Surface topography of enamel and dentine from primary teeth following infrared Nd-YAG laser irradiation: An in vitro study

Laser Application in Dentistry: Irradiation Effects of Nd:YAG 1064 nm and Diode 810 nm and 980 nm in Infected Root Canals-A Literature Overview

Objective. In endodontics, Nd:YAG laser (1064 nm) and diode laser (810 nm and 980 nm) devices are used to remove bacteria in infected teeth. A literature review was elaborated to compare and evaluate the advantages and disadvantages of using these lasers. Methods. Using combined search terms, eligible articles were retrieved from PubMed and printed journals. The initial search yielded 40 titles and 27 articles were assigned to full-text analysis. The studies were classified based upon laser source, laser energy level, duration/similarity of application, and initial and final bacterial count at a minimum of 20 prepared root canals. Part of the analysis was only reduced microorganisms and mechanically treated root canals upon preparation size of ISO 30. All studies were compared to evaluate the most favorable laser device for best results in endodontic therapy. Results. A total of 22 eligible studies were found regarding Nd:YAG laser 1064 nm. Four studies fulfilled all demanded criteria. Seven studies referring to the diode laser 980 nm were examined, although only one fulfilled all criteria. Eleven studies were found regarding the diode laser 810 nm, although only one study fulfilled all necessary criteria. Conclusions. Laser therapy is effective in endodontics, although a comparison of efficiency between the laser devices is not possible at present due to different study designs, materials, and equipment.

Study of the direct bactericidal effect of Nd:YAG and diode laser parameters used in endodontics on pigmented and nonpigmented bacteria

Laser light can be used during endodontic procedures to sterilize the root canal by destroying bacteria. Previous in-vitro studies that investigated the mechanism of the destruction of bacteria inhabiting the root canal by 1,064-nm Nd:YAG and 808-nm diode laser light used substrates that absorb light in the near-infrared (NIR) spectrum. These substrates heat the bacterial microenvironment, which possibly contributes to cell death. To determine the direct effect of laser light on the bacterial sample in the absence of detrimental heating, a sapphire substrate, which is virtually transparent in NIR spectrum, was inoculated with bacterial samples and subjected to laser irradiation at 1,064 nm (1.5 W, 15 Hz) and at 808 nm (1.5 W, 20 Hz). Enterococcus faecalis, Escherichia coli, and Porphyromonas gingivalis bacteria were used. E. faecalis and E. coli were largely unaffected by laser light. The viability of P. gingivalis, a pigmented bacterium, was directly affected by both NIR wavelengths (a 57% decrease of viability at 1,064 nm and a 31% decrease at 808 nm). Our results indicate that the primary mediator of cell death appears to be the interaction between NIR laser light and the bacterial microenvironment, most likely in the form of heating. Our research suggests that when optimizing the efficacy of laser-assisted endodontic sterilization of the root canal, the optical characteristics of the bacterial microenvironment play a key role, as nonpigmented bacteria appear to be virtually transparent at 808 nm and 1,064 nm.

Nanoscratch resistance of human tooth enamel treated by Nd: YAG laser irradiation

The purpose of this study was to investigate the friction behaviour of human tooth enamel irradiated by Nd:YAG laser. Forty specimens were randomly divided into four groups, and received the Nd:YAG laser irradiation with different energy densities (without irradiation; 20, 40, and 80 J/cm2). Subsequently, nano-scratch tests were conducted on the treated enamel surfaces, with progressive loads from 0.1 to 80 mN. The morphologies of the treated enamel surfaces and the scratch scars were observed via a field emission scanning electron microscope and an AMBIOS XP-2 stylus profilometer. The results indicated that the Nd:YAG laser promoted slight morphological alterations under a lower energy density (20 J/cm2), but different morphologies occurred under a higher energy density (40 and 80 J/cm2). The irradiated enamel surfaces had inferior nano-scratch resistance, and the nano-scratch resistance decreased as the energy density increased. Nd:YAG laser irradiation decreased the nano-scratch resistance of the enamel. The main damage mechanisms of the irradiated enamel under nano-scratch consisted of brittle delaminations and formation of cracks.

Immunohistochemical study on pulpal response in rat molars after cavity preparation by Er:YAG laser

While Er:YAG laser systems are in extensive use for caries removal and cavity preparation, the effects of such treatment on pulp tissue remain unclear. This study evaluates these systems using immunohistochemical methods and compares the results with information gained from treatment using conventional burs. Cervical cavities were prepared in the upper first molars of rats, using either an Er:YAG laser or a conventional tungsten-carbide bur. At intervals of 5 min, 6 h, 12 h, 1 d, 3 d and 7 d after cavity preparation, the teeth were processed for immunohistochemical analyses of tissue non-specific alkaline phosphatase, OX6-positive major histocompatibility complex class II antigen-expressing cells and PGP 9.5-immunoreactive nerve fibers. DNA fragmentation was detected by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) method. Tissue non-specific alkaline phosphatase was observed mainly in the subodontoblastic layer under the cavity lesion, from 5 min, in both groups. The immunoreactivity was more pronounced in the laser group, but by 7 d no significant differences were recognizable. At 12 h, TUNEL-positive cells were detected around the odontoblastic layer in both groups. From 3 d to 7 d, a limited number of positive cells were still visible in the group that underwent standard treatment. Clear similarities in the distribution patterns of OX6-immunopositive cells and PGP 9.5-immunoreactive nerve fibers were also noted. From 12 h to 1 d, OX6-positive cells accumulated along the pulp-dentin border, extending their processes into the dentinal tubules. Numerous bead-like PGP 9.5-immunoreactive nerve fibers were observed under the odontoblastic layer at 7 d. These results demonstrated that there was no appreciable difference in the manner in which pulp tissue responded to treatment with either Er:YAG laser or a conventional drill. This would seem to indicate the usefulness of the Er:YAG laser system in the removal of caries and cavity preparation.