Fatigue behavior of bonded lithium disilicate glass-ceramic simplified restorations is not damaged by the finishing/grinding of the bonding surface of dentin analogue material
Introduction
Prosthetic rehabilitation of lost or damaged dental elements using fixed dental prostheses aims to restore esthetic and function following biomechanical principles during tooth preparation, and thus to promote success and longevity of ceramic restorations [1]. The roughness surface of tooth preparation encourages the mechanical interlocking of cement influencing the prosthesis retention. Therefore, a grinded preparation surface, which promotes micro retentions is desirable, thereby enabling micromechanical bonding with the cement without damaging the internal and marginal adaptation of the restoration [2,3].
The adhesion of ceramic restorations to the dental structure depends on several factors, including the ceramic surface treatment, proper selection of the cementing agent and correct treatment of the dental tissue [4,5]. The surface characteristics of the substrate after prosthetic preparation can affect the adhesion effectiveness. However, this may depend on the type of adhesive system used, since the quality of the smear layer can influence the penetration of monomers, making total-etching adhesives less affected by surface characteristics than self-etching adhesives [6,7].
In addition, surface roughness of the hard tissues plays an important role in restorative dentistry, as it influences the restoration's adaptation to the dental structure [8]. A smooth dental surface provides a better impression of the tissues, improves the flow of resin cement and enables a narrow adaptation between ceramic restoration and teeth [7,8]. However, other studies claim that a rougher surface increases the adhesion area, provides micromechanical interlocking, and consequently increases the adhesive potential [7,9].
Several dental surface finishing procedures have been used in dental clinical practice. These procedures influence the introduction of surface defects (shape, amount) and consequently promote distinct surface topographies [7,8]. In this sense, bonding to the prepared substrate can be affected by the type of dental burs used [7], which might have dichotomic consequences. For instance, higher surface roughness generated by rotary instruments might result in a larger area available for adhesion, and therefore facilitate surface wettability [7]. Conversely, deep and narrow grooves may lead to an inclusion of air bubbles between substrate and resin cement, decreasing the bond strength [7,9]. Moreover, the introduction of distinct critical defects on assembly surfaces (mainly on surfaces under tensile stresses) composed by a ceramic (brittle behavior) might affect the mechanical behavior of this assembly [10,11]. Finally, strong adhesion between the ceramic restoration and tooth substrate provides good support for the restoration and dissipates forces throughout the bonded interface, thus minimizing crack formation and consequently improving clinical success [12,13].
Taking into consideration that the use of distinct diamond burs for tooth preparations affect the surface roughness, topography, introduction of surface defects, and adhesive potential, as well as the clinical relevance of this topic, a research question still remains: What will be the effects of the surface finishing procedures promoted by distinct grit-size diamond burs on the fatigue behavior of bonded lithium disilicate glass-ceramic restorations?
Therefore, the present study aims to evaluate the influence of finishing by grinding the bonding surface of dentin analogue material (epoxy resin) on the fatigue behavior of adhesively cemented lithium disilicate glass-ceramic simplified restorations. The null hypothesis is that the different finishing protocols with diamonds burs will promote similar fatigue behavior.
Section snippets
Materials and methods
The general description of the materials used in the present study, their manufacturers, composition, and batch numbers are presented in Table 1.
Results
The CTRL group had the lowest fatigue performance (fatigue failure, number of cycles for failure and survival probabilities) compared with the ‘grinding’ groups. However, no statistically significant difference could be observed among the ground substrates (G, G + F, G + F + FF), regardless of the sequence of diamond burs used (Table 2, Table 3 and Fig. 1). The Weibull analysis showed no statistically significant difference in mechanical structural reliability (Weibull modulus) among all the
Discussion
The assumed null hypothesis was accepted, since the distinct finishing protocols led to similar fatigue behaviors. The grinding conditions were higher than the CTRL group (the lowest fatigue performance).
The clinical performance of the ceramic restoration/tooth structure assembly depends on the correct combination of restorative material, cementation strategy, and surface treatment of the prepared tooth structure and the ceramic surface. Several tooth surface finishing procedures have been used
Conclusion
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The distinct approaches to finish/grind the bonding surface of dentin analogue material (course grinding followed or not by fine/extra-fine diamond burs) provided similar fatigue behavior of the adhesively cemented lithium disilicate simplified restorations.
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The distinct finishing/grinding procedures of the dentin analogue material's surface induced fatigue behavior improvements compared to non-ground surfaces (control).
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As unground surfaces induce lower fatigue behavior, it is important to pay
Acknowledgements
The authors declare no conflicts of interests and emphasize that this study was partly financed by the Brazilian Federal Agency for Coordination of Improvement of Higher Education Personnel (CAPES) (Finance code 001; Doctorate Scholarships of A. C. C-R, R. V. M.), and the Foundation for Research Support of the Rio Grande do Sul State, Brazil – FAPERGS (post-doctorate scholarship of A.B.V.; # 18/2551-0000520-7). We especially thank Ivoclar Vivadent for donating some materials, and finally we
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