Sensory nerves, but not sympathetic nerves, promote reparative dentine formation after dentine injury via CGRP‐mediated angiogenesis: An in vivo study

Abstract

AimDental pulp is richly innervated by nerve fibres, which are mainly involved in the sensation of pain. Aside from pain sensation, little is known regarding the role of dental innervation in reparative dentine formation. We herein generated a mouse model of experimental dentine injury to examine nerve sprouting within the odontoblast and subodontoblastic layers and investigated the potential effects of this innervation in reparative dentinogenesis.MethodologyMouse tooth cavity model (bur preparation + etching) was established, and then nerve sprouting, angiogenesis and reparative dentinogenesis were determined by histological and immunofluorescent staining at 1, 3, 7, 14 and 28 days postoperatively. We also established the mouse‐denervated molar models to determine the role of sensory and sympathetic nerves in reparative dentinogenesis, respectively. Finally, we applied calcitonin gene‐related peptide (CGRP) receptor antagonist to analyse the changes in angiogenesis and reparative dentinogenesis.ResultsSequential histological results from dentine‐exposed teeth revealed a significant increase in innervation directly beneath the injured area on the first day after dentine exposure, followed by vascularisation and reparative dentine production at 3 and 7 days, respectively. Intriguingly, abundant type H vessels (CD31+Endomucin+) were present in the innervated area, and their formation precedes the onset of reparative dentine formation. Additionally, we found that sensory denervation led to blunted angiogenesis and impaired dentinogenesis, while sympathetic denervation did not affect dentinogenesis. Moreover, a marked increase in the density of CGRP+ nerve fibres was seen on day 3, which was reduced but remained elevated over the baseline level on day 14, whereas the density of substance P‐positive nerve fibres did not change significantly. CGRP receptor antagonist‐treated mice showed similar results as those with sensory denervation, including impairments in type H angiogenesis, which confirms the importance of CGRP in the formation of type H vessels.ConclusionsDental pulp sensory nerves act as an essential upstream mediator to promote angiogenesis, including the formation of type H vessels, and reparative dentinogenesis. CGRP signalling governs the nerve‐vessel‐reparative dentine network, which is mostly produced by newly dense sensory nerve fibres within the dental pulp.

Impaired Tertiary Dentin Secretion After Shallow Injury in Tgfbr2-Deficient Dental Pulp Cells Is Rescued by Extended CGRP Signaling

“…A different group reported that CGRP inhibits mineralization [21]. It should be noted that these reports experimented directly on DPSCs, while we and others have shown an intimate, bi-directional communication between the DPSCs and trigeminal neurons [11,15,[22][23][24][25][26][27][28][29][30]. Interestingly, bone research has also found that sensory afferents assist bone healing via CGRP signaling.…”

“…A shallow dentin injury without pulp exposure has been shown to initiate the expression of neurotrophic factors, such as nerve growth factors (NGF), by odontoblasts [5][6][7]. This triggers a neuroinflammatory response in which sensory afferents sprout and secrete CGRP [8,9] to activate odontogenic activities for dentin repair [11,14]. In this report, we sought to determine whether the signaling downstream of Tgfbr2 in the developing dental pulp mesenchyme also regulates reactionary dentinogenesis and odontoblast secretion of neurotrophic signals that promote axon sprouting.…”

“…This prompted us to question whether the response to dentin injury also requires TGFβ signaling and whether the absence of Tgfbr2 would result in aberrant tertiary dentin formation. Additionally, sensory afferents sprout and provide peptidergic signals following injury of the dentin-pulp complex, and this mediates the healing process [11][12][13][14][15]. Several studies reported that CGRP moderates the neuroinflammatory response to dentin injury [11,14,16], yet the roles of CGRP in pulp repair, particularly in the absence of pulp exposure, are not yet fully understood.…”

“…Additionally, sensory afferents sprout and provide peptidergic signals following injury of the dentin-pulp complex, and this mediates the healing process [11][12][13][14][15]. Several studies reported that CGRP moderates the neuroinflammatory response to dentin injury [11,14,16], yet the roles of CGRP in pulp repair, particularly in the absence of pulp exposure, are not yet fully understood. Since Tgfbr2 signaling in the dental pulp cells promotes axon sprouting during tooth development [3,17], we hypothesized that this could be recapitulated during dentin repair.…”

The anatomy, neurophysiology, and cellular mechanisms of intradental sensation

“…The distribution and patterning of free sensory nerve endings within the pulp-dentin complex of a fully developed tooth is not static, but can dynamically remodel in response to injury or infection. CGRP+ sensory endings exhibit branch sprouting surrounding sites of pulp damage, although prolonged and extensive damage leads to eventual pruning and denervation at the damage site ( 48 , 87 ). Denervation by resection of the inferior alveolar nerve is shown to accelerate necrosis induced by pulp damage ( 88 ), suggesting that sensory fibers may contribute to pulp-dentin regeneration in response to injury.…”