Impact of Dentin Pre-treatment Strategies on Colour Stability of Nanohybrid Composite Resin: An In Vitro Spectrophotometric Analysis.

INTRODUCTION

Matrix metalloproteinases (MMPs) are endogenous dentinal enzymes that remain latent until activated in acidic environments. During self-etch or etch-and-rinse adhesive procedures, activated MMPs degrade the dentin matrix, breaking down type I collagen fibres and thereby compromising the hybrid layer and bond strength. To mitigate this degradation, MMP inhibitors are employed as dentin pre-treatment agents, effectively limiting collagen fibre degradation and enhancing bond strength. MMP inhibitors help preserve the integrity of the adhesive interface between the resin composite and dentin. Chlorhexidine (CHX), a widely used MMP inhibitor, is associated with a potential adverse effect of dental staining. A recently introduced collagen crosslinker, riboflavin, shows promising potential for enhancing bond strength. However, the influence of riboflavin on the colour stability of composite resin has not been evaluated.

AIM

To evaluate the effect of various dentin pre-treatment strategies on the colour stability of nanohybrid composite resin.

METHODS

Thirtyextracted permanent molars were collected and subjected to thorough scaling and pumice polishing. The teeth were stored in 0.1% thymol until further use. Thirty mid-coronal dentin discs were prepared from the specimens. Each sample was etched with 37% phosphoric acid for 15 s, rinsed with water, and blot-dried. The samples were randomly divided into three groups, with 10 specimens in each group. Group I (control) received no pretreatment prior to bonding. Group II involved the application of 2% CHX gel (Chlorex Gel, Waldent, New Delhi, India) for 60 s, followed by blot drying. In group III, a 0.1% riboflavin solution was prepared by dissolving a 10 mg tablet in distilled water and applied to the dentin surface, followed by irradiation with blue light-emitting diode light for two minutes, maintaining a distance of 1 mm from the dentin disc. Subsequently, two thin layers of fifth-generation bonding agent (Meta-P&Bond, Meta Biomed Co., Ltd., Chungcheongbuk-do, South Korea) were applied and light-cured for 20 s, followed by placement of a nanohybrid composite resin (Beautifil II, Shofu Inc., Kyoto, Japan). The baseline colour change was measured in the spectrophotometer (CM-5, Konica Minolta, Tokyo, Japan). Subsequently, the samples were subjected to 1,000 thermal cycles in a thermocycler to simulate six months of ageing. The immediate colour change and the colour change after thermocycling were measured using spectrophotometric analysis. The colour change was assessed using the CIELAB colour system, and the ΔE* values were calculated.

RESULTS

The Kolmogorov-Smirnov test was conducted to evaluate the normality of the data, followed by one-way ANOVA and Tukey's Post-hoc test for multiple pairwise comparisons. The highest mean discolouration was observed in group II (CHX), with a value of 4.09, followed by group III, with a ΔE* value of 3.91. The lowest mean discolouration was observed in group I, with a value of 2.69. Pairwise comparison revealed a statistically significant difference between groups I and II.

CONCLUSION

Preserving bond strength without compromising aesthetic outcome is crucial in restorative dentistry. Riboflavin, a collagen crosslinking agent, emerges as a promising alternative. Its potential to stabilise the dentin collagen matrix may enhance the durability of adhesive interfaces while maintaining the optical properties necessary for aesthetic restorations.