An in vitro study of enamel surface microhardness following argon laser irradiation and acidulated phosphate fluoride treatment.

PURPOSE The purpose of this in vitro study was to evaluate the effect of low-fluence argon laser (AL) irradiation and acidulated phosphate fluoride (APF) gel treatment on enamel microhardness. METHODS Twelve mandibular permanent molars were selected for this study. The teeth were sectioned generating 4 flat enamel surfaces per tooth. The flattened enamel tooth surfaces were randomly assigned to 1 of 4 treatment groups: (1) no treatment (control); (2) the enamel surface was exposed to a 4-minute, 1.23% APF gel treatment; (3) the enamel surface was exposed to AL irradiation of 11.5 J/cm2 (0.23 1-W, 5-mm beam size, 10 seconds); and (4) the enamel surface was exposed to the same AL irradiation followed by an APF gel treatment. Using a Buehler Micromet II Digital Microhardness Tester, Knoop hardness was determined using a 1,000-gram load and a dwell time of 12 seconds. Five hardness values were recorded for each enamel surface. Data were analyzed using ANOVA and Fisher's least significant difference post-hoc test. RESULTS Mean surface hardness values (+/-SD) were 298+/-37 Knoop hardness (HK) for the no treatment (control), 270+/-70 HK for the APF-only group, 316+/-5 HK for the AL-only group, and 317+/-25 HK for the AL-before-APF group. The AL-only and AL-before-APF groups had significantly higher (P<.05) surface hardness values vs the APF-only group. CONCLUSIONS Enamel surface microhardness is higher when exposed to low AL irradiation only or AL before APF vs a no treatment (control) enamel surface.