Influence of Pre-Curing Different Adhesives on the Color Stability of Cemented Thin Ceramic Veneers

Brazilian Dental Journal (2019) 30(3): 259-265 http://dx.doi.org/10.1590/0103-6440201902369 ISSN 0103-6440 Influence of Pre-Curing Different Adhesives on the Color Stability of Cemented Thin Ceramic Veneers 1Graduate Program in Dentistry, UP - Universidade Positivo, Curitiba, PR Brazil Correspondence: Carla Castiglia Gonzaga, Rua Prof. Pedro Viriato Parigot de Souza, 5300, 81280330 Curitiba, PR, Brasil. Tel: +55-41-3317-3180. e-mail: Orides Ferrari de Oliveira Jr1 , Patrícia Valéria Manozzo Kunz1 , Flares Baratto Filho1 , Gisele Maria Correr1 , Leonardo Fernandes da Cunha1 , Carla Castiglia Gonzaga1 The objective was to evaluate the color stability of thin ceramic veneers as a function of the curing mode (with and without pre-cure) of different adhesive systems applied to the internal surface of ceramics. Five adhesive systems (Scotchbond Multi-Purpose, Single Bond Universal, Gluma 2 Bond, Ambar, and Ambar APS) and photo-cured resin cement (Allcem Veneer) were used for cementing 0.6 mm-thick feldspathic veneers (Mark II) on composite resin substrates (Charisma Diamond). The groups, according to adhesive system, were divided into two subgroups (n=10): i) adhesive and resin cement were polymerized separately (pre-cure of the adhesive), ii) adhesive and resin cement were polymerized simultaneously. The CIELab color parameters were determined with a spectrophotometer at 24h (baseline), 7 days, 30 days and 12 months. Data were analyzed by two-way ANOVA and Tukey’s test (α=0.05). The results indicated statistically significant differences for adhesive systems and time. The mode of curing of the adhesive system was not statistically significant: pre-cured adhesives (2.6±1.3) and not pre-cured adhesives (2.8±1.4). For the adhesives, ΔE values varied in the following order: Ambar-APS (1.6±0.5) < Scotchbond Multi-Purpose (2.6±1.2) = Gluma 2 Bond (2.7±1.2) = Ambar (2.9±1.2) < Single Bond Universal (3.5±1.5). For time, ΔE values were: 7 days (1.7±0.7), 30 days (3.5±1.2) and 12 months (2.9±1.3). It can be concluded that the different adhesive systems used for cementing thin ceramic veneers influenced the final color of the indirect restorations. The adhesives curing mode did not present a significant effect in the color stability of thin ceramic veneers. Introduction All-ceramic restorations with a high degree of translucency allow the passage of light (1); therefore, the color characteristics of the dental substrate on which they are cemented as well as the materials used for cementation greatly influence the overall color (2). Several studies report that color changes in the resin cement used for cementation may become visible, affecting the final aesthetic appearance of the restoration, which in turn leads to treatment failure (2-4). However, for cementing ceramic laminates to the dental substrate with conventional resin cements, two layers of adhesive system are used: one between the ceramic and the cement, and another between the cement and the dental structure. Yet, little is known about the influence of the adhesive system and its pre-cure on the color stability of thin ceramic laminates. It has been reported that different adhesive systems used in composite resin direct restorations influenced the final color of the restoration (5). It is not yet known whether the adhesive layer used on the internal surface of indirect ceramic restorations causes a similar effect; especially in thin ceramic laminate veneers, which may also interfere Key Words: dental adhesives, color stability, photo-activation, aging, ceramic laminates. with the color stability and final aesthetic result of these restorations in the short and long term. The cementation of ceramic laminates can be achieved using photo-activated resin cements, or either flowable or pre-heated composite resins, which require the application of an adhesive system for bonding to the dental substrate. In general, these adhesives are applied as a surface treatment on the inner surface of ceramic restorations, after conditioning with hydrofluoric acid and silanization. Simplified conventional adhesives have, in general, a relatively high amount of solvent in their composition. Consequently, nano-infiltration from the environment into the hybrid layer of these adhesives may possibly occur (6). In contrast, an adhesive system containing a hydrophobic layer, such as the three-step etch-and-rinse and two-step self-etching adhesives, tend to present lower hydrolytic degradation and increased longevity at adhesion interfaces when compared to simplified adhesives (7). Universal adhesives have proven to be more stable in regard to hydrolytic degradation due to changes in their chemical composition (8). It must be highlighted that the greater the hydrophilic characteristics and solvent content O. F. Oliveira Jr et al. Braz Dent J 30(3) 2019 in an adhesive system or composite are, the higher the degradation rate and, possibly, color change are expected to be (9). Among adhesive system components, the photoinitiator may play a particularly important role regarding the coloring and color stability of adhesive systems and composites. Camphorquinone is the main photoinitiator (a photosensitive molecule that absorbs light and leads to the formation of reactive species) used in most resin-based materials. However, despite promoting the polymerization of monomers and assuring good mechanical properties, camphorquinone has the significant disadvantages of having an intense yellow color and the need for a co-initiator component, which oxidizes over time (10). Depending on the quantity and concentration of camphorquinone in the material, it may develop an undesirable yellowish color, even influencing the color stability in the long term (11). This yellowish color in adhesive systems, for example, may affect the final aesthetic result in the cementation of thin ceramic laminates. For this reason, in order to minimize aesthetic problems due to discoloration, camphorquinone has been partially or completely replaced by other photosensitive molecules in some adhesive systems and composites. More recently, virtually colorless adhesive systems have been introduced with the purpose of causing less interference with the final aesthetic result of thin ceramic restorations. Since each adhesive system may present a coloration resulting from its monomeric composition and type and amount of photoinitiator, it becomes important to know how adhesive use in the internal treatment of thin ceramic restorations can influence the final color stability of the restoration, after definitive cementation. Regarding the photo-activation time, there is still no consensus in the literature as to whether the adhesive system layer in the ceramic laminate inner surface must be pre-cured or photo-activated simultaneously to the resin cement (12,13). On one hand, pre-curing the adhesives can increase the degree of conversion, but can interfere with the fit of the vene (...truncated)