To compare load & strain in various teeth by hand (HS) & finger spreaders (FS).
N: 60 total teeth. 10 each of maxillary central incisor, premolar and molar; and mandibular incisor, pre-molar and molar.
M&M: Teeth excised 2 mm coronal to CEJ, gauges placed (apical & middle 1/3 on Buccal), cleaning and shaping , each tooth obturated twice (hand and finger spreader, randomly assigned order), strain recorded during obturation. Measured force necessary to induce Vertical root fracture (VRF) with spreader.
Exclusion criteria: fracture, craze lines, gross caries, immature apex
- Apical load & overall strain: HS; D11T > FS (statistically significant)
- No significant difference in loads recorded b/w apical & middle 1/3 gauges
- Differences in mean load fracture observed among different tooth types. Weakest tooth = mandibular incisors, then M root of mandibular molars.
- Fracture site usually BL. ↑ variation in location with maxillary premolar and MB root of mx molars.
- LC does not appear to be a direct cause of VRF unless excessive force used. Previous study states 4.9kg is safe. Pitts recommended “safe-limited load” is 70% min force required to cause fracture.
- Many fractures take place in the apical third and are due to transmission of the force from the gutta percha and average time is over 20 months.
In cases of mandibular incisors, overinstrumented root(s), thin dentinal walls, recommended obturation by finger spreaders to decrease risk of fracture.