Chronology and sequence of emergence of permanent premolar teeth in the horse: study of deciduous premolar ‘cap’ removal in Thoroughbred racehorses.

The study takes a closer look at the timeline and order of permanent premolar tooth emergence in Thoroughbred racehorses. The researchers found that these factors were more complex than previously assumed, with a significant trend for later cap extraction age associated with lower jaw teeth, those further back in the mouth, and female horses.

Methodology and Results

• This research was a prospective study. Data collection took place over a period of time with observations being recorded of deciduous premolar “cap” extractions during routine dental exams in Thoroughbred racehorses.
• The researchers used mixed effects multiple regression analysis to correspond the observed ages, noted in days, of PM ‘cap’ extractions with various predictive variables.
• The team made sure to account for multiple observed outcomes within individual horses.
• In total, 508 deciduous premolar ‘caps’ were removed from 207 horses. The average ages at removal from the second, third, and fourth premolars (PM2, PM3, PM4) were 35.1, 37.7, and 45.1 months respectively.
• The research team found the age at which deciduous ‘cap’ removal occurred was significantly associated with the tooth row, whether the tooth was in the upper or lower jaw, and the gender of the horse. The extraction age was typically later for teeth located further back (‘caudal’) in mouth, teeth in the upper jaw, and female horses.

Significance and Further Recommendations

• The ages at which the deciduous premolar ‘caps’ were removed in this study varied greatly from those published previously in equine research.
• The findings provided the first recorded evidence of sexual dimorphism, or a noticeable difference between males and females beyond the reproductive organs, in the eruption of the permanent premolar dentition in horses.
• The variations found strongly suggest a model of cheek tooth eruption in horses where the chronology and sequence of emergence are more intricate than previously assumed. This aligns with existing understanding of tooth eruption in other species which have been studied more extensively.
• Abnormal cheek tooth eruption is believed to be a factor in the development of various dental conditions. Hence, a thorough understanding of the eruption process is essential to devise effective prevention and treatment strategies.