30 December 2022

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Effect of pre-heating on surface wear, color stability of bulk-fill and conventional resin composites

Lorenzo Breschi

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Introduction: Composite resins are widely used in daily clinical practice thanks to their increasingly performant physio-mechanical properties. Incremental layering of conventional resin composites — up to 2 mm-thick each layer — has been recommended to reduce the shrinkage stresses derived from polymerization mechanism. However, the incremental technique results to be operator-sensitive and time-consuming. 

Bulk-fill resin composites have been designed to simplify and improve the restorative procedures: they allow thicker increments — more than 2 mm and up to 4-5 mm — without compromising the polymerization shrinkage and degree of conversion. High-viscosity bulk-fill resin composites have excellent mechanical and optical properties, while they are limited in terms of wettability and cavity adaptation because of their reduced flowability. Pre-heating (PH) resin composites before application has become a popular technique in many dental branches to reduce the viscosity and improve the marginal adaptation and microleakage. Moreover, increasing the temperature of the resin composites has been shown to maximize polymerization and increase surface hardness. 

However, the effects of PH on the optical properties, wear resistance and clinical performance of bulk-fill resin composites have yet to be investigated. In this regard, Abdulmajeed et al. have conducted an in vitro study to evaluate the effect of PH on wear and color stability of high-viscosity bulk-fill resin composites vs. conventional resin composites.

Materials and methods: 32 disc-shaped specimens (10×3 mm) were prepared with Filtek One Bulk Fill Restorative (FOBFR, 3M ESPE) and Filtek Supreme Ultra (FSU, 3M ESPE) (n=16) to determine wear. Subgroups were formed (n=8) according to preparation conditions, respectively PH and room temperature (RT). 

A chewing simulator (CS-4.8, SD Mechatronik) with simultaneous thermocycling (120.000 cycles, 5°C-55°C) was applied to specimens and volumetric material loss was calculated using a laser scanner (LAS-20, SD Mechatronik) and three-dimensional imaging software (Geomagic, 3D Systems). 

Additional 128 disc-shaped specimens (10×1 mm) were prepared with FOBFR and FSU (n=64) and randomly divided into groups according to preparation conditions (PH and RT) to determine color stability (n=32). Specimens were aged for 14 days in coffee, grape juice, distilled water and thermocycling (20.000 cycles, 5°C–55°C). The lightness (L), chroma (C) and hue (H) values were measured at baseline and after 14 days to determine color changes, using the CIEDE2000 formula. All data were statistically analysed using analysis of variance (ANOVA) at a 95% confidence interval (p<0.05).

Results: In both the PH and RT groups, FSU exhibited greater wear than FOBFR (p<0.05). When compared with the RT groups, the PH groups of both materials showed increased material volumetric loss (p<0.05). A significant difference in color change based on the aging solution was observed (p<0.05) when controlling for time and resin composite type, except for deionized water and thermocycling (p>0.05). PH had no effect on the color stability of the resin composite at any time (p<0.05).

Conclusion: The authors concluded that high-viscosity bulk-fill resin composites exceeded conventional resin composites in terms of wear resistance, while displaying a similar color stability. Moreover, aging solutions significantly influenced the color stability of both materials, with coffee determining the most significant effect. Finally, PH may increase volumetric wear irrespective of the material type, but it has no effect on color stability.

Abdulmajeed AA, Suliman AA, Selivany BJ, Altitinchi A, Sulaiman TA. “Wear and Color Stability of Preheated Bulk-fill and Conventional Resin Composites.” Oper Dent. 2022 Sep 1;47(5):585-592. Doi: 10.2341/21-077-L. PMID: 36136611.