EFFECT OF DIFFERENT POLISHING SYSTEMS ON PROPERTIES OF CONTEMPORARY COMPOSITE RESINS

Objectives: This study aimed to evaluate the effects of different polishing systems on the surface roughness and surface micro-hardness of three types of composites.
Materials and Methods: One hundred and eighty samples were prepared in disc-shaped stainless steel molds with a uniform size of 6 mm in diameter and 4 mm in thickness. The samples were divided according to the materials used into three groups of 60 samples for each material, and each group was then subdivided into subgroups according to the polishing instruments with 20 samples in each subgroup: Group I (control group) (Mylar’s strip) with no finishing and polishing. Group II, polishing with Spiral polishing wheels and Group III, polishing with Sof-lex Pop-on discs. Each subgroup was divided into two groups according to measurements of surface roughness and microhardness (n=10). Restorative materials were handled according to the manufacturers’ instructions. The molds were placed on flat glass plates covered with Mylar’s strips and then were filled with restorative materials. The materials were covered with Mylar’s strips, and a glass slide was pressed against the mold to adapt the materials completely to the inner portions of the molds. The excess material was removed, and the samples were photo-activated for 40 sec at the top surface using high intensity Elipar TM LED light curing unit, all samples were light cured following the manufacturers’ instructions. The specimens’ surfaces in groups II and III were finished with an ultrafine diamond finishing. After finishing the group II specimens were polished using Spiral polishing wheel. Group III specimens were polished using Sof-Lex Pop-on discs, strictly following the manufacturer’s instructions. All of the groups were stored in saline for 24 hr. All of the specimens were equally subdivided for both the surface roughness and micro-hardness test. The data were analyzed using one-way ANOVA at a significance level of 0.05 for both the surface roughness and microhardness tests, followed by Tukey,s post hoc test, using SAS software.
Results: Comparing between the three polishing techniques, the Mylar’s strips (control group) exhibited significantly lower roughness values (smoothest surface) than the polishing systems (p <0.0001). Nanocomposite had the lowest surface roughness comparing to other materials. Comparing between the three materials, the greatest microhardness mean value was recorded with Sonic bulkfill, using Mylar’s strips or Spiral wheel or Solfex disc polishing techniques(p <0.0001).
Conclusions: The control group had the lowest surface roughness and microhardness values compared to the polishing groups. No significant difference on surface roughness between Spiral wheel disc values and Soflex disc. The lowest surface roughness material was Nano-composite in each of the used techniques and Sonic bulkfill had the highest mic-ohardness than bulkfill and nanocomposite