Root Surface Caries-preventive Effects Of Combining Pulsed Nd: YAG Laser And Sodium Fluoride Solution

Objective: Caries is a kind of familiar and high incident disease, seeking for a more simple and effective method is important. It is well known that Nd:YAG laser and fluoride have caries-preventive effects. The purpose of this study in vitro is to evaluate preventive effects of combining pulsed Nd:YAG laser and 2%NaF solution the root caries by observing the morphological changes and the progression of primary root surface caries with scanning electron microscope(SME) and light microscope(LM) ; and to seek better caries-prevention methods. Methods: Forty-six caries-free(diagnostic standard: the surface of cementum is lubricous and its color, character, shape are normal ) permanent human premolars extracted for orthodontic reasons are selected for this study. Bloodiness,soft tissues and calculus on the root surface are absolutely eliminate and all the specimen are deposited in 10% formaldehyde solution with ketoconazole (nigoral), stored in 4℃ refrigeratory for use. Each specimen is coated with acid-resistant nail varnish leaving a rectangular window of 3×3mm on adaxial root surface near CEJ area. Then, they are randomly divided into four groups and disposed respectively: control group( dipping in distilled water 37℃constant temperature for 5min ), NaF treated group( dipping in 2%NaF solution 37℃constant temperature for 5min), laser irradiated group(laser irradiated), laser and NaF related group(dipping in 2%NaF solution 37℃constant temperature for 5min after laser irradiated). Laser irradiation: using air gun dry teeth and coating mediator(Chinese ink) on window surface; irradiation parameters: power(P): 0.5W, time(t): 30s, repetition power per second (pps): 15pps, irradiation area: 3mm×3mm, energy density (ED)= P×t／A,33.3mJ/cm2 , repeating twice. Symmetrical scanning irradiation, light fibre approaching but not touching root surface; using LM-91 interpolator to proofread laser device for precision, power range: 0~200W. Choosing one tooth from control group and laser irradiated group respectively, using emery disc chip teeth into 4mm×4mm diamonds including the window, fixation, dehydration, drying for SME observing morphology of normal and laser irradiated root surface. Artificial test: in 37deg conditions, resuscitating S.mutans stored in －20℃ refrigeratory then inoculating on blood culture medium, 37℃constant temperature cultivating for 2days. Choosing a little bacteric gobbet, observing under light microscope to confirm S.mutans. inoculating in cultivation fluid for 1day to make bacteric fluid . Irridiating left forty-four teeth with high intensity ultraviolet radiation for 60min librating them to make sure all the teeth surfaces are listerized .Every the specimen individually immerge in cultivation fluid, after 10days are taken out. Selecting one specimen from each group to obseve morphological changes of root surface after artificial caries. Others are abraded into slices that are translucent and 100μm depth, and made into discs by balata for light microscope observation. Observing the depths of caries lesions and exterior layers, at the same time, mensurating theirs numerical value for statistical disposal. Results: SME observation show: normal root surfaces take on boskage-like form and often attend by a little of spots; the root surfaces are clear and have significant changes such as mang dense irregular honeycomb-like structures globose protuberances and lava structures and so on ;after laser irradiation. And there is obviously difference between root surface laser irradiated with mediator and root surface with no-mediator, the former more visible. The changes after artificial caries are different too: severe caries lesion can be observed in control group with demineralization , a mass of matrix fibre ruptured. The lesions of root surfaces with NaF or laser irradiated alone is lighter than control group,with lesser matrix fibre ruptured. Laser irradiated and NaF related group caries lesion is lightest hardly any matrix fibre ruptured. Light microscope observation...