Lasers in dentistry

Morphological changes induced by short pulse hydrogen fluoride laser radiation on dental hard tissue and restorative materials

BACKGROUND AND OBJECTIVE

The potential benefits of the effects of lasers on dental tissues have yet to be realized but may be brought closer through the availability of a suitable laser. The objective of this project is to examine the surface morphological changes resulting from hydrogen fluoride (HF) laser radiation on tooth and restorative material surfaces.

STUDY DESIGN/MATERIALS AND METHODS

A hydrogen fluoride laser emitting at 2.9 microns is used to interact with a range of dental hard tissue and restorative materials. The surface morphological changes induced by 100 mJ pulses of < 1 microsecond duration is studied using a SEM.

RESULTS

The irradiated surfaces displayed microstructures similar to those of a mechanically fractured surface with no evidence of melting.

CONCLUSION

This study suggests that tissue is removed by microexplosion, leaving a surface free from thermal damage with surface characteristics that would appear to facilitate the adhesion of restorative materials.

Pulsed Nd:YAG laser irradiation of the tooth pulp in the cat: I. Effect of spot lasing

BACKGROUND AND OBJECTIVE

The purpose of the present study was to evaluate physiologically pulpal nerve responses and to elucidate histopathologically the pulp tissue reactions to "spot irradiation" with a pulsed Nd:YAG laser.

STUDY DESIGN/MATERIALS AND METHODS

Antidromic compound action potentials and the pulpal blood flow (PBF) were recorded from the canine tooth of a sodium pentobarbitone-anesthetized cat. The laser irradiation-induced pulp tissue changes were histologically investigated.

RESULTS

The coronal antidromic compound action potentials disappeared in all the teeth tested during lasing, and the time needed to erase them was significantly shortened with increases in lasing power (P < 0.05). The radicular PBF increased when spot irradiation was performed, and the coronal PBF also temporarily increased with low-powered lasing. Histologic investigation revealed that spot irradiation with the laser produced severe damage in the pulp tissue in a dose-dependent manner.

CONCLUSION

The present study suggests that spot irradiation with a pulsed Nd:YAG laser risks producing nerve injury and irreversible tissue damage in the pulp with lasing for the purpose of desensitizing hypersensitive dentin.

Morphological and atomic analytical studies on enamel and dentin irradiated by an erbium, chromium:YSGG laser

OBJECTIVE

The purposes of this study were to investigate the morphological and atomic analytical changes and to evaluate the cutting effect on dental hard tissues of this laser in vitro.

BACKGROUND DATA

There have been few reports on morphological and atomic analytical study of dental hard tissues after erbium,chromium:yttrium,scandium,gallium,garnet (Er,Cr:YSGG) laser irradiation.

METHODS

Eighteen extracted human molars were sectioned into 3-mm-thick slices, which were irradiated with water-air spray by an Er,Cr:YSGG laser at 6.0 W and 20 Hz for 5 sec for enamel and 5.0 W and 20 Hz for 5 sec for dentin. The samples were then morphologically observed and examined atomic-analytically.

RESULTS

Regular holes having sharp edges and smooth walls, but no melting or carbonization, were observed in both samples. An atomic analytical examination showed that the calcium ratio to phosphorus showed no significant changes between the lased areas and unlased areas (p > 0.01).

CONCLUSION

These results showed that the Er,Cr:YSGG laser has a good cutting effect on dental hard tissues and offers advantages of no burning or melting after laser irradiation.

Dentine caries excavation: a review of current clinical techniques

Since the invention and application of rotary instruments, the operative treatment of carious lesions has often resulted in considerable removal of tooth structure. More recently, newer techniques for removal of carious dentine have been developed in an attempt to minimise this excessive tissue loss. The following article reviews and discusses some of the techniques available to excavate demineralised dentine clinically. These methods can be classified as mechanical and non-mechanical, rotary and non-rotary and include: dental handpieces/burs, manual excavators, air-abrasion, air-polishing, ultrasonication, sono-abrasion, chemo-mechanical methods, lasers and enzymes. The advantages and disadvantages of each technique are discussed.

Effects of pulsed Nd:YAG laser irradiation on smear layer at the apical stop and apical leakage after obturation

AIM

This study evaluated the removal of smear layer at the apical stop by pulsed Nd:YAG laser irradiation with or without black ink, and the degree of apical leakage after obturation in vitro.

METHODOLOGY

Sixty extracted human single-rooted teeth were used in this study. The teeth were instrumented up to a size 40 K-file, and then divided into three groups of 20 teeth each: group 1 was unlased as a control group; group 2 was treated with a laser; group 3 was treated with a laser and black ink. The laser was operated at 2 W and 20 pp for 2 s, and irradiation was performed twice with a 30-s interval. In each group, 10 teeth for the leakage study were obturated and immersed in rhodamine B solution for 48 h at 37 degrees C, and the others were used for evaluation of remaining smear layer. All teeth were bisected longitudinally and observed by stereoscopy or scanning electron microscopy.

RESULTS

The smear layer in the laser-treated groups almost melted or evaporated, and was removed significantly compared with the control group (P < 0.05). Leakage was observed in 60% of samples in group 1 and in 20% of samples in group 2. No leakage was observed in group 3, which was significantly different from the control (P < 0.05).

CONCLUSIONS

These results suggest that pulsed Nd:YAG laser irradiation with black ink increases the removal of smear layer compared with that without black ink, and reduces apical leakage after obturation significantly.

Lasers in endodontics: a review

Since the development of the ruby laser by Maiman in 1960 and the application of the laser for endodontics by Weichman in 1971, a variety of papers on potential applications for lasers in endodontics have been published. The purpose of this paper is to summarize laser applications in endodontics, including their use in pulp diagnosis, dentinal hypersensitivity, pulp capping and pulpotomy, sterilization of root canals, root canal shaping and obturation and apicectomy. The effects of laser on root canal walls and periodontal tissues are also reviewed. The essential question is whether a laser can provide equal or improved treatment over conventional care. Secondary issues include treatment duration and cost/benefit ratio. This article reviews the role of lasers in endodontics since the early 1970s, summarizes many research reports from the last decade, and surmises what the future may hold for lasers in endodontics. With the potential availability of many new laser wavelengths and modes, much interest is developing in this promising field.

Caries-preventive effect of Er:YAG laser irradiation with or without water mist

OBJECTIVE

This investigation was performed to evaluate the effect of Er:YAG laser irradiation on the acquired acid resistance of sound dental hard tissues to artificial caries formation by spectrophotometry, and the ultrastructure of lased areas was investigated by scanning electron microscopy (SEM) in vitro.

BACKGROUND DATA

Although an Er:YAG laser has shown the most promise for hard tissue ablation, there have not been any dissolution studies to determine if this laser is suitable for caries preventive treatments.

METHODS

An Er:YAG laser was used to irradiate the enamel and dentin samples from 20 extracted human molars at 400 mJ pulse energy with or without water mist. Samples were subjected to 2 microL of 0.1 M lactic acid solution (pH 4.8) for 24 hours at 36 degrees C. The parts per million (ppm) of calcium ion (Ca2+) dissolved in each solution was determined by atomic absorption spectrophotometry and the morphological changes were investigated by SEM.

RESULTS

The lowest mean Ca2+ ppm was recorded in the samples irradiated without water mist, in those by irradiated with water mist, and in the unlased samples. SEM observation showed that the lased areas had melted and seemed to be thermally degenerated when irradiated without water mist. After acid demineralization, the thermally degenerated enamel or dentin surfaces were almost unchanged.

CONCLUSIONS

The results of this study suggest that Er:YAG laser irradition with and without water mist appears to be more effective for caries prevention.

Treatment of tooth fracture by medium energy CO2 laser and DP-bioactive glass paste: compositional, structural, and phase changes of DP-bioglass paste after irradiation by CO2 laser

Nowadays, fractured teeth are difficult to treat effectively. Currently, root fractures are usually treated by root amputation, hemisection or tooth extraction. If the fusion of tooth fracture by laser were possible, it would offer a different therapy to repair fracture teeth. We tried to use a developed DP-bioactive glass paste to fuse or bridge the tooth crack line by a medium energy continuous-wave CO2 laser. The study is divided into three parts: (1) The compositional and structure changes in tooth enamel and dentin after laser treatment; (2) The phase transformation and recrystallization of DP-bioactive paste during exposure to the CO2 laser; (3) The thermal interactions and bridge mechanism between DP-bioactive glass paste and enamel/dentin when they are subjected to CO2 laser. The present report will focus on the second part that will examine the changes of laser-exposed DP-bioactive glass paste by means of X-ray diffractometer (XRD), Fourier transforming infrared spectroscopy (FTIR), differential thermal analysis/thermogravimetric analysis (DTA/TGA), and scanning electron microscopy (SEM). From the study, we could find that the temperature increase due to laser irradiation is greater than 900 degrees C and that the DP-bioactive glass paste could be melted in a short period of time after irradiation. In the study, we successfully developed a DP-bioactive glass paste which could form a melting glass within seconds after exposure to a medium energy density continuous-wave CO2 laser. The paste will be used in the near future to bridge the enamel or dentin surface crack by the continuous-wave CO2 laser.

Study on removal effects of filling materials and broken files from root canals using pulsed Nd:YAG laser

OBJECTIVES

The aims of this study were to investigate the capability of removing the filling materials or broken files from root canals with pulsed Nd:YAG laser irradiation at three parameters, and to evaluate the temperature rises on root surfaces and morphological changes of root canal walls in vitro.

SUMMARY BACKGROUND DATA

There has been no report on removing the filling materials and broken instruments from root canals with laser irradiation.

MATERIALS AND METHODS

Thirty-six extracted human incisors were divided into two groups of 18 each. Eighteen root canals were shaped and obturated with gutta-percha and root canal sealer. In another 18 specimens, 3-mm long fractures of files were performed intentionally during root canal preparation. A pulsed Nd:YAG laser irradiation was performed repeatedly at three parameters of 1, 2, and 3 W to remove the filling materials or file fragments. Temperature rises on root surfaces during laser irradiation were measured by thermography, and the remaining of obturated materials and morphological changes of root canal walls were evaluated by stereoscopy and scanning electron microscopy.

RESULTS

In more than 70% of the teeth, the obturated materials were completely removed by laser, and in more than 55% of the teeth, the broken files were successfully removed. Temperature rises ranging from 17 degrees C to 27 degrees C were measured from 6 to 11 repeated times.

CONCLUSION

These results demonstrated that a pulsed Nd:YAG laser irradiation has the capability of removing the obturated materials in root canals and is useful for removing the broken files in same if the counter-measure reducing the temperature rise is performed.

A comparative study on the effects of three types of laser irradiation at the apical stop and apical leakage after obturation

OBJECTIVE

The purposes of this study were to determine the degree of apical leakage using a dye penetration method after argon, pulsed Nd:YAG with or without black ink, or Er:YAG laser treatment and obturation, and to compare the results of three types of laser irradiation in vitro.

SUMMARY BACKGROUND DATA

There have been only a few reports of the laser effect on apical leakage after laser treatment and obturation.

METHODS

Seventy-five human extracted single root teeth were divided into five groups of 15 teeth each and prepared up to a #60 K-file size. One group served as the control and was not irradiated. The other four groups were irradiated with an argon laser at 0.3 W for 3 seconds at continuous mode, pulsed Nd:YAG laser at 2 W and 20 Hz for 4 seconds with or without black ink, and Er:YAG laser at 50 mJ per pulse and 4 Hz for 5 seconds. In each group, ten teeth for the apical leakage study were obturated and immersed in rhodamine B solution for 48 hours at 37 degrees C, and the others were used for the observation by scanning electron microscopy (SEM). All teeth were longitudinally bisected and observed by stereoscopy or SEM.

RESULTS

After pulsed Nd:YAG laser treatment with black ink and obturation, the apical leakage degree (mean score: 0) was reduced compared to that in the control (mean score: 1.2) significantly (p < 0.05). SEM findings showed that specimens irradiated by pulsed Nd:YAG laser with black ink presented clean root canal walls with debris and smear layer evaporated, melted, fused, and recrystallized in most cases.

CONCLUSION

These results suggest that pulsed Nd:YAG laser irradiation with black ink at the apical stop is useful for the reduction of apical leakage after obturation.

Effects of copper vapor laser irradiation in human enamel and dentin: ablation and morphological studies

OBJECTIVE

This investigation was performed to determine the ranges of ablation quantitatively and to evaluate the morphological changes in human enamel and dentine irradiated by a green copper vapor laser.

SUMMARY BACKGROUND DATA

Recently, green copper vapor laser (CVL), which is said to have characteristics similar to the argon laser has been introduced in dentistry.

METHODS

Extracted noncarious human teeth were used in this study. A CVL was used to ablate human dental hard tissues with the output powers of 2.0 W. Ablation extent without water spray using red or black ink was measured, and the morphological changes on enamel and dentin were also investigated by stereoscopy and scanning electron microscopy (SEM).

RESULTS

In the samples, irradiated by a CVL after painting red ink on the surface, the ablation depth was increased more than that of irradiation after painting with black ink. Morphological findings by SEM indicated that when irradiated with red ink, brown carbonization was recognized on enamel and dentin surfaces. In addition, cavities with a molten lava-like appearance were produced and an irregular structure with many microholes was observed in the enamel and dentin. Alternatively, a shallow cavity with little carbonization was produced with black ink.

CONCLUSIONS

Removal of dental hard tissues appears to be possible using the CVL. However, further studies should be performed on the selection of radiation conditions that achieve the desired ablation with minimal side effects.

In vivo caries-like lesion prevention with argon laser: pilot study

OBJECTIVE

This clinical pilot study was conducted to investigate the effectiveness of argon laser irradiation to reduce demineralization or loss of tooth structure in vivo.

SUMMARY BACKGROUND DATA

In vitro research previously demonstrated the ability of argon laser irradiation to reduce demineralization or loss of tooth structure.

METHODS

Using the Ogaard model of producing demineralization, the experimental teeth were irradiated with argon laser of 250 mW (producing approximately 12 J/cm2) prior to banding. Polarized light evaluation of the sectioned, extracted teeth was used to determine the amount of demineralization.

RESULTS

Results showed a 29.1% reduction in demineralization in the experimental teeth as compared to the bilateral control teeth.

CONCLUSION

Low-power argon laser irradiation significantly reduced demineralization clinically.

Treatment of cervical dentin hypersensitivity by various methods using pulsed Nd:YAG laser

OBJECTIVE

The purpose of this study was to evaluate the results of two irradiated regions, the cervical and apical, for cervical dentin hypersensitivity treatment using pulsed a Nd:YAG laser with or without black ink.

SUMMARY BACKGROUND DATA

There has been no reports on the irradiated area(s) except the cervical region for dentin hypersensitivity treatment using pulsed Nd:YAG laser.

METHODS

A total of 180 teeth diagnosed with cervical dentin hypersensitivity in 54 (39 females, 15 males, aged 21 to 73) healthy adult patients were included in this study, and teeth were randomly divided into four groups of 45 each. Sensitivity was rated using a blast from a fully depressed air syringe on a four-grade scale both before and up to 2 months after laser treatment. The effectiveness was evaluated on the change in the degree of hypersensitivity after laser treatment. The tooth surfaces in groups 1 and 2 were observed by the replica model method using scanning electron microscopy (SEM).

RESULTS

The methods of irradiation at the cervical regions were better than those at the apical regions except for the period 2 months later. The laser effect was enhanced by black ink at both areas. The effective (excellent and good) rate was decreased depending on the time in every group. SEM observation at the tooth surfaces from group 2 showed that dentinal tubules were occluded or narrowed after laser irradiation.

CONCLUSIONS

These results show that the method of irradiation by a pulsed Nd:YAG laser at cervical regions with black ink is the most effective for cervical dentin treatment of hypersensitivity and recurrence by this method is less than in other methods.

A study on the morphological changes of the rat mandibular bone with TEA CO2 laser

OBJECTIVE

The purpose of this study was to investigate the morphological changes of the bone structure induced by transversely excited, atmospheric TEA pressure CO2 laser irradiation. Moreover, the healing process at 3 weeks was also observed.

SUMMARY BACKGROUND DATA

It has been demonstrated that dental hard tissue can be removed by a long pulse of TEA CO2 laser irradiation with minimal thermal damage. However, there are few studies on the morphological changes of the TEA CO2 laser on bone tissue.

METHODS

The TEA CO2 laser was irradiated on the surface of the rat mandibular bone under the following irradiation conditions: wavelength, 10.6 microns; output, 95 mJ/pulse; pulse repetition rate, 1 Hz; irradiation time, 7.5 microseconds/shot; spot size, 0.8 x 1.5 mm; energy density, 7.9 J/cm2. Histological and scanning electron microscopic examinations were performed.

RESULTS

In the stereoscopic examination, a defect with clean-cut margins was produced. In the light microscopic examination, a basophilic line at the bottom of the defect was noted. Examining the defect with SEM, a smear-like appearance and cone structures were found. In the histological examination, a healing process by formation of new bones at the junction site was recognized.

CONCLUSIONS

These findings suggest that it is possible to remove bone tissues by TEA CO2 laser irradiation. However, a particle-like structure associated with a basophilic line and melted surface indicated that some thermal damage was produced during the laser irradiation.

Ablation depths and morphological changes in human enamel and dentin after Er:YAG laser irradiation with or without water mist

OBJECTIVE

This investigation was performed quantitatively to determine the ranges of ablation and to evaluate the morphological changes in human enamel and dentin irradiated by Er:YAG laser with or without water mist.

SUMMARY BACKGROUND DATA

Recently, several infrared lasers have been introduced in the dental clinic to remove carious dental hard tissues in anticipation of replacing the high-speed dental drill. Among them, the Er:YAG laser has shown the most promise for hard tissue ablation.

METHODS

An Er:YAG laser was used to ablate human dental hard tissues using a pulse energy that ranged from 100 to 400 mJ at a frequency of 2 Hz for 5 seconds. Ablation rates with or without water mist at different pulse energies were measured, and the morphological changes on enamel and dentin were also investigated by stereomicroscopy and scanning electron microscopy (SEM).

RESULTS

The relationship between ablation depths and energies was almost linear at both enamel and dentin samples. The irradiation with water mist reduced the ablation depths, but only minimally, when compared to those irradiated without water mist. Morphological findings by SEM indicated that Er:YAG laser irradiation with water mist could produce the cavities without signs of thermal damage to the surrounding enamel and dentin.

CONCLUSIONS

The results of this study suggest that addition of a fine water mist directed at the ablation sites does not greatly decrease the ablation, and does not cause any carbonization and melting in the surrounding dental hard tissues.

A clinical study on the effects of pulsed Nd:YAG laser irradiation at root canals immediately after pulpectomy and shaping

OBJECTIVE

The effects of pulsed Nd:YAG laser irradiation for the treatment of root canals immediately after pulpectomy and shaping with regard to improvement of symptoms were evaluated clinically.

SUMMARY BACKGROUND DATA

The effects of pulsed Nd:YAG laser irradiation for the treatment of root canals were experimentally investigated using an animal model, but not under clinical conditions.

MATERIALS AND METHODS

Thirty-eight teeth from 29 patients were diagnosed as normal or irreversible pulpitis were used. After extirpation of pulp and shaping using a step-back technique and cleansing with 5% sodium hypochlorite (NaOCl) and 3% hydrogen peroxide (H2O2), laser irradiation was applied at 1 W and 15 pps for 1 second in 23 teeth (laser-treated group). Root canals were then obturated with gutta-percha points and sealer by the lateral condensation method. The condition of the obturations was confirmed radiographically. The control teeth were treated in the same way, but without laser irradiation. Occurrence of spontaneous pain was recorded 1 day after treatment and occurrence of percussion pain was recorded 1, 2, and 3 weeks after treatment.

RESULTS

Effective ratio, which was the ratio of the number of "none" teeth to total teeth number in the laser-treated group, was higher than that in the control group, but there was no significant difference between 2 groups with regard to spontaneous and percussion pain (p > 0.05).

CONCLUSION

These results suggest that the clinical application of pulsed Nd:YAG laser might be advantageous for the one-visit treatment of root canals immediately after pulpectomy shaping and to reduce postoperative pain.

Post-operative symptoms and healing after endodontic treatment of infected teeth using pulsed Nd:YAG laser

Forty-four teeth in 38 patients, diagnosed with chronic apical periodontitis, were endodontically treated. Root canals were shaped using a step-back technique with 5% NaOCl and 3% H2O2 as irrigants. In half of the teeth the canal terminus was irradiated with pulsed Nd:YAG laser (1 W, 15 pps, 1 s). All canals were then obturated with laterally condensed gutta-percha points and sealer, and final radiographs were obtained. Occurrence of spontaneous pain was recorded 1 day after treatment. Percussion pain was recorded after 1 week, and then at 3 and 6 months after treatment. Radiographic follow-up was performed at 3 and 6 months. Percussion pain was significantly less (P < 0.05) in the laser-treated group than in the control group, both 1 week and 3 months after treatment. Other differences between the groups were not significant. These results suggested that the clinical application of pulsed Nd:YAG laser might be advantageous for the treatment of infected root canals.

Morphological and atomic analytical changes of root canal wall dentin after treatment with thirty-eight percent Ag(NH3)2F solution and CO2 laser

OBJECTIVE

The morphological and atomic analytical changes of the root canal wall dentin, treated with 38% diamine silver fluoride [Ag(NH3)2F] solution and irradiated by carbon dioxide (CO2) laser at the continuous wave mode were evaluated in vitro.

SUMMARY BACKGROUND DATA

There has been no report on the morphological or atomic analytical changes of the effect of Ag(NH3)2F solution and CO2 laser on root canal walls.

METHODS

Eighty extracted human single-rooted teeth were instrumented using a conventional technique and randomly divided into 8 groups of 10 teeth each. The teeth in group 1 were neither treated with Ag(NH3)2F solution nor lased. Groups 2, 3, and 4 were irradiated by laser at the parameters of 1, 2, and 3 W for 10 seconds, respectively. Group 5 was treated with Ag(NH3)2F solution only. The other 3 groups were treated with Ag(NH3)2F solution and then lased by the same method as groups 2, 3, and 4. After this treatment, 4 specimens each from group 1, 5, and 6 were analyzed by scanning electron microscope-energy dispersive x-ray spectroscopy (SEM-EDX) and other specimens in all groups were examined by scanning electron microscopy (SEM).

RESULTS

The smear layer and debris of the control and lased specimens were not completely removed, but the areas of carbonization of evaporation of smear layer and open dentinal tubules were observed on the specimens treated with Ag(NH3)2F and lased at 1 W (group 6). After laser irradiation, the amount of silver on the root canal surfaces was significantly reduced to approximately one-third level on the measurement of SEM-EDX (p < 0.01).

CONCLUSION

These results suggest that CO2 laser is an effective method to remove or melt smear layer of root canal walls after treatment with 38% Ag(NH3)2F solution if an appropriate parameter is selected.

Study of microleakage at Class I cavities prepared by Er:YAG laser using three types of restorative materials

OBJECTIVE

The purpose of this in vitro study were to investigate microleakage at class I cavities filled with amalgam, composite resin, or glass-ionomer after preparation by Er:YAG laser and to compare the results with those by a conventional method using an air turbine.

SUMMARY BACKGROUND DATA

There has been no report of a study of microleakage on class I cavities prepared by Er:YAG laser.

METHODS

Ninety-six extracted human premolar and molar teeth were used in this study. Forty-eight class I cavities were prepared by Er:YAG laser and 48 class I cavities by air turbine. After preparation, each of the 2 groups was further subdivided into 3 groups, respectively, and cavities in each of these subgroups were filled by 1 of 3 types of restorative materials. Microleakage at the restored cavities was assessed by the dye penetration method and scanning electron microscopy (SEM).

RESULTS

Minimal or moderate leakage was evident at most of the composite resin or glass-ionomer restorations, whereas moderate or severe leakage was observed at most of the amalgam restorations as shown by the dye penetration method. There was significant difference among the 3 restorative materials (p < 0.05), but there was no significant difference in microleakage between the cavities prepared by Er:YAG laser and those by air turbine (p > 0.05). SEM evaluation demonstrated good adaptation with most of the composite resin or glass-ionomer restorations, but amalgam restorations showed slightly poorer adaptation.

CONCLUSION

These results suggest that Er:YAG laser is useful for class I cavity preparation from the viewpoint of microleakage.

Treatment of oral granulation tissue with the flashlamp pulsed dye laser

BACKGROUND

Surgical excision and debridement is the standard therapy for cutaneous and intraoral pyogenic granulomas (PGs). Occasionally the mass of granulation tissue proves unresponsive to the usual treatment methods.

OBJECTIVE

We report a case in which the flashlamp pulsed dye laser (PDL), previously reported as useful in cutaneous PGs, was used in a patient with persistent granulation tissue around dental implant posts.

METHODS

An illustrative case is presented with a brief discussion of the use of lasers in dentistry and in the treatment of PGs.

RESULTS

Previously resolute tissue responded well to a series of treatments with the PDL.

CONCLUSION

The PDL may have utility in this oral condition, providing a new venue for cooperation between dentists and dermatologists.

Pulsed Nd:YAG laser application to one-visit treatment of infected root canals in dogs: a histopathological study

OBJECTIVE

In this study, the effects of pulsed Nd:YAG laser irradiation during root canal treatment of infected teeth were investigated histopathologically in dogs.

SUMMARY BACKGROUND DATA

Effects of Nd:YAG laser on infected root canal treatment have not been reported in vivo.

METHODS

One hundred thirty-five teeth with a single root, including incisors and premolars, in 15 healthy adult beagle-strain dogs were used in this study. After inducing infection in the teeth, each root canal was shaped with at least a # 40 K-file, then the canal was irradiated using the following parameters: 1 W, 30 pps for 1 and 2 sec; 2 W, 30 pps for 1 and 2 sec. Efficacy of debris removal and evaporation on the root canal walls at 2 weeks, and the degree of inflammation of the periapical region at 2, 4, and 8 weeks after laser irradiation were examined histopathologically by light microscopy.

RESULTS

Effective debris removal was observed in all cases of the laser-treated groups. No evaporation was observed except at the conditions of 2 W for 2 sec. Inflammation of periapical region in the laser-treated groups was similar in the control group at 2 weeks, but was significantly less than that in the control group at 8 weeks (p < 0.05).

CONCLUSION

These results suggest that pulsed Nd:YAG laser is useful for one-visit root canal treatment of infected teeth in dogs, if appropriate parameters are selected, and this is a potential therapy for human apical lesions of teeth.

A study on microleakage after resin filling of Class V cavities prepared by Er:YAG laser

OBJECTIVE

The aims of this study were to investigate microleakage after composite resin filling to class V cavities prepared by Er:YAG laser and to compare the results with those obtained by a conventional method using an air turbine in vitro.

SUMMARY BACKGROUND DATA

There has been no report of the microleakage study on class V cavities prepared by Er:YAG laser.

METHODS

Forty-eight human extracted single root teeth were used in this study. Teeth were divided into three groups of sixteen each and class V cavities of the same size were prepared by Er:YAG laser for two groups and by air turbine for one group (control). For one group prepared by Er:YAG laser and the control group, the teeth were treated with 30% phosphoric acid. After the cavities were filled with the composite resin, the teeth except the areas of cavities and margins were covered by nail varnish and dye penetration was performed under the 0.6% Rhodamine B at 36 degrees C for 48 hrs. The teeth were sectioned at a thickness of 2 mm transversally and the slices were evaluated by stereoscopy and scanning electron microscopy (SEM).

RESULTS

Microleakage at the cavity margins was observed in all three groups using the dye penetration method, but there was no significant difference among the three groups. SEM results showed similar results with the dye penetration method.

CONCLUSION

These results suggest that microleakage at the cavities prepared by Er:YAG laser is at the same level as for prepared by air turbine using dye penetration and SEM methods.

Effects of pulsed Nd:YAG laser radiation on action potential conduction in nerve fibres inside teeth in vitro

OBJECTIVE

This study aimed to simulate the effects of lasing dentine on pulpal nerve function.

METHODS

Rat spinal nerve roots were threaded through the prepared pulp canal of a 10 mm long tooth root segment which was mounted in a perspex bath. The protruding ends of the nerve were placed on platinum wire electrodes used to elicit and to record compound nerve action potentials (CAPs). Laser energy (average power = 0.3-3.0 W) was applied to the surface of the root segment using a pulsed Nd:YAG dental laser (dLase 300).

RESULTS

With the laser probe tip placed in static contact with the tooth surface, the nerve CAP was irreversibly abolished within 60 s of lasing at 1.0-3.0 W power. When the laser tip was moved to and fro over the root surface in a scanning mode, similar levels of radiation produced less marked effects. In the latter mode, CAP attenuation increased with increasing power and duration of lasing. After 60 s lasing at 0.3 W, the CAP size was 95% (+/- 5, S.D.) of the prelasing controls value; with 2.0 W the CAP was reduced to 54% (+/- 33). The CAP recovered to 90% of control levels after lasing at powers up to 1.5 W, but reached only 72% of control values after lasing at 2.0 W power.

CONCLUSIONS

Laser radiation applied to dentine caused a dose-dependent block of action potential conduction in nerve fibres in the underlying pulp chamber.

Morphological and atomic analytical changes after CO2 laser irradiation emitted at 9.3 microns on human dental hard tissues

OBJECTIVE

The purposes of this study were to examine the effects of CO2 laser emitted at 9.3 microns on human sound and carious dental hard tissue ablation with a stereoscope, scanning electron microscope (SEM), and energy dispersive X-ray spectrometer (SEM-EDX) and to identify possible applications of this laser in clinical treatment.

SUMMARY BACKGROUND DATA

There has been no report of morphological changes or atomic analytical studies on carious hard tissues after laser irradiation with 9.3 microns CO2 laser.

METHODS

Sixty extracted human teeth with no caries and sixty teeth with enamel or dentin caries were used for this study. All teeth were horizontally sectioned into slices (approximately 3 mm in thickness) and the samples were irradiated with CO2 laser using the following two parameters: a fluence of 78 J/cm2 and 5 pps for 2 sec. After laser irradiation, half of the samples were observed by stereoscopy and SEM and the other half were analyzed by SEM-EDX.

RESULTS

The lased sound enamel and dentin surfaces showed crater-like structures which had been produced by the high laser energy. On the other hand, some portions of carious hard tissues were evaported by the laser. A slight amount of carbonization was observed by stereoscopy. Calcium (Ca) and phosphorus (P) content of sound or carious hard tissues was increased significantly (p < 0.01) after laser irradiation, but the ratio of Ca to P after laser irradiation was significantly increased (p < 0.01) on sound hard tissue only.

CONCLUSION

These results suggest that the 9.3 microns CO2 laser may be useful for the prevention or removal of caries in clinical situations.

Comparison between Er:YAG laser and conventional technique for root caries treatment in vitro

Effective ablation of dental hard tissues by means of the erbium-doped:yttrium-aluminum garnet (Er:YAG) laser has been reported recently, and its application to caries removal and cavity preparation has been expected. However, few studies have investigated the capability of the Er:YAG laser to treat caries. In the present study, the effectiveness of caries removal by using an Er:YAG laser in vitro was compared with that of conventional mechanical treatment. Thirty-one extracted human teeth with root caries were used. Half of the caries in each tooth was treated with the Er:YAG laser, and the other was removed with a conventional bur or was left untreated as a control. Laser treatment was performed by means of a combination of contact and non-contact irradiation modes with cooling water spray, with a new fiber delivery and contact probe system. Conventional bur treatment was conducted by means of a low-speed micromotor. Measurements of the time required for caries removal, histopathological observations of decalcified serial sections, scanning electron microscope (SEM) observations, and hardness measurements of the treated cavity-floor dentin were performed for each treatment. Due to the careful irradiation technique, a longer treatment time was required for the complete removal of carious dentin by the Er:YAG laser. However, the Er:YAG laser ablated carious dentin effectively with minimal thermal damage to the surrounding intact dentin, and removed infected and softened carious dentin to the same degree as the bur treatment. In addition, a lower degree of vibration was noted with the Er:YAG laser treatment. The SEM examination revealed characteristic micro-irregularities of the lased dentin surface. Our results show that the Er:YAG laser system is promising as a new technical modality for caries treatment.

Caries prevention by CO2 laser treatment: dependency on the number of pulses used

The aim of this study was to assess the caries-preventive potential of various carbon dioxide laser conditions and to explore the effect of the number of laser pulses used. The authors irradiated unerupted human molars at two wavelengths--10.6 or 9.6 micrometers--and at 1, 5, 25 or 100 pulses. All teeth were then subjected to pH cycling simulating the conditions for caries progression. Pulsed CO2 laser-preventive treatment inhibited caries-like lesion progression by up to 87 percent. This effect was dependent on the number of pulses used, but there was no correlation between caries resistance and enamel surface morphological changes.

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.

High-peak-power, pulsed CO(2) laser light delivery by hollow glass waveguides

Flexible hollow glass waveguides with internal metallic and dielectric coatings have been used to deliver high-peak-power transversely excited atmosphere CO(2) laser energy. The straight guide loss is as low as 0.17 dB/m for 1000-mum-bore guides and 0.46 dB/m for 530-mum-bore guides propagating the HE(11) mode. The loss increases to 0.93 and 1.36 dB/m, respectively, when guides are bent to a radius of 0.25 m. The hollow glass waveguides have been used to deliver pulsed CO(2) laser energy successfully with a peak power of 0.7 MW and an energy of 350 mJ per pulse with a gas purge through the hollow core. The delivered average power is as high as 27 W. It is concluded that these waveguides are promising candidates for pulsed CO(2) laser delivery in medical and surgical applications.

The effects of cooling systems on CO2-lased human enamel

The thermal effects on dentin during CO2 laser irradiation on human enamel were investigated. To simulate the clinical practice, two cooling methods (air and water spray) were applied immediately after laser exposure, whereas one group without cooling was served as control. Three hundred and sixty uniform tooth blocks were obtained from freshly extracted human third molars. Temperature change measurements were made via electrical thermocouple implanted within the tooth block 2 mm away from the enamel surface. Experimental treatments consisted of lasing without cooling, lasing with 0.5-ml/sec water cooling, and lasing with 15-psi air cooling. Our results indicated that (1) both air- and water-cooling groups could reduce temperature elevation significantly; (2) the larger power energy resulted in the higher temperature elevation. In conclusion, for CO2 laser irradiation on human enamel both water- and air-cooling methods may be effective on prevention of thermal damage of pulp.

Effects of an erbium, chromium: yttrium, scandium, gallium, garnet laser on mucocutanous soft tissues

OBJECTIVES

Lasers are effective tools for soft tissue surgery. The erbium, chromium: yttrium, scandium, gallium, garnet laser is a new system that incorporates an air-water spray. This study evaluates the cutting margins of this laser and compares healing with laser and conventional scalpel and punch biopsy-induced wounds.

STUDY DESIGN

New Zealand white rabbits were divided into serial sacrifice groups; the tissues were grossly and microscopically analyzed after laser and convential steel surgical wounding.

RESULTS

Wound margins were found to show minimal edge coagulation artifact and were 20 to 40 mm in width. Laser wounds showed minimal to no hemorrhage and re-epithelialization and collagenization were found to occur by day 7 in both laser and conventional groups.

CONCLUSIONS

The new laser system is an effective soft tissue surgical device; wound healing is comparable to that associated with surgical steel wounds. The minimal edge artifact observed with this laser system should allow for the procurement of diagnostic biopsy specimens.

Flexible waveguides for Er-YAG laser radiation delivery

Flexible plastic waveguides (FPW) were devised for the delivery of Er-YAG laser radiation. The FPW characteristics were studied under various conditions. In vitro studies were carried out to explore the drilling procedure on extracted teeth and the FPW-tissue mutual effects. The results which were obtained proved that the FPW as a delivery device might be a substitute hand applicator for the pneumatic turbine for drilling in teeth.