Enhancing Caries Resistance in Occlusal Fissures with a Short-Pulsed 9.6μm Carbon Dioxide Laser and Fluoride

Background and Objectives: High caries prevalence in occlusal pits and fissures warrants novel prevention methods. Treatment of occlusal surfaces with a short-pulsed CO2 9.6 µm wavelength laser has previously been proposed as a method for caries prevention. The objective of the in vitro study part was to determine which non-destructive diagnostic method is clinically applicable and reliable at resolving early enamel changes in occlusal fissure caries created in the laboratory.The objective of the in vivo study part was to conduct a single-blinded, randomized clinical trial of occlusal caries inhibition using short-pulsed 9.6µm CO2-laser irradiation and fluoride varnish (FV) compared to FV alone, quantified by ICDAS II visual inspection, DIAGNOdent, quantitative light-induced fluorescence (QLF), optical coherence tomography (OCT), and SoproLife.In Vitro Methods and Results: A sample of 20 extracted human molars were measured before and after demineralization-remineralization pH-cycling with ICDAS II visual inspection, DIAGNOdent (Kavo, Charlotte, NC), QLF (Inspektor Research Systems, Inspektor Pro, Amsterdam, Holland), SoproLife white daylight and blue light-induced fluorescence modes (Acteon Imaging, SoproLife, Marseille, France), OCT (NRC-IBD, Winnipeg, MB) and polarized Raman spectroscopy (PRS). Per tooth, one part of the fissure was subjected to laser treatment using a short-pulsed CO2 laser at 9.6 μm wavelength with a fluence of 3.5 J/cm2, 20 Hz pulse repetition rate, 20 µs pulse duration, angulated handpiece, and focus diameter of 600 µm, while the other fissure part was left untreated as control. The teeth were subjected to a demineralization-remineralization pH-cycling for 9 days. Cross-sectional micro-hardness testing was done as a gold standard to compare results with findings from the other detection methods used. Due to the small sample size reported, the trend observed was that laser treated fissures demonstrated a smaller relative mineral loss ΔZ than the controls. QLF findings followed a similar trend. Using a rotary catheter probe, OCT measurements were acquired from the various fissures to generate circularly mapped OCT depth images. PRS measurements of parallel- and cross-polarized spectra were acquired with a Raman microscope system. Preliminary OCT images showed differences in the initial air-tooth interface, with PRS results indicating a change in the surface property along with biochemical alterations after pH-cycling. Also following pH-cycling, an increase in the OCT subsurface light backscattering intensity in the control fissures was observed compared to the laser test fissures. Porphyrin based fluorescence methods like DIAGNOdent and SoproLife, respectively demonstrated only additional light scattering due to the demineralization process. In Vivo Methods and Results: Twenty high caries risk participants, ages 10-17, were recruited from UCSF Dentistry clinics. Untreated, non-cavitated cross-arch permanent second molars were randomly assigned to test or control groups. A baseline assessment included: QLF, visual inspection (ICDAS-II), SoproLife, DIAGNOdent, and OCT. Test teeth were irradiated with the same parameters as described in the in vitro study part, and then reassessed with all methods. FV was then applied to all molars. At 6-months, all clinical assessments performed at baseline were repeated. In the in vivo study, ICDAS II visual examination was the only detection method to demonstrate with statistical significance (P<0.05) that 9.6 μm short-pulsed CO2 laser inhibited early caries after 6-months in high caries risk subjects. A strong tendency supporting this result was found with QLF and SoproLife images captured under both white and blue light sources. The author hopes that OCT data may add power to the current findings and analysis of future 12-month data may show current trends becoming statistically significant.Conclusion: ICDAS II visual detection demonstrated that short-pulsed 9.6 μm CO2 laser inhibits occlusal caries and that at this time ICDAS II appears to be the most accessible and relevant method of assessing early carious changes of the pit and fissure system