Laser interactions with dental hard tissues - Effects on the pulp/dentin complex

The successful use of laser energy for a variety of hard tissue treatments is determined byatraumatic effects on the pulp/dentin complex. A series of studies were undertaken using a fiberoptic-delivered pulsed (120 mu s) Neodimium:Yttrium-Aluminum-Garnet laser (Nd:YAG lambda = 1.06 mu m) to determine its effects on dentin and pulp. Optical properties of carious and sound dentin were determined for reflectance and transmittance with absorbance calculated from those values. Absorbance was the same in both forms of dentin. The physical modification threshold of dentin subjected to laser energy was established determining the first physical change occurring in dentin from laser exposure. Microhardness measurements indicated that laser modification increased dentin microhardness which was resistant to acid demineralization. FTIR evaluation confirmed the removal of collagen with mineral changes occurring in dentin altered by laser and by phosphoric-acid modification. These studies describing the physical properties of laser-treated dentin established the basis for investigations into the laser's effects on dental pulp. Rat and monkey studies determined laser energy levels and remaining dentin thicknesses as safe parameters for laser treatment of dentin which caused no pulpal damage. These parameters were then applied to the treatment of third molars in humans, confirming that no adverse pulpal effects occurred at powers less than 2 W, 10 Hz and at 3 W with air/water coolant. Patients remained asymptomatic and histology remained normal. A three year retrospective study confirmed that no pulpal involvement occurred after laser cavity preparation in enamel. Thus, at the parameters described in these studies, the laser has demonstrated its ability to remove carious enamel and dentin, and improve microhardness and acid resistance without untoward pulpal effects.