Occlusal Considerations in Determining Treatment Prognosis

To function in occlusal harmony, the masticatory apparatus -- composed of the teeth and its supporting structures, temporomandibular joints, and associated neuromusculoskeletal structures -- must operate in an integrated and dynamic manner. Loss of integrated function, or of homeostasis in response to functional demand, may generate problems in occlusion. In health, adaptive changes occur with the teeth and periodontium in response to functional occlusal forces. With periodontal and endodontic disease, this adaptive capacity diminishes. The ability to foresee how these changes may influence dental treatment is important in the art of determining treatment prognosis.

Prognosis is the prediction or forecasting of the probable course and outcome of a disease. In clinical dentistry, the definition of prognosis has been extended to include the probable outcome that can be achieved with treatment. With clinical experience, the mechanics of dental procedure become less challenging. Rather, the ability to appropriately diagnose the condition and determine which procedure will provide the optimal outcome is the more difficult task. Unlike clinical procedures, which are technique-oriented, the art of determining prognosis is based on each individual’s collective learned and clinical experiences. Due to the variety of past experiences, views of treatment prognosis may vary.

Numerous factors influence dental prognosis (Table 1). These determinants can influence either or both the prognosis of individual teeth and overall treatment prognosis. Whereas the prognosis of the individual teeth will define which teeth are available for incorporating into the various treatment plan, the overall treatment prognosis will define whether a treatment should be undertaken, which of the available teeth conforms to the treatment, and whether it is likely to be successful.

This review paper will describe how occlusion influences the prognosis of the individual teeth and, subsequently, the overall treatment prognosis. Occlusal harmony exists when the various components of the masticatory system are healthy and can withstand the functional stress (Figure 1). When the tooth is affected by periodontal and endodontic diseases, the tooth becomes weakened. Despite therapy, the adaptive capacity of the tooth has been compromised, which changes the prognosis of the tooth. This paper will review how these occlusal variables influence prognosis.

Factors that Influence Functional Demand

Intensity of Occlusal Forces

Classically, occlusal forces are evaluated based on local factors such as periodontal health, surface area of periodontal support, clinical crown height, and the contact angle to the opposing dentition. Also important is the number of posterior tooth-to-tooth stops, which distribute the occlusal force. New insights have come from computer modeling and orthodontic studies that indicate that other variables can also be significant. Musculoskeletal factors can influence the forces placed on the dentition. Profit¹ has shown that an individual with a high Frankfort mandibular plane angle will generate about half of the first molar occlusal forces as an individual with a low angle. Additionally, Hannam and Wood² have shown the first molar occlusal force to be strongly influenced by the cross-sectional area of the masseter muscle. The masseter is readily evaluated clinically and accounts for 66 percent of the occlusal forces the patient is capable of generating. The role of these musculoskeletal factors on the occlusion of teeth as opposed to dental implants has been reviewed in detail by Curtis and colleagues ("Occlusal Considerations for Implant Restorations in the Partially Edentulous Patient," in this issue). Though these occlusal factors cannot be altered, the clinician must learn to appreciate their significance in determining prognosis.

During normal occlusal activities, occlusal contact and wear are minimal, occurring briefly during chewing and swallowing. With the presence of parafunctional habits such as clenching and bruxism, occlusal forces can become extensive. Trenouth³ showed that in subjects with bruxism, total occlusal contact time (38.7 minutes) was approximately seven times longer than in control subjects (5.4 minutes). With longer periods of occlusal contact, there is an increase in frequency and the total amount of occlusal force. Some have postulated that this increases stress on the periodontium. This idea, however, is not supported by clinical studies. Shefter and McFall,⁴ in a clinical survey of 66 adults, studied the occlusal relation as it relates to periodontal status. Collected data included dental histories, periodontal analysis, analysis of malocclusion, centric discrepancies, patterns of excursive movements, and patterns of occlusal contact and wear. Periodontal analysis indicates that occlusal factors play a minimal role in the progression of periodontal disease in healthy dentitions. An issue not addressed is the effect that parafunctional habits may have on unhealthy dentition, i.e., periodontally involved teeth with mobility. The difficulty in addressing this question scientifically is that mobile teeth are difficult to manage; the quantifying of mobility is controversial; and increases in mobility may be caused by multiple factors, including failing periodontium, increased occlusal trauma, parafunctional habits, extent of functional load, and existing dentition present to provide protection from occlusal load. Finding an answer to this question is complicated by the fact that it would require a prospective study allowing a harmful destructive habit to persist. The need for control and the ethical issues involved are such that this type of study can never be undertaken. For practicing clinicians, the solution is one of eliminating as many etiologic variables as possible to achieve the best possible prognosis. Thus, if parafunctional habits exist, they should be managed.

Age

In determining the overall treatment prognosis, age is perhaps the most important determinant. A treatment is a success if it is functional and survives the life span of the patient. A prognosis for a treatment plan may be fair for a patient 70 years of age (if the anticipated life span is 95 years old), but have a more dismal outlook for a patient 30 years of age. This is often seen in cases where a 30-year-old patient with 5 to 6 mm of attachment loss may require more aggressive treatment than a patient 70 years of age. Likewise, in a young patient, delaying the fully edentulous state through the use of a partial denture or an implant-supported prosthesis is preferable because the fourth or fifth set of full dentures will not be functionally ideal. Similarly, in medicine, the orthopedic surgeon will try every means to avoid placing hip implants in patient until he or she is well over 50. This is due to the limitation in the number of successful hip implants that can be placed. With technological advances, osseointegration has improved the situation in the partially dentate patient as well as patients requiring hip implants. So as technological improves, these limitations decrease and the prognosis improves. This notion of considering age in the overall treatment prognosis needs to be a more consistent theme in patient evaluation.

Age also plays an important role in the prognosis of individual teeth. With age, the signs of attrition and abrasion result in loss of tooth structures, crazing, and an increased presence of fracture lines (Figure 2). The limitation of restorations becomes more apparent over time as amalgam expands, corrodes, and fractures or as the composite seal is lost due to the differential expansion coefficient and restorative wear. All of these events will dictate replacement and additional removal of tooth structure as the restoration gets larger. This weakens the tooth structure to functional occlusal load so the probability of tooth fracture is increased. With tooth fracture, there may be the need for root canal therapy, a post-core, and a crown. The subsequent failure of this endodontically treated tooth may result in extraction and replacement with a bridge. Due to the harsh environment of the oral cavity, there tends to be a need to replace existing restorations. Thus the age of the patient and the characteristics of the existing restorations may influence the prognosis of the tooth and subsequently the prognosis of the overall case.

Age may also influence individual tooth prognosis. Traditionally, increased incidence of attachment loss and gingival recession correlate with increasing age. An excellent review⁵ on the epidemiology of periodontal disease among older adults indicates that moderate levels of attachment loss, bone loss, and recession are found in a high percentage of elderly adults, especially minorities. When one examines the various epidemiological studies closely, one finds that the rate and pattern of disease was similar to other adult populations. Being older does not increase the risk nor incidence, nor change the episodic pattern of periodontal disease. The amount of periodontal disease is still based on individual risk factor and oral hygiene. And as people get older, the accumulation of destructive events as the consequence of disease activity and poor oral hygiene become more evident. The amount of accumulated periodontal disease in relation to the patient’s age should be factored into the prognosis.

Role of Pulpal Health in Response to Occlusal Force

Although healthy teeth can withstand normal occlusal force, nonvital and/or endodontically treated teeth have an increased potential for root fracture (Figure 3). Based on the research of Helfer and colleagues,⁶ many dentists assume that endodontically treated teeth are weakened and fracture-prone because of the desiccation of the tooth structure. This is not the case since photoelastic study indicates that there is little difference in fracture resistance between vital and nonvital teeth. This section will review findings that suggest that increased susceptibility to fracture is associated with the role of the endodontically treated tooth in the restorative design and the amount of tooth structure removed.

Several classical studies have examined the relative amount of stress placed on a tooth based on its role in a prosthetic design. Teeth that serve as fixed prosthetic abutments bear greater stresses in function than a single crown.^7-8 When teeth are used as a removable partial abutment, the amount of stress increases.^9-10 It further increases when a tooth serves as the distal abutment tooth in a distal-extension partial denture design.^11-14 These stresses can fracture teeth weakened by endodontic therapy and dowel space preparation.

A selected review of retrospective chart review studies confirms the increased rate of fracture failure in endodontically treated teeth. In a review of 6,000 patient records by Sorensen and Martinoff,¹⁵ root fracture was shown to be up to five times more frequent in endodontically treated teeth than in healthy teeth. Further analysis indicated that the failure rate of endodontically treated teeth in removable partial dentures (22.6 percent) was twice that of those in fixed prostheses (10.2 percent) and four times that of teeth with crowns (5.2 percent). The incidence of root fracture increases with age and occurs more frequently in posterior dentition.¹⁶ Resistance to fracture increases when more tooth structure is available.¹⁷ In a longitudinal five- to eight-year review of 299 patients who were treated for periodontal-prosthetic therapy, Nyman and Lindhe¹⁸ noted that 75 percent of the abutment teeth that fractured were endodontically treated and serving as terminal abutments.

The main risk factor of root fracture is the loss of dentin during endodontic treatment. Excessive removal of dentin during access preparation, canal fill, and post preparation weakens the tooth and makes it prone to fracture.^19-20 Therefore, it is important to minimize dentin removal and post preparation. Since the placement of a post does not reduce nor improve the distribution of occlusal forces,^21-22 the use of posts should be limited to situations where they are required to provide retention for a core.²³ To achieve optimal fracture resistance of crowns on endodontically treated teeth, Ketac-Silver cores have been shown to be superior to amalgam or bonded amalgam.²⁴ Lastly, having at least 2 mm of crown margin apical to a core buildup is important for retention and resistance to occlusal forces.^19,25

These studies indicate the pulpal status of the tooth and its relationship to the amount of occlusal stress may significantly influence its prognosis. An endodontically treated tooth may have a fair prognosis in a fully dentate occlusion, but the same tooth may have a guarded prognosis in a partially dentate dentition. Furthermore, when this same tooth is the distal abutment in a long leverage free-distal extensional partial denture design, the prognosis is poor. This is an example of how an individual tooth may have a fair/guarded prognosis but because of the overall treatment plan, the prognosis may be significantly worse. In fact, the treatment plan may even dictate a poor/hopeless prognosis and result in strategic extraction or the use of implant-supported prosthesis.

Role of Periodontal Health in Response to Occlusal Force

Occlusion in Healthy Teeth vs. Periodontally Involved Teeth

In evaluating the prognosis of individual teeth to occlusal forces, an important determinant is the health of the periodontium. This relationship, termed "occlusal trauma,"^26-27 describes the pathologic alterations or adaptive changes in the periodontium in response to occlusal forces. Other terms used in the literature include "trauma from occlusion," "traumatizing occlusion," and "occlusal overload." The interrelationship of occlusion and periodontal disease has been recently reviewed.²⁸

Occlusal trauma can be classified as either primary or secondary.²⁶ Primary occlusal trauma is the effect of excessive or abnormal forces acting on a normal and healthy periodontium. Secondary occlusal trauma refers to the effect of normal or excessive forces acting on a reduced periodontium. While the literature and many textbooks emphasize this distinction, it is of little clinical relevance since the consequences of trauma from occlusion are similar and independent of the height of the periodontium. The more important fact is that occlusal trauma is dependent on how well the periodontium can withstand and distribute the occlusal forces. With a reduced periodontium, it takes a comparatively small force to cause occlusal trauma that will result in either adaptive or pathologic compensatory changes.

Clinical Diagnosis of Occlusal Trauma and Its Therapeutic Implications

The major clinical findings in patients with occlusal trauma include the presence of tooth mobility, fremitus, and pain from damaged supporting tissue when in the presence of excessive occlusal forces. Though clinical and radiographic signs such as widening of the periodontal ligament space, angular bony defects, abnormal occlusal contacts, infrabony pockets, crestal funneling, cervical notching, furcation rarefaction, vertical bone loss, hypercementosis, condensation of trabecular bone, and gingival recession are frequently associated with occlusal trauma, the clinician must remember their presence is only suggestive but not pathognomonic of occlusal trauma.^3,29-32 Many of these changes can be produced by a variety of other factors.

Increasing tooth mobility is the hallmark of occlusal traumatism. Mobility, per se, is a reflection of past and present disease experience and/or adaptive changes of a tooth and describes the ability of the tooth to withstand occlusal forces. This ability is highly influenced by past pathologic conditions resulting in attachment loss, the height of the remaining alveolar bone, and root morphology. These factors, added together, give the crown-to-root ratio, which dictates the mechanical resistance of the tooth to an applied force. Though many clinicians emphasize the importance of fremitus, it is not indicative of occlusal trauma. Fremitus is simply a functionally induced form of mobility that is reflective of past and present disease and/or adaptive changes. The clinical dilemma is to decide if the tooth movement observed is reflective of a past or ongoing pathologic condition.

Determining detrimental change involves observation of increasing tooth mobility over time. Unfortunately, this is a clinically difficult task. It would require multiple visits and a sensitive mobility-monitoring mechanism that can only be provided with a periodontometer or a Periotest (Siemens). This is not clinically practical due to the time requirement and the lack of sensitivity associated with most clinically used mobility indices. Operationally, the diagnosis of increasing mobility is made based on patient history of changes in tooth positions, increase in diastema, movement and shifting of teeth, and change in occlusion (Figure 4). This is followed by an occlusal analysis of the resulting changes and existing mobility pattern. From this information, one can diagnose presumptive situations of occlusal trauma. Due to the presumptive nature of the diagnosis, treatment and outcome analysis needs to be performed over time. In extensive restorative cases, evaluation of tooth mobility and suitability as abutment teeth may require long-term provisionalization of the prosthodontic case.

Several factors can influence tooth mobility. Mobility has been shown to influence clinical prognosis. If mobility is deemed clinically significant in treatment outcome, there are several strategies to decrease mobility.

The Influence of Mobility on Therapeutic Prognosis

The clinical implication of tooth mobility and increasing tooth mobility has been the focus of several recent studies. Rosling and colleagues³³ investigated the importance of mobility in patients with advanced periodontal disease. These patients were treated by open flap curettage and placed on supportive periodontal therapy. It was found that mobile and nonmobile teeth responded equally well to periodontal therapy. The maintenance and survival rates for treated mobile teeth were similar to those of nonmobile teeth as long as the patient complied with a rigorous two-week recall schedule during the supportive periodontal therapy phase. This study suggests mobility has no long-term detrimental effect as long as good oral hygiene is maintained. The problem with this study is that the compliance and frequency of maintenance visits required are not practical.

Investigators at the University of Michigan have published a series of studies addressing this issue with more realistic clinical conditions. The initial report by Fleszar and colleagues³⁴ focused on a subpopulation of patients in the University of Michigan longitudinal study on periodontal response to therapy that included 72 patients who had undergone periodontal therapy and completed at least one year of recall. These cases were followed for four additional years. At the end of that period, the investigators concluded that periodontal pockets associated with mobile teeth do not respond as favorably to treatment as compared to nonmobile teeth. Furthermore, there was attachment loss that occurred during the first two years following surgical therapy. These conclusions were confirmed in another subpopulation of the University of Michigan study by Wang and colleagues.³⁵ In examining 24 patients, they found that molar teeth exhibiting mobility at baseline or during the first year of treatment had more attachment loss at the end of eight years than molars without mobility. These findings are consistent with findings by Wagner,³⁶ which demonstrated that initial mobility, gingivitis, and mean probing depth together were significant risk factors for predicting future attachment level changes following periodontal treatment. Epidemiological data obtained by Ismail and colleagues³⁶ confirmed that the presence of tooth mobility was a significant risk factor for future attachment loss. These studies suggest tooth mobility, especially when unmanaged, will increase the risk of attachment loss.

Clinical Management of Occlusal Trauma and Tooth Mobility

Since occlusal trauma may result from two concurrent etiologic factors -- excessive occlusal force and inflammatory periodontal disease -- each problem is treated separately. Occlusal therapy is generally addressed following, or in conjunction with, periodontal therapy. Controlling or decreasing tooth mobility is the clinical measure for therapeutic success. The sequence for clinical management of occlusal trauma consists of three basic strategies: the re-establishment of periodontal health, occlusal adjustment, and dental splint therapy.

Re-establishment of Periodontal Health

Tooth mobility associated with periodontally diseased tissue can be decreased with periodontal therapy. Measurements with Muhlemann’s periodontometer have demonstrated an average decrease of mobility by 20 percent within four months after plaque and calculus removal.³⁸ Goldberg³⁹ found a 25 percent decrease in mobility shortly after scaling and curettage. Ferris⁴⁰ showed a reduction in tooth mobility ranging from 13.6 percent to 77.3 percent two months after initial therapy; the average reduction for the entire test group was 24.6 percent. Although periodontal surgical healing is not influenced by tooth mobility, surgical treatment can decrease tooth mobility by 40 percent to 50 percent.^39-40 These studies indicate that initial therapy can decrease tooth mobility by approximately 20 percent to 25 percent, whereas surgical treatment can decrease mobility by an additional 40 percent to 50 percent.

Occlusal Adjustment

Since mobility is a risk factor for future attachment loss, it is questioned whether occlusal equilibration should be performed to minimize these risks and whether it is effective. There are differences in opinion over this issue.

Occlusal adjustment has long been proposed as a method for the management of occlusal trauma. Muhleman²⁷ reported that mobility values are 30 percent higher in hypofunctional teeth than in hyperfunctional. With the re-establishment of bilateral balanced function by occlusal adjustment, mobility was reduced on the hypofunctional side by 18.1 percent and on the hyperfunctional side by 8.7 percent. Vollmer and Rateitschak⁴¹ confirmed that occlusal adjustment could result in mobility reductions of 18 percent to 28 percent after seven to 30 days. While it is generally agreed that occlusal adjustment can reduce tooth mobility, views differ as to when in the therapeutic sequence occlusal adjustment is indicated.

Reflecting the European philosophy of prosthetic rehabilitation of patients with advanced periodontal disease, Nyman and Lindhe^42-45 demonstrated that splinting or occlusal equilibration is indicated only if tooth mobility is extensive and may interfere with masticatory function or patient’s comfort. Additionally they demonstrated that once mobility and periodontal disease have been controlled, teeth with secondary occlusal trauma and a history of increased mobility can be used as abutments for fixed prostheses or splints. Teeth with severe attachment loss may still be used if inflammation is controlled. It was advocated that these teeth be splinted cross-arch in prosthetic design for a favorable distribution of occlusal force. Conversely, teeth with persistently increasing mobility are not acceptable abutments and should not be used.

Based on various studies performed at the Eastman Dental Clinics, Zander and Polson⁴⁶ concluded that the single most important factor for successful periodontal disease management is plaque control, and most cases do not require occlusal adjustment or splinting. This is consistent with this group’s experimental animal studies, which suggested occlusal trauma is not a co-destructive factor for further attachment loss. Occlusal adjustment was advocated only to improve a patient’s comfort and function.

Caffessee,⁴⁷ Ramfjord and Ash⁴⁸ stated that occlusal therapy should be performed as part of the initial preparation phase of periodontal treatment whenever there is a functional indication for it. After the inflammation has been controlled, appropriate occlusal management may include occlusal adjustment, temporary or long-term splinting, stabilization appliances, orthodontic treatment, and restorative dentistry. The latter two definitive treatments were recommended to be performed at least one to two months or more after completion of periodontal surgery. Splinting was advocated only when mobility interferes with the health and comfort of the patient or when the mobility is progressively increasing.

This philosophy is supported by the findings by Burgett and colleagues⁴⁹ who studied 50 treated patients in the Michigan longitudinal periodontal study who were placed into the periodontal maintenance phase. Of this total population, 22 patients received occlusal adjustment and 28 patients were placed in the control nonadjustment group. After two years, it was concluded that those in the occlusal adjustment group who received conventional periodontal therapy, whether surgical or nonsurgical, had a more favorable clinical attachment level and gain of attachment than those in the nonadjustment group. In addressing the issue of whether initial tooth mobility is a risk factor for future attachment loss, these investigators noted that with occlusal adjustment, initial tooth mobility did not affect attachment response during this limited two-year period of study.

Dental Splint Therapy

A dental splint is an appliance designed to stabilize mobile teeth and allow for "normal" function within the limits of the reduced periodontium. The premise is that splinting will aid in the reduction of tooth mobility and create a more stable and favorable situation for periodontal repair. Splints are classified according to the length of service time and the therapeutic objectives. Temporary splints are utilized in the short term to help stabilize teeth during periodontal treatment. Provisional splints are used for limited duration, from months to several years, for diagnostic purposes. Permanent splints are for long-term use and may be of fixed or removable design.

Splinting has been advocated for stabilizing moderate to advanced tooth mobility. The goal of splint therapy is to reduce occlusal trauma and provide comfort during masticatory function. It may be a treatment of last resort, short of extracting the tooth. Restoratively, permanent splinting is used to stabilize teeth after orthodontic treatment and to prevent extrusion of unopposed teeth. Dental emergency providers and oral surgeons use splints to stabilize subluxated or avulsed teeth following acute trauma or transplantation procedures. Periodontally, splinting is used to stabilize the teeth and to facilitate therapy such as initial preparation, occlusal adjustment, and surgery.

The benefits of splinting teeth are based on clinical impressions rather than on scientific studies. Splinting has not been shown to reduce individual tooth mobility or enhance tissue healing. Several studies^50-52 indicate that although splinting teeth may temporarily improve their mobility status, it does not reduce their mobility once the splint has been removed. The splint, in effect, masks the mobility status. This results in making the accurate assessment of individual tooth mobility a difficult task. Renggli and Schwizer⁵¹ evaluated teeth splinted with copings and telescopic-designed prostheses. After 12 months, no improvement was observed after the splint was removed. These findings have been supported by Rateitschak and coworkers.^50,52 Kegel and colleagues⁵³ used a split-mouth design to evaluate the effect the effect of splinting on tooth mobility during initial periodontal therapy. After 15 weeks, the reductions in tooth mobility observed in the splinted and unsplinted teeth were similar, and any reduction in mobility could only be attributed to improved occlusal relationships and reduction in inflammation. Galler and colleagues⁵⁴ designed a similar split-mouth study to evaluate the effect of splint on tooth mobility following periodontal surgical procedures. After healing, postsurgical mobility was similar for both splinted and unsplinted teeth. Despite the lack of objective improvement in therapeutic response, it is reasonable to splint teeth during periodontal therapy not only to reduce mobility, but also to provide for patient comfort and normal masticatory function during therapy.

Despite the lack of scientific support for splinting, many clinicians are of the opinion that it is valuable in achieving therapeutic success. Clinical reports by Amsterdam,⁵⁵ Cohen and Chacker,⁵⁶ and Nyman and colleagues⁴⁴ described periodontally handicapped patients with multiple missing teeth and advanced mobility who were treated successfully over the long term (Figure 5). In these reports, features contributing to the success of the reported cases included control of periodontal inflammation, good oral hygiene in the presence of healthy periodontal tissue, adequate number and distribution of abutment teeth, cross-arch stabilization, and control of the occlusion. Though the success of these cases is dramatic and impressive, it is important to recognize that these are case reports of highly motivated patients with a high degree of commitment toward oral hygiene and periodontal maintenance. Detail assessment of clinical findings as well as patient compliance is critical for success in defining the prognosis in this type of advanced prosthetic treatment.

The health of the periodontium greatly influences the ability of each tooth to withstand occlusal force. Prognostically, it is important that there is a distribution of occlusal stops with healthy periodontium. A case in point is the dentition where only maxillary and mandibular anteriors are present and the patient refuses to wear a partial denture. The occlusal forces can be such that all of these teeth may be mobile despite adequate periodontal support. The good news is that with the elimination of periodontal inflammation and the addition of posterior support, there is often decreased mobility. Additionally, with the wider acceptance of dental implants, dental prostheses may provide occlusal support that previously was not biomechanically possible based on conventional prosthetic design (Figure 6). Advances in dental implants and restorative materials have created greater opportunities to better manage the distribution of occlusal forces. These advances can improve case prognoses in ways previously thought to be clinically impossible.

Conclusion

The thesis of this paper is to discuss how individual tooth and overall treatment prognosis is affected by the occlusal harmony of the masticatory apparatus. In a healthy situation, the masticatory apparatus -- composed of the teeth and its supporting structures, temporomandibular joints, and associated neuromusculoskeletal structures -- operates in an integrated and dynamic manner. Loss of integrated function, such as the structural integrity of the tooth through endodontic treatment or periodontal disease, can result in adaptive changes in response to occlusal force. Should the adaptive responses not be able to compensate for the occlusal forces, the prognosis may worsen significantly.

Authors

Richard T. Kao, DDS, PhD, is an associate adjunct professor in the Periodontology Department at the University of the Pacific and has a private practice limited to periodontics and dental implants in Cupertino, Calif. He is a diplomate of the American Board of Periodontology.

Raymond Chu, DMD, is an assistant clinical professor in the Restorative Department at the University of California in San Francisco and has a private practice limited to prosthodontics in Cupertino, Calif.

Donald Curtis, DMD, is professor in the Restorative Department at UCSF and has a private practice limited to prosthodontics in Berkeley, Calif.

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To request a printed copy of this article, please contact: Richard T. Kao, DDS, PhD, 10440 S. DeAnza Blvd., Suite #D-1, Cupertino, CA 95014 or at richkao@value.net.

Legends

Figure 1. Occlusal harmony is dependent on each components of the masticatory system to withstand functional occlusal demand.

Figure 2. With periodontal and endodontic health, heavy occlusal stress is compensated with crazing, increase fracture lines, and attrition. This may lead to the loss of vertical dimension. To withstand this type of constant occlusal stress, the compensatory requirement is good periodontal and endodontic health.

Figure 3A. A patient with signs of heavy attrition (photo courtesy of Dr. R. Gurrola).

Figure 3B. The heavy attrition shown in Figure 3A led to the fracture of this endodontically treated tooth (photo provided by Dr. R. Gurrola).

Figure 4. A history of increasing tooth mobility should be investigated when there are signs of increase in diastema spacing, shifting of teeth, and change in occlusion.

Figure 5A. With the re-establishment of periodontal health, cross-arch splinting can be successful as demonstrated in this case. Pre-treatment photo.

Figure 5B. Extraction of hopeless teeth and re-establishment of periodontal health.

Figure 5C. Coping placement for the abutment teeth.

Figure 5D. The placement of a splinted cross-arch prosthesis.

Figure 6A. With implant-supported prosthesis, biomechanical distribution of occlusal forces can be better distributed as exemplified in this case. Pretreatment photo.

Figure 6B. Removal of hopeless teeth and periodontal treatment.

Figure 6C. Four implants were placed in the Nos. 5, 8, 9, and 10 positions so biomechanical forces can be distributed. The prosthesis is also segmented into six pieces so repairs and obsolescence can be accommodated.

Figure 6D. Radiographs of the final prosthesis.

Table 1. Factors Influencing Prognosis

The prognosis of individual teeth
* Mobility
* Attachment level and relative bone support
* Periodontal pockets
* Tooth and root morphology
* Infrabony defects
* Furcation involvement
* Relationship to adjacent teeth and edentulous area
* Tooth vitality and endodontic status
* Extent of restoration present
* Caries and root resorption

The overall prognosis
* Age
* Medical and systemic background
* Patient compliance
* Individual tooth prognosis
* Strategic position and pulpal status of remaining teeth
* Present periodontal status (height of bone, attachment level, mobility, inflammation)
* Assessment of past periodontal response to disease
* Estimation of present level of disease of activity
* Occlusion, malocclusion, and anatomical determinants of occlusal force
* Number of remaining teeth