Caries inhibition with a CO2 9.3 µm laser: An in vitro study.

BACKGROUND AND OBJECTIVES: The caries preventive effects of different laser wavelengths have been studied in the laboratory as well as in pilot clinical trials. The objective of this in vitro study was to evaluate whether irradiation with a new 9.3 µm microsecond short-pulsed CO2 -laser could enhance enamel caries resistance with and without additional fluoride applications. STUDY DESIGN/MATERIALS AND METHODS: One hundred and one human tooth enamel samples were divided into seven groups. Each group was treated with different laser parameters (CO2 -laser, wavelength 9.3 µm, 43 Hz pulse-repetition rate, pulse duration between 3 µs at 1.5 mJ/pulse to 7 µs at 2.9 mJ/pulse). A laboratory pH-cycling model followed by cross-sectional microhardness testing determined the mean relative mineral loss delta Z (ΔZ) for each group to assess caries inhibition in tooth enamel by the CO2 9.3 µm short-pulsed laser irradiation. The pH-cycling was performed with or without additional fluoride. RESULTS: The non-laser control groups with additional fluoride had a relative mineral loss (ΔZ, vol% × µm) that ranged between 646 ± 215 and 773 ± 223 (mean ± SD). The laser irradiated and fluoride treated samples had a mean ΔZ ranging between 209 ± 133 and 403 ± 245 for an average 55% ± 9% reduction in mineral loss (ANOVA test, P < 0.0001). Increased mean mineral loss (ΔZ between 1166 ± 571 and 1339 ± 347) was found for the non-laser treated controls without additional fluoride. In contrast, the laser treated groups without additional fluoride showed a ΔZ between 470 ± 240 and 669 ± 209 (ANOVA test, P < 0.0001) representing an average 53% ± 11% reduction in mineral loss. Scanning electron microscopical assessment revealed that 3 µs pulses did not markedly change the enamel surface, while 7 µs pulses caused some enamel ablation. CONCLUSION: The CO2 9.3 µm short-pulsed laser energy renders enamel caries resistant with and without additional fluoride use. The observed enhanced acid resistance occurred with the laser irradiation parameters used without obvious melting of the enamel surface as well as after irradiation with energies causing cutting of the enamel. Lasers Surg. Med. 48:546-554, 2016. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

The Featherstone laboratory pH cycling model: a prospective, multi-site validation exercise.

PURPOSE: To demonstrate the robustness of the Featherstone pH cycling model when tested in three independent laboratories and to evaluate the use of "non-inferiority" testing at those laboratories. METHODS: The fundamental principles for the Featherstone laboratory pH cycling model to be an appropriate alternative to animal testing is that it must demonstrate equivalent accuracy to the "Gold Standard" (rat caries model) by: (1) providing a meaningful representation of the caries process; (2) demonstrating a proportionate response to fluoride dose (or concentration); (3) being able to show that clinically proven formulations perform similarly relative to the controls; and (4) differentiating products that have attenuated fluoride activity. RESULTS: This cross-validation study confirmed the ability of the three independent laboratories to discriminate between various concentrations of fluoride-containing dentifrice formulations, demonstrated that clinically proven formulas perform as expected and identified an attenuated fluoride formulation (NaF/CaCO3 dentifrice - 1100 ppm NaF) as inferior compared to the 1100 ppm F (NaF/silica) positive control.

In vitro evaluation of erbium, chromium:yttrium-scandium-gallium-garnet laser-treated enamel demineralization.

This study evaluated the effect of different parameters of erbium, chromium:yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser irradiation on enamel mineral loss in a simulated caries model. Forty-five enamel samples obtained from third molar teeth (3 mmx 3 mm) were randomly divided into five groups (n = 9): G1-Er,Cr:YSGG laser at 0.25 W, 20 Hz, 2.8 J/cm(2); G2-Er,Cr:YSGG laser at 0.50 W, 20 Hz, 5.7 J/cm(2); G3-Er,Cr:YSGG laser at 0.75 W, 20 Hz, 8.5 J/cm(2); G4-sodium fluoride (NaF) dentifrice (positive control); G5-no treatment (negative control). After irradiation, the samples were submitted to 2 weeks of pH cycling. After the acid challenge, the samples were assessed by cross-sectional microhardness at different depths from the enamel surface. Analysis of variance (ANOVA) and Student-Newman-Keuls tests were performed (alpha = 5%). The percentage of lesion inhibition for each group was: G1 37%; G2 38%; G3 64%, and G4 50.5%. Regarding the relative mineral loss values (micrometers x volume percent), groups G1 (1,392 +/- 522) and G2 (1,292 +/- 657) did not differ significantly from each other, but both had higher values than group G3 (753 +/- 287); the groups irradiated with Er,Cr:YSGG laser did not differ from group G4. Although the findings of the study revealed that Er,Cr:YSGG laser irradiation at 8.5 J/cm(2) can be an alternative for the enhancement of the enamel's resistance to acid, lower energy densities also produced a cariostatic potential comparable to the use of fluoride dentifrice.

Anticaries potential of a stabilized stannous fluoride/sodium hexametaphosphate dentifrice.

The objective of this research was to evaluate the anticaries potential of stabilized stannous fluoride and sodium hexametaphosphate dentifrice using a series of laboratory studies. In a study of fluoride uptake into demineralized enamel, the stannous fluoride/sodium hexametaphosphate dentifrice exhibited fluoride uptake comparable to the clinically proven stannous fluoride and silica dentifrice. Under lesion progression pH-cycling conditions, the stabilized stannous fluoride/sodium hexametaphosphate dentifrice was shown to protect teeth against lesion initiation and progression almost completely, and was comparable to conventional, clinically proven dentifrices. This series of well-controlled and validated in vitro studies demonstrates the anticaries potential of the stabilized stannous fluoride/sodium hexametaphosphate dentifrice. These in vitro results suggest that the stabilized stannous fluoride/sodium hexametaphosphate dentifrice may provide enhanced anticaries performance relative to a sodium fluoride control dentifrice. These results are reflective of the clinical benefits previously reported for stabilized stannous fluoride/sodium hexametaphosphate dentifrices.

Anticaries and hard tissue abrasion effects of a "dual-action" whitening, sodium hexametaphosphate tartar control dentifrice.

A series of "profile" laboratory studies was conducted to confirm the anticaries potential and hard tissue safety of a novel sodium hexametaphosphate dentifrice technology which provides dual-action tooth whitening (i.e., stain prevention as well as stain removal), while simultaneously providing improved anticalculus action. Under remineralization pH cycling conditions, the dual-action whitening dentifrice produced lesion fluoridation comparable to a conventional NaF dentifrice. Under lesion progression pH cycling conditions, the dual-action whitening dentifrice produced enamel protection against caries initiation and progression comparable to a conventional NaF dentifrice, as well as comparable to a conventional tartar control dentifrice, also containing NaF. These results are consistent with clinical data supporting the anticaries effectiveness of NaF dentifrices combined with anionic tartar control inhibitors, such as pyrophosphate. Abrasion assessments were made using Radioactive Dentin and Enamel Abrasivity (RDA and REA) methods. These laboratory studies demonstrated that the new, dual-action whitening dentifrice produces dentin and enamel abrasivity similar to conventional silica-based dentifrice formulations. These in vitro studies verify the anticaries potential and demonstrate the hard tissue safety of the dual-action, sodium hexametaphosphate dentifrice.

Caries inhibition in vital teeth using 9.6-µm CO2-laser irradiation.

The aim of this study was to test the hypothesis that in a short-term clinical pilot trial short-pulsed 9.6 µm CO(2)-laser irradiation significantly inhibits demineralization in vivo. Twenty-four subjects scheduled for extraction of bicuspids for orthodontic reasons (age 14.9 ± 2.2 years) were recruited. Orthodontic brackets were placed on bicuspids (Transbond XT, 3M). An area next to the bracket was irradiated with a CO(2)-laser (Pulse System Inc, Los Alamos, New Mexico), wavelength 9.6 µm, pulse duration 20 µs, pulse repetition rate 20 Hz, beam diameter 1100 µm, average fluence 4.1 ± 0.3J∕cm(2), 20 laser pulses per spot. An adjacent nonirradiated area served as control. Bicuspids were extracted after four and twelve weeks, respectively, for a quantitative assessment of demineralization by cross-sectional microhardness testing. For the 4-week arm the mean relative mineral loss ΔZ (vol% × µm) for the laser treated enamel was 402 ± 85 (mean ± SE), while the control showed significantly higher mineral loss (ΔZ 738 ± 131; P = 0.04, t-test). The difference was even larger after twelve weeks (laser arm ΔZ 135 ± 98; control 1067 ± 254; P = 0.002). The laser treatment produced 46% demineralization inhibition for the 4-week and a marked 87% inhibition for the 12-week arm. This study shows, for the first time in vivo, that the short-pulsed 9.6 µm CO(2)-laser irradiation successfully inhibits demineralization of tooth enamel in humans.