Preclinics of Prosthetic Dental Medicine PDF

B. Yordanov J. Kamenova PRECLINICS OF PROSTHETIC DENTAL MEDICINE 2013, SOFIA  Contents 1. Introduction (B.Yordanov) 2. Teeth. Planes and sides for tooth orientation. Functional groups of teeth and numbering systems. Size of teeth. Tooth identifica...

B. Yordanov J. Kamenova PRECLINICS OF PROSTHETIC DENTAL MEDICINE 2013, SOFIA  Contents 1. Introduction (B.Yordanov) 2. Teeth. Planes and sides for tooth orientation. Functional groups of teeth and numbering systems. Size of teeth. Tooth identification - markers. Morphology of teeth – general characteristics (B.Yordanov) 3. Morphology of permanent incisors and canines (B.Yordanov) 4. Morphology of permanent premolars (B.Yordanov) 5. Morphology of permanent molars (B.Yordanov) 6. Phylogenetic evolution of the masticatory system and the maxillofacial region. Ontogenetic development. Development and eruption of teeth – basic theories (J.Kamenova) 7. Dental wax modeling techniques. Addition wax modeling technique. Anatomical and functional wax modeling of tooth crowns on dental stone models (B.Yordanov) 8. Functional anatomy of the masticatory system. Oral cavity. Salivary glands. Bones of the masticatory system: maxilla and mandible. Innervation of the masticatory system (B.Yordanov) 9. Functional anatomy of the masticatory system. Temporomandibular joint. Function of the muscles of the masticatory system: masticatory and mimic muscles (B.Yordanov) 10. General classification of prosthetic restorations. Artificial veneer crowns. Tooth preparation for complete veneer crowns. Impressions and master casts. Pouring the impression and fabricating a master cast with removable dies (B.Yordanov) 11. Technology of complete metal crown and resin veneer crown - “Adapta” system. Technology of complete metal crown with a wax cap – dipping technique. Wax pattern fabrication (B.Yordanov) 12. Gnathology and Occlusodontics. Basic positions of the mandible. Central occlusion, centric relation, myocentric occlusion. Lateral and anterior occlusion. Occlusal morphology (B.Yordanov) 13. Functional-mechanical equilibrium of the periodontium. Muscle forces. Masticatory pressure. Periodontal pressure (B.Yordanov) 14. Biomechanics of mandibular movements. Basic movements. Theory of mandibular movements. General types of articulators (B.Yordanov) 15. Custom cast post and core (B.Yordanov) 16. Contouring and polishing of prosthetic restorations (B.Yordanov) 17. Technology of ceromeric and acrylic resin crown (B.Yordanov) 18. General types of resin veneer crowns and porcelain fused to metal crowns (B.Yordanov) 19. Methods for the functional diagnostics of the masticatory system. Orthopedic diagnostic tests (J.Kamenova) 20. Partial veneer crowns. Classification and technology (B.Yordanov) 21. Bridge restorations – components, abutment retainers and pontic. Technology of mandibular bridge prosthesis - “Adapta” system (J.Kamenova) 22. Bridge restorations - classification. Technology of maxillary esthetic bridge with a modified ridge lap pontic design - “Adapta” system (J.Kamenova) 23. Bridge prostheses – basic construction principles (J.Kamenova) 24. Types of bridge prostheses. Cantilevers. Immediate bridge restorations. FDPs with special rigid and non-rigid connectors. Fixed bridge restorations with resin-bonded retainers - selectively opened partial retainers and Maryland retainers. Model-cast bridge (J.Kamenova) 25. Implant supported fixed bridge restorations (B.Yordanov) 26. Technologic characteristics of bridge restorations fabricated by different technologies. Failures (J.Kamenova) 27. Acrylic resin partial dentures. Types of retainers. Impressions for partial dentures and master cast fabrication. Technology of bent clasps (single-arm, double-arm and Jackson clasp) (J.Kamenova) 28. Other components of removable partial dentures (RPD): precision attachments, telescopic and bar attachments. Major connectors - technology. Indirect retainers. Mounting master casts on an articulator (J.Kamenova) 29. Basic construction principles and planning of RPD. Construction principles of resin- based partial dentures. Technology of maxillary and mandibular resin-based RPD (J.Kamenova) 30. Designing one-piece cast framework RPD. Investing (J.Kamenova) 31. Technology of one-piece cast framework RPD (J.Kamenova) 32. Technology of immediate RPD.Repair of broken or damaged RPD (J.Kamenova) 33. Processing failures in the partial denture fabrication (J.Kamenova) 34. Types of partial dentures. Combined prosthetic restoration of partially edentulous dentitions with fixed and removable prostheses (J.Kamenova) 35. Fundamentals of prosthetic splinting – basic principles (J.Kamenova) 36. Technology of complete dentures. Impression trays, impressions and master casts. Custom made impression trays (J.Kamenova) 37. Fabrication of master casts. Outlines of complete dentures. Fabrication of baseplates and occlusion rims. Registration of interocclusal relationship and placing reference marks on the models (J.Kamenova) 38. Selection of artificial teeth and esthetic aspects of the dentition. Orthognathic arrangement of artificial teeth after Gysi (J.Kamenova) 39. Types of complete dentures – comparative assessment. Technologic characteristics of complete dentures. Failures (J.Kamenova) 40. Retention and stability of complete dentures – biomechanical and biophysical methods (B.Yordanov) 41. Technology of maxillofacial prostheses (J.Kamenova)  PRECLINICS OF PROSTHETIC DENTAL MEDICINE 1. Introduction 1. 1. Object Prosthetic Dental Medicine explores the morphological changes, which violate the normal function of the masticatory system. The object of Prosthetic Dental Medicine is the exploration, prevention and treatment of permanent alterations in the dental arches and maxillo-facial region, which violate mastication, speech and esthetics. The masticatory system is composed of separate organs and tissues in the maxillo-facial region, united in a complex, responsible for the masticatory function – chewing, mastication. Completely formed masticatory system is made up of the following 5 basic sections: - supporting section – maxillo-facial bones, cranio-mandibular joint (CMJ), teeth, periodontium; - motor section – masticatory and mimic muscles; - secretory section – salivary glands; - neuro-trophic (nutritional) section – nerves, blood and lymphatic vessels; - soft (covering) tissues – cheeks, lips, mucous membranes, skin, tongue; The permanent alterations in the dental arches and maxillo-facial region, that can be explored by PDM, are as follows: loss of hard tissue as a result of tooth decay, tooth fracture from trauma, single or multiple tooth loss, congenital jaw deformities, acquired jaw and facial defects usually as a result of cancer and the subsequent surgical interventions, completely edentulous dental arches. 1.2. Prosthetic restorations The restorative devices for prevention and treatment in prosthetic dental medicine are special individual constructions, named prosthetic constructions, prostheses, or simply dentures. They restore or replace organs and tissues of the masticatory system, which had been destroyed, lost or not esthetic; they consolidate them in case of injury and prevent them from diseases or destroying. Prothesis is a greek word, meaning an artificial device for replacing part of the body. There are two basic types of prosthetic restorations. Fixed prosthetic restorations are permanently fixed to natural teeth by means of special glue (cement), and can not be removed by the patient himself. The prosthetic devices in the second group - removable restorations, can be removed and should be removed by the patient for cleaning and disinfection. Examples for fixed prosthetic restorations – inlay, onlay, partial crown, complete crown, fixed bridge, splint. 1  PRECLINICS OF PROSTHETIC DENTAL MEDICINE Although fixed restorations are always preferred by patients and clinicians, sometimes the best choice is not a fixed, but a removable denture - acrylic resin partial dentures, one-piece cast framework partial dentures, partial dentures with precision attachments, complete (full) dentures, removable surgical prostheses and facial prostheses. 2. Teeth. Planes and sides for tooth orientation. Functional groups of teeth and numbering systems. Size of teeth. Tooth identification - markers. Morphology of teeth – general characteristics. 2.1. Teeth Teeth are a major component of the supporting section of masticatory system. Dens (dentes in the plural), is the Latin word for tooth, teeth. The word dentition refers to all of the teeth in the upper jaw bone named maxilla, and the lower jaw bone named mandible (mandibula in Latin). Due to their location the upper teeth are called maxillary teeth. Together they form an arch shape, known as the maxillary dental arch (in Latin - arcus dentalis superior). The teeth in the lower jaw are called mandibular teeth. Together they form the mandibular dental arch (arcus dentalis inferior in Latin). Occlusal surface is the chewing surface of posterior teeth consisting of a number of specific features. This specific relief of the chewing surface includes two basic forms, or groups of details – bumps or convexities and depressions or concavities. Cusps and ridges (tuberculum, margo in Latin) are examples for convexities; the concavities can be: groove, fossa, sulcus, fissure. Depending on the number, shape and size of the cusps the dentitions can be Homodontes – with uniform conical monotubercle teeth (sharks for example), and Heterodontes – teeth with a variety of form, size and number of tubercles. Human teeth are Heterodontes. According to presence or absence of teeth in animals, and how many times they are replaced by another set of teeth, the dentition can be defined as: Anodontia – without any teeth (birds, ant-eaters, turtles); Polyphyodontia – continuous growing and losing, continuous replacement of teeth throughout life (it happens with sharks for instance); Diphyodontia – means with two dentitions, primary and permanent (typical for humans and most mammals); Monophyodontia – with only one dentition throughout life (usually found in some whales); 2  PRECLINICS OF PROSTHETIC DENTAL MEDICINE According to this classification, humans are Heterodontes and Diphyodontes. It is clear that humans have a primary and a permanent dentition (dentes lactici and dentes permanentes in Latin). Primary teeth are often called deciduous teeth. There are 20 teeth in the primary dentition – 10 in the maxillary arch and 10 in the mandibular dental arch. Primary teeth emerge in children between the ages of 6 months and 2 years. Starting at the age of 6, they are gradually replaced by the teeth of the permanent dentition, usually by age 12 or 13. 2.2. Planes and sides for tooth orientation When we study the anatomy of human skull, teeth and jaws, we use as reference points certain planes which do not depend on the 3-dimentional position of the head. The sagittal plane divides the dentition into two symmetric halves – left and right. It is also called the midline of the dental arch, the plane between the right and left central incisors. The horizontal plane is the plane between the upper and lower jaw. This plane separates the maxilla from the mandible and is also called occlusal plane. The transversal plane is the plane between the anterior and posterior half of the head and dentition. When this plane is in contact with the facial surfaces of the upper central incisors, it is called the frontal plane. Mesial surface is the surface of the tooth nearest the midline of the dental arch. Distal surface is the surface of the tooth farthest from the midline of the dental arch. The mesial surface of all teeth face the distal surface of the adjacent tooth, except between the central incisors with their mesial surfaces facing each other. Tooth crown is a cube with 6 sides, 5 of them are free, one is facing the root. Free surfaces are as follows: Facial surface or vestibular surface (facies vestibularis in Latin). Facies means surface in Latin, and vestibularis means that this surface is next to the oral vestibule (vestibulum oris). This is the outer surface of a tooth in the mouth, positioned next to the cheeks or lips. Buccal surface (from the Latin word bucca, meaning cheek) is another name for the facial surface of the posterior teeth, because they are next to the cheek. Labial surface (from the Latin word labium, meaning lip) is another name for the facial surface of anterior teeth, because they are next to the lip. Lingual surface is the surface of maxillary and mandibular teeth tongue facing the tongue. The term lingual is more commonly used, regardless of the jaw – maxilla or mandible. 3  PRECLINICS OF PROSTHETIC DENTAL MEDICINE Proximal surface is the side of a tooth that is next to an adjacent tooth. The proximal surfaces have tight contacts with each other, named contact areas or contact points. Mesial surface is the surface of the tooth nearest the midline of the dental arch. Distal surface is the surface of the tooth farthest from the midline of the dental arch. Occlusal surface (facies masticatoria, facies occlusalis in Latin) is the chewing surface of posterior teeth consisting of cusps, ridges and grooves. Anterior teeth – incisors and canines do not have an occlusal surface, they have a cutting edge (incisal edge, ridge). Occlusion means contact of the chewing surfaces of opposing maxillary and mandibular teeth. The contacts of opposing teeth are point contacts. Sometimes there is no contact area between adjacent teeth, but a space between two adjacent teeth, named diastema. 2.3. Functional groups of teeth and numbering systems. The complete primary dentition has 10 teeth in each jaw. The basic tooth categories or classes are: Incisors – dentes incisivi; Canines – dentes canini; Molars – dentes molares. Incisors and canines are called anterior teeth, molars are posterior teeth. The number of the teeth in the 3 classes is as follows: 8 incisors (4 maxillary and 4 mandibular), 4 canines, two in each jaw, and 8 primary molars (4 maxillary and 4 mandibular). Permanent dentition is composed of 32 teeth – 16 maxillary and 16 mandibular. Permanent dentitions have a new category of teeth called premolars, which are positioned in the spaces left where the primary molars had been. Premolars closest to the midline are called first premolars, followed behind by second premolars. The basic permanent tooth categories are: Incisors (dentes incisivi), 4 in each dental arch; Canines (dentes canini), 1 in each dental arch; Premolars (dentes praemolares), 4 in each dental arch, and Molars (dentes molares), 6 in each dental arch. Tooth identification systems The making and storage of accurate dental records is an important task in any dental practice. It would be a great loss of time to write down for each tooth its full description – for example: Dens incisivus inferior primus dexter permanens, or Dens molaris superior secundus sinister permanens. The names are about the same in English: First permanent mandibular right central incisor tooth; Second permanent maxillary left molar tooth. To save our time, it is necessary to adopt a type of code or numbering system for teeth. - Universal Numbering System. It was first suggested by Parreidt in 1882, officially adopted by the American Dental Association in 1975. Basically it uses 4  PRECLINICS OF PROSTHETIC DENTAL MEDICINE numbers 1 through 32 for the permanent dentition starting with 1 for the maxillary right third molar, to 32 for the lower right third molar. For the primary dentition, letters of the alphabet are used from A through T. A is the maxillary right second molar, to T for the mandibular left second molar. - Palmer Notation System. This system utilizes brackets to represent the four quadrants of the dentition as if you are facing the patient. 2/ is upper right, /3 is upper left, 6/ is lower right and /6 is lower left (on the scheme). The permanent teeth are numbered from 1 to 8 on each side from the midline, so 1 is central incisor, 3 is canine, 6 is the first molar, etc. The number is placed within the bracket. Fig 1. Palmer Notation System for permanent teeth On deciduous teeth, the same four brackets are used, but letters of the alphabet A through E represent the primary teeth, central incisors becoming A, lateral incisors – B, canines C, etc. Fig 2. Palmer Notation System for primary teeth The formula for tooth identification of Zigmondi is a modification of the Palmer Notation System. The difference is that for the deciduous dentition not letters, but 5  PRECLINICS OF PROSTHETIC DENTAL MEDICINE Roman numbers are used to represent the primary teeth, central incisors becoming I, lateral incisors II, canines III, molars IV and V. - International Numbering System (Viohla, 1970). Approved by the International Dental Federation, uses 2 digits (figures) for each tooth, permanent of primary. The first digit always denotes the dentition, arch and side, and the second digit denotes the tooth – 1 to 8 for permanent and 1 to 5 for deciduous teeth from the midline posteriorly. Fig 3. Formula for tooth identification after Zigmondi 1 is Permanent dentition, maxillary, right side; 2 is Permanent dentition, maxillary, left side; 3 is Permanent dentition, mandibular, left side; 4 is Permanent dentition, mandibular, right side; 5 is Deciduous dentition, maxillary, right side; 6 is Deciduous dentition, maxillary, left side; etc. Examples for permanent teeth: 11 – maxillary right central incisor; 23 – maxillary left canine tooth; 35 – mandibular left second premolar; 46 – mandibular right first molar, etc. Examples for primary teeth: 52 – maxillary right lateral incisor; 63 – maxillary left canine; 74 – mandibular left first molar; 85 – mandibular right second molar; A 6  PRECLINICS OF PROSTHETIC DENTAL MEDICINE B Fig 4. International Numbering System (FDI). A-permanent dentition, B – primary dentition Instead of the long descriptions in Latin or in English, we can use the International Numbering System, accepted and approved all over Europe – with two digits and additional explanations for proper diagnostics for example. This is how we can denote definite teeth, or diseases like caries, or types of treatment and restorations. Examples: Teeth 13, 15, 24, 37; Caries profunda 23, 26; Obturatio dentis 45; Obturatio dentium 34, 35, 46, etc. 2.4. Size of teeth Teeth vary in form and size, they have general characteristics and individual peculiarities. Average dimensions of teeth are presented in tables, on the basis of numerous measurements on extracted teeth. These data are useful for determining the tooth with the longest crown, the longest overall length, the shortest root, and so forth. The average dimensions of each type of tooth serve as the basis for many statements and research work, and could help the clinician in diagnostics and proper treatment. Tables for average tooth size contain information for the overall length of a particular tooth, length of the crown, length of the root, diameter of the crown in two dimensions - mesiodistal and faciolingual, and diameter of the cervix - mesiodistal and faciolingual. Dental medicine students use these dimensions at a scale of 3:1 for drawing and carving teeth. 7  PRECLINICS OF PROSTHETIC DENTAL MEDICINE 2.5. Morphology of teeth – general characteristics 2.5.1. Parts of a tooth Each tooth has 3 basic anatomic parts: crown – corona dentis; root – radix dentis and cervix (neck) – collum dentis. If we examine an extracted tooth, we can distinguish an anatomic crown and an anatomic root. The line that separates the anatomic crown from the anatomic root is called cervical line. This is also called cement-enamel junction (CEJ), because it separates the crown covered by enamel from the root which is covered by cementum – they both are hard tissues on the surface of the tooth. The root is that part of the tooth which is under the gingiva – the root is usually not visible. The crown is the visible part of the tooth, located in the oral cavity. The cutting edge (ridge, surface) of anterior teeth is called incisal edge – margo incisivus. Occlusal surface (facies masticatoria) is the chewing surface of posterior teeth consisting of cusps, ridges and grooves – or convexities and concavities in general. The number of roots can be one, two, three or more, depending on tooth category. Furcation is the place on multi-rooted teeth where the root base divides into separate roots – bifurcation on two-rooted teeth and trifurcation on three-rooted teeth. The gingiva is that part of the oral mucous membrane that covers the jaw bone, and surrounds the cervical portions of the teeth. Gingival margin (margo gingivalis) is the occlusal (incisal) border at which the gingiva meets the tooth. Usually the gingival margin approximately follows the curvature of the cervical line, it is usually at the same level as the cervical line and the neck of the tooth is tightly embraced by the gingival margin. Anatomic crown is that part of a tooth, visible in the oral cavity, that has an enamel surface. The anatomic root is the part of a tooth that has a cementum surface. The line that separates the anatomic crown from the anatomic root is called cervical line. This relationship does not change over a patient’s lifetime. Usually the gingival margin approximately follows the cervical line. Clinically, when the tooth is in the mouth, this relationship is not always the same. However, the gingival margin is not always at the level of the cervical line because of the eruption process or gingival recession. The clinical crown is the part of a tooth that is visible in the oral cavity. The clinical crown may be larger or smaller than the anatomic crown. It may include all of the anatomic crown and some of the anatomic root if there has been recession of the gingiva. The clinical crown may include only part of the anatomic crown if the cervical part of the crown is still covered by gingiva, for example during the eruption process (especially on newly erupted teeth). 8  PRECLINICS OF PROSTHETIC DENTAL MEDICINE The clinical root is that part of a tooth which is under the gingiva and is not exposed to the oral cavity. In an elderly person with considerable recession of the gingiva, the clinical root would be shorter than the anatomic root because the portion of the root that is exposed is considered to be a part of the clinical crown. The clinical root may be longer than the anatomic root. On newly erupted teeth, any part of the crown not erupted is considered to be part of the clinical root. The crest of curvature is the highest point of a curve or the greatest convexity. The crest of curvature is where this convexity would be touched by a tangent line drawn parallel to the root axis. Contact areas are the crests of curvature on the proximal surfaces of tooth crowns where a tooth touches the tooth adjacent to it in the same arch. If we move a pencil parallel to the root axis of the tooth, we shall draw a line called anatomic crest of curvature. This line divides the tooth surface into two parts – occlusal (above the crest of curvature) and cervical (below the crest of curvature). During chewing, these convexities divert food away from the gingiva that surrounds the neck of tooth, thus preventing trauma to the gingiva. The active parts of some retainers for re movable dentures, like clasps, are positioned in the cervical part, below the crest of curvature. The tooth cavity – pulp cavity or cavum dentis in Latin is positioned in the center part of the tooth and has a similar outline as the tooth itself. The pulp cavity is surrounded by dentin except at a hole near the root apex, called apical foramen. Pulp is the soft, not calcified tissue in the pulp chamber. It is normally not visible except on a dental radiograph. The pulp cavity has a coronal portion – pulp chamber (cavum coronae dentis) and a root portion – pulp canal or canals, depending on the number of roots. The pulp canals are also called root canals – canalis radicis dentis. 2.5.2. Tooth composition A tooth is composed of several basic structures: cuticula, enamel, dentin, cementum, pulp. The crown of the tooth is covered by a thin membrane, named cuticula dentis, composed of a great number of collagen fiber bundles. The most external tissue layer underlying the dental cuticula is named tooth enamel, substantia adamantina. It is the hard, white shiny surface of the anatomic crown. The composition of enamel is: 95% calcium hydroxyapatite (mostly inorganic substance), 4% water and 1% enamel matrix – organic matter. Enamel is the hardest tissue in human body, almost as hard as the mineral quartz - 200-500 kg/mm². Enamel is composed of enamel rods – prismata adamantina. The 9  PRECLINICS OF PROSTHETIC DENTAL MEDICINE diameter of the rods is about 4 μm. The chemical composition of the rods is Calcium Hydroxyapatite - Ca10(PO4)6(OH)2. Enamel gradually gets thinner toward the root and terminates at the cervical line. Cementum is the yellowish external surface of the anatomic root, covering the dentin. The composition of cementum is: 65% calcium hydroxyapatite (inorganic calcified substance), 12% water and 23% organic matter – collagen fibers. The thickness of the cementum layer is lowest near the CEJ, no more than 50-100 μm. The periodontal fibers, connecting the root to the alveolar (jaw) bone are incorporated into the cementum. The CEJ is the transitional zone between the enamel of the crown and the cementum of the root. Dentin is the basic, mostly inorganic, calcified substance of a tooth. It is a hard yellowish tissue underlying the enamel and cementum, making up the major bulk of the tooth. The dentin is not visible, except on radiographic images, or when the enamel is worn out, or on a cross-sectional slices for microscopic examination. The composition of Dentin is: 70% calcium hydroxyapatite (inorganic calcified substance), 12% water and 18% organic matter – collagen fibers. The dentin is composed of a great number of dentine tubules – 65 000/mm² near the pulp and 15 000 – 20 000/mm² near the CEJ. Pulp is the soft non-calcified tissue in the pulp chamber – the cavity in the centre of the crown and root. The pulp is completely surrounded by dentin, except the root apex. It is composed of loose connective tissue, fibroblasts, blood vessels for an abundant, rich blood supply, and a great number of nerve endings, penetrating the pulp through the root apex. The ground substance consists of water, carbohydrates and proteins. Important component of the pulp are the undifferentiated mesenchymal cells that serve to replace injured or destroyed odontoblasts – a repairing (regenerative) function of the pulp. Functions of the pulp: - forming function – at the borderline to the dentin there are cells named odontoblasts. These cells produce new dentin throughout the whole lifetime. It is named secondary dentin. The odontoblasts have cytoplasm processes penetrating into the dentin tubules. That’s why the dentin is extremely sensitive to mechanical, physical and chemical irritating factors – they are directly transferred by the odontoblast processes to the nerve endings into the pulp. - senory function – this means strong sensitivity to hot, cold, sweet, tooth decay, instrumental preparation for treatment, trauma, infection, etc. 10  PRECLINICS OF PROSTHETIC DENTAL MEDICINE - trophic, nutritive function – it is realized through the rich vascular structures – blood vessels, even into the dentin. - protective function – the odontoblasts produce secondary dentin (repairing, protective dentin) as a reaction to the injuring of the hard tooth tissues, from caries for example. - repairing function – through the undifferentiated mesenchymal cells that serve to replace injured or destroyed odontoblasts. The alveolar process comprises all of the bone surrounding the tooth from the alveolar crest (top of the bone) to the root apex. It is the dental arch of bone which surrounds and supports the teeth, with eight sockets in each quadrant. The roots of the teeth are embedded in sockets or pits called alveoli, in the maxillary and mandibular bones. The alveolar bone, named also supporting bone is made up of an inner and outer cortical plate with trabecular bone between the two plates. Trabecular bone (synonyms: cancellous bone, spongy bone) is composed of many platelike bone partitions that separate the irregularly shaped bone marrow spaces located within this trabecular bone. Lamina dura is the thin, compact bone that forms the wall of each tooth socket or the alveolus. The only space between the outer layer tooth root (cementum) and lamina dura is the space occupied by the periodontal ligament. The roots of the teeth are attached to the bone, to lamina dura, by the fibers of the periodontal ligament. Therefore the periodontal ligament suspends and attaches each tooth to the bone. The periodontal ligament is between 0,12 и 0,33 mm thick and is composed of cells and fibrous intercellular substance. In function the tooth sinks into the bone socket and all fibers are stretched out. This movement of the tooth into the alveolus at the time of function (chewing, mastication) is called physiologic tooth mobility. The masticatory pressure is transferred and distributed to lamina dura and the alveolar bone without trauma. Physiologic tooth mobility into the bone socket is about 0,10 – 0,15mm. The periodontal ligament also contains proprioceptive (sense of position) nerve endings, which continually send messages to the brain as to the location of the mandible in space. This has a tremendous influence on jaw position, movement and occlusion of the teeth. 11  PRECLINICS OF PROSTHETIC DENTAL MEDICINE 2.5.3. Basic forms of occlusal surfaces Occlusal surface is the chewing surface of posterior teeth consisting of a number of specific details. The basic groups of details (forms) are convexities and concavities, or in general - grooves and ridges. In the study of tooth morphology, the grooves and ridges on the various surfaces are described and named. A knowledge of the character and location of these ridges, grooves, convexities and concavities on teeth is invaluable in describing and identifying teeth in regard to arch, class, type and side of the mouth. Convexities - cusp, tubercle (tuberculum) – this is a point or peak on the chewing surface of molar and premolar teeth, and on the incisal edge of canines - cusp ridges (cusp slopes) are the inclined surfaces that form an angle at the cusp tip when viewed from the facial or lingual aspect. These cusp slopes may also be called cusp arms. All cusps are basically a gothic pyramid with 4 ridges: mesial cusp ridge, distal cusp ridge, buccal cusp ridge (labial ridge on canines), triangular ridge on posterior teeth (lingual ridge on canines). - cingulum is the enlargement or bulge on the cervical third of the lingual surface of the crown of anterior teeth – incisors and canines - labial ridge (margo labialis) – a ridge running cervicoincisally in approximately the centre of the labial surface of canines - buccal ridge, cusp ridge (margo buccalis) – a ridge running cervicoocclusally in approximately the centre of the buccal surface of premolars - cervical ridge (margo cervicalis) is a ridge running mesiodistally on the cervical one-third of the buccal surface of the crowns, found on all primary teeth but only on the permanent molars - marginal ridge – it is located on the mesial and distal border of the lingual surface. For posterior teeth – on the mesial and distal border of the occlusal surface. - triangular ridge (margo triangularis) – on the occlusal surface of posterior teeth, it is the ridge from any cusp tip to the centre of the occlusal surface. Some cusps have more than one triangular ridge - the mesiolingual cusp on maxillary molars has two triangular ridges - oblique ridge (margo obliquus) – a ridge found only on maxillary molars. Crosses the occlusal surface obliquely and is made up of the triangular ridges of the mesiolingual and the distobuccal cusps - transverse ridge – this is a ridge crossing the occlusal surface of most posterior teeth in a buccolingual direction. This ridge is made up of connecting triangular ridges. Example: between the mesiolingual and mesiobuccal or between the distolingual and 12  PRECLINICS OF PROSTHETIC DENTAL MEDICINE distobuccal cusps on molars. The transverse ridge is also running between buccal and lingual cusps on premolars. Depressions and grooves - sulcus - a broad depression or valley on the occlusal surfaces of posterior teeth, the inclines of which meet in the central groove and extend outward to the cusp tips - developmental grooves – this is a sharply defined, narrow and linear depression, short or long, formed during tooth development and usually separating lobes or major portions of a tooth. The major grooves are named according to their location (central,mesial, distobuccal, mesiobuccal, etc.) - fissure – this is a narrow channel (cleft, crevice), formed at the depth of a developmental groove, extending inward toward the pulp. NB! Decay (dental caries) often begins in a deep fissure - supplemental grooves - small, irregularly placed grooves, not at the junction of lobes or major portions of a tooth, found usually on occlusal surfaces. They can be named for the part of the tooth on which they are found - mesiobuccal supplemental groove, distolingual supplemental groove, etc. - fossa (fossae in plural) – fossa is a depression found on the lingual surfaces of some anterior teeth (particularly maxillary incisors) and on the occlusal surfaces of all posterior teeth - central fossa, mesial triangular fossa, distal triangular fossa, etc. - pits - just like fissures, often occur at the depth of a fossa where two or more grooves join. Similar to fissures at the depth of grooves, pits are areas where dental decay may begin. 3. Morphology of permanent incisors and canines 3.1.Incisors There are 4 maxillary incisors – two central incisors and two lateral incisors, and 4 mandibular incisors - two central incisors and two lateral incisors. The incisors are marked by the symbols 12, 11, 21, 22, 32, 31, 41, 42 according to the International Numbering System. 3.1.1. Functions.The mandibular incisors function with the maxillary incisors in cutting food; enabling articulate speech; helping to support the lip and maintain a good appearance; Their fourth function is to help guide the mandible posteriorly during the final phase of closing just before the posterior teeth contact. In this way the anterior teeth protect the posterior teeth from overloading. 3.1.2. General description. From the facial aspect, the crowns of incisors are relatively rectangular, longer incisogingivally than wide mesiodistally. They are 13  PRECLINICS OF PROSTHETIC DENTAL MEDICINE narrowest in the cervical third and broader toward incisal third. They are more convex on the distal than on the mesial sides, except the mandibular central incisor which is symmetrical. The mesioincisal corner nearly forms a right angle, although this angle is slightly rounded. The distoincisal corner is more rounded. This is a very important marker for distinguishing the incisors from other teeth. The cervical line is convex toward the apex on the facial and lingual sides. Mamelon is one of the three tubercles sometimes present on the incisal edge of an incisor tooth that has not been subjected to wear. Mamelons are usually present on newly emerged teeth and they are soon worn off by functional contacts against the incisors of the opposite dental arch – a phenomenon named attrition. The roots are wider faciolingually than mesiodistally, except for the maxillary central incisor, and when they bend in the apical third, it is usually to the distal. N.B. The central incisor root is the only maxillary tooth that is as thick at the cervix mesiodistally as faciolingually. This is the reason for its conical shape. Because of its shortness and conical shape, the maxillary central incisor is generally considered to be a poor support for any fixed bridge, due to its low mechanical stability. The two shallow vertical depressions on the labial surface of incisors divide this surface into three portions, usually called the mesial, middle and distal lobes. These depressions are named developmental depressions. The crowns have a narrower lingual surface because the mesial and distal sides converge lingually. When viewed from the proximal, the crowns are wedge shaped. The labial and lingual crest of curvature is in the cervical third, close to the cervical line. The lingual outline is S-shaped, being convex over the cingulum and concave from the cingulum nearly to the incisal edge. The labial outline is broader and less curved than the lingual outline. The functional wear of the incisal edges of incisors is an important mark for identification. Due to the contacts between upper and lower incisors in function their incisal edges are subjected to wear in a specific pattern – maxillary incisors demonstrate wear on the lingual side, and the mandibular incisors – on the facial side of the incisal edge. 3.1.3. Maxillary central incisor The crown of the maxillary central incisor is the longest of all human teeth, including that of the canines. The crown is narrowest in the cervical third and becomes broader toward the incisal third. The broad depression (concavity) on the lingual surface of the maxillary central incisor is called lingual fossa – fossa lingualis, positioned immediately incisal to the 14  PRECLINICS OF PROSTHETIC DENTAL MEDICINE cingulum – an enlargement on the cervical third of the lingual surface of the crown on anterior teeth. The lingual fossa is bounded by the mesial and distal marginal ridges. Due to the slightly distal placement of the cingulum, the mesial marginal ridge is longer than the distal marginal ridge. From the incisal aspect the crown has a triangular shape, with a slightly curved labial outline. The incisal ridge is the widest part of the crown. The labial outline of the crown is broadly convex, with a mesial and distal depression on the labial surface, located in the middle and incisal thirds. 3.1.4. Maxillary lateral incisor Maxillary lateral incisor demonstrates great morphologic variability. It may resemble a small version of a maxillary central incisor, it may be quite asymmetrical and it may be peg-shaped. It may be missing altogether, a state called hypodontia. The labial surface is more convex compared to that of the central incisor. Labial depressions are less prominent and less common than on the central incisor. The mesioincisal angle is more acute and the distoincisal angle is wider than on the central incisor. Both angles are more rounded on the lateral incisor than on the central incisor. The lingual fossa is smaller but more pronounced than on the central incisor. The cingulum is narrower than on the central incisor and it is almost centered on the root axis line. Frequently, a lingual pit is present, next to the cingulum and it should be checked and restored by the dentist in case of need to stop decay. From the occlusal aspect, the labial outline of the crown is noticeably more convex than that of the central. This is a characteristic difference. 3.1.5. Mandibular central incisor The surface of the crown is nearly smooth. The crown is very narrow with respect to its length. The mesioincisal and distoincisal angles are nearly right angles, or only a little rounded. N.B. This tooth is so symmetrical that it is quite difficult to tell lefts from rights unless on models or in the mouth. Both mesial and distal contact points are in the incisal third, almost level with the incisal edge. This phenomenon is unique to mandibular central incisors. The root is very narrow mesiodistally, but wide faciolingually. The lingual surface is smooth and shallow, without any grooves, accessory ridges or pits. The labiolingual dimension is greater than the mesiodistal dimension. This is quite different from the measurements of the maxillary incisors and an important mark to distinguish mandibular incisors from maxillary incisors. 15  PRECLINICS OF PROSTHETIC DENTAL MEDICINE 3.1.6. Mandibular lateral incisor The mandibular lateral incisor is a little larger in all dimensions than the mandibular central incisor in the same mouth. The crown of the mandibular lateral incisor resembles that of the mandibular central incisor, but it is not as bilaterally symmetrical. The distal outline is rounded compared to a flatter mesial crown outline. The crown of the lateral incisor is tilted distally on the root, giving the impression that the tooth has been bent at the cervix. The distoincisal angle is noticeably more rounded than the mesioincisal angle, but before attrition. This is an important mark to distinguish lefts from rights but prior to attrition. The distal contact point is cervical to the level of the mesial one. The two contact areas are not at the same level unlike the contact areas on the central incisor – on the same level. From the incisal aspect, the incisal edge does not follow a straight line mesiodistally. It has a distolingual twist - the distal half of the incisal edge is bent lingually. 3.2. Canines There are 4 canines: one on either side in the maxillary and mandibular arches. They are longest of the permanent teeth – 26 mm on the average! The canines are marked by the symbols 13, 23, 33, 43 according to the International Numbering System. 3.2.1. Functions The canines usually function with the incisors to support the lip and the facial muscles; to cut, pierce or shear food morsels; act as important guideposts in occlusion and protect posterior teeth against the damaging horizontal forces - this is called canine protected occlusion; canines, because of their large, long roots, provide excellent support as abutments for fixed bridge prostheses or removable partial dentures. 3.2.2. General description.The canines are the longest teeth in the mouth. They have particularly long thick roots, 16.2 mm on the average, that help to anchor them securely in the alveolar process of the jaw bone. The incisal ridge is divided into two slopes by a cusp, therefore resembling a pentagon shape. The mesial slope (cusp ridge) is shorter than the distal slope. NB! This is an important mark to distinguish lefts from rights. The mesial segment of the incisal edge is shorter and less inclined compared to the distal segment. Canine teeth usually do not have mamelons, but may have a notch on either cusp slope. 16  PRECLINICS OF PROSTHETIC DENTAL MEDICINE The labial surface of a canine is prominently convex with a vertical labial ridge. Canines are the only teeth with a labial ridge although premolars have a similar ridge called the buccal ridge. The measurement of the crown and root is greater labiolingually than it is mesiodistally. Similar to the incisors, canines are wedge-shaped proximally. 3.2.3. Maxillary canine The facial side of the crown is made up of three labial lobes. The cingulum on the lingual surface is the fourth lobe. The middle lobe forms the prominent labial ridge. Shallow depressions lie mesial and distal to the labial ridge. The mesial and distal cusp ridges form an angle that approaches the right angle – 105 degrees. There is a lingual ridge running cervicoincisally from the cusp to the cingulum, and a mesial and a distal shallow lingual fossae, lying on either side of the lingual ridge. From the proximal aspect the crown is wedge-shaped and quite bulky due to the prominent labial and lingual ridges. The apical third of the root is narrow mesiodistally and the apex may be pointed or sharp. The apical third of the root often bends distally. The root is noticeably broad faciolingually in its cervical and middle thirds. From the incisal aspect the mesial half of the labial outline is quite convex, whereas the distal half of the labial outline is frequently somewhat concave. This observation is most helpful in determining right from left maxillary canines. 3.2.4. Mandibular canine The labial surface is smooth and convex. The labial ridge is not as pronounced as on the maxillary canines. The crown appears long and narrow compared with the crown of the maxillary canine. The mesial and distal cusp ridges form a more obtuse angle (120˚) than the maxillary canine. The apical end of the root is more often straight than curving toward the mesial or distal sides. Therefore, on mandibular canines, the root curvature should not be used to distinguish rights and lefts. Roots are shorter than the roots of upper canines. The labiolingual dimension of the crown is noticeably larger than the mesiodistal dimension. This oblong faciolingual outline is characteristic for mandibular canines. The position of the distoincisal angle is lingual to the position of the cusp tip. This displacement gives the incisal part of the crown a slight distolingual twist like the mandibular lateral incisor. The functional attrition of the incisal edges of canines is an important mark for identification. Due to the contacts between upper and lower canines in function their 17  PRECLINICS OF PROSTHETIC DENTAL MEDICINE incisal edges are subjected to wear in a specific pattern – maxillary canines demonstrate wear on the lingual side, and the mandibular canines – on the facial side of the incisal edge. 4. Morphology of permanent premolars The term premolar is used to denote any tooth in the permanent dentition of mammals that replaces a primary molar. There are 8 premolars – 4 in the maxillary arch and 4 in the mandibular arch. They can be identified by the International Numbering System (the formula of Viohla) as teeth 14, 15, 24, 25 for maxillary premolars and 34, 35, 44, 45 for mandibular premolars. 4.1. Functions. The premolars function with the molars in the mastication of food and in maintaining the vertical dimension of the face. They assist the canines in shearing and cutting food morsels. All premolars support the corners of the mouth and cheeks from sagging, which is more visible in older people. 4.2. Morphology of maxillary premolars From the buccal aspect the crown is shaped like a pentagon. The tip of the buccal cusp is slightly mesial to the vertical axis line of the tooth. Therefore: The mesial slope of the buccal cusp is shorter than the distal slope. Except for tooth 14, 24 where the tip of the buccal cusp is slightly distal to the vertical axis line. Therefore the mesial slope of the buccal cusp is longer than the distal slope. This mark is characteristic for this tooth only! The buccal surface is convex, with a buccal ridge that is most prominent on the maxillary first premolars. The apical third of the root is usually bent distally. The first maxillary premolar has two roots or a divided root in the apical third in 61%, with buccal and lingual roots. The root of the second premolar is nearly twice as long as the crown, with a root to crown ratio 1,8/1 which is the highest for any maxillary tooth. The lingual cusp is shorter than the buccal cusp, more noticeable on the first premolar. The tip of the unworn lingual cusp of both maxillary premolars always bends toward the mesial. This makes it easy to tell rights from lefts. The lingual roots of maxillary first premolars are shorter than the buccal roots. From the proximal the crown shape is trapezoid-like. Maxillary first premolars have a prominent mesial depression continuing onto the root! Second premolars do not have such concavity idepression. The distal marginal ridge of both premolars is more cervical in position than the mesial marginal ridge. This phenomenon is true of all posterior teeth, with the exception of the mandibular first premolar. 18  PRECLINICS OF PROSTHETIC DENTAL MEDICINE From the occlusal aspect maxillary premolars are considerably wider faciolingually than mesiodistally. The buccal and lingual triangular ridges extend from the tips of the cusps to the central groove. Combined, these 2 triangular ridges make up the transverse ridge. The central developmental groove runs mesiodistally across the occlusal surface and ends mesially and distally in the mesial and distal triangular fossae. In the distal triangular fossa, the distal end of the central groove meets the distobuccal and distolingual supplemental or developmental grooves, sometimes forming a distal pit. The mesial end of the central groove meets the mesiobuccal and mesiolingual developmental or supplemental grooves, forming a mesial pit in the mesial triangular fossa. An important mark to distinguish first and second premolars is the number of the supplemental grooves. There are fewer supplemental grooves on maxillary first premolars. On the second premolars, there are many supplementary grooves radiating buccally and lingually from the depth of each triangular fossa. On the first premolar, a mesial marginal groove crosses the mesial marginal ridge. This is one of the distinguishing characteristics of the first premolar with a frequency of 97%. From the occlusal aspect, the shape of the buccal surface is a wide and inverted V because of the prominent buccal ridge. The lingual portion of the tooth seems to be bent mesially. This asymmetrical occlusal design is a distinguishing feature of first premolars and is not found on second premolars. The second premolars are less angular, more oval shaped and much more symmetrical. Distal contacts are in the middle third on second premolars, located more lingually than mesial contacts. Just the opposite is true on first premolars with their asymmetry, where the distal contact is more buccal than the mesial contact. 4.3. Morphology of mandibular premolars There are two common types of mandibular second premolars: a two-cusp type with one lingual cusp (frequency 43%), and a three-cusp type with two lingual cusps (frequency 54,2%). The buccal cusp on first premolars is longer, sharper and more pointed than the buccal cusp on second premolars. The cusp slopes meet at a nearly right angle - 110º, while the cusp slopes of the second premolar meet at a more obtuse angle of about 130º. A common phenomenon is the occurrence of shallow notches on both cusp ridges on unworn premolars, called Thomas notches (named after a dentist P.K. Thomas). The lingual cusp of the first premolar is very small and is often pointed at the tip. It is nonfunctional. 19  PRECLINICS OF PROSTHETIC DENTAL MEDICINE On mandibular first premolars there is frequently a mesiolingual groove separating the mesial marginal ridge from the mesial slope of the small lingual cusp. This groove is called the mark of Adloff. Due to this groove the mesial marginal ridge of the first premolar slopes cervically at nearly a 45 degree angle from the buccal cusp and is nearly parallel to the triangular ridge of the buccal cusp. An exception to all other permanent teeth is the mandibular first premolar, the only tooth where the mesial marginal ridge is more cervically located than the distal marginal ridge. As on all mandibular posterior teeth, the crown of the mandibular first and second premolar tilts noticeably toward the lingual surface at the cervix. From the occlusal aspect the crown of the mandibular first premolar has the shape of a diamond, converging lingually from the contact areas. The outline of the crown is not symmetrical. It often looks as though the mesial side of the crown has been pushed inward on the mesiolingual corner. The distal crown outline is considerably more convex. The crown of the two-cusp second premolars is round or oval shaped and tapers to the lingual. On the three-cusp second premolars, the occlusal surface is more square because the crown is broad on the lingual side. When the lingual cusps are large, the occlusal surface is broader on the lingual side than on the buccal side. The triangular ridge of the buccal cusp is long and slopes lingually from the cusp tip to the line where it joins the short triangular ridge of the lingual cusp. The grooves on the first premolars are fewer in number but deeper than those on the second premolars. The mesial and distal fossae are circular, not triangular, each fossa has a pit. The distal fossa is usually larger or deeper. On the two-cusp type mandibular second premolars, the lingual cusp is smaller than the buccal cusp, with a large triangular ridge on the buccal cusp and a smaller one on the lingual cusp. These two ridges form a transverse ridge. The curved central developmental groove extends mesiodistally across the occlusal surface and ends in the circular mesial and distal fossae, where it joins the supplemental grooves. The three-cusp second premolar has three triangular ridges converging toward the central fossa. There is no transverse ridge. The large central fossa is located quite distal to the centre of the occlusal surface. Three-cusp second premolars do not have a central groove. There is a long mesial groove extending from the central fossa to a small mesial triangular fossa. The short distal groove extends from the central fossa to the very small distal triangular fossa. 20  PRECLINICS OF PROSTHETIC DENTAL MEDICINE The lingual groove extends from the central fossa lingually between the mesiolingual and distolingual cusps and onto the lingual surface of the crown. This results in a Y-shaped occlusal groove pattern. 5. Morphology of permanent molars There are 12 permanent molars – 6 maxillary and 6 mandibular. They are the first, second and third molar in each quadrant, and the 6th, 7th and 8th teeth from the midline. Using the International Numbering System (the formula of Viohla) the maxillary molars are 16, 17, 18; 26, 27, 28; The mandibular molars are 36, 37, 38; 46, 47, 48; The first molars are the largest and the strongest teeth in each arch. The second molars are distal to the first molars. The third molar is the last tooth in the arch, its distal surface is not in contact with any other tooth. 5.1. Functions The permanent molars play a major role in the mastication of food – chewing and grinding; maintain the vertical dimension of the face; important in maintaining continuity within the dental arches, thus keeping other teeth in proper alignment; they have a role in aesthetics by keeping the cheeks normally full or supported, and maintain the occlusal vertical dimension. 5.2. Morphology of maxillary molars Maxillary molars are the largest maxillary teeth. On both maxillary molars, there are two cusps on the buccal side – a mesiobuccal cusp and a distobuccal cusp. The mesiobuccal cusp is usually longer and wider than the distobuccal cusp. The buccal groove lies between the buccal cusps and extends cervically on the buccal surface to the middle third of the crown. The roots are normally three, the lingual is longest, then the mesiobuccal and the distobuccal is the shortest root. At the cervical line the crown is attached to a broad undivided base called the root trunk. It is longer on the second molars. The point of furcation is often near the junction of the cervical and middle thirds of the roots. It is called trifurcation since three roots come off the trunk. On first molars, the mesiobuccal and distobuccal roots are well separated. The roots of the second molar are often close together, and more parallel with each other. The crown of the second molar usually appears smaller than that of the first molar on the lingual side, because of the smaller or nonexistent distolingual cusp. On the first molar there are two well defined cusps on the lingual surface – the large mesiolingual 21  PRECLINICS OF PROSTHETIC DENTAL MEDICINE cusp and the smaller distolingual cusp. The mesiolingual cusp is the largest and highest cusp on any maxillary molar. There is often a small fifth cusp or cusplet attached to the lingual surface of the mesiolingual cusp. It is called the cusp of Carabelli, or the tubercle of Carabelli, after the Austrian dentist George von Carabelli who described it in 1842. There are two types of maxillary second molars based on the number of cusps – four and three. On the four-cusp molar, there are two lingual cusps – mesiolingual and distolingual (smaller). They are separated by a lingual groove, extending onto the lingual surface. The three-cusp type of second molar is one in which the distolingual cusp is absent, leaving just one lingual large lingual cusp. The maxillary first molar crown appears short and broad faciolingually from the proximal aspect. There is a noticeable convergence or narrowing of the crown toward the occlusal surface from the buccal and lingual crests of curvature resulting in a relatively narrow occlusal table. The cusps of the first molar, in order of their height, are: the longest is the mesiolingual, followed by mesiobuccal, distobuccal and distolingual cusp. The lingual root of the first molar is the longest of the three roots, it is banana shaped, and on first molars extends conspicuously beyond the crown lingually. It tapers apically and usually is curved buccolingually. On the maxillary second molars, the roots are much less spread apart than the roots of the first molar. The lingual root is straighter than on first molars and usually does not extend beyond the lingual surface of the crown. On the maxillary first molar, the outline of the occlusal surface is not square – actually it is a parallelogram, or rhomb, with two acute and two obtuse angles. The parallelogram is larger buccolingually than mesiodistally. In many first molars the lingual side of the crown is slightly wider mesiodistally than the buccal side. The second molar is also wider buccolingually than mesiodistally, but tapers more from buccal to lingual due to the smaller of absent distolingual cusp. When the disltolingual cusp is absent, the tooth has only three cusps and is triangular or heart-shaped. Each of the 4 major cusps has a definite triangular ridge. The triangular ridges of the mesiolingual cusp and the distobuccal cusp meet and form a diagonal ridge called the oblique ridge. The mesiolingual cusp usually has two triangular ridges. The mesial one meets the triangular ridge of the mesiobuccal cusp and the two make up the transverse ridge. On maxillary molars with four major cusps, there are usually 4 fossae on the occlusal surface. The large central fossa, the small mesial triangular fossa, the distal 22  PRECLINICS OF PROSTHETIC DENTAL MEDICINE triangular fossa (very small); The distal fossa is an elongated fossa, extending between the mesiolingual and the distolingual cusps. The buccal groove extends buccally from the central fossa and continues onto the buccal surface of the crown as the buccal groove. The central groove extends mesially from the central fossa and ends in the mesial triangular fossa. Occasionally there is a distal continuation of the central groove to the distal triangular fossa named transverse groove of the oblique ridge. The distal oblique groove extends from the distal triangular fossa lingually between the mesiolingual and the distolingual cusps and continues onto the lingual surface as the lingual groove. Maxillary third molars are the shortest of the permanent teeth and have the greatest morphologic variabilty compared to all other teeth. The crown may have only one or up to 8 cusps. Short, less separated roots and numerous supplemental grooves and ridges – a wrinkled appearance. The mesiolingual cusp is usually larger an longer than the others. Three roots – mesiobuccal, distobuccal and lingual that may be separated, but more commonly fused together. The roots, fused or not, are often very crooked and curved distally in their apical third. 5.3. Morphology of mandibular molars Mandibular first molars have five cusps, arranged in height from longest to shortest: mesiolingual, distolingual, mesiobuccal, distobuccal and a smaller distal cusp. Mandibular second molars have four cusps, in order from the longest to shortest – mesiolingual, distolingual, mesiobuccal and distobuccal. The crown of the mandibular second molar is usually smaller than that of the first molar. The mandibular first molar has the largest mesiodistal dimension of any tooth – 11.4 mm on the average. The mesiolingual cusp is highest and widest. The mandibular first molar usually has 3 buccal cusps (81%) – mesiobuccal, distobuccal and distal. The mesiobucal cusp is the largest, widest and highest cusp on the buccal side. The distobuccal cusp is slightly smaller, shorter, and sharper than the mesiobuccal cusp. The distal cusp is the smallest of the 5 cusps, and is missing in about 20%. The mesiobuccal groove separates the mesiobuccal cusp from the distobuccal cusp. Sometimes there is a deep pit at the cervical end of this groove. The distobuccal groove separates the distobuccal from the distal cusp. NB! In the mouth, the lingal cusp tips are at a lower level than the buccal cusps due to the lingual tilt of the root axis in the mandible. The mandibular second molar has 4 cusps – mesiobuccal, distobuccal, mesiolingual and distolingual. As on the first molar, the mesiobuccal cusp is usually 23  PRECLINICS OF PROSTHETIC DENTAL MEDICINE wider mesiodistally than the distobuccal cusp. The lingual cusp tips are visible from the buccal side. There is only one groove – buccal groove, that separates the mesiobuccal and distobuccal cusps, and extends to the middle of the buccal surface in a pit. Distal contacts more cervical than mesial contacts. The cervical line of both mandibuar molars runs nearly straight across the buccal surface. Both mandibular first and second molars have two roots, a mesial root and a distal root, approximately the same length. The roots are nearly twice as long as the crown. The root bifurcation of the mandibular first molar is near the cervical line, with a depression between them. The root trunk is shorter than on the second molars. The roots of the first molar are widely separated, on the second molar they are more parallel. The apical half of the roots curve distally. The distal root is straighter than the mesial root and may have a more pointed apex. The roots of the second molar are more pointed than the roots of the first molar. Both roots may curve distally, and the mesial one is slightly longer than the distal. Mandibular first and second molar crowns are narrower on the lingual side, more so on first molars. The lingual cusps of mandibular molars are both slightly longer and more pointed or conical than the buccal cusps, which are hidden behind them. The lingual groove separates the mesiolingual from the distolingual cusp, terminating on the lingual surface. The cervical line is relatively flat or irregular. From proximal - wide and short crowns. Mandibular molar crowns are relatively shorter cervico-occlusally compared to buccolingually. The crowns of both mandibular molars are tilted lingually from the root base – distinguishing mark for all mandibular posterior teeth. The crest of curvature of the buccal surface is in the cervical third. It is called the buccal cervical ridge (margo buccalis cervicalis), running in a mesiodistal direction on the buccal surface of the crown. The mesial marginal ridge is concave buccolingually, usually V-shaped on the second molar. The distal marginal ridge is more cervically located than the mesial one and it may have a groove crossing it. Roots: From the mesial aspect, the mesial root of the first molar is broad buccolingually, hiding the distal root. It has a blunt apex. On the second molar, the mesial root is less broad buccolingually, narrow in the cervical third, and with a more pointed apex. The mesial root always has two root canals – one buccal and one lingual. The distal root is shorter and more pointed at the apex. 24  PRECLINICS OF PROSTHETIC DENTAL MEDICINE From the occlusal aspect the shape of the second molar is rectangular, whereas the first molar is like a pentagon due to the small distal cusp. The two mesial cusps are larger than the two distal cusps. Considerable portion of the buccal surface is visible due to the lingual inclination of the crown. Both molars are wider mesiodistally than faciolingually. The crown tapers two ways – distally and lingually. This mark is helpful in distinguishing lefts from rights and mesial from distal. The widest buccolingual dimension of the crown is at the buccal cervical ridge. On both first and second molars, the triangular ridges of the mesiobuccal and mesiolingual cusps meet to form a transverse ridge. Another transverse ridge is formed by the triangular ridges of the distobuccal and distolingual cusps. There are three fossae on mandibular molars – large central fossa, mesial triangular fossa, and a small distal triangular fossa. The groove pattern on second molars resembles a cross. The central groove extends through the central fossa from the mesial triangular fossa to the distal triangular fossa. The buccal groove separates the mesiobuccal and distobuccal cusps and is usually continuous with the lingual groove that separates the two lingual cusps. Marginal ridge grooves occur more frequently on the mesial. Supplemental grooves are named according to their location. Supplemental ridges are positioned between major and supplemental grooves and serve as additional cutting blades. The grooves on the mandibular first molar separate five cusps and the pattern is more complicated. There are several grooves - the central groove is zigzag-shaped and extends through the central fossa from the mesial triangular fossa to the distal triangular fossa. The lingual groove extends lingually between the mesiolingual and distolingual cusps onto the lingual surface. The mandibular first molar has two buccal grooves – mesiobuccal groove and distobuccal groove, separating the three buccal cusps. There are numerous supplemental ridges and grooves named according to their location. The marginal ridges are crossed by a groove, more often on the mesial. In 19% the mandibular first molar has four instead of five cusps. The crown of the mandibular third molar resembles the crown of the first of second mandibular molar, but is extremely variable. It is generally characterized by a very convex crown and short roots. The lingual cusps are larger and longer than the buccal cusps. The mesiobuccal cusp is the largest of the buccal cusps. Irregular groove pattern with numerous supplemental grooves and pits on the occlusal surface that produce a wrinkled appearance. Occlusal otline – rectangular of oval mesiodistally, with small occlusal table. Two roots, mesial and distal, often fused together, more curved 25  PRECLINICS OF PROSTHETIC DENTAL MEDICINE distally compared to first and second molars and sometimes with extreme curvature. Frequently one or more extra roots. 6. Phylogenetic evolution of the masticatory system and the maxillofacial region. Ontogenetic development. Development and eruption of teeth – basic theories In biology Phylogenetics is the study of evolutionary relationship among groups of organisms (species and populations), which is discovered through molecular sequencing data and morphological data matrices. The term derives from the Greek terms “phyle” and “phylon” denoting “tribe” and “birth”. “Arthropods”–man, human and “ Logos” - is a science of humans in all the times and époques around all pleases of the Earth. In 1859 Darwin describes Neanderthals. Later in 1924 Magnon founds pithecanthropus erectus and Milford created human evolution model. Physical anthropology is one of the most important division of phylogeny and it is defined as a science of humans in biological aspect: origin, anatomy and physiology of the different nationalities. Other branches are paleontology, anthropometry and Forensic anthropology. Paleontology (from Greek is “old, ancient) is a study of fossils to determine organisms evolution and interactions with each other and their environments – paleoecology. As a historical science it explains causes rather than conduct experiments to observe effects. Body fossils and trace fossils are the principal types of evidence about ancient life, and geochemical evidence has helped to investigate the evolution of life before there were organisms large enough to leave fossils. The objects of investigation of paleodentistry are: teeth anatomy, skeleton variations, TMJ and cheek – bone alterations and craniometry. The specific parts are observations on Carabelli George cusp, spacing and diastemi; groves depths, dental crowns eminence and dental caries and erosions appeared in different types of humans. Construction of a phylogenetic evolution is regarded as a branching process, whereby populations are altered over time and may specialty into separate branches, hybridize together or terminate by extinction this may be visualized in a phylogenetic tree. Construction of a phylogenetic evolution is regarded as a branching process, whereby populations are altered over time and may speciate into separate branches, hibridize together or terminate by extinction this may be visualized in a phylogenetic tree. Medical antrhopology has a long lasting development. It can be described as follows: early ages before 4,5 Bill years characterized by the appearance of archeocraniobactery. Next époque obtains the period before 3,5 Bill years during which strmatolites and multicellular organisms are appeared. What is followed is Cambrial period. The evolution of fish, amphibias, reptilians, birds and mammals takes a long period after which, before about 65 MLN 26  PRECLINICS OF PROSTHETIC DENTAL MEDICINE years, evolution of primates have been started. The goal of anthropometry is measuring of physical characteristics of the people. The goal of Anthropometry is measuring of physical characteristics of the people. Phylogenesis (Phylum – order, class; genesis - origin) involves: Morphological characteristics of organisms into categories and periods Morphogenesis; Development and evolutionary history of species in taxonomic groups Origin and history of the evolution of species. Taxonomy is a classification, identification and naming of organisms richly informed by phylogenetics, but remains methodologically distinct. The fields of phylogenetics and taxonomy overlap in the science of phylogenetic systematics – one methodology used to create cladograms and delimit taxa ( clades). In biological systematic as a whole phylogenetic analyses have become essential in researching the evolutionary tree of life. Stoma, cartilage movable jaws, language and number of teeth (homodontia and polifiodontia) are the most often used futures for classification. Grouping of organisms is the main method – there are phylogenetic terms that describe the nature of a grouping in such trees. All birds and reptiles are believed to have descended from a single common ancestor so this taxonomic grouping is called monophyletic. The evolutionary connections between organisms are represented graphically trough phylogenetic trees. Due to the fact that evolution takes place over long periods of time that cannot be observed directly, biologist must reconstruct phylogenies of time inferring the evolutionary relationships among present – day organisms. Phylogenetic relationships in the past were reconstructed by looking at phenotypes, often anatomical characteristics. Today, molecular data, which molecules includes protein and DNA sequences are used to construct phylogenetic ranges. Paleogenesis gives us information about human organs evolution. For example : in Amphibians first mouth formation is founded, in Reptiles – the palate, bone and glands appear first, in Crocodile - they are developed cement and periodontium can be observed for the first time. Comparative anatomy as a part of Primatology investigating different humans types as: human from Paleocene age, Australopitecus from Africa, Parantropus , Neandertal, Homo erectus from Europe and Homo sapiens. Phylogenetics observes modern human epoques as Pleistocene, Upper Paleolitic, and Holocene. The beginning of real Human evolution has been started before 4,5 MLN. God. , when bipedal primates have been 27  PRECLINICS OF PROSTHETIC DENTAL MEDICINE appeared. This period is characterized by human brain evolution. Before 45,000 years the late glacial period have been developed. Cultural development, before 11,000 years, is a last period, involves industry, agriculture, science and mathematics evolution. This period is the beginning of contemporary urbanization. The study of human dentition have raised the interest not only of the Dental community, but also Paleontologists, Anthropologists, Geneticist and has focused their attention to dental anatomy and phylogenesis of human dentition as result of an evolutionary process. The main goal is to study comparative anatomy, dental phylogenesis and anthropology allows the dentist to understand present form and function of human dentition. The shape of human dentition reflects all functions. Human dento-maxiilary anatomy is the expression of the phylogenies evolution. Human primates are featured by their inkongruent TM joints and they are different in their acute angle of the articular heads. Ontogeny recapitulates phylogeny – the development of an organism exactly mirrors the evolutionary development of the species. This theory states that the embryo mirrors adult evolutionary. During the last 19th Century EH RTH was called biogenetic law, most widely accepted. Ontogenesis – its origin and development of the human organism as individuality starts its development after creation of variety of heories. The most important are listed: Darwin Evolution Theory, Remark Cells Theory and Ernst Haeckel statement - Ontogenesis is a repetion of the phylogenies concerning the digestive physiological function and reproducing. Hystory of the embrion is a base foundation of Embriology. Embryo drawings Romanes’S in 1892. Ontogenesis or morphogenesis – is the origin and development of an organism from the fertilized egg to mature form. Term comes from the Greek “onto” – to be and from “geny” – mode of production. Ontogeny is defined as the history of structural change in unity, which can be a cell, an organism, society of organisms, without the loss of then organization which allows that unity to exist. The Theory of recapitulation also called biogenic law or embryological parallelism often expressed as “ontogeny recapitulates phylogeny "is a hypothesis that in developing from embryo to adult, animals go trough stages resembling or representing successive stages in the evolution of their remote ancestors. Several periods are important for the dentists as : nonfunctional and functional periods of life, intrauterine life prenatal (nonfunctional), embrional period, stomadeum development period, Mandibular and Maxillary growths period, Primary embryonic undershot - up to 2 months and Fetal period, characterized by primary embryonic progeny. Functional periods are - period of secondary undershot, Orthognathic bite after break and to 6 months postnatal temporary dentition and Mixed dentition of 6-14 year. Teeth eruption is described by several theories as root theory, pulp theory, occlusal forces interaction, hormone kinetic theory and increased 28  PRECLINICS OF PROSTHETIC DENTAL MEDICINE hydrostatic theory. Tooth development or odontogenesis is the complex process by which teeth form embryologic cells, grow and erupt into the mouth. For human teeth to have a healthy oral environment, enamel, dentin, cementum and the perodontium must all develop during appropriate stages of fetal development. Primary ( baby) teeth start to form between the sixth and eight weeks, and permanent teeth begin to form in the twentieth week. The enamel organ is composed of the outer enamel epithelium, inner enamel epithelium, stellate reticulum and stratum intermedium. These cells give rise to ameloblasts, which produce enamel and the reduced enamel epithelium. The location where the outer enamel epithelium and inner enamel epithelium join is called the cervical loop. The growgth of cervical loop cells into the deeper tissues forms Hertwig’s Epithelial Root Shape. The removed permanent teeth is poisoned below the roots of primary teeth. 7. Dental wax modeling techniques. Addition wax modeling technique. Anatomical and functional wax modeling of tooth crowns on dental stone models. During central closure in the normal dentition the lingual cusps of the maxillary posterior teeth and the buccal cusps of the mandibular posterior teeth make contact with the occlusal fossae or the marginal ridges of the opposing teeth. They grind food like a mortar during mastication and are called functional (supporting) cusps. On the other hand, the buccal cusps of the maxillary molars and premolars and the lingual cusps of the mandibular posterior teeth do not contact the opposing teeth. These cusps prevent food from overflowing, confine food within the sulcus, and protect the buccal mucosa and the tongue by keeping them away from the functional cusps. Since these cusps do not make direct contact with opposing teeth, they are called nonfunctional cusps. The type, number and distribution of occlusal contacts is called an occlusal scheme. The occlusal scheme can be classified by the location of the occlusal contact made by the functional cusp on the opposing tooth in centric relation. There are two types of occlusal schemes: cusp-fossa and cusp-marginal ridge. - cusp-marginal ridge - the cusp-marginal ridge relation is the type of occlusal scheme in which the functional cusp contacts the opposing occlusal surfaces on the marginal ridges of the opposing pair of teeth, or in a fossa. Therefore, a cusp-marginal ridge occlusion is basically a one-tooth-to-two-teeth arrangement. This is the most 29  PRECLINICS OF PROSTHETIC DENTAL MEDICINE natural type of occlusion and is found in 95% of all adults. Since the majority of adults exhibit the cusp-marginal ridge type of occlusion, it is an occlusal pattern widely utilized in daily practice. It can be used for single restorations. The waxing technique used for cusp-marginal ridge occlusion was originally devised by E.V. Payne and was the first wax-added (addition) technique for functional waxing. The same technique, modified by the use of color-coded waxes, has become a widely used method for teaching functional waxing. - cusp-fossa - the cusp-fossa relation is an occlusal pattern in which each functional cusp is positioned (contacts) into the occlusal fossa of the opposing tooth. It is a tooth-to-tooth arrangement. Although considered to be an ideal occlusal pattern, it is rarely found in its pure form in natural teeth. Each centric cusp should make contact with the occlusal fossa of the opposing tooth at three points. The contact points are on the mesial and distal ridge (incline) and the inner facing incline of the cusp, producing a tripod contact. Since the cusp tip itself never comes in contact with the opposing tooth, the cusp tip can be maintained for a long time with a minimum of wear. The technique used for producing wax patterns with an exclusively cusp-fossa occlusion was developed by P.K. Thomas. It is important to keep in mind, however, that the same technique, utilizing the same sequence of morphologic development, can be used with excellent results for developing a cusp-marginal ridge occlusal relationship. When the cusp-marginal ridge arrangement is the desired end result, cusp placement is altered slightly. Occlusal forces are directed parallel to the long axis of the tooth. These forces are near the center of the tooth – placing very little lateral stress on the tooth. Since this type of occlusion is rarely found in natural teeth, it usually can be used only when restoring several contacting teeth and the teeth opposing them, as well as for full mouth reconstruction. The basic purpose of wax modeling and developing optimal occlusal contacts between the maxillary and mandibular dental arch is to reconstruct the lost anatomic shape and function without trauma to the supporting structures and with a uniform distribution of forces during mastication. All this depends on the type of occlusal scheme and the proper distribution of the occlusal contacts. A good restoration adapts perfectly to the prepared tooth and the gingival margin, restores the proximal contacts, the continuity of the dental arch, the interocclusal relationship and the lost harmony of the dental arch. With the wax modeling we restore (reconstruct) the shape, size, proportion and all characteristics of the destructed or completely lost tooth crown. In young persons, the purpose of wax modeling usually is 30  PRECLINICS OF PROSTHETIC DENTAL MEDICINE to restore the ideal anatomic shape and occlusal surface of teeth. In elderly persons we should take account of the functional alterations in tooth morphology – occlusal wear (abrasio dentis) and the evolution of the proximal contacts - contact points are gradually modified into contact surfaces. Wax addition technique provides a possibility to develop a functional occlusal morphology with convex elements and point interocclusal contacts. The finest details of the occlusal morphology are successfully reproduced – secondary grooves and ridges, on which the point occlusal contacts are positioned. The waxing instruments can be categorized by the intent of their design: wax addition, carving and burnishing. Of the popular PKT’s kit (set) of 5 tools: - № 1 and № 2 are wax addition instruments - № 3 is a burnisher for refining occlusal anatomy - № 4, № 5 are wax carvers Instruments № 1 and № 2 are used to guide the wax drop. Their working tips are arch-shaped and rounded, each with two diameteres - 0.6mm/0.9mm и 0.9mm/1.2mm. Wax is added by heating the instrument in the flame, touching it to the wax, and quickly reheating its shank in the flame. You should never heat the tip of the instrument the place to heat is about 1cm from the tip, for 2-3 sec. Wax flows away from the hottest part of the instrument, so that if the shank is heated, a bead of wax will flow off the tip. However, if the tip is heated, the wax will flow up the shank of the instrument. With these tools we develop all convex shapes (elements) of tooth morphology – cusps with cusp tips, cusp ridges (slopes, inclines) and marginal ridges. Modeling wax - inlay casting wax is the name given to all wax used in forming the pattern of cast restorations. It is composed of several waxes; paraffin is usually the main constituent (40%-60%). The remaining balance consists of dammar resin, carnauba, ceresin or candelilla wax to raise the melting temperature. It should be hard at room temperature. Dyes are added to provide color contrasts – usually 4 different colors: yellow, red, green and blue. Waxing with one-colored wax is not recommended, because the fine details of occlusal anatomy are unnoticeable. A step-by-step waxing technique is recommended. Each step is evaluated before proceeding to the next, which allows corrections and minimizes extra work. The finished wax patterns should be an accurately shaped anatomic replica of the original teeth. Information needed to shape the restoration correctly is derived from the contours of the adjacent teeth and tooth surfaces, and the opposing occlusal surfaces. However, you need a comprehensive knowledge of tooth anatomy and the ability to copy 3D structures accurately. 31  PRECLINICS OF PROSTHETIC DENTAL MEDICINE For your practical training first you will get a small study model, a tile, on which you will develop the three basic wax details, used in addition wax technique – a cone, an arch and a prism. The second study model has four cross-sections of the maxillary first premolar – the occlusal surfaces have been cut off (removed). The preliminary preparation of the model includes: a/ mark the sides or directions of the model – vestibular (buccal), lingual, mesial and distal b/ draw (trace) two lines perpendicular to each other, forming a cross and dividing each cross-section into 4 parts – buccal, lingual, mesial and distal. c/ determine the positions of the cones (corresponding to the cusps): the buccal cone is 0.5mm buccally to the midpoint of the segment OC; the lingual cone is 0.5mm lingual to the midpoint of the segment OD and slightly to the mesial. The tip of the lingual cusp is always positioned slightly mesial to the buccolingual line! This asymmetric design is a characteristic feature of the maxillary first premolar. Sequence of modeling steps The first step is to place cones for the buccal and lingual cusps with the №1 waxing instrument. The cusp tip itself never comes in contact with the opposing tooth, but should be accurately directed to the corresponding fossa or marginal ridge. The cones are usually about 2 mm in height, with the lingual cone being slightly shorter. 32  PRECLINICS OF PROSTHETIC DENTAL MEDICINE The second step is to form the buccal and lingual contour ridges of the cusps by adding wax to the buccal aspect of the buccal cone and the lingual aspect of the lingual cone. Then add the triangular ridges with the proper instrument (number 1). Each triangular ridge extends from the central groove to the cusp tip. They should be convex to allow for occlusal contact points positioned along the slopes. The cusp tip remains free from wax – do not add wax on the tip. The third step is to form the mesial and distal cusp ridges, first on the buccal cone, then on the lingual cone. 33  PRECLINICS OF PROSTHETIC DENTAL MEDICINE The inclines of the buccal cusp ridges should not touch the opposing teeth – they are nonfunctional cusps! On the cusp ridges of the lingual cusp, contacts should occur on the sides of the cone near the tip, but not actually on the tip itself. The fourth step is to form the marginal ridges by uniting the mesial and distal cusp ridges. The height of the marginal ridges is determined by the height of the cusp tips of the opposing teeth. The last stage is the final forming of the grooves, fossae and ridges. Supplemental anatomy is formed by the junction between triangular ridges and adjacent cusp ridges or marginal ridges. Use the PKT instrument № 5 to refine the ridges, and smooth the grooves with a PKT instrument № 3. Do not carve the grooves with these instruments. The central groove is sharp-bottomed, and the buccal and lingual developmental grooves, as well as the supplemental grooves are round-bottomed grooves. The development of the occlusal anatomy of molars usually includes 22 stages, in a similar sequence. 34  PRECLINICS OF PROSTHETIC DENTAL MEDICINE First year students practice wax addition technique on study models prepared for modeling by themselves. The teeth for wax modeling are 11, 15, 17 and 31, 34, 36. 8. Functional anatomy of the masticatory system. Oral cavity. Salivary glands. Bones of the masticatory system: maxilla and mandible. Innervation of the masticatory system 8.1. Oral cavity, salivary glands The oral cavity is bounded anteriorly by the lips, laterally by the cheeks, superiorly by the palate and inferiorly by the floor of the mouth. The oral cavity can be devided into two segments: - oral vestibule – the space between the dental arches and lips / cheeks - oral cavity proper – the internal segment beyond the dental arches and alveolar processes The oral cavity is lined with the oral mucous membrane, made up of two layers – stratified surface epithelium and the underlying connective tissue. The palate and alveolar process are covered with a toughened layer of keratinized mucosa. The mucosa of the cheeks and floor of the mouth is thin and has no keratin layer. The upper and lower lips are the borders of the mouth, joining at the left and right commissure. The upper lip is bounded by the cheeks at the nasolabial groove, and by the nose. The lower lip is also bounded laterally by the cheeks, and inferiorly by the labiomental groove. 35  PRECLINICS OF PROSTHETIC DENTAL MEDICINE The nasolabial groove is running diagonally on each side of the nostril toward the corner of the lip. The labiomental groove is a horizontal groove between the lower lip and the chin. Vermilion border is the red transitional zone of the lips, where they merge into labial mucosa. Mucocutaneus margin of the lips is the junction between vermilion border and the skin of the face. Tubercle is a small rounded nodule of tissue in the centre of the upper lip. The depression running from the tubercle to the nostrils is named philtrum. The vestibular fornix is the depth in mandible or height in maxilla, of the vestibule. The labial frenum is a thin sheet of tissue that attaches the centre of the upper or lower lip to the mucosa between the central incisors. The buccal frenum, in the premolar area, loosely attaches the cheek to the mucosa of the jaw. The buccal frena are moved by the facial muscles to various directions in eating, and can dislodge complete denures. The horizontal line running posteriorly on each side of the cheek mucosa at the level of the commissural area is called the linea alba buccalis – buccal white line. The parotid papilla (left and right) is a round elevation of tissue in the upper vestibule, next to the first and second molars. These papillae cover the duct opening from the large parotid glands located in front of each ear. They produce 23-33% of our saliva (serous type). The gingiva is that part of the oral mucous membrane that covers the jaw bone, and surrounds the cervical portions of the teeth. Gingival margin (margo gingivalis) is the occlusal (incisal) border at which the gingiva meets the tooth. Usually the gingival margin approximately follows the curvature of the cervical line, it is usually at the same level as the cervical line and the neck of the tooth is tightly embraced by the gingival margin. The tongue is a broad, flat organ composed of muscle fibers and glands. It rests in the floor of the mouth within the curvature of the body of the mandible. The posterior one-third on the tongue is the tongue root or tongue base. It has numerous functions – principal organ of taste, invaluable for speech, mastication, swallowing. The dorsal surface (dorsum) of the tongue is covered by two kinds of papillae: filiform papillae – most numerous, hair-like, covering the anterior two-thirds of the dorsum. The fungiform papillae have a round mushroom shape, deep red colour, larger, scattered and located near the tip of the tongue. Foliate papillae are large, red, leaf-like, found on the lateral surfaces of the tongue in the posterior one-third. 36  PRECLINICS OF PROSTHETIC DENTAL MEDICINE The circumvallate papillae are 8 to 12 large, flat papillae that form a V-shaped row on the dorsum near the posterior third of the tongue. Contain numerous taste buds. The ventral surface of the tongue is shiny and blood vessels are visible. The lingual frenum is a thin sheet of tissue that attaches the center of the tongue to the floor of the mouth. Sublingual folds, called plica sublingualis, are located on each side of the floor of the mouth, between the first molars and the lingual frenum. Here are the openings of ducts from underlying sublingual salivary glands. They secrete purely mucous saliva, producing 5-8% of our saliva. In the center line at the junction between the right and left sublingual folds on either side of the frenum, is a pair of sublingual caruncles, each with an opening from ducts of salivary glands. They drain the larger, more posteriorly located submandibular glands,which produce about two-thirds of our saliva. Mandibular torus is a bulbous protuberance of bone beneath a thin mucous membrane covering on the lingual side of the mandible, usually found in the premolar region. A similar torus may occur in the middle of the palate – torus palatinus. The hard palate is the firm anterior part of the roof of the mouth, ending opposite the third molars and immediately anterior to foveae palatinae. The movable part of the roof of the mouth, just posterior to the hard palate, is called the soft palate. Incisive (nasopalatine) papilla is the small rounded elevation of tissue on the midline just lingual to the central incisors. Palatine raphe (raphe palatinum) – slightly elevated center line running anteroposteriorly in the hard palate. The mucosa over the raphe is firmly attached to the underlying periosteum. There are numerous salivary glands beneath the mucosa on both sides, in the posterior third of the raphe. Palatine rugae (rugae palatinae) are a series of elevations, running from side to side, on the anterior portion of the palate, from the palatine raphe. They function as tactile sensing objects and in production of certain speech sounds. Uvula is a small soft tissue structure hanging from the center of the posterior border of the soft palate. Vibrating line – the place or line where the beginning of the soft palate can be observed. Foveae palatinae (Latin) – a pair of pits in the soft palate, on etither side of the center line, just posterior to the vibrating line. They areo openings of ducts of minor palatine mucous glands. 37  PRECLINICS OF PROSTHETIC DENTAL MEDICINE 8.2. Bones of the masticatory system: maxilla and mandible 8.2.1. Maxilla The osseous structures supporting the teeth are the maxilla and the mandible. The maxilla, or upper jaw, consists of two bones – a right maxilla and a left maxilla sutured together at the median line. Both maxillae are joined to other bones of the head. Each maxilla is an irregular bone, which consists of a body and four processes – the zygomatic, frontal, palatine, and alveolar processes. The maxilla is hollow and contains the maxillary sinus air space. The body of the maxilla has the following four surfaces: anterior or facial, infratemporal, orbital and nasal. Several landmarks on this bone are among the most important, including the incisive fossa, canine eminence, infraorbital foramen, posterior alveolar foramina, maxillary tuberosity, pterygopalatine fossa, and incisive canal. The zygomatic process is a roughly triangular eminence whose apex is placed inferiorly directly over the first molar roots. The lateral border is rough and spongelike in appearance, where it has been disarticulated from the zygomatic or cheek bone. The frontal process arises from the upper and anterior body of the maxilla. Part of it is formed by the upward continuation of the infraorbital margin medially. Its edge articulates with the nasal bone. Superiorly, the process articulates with the frontal b