Effects of CO2 laser irradiation on matrix-rich biofilm development formation-an in vitro study

CO2 laser irradiation combined with fluoridated dentifrice improved its protective effect on caries lesion progression regardless of the acidulated phosphate fluoride gel application: An in situ study

OBJECTIVE

This in situ study aimed to investigate the efficacy of CO2 laser at a 10.6-µm wavelength combined with 1.23% acidulated phosphate fluoride (APF) and fluoridated dentifrice with 1100 µg F/g (FD) to control enamel caries progression.

MATERIALS AND METHODS

Sixteen volunteers wore palatal appliances containing eight demineralized enamel specimens for four 14-day phases under sucrose exposure. These specimens were submitted to CO2 laser irradiation and APF alone or combined with FD. Treatment groups were non-fluoridated dentifrice-NFD, NFD + CO2 laser, NFD + APF, NFD + CO2 laser + APF, FD, FD + CO2 laser, FD + APF, and FD + CO2 laser + APF. Mineral loss, calcium fluoride (CaF2), fluorapatite (FAp), and fluoride in the biofilm were analyzed by analysis of variance followed by the Student-Newman-Keuls test, p < 0.05.

RESULTS

The highest mineral loss inhibition was noted when FD and CO2 laser irradiation were combined, which did not significantly differ from the FD + CO2 laser + APF group. The CaF2, FAp, and F in the biofilm were more pronounced when the FD and APF were combined. The CO2 laser irradiation promoted a slightly higher concentration of CaF2 in the enamel and F in the biofilm.

CONCLUSION

Although APF promotes the high formation of CaF2 and FAp, the combined use of FD with CO2 laser overcomes the APF effect in inhibiting the progression of artificial caries-like lesions in situ.

CLINICAL SIGNIFICANCE

Under the in situ design of this study, remineralization of white spot lesions was achieved through CO2 laser irradiation and daily use of fluoridated dentifrice. Future clinical trials are encouraged to substantiate this finding.

Use of a novel 9.3-μm carbon dioxide laser and silver diamine fluoride: Prevention of enamel demineralisation and inhibition of cariogenic bacteria

OBJECTIVE

To investigate the effects of a 9.3-μm carbon dioxide (CO₂) laser and silver diamine fluoride (SDF) on the prevention of enamel demineralisation and inhibition of cariogenic bacteria.

METHODS

Enamel blocks were applied with Laser (Group-1), SDF (Group-2), Laser + SDF (Group-3) and no treatment (Group-4), and then subjected to an 8-day pH-cycling for cariogenic challenge. Lesion depth and cross-sectional micro-hardness were assessed. Surface morphological and chemical changes were studied using scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS). For the antibacterial activity, treated enamel blocks were incubated with Streptococcus mutans. The biofilm morphology, kinetics and viability were assessed by SEM, colony-forming units (CFUs) and confocal laser scanning microscope (CLSM), respectively.

RESULTS

Lesion depths (μm) for Group-1 to Group-4 were 88 ± 21, 26 ± 11, 13 ± 9 and 115 ± 25, respectively (p < 0.001; Group-2 and Group-3 < Group-1 < Group-4). Group-3 had a significantly higher cross-sectional micro-hardness than the other three groups. EDS determined that Group-4 had the lowest calcium-to-phosphorus molar ratio among the groups (p < 0.001). SEM images showed apparent bacteria accumulation on enamel surfaces in Group-4, but not in other groups. Log CFUs for Group-1 to Group-4 were 6.2 ± 0.6, 2.9 ± 0.8, 2.2 ± 1.1 and 7.3 ± 0.3, respectively (p < 0.001; Group-2 and Group-3 < Group-1 < Group-4). CLSM images revealed that live bacteria dominated in Group-4, but not in other groups.

SIGNIFICANCE

The irradiation with a 9.3-μm CO₂ laser alone can prevent the demineralisation of enamel and reduce the adhesion of cariogenic bacteria. Moreover, adding SDF can significantly increase the preventive effect and antibacterial ability.

Bioactive Dental Adhesive System With tt-Farnesol: Effects on Dental Biofilm and Bonding Properties

Background

Composite dental restorations are commonly used to restore cavitated carious lesions. Unfortunately, the main reason for failure is the development of secondary caries adjacent to the restoration. To improve the long-term survival of restorations, antibacterial agents have been added into dental materials. In this study, we assessed the antibacterial and bonding capacity of a commercial universal dental adhesive incorporated with the antibacterial agent tt-farnesol creating 3 experimental adhesives: 0.38% (v/v), 1.90% (v/v), and 3.80% (v/v), plus a control (no incorporation of tt-farnesol).

Methods

The antibacterial activity was evaluated by assessing colony-forming units (CFU), biofilm dry weight (DW) and production of extracellular insoluble polysaccharides (EIP) at day 2, 3, and 5 of biofilm growth post surface treatment on the surface of composite disks. The effect of tt-farnesol on the chemical and bonding capacity of the adhesive system was assessed via pH analysis, degree of conversion (DC), and microtensile bond strengths to human dentin in both self-etch and etch-and-rinse application modes. A qualitative analysis of the effects of tt-farnesol on biofilm formation was evaluated using scanning electron microscopy (SEM). The sealing capacity of all adhesive systems tested was evaluated using confocal laser scanning microscopy (CLSM).

Results

The 3.80% (v/v) experimental adhesive exhibited the lowest CFU count and lowest production of EIP at day 5. DW and pH values did no exhibit statistical differences among all tested groups. Bond strengths and DC decreased with the incorporation of the antibacterial agent into the adhesive system regardless of the concentration of tt-farnesol.

Conclusion

The incorporation of tt-farnesol into the adhesive system significantly reduced bacterial viability and production of EIP; however, the bonding properties of the experimental dental adhesives were altered.

The Impact of CO2 Laser Treatment and Acidulated Phosphate Fluoride on Enamel Demineralization and Biofilm Formation

Introduction: This study evaluated the impact of CO₂ laser treatment and acidulated phosphate fluoride (APF) on enamel demineralization and biofilm formation, using in vitro and in situ designs. Methods: Demineralized enamel slabs were distributed among 8 groups: placebo, placebo + continuous CO₂ laser, placebo + repeated CO₂ laser, placebo + ultrapulsed CO₂ laser, 1.23% APF, APF + continuous CO₂ laser, APF + repeated CO₂ laser and APF + ultrapulsed CO₂ laser. In the in vitro study, 15 enamel slabs from each group were subjected to a pH-cycling regimen for 14 days. In the cross over in situ design, 11 volunteers wore palatal appliances with demineralized enamel slabs for 2 periods of 14 days each. Drops of sucrose solution were dripped onto enamel slabs 8×/day. Biofilms formed on slabs were collected and the colony-forming units (CFU) of Streptococcus mutans and Lactobacillus were determined. Results: For both in vitro and in situ studies, there was no significant difference between treatments (P>0.05). However, all treatments increased microhardness of demineralized enamel (P<0.05). After a further in situ cariogenic challenge, with the exception of the placebo, all treatments maintained microhardness values (P<0.05). Microbiological analysis showed no difference in Streptococcus mutans (P>0.05) or Lactobacillus (P>0.05) counts between groups. Conclusion: The results suggest that APF gel combined with the CO₂ laser, regardless of the pulse emission mode used, was effective in controlling enamel demineralization, but none of the tested treatments was able to prevent bacterial colonization.

Effects of 10,600 nm Carbon Dioxide Laser on Remineralizing Caries: A Literature Review

Objective: To study the effects of carbon dioxide (CO₂) lasers (λ = 10,600 nm) on remineralizing dental caries. Methods: This study involved performing a systematic search of English articles archived in the PubMed, Scopus, and Web of Science databases. The keywords used to identify the relevant articles were ((CO₂ laser) OR (carbon dioxide laser)) AND ((dental caries) OR (tooth remineralization)). Publications before 2019 were selected. The titles and abstracts of the initially identified articles were screened. Duplicate records, reviews, and irrelevant studies were removed. Full texts were retrieved for publications that studied the effects of CO₂ lasers on remineralizing dental caries. Results: The search identified 543 potentially relevant publications. A total of 285 duplicate records were removed. Sixteen articles were included in this review. Four studies reported that CO₂ lasers inhibited bacterial growth. The growth of cariogenic bacteria, mainly Streptococcus mutans, on an irradiated tooth surface was slower compared with nonirradiated ones. Four studies investigated the reduction of the demineralization of enamel with cariogenic challenge. They found that CO₂ lasers reduced the carbonate content of mineralized tissues and increased the microhardness of enamel. Nine studies used CO₂ lasers associated with topical fluorides in remineralizing dental caries. The results of the synergistic effect of laser irradiation and fluoride application with regard to the inhibition of caries progression varied among these studies, whereas laser irradiation could enhance fluoride uptake to demineralized mineral tissues. Conclusions: CO₂ laser irradiation increased acid resistance and facilitated the fluoride uptake of caries-like lesions. In addition, it reduced the growth of cariogenic bacteria.

Evaluation of the effect of two types of laser on the growth of streptococcus mutans

Background and aims

This study was done to compare the antibacterial effect of Photodynamic therapy (PDT) on streptococcus mutans (S. mutans) using two different light sources and photosensitizers (PS).

Materials and methods

Five groups were studied in this research:no light and no toluidine blue ortho (TBO) as PS for control group, irradiation only (CO₂ laser or Nd:YAG laser), and irradiation with PS (CO₂ laser and TBO or Nd:YAG laser and TBO). Standard suspensions of S. mutans, based on the type of group, were used in different PDTs. Bacterial suspension from each treatment was subcultured onto the surface of Mueller-Hinton agar plates, and bacterial growth was assessed. The results were analyzed by analysis of variance (ANOVA).

Results

There was a statistically significant reduction in the viability of S. mutans in TBO with CO₂ laser and TBO with Nd:YAG laser groups (p value < 0.05). However, there was no significant difference between control and groups treated with lasers only. The highest number of the colonies of S. mutans in treated groups was observed in CO₂ laser irradiation only and the lowest number was seen in CO₂ laser with TBO. In the groups irradiated alone (without TBO), no significant reduction of colonies was observed. There was no significant difference between the experimental groups.

Conclusions

The colonies of S. mutans were susceptible to either CO₂ laser or Nd:YAG laser in the presence of TBO with no significant difference. So these lasers with this photosensitizer may be useful in prevention of dental caries and antimicrobial treatment protocols.