A study of sub-occlusal secondary dentine thickness in overgrown equine cheek teeth

The presence of cheek tooth loss or defects, with subsequent overgrowth of the opposing teeth, is common in horses. Little is known about the factors that control the deposition of sub-occlusal secondary dentine (SO2D) in normal equine teeth, but these are likely to include stimulation of the occlusal surface. There appears to be no information on the possible alterations to this process when teeth develop overgrowths and, consequently, of the net effect on SO2D thickness caused by reduced stimulation of the occlusal surface and of absent/reduced normal occlusal wear (attrition). Knowledge of the likely thickness of SO2D in overgrown teeth may help reduce the risks of pulp horn exposure or thermal damage during therapeutic reduction of overgrowths. This study utilised 24 permanent cheek teeth (CT) with overgrowths (mean overgrowth height: 9.5 mm; range, 3.4-17.9 mm), and 18 control CT obtained from 15 horses of different breeds and ages. The thickness of SO2D was measured above 94 matched pulp horns in control and overgrown CT and showed a mean value of 12.14 mm (range 1.87-36.02 mm) in overgrown teeth and of 10.25 mm (range 2.64-17.26 mm) in controls. There was no significant difference between SO2D thickness in overgrown (mean 11.38 mm) and control (11.41 mm) mandibular CT, but SO2D was significantly thicker in overgrown (mean 12.57 mm) as compared to control maxillary (9.41 mm) CT. A comparison of SO2D thickness above the 94 matched pulp horns in overgrown and control teeth showed that 49% (46/94) of pulps in overgrown teeth had less SO2D overlying them than had control teeth. Of major clinical relevance was that the height of dental overgrowths was greater than SO2D thickness over one or more pulp horns in 14/24 overgrown teeth. Consequently, reduction of these overgrown teeth to the level of adjacent normal-height teeth would cause occlusal pulp exposure in 58% of teeth, in addition to possible thermal damage to additional pulp horns. It was concluded that equine CT overgrowths should be gradually reduced, by a few millimetres at a time, over a prolonged period.