Photomedicine and Laser Surgery Volume 26, Number 4, 2008 © Mary Ann Liebert, Inc. Pp. 313–319 DOI: 10.1089/pho.2007.2140 Investigation of Mast Cells in Human Gingiva Following Low-Intensity Laser Irradiation L.B. Silveira, 1,2 R.A. Prates, 3 M.D. Novelli, 4 H.A. Marigo, 5 A.A. Garrocho, 5 J.C.F. Amorim, 2 G.R. Sousa, 2 M. Pinotti, 2 and M.S. Ribeiro, Ph.D. 1,3 Abstract Objective: The aims of the present study were to investigate the effect of low-intensity laser irradiation on the total number of mast cells as well as the percentage of degranulation in human gingiva. Blood vessel dilation was also evaluated. Background Data: It has been proposed that low-intensity laser irradiation can ameliorate pain, swelling, and inflammation. In periodontal tissue, mast cells may influence either the destructive events or the defense mechanism against periodontal disease via secretion of cytokines and through cellular migra- tion to improve the healing process. Mast cells play an important role in the inflammatory process. Methods: Twenty patients with gingival enlargement indicated for gingivectomy were selected. Gingival fragments were obtained from each patient and divided into three different groups before surgery. One fragment was removed without any irradiation. The two others were submitted to punctual irradiation with an energy density of 8 J/cm 2 at an output power of 50 mW at 36 Hz for 36 sec before gingivectomy. Nondegranulated and degranu- lated mast cells were counted in five areas of the gingival fragment connective tissue. Major and minor diam- eters of the blood vessels were also measured. Results: Both red and infrared radiation promoted a significant increase in mast cell degranulation compared to controls; however, no statistically significant differences (p  0.05) were observed between the irradiated groups. No significant differences among the groups were observed regarding blood vessel size. Conclusion: The results suggests that red and infrared wavelengths promote mast cell degranulation in human gingival tissue, although no dilation of blood vessels was observed. The effects of premature degranulation of mast cells in human tissue and the laser radiation protocol applied in this study encourage further investigations to extend these results into clinical practice. 313 Introduction G INGIVAL ENLARGEMENT, or an increase in the size of the gingiva, can be caused by various stimuli. The most common is chronic inflammatory gingival enlargement; the clinical signs are a soft and discolored gingiva. This is due to tissue edema and infective cellular infiltration caused by prolonged exposure to bacterial biofilm, and it is treated with conventional periodontal treatment, such as scaling and root planing. Portions in which the chronic inflammatory gingi- val enlargement includes significant fibrotic components that do not respond to treatment and do not undergo shrink- age after scaling and root planing are surgically removed to eliminate the excess tissue, most often with a procedure known as gingivectomy. 1–3 In inflamed gingival lesions, a variety of cytokines are produced by lymphocytes and monocytes as well as by non-immune cells like fibroblasts and epithelial and endothelial cells. 4 Low-intensity laser radiation as a therapeutic modality for acceleration of wound healing was first introduced by Mester and others in the 1960s. 5 This therapy is widely used as a tissue stimulator 6–9 and to promote anti-inflammatory and analgesic effects. 10 Despite its widespread use in clini- cal trials, 11,12 the biological basis for its effectiveness has not been elucidated. It is proposed that the healing acceleration may be due to a reduction in the duration of acute inflam- mation. Primary mechanisms that stimulate cell activity leading to enhanced mast cell recruitment and degranula- 1 Professional Master Lasers in Dentistry, IPEN-CNEN/SP, Cidade Universitária, São Paulo, 2 Bioengineering Laboratory, Universidade Federal de Minas Gerais, Belo Horizonte, 3 Center for Lasers and Applications, IPEN-CNEN/SP, Cidade Universitária, São Paulo, 4 School of Dentistry, Universidade de São Paulo, São Paulo, and 5 School of Dentistry, Pontifícia Universidade Católica de Minas Gerais, Belo Hor- izonte, Brazil.