The International Journal of Prosthodontics, 06/1998

Purpose: This article describes the concept of the Marburg double crown system (MDC system) in the treatment of partially edentulous patients. Long-term success is assessed by a review of patient records. Materials and Methods: Double crowns with clearance fit are used to retain tooth-, mucosa-, and implant-supported removable partial dentures (RPD). To achieve retention, an additional attachment, the TC-SNAP system, is used. All metal components are fabricated in a single cobalt-chromium-molybdenum alloy; the framework (including outer crowns) is cast in one piece. Because of the framework's rigidity, the RPD can be constructed without major and minor connectors. The denture base adjacent to the abutments is fabricated using a perioprotective design that is similar to fixed partial dentur es. One hundred eleven dentures, of which 49 (44%) were fabricated for patients with intraoral defects, were evaluated by reviewing patient records. Results: The mean age of the patients at the time of insertion was 57.5 years (± 12.3). The mean number of double crowns per denture was 3.5 ± 2.1 (range, 1 to 9). The probability that a patient will have lost all abutment teeth 10 years after insertion of the denture is 4%. The probability that a patient will have kept all teeth that abut the denture 5 years after insertion is 87%; 10 years after insertion the probability is 80%. Conclusion: The Marburg double crown system is a versatile and successful means of achieving the long-term restoration of the partially edentulous jaw. Insertion and removal of the denture and routine oral hygiene are easy to perform, even for patients with limited manual dexterity. As a full-arch reconstruction, the MDC system enables easy adjustment, modification, and relining with low follow-up costs.

Purpose: The aim of this study was to evaluate the clinical and radiographic performance of patients who received implants and fixed prostheses with laser-welded titnaium frameworks. Materials and Methods: Fifty-eight consecutive patients were treated with 349 osseointegrated implants ad modum Branemark in the edentulous maxilla at 6 implant centers. The patients were randomly arranged into 2 groups at the time of final imperssion. Twenty-eight patients received laser-welded titanium frameworks and 30 patients received conventional cast frameworks. Clinical and radiographic data were collected for 2 years in function. Results: The 2 groups of patients showed similar results. The 2-year overall cumulative implant survival rate from the time of implant placement and prosthesis insertion was 93.7% and 96.2%, respectively. The corresponding cumulative survival rate for prostheses was 96.6%. Two patients, 1 from each group, failed completely and resumed using conventional complete dentures. The only obvious factor that could possibly be related to the 2 complete failures was a smoking habit. However, it was not possible to significantly correlate implant failures to smoking habits in this study. No fractures were observed in teh frameworks or implant components, and both groups experienced the same frequency of resin veneering material fractures. The overall average marginal bone loss was 0.4 mm (SD 0.8 mm). Conclusion: Patients treated with implant-supported prostheses fabricated with laser-welded titanium frameworks in the edentulous maxilla presented comparable results to patients with conventional cast frameworks after 2 years in function.

Purpose: This study compared the number of cycles to failure of central incisors restored with full cast crowns and then cemented with 3 different luting cements. Materials and Methods: Fifteen human maxillary central incisors received cast post-and-core restorations. These were cemented with zinc phosphate. The teeth were then divided into 3 gruops of 5 samples each. Each tooth had a ferrule length of 1.0 mm and was prepared for a full crown. A waxing jig was used to standardize the load application point on all waxed crowns. Complete cast crowns were cemented to the compromised teeth using 3 different luting cements: a zinc phosphate cement (control group), a resin-modified glass-ionomer cement, and a resin cement with a dentin bonding agent. A fatigue load of 1.5 kg was applied at a rate of 72 cycles per minute until failure of the cement layer occurred between teh crown and the tooth (preliminary failure). The independent variable was the number of load cycles required to create preliminary failure. An electrical resistance strain gauge was used to provide evidence of preliminary failure. An electrical resistance strain gauge was used to provide evidence of preliminary failure. Results and Conclusion: The resin cement samples had a significantly higher number of load cycles to preliminary failure than both the zinc phosphate and the resin-modified glass ionomer (P - 0.05). There was no significant difference between the zinc phosphate and the resin-modified glass-ionomer cements.

Purpose: To investigate the performance of different rotary instruments when machining cobalt-chromium alloy. Materials and Methods: One tungsten carbide bur, 1 diamond bur, and 2 aluminum oxide abrasive points (pink stones) of different diameter were used to machine cobalt-chromium alloy under standardized conditions. The rate of metal removal was determined and the resulting surfaces and bur wear were investigated using scanning electron microscopy and energy dispersive analysis. Results: Although the larger diameter pink stone was shown to be the most efficient instrument, the tungsten carbide bur produced the smoothest surface. Conclusion: Because of its low cost and high cutting efficiency, the pink stone is well suited for laboratory use. The tungsten carbide bur is the preferred instrument for clinical use.

Purpose: The aim of this study was to analyze the techniques, production problems, and 2-year results of attachment-retained removable partial denture (RPD) treatment provided by general practitioners in Sweden. Materials and Methods: At a major dental laboratory, consecutive cases involving new production of crowns, or of fixed partial dentures (FPDs) and RPDs retained with precision attachments, were studied. Parameters of the dentition, crown or FPD, type and brand of attachment, etc, as well as early satisfaction by dentist and patient, were recorded using specially designed forms at the dental laboratory and questionnaires for the dentists. After 2 years, questionnaires were again sent out to the dentists to record complications and patients' and dentists' opinions of the results. The sample gathered totaled 83 constructions. After 2 years, responses for 57 patients, all of whom had distal-extension RPDs, were received. Most drop-outs in the study were explicable. Results: The most frequently cited reasons for using attachments were esthetics and need for crowning the teeth abutting the RPD. McCollum rigid slide attachment was the pred ominant brand used (43% of constructions). Dentists and patients were dissatisfied with 6% of the constructions. During the first 2 years, 22 of 57 constructions were complication-free. Seventeen had attachment complications and 9 had serious complications related to the abutment teeth or RPDs. A comparison between these 2 groups revealed that those with complications had every second abutment root-canal treated and a root post, while the group without complications had every fifth abutment root-canal treated. Conclusion: There were many technical and biotechnical complications and failures; the exact ratio, however, depended on the definition of complications and failure. The 2-year results also deviated considerably from the dentists' opinions of the early results.

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 um), compared with the chamfer finish line (64 ± 38 um), the 0.8-mm rounded sho ulder (51 ± 34 um), and the 0.5-mm rounded shoulder (68 ± 56 um). 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 cuspt 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 sytem, but all other finish-line forms and design variations are accurately and clinically acceptably reproduced using this system.

Puprose: The most direct method to clinically evaluate marginal openings in fixed partial dentures is to use manual explorers for tactile perception. The purpose of this in vitro study was to establish the reliability of different instruments for discovering marginal openings. Materials and Methods: The materials used in this study included a dull stylet and a sharp-tipped explorer as well as a metal cylinder surface featuring 9 V -shaped circumferen tial grooves ranging in size from 20 to 165 um. A group of 42 subjects were asked to discover the grooves using both instruments. Results: The data revealed high reliability in the use of the sharp-tipped explorer. With this instrument, a defect of 36 um could be perceived by 95% of the subjects. The dull, worn instrument gave significantly inferior results (P 0.05). Conclusion: Using a sharp-tipped explorer on a smooth metal surface, tactile perception is a reliable means of detecting open margin defects up to 36 um wide. As has been suggested in previous studies, the difficulty seems to be not in defect detection but in the evaluation of the clinical acceptability once it is detected.

Purpose: This article proposes a classification protocol for reporting the outcome of implant-supported fixed partial dentures. Materials and Methods: A review of the literature revealed a contrast between the accepted criteria for assessing and presenting the outcome of osseointegrated implants and the deficient and misleading assessment and presentation of the outcome of the prostheses supported by these implants. A classification protocl comprising 6 well-defined fields with objective standards that accounts for retreatment as well as failure is proposed. This protocol has been applied where possible to reports on the outcome of fixed partial dentures in several published articles. Results: In all cases there was a stark difference between the authors' claims of success and the outcome according to the 6-field protocol. It is accepted that the outcome of a given prosthesis does not necessarily correspond to the outcome of the overall prosthodontic treatment, as the latter also invovles an assessment of outcome as perceived by the patient and accounts for planned revisions. Conclusion: If adopted, the proposed protocl would allow meaningful comparisons between prosthesis designs and between different implant systems' capacities to support such designs. It would also assist in evaluating the cost-effectiveness of implant-supported treatments.

Purpose: The purpose of this study was to evaluate the fracture resistance of 5 different all-ceramic crown systems (In-Ceram, Empres staining technique, Empress veneering technique, Celay feldspathic system, and Celay In-Ceram system) before and after cyclic preloading in an artificial mouth. Materials and Methods: Extracted natural maxillary incisors we re prepared with a 90-degree shoulder. The crowns were adhesively luted to the abtuments using dual-cured composite cement. Half of the specimens were artificially aged via a chewing simulation and thermocycling, and all specimens were tested for fracture strength. The results were compared with those of porcelain-fused-to-metal (PFM) crowns with circular porcelain-butt margins that were cemented with zinc phosphate cement. Results: The chewing simulation and the thermocycling significantly decreased the fracture strength of all tested crown systems (P 0.01). There were no statistically significant differences between the all-ceramic crown groups and the PFM crowns. Conclusion: All-ceramic crowns can be used for anterior restorations. However, in vivo investigations of all-ceramic crown systems should be undertaken before introducing them into routine clinical use.

Purpose: The purpose of this study was to evaluate the clinical effectiveness of hydroxyapatite-coated cylindrical implants to support overdentures. These implants were placed between 1990 and 1994 and have been followed up over a period of 3 to 6 years. Materials and Methods: One hundred thirty-nine Calcitek dental implants were placed in 43 patients to support 14 maxillary and 30 mandibular overdentures. Standardized clinical review procedures were used. Results: At exposure all the implants were found to be osseointegrated. To date only 7 implants (5%) have completely failed and two associated overdentures (5%) have been lost. The cumulative survival rate of all implants over 6 years was 92%. However, if failure is defined by the loss of more than 4 mm of cervical bone, 33 implants could be classified as being in the process of failing. Using these figures, interval success rates as low as 82% were found by year 6, and the cumulative success rate would fall to 39%. Maxillary survival and success rates were siginficantly lower than mandibular rates, at 38% and 10%, respectively, by year 5. Conclusion: Failure rates were higher in the maxillary arch, in poor quality bone, in smokers, and where implants were opposed by a natural dentition or an implant-supported prosthesis. The results suggest that the cervical bone level adjacent to the Calcitek cylindrical hydro xyapatite-coated implant failed to establish a steady state, particularly in the maxillary arch. Doubts remain regarding the long-term prognosis of these cylindrical implants.