Application of the horse grimace scale in horses with dental disease: Preliminary findings

Background: Dental disease is a common but often under-recognised condition in horses, possibly due to an inability to recognise clinical signs of oral discomfort. Some dental disorders are reportedly more painful than others, but there is no current metric by which dental pain can be objectively assessed. This study aimed to determine whether a facial expression-based pain scale offered an objective and reliable method for assessing dental pain in horses. It was hypothesised that dental disorders affecting the periodontium would produce high pain scores.

Methods: Twelve horses with dental disease were evaluated for pain using a numerical rating scale (NRS) and a horse grimace scale (HGS) by blinded observers using still, lateral photographs.

Results: Interobserver reliability was poor across all observers when both the NRS (intraclass correlation coefficient [ICC] = 0.36) and the HGS (ICC = 0.27) were used in horses with dental disease. The highest mean scores were given for horses with equine odontoclastic tooth resorption and hypercementosis (EOTRH) and periodontal disease (PD).

Limitations: This study has a small sample size of both horses and questionnaire respondents, and the respondent demographics are not representative of the wider veterinary population Furthermore, no positive or negative controls were used for the pain scoring.

Conclusions: The results of this study indicate the unreliability of tools designed for identifying acute pain for assessing chronic pain, such as dental pain. A more dental-specific ethogram is required to accurately identify dental pain in horses. Both the NRS and HGS produced the highest mean scores for EOTRH and PD, supporting existing literature that these conditions are associated with more obvious signs of pain.