JOVD 2017: The Influence of Force Direction on the Fracture Pattern and Fracture Resistance of Canine Teeth in Dogs

Question 1

Authors?

Answer 1

stephanie goldschmidt

Jason Soukup and al.

Question 2

Aim of study?

Answer 2

Evaluate the influence of force direction on fracture resistance and fracture pattern of canine teeth.

Question 3

What did the cadaver models and finite element analysis (FEA) studies had previously found?

And what were the drawbacks of these studies?

Answer 3

• Foundings:
  
  • when the height to diameter ratio of the crown base (tooth crown excluding the cusp) exceeds 1, vertical crack propagation will arrest approximately one-third of the way down the cylindrical base of the tooth, even with increasing load
  • increasing height of crown base (e.x. tooth elongation) confers a protective factor to the tooth preventing vertical fractures when exposed to axial loads.
  • Small rounded cusp of canine teeth protects tooth from chip fractures when exposed to off-axial loading
  • greater loads are required with increasing base radius & dental toughness
  • lower loads are required to fracture teeth with longer crowns (longer tooth more susceptible to bending stress and fracture)
  • decreasing the height of canine tooth protect integrity of that tooth but increase fracture susceptibility of the remaining canine teeth
• Drawbacks:
  
  • dentin and enamel Ø homogenous unit (fractures can stall at DEJ);
  • thickness & material properties Ø homogenous throughout the entirety of the tooth;
  • material properties of teeth (elasticity, toughness) based on values for human teeth;
  • morphological features of canine tooth (distal curvature) has not been taken into account.

Question 4

Describe the loading forces that cause vertical, chip and transverse fractures

Answer 4

Vertical fractures: cracks that extend vertically through enamel from the occlusal cusp (radial cracks) or base of tooth (marginal cracks); occur with a_xial (ie, occlusal/compressive) loading of tooth_.

Chip fractures: scallop-shaped segments coming off the side of enamel; caused by off-axial loading.

Transverse fractures: course through transverse plane of entire tooth; occur under lateral loads.

Oblique fractures: known in human and veterinary literature, but no study.

Question 5

What is the most common type of fracture for canine teeth?

Answer 5

Transverse

Question 6

What fracture type does a load applied in distal-mesial direction result in?

Answer 6

Group A (distal-mesial force direction): 85% oblique distal-mesial fx pattern; 14% transverse fx pattern

N.B.: more enamel–dentin fractures with distal–mesial direction (these lesions, considered “abrasion” injuries, may be more acute traumatic dentoalveolar injuries that may require different therapeutic and preventative approach

Question 7

What fracture type does a load applied in labial-lingual direction result in?

Answer 7

Group B (labial-lingual): 58% obique lateral-lingual fx pattern and 41% transverse fx pattern

Question 8

What fracture type does a load applied in mesial-distal direction result in?

Answer 8

Group C (mesial-lingual): 66% oblique mesial-distal fx pattern; 25% transverse fx pattern; 8% lingual-lateral fx pattern.

Question 9

In the combined loads of axial compression, bending, and transverse shear, which force is dominate the failure force?

Answer 9

Transverse shear force; which explains the presence of transverse fx pattern in all force direction groups

Question 10

In what direction is the tooth the weakest?

Answer 10

Regardless of force direction a similar force to fracture is required for clinical failure

Force to fracture was lower for labial-lingual direction although not statistically significant

Question 11

Is root involvement of the fracture predictable?

Answer 11

no

Question 12

Why increase susceptiblity of fracture was expected with labial-lingual direction and to lesser extent with mesial-distal direction?

Answer 12

Because natural shape of the canine tooth has evolved for resisting force in biting pulling motion (distal–mesial force dir.); the crane hook shape of dog’s canine tooth make it more resistant to bending moment caused by force in the distal–mesial direction; but surprisingly no difference in mean force to fracture was found between groups (can be due to the small sample size and large variance in groups)

Question 13

What factors dictate the force to fracture values?

Answer 13

• Amount of dentin is key factor dictating ultimate force to fracture values; more hard tissue that is removed with cavity and root canal preparation, the greater the risk of fracture.
• Teeth with smaller base radius have an increased susceptibility to transverse fractures; hard tissue CSA was significantly correlated with force to fracture.
  
  • Hard tissue cross-sectional area (CSA):
    
    • D1: mesial to distal diam. at CEJ; D2: pulp chamber diam. at same place as D1; CSA = pie (D1² – D2²)/4

Question 14

Why this study showed lower force to fracture than Correas and Soukup prevous study?

Answer 14

• In Correas: loading force was applied perpendicular to long axis of tooth at 4 mm from CEJ, while in the present study the loarding force was applied at tip of tooth at 45 degree to long axis of tooth.
• In Soukup: loading force was applied at 45 degree and at tip of tooth but only in distal-mesial direction, while in the present study the lower to fracture forces were found in the labial-lingual direction group.