Tooth preparations for complete crowns: an art form based on scientific principles.

STATEMENT OF THE PROBLEM: No recent literature has reviewed the current scientific knowledge on complete coverage tooth preparations. PURPOSE: This article traces the historic evolution of complete coverage tooth preparations and identifies guidelines for scientific tooth preparations. MATERIAL AND METHODS: Literature covering 250 years of clinical practice was reviewed with emphasis on scientific data acquired during the last 50 years. Both a MEDLINE search and an extensive manual search were used to locate relevant articles written in English in the last 50 years. RESULTS: Teeth should be prepared so that they exhibit the following characteristics: 10 to 20 degrees of total occlusal convergence, a minimal occlusocervical dimension of 4 mm for molars and 3 mm for other teeth, and an occlusocervical-to-faciolingual dimension ratio of 0.4 or greater. Facioproximal and linguoproximal line angles should be preserved whenever possible. When the above features are missing, the teeth should be modified with auxiliary resistance features such as axial grooves or boxes, preferably on proximal surfaces. Finish line selection should be based on the type of crown/retainer, esthetic requirements, ease of formation, and personal experience. Expectations of enhanced marginal fit with certain finish lines could not be validated by recent research. Esthetic requirements and tooth conditions determine finish line locations relative to the gingiva, with a supragingival location being more acceptable. Line angles should be rounded, and a reasonable degree of surface smoothness is desired. CONCLUSIONS: Nine scientific principles have been developed that ensure mechanical, biologic, and esthetic success for tooth preparation of complete coverage restorations.

Flapless anterior implant surgery: a surgical and prosthodontic rationale.

Full-thickness periosteal flap surgery is often accompanied by potential marginal bone loss and/or soft tissue recession. This is critical, particularly for the single-unit implant-supported restoration in the anterior maxilla, where the harmony of the soft and hard tissue architecture is of paramount importance to the development of natural aesthetics and function. This article demonstrates a flapless implant surgery technique in the anterior maxilla for optimal aesthetic results. The indications and limitations of this procedure are also discussed.

Effects of smoking on implant success in grafted maxillary sinuses.

STATEMENT OF THE PROBLEM: Cigarette smoking has been identified as a significant risk factor for dental implant treatment. PURPOSE: This retrospective study evaluated the effect of smoking and the amount of cigarette consumption on the success rates of the implants placed in grafted maxillary sinuses. MATERIAL AND METHODS: Sixty patients (16 smokers and 44 nonsmokers) were evaluated for the effects of smoking on osseointegrated implants placed in 84 grafted maxillary sinuses that contained a total of 228 endosseous root-form implants. Seventy implants were placed in 26 maxillary sinuses in smokers, whereas 158 implants were placed in 58 sinuses in nonsmokers. The number of implant failures and the amount of cigarette consumption were recorded. RESULTS: Of the 228 implants, 205 (89.9%) remained in function, after a mean follow-up period of 41.6 months (2 to 60 months). There was a significantly higher cumulative implant success rate in nonsmokers (82.7%) than in smokers (65.3%) (P =.027). Overall cumulative implant success rate was 76%. There was no correlation between implant failures and the amount of cigarette consumption (P >.99). CONCLUSION: Within the limitations of this study, cigarette smoking appeared to be detrimental to the success of osseointegrated implants in grafted maxillary sinuses regardless of the amount of cigarette consumption.

Clinical complications of osseointegrated implants.

STATEMENT OF PROBLEM: There is no comprehensive review of the literature that identifies the complications reported in clinical dental implant studies. PURPOSE: This article attempted to determine the types of complications that have been reported and to provide data regarding their frequency. METHODS: All available clinical studies from 1981 to 1997, published in English or with English abstract, that presented success/failure data regarding implant treatment were evaluated to determine the types of reported complications and to quantify implant loss as it relates to type of prosthesis, arch, time, implant length, and bone quality. RESULTS: Greater implant loss occurred with overdentures than with other types of prostheses. There was greater loss in the maxilla than mandible with fixed complete dentures and overdentures, whereas little arch difference was noted with fixed partial dentures. Implant loss increased with short implants and poor bone quality. The time of implant loss (preprosthetic vs postprosthetic) varied with type of prosthesis. Surgical complications included neurosensory disturbance, hematoma, mandibular fracture, hemorrhage, and tooth devitalization. Initial and long-term marginal bone changes were identified. Peri-implant soft tissue complications included dehiscence, fistulas, and gingival inflammation/proliferation. Mechanical complications were screw loosening/fracture, implant fractures, framework, resin base and veneering material fractures, opposing prosthesis fractures, and overdenture mechanical retention problems. Some studies also presented phonetic and esthetic complications. CONCLUSIONS: Although the literature presents considerable information on implant complications, variations in study design and reporting procedures limited the available data and therefore precluded proper analysis of certain complications.

Clinical methods for evaluating implant framework fit.

STATEMENT OF PROBLEM: Passive fit of implant-supported-prosthesis frameworks has been suggested as a prerequisite for successful long-term osseointegration. However, there are no scientific guidelines as to what is passive fit and how to achieve and measure it. PURPOSE: The purpose of this article is to discuss passive fit and to review the various clinical methods that have been suggested for evaluating implant framework fit.Methods. The dental literature was reviewed to identify the clinical methods that have been used to evaluate implant framework fit. CONCLUSIONS: The suggested levels of passive fit are empirical. Numerous techniques have been advocated to evaluate the prosthesis-implant interface, but none individually provides objective results. It is suggested that clinicians use a combination of the available methods to minimize misfits.

The effect of tooth preparation form on the fit of Procera copings.

PURPOSE: This study evaluated the marginal and internal adaptation of Procera copings using different tooth preparations. The variations comprised 4 finish line forms, 3 occlusal forms, 3 occlusocervical undulation forms to the proximal finish line, and 3 proximal auxiliary retention forms. MATERIALS AND METHODS: One hundred twenty preparations were made and copings were fabricated, cemented, embedded in an epoxy resin, sectioned, and measured at 14 sites. RESULTS: The feather-edge finish line had the highest mean external marginal opening (135 +/- 79 microns), compared with the chamfer finish line (64 +/- 38 microns), the 0.8-mm rounded shoulder (51 +/- 34 microns), and the 0.5-mm rounded shoulder (68 +/- 56 microns). All 3 forms of occlusal reduction produced comparable internal adaptation at the axial wall. Specimens with normal occlusal reduction had the best occlusal adaptation at the cusp tip but not to a statistically different degree from the exaggerated form. Variations in the vertical height of interproximal finish lines did not significantly affect marginal opening. However, proximal retentive features less than 2.5 mm wide and more than 0.5 mm deep cannot be accurately reproduced with the present Procera scanner tip. CONCLUSION: Feather-edge finish-line forms, deep retentive grooves, and deep occlusal morphology are not well reproduced using this system, but all other finish-line forms and design variations are accurately and clinically acceptably reproduced using this system.

Using a colorimeter to develop an intrinsic silicone shade guide for facial prostheses.

PURPOSE: To determine if using CIE L*a*b* color measurements of white facial skin could be correlated to those of silicone shade samples that visually matched the skin. Secondly, to see if a correlation in color measurements could be achieved between the silicone shade samples and duplicated silicone samples made using a shade-guide color formula. MATERIALS AND METHODS: A color booth was designed according to ASTM specifications, and painted using a Munsell Value 8 gray. A Minolta colorimeter was used to make facial skin measurements on 15 white adults. The skin color was duplicated using custom-shaded silicone samples. A 7-step wedge silicone shade guide was then fabricated, representing the commonly encountered thicknesses when fabricating facial prostheses. The silicone samples were then measured with the Minolta colorimeter. The readings were compared with the previous L*a*b* readings from the corresponding patient's skin measurements, and the relative color difference was then calculated. Silicone samples were fabricated and analyzed for three of the patients to determine if duplication of the visually matched silicone specimen was possible using the silicone color formula, and if the duplicates were visually and colorimetrically equivalent to each other. The color difference Delta E and chromaticity was calculated, and the data were analyzed using a coefficient-of-variation formula expressed by percent. A Pearson Product Moment Correlation Coefficient was performed to determine if a correlation existed between the skin and the silicone samples at the p < or = .05 level. RESULTS: The highest correlation was found in the b* dimension for silicone thicknesses of 1 to 4 mm. For silicone thicknesses of 6 to 10 mm, the highest correlation was found in the L* dimension. All three dimensions had positive correlations (R2 > 0), but only the 1-mm and 4-mm b* readings were very strong. Patient and silicone L*a*b* measurement results showed very little change in the a* axis, while the L* and b* measurements showed more change in their numbers, with changes in depth for all patient silicone samples. Delta E numbers indicated the lowest Delta E at the 1-mm depth and the highest Delta E at the 10-mm depth. All duplicated samples matched their original silicone samples to a degree that visual evaluation could not distinguish any color differences. Using volumetric measurements, a shade guide was developed for all 15 patients. CONCLUSIONS: There was good correlation between the patient's colorimeter measurements and the silicone samples, with the b* color dimension the most reproducible, followed by the L* and the a*. Silicone samples at 6, 8, and 10 mm matched the patient the best, and this study showed that silicone samples can be duplicated successfully if a good patient-silicone match is obtained. Rayon flocking fibers and liquid makeup are effective at matching facial prostheses and can be used to develop a simple shade guide for patient application.

Mandibular fracture after endosseous implant placement in conjunction with inferior alveolar nerve transposition: a patient treatment report.

A patient with a severely atrophic right posterior mandible had three endosseous implants placed in conjunction with transposition of the inferior alveolar nerve. Three weeks following implant placement surgery, the patient experienced a spontaneous fracture of the mandible involving the two anterior implants. The two implants were removed, and the fracture was treated with open reduction and fixation with titanium mesh. The fracture healed, and the posterior implant integrated. This report suggests that the buccolingual and superior-inferior position of the mandibular canal can increase the possibility of mandibular fracture by increasing the size of the buccal cortical plate that is removed to expose the nerve during surgery.

Endosseous implant placement in conjunction with inferior alveolar nerve transposition: an evaluation of neurosensory disturbance.

This retrospective study evaluated neurosensory dysfunction and the implant success rate associated with 64 implants placed in 15 patients following transposition of the inferior alveolar nerve. A total of 21 inferior alveolar nerve mobilization surgeries were performed. The mean postoperative follow-up time was 41.3 months, with a range of 10 to 67 months. The effects of surgical technique and implant surface geometry on neurosensory dysfunction were evaluated by using light touch, brush stroke direction, and two-point discrimination. The implant success rate was 93.8% (60/64). The surgical technique that involved detaching the mental foramen resulted in a significantly greater incidence of neurosensory disturbance (77.8%, 7/9) than did the technique that left the bony foramen intact (33.3%, 4/12). The overall incidence of neurosensory disturbance was 52.4% (11/21).

Prosthodontic considerations when using implants for orthodontic anchorage.

STATEMENT OF PROBLEM: The use of implants for orthodontic anchorage can produce superior preprosthetic tooth positions. Their use often requires a crown or prosthesis to be fabricated for use as a connection between the orthodontic devices and the implant. PURPOSE: In this article, factors that affect the design of prostheses required for orthodontic movement and examples of prosthesis designs and materials, based on the authors' experience, are presented.

An evaluation of microwave-polymerized resin bases for removable partial dentures.

PURPOSE: The hardness, porosity, and adaptation of removable partial dentures fabricated with one heat-polymerized denture base resin and two resins designed for microwave polymerization were evaluated. MATERIALS AND METHODS: Five prostheses were evaluated for each resin. Adaptation of the denture bases to the master cast was evaluated by spatial orientation and mean weight of residual impression material. The prostheses were than embedded in epoxy resin and sectioned for evaluation of resin hardness (Knoop hardness) and microporosity. RESULTS: There were no significant differences in the adaptation of the acrylic resin bases for Acron MC and Ch Lucitone. There was no significant difference in the mean Knoop hardness values for any of the resin bases near and away from the metal. None of the denture bases showed porosity greater than 100 microns. CONCLUSIONS: Both resin bases formulated for microwave polymerization were effectively polymerized around metal frameworks without adverse effects on resin hardness or porosity. Justi Denture Base material had poorer base adaptation than the other two resins.

The effect of using custom or stock trays on the accuracy of gypsum casts.

This study examined the linear dimensional stability of nonaqueous elastomeric impressions made from stock and custom trays by measuring casts derived from those impressions at 1 hour, 1 day, and 1 week. There was a small statistical difference among casts produced from stock versus custom trays compared to the master model. However, there was no significant difference in casts produced from impressions poured at 1 hour, 1 day, and 1 week. A custom tray with a 2.0 to 2.5 mm tray spacing had the least amount of variation, yet the differences between custom and stock trays may not be clinically significant.

Effect of two opaquing techniques and two metal surface conditions on metal-ceramic bond strength.

The optimal conditions for opaquing techniques during porcelain application have not been confirmed. In this study the metal-ceramic bond strength was measured among one porcelain and three dental alloys, namely a gold-platinum-palladium alloy, a silver-free gold-palladium alloy, and a base metal alloy, with two opaquing techniques (a single masking layer versus a thin overfired layer followed by a second masking layer). In addition, the opaque porcelain was fired over an oxidized and nonoxidized alloy surface for the silver-free gold-palladium alloy. No significant differences in bond strength were recorded between the two opaquing techniques with the gold-platinum-palladium and base metal alloys. There was no substantial differences between the two opaquing techniques when opaque was applied over an oxidized gold-palladium alloy surface and bond strengths were substantially greater over an oxidized surface. However, when the opaque was applied to a nonoxidized gold-palladium surface the two-layer technique created a significantly greater bond strength.

The prosthodontic management of endodontically treated teeth: a literature review. Part III. Tooth preparation considerations.

The final part of this literature review series presents guidelines for the optimal preparation of teeth to receive posts and cores.

The prosthodontic management of endodontically treated teeth: a literature review. Part II. Maintaining the apical seal.

Part II of the three-part literature review series addresses factors related to prosthodontic treatment that can affect the apical seal and endodontic success.

A comparison of the marginal and internal adaptation of titanium and gold-platinum-palladium metal ceramic crowns.

The marginal and internal adaptation of metal ceramic crowns fabricated by electrical discharge machining and conventional metal ceramic alloys were compared. The crowns were cemented using zinc phosphate cement, embedded in epoxy resin, and sectioned in two planes: diagonal and buccolingual. The crowns were then measured at nine sites. The results showed that there were no statistical differences between the external marginal opening of the titanium and the gold-platinum-palladium crowns. The overall marginal discrepancies for the restorations in this study were 61 microns (+/- 34 microns) for the titanium metal ceramic crowns and 47 microns (+/- 17 microns) for the gold-platinum-palladium metal ceramic crowns.

The prosthodontic management of endodontically treated teeth: a literature review. Part I. Success and failure data, treatment concepts.

Part I of this three-part literature review discusses the incidence of endodontic treatment required after prosthodontic procedures, whether crowns are needed on endodontically treated teeth, the primary purpose of posts, the causes of post and core failure, root fracture incidence data, and post design considerations. Pertinent questions are addressed based on the past 25 years of dental literature.

Recent graduates' and current dental students' evaluation of their prosthodontic curriculum.

This survey of recent graduates and third- and fourth-year dental students at Indiana University School of Dentistry determined whether the prosthodontic curriculum adequately prepared students for the prosthodontic portion of dental practice and whether there was material that should be added to or omitted from the prosthodontic curriculum. The survey evaluated 106 topics in the prosthodontic curriculum and areas related to prosthodontics. On the basis of their importance to the respondents, 59.4% of the topics were considered adequately emphasized, 2.9% of the topics were overemphasized and should be reduced in emphasis or eliminated, and 37.7% of the topics were underemphasized, which indicated the need to increase time devoted to these topics. Most of the underemphasized topics dealt with new materials, alternate techniques, private practice and its management, and the prosthodontic needs of special types of patients.

The effect of finish line form and luting agent on the breaking strength of Dicor crowns.

Molar teeth were prepared to a standardized cylindric form using a lathe. Dicor crowns were luted on these preparations using zinc phosphate, glass-ionomer, and resin cements. The crowns were thermocycled and subjected to fracture loading to compare the effect of the different luting agents on fracture strength. Five finishing lines were used to determine if resin cement and associated bonding procedures could counteract the negative effect certain finish lines produce on all-ceramic crowns. When resin cement was used in conjunction with restoration and tooth precementation bonding treatments, the crowns were significantly stronger than when glass-ionomer or zinc phosphate cements were used. No difference in strength was found between the five finish lines when the crowns were cemented with resin and associated bonding procedures.