Behavioural indicators of oral pain in horses: Towards the development of an equine dental ethogram

Introduction: Headshaking in horses is a commonly encountered syndrome, recognized
by spontaneous and often repetitive uncontrolled movements of the head and neck, which can occur intermittently or persistently (Newton, 2005; Madigan & Bell, 2001). The majority of horses presenting with signs of headshaking are diagnosed with trigeminal-mediated headshaking (Pickles et al., 2014). Other causes can be local diseases such as dental problems, periapical dental osteitis, rhinitis, intranasal masses, and sinusitis (Pickles at al. 2014; Newton et al. 2000; Gilsenan et al. 2014) infraorbital canal changes (Edwards et al. 2019). We couldn’t find publication considering supernumeric tooth induced headshaking. Our objective is to present a successfully treated headshaking caused by a non-erupted supernumeric and other misaligned incisors. Materials and methods: A 12 years old dutch warmblood showing spontaneous, intermittent and repetitive vertical/horizontal movements of the head and neck during exercise. Priorly the horse had detailed physical and edoscopic examination at different clinics. Nose cover was used by the owner without satisfactory result. Former examinations diagnosed misaligned, mispositioned, malformed 102-103 and a remnant 503. At our clinic x-ray of the incisors and transverse CT images of the head were acquired on a standing sedated horse from the occipital region until the incisors. The images revealed a non-erupted supernumerary incisor positioned deeply within the right incisive bone, thinning and bulging out the dorsal compacta of the bone at the alar fold region. The right sided infraorbital nerve block caused mild improvement. The CT did not reveal any other changes in the rest of the head that could correlate to the actual headshaking condition. Based on the results we decided to extract the 503 remnant, the 102-103 and the supernumeric incisor. The surgery was performend on a standing sedated (0,01 mg/bwkg Detomidin-hydroclorid and 0,01 – 0,02 mg/bwkg butorphanol) horse using infraorbital nerve block and local lidocaine infiltration. For packing platelet rich plasma covered with calcium/sodium alginate were used and changed 2-4 days intervalls until the granulation level made the packing unnecessary. For oral hygiene 0,2% chlorhexidine was used twice daily. NSAID and combinated penicillin were administerd in the first 5 days following extraction. Results: 2,5 months after the operation the horse could start working again without any signs of headshaking. Conclusions: In the horse, clinical signs attributed to supernumerary incisor teeth are rarely noted and therefore treatment is not sought (Baker 1991; Dixon et al.1999b; Baker 1999). Although we could not prove 100% our final diagnosis but the negative results of the complex examinations focusing on the frequent causes of the headshaking turned us towards the pathological conformity of the incisors including the supernumerary one.