Quantifying light energy delivered to a Class I restoration.

PURPOSE: To measure the amount of light energy that dental students actually deliver to a Class I preparation in a dental mannequin. MATERIALS AND METHODS: Approval for the study was obtained from the Dalhousie University Health Sciences Research Ethics Board. Each of 20 third-year dental students light-cured a Class I preparation in tooth 27 in a mannequin head. A photodetector located at the bottom of the cavity preparation measured how much light would be received by a restoration. Each student cured the simulated restoration for 20 seconds using a quartz-tungsten-halogen curing light (Optilux 401). The irradiance received (mW/cm2) was recorded in real time, and the energy per unit area (J/cm2) delivered to the detector by each student was calculated. The students were then given detailed instructions on how to effectively use the curing light, and the experiment was repeated. RESULTS: When the curing light was fixed directly over the tooth, the greatest amount of light energy delivered to the detector in 20 seconds was 13.9 +/- 0.4 J/cm2. Before instruction, the students delivered between 2.0 and 12.0 J/cm2 (mean +/- standard deviation [SD]: 7.9 +/- 2.7 J/cm2). After receiving detailed instructions, the same students delivered between 7.7 and 13.4 J/cm2 (mean +/- SD: 10.0 +/- 1.4 J/cm2). A paired student"s t test showed that instruction resulted in a significant improvement (p < 0.001). CONCLUSIONS: Although instruction yielded improvements, the mean energy delivered was much less (7.9 J/cm2 before instruction and 10.0 J/cm2 after instruction) than the expected 13.9 J/cm2. To maximize the energy delivered, the operator should wear eye protection, should watch what he or she is doing and should hold the light both close to and perpendicular to the restoration.

Effect of configuration factor on shear bond strengths of self-etch adhesive systems to ground enamel and dentin.

Self-etch bonding systems are easy to use and popular in dental practice. The current study examined the in vitro shear bond strengths to dentin and ground enamel of four self-etch bonding systems and a two-step etch-and-rinse bonding system. Two hundred extracted non-carious human molars were used. Approximately 0.5 mm of enamel was removed from the buccal surface of 100 teeth and the bond strengths of this enamel surface were determined. The buccal surface of the remaining 100 teeth was ground away to create a standardized smear layer on dentin. Five adhesive systems were used: Adper Single Bond Plus (ASB): two-step etch-and-rinse); Adper Scotchbond SE (AS), Clearfil SE Bond (CSE-both two-step self-etch); XENO V (X) and Adper Easy Bond (AE): both one-step self-etch). Filtek Z250 composite was bonded to the tooth using each adhesive system in a low configuration (C) factor (0.2) and a high C-factor (4.4) mold (10 teeth in each group). The specimens were thermal cycled 2,000x, then subjected to a shear bond strength test. The data were compared with analysis of variance using the Fisher's PLSD multiple comparison tests. A three-factor ANOVA showed that, overall, the shear bond strength was significantly higher in the low C-factor group 4.33 MPa (p < 0.0001). There was also a significant difference in the shear bond strengths among the bonding systems (p < 0.0001). The higher C-factor molds had the same adverse effect on all bonding systems and on both enamel and dentin, but the bonding systems acted differently on enamel and dentin (three-factor ANOVA p < 0.0001). The two-step etch-and-rinse system (ASB) consistently delivered the highest bond strengths (34.6-41.5 MPa). Fisher's PLSD comparisons showed that, in the high C-factor mold, there was no significant difference between the shear bond strengths of SB, EB and CSE to dentin, and SB, X and SE to enamel (p > 0.05). The one-step self-etch AE system delivered the lowest shear bond strengths (23.9 MPa) to enamel (p < 0.05). The two-step self-etch system AS delivered the lowest shear bond strengths (23.9 MPa) to dentin (p < 0.05).