Lasers in periodontal therapy

Treatment with low-intensity lasers to improve wound healing has been applied since 1967, when Mester first showed acceleration of wound healing in mice stimulated with a ruby laser (90). Two theories are accepted to explain the effects of laser irradiation on tissues: the first theory states that the light of a specific wavelength activates the cells’ mitochondrial respiratory chain (71); and the second theory assumes that the light acts by opening the calcium channels on the cell membrane (135). Both mechanisms result in an increase of cellular metabolism with a higher production of adenosine triphosphate. A number of studies have investigated the use of phototherapy to improve wound healing, with conflicting results. Animal studies show either beneficial effects (70, 90, 166) or no effect at all (21, 62, 66, 80, 158). The same applies for human studies, some of which show beneficial effects of laser therapy on wound healing (7, 90), whereas no improvement is reported by others (22, 42, 122). Conversely, cell-culture studies revealed promising results for the action of phototherapy on various biological mechanisms (60, 75, 79, 89, 134). In our first studies, the effects of phototherapy with a low-intensity laser were investigated on wound healing after gingivoplasty in humans (30, 31). A GaAlAs diode laser with a wavelength of 670 nm (red) and 15mW power was applied point by point on the mucosa corresponding to the incisors and canines. This study had a split-mouth design and the test side received 4 J/cm2 energy density per point, for a total of three points. The application was repeated every 48 h for 1 week (i.e. four sessions in total). Postsurgical clinical evaluation was performed at 7, 15, 21, 30 and 60 days by five blinded experienced periodontists who were asked to choose the side presenting the more advanced gingival healing based on the parameters gingival color, texture and contour. This evaluation resulted in no statistical differences between nontreated sites and sites treated with the low-intensity laser (30). Incisional biopsies taken sequentially at 7, 14, 21 and 60 days postgingivoplasty showed no significant differences in histomorphometric evaluation of the gingival epithelium and connective tissue (31). In contrast to our findings, improved wound healing was found after gingivoplasty in another study using a similar laser-application protocol (7). A visible red laser (685 nm), of 4 J/cm2 energy density, was applied by scanning immediately after surgery and 24 h, 3 days and 7 days postoperatively. Clinical measurements of the width of the attached gingiva and the probing depth of the gingival sulcus were made before and immediately after surgery, and at 24 h, and 7, 14, 21, 28 and 35 days postoperatively. At 21 and 28 days the values for probing depth were significantly higher in the control group compared with the laser group (P < 0.05), and there were no significant differences in the width of the attached gingiva. Based on these data, the authors assumed that the laser stimulated faster tissue repair compared with no treatment (7). Challenged by this controversy and aware of the positive effects of laser therapy in cell cultures, we