Search

Purpose: To evaluate the stress distribution along a premolar's root dentin, its post, and its post-luting agent when materials with different elastic moduli are used to fabricate one-piece post-and-cores in two different designs., Materials and Methods: Two 3D virtual models (for cylindrical and conical post designs) of a mandibular premolar restored with one-piece post-and-core restorations were obtained using a software. A total of eight post-and-core materials were tested: polyetheretherketone (PEEK), polyetherketoneketone (PEKK), glass fiber-reinforced polyetheretherketone (GFR-PEEK), carbon fiber-reinforced polyetheretherketone (CFR-PEEK), gold-palladium alloy (Au-Pd), titanium (Ti), zirconia (Zi), and chromium-nickel (Cr-Ni). Maximum principals stress (MPS) in the post, post-luting agent, and root dentin were determined. A load of 150 N was applied to the buccal cusp in the linguo-labial direction at an angle of 45 degrees oblique to the longitudinal axis of the crown., Results: The highest MPS value in post structure was observed with Cr-Ni material for both post designs. Similarly, the highest MPS value in the post-luting agent was observed for Cr-Ni, the material with the highest elastic modulus. However, in the root dentin, the highest value was observed in PEEK, the material with the lowest elastic modulus., Conclusions: Post material and design influenced the stress concentration in the post, post-luting agent, and root dentin. The stress at the root dentin was slightly higher for polymeric materials. Cylindrical post design revealed lower stresses than conical post design at root dentin for all post-and-core materials tested.

Purpose: To investigate the clinical usefulness, a customized abutment produced with the Pd-Ag-In alloy was compared with a customized abutment produced with the conventional titanium alloy for discoloration and mechanical accuracy., Materials and Methods: Discoloration and resistance to corrosion of the Pd-Ag-In alloy were evaluated using chemical solutions. Marginal adaptation of internal-type implants and abutments was compared using 10 titanium abutments and 10 Pd-Ag-In abutments using a surface measuring system. A detorque test was performed on 12 implant-abutment complexes of each control and experimental group to investigate screw joint stability. Cyclic loading simulating a human's mastication movement for 1 year was applied after 30 Ncm initial tightening, and the removal torque was measured using a digital torque gauge. The noninferiority test was conducted to compare the Pd-Ag-In alloy with a titanium abutment with a 10% margin., Results: The Pd-Ag-In alloy had a warm yellow color and displayed stable resistance to discoloration and corrosion, resulting in an advantageous esthetic property. When compared to the titanium alloy, it did not show noninferiority with respect to the gap between the implant and the abutment; the gap was approximately 13.3 μm on average, which was not significantly different from those observed in previous studies. After long-term use, it displayed statistically significant noninferiority in the removal torque value compared to the titanium group., Conclusion: The Pd-Ag-In alloy-based customized abutment had good mechanical properties of the implant-abutment complex as well as a superior esthetic property, and can provide favorable outcomes in anterior implant restoration.

Purpose: Ceramic defects in porcelain-fused-to-metal (PFM) restorations may depend on framework alloy type. This study assessed ceramic defects on cobalt-chromium- (Co-Cr-) and gold-platinum- (Au-Pt-) based PFM restorations., Materials and Methods: In this study, 147 Co-Cr-based and 168 Au-Pt-based PFM restorations inserted between 1998 and 2010 (139 patients) were examined for ceramic defects. Detected defects were assigned to three groups according to clinical defect relevance., Results: Ceramic defect rates (Co-Cr-based: 12.9%; Au-Pt-based: 7.2%) revealed no significant difference but a strong statistical trend (U test, P = .082). Most defects were of little clinical relevance., Conclusions: Co-Cr PFM restorations may be at higher risk for ceramic defects compared to Au-Pt-based restorations.

Purpose: This in vitro study evaluated the adhesive strength of a technique to lute implant cylinders to metal frameworks in implant-supported prostheses and ensure a good passive fit., Materials and Methods: Different height samples were tested: In group 1, implant cylinders were 5 mm long; in group 2, they were 10 mm long. A universal testing machine (Instron) was used to perform pullout tests., Results: The luting technique provided enough adhesive strength for clinical use with greater adhesive strength in group 2 (mean pull-out strength: 2.85 kN in group 1 versus 3.79 kN in group 2)., Conclusions: The luting technique provides enough adhesive strength for clinical use. Moreover, specimens with a larger surface for adhesion demonstrated higher adhesive strength compared with shorter specimens.

Purpose: To use a novel approach to measure the amount of vertical marginal gap in computer numeric controlled (CNC)-milled titanium frameworks and conventional cast frameworks., Materials and Methods: Ten cast frameworks were fabricated on the mandibular master casts of 10 patients. Then, 10 CNC-milled titanium frameworks were fabricated by laser scanning the cast frameworks. The vertical marginal gap was measured and analyzed using the Contura-G2 coordinate measuring machine and special computer software., Results: The CNC-milled titanium frameworks showed an overall reduced mean vertical gap compared with the cast frameworks in all five analogs. This difference was highly statistically significant in the distal analogs. The largest mean gap in the cast framework was recorded in the most distal analogs, and the least amount was in the middle analog., Conclusions: Neither of the two types of frameworks provided a completely gap-free superstructure. The CNCmilled titanium frameworks showed a significantly smaller vertical marginal gap than the cast frameworks.

Purpose: Micromotion at the implant-abutment level has been reported to be a major determinant of longterm implant success, as technical problems ranging from screw loosening to screw fracture may occur as a consequence of excessive micromotion., Materials and Methods: Following published standards, implant-abutment assemblies were fixed in a universal testing machine at a 30-degree angle. A cyclic load of 200 N was applied to the specimens 10 times at a crosshead speed of 100 N/s while relative displacement between the implant and the abutment was quantified using extensometers. For five consecutive loading cycles per specimen, micromotion was recorded as a basis for statistical analysis, with two-sample t tests (Welch test) applied., Results: Micromotion at the implant-abutment interface ranged from 1.52 to 94.00 μm. While a significant effect of tightening torque was found, implant shoulder design did not reveal a significant effect in all cases. Lack of engagement of antirotational features of the implants resulted in increased micromotion. Casting onto prefabricated gold cylinders resulted in abutments with significantly less micromotion as compared to copy-milled and stock abutments. Computer-aided design/computer-assisted manufacture (CAD/CAM) zirconia abutments showed less micromotion than CAD/CAM titanium abutments. Inconsistent levels of micromotion were recorded for CAD/CAM abutments coupled to proprietary and competing implant systems. Great variations in micromotion were found with clone abutments and clone implant systems., Conclusion: A broad range of micromotion values was observed with the implant abutment combinations investigated. There seems to be no perfect implant shoulder geometry or perfect fabrication technique that would result in no detectable micromotion.

Purpose: The purpose of this study was to evaluate and compare the strain development at different occlusal heights of an implant prosthesis and adjacent teeth through the use of strain gauges., Materials and Methods: A test model was constructed using autopolymerizing polyurethane resin, artificial composite resin teeth, and an implant gold crown in the mandibular first molar area. The resin block containing the implant and the gold crown was sectioned, and two expansion screws were attached perpendicular to the bottom of the resin block on the buccal and lingual sides. The expansion screws were turned to create a gap. Four groups were created based on the occlusal height of the implant gold crown. Three strain gauges were attached to the buccal surfaces of the mandibular right second premolar, implant gold crown, and second molar. Beef jerky, carrot, and bread were used as test foods. A universal testing machine was used to apply compressive forces of 300 N (beef jerky), 250 N (carrot), and 50 N (bread), and the occlusal force was measured in each group., Results: With 300 N, occlusal forces were concentrated on the adjacent teeth when the occlusal height of the implant prosthesis decreased. With 250 and 50 N, when the occlusal height of the implant prosthesis increased, the occlusal force applied to the implant prosthesis increased, but alterations in the implant crown height had little effect on the adjacent teeth., Conclusion: Different amounts of strain in the implant prosthesis and adjacent teeth were recorded depending on the occlusal height of the prosthesis. With 250 or 50 N of force, an increased prosthesis height affected the implant itself. With 300 N of force, decreased occlusal height of the prosthesis resulted in increased force on the adjacent teeth.

Purpose: This retrospective study investigated the frequency and time history of chipping and facing failures, recurrent caries (RC), periodontitis (PE), and loss of retention (LR) of porcelain-fused-to-metal (PFM) single crowns., Materials and Methods: A total of 997 PFM single crowns had been inserted according to a standardized treatment protocol from January 1984 to May 2009. The frequency and time history of chipping and facing failures were evaluated, as were possible risk factors from historical clinical data. Risk factors were bruxism, the type of antagonist, and the location of crowns (mandible, maxilla, anterior, posterior). The survival times of crowns were estimated using Kaplan-Meier (KM) analysis., Results: The median follow-up time calculated with the inverse KM method was 4.33 years. Anterior and posterior PFM crowns showed 5-year survival rates (time to crown replacement) of 96.4% and 97.5% and 10-year survival rates of 92.3% and 95.9%, respectively. Chipping was found in 17 (1.7%) of the 997 PFM crowns. According to the KM method, the 5- and 10-year free-of-event-rates for chipping of anterior crowns were both 98.9%, and the rates for posterior crowns were 98.2% for 5 years and 97.3% for 10 years. Thirteen patients showed RC (1.3%) and 144 (14.4%) PE. The 5-year free-of-event-rate for RC was 98.7% and the 10-year free-of-event rate was 97.2%. For PE, the 5-year free-of-event-rate was 85.8% and the 10-year free-of-event rate was 72.2%. The 5- and 10-year free of- event-rates for LR were 92.2% each for anterior teeth and 97.1% each for posterior teeth., Conclusions: Patients with PFM crowns may expect long-term survival for their restoration. Clinical complications are rare. Chipping of the veneer or loss of retention may occur during the first few years. While chipping of the veneer may occur during the first few years, the frequency of caries or periodontitis increases with the length of oral service and with age.

The aims of this study were to determine the fracture origins and crack paths in the porcelain of clinically failed bilayer ceramic restorations and to reveal the correlation between the porcelain failures and material properties. Three clinically failed crowns of each material (bilayer zirconia crowns, galvano-ceramic crowns, and porcelain-fused-to-metal crowns) were collected and underwent failure analysis. The fractures found in porcelain veneers showed several characteristics including wear, Hertzian cone crack, chipping off, and delamination. The results indicated that the fracture origins and features of the porcelain in bilayer ceramic restorations might be affected by the rigidity of core materials and thickness of copings.

Objectives: The primary goal of the present finite element (FE) analysis of a special removable prosthesis, the conical telescopic crown (CTC), was to validate established results based on a rigid model of the CTC and to analyze its characteristic features as a function of the essential material and geometric parameters. Furthermore, the effectiveness of a new element, the composite stop (CS), was investigated., Materials and Methods: The study used an axisymmetric FE model containing the inner and outer crown including resin or ceramic veneer, the CS, the cement layer between the interior crown and the tooth, and the upper part of the tooth itself., Results: For a convergence angle (half-cone angle) α = 4 degrees and a moderate chewing force F = 150 N the loosening force decreased from - 50 N without to - 10 N with CS. Increasing α values yielded a decrease of the loosening force. Adherence between the inner (IC) and outer crown (OC) was achieved for all configurations (α = 2 degrees, 4 degrees, and 6 degrees), except for zirconium crowns with α = 6 degrees. In systems without CS, the maximum tensile stress in the veneer increased proportionally to F, but remained limited in those with CS., Conclusions: The angle a and the coefficient of static friction μ0 emerged as the decisive parameters of the CTC. The computed fitting/loosening behavior agreed well with results of a simple rigid-body model and experiments. The incorporation of a CS allows ceramic veneering of the outer crown., Clinical Relevance: The optimal angle α of the CTC is ascribed to a number of customary material combinations for IC and OC. The CS limits the loosening forces of the CTC to values which guarantee non-traumatic removal of the prosthesis.

Purpose: The aim was to evaluate the stress concentration caused by different cross sections of bar frameworks and clip materials used to retain overdentures., Materials and Methods: Three-dimensional models of a severely resorbed arch, an overdenture retained by two implants, and a bar-clip attachment system were made. A total of twelve models were made according to the cross section of the bar framework (round, oval, or Hader), clip material (gold or plastic), and presence of misfit. A vertical misfit of 100 μm between the implant and the bar framework was made on the right implant. Finite element models were obtained by importing the solid model into mechanical simulation software. The base of the mandible was set to be the fixed support, and a pressure of 100 MPa was applied to the right mandibular first molar. The analysis was made by means of von Mises stress for the prosthetic components and microstrain to the bone tissue., Results: Round bars led to lower values of stress in the clip and prosthetic screw of the ill-fitted component and lower microstrain values in the periimplant bone tissue. The lowest values of stress in the bar were observed in the Hader groups. Plastic clips reduced the stress concentration in all structures compared with gold clips., Conclusion: The clip material and the cross section of the bar framework influenced the stress distribution in overdentures retained by a bar-clip system presenting vertical misfit.

Purpose: To measure the vertical occlusal forces transmitted through crowns made of different restorative materials onto simulated peri-implant bone., Materials and Methods: The study was conducted using a masticatory robot that is able to reproduce the mandibular movements and forces exerted during mastication. During robot mastication, the forces transmitted onto the simulated peri-implant bone were recorded using nine different restorative materials for the simulated single crown: zirconia, two glass-ceramics, a gold alloy, three composite resins, and two acrylic resins. Three identical sample crowns for each material were used. Each crown was placed under 100 masticatory cycles, occluding with the flat upper surface of the robot to evaluate the vertical forces transmitted. Two-way analysis of variance was used. Alpha was set at .05., Results: The statistical evaluation of the force peaks recorded on the vertical z-axis showed mean values of 641.8 N for zirconia; 484.5 N and 344.5 N, respectively, for the two glass-ceramics; 344.8 N for gold alloy; 293.6 N, 236 N, and 187.4 N, respectively, for the three composite resins; and 39.3 N and 28.3 N, respectively, for the two acrylic resins. Significant differences were found between materials (P < .0001), except for the comparison between gold alloy and one of the glass-ceramics., Conclusion: Composite and above all acrylic resin crowns were more able to absorb shock from occlusal forces than crowns made of zirconia, ceramic material, or gold alloy.

Purpose: To evaluate telescopic crown (TC), bar, and locator attachments used in removable four implant-supported overdentures for patients with edentulous maxillae., Materials and Methods: A total of 30 maxillary edentulous patients were enrolled in a 3-year prospective study. Ten patients (group A) were treated with overdentures supported by TCs, 10 patients (group B) with overdentures supported by bar attachments, and 10 patients (group C) with overdentures supported by locator attachments. A total of 120 implants were used to restore oral function. During the 3-year follow-up period, implant survival and success rates, biologic and mechanical complications, prosthodontic maintenance efforts, and patient satisfaction were evaluated., Results: All 30 patients were available for the 3-year follow-up and exhibited 100% implant survival and success rates. Peri-implant marginal bone resorption was not statistically significant for the three groups. There were lower plaque, bleeding, gingiva, and calculus indices in group C compared with groups A and B. The number of prosthodontic maintenance visits revealed eight complications in the TC group, seven complications in the bar group, and four complications in the locator group. However, there were no differences in the clinical effects of the overdentures in the three groups., Conclusion: Within the limits of this prospective study, it was concluded that the locator system produced superior clinical results compared with the TC and bar attachments in terms of peri-implant hygiene parameters, the frequency of prosthodontic maintenance measures, cost, and ease of denture preparation. However, longer-term prospective studies are required to confirm these results.

Purpose: The objectives of this study were to evaluate the galvanic corrosion behavior between titanium and nickel-chromium (Ni-Cr) alloy, to investigate the effect of diamondlike carbon (DLC) coating over titanium on galvanic corrosion behavior between titanium and Ni-Cr alloy, and to evaluate the effect of DLC coating over titanium abutments on the fit and integrity of prosthetic assemblies by scanning electron microcopy (SEM)., Materials and Methods: Five Ni-Cr and 10 titanium disks with a diameter of 5 mm and thickness of 3 mm were prepared. DLC coating was applied to five titanium disks. Electrode samples were prepared, and open circuit potential measurements, galvanic current measurements over platinum electrodes, and potentiodynamic polarization tests were carried out. For the SEM evaluation, 20 Ni-Cr alloy and 10 gold alloy superstructures were cast and prepared over 30 abutments. DLC coating was applied to 10 of the abutments. Following the fixation of prosthetic assemblies, the samples were embedded in acrylic resin and cross sectioned longitudinally. Internal fit evaluations were carried out through examination of the SEM images., Results: Titanium showed more noble and electrochemically stable properties than Ni-Cr alloy. DLC coating over the cathode electrode served as an insulating film layer over the surface and prevented galvanic coupling. Results of the SEM evaluations indicated that the DLC-coated and titanium abutments showed no statistically significant difference in fit. Hence, no adverse effects on the adaptation of prosthetic components were found with the application of DLC coating over abutment surfaces., Conclusions: DLC coating might serve as a galvanic corrosion barrier between titanium abutments and Ni-Cr superstructures.

Purpose: This study aimed to compare the fit of computer-aided design/computerassisted manufacture (CAD/CAM) abutments provided by a single system with proprietary prefabricated abutments on various implant systems., Materials and Methods: Titanium CAD/CAM abutments were compared with prefabricated abutments on five different implant types. The samples were embedded in epoxy resin, sectioned longitudinally, and polished. Scanning electron microscopy was used to measure the gap between the implants and abutments at the connecting flanges and internal features. Independent t tests were used to compare data., Results: A mean difference of 1.86 μm between the gold synOcta and CAD/CAM abutments on the Straumann Standard Plus implant was observed to be statistically significant (P = .002). Less than 0.4 μm of difference was found between the CAD/CAM and prefabricated abutments for the remaining implant types, and statistical significance was not observed. Mean differences of 34.4 μm (gold) and 44.7 μm (titanium) were observed between the CAD/ CAM and prefabricated abutments on the Straumann Standard Plus implants, which were statistically significant (P < .001). A mean difference of 15 μm was also observed between the CAD/CAM and prefabricated abutment on the NobelReplace implant, which was statistically significant (P = .026). All other groups had less that 4 μm of difference, and statistical significance was not observed., Conclusion: The CAD/CAM abutments appeared to have a comparable fit with prefabricated abutments for most of the systems evaluated. Design differences between the abutment connections for both Straumann implants were observed that affected the fit of internal components of the implant-abutment connections.

The purpose of this study was to examine the influence of reinforcing the structure of an overdenture on stress distribution in the residual ridge using the three dimensional finite element method. Four models of mandibular overdentures with various reinforcement methods were analyzed, including (1) without reinforcement, (2) with chrome-cobalt reinforcing wire, (3) with a reinforcing structure (a cast metal framework) and no reinforcement on the coping top, and (4) with a reinforcing structure and reinforcement on the coping top. The reinforcement adjacent to the top of the coping and the medial part reduces the stress beneath the loading side of dentures and widely and evenly distributes the stress of the residual alveolar ridge.

Purpose: This study aimed to present the up to 25-year clinical performance and survival of 2,340 high gold-based metal-ceramic single crowns placed in a specialist prosthodontic practice., Materials and Methods: All crowns provided to 670 patients between 1984 and 2008 were sequentially recruited. Each crown/tooth combination was given a prognostic evaluation at cementation. Patients were recalled in 2008 and 2009 for examination, and patient records were scrutinized for any retreatment. Estimated cumulative survival, standard error, and differences in survival between groups were calculated using the Kaplan-Meier method, Greenwood formula, and log-rank test, respectively. Crown status (six-field classification) was reported within 5-year groupings and for 7, 10, and 12 years., Results: The up to 10-year and 25-year estimated survival rates of the 2,211 favorably rated crowns were 97.08% ± 0.45% and 85.40% ± 2.19%, respectively. The up to 12-year survival for crowns in the postimplant era was 94.4% ± 2.78%. No significant differences related to sex, tooth type, or tooth position were demonstrated. Nonvital teeth had lower overall survival rates than vital teeth, but not in crowns placed in the postimplant era. Actual 10-year outcomes closely matched the estimated 10-year survival. Biologic factors accounted for 101 of the 133 failures, while mechanical factors accounted for 8 failures and patient concerns accounted for 24 failures. Porcelain fracture requiring replacement occurred in 4 crowns., Conclusions: The clinical performance of the crowns was excellent. Biologic factors accounted for the majority of failures. Material stability was excellent. Patient complaints of unacceptable esthetics resulted in 22 crowns being replaced after a mean clinical service time of 14 years.

This study presents the results of a long-term clinical evaluation of conical crown-retained dentures fabricated using different technologies. Four different material connections between the outer and inner crowns were used: cast gold/cast gold, cast gold/electroforming, nonprecious alloy/electroforming, and titanium abutment/electroforming. Technical failures and retention values were assessed. The best clinical outcome was found with dentures in which both crowns were cast from gold alloy. The most frequent technical failures were observed in restorations with electroformed outer crowns. Better clinical outcomes were noted when the electroformed outer crowns were used in dentures retained by implants as compared to dentures on natural dentition.

Excessive cantilever lengths of fixed implant-supported prostheses may have functional and biomechanical disadvantages. This study reports the clinical outcomes of unconventional implants placed for distal support of a fixed implant-supported prostheses. Seven extraoral implants with intraosseous lengths of 2.5 to 4.0 mm were placed in four patients. Distal cantilevers had a mean length of 29.8 mm (range, 18.6 to 39.3 mm). No bone loss or other adverse events were found. The prosthetic plan was maintained in all patients. Within the limits of the employed research design, this concept seems to be a successful option for fixed complete implant-supported prosthesis treatment.

This study evaluated secondary caries and periodontal conditions associated with metal (MCs) and composite resin copings (RCs) of abutment teeth for overdentures. The rates of secondary caries and periodontal problems in 70 root copings (41 MCs, 29 RCs) in 35 patients were retrospectively investigated for a period of 6.9 years. Statistical analysis was performed using chi-square tests and logistic regression (P < .05). No significant differences in secondary caries or periodontal conditions were detected between MCs and RCs. These results suggest that RCs and MCs can be used as root copings of abutment teeth for overdentures.

Purpose: The aim of this study was to evaluate the effect of retightening and mechanical cycling on the maintenance of preload in the retention screws of implant-supported crowns., Materials and Methods: Five groups (n = 12 in each group) of implant-crown assemblies were created according to different abutments and veneering materials: Gold UCLA abutments cast in gold alloy veneered with ceramic (group 1) and light-curing resin (group 2), UCLA abutments cast in titanium veneered with ceramic (group 3) and light-curing resin (group 4), and zirconia abutments with ceramic veneering (group 5). The crowns were attached to implants by gold retention screws. The assemblies were submitted to mechanical cycling for a total of 1 million cycles. Removal torque measurements were performed initially and after each period of 100,000 cycles; this was followed by screw retightening with 35 Ncm of torque. Data were evaluated with analysis of variance, the paired t test, and the Student t test., Results: All groups exhibited reduced removal torque values in comparison to insertion torque initially and after all periods of mechanical cycling. Analysis of variance revealed statistically significant differences among the groups, but there were no differences among the periods of mechanical cycling or for the interaction between groups and cycling. Group 1 was the only group that did not show a difference between removal torque values of different cycling periods. The Student t test did not reveal statistically significant differences between mean removal torque values obtained before and after mechanical cycling, except for group 4., Conclusions: Torque maintenance allowed screw joint stability in the present study. Mechanical cycling associated with the retightening of abutment screws did not influence the maintenance of insertion torque.

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.

This study evaluated the clinical outcome of posterior single-unit metal-ceramic crowns fabricated using computer-aided design/computer-assisted manufacture laser-sintering technology. Sixty restorations were placed in 39 patients and cemented with glass-ionomer cement. Follow-ups were performed annually. During a mean observation period of 47 months, one restoration was regarded a dropout, one crown failed (biologic failure), and one debonded. One abutment tooth had to be treated endodontically, and three teeth were treated because of caries. No further technical complications, eg, veneering ceramic chipping, occurred during the observation period. The results suggest that the clinical outcome of posterior single-unit metal-ceramic crowns fabricated using laser-sintering technology is promising.

Purpose: This study compared the removal torque values (RTVs) of different abutments (straight, angled, and gold premachined UCLA-type) in external- and internal-hex implants after dynamic cyclic loading with the clinical situation of the anterior maxilla simulated., Materials and Methods: An ideal cast of a maxilla with a missing right central incisor was fabricated in dental stone, and an implant analog was embedded in this model at a 15-degree angle labial to the long axis of the left central incisor. Thirty external-hex and 30 internal-hex implants were used. A total of 10 straight abutments, 10 angled abutments, and 10 gold premachined UCLA-type abutments of each system and 60 abutment screws were tested. Initial RTVs were measured after each assembly was tightened to 30 Ncm. Straight abutments and angled abutments were prepared and gold-premachined UCLA-type abutments were waxed and cast with low-fusing gold alloy for the central incisor. RTVs were then measured again. After each assembly was tightened, a metal crown was temporarily cemented. After cyclic loading of 20 to 200 N was applied 1 million times, RTVs were measured for a third time. Statistical analysis (alpha = .05) was performed to evaluate the results., Results: The angled abutment group showed significantly higher RTVs than the straight abutment and gold premachined UCLA-type abutment groups in external-hex implants. However, no significant difference in RTVs was found among abutments in internal-hex implants. The time of analysis of RTV was found to significantly influence mean RTVs. Mean RTVs of external- and internal-hex implants showed significant differences., Conclusions: Within the limitations of this study, there were significant differences in RTVs among different abutment groups in external-hex implants. There were no significant differences in RTVs among different abutment groups in internal-hex implants.

Purpose: The purpose of this study was to analyze and compare the implant-bone interface stresses in anisotropic three-dimensional finite element models of an osseointegrated implant with platform switching and a conventional matching-diameter implant platform and abutment in the posterior maxilla., Materials and Methods: Three-dimensional finite element models were created of a first molar section of the maxilla and embedded with a single endosseous implant (4.1 3 10 mm). One model simulated a 4.1-mm-diameter abutment connection and the other was a narrower 3.4-mm-diameter abutment connection, ie, simulating a platform-switching configuration. A gold alloy crown with 2-mm occlusal thickness was applied over the titanium abutment. Material properties of compact and cancellous bone were modeled as fully orthotropic and transversely isotropic, respectively. Oblique (200-N vertical and 40-N horizontal) occlusal loads were applied and perfect bonding was assumed at all interfaces., Results: Maximum von Mises, compressive, and tensile stresses in compact bone were lower in the platform-switching model than in the conventional model. However, the maximum von Mises stress in cancellous bone was higher in the platform-switching model than in the conventional model., Conclusion: The platform-switching technique reduced the stress concentration in the area of compact bone and shifted it to the area of cancellous bone during oblique loading.

The aim of this study was to measure in vitro retention of cast gold crowns cemented with traditional and resin cements. Forty-eight human molars were prepared on a lathe to produce complete crown preparations with a consistent taper and split into six groups, eight crowns in each group. Crowns were cast in a high-gold alloy and then cemented. After 24 hours, the retention force (N) was recorded and mean values were analyzed by one-way analysis of variance and the Fisher post-hoc least significant difference (PLSD) multiple comparisons test (a = .05). Failure sites were examined under 3100 magnification and recorded. Mean values (SD) for each group in increasing order of retention force were: Harvard Cement: 43 N (27), TempoCem: 59 N (16), PermaCem Dual: 130 N (42), RelyX Luting Cement: 279 N (26), Contax and PermaCem Dual: 286 N (38), and TempoCem with Contax and PermaCem Dual: 340 N (14). The Fisher PLSD interval (P = .05) for comparing cements was 29 N. Zinc-phosphate cement and provisional resin cements had the lowest retention forces. Resin cement with a bonding agent and the hybrid-ionomer cement had similar retention forces. Resin cement with a bonding agent applied after use of a provisional resin cement had a significantly higher retention force than the other cements tested.

Purpose: This study aimed to investigate the electrochemical behavior of commercially pure titanium (grade II) coupled with type IV gold alloy and nickel-chromium alloy at different surface area ratios in 3 different electrolytes., Materials and Methods: Titanium was coupled with gold (Ti/Au) and nickel-chromium (Ti/Ni-Cr). For each couple, 9 surface area ratios between titanium and gold or nickel-chromium were prepared. The electrolytes used were 1% lactic acid, tryptic soy broth media, and Streptococcus mutans culture supernatant. The corrosion polarization curves were obtained, and average values of corrosion potential and corrosion current density were calculated., Results: Both Ti/Au and Ti/Ni-Cr were affected by surface area ratios and different electrolytes, showing the least corrosion rate when the ratio was 1:1 and when the lactic acid was used as an electrolyte., Conclusions: The greater the difference in surface area between titanium and restorative materials, the more corrosive behavior the materials show. The existence of bacteria such as S mutans may aggravate corrosive behavior between different metals.

The aim of this study was to test the color-change effect of all-ceramic restorations compared with porcelain-fused-to-metal (PFM) restorations on marginal peri-implant soft tissue. Thirty patients were randomly divided into 2 groups of 15 subjects each. The all-ceramic group received all-ceramic crowns on aluminum oxide-based abutments, while the PFM group received crowns on titanium or gold abutments. A reflectance spectrophotometer was used to measure the color difference (deltaE(Implant)) between the midfacial peri-implant mucosa before and after restoration insertion. The color difference (deltaE(Tooth-implant)) between the midfacial peri-implant mucosa and the gingival margin of the corresponding neighboring tooth was tested. The mucosal thickness was measured midfacially around the implant (MT(Implant)) and neighboring tooth (MT(Tooth)). deltaE(Implant) values were similar for the all-ceramic (7.4 +/- 2.7) and PFM groups (7.6 +/- 2.8). The all-ceramic group induced significantly less visible mucosal color change (3.4 +/- 1.4) compared to the PFM group (5.2 +/- 2.3). The MT(Implant) value of the all-ceramic group was 3.4 +/- 0.8 mm, while that of the PFM group was 2.9 +/- 0.9 mm, which was not significantly different. Significant differences were found when comparing MT(Implant) (3.1 +/- 0.9) and MT(Tooth) (1.2 +/- 0.3) values for test and control groups. All-ceramic restorations revealed a better color match to the neighboring teeth than PFM restorations.

Purpose: The aim of this study was to quantitatively measure tooth and ceramic wear over a 2-year period using a novel superimposition technique. Three ceramic systems--experimental hot-pressed ceramic (EC), Procera AllCeram (PA), and metal-ceramic--were used., Materials and Methods: A total of 90 posterior crowns in 48 patients were randomized into 3 groups, and impressions were made at baseline and at 6-month intervals for 2 years. Clinical images were taken after using a dye to highlight surface changes. The impressions were digitized and modeled as superimposable 3-dimensional colored surface images. The depth of wear at the occlusal contact areas was quantitatively measured at 6, 12, 18, and 24 months., Results: The quantitative evaluation showed more wear in Procera AllCeram at the occlusal contact areas, whereas the experimental and metal-ceramic systems showed less wear. There was a significant difference in the amount of enamel worn between all types of restorations (P < .05). There was a statistically significant difference (P < .05) in the mean depth of wear between all systems., Conclusions: The metal-ceramic and experimental systems showed less change, indicating improved wear resistance compared with Procera AllCeram. In addition, enamel opposing metal-ceramic and experimental crowns showed less wear compared to enamel opposed by Procera AIICeram crowns.

Purpose: This study evaluated treatment outcomes of 4-unit porcelain-fused-to-gold fixed dental prostheses (FDPs) replacing 2 adjacent missing teeth., Materials and Methods: A total of 102 FDPs made in an undergraduate university clinic for 73 patients were evaluated for up to 20 years, with a mean survival follow-up time of 11.4 years. All patients were offered an oral health maintenance program. Treatment failures were divided into irreversible (loss of FDPs/finish line involved) or reversible (FDPs and finish line intact after conservative treatment) complications and into biologic and technical/patient-related failures., Results: The Kaplan-Meier overall estimated survival rate was 68.3% at year 20. There was a statistically significant difference (P = .007) between the survival rates in the maxilla for the vital group (73.8%) and those for the root canal-treated group (25.1%). Comparing the survival rate in the root canal-treated group for the restorations in the maxilla (25.1%) versus the mandible (66.8%), a statistically significant difference (P = .011) was found. The main reason for irreversible failure was caries (32.0%)., Conclusion: The estimated successful outcome of 4-unit FDPs over an up to 20-year period is considered favorable and should be compared with the survival rates of other treatment options for the replacement of 2 adjacent teeth. Occurrence of a previously reversible complication appears to be a predictive factor for an irreversible complication later on. A reversible complication within the first 2 years will lead to an early irreversible complication.

This in vitro study evaluated the 6-month fatigue retention provided by 5 paired overdenture attachments placed at 3 different interimplant distances (19, 23, and 29 mm). Mean fatigue retention was calculated for each attachment type and compared with the retention produced by the other attachments tested and the initial retention values published earlier. Interimplant distance was found to play a significant role only in the retention of the Hader bar with red and yellow clips. A significant reduction in retention values was observed for 4 of 5 attachment types.

Purpose: This study of short-span fixed dental prostheses (Ss-FDPs) versus long-span FDPs (Ls-FDPs) evaluated the long-term efficacy and determined the frequencies and causes of failures., Materials and Methods: A total of 236 Ss-FDPs and 86 Ls-FDPs made in an undergraduate university clinic for 149 and 70 patients, respectively, were evaluated over a 20-year period. Kaplan-Meier analysis with a 95% confidence interval was used to estimate the survival probability. Failures of the FDPs were divided into irreversible (loss of FDPs or finish line involvement) or reversible (FDPs and abutments intact after conservative treatment) complications and into biologic and technical/patient-related failures., Results: The overall survival estimations for Ss-FDPs (70.8%; 95% Cl: 63%-79%) and Ls-FDPs (52.8%; 36%-70%) at year 20, were statistically significantly different (P = .030). There was no statistically significant difference (P = .126) for the survival estimations for Ss-FDPs (60.4%; 48%-73%) versus Ls-FDPs (59.0%; 44%-74%) at year 19 in the root-canal treated (RCT) group. For the Ss-FDPs group there was a statistically significant difference (P = .009) between the vital (82.4%; 73%-92%) and RCT (60.4%; 49%-73%) groups at year 20. The reason for failure in the Ss-FDP group was of biologic origin in 55.6% to 66.7% of cases, but for the Ls-FDP group the failures were of technical origin in 56.0% to 84.0% of cases., Conclusion: The survival of Ss-FDPs and Ls-FDPs over a 20-year period was favorable. The overall survival estimation for Ss-FDPs was statistically significantly better than for Ls-FDPs at year 20. The use of an RCT abutment becomes more significant in fixed prosthetic restorations with 4 or more units. Occurrence of a previously reversible complication is a predictive factor for an irreversible complication later on. A reversible complication within the first 2 years for an Ss-FDP will lead to an irreversible complication.

The provision of patients with removable partial dentures on all-ceramic primary crowns with electroplated gold secondary parts is described as an alternative worthy of consideration in dental journals, lectures and in further training courses. The mode of operation is based on a precise, frictionless, passive fit between female and male components. To guarantee this even over large spans, intraoral joining of the individual components is necessary. However, this requires a different sequence of the treatment steps. The different procedures (conventional, procedure by Weigl, modified concept) are described in the following article. Clinical considerations, design principles, and special characteristics involved in producing the partial denture are explained.

Purpose: To investigate the effects of thermal cycling and surface roughness of metal implant abutments and the intaglio surface of the copings on the retentive properties of 4 provisional luting agents commonly used in the cementation of implant-retained fixed partial dentures (FPDs)., Materials and Methods: A 2-unit implant-retained FPD and a 4-unit implant-retained FPD were fabricated using gold-palladium alloy. The abutments used were 5 mm in height. The FPDs were cemented with 4 commonly used provisional luting agents and thermocycled for 700 cycles from 5 degrees C to 36 degrees C to 55 degrees C and were then subjected to tensile strength testing. After thermal cycling, the intaglio surfaces of the same FPDs and the abutments were air-abraded with 50 microm Al2O3 particles. FPDs were cemented using the same provisional cements, and after 24 hours of storage in 100% humidity, tensile strength tests were performed. Descriptive statistics, 2-way analysis of variance, Friedman's 2-way ANOVA, and Tukey's HSD test (alpha = .05) were performed., Results: Both thermal cycling and air abrasion had a significant effect (P < .001) on the retentive values of all cements tested. A noneugenol provisional cement (Nogenol) exhibited the lowest mean retentive value after both thermal cycling and air abrasion for both the 2- and 4-unit FPD models. The urethane resin provisional cement (Improv) exhibited the highest mean retentive strength for both the 2- and 4-unit FPDs after thermal cycling and air abrasion treatments., Conclusions: Thermal cycling had a detrimental effect on the retentive properties of all cements tested. Air abrasion significantly improved the cement failure loads of the provisional luting agents used in the study and seems to be an effective way of increasing the retention of implant-retained FPDs.

This study evaluated the effects of recasting on high noble, noble, and nickel-based alloys, as well as on titanium. Four specimens of each material were cast and recast 7 times. Chemical composition, microstructure, microhardness, and ion release were determined before and after the first cast and following each recast. Zinc and tin concentrations in the high noble alloy decreased significantly with recasting; consequently, the release of these ions decreased as well. A significant increase in Vickers hardness appeared in the fifth recast in both the high noble alloy and titanium. The noble alloy and the nickel-based alloy demonstrated great stability after 7 recasts. The results suggest not recasting titanium.

Purpose: To compare the in vitro 3-dimensional (3D) accuracy of fit of laser-scanned Computer Numeric Controlled (CNC)-milled implant titanium frameworks to that of conventional cast frameworks., Materials and Methods: Nine cast frameworks were fabricated on the mandibular master casts of 9 patients with 5 implants each following the well-established conventional fabrication technique. The frameworks were then laser scanned, and 9 CNC-milled titanium frameworks matching the outline of the conventional frameworks were fabricated. The accuracy of fit of both framework types was measured using a contact-type coordinate measuring machine and a computer program developed specifically for this purpose. Statistical analysis was done by a series of paired ttests., Results: The laser-scanned CNC-milled frameworks showed significantly less distortion along the x-axis (transversal, d(x)) compared with the conventional frameworks (means: 33.7 microm and 49.2 microm, respectively) (P = .011). The titanium frameworks also demonstrated significantly less distortion on the horizontal plane compared with the conventional frameworks (means: 56 microm and 85 microm, respectively) (P = .012). The d(y) (sagittal) and d(z) (vertical) axes and total 3D distortion (square root of dx(2) + dy(2) + dz(2)) showed less distortion overall in the laser-scanned CNC-milled frameworks, but this was not statistically significant (mean: 22.3 vs 35.6 microm, 13.3 vs 59.2 microm, 51 vs 114.1 microm, respectively, for y, z, and 3D distortion)., Conclusion: Within the limitations of this study, fabrication of an implant-prosthodontic framework using the CNC milling technique yields a more accurate fit than the currently used cast technique. In vivo studies are needed to investigate the clinical significance of this recorded difference.

The purpose of this study was to compare misfit-induced strains on implant-supported superstructures fabricated by two impression techniques and two different elastomeric impression materials. A master cast hosting four Straumann implants was constructed. On this cast, a total of 21 implant-level impressions were made by the direct technique using a polyether impression material and synOcta screwed aluminum impression caps (PE-D), and by the indirect technique using polyether (PE-IN) or polyvinylsiloxane impression material (VPS-IN) with snap-on impression caps and synOcta plastic positioning cylinders. Two casts were randomly selected from each group of seven, and a total of four screw-retained superstructures, supported by either two or four implants (one of each type on both casts), were cast in a gold alloy for each group. Linear strain gauges were bonded on the superstructures, and misfit-induced strains were recorded during superstructure connection on each of the working casts and on the master cast using a data acquisition system and corresponding software at a sample rate of 10 kHz. Connection on the implants in the master cast increased strains considerably on most of the superstructures, in comparison with strain gradients measured when the superstructures were connected on the casts from which they were fabricated (P <.05). The differences in strain amplitude between connection on the cast from which the superstructure was fabricated and on the master cast were higher for superstructures fabricated by PE-D than for those fabricated by PE-IN and VPS-IN. The snap-on indirect impression technique for Straumann implants leads to acceptable superstructures, regardless of the impression material used.

Large-span fixed restorations in the treatment of periodontally compromised patients are technically difficult to realize. Despite existing techniques of regenerative periodontal surgery and implant therapy aimed at preventing large spans by increasing the number of abutments, prosthetic complications do occur. The present article describes a method that introduces galvanic caps to conventional prosthetic technology, which facilitates clinical procedures and reduces complications by improving precision of fit.

Purpose: This study examined the retentive forces of intracoronal precision attachments after wear cycling., Materials and Methods: Three material combinations of an intracoronal cylindric T-attachment were tested. A total of 10,000 separating and joining movements were performed, and retentive forces were measured., Results: Components made of gold alloy performed significantly better (P = .002) than other materials. The average proportional loss of retention was 90% for titanium and 47% for gold alloy components., Conclusion: Cyclic loading of metal precision attachment components results in loss of retention, which can be fully compensated by reactivating internal screws in the patrices. Machined, high-noble gold alloys show less wear than other materials.

Purpose: The aim of this study was to evaluate the clinical performance of metal-ceramic crowns placed in 10 private practices., Materials and Methods: In this prospective clinical trial, 95 patients were provided with 190 noble-metal metal-ceramic single crowns., Results: The 7-year survival rates of the crowns were 95.5% (target event: any removal), 99.5% (target event: removal because of defective veneer), and 92.4% (target event: metal-ceramic complication of any kind). No significant explanatory variables for metal-ceramic complications could be detected by bivariate and multivariate testing. The consequences resulting from metal-ceramic defects were of minor clinical significance in most cases., Conclusion: The findings support previous claims that metal-ceramic restorations perform very well clinically, including in practices outside academic environments.

Purpose: The aim of this clinical simulation study was to investigate the effect of anatomic and nonanatomic occlusal preparation design on stress distribution in different metal-ceramic crowns and tooth and bone., Materials and Methods: For the finite element analysis method, a 2-dimensional mathematical model of a mandibular second premolar tooth and its supporting tissues was used. The analysis was performed by using a structural analysis program. Four groups were designed: gold-palladium alloy/anatomic occlusal preparation (Au-Pd/A), Au-Pd alloy/nonanatomic (flat) occlusal preparation (Au-Pd/N), nickel-chromium alloy/anatomic occlusal preparation (Ni-Cr/A), and Ni-Cr alloy/nonanatomic occlusal preparation (Ni-Cr/N). A distributed type load of 400 N (total) was applied to the centric stop points on the tip of the buccal cusp and on the central developmental groove in centric occlusion to all types of restorations., Results: The results demonstrated that shear stresses in the dentin tissues and restorations in Au-Pd/A and Ni-Cr/A were similar. The shear stresses within the restorations in Au-Pd/N and Ni-Cr/N were similar., Conclusion: Anatomic occlusal preparation designs were advantageous in stress distribution in the dentin tissue. Nonanatomic occlusal preparation designs were found to be advantageous in the stress amount and distribution in the porcelain structure. Occlusal preparation designs and restorative materials showed no differences in stress distribution and amount in the pulp tissue and bone tissues.

There are no long-term clinical studies concerning the treatment outcome of CAD/CAM generated porcelain laminate veneers. The objective of this study was to conduct a longitudinal evaluation of CAD/CAM fabricated porcelain laminate veneers. A single practitioner placed 715 CAD/CAM generated porcelain laminate veneers produced chairside with the Cerec system on 307 patients between December 1989 and December 1997. 260 patients with 617 veneers were available for recall examination. Forty-seven patients with 98 veneers (13.7%) were unable to be located or return for recall examination. Fourteen restorations had been lost. The Kaplan-Meier survival rate was 94% after up to 9 years (95% confidence interval: 90.7 to 97.8%). Of the surviving restorations, 98% were classified as clinically acceptable after 9 years. 97.3% of the teeth examined tested vital, 96.2% of the veneers were asymptomatic since their production, 98.8% of the veneers were considered successful by the patient. CAD/CAM veneers fabricated with the Cerec System achieved comparable long-term clinical results to those reported for laboratory processed porcelain laminate veneers. The high survival rate and favorable clinical results would support the use of CAD/CAM porcelain laminate veneers in clinical situations similar to those for laboratory processed porcelain veneers. CAD/CAM generated porcelain laminate veneers may provide equally good clinical results and longevity as conventional laboratory-processed porcelain laminate veneers.

Restoration of endodontically treated teeth is a routine procedure in everyday clinical practice. Placement of posts and cores is often required for replacement of the missing coronal aspect of teeth. Use of traditional post-and-core systems (gold and titanium) in conjunction with all-ceramic restorations results in poor esthetics because of the reflection and lack of light transmission. For a highly esthetic outcome, there is a need to use a material that transmits and refracts light in much the same manner as a natural tooth. The purpose of this study was to clinically evaluate the light transmission of a (1) ceramic post (Celay), (2) polyester post reinforced with zirconium fibers (Snowlight), and (3) zirconia post (Cosmopost), in comparison with a cast-metal post and core covered with opaque porcelain (control). The light transmission of these systems when used in conjunction with IPS Empress all-ceramic crowns was evaluated.

Purpose: This investigation was concerned with the effect of 3 superstructure materials on the strain around an implant under static and nonimpact dynamic loading., Materials and Methods: Five highly filled composite resin-veneered crown analogs, 5 autopolymerized acrylic resin-veneered crown analogs, and 5 gold-alloy full cast crown analogs were prepared. The resin veneers were applied to gold-alloy frameworks. These crown analogs were prepared to fit an ITI implant-abutment assembly, which was screwed into a block of acrylic resin to simulate implantation in bone. The crown analogs were successively placed on the abutment, and a lateral load of 100 N was applied to the superstructure by a lever-type testing machine. Strains were recorded under static and dynamic loading by a 2mm-long strain gauge bonded to the surface of the bone simulant tangential to the implant. The dynamic load simulated masticatory cycles (75 strokes/min)., Results: Although the strain values differed significantly between the static and dynamic loading (P < .05), there was no significant difference among the superstructure materials under either loading condition (P > .05)., Discussion: These findings are in agreement with in vivo measurements, thus suggesting that cyclic rather than impact loading should be used in the investigation of occlusal material behavior under functional loading., Conclusion: Under static and nonimpact dynamic loading, the 3 superstructure materials tested (highly filled composite resin, acrylic resin, and gold alloy) had the same influence on the strain transmitted to a bone simulant that surrounded a single implant.

Purpose: Critical bending moment (CBM), the moment at which the external nonaxial load applied overcomes screw joint preload and causes loss of contact between the mating surfaces of the implant screw joint components, was measured with 2 types of implants and 2 types of abutments., Materials and Methods: Using 4 test groups of 5 implant-abutment pairs, CBM at the implant-abutment screw joint was measured at 25%, 50%, 75%, and 100% of the manufacturer's recommended torque levels. Regular Platform (RP) Nobel Biocare implants (3.75 mm diameter), Wide Platform (WP) Nobel Biocare implants (5.0 mm diameter), CeraOne abutments, and Multiunit abutments were used. Microstrain was measured as loads were applied to the abutment at various distances from the implant-abutment interface. Strain instrumentation logged the strain data dynamically to determine the point of gap opening. All torque applications and strain measurements were repeated 5 times., Results: For the CeraOne-RP group, the mean CBMs were 17.09 Ncm, 35.35 Ncm, 45.63 Ncm, and 62.64 Ncm at 25%, 50%, 75%, and 100% of the recommended torque level, respectively. For the CeraOne-WP group, mean CBMs were 28.29 Ncm, 62.97 Ncm, 92.20 Ncm, and 127.41 Ncm; for the Multiunit-RP group, 16.08 Ncm, 21.55 Ncm, 34.12 Ncm, and 39.46 Ncm; and for the Multiunit-WP group, 15.90 Ncm, 32.86 Ncm, 43.29 Ncm, and 61.55 Ncm at the 4 different torque levels. Two-way analysis of variance (ANOVA) (P < .001) revealed significant effects for the test groups (F = 2738.2) and torque levels (F = 2969.0)., Discussion: The methodology developed in this study allows confirmation of the gap opening of the screw joint for the test groups and determination of CBM at different torque levels., Conclusion: CBM was found to differ among abutment systems, implant diameters, and torque levels. The torque levels recommended by the manufacturer should followed to ensure screw joint integrity.

Purpose: This laboratory study compared the effect of different surface treatments of a medium-gold, high-noble alloy on the shear bond strength of an indirect, highly filled resin composite to the alloy and on the elemental composition of the alloy surface., Materials and Methods: Ninety disks, cast in a medium-gold, high-noble porcelain-fused-to-metal alloy (V-Deltaloy), received three different surface treatments: sandblasting with 50-microm Al2O3 (group 1) or 250-microm Al2O3 (group 2) and chemical agents, or with 250-microm Al2O3 without chemical agents (group 3) prior to bonding of an indirect resin composite (Artglass, and chemical agents Siloc-pre and Siloc-bond). The specimens were tested in shear, half of them after 24-hour dry storage at room temperature and the rest after 10-day storage in normal saline solution at 37 degrees C and thermocycling (2,500 cycles between 5 and 55 degrees C). Morphologic and qualitative changes on the alloy surface after sandblasting with 50- or 250-microm Al2O3 were examined by SEM using EDS analysis and compared with polished specimens. Statistical analysis was performed using two-factor ANOVA., Results: The mean shear bond strengths (in MPa) after dry or wet storage and thermocycling were 29 and 24 for group 1, 21 and 18 for group 2, and 17 and 12 for group 3, respectively; there was a statistically significant difference among the groups. Sandblasting of the alloy surface led to statistically significant changes in elemental composition. These changes were of greater magnitude when 50-microm Al2O3 particles were used., Conclusion: The particle size used for sandblasting influences the shear bond strength between a high-noble alloy and a highly filled indirect resin composite, as well as the elemental composition of the alloy surface.

Purpose: This laboratory study compared the shear bond strength between three indirect resin composites and a noble alloy using their respective bonding systems., Materials and Methods: One hundred twenty disks cast in a medium-gold, high-noble metal-ceramic alloy (V-Deltaloy) were divided equally into four groups and received different treatments for veneering: Conventional feldspathic porcelain (Omega) was applied on one set of specimens to be used as a control, and three indirect resin composites (Artglass, Sculpture, Targis) with their respective bonding systems were used for the other groups. The specimens were tested in a parallel shear test, half of them after 24-hour dry storage at room temperature and the rest after 10-day storage in normal saline solution at 37 degrees C and thermocycling. The fractured specimens were evaluated to determine the nature of the failure., Results: The mean shear bond strength values (in MPa), before and after wet storage and thermocycling, were 30 and 23 for the metal-ceramic group, 29 and 23 for the Artglass group, 20 and 19 for the Sculpture group, and 17 and 14 for the Targis group, respectively. The metal-ceramic and Artglass groups exhibited significantly higher bond strengths than the other two groups. All specimens, with the exception of the Sculpture group, showed a significant decrease in bond strength after wet storage and thermocycling., Conclusion: No group exceeded the shear bond strength of the metal-ceramic group, but the Artglass group with its respective metal-resin bonding system exhibited similar bond strengths. The Sculpture group showed a stable bond after water storage and thermocycling.

Purpose: The purpose of this retrospective study was to present treatment outcome and patient reactions to rehabilitation with implant-supported fixed partial prostheses., Materials and Methods: Eighty-three patients were consecutively treated with implant-supported fixed partial prostheses (Brånemark system) from 1986 to 1995. Seventy-six of these 83 patients were examined (66 maxillary and 31 mandibular prostheses). The mean observation time was 53.9 months. In total, 285 implants were placed. Eleven implants were lost before loading. The first 41 prostheses were removed and the implants examined regarding the criteria for "success" and tightness of the screw joints. Only one implant had lost integration., Results: The survival rate before and after loading was 96%, which included implants placed in augmented bone. All prostheses were stable at the time of examination. In prostheses with cantilevers (98 implants), 12% of the gold screws and 17% of the abutment screws showed a "not acceptable" loosening, compared to none in the prostheses without cantilevers (17 implants). The difference was not statistically significant. The mean marginal bone loss was 0.4 mm for the first year after prosthesis insertion and less than 0.1 mm per year in the following years. The most frequent prosthesis design was one pontic supported by two implants. Prostheses made in gold acrylic and titanium acrylic had more complications and showed a higher need for repair than metal-ceramic restorations. Patients reacted very positively to the esthetic results and comfort with eating, and were overall satisfied with their prostheses., Conclusion: Implant-supported fixed partial prostheses seem to have a very good prognosis and are well-accepted by patients.

Purpose: The purpose of this study was to investigate and compare the precision of fabrication in repeatqdly produced computer numeric controlled (CNC)-milled frameworks with consventional castings, and to analyze the distortion from application of different veneering materials., Materials and Methods: Twenty identical titanium frameworks were fabricated by means of a CNC milling technique for the same master model. Five conventional frameworks were cast as a control group to the same model. The frames were measured with regard to fit in a coordinate measuring machine linked to a computer. Measurements were made during different stages of handling of the titanium framework, and after veneering materials had been applied., Results: The CNC frameworks showed a statistically better fit and precision of fabrication compared to conventional castings (P < .05). The application of veneering material did not statistically affect the fit of the titanium frameworks (P > .05)., Conclusion: It is possible to fabricate implant-supported frameworks by means of the present CNC technique with a very high precision and repeatability.

Purpose: This study reported on the modes of failure and the influence of various clinical characteristics on the outcome of 515 metal-ceramic fixed partial dentures (FPD) involving 1,209 abutment and 885 pontics placed by one operator in a specialist prosthodontic practice between January 1984 and December 1997., Materials and Methods: Fifty-three percent of maxillary and 84% of mandibular FPDs involved one or more nonrigid abutment-pontic connections. Patients were recalled in 1993 (review 1) and 1998 (review 2) and clinically examined by the author. The modes of failure and influence of clinical characteristics, including abutment-pontic connection, post design in nonvital abutments, and regularity of professional maintenance, were evaluated., Results: At review 2, 80% of the FPDs were still in function, while 9% required retreatment. Tooth fracture accounted for 38%, caries for 11%, loss of retention for 13%, and periodontal breakdown for 27% of retreatments. Nonrigid abutment-pontic connection in posterior FPDs and regular professional maintenance were associated with significantly reduced failure rates. Except in posterior molars, there was no difference in failure rates between parallel-sided preformed stainless steel serrated posts and cast-gold alloy posts., Conclusion: Tooth fracture was the most common reason for retreatment of the FPDs, although the rate of periodontal breakdown and caries increased significantly with time. Nonrigid abutment-pontic connection and regular professional maintenance were associated with significantly reduced failure rates. Post design and composition were not related to outcome.