Circumferential Strains in Maxillary Central Incisor Roots During Lateral Condensation

Objectives: Lateral condensation using cold gutta-percha has been "blamed" as a possible cause of vertical root fracture (VRF). The aim of this study was to characterize the circumferential strains that develop in the root during lateral condensation of a root filling. Methods: Twelve human central incisors were collected and tested within 2 weeks from extraction A crown-down technique with final apical filing to No. 50 was used to shape the root canal. Three pairs of 031-EC or 031-DE strain gauges were bonded on the buccolingual or mesiodistal sides in the center of the apical, middle and coronal third of the root. Teeth were embedded to the CEJ level in a cylindrical tube containing impression material located on a weighting load cell. Gauges were wired and attached to a data acquisition system. The strain in each gauge was continuously recorded at a 10 Hz frequency during a lateral condensation process which completely mimicked the clinical procedure, using a stainless steel finger spreader, gutta-percha and Ah-26. Results: The highest strains developed in the apical third of the root (2-3 fold higher compared to midroot). Mean apical proximal strains (mesial = 359 ± 243 µs; distal = 289 ± 187 µs) were higher compared to buccolingual strains (buccal = 135 ± 107 µs; lingual = 95 ± 89 µs) (p<0.02). Maximal apical proximal strains (mesial = 661 ± 493 µs; distal = 528 ± 305 µs) were higher compared to buccolingual strains (buccal = 248 ± 201 µs; lingual = 156 ± 162 µs) (p<0.05). Conclusions: The highest circumferential strains in lateral condensation develop in the apical third of the root in a direction (proximal) perpendicular to the anticipated plane of the VRF.