The International Journal of Prosthodontics, 06/1999

Purpose: The main purpose of this retrospective study was to investigate the clinical outcome of the treatment with 259 consecutively placed Brånemark system implant-supported single crowns. Materials and Methods: There were 259 implants placed in 183 patients with a mean age of 29.8 years; 230 (89%) were placed in the maxilla and 29 (11%) were placed in the mandible. Of the prosthetic restorations, 165 were all-ceramic (68%), 79 were metal-ceramic (31%), and 4 were gold-acrylic (1%). The observation period ranged from 1 to 9 years. Results: A total of 9 patients (10 implants) was lost to follow-up. There were 3 implant failures registered, one before loading and one during the first year in function; one implant fractured after 6 years in service, giving a cumulative success rate for implants of 98.3%. A total of 8 crowns was remade following prosthetic complications; otherwise, the frequency of adverse events was low. The bone loss was of the same magnitude as in other studies on Brånemark implants as support for single crowns. In general, the soft tissue conditions around the restorations were healthy and comparable to those of the patients' natural teeth. Conclusion: This study confirms the favorable results presented in other studies on Brånemark implants to support single-tooth restorations.

Purpose: The aim of this study was to determine whether a condition similar to Combination Syndrome occurs in patients rehabilitated with a maxillary complete denture opposing a mandibular implant-supported fixed prosthesis. Materials and Methods: Standardized clinical procedures measured fit, occlusal integrity, and bone loss in the anterior maxilla in 11 edentulous subjects meeting these requirements, from the patient pool of the Implant Centre, United Dental Hospital, Sydney. Results: A mean annual loss of 0.17 mm in the anterior maxillary ridge height was not statistically significant (P > 0.05). However, increased pressure in the anterior maxillary ridge during occlusion and loss of posterior occlusal contacts in retruded position were noted on one or both sides in all subjects. Conclusion: Loss of posterior occlusion could not be related to anterior maxillary bone loss. However, to maintain the integrity of the prostheses and their supporting structures, it is important to schedule periodic recall appointments for review of the occlusion.

Purpose: The purpose of this study was to investigate the influence of certain defined variables on color and opacity of silicone elastomers for maxillofacial prostheses. Materials and Methods: Three condensation-type and five addition-type silicone elastomers were tested for their changes in color and opacity as a result of aging. The specimens were aged under a xenon light source, dry or wet, and in darkness, also dry (control specimens) or wet. The aging times were 24, 96, 168, 336, 504, 840, 1176, and 1512 hours. The changes in appearance were measured with a spectrophotometer. Results: The condensation-type polymers increased in opacity in an aqueous environment, while the addition-type polymers, as a group, showed the smallest color changes. Although the addition-type polymers generally had a higher filler content than the condensation types, they had a lower opacity. However, because of their higher viscosity, the condensation-type polymers offer better possibilities for intrinsic coloring of the prosthesis. Conclusion: Under the experimental conditions studied, significant differences between the silicone elastomers regarding color and opacity changes were demonstrated. However, for a proper choice of material in a given case, these factors have to be related to biologic and mechanical properties of the material.

Purpose: Currently available clinical studies on porcelain laminate veneers seem to support their use as a standard treatment method in modern restorative dentistry. The purpose of this study, which comprises 3 parts, was to evaluate the clinical applicability and the survival probability of porcelain laminate veneers for an observation period of up to 10 years. This first part of the study describes the step-by-step clinical procedure. Materials and Methods: The reasons for provision of porcelain laminate veneers were mainly for the treatment of worn anterior teeth, surface enamel defects, intrinsic discolorations, and hypoplasia. As the treatment time for try-in, cementation, and finishing of veneers differs significantly from that needed for conventional restorations, the total time required for veneer treatment was evaluated. Results: A total of 205 porcelain laminate veneers, 117 in the maxilla and 88 in the mandible, was placed in 72 patients (43 females and 29 males). Mean cementation time was 38.7 minutes, which increased significantly to 43.9 minutes if single discolored teeth were being restored. Clinical experience and a familiarity with the strict step-by-step procedure followed throughout the study reduced the mean treatment time from 40.8 minutes during the first 5 years to 36.7 minutes in the following years. Conclusion: The porcelain laminate veneer concept provides excellent esthetic and conservative restorations, but it should be stated that the cementation and finishing procedure is highly time consuming.

Purpose: The purpose of this study was to describe a mandibular envelope of motion during speech for 2 subject groups. One subject group had experienced no tooth wear and the other had incisal tooth wear. The speech envelope was to be described with regard to its maximal dimensions in the vertical, anteroposterior, and lateral directions, and its most superior and anterior positions in relation to intercuspal position. Materials and Methods: An electromagnetic method of jaw tracking was employed to record mandibular speech movements for 60 subjects whose teeth exhibited no tooth wear and 30 subjects with incisal dental attrition. The test speech exercise contained all of the word sounds that occur in the English language. The test was recorded 3 times, and mean values for parameters were reported. Results: The speech envelope of the tooth wear group was significantly smaller (Student's t test, P 0.01) in all 3 dimensions than that of the normal group. The tooth wear group speech envelope was also located closer to the intercuspal position in the vertical dimension (P 0.01) and was not as anteriorly placed (P 0.01). In the normal group, correlations were found between the vertical incisor overlap and the most superior speech position (r = 0.48, P 0.0001), and between the horizontal incisor overlap and the most anterior mandibular speaking position (r = 0.63, P 0.0001). Conclusion: The envelope of mandibular movement during speech differed in dimension and position between the 2 groups investigated

Purpose: The purpose of this study was to report on the clinical characteristics and outcome of 688 single-unit metal-ceramic crowns placed in a specialist prosthodontic practice between January 1984 and December 1992. Materials and Methods: Clinical and laboratory techniques were standardized and patients were recalled by the author between June and December of 1993. The outcome of all crowns was allocated to one of 6 fields in this assessment period. Results: Clinical review examination by the author covered 87% of the crowns. Of these, 52% had been in service for 5 to 10 years and 48% for less than 5 years but more than 1 year; 67% of the crowns were placed on vital teeth and 94% were given a 'good prognosis' rating at examination. The repair and failure rates of crowns in the 5 to 10 years in clinical service group were both 3%. Crowns on nonvital teeth in the same grouping had a significantly greater failure rate (5%) than crowns on vital teeth (1%), and anterior teeth had a significantly greater retreatment rate than posterior teeth. Retreatment for all 25 crowns occurred within 66 months after cementation. Tooth fracture accounted for 56% of retreatments, while caries and loss of retention accounted for only 24% of retreatments; 2% of initially vital teeth were endodontically treated during the survey period. Conclusion: Single-unit metal-ceramic crowns have a high expectancy of exceeding 10 years of clinical service when the described clinical and laboratory protocol is applied.

Purpose: The purpose of this study was to describe how dentists evaluated various items related to a treatment choice between fixed partial dentures (FPD) and removable partial dentures (RPD), and to determine if the differences could be explained by dentist-related variables ('social and demographic attributes,' 'job situation,' and 'attitudes'). Materials and Methods: Questionnaires were sent to a random sample of 2,059 Swedish general dentists, with a response rate of 76%. In the questionnaire, the choice between FPDs and RPDs in a clinical situation was presented. The dentists were asked to mark on 14-item visual analogue scales the relative importance he or she gave the different items. The items were analyzed through principal components analysis, where a 3-factor solution was obtained; the factors were labeled as 'time,' 'health,' and 'comfort.' The factors were run as dependent variables in multiple regression analyses. Results: Great individual variations were seen, but the differences between groups of dentists were small. The items evaluated as most important were 'patient's wish,' 'condition of possible abutment teeth,' and 'prognosis for delivered treatment.' Male dentists gave significantly greater importance to the 'health' factor compared to female dentists. The attitudinal variable 'patient information' showed significant associations with all 3 factors in the multivariate models. Conclusion: Great individual differences were seen regarding the importance of the various items. In multiple regression models, several independent variables showed significant associations, most interestingly the attitudinal variable 'patient information.' Low explanatory (R2) values indicate that it is necessary to capture more variables of importance for the prosthodontic decision-making process.

Purpose: The biaxial flexural strength and fracture toughness for 3 representative types of ceramic core materials were studied to (1) ascertain the ranking of the 3 ceramic types for strength and toughness, and (2) provide clinicians with more information to predict clinical outcomes. The former aim was deemed important in view of the importance of flaw size in the relationship between failure stress and fracture toughness of brittle materials. Materials and Methods: The 3 representative ceramic types included a leucite-reinforced glass, a glass-infiltrated sintered alumina, and a high-purity, high-density alumina. The biaxial flexural strength was measured with the piston-on-3-ball method. The plane-strain fracture toughness was measured with the short-bar chevron-notch method. Results: The biaxial flexural strengths of the high-purity, high-density alumina and glass-infiltrated sintered alumina ceramic core types were significantly higher than that of the leucite-reinforced glass ceramic type. The glass-infiltrated sintered alumina was significantly higher in fracture toughness than the high-purity, high-density alumina type, which was significantly higher than the leucite-reinforced glass. Conclusion: All materials surpassed the minimum strength requirement outlined by the International Standards Organization, and they also had similar strength variability according to their Weibull moduli. The glass-infiltrated sintered alumina and the high-purity, high-density alumina types were significantly stronger and tougher than currently used core materials. However, while the glass-infiltrated sintered alumina had a higher fracture toughness than the high-purity, high-density alumina, it had a lower flexural strength.

Purpose: The fracture of acrylic resin dentures remains an unresolved problem. Over the years, various approaches to strengthening acrylic resin have been suggested, including modifying or reinforcing the resin. The aim of this study was to investigate the effect of chopped poly(methyl methacrylate) (PMMA) fibers on some properties of acrylic resin denture base material. Materials and Methods: PMMA in the form of fibers 0.75 mm in diameter and 5 mm in length was added to acrylic resin denture base material in various percentages to form a composite material. The influence on doughing and manipulation times and transverse strength was examined. The results were subjected to statistical analysis using a one-way analysis of variance and, where appropriate, the Scheffé test. Results: The results showed that the doughing time was decreased by the addition of fibers, with the manipulation and setting times showing inconsistent changes. There was a significant difference between the materials in terms of the transverse strength. When the amount of PMMA fibers in the acrylic resin was increased, there was a decrease in the modulus of rupture and a decrease in the modulus of elasticity. The differences were shown to be statistically significant in some groups. Conclusion: The doughing time was decreased by the addition of fibers, while the manipulation and setting times showed inconsistent changes. The incorporation of chopped, randomly oriented PMMA fibers into acrylic resin had no advantage over the unmodified polymer in terms of strength and cannot be recommended as a reinforcing agent for acrylic resin denture base material.

Purpose: The purpose of this study was to evaluate the bonding characteristics of porcelain-fused-to-metal (PFM) systems by determining the strain energy release rate associated with interface fracture of porcelain and metals. Materials and Methods: Porcelain-veneered metal plates cast from commercially pure titanium and 3 metal alloys (gold, palladium, and nickel-chromium alloys) were made to dimensions of 25 mm 3 8 mm 3 2.5 mm with comparable thicknesses of porcelain and metal. The porcelain side of the specimens was notched to the interface with a thin diamond saw, and a small precrack was initiated at the metal-porcelain interface. The samples were subjected to a limited number (typically less than 4) of load-unload cycles under 4-point bending at a crosshead speed of 0.1 mm/min. The loading and unloading force displacements associated with stable crack extension were recorded. The strain energy release rate was calculated. The interfacial area was also examined under scanning electron microscope (SEM) after the test. Results: The mean strain energy release rates were 72.7 ± 10.0 J/m2, 58.5 ± 13.5 J/m2, 39.4 ± 4.3 J/m2, and 16.6 ± 2.5 J/m2 for the samples of gold, palladium, nickel-chromium alloys, and titanium, respectively. The SEM photographs showed that the crack occurred in the porcelain layer close to the interface. Conclusion: The bonding characteristics of PFM systems were determined with 3 types of metal alloys and commercially pure titanium by a fracture mechanics approach. The gold alloy and titanium are considered to obtain the greatest and least adhesion, respectively. The test system has proven to be a simple and reliable approach to determine the bonding in bimaterial systems.