Duncan Yu

Combined Effects of Laser Irradiation and Chemical Inhibitors on the Dissolution of Dental Enamel

It has previously been shown that the susceptibility of human teeth to acid dissolution can be reduced by the presence of various chemical agents in the dissolution medium or by pretreatment of the teeth with laser irradiation. Now synergism between these two approaches to improving acid resistance has been demonstrated. Extracted human teeth were irradiated with a continuous-wave carbon dioxide laser at a wavelength of 10.6 microns. Energy doses of either 65 or 130 J/cm2 given over periods of 2 or 4 s, respectively, were applied and the teeth subjected to a severe acid challenge (0.1 M acetate buffer, pH 4.5, no calcium or phosphate common ion present) for 24 h. Mineral loss was assessed by measurement of mineral density profiles with quantitative microradiography. Experiments were carried out in the presence or absence of three chemical inhibitors with distinctly different mechanisms of action: ethane-1-hydroxy-1, 1-diphosphonic acid, fluoride, and dodecylamine HCl. Laser irradiation alone was found to lead to increased resistance of the teeth to acid challenge, with the higher energy dose being more effective than the lower dose. Each of the chemical inhibitors was effective on both lased and unlased teeth, with the percent reduction of dissolution greater when the inhibitors were applied to teeth lased with an energy dose of 130 J/cm2 which were already more resistant to acid challenge than were unlased teeth or teeth lased with a dose of 65 J/cm2.(ABSTRACT TRUNCATED AT 250 WORDS)

Initial Dissolution Rate Studies on Dental Enamel after CO2 Laser Irradiation

The influence of CO 2 laser irradiation on the dissolution behavior of human dental enamel has been investigated. Human enamel was irradiated by a continuous-wave CO 2 laser at 10.6 μm and initial dissolution rates (IDRs) were measured in 0.1 mol/L acetate buffer, pH = 4.5, both with and without calcium and/or phosphate common ion, by means of a rotating disk assembly. The effects of (1-hydroxyethylidene) bisphosphonic acid (EHDP), fluoride (F), and dodecylamine HCI (DAC) at various levels upon the IDR were also determined. All of the findings were consistent with the hypothesis that CO2 laser irradiation converts dental enamel to hydroxyapatite (HAP) possessing site #2 character (Yamamoto et al., 1986). The dissolution driving force function, KHAP = aca 10apO4 6aOH2, was found to have a value of 10-129.9 after being lased, as compared with 10-121.4 before being lased. The IDR values for EHDP (3 mmol/L) and DAC (3 mmol/L) were essentially zero as expected for site #2 HAP. For solution F, the deduced dissolution driving force function, K FAP = aca 10aPO46aF2 was 10-128.6 after being lased as compared with 10-116.3 before being lased. These results all support the hypotheses (1) that laser irradiation may convert the surface of human dental enamel to an apatite of significantly lower effective solubility (i.e., site #2 HAP) than that of unlased enamel; and (2) that there is significant synergism between laser treatment and these chemical dissolution rate inhibitors (again consistent with site #2 HAP). Simple model calculations indicate that, in both the presence and absence of fluoride, these laser-induced changes in the driving force for dissolution should dramatically lessen the susceptibility of enamel to the types of acid challenge that might be encountered in the mouth

Argon laser effect on demineralization of human enamel

Previous studies have recorded the reduction of caries-like lesions in extracted human teeth that have been irradiated with CO2 laser. Other studies have shown a decrease in dissolution rate of enamel that has been irradiated with CO2 laser and acid resistance. This study was conducted to evaluate the effects of Argon laser irradiation on acid resistance and demineralization of dental enamel. Human enamel was laser irradiated with approximately 60 J/cm2 and 120 J/cm2. The amount of demineralization was determined in a rotating disk assembly (0.1 M acetate buffer, pH-4.5) for 24 hours and the results determined and plotted against the nonlased control using microradiographs and computerized imaging. The amount of dissolution of tooth structure lost to demineralization in 4.5 pH acid bath in a 24 hour period was reduced from approximately 140 micrometers to approximately 70 micrometers . This study show that demineralization is reduced when human enamel is exposed to Argon laser irradiation.

Computer simulation of surface temperature profiles during CO2 laser irradiation of human enamel

The surface temperature profiles of human enamel blocks following laser irradiation are examined using a mathematical model. A physical model for calculating this surface temperature is developed and then solved by the Laplace transform technique. The enamel block is modeled as a homogeneous cylinder in one dimension with the entire surface exposed to laser beam irradiation. Both the photon absorption/transmission and convective heat loss are taken into consideration in the proposed model. This model allows the surface temperature to be calculated under arbitrary combinations of laser wavelength, pulse pattern, and energy density. Results indicate that (1) surface temperature depends on the wavelength, energy density, and duration of the pulse; (2) high surface temperatures (~ 300°C) can be achieved with associated inside temperature changes of less than 5°C; and (3) the surface temperature depends strongly on the environmental heat transfer coefficients. These results will facilitate the rational development of lasers as potential tools in preventive dentistry.

Comparison of three lasers on demineralization of human enamel

Previous studies have recorded the reduction of caries-like lesions or demineralization in extracted human teeth that had been irradiated with CO2 laser, Nd:YAG laser, and Argon laser. This study was conducted to evaluate the effects of three different cw lasers on acid resistance and demineralization of dental enamel. Human enamel was laser irradiated with either Argon, CO2, or Nd:YAG energy densities of 60 - 65 J/cm2 or 120 - 130 J/cm2. The amount of demineralization was determined in a rotating disk assembly (0.1 M acetate buffer, pH - 4.5) for 24 hours and the results determined and plotted against the non-lased control using microradiographs and computerized imaging. The amount of dissolution of tooth structure lost to demineralization in 4.5 pH acid bath in a 24 hour period was reduced from approximately 140 microns for the unlased control to approximately 90 microns for the Argon laser and 70 microns for the CO2 laser at 60 - 65 J/cm2. At 120 - 130 J/cm2 the results were: 120 microns for the Nd:YAG, 70 microns for the Argon, and 45 microns for the CO2 laser. This study shows that demineralization is reduced significantly in vitro when human enamel is exposed to Argon and CO2 laser irradiation.