The aim of this research was to evaluate the fatigue behavior and reliability of monolithic computer-aided design/computer-assisted manufacture (CAD/CAM) lithium disilicate and hand-layer-veneered ...zirconia all-ceramic crowns.
A CAD-based mandibular molar crown preparation, fabricated using rapid prototyping, served as the master die. Fully anatomically shaped monolithic lithium disilicate crowns (IPS e.max CAD, n = 19) and hand-layer-veneered zirconia-based crowns (IPS e.max ZirCAD/Ceram, n = 21) were designed and milled using a CAD/CAM system. Crowns were cemented on aged dentinlike composite dies with resin cement. Crowns were exposed to mouth-motion fatigue by sliding a WC-indenter (r = 3.18 mm) 0.7 mm lingually down the distobuccal cusp using three different step-stress profiles until failure occurred. Failure was designated as a large chip or fracture through the crown. If no failures occurred at high loads (> 900 N), the test method was changed to staircase r ratio fatigue. Stress level probability curves and reliability were calculated.
Hand-layer-veneered zirconia crowns revealed veneer chipping and had a reliability of < 0.01 (0.03 to 0.00, two-sided 90% confidence bounds) for a mission of 100,000 cycles and a 200-N load. None of the fully anatomically shaped CAD/CAM-fabricated monolithic lithium disilicate crowns failed during step-stress mouth-motion fatigue (180,000 cycles, 900 N). CAD/CAM lithium disilicate crowns also survived r ratio fatigue (1,000,000 cycles, 100 to 1,000 N). There appears to be a threshold for damage/bulk fracture for the lithium disilicate ceramic in the range of 1,100 to 1,200 N.
Based on present fatigue findings, the application of CAD/CAM lithium disilicate ceramic in a monolithic/fully anatomical configuration resulted in fatigue-resistant crowns, whereas hand-layer-veneered zirconia crowns revealed a high susceptibility to mouth-motion cyclic loading with early veneer failures.
Abstract Objective To evaluate the effects of clinically relevant variables on the maximum principal stress (MPS) in the veneer layer of an anatomically correct veneer–core–cement–tooth model. ...Methods The average dimensions of a mandibular first molar crown were imported into CAD software; a tooth preparation was modeled by reducing the proximal walls by 1.5 mm and the occlusal surface by 2.0 mm. ‘Crown systems’ were composed by varying characteristics of a cement layer, structural core, and veneer solid, all designed to fit the tooth preparation. The main and interacting effects of proximal wall height reduction, core material, core thickness, cement modulus, cement thickness, and load position on the maximum stress distribution were derived from a series of finite element models and analyzed in a factorial analysis of variance. Results The average MPS in the veneer layer over the 64 models was 488 MPa (range = 248–840 MPa). MPS increased significantly with the addition of horizontal load components and with increasing cement thickness. In addition, MPS levels varied as a function of interactions between: proximal wall height reduction and load position; load position and cement thickness; core thickness and cement thickness; cement thickness and proximal wall height reduction; and core thickness, cement thickness and proximal wall height reduction. Conclusion Rational design of veneered structural ceramics must consider the complex geometry of the crown–tooth system and integrate the influence of both the main effects and interactions among design parameters.
Purpose: The purpose of this study was to test the hypothesis that all‐ceramic crown core‐veneer system reliability is improved by modifying the core design and as a result is comparable in ...reliability to metal‐ceramic retainers (MCR). Finite element analysis (FEA) was performed to verify maximum principal stress distribution in the systems.
Materials and Methods: A first lower molar full crown preparation was modeled by reducing the height of proximal walls by 1.5 mm and occlusal surface by 2.0 mm. The CAD‐based preparation was replicated and positioned in a dental articulator for specimen fabrication. Conventional (0.5 mm uniform thickness) and modified (2.5 mm height, 1 mm thickness at the lingual extending to proximals) zirconia (Y‐TZP) core designs were produced with 1.5 mm veneer porcelain. MCR controls were fabricated following conventional design. All crowns were resin cemented to 30‐day aged composite dies, aged 14 days in water and either single‐loaded to failure or step‐stress fatigue tested. The loads were positioned either on the mesiobuccal or mesiolingual cusp (n = 21 for each ceramic system and cusp). Probability Weibull and use level probability curves were calculated. Crack evolution was followed, and postmortem specimens were analyzed and compared to clinical failures.
Results: Compared to conventional and MCRs, increased levels of stress were observed in the core region for the modified Y‐TZP core design. The reliability was higher in the Y‐TZP‐lingual‐modified group at 100,000 cycles and 200 N, but not significantly different from the MCR‐mesiolingual group. The MCR‐distobuccal group showed the highest reliability. Fracture modes for Y‐TZP groups were veneer chipping not exposing the core for the conventional design groups, and exposing the veneer‐core interface for the modified group. MCR fractures were mostly chipping combined with metal coping exposure.
Conclusions: FEA showed higher levels of stress for both Y‐TZP core designs and veneer layers compared to MCR. Core design modification resulted in fatigue reliability response of Y‐TZP comparable to MCR at 100,000 cycles and 200 N. Fracture modes observed matched with clinical scenarios.
To compare the bone bonding capabilities of 2 different surface treatments at an early healing period. Titanium alloy (Ti6Al4V) custom-made rectangular plates (1.4 × 2.4 × 4 mm) were either dual acid ...etched (Ti6Al4V-DAE) or DAE/nanotextured blasted (Ti6Al4V-NTB).
Implants were placed in the distal femurs of 10 Wistar rats and were allowed to heal for 9 days. After euthanasia, the bone immediately proximal and distal to the implant was removed to test the bone bonding force with a universal testing machine. Ultrastructure of the bone/implant interface was assessed by scanning electron microscopy.
Ti6Al4V-NTB samples exhibited significantly greater bond strength than Ti6Al4V-DAE samples. Morphologically, the Ti6Al4V-NTB surfaces presented intimate interaction with bone, whereas little interaction between the Ti6Al4V-DAE surface and bone was observed.
The results of this study indicated a significant increase in bone bonding for the DAE/nanotextured blasted surface, which is suggested to be the outcome of the nanotexturing.
Because the mechanical behavior of the implant-abutment system is critical for the longevity of implant-supported reconstructions, this study evaluated the fatigue reliability of different ...implant-abutment systems used as single-unit crowns and their failure modes.
Sixty-three Ti-6Al-4V implants were divided in 3 groups: Replace Select (RS); IC-IMP Osseotite; and Unitite were restored with their respective abutments. Anatomically correct central incisor metal crowns were cemented and subjected to separate single load to failure tests and step-stress accelerated life testing (n = 18). A master Weibull curve and reliability for a mission of 50,000 cycles at 200 N were calculated. Polarized-light and scanning electron microscopes were used for failure analyses.
The load at failure mean values during step-stress accelerated life testing were 348.14 N for RS, 324.07 N for Osseotite, and 321.29 N for the Unitite systems. No differences in reliability levels were detected between systems, and only the RS system mechanical failures were shown to be accelerated by damage accumulation. Failure modes differed between systems.
The 3 evaluated systems did not present significantly different reliability; however, failure modes were different.
Statement of Problem. Removable partial dentures are affected by fatigue because of the cyclic mechanism of the masticatory system and frequent insertion and removal. Titanium and its alloys have ...been used in the manufacture of denture frameworks; however, preventive agents with fluorides are thought to attack titanium alloy surfaces. Purpose. This study evaluated, compared, and analyzed the corrosion-fatigue life of commercially pure titanium and Ti-6Al-4V alloy in different storage environments. Material and Methods. For each metal, 33 dumbbell rods, 2.3 mm in diameter at the central segment, were cast in the Rematitan system. Corrosion-fatigue strength test was carried out through a universal testing machine with a load 30% lower than the 0.2% offset yield strength and a combined influence of different environments: in air at room temperature, with synthetic saliva, and with fluoride synthetic saliva. After failure, the number of cycles were recorded, and fracture surfaces were examined with an SEM. Results. ANOVA and Tukey's multiple comparison test indicated that Ti-6Al-4V alloy achieved 21,269 cycles (SD = 8,355) against 19,157 cycles (SD = 3,624) for the commercially pure Ti. There were no significant differences between either metal in the corrosion-fatigue life for dry specimens, but when the solutions were present, the fatigue life was significantly reduced, probably because of the production of corrosion pits caused by superficial reactions. (J Prosthet Dent 2000;84:274-9.)
This study evaluated the effect of fiber post customization and laser application on the results of pull-out tests in endodontically treated teeth. Forty-eight bovine incisors were stored in aqueous ...2% formaldehyde (pH 7.0) for 30 days. At the end of the storage period, the incisors were scraped with No. 11/12 periodontal curettes, rinsed with water and sodium bicarbonate, and stored in 0.9% saline solution for 7 days. Roots with similar shape and dimensions were selected and sectioned to a standard 17-mm length. Root canals were prepared and filled to a depth of 12 mm. The roots were divided into 4 groups (n = 12): 1, conventional fiber post and no laser application; 2, customized fiber post and no laser application; 3, conventional fiber post and laser application; and 4, customized fiber post and laser application. After removal of the obturation material for post space preparation, the canals were enlarged, and a laser beam was applied to the roots of teeth in groups 3 and 4 as an auxiliary disinfection procedure. After cementation of the posts, a pull-out test was performed using an axial tensile load at 0.5 mm/min in a universal testing machine. Analysis of variance and the Tukey test were used for statistical analysis of the results. The mean (SD) maximum tensile force was 10.18 (4.73) kgf in group 1, 38.89 (6.49) kgf in group 2, 27.74 (10.07) kgf in group 3, and 38.92 (6.89) kgf in group 4. These values were significantly higher in groups 2 and 4 than in group 1 (P < 0.05). The customization of fiber posts used for the restoration of pulpless teeth resulted in significantly (P < 0.05) greater pull-out test values, a thinner cement layer, and improved retention.
ABSTRACT Objective: The aim of this study was to evaluate the satisfaction of patients rehabilitated with fixed partial denture and the incidence of failures/clinical complications of prostheses ...after one year. Methods: The patients answered a questionnaire about the satisfaction degree with dental treatment performed and care maintenance for prosthesis conservation. Clinical and radiographic evaluations of the prosthesis were performed. Data were tabulated for descriptive analysis of the factors assessed, with calculation of absolute frequencies and percentages, and chi-square and Fisher’s exact test.. Results: A total of 9.67% failures were found. The most common was the prosthesis loosening (57.14%), followed by ceramic fracture (28.57%), and abutment tooth fracture (14.29%). Biological failures were observed in 30.65%. The most common failure was gingival recession (52.00%), periodontal pocket (24.00%), support periodontal involvement (16.00%), and recurrent caries (4.00%). Radiographic examination showed that 70.97% of the total number evaluated had some kind of failure. There was statistically significant association between satisfaction degree and technical failure (p=0.04). Conclusion: Patients were satisfied after observation period of 1 year. The main failures detected were: crown cementation failure and ceramic fracture; gingival recession, periodontal pocket; manufacture and cementation of short intraradicular post with increased diameter and crown cervical misfit.
RESUMO Objetivo: O objetivo deste estudo foi avaliar a satisfação dos pacientes reabilitados com prótese parcial fixa e a incidência de falhas/complicações clínicas das próteses instaladas após um ano. Métodos: Os pacientes responderam um questionário abrangendo o grau de satisfação pelo tratamento odontológico efetuado e os cuidados de manutenção realizados para a conservação da prótese. Na sequência foi realizada avaliação clínica e radiográfica das próteses. Os dados obtidos foram tabulados para análise descritiva dos fatores avaliados com cálculo de frequência absoluta e percentual, e teste de Qui-quadrado e Fischer. Resultados: Foram encontradas 9,67% de falhas, sendo a mais comum a descimentação (soltura da prótese) (57,14%), seguida da fratura da cerâmica (28,57%), e um caso de fratura no dente pilar (14,29%). As falhas biológicas foram observadas em 30,65%. A falha mais comum foi a recessão gengival (52,00%), seguida por bolsa periodontal (24,00%), envolvimento periodonto de suporte (16,00%), e recidiva de cárie (4,00%). No exame radiográfico 70,97% do número total avaliado apresentaram algum tipo de falha. Houve associação estatisticamente significante entre grau de satisfação e falhas mecânicas (p=0,04). Conclusão: Os pacientes ficaram satisfeitos após um período de acompanhamento de 1 ano. As principais falhas detectadas foram: falha de cimentação da coroa e fratura da cerâmica; Recessão gengival, bolsa periodontal; confecção e cimentação de pino intraradicular curto, pino com diâmetro aumentado e desajuste cervical da coroa.
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