Correction of Existing Disease

Existing disease is revealed during the clinical examination. The disease process can usually be arrested by identification and reduction of the initiating factors, identification and improvement of the resistive factors, or both (Fig. 3-1). For example, oral hygiene instruction helps reduce the amount of residual plaque, an initiating factor, and thus helps reduce the likelihood of further dental caries. It also helps improve gingival health, and the resulting healthy tissue is more resistant to disease.

Fig. 3-1 Poor plaque control with dental caries.

Additional fluoride intake (e.g., mouth rinses) is also recommended in a patient with a caries problem. Restorative care replaces damaged or missing tooth structure, but additional treatment is essential for controlling the disease that caused the damage.

Prevention of Future Disease

The likelihood of future disease can be predicted by evaluating the patient’s disease experience and by knowing the prevalence of the disease in the general population. Treatment should be proposed if future disease seems likely in the absence of such intervention.

Restoration of Function

Although objective measurement may be difficult, the level of function is assessed during the examination. Treatment may be proposed to correct impaired function (e.g., mastication or speech).

Improvement of Appearance

Patients often seek dental treatment because they are dissatisfied with their appearance. However, it is difficult to objectively assess dental esthetics. The dentist should develop expertise in this area and should be prepared to appraise the appearance of the patient’s dentition and listen carefully to the patient’s views. If the appearance is far outside socially accepted values, the feasibility of corrective procedures should be brought to the patient’s attention. Long-term dental health should not be compromised by unwise attempts to improve appearance. Patients should always be made aware of the possible adverse consequences of treatment.

Plastic Materials

Plastic materials (e.g., silver amalgam or composite resin) are the most commonly used dental restoratives. They allow simple and conservative restoration of damaged teeth. However, their mechanical properties are inferior to those of cast metal or metal-ceramic restorations. Their continued service depends on the strength and integrity of the remaining tooth structure. When the remaining tooth substance needs reinforcement, a cast metal restoration should be fabricated, usually with amalgam as the foundation or core (see Chapter 6).

Large amalgam restorations (Fig. 3-2A) are shaped or carved directly in the mouth. The great degree of difficulty associated with this direct approach often results in defective contours and poor occlusion. The indirect procedure, used in making cast metal crowns (Fig. 3-2B), facili-tates the fabrication of more accurately shaped restorations.

Fig. 3-2 A, The large amalgam restoration is hard to condense and contour accurately. B, The complete cast crown is stronger and can be shaped by an indirect procedure in the dental laboratory.

Cast Metal

Cast metal crowns are fabricated outside the mouth and are cemented with a luting agent. To minimize exposure of the luting agent to oral fluids, a long-lasting restoration must have good marginal adaptation. The highly refined techniques for overcoming the problem of marginal fit also permit the manufacture of cast metal crowns with precisely shaped axial and occlusal surfaces. This ensures continued periodontal health and good occlusal function. The internal dimensions of a casting must seat without binding against the walls while remaining stable and not becoming displaced during function. Preparation design for cast metal restorations is crucial and is discussed in detail in Chapter 7, Chapter 8, Chapter 9 and Chapter 10.

Intracoronal restorations

An intracoronal cast metal restoration (Fig. 3-3), or inlay, relies on the strength of the remaining tooth structure for support and retention, just as a plastic restoration does. However, greater tooth bulk is needed to resist any wedging effect on the preparation walls. Therefore, this restoration is contraindicated in a significantly weakened tooth. When fabricated correctly, it is extremely durable because of the strength and corrosion resistance of the gold casting alloy; in a tooth with a minimal proximal carious lesion, however, it usually requires greater removal of tooth structure than does an amalgam preparation. Inlays do not have sufficient resistance or retention to be used as abutment retainers for FDPs.

Fig. 3-3 A, The mesio-occlusal-distal (MOD) inlay is generally contraindicated because there is the risk of tooth fracture. However, it can be a very long-lasting restoration. These, placed in 1948, are still satisfactory after 58 years. B, These small gold foil restorations were placed in 1943.

Extracoronal restorations

An extracoronal cast metal restoration (Fig. 3-4), or crown, encircles all or part of the remaining tooth structure. As such, it can strengthen and protect a tooth weakened by caries or trauma. To provide the necessary bulk of material for strength, considerably more tooth structure must be removed than for an intracoronal restoration. The margins of an extracoronal restoration often must be near the free gingiva, which can make maintenance of tissue health difficult. Tooth preparation for an extracoronal restoration may be combined with intracoronal features (e.g., grooves and pinholes) to gain resistance and retention.

Fig. 3-4 A, Complete cast crowns. B, C, Partial veneer crowns.

Metal-Ceramic

Metal-ceramic restorations (Fig. 3-5) consist of a tooth-colored layer of porcelain bonded to a cast metal substructure. They are used when a complete crown is needed to restore appearance as well as function. Sufficient reduction of tooth structure is necessary to provide space for the bulk of porcelain needed for a natural appearance. Thus, the preparation design for a metal-ceramic crown is among the least conservative, although tooth structure can be conserved if only the most visible part of the restoration is veneered.

Fig. 3-5 A, B, Metal-ceramic restorations.

The labial margins of a metal-ceramic restoration are often discernible and may detract from its appearance. They can be hidden by subgingival placement, although they then have the potential for increasing gingival inflammation; this should be avoided when possible.¹ Appearance can be improved by omitting the metal shoulder and making the labial margin in porcelain. As discussed in Chapter 24, this is a more demanding laboratory procedure.

Resin-Veneered

Resin-veneered restorations were popular before the metal-ceramic technique was fully developed, but problems with wear and discoloration of the polymethyl methacrylate veneer (Fig. 3-6) limited their use to long-term interim restorations. Current resin-veneer techniques² incorporate bis-GMA–based materials (bisphenol-A glycidyl dimethacrylates), which have better physical properties than do the earlier acrylic resins, and adhesive techniques to improve the bond to the supporting metal.^3,4

Fig. 3-6 Worn acrylic resin veneer.

Fiber-Reinforced Resin

Advances in composite resin technology, especially the introduction of glass and polyethylene fibers,^5–7 have prompted the use of indirect composite resin restorations for inlays, crowns, and FDPs. Excellent marginal adaptation and esthetic results are achievable (Fig. 3-7), but because these are newer technologies, little is known about their longer-term performance (see Chapter 27).

Fig. 3-7 Fiber-reinforced fixed dental prosthesis.

Complete Ceramic

Crowns, inlays, and laminate veneers made entirely of dental porcelain can be the most esthetically pleasing of all fixed restorations (Fig. 3-8). Drawbacks include a comparative lack of strength and the difficulties associated with achieving an acceptable marginal fit. The current focus in improving strength lies with either veneering a high-strength alumina, zirconia, spinel, or lithium disilicate core^8–10 with a more translucent porcelain or using a leucite-reinforced translucent material^11–13 (see Chapter 25). Complete ceramic restorations are fabricated by an indirect technique and generally retained with composite resin. Acid etching is used to provide retention “keys.”

Fig. 3-8 Complete ceramic restoration.

Fixed Dental Prostheses

An FDP (Fig. 3-9) is often indicated when one or more teeth require removal or are missing. Such teeth are replaced by pontics that are designed to fulfill the functional and often the esthetic requirements of the missing teeth (see Chapter 20). Pontics are connected to retainers, which are the restorations on prepared abutment teeth.

Fig. 3-9 A, A three-unit fixed dental prosthesis showing the main components. B, The pontic rigidly attached to crowns on the abutment teeth. The connectors should occupy the normal interproximal contact area and be large enough for strength but not so large as to impede plaque control.

All the components of an FDP are fabricated and assembled in the laboratory before cementation in the mouth. This requires precise alignment of tooth preparations. Because unseating forces on individual retainers can be considerable, highly retentive restorations are essential. FDPs have been demonstrated to have exceptional long-term success,¹⁴ which is ensured by controlling the magnitude and direction of forces and by making sure the patient practices appropriate oral hygiene measures.

Implant-Supported Prostheses

Single or multiple missing teeth can be replaced with an implant-supported prosthesis (Fig. 3-10). For the successful “osseointegrated” technique, the bone is atraumatically drilled to receive precisely fitting titanium cylinders.¹⁵ These are left in place without loading for some months until they are invested with bone. Only then are function and esthetics restored with a prosthesis (see Chapter 13).

Fig. 3-10 Four-unit fixed dental prosthesis supported by four dental implants.

Partial Removable Dental Prosthesis

A partial removable dental prosthesis (RDP) (Fig. 3-11) is designed to replace missing teeth and their supporting structures. Forces applied to a well-designed prosthesis are distributed to the remaining teeth and the residual alveolar ridges. These forces are most accurately controlled if the abutment teeth are provided with fixed cast restorations that have carefully contoured guide planes and rest seats (see Chapter 21).

Fig. 3-11 The component parts of a partial removable dental prosthesis.

Complete Dentures

Some of the difficulties encountered with complete dentures relate to the lack of denture stability and a gradual loss of supporting bone. Stability is enhanced if the denture has a carefully designed occlusion. Problems with stability can be especially severe when the mandibular incisors are the only teeth retained, with ensuing damage to the opposing premaxilla,¹⁶ although any treatment plan that involves a complete denture opposing fixed restorations requires careful planning of the occlusion (Fig. 3-12). For selected patients, providing an overdenture that rests on endodontically treated roots may help preserve the residual ridge and enhance the stability of the complete denture.¹⁷

Fig. 3-12 Special planning is required when a combination of a complete maxillary denture is planned opposing a fixed mandibular prosthesis. In general, a trial maxillary denture is indicated so the fixed prosthesis can be fabricated to a well-aligned occlusal plane. A, Preoperative appearance. B to E, Completed restoration.

(Courtesy of Dr. J. A. Holloway.)

Decision to Remove a Tooth

The decision to remove a tooth is part of the treatment-planning process and is made after assessing the advantages and disadvantages associated with retention of the tooth. Sometimes it is possible to retain a tooth with an apparently hopeless prognosis by using highly specialized and complex techniques. In other cases, removing the tooth is the treatment of choice (Fig. 3-13). A decision about replacing a missing tooth is best made at the time its removal is recommended, rather than months or years after the fact.

Fig. 3-13 Poor treatment planning. The displaced premolar should never have been restored under these circumstances.

(Courtesy of Dr. P. B. Robinson.)

Consequences of Removal without Replacement

The decision to replace or not replace missing teeth requires a careful analysis of the costs and benefits of the action. The loss of posterior occlusion may lead to excessive forces on the remaining dentition with consequent damage and poor function. However, studies have demonstrated that adequate function is possible with reduced posterior occlusion.¹⁸ Deciding not to replace a tooth may lead to a situation in which the balance of the forces exerted on that tooth by the adjacent and opposing teeth and supporting tissues and by the soft tissues of the cheeks, lips, and tongue is upset (Fig. 3-14). The consequences may be supraclusion of the opposing tooth or teeth, tilting of the adjacent teeth, and loss of proximal contact (with resulting disturbances in the health of the supporting structures and the occlusion). However, the teeth adjacent to an edentulous space have not been shown to be at greater risk of damage,¹⁹ and the rate of change of teeth adjacent to an edentulous space is usually slow.²⁰

Fig. 3-14 Loss of a mandibular first molar not replaced with a fixed dental prosthesis. The typical consequences are supraclusion of opposing teeth (1), tilting of adjacent teeth (2), and loss of proximal contacts (3).

(A, Redrawn from Rosenstiel SF: Fixed bridgework—the basic principles. In Rayne J, ed: General Dental Treatment, London, Kluwer Publishing, 1983.)

However, if the situation is not carefully monitored and significant movement of adjacent teeth has occurred, simple replacement of the missing tooth at this late stage may prevent further disruption, although it may be insufficient to return the dentition to full health. Extended treatment plans, including orthodontic repositioning and additional cast restorations (to correct the disturbed occlusal plane), may be needed to compensate for the lack of treatment at the time of tooth removal.

Replacement of a Single Missing Tooth

Unless bone support has been weakened by advanced periodontal disease, a single missing tooth can almost always be replaced by a three-unit FDP that includes one mesial and one distal abutment tooth. An exception is when the FDP is replacing a maxillary or mandibular canine. Under these circumstances, the small anterior abutment tooth needs to be splinted to the central incisor to prevent lateral drift of the FDP.

Cantilever fixed dental prostheses

FDPs in which only one side of the pontic is attached to a retainer are referred to as cantilevered. An example would be a lateral incisor pontic attached only to an extracoronal metal-ceramic retainer on a canine. Cantilevered FDPs remain popular because some of the difficulties encountered in making a three-unit FDP are lessened. Also, many clinicians are reluctant to prepare an intact central incisor, preferring instead to use a cantilever.

However, the long-term prognosis of the single-abutment cantilever is poor.²¹ Forces are best tolerated by the periodontal supporting structures when directed in the long axes of the teeth.²² This is the case when a simple three-unit FDP is used. A cantilever induces lateral forces on the supporting tissues, which may be harmful and lead to tipping, rotation, or drifting of the abutment (Fig. 3-16). Laboratory analysis^23,24 has confirmed the potential harmful nature of such FDPs. However, clinical experience with resin-retained FDPs has suggested that cantilever designs may be preferred, especially because re-adhesion after failure is greatly facilitated²⁵ (see Chapter 26).

Fig. 3-16 A, Forces applied to a cantilever fixed dental prosthesis are resisted on only one side, leading to imbalance. Vertical forces can cause tipping, and horizontal forces, rotation, of abutment teeth. B, By including both adjacent teeth in the prosthesis, it is possible to resist forces much better since the teeth have to be moved bodily rather than merely rotated or tipped.

(Redrawn from Rosenstiel SF: Fixed bridgework—the basic principles. In Rayne J, ed: General Dental Treatment, London, Kluwer Publishing, 1983.)

When multiple missing teeth are replaced, cantilever FDPs have considerable application (see Fig. 3-20). The harmful tipping forces are resisted by multiple abutment teeth, and movement of the abutments is unlikely. Cantilevers are also successfully used with implant-supported prostheses (see Chapter 13).

Fig. 3-20 A, A five-unit fixed dental prosthesis (FDP) replacing the maxillary first molar and first premolar. The middle abutment can act as a fulcrum during function, with possible unseating of one of the other retainers. To be successful, this type of FDP needs extremely retentive retainers. B, An alternative approach is a nonrigid dovetail connector between the molar pontic and the second premolar. C, Where periodontal support is adequate, a much simpler approach would be to cantilever the first premolar pontic.

(Redrawn from Rosenstiel SF: Fixed bridgework—the basic principles. In Rayne J, ed: General Dental Treatment, London, Kluwer Publishing, 1983.)

Unrestored abutments

An unrestored, caries-free tooth is an ideal abutment. It can be prepared conservatively for a strong retentive restoration with optimum esthetics (Fig. 3-17). The margin of the retainer can be placed without modifications to accommodate existing restorations or caries. In an adult patient, an unrestored tooth can be safely prepared without jeopardizing the pulp as long as the design and technique of tooth preparation are wisely chosen. Certain patients are reluctant to have a perfectly sound tooth cut down to provide anchorage for an FDP. In these cases, the overall dental health of the patient, rather than the condition of each individual tooth, should be emphasized.

Fig. 3-17 A, B, Unrestored abutment teeth can be prepared for conservative retainers. C, An esthetic fixed dental prosthesis replacing a maxillary incisor.

Mesially tilted second molar

Loss of a permanent mandibular first molar to caries early in life is still relatively common (Fig. 3-18). If the space is ignored, the second molar may tilt mesially, especially with eruption of the third molar. It then becomes difficult or impossible to make a satisfactory FDP, because the positional relationship no longer allows for parallel paths of insertion without interference from the adjacent teeth.

Fig. 3-18 A, Early loss of a mandibular first molar with mesial tilting and drifting of the second and third molars. B, A conventional three-unit fixed dental prosthesis will fail because its seating is prevented by the third molar. C, A modified preparation design can be used on the distal abutment. D, A better treatment plan would be to remove the third molar and upright the second molar orthodontically before fabricating a fixed dental prosthesis.

(Redrawn from Rosenstiel SF: Fixed bridgework—the basic principles. In Rayne J, ed: General Dental Treatment, London, Kluwer Publishing, 1983.)

In such circumstances, an FDP is sometimes made with modified preparation designs or with a nonrigid connector, or a straightforward solution²⁷ may be considered: uprighting the tilted abutment orthodontically with a simple fixed appliance. However, the problem can be avoided altogether if a space-maintainer appliance (Fig. 3-19) is fabricated when the first molar is removed. This device may be as simple as a square section of orthodontic wire bent to follow the edentulous ridge and anchored with small restorations in adjacent teeth.

Fig. 3-19 Square section orthodontic wire can be used as a simple stabilizing appliance to prevent drifting of abutment teeth after exodontia. The wire is retained by placing small restorations. As an alternative, orthodontic bands can be used as the retainer. Note that these simple stabilizers do not prevent supraeruption of opposing teeth; in areas where this is anticipated, a provisional fixed dental prosthesis is needed.

Replacement of Several Missing Teeth

Fixed prosthodontics becomes more difficult when several teeth must be replaced. Problems are encountered in restoring a single long, uninterrupted edentulous area or multiple edentulous areas with intermediate abutment teeth (Fig. 3-20), especially when anterior and posterior teeth are to be replaced with a single fixed prosthesis. Underestimation of the problems involved in extensive prosthodontics can lead to failure. One key to ensuring a successful result is to plan the prostheses by waxing the intended restorations on articulated diagnostic casts. This is essential for complex fixed prosthodontic treatments, particularly when an irregular occlusal plane is to be corrected, the occlusal vertical dimension is to be altered, an implant-supported prosthesis is recommended, or a combination of fixed and removable prostheses are to be used. The precise end point of such complicated treatments can be far from evident, even to an experienced prosthodontist (see Fig. 2-39).