Du-Hyeong Lee1, Beom-Jun Lee2, Sung-Hun Kim3, Kyu-Bok Lee4. 1. Assistant Professor, Department of Prosthodontics, Kyungpook National University, Daegu, South Korea. 2. Graduate student, Department of Prosthodontics, Kyungpook National University, Daegu, South Korea. 3. Professor, Department of Prosthodontics, Seoul National University, Seoul, South Korea. 4. Associate Professor, Department of Prosthodontics, Kyungpook National University, Daegu, South Korea. Electronic address: kblee@knu.ac.kr.
Abstract
STATEMENT OF PROBLEM: A recently introduced presintered cobalt-chromium (Co-Cr) alloy for metal ceramic restorations can be efficiently processed with computer-aided design/computer-aided manufacturing (CAD/CAM) techniques. However, little or no reliable study data are available regarding the bonding ability of porcelain to milled Co-Cr alloys. PURPOSE: The purpose of this study was to evaluate the shear bond strength of veneering porcelain to the presintered Co-Cr alloy and to a conventional castable alloy. MATERIAL AND METHODS: Ninety-six cylindrical cores (6.8 mm in diameter, 9 mm in height) were made of millable alloy (Ceramill Sintron) and castable alloy (4-all) by means of CAD/CAM or casting, 48 cores for each alloy. Four types of veneering porcelain were fired or pressed to the cores; these specimens had dimensions of 4×4×3 mm. After firing, the specimens were put in resin molds, fixed in a universal testing machine, and subjected to a shear force test. Loading was applied to each specimen through the attached crosshead at a constant drive speed of 0.5 mm/min until fracture occurred. Shear bond strengths (MPa) were calculated by dividing the maximum failure force over the cross-sectional area of each specimen. Failure patterns of the specimens were also investigated and characterized as adhesive, cohesive, or mixed. One-way ANOVA and the Duncan post hoc test were used to analyze statistically significant differences between groups (α=.05). RESULTS: The means of the shear bond strengths of (millable) Ceramill Sintron were similar to or higher than those of (castable) 4-all cores. The shear bond strength was significantly lower for Press-To-Metal veneer than for the other fired veneers in the test (P<.001). The pattern of failure in most specimens was mixed, except for Press-To-Metal veneer, where cohesive failure occurred. CONCLUSIONS: The bonding ability of the traditional castable alloy was similar to that of the presintered millable Co-Cr alloy.
STATEMENT OF PROBLEM: A recently introduced presintered cobalt-chromium (Co-Cr) alloy for metal ceramic restorations can be efficiently processed with computer-aided design/computer-aided manufacturing (CAD/CAM) techniques. However, little or no reliable study data are available regarding the bonding ability of porcelain to milled Co-Cr alloys. PURPOSE: The purpose of this study was to evaluate the shear bond strength of veneering porcelain to the presintered Co-Cr alloy and to a conventional castable alloy. MATERIAL AND METHODS: Ninety-six cylindrical cores (6.8 mm in diameter, 9 mm in height) were made of millable alloy (Ceramill Sintron) and castable alloy (4-all) by means of CAD/CAM or casting, 48 cores for each alloy. Four types of veneering porcelain were fired or pressed to the cores; these specimens had dimensions of 4×4×3 mm. After firing, the specimens were put in resin molds, fixed in a universal testing machine, and subjected to a shear force test. Loading was applied to each specimen through the attached crosshead at a constant drive speed of 0.5 mm/min until fracture occurred. Shear bond strengths (MPa) were calculated by dividing the maximum failure force over the cross-sectional area of each specimen. Failure patterns of the specimens were also investigated and characterized as adhesive, cohesive, or mixed. One-way ANOVA and the Duncan post hoc test were used to analyze statistically significant differences between groups (α=.05). RESULTS: The means of the shear bond strengths of (millable) Ceramill Sintron were similar to or higher than those of (castable) 4-all cores. The shear bond strength was significantly lower for Press-To-Metal veneer than for the other fired veneers in the test (P<.001). The pattern of failure in most specimens was mixed, except for Press-To-Metal veneer, where cohesive failure occurred. CONCLUSIONS: The bonding ability of the traditional castable alloy was similar to that of the presintered millable Co-Cr alloy.