Application of optical coherence tomography to identify pulp exposure during access cavity preparation using an Er:YAG laser.

OBJECTIVE: The study aimed to evaluate the ability of optical coherence tomography (OCT) to guide and identify pulp exposure using an erbium: yttrium-aluminum-garnet (Er:YAG) laser. BACKGROUND DATA: The Er:YAG laser has been proven to be effective in ablating dental hard tissue and offers advantages, as there is none of the vibration and noise you get with conventional methods, but it has limitations in relation to the tactile feedback that would aid in identification of entry into the pulp chamber. Based on depth-resolved optical reflectivity, OCT technology has been developed to provide high-resolution, cross-sectional images of the internal structure of biological tissues. MATERIALS AND METHODS: The pulp chambers of 20 human mandibular incisors were examined, and the average thickness of hard tissue covering the pulp chamber was assessed using micro-computed tomography (micro-CT) images. An Er:YAG laser was used to gradually penetrate the hard tissue over the pulp chamber under microscopic guidance. The preparation was constantly imaged using a swept-source OCT at 10 sec intervals until a pulp chamber exposure was identified using the technology. The pulp exposure was re-examined under the microscope and compared with micro-CT images for verification. RESULTS: The pulp exposures of 20 incisors were all verified microscopically and with micro-CT images. The thickness of hard tissue penetrated by the laser ranged from 0.44 to 1.69 mm. CONCLUSIONS: Swept-source OCT is a useful tool for identifying pulp exposure during access opening with the Er: YAG laser.

Shaping of the root canal using Er:YAG laser irradiation.

OBJECTIVE: The purpose of the present study was to investigate the degree of Er:YAG laser irradiation at the apical area in vitro. BACKGROUND DATA: Since the laser was developed, advancement of laser treatment has been seen in various fields. However, few reports exist on shaping of the root canal using Er:YAG laser irradiation. METHODS: Six single-rooted human teeth were used. The working length of root canals was set at 6.5 mm, and they were enlarged to apical file size #25. An Er:YAG laser and cone-shaped irradiation tips (R135T and R200T) were used. Laser irradiation conditions were 30 m J, 20 pps, and water flow of 5 mL/min. Samples were irradiated three times for 10 sec each using each tip. To evaluate the cutting degree of horizontal area of the root canal, the laser-irradiated surfaces were observed using microfocus X-ray computed tomographic photography before and after every irradiation. The samples were observed under a scanning electron microscope. Measurement of pixels in an area was performed by image-editing software (Adobe Photoshop 7.0). Statistical analysis was performed using StatView (version 5.0). One-way ANOVA and the Tukey-Kramer tests were used; p<0.05 indicated statistical significance. RESULTS: When root canals were irradiated with R200T for 10 sec (p<0.05), a large amount of evaporation (0.12 ± 1.07 mm(2)) was acquired in their cut area compared with the other irradiation conditions. In scanning electron microscopic observation, there was no smear layer and the dentinal tubules were open. CONCLUSIONS: When the distance between the tip and root dentin was adjacent, the shaping of root dentin by Er:YAG laser irradiation was definitely observed.

Effects of dentin surface modifications treated with Er:YAG and Nd:YAG laser irradiation on fibroblast cell adhesion.

OBJECTIVE: The purpose of this in vitro study was to evaluate the effect of surface modifications induced by erbium (Er):YAG and neodymium (Nd):YAG laser irradiation on cell adhesion by comparing it to that of conventional methods for surface preparation after root-end resection. BACKGROUND DATA: Many studies have been seeking a favorable method to produce a resected root end with optimal conditions for cell response. However, little improvement has been achieved. This study evaluated the biocompatibilities of resected root surfaces after Er:YAG or Nd:YAG laser irradiation on initial cell adhesion. MATERIALS AND METHODS: Dentin disks were divided into three groups. Group A was left untreated, Group B was treated with Er:YAG laser irradiation (60 mJ/pulse, 10 pps, 60 sec), and Group C with Nd:YAG laser irradiation (60 mJ/pulse, 10 pps, 60 sec). After laser irradiation, the dentin disks were incubated with NIH/3T3 fibroblasts cultured in Dulbecco's modified Eagle's medium. A morphological analysis of the dentin surface and cell adhesion was observed under a scanning electron microscope. Surface roughness was measured using a confocal laser scanning microscope. The statistical analysis was undertaken using ANOVA at a level of significance of 5% (p<0.05). RESULTS: Morphological analysis and roughness measurement showed that dentin surfaces treated with Er:YAG laser irradiation were rougher than those in Groups A and C. Group B (Er:YAG) exhibited the greatest number of attached cells among all groups after 12 and 24 h. CONCLUSIONS: Morphological alteration induced by Er:YAG laser irradiation showed a favorable effect on the attachment of fibroblasts to dentin surfaces.

Dentin strain induced by laser irradiation.

The purpose of this study was to investigate the strain and temperature change in dentin induced by laser irradiation of human root canals with or without water cooling. Twenty-eight palatal roots of extracted human maxillary first molars were used. The strain in dentin was measured using strain gauges fixed on the apical third of the buccal root surface. The temperature change of the root dentin was monitored using thermocouples embedded into dentin near the apex. The root canal was irradiated with Er:YAG or Nd:YAG laser at an output of 1 W (100 mJ, 10 pps) for 5 s. The tip of the irradiation fibre was located 2.0 mm from the root apex. With water cooling, the mean maximum strain induced by Er:YAG laser was significantly lower than that by Nd:YAG laser (P < 0.05). However, without water cooling, no significant difference between the two lasers (P > 0.05) was found. The results suggest that the strain induced by Er:YAG laser irradiation in dentin with water cooling may be minimal, but there still might be a risk of root micro-fracture if cooling is not sufficient.

Safety of laser use under the dental microscope.

The aim of this study was to investigate the safety of laser use under the dental microscope. Nd:YAG, Er:YAG and diode lasers were used. The end of the tips was positioned at a distance of 5 cm from the objective lens of a dental microscope. Each eye protector was made into a flat disc, which was fixed on the lens of the microscope. The filters were placed in front of the objective lens or behind the eye lens. Transmitted energy through the microscope with or without the filters was measured. No transmitted laser energy was detected when using matched eye protectors. Mismatched eye protectors were not effective for shutting out laser energy, especially for Nd:YAG and diode lasers. None or very little laser energy was detected through the microscope even without any laser filter. Matched filters shut out all laser energy irrespective of their positions.

Removal of two types of root canal filling material using pulsed Nd:YAG laser irradiation.

OBJECTIVE: The aim of this study was to examine the usefulness of a pulsed Nd:YAG laser in removing two types of endodontic obturation material from the root canal in vitro. BACKGROUND DATA: Recently, a fine flexible glass fiber made of quartz has been developed to transmit the laser beam more effectively and permit its concentration in a specific area. This has increased the potential usefulness of the Nd:YAG laser in root canal treatment. METHODS: The time required for removing the root canal obturation material (Gutta-percha cones and, Sealapex or AH26) by means of either Nd:YAG laser irradiation or a conventional method (Gates Glidden drills and K files) was measured. Contact microradiography was used to assess the radiopacity of the root canals before and after the removal of obturation material. The surfaces of the root canal after removal of the obturation materials were also observed by scanning electron microscopy. RESULTS: Although none of the methods used in this study resulted in complete removal of debris from the root canal wall, the time required for the removal of any of the root canal obturation materials using laser ablation was significantly shorter than that required using the conventional method (p < 0.05). It appeared that some orifices of the dentinal tubules were blocked with melted dentin following laser irradiation. CONCLUSIONS: Nd:YAG laser irradiation is an effective tool for the removal of root canal obturation materials, and may offer advantages over the conventional method.

The possibility of dowel removal by pulsed Nd:YAG laser irradiation.

BACKGROUND AND OBJECTIVES: Nd:YAG laser is one of the popularly used laser, in dentistry for treatment and technologic processing. Removal of dowel from root canal is very troublesome at endodontic retreatment. This study aimed to examine the possibility and efficiency of dowel removal from the root canal using the Nd:YAG laser in vitro. STUDY DESIGN/MATERIALS AND METHODS: Irradiation time and energies required for complete removal of the dowel set in the root canal using the laser were measured. The dowel ablation was observed by contact microradiographs (CMRs). The surface of the root canal after lasing was observed by a scanning electron microscope (SEM). RESULTS: A significant difference existed in irradiation times and energies to remove dowels among various combinations of metal and cement (P < 0.05). The CMRs showed that both dowel and dentin were ablated, and the SEM observation demonstrated that root canal surface was melted. CONCLUSIONS: The Nd:YAG laser irradiation could remove set dowels from the root canal.