A resin composite restoration can be imperceptible to the naked eyes when its surface closely resembles the surrounding enamel surface. Thus, polished restoration should demonstrate an enamel-like surface texture and gloss. In this study, the smoothest surfaces were obtained by curing both materials against a matrix strip. This finding was in agreement with previous studies[6,12–14] on resin composites. Although the surface obtained with a mylar strip is perfectly smooth, it is rich in resin organic binder. Therefore, the removal of the outermost resin by finishing and polishing procedure would tend to produce a harder,[15] more wear resistant and hence a more esthetically stable surface.[14] Therefore, it is clinically important to determine the finishing techniques that result in the smoothest surface with minimum time and instruments.
Improper application of finishing/polishing instruments could lead to decreased effectiveness and less than optimal results.[16] Strict adherence to manufacturers' instructions on finishing/polishing procedures was thus observed. Efforts were also made to standardize the different aspects of the methodology including handpiece speed, type of motion used and the total number of strokes employed for each finishing/polishing system. The slight variations in Ra values with-in each treatment group may be accounted for by the unequal distribution of abrasives in the delivery medium and the differences in pressure exerted during finishing/polishing procedures. The differences in pressure exerted during finishing/polishing procedures were minimized by using a single operator for the experiment. The term finishing/polishing was employed instead of finishing and polishing, as the two processes are inter-related and cannot be easily demarcated.
According to Stoddard and Johnson,[14] the effectiveness of finishing/polishing systems depends on material (filler size and content), type of abrasive used, time spent with each abrasives, strokes, amount of pressure applied, orientation of abrading surfaces and geometry (discs, cups, cones) of abrasive instruments.
For years, specially designed diamonds with very fine abrasive particle size and white Arkansas stones have been used to polish resin composite restorations.[17] However, the use of diamond burs is limited to initial contouring because of their ability to remove equal amount of adjacent enamel.[18] Later, importance was given to the application of progressive finer grits of abrasives to polish resin composites with little concern for the type of motion employed during their use.
Fruits and others,[11] have reported that three types of motion may be equally critical to the development of optimal surface smoothness: A rotary motion (circular), a planar motion and a reciprocating motion. They concluded that, for all possible combinations of materials and abrasive grits, the planar motion achieved the lowest roughness values. In the current study, a planar motion was used for both the polishing systems.
Most investigators have concluded that flexible aluminum oxide disks are the best instruments for providing low roughness on composite surfaces.[6,19,20] However, aluminum oxide disks (Super snap) have limitations due to their geometry. While using the disks, it is often difficult to efficiently create, finish and anatomically polish contoured surfaces, especially in the posterior region of the mouth.
To reduce the clinical time, the technology for two and one-step finishing/polishing system has evolved over the past few years and current systems appear to be as effective as multi-step systems for finishing and polishing dental composites. The obvious advantage of the one-step system is the convenience and efficiency of producing a very smooth surface without having to switch to finer polishing items or having to wash and dry between each step to ensure removal of the larger abrasives from the previous step.
For this study, PoGo is used as a one-step micro-polisher, but the manufacturer recommends pre-treatment with the Enhance system to obtain favorable results. As per the definition, PoGo is a one-step method and indeed, some authors use this system without any pre-treatment.[1,21] For this reason, the authors of this study classified and applied PoGo as a one-step method.
The surface micro-morphology of resin composite after finishing and polishing has been shown to be influenced by the size, hardness and amount of filler particles.[22] In this study, the surface finish of minifill-hybrid composite (Esthet-X) was significantly better than packable composite (Solitaire II) when PoGo system was used. In composites, where the filler particles are significantly harder than the matrix, the resin phase may suffer a preferential loss during finishing and polishing. This will result in the filler phase showing positive relief on the surfaces.[6,22] Materials with larger and harder filler particles are therefore expected to have higher Ra values after finishing/polishing. The filler particle size of Esthet-X ranged from 0.85 to 0.9 μm, while that of Solitaire II ranged from 2 to 20 μm. In view of the aforementioned, the significantly higher Ra values observed with Solitaire II after finishing/polishing is expected.[6]
According to Marigo and others,[23] the final glossy surface obtained by polishing depends on the flexibility of the backing material in which the abrasive is embedded, the hardness of the particles, the instruments and their geometry (cups, discs and cones). In this study, PoGo achieved a smoother surface compared to Super Snap for Esthet-X group. This result is in accordance with that of previous studies.[21] The superior performance of PoGo may be attributed in part to the use of fine diamond powders instead of aluminum oxide (Super Snap) and the cured urethane dimethacrylate resin delivery medium. According to Roeder,[15] aluminum oxide disks produced the smoothest surface for packable composites (Solitaire II). In this study, no significant difference was observed between PoGo and Super Snap for Solitaire II group. Results of this study correlate well with that of previous studies.[21,24] The PoGo system is very sensitive to the mode of application because it requires polishing at two different loads. Therefore, by using this system, inter-individual differences with respect to manual application and polishing could have a greater effect on results than is the case of the other method.
Many studies on the polishing of resin composites have been introduced and the most commonly used parameter to describe surface roughness is Ra.[3,15,20] Surface roughness is a function of the microstructure created by the series of physical processes used to modify the surface and is related to the scale of the measurement. Profilometers have been used for years to measure the surface roughness for in-vitro investigations. They provide limited two-dimensional information. However, an arithmetic average roughness can be calculated and used to represent various material-polishing surface combinations that assist clinicians in their treatment decisions.[23,25] However, the complex structure of a surface cannot be fully characterized by the use of only surface roughness measurements. Therefore, it is not appropriate to draw conclusions on the clinical suitability of a finishing instrument exclusively on the basis of roughness average results. However, in combination with atomic force microscopy (AFM)[26] and scanning electron microscope (SEM) analysis that permits evaluation of the destructive potential of the finishing tool, more valid predictions of clinical performance can be made.[26] In this study, surface roughness measurements were used only for relative comparisons.
Further studies are needed to determine which finishing technique is best suited to clinical situations, where access is limited and restoration surfaces are not flat along with AFM and SEM analysis to obtain more valid results.