The impact of resin-coating on sub-critical crack extension in a porcelain laminate veneer material

Xu Cao,Garry J.P Fleming,Owen Addison

doi:10.1016/j.dental.2017.02.004

Abstract

ObjectivesCharacterisation of the interaction between crack extension, crack stabilisation and stress/strain relaxation in the polymeric matrix, the interplay between stress corrosion cracking and the mechanical response of a resin-based luting adhesive within a surface defect population could extend PLV restoration longevity by optimising cementation protocols. The aim was to investigate the influence of stress corrosion cracking and the viscoelastic behaviour of a resin-based luting adhesive independently by controlling the environmental conditions operative during test specimen fabrication. MethodsThe effects of stress corrosion at ceramic crack tips and potential viscoelastic responses to loading of the resin-coated impregnating cracks were isolated. Resin-coated feldspathic ceramic test specimens were fabricated in ambient humidity or following moisture exclusion. Bi-axial flexure strengths of groups (n = 20) were determined at constant loading rates of 2.5, 10, 40, 160 or 640 N/min and data was compared with uncoated controls. Fractographic analyses were performed on all fractured test specimens. ResultsResin-cement coating resulted in significant ceramic strengthening in all conditions tested (p < 0.01). A two-way ANOVA demonstrated that the exclusion of moisture during resin- coating significantly increased mean BFS (p<0.01) but post-hoc Tukey tests identified that moisture exclusion resulted in significant increases in BFS values only at intermediate loading rates with no significant differences observed at either the fastest or slowest loading rates (640 and 2.5 N/min, respectively). SignificanceMechanical reinforcement of PLV materials by resin-cement systems is yet to be optimized. The viscoelastic behavior of the resin-cement itself can influence the magnitude of reinforcement observed and sub-critical crack growth.

Highlights

Porcelain Laminate Veneers (PLVs) are a minimally invasive treatment modality used routinely by dental practitioners to modify the esthetics of the anterior dentition [1]
The loading rate applied during testing significantly impacted on the mean bi-axial flexure strength (BFS) values with an increase in mean BFS values observed with increasing loading rate (p < 0.01), but the effect was not influenced by the presence or absence of the resincoating (p = 0.49)
A further two-way analysis of variance (ANOVA) identified that the exclusion of moisture during resin-coating significantly increased the mean BFS values (p < 0.01), there was no significant interaction between loading rate and the environmental processing conditions on the mean BFS (p = 0.57)

Summary

Introduction

Porcelain Laminate Veneers (PLVs) are a minimally invasive treatment modality used routinely by dental practitioners to modify the esthetics of the anterior dentition [1]. Investigators have made comparisons with similar systems in the engineering literature where brittle coatings were intimately bonded to relatively compliant substrates namely, laminated glass and thermal barrier coatings [6,7,8]. Radial crack extension is understood to be the dominant failure mechanism when the ceramic coating is thin and the supporting substrate is relatively compliant [6,10,11]. This failure mechanism has been demonstrated to predominate in the failure of PLVs in service [12,13]

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