The International Journal of Prosthodontics, 03/2004

Prosthodontics offers an extraordinary range of treatment possibilities for oral rehabilitation. However, its reliance on the high-technology end of the spectrum of possibilities inevitably limits it to relatively few people. There is nothing wrong with "high-tech" solutions, for it is the research into such solutions that has provided astonishing advances. But it is my contention that by emphasizing such solutions, health professionals risk usurping their professional mandate.

Purpose: This study sought to develop an understanding of the magnitude and types of loads generated on craniofacial implants supporting an auricular prosthesis. Materials and Methods: Strain gauges were used to measure the in vitro and in vivo misfit loads generated when connecting auricular-style superstructures to implants and the in vivo functional load generated during the removal and insertion of the auricular prostheses. In addition, the vertical misfit of the 11 custom-built two-implant superstructures used in the in vitro study was measured. Results: Superstructures used in the in vitro study that were considered clinically passive still had considerable preloads. In addition, the calibrated loads, which would result from the vertical misfit alone, did not account for the magnitude of the generated preloads. Conclusion: The clinical definition of misfit based on vertical distortion of the superstructure did not quantify the resulting misfit load. Measured in vivo functional loads were smaller than the misfit loads.

Purpose: Reports of irreversible alteration in jaw posture and destructive occlusal contact relationships in individuals using mandibular advancement devices for obstructive sleep apnea are beginning to appear. This study sought cephalometric means of identifying such individuals before commencing therapy. Materials and Methods: Cephalograms of 34 obstructive sleep apnea sufferers who had worn mandibular advancement devices for 2 years were compared retrospectively with baseline films taken at commencement of therapy and analyzed for signs ofmorphologic changes in jaw position and occlusal relationship. In affected patients, two distinct morphologic species of mandibular reposturing became evident: (1)bilateral posterior open bite with destructive incisal attrition; and (2)less destructive intermediate open bite over the premolar and first molar regions. From the observed morphology patterns, gonial angle and maxillary-mandibular plane angle were analyzed as possible vertical cephalometric risk predictors, with newly defined pterygoid advancement proportion (PtAP) as a horizontal predictor. Results: Three patients displayed the posterior open bite pattern and had gonial angles = 119 degrees and maxillarymandibular plane angles = 16 degrees, with PtAP values >= 0.48. Prediction intervals for the five intermediate open bite cases were 118 degrees = gonial angle = 128 degrees, and 23 degrees = maxillary-mandibular plane angle = 32 degrees. PtAP values were >= 0.52. Conclusion: Cephalometric analysis can help practitioners identify which apnea patients might be likely to develop irreversible mandibular postural changes from wearing a jaw-repositioning device.

Purpose: This review article evaluated the clinical performance of two-unit cantilevered, single-abutment, single-pontic, resin-bonded fixed partial dentures (FPDs) by comparing them to noncantilevered resin-bonded FPDs with two abutments and a single pontic. Materials and Methods: One publication on design principles and 11 clinical research studies were selected by searching two databases. Results: Six of the studies dealt exclusively with two-unit cantilevered resin-bonded FPDs, and five studies compared fixed-fixed design resin-bonded partial dentures with cantilevered resin-bonded FPDs. Two-unit cantilevered resin-bonded FPDs for singletooth replacement appear to be reliable and predictable restorations, provided their preparations meet the right standards. Conclusion: According to the studies reviewed, two-unit cantilevered FPDs show better longevity than resin-bonded fixedfixed partial dentures in similar situations.

Purpose: This prospective clinical study evaluated an experimental implant abutment made of densely sintered zirconia with respect to peri-implant hard and soft tissue reaction as well as fracture resistance over time. Materials and Methods: Twenty-seven consecutively treated patients with 54 single-tooth implants were included. Zirconia abutment ingots were individually shaped and set on the implants with gold screws. All-ceramic (Empress I) crowns were cemented using a composite cement. At the 1- and 4-year examinations, reconstructions were evaluated for technical problems (fracture of abutment or crown, loosening of abutment screw). Modified Plaque and simplified Gingival Indices were recorded at implants and neighboring teeth, and periimplant bone levels were radiographically determined. Results: All but 1 of the 27 patients with 53 restorations could be evaluated at 1 year, and 36 restorations in 18 patients were evaluated 4 years after abutment and crown insertion. The median observation period for the reconstructions was 49.2 months. No abutment fractures occurred. Abutment screw loosening was reported for 2 restorations at 8 months and 27 months, respectively. Mean Plaque Index was 0.4 (SD 0.6) at abutments and 0.5 (SD 0.6) at teeth; mean Gingival Index was 0.7 (SD 0.5) at abutments and 0.9 (SD 0.5) at teeth. Mean marginal bone loss measured 1.2 mm (SD 0.5) after 4 years of functional loading. Conclusion: Zirconia abutments offered sufficient stability to support implantsupported single-tooth reconstructions in anterior and premolar regions. The soft and hard tissue reaction toward zirconia was favorable.

Purpose: The present report describes a relatively simple but effective prosthodontic treatment following removal of a moderately well differentiated osteogenic chondrosarcoma in the premaxillary region. Materials and Methods: Following removal of a rare tumor, a young man was treated with gold crowns on three molars and a metal-ceramic crown on a first premolar, with attachments in the areas facing the defect for esthetic reasons. A removable partial denture was retained by the attachments and conventional cast retentive circumferential clasps, including a hollow obturator filling the defect. Results: The restoration has served the patient for 16 years, seemingly without discomfort, and it has not required any maintenance. The patient has kept up with his oral hygiene, using conventional methods for the teeth and prosthesis, with periodic flushing with chlorhexidine solution. He has lived a normal family life and finished his university education. Conclusion: The problem-free use of the appliance can be at least partly explained by the patient taking oral hygiene measures seriously from the beginning. This report explains how relatively uncomplicated prosthodontic measures can enormously affect quality of life.

Purpose: This in vitro study evaluated the effects of surface treatments and thermocycling on the bonding of autopolymerizing silicone soft denture liner (Sofreliner) to denture base resin. Materials and Methods: The bonding surfaces of denture base cylinders were polished with 600-grit silicon carbide paper and pretreated with applications of Sofreliner Primer, Sofreliner Primer after air abrasion, Reline Primer, or Reline Primer after air abrasion. Failure loads and elongation at failure were measured after subjecting specimens to 0, 10,000, 20,000, and 30,000 thermocycles. Failure modes were assessed for all specimens. Seven specimens were fabricated for each of 16 groups, including four pretreatments and four thermocycle groups. Results: Failure loads of the Sofreliner Primer group were significantly higher than those of the air-abrasion group up to 20,000 thermocycles; both groups showed cohesive failures of the soft denture liner. Failure loads of the Reline Primer group were significantly higher than with Reline Primer after air abrasion up to 10,000 thermocycles. Failure mode after 10,000 thermocycles was cohesive for the Reline Primer group and mixed cohesive/adhesive for Reline Primer after air abrasion. Failure loads of the Sofreliner Primer group were significantly higher than those of the Reline Primer group at each thermocycling interval. Elongation values decreased after 10,000 thermocycles for all groups. Conclusion: Air abrasion on the denture base resin surface was not effective in enhancing failure load. Cyclic thermal stress is one factor degrading the bond between soft denture liner and acrylic resin denture base.

Purpose: This study performed a clinical evaluation of two ceramic systems retained with resin-bonded cement, observed clinical outcomes over time, and compared the two systems used (IPS Empress and Vitadur Alpha) and differences between inlays and onlays. Materials and Methods: Three general practitioners placed 317 restorations (215 IPS Empress and 102 Vitadur Alpha) in 153 patients. The first clinical registration was performed 6 to 36 months after placement of the restorations by calibrated investigators using the CDA criteria. A second follow-up was performed 36 months later. The mean time in function for all restorations at follow-up was 60 months. Results: At the first examination, five restorations were not clinically acceptable because of fractures and caries. At follow-up, another 16 restorations were judged as failures. The most significant changes over time were an increase in rough surfaces, evidence of increasing marginal discrepancy, and slight mismatch in color between restored tooth and ceramic restoration. When comparing IPS Empress to Vitadur Alpha, there was no difference in clinical performance. When comparing inlay and onlay restorations, there was a tendency toward a higher number of failures in the inlay group. The overall success rate was 92%. Conclusion: Ceramic restorations performed well after 5 years in function and provide a good treatment alternative that can be successfully managed in general dental practice.

Purpose: This study evaluated the effect of cement, post material, surface treatment, and shape (1) on the retention of posts luted in the root canals of extracted human teeth and (2)on the failure morphology. Materials and Methods: Posts of titanium alloy (ParaPost XH), glass fiber (ParaPost Fiber White), and zirconia (Cerapost) received one of several surface treatments-sandblasting, CoJet treatment, application of Metalprimer II, or sandblasting followed by silane application-and were then luted in the prepared root canal of human incisors and canines (n = 10). Following water storage at 37°C for 7 days, retention was determined by extraction of the posts. Failure morphology of extracted posts was analyzed and quantified stereomicroscopically. Results: Type of luting cement, post material, and shape of post influenced the retention and failure morphology of the posts. Because of limited adherence of the cement to the root canal, surface treatments did not always have a positive effect on retention. Conclusion: Choice of luting cement was critical for all three types of posts. Parallel posts showed superior retention to tapered posts.

Purpose: This study assessed the influence of palatal cuspal coverage on the in vitro fatigue resistance and failure mode of Class II resin composite restorations including replacement of the buccal cusp in premolars. Materials and Methods: A master model was made of a maxillary premolar with an MOD amalgam cavity and a simulated fracture of the buccal cusp from the isthmus floor to the CEJ. Using a copymilling machine, this preparation was copied to 20 extracted human maxillary premolars (group A). Subsequently, the palatal cusp was reduced by 1.5 mm; this modified preparation was copied to 20 additional maxillary premolars (group B). Direct resin composite restorations were made in all teeth. Cyclic load (5 Hz) was applied, starting with a load of 200 N (10,000 cycles), followed by stages of 400, 600, 800, and 1,000 N at a maximum of 50,000 cycles each. Samples were loaded until fracture or to a maximum of 210,000 cycles. Results: Of the restored premolars of group A, 20% withstood all 210,000 loading cycles; in group B, this figure was 55%. In group A, 19% of the fractures ended below the CEJ; in group B, 78% did. Conclusion: Palatal cuspal coverage increased the fatigue resistance of Class II resin composite restorations with replacement of the buccal cusp in premolars. However, fractures of restorations with cuspal coverage led to more dramatic failures that made restoration virtually impossible. This suggests caution in lowering remaining cusps for these adhesive restorations in the clinical situation.

Purpose: The effect of glass-fiber reinforcement and water storage on the fracture toughness (KIC) of polymer-based provisional crown and fixed partial denture (FPD) materials was investigated. Materials and Methods: Five unreinforced single-edged, notched control specimens and five test specimens reinforced with unidirectional Eglass fibers (Stick) were fabricated from three dimethacrylate-based provisional materials and one monomethacrylate-based provisional material. The specimens were stored in water at 37°C for 1, 7, 30, or 60 days. Specimens were loaded in three-point bending at a cross-head speed of 0.1 mm/s. Mode I plane-strain KIC was calculated using the maximum load, and results of the two groups were compared. The water storage effect on KIC with time was also evaluated. Results: The KIC of provisional materials reinforced with glass fibers (range 7.5 to 13.8 MNm-1.5) was significantly higher than that of unreinforced materials (range 1.3 to 3.1 MNm-1.5), by a factor of 4.4 to 5.5. A small, gradual decrease of KIC in reinforced specimens occurred with aqueous storage, but it was not statistically significant. Conclusion: The KIC of polymer-based provisional crown and FPD materials was significantly increased when they were reinforced with unidirectional E-glass fibers. Water storage for up to 2 months still left the reinforced materials with KIC values in excess of 7 MNm-1.5. Hence, their performance was satisfactory.

Purpose: This study evaluated the long-term survival of anterior porcelain laminate veneers placed with and without incisal porcelain coverage. Materials and Methods: Two prosthodontists in a private dental practice placed 110 labial feldspathic porcelain veneers in 50 patients; 46 veneers were provided with incisal porcelain coverage, and 64 were not. The veneers were evaluated retrospectively from case records for up to 7 years (mean 4 years). Results: At 5, 6, and 7 years, the cumulative survival estimates were 95.8% for veneers with incisal porcelain coverage and 85.5% for those without incisal coverage. The difference was not statistically significant. Six of the nine failures occurred from porcelain fracture in the veneers without incisal coverage. Conclusion: Although there was a trend for better long-term survival of the veneers with incisal porcelain coverage, this finding was not statistically significant.

Purpose: This study undertook a systematic overview of the literature on the description and visual measurement of gingival color. Materials and Methods: Two research questions were formulated. The first addressed the description of gingival color, while the second aimed at visual color measurement techniques. An electronic search was performed in 22 literature databases. The electronic search was complemented by hand searching. The retrieved articles were independently reviewed by two members of the research team. The levels of evidence of the articles were classified following the guidelines of the Oxford Centre for Evidence-Based Medicine. Results: Of the nine articles retrieved by the two searches, six applied to the first question, two applied to the second question, and one applied to both questions. Three articles were published in Japanese and dealt with the color of gingival and alveolar mucosa. The clinical studies showed that the intraoral tissues of younger persons are of a lighter color. Evidence levels were no higher than 4. Conclusion: Studies on the description of gingival color used a narrative approach. Studies on visual gingival color measurement had diverse aims, methods, and parameters. It is impossible to compare or even combine their outcomes in a scientifically meaningful manner. Since none of the investigations used a controlled or randomized design, they represent low levels of evidence.

Purpose: Using a population-based sample of the cross-sectional epidemiologic "Study of Health in Pomerania" (SHIP), this study evaluated whether certain occlusal and sociodemographic factors besides age and gender are risk factors for high dental wear. Materials and Methods: Medical history and dental and sociodemographic parameters of 2,529 dentate subjects selected representatively and according to age distribution were checked for correlations with the occurrence of high occlusal wear symptoms using a multivariate logistic regression model. Occlusal wear was recorded using the attrition index by Ekfeldt et al and was age adjusted by determining high occlusal wear for every 10-year age group as index values = 90th percentile. Results: The following independent variables were found to be correlated with high occlusal wear: male gender, odds ratio 2.2; frequent bruxism, odds ratio 2.5; loss of molar occlusal contact (Eichner classification), odds ratio from 1.5 to 3.1; edge-to-edge relation of incisors, odds ratio 1.7; unilateral buccolingual cusp-to-cusp relation, odds ratio 1.8; and unemployment, odds ratio 1.6. In contrast, anterior cross-bite, unilateral posterior crossbite, and anterior crowding were protective for high occlusal wear levels, as shown by significantly reduced odds ratios. Gender-separated analysis showed that self-reported bruxism was a risk factor only for men. Conclusion: In addition to some occlusal factors, the main factors associated with occlusal wear were bruxism and gender.

Purpose: This study compared the effect of two postpolymerization heat treatments on the cytotoxicity of three denture base resins on L929 cells using 3H-thymidine incorporation and MTT assays. Materials and Methods: Sample disks of Lucitone 550, QC 20, and Acron MC resins were fabricated under aseptic conditions and stored in distilled water at 37°C for 48 hours. Specimens were then divided into three groups: (1) heat treated in microwave oven for 3 minutes at 500 W; (2)heat treated in water bath at 55°C for 60 minutes; and (3)no heat treatment. Eluates were prepared by placing three disks into a sterile glass vial with 9 mL of Eagle's medium and incubating at 37°C for 24 hours. The cytotoxic effect from the eluates was evaluated using the 3H-thymidine incorporation and MTT assays, which reflect DNA synthesis levels and cell metabolism, respectively. Results: The components leached from the resins were cytotoxic to L929 cells when 3H-thymidine incorporation assay was employed. In contrast, eluates from all resins revealed noncytotoxic effects as measured by MTT assay. For both MTT assay and 3H-thymidine incorporation, the heat treatments did not decrease the cytotoxicity of the materials tested. Conclusion: Resins were graded by 3H-thymidine incorporation assay as slightly cytotoxic and by MTT assay as noncytotoxic. Cytotoxicity of the denture base materials was not influenced by microwave or water bath heat treatment.

Purpose: The purpose of this study was to determine the proper prerequisite conditions for gas injection and the steps for applying gas injection for obturator fabrication. Materials and Methods: Optimal prerequisite conditions were investigated by using thermocoupling to verify exothermic changes in the resin during polymerization. Three experimental groups were designated: in the control group (C), resin was packed into the mold without argon gas injection; in the gas injection group (GI), after resin packing, gas was injected into the resin bulb in the mold; and in the plunger/gas injection group (PGI), after resin packing, the syringe plunger was drawn out before gas injection. Results: The 55°C mold temperature and addition of 0.3% DMPT to the monomer liquid caused differences in exothermic temperature increase in various parts of the resin. Without gas injection and plunger drawing, porosity was observed in the thick bulbs of groups C and PGI. In group PGI, a balloon-like elliptic hollow was observed. Compared to group C, the weight reduction in group PGI was approximately 10%. Conclusion: Proper mold temperature with secondary venting and the addition of DMPT were required before the injection of gas. The resulting prosthesis could be fabricated in one step and required no resin seal.

Purpose: This study reviewed the wear of commonly used dental restorative materials and their effects on the opposing dentition. Materials and Methods: Key words were used with PubMed to retrieve pertinent references to publications on tooth and restoration wear. Results: The wear resistance of newer esthetic restorative materials has generally improved, and the damage caused by several materials to the opposing dentition has been reduced. However, the different structures and physical properties of tooth substance and restorative materials will eventually lead to varying degrees of differential wear. The extent and rate of wear are influenced by many intraoral factors. Conclusion: Selection of restorative materials must be based on knowledge of their wear behavior and the individual needs of each patient. The lowest wear rates for restorations and the opposing dentition occur with metal alloys, machined ceramics, and microfilled and microfine hybrid resin composites.

Purpose: This study evaluated the surface microhardness and flexural and compressive strengths of five luting cements and compared the degree of conversion of dual and autopolymerized forms of four resin-based luting cements. Materials and Methods: Four resin composite luting cements-Panavia F, Variolink 2, RelyX Unicem Applicap, and RelyX ARC-and a polycarboxylate cement (Durelon, control group) were used in three-point bending, compression, and Vickers hardness tests following water storage for 1 week. Resin composite cements were additionally investigated with both dual and autopolymerization techniques under Fourier transformed infrared spectroscopy. Differences were analyzed using one-way ANOVA. Results: The highest flexural strengths were obtained with Variolink 2 (90 MPa, SD 22), whereas the lowest were observed with Durelon (28 MPa, SD 4). RelyX Unicem showed the highest hardness values (44 HV, SD 5), whereas Variolink 2 gave the lowest (32 HV, SD 6). The highest compressive strengths were obtained with RelyX Unicem (145 MPa, SD 32), whereas the lowest were observed with Durelon (41 MPa, SD 17). For both dual and autopolymerized groups, RelyX ARC showed the highest degrees of conversion (81% and 61%, respectively) and RelyX Unicem had the lowest (56% and 26%, respectively). Conclusion: Resin composite luting cements of similar chemical characterizations differed in their physical properties, and polymerization method influenced their degree of conversion.

Purpose: This study examined the influence of the adhesive strength between fiberreinforced composites (FRC) and veneering composites on the fracture load of combinations of these materials. Materials and Methods: Six materials were used. An experimental material called BR-100, Vectris, and FibreKor were the types of FRC. Estenia, Targis, and Sculpture were used as veneering composites. With the Estenia/BR-100 combination, the surface of the FRC was subjected to three different conditions before veneering. Ten specimens of each combination were fabricated and divided into two groups: One group was stored in 37°C distilled water for 24 hours, and the other was thermocycled (4°C/60°C, 10,000 cycles). Adhesive strength between FRCs and veneering composites was determined using the compressive shear strength test. In addition, fracture loads of laminate specimens were determined. Results: Good adhesive strength was obtained by leaving an unpolymerized layer on the surface of the FRC or by performing silane and bonding treatment. In the Estenia/BR-100 combination, when the adhesive strength was low, the fracture load of the laminate specimens was also low. However, the difference in fracture load was not as large as that seen in adhesive strength. The fracture load of each laminate specimen was significantly lower after thermocycling. Conclusion: The adhesive strength between the FRCs and veneering composite had an effect on the fracture load of the combination.

Purpose: This article presents a review of the literature on biomechanical factors affecting the treatment outcome of prosthetic treatment of structurally compromised dentitions, with the main emphasis on often-compromised endodontically treated teeth. Materials and Methods: Articles cited in a MEDLINE/PubMed search were reviewed with a focus on factors influencing the risk for fatigue failures. Results: Technical failures in connection with fixed prosthodontics are often caused by fatigue fractures. The abutments, cement, and reconstruction are all subjected to stress caused by occlusal forces, and fatigue fracture may occur at the weakest point or where the maximum stress occurs. The weakest point is frequently in connection with endodontically treated teeth restored with posts and cores. Conclusion: The literature points to nonaxial forces as a risk for fatigue fracture of teeth, cement, and restorative material. Favorable occlusal prosthesis design is probably more important for survival of structurally compromised endodontically treated teeth than is the type of post used.