Effects of home bleaching agents on the surface properties of CAD CAM esthetic restorative materials

Abstract

Objectives

The aim of the study was to investigate surface characteristics of three different esthetic restorative materials for CAD/CAM following application of two different home bleaching agents.

Materials and methods

Three different esthetic restorative materials for CAD/CAM were used in this study; zirconia (Easy one Zr S2), lithium disilicate (IPS e.max CAD), and hybrid ceramic (Lava Ultimate CAD/CAM). For all of test group, A2 shade was selected as it was most commonly used shade in clinic. All blocks in these tests were made to size with 6.0 mm x 12.0 mm x 1.2 mm.

Two type of home bleaching agents were used in this study; 3% hydrogen peroxide (ZOOMREAL KIT2 LIMITED EDITION) and 15% carbamide peroxide (Opalescence tooth whitening systems). Commercially available products were used for both types, where hydrogen peroxide was available easily through internet while carbamide peroxide was obtained from dental clinic.

All of specimens were first washed in flowing water for 1 min. The specimens were then placed and kept for 24 hours in screw-top conical tube (GeneDrireX, Inc., USA) filled with 10 ml of distilled water (PISCO, Inc., Gyeonggi-do, Korea) in room temperature. All of 3 different types of restorative materials were grouped randomly into 3 groups; 2 test groups and 1 control group (n=10). For test group for carbamide peroxide, the bleaching agent was applied for 4 hours and washed with flowing distilled water for 1 min. Meanwhile, test group for hydrogen peroxide was applied with bleaching agent for 30 min, followed by washing with flowing distilled water for 1 min. The process was repeated on each of test group at day 7, 14 and 21, where test groups were continuously kept in thermostatic water bath of 37 °C (JS reacerch Inc., Chungcheongnam-do, Korea) during entire experimental days. Control group was kept in thermostatic water bath of 37 °C for 21 days without the application of home-bleaching agents.

pH tape (Test paper, UNIV, Japan) was used to measure the pH of the agents. Optical 3D surface measurement profiler (BRUKER, Massachusetts, USA) was used to measure the surface roughness of each specimen. The point of measuring the roughness on the sample was selected randomly, and repeated measurements were taken at the point that was in clock wise direction from the initial point. The colors of specimen before and after use of home bleaching agents were analyzed with spectrophotometer (CM-3500d, MINOLTA, Japan). Value of L*, a*, and b* were measured and the difference in color (ΔE*). Surface hardness of each specimen was measured by Vicker’s Hardness Tester (DMH-2, Matsuzawaseiki, Japan). The measurement was carried out according to KS L 1603: 2013 standard using 1 Kg of weight. Surface of randomly selected test and control specimen were observed under scanning electron microscope (JSM-7001F, JEOL Ltd., Japan), (S-3000N, HITACHI, Japan) at 21 days of the experiment. Magnifications at 300 X, 3000 X were used.

Results

All of measurements were carried out by single tester, and ANOVA analysis with post-hoc Tukey method was used for statistical analysis of each data. Probability less than 0.05 were considered to be significant.

1. In terms of pH, ZOOMREAL KIT2 LIMITED EDITION (3% HP) was 4~5 while Opalescence tooth whitening systems (15% CP) of was 5~6.

2. Mean difference of color for each of test sample at each experimental day showed that there was no significant difference in mean color difference, as indicated by ΔE* value between all of test sample at all of experiment days, even at 21 days of experiment (p> 0.05).

3. In terms of SEM images, there was no difference in surface morphology between control zirconia sample with both of test zirconia sample that were treated with 3% hydrogen peroxide or 15% carbamide peroxide for 21 days. However, SEM images on lithium disilicate sample following 21 days of 3% hydrogen peroxide treatment clearly showed changes on surface sample compared to both control lithium disilicate and lithium disilicate treated with 3% hydrogen peroxide for 21 days. Finally, both test hybrid ceramic sample following 21 days of 3% hydrogen peroxide or 15% carbamide peroxide exposure showed that there was change in surface compare to the control hybrid ceramic sample.

4. The average roughness value (Ra) for surface of each test and control samples following exposure to bleaching agents were calculated from 3D optical profiler results.

In case of zirconia sample, application of 15% carbamide peroxide for 21 days resulted in significant change in surface roughness compare to the control (p< 0.05). Meanwhile, there was significant difference in Ra value between control and test sample for lithium disilicate on 7, 14 and 21 days of 3% hydrogen peroxide application as well as on 7 days of 15% carbamide peroxide application (p< 0.05). The result for the hybrid ceramic was significant difference in Ra value on 7, 14, and 21 days of 3% hydrogen peroxide application as well as on 14 days of 15% carbamide peroxide application (p< 0.05).

5. The average surface hardness value measured as Vicker’s hardness for each of test and control on each of experimental days showed that there was significant reduction (p< 0.05) in Vicker’s hardness on lithium disilicate and hybrid ceramic blocks following exposure to 3% hydrogen peroxide for 14 and 21 days. However, test block showed significant reduction of Vicker’s hardness for 15% carbamide peroxide only at 21 days of experiment (p< 0.05). Finally, there was significant difference between two bleaching agents, 5% hydrogen peroxide and 15% carbamide peroxide (p< 0.05).

Significance

All three CAD/CAM prosthetic materials had no change in color following exposure to home bleaching agents of 3% hydrogen peroxide and 15% carbide peroxide. However, there was significant change in surface roughness between all three groups at each experimental day while effect on surface hardness was noted for lithium silicate and hybrid cement. Hence, careful cautions must be given when applying bleaching agents on patient with such CAD/CAM prosthesis, and enough information must be given to patient with regard to safe home bleaching.