Thermal effects of lasers on dental tissues

Emissivity evaluation of human enamel and dentin

Background: Human enamel and dentin temperatures have been assessed with non-contact infrared imaging devices for safety and diagnostic capacity and require an emissivity parameter to enable absolute temperature measurements. Emissivity is a ratio of thermal energy emitted from an object of interest, compared to a perfect emitter at a given temperature and wavelength, being dependent on tissue composition, structure, and surface texture. Evaluating the emissivity of human enamel and dentin is varied in the literature and warrants review. The primary aim of this study was to evaluate the emissivity of the external and internal surface of human enamel and dentin, free from acquired or developmental defects, against a known reference point. The secondary aim was to assess the emissivity value of natural caries in enamel and dentin.

Method: Fourteen whole human molar teeth were paired within a thermally stable chamber at 30°C. Two additional teeth (one sound and one with natural occlusal caries–ICDAS caries score 4 and radiographic score RB4) were sliced and prepared as 1-mm-thick slices and placed on a hot plate at 30°C within the chamber. A 3M Scotch Super 33 + Black Vinyl Electrical Tape was used for the known emissivity reference-point of 0.96. All samples were allowed to reach thermal equilibrium, and a FLIR SC305 infrared camera recorded the warming sequence. Emissivity values were calculated using the Tape reference point and thermal camera software.

Results: The external enamel surface mean emissivity value was 0.96 (SD 0.01, 95% CI 0.96–0.97), whereas the internal enamel surface value was 0.97 (SD 0.01, 95% CI 0.96–0.98). The internal crown-dentin mean emissivity value was 0.94 (SD 0.02, 95% CI 0.92–0.95), whereas the internal root-dentin value was 0.93 (SD 0.02, 95% CI 0.91–0.94) and the surface root-dentin had a value of 0.84 (SD 0.04, 95% CI 0.77–0.91). The mean emissivity value of the internal enamel surface with caries was 0.82 (SD 0.05, 95% CI 0.38–1.25), and the value of the internal crown-dentin with caries was 0.73 (SD 0.08, 95% CI 0.54–0.92).

Conclusion: The emissivity values of sound enamel, both internal and external, were similar and higher than those of all sound dentin types in this study. Sound dentin emissivity values diminished from the crown to the root and root surface. The lowest emissivity values were recorded in caries lesions of both tissues. This methodology can improve emissivity acquisition for comparison of absolute temperatures between studies which evaluate thermal safety concerns during dental procedures and may offer a caries diagnostic aid.

Comparison of Different Energy Levels of Er:YAG Laser Regarding Intrapulpal Temperature Change During Safe Ceramic Bracket Removal

OBJECTIVE

This study was done to compare the intrapulpal temperature change generated by different energy levels of Er:YAG laser used during debonding of ceramic brackets and find the most suitable level for clinical use.

MATERIAL AND METHODS

Eighty polycrystalline alumina brackets were bonded on bovine incisor teeth, which were randomly divided into 4 groups of 20. One group was assigned as control. In the study groups, after laser exposure with 2, 4, or 6 Watt energy levels, brackets were debonded using an Instron Universal Testing machine. Adhesive remnant index (ARI) scores were recorded to evaluate the site of debonding. To assess intrapulpal thermal increase, 60 human premolar teeth that were prepared in the same way, at the same energy levels, by a thermocouple were used.

RESULTS

When the debonding forces, intrapulpal temperature increases, and ARI of the groups were examined, statistically significant difference was observed between the groups. Mean temperature increases of 0.67°C ± 0.12°C, 1.25°C ± 0.16°C, and 2.36°C ± 0.23°C were recorded for the 2, 4, and 6 Watt laser groups. The mean shear bond strength was 21.35 ± 3.43 megapascals (MPa) for the control group, whereas they were 8.79 ± 2.47, 3.28 ± 0.73, and 2.46 ± 0.54 MPa for the 2, 4, and 6 Watt laser groups, respectively.

CONCLUSIONS

Four watts is the most efficient and safe energy level to be used, utilizing Er:YAG laser with water cooling spray for 6 sec by scanning method during debonding of polycrystalline alumina brackets without any carbonization effects and detrimental temperature changes at debond sites.

Evaluation of Nd:YAG laser on partial oxygen saturation of pulpal blood in anterior hypersensitive teeth

Dentine hypersensitivity has of long been known to be a common clinical problem in dental practices. Lasers have recently come to play a prominent role in the treatment of this disorder. They might, however, cause dental pulp damage. This study was conducted to evaluate the effect of Nd:yttrium-aluminum-garnet (YAG) laser on partial oxygen saturation of pulpal blood in sensitive anterior teeth. In this clinical trial, 65 hypersensitive teeth were selected and randomly allocated to two groups. The study group involved Nd:YAG laser treatment, while no treatment was employed for the control group. Using a pulse oximetry system, evaluations were preformed of the partial oxygen saturation in the pulpal blood before, immediately after, 1 week after, and 1 month after the treatment. The results were analyzed using the SPSS software and repeated-measures analysis of variance and paired-samples t tests. The mean partial oxygen saturation of the blood was found to be 85.4% in the study group, which was not significantly different from that of the control group. No significant differences were observed in the control group between the means obtained from pretreatment and post-treatment intervals (P > 0.05). The Post-treatment partial oxygen saturation mean rose to 89.3% (P = 0.001) and remained constant throughout the following week after it. However, no significant differences were found between the pretreatment partial oxygen saturation mean and the same measurement 1 month after treatment (P = 0.702). Nd:YAG laser therapy for dentine desensitization of anterior teeth caused no persistent changes in the partial oxygen saturation of pulpal blood. It may, therefore, be concluded that the diffusion of heat induced by the Nd:YAG laser into the pulp within the limit of the desensitization parameters cause no irreversible damages in the dental pulp.

Verifiable CPD paper: laser-tissue interaction

The oral cavity is a unique and complex environment, where hard and soft tissues exist in close proximity, within bacteria-laden saliva. All oral tissues are receptive to laser treatment, but the biophysics governing laser-tissue interaction demands a knowledge of all factors involved in delivery of this modality; through this knowledge, correct and appropriate treatment can be delivered in a predictable manner.

The feasibility of using infrared thermography to evaluate minor salivary gland function in euhydrated, dehydrated and rehydrated subjects

BACKGROUND

Infrared thermography technique (IRT) is utilized by a growing number of disciplines within medicine and dentistry. However, IRT has not been employed in the evaluation of salivary gland dysfunction. The purpose of this study was to examine the feasibility of using thermographic imaging in the evaluation of minor labial salivary gland function in subjects during euhydration, dehydration, and rehydration states.

METHODS

Ten subjects were studied. Upper labial minor salivary gland secretion was quantified whilst simultaneously visualizing lower minor salivary gland output thermographically during each state.

RESULTS

A significant difference was observed in the minor labial salivary flow among euhydrated, dehydrated and rehydrated, states. Despite the lack of statistical difference in the thermographic findings, IRT images reflected noticeable differences among the three hydration states.

CONCLUSION

The overall results of this study suggest that IRT could potentially provide a valuable non-invasive tool for evaluating the relationship between minor labial salivary gland function and hydration status.

Increases in intrapulpal temperature during polymerization of composite resin

STATEMENT OF PROBLEM

The polymerization of dental composite resins can generate increases in intrapulpal temperature that may damage the pulp. The development of new polymerization devices such as the argon laser makes the assessment of these temperatures important.

PURPOSE

This study compared increases in temperature generated by argon laser and halogen light when polymerizing a bonding system and a composite resin, and also sought to determine whether both types of polymerization lights generate temperature increases below the safe limit of 5.5 degrees C.

MATERIAL AND METHODS

Thermocouples linked to a temperature reading system were positioned in the pulp chamber of 10 extracted bovine incisors. Class V cavities were prepared, etched, and filled with a 1-bottle bonding system (Single Bond) and composite resin (Z-100). The test groups were as follows (n = 5 for all groups): halogen light for bonding system (HB); halogen light for composite resin (HC); argon laser for bonding system (LB), and argon laser for composite resin (LC). The polymerization parameters were halogen light operated at 600 mW/cm2 for 40 seconds, which served as control, and argon laser operated at 200 mW for 10 seconds. Data were analyzed by a 2-way (light versus material) analysis of variance (ANOVA) (alpha = .05).

RESULTS

The average temperature increases were 2.35 degrees C (HB), 2.69 degrees C (HC), 1.25 degrees C (LB), and 1.5 degrees C (LC). Significant differences between halogen light and argon laser (P = .002), but not between composite and bonding system, were demonstrated.

CONCLUSIONS

The argon laser produced significantly lower increases in pulpal temperature than the halogen light, independent of the thickness of the polymerized material.

Nd: YAG laser for debonding ceramic orthodontic brackets

INTRODUCTION

The purpose of this study was to develop an effective method for debonding ceramic orthodontic brackets with a high-peak power Nd:YAG laser.

METHODS

Two types of ceramic brackets (single crystal and polycrystalline) were bonded to mandibular bovine teeth with 2 types of bonding resins (4-META/MMA and Bis-GMA). The laser was applied to 2 points on each bracket, each with a 1-pulse-per-second shot. Bond strength and thermal effects of the laser on the dentin surface were assessed at 3 laser energy levels: 1.0, 2.0, and 3.0 joules (J). Shear tests were performed on the irradiated test group and on a nonirradiated control group. ANOVA was used to determine significant differences.

RESULTS

The shear test (P < .05) showed that every specimen in the 2.0-J and 3.0-J groups underwent a significant decrease in bonding strength compared with the nonirradiated group. However, the 1.0-J group did not exhibit any such difference. In the 2 former groups, laser irradiation alone was sufficient to debond some specimens. No significant difference was found between bonding resins. The maximum temperature rise measured on the pulpal walls at the lasing points was 5.1 degrees C.

CONCLUSIONS

The application of a high-peak power Nd:YAG laser at 2.0 J or more is effective for debonding ceramic brackets.

Argon laser oral safety parameters for teeth

Argon lasers have been reported to prevent or reduce demineralization of enamel in extracted teeth and to polymerize dental composites (using 25-100 J/cm2). Prior to clinical trials on caries prevention and curing composites, safety parameters for intraoral use of the argon laser need to be established. This study was conducted to determine the enamel damage, pulp temperature changes, and associated pulpal tissue damage following irradiation at various argon laser energy levels using 1.6-6.0 watts, approximately 1 and 2 mm diameter beam for 0.2-5.0 seconds. To evaluate pulpal damage, selected dogs' teeth were irradiated in vivo, extracted 7 days postlasing, fixed, decalcified, sectioned, stained, and read for pulpal damage. Pulp temperature and enamel damage tests utilized extracted dog and human teeth. Temperature probes were inserted in the pulp chambers and temperature changes recorded as enamel surface was lased. Enamel surface damage was evaluated by visual and microscope examination. Results showed that histologic pulpal damage occurred at > 600 J/cm2. Temperature changes were < 6 degrees F in human teeth with approximately 900 J/cm2. No enamel damage was observed at these energy densities. At energy densities needed for proposed uses, no apparent damage would be expected to pulp or enamel.

Pulpal and periodontal temperature rise during KTP laser use as a root planing complement in vitro

OBJECTIVE

The purpose of this study was to define the optimal irradiation conditions of a KTP laser during root planing treatment.

METHODS

The surfaces of 60 single-root human teeth were scaled with conventional instruments before lasing. The pulpal temperature increase was measured by means of one thermocouple placed in the pulp chamber and a second one placed on the root surface at 1 mm from the irradiation site. The influence of variables of coloration by Acid Red 52 (photosensitizer), scanning speed, dentin thickness, and probe position was analyzed for a constant exposure time of 15 sec and 500 mw (spot size diameter, 0.5 mm). The pulpal temperature was below 3 degrees C for the adjustments.

RESULTS

The irradiation on one point of root surface had the following results: The application of photosensitizer on the root surface before lasing produced a 50% higher temperature rise within the pulp than in the case without the application of the photosensitizer. The temperature rise in the pulp chamber was below 3 degrees C with the following settings of 500 mw: PW = 10 msec and PRR < 35; or PW= 20 msec and PRR < 20 Hz. On the other hand, for the same irradiation conditions, the temperature rise on the surface of the root was always below 7 degrees C. However, the temperature increase became higher than 7 degrees C (on the surface of the root) in the case of P > 500 mw, PW > 50 msec and PRR > 10 Hz of root surface or a scanning speed of irradiation of 1 mm/sec for a linear irradiation of 4 mm.

CONCLUSION

The KTP laser may be used safely without thermal damage to pulp and periodontal tissue with respect to the biologically acceptable previously described parameters.

Effects of copper vapor laser irradiation (lambda = 510.6 nm) on the enamel and dentine of human teeth: an ultra-structural morphologic study

OBJECTIVE

A morphological and ultra-structural study of copper vapor laser (lambda = 510.6 nm) effects on enamel and dentine was performed to show the effects of this radiation.

METHODS

A total of 15 human molars were cut in half; 15 pieces were separated for irradiation on enamel and 15 for dentine. These two groups were further divided into five experimental groups, including a control group, comprised of three half-sections each, irradiated by a CVL laser with a power of 7 W, a repetition rate of 15,000 pulses/sec and exposed at 500, 600, and 800 msec and 1 sec irradiation times with a 5-sec interval between irradiations.

RESULTS

In an ultra-structural SEM exam, we observed that on the enamel surfaces irradiated for 1 sec there was morphological alteration that consisted of catering, flaking, and melting on the surfaces. There was no alteration for the other exposure times. On the dentine teeth irradiated for 1 sec, we observed an evident ultra-structural alteration of melted tissue and loss of morphological characteristics. In the dentine group irradiated by 800 msec, we observed ablation and a partial loss of morphological characteristics. In the dentine groups irradiated by 500 and 600 msec, no alteration was observed.

CONCLUSIONS

The results showed that irradiation with CVL promoted morphologic changes in the enamel as well as in the dentine and demonstrated a need for future studies in order to establish a safe protocol for further use in the odontological practice.

Safety parameters for pulp temperature during selective ablation of caries by KTP laser in vitro

OBJECTIVE

To define the optimal parameters of KTP laser irradiation during a selective caries removal.

MATERIALS AND METHODS

Twelve decayed human teeth, recently extracted were used. Their root canals were prepared for insertion of a thermocouple probe into the pulp chamber. The demineralized tissues were colored by Acid Red 52 before proceeding to different conditions of irradiation.

RESULTS

Pulpal temperature increases (below 3 degrees C) were found under the following parameters with 15 sec of continuous lasing: 400 mWatts, 0.10-msec pulse width, PRR <50 Hz for efficient caries removal. A resting time average of 70 sec was necessary to allow pulp temperature to get back to its baseline.

CONCLUSION

KTP laser can be used safely and without any pulp over-heating under certain irradiation conditions.

Wavelength and average power density dependency of the surface modification of root dentin using an MIR-FEL

BACKGROUND AND OBJECTIVES

Surface modification of root dentin by mid-infrared (MIR) pulsed-laser irradiation is one of the candidates for a novel, non-invasive treatment to prevent root surface caries. To modify root dentin effectively and non-invasively it is essential to estimate quantitatively and qualitatively the laser parameters, such as the wavelength and power density, required for surface modification. The key aspect is to bring about effective surface modification of the root dentin while minimizing the unwanted removal of the underlying dentin.

STUDY DESIGN/MATERIALS AND METHODS

Using a tunable, MIR Free Electron Laser with lambda = 8.8-10.6 microm, we have investigated macroscopically the extent of the surface modification (morphological and chemical changes) of root dentin. We have obtained experimental results related to the ablation depth, the MIR absorption spectrum, and the elemental chemical composition.

RESULTS

The observations showed that the surface modification of root dentin was inclined toward well-recrystallized HAp-like material, leading to an increase in the acid resistance and dentinal tubule sealing. The laser parameters, at which efficient surface modification without enhanced ablation occurred, were estimated to be approximately in the wavelength region around lambda = approximately 9.0 or approximately 9.7 microm and in the average power density region of approximately 10-20 W/cm2 (resulting in total energy density and peak power density regions of approximately 1-2 kJ/cm2 and approximately 0.67-1.2 kW/cm2).

CONCLUSIONS

The surface modification of root dentin strongly depends on the laser parameters applied. We conclude that the optimum wavelengths for laser treatment of root surface caries are lambda = approximately 9.0 or approximately 9.7 microm, corresponding to the absorption peak due to P-O stretching.

Sintering mechanism of the CaF2 on hydroxyapatite by a 10.6-l microm CO2 laser

BACKGROUND AND OBJECTIVES

Laser has been reported as a heat source for melting and re-crystallization. Occurring at about 1100 degrees C, the melting of surface dental enamel along with re-crystallization might have an assistant role in the therapy of hypersensitive tooth, apical sealing of endodontic surgery in dentistry, preventive dentistry for pit and fissure sealing, and fluoridation. For laser to be accepted in clinical applications, it is desired that, studies must show the incorporation of CaF(2) into hydroxyapatite could reduce the sintering temperature for the sake of safety.

STUDY DESIGN/MATERIALS AND METHODS

In this study, the Sharplan 20XJ CO(2) laser with 10.6- microm wavelength was set under the following parameters: power, 5 W; repetitive mode, 0.1 second; beam, focused. Fluorite was added to hydroxyapatite as a synthetic compound to lower the sintering temperature. Human dental enamel without caries was used for in vitro sintering test. Scanning electron microscopy (SEM), X-ray diffractometer (XRD), Fourier transforming infrared spectroscopy (FTIR), and differential thermal analysis/thermogravimetric analysis (DAT/TGA) were used for the investigation of sintering mechanism of CaF(2).

RESULTS

Fusion between hexagonal shape crystals and cubic shape crystals (CaF(2)) were observed under SEM study. Hexagonal shape crystals indicated the formation of fluorapatite under XRD analysis. Under FTIR study, we examined reductions of water (3445 cm(-1)) and hydroxyl bands (3567 and 627 cm(-1)) in irradiated compounds. From the DTA pattern of synthetic compound, it showed the endothermic reaction reaching its peak point around 1180 +/- 20 degrees C. It was attributed to the phase transformation and/or initial melting.

CONCLUSIONS

In this study, we proposed the interrelationship of the eutectics between initiator (CaF(2)) and the reaction product (calcium hydroxide) that reduced the sintering temperature. It appeared that the co-eutectics interacted to reduce the sintering temperature of hydroxyapatite below 800 degrees C and that the key eutectic was calcium hydroxide. The clinical feasibility of the melting and re-crystallization of hydroxyapatite under 10.6-microm CO(2) laser would be therefore enhanced.

Selective ablation of surface enamel caries with a pulsed Nd:YAG dental laser

BACKGROUND AND OBJECTIVE

High intensity infrared light from the pulsed Nd:YAG dental laser is absorbed by carious enamel and not absorbed by healthy enamel. Consequently, this system has potential for selective removal of surface enamel caries. Safety and efficacy of the clinical procedure was evaluated in two sets of clinical trials at three dental schools. Selective ablation was evaluated with FTIR spectroscopy.

STUDY DESIGN/MATERIALS AND METHODS

Carious lesions were randomized to drill or laser treatment. Pulp diagnosis, enamel surface condition, preparations, and restorations were evaluated by blinded evaluators. In Study I, surface caries were removed from 104 third molars scheduled for extraction. One-week post-treatment teeth were evaluated clinically, extracted, and the pulp was examined histologically. In Study II, 90 patients with 462 lesions on 374 teeth were randomized to laser or drill and followed for 6 months.

RESULTS

Pulsed Nd:YAG laser removal of surface enamel caries was demonstrated to be both safe and effective. Caries were removed in all conditions. There were no adverse events and both clinical and histological evaluations of pulp vitality showed no abnormalities. A significantly greater number of preparations in the drill groups vs. laser groups entered dentin (drill = 11, laser = 1, P = 0.007).

CONCLUSION

The more conservative laser treatment removed the caries but not the sound enamel below the lesion. The pulsed Nd:YAG dental laser was found to be both safe and effective for surface caries removal.

The effect of Nd:YAG radiation at nanosecond pulse duration on dentine crater depth

The effect of laser parameters on laser-dentine interaction is little known. The aim of this in vitro study was to determine the effect on dentine crater depth of Nd:YAG laser radiation in relation to pulse repetition rate, total delivered energy, dentine site and the presence or absence of a dye. One hundred and forty-four sound third molars were extracted and sectioned transversely to provide 288 upper and lower cut surfaces. The upper surfaces were painted with a layer of dye (IR5) suitable for absorption at 1064 nm. The specimens were divided into 12 sub-groups each containing 12 upper and 12 lower specimens. These were exposed to a Nd:YAG laser with a 30 nanosecond (ns) pulse duration. This laser operated in a non-contact mode (spot diameter 165 microm) with pulse repetition rates of 2.5, 5.4 and 10.5 Hz. Four total energies were delivered at each repetition rate; 2.3, 3.63, 3.96, 4.29 joule (J) at 2.5 Hz repetition rate; 2.3, 2.64, 3.63, 4.29 J at 5.4 and 10.5 Hz repetition rates. Five outer and three inner sites were irradiated on each specimen. Each dentine crater depth was measured five times using a Reflex Microscope and a three-dimensional centre of gravity derived. An upper and lower specimen were taken from each sub-group and viewed under a scanning electron microscope (SEM). ANOVA was applied: total delivered energy and dyed/undyed were found to have a statistically significant effect on crater depth (p<0.0001). In general increasing energy and the presence of dye produced deeper craters. Inner/outer dentine location and repetition rate were not found to be statistically significant. All craters were carbonised.

Effect of pulsed Nd:YAG laser irradiation on acid demineralization of enamel and dentin

OBJECTIVE

The purpose of this study was to investigate the effect of Nd:YAG laser irradiation on the acid demineralization of enamel and dentin by spectrophotometry. A mechanism of acquired acid resistance is also proposed.

SUMMARY BACKGROUND DATA

The ability of Nd:YAG laser irradiation to the enhanced resistance to artificial caries formation is still controversial.

METHODS

A pulsed Nd:YAG laser at 1.064-micron wavelength was used to irradiate the human enamel and dentin samples from 20 extracted human molars at the parameters of 1, 2, and 3 W and 20 pps for a total of 9 sec after painting with black ink. Samples were then subjected to 2 microliters of 0.1 M lactic acid solution (pH 4.8) for 24 h 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 also investigated by scanning electron microscopy (SEM).

RESULTS

The lowest mean Ca2+ ppm was recorded in the samples irradiated at 3 W, in those by irradiated at 2 W and 1 W. The unlased samples showed the highest Ca2+ ppm. SEM observation showed that in the lased areas, the smear layer was partially melted and the underlying primary enamel or dentin seemed to be thermally degenerated.

CONCLUSIONS

The results of this study suggested that melted smear layer and underlying enamel or dentin degenerated thermally by the heat treatment of Nd:YAG laser might play a major role to enhance resistance to artificial caries-like formation.

Pulsed Nd:YAG laser irradiation of the tooth pulp in the cat: II. Effect of scanning lasing

BACKGROUND AND OBJECTIVE

The purpose of the present study was to assess whether "scan irradiation" with a pulsed Nd:YAG laser could produce changes in intrapulpal nerve activities and pulpal blood flow and to investigate whether it would cause tissue damage in the pulp.

STUDY DESIGN/MATERIALS AND METHODS

The pulsed Nd:YAG laser was used to irradiate, in a scanning manner, the canine tooth pulp in sodium pentobarbitone anesthetized cats. The compound action potentials and spike response in the functional single afferent nerve fibers were recorded while responding to various external stimuli applied to the exposed dentin. Histologic observation was performed to detect lasing-induced tissue changes.

RESULTS

Pulpal compound action potentials evoked by various external stimuli were significantly reduced (P < 0.05) and unit firings were observed in both functional single A delta- and C-fibers during irradiation. Unit responses to external mechanical stimulation of the dentin completely disappeared after "scan irradiation" with the pulsed Nd:YAG laser. Histologic observation revealed that irradiation with the laser produced tissue damage in the pulp.

CONCLUSION

"Scan irradiation" with the pulsed Nd:YAG laser of cat's teeth produced alterations in the intrapulpal nerve activities, as well as caused tissue damage in the pulp.

Morphological effects of ArF excimer laser irradiation on enamel and dentin

BACKGROUND AND OBJECTIVE

The aim of this investigation to determine the range of morphological and ablative effects that can be achieved on dental enamel and dentin using ArF excimer laser irradiation at a wavelength of 193nm.

STUDY DESIGN/MATERIALS AND METHODS

Caries-free coronal enamel and dentin surfaces of 20 extracted human teeth were subjected to irradiation at 193nm using a Lamda-Physik model EMG 103 MSC and ArF fill. Morphology of cavity floors and walls were assessed by light microscopy and SEM.

RESULTS

Morphological surface effects and ablation could be controlled effectively and reliably by choice of parameter combination, allowing the operator to achieve either a smooth, flat, or increasingly rough surface with differing degrees of selective ablation. No signs of thermal damage were apparent.

CONCLUSION

Excimer laser irradiation at 193nm provided clinically useful cavity preparations and surface morphological effects.

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.

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.

Acquired acid resistance of dental hard tissues by CO2 laser irradiation

OBJECTIVE

This investigation was performed to evaluate the effect of CO2 laser irradiation on the acquired acid resistance of dental hard tissues to artificial caries-like formation and the ultrastructure of lased areas was morphologically investigated in vitro.

SUMMARY BACKGROUND DATA

In recent years, many studies have been carried out to evaluate the effect of the CO2 laser on the enhanced resistance to artificial caries formation of enamel. However, a limited number of papers concerning its effect on dentin have been published.

METHODS

A CO2 laser of 10.6 microns wavelength was used to irradiate human enamel and dentin samples from 20 extracted human molar teeth, and samples were subjected to 2 microliters of 0.1 M lactic acid solution (pH 4.8) for 24 h 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 scanning electron microscopy (SEM).

RESULTS

The lowest mean Ca2+ ppm was recorded in the samples irradiated at 3 W, followed by 2 W, 1 W, and unlased samples. SEM observation showed that the lased areas were melting with solidification of the smear layer. Even after acid demineralization, the lased surfaces were almost unchanged.

CONCLUSIONS

The results of this study suggested that CO2 laser irradiation could sufficiently melt and solidify the enamel and dentin surfaces and thus enhance resistance to artificial caries-like formation.

Dye-assisted diode laser ablation of carious enamel and dentine

Carious dentine and enamel from extracted human teeth were ablated using a semiconductor diode laser in conjunction with an applied dye, indocyanine green. This technique offers selective ablation with minimal risk of thermal damage to surrounding dental tissues because uptake of the dye and its irradiation by the laser together control the ablation. In this study, various laser powers and dye concentrations were used to ablate previously extracted human teeth with moderate caries. The mass of material ablated and the temperature rise in the pulp and at the surface were recorded, and the ablated surface was examined by microscopy. The ablation was efficient and the rise in the pulp temperature slight. Ablation efficiency and surface temperature were both found to increase with laser irradiance and with dye concentration. No surface cracks or fissures were seen in electron microscope examination and the hardness of the laser-treated surfaces was comparable to that of healthy tissue. The dye-assisted laser ablation technique offers considerable potential for clinical caries removal and dentine, enamel and pulp sterilization, whilst leaving healthy tissue intact. The diode laser can deliver its energy via simple optical fibre and is cheaper and much smaller than the conventional high power lasers used in other studies.

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.

Effects of Nd: and Ho:yttrium-aluminium-garnet lasers on human dentine fluid flow and dental pulp-chamber temperature in vitro

Dentine specimens were prepared from freshly extracted third molars and initial permeability measured. Each specimen was subjected to Nd:yttrium-aluminium-garnet (YAG) (1.06 or 1.32 microns wavelength) or Ho:YAG (2.10 microns wavelength) laser energy while temperatures in the pulp chambers were recorded. Permeability was again measured and the surfaces examined by scanning electron microscopy. Six crown segments were used for each laser variable and eight permeability measurements were taken before and eight after laser exposure, while temperature was recorded during treatment. All wavelengths reduced permeability but temperature rises were high enough to have caused pulpal damage, indicating that shorter treatment times and lower power settings may be necessary if used in vivo.

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.

Pulpal response to cavity preparation with the Er:YAG and Mark III free electron lasers

OBJECTIVE

The purpose of this investigation was to evaluate the pulp response to class V cavity preparation with the use of the Er:YAG laser and free electron laser.

STUDY DESIGN

Class V cavities were prepared in 133 teeth of four beagle dogs by one of three methods: (1) Er:YAG laser, (2) free electron laser, (3) high-speed handpiece. Treatment occurred at 1 hour, 1 day, 7 days, and 28 days. The teeth were removed and the pulp evaluated. Histologically, the data were evaluated with Mantel-Haenszel analysis.

RESULTS

The Er:YAG laser, free electron laser, and handpiece treatment groups resulted in specimens with normal or mild pulp reactions in 36, 46, and 42 teeth, respectively; moderate or severe reactions were observed in 7, 1, and 1 teeth, respectively. No statistically significant difference in the pulp response to the three treatment modalities was observed.

CONCLUSION

The pulp response to Er:YAG laser and free electron laser application would appear to be similar to the response from high-speed handpiece application.

Infrared thermography. Its role in dental research with particular reference to craniomandibular disorders

The use of infrared thermography in dentistry has been minimal, principally due to technological inadequacies of previous thermal imaging systems. However, with the ever-developing advancement in technology, current systems are capable of producing real-time, highly sensitive digitized thermal images. This development has led to an increased use of infrared imaging within both medical and dental research. The present paper describes these techniques and their previous applications within dentistry, and, through the use of a pilot study, highlights possible future applications in the assessment of craniomandibular disorders.

Effects of the argon laser on primary tooth pulpotomies in swine

This study evaluated the clinical, radiographic, and histologic effects of the HGM PC Oralase argon laser on vital pulps of swine teeth. Pulpotomies were performed in vivo on 42 primary teeth from three young pigs and observed for 7 or 60 days. For each time period nine experimental teeth received an argon laser dose of 1 W, 2 sec (24.88 J/cm2), and nine experimental teeth received a dose of 2 W, 2 sec (49.74 J/cm2). Controls consisted of three teeth for each time period and did not receive exposure from the argon laser. There were no significant differences noted between the two energy densities with respect to clinical, radiographic, or histological parameters for either time period. All soft tissues remained normal and all teeth exhibited normal mobility at weekly assessments. Other than physiologic root resorption, there were no differences in pre- and postoperative radiographs in the 7 day sample; calcifications coinciding to dentinal bridges were visible radiographically in 8 of the 60-day samples. Reparative dentin formation was noted histologically in a total of 9 roots in the 7-day group and in 13 roots in the 60-day group. With the exception of teeth which had early restoration loss with resultant bacterial contamination, all other pulps appeared to retain their vitality and capability of normal pulpal healing. Use of the argon laser at the parameters described in this study did not appear to be detrimental to pulpal tissues.

The radicular dentine temperature during laser irradiation: an experimental study

The detoxification and sterilization radicular surfaces that have been produced by periodontal diseases could be accomplished after polishing (root planing) using the thermal elevation resulting from CO2 laser on continuous emission. In vitro experiments reveal that thermal elevations reached on the surfaces or in the depth are proportional to the dispersed energy. The thermal elevation in the depth (0.5-1 mm from the impact point) remained moderate because of the water absorption potentials of the radiations. Energies from 2 to 4.5 J can help obtain the combination of surface temperature elevation, which allows detoxification, and of a thermal elevation in the depth, compatible with vital tissues. This energy has to be delivered at an application time under 0.6 sec in continuous mode.

Light deposition in dental hard tissue and simulated thermal response

Near-IR (approximately 1 micron) lasers are presently used for a variety of intra-oral applications including dental hard tissue ablation, although the light intensity distribution and subsequent heating of the hard tissue are still poorly understood. This paper presents a detailed numerical study of the scattered light intensity distribution along with the corresponding predicted thermal response. The calculations are based on recently published scattering and absorption data for dental hard tissue around 1 micron. Our simulations indicate strongly enhanced energy deposition and concomitant heating near the dentino-enamel junction (DEJ), mainly due to the higher absorption in dentin. We predict from 10 to 20 times higher internal temperatures near the DEJ compared with the surface. For example, for 50-ms pulses of 5-J energy on a 3-mm-diameter spot (approximately 1 kW/cm2 or approximately 50 J/cm2), one can expect internal temperatures near the DEJ in excess of 100 degrees C. Elevated temperatures are predicted to extend far into the dentin, endangering the vitality of the pulp several millimeters below the surface. Our results are compared with published experimental data taken under similar conditions and are found to be in good general agreement. The results of this study do not contradict recently reported ablation of dentin with Nd:YAG laser radiation by contact fiber probes. In this case, the irradiation intensities are 3 to 4 orders of magnitude higher, so plasma formation and plasma shielding of the interior of the tooth are likely.

Damage to dental composite restorations following exposure to CO2 laser radiation

Damage to tooth structure is a major hazard in the use of infrared lasers for oral surgical procedures. While the effects of laser exposure on dental enamel and dentine are well characterized, there are no data on the effects of laser exposure on dental composite materials, which are widely used in tooth-colored restorations. This study examined surface changes in several dental composites exposed to CO2 laser radiation for 200 msec. Surface changes, such as ablation, combustion, and melting, occurred even at relatively low power densities (340 W/cm2), with greater effects occurring in composites than in "compomers" (glass iomomer-composite mixtures). These findings indicate that nonmetallic dental restorations are prone to damage from inadvertent laser exposure. Clinicians must be aware of this hazard and employ measures to protect both natural tooth structure and restorations when performing intraoral laser surgery.

Nature of light scattering in dental enamel and dentin at visible and near-infrared wavelengths

The light-scattering properties of dental enamel and dentin were measured at 543, 632, and 1053 nm. Angularly resolved scattering distributions for these materials were measured from 0° to 180° using a rotating goniometer. Surface scattering was minimized by immersing the samples in an index-matching bath. The scattering and absorption coefficients and the scattering phase function were deduced by comparing the measured scattering data with angularly resolved Monte Carlo light-scattering simulations. Enamel and dentin were best represented by a linear combination of a highly forward-peaked Henyey-Greenstein (HG) phase function and an isotropic phase function. Enamel weakly scatters light between 543 nm and 1.06 µm, with the scattering coefficient (µ(s)) ranging from µ(s) = 15 to 105 cm(-1). The phase function is a combination of a HG function with g = 0.96 and a 30-60% isotropic phase function. For enamel, absorption is negligible. Dentin scatters strongly in the visible and near IR (µ(s)≅260 cm(-1)) and absorbs weakly (µ(a) ≅ 4 cm(-1)). The scattering phase function for dentin is described by a HG function with g = 0.93 and a very weak isotropic scattering component (˜ 2%).

Lasers in dentistry

Since the development of the ruby laser by Maiman in 1960, there has been great interest among dental practitioners, scientists, and patients to use this tool to make dental treatment more pleasant. Oral soft tissue uses are becoming more common in dental offices. The possible multiple uses of lasers in dentistry, beyond soft tissue surgery and dental composite curing, unfortunately, have not yet been realized clinically. These include replacement of the dental drill with a laser, laser dental decay prevention, and laser decay detection. The essential question is whether a laser can provide equal or improved treatment over conventional care. Safe use of lasers also must be the underlying goal of proposed or future laser therapy. With the availability and future development of different laser wavelengths and methods of pulsing, much interest is developing in this growing field. This article reviews the role of lasers in dentistry since the early 1960s, summarizes some research reports from the last few years, and proposes what the authors feel the future may hold for lasers in dentistry.

Dye-enhanced ablation of enamel by pulsed lasers

Laser removal of dental hard tissue has been proposed as a replacement for or augmented approach to the dental handpiece. The main limitation for widespread usage of lasers in dentistry has been inefficient ablation of dental hard tissue, accompanied by potential laser-induced damage to the surrounding tissue. The research focuses on a novel approach for enhancement of tissue ablation and confinement of laser interaction to a small tissue volume by controlled placement of an exogenous dye on the enamel surface. Studies were done with both pulsed alexandrite and pulsed Nd:YAG lasers, with indocyanine green and India ink, respectively, used as photo-absorbers. These dye-enhanced laser processes demonstrated the feasibility of this technique for cavity preparation. While control studies produced little or no appreciable crater, average preparation depth for the dye-enhanced ablation was from 1 to 1.5 mm, with a diameter of approximately 0.6 mm. Knoop hardness measurements show that, surrounding the crater, there is small annular region slightly softened by the laser action. SEM studies of the interior structure of the tooth did not show significant damage to the surrounding tissue. Temperature measurement studies indicated that the pulsed nature of the laser, combined with the photo-absorbing dye, effectively prevented significant temperature rise at the pulp. The remarkable effectiveness of this technique in creating cavity preparations and the absence of any notable collateral damage to the surrounding tissue suggest that dye-enhanced pulsed-laser ablation could be used as an alternative to the dental handpiece in selected procedures.

Histologic effects of a thermally cooled Nd: YAG laser on the dental pulp and supporting structures of rabbit teeth

The histologic response of the pulp, periapical tissues, supporting periodontal ligament, and alveolar bone adjacent to the incisor teeth of adult rabbits was compared after laser treatment (etching) or drilling with a high-speed dental rotary handpiece (enamelplasty) on the buccal enamel surface. Observations were made at four time periods, 2 days, 14 days, 60 days, and 180 days after treatment. Block sections were removed, and serial sections were prepared and examined by an independent veterinary pathologist for occurrences of histopathologic changes with untreated control teeth used for comparison. Under the conditions of this study, there were no differences between either the laser-treated or the drilled specimens compared with the untreated control teeth on the basis of the histologic appearance.

Intrapulpal temperatures during pulsed Nd:YAG laser treatment of dentin, in vitro

Lasers are being used for soft tissue removal, caries removal, and treatment of root surface sensitivity. One concern for laser safety is that the heat produced at the irradiated root surface may diffuse to the pulp causing irreversible pulpal damage. To test this heat diffusion, copper-constantan thermocouples were inserted into the radicular pulp canals of extracted teeth. Simulating direct exposure which might occur during gingival excision, superficial caries removal, and modification of the dentin surface for treatment of root surface sensitivity, a 2 mm2 area of the external root surface was uniformly irradiated with a pulsed Nd:YAG laser using a 320 microns diameter fiber optic contact probe. Power was varied from 0.3 to 3.0 W with frequencies of 10 and 20 Hz. Temperature changes during cavity preparations using a high speed handpiece with air coolant were also recorded. Repeated measures ANOVA (P < or = 0.05) indicated that intrapulpal temperatures increased as a function of power, frequency, and time. Intrapulpal temperatures decreased as remaining dentin thickness (0.2 to 2.0 mm) increased for each laser parameter. Irradiation of dentin using a Nd:YAG pulsed laser, within the treatment times, powers, and frequencies with adequate remaining dentin thickness, as outlined in this paper, should not cause devitalizing intrapulpal temperature rises.

Clinical evaluation of dental hard tissue applications of carbon dioxide lasers

This clinical study examined the pulpal safety of selected CO2 laser hard tissue applications. A total of 187 hard tissue procedures were performed on 54 patients. The mean period of follow-up following laser treatment was 13.5 months (range 2-24 months). The procedures included etching (n = 96), desensitizing (n = 56), laser-enhanced fluoride (n = 28), treatment of external resorption (n = 4), and pulp capping or pulpotomy (n = 3). Only the latter two procedure types were performed with anesthesia. The total irradiation received during these procedures ranged from 2 to 12 J. No patients complained of sensation or discomfort during any procedure. Pulp vitality was maintained in all teeth, and no instances of postlasing thermal sensitivity or pulpitis were reported. These results indicate that pulp vitality can be maintained provided that conditions of irradiance are controlled carefully to minimize thermal effects.

Power density and external temperature of laser-treated root canals

The purpose of this study was to determine the power and time parameters for an argon laser that would result in the removal of pulpal tissue without excessively elevating the external temperature of the root. External temperatures were measured by attaching thermistors to the surfaces of the teeth at the cemento-enamel junction (CEJ) areas and at the root apices. Results indicate that a 1-W power setting with a pulse duration of 0.1 sec and a 1 sec interval between pulses produced a mean temperature rise of 0.89 +/- 0.27 degrees C at the cemento-enamel junction area and a mean temperature increase of 2.04 +/- 0.47 degrees C at the apex. A 2-W power setting with a 0.1 sec pulse duration and a 1 sec interval between pulses resulted in a mean temperature increase of 1.58 +/- 0.45 degrees C at the CEJ and a mean temperature rise of 2.59 +/- 0.20 degrees C at the apex. Based upon the results of this study, it was concluded that an argon laser operating at 1 or 2 W of power with a 0.1 sec pulse duration could be used to remove pulpal tissue without creating an excessive increase in the external temperature of the tooth.

Temperature and surface changes of dentine and cementum induced by CO2 laser exposure

The thermal effects of a CO2 laser on the external root surface and inside the root canal were studied in vitro by means of computerized infrared (IR) thermography and a digital thermometer. One-hundred-and-eighty tooth roots with single root canals were irradiated internally and externally with laser power set at 0.5, 1, 1.5, 2, 3 and 4 W. The laser was used in two operating modes: pulsed (pulse 0.5 s) and continuous mode with exposure time of 10 s. Under the conditions of this experiment, temperature rises of between 1.5 and 19.1 degrees C at the external root surface and 1.5 and 12 degrees C inside the root canal and horizontally across the sectioned root surface were recorded. The results obtained with IR camera showed a higher temperature on the external root surface than the digital thermometer during and after lasing the root canal. Scanning electron microscope (SEM) analysis revealed that even low laser energy significantly damaged the external root cementum surfaces.