Purpose: This study investigated the effects of curing light convergence and irradiation distance on the microtensile bond strength of resin composite to dentin using three light emitted diode (LED) light-curing units.
Materials and Methods: Three light curing units were investigated in this study; Flash Lite (FL), Pencure (PN), and an experimental light-curing hand-piece developed for Dentaport ZX (DP), which was designed to emit convergent light. The light intensity of each unit was measured at irradiation distances up to 10 mm. For bond strength test, bonding area was demarcated on prepared dentin using black plastic rings, in which a self-etching adhesive and a resin composite (Clearfil Liner Bond IIΣ and Clearfil Photo Core) were light-cured at different distances (2, 4, 6, 8, and 10 mm). After 24 hours storage in 37ºC water, the specimens were sectioned into beams. Microtensile bond strength was then measured and failure modes were observed.
Results: The light intensity of all units significantly decreased with increasing irradiation distance. DP showed a smaller range of decrease, significantly higher intensity values at irradiation distances over 2 mm and significantly higher bond strengths at 8 and 10 mm compared to FL and PN (p<0.05). Percentage of cohesive failures in dentin decreased at 8 and 10 mm for FL and PN. Irradiation distance did not significantly affect light curing performance of DP.
Conclusion: Convergent light-irradiation was effective in maintaining adequate light intensity and bond strength as the irradiation distance increased.

Purpose: The aim of this study was to assess the efficacy of alkali-ion water (AW) on removal of Streptococcus mutans (S. mutans) single species biofilms from bovine enamel surfaces in vitro.
Materials and Methods: AW solutions were produced by electrolyzing tap water using a water electrolyzing device. S. mutans biofilms were formed on bovine enamel blocks in an oral biofilm reactor for 8 hours and 12 hours, respectively. AW solutions, AW-H (pH 11.5) and AW-L (pH 10.5), were tested for their efficacy in dissolving water insoluble glucans (WIG) from the above biofilms. Sodium hydroxide solution (NaOH pH 13.5) and mineral water (MW pH 7.5) were also compared as controls. Biofilms were tried to disintegrate employing two different methods; 1) assisted by a driving force (shaking) which was a simulation of gargling by an adult, and 2) incubation without applying any driving force to observe biofilm disintegration effect on self-penetration by the solutions on their sole chemical potentiality.
Results: One-way ANOVA and Tukey’s HSD tests indicated that amount of dissolved glucan was significantly (p<0.05) more in AW-H compared to MW and AW-H yielded significant differences (p<0.05) in all tests with or without application of a driving force equivalent to NaOH. AW-L also dissolved more glucan than MW. Longer incubation period without any driving force dissolved more glucan by AW time dependently.
Conclusion: It was suggested that AW has the efficacy to remove a remarkable amount of biofilms by disintegrating glucans from the S. mutans artificial biofilms.

Purpose: This in vitro study assessed the potency of cariogenic biofilms in developing secondary caries in human extracted teeth.
Materials and Methods: Cavities (3x2x2 mm³) were prepared in the blocks of mid-buccal human extracted molars. Cavities were filled with Clearfil AP-X composite with (SE-Bond) or without (No-bond) application of an adhesive. Biofilms were formed on both groups of specimens using three species of cariogenic bacteria inside an oral biofilm reactor for 20 hours and specimens were further incubated separately for 7 days or 30 days dividing into two groups. Developed secondary caries lesions were examined using fluorescence microscope and scanning electron microscope. Sizes of the lesions were measured by using image analysis software. Data were statistically analyzed by one-way ANOVA and Turkey’s HSD methods.
Results: The secondary caries were visible at resin-enamel interfaces in all cases including the 7-day specimens. Photomicrographs and data on image analysis clearly showed that the lesion size was smaller in SE-Bond sample compared to No-bond samples, which was statistically significant (p<0.05).
Conclusion: It is suggested that sucrose supplemented biofilms of mutans streptococci have the potency in developing secondary caries lesion within a week time indicating high caries risks in case plaque-biofilms left undisturbed in the oral cavity.