The Influence of Crown Height to Diameter Ratio on the Force to Fracture of Canine Teeth in Dogs

Abstract

Summary Previous work suggests that the tooth height to diameter ratio (H/D) may have an influence on the fracture resistance of dog canine teeth. Thus, it can be hypothesized that canine teeth with distal abrasion or teeth already requiring pulpal manipulation may benefit from a reduction in height and that an ideal H/D exists that balances tooth fracture resistance and tooth function. Therefore, a study was performed to investigate the influence of H/D on force to fracture and probability of fracture of canine teeth in dogs. Thirty extracted canine teeth from laboratory Beagle dogs were standardized by hard tissue volume and evenly distributed among three groups; unaltered H/D (group A), 10% reduction in H/D (group B) and 20% reduction in H/D (group C). The teeth were potted in clear auto-polymerizing orthodontic acrylic and then secured within a universal materials testing machine. A displacement was applied at a speed of 1 mm/min to the distoocclusal line angle at 45° angle to the long axis of the crown. The maximum measured force at the time of fracture represented the maximum force to fracture. A linear regression model showed a significant inverse relationship between H/D and force to fracture (p=0.043; 95% CI -55.2 to -0.09). A margin of safety (MoS) analysis was performed to determine the probability of fracture by comparing normal force distributions of the measured force at fracture to that reported in a previous study, representative of normal biting-pulling loads on canine teeth. When 100% of the load was applied to a single unaltered canine tooth the probability of fracture was 36.7%. Decreases in H/D of 10% and 20% resulted in a decreased probability of fracture by 24.1% and 60.4%, respectively. A paired MoS analysis was conducted wherein the applied loads were distributed across two maxillary canine teeth according to their relative heights. Within the pair, a 20% decrease in H/D decreased the probability of fracture of that tooth by 86.5%, but increased the probability of fracture of the unaltered contralateral canine tooth by 54.4%. The results of this study may have implications on the successful long-term management of traumatized canine teeth in dogs. The findings of this study support the hypothesis that teeth with a lower H/D are more resistant to fracture. However, given the potential impact of crown reduction of a single canine tooth on the load redistribution to the remaining unaltered canine teeth, further investigation is needed to determine what H/D would be ideal. In addition, future studies could elucidate in which clinical scenarios the concept of H/D reduction could be implemented.

Fracture Limits of Maxillary Fourth Premolar Teeth in Domestic Dogs Under Applied Forces

“…There is an inherent variability in the ability of a tooth to resist fracture that would commonly occur during chewing on a treat or toy. The average maximum force sustained by the tested teeth was higher than what has previously been reported for strategically important teeth 2 (21). The range of data was not unexpected when published information on the fracture performance of human teeth (22) or the fracture behavior of canine teeth of dogs under pulling forces is considered (18).…”

“…For the purpose of evaluating the potential effects of material texture on the risk of inducing a maxillary fourth premolar tooth fracture during chewing, it is necessary to combine the referenced knowledge for chewing forces with an understanding of the forces required to induce a clinically observed tooth fracture. Mechanical testing has previously been conducted on extracted canine teeth from dogs, using a universal materials testing machine after potting the teeth in acrylic and applying the force at a speed of 1 mm/min to the disto-occlusal line angle at an angle of 45° to the long axis of the crowns (21). The mean forces required to fracture canine teeth ranged from 494 to 630 N depending on the crown height to diameter ratio.…”

“…One study explored the effect of dental restoration technologies on the subsequent fracture forces of teeth post restoration 3 . A lower crown height to diameter ratio has been found to increase fracture resistance of canine teeth that have undergone endodontic and prosthodontic therapy (21). Further literature on this subject is sparse at best, and this in part explains the lack of established guidelines for recommended chewing textures of treats and toys.…”

Assessment of 68 Prosthodontic Crowns in 41 Pet and Working Dogs (2000–2012)

“…35 However, the recommendation for a higher height/diameter ratio for crown preparation has been subsequently contradicted. 36 Additionally, this review concluded that the…”

“…Along with multiple anesthetic episodes come additional costs to the client related to equipment, instruments and materials, and pertinent laboratory fabrication fees. 36 Adjunct periodontal surgery and crown preparation may mean time "off work" that could interfere with training or the on-duty schedule of working dogs. It is recommended that prosthodontic therapy should be performed on a case-by-case basis with the clients understanding the associated risks and financial requirements.…”