In situ mineral loss inhibition by CO2 laser and fluoride

Laser and fluoride treatments have been shown to inhibit enamel demineralization in the laboratory. However, the intra-oral effects of this association have not been tested. This study assessed in situ the effect of a Transversely Excited Atmospheric CO2 laser (lambda = 9.6 mum) and the use of pressure fluoridated dentifrice on enamel demineralization. During two 14-day phases, 17 volunteers wore palatal appliances containing human enamel slabs assigned to treatment groups, as follows: (1) non-fluoride dentifrice, (2) CO2 laser irradiation plus non-fluoride dentifrice, (3) fluoride dentifrice, and (4) CO2 laser irradiation plus fluoride dentifrice. A 20% sucrose solution was dripped onto the slabs 8 times per day. The specimens treated with laser and/or fluoridated dentifrice presented a significantly lower mineral loss when compared with those from the non-fluoride dentifrice group. The results suggested that CO2 laser treatment of enamel inhibits demineralization in the human mouth, being more effective when associated with fluoride.     

Effects of CO2 laser on fluoride uptake in enamel

OBJECTIVES: The objective of this study was to investigate the effects of CO(2) laser on fluoride uptake in the loosely- and firmly-bound forms in enamel. METHODS: Five human molars were cut into halves before being treated with 2.0% NaF topical gel. Each half had three windows on the enamel surface, including one control and two experimental windows irradiated by two laser therapies. One half of each tooth was treated with 1 M KOH solution to remove the loosely-bound fluoride (calcium fluoride). A tooth section was obtained from each window and the relative fluorine concentration was analyzed with Secondary Ion Mass Spectrometry (SIMS). The morphology of the enamel surfaces in the windows was examined using an Environmental Scanning Electron Microscope (ESEM). RESULTS: Significant laser-induced increases in the uptake of fluoride were revealed in both loosely-bound and firmly-bound apatitic fluoride, with both laser treatments (all p<0.001). Calcium fluoride-like deposits on the enamel surfaces receiving the combined laser-fluoride treatment were revealed by ESEM. CONCLUSIONS: The finding of this study substantiated the laser effect in increasing the fluoride uptake into enamel.     

Rehardening of acid-softened enamel and prevention of enamel softening through CO2 laser irradiation

Objectives

The aims of the present study were to investigate whether irradiation with a CO₂ laser could prevent surface softening (i) in sound and (ii) in already softened enamel in vitro.

Methods

130 human enamel samples were obtained and polished with silicon carbide papers. They were divided into 10 groups (n = 13) receiving 5 different surface treatments: laser irradiation (L), fluoride (AmF/NaF gel) application (F), laser prior to fluoride (LF), fluoride prior to laser (FL), non-treated control (C); and submitted to 2 different procedures: half of the groups was acid-softened before surface treatment and the other half after. Immersion in 1% citric acid was the acid challenge. Surface microhardness (SMH) was measured at baseline, after softening and after treatment. Additionally, fluoride uptake in the enamel was quantified. The data were statistically analysed by two-way repeated measurements ANOVA and post hoc comparisons at 5% significance level.

Results

When softening was performed either before or after laser treatment, the L group presented at the end of the experiments SMH means that were not significantly different from baseline (p = 0.8432, p = 0.4620). Treatment after softening resulted for all laser groups in statistically significant increase in SMH means as compared to values after softening (p < 0.0001). Enamel fluoride uptake was significantly higher for combined laser-fluoride treatment than in control (p < 0.0001).

Conclusion

Irradiation of dental enamel with a CO₂ laser at 0.3 J/cm² (5 μs, 226 Hz) not only significantly decreased erosive mineral loss (97%) but also rehardened previously softened enamel in vitro.     

Measurement of vaporization cavity after CO2 laser irradiation on bovine dentin

Lasers are used for various clinical applications in dental practices, and many studies have examined the effects of lasers with different applications on enamel and dentin. The CO₂ laser was introduced into the dental clinic for the removal of caries and for cavity preparation of hard tissues, in anticipation of replacing air turban and micromotor devices. The aim of this study was to examine dentin structural changes by measuring 3-dimensional diameter, depth, and volume in bovine teeth irradiated with a CO₂ laser at 1, 3, or 5 W. According to our measurements, a vaporization depth of 400 μm was created by irradiation for a mere 100 ms in the case of 3 W irradiation and 500 μm in the case of 5 W irradiation. Further, at the same output power, the pulse mode transmitted energy to deeper layers of the tooth as compared with the continuous wave mode, indicating that the pulse mode has more penetrating power than the continuous wave mode. Moreover, the depth of cavity that after laser irradiated was > 500 μm at output power 5 W. Thus, irradiation at high output power and the influence of pulse mode on the pulp tissue cannot be disregarded. That is to say, it is important to consider irradiation output power, mode, direction, and distance when lasers are used for adjacent to pulp of tooth that primary incisors and deep cavities.     

Chemical analysis and surface morphology of enamel and dentin following 9.6mu CO2 laser irradiation versus high speed drilling

OBJECTIVES: The purpose of the present in vitro study was to determine whether there is a change in the chemical composition and surface morphology of enamel and dentin following 9.6mu CO2 laser irradiation and high-speed drilling. MATERIALS AND METHODS: Ten permanent, non-carious, young premolars, extracted for orthodontic reasons, were selected. The crowns were separated longitudinally into two equal parts at their mesiodistal axis. Two areas on the inner enamel surface of each specimen and two on the dentinal surface were selected. A high-speed drill and 9.6mu CO2 laser irradiation were applied to the selected enamel and dentinal areas. A random area on the unlased enamel and on the unlased dentin of each specimen served as controls. The morphology of the specimens was evaluated using scanning electron microscopy. Calcium, phosphorus and oxygen levels were measured using an energy dispersive spectrometer. RESULTS: Mineral analysis revealed no significant difference in the mineral content of the enamel and dentin after laser irradiation or high speed drilling versus the control. Use of the high-speed drill on enamel and dentin resulted in very clear cavity margins, with characteristic grooves, whereas laser irradiation of enamel and dentin did not produce clear margins and the floor of the cavity displayed an irregular surface. CONCLUSIONS: The 9.6mu CO2 laser appears to be a promising tool in the clinical setting. However, further investigation is indicated to ensure maximum effectiveness.     

Initial dissolution rate studies on dental enamel after CO2 laser irradiation.

The influence of CO2 laser irradiation on the dissolution behavior of human dental enamel has been investigated. Human enamel was irradiated by a continuous-wave CO2 laser at 10.6 microns 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 HCl (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 = aCa10aPO4(6)aOH2, 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, KFAP = aCa10aPO4(6)aF2 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.     

Pulpal response to irradiation of enamel with continuous wave CO2 laser

Selected dog's teeth, in vivo, were exposed to carbon dioxide (CO2) laser power densities ranging from 13 to 102 J per cm2. The teeth were extracted 48 h postlasing, fixed with 10% neutral buffered formalin, decalcified with Kristensen's solution, processed, sectioned, stained, and evaluated for pulpal damage. No pulpal damage was observed when compared with nonlased control teeth. It appears that carbon dioxide laser power densities of approximately 13 to 102 J per cm2 could be used to irradiate enamel of teeth without damage to the pulp.     

Effects of CO2 laser irradiation on microstructure of dentin, dentin adhesion of resin composites and dental pulp

This study was designed to investigate the effects of CO2 laser irradiation on the dentin microstructure, dentin adhesion of resin composites and dental pulp. An artificial caries lesion was produced on the bovine dentin, immersing in 0.4 mol/l acetic acid. Three kinds of dentin (sound dentin, outer or inner caries dentin) surfaces were pretreated by the laser irradiation, acid etching or no-treatment. The tensile adhesion-test of these pretreated dentin surfaces was performed. The changes in these dentin surfaces by the various treatments including the laser irradiation and the resin-dentin interfaces were examined by the SEM. Furthermore, histopathological study using monkey teeth was conducted to examine the effect of the laser irradiation on the dental pulp. Histopathological changes in the pulp were found at 3 and 90 days after the operation. The findings were as follows: 1. The outer highly and inner partially decalcified layers produced in the bovine dentin were each approximately 200 microns in thickness. 2. The bond strength of the resin composites to the laser pretreated sound dentin was approximately 40 kgf/cm2. Those of the laser pretreated outer and inner decalcified dentins were about 60 kgf/cm2. 3. At the initial stage, the laser irradiation (output power 3W : irradiation period 0.5 second) exhibited a slight pulpal response, producing irritation dentin formation in the latter stage without any severe histopathological change.     

Effects of chlorhexidine and fluoride on irradiated enamel and dentin

The effectiveness of mouthwash protocols in preventing gamma irradiation therapy damage to the ultimate tensile strength (UTS) of enamel and dentin is unknown. It was hypothesized that the use of chlorhexidine and fluoride mouthwash would maintain the UTS of dental structures. One hundred and twenty teeth were divided into 2 groups: irradiated (subjected to 60 Gy of gamma irradiation in daily increments of 2 Gy) and non-irradiated. They were then subdivided into 2 mouthwash protocols used 3 times per day: 0.12% chlorhexidine, 0.05% sodium fluoride, and control group (n = 10). The specimens were evaluated by microtensile testing. The results of the Tukey test (p < 0.05) indicated that the gamma irradiation therapy significantly reduced the UTS of the enamel, crown, and root dentin. Macromolecular alterations were suggested by optical retardation data in dentin. Structural alterations, in both substrates, were detected by scanning electron microscopy analysis. Mouthwash with 0.12% chlorhexidine partially prevented the damage to the mechanical properties of the irradiated crown dentin, whereas the 0.05% sodium-fluoride-irradiated enamel showed UTS similar to that of non-irradiated enamel.     

Effects of low-energy CO2 laser irradiation and the organic matrix on inhibition of enamel demineralization

In the past two decades, accumulated evidence has clearly demonstrated the inhibitory effects of laser irradiation on enamel demineralization, but the exact mechanisms of these effects remain unclear. The purpose of this study was to investigate the effects of low-energy CO2 laser irradiation on demineralization of both normal human enamel and human enamel with its organic matrix removed. Twenty-four human molars were collected, cleaned, and cut into two halves. One half of each tooth was randomly selected and its lipid and protein content extracted. The other half of each tooth was used as the matched control. Each tooth half had two window areas. All the left windows were treated with a low-energy laser irradiation, whereas the right windows served as the non-laser controls. After caries-like lesion formation in a pH-cycling environment, microradiographs of tooth sections were taken for quantification of demineralization. The mean mineral losses (with standard deviation) of the enamel control, the lased enamel, the non-organic enamel control, and the lased non-organic enamel subgroups were 3955 (1191), 52(49), 4565(1311), and 1191 (940), respectively. A factorial ANOVA showed significant effects of laser irradiation (p = 0.0001), organic matrix (p = 0.0125), and the laser-organic matrix interaction (p = 0.0377). The laser irradiation resulted in a greater than 98% reduction in mineral loss, but the laser effect dropped to about 70% when the organic matrix in the enamel was removed. The results suggest that clinically applicable CO2 laser irradiation may cause an almost complete inhibition of enamel demineralization.     

Prevention of toothbrushing abrasion of acid-softened enamel by CO(2) laser irradiation

Objective

The aim of the present study was to evaluate the effect of CO₂ laser irradiation (10.6 μm) at 0.3 J/cm² (0.5 μs; 226 Hz) on the resistance of softened enamel to toothbrushing abrasion, in vitro.

Methods

Sixty human enamel samples were obtained, polished with silicon carbide papers and randomly divided into five groups (n = 12), receiving 5 different surface treatments: laser irradiation (L), fluoride (AmF/NaF gel) application (F), laser prior to fluoride (LF), fluoride prior to laser (FL), non-treated control (C). After surface treatment they were submitted to a 25-day erosive-abrasive cycle in 100 ml sprite light (90 s) and brushed twice daily with an electric toothbrush. Between the demineralization periods samples were immersed in supersaturated mineral solution. At the end of the experiments enamel surface loss was determined using a contact profilometer and morphological analysis was performed using scanning electron microscopy (SEM). For SEM analysis of demineralization pattern, cross-sectional cuts of cycled samples were prepared. The data were statistically analysed by one-way ANOVA model with subsequent pairwise comparison of treatments.

Results

Abrasive surface loss was significantly lower in all laser groups compared to both control and fluoride groups (p < 0.0001 in all cases). Amongst the laser groups no significant difference was observed. Softened enamel layer underneath lesions was less pronounced in laser-irradiated samples.

Conclusion

Irradiation of dental enamel with a CO₂ laser at 0.3 J/cm² (5 μs, 226 Hz) either alone or in combination with amine fluoride gel significantly decreases toothbrushing abrasion of softened-enamel, in vitro.     

A comparison of the morphological changes after Nd-YAG and CO2 laser irradiation of dentin surfaces

The purpose of this study was to compare the morphological changes after Nd-YAG and CO2 laser irradiation on dentin surfaces with or without the smear layer. Eighty-one 3-mm-thick dentin specimens collected from the middle third of molar crowns were used. The dentin surfaces were ground to #320, #400, and #600 grit in series to create a smear layer. Half of the specimens were treated with 14% EDTA for 2 min to remove the smear layers. The lasers were applied on each specimen perpendicularly with 1-mm focus distance to the dentin surface for 4 s. The parameters for the Nd-YAG laser were 50 mJ, 100 mJ, and 150 mJ at 10 pps, 20 pps, and 30 pps, and for the CO2 laser were 2 W, 3 W, and 4 W at 5 ms x 20 pps, 10 ms x 10 pps, 20 ms x 20 pps, 50 ms x 2 pps, 100 ms x 2 pps, and 200 ms x 2 pps. The results showed that the Nd-YAG laser caused crater and melting of the dentin surface, especially in dentin specimens with smear layers. The CO2 laser produced extensive cracking lines on dentin surfaces with a smear layer, whereas surface erosion and crater formation were found on specimens without a smear layer. In conclusion, both the laser types and smear layer have a significant influence on the morphological changes of dentin surfaces irradiated by lasers.     

Effects of CO2 laser energy on dentin permeability.

The effect of a CO2 laser on the structure and permeability of smear layer-covered human dentin was evaluated in vitro. Three different energy levels were used (11, 113, and 566 J/cm2). The lowest exposure to the laser energy increased dentin permeability, measured as a hydraulic conductance, due to partial measured as a hydraulic conductance, due to partial loss of the superficial smear layer and smear plugs. The intermediate energy level also increased dentin permeability by crater formation, making the dentin thinner. The lack of uniform glazing of the surface of the crater, leaving its surface porous and in communication with the underlying dentinal tubules also contributed to the increase in dentin permeability seen with the intermediate laser energy. The highest laser energy produced complete glazing of the crater surfaces and sealed the dentinal tubules beneath the crater. However, it also completely removed the smear layer in a halo zone about 100-microns wide around each crater which increased the permeability of the pericrater dentin at the same time it decreased the permeability of the dentin within the crater. The combined use of scanning electron microscopy and permeability measurements provides important complementary information that is essential in evaluating the effects of lasers on dentin.     

In vivo caries formation in enamel following argon laser irradiation and combined fluoride and argon laser treatment: a clinical pilot study.

OBJECTIVE: This in vivo pilot study investigated the role of argon laser irradiation and combined fluoride and argon laser treatment in accelerated natural caries development in sound enamel surfaces beneath plaque-retentive orthodontic bands. METHOD AND MATERIALS: Five patients (3 female, 2 male, ages 19 to 28 years) requiring tooth extraction prior to orthodontic treatment, participated in the study. Buccal surfaces were treated with either: (1) argon laser (250 mW for 10 seconds, ARGO-MOD); (2) topical fluoride (0.5% fluoride ion, Thera-Flur-N) followed by argon lasing; or (3) no treatment (control). Orthodontic bands with plaque-retentive slots on buccal surfaces were placed on the teeth slated for extraction (n = 14). Following a minimum of 5 weeks of intraoral exposure, the teeth were extracted for laboratory analysis. The teeth underwent serial longitudinal sectioning (12 sections per tooth). The sections were imbibed in water, and lesion depths were determined with each section, using polarized light microscopy. Comparisons were made among treatment groups (analysis of variance, Duncan's multiple range test for paired samples). RESULTS: Mean lesion depths were: 261 +/- 24 microm for the no treatment control group (n = 84 sections); 147 +/- 18 microm for the argon laser group (n = 24 sections); and 99 +/- 12 microm for the fluoride and argon laser group (n = 60 sections). Both the argon laser (44%) and the fluoride and argon laser groups (62%) had significant lesion depth reductions compared to controls. The addition of fluoride treatment prior to argon lasing resulted in a 32% reduction in lesion depth compared to argon laser treatment alone. CONCLUSIONS: Within this clinical pilot study, in vivo natural caries formation was affected significantly by a single exposure to low fluence argon laser irradiation. Topical fluoride treatment in combination with argon lasing provided an even greater degree of resistance against in vivo enamel caries development. A simple technique for reducing the caries susceptibility of enamel may be a clinical reality.     

Effects of CO2 laser irradiation on gingiva

A CO2 laser (Coherent Medical Model 400) was used to irradiate the gingival tissue of a cynomolgous monkey to determine laser effects on the epithelium and underlying connective tissue. A focal length of 400 mm and a 10-watt power setting at 0.2- and 0.5-second exposure was used. Biopsy results indicated that a 0.2-second duration of CO2 laser irradiation was inadequate to completely de-epithelialize the gingival tissue. A 0.5-second exposure exhibited complete epithelial destruction with little or no disturbance of the underlying connective tissue layer and viable connective tissue 1.0 mm below the impact site.     

The effect of a desensitizer and CO2 laser irradiation on bond performance between eroded dentin and resin composite

PURPOSE

This study was aimed to evaluate effect of the desensitizing pretreatments on the micro-tensile bond strengths (µTBS) to eroded dentin and sound dentin.

MATERIALS AND METHODS

Forty-two extracted molars were prepared to form a flat dentin surface, and then they were divided into two groups. Group I was stored in distilled water while group II was subjected to a pH cycling. Each group was then subdivided into three subgroups according to desensitizing pretreatment used: a) pretreatment with desensitizer (Gluma); b) pretreatment with CO₂ Laser (Ultra Dream Pluse); c) without any pretreatment. All prepared surfaces were bonded with Single Bond 2 and built up with resin composite (Filtek Z250). The micro-tensile bond test was performed. Fracture modes were evaluated by stereomicroscopy. Pretreated surfaces and bonded interfaces were characterized by scanning electron microscope (SEM). The data obtained was analyzed by two-way ANOVA (α=0.05).

RESULTS

For both sound and eroded dentin, samples treated with desensitizer showed the greatest µTBS, followed by samples without any treatment. And samples treated with CO₂ laser showed the lowest µTBS. SEM study indicated that teeth with eroded dentin appeared prone to debonding, as demonstrated by existence of large gaps between adhesive layers and dentin.

CONCLUSION

Pretreatment with Gluma increased the µTBS of Single Bond 2 for eroded and sound teeth. CO₂ laser irradiation weakened bond performance for sound teeth but had no effect on eroded teeth.