The effects of finishing and polishing techniques on surface roughness and color stability of nanocomposites

Abstract

Objectives

The aim of this in vitro study was to evaluate the effects of different finishing and polishing techniques on the surface roughness and color stability of nanocomposites.

Methods

Two nanohybrid (Grandio, Aelite Aesthetic Enamel), two nanofill (Filtek Supreme XT Dentin and Translucent), and a microhybrid (Filtek Z250) composites were used. Two hundred and eighty disc-shaped specimens were cured under a mylar strip. Seven specimens of each resin composite were randomly assigned to one of the seven polishing systems. A profilometer was used for assessing surface roughness. ΔE was calculated with a colorimeter at baseline and 48 h after storage in a coffee solution. The results were analysed by two-way ANOVA and Tukey's HSD test (α = 0.05). Regression analysis was used to examine the correlation between surface roughness and color stability (α = 0.01).

Results

There was no significant difference in R_a values between mylar strips and Sof-Lex polishing discs (p > 0.05). The highest ΔE and R_a values were obtained from Grandio (p < 0.05), and Aelite Aesthetic Enamel had the lowest ΔE values (p < 0.05). The Enhance system showed the lowest color differences among all the finishing systems. The highest ΔE values were found in the composite resin groups under mylar strips and finished with diamond burs (p < 0.05).

Conclusions

While the Sof-Lex discs provided the lowest surface roughness, the Enhance Polishing system provided the most stain-resistant groups. Grandio presented the highest surface roughness and staining susceptibility after storage in coffee solution. Aelite Aesthetic Enamel, which did not include TEGDMA in its composition, showed the least discoloration.

Clinical significance

The composites with smaller filler size did not necessarily show low surface roughness and discoloration. Staining of composite resins was dependent on monomer structure, as well as surface irregularities.

Introduction

Resin composites have been widely used for the direct restorations of both anterior and posterior teeth, due to their aesthetics, improved physical properties, better bonding systems, curing refinements, and environmental concerns over amalgam.1, 2 Resin composites have been classified according to various characteristics, such as filler type, filler distribution, average particle size of filler, and physical and mechanical properties of the materials. Currently, three categories have been proposed for widely used resin composites: microfilled, microhybrid, and nanocomposite (nanofill or nanohybrid resin composite).³

Nanotechnology, also known as molecular nanotechnology or molecular engineering, is the production of functional materials and structures, at a range of 0.1–100 nanometers, by various physical and chemical methods.⁴ Nanofill is a composite resin that is composed of both nanomer and nanocluster, whereas nanohybrid is a hybrid resin composite with nanofiller in a prepolymerised filler (PPF) form. Microhybrid composites and nanocomposites are widely used on both anterior and posterior teeth as universal resin composites.3, 5

The longevity and aesthetic appearance of tooth-colored dental restorative materials greatly depend on the quality of the finishing and polishing techniques employed.6, 7, 8 High-quality finishing and polishing improve both the aesthetics and the longevity of composite restorations, whereas rough, poorly polished surfaces contribute to staining, plaque accumulation, gingival irritation, recurrent caries, and discoloration of the restoration. In adhesive restorations, it is important to determine the best finishing/polishing technique to obtain the best results.9, 10

Finishing and polishing in restorative dentistry refers to the following steps:

• Gross contouring of the restoration to obtain the desired anatomy.

• Reduction and smoothing of surface roughness and scratches created by finishing instruments in the process of gross reduction and initial polishing.

• Process of producing a highly smooth, light-reflective, enamel-like surface through final polishing.¹¹

A wide variety of finishing and polishing devices is available for the clinician today. Multifluted carbide finishing burs, hard-bonded/surface-coated ceramic diamond rotary instruments, impregnated rubber or silicon discs and wheels, and silicon carbide-coated or aluminium oxide-coated abrasive discs are among the most common devices used to finish dental restoratives.¹²

An unacceptable color match is a major reason for replacement of composite restorations. Intrinsic factors due to changes in the filler, matrix, or silane coating, or extrinsic factors such as absorption of stains, may cause discoloration of aesthetic materials.⁶ The resin plays a major role in the color stability of resin composites. The resin's affinity for stains is modulated by its conversion rate and its chemical characteristics.6, 13, 14

Discoloration can be evaluated with various instruments. Because instrument measurements eliminate the subjective interpretation of visual color comparison, spectrophotometers and colorimeters have been used to measure color change in dental materials.15, 16, 17

The purpose of this study was to evaluate the effects of different finishing and polishing techniques on the surface roughness and color stability of nanofill and microhybrid composites.

The null hypothesis tested was that different finishing and polishing techniques would not affect the surface roughness and stainability of composite resin restorations.