Mandibular separation: an epidemic of significance (Proceedings)
What began as an astute observation by a very sharp dental technician has resulted in discovery that the mandibular symphysis of the cat is very easily and frequently separated.
The mandible is comprised of two halves joined together on the midline at the mandibular symphysis. Unlike dogs and humans, this joint is not ossified. Rather, there is a fibrocartilagenous plate between the two halves of the mandible. This plate is composed of a layer of fibrous connective tissue and cartilage that is radiolucent. This means that when the mandibular symphysis is radiographed, there is a "space" between the two bony halves.Incidence
After observing several cats with this abnormality, my technicians begin to incorporate a mandibular symphyseal examination as part of all dental procedures. During a 12 month period, 417 cats underwent dental therapy; 67 (16%) of them had mandibular separation. Of those 67 cats, 69% were 10 years of age or more, and 21 (31%) were less than 10 years old. Thus, there appears to be a propensity for this disease in older cats.
The two halves of the mandible are moved in opposite vertical directions easily demonstrating joint laxity. It is notable that this condition is rarely detectable in awake cats, but it is easily diagnosed with the cat under anesthesia.
When queried about clinical signs, some owners report that none are observed. However, we frequently hear two things: 1) The cat is making awkward movements of the mandible during chewing ("jawing"). 2) The cat that eats dry food has small particles of food drop from the mouth as it is chewing. Occasionally, following repair, owners report that their cats eat significantly better; however, this is a retrospective observation.
Initially, there was concern that renal secondary hyperparathyroidism might be involved in the etiology; however, blood panels of the affected and non-affected cats were not significantly different in regard to renal or electrolyte (calcium and phosphorus) levels. If renal disease was detected, it was almost always with creatinine values less than 3.5 and with normal total calcium and phosphorus levels.
Because of the significantly higher incidence in cats over 10 years of age, our working etiologic explanation is simply years of chewing on hard objects; dry cat food is a likely object. However, some of the older cats with the disease are primarily or exclusively canned cat food eaters.