The effects of finishing and polishing techniques on surface roughness and color stability of nanocomposites
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:
- (1)
Gross contouring of the restoration to obtain the desired anatomy.
- (2)
Reduction and smoothing of surface roughness and scratches created by finishing instruments in the process of gross reduction and initial polishing.
- (3)
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.
Section snippets
Materials and methods
The composite resins and finishing and polishing systems used in this study are shown in Table 1, Table 2, respectively.
Fifty-six cylindrical specimens were prepared for each of five resin composite groups using a brass mould with a central hole (15 mm in diameter; 2 mm deep), and a total of 280 discs were obtained. Each composite resin was covered with a mylar strip, pressed flat with a glass slide, and light-cured with a tungsten halogen curing light (Lunar Light Curing Unit, Benlioğlu Dental,
Surface roughness
According to the two-way ANOVA results of the restorative materials, surface polishing procedures and interaction between materials and surface procedures were significant (p < 0.001).
The average surface roughness for combinations of composite resin restorations and polishing systems are shown in Table 3. The lowest Ra values were found in Group K (control group) among all composite resins tested. However, no significant differences were found between Group K and Group TS (p > 0.05).
Comparing the
Discussion
Surface roughness, associated with improper finishing and polishing, can cause increased wear rates and plaque accumulation, which compromise the clinical performance of the restoration.6, 18 There is a wide variety of finishing and polishing instruments described in the literature for resin restorations to obtain smooth surfaces.19, 20, 21, 22, 23 However, the controversial results of existing reports, as well as the continuous appearance of new finishing and polishing products on the markets,
Conclusion
Among the resin composites tested, Grandio showed, significantly, the highest surface roughness and discoloration due to storage in coffee solution. Final finishing with Sof-Lex discs was satisfactory in all the composite resin groups. Discoloration of composite resins was found to be related to surface treatments, as well as resin composition.
Conflict of interest statement
The authors wish to state that this study was financially supported by “The Scientific and Technological Research Council of Turkey”.
Acknowledgements
The authors thank to The Scientific and Technological Research Council of Turkey for supplying financial support for commercial products used in this project (project no: 107S314) and Dr. Ahmet Umut Güler for sharing his valuable experiences and advices in this study. We also thank to Soner Çankaya for statistical advice and assistance.
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