The International Journal of Prosthodontics, 02/2011

Purpose: The aim of this systematic literature review was to investigate the survival rates of teeth, implants, and double crown-retained removable dental prostheses (RDPs). Materials and Methods: A systematic review of the literature published from January 1973 through May 2010 was conducted using electronic databases and hand-searching to assess the clinical outcomes of teeth, implants, and double crown-retained RDPs. Results: This review yielded 512 articles, which were narrowed down to 11. The included studies demonstrated tooth survival rates between 60.6% and 95.3% after an observation period of 4 to 10 years. The survival rates of RDPs supported by teeth ranged between 90.0% and 95.1% after 4 and 5.3 years, respectively. The survival rates of implants supporting prostheses in the mandible were between 97% and 100% after an observation period between 3 and 10.4 years. The survival rates of implant-retained RDPs in the mandible ranged between 95% and 100% after 9 and 10.4 years. Teeth and implants supporting prostheses in the maxilla, as well as the RDPs themselves, demonstrated a survival rate of 100% after 3.2 years. Conclusion: The current literature does not provide sufficient information regarding the long-term outcome of double crown-retained RDPs. Further studies based on a higher level of evidence are needed to validate the outcomes of this treatment modality.

Purpose: Insufficient coronal tooth structure may require restoration of endodontically treated (ET) teeth with cast posts and cores (CPCs). The prognosis for these teeth is a matter of scientific debate, especially if they serve as distal abutments in cantilever fixed dental prostheses (FDPs). The purpose of this study was to study stress field development in distal abutments in two types of FDPs with different pulp cavity conditions. Materials and Methods: The methodology involved the development of four digital models in which the right mandibular premolars were splinted via an FDP with: (1) no cantilever and a vital distal abutment, (2) no cantilever and an ET CPC distal abutment, (3) a single-unit cantilever and a vital distal abutment, and (4) a single-unit cantilever with an ET CPC distal abutment. The models were analyzed using a three-dimensional finite element program, and von Mises stress values and patterns were evaluated. Results: The results revealed that although the stress distribution patterns in dentin were dissimilar, the von Mises stress values registered for the vital and ET CPC distal abutment were not considerably different. However, higher stress values were detected in the dentin area surrounding the post-gutta-percha interface after CPC placement. The addition of the cantilever resulted in a considerable increase in stress on the dental tissue structures. Conclusions: CPCs appear to create a risk of potential fracture that is initiated in the dentin at the apex of the post. The type of restoration appears to have a much more serious impact on the stress pattern developed in the distal abutment, and the addition of a cantilever appears to biomechanically compromise both biologic and restorative structures.

The retentive and morphologic changes of overdenture attachments were evaluated independently after repeated insertion and sinusoidal loading on implant abutments. Stud and magnetic attachments were embedded in overdenture housings (n = 5). The overdentures were subjected to either repeated insertion and removal for 5,400 cycles or sinusoidal cyclic loading for 100,000 cycles. A 67.8% decrease in retentive force was observed after 100,000 loading cycles (P .05), and a 73.9% decrease of retentive force occurred after 5,400 insertion-removal cycles (P .05). Stud attachments showed more loss of retention and physical deterioration than magnetic attachments tested under identical conditions.

Seven implants provided with strain gauges were placed in an acrylic block to evaluate the biomechanical performance of short implants in splinted restorations. Two 7-mm-long implants with the same diameter (3.8, 4.4, or 5.0 mm) were splinted together (short-short implant splinted restoration [SS]) or individually with a 4.4 × 12.0-mm implant (short-long implant splinted restoration [SL]), and a 50-N oblique load was applied to both restorations. The strain decreased significantly with an increase in implant diameter in both the SS and SL restorations, and the observed strain was identical between splinted implants of the same diameter and those splinted with the long implant, suggesting that splinting of two short implants has the same biomechanical effectiveness as splinting with a single long implant.

This pilot study aimed to explore whether occlusal contacts during lateral excursions are influenced by tilted body positions. Occlusal contacts in lateral excursions were verified for 30 dental students and 22 dental staff members using articulation foil while patients were seated in a dental chair. The number and location of dynamic tooth contacts (initial and halfway) were registered with the back of the dental chair in three positions: upright, 45 degrees, and supine. For the majority of subjects (96%), dynamic occlusal contacts changed when the body position was altered.

This study evaluated a newly developed online color training system. The system incorporated basic color training, shade guide matching, and clinical shade selection simulation exercises. Thirty-seven dental students went through baseline Vita-Vita testing with VITA Classical shade guides and then practiced color training exercises with the system for 4 days; the same test was performed after the training program. The average correct match increased from 6.7 (41.88%) to 11.38 (71.13%) using the shade guides (P .001) and from 9.67 (60.42%) to 13.06 (81.63%) using the color training system (P .001). The effectiveness of the color training system in improving color-matching quality was confirmed.

This study investigated the effect of occlusal design on the strain developed in simulated bone of implant-supported single crown models. Triaxial strain gauges were attached at the cervical area of each model. Occlusal design, load location, and magnitude were examined to determine the maximum axial principal strains (µε) of four occlusal designs: 30-degree cusp inclination with 4- and 6-mm occlusal table dimensions and a 10-degree cusp inclination with 4- and 6-mm occlusal table dimensions. Statistical differences were found for peak average maximum principal strains between each occlusal design when the applied load was directed along the central fossa and 2 mm buccal to the central fossa along the inclined plane, with strain gauges attached at the cervicobuccal (P .001) and cervicolingual (P = .001) aspects. In all loading conditions, the 30-degree cusp inclination and 6-mm occlusal table dimension consistently presented the largest strains compared with the other occlusal designs. A reduced cusp inclination and occlusal table dimension effectively reduced experimental bone strain on implant-supported single crowns. The occlusal table dimension appeared to have a relatively more important role than cusp inclination.

The aim of this study was to evaluate the radiopacity of the core and veneer ceramics in four zirconia-based crown systems: In-Ceram Zirconia, In-Ceram YZ, Procera Zirconia, and Cercon. Two-millimeter-thick restoration slices were prepared and digitally radiographed alongside an aluminum stepwedge. The grayscale data were converted into millimeters of aluminum by an image analysis program. The two-way analysis of variance test detected significant differences with respect to all-ceramic system, layer ceramic, and the interaction of the two factors (P = .0001). All materials presented radiopacity values above the minimum recommended by the International Organization for Standardization.

Purpose: The aim of this study was to develop a protocol to analyze the microstructure of mandibular and maxillary bone in association with implant placement in ectodermal dysplasia (ED) and anodontia conditions compared to patients not suffering from such conditions. Materials and Methods: This study was not additionally invasive, since the bone harvesting was completed at the time and site of implant placement. Bone samples were allocated into two groups (ED and control patients) and specified by the site of bone harvesting. Microcomputed tomography (micro-CT) analysis at 5-µm resolution was conducted on each bone sample. Computer analysis applying specialized CT analysis and software allowed evaluation of the three-dimensional microstructure of alveolar and basal bone samples for comparison of structural parameters. Results: Ten bone samples (five alveolar and five basal) were harvested. Preliminary data confirmed the structural features and significant differences between alveolar and basal bone. Basal bone had greater absolute and percent bone volume, greater bone surface, and a lower trabecular bone pattern factor than alveolar bone. Conclusion: Preliminary data were derived from bone harvested from both the maxilla and mandible of control patients, while bone samples from ED patients were harvested from only the anterior mandible. Further bone samples will provide more data on whether broader areas of bone harvesting, age, or sex affect the quality and quantity of the bone and influence implant treatment outcomes.

The aim of this study was to evaluate the effects of carbamide peroxide (CP) on surfaces of different restorative materials. Porcelain, composite resin, glass ionomer, and amalgam were analyzed in this study. Surface roughness (Ra) was measured before and after treatment with 10% and 15% CP. Fifteen percent CP increased Ra values in both the glass ionomer and amalgam subgroups, while 10% CP increased Ra values in the glass ionomer subgroup only. Changes in restorative material surfaces can be more severe when bleaching is completed without a clinician's supervision. Hence, thorough patient examinations must be done before, during, and after bleaching treatment.

Purpose: Long-term comparisons of frameworks at the implant or abutment level are not available, and knowledge of the clinical function of cobalt-chromium (Co-Cr) alloy frameworks is limited. Primarily, the aim of this study was to compare the 5-year clinical performance of frameworks with or without abutment connections to implants. Secondly, the outcomes of prostheses made from Co-Cr alloy with porcelain veneers to those made of commercially pure titanium (CP Ti) with acrylic veneers were compared. Materials and Methods: The test groups comprised patients treated with screw-retained fixed prostheses made at the implant level according to the Cresco method in either dental porcelain-veneered Co-Cr alloy (n = 15) or acrylic-veneered CP Ti (n = 25). A control group of 40 randomly selected patients were provided with prostheses made at the standard abutment level in CP Ti with acrylic veneers. For all patients, clinical and radiologic 5-year data were retrospectively collected and evaluated. Results: Five-year implant cumulative survival rates (CSRs) were 98.6% and 97.6% for test and control groups, respectively (P > .05). No major differences in bone level were demonstrated between the groups after 5 years (P > .05). Significantly more complications occurred in the test groups compared to the control group (P .01), with the most common complications being mucositis and fracture of veneers. Conclusions: After 5 years, the clinical outcomes of implant-level prostheses made of porcelain-veneered Co-Cr or acrylic-veneered CP Ti seem comparable to acrylic-veneered titanium prostheses made at the standard abutment level regarding implant CSR and bone levels. However, more complications were registered in implant-level prostheses compared to the standard abutment-level prostheses.

This study investigated the fracture resistance of three different zirconia fixed partial dentures (FPDs) with different cementation methods. Forty-eight three-unit FPDs were adhesively bonded (AB) or conventionally cemented (CC). Sixteen glass-infiltrated zirconia FPDs were used as a control. Fracture resistance was determined after aging. The zirconia systems showed no significant different fracture forces with the different bonding methods (CC: Cercon [1,231.5 ± 410.1 N], Ceramill [1,311.3 ± 318.3 N], Vita YZ [1,269.0 ± 317.4 N]; AB: Cercon [1,072.3 ± 516.7 N], Ceramill [1,358.6 ± 176.4 N], Vita YZ [1,270.6 ± 267.6N]) or between the different materials. The control group provided significantly lower fracture strength. Regarding fracture resistance, adhesive bonding or conventional cementation of zirconia FPDs showed no restrictions for posterior application.

The aim of this study was to evaluate the damage tolerance of different zirconia-based materials. Bars of one hard machined and one soft machined dental zirconia and an experimental 95% zirconia 5% alumina ceramic were subjected to 100,000 stress cycles (n = 10), indented to provoke cracks on the tensile stress side (n = 10), and left untreated as controls (n = 10). The experimental material demonstrated a higher relative damage tolerance, with a 40% reduction compared to 68% for the hard machined zirconia and 84% for the soft machined zirconia.

The aims of this study were to evaluate the retentive effect of different denture adhesives on maxillary complete dentures and examine the use of an intraoral transducer in assessing denture retention. The quantification of maxillary complete denture retention in 26 patients with five different adhesives was completed using vertical tensile tests and an intraoral resistance transducer. The means of the values obtained were analyzed statistically for comparative purposes. The experimental design revealed that all tested denture adhesives improved retention and that the intraoral transducer used proved to be appropriate for this evaluation. The intraoral transducer demonstrated that denture adhesives can improve retention of complete maxillary dentures.