Temperature response in the pulpal chamber of primary human teeth exposed to Nd:YAG laser using a picosecond pulsed regime.

OBJECTIVE: This study was conducted to analyze temperature variation in the pulpal chamber using the (Nd:YAG) picosecond-pulsed laser to promote ablation in enamel and dentin of primary teeth. BACKGROUND DATA: Several previous studies reported the temperature rise in pulpal chamber during laser irradiation. Since there are no reports about pulp chamber temperature changes during irradiation with picosecond-pulsed laser, the purpose of our investigation is to quantify the intrapulpal temperature changes following picosecond-pulsed Nd:YAG laser irradiation of enamel and dentin of primary teeth. METHODS: In this study, we used 10 intact primary exfoliated teeth: five molars and five incisors. We used a commercial neodymium:- yttrium-aluminum-garnet continuous-wave (CW)-pumped Q-switched and mode-locked Nd:YAG laser, with varying power levels (200, 300, and 350 mW) operating with 100-psec pulsed duration. RESULTS: Typical plots show differences between heating and cooling of enamel and dentin of anterior and posterior teeth. Whereas for enamel the time evolution curves are dependent on power used for the investigated range (200-350 mW), for dentin the differences are not so evident. Observing temperature enhancement for each power, we were able to analyze operational conditions where temperature changes do not exceed 5.5 degrees C. Power-time-temperature (PTT) diagrams for clinical operations were determined based on varying power level and exposition time. Through the heating-cooling cycle, we could extract conventional heating and cooling times for enamel and dentin. CONCLUSION: We have shown that the Nd:YAG picosecond-pulsed laser is a safe tool for ablation of primary teeth in a broad range of operational parameters.

A comparative in vitro study to diagnose decayed dental tissue using different methods.

OBJECTIVE: The purpose of this study was to compare diagnoses of decayed dental tissue (occlusal) using five different methods in vitro. BACKGROUND DATA: Previous studies have showed occlusal surface caries are very difficult to diagnose at early stages. Early carious lesions detection through conventional diagnosis methods, including radiographic, visual and tactile exams, is questionable because they can end up with a risk of a false-positive or false-negative diagnosis. MATERIALS AND METHODS: We used 22 teeth in vitro, premolars and molars, which suggested carious lesions. Three calibrated examiners using pre-determined scores made the exams. The methods used were GI, visual inspection; GII, tactile inspection (explorer probe); GIII, conventional radiographic exam; GIV, digital radiographic exam (Digora for Windows 1.51 and 1.51N, SoredexOrion Co.); GV, low-intensity laser for diagnosis (DIAGNOdent, KaVo, Germany); and GVI, histological inspection. The examiners did not communicate among themselves during the exams. RESULTS: There was significant statistical difference among the evaluated methods. Under the Friedman statistical test, GI, GIII, and GIV were different from GV at the 0.1% level. Comparing GII with GV, we observed statistical difference at the 1% level. CONCLUSION: GV was highly statistically different from the others groups, even when compared with GVI, which means that dentists must use every method they can get to avoid a false-negative diagnosis.

Study of microleakage at class V cavities prepared by Er:YAG laser using rewetting surface treatment.

OBJECTIVE: This study was conducted to analyze microleakage in Class V cavity preparation, using rewetting (or not) just after burr or Er:YAG laser preparation of enamel and dentin walls in permanent teeth. BACKGROUND DATA: Several studies reported microleakage around composite restorations when cavity preparation was done or treated by Er:YAG laser. As the hybridized laser is removed when this laser is used to cut dental hard tissue, there is a need for new materials or techniques to minimize gaps and microleakage. RESULTS: Primer solution showed significant effect in enamel and dentin, at the level of 5%, when Er:YAG laser was used as a cutting tool. Using primer solution after phosphoric acid in preparations with the laser, microleakage was similar in degree to when cavities were prepared with the burr. CONCLUSION: Re-wetting surface just after Er:YAG irradiation and chemical treatment with phosphoric acid using HEMA aqueous solution seems to improve the quality of bioattachment between the adhesive system and enamel/dentin, showing similarities between restoration behaviors independently of the cutting tool, whether burr or laser.

Clinical evaluation of low-level laser therapy and fluoride varnish for treating cervical dentinal hypersensitivity.

The aim of this study was to evaluate in vivo the use of low-level galium-aluminium-arsenide (GaAlAs) (BDP 600) laser and sodium fluoride varnish (Duraphat) in the treatment of cervical dentine hypersensitivity. Twelve patients, with at least two sensitive teeth were selected. A total of 60 teeth were included in the trial. Prior to desensitizing treatment, dentine hypersensitivity was assessed by a thermal stimulus and patients' response to the examination was considered to be a control. The GaAlAs laser (15 mW, 4 J/cm2) was irradiated on contact mode and fluoride varnish was applied at cervical region. The efficiency of the treatments was assessed at three examination periods: immediately after first application, 15 and 30 days after the first application. The degree of sensitivity was determined following predefined criteria. Data were submitted to analysis and no statistically significant difference was observed between fluoride varnish and laser. Considering the treatments separately, there was no significant difference for the fluoride varnish at the three examination periods, and for laser therapy, significant difference (P < 0.05) was found solely between the values obtained before the treatment and 30 days after the first application. It may be concluded that both treatments may be effective in decreasing cervical dentinal hypersensitivity. Moreover, the low-level GaAlAs laser showed improved results for treating teeth with higher degree of sensitivity.

A comparative study of nanosecond and picosecond laser ablation in enamel: morphological aspects.

OBJECTIVE: We have investigated and compared the main morphological features of human enamel tissue under Nd:YAG nanosecond and picosecond laser ablation. BACKGROUND DATA: The use of ultrashort laser pulses on teeth ablation is an alternative to avoid overheating and presents the advantage of minimizing the volume of damaged material during laser ablation. Comparison of the morphology obtained in laser ablation using nanosecond and picosecond laser pulses is a way to investigate the advantages of ultrashort laser pulses for ablation. METHODS: Trains of pulses with picosecond duration from a Q-switched and mode-locked Nd:YAG laser and pulses with nanosecond duration from a Q-switched Nd:YAG laser, both operating at 15 Hz kept at the same average power, were focused in human sound molars for 30 sec. Drilled holes with different morphological characteristics were observed using several laser intensity regimes. Enamel surfaces were examined using a scanning electron microscope (SEM) and their morphological characteristics compared. RESULTS: An interesting contrast between the morphology of the enamel when treated with different level of laser power and pulse duration was observed. Picosecond pulses promote a better-defined material removal with a minimum intermediate region, whereas nanosecond pulses at the equivalent average power level cause a large intermediate modified region between ablated and normal tissue, as well as a complete superficial modification of the existent original structure. CONCLUSION: Our results show an important correlation between the surface morphology and the pulse width of the lasers, suggesting advantages toward the use of ultrashort laser pulses in dentistry.

Characterization of enamel and dentin response to Nd:YAG picosecond laser ablation.

OBJECTIVE: We investigated the main characteristics of human dental tissue under Nd:YAG picosecond laser ablation. SUMMARY BACKGROUND DATA: The use of ultrashort laser pulses for teeth ablation prevents overheating and is an alternative for mechanical material removal; it also minimizes the volume of damaged material. METHODS: Laser pulses of picosecond at 15 Hz repetition rates from a Q-switched and mode-locked Nd:YAG laser were focused on sound human molars for 30 seconds. Variation of light intensity in the pulse train allowed us to obtain drilled holes with different characteristics. Enamel and dentin surfaces were examined by optical and scanning electron microscope (SEM). The samples consisted of three sound human molars. The ablation rate was determined after taking an average of all samples. RESULTS: Images from the SEM showed an interesting contrast between the morphology of the ablated enamel and dentin regions. In enamel, the ablated region appears to be more superficial than in dentin. The dentin fragility normally causes cracks that originate in the ablated region. The ablation rates in both enamel and dentin demonstrate a saturation behavior as the laser intensity increases. Furthermore, the ablation rate in dentin is about eight times greater than in enamel for the same laser fluence. CONCLUSION: Our results show an important correlation between the surface morphology and the pulsed laser fluence, which is compatible to the ablation mechanisms presented when ultrashort laser pulses are used.