Argon laser oral safety parameters for teeth

Thermal, morphological, and spectral changes after Er, Cr:YSGG laser irradiation at low fluences on primary teeth for caries prevention

The aim of this study was to determine the temperature increase in the pulp chamber and possible thermal effects on molecular structure of primary teeth during the irradiation with Er,Cr:YSGG laser. Primary central incisors were divided into three groups (n = 20). Labial surfaces in each group were irradiated by Er,Cr:YSGG laser within different power and frequencies as following groups: I: 0.25 W, 20 Hz, II: 0.50 W, 20 Hz, III: 0.75 W, 20 Hz. A thermocouple was placed inside the pulp chamber so that the temperature increments were recorded during the enamel irradiation. Morphological changes of enamel surfaces were experimentally evaluated by SEM. Fourier-transform infrared spectroscopy and RAMAN analyses were carried out to determine the differentiations in the molecular structure. The experimental results obtained were analyzed statistically by means of one-way analysis of variance. Statistically significant differences were detected between groups (p < .05). Group III exhibited the highest values for the temperature parameters. Besides, the conical craters, cracks, and formation of ablation areas were observed for all the groups. Also, it was obtained that the hydroxyapatite lost the hydroxyl ions due to the thermal effect of the laser. Temperature rise throughout the Er,Cr:YSGG laser irradiation for prevention of primary enamel demineralization presented a positive correlation with the laser output power level. The formations of adverse morphological and spectral changes were detected on the surface of teeth after the laser application. On this basis, the Er,Cr:YSGG laser applications should be treated with much more caution considering enamel surface and pulpal tissues in primary teeth.

Effect of Erbium:Yttrium-Aluminum-Garnet Laser Combined with Mineralizing Agents on Microhardness of Demineralized Dentin

Objective The aim of this study was to assess the combined effect of erbium:yttrium-aluminum-garnet (Er:YAG) laser and mineralizing agents including casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) and fluoride in improving the resistance of demineralized dentin at new demineralization process.

Materials and Methods One hundred and twenty healthy dentin surfaces were prepared and demineralized using acidic solutions. Primary microhardness was measured (h1), and samples were randomly divided into six groups. Each group received a different protocol as follows: Group A (control group): no additional treatment, Group B: applying a fluoridated gel, Group C: applying a CPP-ACP-containing cream, Group D: irradiation of Er:YAG laser, Group E: irradiation of Er:YAG laser combined with the application of a fluoridated agent, and Group F: irradiation of Er:YAG laser combined with the application of CPP-ACP-containing cream. Microhardness values were measured afterward (h2). Then, all the groups were re-exposed to acidic solution, and microhardness was measured for the third time (h3). The microhardness data were analyzed using analysis of variance and Scheffe's post hoc test.

Results Although application of mineralizing agents increased the microhardness of demineralized dentin in comparison with the control group, no significant difference was observed using two agents. Comparison of laser groups showed an increase in microhardness only after the irradiation of Er:YAG laser combined with the application of a fluoridated agent. Demineralizing process reduced the microhardness values in all the groups, but the application of a CPP-ACP agent caused the least reduction among the laser irradiated groups. Comparison of hardness changes at the beginning and end of the experiment did not show any significant differences between the groups.

Conclusion Comparison of treatment modalities used in this study exhibited that fluoride had the greatest impact on dentin resistance. Laser irradiation on demineralized dentin did not increase the hardness or resistance to acidic attacks.

Use of light-curing units in orthodontics

Because of their wide field of applications, light-curing units are now indispensable for orthodontists and general dentists; thus, it is important to be familiar with the various types of light-curing units, their history, specifications, advantages, and disadvantages. For this review, a search of the PubMed database (from 1966 to March 2010) was conducted using the search term "curing lights orthodontics". Eligibility of the selected studies was determined by reading the abstracts of articles identified by the search. All the articles that met the inclusion criteria were selected, and the articles collected. The reference lists of the retrieved articles were also hand searched for any applicable studies that might have been missed in the database searches. When selecting curing lights for an office, many variables need to be considered. Armed with knowledge about each curing-light category, orthodontists can evaluate their unique practice style and select the appropriate light/lights.

Lasers in periodontics

Laser is one of the most captivating technologies in dental practice since Theodore Maiman in 1960 invented the ruby laser. Lasers in dentistry have revolutionized several areas of treatment in the last three and a half decades of the 20^th century. Introduced as an alternative to mechanical cutting device, laser has now become an instrument of choice in many dental applications. Evidence suggests its use in initial periodontal therapy, surgery, and more recently, its utility in salvaging implant opens up a wide range of applications. More research with better designs are a necessity before lasers can become a part of dental armamentarium. This paper gives an insight to laser in periodontics.

Argon ion laser curing depth effect on a composite resin

The aim of this study was to define optimal power settings as well as curing time associated with evaluating the curing depth of a composite resin as a function of Vickers hardness. The tests were performed with a hybrid composite resin cured with a halogen lamp and argon ion laser, with different exposure times and power settings. The composite resin bulk technique was used using a black polypropylene matrix with thicknesses ranging from 1 to 4 mm and Vickers microhardness was measured on the opposite surface of the light activation. ANOVA and Tukey statistical tests were used. The results showed that the groups activated by the laser for 20 s, at 200 and 250 mW, did not present statistically significant differences regarding the halogen lamp with 1 mm thickness, but the halogen lamp showed better results with thickness values more than 2 mm (p < 0.05).

Intrapupal temperature variation during Er,Cr: YSGG enamel irradiation on carries prevention

Studies have shown the cariostatic effect of Er,Cr:YSGG (2.78 mm) laser irradiation on human enamel and have suggested its use on caries prevention. However there are still no reports on the intrapulpal temperature increase during enamel irradiation using parameters for caries prevention. The aim of this in vitro study was to evaluate the temperature variation in the pulp chamber during human enamel irradiation with Er,Cr:YSGG laser at different energy densities. Fifteen enamel blocks obtained from third molars (3 x 3 x 3 mm) were randomly assigned to 3 groups (n=5): G1--Er,Cr:YSGG laser 0.25 W, 20 Hz, 2.84 J/cm(2), G2--Er,Cr:YSGG laser 0.50 W, 20 Hz, 5.68 J/cm(2), G3--Er,Cr:YSGG laser 0.75 W, 20 Hz, 8.52 J/cm(2). During enamel irradiation, two thermocouples were fixed in the inner surface of the specimens and a thermal conducting paste was used. One-way ANOVA did not show statistically significant difference among the experimental groups (alpha=0.05). There was intrapulpal temperature variation < or = 0.1 degrees C for all irradiation parameters. In conclusion, under the tested conditions, the use of Er,Cr:YSGG laser with parameters set for caries prevention lead to an acceptable temperature increase in the pulp chamber.

Intrapulpal Temperature during Preparation with the Er:YAG Laser: Anin VitroStudy

OBJECTIVE

This investigation evaluated the variation of the intrapulpal temperature when dentine was irradiated by the Er:YAG laser.

BACKGROUND DATA

The effect of preparation with the Er:YAG laser on the intrapulpal temperature is probably the biggest problem in using the laser for preparation of dental hard tissue.

MATERIALS AND METHODS

Seventy-two bovine incisors were studied that had the enamel and dentine of the buccal surface polished to a thickness of 2.0 mm. The teeth were divided into three groups, according to the repetition rate used (Group I = 2 Hz, Group II = 4 Hz, and Group III = 6 Hz), and irradiated, with or without water cooling, using 250, 300, and 350 mJ of energy per pulse. Thermocouples were introduced inside the pulp chamber through the palatine opening of the samples and fixed to the vestibular wall of the pulp chamber using a thermal paste.

RESULTS

It was verified that there was a decrease of the intrapulpal temperature for all of the parameters in the Group I irradiated with water cooling and for the parameters of 350 mJ/4 Hz with water cooling. The other irradiations showed an increase of the intrapulpal temperature, varying from 0.03 degrees to 2.5 degrees C.

CONCLUSION

We conclude that the use of the Er:YAG laser promoted acceptable temperature increases inside the pulp chamber. However, we do not recommend this procedure without water cooling because macroscopic observations of the dentine irradiated without water cooling showed dark lesions, suggesting carbonization of this tissue.

Increase of enamel fluoride retention by low fluence argon laser beam: A 6-month follow-up study in vivo

BACKGROUND AND OBJECTIVES

The aim of this 6-month in vivo study was to investigate if argon laser irradiation of enamel can increase the retention of fluoride.

STUDY DESIGN/MATERIALS AND METHODS

Ninety-eight teeth in 12 patients were randomly divided into three groups: (1) EF group: 40 teeth were only treated with fluoride gel (applied for 5 minutes followed by a 1 minute rinsing with distilled water). (2) EFL group: 40 teeth were treated the same way as in the EF group but they were lased after fluoridation. (3) E group: 18 teeth were kept without any treatment as a control group. In order to quantify the fluoride content in the enamel samples, the teeth were analyzed by proton beam delivered by a tandem accelerator (PIgE, particle induced gamma-ray emission). A low energy density of argon laser beam was used: 10.74 J/cm2 (11 mm of beam diameter, irradiation time of 30 seconds, and an output power of 340 mW in continuous mode).

RESULTS

The results after 6 months showed that the lased enamel still retained 52.55+/-8.47 ppm or 14.12% of fluoride after the fluoridation process, whereas the unlased enamel retained only 12.18+/-6.82 ppm or 3.27% of fluoride. The untreated and control enamel (E group: unlased and without fluoride treatment) had 1.16+/-4.27 ppm value of fluoride. The statistical test (ANOVA tests at 95% level) showed that the difference is significant between the fluoride retention in the group EFL and the group EF 6 months after fluoridation.

CONCLUSIONS

The use of argon laser at low energy density (10.74 J/cm2) significantly increased the fluoride retention in lased enamel that had approximately 400 times more fluoride than the unlased enamel. We consider this procedure as an alternative clinical procedure to increase the fluoride content of enamel surface.

Increase of enamel fluoride retention by low fluence argon laser in vivo

BACKGROUND AND OBJECTIVES

The aim of this in vivo study was to investigate if argon laser irradiation of enamel can increase the retention of fluoride.

STUDY DESIGN/MATERIALS AND METHODS

Ninety-eight teeth in 12 patients were randomly divided into three groups: (1) EF group: 40 teeth were only treated by fluoride gel (application for 5 minutes followed by 1 minute rinsing with distilled water). (2) EFL group: 40 teeth were treated the same way as in the EF group but they were lased after fluoridation. (3) E group of 18 teeth were kept without any treatment and considered as reference. In order to quantify the fluoride content in the enamel samples, the teeth were analyzed by proton beam delivered by a tandem accelerator (PIgammaE, particle induced gamma-ray emission). The fluoride content of enamel surface is not homogeneous. Therefore, it is necessary to analyze the same enamel area after each treatment. Each tooth was maintained in a fixed tooth holder which was designed to analyze the tooth enamel surface at the same place (1 mm(2) and around 20 mum in depth) after various treatments. A low energy density of argon laser beam was used: 10.74 J/cm(2), 30 seconds of irradiation time and 340 m W of output power.

RESULTS

The results after 7 days showed that the lased enamel still retained 157.4 +/- 23.371 ppm or 42.29% of fluoride after fluoridation process whereas the unlased enamel retained 45.59 +/- 9.377 ppm or 12.25% of fluoride.

CONCLUSIONS

We concluded that the use of argon laser at low energy density (10.74 J/cm(2)) significantly increases the fluoride retention in lased enamel which had approximately three times more fluoride than the unlased enamel.

The effects of argon laser irradiation on enamel decalcification: An in vivo study

Enamel decalcification is a significant problem in orthodontic patients. The argon laser has been shown to reduce decalcification during an acidic challenge in vitro. The purpose of this study was to investigate the in vivo effects of argon laser irradiation on enamel decalcification during orthodontic treatment. Nine volunteers whose treatment plans included 4 first premolar extractions were enrolled in the study. The 36 extracted premolars were assigned to 1 of the following 4 groups: group 1, control group with no treatment; group 2 (pumice-laser), teeth were pumiced for 3 seconds and treated with a 325 mW, 5-mm diameter laser beam for 60 seconds; group 3 (pumice-etch-laser), teeth were pumiced for 3 seconds, acid-etched with 30% phosphoric acid for 30 seconds, and treated for 60 seconds with laser; and group 4 (laser only), teeth were treated for 60 seconds with laser. A specially designed (oversized) orthodontic band was fitted on each of the premolars to create a pocket for decalcification. The bands were cemented in place for 5 weeks. After extraction, the teeth were sectioned and examined under polarized light microscopy. Images of lesions were digitally analyzed and measured. Average lesion depths were calculated from 3 depth measurements recorded 10 microm apart. Average lesion area was calculated with the aid of imaging analysis software. Data were analyzed with analysis of variance (P <.05) and Student t tests. Significant differences were found in lesion depth (P <.001) and lesion area (P <.01) among the 4 test groups. The average lesion depths were 15.93 +/- 9.31 microm (control), 6.45 +/- 8.70 microm (pumice-laser), 1.71 +/- 4.82 microm (pumice-etch-laser), and 1.34 +/- 3.80 microm (laser only). The average lesion areas were 1028.67 +/- 725.68 microm (2) (control), 555.49 +/- 948.20 microm (2) (pumice-laser), 79.91 +/- 226.03 microm (2) (pumice-etch-laser), and 55.71 +/- 157.59 microm (2) (laser only). The average lesion depth in the laser-only group was reduced by 94.1% and the average lesion area was reduced by 94.4% when compared with the control group. In the pumice-etch-laser group, the average lesion depth was reduced by 89.1% and the average lesion area was reduced by 92.2% when compared with the control group. There were no significant differences in lesion depth and lesion area between maxillary and mandibular teeth (P <.06 and P <.08, respectively) and between the teeth on the right and left sides (P <.68 and P <.55, respectively). These results show that argon laser irradiation is effective in reducing enamel decalcification during orthodontic treatment. Pumicing and etching do not appear to reduce the effect of laser on enamel solubility.

A comparison of shear bond strengths of orthodontic brackets using various light sources, light guides, and cure times

The objective of this study was to evaluate the effects of different cure times, light sources, and light guides on shear bond strength of orthodontic brackets bonded with Transbond XT (3M Unitek, Monrovia, Calif) to bovine enamel. Specifically, the Power Slot (Reliance Orthodontic Products, Itasca, Ill) light guide was placed on 4 visible light sources to compare shear bond strengths and recommended cure times with the light guides provided with each light source. We randomly divided 240 bovine mandibular incisors into 16 groups; each group consisted of 15 teeth mounted in an acrylic block. Each group of teeth was polymerized with a specific light and light guide combination. Eight groups were sheared after 5 minutes and the remaining 8 groups after 24 hours. After bonding, all brackets were subjected to a shear force with a testing machine. Overall, there was a significant increase in bond strengths of the 24-hour groups compared with the 5-minute shearing groups. However, there were no statistical differences (P =.05) within the 24-hour test groups or the 5-minute test groups. The results of this study indicate that, compared with standard light guides, the Power Slot and the Turbo Tip (Ormco Sybron Dental Specialties, Orange, Calif) light guides can significantly reduce the curing times (10 seconds per bracket; 5 seconds each from mesial and distal) without affecting their shear bond strengths. Therefore, the Power Slot and the Turbo Tip light guides with their collimation of visible light to increase its intensity can be recommended as advantageous alternatives for curing composite resins for orthodontic bonding procedures.

The Nd-YAG laser is useful in prevention of dental caries during orthodontic treatment

Plaque control during the course of orthodontic treatment is not an easy task, and dental caries are not an unlikely complication. We examined the possibility of controlling dental caries with Nd-YAG laser irradiation in orthodontic patients. As a preliminary experiment, we used the Nd-YAG laser to irradiate an extracted tooth and then left it to soak in lactic acid. The decay of the tooth was evaluated with a scanning electron microscope (SEM); tooth decay was inhibited by the action of the laser. Twenty patients undergoing orthodontic treatment for early decalcification of the teeth (white spot lesions) were selected, and photographs were taken of their oral cavities. White spot lesions on the four incisors and two canines of the maxilla were traced on tracing paper, and their areas were calculated by computer. Ten of the patients received laser treatment and acidulated phosphate fluoride solution (APF); the other ten acted as the control group. Between 11 and 12 months later, we photographed the oral cavity as we had previously; the white spot lesions were again traced and their areas calculated. The changes in the areas of the white spots of the laser-irradiated and control groups showed the following increases: laser-irradiated group, 1.41 times; controls, 2.87 times. The difference was statistically significant. These results demonstrate that Nd-YAG laser irradiation with application of APF acts as an effective method of caries control during orthodontic treatment.

Response of associated oral soft tissues when exposed to Argon laser during polymerization of dental resins

BACKGROUND AND OBJECTIVE

Polymerization of dental resins with Argon laser produces restorations with improved physical properties when compared to conventional visible-light polymerization techniques. However, the possibility of damaging adjacent soft tissues has not been addressed.

STUDY DESIGN/MATERIALS AND METHODS

In this study, Argon laser (488/514 nm) was used for the polymerization of composite resins to determine effects on the parakeratinized gingiva adjacent to both restored and unrestored teeth in six dogs, using 10-, 20-, and 30-second polymerization exposures.

RESULTS

Gingival tissues removed at 24 hours, 72 hours, or 5 days revealed desiccated, disrupted, hyalinized connective tissue. Tissues exposed for 10 seconds showed minimal change. This minimal degree of change was most evident at 72 hours and returned to normal limits at 5 days. The 20-second exposure produced alterations evident through all time periods. Tissues exposed for 30 seconds exhibited necrosis, severe disruption, and vessiculation, which was still unresolved at 5 days.

CONCLUSION

This study demonstrates that clinically relevant Argon laser exposure (10 seconds) of parakeratinized gingiva adjacent to teeth undergoing restoration does not cause lasting damage.

In vitro temperature change at the dentin/pulpal interface by using conventional visible light versus argon laser

BACKGROUND AND OBJECTIVE

The argon laser has been promoted as a competing technology to multi-wavelength visible light as a curing source for dental restorative resins. However, the comparative thermal risk to the pulp between these two sources of light energy requires determination. The objective of this study is to compare the temperature induced at the dentin-pulpal interface between the argon laser and visible light curing unit at a variety of exposure regimens and conditions.

STUDY DESIGN/MATERIALS AND METHODS

In vitro temperatures were measured and recorded at the dentin-pulpal interface upon external light exposure. Independent variables included the dentin thickness, duration and waveform of exposure, and presence of composite resin.

RESULTS

In most instances, the argon laser resulted in less temperature rise on the pulpal-dentin interface.

CONCLUSION

The argon laser should not pose a serious thermal risk to the pulp if used at recommended energies.

Human teeth exposed to argon laser irradiation: determination of power-time-temperature working conditions

OBJECTIVE

This study was conducted to establish the operating parameters of the argon laser without thermal damage to the pulp tissue for clinical applications.

SUMMARY BACKGROUND DATA

Previous studies have mainly compared the temperature modifications of the pulp chamber in a very limited situation, where a complete view of the thermal history cannot be obtained nor even extrapolated to new applications.

METHODS

We used samples of molar and premolar tooth where a class V cavity was prepared and illuminated with an argon laser at different power levels, fixing the exposition area for all cases. Situations including open cavity and teeth restoration were analyzed. High-precision thermistors were placed in four different positions, one of which was inside the pulp chamber. The temperature evolution was monitored continuously by an interfaced computer during all laser exposure. Special attention was paid to the intrapulpal temperature variation because it is considered the most vulnerable thermal region. The temperature time evolution allowed the determination of the operating conditions (power-time-temperature variation) in which the use of the argon laser causes no pulpal damage. As a function of temperature variation, we divided the whole parameter space (power-time-temperature) into zones and the optimum zone of operation was determined.

CONCLUSIONS

We created a diagram called power-time-temperature (PTT) where zones of temperature increased under laser irradiation allow the verification of which condition is safe for clinical laser application. The results have a broad use when this type of analysis is applicable.

Dentistry for the 21st century? Erbium:YAG laser for teeth

The first dental laser for use in cutting human teeth in vivo was cleared by the Food and Drug Administration for marketing in the United States. The authors explored, in summary form, the data provided to the FDA for the clinical use of the erbium:yttrium-aluminum-garnet, or Er:YAG, laser. The authors concluded that using the Er:YAG laser to treat dental hard tissue is both safe and effective for caries removal, cavity preparation and enamel etching.

The results of 1328 periodontal pockets treated with the argon laser: selective pocket thermolysis

A study of 30 randomly selected cases of type II-IV periodontitis was done from a group of 130 patients who had been treated with argon laser pocket thermolysis and root planing between January 1993 and April 1994. The group consisted of 12 males and 18 females with a mean age of 47. No antibiotics were taken 6 months prior or during the treatment. A pocket charting and bleeding index was done at a mean of 4.6 months after treatment. A total of 1328 pockets were treated using a 300-microns fiber in contact at 0.4 W for 20-30 sec per pocket with coaxial irrigation. The 4-5 mm pockets were reduced by 1.62 mm, 6-7 mm pockets by 2.85 mm, and 8-9 mm by 3.30 mm. The bleeding of probing was reduced by 75%. The mean postoperative pain medication was 400 mg/day of ibuprofen for 1-2 days. Laser pocket thermolysis with subgingival thermodynamic debridement may eliminate or greatly reduce the need for additional treatment. There is a great need for further investigation.

Argon laser irradiation in root surface caries: in vitro study examines laser's effects

Recent research shows that laser irradiation can improve enamel's resistance to caries. This in vitro study examines the effects of argon laser irradiation on root surface caries. Treated surfaces seemed more resistant to an artificial caries medium than control surfaces.