Effect of CO2-laser-irradiation and Fluoride-application on Root Surface Demineralization

Objective: The purpose of this study was to evaluate the acid resistance of root surface with and without various conditioned CO₂ laser irradiation and various concentrations of fluoride application.

Method: Thirty-five roots of extracted human premolars were cleaned, and all surfaces except for a window (2x3 mm) on the proximal surfaces were coated with an acid-resistant varnish. The root specimens were divided into 7 experimental groups (n=5) as shown in the table below. After each treatment was applied to the windows, the specimens were subjected to a pH-cycling test, which the roots were placed in a cycle of demineralization (pH4.7 for 18 hours) and remineralization (pH7.0 for 6 hours) for 2 days. From each window, 3 sections (100μm thick) were obtained. The lesion-depth (LD) on the sections was measured under polarized-light-microscopy. Data were statistically analyzed with ANOVA and the Tukey’s post-hoc-test. 

Result: Results of the LD are presented in the table below. The LD values of group 3, 4, 5 and 6 were significantly lower than that of the control (p<0.05), however, there were no significant differences among groups 1, 2 and the control (p>0.05).

Group	Condition of laser irradiation				Fluoride application	Lesion-depth (μm) (Mean ± S.D.)*
	Power	Duration	Interval	Energy
1	0.5W	5msec	10msec	17J/cm2	None	41.0 ± 3.4 a,b
2	0.5W	10msec	10msec	25J/cm2	None	42.3 ± 2.9 a,b
3	0.5W	50msec	10msec	41J/cm2	None	38.4 ± 10.8 b
4	None				0.05%NaF	37.9 ± 4.2 b,c
5	None				0.2%NaF	32.6 ± 3.4 c,d
6	None				2.0%NaF	28.3 ± 3.2 d
Control	None				Non	45.9 ± 2.7 a

* The same superscript letters indicate no significant difference (p>0.05).

Conclusion: The fluoride application to root surface significantly increased the acid resistance, but the laser irradiation except 41J/cm² showed no effect on the acid resistance increase.