The International Journal of Prosthodontics, 02/2002

Purpose: The purpose of this study was to evaluate the compatibility of three-dimensional finite element stress analysis and in vitro strain gauge analysis in the measurement of strains on a dental implant. Materials and Methods: Two vertically placed implants embedded in a poly(methyl methacrylate) model were used. Strain gauges were bonded to the cervical parts of the implants, and seven cement-retained fixed partial dentures were fabricated. A three-dimensional model of the strain gauge analysis model was constructed, and an additional model in which human bone simulation was provided was also constructed. A static vertical load of 50 N was applied at certain locations to simulate centrally positioned axial and laterally positioned axial loading for strain gauge analysis and three-dimensional finite element stress analysis. Results: Statistically significant increases in strain levels were recorded between loading types in the strain gauge analysis (P .05). Strains obtained from strain gauge analysis were higher than for three-dimensional finite element stress analysis. There was a remarkable difference between the two finite element models under the conditions of laterally positioned axial loading. Conclusion: There are differences regarding the quantification of strains between strain gauge analysis and three-dimensional finite element stress analysis. However, there is a mutual agreement and compatibility between three-dimensional finite element stress analysis and in vitro strain gauge analysis on the determination of the quality of induced strains under applied load.

Purpose: The objective of this follow-up study was to examine the performance of Cerec inlays and onlays in terms of clinical quality over a functional period of 10 years. Materials and Methods: Of 200 Cerec inlays and onlays placed in a private practice between 1989 and early 1991, 187 restorations were observed over a period of 10 years. The restorations were fabricated chairside using the Cerec-1 computer-aided design/manufacturing (CAD/CAM) method and Vita MK I feldspathic ceramic. An adhesive technique and luting composite resin were used for seating the restorations. After 10 years, the clinical performance of the restorations was evaluated using modified USPHS criteria. The results were used to classify success and failure. Results: According to Kaplan-Meier analysis, the success rate of Cerec inlays and onlays dropped to 90.4% after 10 years. A total of 15 (8%) failures were found in 11 patients. Of these failures, 73% were caused by either ceramic fractures (53%) or tooth fractures (20%). The reasons for the remaining failures were caries (20%) and endodontic problems (7%). The threesurface Cerec reconstructions were found to have the most failures. Conclusion: The failure rate of 8% and the drop of the survival probability rate to 90.4% after 10 years of clinical service of Cerec-1 CAD/CAM restorations made of Vita MK I feldspathic ceramic appear to be acceptable in private practice. This is particularly true in light of the very high patient satisfaction.

Purpose: The conventional impression technique for manufacturing facial prostheses has the disadvantage of deforming the soft tissues because of the tension caused by the impression material, as well as causing discomfort to the patient. The purpose of this study was to establish a system that allows contact-free reproduction of the facial surface combined with computer-assisted design and fabrication of facial prostheses. Materials and Methods: Three-dimensional data of the facial surface were obtained using an optical acquisition system based on the method of phase-measuring profilometry. A sensor head with a fringe projector and two CCD cameras for photogrammetric triangulation were used in connection with a PC for measurement control and data evaluation. Software for computer-assisted design of the facial surface to be reconstructed was developed. A prototype facial prosthesis was fabricated using stereolithography. The system was tested using a modified puppet head. First clinical tests were performed with a patient who had undergone maxillofacial surgery including the resection of one eye. Results: Threedimensional data acquisition and imaging allow visualization of a whole face without causing tension or neuromuscular reaction. As surface brightness is also part of the digital model, it is even more realistic than a plaster cast. The stereolithographic object showed good marginal fit and satisfactory shape. Conclusion: The presented technique allows three-dimensional data reproduction of the facial surface, computer-assisted design of a facial prosthesis, and transfer to a rapid prototyping unit. The system has obvious advantages over conventional impression techniques. Further clinical trials are planned to evaluate the clinical success of the technique.

Purpose: A longitudinal 5-year clinical investigation was carried out to compare screwretained frameworks constructed from two alloys with different mechanical properties, either gold or silver-palladium, supported in the mandible by the Astra Tech implant system. Materials and Methods: Twenty-six edentulous patients with mandibular implants were divided into two groups: group A was provided with Chicago IV gold alloy superstructures, and group B was provided with Palliag M silver-palladium alloy superstructures. The surgical procedures for placing the mandibular bone implants and the prosthodontic and laboratory techniques for constructing the prostheses were carried out according to standard, well-documented practices. All patients wore conventional maxillary complete dentures. The integrity of prostheses and health of supporting tissues were compared over a 5-year period. Results: Both materials had similar accuracy of fit and resistance to functional stress, although silver-palladium was technique sensitive and necessitated meticulous laboratory practice to achieve accuracy of casting. Clinical performance of both prostheses was similar, and radiographic assessment showed no statistically significant differences in periimplant bone changes. Conclusion: There were no differences in clinical performance and radiographic changes between the two materials. Therefore, silver-palladium alloy may be considered a suitable low-cost substitute for gold alloy for fixed implant-supported prostheses.

Purpose: Speech outcome measurements are valuable in guiding treatment and determining the effectiveness of rehabilitation with a maxillary obturator prosthesis in individuals with palatal resection. Although speech outcome data exist in the literature for such patients, relatively few reports have used clinical tools designed to measure the acoustic, physiologic, and perceptual bases of speech. This investigation reports these measures for individuals rehabilitated with a maxillary obturator. Materials and Methods: Speech measurements were collected prospectively at three clinical visit times(preoperative, postresection without an obturator, and with a definitive obturator) for 12 patients assigned to three groups based on the extent of their resection ( half the hard palate, >= half the hard palate, hard and soft palates). Acoustic data were obtained with the Nasometer, aeromechanical data were collected with the PERCI-SARS, and perceptual ratings of speech intelligibility were obtained through listener analysis. Results: Significant differences existed among the three treatments for all dependent variables and revealed that speech without an obturator is significantly different from the preoperative state, while speech with an obturator does not differ significantly from preoperative function. Individuals with soft palate involvement exhibited significantly poorer nasalance values than individuals with involvement of the hard palate only. Conclusion: Rehabilitation with a maxillary obturator is successful in restoring preoperative speech function. Rehabilitation of individuals with involvement of the soft palate may be more challenging.

Purpose: The purpose of this study was to describe oral prosthetics in a context intended for other, primarily Nordic, health professionals and health authorities. Materials and Methods: An article describing oral prosthetics for the general public was formulated on the basis of recent data and publications in prosthodontics from Scandinavian authors. A draft was presented to the educational committee of the Scandinavian Society for Prosthetic Dentistry for verification and consensus. Following modifications and amendments by representatives from the 11 dental schools in the Nordic countries, the educational committee has approved the present article. Results: The report consists of four sections describing oral prosthetics, prosthetic therapy, undergraduate teaching in oral prosthetics, and advanced oral prosthetics, from a Nordic perspective. The report appraises the various factors in context with demographic, cultural, and professional circumstances and suggests strategies for improvement of present conditions. Conclusion: The relationship between the undergraduate curriculum in oral prosthetics and the public need for advanced oral prosthetics must continuously be monitored so that patients can obtain optimal care from the profession.

Purpose: All-ceramic post-and-core restorations offer a number of advantages compared with systems that use metal cores. In certain clinical cases, however, fractures at the junction between the post and the core have been reported. The objective is therefore to improve the strength between the post and the core. Materials and Methods: Three different methods were used to fabricate all-ceramic post-and-core restorations: pressing IPS Empress cores directly to CosmoPost zirconia posts, adhesively luting IPS Empress cores to CosmoPost zirconia posts, and Celay milling In-Ceram zirconia blanks to onepiece post-and-core restorations. Ten restorations were prepared with each of the three methods. The post-and-core complexes were tested to failure with the load applied perpendicular to the post axis. The load and deflection at fracture were recorded. Results: The highest breaking load and highest deflection were recorded for the luting technique, with values of 25.3 N and 394 µm, respectively. The corresponding values for the pressed cores and the milled zirconia cores were 22 N and 301 µm, and 13 N and 160 µm. All differences were statistically significant at P .05. Regarding the load dependence of the deflection, the luted cores again demonstrated the highest mean value, with 15.5 µm/N, while this value was 13.6 µm/N and 13 µm/N for the pressed-on and milled cores, respectively.These differences were not statistically significant. Conclusion: Adhesively luted all-ceramic cores on zirconia posts offer a viable alternative to the conventional pressed technique.

Purpose: Topographic analysis of etched ceramics provides qualitative surface structure information that affects micromechanical retention mechanisms. This study tested the hypothesis that the etching mechanism changes according to the type of etchant and the ceramic microstructure and composition. Materials and Methods: Quantitative and qualitative analyses of 15 dental ceramics were performed using scanning electron microscopy, back-scattered imaging, X-ray diffraction, optical profilometry, and wavelength dispersive spectroscopy based on Phi-Rho-Z correction. All ceramic specimens were polished to 1 µm with diamond compound, and the following etchants and etching times were used: ammonium bifluoride (ABF) for 1 minute, 9.6% hydrofluoric acid (HF) for 2 minutes, and 4% acidulated phosphate fluoride (APF) for 2 minutes. Results: HF produced an irregular etching pattern in which pores were the characteristic topographic feature. ABF-etched ceramic surfaces showed mostly grooves, and APF etchant caused a buildup of surface precipitate. Core ceramics showed less topographic change after etching because of their high alumina content and low chemical reactivity. Conclusion: The observations suggest that the etching mechanism is different for the three etchants, with HF producing the most prominent etching pattern on all dental ceramics examined.

Purpose: This study evaluated the dimensional accuracy of various impression materials for monophase elastic impression making. To isolate this parameter, a direct measurement of the impressions was made without taking the model material into consideration. Materials and Methods: A total of eight materials were tested; six impression materials were addition-curing silicones, and two were polyether impression materials. All materials were processed according to the manufacturers' instructions. A specially developed precision mold made of stainless steel served as a basis for measuring the elastomeric impression materials. Using a stereomicroscope at a temperature of 23.0 ± 1.0°C and with a precision linear adjustment and lathe, sights were set on the marking points of customized posts. The measurement was performed after the earliest time possible for fabricating the model according to the manufacturer (time 1) and after 90 minutes (time 2). In a one-way analysis of variance, multiple average comparisons of dimensional accuracy were made (P = .05) between the impression materials under investigation. Results: Under the conditions of this study, the impression materials tested demonstrated a very high dimensional accuracy. The arithmetic means of the dimensional changes ranged from -11 to 19 µm for both measuring times. Conclusion: Since as a rule, no significant dimensional changes occurred for the different impression materials between time 1 and time 2, this time interval for fabricating a model can be recommended.

Purpose: This study determined the effect of bonding a composite core on the number of load cycles to cement failure for teeth restored with complete crowns. Materials and Methods: Ten extracted human maxillary central incisors were divided into two groups of five each. The tooth roots were at least 11 mm long, allowing an 8-mm post. Under copious irrigation, each tooth was cut to a flat plane 1 mm coronal to the buccal cementoenamel junction, perpendicular to the long axis of the tooth. The canal space was prepared to a final diameter of 1.25 mm, 8 mm deep. Each tooth was rebuilt with a 050 Parapost and Corestore. Final preparation height was 7 mm, including a 1-mm ferrule. For group 1, the core was bonded to the dentin using autocured Scotchbond Multipurpose Plus. For group 2, the core was not bonded. Following crown cementation, all teeth were subjected to a fatigue load of 4 kg at a rate of 280 cycles per minute. Results: One tooth with a bonded core failed at 19,880 cycles, and the other four in this group did not fail after 100,000 cycles. All of the teeth without a bonded core failed at a cycle count of less than 100. The Mann-Whitney nonparametric test showed a significant difference between the two groups (P .01). Conclusion: Bonding of a composite core to dentin prior to crown cementation provided a significantly stronger crown retention under fatigue loading.

Purpose: The study compared the probability of failure of three highly filled resin-veneered restorations to that of conventional metal-ceramic restorations when used as implantsupported prostheses. The effect of the location of load application on the fracture resistance of the restorations was also studied. Materials and Methods: Twenty samples each of the three resins, Artglass, Targis, and Estenia, were applied on Type IV gold frameworks. Twenty metal-ceramic restorations of equal dimensions (VMK 95 and Degudent Universal) were used as controls. Compressive load was applied vertically at 1 mm (n = 10) and 2 mm (n = 10) from the periphery of the occlusal table until the restorations failed. Weibull analysis was applied to the data. Results: There was no significant difference in the probability of failure among the metal-ceramic restorations and three resin-veneered restoration systems. Loading the resin-veneered restorations at the 1-mm location significantly increased their probability of failure when compared to the 2-mm loading location. The loading location did not significantly change the probability of failure of the metal-ceramic restorations. Conclusion: The probability of failure of resin-veneered restorations tested was not significantly different from that of the metal-ceramic restoration under two compressive loading conditions. Eccentric loading of resin-veneered restorations should be minimized in light of the higher probability of failure associated with such a loading condition.

Purpose: The study compared the flexural strength of In-Ceram alumina and In-Ceram zirconia systems. The probability of failure of the two glass-infiltrated ceramic core materials was analyzed with and without lamination with Vitadur-α porcelain. Materials and Methods: Ten uniform beams of core materials as well as 10 beams of laminated core materials were fabricated for In-Ceram alumina and In-Ceram zirconia. The samples were subjected to three-point bending tests. Flexural strength for both ceramic core materials was determined with and without their porcelain laminations. The strength data were analyzed using the Weibull method. Modes of failure for both systems were determined using scanning electron micrography. Results: The strength of the In-Ceram zirconia system was significantly higher than In-Ceram alumina when comparing their core materials with and without porcelain lamination. The failure mode for both systems was predominantly transgranular fracture of alumina platelets. Conclusion: In-Ceram zirconia demonstrated higher flexural strength than In-Ceram alumina.

Purpose: The purpose of this study was to use three-dimensional finite element analysis to analyze stress distribution patterns in Re-Implant implants made of commercially pure titanium (cpTi) and yttrium-partially stabilized zirconia (YPSZ). Materials and Methods: Two three-dimensional finite element analysis models of a maxillary incisor with Re- Implant implants were made, surrounded by cortical and cancellous bone. A porcelainfused-to-metal crown for the cpTi implant and a ceramic crown for the YPSZ implant were modeled. Stress levels were calculated according to the von Mises criteria. Results: Higher stresses were observed at the area where the implant entered the bone. Stresses were higher at the facial and lingual surfaces than the proximal ones. In cortical bone and at the junction of cortical and cancellous bone, stress distribution presented a pattern of alternating higher (4.0 to 5.0 MPa) and lower (1.3 to 2.0 MPa) stress areas. Higher stresses were found at the apical third of the implant-to-bone junction as well. Conclusion: Re-Implant implants presented a pattern of low, well-distributed stresses along the entire implant-to-bone interface. YPSZ implants had very similar stress distribution to cpTi implants and may be viable esthetic alternatives, especially in maxillary anterior regions.