Wafa El-Badrawy

Chemical versus dual curing of resin inlay cements.

Dual-cure inlay resin cements polymerize both chemically and through light activation; however, clinically some aspects of the cement are not readily accessible to the light source. This study investigated the degree of cement hardening achieved through chemical curing only versus dual curing and the effect of inlay thickness on cement hardness. Disks 6 x 2.5 mm were prepared from seven commercially available cements. Eight specimens were prepared from each material; half of the specimens were cured chemically only, and the remainder were dual-cured. Knoop hardness measurements were then recorded at 1-hour, 1-day, and 1-week intervals. In addition, 24 specimens of the same dimensions were prepared from each cement. Twelve specimens were dual-cured through resin composite spacers of varying thicknesses (1 to 6 mm), and the others were cured through similar ceramic spacers, and hardness measurements were recorded. Multivariate analysis of variance revealed significant differences in hardness of chemically cured versus dual-cured specimens at the 5% level of significance for all examined cements. Significant differences were also found in the hardness of specimens dual cured through ceramic or resin composite spacers 2 to 3 mm in thickness or more versus those that were dual cured without spacer regardless of the spacer material. It is concluded that chemical curing alone was not sufficient to achieve maximum hardening of the examined cements. Cement hardness was significantly reduced when inlay thickness was 2 to 3 mm or more.

Effect of LED Light-curing on the Relative Hardness of Tooth-colored Restorative Materials

OBJECTIVE To determine the relative hardness of GI-based restorative materials using both LED and QTH curing lights at different post-irradiation intervals. METHODS Four restorative materials (Z250, Beautifil, Dyract AP and Fuji II LC) with shade A3.5 were tested in conjunction with three LCUs (Astralis 3, Blue phase and Radii). The specimens were prepared using specially constructed molds, irradiating only the top surface to an equivalent energy density (J/CM). Vickers microhardness measurements were performed for both the top and bottom surfaces of all specimens following dry storage for 15 minutes in the dark. The measurements were repeated after 24 hours and 7 days. Mean VHNs and SD of the top and bottom surfaces of each specimen were calculated. Relative hardness values (RH) were also determined and mean RH was calculated for each group. RESULTS The top surface of the Z250, Beautifil and Dyract materials were significantly harder than the bottom surface (p < 0.05) with all LCUs and at all time intervals. Conversely, a different trend was observed with Fuji II LC, where bottom surface VHNs were significantly higher than top surface values (p < 0.05). Blue phase was the only LCU that recorded RH values above 80% for all tested material at all post-irradiation intervals. CONCLUSIONS A high-intensity LED LCU used for 10 seconds resulted in RH values greater than 80%, with all four restoratives tested indicating a sufficient degree of monomer conversion with such a short curing cycle.

Effect of pretest storage conditions of extracted teeth on their dentin bond strengths

STATEMENT OF PROBLEM It is becoming increasingly difficult to obtain sufficient freshly extracted human teeth to utilize in in vitro studies, particularly for bonding investigations. PURPOSE The purpose of this study was to investigate the effect of different storage conditions for human extracted teeth prior to their use in microtensile bond strength (microTBS) testing. MATERIAL AND METHODS Thirty incisors were divided into groups according to their storage time and condition. The first group consisted of freshly extracted teeth. Teeth of the second group were stored in chloramine-T at 4 degrees C for 2 years +/-1 month. The last group was stored dry for up to 2 years +/-2 months, after which teeth were rehydrated in distilled water for 2 weeks before use. All teeth were disinfected using 0.5% chloramine-T. Dentin surfaces were exposed and then bonded using Scotchbond Multi-Purpose or Clearfil SE Bond to composite resin foundations (Esthet-X). Following 24-hour storage, bonded teeth (n=30) were sectioned into beams with a cross-section of 0.9 +/-0.1 mm(2) and subjected to microTBS testing using a microtensile testing machine (Micro Tensile Tester). Data were calculated and statistically analyzed using Kruskal-Wallis and Mann-Whitney tests (alpha=.05). Failure modes were determined using a stereomicroscope at x40 magnification. RESULTS Statistical analysis revealed no significant difference between the different storage conditions nor between the 2 adhesive systems for each storage condition (P>.05). Modes of failure for all tested groups were predominantly adhesive followed by mixed. CONCLUSIONS Within the limitations of this study, it was concluded that aging of teeth and storage conditions had no significant effect on dentin microtensile bond strength to composite resin.

Cuspal Deflection of Premolars Restored with Bulk‐Fill Composite Resins

OBJECTIVE This in vitro study compared cuspal deflection of premolars restored with three bulk-fill composite resins to that of incrementally-restored ones with a low-shrinkage silorane-based restorative material. MATERIALS AND METHODS Forty freshly-extracted intact human upper premolars were used. Reference points at buccal and palatal cusp tips were acid-etched and composite rods were horizontally bonded to them (TPH-Spectra-HV, Dentsply). Two acrylic resin guiding paths were made for each premolar to guide beaks of a digital micrometer used for cuspal deflection measurements. Standardized MOD cavities, 3 mm wide bucco-lingually and 3.5 mm deep, were prepared on each premolar. Prepared teeth were then equally divided into four groups (n = 10) and each group was assigned to one of four composite resin (QuiXX, Dentsply; X-tra fil, Voco; Tetric EvoCeram Bulk Fill, Ivoclar Vivadent; low-shrinkage Filtek LS, 3M/ESPE). Adper Single Bond-Plus, 3M/ESPE was used with all bulk-fill restoratives. LS-System Adhesive, 3M/ESPE was used with Filtek LS. For each prepared premolar, cuspal deflection was measured in microns as the difference between two readings between reference points before and after restoration completion. Means and SDs were calculated and data statistically-analyzed using One-way ANOVA and Tukeys test. RESULTS Filtek LS showed the lowest mean cuspal deflection value 6.4(0.84)μm followed by Tetric EvoCeram Bulk Fill 10.1(1.2) μm and X-tra fil 12.4(1.35)μm, while QuiXX showed the highest mean 13(1.05)μm. ANOVA indicated significant difference among mean values of groups (p < 0.001). Tukeys test indicated no significant difference in mean values between QuiXX and X-tra fil (p = 0.637). CONCLUSIONS Tetric EvoCeram Bulk Fill had significantly lower mean cuspal deflection compared with the two other bulk-fill composite resins tested. Filtek LS had the lowest significant mean cuspal deflection in comparison to all tested bulk-fill restoratives. CLINICAL SIGNIFICANCE The use of Tetric EvoCeram Bulk fill composite resin restorative for class II MOD cavities resulted in reduced cuspal deflection in comparison to the two other bulk-fill composite resins tested. The silorane-based Filtek LS restorative resulted in the least cuspal deflection in comparison to all tested bulk-fill composite restoratives.