The International Journal of Prosthodontics, 01/2003

Purpose: This study investigated the cytotoxicity of a high-noble alloy (Bioherador N) and six commercially available base-metal alloys, including four Ni-Cr alloys (Remanium CS, Heranium NA, Wiron 99, CB Soft), one Co-Cr alloy (Wirobond C), and one Cu-based alloy (Thermobond). Materials and Methods: Ten specimens from each alloy were prepared in the form of disks, which were placed in 24-well tissue culture plates together with a suspension containing Balb/C 3T3 fibroblasts (5 = 105 cells/mL). After 3 days of incubation at 37°C, cell viability was determined by the MTT method. Results: Variations in cytotoxicity of the alloys were observed and related to their composition. One-way ANOVA showed statistically significant differences in cytotoxicity of the alloys (P .001). Tukey's multiple comparisons (>= = .05) revealed that Bioherador N was significantly less cytotoxic than all the other alloys. Thermobond was the most cytotoxic, followed by CB Soft, and both of these alloys were significantly more cytotoxic than all the others. Conclusion: The cytotoxicity of casting alloys tested in this study was markedly affected by their composition. Differences were found in the cytotoxicity of alloys classified within the same category. The presence of Cu in the composition of the alloy adversely affected cell viability.

Purpose: The aim of this study was to introduce a newly designed die for ceramometal restoration, and to compare the dimensional accuracy with the traditional complete-crown design. Two methods of dimensional accuracy assessment, vertical axial discrepancy and transverse diametral percentage, were compared. Materials and Methods: Patterns were prepared from two different die designs-complete crown and ceramometal. Two investments available for titanium crown casting were used, Titavest CB and T-invest C & B. Titanium castings were made from each investment with a high-pressure casting machine. Vertical axial discrepancy of casting was determined by measuring the discrepancy for each set of wax patterns and their castings on the same die under a traveling microscope. Dimensional accuracy was expressed as vertical axial discrepancy and by transforming the vertical axial discrepancy into transverse diametral percentage. Results: Both dies produced undersized castings with T-invest C & B and oversized castings with Titavest CB. Dimensional accuracy assessment of the two different types of crown casting design showed no significant difference in vertical axial discrepancy. Conclusion: Compared to the traditional transverse diametral percentage calculation, the vertical axial discrepancy assessment is independent of the die's dimensions. The two types of investment materials studied resulted in castings with different dimensional accuracies.

Purpose: The purpose of this study was to clinically evaluate the mucosal condition and the esthetic and functional results of distraction implants loaded with fixed or removable implant-supported restorations. Materials and Methods: A total of 35 patients were treated with 62 distraction implants for correction of alveolar ridge deficiency. The distraction implants were loaded with prosthetic superstructures 4 to 6 months after distraction. Nine patients were provided with single-crown restorations, 16 received metal-ceramic fixed partial dentures, and 10 received removable overdentures. Recall was scheduled before and 3, 6, and 9 months after implant loading. Periotest values, periimplant probing depths, and radiographic marginal bone levels were recorded, along with any biologic or mechanical complications. Results: Patients were followed for 9 months after implant loading. Two distraction implants were lost before abutment connection. After fabrication and placement of individual abutments, all implants were loaded with prosthetic superstructures. The results showed a decrease of the Periotest values, and thus an increase of implant stability, during the following 9 months. Periimplant probing depths also decreased in the first months after implant loading. Soft tissue around the superstructures and adjacent teeth was healthy. Conclusion: The distraction implant system has a high potential for osseointegration. Because of the gentle distraction technique and the possibility of using individual abutments at almost any angulation, satisfying esthetic and functional results are possible. The rate of complications was low in this short-term study.

Purpose: When performing clinical trials, missing data from withdrawn patients should be evaluated differently, depending on the reason for the withdrawal of the patients. The question is, if a certain type of patient drops out, will that affect the result? Could a randomly selected sample of a study population be used for analyses instead of evaluating each and every patient? The purpose of this study was to answer these questions. Materials and Methods: Detailed information on 1,738 implants in 487 patients was pooled together in a new database and used for statistical evaluations. Random or selected withdrawals were pulled from the database. Chi-squared tests were used for significance tests, and lifetables were used for survival analysis. Results: There was a difference in the outcome depending on whether the withdrawals were randomly chosen or selected. Random withdrawals could represent, in this study, as much as 50% of the included patients without changing the statistical results. If selected withdrawals were based on which jaw was treated, the statistical outcome did change, but it did not change if withdrawals were based on gender or age. Conclusion: Evaluation of reasons for withdrawals and withdrawn patient characteristics are of utmost importance when evaluating clinical trials. A randomly selected sample of the entire population could, however, be expected to give the same statistical value as the entire group, if the original material were large enough. Therefore, the use of study samples may more easily enable clinicians to do follow-up investigations.

Purpose: The purpose of this study was to explore possible associations between prosthodontic, occlusal, endodontic, and periodontal factors and the endodontic status of endodontically treated teeth. Materials and Methods: Forty-six patients who had received endodontic treatment followed by a fixed restoration for at least one of their teeth were recalled and examined clinically and radiographically according to a predetermined set of evaluation criteria. A total of 89 teeth were included, and data obtained included assessments of the coronal restoration and post and core, occlusal contact relationships, a number of endodontic parameters, and periodontal status of the study teeth. For the latter assessment, 54 contralateral teeth were available for purposes of comparison. Teeth were grouped into those with and without periapical radiolucencies, and differences between the groups, with respect to all parameters, were analyzed by logistic regression. Results: Three factors were significantly associated with the presence of radiolucency: confirmed occlusal contact, by virtue of the tooth being either involved in group function or the only contact in working-side and protrusive movements, and endodontic filling and crown margins of poor quality. None of the other independent variables showed significant associations with the dependent variable of periapical radiographic appearance. Contralateral teeth had better periodontal conditions than restored study teeth. Conclusion: The finding that a good-quality endodontic filling and crown margin improve endodontic outcome corroborates many other similar reports; however, with occlusal contact shown to be associated with failing endodontic treatment, the range of factors that may influence endodontic outcome appears to have widened.

Purpose: This prospective clinical follow-up evaluated the acceptability of quartz fiber-reinforced epoxy posts used in endodontically treated teeth over a 30-month period. Materials and Methods: In 132 patients, 180 endodontically treated teeth were restored using Æstheti-Plus quartz-fiber posts. The posts were luted with the All-Bond 2 adhesive system and C&B Resin Cement according to the manufacturer's recommendations. The core was made with Core-Flo or Bis-Core, and all-ceramic crowns or metalceramic crowns were applied as final restorations. The parameters considered as clinical failure were displacement, detachment, or fracture of posts; core or root fracture; and crown or prosthesis decementation. Patients were reevaluated at 6, 12, 24, and 30 months. Results: One cohesive failure involving a margin of the composite core was observed after 2 weeks, and two adhesive fractures were seen after 2 months. These failures were located between the cement and the dentin walls of the canals. All three failures occurred during removal of the temporary crown. The percentage of failures was thus 1.7% over a 30-month period, but it was possible to successfully replace the restoration in all three failed cases. Conclusion: Over a 30-month period, the rehabilitation of endodontically treated teeth using quartz-fiber posts showed good clinical results. No crown or prosthesis decementation was observed, and no post, core, or root fractures were recorded.

Purpose: The purpose of this study was to examine the correlation between patient satisfaction with complete dentures and parameters of denture quality, oral condition, and flow rate of the submandibular and sublingual salivary glands. Materials and Methods: The parameters were evaluated on 50 denture wearers using semiquantitative scales and a recently described submandibular/sublingual saliva collector. Results: Most patients had a medication-induced reduced salivary flow rate (mean 0.024 mL/min/gland; SD 0.040). Submandibular/sublingual salivary flow rate correlated statistically with six denture satisfaction parameters: maxillary denture retention and comfort, mandibular denture retention and comfort, abilities of chewing, and speech. Residual alveolar ridge resilience, maxillary ridge shape, and denture quality did not significantly correlate with denture satisfaction. Characteristics of musculature correlated significantly only with subjective maxillary denture retention, and mandibular ridge shape correlated with comfort. Conclusion: Submandibular/sublingual salivary flow rate is an important factor in denture satisfaction. The retention of the maxillary denture was correlated to the oral musculature characteristics, and the mandibular denture comfort was correlated to the mandibular ridge shape. Denture satisfaction was not affected by other anatomic or denture quality-related parameters.

Purpose: The purpose of this investigation was to examine the changes in wettability of dental impression materials during setting. This study compared the properties of the initial water contact of two different dental impression materials and their subsequent development during polymerization. Materials and Methods: Two dental impression materials (Impregum Penta Soft and Aquasil) with different chemical compositions (polyether and polyvinyl siloxane, respectively) were investigated with respect to their changing wetting properties by time-resolved static contact angle measurements. Ten sets of measurements each were taken over a period of 400 seconds with 150 points of data each; the first pictures were used for further characterization of the initial interaction. Results: With 73 degrees, Impregum Penta Soft exhibited a significantly lower contact angle, which stayed lower during the process of setting, compared to the silicone-based material. The initial interaction of the droplet showed a repulsive interaction of Aquasil with the water droplet. Conclusion: Impregum Penta Soft showed a more hydrophilic behavior during the process of setting compared to Aquasil and can therefore be expected to exhibit better flow properties. The method of time-resolved static contact angle measurements is a well-suited analytic instrument to monitor temporally changing wetting phenomena.

Purpose: The aim of this study was to investigate the effect of occlusal veneer porcelain thickness on the load at fracture of Procera AllCeram crowns. Materials and Methods: Fifty resin dies were manufactured to incorporate the features of an all-ceramic crown preparation on a premolar tooth. Fifty corresponding crowns were constructed and divided into five groups. Groups 1, 2, 3, and 4 were crowns with 0.6-mm-thick Procera cores and 0.4-mm-thick axial veneer porcelain and occlusal veneer porcelain thicknesses of 0.0 mm, 0.4 mm, 0.9 mm, and 1.4 mm, respectively. Group 5 specimens consisted of 0.6-mm-thick In-Ceram cores with 0.4 mm of axial porcelain and 0.4 mm of occlusal porcelain. The crowns were cemented onto their respective dies with a resin luting agent. Specimens were stored in distilled water at 37°C for 24 hours prior to placing them in a universal testing machine and applying a controlled compressive load at a cross-head speed of 0.1 mm/min until fracture occurred. Results: The mean loads at fracture were 419 N (group 1), 702 N (group 2), 1,142 N (group 3), 1,297 N (group 4), and 732 N (group 5). Statistical analysis revealed significant differences (P .05) in the load at fracture between the groups, except for between groups 2 and 5. Conclusion: Increasing the thickness of the occlusal veneer porcelain increased the load at fracture for Procera AllCeram crowns. There was no significant difference in load at fracture between the Procera and In-Ceram crowns.

Purpose: The purposes of this study were to investigate the periodontal status and susceptibility to periodontal disease progression of the teeth in contact with removable partial dentures (RPD) and to compare them with control teeth in mouths not restored with a partial denture, by means of both clinical parameters and interleukin (IL)-1ß levels in gingival crevicular fluid. Materials and Methods: Twenty-eight periodontally healthy patients were selected for the study; 14 of them were treated with mandibular Kennedy Class I RPDs, and the other 14 patients were not restored for control. Clinical periodontal measurements were assessed, and crevicular fluid samples were collected from both abutment and control teeth to determine IL-1ß levels, which were measured by enzymelinked immunosorbent assay. These procedures were performed both at baseline and 9 months after the insertion of the dentures. Results: The wearing of RPDs resulted in statistically higher clinical scores and total IL-1ß levels compared to the baseline examination. In contrast, no statistically significant differences were found between baseline and 9-month examinations in the control group. Conclusion: RPDs are a risk factor for periodontal disease progression because of increased plaque accumulation associated with increased total IL-1ß levels and impaired clinical periodontal parameters.

Purpose: This study compared the fatigue life of human maxillary premolars restored with direct composites and indirect ceramic inlays in mesio-occlusodistal (MOD) cavities. Materials and Methods: Ten human maxillary premolars were divided into two groups of five and restored with (1) direct composite restorations, or (2) pressed ceramic restorations. Standardized MOD cavities were prepared for both groups. Teeth in the direct composite group were restored with Z250 composite and Single Bond adhesive, and those in the ceramic group were restored with IPS Empress ceramic inlays. The ceramic inlays were luted with Single Bond and RelyX ARC cement. Under the applied test load of 11.17 kg, strain measurements were recorded from an electric resistance stain gauge bonded to the buccal surface. These strains were recorded for the (1) intact tooth, (2) cavity preparation, and (3) restored tooth. These strain measurements were used to calculate the relative tooth compliance values for each tooth. The fatigue loading was applied until reinforcement loss was registered by the strain gauge. Results: A one-way ANOVA showed no significant compliance difference between the intact and restored tooth conditions, and no significant difference in fatigue cycles to failure between the two groups. Conclusion: There were both adhesive and cohesive failures in both restoration groups, indicating that the adhesive joint is not the only weak link in these restorations.

Purpose: Earlier studies on low-fusing ceramics have shown the occurrence of changes over time regarding surface and color. The present prospective study is an ongoing follow-up of an intraindividual comparison between two metal-ceramic systems, the Procera system (titanium copings veneered with a low-fusing ceramic) and noble-alloy copings veneered with a medium-fusing ceramic. Materials and Methods: Twenty-one crown pairs were fabricated for 18 patients. After 5 years, 18 crown pairs in 15 patients were available for comparison. The crowns were examined shortly after cementation (baseline), and after 1, 2, and 5 years. The crowns were rated according to the CDA system. Bleeding index and margin index were also evaluated. Results: Obvious changes regarding surface and color were noted for the titanium-ceramic crowns. The difference between the two types of crowns was statistically significant at 5 years (P = .004). The differences between the two systems regarding anatomic form, margin integrity, bleeding index, and margin index were small. Conclusion: Within the limitations of this study, it is concluded that low-fusing ceramic-veneered titanium copings are inferior to mediumfusing ceramic-veneered conventional copings regarding surface and color of the ceramic. Therefore, conventional ceramic-veneered crowns seem to be preferable, at least in the anterior area, where the esthetic requirements are greater than in premolar and molar regions. Whether possible changes in the properties of low-fusing ceramics will reduce the differences between the two types of metal-ceramic crowns remains to be proven.

Purpose: Occlusal adjustment of ceramic restorations may be necessary to correct interferences. A rough surface may abrade opposing tooth or restorative materials, thereby increasing plaque accumulation. The aim of this study was to compare the effect of four finishing systems and diamond paste on ceramic roughness. Materials and Methods: Forty ceramic disks were distributed into four randomized groups. The initial roughness of all samples was increased with a diamond bur. Samples in group 1 were finished with white silicon and black rubber; group 2 samples were finished with Shofu rubbers; group 3 samples were finished with diamond burs; and group 4 samples were finished with Sof-Lex disks. All samples were then polished by Yeti diamond paste. The surfaces were characterized by means of a surface roughness analyzer. The parameters Ra, Rpm, and Rz were determined. Four roughness recordings were made before and after diamond bur finishing, and before and after Yeti paste polishing. ANOVA was used to test the significance of differences between groups at each stage of the procedures. Results: All four methods reduced the average roughness of the samples. The most effective system was Sof-Lex disks. Diamond paste can round the profile shape and reduce the height of maximum peaks of the surface, but it may not improve the average roughness. Conclusion: All systems tested reduced the roughness of ceramic samples, but the Sof-Lex disk finishing system may be more efficient than other methods. The efficiency of the diamond paste is not clear.

Purpose: Acrylic resin complete dentures exhibit dimensional changes mainly because of processing shrinkage and expansion because of water uptake. The aim of this 5-year clinical study was to determine the dimensional changes occurring during construction and in service in maxillary complete dentures made of two types of acrylic resin. Materials and Methods: Complete dentures were constructed for 17 edentulous patients. Nine patients received dentures made of conventional heat-cured acrylic resin, and eight patients received dentures made of rapid heat-cured acrylic resin. Measurements were taken across three reference points (second molars bilaterally and central incisors) on six occasions: at the flasking stage, at the denture insertion appointment, and after 1 week, 1 month, 3 months, and 5 years of use. The data obtained were analyzed using one-factor repeated-measures ANOVA, one-way ANOVA, and Duncan's multiple comparisons test. Results: The two types of dentures showed the same pattern of dimensional changes. A shrinkage of up to 0.27% was estimated at the insertion stage. During the first 3 months of use, a decrease of the initial dimensional change was observed. After a 3-month period, a gradual compensation for the initial shrinkage started to take place. At the end of the study period (5 years), an expansion of up to 0.35% was measured. Conclusion: Maxillary complete dentures made of either conventional or rapid heat-cured acrylic resin exhibited dimensional changes that were considered clinically acceptable.

Purpose: The purpose of this study was to examine the influence of the elastic modulus of cement and luting thickness on the resulting stresses in an axially loaded crown cemented onto a first premolar. A comparison of these stresses was also made with the strength of the constituent materials making up the crown. Materials and Methods: Examination of the stresses on a restored crown was conducted using finite element analysis. Eight different axisymmetric models containing combinations of In-Ceram or gold coping, using adhesive resin or zinc phosphate cement as the luting agent, with thicknesses of either 0.05 or 0.1 mm were analyzed. Results: The peak tensile principal stresses in the porcelain remained below its material fracture strength. The same was true for the peak stress in the adhesive resin compared to its fracture and chemical bond strength. This was not the case for zinc phosphate. The influence of the luting agent's elastic modulus on the stresses in the crown was minor, and the influence of luting thickness was even less. Conclusion: The role of the luting agent was primarily one that effectively transferred the resulting stresses between the relatively stiff coping and underlying dentin. There was no evidence of the luting agent itself playing a significant