Supervisors info:
Μασούρας Κωνσταντίνος, Επίκουρος Καθηγητής, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Παπάζογλου Ευστράτιος, Καθηγητής, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Παππά Ευτυχία, Επίκουρη Καθηγήτρια, Τμήμα Οδοντιατρικής, Σχολή Επιστημών Υγείας, ΕΚΠΑ
Summary:
Introduction
The development and improvement of modern resin composites, has led to their widespread use, in both anterior and posterior restorations. However, the clinician in a daily practice still encounters problems associated with their use, despite their continuous developments. One of the main problems is, the incomplete polymerization of the material and the reduced rate of double bond conversion.
Another problem is, the marginal and internal adaptation. Due to their high viscosity, resin composites are sticky and difficult to handle, so their proper placement to the walls of the cavity, becomes a demanding procedure. A technique that seems to be gaining the interest, of both clinicians and researchers and has been proposed to address the above problems, is the preheating of resins before placing them in the cavity and polymerizing them.
From 2005, mainly laboratory studies that examine the effect of preheating on the properties of composite resins, began to appear in the literature. Although, several studies have investigated and proved the effect of preheating on the conversion rate and the mechanical properties, there is little evidence about the effect of preheating on the optical properties. Considering the clinical importance of color stability of contemporary resin composites, it is important to evaluate the effect of repeated preheating cycles, on the optical properties of resin composites.
The purpose of the present study was to examine, if the resin composite repeated pre-heating cycles can affect the optical properties of the material, especially the color and the translucency.
Materials and methods
In the current study, four different resin composite systems were selected: two monochromatic systems, Tetric EvoCeram and G Aenial anterior and two enamel-dentin systems, Enamel Plus HRi and Inspiro. The shade that was selected was, A2 for Tetric Evo Ceram and G Aenial and dentin A2 for Enamel Plus HRi and Inspiro. The device used for the preheating of the materials, was Ena Heat (Micerium, Genoa, Italy), and the temperature used, was 55°C. A total of 160 samples, were constructed as follows:
For each resin composite, 5 specimens were made at room temperature, which was the control group, 5 specimens were made after 3 preheating cycles, at 55°C, 5 samples after 6 cycles etc., until the number of 21 cycles. Each specimen was fabricated by using a cylindrical silicone matrix, 10 mm in diameter and 1 mm high. The free surface of the resin was covered, by a transparent celluloid tape and a glass cover, in order to compress the resin into the matrix. Then, the glass cover was removed and each specimen was polymerized for 40s, with the bluephase style Led lamp (Ivoclar Vivadent AG, Schaan, Liechtenstein), at 1100 mW/cm2. After the removal of the celluloid tape, each specimen was removed from the matrix and polished up to 1000 grit, by using sandpapers and then was stored in deionized water, at 37°C, for 24 hours.
The optical properties studied, were the color and the translucency of each specimen. Three successive measurements for each specimen, on a white substrate and 3 measurements on a black substrate were taken, with a hand-held intraoral spectrophotometer, Spectroshade Micro, (MHT Optic Research AG, Niederhasli, Switzerland). The L, a and b color parameters of the CIE Lab were recorded.
Color differences were calculated with the CIEDE2000 equation:
ΔE00 = [(ΔL'/kLSL)2+(ΔC'/kCSC)2+(ΔH'/kHSH)2+RT(ΔC'/kCSC) (ΔH'/kHSH)]1/2
Translucency parameter was calculated with the equation:
TP = [(Lb-Lw)2 + (ab-aw)2 + (bb-bw)2] ½
where b and w refer to black and white substrates respectively. Then, the color changes (ΔΕ) and the translucency changes (ΔTP) were calculated, for each specimen, between the control group and the others.
The non-parametric Friedman test was performed to compare the repeated measures (different cycles) of ΔΕ, TP and ΔTP values, per type of composite resin. In addition, when Friedman test yielded significant results, post-hoc Mann-Whitney U tests were conducted, to detect pairwise significant differences. The statistical level was set at 5% (p<0.05).
Results
The non-parametric Friedman test, showed no statistically significant differences, for the ΔΕ for resin tetric EvoCeram, but statistically significant differences for the ΔΕ of the other three resins and statistically significant differences for the TP for all the resins.
The mean ΔE00 value for Tetric EvoCeram, between the control group and the group of 21 preheating cycles was 0.30, which is not statistically significant. The mean ΔΕ00 value for G-aenial, between the control group and the group of 21 preheating cycles was 1.08, which is statistically significant. The mean ΔΕ00 value for Enamel Plus Hri, between the control group and the group of 21 preheating cycles was 2.33, which is also, statistically significant. Finally, the corresponding ΔΕ00 value for Ιnspiro, was 0.77, which is statistically significant.
The mean value of translucency, between the control group and the group of 21 cycles, increased for Tetric EvoCeram, while the corresponding values for the other three materials, seemed to decrease. The ΔTPab value for Tetric EvoCeram, between the control group and the group of 21 preheating cycles, was 2.31. The corresponding ΔTPab value for G-aenial, was 0.68. The corresponding ΔTPab value for Hri, was 3.92. Finally, the ΔTPab value for Inpsiro, between the control group and the group of 21 preheating cycles, was 0.28.
Conclusions
For the majority of the materials tested, the color and translucency differences, were in clinical acceptable range. Enamel Plus Hri, showed the most significant differences, in both color and translucency.
From the results of this study, it cannot be assumed, that repeated preheating cycles can significantly alter the color and translucency of resin composites, in a clinically significant range.
