Factors Influencing the Intra-Oral Movement of the Bit: A Cadaveric Study

Bit-related trauma is a welfare issue in equestrian sports; therefore, a proper understanding of how the bit behaves inside the mouth is of importance. The objective of this study is to investigate the influence of bit design (snaffle bits/single/double-jointed; ring/eggbutt and curb bits), size, rein tension, and rein angle on the intra-oral movement of the bit in ex vivo specimens. The lateral and posterior movement of different bits was measured on cadaver heads under different circumstances. This ex vivo model, while not fully replicating natural conditions, provided insight into potential bit-related movements. Lateral displacement of the snaffle bit was significantly greater with higher unilateral rein tension. Bits that were too wide exhibited significantly more lateral and posterior displacement under unilateral rein tension. Posterior displacement increased with both unilateral and bilateral rein tensions. Using a bit that is too wide, using reins at a 20° angle, and applying 4 kg of rein tension were identified as risk factors for contact with the mesial gingival tissues of the mandibular 06s. Similar patterns were observed with curb bits, although bit movement was more restricted, and no contact with the mesial gingival tissues of the mandibular 06s was noted. This study demonstrated that bit design, bit size, rein angle, and rein tension all influence bit movement in the horse's mouth.