title: Shear bond strength of porcelain to a new millable alloy and a conventional castable alloy.
abstract: BACKGROUND
  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.
  
  
  OBJECTIVE
  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.
  
  
  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.
authors: Assistant Professor, Department of Prosthodontics, Kyungpook National University, Daegu, South Korea.
authors: Du-Hyeong
authors: DH
authors: Lee
authors: Graduate student, Department of Prosthodontics, Kyungpook National University, Daegu, South Korea.
authors: Beom-Jun
authors: BJ
authors: Lee
authors: Professor, Department of Prosthodontics, Seoul National University, Seoul, South Korea.
authors: Sung-Hun
authors: SH
authors: Kim
authors: Associate Professor, Department of Prosthodontics, Kyungpook National University, Daegu, South Korea. Electronic address: kblee@knu.ac.kr.
authors: Kyu-Bok
authors: KB
authors: Lee
mesh_terms: D000268:Adhesiveness; D000537:Aluminum Oxide / Q000737:chemistry; D002858:Chromium Alloys / Q000737:chemistry*; D017076:Computer-Aided Design; D001840:Dental Bonding; D003734:Dental Casting Investment / Q000737:chemistry*; D045662:Dental Etching / Q000379:methods; D003776:Dental Porcelain / Q000737:chemistry*; D003799:Dental Stress Analysis / Q000295:instrumentation; D003801:Dental Veneers; D006358:Hot Temperature; D006801:Humans; D008422:Materials Testing; D016876:Metal Ceramic Alloys / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D033081:Shear Strength; D013499:Surface Properties
chemical_list: D002858:Chromium Alloys; D003734:Dental Casting Investment; D016876:Metal Ceramic Alloys; D003776:Dental Porcelain; D000537:Aluminum Oxide