A comparison of laser- and acid-etched human enamel using scanning electron microscopy

Cavity preparation using a superpulsed 9.6-microm CO2 laser--a histological investigation

BACKGROUND AND OBJECTIVES

The superpulsed 9.6-microm CO(2) laser is an effective laser for ablating dental tissues and decay. This histological study compares laser class V preparations with conventional treatment to evaluate the resulting formation at the cavity walls.

STUDY DESIGN/MATERIALS AND METHODS

Four class V preparations (one made with a diamond drill and three with the CO(2) laser (9.6 microm, 60 microseconds pulse width, 40 mJ pulse energy, 100 Hz, integrated scanner system, water cooling) were performed on ten extracted teeth. The cavities were filled with a composite resin partly including enamel and dentine conditioning.

RESULTS

After laser preparation, no cracks or signs of carbonisation were detected. The results were comparable to those attained with conventional treatment. Following cavity filling without prior conditioning, gaps were noted at the cavosurface indicating a lack of adhesion. Dentinal bonding decreased gap formation significantly.

CONCLUSION

The 9.6-microm CO(2) laser is an effective tool for cavity preparation.

In vitro analysis of the effects of acid or laser etching on microleakage around composite resin restorations

OBJECTIVES

The aim of the present study was to determine the effect of two conditioning methods, phosphoric acid and XeCl laser application on microleakage at composite resin restorations.

METHODS

Class II MOD (mesio-occluso-distal) cavities were prepared on 90 extracted human wisdom teeth with one proximogingival margin on enamel and the other on dentin. Phosphoric acid (37%) and a XeCl excimer laser system were used for the etching procedure. The prepared teeth were randomly assigned to six groups: In group 1, acid-etching of the enamel margins was followed by application of enamel bonding, in group 2 additionally a dentin bonding system was used. In group 3, acid-etching of the enamel and dentin (total etch) was followed by the application of dentin bonding. In group 4, laser-etching of enamel margins was followed by the application of enamel bonding, in group 5 dentin bonding was used additionally. In group 6, laser-etching of enamel and dentin margins was followed by the application of dentin bonding. All restorations were placed incrementally and polymerized with a halogen light source. After restoration, all samples were thermocycled and stained in 0.5% basic fuchsin and sectioned longitudinally in a mesio-distal plane. Microleakage was scored by means of a stereomicroscope. The margins of the restorations at tooth-resin interface were examined with a scanning electron microscope.

RESULTS

In all groups, marginal leakage was more extensive at the gingival margin that was in dentin than at the gingival margin in enamel. Microleakage scores and the gap at the tooth-resin interface were significantly lower in all acid-etched groups than in laser-etched groups.

CONCLUSION

Acid-etch technique is more effective than the investigated laser-etch technique at 308nm concerning the reduction of marginal leakage in composite restorations.

Subsurface morphologic changes of ND:YAG laser-etched enamel

BACKGROUND AND OBJECTIVE

Etching the enamel surface with a Nd:YAG dental laser produces impact craters with cavities, micropores, and microfissures. This in vitro SEM study examined laser-etched enamel to determine the pattern and extent of subsurface changes.

STUDY DESIGN/MATERIALS AND METHODS

The facial surface of 10 maxillary central incisor teeth were coated with a black initiator and laser-etched with a pulsed Nd:YAG laser (1.06 lambda, 75 mJ, 15 Hz, 320 microns fiber, 94 J/cm2 fluence). The facial surface of five teeth were plastic-embedded under a low vacuum, then demineralized in 10% formic acid. The other teeth were split incisoapically. All samples were prepared for SEM.

RESULTS

Examination of the plastic impressions showed a delicate interlacing pattern of thin partitions and small knob-like expansions. Examination of the split teeth showed the penetration of microfissures into the enamel estimated at 10 microns.

CONCLUSION

These subsurface alterations may provide space for the infiltration and mechanical retention of dental resin.

[The morphological results of the use of a pulsed krypton fluoride excimer laser for enamel conditioning]

Although there have been many advances in the field of acid etching, major problems still present. For the most part, these are the unpredictability of the effects of etching, the lack of control of the depth of etching over the long term, and the development of enamel fractures occurring on debonding. The aim of this study was to investigate the morphological effects of enamel conditioning using a pulsed krypton fluoride excimer laser (wavelength 248 nm). Scanning electron microscopic examination revealed a surface similar to that produced by peripheral etching; no signs of thermal damage were to be seen. The requirements that have to be met by a modern laser considered as a possible alternative to conventional acid etching, are discussed.

Scanning electron microscopic study of laser-induced morphologic changes of a coated enamel surface

A low-energy Nd:YAG laser was used to irradiate extracted human teeth coated with a black energy-absorbent laser initiator in a study to determine the extent of the morphologic changes produced in the enamel surface. The laser initiator was applied to a cleaned enamel surface and irradiated at an energy output of 30 mJ or 75 mJ. Both energy levels produced morphologic changes of the surface. There was a sharp line of demarcation between the coated, irradiated area and the surrounding noncoated enamel surface. The scanning electron microscope view at the lower energy level showed that the surface had melted and reformed with numerous small, bubble-like inclusions. The 75 mJ energy level showed individual impact craters with shallow centers and raised edges containing numerous pores and large, bubble-like inclusions. Etching is a dental procedure in which an acid is normally used to remove a thin outer layer of the tooth structure. This is necessary to create a roughened, irregular surface in order to provide mechanical retention for dental restorative materials. The changes produced by the laser in this study suggest a simple, effective, and controlled method of etching the enamel surface of a tooth by altering its surface characteristics.