Effects of the Oral Examination on the Equine Temporomandibular Joint

• Chondroitin sulfate and hyaluronic acid concentrations in synovial fluid (SF) of healthy temporomandibular joint (TMJ).
• Environmental changes of TMJ followed the use of a full-opened mouth speculum.
• Alterations were mild and mainly of inflammatory nature.
• The results do not indicate increase of extracellular matrix degradation products in SF.

Despite the increasing number of oral examinations performed, reports on temporomandibular joint (TMJ) assessment after the use of full-mouth specula are lacking in the literature. The aim of this study was to investigate whether prolonged application of a full-mouth speculum (60 minutes) would result in alterations in the clinical, thermographic, and synovial fluid (SF) findings. Horses were randomly divided into two groups. In one group, the speculum was kept in place in a closed position (CP group). In the other group, animals remained for 60 minutes with the mouth speculum at full range of aperture (opened position [OP] group). All TMJ joints were evaluated using digital palpation and thermography previous to (baseline values) and 6 hours after the removal of the mouth speculum (M6h). Synovial fluid was collected and analyzed. Six hours after full-mouth speculum use (M6h), pain on digital palpation, skin temperature, and total cell count in the OP group were higher when compared to baseline values. Moreover, pain on digital palpation and total cell count were higher in the OP group when compared to the CP group at M6h. There was no difference in total protein, chondroitin sulfate, hyaluronic acid, and prostaglandin E2 SF concentrations. Based on clinical, thermographic, and SF cell cytological findings, we concluded that TMJs environmental modifications followed the application of a full-opened mouth speculum for 60 minutes. However, these alterations were mild and mainly of inflammatory nature, and there was no indication of an increase in extracellular matrix degradation products in the SF.