Book: Teeth Selection PDF

CHAPTER 17 Selecting and Arranging Prosthetic Teeth and Occlusion for the Edentulous Patient Aaron H. Fenton A knowledge and understanding of a number of physical and biological factors directly related to the patient are required to appropriately select artificial teeth to rehabilitate the occlu...

CHAPTER 17 Selecting and Arranging Prosthetic Teeth and Occlusion for the Edentulous Patient Aaron H. Fenton A knowledge and understanding of a number of physical and biological factors directly related to the patient are required to appropriately select artificial teeth to rehabilitate the occlusion. The goals for this phase of therapy are to construct complete dentures that (1) function well, (2) allow the patient to speak normally, (3) are esthetically pleasing, and (4) will not abuse the tissues over residual ridges. The dentist is the best person to accumulate, correlate, and evaluate the biomechanical information so that the artificial teeth selected will meet the individual needs of the patient. The selection of artificial teeth is a relatively simple non–time-consuming procedure, but it requires the development of experience and confidence. The setting of the selected teeth in wax according to a concept of occlusion is a laboratory procedure that requires the use of accurate record bases and articulator mountings of models. These record bases permit the dentist to transfer the tooth arrangement or occlusal scheme back from the articulator to the patient’s mouth for a final examination of the maxillomandibular jaw relationships, an evaluation of the occlusal concept, and the philosophy of occlusion to be fulfilled. These activities are performed during what is termed the try-in appointment. ANTERIOR TOOTH SELECTION A smile is the most visible record of a dentist’s care of an edentulous patient. It is present for all to see. Anterior tooth selection (ATS) has been based on theories that tooth shape relates to head shape, and tooth appearance is influenced by a patient’s age, sex, 298 and personality. If no other information about ATS is available, these systems can be used to select teeth. The dentist’s professional obligation is to give the patient adequate information, guidance, and opportunity to choose their teeth. ATS is the area of prosthodontic care in which the patient should be given a primary responsibility to determine the esthetic outcome. ATS for dental prostheses has both psychological and dental considerations that are influenced by the societal values for youth and health. Patients may wish to have teeth that look whiter and less restored than what would normally be expected in persons their age. The dentist’s task is to assist a patient in making the best decision. Tooth manufacturers provide a variety of shade guides, mold guides, and measurement charts to assist dentists in the selection of anterior teeth (Figure 17-1). Because each system can produce satisfactory results, select a manufacturer based on local availability and reliable delivery. Future tooth repairs are easier if the prosthetic teeth are readily matched. Although the dental profession seeks to realistically replace the missing dentition, prosthetic teeth are often smaller in size and lighter in color than the range of the natural dentition. This does not seem to be a problem because patients most often object to teeth being too large or too dark. They often prefer teeth that are lighter. Ask your local laboratory which tooth sizes and colors are selected most often. Find out if the laboratory has problems with a manufacturer’s tooth color and size matching or if frequent repairs are needed. Chapter 17 Selecting and Arranging Prosthetic Teeth and Occlusion for the Edentulous Patient Figure 17-1 selection. Shade and mold guides assist in tooth Psychology of Acceptance: Give Patients What They Want The United States is a consumer-oriented society, yet patients leave many dental decisions to the dentist, such as the posterior palatal seal or the retromylohyoid extension. Dentists have knowledge of oral anatomy and esthetics and the physiology of speech and mastication. Teeth can be selected without the patient’s input. This is dentally feasible, but therapeutically dangerous. Everyone sees the anterior teeth, and everyone has an opinion. Patients should be given enough information and assistance and should be guided toward a limited selection of anatomically possible tooth selections so that they can choose the teeth that make them happy. Let the patient decide; then both the patient and dentist will get what each wants. Patients, and perhaps their close personal friends, know what they think teeth should look like, so get them involved in the decision making. Psychologically, this is effective therapy. Patients more readily accept prosthetic care if they have had some input. Satisfied patients tell their friends who treated them; dissatisfied patients tell everyone. The first step in ATS is to listen to the patient. What the patient wants is the reason that she or he came to your office. Do not miss it. Too often, dentists are so keen to make impressions and all those dental things that they alone know about that they underestimate the value of hearing what the patient wants. 299 At the first appointment, ask your patient for his or her opinion about the existing teeth. Write it down in the patient’s own words (e.g., “My teeth don’t show anymore.”) Then restate it in your words to clarify what the patient expects (e.g., “If we make teeth of the same size, but lighter in color, and a little longer at the front, would that make them show the way you want?”) Listen much and talk little. We cannot hear when we are talking. Let the decision maker choose the teeth. A patient may have another person such as a spouse, relative, or friend whose opinion is valued. Ask them. That person may be more the reason why the patient is seeking treatment than the patient. It takes only a few seconds to find out if there is someone else with whom the patient would like to check regarding tooth color and size. You may devote hours of laboratory and chairtime only to find out that the setup that you and the patient agree on in the office is not liked by their spouse, and they demand that you change the teeth or set-up. This will have to happen only once for you to remember it. People vary in how much they value the appearance of their teeth. The importance of ATS to patients can range from the indifferent “it doesn’t matter” to unrealistic expectations that cannot be satisfied. Fortunately, almost all patients are well between these two extremes. Your most important task is to quickly find out where your patients are on this spectrum of interest in the appearance of their smiles. Their responses will indicate how interested they are in change and how much time you will devote to tooth appearance. This affects your cost of providing the service of complete denture treatment. Second, get records of existing and previous teeth and find out the patient’s opinion of them. Ask patients what their teeth looked like before the existing dentures. Explain that to get the best result for them, you need to know what their teeth were like before. Their mouth has probably changed, and present appearances can be misleading. Ask the patient to bring any models, old dentures, and photographs that show them happy and smiling, to the next appointment. The patient will give you credit for trying to provide the best personal service, and you will get some indication of what the teeth were like. Make alginate impressions and plaster models of the dentures that best satisfy the 300 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures patient, and with the patient’s permission, make a photocopy of any relevant pictures (Figure 17-2). You may make good dentures, but patients will never forget if a favorite wedding picture gets too close to a Bunsen burner. If your patients are happy with the appearance of their teeth, use these records to provide a denture service that has similar teeth, but a better vertical dimension of occlusion and adaptation to the tissues. This has been identified as a “conformative approach” to prosthodontic care. The message that you are interested in making their teeth as natural as possible can be personalized further by asking if their teeth were like their direct descendents: their children. Photographs or dental models of adult children are sometimes the best way to create a smile that your patient appreciates. At least ask. The patient can always decline (Figure 17-3). Figure 17-2 Photocopy a patient’s photograph to help in selecting tooth size and positioning. B A C Figure 17-3 A, This patient’s childhood photograph provided assistance in selecting denture teeth for her at age 54. B and C, Diagnostic casts made of her 30-year-old daughter furnished additional assistance. The daughter’s tooth shade (Vita A1 for the centrals and laterals, A2 for the canines) also substantiated her mother’s request for a light tooth shade. Chapter 17 Selecting and Arranging Prosthetic Teeth and Occlusion for the Edentulous Patient On the other hand, your patients may not like their present teeth. Often the most important thing to find out is how not to make teeth because of the patients’ dislike of their own teeth or previous dentures. If the teeth are the wrong color, size, shape, or position, plan on improvements. Also, the teeth may be excessively worn, or tissue changes may be so advanced that making teeth similar to what the patient has would be of little benefit. In these situations, consider a reorganized approach where you plan to change the prostheses to improve them. Even though you are planning improvements, improvements are a change. Assess the tolerance and motivation of your patients for change and work within the range that they can accept. The pleasure of prosthodontics is blending the interpersonal aspects of patient care with the biology of the mouth and the science of dental materials. Third, arrange your practice for ATS. Make it easy for you and your patients to view their faces in good light. Your patient should be able to stand before a north-facing window, and you should have adequate color-corrected lighting. Tall or short patients should stand so that you can see their face and smile as others see them. Position yourself so that the window light comes over your shoulder and onto your patient’s face. Make sure your patients put their glasses on if they need them. Give your patients a hand mirror of about 6 inches (or 15 cm) in diameter so that they can see how their face looks. A smaller mirror does not give an adequate image to the patient; a larger mirror makes it difficult for you to see around it. Fourth, allow your patients to select the color of teeth they prefer. Dentists are familiar with an array of tooth shades and mold guides and charts, but these can be too confusing for patients to decide. They beg off making a decision and tell the dentist to decide what is best for them. Then you are responsible. If your patients like your decision, that is fine. If they, or anyone else, are at all skeptical, suddenly it is your teeth that are the problem, not theirs. Avoid this roadblock by tactfully insisting that your patients decide which teeth are best for them. This is easily done in a nonthreatening manner by giving the patients a simple choice with two options (i.e., a Method of Pair Comparison). Tell your patients that you need their help to get the best results. Explain that you have many colors 301 and sizes of teeth to best treat your patients, but only a few are appropriate for them. A display of all of your shade and mold guides at this point is impressive but confusing to a patient untrained in dental anatomy. Reassure your patients that any required decisions will be simple. They will only have to tell which one of two things they prefer; in other words, make a simple choice. Color is the easiest thing for a patient to decide about teeth. Show the patient a complete shade guide and select the two tabs that are lightest and darkest (Figure 17-4). Point out how different these two are and satisfy yourself that the patient can see the difference and agree. Hold them against the patients’ lips and ask them to note how different they are. Then ask them to point to the one that they prefer. Delete the rejected color. On the basis of the decision, select another shade in the preferred half of the shade guide and repeat the pair comparison. After two selections by the patient, you will probably have a pair of shades that are very close to what the patient wants. To confirm the patient’s decision, reverse the sides of the pair so that the preferred shade is presented on the opposite side. Try another shade that is close to the preferred shade. By now the psychology of decision making is as important as the physiology of color perception. Usually patients can still select the same shade even when you move it from side to side in the pair, but sometimes they are unwilling to state a preference. Figure 17-4 A pair of tooth shades to compare. Ask your patient to point to the one that he or she prefers. 302 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures If patients are unable or unwilling to decide on a shade, their powers of perception can still help to select a tooth color. Ask them to point out which one of the pair of tabs they notice. By default, the tab that they do not notice is less conspicuous and therefore a better color. In the rare situations in which patients still cannot decide, advise them that they are correct. Both shades are appropriate, and a pleasing appearance could be made with either one of them. However, you would still like them to be happy, so they should choose between the two shades when you have the actual teeth. Order two sets of teeth so that the patient can compare them side by side and select the best before they are needed for setup. Fifth, choose a size of tooth that is appropriate. Existing dentures, models of previous teeth, and photographs all give valuable input for selection of the size and shape of teeth. Teeth can be measured in millimeters and teeth of similar size selected (Figure 17-5). Even so, patients may have a clear perception of how large a tooth they prefer. Coupled with actual measurement, again use the Method of Pair Comparison to assist patients to decide what size of tooth they prefer. Set two different sizes of teeth on a piece of wax rope or on the tooth selector rim that some companies provide. Place this under the upper lip and find out which one the patient prefers. The decision is often not one of preference, but rejection. People note and reject the teeth that are, for example, too large, Figure 17-5 Use a Boley gauge to determine the size of teeth in millimeters. A similar-sized tooth can be selected based on this evidence. small, long, or short. By default they prefer the other set of teeth. Sixth, select the mold of the teeth. Teeth of a similar size can have a different appearance because of differences in the crown taper and labial curvature. This is the least obvious of the three judgments to be made, yet it can provide the “finishing touch” to replicate a realistic appearance for your patient. Mold determination requires previous models or photographs for guidance. If the patient is to receive immediate insertion complete dentures, the actual teeth are the best indicator of mold. If teeth are unavailable, allow the patient to select between molds of the same size but different shapes. Set two different molds on the right and left sides of a piece of wax rope and ask patients which they prefer (Figure 17-6). Anterior tooth selection should be completed early in treatment, preferably before final impressions are made. This gives ATS appropriate significance and allows time for judgment of the result before the teeth are needed. Order all of the teeth (1 × 28) because the premolars are part of the smile. Their color, size, and shape should complement the anterior teeth. Show patients the actual teeth at the impression appointment and secure their agreement (Figure 17-7). If the teeth are not what patients think they will be, based on the shade and mold guide estimations, they can be reordered and exchanged before they are needed for setup in Figure 17-6 Pair comparison to identify the best mold of teeth. The two teeth on the left and the two teeth on the right are from different molds. The patient can see them in the mirror, and he is pointing to the ones that he prefers. Chapter 17 Selecting and Arranging Prosthetic Teeth and Occlusion for the Edentulous Patient 303 of pink gingival acrylic. It is harder to make realistic-appearing gingival acrylic compared with teeth. Therefore make a smile with slightly more dental and less gingival display. Limited Interocclusal Space Use acrylic teeth. They can be ground thin, yet they will still chemically bond to the underlying denture base acrylic. Porcelain teeth lose their mechanical retention if the palatal pins are ground off. Figure 17-7 Order the selected teeth early so that the patient can see them at the impression appointment. Confirm their acceptability before they are needed for setup. wax. Otherwise, it is expensive for your laboratory fees and office chairtime to exchange and reset a second set of teeth. Additional Clinical and Technical Considerations in Anterior Tooth Selection Patient preferences, local anatomy, and the opposing dentition can affect the ATS of materials or mold. Patient Preference Patients may want teeth to be porcelain or acrylic, depending on various reasons that they have heard: “Acrylic teeth stain,” “Porcelain teeth are real,” “Porcelain teeth are noisy for chewing,” or “Porcelain teeth are heavy.” There are a variety of opinions. Listen and respond with your knowledge of dental materials, but do not be disheartened if the patient is skeptical. Facts are not always as accepted as opinions. If the denture is not compromised by patients’ requests, you can perhaps accede to their wishes. Make patients aware that you are modifying your therapy personally for them and make a note in the chart. Again, this is an opportunity for patients to accept responsibility for their decisions. Highly Visible Gingiva Select squarer teeth with a long contact point rather than highly tapered teeth. This will minimize the interproximal display Opposing Natural Teeth Porcelain can be very abrasive. Use acrylic teeth for dentures that oppose natural teeth to minimize their wear. The acrylic teeth will wear, but they can be replaced. This is preferable to the porcelain destruction of enamel. Also, acrylic teeth are less brittle than porcelain when additional adjustment is required to match natural occlusion. Overdentures The tooth positioned just over a retained tooth root or implant abutment has to be “hollow-ground,” and a little extra tooth volume is needed for strength. Use a square flat mold in a standard nonlaminated acrylic. Tapered or curved teeth get too thin and weak in the gingival areas. Highly characterized or laminated teeth may become translucent or separate their veneers when ground thin over tooth roots or implants. The Personal Touch: Characterization of Selected Teeth Explain to patients that smiles are more realistic with subtle chips, wear, or restorations. These hint at the presence of a dentition for many years, as opposed to looking “brand new.” Although this service is offered to all patients, lately, more patients seem to prefer an undamaged appearance of light-colored teeth. Fewer patients opt for too-visible characterization. Nevertheless, anterior tooth characterization can produce strikingly realistic effects that make the patient’s smile look as if it is enamel, dentin, and gingiva. Teeth can be modified to create a personal smile in a number of ways and combinations, such as changes in color and position (Figure 17-8), individual grinding and placement (Figure 17-9), placement of restorations and worn appearance (Figure 17-10), and natural proportion and subtle variations in position (Figure 17-11). 304 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures A B Figure 17-8 Characterization with colors: use different tooth colors to create the best effect. A, The prominent position and color of this patient’s maxillary right central were identified from a photograph. B, The maxillary central incisors were Dentsply shade 102; the rest of the smile was Dentsply shade 114. This emphasized the tapered arch form and created the illusion of more prominence for the upper right central incisor than was prosthetically possible. The smile appears real to this patient. A B Figure 17-9 Characterization by grinding: immediate dentures allow for realistic tooth selection and shaping. A, A previous photograph hints at the prominence of the maxillary central incisors, their overlap of the lateral incisors, and the Angle Class II relationship. B, A study model allows selection of the best available mold. Continued Chapter 17 Selecting and Arranging Prosthetic Teeth and Occlusion for the Edentulous Patient C D Figure 17-9 cont’d C, The acrylic teeth are trimmed to recreate the actual tooth shape. It could not be found in any mold guide. D, The completed prosthesis faithfully replicates the irregularity of tooth color, size, mold, and Angle Class II position. This patient’s smile looks real. Figure 17-10 Characterization with restorations and wear. A gold inlay is in the mesial of the upper right canine, the upper left lateral incisor is rotated prominently, and the incisal is chipped, with an Angle Class II Division 2 tooth arrangement. The teeth are a single uncharacterized shade, but all the other natural effects make them appear real. 305 306 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures A B C D Figure 17-11 Characterization by natural arrangement: a standard anterior tooth shade and mold is made to look real by the subtle natural irregularity of tooth positioning. A, The patient’s presenting smile with teeth that are too small and hardly visible. B, The maxillary teeth are a single uncharacterized color, too small, out of proportion to the lower teeth, and too uniform in position. C, The new smile has better lip support and visibility at rest. The midline of the teeth is different from the lip at rest because it is set for the more visible asymmetrical smile. D, The patient’s smile is in proportion to the surrounding tissues. Each tooth has an individual identity because of subtle variations in angle and rotation. The central incisors are at the midline of the smile, but they are not a mirror image of each other. The patient’s left lateral incisor is rotated out at the mesial. The canines and visible premolars vary in gingival prominence and angulation. The gingiva is inconspicuous. This smile is perceived to be real and gives the patient self-confidence. POSTERIOR TOOTH SELECTION Until the middle 1920s, most posterior denture teeth were anatomical in design and represented the forms of natural teeth. In the mid 1920s, dentists began to experiment with tooth forms that, were designed for a specific functional purpose rather than merely reproducing natural forms. Thus emerged a number of nonanatomical denture teeth. The occlusal surfaces of these teeth are not copies from the natural form but are given forms that, in the opinion of the tooth carver, were designed to meet specific patient needs, such as denture base stability and improvements in mastication. Some Chapter 17 Selecting and Arranging Prosthetic Teeth and Occlusion for the Edentulous Patient nonanatomical posterior denture teeth were designed completely without cusps, whereas others were mechanical in design, possessing metal cutters to increase masticatory efficiency. The maintenance of hard and soft tissues of the dental arches has been difficult to relate to tooth forms and occlusal schemes. Other factors, such as (1) properly fitted bases; (2) correct jaw relation records that are transferred to an instrument capable of accepting what is recorded; and (3) the arrangement of teeth for the best stability and other functional and nonfunctional activities, are considered to have an influence on the maintenance of these tissues. Posterior teeth are selected for color, buccolingual width, total mesiodistal width, cusp tip to cervical collar height, material, and the cuspal inclination needed for the concept of occlusion to be used in restoring the patient. Buccolingual Width of Posterior Teeth The buccolingual widths of artificial teeth should be less than the widths of the natural teeth they replace. Artificial posterior teeth that are narrow enhance the development of the correct form of the polished surfaces of the denture by allowing the buccal and lingual denture flanges to slope away from their occlusal surfaces. These narrower forms, especially in the lower denture, assist the cheeks and tongue in maintaining the dentures on the residual ridge. Mesiodistal Length of Posterior Teeth The length of the mandibular residual ridge from the distal of the canine to the retromolar pad will dictate the dimensions of the posterior teeth selected. Artificial posterior teeth are manufactured with varying widths and lengths that easily accommodate the needs of the patient. After the six anterior mandibular teeth have been placed in their final position, a point is marked on the cast landing area at the distal of the canine. A second mark is placed on the landing area of the cast at the point where the mean residual ridge begins to ascend to the retromolar pad. Posterior teeth are not positioned on this inclined plane. The available space will dictate whether three or four posterior teeth are used. The arrangement of only three posterior teeth is more often the norm and will reduce the 307 potential for placement of the second molar too far posterior. Maxillary posterior teeth that extend too close to the posterior border of the maxillary denture may cause the patient to bite the cheek. Vertical Height of the Facial Surfaces of Posterior Teeth It is best to select posterior teeth corresponding to the interarch space and to the height of the anterior teeth. Artificial posterior teeth are manufactured in varying occlusal-cervical heights. The height of the maxillary first premolar should be comparable with that of the maxillary canines to have the proper esthetic effect. Without this relationship, the denture base material will appear unnatural distal to the canines. Ridge lapping the posterior teeth can be done without sacrificing leverage or esthetics. The form of the dental arch should copy, as nearly as possible, the arch form of the natural teeth they replace. Types of Posterior Teeth According to Materials For many years, porcelain was the favorite tooth material because of the rapid wear of acrylic resin. However, with the tendency for porcelain to chip and fracture, acrylic resin teeth have gained in popularity. Improved acrylic resin teeth and newer composite resin teeth are more wear resistant, and they have supplanted porcelain during the past two decades. Acrylic resin or composite resin posterior teeth are specifically called for when they oppose natural teeth or teeth whose occlusal surfaces have been restored with gold. These resin teeth reduce the possibility that the artificial teeth will cause unnecessary abrasion and destruction of the natural or metallic occlusal surfaces of the opposing teeth. Acrylic resin teeth also are desirable when the tooth must be excessively reduced in height because of a small interarch distance. The chemical bonding of the resin teeth with the denture base prevents these teeth from breaking away from the denture base. Types of Posterior Teeth According to Cusp Inclines The cuspal inclines for posterior teeth were described earlier in great detail. Posterior artificial 308 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures teeth are manufactured with cusp inclines that vary from steep to flat. Selecting the tooth to be used is based on the concept of occlusion to be developed, the philosophy of occlusion to be fulfilled, and the accomplishment of both of these goals with the least complicated approach (Table 17-1). ARRANGING TEETH FOR COMPLETE DENTURE OCCLUSION Once the master casts have been mounted on the articulator, the teeth are set in the occlusion rims so a more accurate observation of the jaw relationship can be recorded, and eventually the Table 17-1 Comparison of Denture Tooth Molds and Occlusal Concepts Tooth Mold Occlusal Concept 20- or 30-degree cusped teeth ● ● Monoplane 0-degree teeth ● ● ● ● ● Flat teeth with compensating curve or second molar ramp ● Combinations or “lingualized” occlusion ● ● ● ● ● ● Advantage Centric jaw record, face bow, protrusive records to semiadjustable articulator Set upper anterior and posterior teeth, then lowers to cross-arch contact or “balanced occlusion” Centric relation jaw record only Simple articulator Set 12 anterior teeth with overjet but no overbite Set lower teeth in flat plane to middle of retromolar pad Set upper to match; no attempt on contact on excursions ● Centric relation jaw record Semiadjustable articulator Anterior teeth with overjet and slight overbite Posteriors set to contact on at least 1 point on nonworking or balancing contact Centric jaw record Monoplane lower posterior teeth set to retromolar pad Anatomical upper posterior teeth set with only lingual, not buccal cusps touching ● ● Reported slightly more efficient in chewing tests Posteriors appear more natural Disadvantage ● ● ● ● ● ● ● ● ● ● ● ● ● Simplest of all recordings Simplest articulator Quick arrangement of teeth Wide range of posterior tooth positions possible No lateral stresses on mucosa with parafunction Easier for patients with uncoordinated closures (e.g., patients with dyskinesias, Parkinson’s disease, or stroke) Simple to set up; allows for more esthetic overlap of anterior teeth The posterior point contact maintains denture base stability on excursions or parafunction ● Upper premolars appear natural Some range of posterior tooth position allowed Reported slightly better chewing than monoplane teeth ● ● ● ● ● Most time and complexity of records Limitations of anterior tooth positions Restriction of posterior tooth positions to that allowed by cuspal anatomy Flat premolars may appear less esthetic Reported as less efficient in chewing tests Anterior esthetics need more overjet and no overbite Slightly more laboratory setup time than flat teeth Premolars appear flat if visible Some grinding needed to create upper cusp tip/lower fossa contacts (some manufacturers are now producing molds for this occlusal concept) Chapter 17 Selecting and Arranging Prosthetic Teeth and Occlusion for the Edentulous Patient occlusion established. Most dentists carve the wax occlusion rims as accurately as they can for determining the desired amount of lip support and have their technician make the preliminary arrangement of teeth. The carved occlusion rims provide the technician with reliable guides for placement of the anterior teeth in the wax occlusion rims. Subsequently, these dentists make corrections in the tooth positions when the wax trial dentures are observed in the mouth at the try-in appointment. The incisive papilla is a valuable guide to anterior tooth placement because it has a constant relationship to the natural central incisors (see Figure 17-3, Figure 17-12). The incisive papilla is found in the lingual embrasure between these incisors. Naturally, it should serve to position the midline of the upper denture or, more specifically, the central incisors in the dental arch. However, the mesial surfaces of the central incisors of some people are not exactly in the center of their face or mouth. Therefore information on the center of the upper A B 309 C Figure 17-12 Indications of correct anteroposterior positioning of artificial anterior teeth. A, By measurement from the middle of the incisive fossa on the trial denture base to the labial surfaces of the central incisors. B, By visualization of the imaginary roots of artificial anterior teeth. The imaginary roots will be further in front of the residual ridge when a great amount of resorption has occurred. C, By determining the relationship of a transverse line extending between the middle of the upper canines and the incisive fossa. 310 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures lip or face should be recorded on the carved wax occlusal rim. A line marking the center of the incisive papilla on the wax rim can be extended forward onto the landing area of the cast (Figure 17-13). The central incisors set on either side of this line will have positions similar to those of the natural teeth insofar as right and left orientations are concerned. The incisive papilla is also a good guide for the anteroposterior positioning of the teeth (see Figure 17-13). The labial surfaces of the central incisors are usually 8 to 10 mm in front of the papillae. This distance, for obvious reasons, will vary with the size of the teeth and the labiolingual thickness of A B Figure 17-13 The incisive papilla is used to help locate the midline of the dental arch. A, A mark is made on the cast through the center of the papilla. B, The mark is transferred to the occlusion rim as a guide to placement of the maxillary incisors. the alveolar process carrying the natural teeth, so it is not an absolute relationship. Furthermore, as severe resorption of the residual ridge in a vertical direction occurs, the incisive papilla may be located more posteriorly to the position of the replacement teeth. Thus the distance from the papilla to the labial surface of the teeth may become greater for those patients with excessive bone loss in the maxillary anterior region. Another guide to positioning the central incisors is their relationship to the reflection of soft tissues under the lip or as recorded in the maxillary impression. The labial surfaces and incisal edges of the teeth are anterior to the tissues at the reflection, where the denture borders would be placed. This fact must be kept in mind when placing an artificial incisor in the wax occlusion rim. The root of the natural tooth extends into the alveolar process, with a relatively thin layer of bone over it labially. This means that in some situations the residual ridge can be used as a guide to determine the proper inclination of anterior teeth. However, the accuracy of this guide decreases as resorption of the residual ridge progresses. Clinical judgment is essential in the evaluation and application of these guides. The anteroposterior position of the dental arch should be governed chiefly by consideration of the orbicularis oris muscle and its attaching muscles and by the tone of the skin of the lips. Superficially, this means the position and expression of the lips. The orbicularis oris muscle affects, and is affected by, the following seven muscles: the quadratus labii superioris, caninus, zygomaticus, quadratus labii inferioris, risorius, triangularis, and buccinator. These muscles control expression and reflect the personality and appearance of every person wearing complete dentures. The tone and action of these muscles depend on the anteroposterior support provided by the teeth and the denture base material. Setting teeth over the maxillary anterior ridge may undermine the esthetic result. The greatest harm is done when the maxillary anterior teeth are set too far back on the ridge or under the ridge. In other words, the tooth’s direction is upward and backward. In the resorbed situation, the crest of the ridge is considerably more posterior than it is in a patient with recent extractions. If the rule of setting teeth over the ridge is followed after the residual Chapter 17 Selecting and Arranging Prosthetic Teeth and Occlusion for the Edentulous Patient ridge has resorbed, a prematurely aged appearance will result. If the wax occlusion rims have been accurately carved to support the lips and the maxillomandibular jaw relationship, they will provide an excellent guide to correct anteroposterior tooth positioning in the dental arch. If they have not been accurately carved, the dentist must decide what alterations will be necessary when the teeth are arranged. For example, if the lip needs more support when the occlusion rims are in the mouth, the incisors should be set in front of the labial surface of the wax rim. If the lips are too full at that time, more of the labial surface of the occlusion rims should be cut away before the teeth are set. Arranging the Maxillary Anterior Teeth After selecting the anterior molds for the maxillary and mandibular teeth, the arrangement is left to the discretion of the individual dentist to achieve the esthetic needs of the patient. Remove the maxillary wax occlusal rim on one side from the midline around the arch for a distance of approximately 1 inch (about 25 mm). For the maxillary anterior teeth to be set with the appropriate labial orientation, it may be necessary to grind the acrylic resin to reduce the thickness of the record base. This is a common occurrence in clinical practice and should always be performed before grinding on the neck of the tooth. A longer tooth clinically will provide a better esthetic result. Short, stubby teeth are not natural in appearance. Do not be concerned should you create a hole in the record base because it will be covered with wax in setting the anterior teeth. Often it is helpful to set both central incisors and thus establish the midline before setting the lateral and canine. Maxillary Central Incisor Place a small portion of soft, pink wax on the neck of the maxillary central incisor and attach the tooth to the record base over the anterior region of the residual ridge. Make certain that the long axis of the tooth is perpendicular to the horizontal, with the incisal edge 0.5 mm below the wax occlusal rim. Seal the tooth into position with pink wax, using the no. 7 spatula. Try to use only the amount of wax needed for securely attaching the teeth to the record base. Excess wax should be removed from the teeth. The 311 maxillary central incisor is the most difficult tooth to set because it establishes the midline and the esthetic support of the patient’s lip. The proper arrangement of the maxillary and mandibular anterior and posterior teeth relies on the setting of the maxillary central incisors. Maxillary Lateral Incisor Place the maxillary lateral incisor next to the central incisor, with the neck slightly depressed. Arrange the incisal edge in symmetry with the central incisor and with the remaining anterior occlusal rim. This incisal edge is even with the remaining maxillary wax occlusal rim and is therefore slightly elevated from the central incisor. The incisal edge is parallel with the mandibular wax occlusal rim. After this tooth is arranged in the normal position for a lateral incisor, it may be repositioned with spacing, lapping, or rotation to meet the individual esthetic requirements for the patient. Maxillary Canine Place the maxillary canine so that the anterior one half of the incisal edge is in symmetry with the lateral and central incisors as it curves around the labial contour of the wax occlusal rim. The neck of the tooth must be prominent and the tooth tilted slightly to the distal. Like the central incisor, the incisal tip of the canine must be 0.5 mm below the maxillary wax occlusal rim. Again, after initially setting the tooth to these guidelines, any individual changes necessary for the creation of naturalness for the patient should be performed. Remaining Maxillary Anterior Teeth Arrange the remaining maxillary anterior teeth on the other sides of the arch to complete the anterior setup. The wax supporting the teeth must be heated and sealed both to the teeth and to the record base to maintain the set teeth in position. Arranging the Mandibular Anterior Teeth The wax occlusal rim is removed from the area of the lower midline around the arch for approximately 1 inch (around 25 mm). This is similar to the procedure you performed on the maxillary wax occlusal rim when the maxillary anterior teeth were set. 312 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures Mandibular Central Incisor Position the central incisor next to the midline and tip it slightly to the labial. Direct the long axis of the tooth toward the residual ridge. Be certain that the necks of the teeth are depressed so that they are in from the edge of the record base. The incisal edges of these teeth must be at the height of the mandibular wax occlusal rim. This will result in a 0.5-mm vertical overlap with the maxillary central and canine teeth. A 1- to 2-mm horizontal overlap must exist between the lingual surface of the maxillary anterior teeth and the labial surface of the mandibular anterior teeth. Such an arrangement will create a low incisal guidance, which is exactly what one should achieve for the patient (Figure 17-14). Mandibular Lateral Incisor Position the lateral incisor next to the central incisor, with the long axis of the tooth directed toward the residual ridge. The incisal edge should be at the height of the wax occlusal rim. The 1 to 2 mm of horizontal overlap between the maxillary and mandibular anterior teeth should be continued. Mandibular Canine Place the mandibular canine with the anterior one half of the incisal edge in 0.5 mm 1-2 mm A B Figure 17-14 A, 0.5 mm of vertical overlap and 1 to 2 mm of horizontal overlap must exist between the maxillary anterior teeth and their mandibular antagonists to achieve a low incisal guidance, which is needed for the anterior teeth to function in harmony with most posterior tooth forms. B, The low incisal guide angle is both esthetic and functional. Chapter 17 Selecting and Arranging Prosthetic Teeth and Occlusion for the Edentulous Patient symmetry with the lateral and central incisors. Place the incisal tip at the same level as the lateral and central incisors. The neck of the tooth is slightly prominent and tilted to the distal. After these teeth are adjusted to this ideal arrangement, they may be altered by rotation, spacing, and tilting the teeth to achieve the naturalness requirement of the patient. Remaining Mandibular Anterior Teeth Arrange the remaining anterior teeth on the other side of the arch to complete the anterior setup. Again, be sure to seal all the teeth to the record base with pink baseplate wax and the no. 7 spatula. It is at this point in the clinical management of a patient that you may wish to evaluate the esthetics of all anterior teeth by a try-in with the patient. Anterior artificial teeth should be placed in essentially the same positions previously occupied by the natural teeth, and the labial surface of the denture base material should duplicate, as nearly as possible, the contour and position of the mucous membrane covering the alveolar ridge. Reducing the horizontal and vertical overlaps of the anterior teeth is necessary to reduce the incisal guide angle. It should be recognized that this reduction may have an impact on esthetics. The dangers from a high incisal guidance far exceed the possible impact on esthetics that might be produced when the teeth are set with less horizontal and vertical overlaps. It is not necessary for the anterior teeth to contact in maximum intercuspation. In fact, it is better that they be set just out of contact. If the mandibular ridge is forward of the maxillary ridge (as in a prognathic jaw relationship), the upper anterior teeth should be set end to end, with the incisal edges in light contact with the mandibular anterior teeth. When the prognathism is extreme, it may not be possible to have tooth contact in the incisor region because the maxillary incisors will be placed too far anteriorly and will put the upper lip under too much tension. In such situations, an anterior crossbite is the only alternative. Extremely high ridges may seem to create a problem unless it is realized that natural teeth once projected from these ridges. Insufficient space between the residual ridges is an indication that either the artificial teeth selected are longer than the 313 natural teeth or the vertical dimension of the face may be closed. However, if only parts of the ridges are too close together, the cause may be an incomplete alveolectomy during tooth extraction. Surgical removal of small bony projections may be indicated. Arranging the Posterior Teeth The preliminary arrangement of posterior teeth involves the application of principles similar to those applied in the arrangement of anterior teeth. The artificial posterior teeth should be placed near to where the natural teeth were positioned. This is easier said than done, however, because there are only a few guides for posterior tooth position. The final position of the occlusal plane, the occlusal contacts, and even the number of posterior teeth cannot be determined until the jaw relations are evaluated and found correct. The orientation of the anterior occlusal plane is determined initially by the wax occlusal rim. The anatomical guides most often used in developing the anterior plane of occlusion are the corners of the mouth. In general, the plane should be located either at or slightly below the corners of the mouth. During the arrangement of the mandibular anterior teeth, the position of the incisal edges of the mandibular anterior teeth eventually establishes the level of the anterior plane of occlusion. The posterior plane of occlusion is an extension of this anterior plane level with the junction between the middle and upper third of the retromolar pads bilaterally. These posterior references (retromolar pads) will place the overall plane at a level that is familiar to the tongue. If the plane is located higher or lower, for whatever reason, the dentures will interfere with normal tongue action. This will adversely influence denture base stability (Figure 17-15). The inclination of the occlusal plane is important to the stability or instability of dentures. If the plane is too low in the anterior region or too high in the posterior region, the maxillary denture will tend to slide forward. Ideally, the plane of occlusion should parallel the mean mandibular residual ridge. The height of the occlusal plane is not simply a matter of dividing the maxillomandibular denture space equally. This space is governed by the relative amount of bone lost from the two ridges. More 314 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures bone may have been lost from the maxillae than from the mandible, and the occlusal plane should not be placed an equal distance between the two ridges. It also should not be at a level that would favor the weaker of the two ridges (basal seats). The most reliable guides are esthetics or anterior tooth placement and the retromolar pads. The buccolingual position of the posterior teeth and the posterior arch form are determined anteriorly by the position of the canine and posteriorly by the shape of the basal seat and the location of the retromolar pads. The curvature of the arch of anterior teeth should flow pleasingly toward the posterior teeth. The posterior teeth are positioned in such a way that they are properly related to the bone that supports them and to the soft tissues that contact their facial and lingual surfaces. In the final tooth arrangement, the posterior form of the arch will be determined largely by the “neutral zone” between the cheeks and tongue. This is the space resulting from the removal of the posterior teeth and the loss of bone from the residual ridges. The pressure of the cheeks and tongue against the facial and lingual surfaces of the erupting natural teeth was strong enough to influence their alignment in the dental arch. These forces also are applied against dentures. Therefore the final arrangement of the arch must be developed with respect for the tongue and cheek (see Figure 17-15). The solution to the problem is to position the teeth along a line extending from the tip of the canine to the middle of the retromolar pad. This arbitrary line should pass through the central fossa of the mandibular premolars and molars (Figure 17-16). The basic principle for the buccolingual positioning of posterior teeth is that they should be positioned over the residual ridge. The canine and retromolar pad should provide guides for this arrangement. A B OCCLUSAL SCHEMES FOR COMPLETE DENTURE OCCLUSION The occlusal scheme or the tooth molds selected for occlusal rehabilitation will depend on the concept of occlusion that has been selected to satisfy the needs of the patient. The posterior teeth, arranged according to the occlusal concept selected, should fulfill the dentist’s philosophy of occlusion as well appear esthetically pleasing. Posterior tooth forms have aroused a great deal of controversy among clinicians and researchers. Chewing efficiency tests have shown a slight advantage to cusped teeth. Cuspal anatomy has not been shown to have any significant effect on the supporting tissues. Patient preference surveys have been inconclusive. Prosthetic tooth anatomy seems to be more important to dentists than to the patients who use the teeth. In the absence of clear evidence of the benefits of one tooth anatomy compared with others, dentists should use the least complicated procedures and tooth forms that will satisfy their con- Figure 17-15 A, Mandibular teeth positioned too far toward the buccal of the ridge (r) and too far toward the lingual (l). B, Positions of the mandibular teeth corrected from those shown in A. Chapter 17 Selecting and Arranging Prosthetic Teeth and Occlusion for the Edentulous Patient 315 A B Figure 17-16 A, The mean residual ridge, as well as selected anatomical landmarks, provides the guidances used in the buccolingual and anteroposterior positioning of the mandibular posterior teeth. B, Centering the wax occlusal rim on the mandibular record base with the anatomical guides is essential to the appropriate placement of the artificial teeth. The basal seat, or mean residual ridge, and the retromolar pads bilaterally are used to develop the positioning and height of the wax occlusal rim. cepts of occlusion and articulation of a mucosal supported dentition. There are several schools of thought on the choice of occlusal forms of posterior teeth for the three concepts of occlusion most often selected, namely, (1) bilateral balance, (2) monoplane or nonanatomical, and (3) lingualized articulations. Anatomical molds usually are selected for bilateral balanced articulation; however, nonanatomical teeth can be used in a balanced concept with the use of compensating curves. Nonanatomical or cuspless teeth are generally the choice for monoplane 316 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures articulation, although teeth with cusps also can be used. For the lingualized occlusal concept, a combination of upper anatomical and lower nonanatomical molds has been introduced by several tooth manufacturers. Arranging Anatomical Teeth to a Balanced Articulation The anterior teeth are set with a minimal vertical overlap of 0.5 to 1 mm and 1 to 2 mm of horizontal overlap to establish a low incisal guidance (see Figure 17-14). After these requirements are satisfied, the teeth may be rotated, tipped, overlapped, or spaced to achieve naturalness. In the arrangement of the posterior teeth, most clinicians set the mandibular teeth before the maxillary because this provides better control of the orientation of the plane of occlusion both mediolaterally and superoinferiorly. Number of Posterior Teeth Set The decision on the number of teeth to use will depend on the available space for posterior teeth from the distal of the canine to the retromolar pad. Placing teeth on the residual ridge incline as it ascends to the pad should be avoided. If only three teeth are to be arranged, it is more convenient to drop the first premolar and place the second premolar and the first and second molars into the available space. Eliminating the first premolar is a logical choice because this tooth has less occlusal surface for the mastication of food. Setting the Mandibular Teeth First The primary consideration in positioning the premolars is that they follow the form of the residual ridge. The facial surface of the premolars should be perpendicular to the occlusal rim, and yet slightly facial to the canine, but never farther facially than the buccal flange. In the ideal situation, the mandibular first and second premolars, with their central grooves, are positioned on a line from the canine tip to 1 to 2 mm below the top of the retromolar pad (Figure 1717). Before the first premolar is positioned, a small section of the mandibular wax occlusal rim is removed to accommodate the first and second premolars. A small cone of soft pink baseplate wax is attached to the neck of the first premolar tooth, and it is positioned in the arch in contact with the canine and with its central grooves on the reference line from the tip of the canine to the retromolar pad. The long axis of the tooth is positioned so that the cusp tips are level with the remaining mandibular wax occlusal rim. The second premolar is set in a similar manner. When these lower teeth have been arranged, a segment of the maxillary occlusal rim is removed to accommodate the first maxillary premolar, which is set into maximum intercuspation with the two lower premolars. If a space develops between the maxillary canine and first premolar, the maxillary first premolar is aligned with the canine, and the maxillary second premolar is positioned in the upper arch. Then the two mandibular premolars are repositioned to achieve maximum intercuspation with the maxillary premolars. The mandibular first premolar may need to be adjusted mesiodistally to fit into the available space. Reshaping of the tooth by grinding usually will satisfy the space requirements. Maintenance of the occlusal plane by positioning the mandibular teeth at the appropriate height is of paramount importance as is the placement of their central grooves on the reference line from the tip of the canine to the retromolar pad. The first three premolars set (two mandibular and one maxillary) are the key to the relative anteroposterior intercuspation of all the remaining posterior teeth. Once the premolars are set and properly related to each other, positioning of the remaining mandibular posterior teeth is easily accomplished. In the positioning of the mandibular first molar, the central groove is placed on the canine to retromolar pad reference line. The vertical height of the tooth is adjusted by positioning the cusp tips on the occlusal plane. After these adjustments are completed, the maxillary first molar is articulated with the mandibular first molar. A small segment of the wax occlusal rim is removed, and the tooth is attached to the record base with a small cone of soft baseplate wax. After the tooth is positioned, it is sealed to the record base with molten wax and the hot no. 7 spatula. After the maxillary first molar is positioned, the articulator is closed so that the mandibular tooth will assist in seating the maxillary tooth into maximum intercuspation. The index finger is used to hold the cervical neck of the maxillary tooth in place while the articulator is closed. Chapter 17 Selecting and Arranging Prosthetic Teeth and Occlusion for the Edentulous Patient 317 1-2 mm A B Figure 17-17 A, A point 1 to 2 mm below the top of the retromolar pad and the tip of the positioned mandibular cuspid are guides used in the placement of the mandibular posterior teeth. B, The central grooves of the posterior teeth are positioned on a line between the cuspid tip and the middle of the retromolar pad. When only three posterior teeth are arranged, it is essential that the central grooves of the molars be positioned slightly to the buccal to avoid crowding the tongue. This will develop the desired lingual cusp contact of the maxillary molar in the central fossa of the mandibular antagonist. The same procedure is used for setting the remaining maxillary teeth. The teeth on the opposite side of the dental arches are arranged in a similar manner. Setting the Maxillary Teeth First In arranging the maxillary posterior teeth first, start with the maxillary first premolar and continue the arrangement of the teeth through to the second molar. During the positioning of these teeth, the maxillary lingual cusps are aligned with the reference line that has been scribed on the mandibular wax occlusal rim from the mandibular canine tip to the middle of the retromolar pad. Positioning the maxillary teeth with a slight opening of the contact points between these teeth allows the mandibular teeth to better assume their correct mesiodistal position as they are interdigitated with the maxillary posterior teeth. Because this intercuspation is very exacting, it is best done by placing the mandibular first molar in position first. For the first molar to be placed and still preserve the reference line on the wax occlusal rim, a block of wax approximately the size of the mandibular molar tooth is all that is removed from 318 Part Three Rehabilitation of the Edentulous Patient: Fabrication of Complete Dentures the mandibular wax occlusal rim. When the mandibular first molar is placed in position without adjoining teeth, it is possible to determine its correct anteroposterior position more easily. If the mandibular first premolar is positioned first, the inconstant vertical overlap might crowd the tooth into difficult intercuspation with the maxillary teeth, and this would be continued throughout all the mandibular posterior teeth. Therefore placement of the mandibular first premolar is left until last to take up all the variation in vertical and horizontal overlap of the anterior teeth. The first premolar is then ground to fit the remaining space. The second mandibular molar is placed after the positioning of the first molar, thereby assuring its anteroposterior correctness. The mandibular second premolar is next placed, after another block of wax has been cut away from the occlusal rim. The mandibular first premolar is the last tooth to be placed. It frequently needs to be ground because of the minimal space remaining between the second premolar and the canine after these teeth have been arranged in maximum intercuspation. For this reason, the tooth must be ground and shaped to fit the space available. The teeth on both sides of the dental arches are arranged in a similar manner. Evaluating Bilateral Balanced Articulation The presence of a balanced articulation can be inspected after all the maxillary and mandibular teeth have been arranged. However, it must be remembered that unless the teeth are positioned in exactly the same location in the articulator as they were when their primordial forms were carved in the cutting instrument, they will not balance. Furthermore, if the end-controlling factors recorded from the patient and transferred to the instrument are also not the same as those used in developing the tooth molds, one should not expect a perfect bilateral balance to be present. With luck, what one will see during this exercise is that some minor deflections are observed and tha