Impact of photobiomodulation therapy on the morphological aspects of submandibular gland submitted to excretory duct ligation and hypothyroidism: an animal study.

Abstract

The aim of this study was to evaluate the impact of photobiomodulation therapy (PBMT) on histomorphological aspects of submandibular gland (SMG) submitted to salivary gland duct obstruction in hypothyroid rats. Fifty-six male Wistar rats (250 to 300g) were divided into 4 groups (n = 14): euthyroid (EU), EU + PBMT, hypothyroid (HYPO), and HYPO + PBMT. Duct obstruction of the left submandibular gland (LSMG) was performed in all animals by a ligature procedure. For the induction of hypothyroidism, total thyroidectomy was performed. PBMT groups received irradiation with AlGaInP diode laser (808nm, 0.04W, 0.04cm2 spot size, 60s, 2.4J per point, 60J/cm2, 1W/cm2). Irradiation was performed immediately, 24h, and 48h after the obstruction of the salivary gland duct, in one point, extra oral and perpendicular to the gland. Animals were sacrificed after 24h and 72h after duct ligature. Our results indicated that salivary duct obstruction and hypothyroidism caused negative modifications on the salivary glands' histomorphology, especially acinar atrophy, after 24h and 72h. HYPO + PBMT showed a significant reduction of the inflammatory infiltrate, congested blood vessels, and acinar atrophy in the SMG submandibular salivary gland in 72h compared to 24h (p < 0.05). In conclusion, obstruction of the salivary gland excretory duct and hypothyroidism causes severe sialoadenitis with expressive atrophy of the glandular parenchyma. However, PBMT was able to modulate the inflammatory process and delaying acinar atrophy. This study provided insights to better understand the role of the PBMT on the altered salivary gland by duct ligation and associate hypothyroidism.