[Temperature variation at the external root surface during Nd: YAG laser irradiation in the root canal in vitro]

To assess the temperature variation of the root surface using Nd: YAG laser irradiation in the root canal with different power and to evaluate the safety of laser application on the periodontal region.

Thirty extracted human teeth with single-roots were collected. The teeth were cross-sectioned in the cervical portion, standardizing the roots at a 12-mm length. The roots were used as specimen. The roots were radiographed in the buccal-lingual direction to measure the thickness of the proximal walls, by means of a digital radiographic system. The specimens were divided into three groups according to the laser potency (1.5, 3.0, and 4.5 W). Each group was subdivided into two subgroups according to laser frequency (15 and 30 Hz). With the Nd: YAG laser irradiation for 20 s, the temperature variation of the root surface was monitored by thermocouples located at different parts of the root external wall and recorded by digital thermometers.

The groups irradiated with 4.5 W presented the greatest temperature variation (above 10°C), followed by 3.0 and 1.5 W. The temperatures were statistically different (P < 0.01). The groups irradiated in the same potency, regardless of whether 15 Hz or 30 Hz was used, presented with no statistical difference (P > 0.05). The apical half of the root presented statistically higher temperature rises than the cervical half of the root (P < 0.01).

The temperature variation of the root surface was associated with laser power, irradiation time, and the thickness of dentin. Application of Nd: YAG laser in the root at 1.5 W for 20 s can safely be used in endodontic treatment.