Introduction to Dental Anatomy and Physiology PDF

1 2   Dental anatomy is defined as the study of the development, morphology, function, and identity of each of the teeth in the human dentitions, as well as the way in which the teeth relate in shape, form, structure, color, and function to the other teeth in the same d...

1 2   Dental anatomy is defined as the study of the development, morphology, function, and identity of each of the teeth in the human dentitions, as well as the way in which the teeth relate in shape, form, structure, color, and function to the other teeth in the same dental arch and to the teeth in the opposing arch  Formation of the Dentitions: Humans have two sets of teeth in their lifetime. The first set of teeth to be seen in the mouth is the primary or deciduous dentition, which begins to form prenatally at about 41 weeks in utero and is completed postnatal at about 3 years of age. In the absence of congenital disorders, dental disease, or trauma, the first teeth in this dentition begin to appear in the oral cavity at the mean age of 3, and the last emerge at a mean age of 82 ± 1 months. The deciduous dentition remains intact (barring loss from dental caries or trauma (it is composed of 82 teeth). Until the child is about 3 years of age at about that time the first succedaneous or permanent teeth begin to emerge into the mouth. The emergence of these teeth begins the transition or mixed dentition period in which there is a mixture of deciduous and succedaneous teeth present. The transition period lasts from about 3 to 48 years of age ( ugly duckling stage)it is a transient phase and ends when all the deciduous teeth have been shed {Shedding it is a physiological process for elimination of deciduous teeth by resorption of their roots prior to eruption of their permanent successors}. At that time the permanent dentition period begins. Thus, the transition from the primary dentition to the permanent dentition begins with the emergence of the first permanent molars, shedding of the deciduous incisors, and emergence of the permanent child because of habits, missing teeth, teeth of different colors and hues, 3 crowding of the teeth, and malposed teeth.The permanent, or succedaneous, teeth replace the exfoliate deciduous teeth in a sequence of eruption that exhibits some variance After the shedding of the deciduous canines and molar emergence of the permanent canines and premolars, and emergence of the second permanent molars, the permanent dentition is completed (including the roots) at about 41 years of age, except for the third molars, which are completed at 42 to 82 years of age. In effect, the duration of the permanent dentition period is 48+ years. The completed permanent dentition consists of 38 teeth if none are congenitally missing. Functions of teeth 4-Mastication  Food needs to be broken down and chewed before entering the digestive system so that our body can easily absorb nutrients from them.  Incisors is suitable for incising food  Canine is for tearing  Premolars help in tearing and grind food partialy  Molars for griding food. 2-Speech  Teeth can help us pronounce accurately. 3-Appearance:-  Teeth can help us look better by giving us a good profile. 4-Growth of jaws:-  Deciduous teeth can reserve spaces for permanent teeth. Once the permanent teeth start to erupt, the deciduous teeth will fall out and give room for permanent teeth (play role in growth and maintenance of jaws bone). 4  Nomenclature:-  The first step in understanding dental anatomy is to learn the nomenclature, or the system of names, used to describe or classify the material included in the subject  The term mandibular refers to the lower jaw, or mandible  The term maxillary refers to the upper jaw, or maxilla  The term Primary dentition, deciduous dentition, milk tooth, Also called baby tooth, deciduous tooth they indicate a first dentition  The term succedaneous, permanent, adult, secondary used to describe, permanent dentition.  Dental formula:- It refers to the types and number of teeth The denomination of each tooth is often represented by the initial letter in its name (e.g., I for incisor, C for canine, P for premolar, M for molar). Each letter is followed by a horizontal line and the number of each type of tooth is placed above the line for the maxilla (upper jaw) and below the line for the mandible (lower jaw). The formulae include one side only, with the number of teeth in each jaw being the same for humans. The dental formula for the primary/deciduous teeth in humans is as follows: This formula should be read as: incisors, two maxillary and two mandibular; canines, one maxillary and one mandibular; molars, two maxillary and two mandibular— or 42 altogether on one side, right or left 5 A dental formula for the permanent human dentition is as follows: Premolars have now been added to the formula, two maxillary and two mandibular, and a third molar has been added, one maxillary and one mandibular. (fig4) Maxillary and mandibular arches 6  Fig(8) A deciduous, or primary, dentition. B, permanent dentition. 7  (fig3) The quadrants of dental arch 8 Tooth Numbering Systems:- In clinical practice some ―shorthand‖ system of tooth notation is necessary for recording data. There are three different numbering systems used to identify the teeth in dentistry 1-Palmer Notation System:- In 4282. Palmer published the symbolic system ,The symbolic system is most often referred to as the Palmer notation In this system the arches are divided into quadrants with the entire dentition being notated as follows:-The deciduous teeth are referred by alphabetic letters A. For Central incisor B. For lateral incisor C. For Canine D. For first molar E. For second molar 9 ┘ In upper right └ In upper left ┐ In lower right ┌ In lower left The Zsigmondy/Palmer notation for the permanent dentition is a four- quadrant symbolic system in which, beginning with the central incisors, the teeth are numbered 4 through 2 in each arch. For example, the right 3 maxillary first molar is designated as ┘ , and the left mandibular central incisor as ┌4. The Palmer notation for the entire permanent dentition is as follows: The mouth is divided into four sections called quadrants.The numbers 4 through.The numbering runs from the center of the mouth to the back. In the upper right quadrant tooth, number 4 is the incisor.The numbers continue to the right and back to tooth number 2, which is the third molar.The numbers sit inside an L-shaped symbol used to identify the quadrant. 11 2-Universal Numbering System This system adopted by the ADA and is in use by most general dentists today. Tooth number 4 is the tooth farthest back on the right side of your mouth in the upper (maxillary) jaw. Numbering continues along your upper teeth toward the front and across to the tooth farthest back on the top left side number 43.The numbers continue by dropping down to the lower (mandibular) jaw. Number 48 is the tooth farthest back on the left side of your mouth on the bottom. Numbering continues again toward the front and across to the tooth farthest back on the bottom right side of your mouth number 38. 11 3-A two-digit system (FDI):- This System uses a two-digit numbering system in which the first digit represents a tooth's quadrant and the second digit represents the number of the tooth from the midline of the face. For permanent teeth, the upper right teeth begin with the number, "4". The upper left teeth begin with the number, "8". The lower left teeth begin with the number, "3". The lower right teeth begin with the number, "1". For primary teeth, the sequence of numbers goes 2, 3, 8, and 2 for the teeth in the upper right, upper left, lower left, and lower right respectively. When speaking about a certain tooth such as the permanent maxillary central incisor, the notation is pronounced ―one, one‖, the two digits should be pronounced separately so, the deciduous upper left second molar is 32(six five). 12  For the premenant teeth For deciduous teeth 13 Macro-anatomy of the tooth Each tooth composes of crown and root portion. The crown is covered with enamel, and the root portion is covered with cementum Figure (1) Maxillary central incisor (facial aspect). A, Apex of root; R, root; CL, cervical line; C, crown; IE, incisal edge.  Anatomical crown -: That portion of the tooth which is covered by enamel.  Clinical crown: That portion of the tooth which is visible in the mouth. The clinical crown increase throughout life, while the anatomical crown is a constant value.  Anatomical root: That portion of the tooth which is covered with cementum.  Clinical root: That portion of the tooth which is in visible in the mouth. The clinical root is a changing entity, while anatomical root is constant The clinical root may or may not correspond to the anatomical root 14  Fif(2) The root:- The roots of the teeth may be single or multiple. Both maxillary and mandibular anterior teeth have only one root each. Mandibular first and second premolars and the maxillary second premolar are single rooted, but the maxillary first premolar has two roots in most cases, one buccal and one lingual. Maxillary molars have three roots, one mesiobuc-cal, one distobuccal, and one lingual. Mandibular molars have two roots, one mesial and one distal. 15 Fig(3) Schematic drawings of longitudinal sections of an anterior and a posterior tooth. A, Anterior tooth. A, Apex; AF, apical foramen; SC, supplementary canal; B, bone; C, cementum; PM, periodontal ligament; PC, pulp canal; G, gingiva; GC, gingival crevice; GM, gingival margin; PCH, pulp chamber; D, dentin; E, enamel; CR, crown. B, Posterior tooth. A, Apices; PC, pulp canal; PCH, pulp chamber; PH, pulp horn; F, fissure; CU, cusp; CEJ, cementoenamel junction; BI, bifurcation of roots. 16  Tissues Of The Tooth The tooth has three types of hard tissue enamel,dentin, cementum& One type of soft tissue at the inner side of the tooth called pulp. -Hard tissues: 4. Enamel: the hard, mineralized tissue which covers the dentin of the anatomical crown of a tooth. 8. Dentin: the hard tissue which forms the main body of the tooth. It surrounds the pulp cavity, and is covered by the enamel in the crown, and by the cementum in the anatomical root. 3. Cementum: the hard, bonelike tissue which covers the dentin of the anatomical root.. Its main job is to help attach the root of the tooth to the bone in the socket (and the jaw) A ligament cushions between the cementum and the jaw bone which further secures the tooth to the bone The periodontal ligament is a connective tissue; it contains blood vessels, nerves and bundles of collagen fibers. It is sensitive to pressure and damage. You may experience pain if you are grinding your teeth as this puts pressure onto the periodontal fibers 1-dental pulp is a connective tissue organ containing a number of structures, among which are arteries, veins, a lymphatic system, and nerves. Its primary function is to form the dentin of the tooth. When the tooth is newly erupted, the dental pulp is large; it becomes progressively 17 Smaller as the tooth is completed. The pulp is relatively large in primary teeth and also in young permanent teeth.the teeth of children and young people are more sensitive than the teeth of older people to thermal Change and dental operative procedures (heat generation) The opening of the pulp cavity at the apex is constricted and is called the apical foramen. The pulp keeps its tissue-forming function (e.g., to form secondary dentin), especially with the advance of dental caries toward the pulp. The pulp cavity becomes smaller and more constricted with age. 5-Cemento Enamel junction:- The cementoenamel junction (CEJ) visualized anatomically as the cervical line, the following several types of junctions are found: 4-The enamel overlapping the cementum. 8- An end-to-end approximating junction, 3-The absence of connecting enamel and cementum so that the dentin is an external part of the surface of the root, and 1- Overlapping of the enamel by the cementum these different junctions have clinical significance in the presence of disease (e.g., gingivitis, recession of the gingiva with exposure of the CEJ, loss of attachment of the supporting periodontal fibers in periodontitis); cervical sensitivity, caries, and erosion; and placement of the margins of dental restorations. 18 Anatomical Land Marks of the Crown:- In order to study an individual tooth we must be able to recognize all landmarks of importance by name, these include: 1. Cusp It is an elevation on the occlusal surface of the premolars , molars and incisal portion of the canine Fig (8) landmarks on the maxillary first molar. BCR, Buccocervical ridge; BG, buccal groove; MBC, mesiobuccal cusp; SG, supplemental groove; TF, triangular fossa; MLC, mesiolingual cusp; DG, developmental groove; DLC, distolingual cusp; OR, oblique ridge; DMR, distal marginal ridge; DBC, distobuccal cusp; CF, central fossa. 19 Fig(2) Maxillary right lateral incisor (lingual aspect). CL, Cervical line;CI, cingulum (also called the linguocervical rìdge); MR, marginal ridge; IR, incisal ridge; LF, lingual fossa. B, Mamelons on erupting, noncontacting central incisors. 8- Tubercle: It is a smaller elevation on some portion of the crown produced by an extra formation of enamel. These are deviations from the typical form Fig(9) showing Tubercle 21 3. Cingulum: - a smooth rounded prominence it is the lingual lobe of the anterior teeth makes up the bulk of the cervical third of the lingual surface. Fig(42) showing the cingulum 4. Ridge: it is any linear elevation on the surface of a crown and is named according to its location ( e.g. buccal ridge, incisal ridge, marginal ridge). a.Marginal ridge: these are rounded borders of enamel that formed mesial and distal margins of the occlusal surfaces of premolars and molars and the mesial and distal margins of the lingual surfaces of the incisors and canines. b.Triangular ridge :- these descend from the tips of the cusps of molars and premolars toward the central part of the occlusal surfaces. They are so named because the slopes of each side of the ridge are inclined to resemble two sides of a triangle. They are named after the cusps, to which 21 they belong, e.g. the triangular ridge of the buccal cusp of the maxillary first premolar. c.Transverse ridge: it is the union of two triangular ridges crossing transversely the surface of a posterior tooth. d.Oblique ridge: it is a ridge crossing obliquely the occlusal surfaces of maxillary molars. It is formed by the union of the triangular ridge of the disto-buccal cusp and the distal cusp ridge of the mesio-lingual cusp. 5.Fossa: it is an irregular depression or concavity.a- Lingual fossae: are on the lingual surface of incisors b-Central fossae: are on the occlusal surface of molars. They are formed by the convergence of ridges terminating at a central point in the bottom of the depression where there is a junction of grooves c.Triangular fossa: it is located on the occlusal surfaces of molars and premolars, mesial or distal to marginal ridges. 6.Sulcus: it is a long depression or valley in the surface of a tooth between ridges and cusps, the inclines of which meet at an angle. A sulcus has a developmental groove at the junction of its inclines. 7- Developmental groove: is a shallow groove or line between the primary parts of the crown or root, Buccal and lingual grooves are developmental grooves found on thebuccal and lingual surfaces of posterior teeth. 22 8-supplemental groove: is less distinct, is also a shallow linear depression on the surface of a tooth, but it is supplemental to a developmental groove and does not mark the junction of primary parts. 9.Pit: it is a small pinpoint depression located at the junction of developmental grooves or at terminals of those grooves, e.g. central pit is a term used to describe landmark in the central fossa of molars where developmental grooves join. 42.Mamelon: it is any one of the three rounded protuberances found on the incisal ridges of newly erupted incisor teeth. 11. Lobe: it is one of the primary sections of formation in the development of the crown. Cusps and mamelons are representative of lobes 23  Fig(44) showing mamelones Fig(48) showing occlusal surface of molars 24  Fig(43) Mesial view of a maxillary right first premolar. MR, Marginal ridge;2, sulcus traversing occlusal surface;CR, cusp ridge;ßCR, buccocervical ridge. B, Occlusal view of maxillary right first premolar. CR, Cusp ridge; TR, triangular ridges; Trans R, transverse ridge, formed by two triangular ridges that cross the tooth transversely. C, Occlusal view of a maxillary right first molar. Trans R, Transverse ridge; TR, triangular ridge; P, pit formed by junction of developmental grooves; 2G, supplemental groove; DG, developmental groove; TR, triangular ridge. 25 Fig(41)MMR: mesial marginal ridge. DMR: distal marginal ridge. MP: mesial pit. DP: distal pit. CP: central pit. CDG: central developmental groove. 26  Fig(42)General outlines of some of the lobes. A, Labial aspect of maxillary central incisor, showing the labial grooves marking the division of the lobes. 4, Mesial lobe; 8, labial lobe; 3, distal lobe. The lingual lobe, or cingulum, is not in view. B and E, Mesial and occlusal aspects of maxillary first premolar. 4, Mesial lobe; 8, buccal lobe; 3, distal lobe; 1, lingual lobe. C, Occlusal aspect of mandibular first molar. 4, Mesiobuccal lobe; 8, distobuccal lobe; 3, distal lobe; 1, mesiolingual lobe; 2, distolingual lobe. Lobes on molars are named the same as cusps. D, Occlusal aspects of maxillary first molar. 4, Mesiobuccal lobe; 8, distobuccal lobe; 3, mesiolingual lobe; 1, distolingual lobe; 2, fifth lobe (fifth cusp). 27  Tooth Surfaces There are seven tooth surfaces most commonly used. Three of the surfaces are used on all tooth types, while the use of the remaining surfaces is dependent on the tooth type. All Tooth Types Posterior Only Anterior Only Distal(D) – tooth Incisal(I) – side cutting/biting farthest from the edge of midline(proximal the tooth surface) Lingual(L) – Buccal(B) – Facial(F) or tongue front/cheek side (labial) – side of the tooth the tooth front/visible side of of the tooth the tooth Mesial(M) –side closest to the midline of the tooth (proximal surface) 28 Mesial Surface of a tooth that is closest to the midline of the mouth. This term is used on both anterior and posterior teeth. Distal Surface of the tooth that is farthest from the midline of the mouth. This term is used for both anterior and posterior teeth. Facial (Labial):-Surface of a tooth that faces or touches the lips and it represents the outer surface on an anterior tooth. Buccal:- Surface of a tooth that faces or is towards the cheeks. This term can be used on all maxillary teeth and mandibular posterior teeth. Lingual:- Surface of a tooth that faces or is towards the roof of the mouth or tongue. This term is used on all mandibular teeth. It can also be used on all maxillary teeth (anterior and posteriors) and can be used interchangeably With the term palatal. Occlusal:- Surface of the tooth that is the chewing or occluding surface on a posterior tooth. Incisal:-Surface on a tooth that is the biting surface on an anterior tooth. 29  Fig (43) surfaces of the tooth 31  Division into Thirds, Line Angles, and Point Angles For purposes of description, the crowns and roots of teeth have been divided into thirds, and junctions of the crown surfaces are described as line angles and point angles. When the surfaces of the crown and root portions are divided into thirds, these thirds are named according to their location.these thirds are named according to the areas which they are near to. 4-Horizontally :-(occlusocervically or incisocervically) This is for the crown and apico cervically for the root. Crown:- Occlusal or ncisal middle,cervical thirds. Root:- cervical, middle,apical thirds. 8-Mesiodistally:-Mesial,middle,distal thirds. 3-Labio or buccolingualy:Crown: labial or buccal ,middle and lingual thirds. 31  \ Fig (48) Division of the teeth into thirds 32 A line angle is formed by the junction of two surfaces and derives its name from the combination of the two surfaces that join. For instance, on an anterior tooth, the junction of the mesial and labial surfaces is called the mesiolabial line angle. Because the mesial and distal incisal angles of anterior teeth are rounded, mesioincisal line angles and distoincisal line angles are usually considered nonexistent. They are spoken of as mesial and distal incisal angles only. A point angle:- It is formed by the junction of three surfaces. The point angle also derives its name from the combination of the names of the surfaces forming it. For example, the junction of the mesial, buccal, and occlusal surfaces of a molar is called the mesiobucco-occlusal point angle. -The line angles of the posterior teeth are as follows: mesiobuccal distolingual Buccoocclusal distobuccal mesio-occlusal linguoocclusal mesiolingual disto-occlusal -The line angles of the anterior teeth are as follows: mesiolabial distolingual distolabial labioincisal mesiolingual linguoincisal 33 -The point angles of the anterior teeth are : mesiolabioincisal mesiolinguoincisal distolabioincisal distolinguoincisal -The point angles of the posterior teeth are mesiobucco-occlusal mesiolinguoocclusal distobucco-occlusal distolinguo-occlusal 34  Fig(42)Point angles on anterior teeth. B, Point angles on posterior teeth. 35  Development and Eruption/ Emergence of the Teeth Tooth development can bedivided into 3 phases: 4) Initiation — the sites of the future teeth are established, with the appearance of tooth germs along an invagination of the oral epithelium called the dental lamina. 8) Morphogenesis — the shape of the tooth is determined by a combination of cell proliferation and cell movement. 3) Histogenesis — differentiation of cells forms dental tissues, both mineralized (enamel, dentine, cementum) and unmineralized (dental pulp, periodontium). Fig(82)Stages of tooth development 36 Eruption:- the term eruption was used to denote the tooth’s emergence through the gingiva. Emergence of the primary dentition takes place between the sixth and thirtieth months of postnatal life. It takes from 8 to 3 years for the primary dentition to be completed, beginning with the initial calcification of the primary central incisor to the completion of the roots of the primary second molar The emergence of the primary dentition through the alveolar mucous membrane is an important time for the development of oral motor behavior and the acquisition of masticator skills Calcification of the primary teeth It begins in utero from 43 to 43 weeks postfertilization. By 42 to 82 weeks, all the primary teeth have begun to calcify. Primary tooth crown formation takes only some 8 to 3 years from initial calcification to root completion. However, mineralization of the permanent dentition is entirely postnatal, and the formation of each tooth takes about 2 to 48 years. The variability in tooth development is similar to that for eruption, sexual maturity, and other similar growth indicators Crown formation of the primary teeth It continues after birth for about 3 months for the central incisor, about 1 months for the lateral incisor, about 8 months for the primary first molar, about 2.2 months for the canine, and about 42.2 months for the second primary molar. During these periods before and after birth, disorders in shape, pigmentation, mineralization, and structure sometimes occur 37  Fig(84)Development of the human dentition to the sixth year. The primary teeth are the darker ones in the illustration. 38 39  Fig(88)Development of the human dentition from the seventh year to maturity. Note the displacement of the primar 41  SURFACE ANATOMY OF PERMANENT TEETH The maxillary permanent incisors General features:-  The maxillary incisors are four in number  The maxillary central incisors are centered in the maxilla, one on either side of the median line, with the mesial surface of each in contact with the mesial surface of the other  The maxillary and mandibular central incisors are the only neighboring teeth in the dental arches with mesial surfaces in contact  The maxillary central incisor is larger than the lateral incisor.  The incisors are shearing or cutting teeth. Their major function is to punch and cut food material during the process of mastication  Maxillary Central Incisor -The maxillary central incisor is the widest mesiodistally of any of the anterior teeth - The labial face is less convex than that of the maxillary lateral incisor or canine, which gives the central incisor a appearance. -The maxillary central incisors are the most prominent teeth in the mouth Chronology:- First evidence of calcification 3-4 mo Enamel completed 1-2 yr Eruption 8-2 yr Root completed 42 yr 41 Labial surface:-  The crown of the average central incisor will be 42 to 44 mm long from the highest point on the cervical line to the lowest point on the incisal edge.  The labial surface is convex and flattend incisally  Labial surface shows two shallow developmental grooves that divide it into three lobes  The mesial outline of the crown is slightly convex  The distal outline of the crown is more convex than the mesial outline  The incisal outline is usually regular and straight in a mesiodistal direction after the tooth has been in function lon enough to obliterate the mamelons.  The mesioincisal angle is sharp and nearly form right angle  The distoincisal angle is rounded  The distal contact area is more cevically  The mesial contact area is near the mesioincisal angle Lingual Aspect:-  The lingual outline of the maxillary central incisor is the reverse of that found on the labial aspect  The lingual aspect has convexities and a concavity  Below the cervical line a smooth convexity found called the cingulum.  Mesially and distally confluent with the cingulum are the marginal ridges which extend to the incisal ridge.  The lingual fossa is shallow concavity present between the marginal ridges and the cingulum. 42 Mesial Aspect:-  The crown form is wedge-shaped, or triangular,with the base of the triangle at the cervix and the apex at the incisal ridge  The incisal ridge of the crown is on a line with the center of the root  The labial outline of the crown convex in the cervical third and slightly covex or flat in the middle and incisal thirds  The lingual outline is convex at the crest of at the cingulum; it then becomes concave at the mesial marginal ridge and slightly convex again at the linguoincisal ridge and the incisal edge.  The cervical line outlining the cementoenamel junction(CEJ) is convex toward the incisal edge  The contact area located at the mesioincisal angle. Distal Aspect:-  Little difference is evident between the distal and mesial outlines of this tooth  The crown is thicker toward the incisal third.  The curvature of the cervical line outlining the CEJ is less distal than on the mesial surfaces 43  Incisal Aspect:-  The labial face of the crown is relative broad and flat in comparison with the lingual surface, especially toward the incisal third.  The outline of the lingual portion tapers lingually toward the cingulum.  The cingulum of the crown makes up the cervical portion of the lingual surface.  The crown of this tooth shows more bulk from the incisal aspect(mesiodistal dimension is greater than labiolingual dimensions)  The lingual fossa is seen as broad concavity between the two margina l ridges and incisal to the cinglum. Fig(83) Maxillary right central incisor, lingual and incisal aspects. The labioincisal edge [LIE (4)] and linguoincisal edge [LIE (8)] border the incisal ridge. CL, Cervical line; C, cingulum; MMR, mesial marginal ridge; LF, lingual fossa; DMR, distal marginal ridge 44  Fig (81) Showing maxillary central incisors 45  Maxillary Lateral Incisor The maxillary lateral incisor supplements the central incisor in function, the crowns has close resemblance to the maxillary central incisor.  The lateral incisor is smaller in all dimensions than maxillary central incisor except for root length . Maxillary lateral incisors vary in form more than any other tooth in the mouth except the third molar. If the variation is too great, it is considered a developmental anomaly. A common situation is to find maxillary lateral incisors with a nondescript, pointed form; such teeth are called peg-shaped laterals First evidence of calcification 11-12 mo Enamel completed 4-5 yr Eruption 8-9 yr Root completed 11 yr -Labial Aspect:-  the labial aspect of the maxillary lateral incisor appear similar to that of the central incisor  The mesial outline of the crown from the labial aspect resembles that of the central incisor, with a more rounded mesioincisal angle. 46   The distal outline of the crown from the labial aspect differs somewhat from that of the central incisor The distal outline is always more rounded  The disto incisal angle is more rounded than the mesio incisal angle.  The labial surface of the crown is more convex than that of the central incisor  This tooth is relatively narrow mesiodistally, usually about 8 mm narrower than the central incisor.  The developmental grooves are less prominent than that in central incisor.  The mesial contact area is near or at the junction of incisal and middle thirds  The distal is located more cervically -Lingual Aspect:-  From the lingual aspect, mesial and distal marginal ridges are well marked  The cingulum is usually prominent  Deep developmental grooves within the lingual fossa  The lingual fossa is more concave and circumscribed than that found on the central incisor.  The cingulum encloses a palatal pit 47 -Mesial Aspect:-  The mesial aspect of the maxillary lateral incisor is similar to that of a small central incisor  The crown is shorter  The curvature of the cervical line is marked in the direction of the incisal ridge  the labiolingual measurement of the crown and root is less than that of the maxillary central incisor Distal Aspect:-  The width of the crown distally appears thicker than it does on the mesial aspect.  The curvature of the cervical line is usually less in depth than on the mesial side. -Incisal Aspect:-  It resembles that of the central incisor except in size  All maxillary lateral incisors exhibit more convexity labially and lingually from the incisal aspect than do the maxillary central incisors  If palatal pit is present it seen in the depth of the lingual fossa. 48  Fig(82)Maxillary right lateral incisor. 49  The Permanent Mandibular Incisors  The mandibular incisors are four in number.  The mandibular central incisors are centered in the mandible, one on either side of the median line, with the mesial surface of each one in contact with the mesial surface of the other.  The central incisor is somewhat smaller than the lateral incisor which is the reverse of the situation in the maxilla.  Mamelons on the incisal ridges are worn off soon after eruption Leaves the incisal ridges smooth and straight Mandibular Central Incisor:- Chronology First evidence of calcification 3-4 mo Enamel completed 4-5 yr Eruption 6-7 yr Root completed 9 yr Labial surface:-  The labial aspect of the mandibular central incisor is regular, tapering evenly from the relatively sharp mesial and distal incisal angles to the apical portion of the root( trapezoid)  The labial aspect of the mandibular central incisor is regular tapering evenly from the relatively sharp mesial and distal incisal angles ,giving the crown fan shape.  the mesial and distal outlines of the crown make a straight drop downward from the incisal angles to the contact areas  the contact areas, which are incisal to the junction of incisal 51  and middle thirds of the crown  The mesial and distal sides of the crown taper evenly from the contact areas to the narrow cervix.  newly erupted central incisors show few traces of developmental grooves. Fig(83)Mandibular right central incisor, lingual and incisal aspects. IR, Incisal ridge; DMR, distal marginal ridge; LF, lingual fossa; CL, cervical line; C, cingulum; MMR, mesial marginal ridge. Lingual Aspect:-  The lingual surface of the crown is smooth, with very slight concavity at the incisal third between the less developed marginal ridges  The lingual surface becomes flat and then convex as progression is made from the incisal third to the cervical third. 51   Mesial Aspect  The mesial aspect shows the typical outline of incisor tooth, even though the measurements are small  The curvature labially and lingually above the cervical line is less than that found on maxillary incisor  The outline of the labial face of the crown is straight above the cervical curvature, sloping rapidly from the crest of curvature to the incisal ridge.  The lingual outline of the crown is a straight line inclined labially for a short distance above the smooth convexity of the cingulum; the straight outline joins a concave line at the middle third of the crown, which extends upward to join the rounded outline of a narrow incisal ridge  The curvature of the cervical line representing the cementoenamel junction (CEJ) on the mesial surface is marked, curving incisally approximately one third the length of the crown.  Distal Aspect:-  The cervical line representing the CEJ curves incisally about 4 mm less on the distal aspect than on the mesial aspect  The distal surface of the crown of the mandibular central incisor is similar to that of the mesial surface  Incisal Aspect  The incisal aspect illustrates the bilateral symmetry of the mandibular central incisor. The mesial half of the crown is almost identical with the distal half. 52   The labial surface of the crown is slightly convex at the incisal third  The lingual surface of the crown is slightly concave at the incisal third  The crown tapers ligually ,therefore ,the labial out line is broader than thelingual outline. 53  Fig(88)Mandibular right central inciso 54 Mandibular Lateral Incisor: The mandibular lateral incisor is the second mandibular tooth from the median line, right or left. It resembles the mandibular central incisor so closely as with the mandibular central incisor, the shape of the lateral incisor is uniform compared with that of other teeth. Rarely, it will have a labial and lingual root division in the cervical third. Somewhat more commonly it has two canals in the single root. Chronology:- First evidence of calcification 3-4 mo Enamel completed 4-5 yr Eruption 7-8 yr Root completed 11 yr Labial and Lingual Aspects  The labial and lingual aspects show the added fraction of approximately 4 mm of crown diameter mesiodistally added to the distal half. This, however, is not always true. The lingual aspect of the mandibular incisors in some Mongoloid groups is marked by a deep but short cervicoincisal groove, which is vulnerable to dental caries  Mesial and Distal Aspects  The mesial side of the crown is often longer than the distal side; this causes the incisal ridge, which is straight, to slope downward in a distal direction. The distal contact area is more toward the 55  cervical than the mesial contact area to contact properly the mesial contact area of the mandibular canine.  Except for size, no marked difference is evident between the mesial and distal surfaces of central and lateral incisors. Even the curvatures of the cervical line mesially and distally are similar in extent.  A tendency exists toward a deeper concavity immediately above the cervical line on the distal surface of the mandibular lateral incisor.  Although the crown of the mandibular lateral incisor is somewhat longer than that of the central incisor (usually a fraction of a millimeter), the root may be considerably longer. Therefore in most instances the tooth is a little larger in all dimensions. The root form is similar to that of the central incisor, including the presence of developmental depressions mesially and distally.  Incisal Aspect  The incisal aspect of the mandibular lateral incisor provides a feature that can usually serve to identify this tooth. The incisal edge is not at approximate right angles to a line bisecting the crown and root labiolingually, as was found when observing the central incisor; the edge follows the curvature of the mandibular dental arch, which gives the crown of the mandibular lateral incisor the appearance of being twisted slightly on its root base. It is interesting to note that the labiolingual root axes of mandibular central and lateral incisors remain almost parallel in the alveolar process, even though the incisal ridges are not directly in line. 56  The Permanent Canines: Maxillary and Mandibular General features  The maxillary and mandibular canines bear a close resemblance to each other, and their functions are closely related. The four canines are placed at the "corners" of the mouth; each one is the third tooth from the median line, right and left, in the maxilla and mandible  They are commonly referred to as the cornerstone of the dental arches.  They are the longest teeth in the mouth; the crowns are usually as long as those of the maxillary central incisors, and the single roots are longer than those of any of the other teeth.  The middle labial lobes have been highly developed incisally into strong, well-formed cusps  Crowns and roots are markedly convex on most surfaces. The shape and position of the canines contribute to the guidance of the teeth into the intercuspal position by "canine guidance."  Because of the labiolingual thickness of crown and root and the anchorage in the alveolar process of the jaws, these teeth are perhaps the most stable in the mouth.  The crown portions of the canines are shaped in a manner that promotes cleanliness. This self-cleansing quality, along with the efficient anchorage in the jaws, tends to preserve these teeth . When teeth are lost, the canines are usually the last ones to go. They are very valuable teeth, when considered either as units of the natural dental arches or as possible assistants in stabilizing replacements of lost teeth in prosthetic procedures. 57   Both maxillary and mandibular canines have another quality that must not be overlooked: the positions and forms of these teeth and their anchorage in the bone, along with the bone ridge over the labial portions of the roots, called the canine eminence, have a cosmetic value.  The canines support the incisors and premo-lars, since they are located between these groups. The canine crowns have some characteristics of functional form, which bears a resemblance to incisor form and also to the premolar form. 58   Maxillary Canine:-  The maxillary canine is the third tooth from the midline. Labial Aspect  The outline of the crown is trapezoid with the smallest uneven side cervically.  The crown and root are narrower mesiodistally than those of the maxillary central incisor. The difference is about 4 mm in most mouths. The cervical line labially is convex, with the convexity toward the root portion).  Mesially the outline of the crown may be convex from the cervix to the center of the mesial contact area, or the crown may exhibit a slight concavity above the contact area from the labial aspect.  The center of the contact area mesially is approximately at the junction of middle and incisal thirds of the crown.  Distally the outline of the crown is usually concave between the cervical line and the distal contact area.  The distal contact area is usually at the center of the middle third of the crown. The two levels of contact areas mesially and distally should be noted  The cusp tip is on a line with the center of the root.  The cusp has a mesial slope and a distal slope, the mesial slope being the shorter of the two.  Both slopes show a tendency toward concavity before wear has taken place  The labial surface of the crown is smooth. 59   Shallow developmental depressions mesially anddistally,indicating fusion of the three labial lobes.  The middle labial lobe shows much greater development than the other lobes. This produces a ridge on the labial surface of the crown.  The root of the maxillary canine appears slender from the labial aspect when compared with the bulk of the crown; it is conical in form with a bluntly pointed apex.  Lingual Aspect:-  The outline form is similar to that of the labial surface.  The crown and root are narrower lingually than labially.  The cervical line from the lingual aspect differs somewhat from the curvature found labially and shows a more even curvature. The line may be straight for a short interval at this point.  The cingulum is large and, in some instances, is pointed like a small cusp.  well-developed lingual ridge runs from the cusp tip to the cigulum.  Shallow concavities are evident between this ridge and the marginal ridges. When these concavities are present, they are called mesial and distal lingual fossae.  Mesial marginal ridge is longer than the distal marginal ridge. Mesial Aspect  The mesial aspect of the maxillary canine presents the outline of the functional form of an anterior tooth. However, 61  it generally shows greater bulk and greater labiolingual measurement than any of the other anterior teeth.  The outline of the crown is wedge-shaped, the greatest measurement being at the cervical third and the wedge point being represented by the tip of the cusp.  The labial out line is convex from the cervical line to the cusp tip(more than that of the upper central incisor).the crest of curvature is at the cervical third.  The lingual outline of the crown from the mesial aspect is convex in the cervical third. The crest of the curvature is on the cingulum.in the middle third, The lingual outlineis slightly concave,then becoming convex again in the incisal tip.  The cervical line that outlines the base of the crown from this aspect curves toward the cusp on average by approximately 8.2 mm at the cementoenamel junction  The mesial surface of the canine crown presents convexities at all points except for a small, circumscribed area above the contact area, where the surface is concave and flat between that area and the cervical line.  Distal aspect:-  Similar to the mesial aspect except for  The cervical line has less curvature toward the cusp tip.  Distal marginal ridge is heavier and irregular in its outline.  Distal surface of the crown is more concave cervical to the contact area. 61  Incisal Aspect  In general, the labiolingual dimension is greater than the mesiodistal.  The tip of the cusp is labial to the center of the crown labio- lingually and mesial to the center mesiodistally.  The ridge of the middle labial lobe is very noticeable labially from the incisal aspect. It attains its greatest convexity at the cervical third of the crown, becoming broader and flatter at the middle and incisal thirds.  The cingulum well development makes up the cervical third of the crown lingually  The labial surface is covex more than the incisors. 62  Fig(82)Maxillary right canine. 63  Fig(89)Maxillary right canine, lingual and incisal aspects. CL, Cervical line; C, cingulum; MMR, mesial marginal ridge; MLF, mesiolingual fossa; MCR, mesial cusp ridge; DCR, distal cusp ridge; LR, lingual ridge; DLF, distolingual fossa; DMR, distal marginal ridge.. 64 Mandibular Canine:- Because maxillary and mandibular canines bear a close resemblance to each other, direct comparisons are made with the maxillary canine in describing the mandibular canine. First evidence of calcification 4-5 mo Enamel completed 3-8 yr Eruption 9-42 yr Root completed 48-41 yr Labial Aspect  From the labial aspect, the mesiodistal dimensions of the mandibular canine are less than those of the maxillary canine. The difference is usually about 4 mm.  The mandibular canine is broader mesiodistally than either of the mandibular incisors, for example, about 4 mm wider than the mandibular lateral incisor. The essential differences between mandibular and maxillary canines viewed from the labial aspect described as follows: The crowns of the mandibular canines appear longer. The mesial outline of the crown of the mandibular canine is nearly straight with the mesial outline of the root, with the mesial contact area being near the mesioincisal angle. 65  The cusp angle is on a line with the center of the root, as on the maxillary canine.  The mesial cusp ridge is shorter than the distal slope The distal contact area of the mandibular canine is more toward the incisal aspect than that of the maxillary canine but is not up to the level of the mesial area.  The mesial contact area in the incisal third just below the mesioincisal angle.  The cervical line labially has a semicircular curvature apically.  The distal outline is slightly concave in the cervical third,then it becomes convex incisally  The labial surface is smooth and convex.  Labial surface shows labial ridge that is not as prominent as on the upper canine.  Shallow vertical depressions may be present on either side of the labial ridge in the incisal third.  The incisal third of the crown is slightly flattend. Lingual Aspect In comparing the lingual aspect of the mandibular canine with that of the maxillary canine, the following differences are noted.  The lingual surface of the crown of the mandibular canine is flatter, simulating the lingual surfaces of mandibular incisors.  The cingulum is smooth and poorly developed.  The marginal ridges are less distinct.  The mesial marginal ridge is longer and straighter than the shorter distal marginal ridge. 66 Mesial Aspect From the mesial aspect, characteristic differences are evident between the two teeth in question.  The mandibular canine has less curvature labially on the crown, with very little curvature directly above the cervical line.  The lingual outline of the crown is curved in the same manner as that of the maxillary canine, but it differs in degree.  The cingulum is not as pronounced.  The incisal portion of the crown is thinner labiolingually, which allows the cusp to appear more pointed and the cusp ridge to appear more slender (pointed).  The tip of the cusp is more nearly centered over the root, with a lingual placement in some cases comparable to the placement of incisal ridges on mandibular incisors.  The cervical line curves more toward the incisal portion than does the cervical line on the maxillary canine. Distal Aspect Little difference from the distal aspect can be seen between mandibular and maxillary canines.  The distoincisal angle is slightly more lingual in position because of the distolingual twist of the crown.  The cervical line curvature is 4 mm less than that in the mesial side. 67 Incisal Aspect The outlines of the crowns of mandibular and maxillary canines from the incisal aspect are often similar. The main differences are as follows: The mesiodistal dimension of the mandibular canine is less than the labiolingual dimension. The cusp tip and mesial cusp ridge are more likely to be inclined in a lingual direction in the mandibular canine.  Labialy the masiolabial outline is more convex while the distolabial out line is flat or concave.  The crown tapers lingual and the cingulum is represented by curved line. Fig(32) Mandibular right canine, lingual and incisal aspects. MCR, Mesial cusp ridge; LR, lingual ridge; MMR, mesial marginal ridge; MLF, mesiolingual fossa; C, cingulum; CL, cervical line; DLF, distolingual fossa; DMR, distal marginal ridge; DCR, distal cusp ridge. 68  ‫الحمد هلل الذى تتم بنعمته الصالحات‬ ‫‪69‬‬