Recovery of inferior alveolar nerve by photobiomodulation therapy using two laser wavelengths: A behavioral and immunological study in rat.

Postoperative sensory disturbances of inferior alveolar nerve (IAN) are major challenges in dental procedures. We aimed to investigate the effect of photobiomodulation therapy (PBMT) with 810 nm and 980 nm diode lasers on behavioral and immunological factors in a rat IAN crush model. Seventy-two rats were randomly assigned to the four groups of 810 nm laser (crush injury+810 nm laser; 6 J/cm2, 15 sessions, every 48 h), 980 nm laser (crush injury+980 nm laser; same protocol), control (crush injury without irradiation), and sham surgery (no crush injury and no irradiation). The neurosensory response of IAN was evaluated by Von Frey behavioral test before (baseline) and post-surgery in a period of one month. Changes of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), nuclear factor-kappa B (NF-κB), TNF-α, and IL-1ß, were assessed on days 2 and 30 post injury. Data were analyzed for significant differences by repeated measures and one-way ANOVA (p < .05). One day after surgery, all rats subjected to nerve injury showed significant increase in the withdrawal threshold of von Frey test compared to the baseline (p = .02 for control and p = .03 for laser groups). The threshold gradually returned to the baseline scores in 810 nm, 980 nm, and control groups from days 11, 17, and 29, respectively. There was a significant lower withdrawal threshold in 810 nm and 980 nm laser groups compared to the control group in days 11 to 19 and 9 to 23, respectively. At both time points, the levels of NGF and BDNF were significantly higher in 810 nm laser group compared to the control group. There was a significant difference between laser and control groups regarding NF-κB expression (all p values<.001). TNF-α and IL-1ß were significantly lower in laser groups compared to the control group (all p values < .001). PBMT with 810 and 980 nm diode laser protocol used in this study, promoted the neurosensory recovery of IAN after crush injury in rats. In addition, application of 810 nm diode laser was associated with more improvement in immunological responses compared to that of 980 nm laser.

Inferior alveolar nerve transection disturbs innate immune responses and bone healing after tooth extraction.

Coordination between the nervous and innate immune systems to maintain bone homeostasis is largely uncharacterized. The present study investigated the sensory-immune interaction in resting alveolar bone and healing socket by surgical sensory denervation. Bone histomorphometry and immunohistochemistry showed that sensory denervation resulted in moderate suppression of bone remodeling, with a proinflammatory milieu manifested by increased neutrophil recruitment and possible alternations in macrophage phenotypes along the resting bone surface. This denervation effect intensified when bone remodeling was triggered by tooth extraction, as revealed by disrupted temporospatial variations in macrophage subpopulations and neutrophil infiltration, which were closely associated with a dramatic decline in socket bone filling and residual ridge height. Antagonism of calcitonin gene-related peptide (CGRP) brought about similar antianabolic and proinflammatory effects as sensory denervation, suggesting that sensory nerves may monitor the bony milieu by CGRP. Depletion of macrophages, rather than neutrophils, ruled out CGRP effects, illustrating that macrophages were the primary immune mechanism that linked sensory innervation, innate immunity, and bone. The data support that sensory innervation is required for control of innate immune responses and maintenance of bone homeostasis. Sensory neuropeptides, such as CGRP, are a possible target for the development of proanabolic treatments in bone disease by modulating innate immune responses.