Complete Denture Prosthodontics PDF

Table of contents Chapter I: Introduction to Complete Denture …………….………2 Chapter II: Anatomical Landmarks …………………………….…...…6 Chapter III: Impression Trays and techniques………………..……...28 Chapter IV: Relief Areas…………………………...……….………..43 Chapter V: Record Base and occlusion rim …………..……..……. 55 Ch...

Table of contents Chapter I: Introduction to Complete Denture …………….………2 Chapter II: Anatomical Landmarks …………………………….…...…6 Chapter III: Impression Trays and techniques………………..……...28 Chapter IV: Relief Areas…………………………...……….………..43 Chapter V: Record Base and occlusion rim …………..……..……. 55 Chapter VI: Face Bow……………….. ……………………..……… 68 Chapter VII: Articulators…………………………………………... 70 Chapter VIII: SELECTION, of artificial teeth and WAXING-up.92 Chapter VIII: Processing Dentures ………………...………….…..110 1  Chapter 1 Introduction to complete denture Prosthetics: It is the art and science of designing, supplying and fitting artificial replacement for missing part of the human body. Prosthesis: Is the artificial appliance which replaces a lost part of the human body. Prosthodontics or Prosthetic Dentistry: It is a branch of dental science which deals with replacement of missing teeth and associated structures by using artificial devices to restore function and esthetics. Prosthodontics 1- Fixed prosthodontics. 2- Removable prosthodontics: a- complete denture b- partial denture 3- Maxillofacial prosthodontics. Removable Prosthodontics is the art and science of replacement of missing teeth and oral tissues with a prosthesis designed to be removed by the wearer. It includes removable complete and removable partial prosthodontics. Dentulous: A condition in which natural teeth are present in the mouth. Edentulous: A condition in which all natural teeth are lost. Partially Edentulous: A condition in which some of the natural teeth are lost. Retention: is a quality inherent in a prosthesis acting to resist dislodging forces along the path of placement. Stability is the quality of prosthesis to be firm, steady, or constant, to resist displacement by functional horizontal or rotational forces. 2 Support is the quality of prosthesis to resist vertical tissue ward force. Supporting area is the foundation area on which a dental prosthesis rests. Complete Denture Prosthodontics: Complete denture prosthodontics involves the replacement of the lost natural dentition and associated structure of the maxilla and mandible for patients who have lost all their natural teeth. Objectives of Complete Denture Prosthodontics 1- Restoration of the masticatory function. 2- Restoration of the normal appearance. 3- Correction of speech defects resulting from loss of natural teeth. 4- Preservation of the alveolar bone and tempromandibular joints. 5- Satisfaction and comfort of the patient. Denture surfaces Complete denture consists of denture base that rest on the supporting structure and to which an artificial teeth attached to it. It has three surfaces: 1-Fitting surface: (intaglio surfaces, impression surface) determined by the impression. 2-Polished surface: includes the facial (labial and buccal), lingual and palatal surfaces. 3-Occlusal surface: that makes contact with the opposing denture. Denture borders: The margin of the denture base at the junction of the polished and impression surface. 3 Denture flanges The vertical extension of the denture base that extends from the cervix of the teeth to the borders of the denture flanges; they are named according to location into: Labial flange: the portion of flange that occupies the labial vestibule. Buccal flange: the portion of flange that occupies the buccal vestibule. Lingual flange: the portion of mandibular denture flange that occupies the alveololingual sulcus. The differences between natural teeth and artificial teeth Natural Teeth Artificial Teeth Type of support The teeth are supported by All teeth are on bases and supported periodontal tissue which gives by mucosa which is not created to be support, positional adjustment of covered. teeth and proprioceptive response. Area of support in both jaws About 35 cm square of edentulous About 90 cm square. mouth. Amount of masticatory forces About 10- 15% of its value in natural From 5 - 17.5 pounds. dentition. Effect of masticatory forces The force is not directed to the entire The masticatory forces are alveolar bone but is applied only on transmitted to the bone in the form of its surface in the form of compression. tension through the periodontal This compression has limited 4 ligament. This tension is well accepted tolerance by the bone and may cause by the alveolar bone and may even alveolar bone resorption. service as stimulus for alveolar bone remolding Effect of pressure on teeth Each tooth receives individual Teeth move as a unit on a base. pressure and moves independently. Effect of non-vertical components of Cause trauma to the supporting tissue forces and reduce stability to the denture. Well tolerated. Incising forces Cause tipping of the denture base Not affect posterior teeth. especially if the teeth are not balanced articulated. Proprioceptive response The proprioceptive mechanism act as By the loss of natural teeth there is no a useful alarm protecting both the proprioceptive mechanism. supporting structures of the tooth and the substance of the crown from the effects of excessively vigorous masticatory movements. 5  Steps of Complete Denture Construction: Clinical Steps Laboratory Steps 1-History taking and examination of 3-Casting of the preliminary the mouth. impression (using plaster of Paris). -Preparing the mouth for dentures. 4-Construction of special trays. 2-Taking of preliminary impressions 6-Boxing in and casting of the final (in stock trays) impression (using dental stone). 5-Taking of final impressions (in 7-Construction of occlusion record special trays) and determining of the blocks. posterior 9-Mounting of the casts with the Palatal seal. record blocks on the articulator. 8-Recording of jaws relations, face 10-Setting-up of the teeth and waxing- bow transfer and selection of teeth. up. 11-Trying in the waxed denture. 12-Processing of the denture 15-Registration of new centric (Flasking, wax elimination, packing, relation andface bow transfer for curing and deflasking). clinical remount 13-Laboratory remounting of the (If needed). denture and correction of occlusion 17-Delivery of the finished denture by selective grinding. and instruction for their use. 14-Finishing and polishing. 18-Review of the denture (inspection 16-Remount of the denture on and aftercare). articulator for adjustment of occlusion (if needed). 6 Factors Influencing the Outcome of Prosthetic Treatment The successful outcome of prosthetic treatment depends upon (1) The dentist – who makes a diagnosis, prepares a treatment plan and undertakes the clinical work. (2) The dental technician – who constructs the various items which terminate in the finished dentures. (3) The patient – who is faced with coming to terms with the loss of all the natural teeth and then of having to adapt to the dentures and accept their limitations. 7  Chapter 2 Anatomical Landmarks of Prosthetic Interest These are anatomical guides that help in denture construction. These landmarks are either bony landmarks or soft tissue landmarks. [ I ] Extra-oral Landmarks Of Prosthetic Importance 1- Inter-pupillary line Description - Imaginary line running between the two pupils of the eye when the patient is looking straight forward. Significance helps in establishing the anterior occlusal plane of the artificial teeth of the denture. 2- Ala-tragus line (Camper's line) Description - Imaginary line running from the Inferior border of the ala of the nose to the superior border of the tragus of the ear. Significance Help in establishing the posterior occlusal plane of the artificial teeth of the denture. 3- Canthus-tragus line Description - Imaginary line running from the outer canthus of the eye to the superior border of the tragus of the ear. Significance -Help in locating the position of the condyles. 8 4- Naso-labial sulcus Description - Depression that extends from the ala of the nose in a downward and lateral direction to the corner of the mouth. Significance The sulcus becomes more prominent with aging and due to loss of teeth and vertical dimension. It can be modified by proper degree of jaw separation and tooth positioning. Plumper’s (thick denture flanges) improve the condition but it may interfere with muscular activity. 5- Vermillion border Description - The transitional epithelium between the mucous membrane of the lip and the skin. The amount of vermillion border shown on the lips depends on 1-The bulk of the orbicularis oris muscle. 2- The amount of the labial alveolar bone. 3-The alignment of the anterior teeth. Significance After loss of teeth, the amount of vermillion border shown on the upper lip is reduced. The condition can be corrected by thickening of the labial flange of the denture and proper positioning of the anterior teeth. 6- Mento-labial sulcus Description - Depression runs horizontally between the lower lip and chin. Significance Its curvature indicates the character of the maxillomandibular relationship and the degree of over-closure.  Angle Class 1 normal ridge relationship: The sulcus shows a gentle curvature with obtuse angle  Angle class II (retruded mandibular relation): The sulcus forms an acute angle 9   Angle class III (protruded mandibular relationship): sulcus forms an angle of almost 180 7- Philtrum Description - It is a diamond shaped depression at the center of the upper lip and base of the nose. Significance After loss of teeth, the philtrum becomes flattened. This condition can be improved by construction of proper denture with an appropriate arch-form and tooth alignment. 8- Modiolus Description - The point of meeting of buccinator and other facial muscles distal to the angle of the mouth. The modiolus is held in position by the arch-form of the maxillary teeth. Significance With the loss of teeth the modiolus drops. The appearance can be improved by proper positioning of the maxillary teeth. Narrowing of the lower denture base related to the modiolus is usually necessary to avoid displacement 9- Angle of the mouth (commissure of the lips) Description - Point of meeting between the upper and lower lip. Significance - (Angular Chilitis): Inflammation and ulceration as a result of: 1- Prolonged edentulism. 2- ↓ vertical dimension of complete denture. 3- Vitamin B deficiency. 10 10- The Angle of the Mouth and the Outer Canthus of the Eye Significance The distance from the outer canthus of the eye to the angle of the mouth was used by Wills to determine the vertical dimension of the edentulous patient at rest by making the distance from the base of the nose to the lower edge of mandible equal to it. [II] Intra-oral landmark of prosthetic importance The denture foundation can be divided into: -Supporting structures. -Peripheral limiting or sealing areas Anatomic Landmarks of the Denture Bearing Area (supporting structures): In the Maxilla 1-The residual ridge and hard palate 2- The incisive papilla 3- The palatine rugae 4-Median palatine raphe 5- Maxillary tuberosity 6- Torus palatinus 7- Fovea palatinae 8- Incisive fossae 9- Canine eminence 10- Buttress of the zygomatic bone In the Mandible 1- Residual alveolar ridge 2- Retromolar pad 3- Internal oblique ridge (mylohyoid ridge). 11 4- External oblique ridge 5- Buccal shelf of bone 6- Mental foramen 7- Genial tubercles 8- Torus mandibularis Anatomic Landmarks that Limit the Periphery of the Denture (limiting structures): In Relation to Maxillary Denture 1- Labial frenum 2- Labial vestibule 3- Buccal frenum 4- Buccal vestibule 5- Pterygo maxillary notch (Hammular notch) 6- Vibrating line. In Relation to Mandibular Denture 1- Labial frenum 2- Labial vestibule 3- Buccal frenum 4- Buccal vestibule 5-Masseter muscle influencing area 6-Retromolar pad and inferior border of the ramus 7- Pterygomandibular raphe 8- Plato glossal arch 9- Lingual pouch 10-Mylohyoid muscle influencing area 12 11- Lingual frenum ANATOMIC LANDMARKS OF THE MAXILLA A] The Denture Bearing Area (Supporting Structures) Landmark Description Significance 1- Residual ridge - The portion of the - It covered by a dense alveolar process& it's soft connective tissue fibers tissue covering that so, it act as a 1ry stress remains after extraction. bearing area. 2-vault of the palate The vault of the palate has The moderately high U- different forms according shaped vault is the more to the pattern of common and is more development of the desirable for denture maxillary processes. The stability. palatal arch may be V shaped, U-shaped or flat. 3- Incisive papilla - Pear-shaped elevation - After extraction of teeth present in the midline it migrates to the crest of behind the 2 centrals. the ridge. - It should be relieved to avoid the burning sensation of the palate. 4- Palatine rugae area - It is irregular elevations - 2ry stress bearing area. 13  radiates from the midline - Prevent forward of the anterior part of the movement of the denture. palate. - If it is sensitive or prominent it should be relived. 5- Median palatine - The mucoperiosteum - When it is prominent it raphe that covers the median should be relieved. palatine suture. - Lack of relief cause: 1- rocking of the denture due to bone resorption. 2- Tissue ulceration. 3- Mid-line denture fracture 6- Maxillary tuberosity - Bony prominence - Aid in support, retention located posterior to the and upper 3rd molar. stability of the complete denture. - When it is large: 1- Relieved. 2- Modify the path of insertion.(unilateral enlargement). 3- Surgical removal. 7- Torus palatinus - Bony prominence - present in 20% of the 14  present at population. both sides of the midline - It should be: of the palate. 1- Relieved. 2- Surgical removal. 8- Fovea palatinae - Two openings of minor - It determines the salivary glands present in posterior both sides of the midline extension of the upper posterior to junction of complete denture to be hard 2mm and soft palate. posterior to it. 9- Incisive fossa It is a slight depression in the labial surface of the maxilla opposite the region previously occupied by the root of upper lateral incisor. 10-Canine eminence It is found in the labial surface of the maxilla. It is a rounded bulge at the corner of the mouth opposite the region previously occupied by the root of the maxillary canine. 10-Buttress (root) of the It is formed by the lower This area provides 15 zygomatic bone portion of the zygomatic excellent resistance to process of the maxilla vertical forces as which flares upward and It’s almost at right angles outward from the area to the occlusal forces. above the first - avoid vertical molar overextension in the first molar region, as mucosal injury may result from a sandwiching of the soft tissues between the denture border and the zygomatic process of the maxilla. With resorption the denture may require relief over it 16 B] Border structures that limit the periphery of maxillary denture Landmark Description Significance Maxillary labial frenum It is a fibrous band A labial notch must be covered by mucous provided in the midline of membrane that extends the denture border from the labial aspect of opposite to the frenum. the residual alveolar ridge This notch prevents to the lip. It may be single ulceration of the frenum or multiple and may be or displacement of the narrow or broad. denture. It contains no muscle so it can be surgically exiseced if it attach near the crest of the ridge. Labial vestibule The labial vestibule The labial flange of the extends in both sides maxillary denture between the labial frenum occupies the space and the buccal frenum. bounded by the residual alveolar ridge, and the lip. The major muscle in this area is orbicularis oris. Buccal frenum It is a fold or folds of It requires more clearance mucous membrane extend in the denture flange for from the buccal mucous its action. Inadequate 17  membrane provision for the buccal reflection towards the frenum or excess slope or crest of the thickness of the flange residual ridge. They vary distal to the buccal notch in size, number and can cause dislodgment of position. the denture. Buccal vestibule It extends from the buccal The thickness of the distal frenum to the hamular end of the buccal flange notch. It houses the of the demure must be buccal flange of the adjusted to accommodate denture between the ridge the coronoid process of and the cheek. the mandible; otherwise it will push the denture out of place Pterygomaxillary It is a depression lies It is used as a boundary of (hamular) notch between the pterygoid the posterior border of the hamulous posteriorly and maxillary denture. The the maxillary tuberosity tissue in this notch is anteriorly easily compressed and the It is a displaceable area post dam line of the upper about 2mm wide denture should be carried into this region to ensure an adequate peripheral seal. Bases short of the hamular notch will end on 18  the thin - nonflexible – tissue of the tuberosity and will consequently lack retention. Vibrating line of the The vibrating line is an This line is not well palate imaginary line drawn defined and is better across the posterior part described as an area rather of the palate that marks than a line. the beginning of motion The maxillary denture in the soft palate when the posterior end should patient says "ah.“ It extend to this line. extends from one hamular notch to the other. ANATOMIC LANDMARKS OF THE MANDIBLE A] The Denture Bearing Area (Supporting Structures) Landmark Description Significance 1- residual ridge - The portion of the - Don't used as 1ry stress alveolar process& it's soft bearing area → Covered tissue covering that by movable fibrous remains after extraction. connective tissue. - Don't Provide stability or support. 19 2- External oblique - Bony ridge running In the impression, the ridge downward and forward external oblique ridge from ramus to reach shows a groove. The mental foramen. impression should record the ridge 3- Buccal shelf area - Bony area extends - Used as 1ry stress between the external bearing oblique ridge and the area: residual ridge. The buccal 1- Perpendicular to the shelf area can range from vertical masticatory force. 4-6 mm wide on an 2- Formed from compact average mandible to 2- bone. 3mm or less in narrow 3- Provide support. mandible. 4- Mental foramen - It's located on the - Lack of relief → Buccal surface of the numbness of the lower mandible between the lip. roots of 1st and 2nd premolar. 5- Retromolar pad - Pear-shaped area located - Shock absorbent. distal to the lower 3rd - Gives retention not molar. support. It consists of mucous - Determine the level of 20  glands the , temporal tendon , fibers Occlusal plane. of The buccinators and superior constrictor muscle. 6- Torus mandibularis - Bony prominence - It should be: located at the inner 1- Relieved. surface of premolar area. 2- Surgical removal. 7- Internal oblique ridge - Irregular bony ridge of - It should be relieved (Mylohyoid ridge) median surface of the during complete denture mandible which the construction. Mylohyoid muscle attached. 11-Genial tubercle - Two bony projections - Represent the (Mental spine) present at the median attachment of geniohyiod surface of mandible at and genioglossus muscles. midline of each side of - If it's prominent, it symphesis. should be relieved. 21 B- Border structures that limit the periphery of mandibular denture Landmark Description Significance 1-mandibular labial It is a fibrous band A labial notch must be frenum covered by mucous provided in the midline of membrane that extends the denture border from the labial aspect of opposite to the frenum. the residual alveolar ridge This notch prevents to the lip. It may be single ulceration of the frenum or multiple and may be or displacement of the narrow or broad. denture 2- Labial vestibule The labial vestibule The labial flange of the extends in both sides mandibular denture between the labial frenum occupies the space and the buccal frenum. bounded by the residual alveolar ridge, and the lip. 3- Buccal frenum It is a fold or folds of It requires clearance in the mucous membrane extend denture flange for its from the buccal mucous action. Inadequate membrane reflection provision for the towards the slope or crest buccal frenum or excess of the residual ridge. Like thickness of the flange the labial frenum it distal to the buccal notch contains no muscle fibers. can cause dislodgment of They vary in size, number the denture. 22  and position. 4-Buccal vestibule It extends from the buccal It houses the buccal frenum to the Retromolar flange of the denture pad area. between the ridge and the cheek. 5-Masseter muscle The distobuccal comer of influencing area the mandibular denture must converge rapidly to avoid displacement due to contracting pressure of the masseter muscle 6-Lingual Vestibule It can be divided into three areas – Anterior vestibule/ sublingual crescent area/ – the middle vestibule/ mylohyoid area –the distolingual vestibule/ lateral throat form/ retromylohyoid fossa 7- The lingual pouch Lies at the distal end of Over extension of the the alveolingual sulcus. distolingual border of the The lingual pouch lower denture will cause boundaries: sore throat due to the 23  Medially; lateral aspect of pressure on the the tongue. palatoglossus arch Laterally;the inner surface muscles. of the mandible; The lingual flange of the Posteriorly; the lower denture should palatoglossus arch properly extend in this Anteriorly; the mylohyoid area to increase its muscle. retention. 8- Sublingual salivary Formed by the superior The lingual flanges of the gland area \ Sublingual surface of the sublingual lower denture should not folds glands and the ducts of extend in this area the submandibular glands. 9- Lingual frenum It is the anterior The denture borders attachment of the should be well rounded in undersurface of the this area. tongue to the floor of the A notch should be mouth in the midline. It is provided in the lingual very resistant, active and flange to avoid often wide. displacement of the lower denture. 10-pterygomandibular It is a raphe formed by the The distal extension of the Raphe buccinator muscle fibers mandibular denture is and the superior limited by the Pterygo- constrictor muscle of the mandibular pharynx. Raphe 24 11- Plato glossal The palato glossal arch is The distal end of the Arch formed mainly by the lingual flange is related to palato glossus the palate glossal arch. muscle. Over-extension of the lingual flange in this area will cause sore throat. Extra-oral Landmarks of Prosthetic Importance 25 Intra-oral Landmarks of Prosthetic Importance 26 27  Chapter 3 Impression Trays and Boxing Impression: a negative reproduction of the teeth and adjacent structures for use in dentistry. Impression material: any substance or combination of substances used for making an impression or negative reproduction Impression tray: a device used to carry the impression material into the mouth, maintaining it in position during setting, and supporting it during removal from the mouth and when casting the impression. A cast or model is a positive reproduction of the form of the tissue of the upper or lower arch, which is made in an impression. Preliminary cast: a cast formed from a preliminary impression for use in diagnosis or the fabrication of an impression tray [Diagnostic cast – study cast] Preliminary impression: a negative likeness made for the purpose of diagnosis, treatment planning, or the fabrication of a tray Final impression: An impression made for the purpose of fabricating prosthesis Master cast: A replica of the tooth surfaces, residual ridge areas, and/or other parts of the dental arch and/or facial structures used to fabricate a dental restoration or prosthesis.[Working cast – final cast] Stock tray: a prefabricated impression tray typically available in various sizes and used principally for preliminary impressions Custom tray: an individualized impression tray made from a cast recovered from a preliminary impression. It is used in making a final impression 28 Component parts The tray consists of a body and a handle. The body consists of a floor and flanges. The difference between the upper and lower trays is that the upper has a palatal portion while the lower has lingual flanges. Requirements of impression trays 1- They should be strong and rigid to avoid distortion of the impression on removal. 2- They should be smooth, clean and can be sterilized if they are not disposable. 3- They should confine the impression material and hold it in correct position in the mouth and cover the whole area of the jaw which is required for the impression. 4- They should allow for equal thickness of impression material over the entire fitting surface. 5- The flanges of the tray must reach the functional position of the sulci and frena but not displace them. 6- They should provide for mechanical locking of the impression material to the tray through rim-lock undercut or perforation. Otherwise, adhesives should be used for the elastic impression materials. 7- The stock trays should be available in different size and shapes. 8- They must be inexpensive. Types of impression trays 1- Stock trays. 2- Special, individual or custom trays. 29 I- Stock Trays These are ready-made trays available in different shapes and sizes. Types: 1- Size: Most commonly, they are supplied in small, medium, large and extra-large sizes. 2- The shape of the tray differs according to the case whether it is dentulous, edentulous or partially edentulous. For dentulous patients: The tray has flat floors, high flanges and the handle is in-line with the floor of the tray. The trays for dentulous patients may be perforated, rim-lock trays or water- cooled trays. For edentulous patients: The trays have round floor and short flanges to conform theshape of the ridge. The handle is bent in the form of L-shaped and joined at right angle to the floor of the tray to clear the lip and allows proper border moulding in the labial portion of the impression. For partially-edentulous patients: In this type, part of the tray has flat floor and high flanges in the dentulous area and the other part has rounded floor and short flanges in the edentulous area. 3- Material: The stock trays can be made from different materials Metallic: as nickel silver, stainless steel, aluminum tin Plastics: The plastic stock trays are usually disposable. 4- Stock trays may be perforated or rim lockfor hydrocolloid impression materials. Non perforated trays are used for compound. Water-cooled trays used for reversible hydrocolloid impression materials 30 Uses: The stock trays are used for making the preliminary impression. The tray must be selected to conform nearly the shape and size of the arch. Incorrect selection of the tray results in a distorted impression. Modification Some dentists prefer to modify stock trays to improve their fitness. These modifications include a- Bend the flanges to provide adequate space for impression material. b- Cut theflanges to accommodate for labial or buccal frena or to reduceover extended flanges. c- Modeling plastic may be used toimprove adaptation or to prolong the short flanges. Construction of primary, study or diagnostic casts: The study cast is made from the preliminary impression. The impression should not subject to pressure or tension. 1. The study cast is made by measure powder liquid ratios provided by the manufacturer's instructions appropriate to the models to be poured (approximately one part water to two parts plaster). 2. Mix the material thoroughly assuring that all dry stone is wet, and a smooth mixture with minimal bubbles is achieved. For best results, vacuum mixing is recommended. 3. Gently vibrate the plaster into the impression and allow it to set. 4. When the plaster has set, prepare a thick mix of plaster to form a base and invert the impression onto the plaster patty. Allow to set for at least one half hour. 31 5. Remove the impression tray and alginate and recover the diagnostic cast. In case of compound impression, the impression with the set plaster is immersed in warm water for few minutes to soften compound and facilitates removal of cast. 6. Adjust the peripheries of the diagnostic cast using the model trimmer. Spacer or shim The Special trays are either made directly on the study cast or made over a shim (spacer) to provide a room of even thickness in the special tray for the impression material. The thickness of the shim depends on the impression techniques to be used fortaking the final impression. Advantages of spacer: It provides a space of even thickness in the tray for the impression material. Thus; 1- Any dimensional change in the material will be equal throughout the impression. 2- The shape of the tissues may be recorded with minimal displacement. 3- In case of plaster impression, the suitable thickness will help in reassembling the fractured pieces. Methods of shim constructions a- Modeling wax 1-The outline of the denture bearing is penciled on the cast. The outline for wax spacer is drawn on the cast; the edges are usually 2 mm short of the tray borders 2- The cast is then dusted by talcum powder or immersed in a water for 10 minutes to prevent sticking of the softened wax to it. 3- One or two layers of the modeling wax are adapted evenly on the cast and are cut down to the denture outline. 32 The posterior palatal seal area on the maxillary cast is not covered with the wax spacer. Thus the tray will contact the posterior palatal seal to prevent the final impression material from sliding down into the pharynx. b- Molten wax The outlined cast is immersed in water for few minutes, and then the cast is dipped in molten wax (54.5° C) repeatedly until the desired thickness is built up on the cast. Three dips are usually sufficient to produce the spacer. The excess wax beyond the outline is trimmed away. The use of stops: Placing stops in the tray before checking and correcting the borders ensuring a uniform thickness of about 2–3 mm of impression material, and stabilizing the tray during impression taking. There are several ways that stops can be produced: (1) During construction of an acrylic tray in the laboratory. Windows are cut in the wax spacer at appropriate locations on the cast used to manufacture the impression tray. The stops are produced by the acrylic dough flowing into these windows and contacting the model. This is the preferred method of producingstops as it is accurate and saves chairside time. (2) At the chairside in the mouth. Tracing compound is applied to the tray and tempered in warm water to avoid burning the mucosa. The tray is then seated in the mouth to mould the tracing compound to the ridge tissues creating the required space between the tray and mucosa. (3) At the chairside on the cast. Tracing compound is applied to the tray as in (2) above and the tray is then seated on the dampened cast. This approach has the 33 advantage over method (2) in that it is easier to check visually that the tray is centered correctly on the ridge while the stops are being formed. II- Special trays The need for special trays The edentulous ridges show variation of shape, size and contours. In the same patient the ridge shows different amounts of resorption and irregularities which affect the shape and contour of the ridge. A stock tray can only fit the ridge in a very arbitrary manner, while a specially constructed tray permits even thickness of impression material. For this reason the special trays are used for making the final impression. Advantages of special tray It fits the arch more accurately. It provides even thickness of impression material. It minimizes tissue displacement and sore spots in the finished denture. It allows for proper extension of the flanges and facilitates border moulding which helps in better retention of dentures. the bulk of the impression material is reduced; this is more economic, more comfortable for patients. Materials used for special trays A - Metallic special trays B- Nonmetallic special trays 1- Acrylic resin 2- Shellac-base plates 3- Thermoset plastic vinyl sheets. 4- Compound impression 5- Old denture 34 Special trays are either made directly on the primary cast or made over a shim (spacer) prepared over the cast. A-Metallic special trays This type can be used for any impression materials, but it is required only when compound is to be used. Types: 1- Swaged: can be made by swaging nickel silver 2- Casted metal may be used in construction of special trays. An alloy of tin and lead or tin alone may be used for casting special trays. Swaged or casted metal special trays are not commonly used because the production of these trays is difficult, time-consuming and expensive. B- Nonmetallic special trays 1- Shellac base special trays Disadvantages of shellac special trays: 1- Low strength. 2- Easily distorted by load and temperature. 3- Improper adaptation to the cast. 2- Acrylic resin special trays This type of trays is mainly made from self-curing acrylic resin. It can also be made from heat-curing acrylic resin and Light-cure resins, but the use of heat- curing resin is more difficult and time consuming. Advantages of self-cure acrylic resin special trays: 1- Easier to make. 2- Rigid. 3- Can be easily trimmed. 35 4- Light in weight. 5- Can accept tracing material without Warpage. 3- Thermoset plastic vinyl sheets -A ready-made sheet used for construction of special trays by vacuum. -On the stone cast the undercuts are blocked and a shim is prepared by placing appropriate thickness of wet paper towels. -The cast is placed in its position on the vacuum machine. -Vinyl sheet is inserted in the frame located below the heat source. Heating should be continued until the sheet is softened and begins to sag. -The supporting frame carrying the softened sheet is lowered onto the cast and the vacuum is turned on to adapt the sheet. -The heater is turned off and the base is allowed to cool then removed and trimmed. -A cold cure acrylic handle can be fabricated. 4- Compound impression -Sometimes compound impressions are used as special trays after scraping the fitting surfaces and the flanges of the primary impression to provide space for the impression material. -A scraping of 2mm is sufficient for plaster, 0.5mm for zinc oxide eugenol “ ZOE” and 3-4 mm plus perforation is required for alginate. 5- Old denture The existing denture may be used as a special tray as in case of taking zinc oxide eugenol “ZOE” impression for relining or rebasing the denture. 36 Construction of Shellac base special trays -A shim is made then the depth of vestibule is outlined. -Block-Out Undercuts -The upper tray is made by softening an upper base plate over a flame and adapting it on the shim of the upper cast. -The palatal portion is adapted first and allowed to harden then followed by the outer portion. -The excess shellac is trimmed by scissors to the drawn outline and the edge is smoothed with file. -A handle is made by rolling softened piece of shellac and attaching it to the base of the tray on the anterior area in such a way that avoids distortion of the lip. -The mandibular tray is made by softening a lower base plate and adapting it on the shim of the lower cast, section by section. Excess materials are cut and the edges are rolled out to strengthen the tray. The handle is made in the same manner as the upper tray. Construction of self-curing acrylic special trays -A self-curing special tray may be adapted directly on the cast after blocking out the undercuts by plaster or wax. It may also be constructed over a shim depending upon the impression technique used. - Self curing resin dough is formed by mixing the polymer and the monomer. The dough is flattened to a sheet of 2-3 mm thickness. -This sheet is then adapted over the dusted cast or shim and trimmed to the previously drawn outline. -A resin handle is attached to the anterior region of the upper and lower trays. -When the resin is cured it is separated from the cast and spacer and the periphery is rounded and smoothed with stone. 37  Extension: 2 mm short of the peripheral role Construction of acrylic special trays with stops for mucostatic impression technique The construction of this tray is exactly the same as the usual acrylic trays except that for mucostatic impression technique, stops are made by perforating the shim. Four stops (4 mm squares), two in the anterior and two in the molar regions are usually made. Boxing-in the impression and making the casts: Boxing of impression Boxing-in an impression is the process of building up vertical walls around the final impression to produce the desired size and form of the base of model, preserve certain details of the impression and to keep the stone mix during vibration. Advantages of boxing 1-The borders of impression are preserved. 2-The thickness of the model can be controlled. 3-Since all the mixed stone can be vibrated, the model will contain fewer air bubbles and a stronger model will be produced. 4-It is time saving, because trimming may not be required. 5-Material is economized. Methods of Boxing: I- Wax Boxing Method: 1- On the maxillary impression: 38 A strip of square beading wax 5mm wide is placed around the periphery “buccal and labial” and luted at the non-critical edge (about 2 mm from the impression border) and parallel to it. The beading wax should not be extended across the posterior border of the impression. 2- On the mandibular impression A strip of square beading wax is placed around the entire periphery “buccal, labial and lingual” and luted at the non-critical edges of the impression. The tongue space in the lower impression is blocked with wax before boxing. This wax is attached to the impression at the level of the lingual beading wax to provide a flat lingual shelf in the master cast just below the lingual border on both sides. 3- A sidewall is then wrapped around each impression to contact the beading wax to form a cylinder. The vertical walls of the boxing are made of sheets of bees- wax. This wall should extend ½ inch (10 to 15 mm) above the impression and mainly made of boxing wax or base plate wax. The end of the wax walls is joined together with hot spatula. Wax boxing procedures cannot be used on impression made in hydrocolloid material because the material will not adhere to the impression or because the impression will be distorted. 2- Boxing-in the impression with Plaster of Paris and Pumice: The beading wax does not adhere to alginate and rubber base impression materials, so the plaster & pumice boxing mix is used: 1. A mix of half plaster and half pumice is made, poured on glass slab and smoothed by spatula. 39 2. The tray is placed with the under surface over the mix. The material is raised by the spatula to a height of 3-4mm below the border of the impression and of 5mm thick. 3. The mix around the impression is allowed to set and then it is removed from the slab and trimmed to the desired height and width. 4. Boxing wax is adapted to the impression to be 1cm above the borders and sealed to the outer surface of the mix. The exposed surface of the plaster and pumice is painted with separating medium. 5. Then a mix of stone is vibrated into the impression. Pouring the cast The stone is mixed carefully according to the manufacturer’s instruction and placed in small quantities into the boxed impression. The stone should be carefully vibrated after each pouring to avoid trapping air bubbles. The stone is allowed to set for 30-45 minutes, then the wax strap is removed and the model is carefully separated from the impression. Plaster of Paris is usually used for casting the preliminary impression, and the final impression should be cast into dental stone. Stock tray modification 40 Plastic perforated stock tray Create tissue stops Metallic stock trays Water cooled trays 41 Thermoset plastic vinyl sheets ---- acrylic special trays with stops Wax boxing Plaster of Paris and Pumice boxing 42  Chapter 4 Relief Areas Relief means release or elimination of pressure from a specific area in the denture-supporting structure. The mucous membrane covering the denture bearing area is varying in thickness, softness and sensitivity. So denture relieves are made to reduce pressure on the hard and the sensitive areas. Hard areas: Areas covered by thin mucoperiosteum are usually hard and require relief to avoid pain and/or rocking of the denture. The hard areas which require relief include: 1- Median palatine raphe. 2- Maxillary tuberosity if prominent. 3- Zygomatic process of the maxilla 4- Torus palatinus and torus mandibularis. 5- Mylohyoid ridge of the mandible. 6- Prominent genial tubercles 7- Any bony nodule. Relation between ridge and median palatine raphe If the alveolar ridge is covered by highly compressible mucosa, more relief than average is needed over the hard median palatine raphe. If the alveolar ridge is firm and the palate center is compressible, little or no relief is needed. Sensitive areas: Relief of pressure over sensitive areas is needed for patient comfort and to avoid pain. The sensitive areas requiring relief include: 1- Incisive papilla. 2- Enlarged rugae areas (especially when they are undermined). 3- Mental foramen areas (especially in flat lower ridges). 43 4- Crest of thin lower ridge. Methods of relief A- Automatic relief this type of relief can be obtained at the time of making the impression by using a muco-compression impression technique. B -Direct relief 1) In the impression The final impression is scrapped to the desired width and depth over areas corresponding to the hard or sensitive areas. This method is only used with plaster of Paris impression material. 2) On the cast (The commonly used method) The area to be relieved is outlined on the cast and covered by one or more layers of tin foils of the desired shape and thickness. The tin foil is burnished over the cast by a blunt instrument and fixed in place by cement. Depth and shape of the relief The depth of relief depends mostly upon resistance or yield of the area to be relieved as compared with that of the surrounding area. The shape of the relief is determined according to the extent of the hard or the sensitive areas. Generally, in the upper model the relief area will normally be pear-shapedwith the broadest part anteriorly. It should not extend to the crest of the ridge except over the incisive papilla. 44  On cast Relief Advantages of relief 1- Preventing pain and rocking of the denture and giving comfort to the patient. 2- Improving the denture stability. 3- Compensating for tissue displacement over the ridge during settling of dentures and due to ridge resorption, as resorption takes place mainly in the alveolar process and the central area of the palate changes very little throughout life. 4- Compensating for some technical discrepancies occurring during processing or repairing the denture. Relief in the maxillary denture compensates for the shrinkage of acrylic resin during processing. Shrinkage makes the upper denture slightly narrower across the tuberosities and higher in the palatal vault areas. 45 Disadvantages of relief It may affect the retention gained by accurate adaptation of denture base and oral tissue because there is no actual contact between denture base and the tissue at areas of relief. 46  Chapter 5 Posterior Palatal Seal (Post-damming) The posterior palatal seal area is that area of the soft tissue along the junction of the hard and soft palate on which pressure within the physiological limits of the tissue can be applied by the denture to aid in the retention of the denture. Post dam is a slight elevation at the posterior border of maxillary denture. The post-dam should be placed in the region of compressible tissue just distal to the hard palate, but it must be anterior to the vibrating line. Peripheral seal is the area of contact between the lip and cheek mucosa and the denture borders that prevent passage of air between the base and the tissues. The peripheral seal depends on proper extension (width and height) of the denture borders that fill the mucobuccal space and contact the cheek tissue laterally. There are no cheek tissues posteriorly to seal the denture border. Therefore, the posterior palatal seal is necessary. Functions of post-damming 1- Increases retention of the denture by atmospheric pressure. 2- It slightly displaces the soft tissue at the distal end of the maxillary denture to enhance the posterior border seal 3- Prevents air and food from getting under the denture 4- Decreases reflex irritation and gag by: a- Decreasing patient’s awareness of this area. b- Reducing the thickness of the denture base felt by the tongue. 47 5- Compensates for dimensional changes that are inherent in the laboratory procedures. 6- During taking the impression, the post dam acts as a guide for positioning the tray and prevents the impression material from sliding into the pharynx Dimensions of post-dam The post dam extends from the hamular notch on one side to the other hamular notch of the other side. The post dam is usually narrow in its central part (due to the posterior nasal spine), wider as it extends laterally on each side, and narrow again as it approaches the hamular notch to fade out behind the tuberosity called butterfly post dam or Cupid’s bow. The post dam should be wide to avoid cutting or irritating the tissues (about 4 mm wide in its widest part) the depth or thickness of the post dam should vary for different individuals and, for the same individual from the different parts. The average thickness is 1 mm. Depth of post-dam: The post dam is deepest at a point 1/3 of the distance from the posterior edge of the groove and the midpoint between the midline and hamular notches. It becomes gradually shallower anteroposteriorly and laterally. The depth or thickness of the post dam should vary in different individuals and different parts of the same mouth according to compressibility of the tissue. The mucosa at the midline of the palate is less compressible than that at the sides, so that the deepest area of the seal is located on either side of the midline (1.5-2 mm). Its depth is about 0.5 mm at the midline and at hamular notches. 48 CLASSIFICATION OF SOFT PALATE The width of the posterior palatal seal depends on the curvature of the soft palate. The soft palates are classified into three classes based upon the angle that the soft palate makes with the hard palate. -Class I; -The soft palate has a gentile curve and allows a broad post dam (5-6mm). -Class II; -The soft palate has a medium degree of curvature and allows for a medium width of the post dam (3-4 mm at the widest area). -Class III; -It is seen in conjugation with high V shape palatal vault. There is few mm separation of anterior & posterior vibrating line thus there is small PPS area & less retention. - The soft palate has abrupt curvature allows a narrow area for post damming (1-2 mm at its widest area). Vibrating lines The PPS lies between the anterior and posterior vibrating lines. It is an imaginary line across the posterior part of the palate marking the division between the movable and immovable tissues of the soft palate. This can be identified when the movable tissues are functioning It should be described as area not line Anterior vibrating line it`s located at the junction of attached tissues overlying the hard palate and slightly movable tissues of the immediately adjacent soft palate. This should not be confused with anatomic junction of hard and soft palate. 49  It can be located by instructing patient to say Ah in short vigorous bursts. This places the soft palate inferiorly at its junction with hard palate. Due to projection of posterior nasal spine the anterior vibrating line is not a straight line between the Hammular processes. Posterior vibrating line It is an imaginary line at the junction of tensor veli palatini muscle and muscular portion of soft palate. It is straight line It represents the demarcation between that part of soft palate has limited or shallow movement during function and the remainder of soft palate that is markedly displaced during functional movements. It can be visualized by instructing patient to say Ah in normal unexaggerated fashion. The posterior vibrating line marks the most distal extension of denture base. Determining the position of the post-dam The soft palate is divided into non-movable anterior part that is adjacent to the hard palate and movable posterior part. The operator first discovers the position of the vibrating line by asking the patient to say a prolonged “ah”, with the mouth widely opened, and noting the line from which the soft palate moves. The tissue in front of this line is exposed with a blunt instrument and the area of soft compressible tissue noted. For future reference it is useful to mark this line on the palate with an indelible pencil. The posterior border can be accurately located if it is possible to see the two small pits (fovea palatinae) one on eachside of the midline on the anterior part of the soft palate. The fovea is usually situated just anterior to the vibrating line thus marking the posterior limit of the denture. 50 The posterior palatal seal should extend from one hamular (Pterygomaxillary) notch to the other, following the contour of the hard palate anterior to the vibrating line. Methods of post-damming 1- FUNCTIONAL METHOD: This method is carried out at the time of impression making. After finishing the impression, postdam area will be determined and a strip of melted wax or low fusing compound is traced on the impression over the post dam area. The impression is seated in the mouth under gentle pressure until it hardens. Meanwhile, the patient is asked to raise the soft palate by breathing deeply from the nose. The added material will spread out and form a raised strip across the distal end of the impression. The final impression with the posterior border seal is carefully boxed and poured in stone. Advantages: 1-The displacement of the tissues is within its physiologic limit. Over compression of the tissues is avoided. 2-posterior palatal seal is incorporated in the trial denture base for added retention. 2- ARBITRARY METHOD: This method is carried out during jaw relation recording or at the try-in stage. The vibrating line is observed in the patient's mouth as the patient says a series of short "ah" and marked by indelible pencil. The trial denture base is inserted so the indelible pencil line marked on vibrating line of the soft palate will be transferred from the soft palate to the trial denture base, and then to the cast (The posterior limit of the post dam). 51 The tissues anterior to the vibrating line are palpated with a mouth mirror to determine their compressibility both in width and depth and marked with the indelible pencil, then transferred to the cast (The anterior limit of the post dam). The cast is then scraped to the desired depth and width. 3-SCRAPING OF MASTER CAST: This technique is the least accurate and un-physiologic as the technician attempts to place the posterior palatal seal. A line is drawn across the posterior border of the cast between the two hamular notches passing behind the fovea palatinae. Another line is drawn anterior to the first line in the shape of butterfly. The cast is scrapped by a sharp knife or carver to the post dam between these two lines. The post dam is usually narrow in its central part (due to the projection of posterior nasal spine), wider as it extends laterally on each side, and narrow again as it approaches the hamular notch to fade out behind the tuberosity. It is sometimes called butterfly (Cupid's bow) post dam. Damming of the lower denture A lower denture may be post-dammed at each distal extremity by slightly compressing the Retromolar pads. The amount of compression must be determined at the time of impression taking. ERRORS IN RECORDING OF PPS 1. UNDER EXTENSION This is the most common cause for poor posterior palatal seal. It may be produced due to one of the following reason:- 1. The denture does not cover the fovea palatina. 2. Improper delineation of the anterior & posterior vibrating line. 52 2. OVER EXTENSION 1. The denture base can lead to ulceration of the soft palate & painful deglutition. 2. The most frequent complaint from the patient will be that swallowing is painful& difficult. 3. The hamuli are covered by the denture base; the patient will experience sharp pain, especially during function. 4. The pterygoid hamuli must never be covered by the denture base. 5. The overextension can be removed with a bur & then carefully repolished. 3. UNDER POSTDAMMING This can occur due to improper head positioning & mouth positioning. E.g. the mouth is wide open while recording the posterior palatal seal the mucosa over the hamular notch becomes stretched. This will produce a space between the denture base & tissue. 4. OVER POSTDAMMING This commonly occurs due to excess scraping of the master cast. It occurs more commonly in the hamular notch region. Prevention: Reduction of the denture border with a carbide bur, while maintaining its convexity. CLASSIFICATION OF SOFT PALATE 53 FUNCTIONAL METHOD Scraping method 54  Chapter 5 Recording Bases and Occlusion Rims Record blocks are generally made of occlusion rims attached to well fit trial denture base. Recording bases It is used for recording maxillomandibular jaw relationships and for setting the artificial teeth. Requirements of an ideal recording base 1- Dimensionally stable, both on the cast and in the mouth. 2- They must be rigid and strong. 3- They must be well adapted to the cast and accurately fit the denture area. 4- They should retain their shape at mouth temperature. 5- They should have smooth and round borders. 6- They should be non-irritant 7- They should be easy to manipulate. 8- Easily contoured and polished 9- They should be of proper thickness not interfere with artificial teeth placement Types of recording bases I- Temporary recording bases These bases are used during the various steps and will later be replaced by the permanent denture base. The materials used for temporary bases are: 1- Shellac baseplate 2- Cold curing acrylic resin 3- Vacuum formed vinyl or polystyrene. 4- Baseplate wax. 5- Swaged tin baseplate. 55 II- Permanent recording bases It is the base of the finished denture. The materials used for permanent bases are: 1- Heat-curing acrylic resin 2- Casted metal (gold, chromium-cobalt alloy and chromium nickel). Temporary recording bases 1- Shellac baseplate It is a commonly used material for recording bases. Construction 1- All undercuts of the casts should be blocked out. 2- To prevent the shellac from sticking to the cast, the cast should be treated by one of the following methods: a- Dusting the cast with talcum powder b- Soaking the cast in water for few minutes c- Adapting a layer of tin foil (0.001 inch) to the cast. 3- The shellac is softened on a flame then adapted to the cast by wet fingers. The adaptation is started with the palatal portion of the maxillary cast or with the lingual surface of the mandibular cast followed by the crest of the ridge and the reflections. 4- The material is trimmed with scissors leaving approximately 5mm beyond the edge of the cast. 5- This excess is heated and folded to form a smooth rounded border. To increase strength and rigidity of shellac base plates, reinforcing wires should be embedded across the posterior palatal seal area for the upper trial denture base and in the lingual flange of the lower one. 56 Advantages 1- Easily and quickly made. 2- Stronger than wax. 3- Laboratory time is saved. 4- Inexpensive. Disadvantages 1- It is difficult to obtain good retention. 2- It is not adequately strengthened, distortion may occur when left for a long time in the mouth. 3- It is a brittle material. 4- The bond between the shellac base and the wax is less than that of acrylic base. 2- Cold-curing acrylic resin Non -Flasking method (Finger adapted dough method) 1- The cast is prepared by blocking out the undercuts with wax and applying a separating medium. 2- The auto polymerizing resin is mixed and allowed to reach the dough stage, then rolled to a sheet of 2-3 mm thick. 3- While the acrylic sheet is still soft, it is adapted to the cast and the excess resin is trimmed with sharp knife. 4- After polymerization has been completed, the acrylic base is removed and retrimmed with bur; the external surface of the resin base can be polished with wet pumice. 5- The thickness of the resin base over the crest of the ridge is reduced to about 1mm. 57 Flasking method 1- A wax is adapted to the cast and flasked. After setting of the investment material wax elimination is carried out. 2- An autopolymerizing resin is mixed in a glass jar and packed into the mold when it reaches the doughy stage, then the flask is closed. 3- Resin is allowed to polymerize under pressure for 20 to 30 minutes. 4- The base is removed from the flask, trimmed, and polished. This method requires considerable time for, fabrication and more costly. Advantages 1- They are strong and have accurate fit. 2- Do not soften or warp at mouth temperature. 3- They are not easily distorted 4- Any type of occlusal rims can be mounted to it. Disadvantages 1- The retention may be reduced due to blocking out of the undercuts on the cast. 2- They may take up space needed for setting the teeth, necessitating some grinding of the resin base in required areas. 3- Vacuum -formed vinyl or polystyrene 1- The cast is prepared by blocking out the undercuts. 2- The cast is placed in its position on the vacuum machine. 3- Vinyl or polystyrene sheet is inserted in the frame located below the heat source. 4- Heating should be continued until the sheet is softened and begins tosag. 5- The supporting frame carrying the softened sheet is lowered onto the cast and the vacuum is turned on to adapt the sheet. 6- The heater is turned off and the base is allowed to cool then removed and trimmed. The vacuum method is very easy, fast and gives accurate results. 58 4- Baseplate wax 1- The wax is softened over a flame and adapted. 2- Excess wax is trimmed and the borders are rounded. 3- A strengthening wire is adapted in the posterior palatal seal area of the upper base or incorporated into the lingual flange of the lower base to increase both the rigidity and the resistance to distortion. These types are used in conjunction with wax occlusal rim. To prevent the wax from sticking to the cast, talcum powder is applied to the cast. Advantages 1- Easily to construct. 2- Inexpensive. Disadvantages 1- It is softened and distorted at mouth temperature. 2- It does not withstand the pressure required for recording jaw relationship. 3- It is very weak and not commonly used. To increase stability and retention of shellac, resin, or wax-recording bases reline the recording base with soft liner, zinc oxide eugenol or light body rubber base. 5- Swaged tin base plate 1- Three tin layers of gauge (5) can be swaged one above the other on a metal die and trimmed to the proper extend. 2- The inside layers can be cemented together with wax or zinc oxide eugenol. Advantages 1- It does not warp at mouth temperature. 2- It gives a uniform thickness. 3- It has a suitable fitness. 59 Permanent denture bases 1-Heat-curing acrylic resin These recording bases are permanent and become part of the finished denture. Technique 1- The wax pattern of desired shape is directly adapted onto the cast without blocking out the undercuts. 2- The definite outlines are obtained and the pattern is invested in a flask. The wax is eliminated with hot water, and then tin foil substitute is applied. The mixed acrylic resin is packed into the mold and processed. 3- The denture base is removed from the cast and finished. 4- The artificial teeth are attached to the acrylic base by wax to form the trial denture. When satisfactory, the trial denture is flasked, processed and finished. Either cold-curing or heat-curing resin may be used to attach the teeth to the processed base. Advantages 1- The bases are rigid, accurate and stable. 2- It does not warp at mouth temperature. 3- The bond between the wax rim and the base is strong. 4- Any type of occlusal rim can be used. 5- Retention and stability can be tested in the mouth before finishing of the denture. Disadvantages 1- Time consuming 2- Warpage always occurs when acrylic resin is reprocessed. However, this can be prevented by attaching the teeth to the base by cold-curing acrylic resin. It is not advisable to finish the denture on these bases. 60 2- Cast alloys These recording bases are permanent and become part of the finished denture. Technique 1- Refractory casts are first prepared from the final cast. A wax pattern is formed, spurred, invested, burned out and the molten alloy cast into its mold. 2- On cooling, the casting is removed from the investment, finished and polished and then returned to the final cast. Occlusion rims are attached to these metal bases to register the jaw relationship. The artificial teeth are attached to the metal base by acrylic resin. Advantages 1- The bases are rigid, accurate and dimensionally stable. 2- They add more weight to mandibular denture and more thermal conductivity to maxillary denture. Disadvantages 1- They are more costly than other types of bases. 2- They require more time for fabrication. Occlusion Rims They are horseshoe shaped occluding surfaces attached to the temporary or final denture base for the purpose of recording jaw relations and arranging of teeth. The occlusion rims are used for: 1- Establishing maxillo mandibular jaw relations (vertical dimension and centric relation). 2- Establishing the proper lip and cheek support (fullness of the lips and cheeks). 3- Choice of teeth 61 a- High and low lip lines; the distance between each of them and the occlusal plane determines the length of the upper and lower teeth. b- Canine lines; determines the width of the maxillary anterior teeth. 4- Arrangement of the artificial teeth; occlusion rim helps in the determination of: a- The proper occlusal plane. b- The neutral zone and the shape of the arch. c- The labial surface of the teeth. d- Position of mid line of the arch for the correct placement of the central incisors. e- Generally the occlusion rims form the medium in which the teeth are set up. Types of occlusion rims: 1-Base plate wax rim: Procedures of construction: 1. Dry the record base thoroughly as wax will not adhere to a wet surface. Roughen the area of the record base where the wax will be adapted. 2. Uniformly soften a sheet of hard pink baseplate wax. Flame the wax on a Bunsen burner flame slowly by passing the wax quickly through the flame many times. When the wax is thoroughly softened, fold the wax in half. Continue to flame the wax to soften it. Repeat the folding and warming until the required roll is formed. 3. Form the wax into a horseshoe shape and adapt the wax to the record base over the ridge crest area. Begin at one posterior end and continue to the anterior and to the opposite end. 4. Seal it to the record base with molten wax using a hot spatula. Add wax as needed to contour the rim. Sticky wax can also be used to attach the occlusion rims. 62 5. The rim should approximate the position of the natural teeth. Remember the facial surfaces of the maxillary central incisors are 8-10 mm anterior to the center of the incisive papilla. The wax rim must be anterior to the crest of the maxillary ridge. 6. Use a heated wax spatula to develop a flat occlusal plane. 7. Adjust the height and width of the wax rims to the proper dimensions. 2-The composition (compound) rim: The use of compound rim is indicated when it is desired to obtain more than one jaw relation record or when Gothic arch tracing is to be taken. 3-Plaster and pumice rim: When a functional recording of mandibular movements are to be made, a mixture of plaster and pumice rims is used. In this technique the patient grind the maxillary and mandibular rims together and produces the occlusal plane conforming to the mandibular movements. Characteristics of occlusion rims: 1-The occlusion rims should be approximately the same size and shape as the natural teeth. 2- Wax rims are smooth and have a flat occlusal surface. 3-The occlusal rim must be centered buccolingually over and parallel to the residual ridge crest. 4- The occlusal rim is properly sealed to the baseplate without any voids 63 Dimension of Occlusal Rim 64  Chapter 6 Face-Bows It is a caliper like device that is used to record the relationship of the jaws to the TMJ. and to orient the cast in the same relationship to the opening axis of the articulator. Functions of face-bows: 1. Locate the terminal hinge axis by the use of a kinematic face bow. 2. Relate the maxillary cast to the transverse axis of the articulator in the same relationship as the maxilla is related to the mandibular hinge axis. Types of face-bows: A. kinematic face bow (mandibular, hinge axis locator) B- The arbitrary (maxillary) face bow) Basic components of the face bow U shaped frame Condylar or ear rod Bite fork Anterior reference point(optional) as orbital or nasion Locking clamps A. kinematic face bow (mandibular, hinge axis locator): This face bow aids in finding the kinematic center (terminal hinge axis) of the jaw opening. A-it is used to locate the true terminal hinge axis and transfer this record to the articulator when mounting the maxillary cast. However, use of it can aid in recording centric relation. 65 B-the fork of kinematic face-bow is attached to the mandibular occlusal rim. B- The arbitrary (maxillary) face bow: The maxillary face bow is the one more commonly used in the construction of complete dentures. It is used to record the position of the upper jaw in relation to the hinge axis and transferring the relation to a mounting instrument (articulator). It consists of a U- shaped metal bow with two graduated condylar rods, bite fork and a universal joint. It is either fascia or ear face bow. The ear face bow is arbitrary face bow using the external auditory meatus as the posterior reference point. According to the anterior reference point it may be either infraorbital or nasion. According to the intercondylar distance equilibrationit may be spring, calibrated condylar rod, or slidematic face bow. Errors in maxillary face bow record and transfer: 1. Movement of part of the face bow caused by incomplete tightening of one of the locking screw. 2. Inadequate stabilization of the bite fork record on the maxillary cast. 3. Poor fit of the maxillary cast into the bite fork indentation. 4. Neglect use of maxillary cast support during mounting causing distortion of the face bow record. T- Cast support is mounted on the lower member of the articulator to support the bite fork during mounting the maxillary cast. 66 Maxillary Face Bow Record 1- Bite fork is heated and inserted into the upper occlusion rim. Both are then placed intraorally together with the lower occlusion block. 2-The condylar axis is then determined either arbitrarily or by using mandibular face bow record. The rods are then placed on it, so that the bow surrounds the patient’s face. The stem of the bitefork is slipped into the universal joint. 3- When the patient‘s face is centralized in the bow, all clamps are tightened.. 4- Universal joint once tightened, never opened. Maxillary Face Bow Transfer 1- The slide bar clamp is unscrewed to remove assembly from the face. 2- Assembly is now centralized on the articulator. Again notice position of - condylar rods -infraorbital pointer, - L shaped bitefork, and the incisal pin 3- Upper cast is mounted on the articulator. An arbitrary mounting of the maxillary cast without a face-bow transfer can introduce errors in the occlusion of the finished denture. A face bow transfer is essential when cusp teeth are used, and is also most helpful in supporting the maxillary cast while it is being mounted on the articulator. 67  Mandibular Face bow Parts of Maxillary Face Bow 68 Mounting of Upper cast on the Articulator 69  Chapter 7 THE ARTICULATOR ARTICULATORS An articulator is a mechanical device to which maxillary and mandibular casts may be attached, representing the tempromandibular joints and jaw members. Articulators can simulate but they cannot duplicate the mandibular border movements. Articulators are used to hold casts in one or more positions in relation to each other for the purposes of diagnosis, and arrangement of artificial teeth. USES 1. To simulate the patient in the absence of the patient. 2. To plan the dental procedures based on the relationship between opposing natural and artificial teeth. (Diagnosis and treatment planning) 3. To aid in the fabrication of restorations and prosthodontics replacements. 4. To correct and modify completed restorations. 5. To arrange artificial teeth. Advantages of the articulators: 1- Visualization of the occlusion especially from the lingual side. 2- Patient cooperation is not a factor. 3- Decrease the chair time, and patient appointments time. 4- Working away from saliva, tongue, and cheek. 5- Minimizing the effects of tissue resiliency. 70 Terminology Mounting: it’s a laboratory procedure of attaching the maxillary and /or mandibular cast to an articulator. TERMINAL HINGE AXIS When the condyles are in their most superior position in the articular fossae and the mouth is purely rotated open, the axis around which movement occurs is called the ‘Terminal Hinge Axis’. Condylar guidance : “Mandibular guidance generated by the condyle and articular disc traversing the contour of the glenoid fossa” Condylar path: the path travelled by the condyles in the TMJ during various mandibular movements Incisal guidance “The influence of the contacting surfaces of the mandibular and maxillary anterior teeth during mandibular movements” Incisal path: the path travelled by the incisal edges of the lower incisors on the palatal surface of the upper incisors during protrusion. MANDIBULAR MOVEMENTS Border and intra-border movement Movements on the boundaries of the movement space are called border movements. Movements within the boundaries of movement space can be designated as intra-border movements. Border movements of the mandible are reproducible.The border movements constitute the framework inside which the functional movement patterns take place. 71 Types of articulators I. Simple, hinge or plane line articulators. II. Mean value or fixed condylar path articulators. III. Adjustable articulators. a. Semi-adjustable condylar path articulators. b. Fully adjustable condylar path articulators. I-Simple, hinge or plane line articulators It consists of two metal frames, which are held apart at a certain distance by a setscrew at the back that can raise or lower the distance between the two frames permitting only the hinge like movement. Uses: - Maintaining the centric occlusion relationship only. - Setting-up of teeth. - Representation to the patient. Possible movements: This type of articulators gives only opening and closing movements. Records required: Vertical dimension of occlusion. Centric relation record. Disadvantages: These articulators do not represent the tempromandibular joint and the dynamic mandibular movements. 72 II. Mean value, average or fixed condylar path articulators In this type the two members of the articulator are joined together by two joints, which represent the tempromandibular joint. The condylar path, as represented by the joint and the incisal table is fixed at certain angle, and the angle is used for all patients. As these angles have been obtained by taking an average over many hundreds of patients it may be assumed that a good proportion of cases can be treated successfully with this type of instrument. In some fixed condylar path articulators the upper cast is mounted on the upper member of the articulator with a face bow transfer Other articulators mounting are carried out according to the Bonwill triangle. Bonwill mentioned that the distance between the condyles and the distance from each condyle to the contact point of the lower central incisors is 4 inches. Bonwill, thus, formulated the theory of the equilateral triangle and designed an articulator to this theory. On the fixed and most adjustable condylar path articulators the upper members are movable and the mandibular members are stationary (non-arcon or condylararticulators) the fixed condylar path articulators have their condyles on the upper member and the condylar guides on the lower member. This articulator is classified into two groups: 1- Accept face bow transfer. 2- Does not accept face bow, and transfer mounting is done by: Bonwill triangle. Possible movements: 1- Opening and closing. 2- Protrusive movement at a fixed condylar path angle. 73 Records required: 1- Vertical dimension of occlusion. 2- Centric relation record. 3-Face-bow record: In some designs of these articulators, the upper cast can be mounted by a face bow transfer. Disadvantages: 1-Most of these articulators does not accept face-bow record. 2-The condylar path moves to a fixed angle and it is successful in-patients whose condylar angle approximates that of the articulator. 3- No lateral movements. III. Adjustable articulators The adjustable articulator employs the face bow to transfer the arbitrary or actual terminal hinge axis of the mandible to the articulator and possess condyle mechanisms which can be adjusted to copy condyle positions transferred byinterocclusal, protruded and lateral records from the mouth. A. Semi-adjustable condylar path articulators -A semi adjustable articulator is an instrument whose larger size allows a close approximation of the anatomical distance between the axis ofrotation and the teeth. -With this type of articulators it is said to be possible to adjust the sagittal condyle path to the same inclination as those of the patient. The lateral condyle path inclination can be obtained from the following formula: L=H/8+12 Where L and H are the lateral and horizontal (sagittal) condyle path inclinations, respectively. 74 Arcon versus condylar articulator: The term arcon is commonly used to indicate an instrument that has its condyles on the lower member and the condylar guides on the upper member. Instruments that have the condyles on the upper member and condylar guides on the lower member are commonly referred to as condylar instrument or as nonarcon instruments. Possible movements: Opening and closing. Protrusive movement according to the horizontal condylar path angle determined from the patient. Lateral movement to the angle estimated from the Hanau formula. Some types have Bennett movement (immediate side shift). Records required: 1. A maxillary face bow record to mount the upper cast. 2. Centric occluding relation record (vertical dimension and centric relation) to mount the lower cast. 3. Protrusive record to adjust the horizontal condylar path inclination of the articulator. b. Fully adjustable articulators (axle type articulators) In this type both horizontal (protrusive or sagittal) and lateral condyle path inclinations can be adjusted according to records taken from the patients These articulators are designed to reproduce the entire character of border movements including immediate and progressive side shift and the curvatureand direction of condylar inclination, Intercondylar distance is completely adjustable. 75 This type of instrument is expensive. The techniques required for its use demand a high degree of skill and time consuming to accomplish. For this reason fully adjustable articulators are used primarily for extensive treatment, requiring the reconstruction of an entire occlusion. Some authors believe that unavoidable errors that may occur on using suchinstruments make their value doubtful. Possible movements: It has the same movements of the semi-adjustable articulators. In addition they have Bennett movement. Records required: 1. A maxillary face bow record to mount the upper cast. 2. Centric occluding relation record to mount the lower cast. 3. Protrusive record to adjust the horizontal condylar path inclination. 4. Right lateral record to adjust the left lateral condylar path inclination. 5. Left lateral record to adjust the right lateral condylar path inclination. 6. Intercondylar distance. I. Simple, hinge or plane line articulators. 76  Semiadjustable articulator Left; Hanau non-arcon articulator. Right; Denar, arcon articulator 77  Chapter 8 SELECTION OF ARTIFICIAL TEETH FOR COMPLETELY EDENTULOUS PATIENTS Selection of anterior teeth The objective in selection of the anterior teeth is to obtain a natural appearance. This should be in harmony with age, sex, personality and occupation of the patient. Anterior tooth selection is an unsure step, which can be verified by the dentist and confirmed by the patient and family or friends. There are three basic considerations when selecting the upper six anterior teeth; these are form, size, and shade. 1. Form or shape of teeth Factors that aid in selecting the form of the teeth include: a- Shape of the edentulous upper arch. b- The shape of the face. c- The profile of the face. d- Dentogenic concept a- The shape of the edentulous upper arch There is some relationship between the shapes of the edentulous upper arch form and the upper incisor teeth e.g. square arch form indicates square incisor teeth and V-shaped arch indicates incisors which are narrower at the neck than at the incisal edge. 78 b- The shape of the face or Facial Form It is believed that there is a harmonious relation between the shape of the upper central (labial aspect) and the forms of the face when seen from the front. The face form of the patient must be taken into consideration when selecting the anterior teeth. There are four basic typical forms of faces: square, square-tapering, tapering, and ovoid. Shape of Teeth in relation to Face In order to determine the type of face form, the operator should imagine two lines, one on each side of the face running through the sides of the forehead, the zygomatic bone and the angle of the mandible. - Square: the outline form of the face is square (the imaginary lines are parallel). - Square-tapering: very similar to the square, the difference from the true square occurs from the zygomatic bone to the angle of the mandible (The lower parts of the lines are converging toward the chin). - Tapering: this face form presents a tapering appearance from the sides of the forehead to the angle of the mandible, the widest part at the forehead and the narrowest part at the angle of the mandible. 79 - Ovoid: the zygomatic width is the widest. The forehead and the angle of the mandible are less in width. C- The profile of the face The labial surface of artificial teeth should be in harmony with the profile of the face. The three general types of profile are straight, convex and concave. The labial surface of the artificial teeth when viewed from the mesial aspect should be in harmony with the convexity or flatness of the face D- Dentogenic Concept and: The sex, personality, age, (SPA factor) and occupation of the patient The sex, personality and age of the patient determine the form of the anterior teeth. With age the teeth undergo attrition and characteristic teeth may be used. The color of the teeth also changes with age. Inter-occlusal distance reduces with age. For females and for most professional men whose occupation entails intimate contact with people, appearance is more important and this should be taken into consideration when selecting the anterior teeth. For executives, the teeth should be relatively smaller and more symmetrically arranged 2. Size of the anterior teeth Methods used as a guide to select the size of the teeth: Methods using pre-extraction records Methods using anthropological measurements of the Patient. Methods using anatomical landmarks Clinical methods 80 Methods Using Pre-extraction Records Diagnostic casts They are prepared before the extraction of the teeth. The operator can obtain an idea about the actual size and shape of the teeth from these casts. Pre-extraction photographs Photographs showing the lateral, anterior and anterolateral views of the patient should be taken before extraction. These photographs must show at least the incisal edges of the anterior teeth. This method is useful to determine the exact width and outline of the teeth. Photo interpupillary distance \ patient's actual interpupillary = photo central incisor width \ distance X (X gives the original width of the patient's central incisor) Pre-extraction radiographs This is usually obtained from the patient's previous dentist. Radiographic errors are a major limitation to this method. Teeth of close relatives This method is usually followed only if the other records are not available. The size and contour of the patient's son or daughter's tooth is taken as reference. Preserved extracted teeth This is the best method to determine the size of the anterior tooth. The exact details about the size and contour can be recorded from this method. 81 Methods using Anthropological Measurements of the Patient Anthropological measurements are usually post-extraction records made directly from the edentulous patient. Anthropometric cephalic index The transverse circumference of the head is measured using a measuring tape at the level of the forehead. The width of the upper central incisor can be derived from this measurement. Width of the upper central incisor = Circumference of the head / 13 Width of the nose It is measured with caliper. The width of the nose is equal to the combined width of the anterior teeth. Methods using Anatomical Landmarks Size of the maxillary arch The distance between the incisive papilla and the hamular notch on one side is added with the distance between two hamular notches. This gives the combined width of all the anterior and posterior teeth of the maxillary arch Location of canine eminences The distance between the two canine eminences is measured along the residual ridge. This measured value gives the combined width of the anterior teeth Location of the buccal frenal attachments The attachments of the buccal frenum are marked on the residual ridge. The distance between the two markings recorded along the residual ridge gives the combined width of the maxillary anteriors. 82 Location of the corners of the mouth The corner of the mouth marks the distal end of the canine. The corners of the mouth are recorded on the occlusal rim and the distance is measured between these markings. The anterior teeth are set within these markings The interalar distance: A vertical line extending along the lateral surface of the ala of the nose will pass through the middle of the upper canines. Clinicians need to add 7 mm to the interalar measurement to produce the width of the six maxillary' anterior teeth. Clinical methods  Canine lines at the corners of the mouth these lines are marked on the properly contoured occlusion rim. The distance between the canine lines determines the width of the six anterior teeth.  High lip line: The distance from the lower edge of the upper occlusion rim to the high lip line is used as a guide to determine the length of the upper anterior teeth.  Length: The distance from the high lip line and the lower edge of the upper occlusion rim represents the length of the upper anterior teeth. The lower edge of the upper occlusion rim should be about 2mm below the upper lip at rest. The amount of upper teeth shown below the upper lip depends on: A-Length of the upper lip; short lip shows more tooth and vice versa. B-Mobility of the upper lip; hyper mobile lip shows more teeth. C-Interarch distance: large space between upper and lower ridge require a long teeth. 83 3. Color (shade) of the teeth For complete denture the color of the teeth is affected by the color of the skin, hair and eyes. But it is not a constant factor and can be unreliable & inaccurate. The age: Usually older patients require darker teeth than younger ones. Sex of the patient should be taken into consideration when selecting the shade of the teeth. Women require lighter teeth than men. The characteristics of natural teeth color: a- The neck of the teeth is darker than the incisal edge. b- The incisal edge is more translucent than