Effect Of Polishing Protocol And Exposure To Staining Solutions On The Colour Stability Of Dental Composite Materials

Abstract

Background: Colour instability of dental resin composite materials can result in their failure and subsequently need for replacement. The discolouration may be intrinsic or extrinsic. Intrinsic discolouration is dependent on the materials’ composition while extrinsic discolouration can be due to adsorption of stains which make contact with the restorations. Finishing and polishing is one of the most crucial steps in the placement of dental resin composite restorations. Apart from being essential for oral health and function by ensuring smooth surfaces that prevent accumulation of plaque, allow food to glide more freely over tooth surfaces during mastication and minimise wear to opposing and adjacent dentition, finishing1and1polishing is also an important determinant of extrinsic discolouration of composite restorations. Broad objective: To evaluate the effect of finishing and polishing protocol and exposure to staining solutions on the colour stability1of dental resin composite restorative1materials. Study design: A laboratory based experimental study. Study area: School of Dental Sciences, Prosthetics laboratory and School of Pharmacy, Pharmaceutical Chemistry laboratory, University of Nairobi. Materials1and1methods: Two1commercial dental resin composite materials were evaluated for colour stability: a nano-fill composite, Filtek Z 350 (3M ESPE St Paul, MN, USA) and a micro-hybrid composite, Vit-l-escence (Ultradent1Inc, South1Jordan, UT, USA). The material specimens were prepared from perspex moulds with dimensions of 8mm diameter x 2mm width. A total of 150 specimens were prepared, 75 from Vit-l-escence and 75 from Filtek Z 350 XT. Three finishing and polishing protocols were evaluated, namely, mylar strip finish (Maquria industries, Brazil), Soflex polishing discs (3M1ESPE1St1Paul, MN, USA) and white polishing stone (Prime dental, UK), while the staining solutions were tea, red wine and khat extract (diluted to 2 different concentrations). Distilled water was the control for staining solutions. The method specified in International for standardisation ISO 7496:2000 for determination of colour stability of dental materials was used. There were 5 test specimens for each finishing protocol and staining solution for both materials. Baseline colour measurements were taken before the specimens were placed in the staining solutions. A digital spectrophotometer (Vita Easyshade, Vita Zahnfabrik, Bad Sackingen, Germany) was used for all colour measurements which were xix done using the CIE-Lab-colour (Commission International de l’ Eclairage L*a*b colour) system. The colour measurements were taken at 6hrs, 1, 2, 4, 7, 10 and 14days against a white background and the mean calculated. An Independent-Samples t-test was used to determine the difference in colour at baseline and at the end of staining between the two materials while Two-Way Analysis of Variance (ANOVA) was used to determine the difference in mean colour change within or between the groups of finishing protocols and staining solutions followed by Tukey’s HSD post hoc test at an alpha level of 0.05. Results: Total colour difference (ΔE) above 2.6 units1is considered1to be1clinically perceptible1while ΔE of 5.5 is considered clinically unacceptable. At the1end of1the staining period all1specimens, except Soflex disc finished – microhybrid specimens (Vit-l-escence) in the khat 1 and khat 2 staining solutions, demonstrated a clinically unacceptable ΔE. In the microhybrid group (Vit-l-escence), Soflex disc finished specimens recorded the least mean ΔE whilst mylar finished specimens demonstrated the highest ΔE. Within the Soflex finish – microhybrid group, red wine produced the highest ΔE of 8.2±0.67 units while khat 2 (khat diluted at 1:3) demonstrated the least ΔE of 5.02±0.72 units. Red wine was the only staining solution to produce a statistically significant ΔE, p=0.023 in this group. The pattern in the white polishing stone finish – microhybrid group was similar to the Soflex group with red wine producing the highest ΔE of 9.47±0.85 units and khat 2 producing the lowest ΔE of 8.18±1.62 units. All the 4 staining solutions produced statistically significant ΔE with p<0.001 in red wine, p=0.004 in tea, p=0.008 in khat 1 and p=0.011 in khat 2. In the mylar finish - microhybrid group, khat 2 produced the highest ΔE of 18.3±4.76 units while red wine produced the least ΔE of 10.66±1.02 units. All the 4 staining solutions produced statistically significant ΔE with p<0.001 for all of them. In the nanofill group (Filtek Z 350XT), white polishing stone demonstrated the highest ΔE in all the staining solutions while Soflex discs demonstrated the least ΔE in all the staining solutions with the exception of the red wine staining group where mylar finished specimens demonstrated the least ΔE. In the white polishing stone group, khat 2 produced the highest ΔE of 15.66±1.3 units and red wine produced the least ΔE of 11.81±0.68 units with all 4 staining solutions producing statistically significant ΔE p<0.001. In the mylar finish group tea produced the highest ΔE of 13.65±1.89 while red wine produced the least ΔE of xx 7.82±0.79 units. All 4 staining solutions again produced statistically significant ΔE, p=0.002 with wine and p<0.001with the other 3 solutions. In the Soflex group red wine produced the highest ΔE of 8.17±1.27 while tea produced the least ΔE of 5.96±1.21. In this group only red wine produced a statistically significant ΔE p=0.002. Comparing the two materials, the microhybid composite showed better colour stability compared to the nanofill when finished with Soflex discs and white polishing stone, while the nanofill had better colour stability with the mylar finish in the staining solutions used in the study. The staining solutions did not show any clear pattern as to which produces the highest ΔE. Conclusion: There is a difference in colour stability of resin composites depending on the type of material and the finishing protocol. Overall, Soflex disc finished specimens demonstrated the least ΔE for both materials while white polishing stone finished specimens demonstrated the highest ΔE for the nanofill composite and mylar finished specimens demonstrated the highest ΔE for the microhybrid composite. Clinicians should select the recommended finishing protocol for various materials as guided by the filler content.