Evaluation of the relationship between metallurgical properties and metal-ceramic bond characteristics of Co-Cr alloys manufactured by different techniques.

STATEMENT OF PROBLEM: Metal-ceramic restorations made from cobalt chromium (Co-Cr) alloy have been increasing, but studies on the effects of different manufacturing techniques on metal-ceramic interface characteristics and metal-ceramic bond strength are sparse. PURPOSE: The purpose of this in vitro study was to examine the metal-ceramic interface and the metal-ceramic bond strength of a Co-Cr alloy produced by casting, milling, and selective laser melting (SLM) with or without thermal cycling. MATERIAL AND METHODS: Co-Cr alloys were prepared by casting, milling, and SLM. Two different SLM devices were used. Ninety-six specimens (25×3×0.5 mm) were manufactured. The structure of the oxidation surface of Co-Cr specimens was examined by scanning electron microscopy (SEM) and by X-ray fluorescence spectroscopy (XRFS). After porcelain application, selected specimens were thermal cycled, and the strength of the metal-ceramic bond was measured by the 3-point bend test. All specimens were analyzed for failure type with a stereomicroscope. The elemental composition and morphology of the metal-ceramic interface were examined by XRFS and SEM with energy-dispersive X-ray (EDX). The results of bond strength were analyzed using a 2-way analysis of variance (ANOVA) for manufacturing methods and testing conditions and the Tukey honest significant difference (HSD) test (α=.05). RESULTS: The main effect of the interactions of the testing condition and manufacturing method variables on the bond strength variable was not statistically significantly different. No significant differences were found among the testing conditions tested (P=.638). Significant differences were found among the manufacturing methods tested statistically (P<.001). Statistically significant differences were found in the CAD-CAM and CONSEPT LASER groups, the CAD-CAM and SLM LASER groups, the CAD-CAM and CAST groups, and the CAST-SLM LASER groups (P<.05). Differences were observed among the interface morphologies of casting, milling, and the two SLM groups. CONCLUSIONS: The bond strength between Co-Cr alloy and ceramic is affected by the manufacturing method. The metal-ceramic bond strength is independent of thermal cycling. The bond strength value in all groups was over 25 MPa, which has been considered clinically acceptable. The interface metallurgical structures of Co-Cr alloys were affected by different manufacturing techniques.

The effect of thermo-mechanical fatigue on the retentive force and dimensional changes in polyetheretherketone clasps with different thickness and undercut.

PURPOSE: Esthetic expectations have increased the use of polyetheretherketone (PEEK) clasps as alternatives to Cr-Co in removable partial dentures (RPDs). The objective of this study was to evaluate the retentive force and dimensional change of clasps with different thickness and undercut made from PEEK by the thermo-mechanical fatigue. MATERIALS AND METHODS: PEEK clasps (N = 48) with thicknesses of 1 or 1.50 mm and 48 premolar monolithic zirconia crowns with undercuts of 0.25 mm or 0.50 mm were fabricated. Samples are divided into four groups (C1-C4) and were subjected to 7200 thermal aging cycles (at 5 - 55℃). The changes in the retentive force and dimensions of the clasps were measured by micro-stress testing and micro-CT devices from five measurement points (M1 - M5). One-way ANOVA, paired t-test, two-way repeated ANOVA, and post-hoc tests were used to analyze the data (P < .05). RESULTS: The retentive forces of C1, C2, C3, and C4 groups in initial and final test were found to be 4.389-3.388 N, 4.67 - 3.396 N, 5.161 - 4.096 N, 5.459 - 4.141 N, respectively. The effects of retentive force of all PEEK clasps groups were significant decreased. Thermo-mechanical cycles caused significant dimensional changes at points with M2, M4, and M5, and abraded the clasp corners and increased the distance between the ends of the clasp, resulting in reduced retentive forces (P * = .016, P * = .042, P < .001, respectively). CONCLUSION: Thermo-mechanical aging decreases the retentive forces in PEEK clasps. Increasing the thickness and undercut amount of clasps decreases the amount of dimensional change. The values measured after aging are within the clinically acceptable limits.

The effect of thermo-mechanical fatigue on the retentive force and dimensional changes in polyetheretherketone clasps with different thickness and undercut

PURPOSE@#Esthetic expectations have increased the use of polyetheretherketone (PEEK) clasps as alternatives to Cr-Co in removable partial dentures (RPDs). The objective of this study was to evaluate the retentive force and dimensional change of clasps with different thickness and undercut made from PEEK by the thermo-mechanical fatigue. @*MATERIALS AND METHODS@#PEEK clasps (N = 48) with thicknesses of 1 or 1.50 mm and 48 premolar monolithic zirconia crowns with undercuts of 0.25 mm or 0.50 mm were fabricated. Samples are divided into four groups (C1-C4) and were subjected to 7200 thermal aging cycles (at 5 - 55℃). The changes in the retentive force and dimensions of the clasps were measured by micro-stress testing and micro-CT devices from five measurement points (M1 - M5). One-way ANOVA, paired t-test, two-way repeated ANOVA, and post-hoc tests were used to analyze the data (P < .05). @*RESULTS@#The retentive forces of C1, C2, C3, and C4 groups in initial and final test were found to be 4.389-3.388 N, 4.67 - 3.396 N, 5.161 - 4.096 N, 5.459 - 4.141 N, respectively. The effects of retentive force of all PEEK clasps groups were significant decreased. Thermo-mechanical cycles caused significant dimensional changes at points with M2, M4, and M5, and abraded the clasp corners and increased the distance between the ends of the clasp, resulting in reduced retentive forces (P* = .016, P* = .042, P < .001, respectively). @*CONCLUSION@#Thermo-mechanical aging decreases the retentive forces in PEEK clasps. Increasing the thickness and undercut amount of clasps decreases the amount of dimensional change. The values measured after aging are within the clinically acceptable limits.