Sealant bond strengths of CO(2) laser-etched versus acid-etched bovine enamel.

BACKGROUND AND OBJECTIVE: The purpose of this study was to evaluate sealant shear bond strength on bovine enamel with standard acid etching compared with CO(2) laser etching. STUDY DESIGN/MATERIALS AND METHODS: Bovine enamel was prepared either by acid or laser etching and divided into four experimental groups, either acid or laser-etched teeth with or without a primer. A gelatin capsule was used to place the sealant on the prepared enamel surface and the bond tested in shear. Also surface roughness was evaluated by using a surface analyzer and an atomic force microscope. RESULTS: Shear bond strength results were the following: acid etch = 8.8 +/- 3.8 MPa, acid etch with primer = 10.3 +/- 5.5 MPa, laser etch = 4.0 +/- 1.1 MPa, and laser etch with primer = 6.2 +/- 2.3 MPa. Analysis of variance statistical analysis found no significant difference in bond strength between the acid-etched groups. However, the laser-etched groups had significantly lower bond strengths from the acid-etched teeth. In addition, a significant difference was observed between the laser-etched groups, where the use of the primer helped to increase the bond strength of the sealants. The surface roughness was significantly greater on the laser-etched teeth at the microm level (by using a surface analyzer) from the acid-etched and the control specimens. No difference in roughness (by using an atomic force microscope) was observed at the nanometer level between the laser and acid-etched teeth. CONCLUSION: For these particular settings, the laser-etched teeth resulted in lower bond strengths to enamel and the use of a primer increased the bond strength for laser-etched teeth only.

Erbium laser ablation of dental hard tissue: effect of water cooling.

BACKGROUND AND OBJECTIVE: Several lasers have been explored for hard dental tissue applications; used alone they have resulted in potentially harmful temperature increases in the pulp chamber. MATERIALS AND METHODS: An Er:YAG laser (lambda = 2.94 microns) was used to ablate hard dental tissues. Ablation rates with and without a water-cooling spray were measured. Subsequent experiments investigated the cooling effects of the water. Initially single channels were drilled into dentin; further studies involved ablating rectangular areas with repetition rates up to 10 Hz. RESULTS: The water spray minimally reduced the ablation rates of dentin and did not affect the ablation rates of enamel. The water spray effectively cooled the teeth; while using the maximum average power investigated (10 Hz, 360 mJ/pulse), a water flow rate of 4.5 ml/min limited the temperature rise in the pulp chamber to less than 3 degrees C. CONCLUSION: The studies confirm the feasibility of using an Er:YAG laser in conjunction with a water spray to safely and effectively remove hard dental tissues.

Shear strength of composite bonded to Er:YAG laser-prepared dentin.

An Er:YAG laser coupled with a cooling stream of water effectively removes dental hard tissues. However, before such a system can be deemed clinically viable, some safety and efficacy issues must be addressed. We compared the bonding of composite to dentin following the preparation of the dentinal surface with either an Er:YAG laser (lambda = 2.94 microns) or a standard dental bur and with and without a subsequent acid-etching treatment. The crowns of extracted human molars were removed, revealing the underlying dentin. We removed an additional thickness of material with either a dental handpiece or an Er:YAG laser (350 mJ/pulse at 6 Hz) by raster-scanning the samples under a fixed handpiece or laser. Comparable surface roughnesses were obtained. Several samples from each group received an acid-conditioning treatment. A cylinder of composite was bonded onto the prepared surfaces. The dentin-composite bond was then shear-stressed to failure on a universal testing apparatus. The results indicate that laser-irradiated samples had improved bond strengths compared with acid-etched and handpiece controls. SEM photographs of the surfaces show exposed tubules following the laser treatment: tubules could also be exposed with acid etching. We conclude that Er:YAG laser preparation of dentin leaves a suitable surface for strong bonding or an applied composite material.

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.

Effects of diphenylhydantoin on teeth in rabbit.

The drug diphenylhydantoin (DPH) is well known to affect the gingiva of humans. Among other known unwanted effects is that on calcified tissues. The initial purpose of our study was to examine the effect of chronic administration of DPH on the continuously erupting incisors of the rabbit. While studying the dentin a second investigation was undertaken when it was noticed that the pulps in DPH-treated rabbits were apparently more vascular than those in the control rabbits. After a treatment period of from 5-6.5 weeks the rabbits were killed, the jaws decalcified, sectioned and stained. The results presented here show that the animals treated with DPH developed less dentin. The pulps from the DPH-treated animals showed a greater area occupied by blood vessels. These experimental results are of interest in view of reported clinical findings that some patients treated with DPH develop smaller teeth with blunted apices. The vessel changes remain unexplained.