The International Journal of Prosthodontics, 02/1999

Purpose: The purpose of this study was to investigate the biomimetic principle in porcelain veneer reconstruction, or in other words, to assess the extent to which the restoration can mimic the biomechanics and structural integrity of the original tooth. Using an optimized luting procedure, porcelain veneers are expected to present such features even when bonded to an extensive dentin surface. Methods and Materials: Dentin-bonded porcelain veneers were assessed using functional and cyclic thermal loads with respect to two parameters: coronal stiffness (investigated using experimental strain gauges and finite element analysis) and morphology of the tooth-restoration interface (scanning electron microscope evaluation). Two different application modes of the same dentin-bonding agent, Optimbond FL, were valuated: a traditional method (dentin adhesive applied when proceeding to luting the veneer) and an alternative method (dentin adhesive applied to dentin and cured before taking the impression for the veneer). Results: In the finite element model, the crown compliance increased by a factor of 2.16 after facial enamel removal and returned to 96% of its original value after the placement of the veneer. The finite element values showed a good correlation with strain gauge experimental results (one-sample t test, P > 0.35 after facial enamel removal and P > 0.19 after veneer placement). The dentin adhesive application mode was not critical to the recovery of tooth stiffness (analysis of variance, P = 0.10). However, qualitative scanning electron microscope observations demonstrated that the traditional dentin adhesive application was associated with bonding failures between the hybrid layer and the overlying resin, whereas unbroken and continuous interfaces were obtained with the new mthod using the same dentin adhesive. Conclusion: The results of this study definitely favor the biomimetic behavior of porcelain veneers bonded to teeth using an optimized application mode of dentin adhesives, because this treatment modality proved to restore both the mechanical behavior and microstructure of the intact tooth.

Purpose: The purpose of this study was to retrospectively evaluate leucite reinforced-glass ceramic crowns (Empress) placed in patients who regularly visit general practices. Materials and Methods: One hundred ten Empress crowns, placed in 29 patients who visited a general practice on a regular basis, were evaluated according to the California Dental Association's (CDA) quality evaluation system. In addition, the occurence of plaque and certain gingival conditions was evaluated. All crowns were luted with resin composite cement. The means and median years in function for the crowns were 3.6 and 3.9 years, respectively. Results: Based on the CDA criteria, 92% of the 110 crowns were rated satisfactory. Eighty-six percent were given the CDA rating excellent for margin integrity. Fracture was registered in 6% of the 110 crowns. Of the remaining 103 crowns, the CDA rating excellent was given to 74% for anatomic form, 86% for color, and 90% for surface. No significant differences (P > 0.05) were observed regarding fracture rates between anterior and posterior crowns. With regard to the occurrence of plaque and bleeding on probing, no significant differences (P > 0.05) were observed between the Empress crowns and the controls. Conclusion: Most of the fractured crowns had been placed on molars or premolars. Although the difference between anterior and posterior teeth was not statistically significant with respect to the fracture rates obtained, the number of fractured crowns placed on posterior teeth exceeded that of those placed on anterior teeth. The difference between the fracture rates may have clinical significance, and the risk of fracture has to be taken into consideration when placing crowns on teeth that are likely to be subjected to high stress levels.

Purpose: The purpose of this study was to clarify certain properties of the resulting unpolymerized surface layer on 6 hard, autopolymerizing reline resins. Materials and Methods: Two of the resins examined were the conventional type with a base monomer composition of mainly methyl methacrylate, and the other four were cross-linked reline materials containing difunctional monomers. For curing, the materials were polymerized in air at 24 and 37 degrees C, and in distilled water at 37 degrees C. The powder-to-liquid ratio was changed by ± 20 wt% of the manufacturer's specified ratio. The inhibition depth processed under these conditions was measured with an optical microscope. Each sample was then immersed in methylene blue dye bath for 3 weeks before its surface was observed. Results: Espcially on cross-linked reline materials, the unpolymerized layer was significantly reduced with higher temp erature, lower oxygen presence, and lower powder-to-liquid ratio (P 0.01). The unpolymerized layer was stained in all materials. There were tiny, stained voids in the polymerized region on the conventional type of reline resins, whereas no staining was found in the polymerized region on the cross-linking reline resins. Conclusion: The inhibition depth was strongly affected by the temperature, the presence of air, and viscosity. The unpolymerized layer was easily contaminated in all materials. However, the highly polymerized, cross-linked reline materials might be harder to contaminate than the conventional type of reline resins.

Purpose: The purpose of the present paper was to study the long-term clinical results with ceramic-veneered Procera titanium copings. Materials and Methods: A total of 44 titanium copings (fabricated for 22 patients) veneered with a low-fusing ceramic were followed for 60 to 78 months. The clinical examinations were performed by licensed specialists in prosthetic dentistry. The crowns were rated according to the California Dental Association system. In addition, Bleeding Index and Margin Index were also evaluated. Results: In 3 crowns ceramic fractures necessitated their replacement. Two crowns had to be replaced because of caries. The ratings for surface and color had changed markedly, from excellent to acceptable. Regarding anatomic form, with the exception of the 3 fractured ceramic crowns, there were no obvious changes. The margin integrity, aside from the 2 crowned teeth with caries, was recorded as satisfactory (excellent or acceptable) for all other crowns; in fact, a large majority were rated excellent. Regarding Bleeding Index, there were no differences between crowned teeth and control teeth. Changes in Margin Index showed that the gingiva of the crowned teeth had retracted. Conclusion: Of the various clinical factors evaluated, only surface and color-related to the low-fusing ceramic used for veneering-showed any obvious change during the follow-up period. Otherwise the veneered titanium copings had, in general, performed well.

Purpose: Previous studies have disclosed the unsatisfactory color stability of autopolymerizing, hard direct denture reliners (HDDR). The present study investigated the color stability of the newly introduced visible light-cured and dual-cured HDDRs. Materials and Methods: Five HDDRs were evaluated after 1 hour, 1 day, 7 days, and 30 days of immersion in coffee, tea, and water. Color measurements were obtained with a tristimulus colorimeter, and color differences (AE*) were calculated. Results: After 30 days of immersion one visible light-cured material exhibited the highest AE* value (17.8). The other materials showed acceptable color stability in water and coffee. However, tea strongly affected their color. Conclusion: Reliners, staining solutions, and immersion time are significant factors that affect color stability. After 7 days of immersion, all of the materials showed perceptible color differences. Tea exhibited higher staining capacity than coffee.

Purpose: The purpose of this study was to evaluate denture base displacement caused by tongue movements during speech. Materials and Methods: Ten patients with new Kennedy Class I mandibular removable partial dentures participated in this study. All prostheses were made according to a standardized protocol. Denture base displacements when speaking a test sentence were measured with a computer-aided device that was developed for this purpose. It included 4 Hall sensors, mounted on a paraocclusal splint and magnets, embedded in the denture bases. Vertical and transverse base displacements were calculated from Hall voltages. Clasp retention was measured with a dynamometer. Results: Mean displacements were 145 um seating, 72 um unseating, 87 um buccally, and 74 um lingually. Seating and unseating displacements differed statistically significantly in absolute values. Mean clasp retention was 2.5 N. No correlation was found between clasp retention and unseating base displacements. Conclusion: Tongue movements during speech induced only minimal displacements in the dentures investigated. Additionally, tongue activity was found to be denture stabilizing rather than denture displacing in this study.

Purpose: This review summarizes the methods employed to evaluate denture cleansers and makes some suggestions on the methodology of evaluation. Materials and Methods: More than 20 articles evaluating the efficacy of denture cleansers were compared, and the advantages and disadvantages of each method were evaluated. Results: The results obtained vary depending on the methods used to evaluate the efficacy of denture cleansers, particularly among in vitro and in vivo assays. In addition, it is pointed out that chemical denture cleansers are not as efficacious in clinical use as in the in vitro assay. The uncertainty over efficacy may be caused by nonstandardized methodology and reports of conflicting results. Conclusion: A standardization of the methodology is needed. This should include evaluation of the efficacy of cleansers through both in vivo and in vitro assay methods; standardization of the materials and methods used in studying the efficacy of denture-cleansing regimens; and the examination of not only selected microorganisms from limited surface areas of a denture, but the microorganisms in denture plaque from the whole surface of a denture. It would also be preferable to use methods and/or media that make it possible to not only qualify but also quantify the microbial plaque.

Purpose: When evaluating the outcome of oral implant treatment, a statistically important aspect to consider is whether any dependency exists among implants placed within the same patient/jaw. If one implant fails, will the risk of subsequent failures increase, ie, will any of the remaining implants also fail? In an attempt to study this question, the aims of the persent study were to statistically determine if the suggested hypothesis was valid, ie, whether dependency exists among implants in the same patient/jaw, and to determine how failure lifetable analysis should be calculated. Materials and Methods: In the present study, multicenter trial material consisting of 1,738 oral implants in 487 patients from 4 separate studies was used. First, any dependency among implants within the same patient/jaw was determined; thereafter, cumulative success rates were calculated for one implant per patient (chosen randomly), and the range of variations in the randomized success rates was also calculated. This was then compared with the cumulative success rates based on the entire material. Results: The statistical analysis showed that a dependency among the implants existed prior to their functional loading, ie, the risk for an implant failure among the remaining implants in the same patient/jaw increased after the first failure had occurred. Conclusion: Both study design and statistical analysis are of importance when comparing success rates from various investigations, since dependency among implants in the same patient/jaw does exist and may influence the success rates. Consequently, it is suggested that only one randomly selected implant from each patient should be considered when calculating implant success rates.

Purpose: This paper reviews the literature on advanced strategies that attempt to improve fit in implant prosthodontics with reference to the concept of the distortion equation. Materials and methods: The majority of the articles reviewed were either clinical or technique articles that advocated strategies to improve fit in implant prosthodontics. A limited number of retrospective and prospective clinical trial studies were included as they related to the topic. Reviewed articles were limited to those that addressed advanced strategies to improve fit. All of the scientific studies included in this review used an in vitro experimental design. The advanced strategies were categorized into methods that address intraoral indexing and methods that use the implant master cast. Results: Relatively few methods have been scientifically proven to improve fit in implant prosthodontics. Most of the tested strategies still resulted in a slight misfit of the frameworks to the implant abutments/analogues. Conclusion: Multiple factors preclude that the concept of passive fit can be achieved in implant prosthodontics, even with the use of advanced strategies. The use of meticulous, accurate implant prosthodontic procedures and the appropriate use of advanced strategies continue to be the recommended means of achieving precise fit of the implant prosthesis to the intraoral abutments.

Purpose: The purpose of this study was to examine the influence of ozone on the surface of removable partial denture (RPD) alloys to determine its usefulness as a cleaning method for RPDs, since ozone has powerful sterilizing and deodorizing properties. Materials and Methods: Two types of ozone cleaning were used. The quantities of ozone generated by both methods were the same (20 mg/h). In method A, ozone was generated for 10 minutes every 12 hours and in method B, ozone was generated over 24 hours a day. Test specimens of 3 types of dental alloy (Co-Cr, Au-Ag-Pt, and Au-Cu-Ag-Pd) were subjected to different cleaning methods for 7 days and measured in terms of reflectance, surface roughness, and weight. Five different cleaning solutions (three commercial denture cleaners, acid-electrolyzed water with a pH of 2.4, and pure water) were used for comparison with the ozone treatments. Results: No significant changes were detected after treatment of the Co-Cr and Au-Ag-Pt alloys with ozone. Ozone caused a slight change in the Au-Cu-Ag-Pd alloy in terms of reflectance, but the changes were significantly less than those caused by acid-electrolyzed water and one of the commercial denture cleaners. Conclusion: Ozone had little influence on the oxidation of dental alloys.

PURPOSE: This report demonstrates the use of root-analogue titanium implants for single-tooth replacement. MATERIALS AND METHODS: A maxillary lateral incisor was removed and a custom-made one-stage, root-analogue titanium implant (Re-Implant) with an apical extension and a healing cap was fabricated and placed immediately after tooth extraction. Six months later the healing cap was removed, an impression was taken, and a porcelain-fused-to-metal crown was fabricated and cemented. RESULTS: No complications occurred during the healing period. A good esthetic result was achieved with the final ceramometal crown. Bony resorption and buccal soft tissue recession led to a slight discoloration of the marginal periimplant mucosa. CONCLUSION: Further research into the modalities of the immediate placement of root-analogue implants is needed to obtain predictable esthetic results concerning the soft tissue environment.