Occlusion of dentinal tubules and selective block of pulp innervation prevent the nociceptive behaviour induced in rats by intradental application of irritants.
OBJECTIVE
Application of irritants on the exposed dentine of the incisors has been shown to produce aversive behaviour in awake rats. This study aims to demonstrate that the observed aversion is due to the infiltration of irritants through the dentinal tubules and the activation of capsaicin sensitive fibres in the tooth pulp.


METHODS
Different groups of rats were subjected, under anaesthesia, to cutting of the distal 2 mm of their lower incisors and the fixation of an artificial crown that allows the application of 10-15 microl of solution. Several procedures were followed to prevent the action of the irritants including occlusion of the dentinal tubules, local application of lidocaine, selective ablation of the capsaicin sensitive primary afferents (CSPA) or incisor pulpectomy; the reactions to intradental application of either capsaicin (1%) or formalin (2.5%) were tested using a newly designed behavioural score.


RESULTS
Occlusion of dentinal tubules produced significant attenuation of the nociceptive behaviour induced by dentinal application of either capsaicin or formalin. Similar results were observed following either local block with lidocaine (2%), selective ablation of capsaicin sensitive afferents or total denervation by pulpectomy.


CONCLUSIONS
The present results confirm the hypothesis of infiltration of irritants to the incisor pulp through the dentinal tubules and suggest that the reported inflammatory reaction and hyperalgesia are mediated, to a large extent, by capsaicin sensitive primary afferents.
Rifai
Khaldoun
K
Department of Prosthodontics, School of Dentistry, Lebanese University, Beirut, Lebanon.
Chidiac
Jose J
JJ
Hawwa
Nadim
N
Baliki
Marwan
M
Jabbur
Suhayl J
SJ
Saadé
Nayef E
NE
D000779:Anesthetics, Local / Q000494:pharmacology; D000818:Animals; D002211:Capsaicin / Q000494:pharmacology*; D003782:Dental Pulp / Q000187:drug effects / Q000294:innervation*; D005260:Female; D007180:Incisor / Q000187:drug effects*; D007509:Irritants / Q000494:pharmacology*; D008012:Lidocaine / Q000494:pharmacology; D008297:Male; D023421:Models, Animal; D009407:Nerve Block; D009475:Neurons, Afferent / Q000187:drug effects; D009619:Nociceptors; D010070:Oxalates / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011955:Receptors, Drug / Q000187:drug effects
D000779:Anesthetics, Local; D007509:Irritants; D010070:Oxalates; D011955:Receptors, Drug; D008012:Lidocaine; D002211:Capsaicin