Davide Cortellini1, Angelo Canale2, Rodrigo O A Souza3, Fernanda Campos4, Julia C Lima4, Mutlu Özcan5. 1. Private Practice, Riccione, Italy. 2. Dental Laboratory, Rimini, Italy. 3. Department of Dentistry, Division of Prosthodontics, Federal University of Rio Grande do Norte, Natal,, RN, Brazil. 4. São Jose dos Campos Dental School, Department of Prosthodontics and Dental Materials, São Paulo State University, São José dos Campos, Brazil. 5. Dental Materials Unit, Center for Dental and Oral Medicine, Clinic for Fixed and Removable Prosthodontics and Dental Materials Science, University of Zurich, Zurich, Switzerland.
Abstract
PURPOSE: The aim of this study was to evaluate the durability of lithium disilicate crowns bonded on abutments prepared with two types of finish lines after long-term cyclic loading. MATERIALS AND METHODS: Pressed lithium disilicate all-ceramic molar crowns were bonded (Variolink II) to epoxy abutments (height: 5.5 mm, Ø: 7.5 mm, conicity: 6°) (N = 20) with either knife-edge (KE) or large chamfer (LC) finish lines. Each assembly was submitted to cyclic loading (1,200,000×; 200 N; 1 Hz) in water and then tested until fracture in a universal testing machine (1 mm/min). Failure types were classified and further evaluated under stereomicroscope and SEM. The data (N) were analyzed using one-way ANOVA. Weibull distribution values including the Weibull modulus (m), characteristic strength (0), probability of failure at 5% (0.05), 1% (0.01), and correlation coefficient were calculated. RESULTS: Type of finish line did not significantly influence the mean fracture strength of pressed ceramic crowns (KE: 1655 ± 353 N; LC: 1618 ± 263 N) (p = 0.7898). Weibull distribution presented lower shape value (m) of KE (m = 5.48; CI: 3.5 to 8.6) compared to LC (m = 7.68; CI: 5.2 to 11.3). Characteristic strengths (0) (KE: 1784.9 N; LC: 1712.1 N) were higher than probability of failure at 5% (0.05) (KE: 1038.1 N; LC: 1163.4 N) followed by 1% (0.01) (KE: 771 N; LC: 941.1 N), with a correlation coefficient of 0.966 for KE and 0.924 for LC. Type V failures (severe fracture of the crown and/or tooth) were more common in both groups. SEM findings showed that fractures occurred mainly from the cement/ceramic interface at the occlusal side of the crowns. CONCLUSION: Lithium disilicate ceramic crowns bonded onto abutment teeth with KE preparation resulted in similar fracture strength to those bonded on abutments with LC finish line. CLINICAL SIGNIFICANCE: Pressed lithium disilicate ceramic crowns may not require invasive finish line preparations since finish line type did not impair the strength after aging conditions.
PURPOSE: The aim of this study was to evaluate the durability of lithium disilicate crowns bonded on abutments prepared with two types of finish lines after long-term cyclic loading. MATERIALS AND METHODS: Pressed lithium disilicate all-ceramic molar crowns were bonded (Variolink II) to epoxy abutments (height: 5.5 mm, Ø: 7.5 mm, conicity: 6°) (N = 20) with either knife-edge (KE) or large chamfer (LC) finish lines. Each assembly was submitted to cyclic loading (1,200,000×; 200 N; 1 Hz) in water and then tested until fracture in a universal testing machine (1 mm/min). Failure types were classified and further evaluated under stereomicroscope and SEM. The data (N) were analyzed using one-way ANOVA. Weibull distribution values including the Weibull modulus (m), characteristic strength (0), probability of failure at 5% (0.05), 1% (0.01), and correlation coefficient were calculated. RESULTS: Type of finish line did not significantly influence the mean fracture strength of pressed ceramic crowns (KE: 1655 ± 353 N; LC: 1618 ± 263 N) (p = 0.7898). Weibull distribution presented lower shape value (m) of KE (m = 5.48; CI: 3.5 to 8.6) compared to LC (m = 7.68; CI: 5.2 to 11.3). Characteristic strengths (0) (KE: 1784.9 N; LC: 1712.1 N) were higher than probability of failure at 5% (0.05) (KE: 1038.1 N; LC: 1163.4 N) followed by 1% (0.01) (KE: 771 N; LC: 941.1 N), with a correlation coefficient of 0.966 for KE and 0.924 for LC. Type V failures (severe fracture of the crown and/or tooth) were more common in both groups. SEM findings showed that fractures occurred mainly from the cement/ceramic interface at the occlusal side of the crowns. CONCLUSION:Lithium disilicate ceramic crowns bonded onto abutment teeth with KE preparation resulted in similar fracture strength to those bonded on abutments with LC finish line. CLINICAL SIGNIFICANCE: Pressed lithium disilicate ceramic crowns may not require invasive finish line preparations since finish line type did not impair the strength after aging conditions.