Polishing Performance And Water Sorption Of Six Resin Composites

The clinical use of resin composites has increased over the past few years due to increased esthetic demands by patients, modification of resin components, improvements of many characterizations and simplification of clinical procedures. Finishing and polishing of resin composite restorations are essential steps in restorative dentistry. The esthetics and life span of tooth-colored restorative materials are dependent on the qualities of the surface finishing. The presence of surface irregularities arising from poor finishing/polishing techniques and/or instruments may create clinical complications such as staining, plaque retention, gingival irritation, and recurrent caries. Proper polishing of restorations is desirable not only for esthetics and comfort for patients but also for oral health considerations by preventing plaque retention.Resin composites surface roughness is usually dictated by the size, hardness, and amount of filler and by the ?exibility of the backing material and hardness and grit size of the abrasive.This study would evaluate the polishing effect of three different finishing and polishing procedures on six different resin compsites. These finishing and polishing procedures include Composite Polishing Kit CA 0310(Shofu), Super-Snap polishing system (Shofu) and diamond finishing bur with polishing rubber cup and paste. These resin composites include Venus(micro-hybrids), Solitaire 2(packable),Te-Econom (midi-hybrids), Charisma(micro-hybrids), Composan LCM (micro-hybrids) and Swiss TEC(midi-hybrids).As direct filling materials, resin composites would exist in oral cavities and contact with saliva for a long time. The effects of water on resins include water sorption, dissolution and hydrolysis. These effects are considered to in?uence strength, abrasion resistance, volume, color stability and biocompatibility of filling materials. This study would compare the weight change of six resin composites stored in water. Water sorption of resins may influence its polishing characterization and surface roughness. The literature about this is little. Specimens were prepared utilizing a sectional metal mold (6.6mm diameter×2.0 mm deep). Fifteen specimens were prepared for each materials and divided into three groups randomly. Each group contains five specimens. Three groups was finishing and polishing with Composit Polishing Kit CA 0310, Super-Snap polishing system and diamond finishing bur with rubber cup and polishing paste respectively.The surface roughness was measured in three different positions on each sample using a Surface Roughness Tester. The average surface roughness was calculated by taking the arithmetic mean from the three positions. Specimens were removed from the water, wiped their surface using a drying paper and weighed after 3 minutes. The weights of the specimens were measured using an electronic analytical balance with an accuracy of 0.0001g. Total specimens were stored in distilled water in 37℃. The weights and surface roughness were measured after three days, one week, two weeks, six weeks and twelve weeks.Polishing instruments have an important impact on the surface roughness of resins. For a composite finishing system to be effective, the cutting particles must be relatively harder than the filler materials. Otherwise, the polishing agent will only remove the soft resin matrix and leave the filler particles protruding from the surface. For six resin composites studied in this research, the Ra, Rz and Ry were no statistically significant difference between Composite Polishing Kit group and Super-Snap group (p>0.05). The average Ra value is below 0.2μm. Composite Polishing Kit CA 0310 and Super-Snap polishing system contain various grade aluminum oxide particles. Because the hardness of aluminum oxide is significantly higher than that of silicone oxide as well as most filler particles in composites, these two polishing systems could remove resin matrix and filler particles uniformly and create smooth surface. The group finishing with diamond finishing bur and polishing with rubber cup create the most roughest surface. There is a statistically significant difference between the third group with other two groups(P<0.05).The average Ra value is from 0.442μm to 0.548μm. The possible explanation is diamond finishing bur can't remove resin matrix and filler particles uniformly , rubber cup and polishing paste are soften than filler particles.Another factor influenced surface roughness is the size of filler particles. Materials with fillers of larger sizes generally show more surface roughness than those with fillers of smaller sizes. In present research, five hybrids resin composites of Composite Polishing Kit group and Super-Snap group acquired smooth surface. The average Ra value is below 0.2μm. There is a high correlation between smoother surface and smaller sizes of filler particles. Solitaire 2 contains special filler particles with diamater varies from 0.02mm to 2mm. Theoretically, the surface of Solitaire 2 should be more roughness. Nevertheless, the results of present research is different. In Composite Polishing Kit group, the Ra value and Ry value of Solitaire 2 are similar with other five resins (p>0.05), the Rz value is maximum. In Super-Snap group, the Ra, Rz and Ry value of Solitaire 2 are similar with other five resins (p>0.05). In the group polishing with rubber cup and polishing paste , the Ra, Rz and Ry value of Solitaire 2 is maximum in six materials, but statistical difference is not found with other five resins.This can be explained by the hardness of aluminum oxide is higher than the hardness of most filler particles in composites.When specimens were immersed in water, water sorption and dissolution would take place. During this process, increases in these weights by water absorption and decreases in weight by dissolution of the material into water occurred simultaneously. The weight changes which were measured in this research are the outcomes of above two effects.In this study, water absorption reacheded equilibrium for Venus, Te-Econom, Charisma, Composan LCM and Swiss TEC in six weeks. The water absorption of Solitaire 2 increased over six weeks. After stored in water for twelve weeks, the weight change of Venus is maximum. There ia a statistical significant difference between Venus with other materials(P<0.05).The weight change of Swiss TEC is minimum. There is a statistical significant difference between Swiss TEC with other materials(P<0.05). The ranking of weight change was as follows: Venus>Solitaire 2≈Composan LCM>Charisma≈Te-Econom>Swiss TEC.When resin composites is stored in water, water is the main factor responsible for the appearance and propagation of interfacial debonding, matrix cracking, superficial ?aws, and filler particle dislodgment. Indeed, water sorption reduces the hoop stresses around fillers, which facilitates the plucking out of particles. As a probable consequence, the inorganic particles are no longer provided with a stable structure, which could predispose to filler dislodgment and elution. Therefore, one could expect that the decreased surface hardness should be accompanied by increased surface roughness. In present research, the surface roughness in most of groups did not change significantly during twelve weeks. It is different from theoretical analysis. Therefore, the influence of water on surface roughness of resin composites needs further evaluation.Within the limitations of this in vitro study the following conclusions were drawn:①Composite Polishing Kit CA 0310 and Super-Snap polishing system can acquire ideal polishing effectiveness. The average Ra value is below to 0.2μm.②As a commonly used polishing method, the procedure polishing with rubber cup and polishing paste after finishing with diamond finishing bur produced clinically acceptable surface roughness for all six resins. The average Ra value is between0.442μm and 0.548μm.③The polishing effect of six resins is similar.④In this study water absorption reacheded equilibrium for Venus, Te-Econom, Charisma, Composan LCM and Swiss TEC in six weeks. The water absorption of Solitaire 2 increased over six weeks. After immersed in water for twelve weeks, the weight of six resins is increasing steadily. The ranking of weight change was as follows: Venus>Solitaire 2≈Composan LCM>Charisma≈Te-Econom>Swiss TEC.⑤The surface roughness of six resins did not change significantly during a 12-week storage period.