Effect of bleaching on microleakage, surface hardness, surface roughness, and color change of an ormocer and a conventional hybrid resin composite
N Ayad, A Bedewi, S Hanafy, S Saka
bleaching, color change, hardness, microleakage, ormocer, roughness
N Ayad, A Bedewi, S Hanafy, S Saka. Effect of bleaching on microleakage, surface hardness, surface roughness, and color change of an ormocer and a conventional hybrid resin composite. The Internet Journal of Dental Science. 2008 Volume 6 Number 2.
The esthetic of an existing restoration is important in affecting clinical success. Although the initial color match of a light-polymerized restoration may be established, long term color changes may occur because of surface staining, microleakage, and wear-dependant surface changes.
Bleaching has become a popular treatment to remove surface stains and restore esthetics. Although bleaching is safe from a procedure stand point, it may not be safe for dental materials that have high degradation characteristics. Peroxide-based agents provide whitening through decomposition of their peroxides into unstable free radicals that breakdown large pigmented molecules either through an oxidation or a reduction reaction. Accordingly, these agents may possibly affect sealing ability or surface quality of the restoration. (1,2,3)
The aim of this study was to evaluate the effect of two carbamide peroxide bleaching systems on microleakage, surface hardness, roughness, and color change of an ormocer and a conventional hybrid resin composite.
Materials and methods
An ormocer-based material, Admira(Voco, Cuxhaven, Germany) and a hybrid composite, Glacier(South Dental Industries, Australia) together with two bleaching systems, Vivastyle paint-on (VSP)and Vivastyle(VS) / Ivoclar-vivadent, Schaan, Liechtenstein, were utilized for this study, All materials were handled according to the manufacturers' instructions.
Thirty recently extracted sound permanent human upper premolars were cleaned from any calculus deposits or soft tissue debris using an ultrasonic scaler. All teeth were microscopically examined at X20 magnification to assure the absence of cracks or defects. Then, the teeth were stored in distilled water that contained an antibacterial agent (0.2 % sodium azide), until being used. (4) A trapezoidal class V cavity with dimensions of 3, 2, 2, 2 mm was prepared on the buccal surface of each tooth 0.5 mm coronal to cemento-enamel junction using No. 56 fissure carbide bur
Thirty disc-shaped samples were prepared in a split stainless steel mold (6 mm in diameter and 3 mm in thickness). The mold was slightly over-filled with the restorative material under evaluation, placed between two celluloid matrix strips and then sandwiched between two microscopic glass slides to extrude the excess material. The samples were light-cured from the top and the bottom for 40 seconds, then removed from the mold and stored in distilled water at 37 ° C for 24 hours in the incubator. The samples were thermocycled, then fixed in acrylic resin boxes with one of their surfaces exposed. The surface hardness testing was accomplished using
Thirty disc-shaped samples were prepared in a split stainless steel mold (9 mm in diameter and 3 mm in thickness). The samples were prepared and fixed in acrylic resin boxes as mentioned in the preparation of surface hardness samples. Then, they were stored in distilled water at 37 ° C. Surface roughness measurement was carried-out using an electronic surface roughness measuring apparatus Talysurf,
Thirty disc-shaped samples were prepared in a split stainless steel mold (13 mm in diameter and 1 mm in thickness) as mentioned in the preparation of surface hardness samples. Due to the larger surface area of the sample relative to the exit window of the light source, each sample was cured at the center for 30 seconds and then selecting a north, south, east, and west corners of the disc sample and curing each location for 30 seconds. Then, they were stored in the incubator. The color shifts of the samples were determined using the
The data obtained were tabulated for statistical analysis using SPSS version 10. The Mann-Whitney test and the paired sample t-test were used to detect the significant differences among the variables tested in this study.
Admira and Glacier decreased significantly after bleaching but Admira was less affected and the difference was of extremely high significance (p≤ 0.001). Also, there was an extremely high significant difference between the mean (VHN) values of all test groups for each tested material separately, (p≤ 0.001),
Surface roughness values of both Admira and Glacier increased after carbamide peroxide bleaching but Admira values were higher and the difference was highly significant in case of using VSP system (p≤ 0.01), and of extremely high significance in case of VS system (p≤ 0.001) as apparent in
Bleaching has become a popular treatment to remove surface stains and restore esthetics. Numerous bleaching agents have been used, including carbamide peroxide which is considered as one of the best bleaching agents. Restorative materials with different monomer systems, such as composites or organically modified ceramics (ormocer), may react in different ways to the application of bleaching agents. Accordingly, this study has got the concern of evaluating the effects of two bleaching systems (Vivastyle paint-on/ Vivadent), and (Vivastyle/ Vivadent) on microleakage, surface hardness, roughness, and color change of an ormocer (Admira/Voco), and a hybrid composite (Glacier/SDI). (2,6,13,14)
The results of this study revealed that carbamide peroxide bleaching had a significant adverse effect on the sealing ability at the tooth-restoration interface and that the higher the concentration of the bleach, the stronger are its deleterious effects. Some studies revealed the adverse effects of carbamide peroxide on the bond strength of resin composite to enamel and dentin and on marginal seal at the tooth-restoration interface, together with the directional proportionality between the bleach concentration and the severity of its effects on the restoration. (2,14,15,16,17,18)
Residual peroxides from the bleaching agent could explain the increase in microleakage as they would interfere with resin attachment to the tooth, hence, increasing the gap between the restoration and the tooth. This explanation coincide with that of
On the other hand,
The results of this study also showed that, the score of microleakage values was lower for Admira than for Glacier in all test groups, and the difference was highly significant, this could be attributed to the difference in composition between the restorative materials used. Ormocer-based composite possesses a modified organic matrix, formed by monomers with a single polymerizable end. The other end is formed by an alkoxy group, resulting in an inorganic area, bonded to other monomers by a condensation reaction, converting the monomer precursors, creating a complex structure with the formation of the Si-O-Si chain in the inorganic area of the polymer. The combination of this inorganic-organic matrix and filler particles in high concentration would result in lower polymerization shrinkage and superior sealing ability to that of hybrid composites, whose matrix is composed of the traditionally-known resins that undergo a relatively higher degree of polymerization shrinkage. (11,22,23)
The results of this study demonstrated that carbamide peroxide bleaching lowered the surface hardness values of Admira and Glacier restorative materials, but Admira was less affected than Glacier and the difference was of extremely high significance in all groups. This could be attributed to the difference in composition as mentioned earlier. It has also been shown that higher concentrations of carbamide peroxide resulted in lower values of VHN. This can be explained by the fact that the quantity of released hydrogen peroxide is directly proportional to the bleach concentration. The oxidizing agent H2O2 releases free radicals that have a great oxidative power to break up larger macromolecular stains into smaller ones and by diffusion expel them to the surface. The free radicals eventually combine to form molecular oxygen and water. Some aspects of this chemical process might accelerate the hydrolytic degradation of composite leading to surface dissolution and lowering surface hardness. This explanation is in agreement with
On the other hand, the results of another study were in disagreement with ours, where, it was shown that restorative resins exposed to home-use carbamide peroxide gels exhibited an increase in surface hardness values. Those results may be attributed to the composition of the materials under investigation where, they consisted of an organic matrix with considerably low surface hardness value into which were dispersed inorganic filler particles with higher surface hardness value. Bleaching abraded the softer matrix phase leaving the filler particles protruding. Accordingly, the Vickers' diamond indenter hit the filler particles rather than the organic matrix resulting in higher VHN records. (29)
The surface roughness of composite restorative materials is the result of the interaction of multiple factors among which are the filler type, size and distribution of particles, type of resinous matrix of the material, and the bond of filler and matrix at the interface. High surface roughness is responsible for undesirable deterioration of the esthetic of the restoration, due to the loss of surface gloss, dental plaque accumulation and increasing the risk of caries. (2,22,30)
In agreement with
The results of this study also demonstrated that bleaching had an adverse effect on the surface roughness of the tested materials which could be explained by selective softening of the resin matrix and dislodgement of filler particles by bleaching. Also, higher concentrations of carbamide peroxide were found to cause more increase in surface roughness values. There was an extremely high significant difference between different test groups where bleaching is supposed to abrade the softer phases of the surface, thus reducing its smoothness. This explanation is in agreement with those of
On the other hand,
Before application of the bleaching agent, there was no significant difference between the recorded basic color values of the tested materials. This could be attributed to the use of the same color shade with the same filler size (0.7µm). This explanation is in agreement with
After application of the bleaching agent, both Admira and Glacier have shown a tendency to become lighter and the difference between the test groups of each material separately was of extremely high significance. In agreement with,
Within the limitation of this study, the following conclusions were obtained:
Carbamide peroxide bleaching of Admira and Glacier could achieve lighter color change but this was associated with an increase in microleakage, surface roughness and a decrease in surface hardness.
The higher the concentration of the carbamide peroxide used, the greater the formerly- mentioned affections.
Admira exhibited greater resistance than Glacier to adverse effects of bleaching except for surface roughness.
The authors would like to thank Prof. Dr. Abdalla Shahin, Dr. Mahrous Abu El Ein, faculty of Science, and Dr. Osama Badie, faculty of Engineering, Mansoura university, Mansoura, Egypt, for their valuable assistance in the applied part of this work.
Dr Neveen Mokhtar Ayad, Department of Dental Biomaterials, Faculty of Dentistry,
Mansoura University, Mansoura, Egypt.