Correlation between metal-ceramic bond strength and coefficient of linear thermal expansion difference

Stella Crosara Lopes,João Manuel Domingos De Almeida Rollo,Mônica Barbosa Leal,Valéria Oliveira Pagnano,Osvaldo Luiz Bezzon

doi:10.1590/s1678-77572009000200010

Stella Crosara Lopes, João Manuel Domingos De Almeida Rollo + Show 3 more

Open Access

https://doi.org/10.1590/s1678-77572009000200010

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Abstract

The purpose of this study was to evaluate the metal-ceramic bond strength (MCBS) of 6 metal-ceramic pairs (2 Ni-Cr alloys and 1 Pd-Ag alloy with 2 dental ceramics) and correlate the MCBS values with the differences between the coefficients of linear thermal expansion (CTEs) of the metals and ceramics. Verabond (VB) Ni-Cr-Be alloy, Verabond II (VB2), Ni-Cr alloy, Pors-on 4 (P), Pd-Ag alloy, and IPS (I) and Duceram (D) ceramics were used for the MCBS test and dilatometric test. Forty-eight ceramic rings were built around metallic rods (3.0 mm in diameter and 70.0 mm in length) made from the evaluated alloys. The rods were subsequently embedded in gypsum cast in order to perform a tensile load test, which enabled calculating the CMBS. Five specimens (2.0 mm in diameter and 12.0 mm in length) of each material were made for the dilatometric test. The chromel-alumel thermocouple required for the test was welded into the metal test specimens and inserted into the ceramics. ANOVA and Tukey's test revealed significant differences (p=0.01) for the MCBS test results (MPa), with PI showing higher MCBS (67.72) than the other pairs, which did not present any significant differences. The CTE (10-6 °C-1) differences were: VBI (0.54), VBD (1.33), VB2I (-0.14), VB2D (0.63), PI (1.84) and PD (2.62). Pearson's correlation test (r=0.17) was performed to evaluate of correlation between MCBS and CTE differences. Within the limitations of this study and based on the obtained results, there was no correlation between MCBS and CTE differences for the evaluated metal-ceramic pairs.

Highlights

Metal-ceramic compatibility is an important factor in manufacturing metal-ceramic restorations
Some authors reported that metal-ceramic specimens with a negative coefficient of linear thermal expansion (CTE) difference failed at significantly lower flexural loads than specimens did with positive CTE difference[2,10]
Two Ni-Cr alloys - Verabond (VB) with Be and Verabond II (VB2) without Be -and one Pd-Ag alloy - Pors-on 4 (P4) - were fused to 2 ceramics - IPS (I) and Duceram (D) (Table 1) to form six metal-ceramic pairs (VBI, VBD, VB2I, VB2D, PI, and PD)

Summary

Introduction

Metal-ceramic compatibility is an important factor in manufacturing metal-ceramic restorations. The general consensus is that the alloy should have higher CTE than the porcelain (a positive expansion coefficient mismatch) in order to produce compressive stress in the porcelain when cooling[11,24]. A variation ranging from 0.5 to 1.0 x 10-6 oC-1 between the CTEs of the alloy and ceramic is considered adequate when the metal coefficient is higher than that of the ceramic. It keeps the ceramic compressed; increasing the lifetime of the restoration[3]. Some authors reported that metal-ceramic specimens with a negative CTE difference failed at significantly lower flexural loads than specimens did with positive CTE difference[2,10]

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