Scientific Arl:icle Argon laser irradiation and acidulated phosph.ate fluoride treatment in caries-like lesion formation in enamel: an in vitro study

The purpose of this in vitro study was to determine the combined effects of argon laser irradiation (ArI) and acidulated phosphate fluoride treatment (APF) on caries-like lesion formation in human enamel. Each specimen was divided into tooth quarters with each quarter assigned to one of four groups: 1) control; 2) ArI Only; 3) ArI before APF treatment; 4) APF treatment before ArI. After a fluoride-free prophylaxis, acid-resistant varnish was applied to the tooth quarters, leaving sou nd enamel windows exposed on buccal and lingual surfaces. Argon laser irradiation was at 2 watts for 10s (100 J/cm2 ). AP F treatment was with a 1.23 % APF gel for 4 min. Lesions were created in sound enamel windows with an acidified gel. After lesion formation, sections were obtained and imbibed with water for polarized light study. Body of the lesion depths were determined and compared among the four groups. Lesion depths were: 195 + 23 ~m for control; 129 + 17 ~m for ArI only; 96 + 14 [~mfor ArI before APF; and 88 + 11 I~mfor APF before ArI. Significant differences (P < 0.05) were found between the control group and all treatment groups, and between the Arl only group and both combined AP F and Arl groups. Significant difference (P > 0.05) was not found between the ArI before APF and the APF before ArI groups. Laser irradiation alone reduced lesion depth by 34% compared with control lesions. When ArI was combined with APF treatment, lesion depth decreased by more than 50% compared with control lesions, and by 26 to 32% when compared with lased-only lesions. Combining ArI and APF treatment significantly enhances the resistance of sound enamel to an in vitro cariogenic challenge. (Pediatr Dent 17:31-35, 1995) A lthough recent epidemiologic studies have reported a decline in dental caries in the pediatric and adolescent population in the United States, dental caries represents the most prevalent disease process occurring during childhood and adolescence, with only about 15% of 17-yearoolds remaining caries free. 1 Especially disconcerting is the fact that approximately one-sixth of this population accounts for two-thirds of the total caries experience2 These facts emphasize the need for optimizing current cariespreventive regimens and introducing innovative preventive techniques. The role of systemic and topical fluoride in the decline of caries is well known. ~4 Fluoride has become the mainstay in the battle against caries, with more than 60% of children residing in communities with optimal water fluoridation. 2, 3 In addition to professionally applied topical fluorides, fluoridated dentifrices and mouth rinses are readily available without prescription. More recently, the role of lasers in caries prevention has been explored. Several different types of lasers have been shown to reduce enamel solubility and dissolution rates substantially, as well as affect caries-like lesion formation,s-~5 Laser irradiation of sound enamel at relatively low energy levels results in significant resistance to a cariogenic challenge,~-15 and avoids thermal temperatures ~6 that would harm both hard and soft tissue, including the dental pulp. It would appear that laser irradiation of enamel in combination with topical fluoride application may provide a synergistic effect on caries resistance in enamel and provide further benefit over either treatment modality alone. The purpose of this in vitro study was to determine the combined effect of argon laser irradiation (ArI) and acidulated phosphate fluoride (APF) treatment on caries-like lesion formation in human dental enamel using polarized light techniques. Methods and materials Twenty caries-free human molar teeth were selected for this in vitro study. The buccal and lingual surfaces were examined with a binocular, dissecting microscope at a magnification of 16x to ensure that these surfaces were free of clinically detectable White spot lesions. The specimens were sectioned into tooth quarters, then quarters from each tooth were assigned to one of four treatment groups: 1) control (no treatment); 2) ArI only; 3) ArI before APF treatment; and 4) APF treatment Pediatric Dentistry 17:1, 1995 American Academy of Pediatric Dentistry 31 TABLE. ARGON LASER IRRADIATION AND ACIDULATED PHOSPHATE FLUORIDE TREATMENT~ EFFECT ON CARIES-LIKE LESION FORMATION IN ENAMEL Surface Zone Depth Body of:Lesion Depth Reduction in Body (Mean +SD) (Mean .-+ SD) of Lesion Depth Control lesions 8 -+ 3 ~tm a-c 195 -+ 23 ~tma-f ~--]~ ~ Argon laser irradiation 16 5 ~tm a 129 17 p,md’g’h _A 51% 5~ Argon laser irradiation 18 4 [xm b 96 14 ~tme, g ~ before APF treatment APF treatment before 21 _+ 5 ~tm c 88 -+ 11 p~m Lh -argon laser irradiation 32% -~ I ANOVA and DMR-paired sample results: means with same letters are significantly different at P< 0.05. before ArI. Following a fluoride-free prophylaxis, an acid-resistant varnish was placed, leaving two windows of sound enamel exposed on the buccal and lingual surfaces. Argon laser irradiation (HGM Corporation, Salt Lake City, UT) of the sound enamel windows was at 2 watts for 10 sec (100 Joules/cm2) using a 320~tm bare fiber with an effective spot size of 5 mm. APF treatment was with a 1.23% APF gel (Oral-B Laboratories, Redwood City CA) for 4 min. After the fluoride treatment, the APF gel was removed by a copious, airwater spray rinse followed by a 24-hr deionized-distilled water rinse. Caries-like lesions were created in the sound enamel windows using a dialyzed-reconstituted acidified gelatin gel containing 1.0 mM calcium, 0.6 mM phosphate and < 0.05 mM fluoride at pH 4.25 + 0.02.17 Following a 10-week exposure period to the artificial caries medium, longitudinal sections were prepared from the tooth quarters for polarized light evaluation. The sections were imbibed with water and photomicrographs were taken. Mean surface zone and body of the lesion depths were obtained using a digitized tablet and taking five measurements along the inner aspect of the surface zone and body of the lesion. Forty paired lesions from each of the four treatment groups were available for statistical analyses. Because of the paired research design, the surface zone and body of the lesion depths from the treatment and control groups were compared using analysis of variance and Duncan’s multiple range analysis for paired samples, thereby limiting tooth-to-tooth variability in the statistical analysis.