Influence of remaining coronal tooth structure on fracture resistance of endodontically treated maxillary incisors

Statement of problem. Although endodontically treated tooth is less likely to break when there is enough remaining tooth structure, controversy exists concerning the remaining coronal tooth structure of endodontically treated maxillary incisors.
Purpose. The aim of this investigation was to access the resistance to fracture of endodontically treated maxillary incisors with four walls and those with three walls of remaining coronal tooth structure and the influence of the site of the missing coronal wall.
Material and methods. Forty endontically treated maxillary central incisors were decoronated according to the criteria of each group, leaving 3 mm above the cemento-enamel junction (CEJ). A 0.5-mm-wide chamfer was prepared 1 mm above the CEJ. The teeth were randomly divided into four groups (n=10) Group 1 had four walls of coronal tooth structure (control group), whereas groups 2, 3, and 4 had only three walls, missing the labial, palatal, and mesial wall respectively (test groups). The cast dowel and cores and crowns Ni–Cr-Be base metal alloy were fabricated and cemented with Panavia 21 cement. A compressive load was applied 45-degree to the long axis with an Instron machine until failure at a crosshead speed of 0.5 mm/min. Failure load was recorded in N and data were analyzed with 1-way ANOVA, followed by multiple comparisons using Tukey HSD test (α=.05).
Results. The mean failure load (N) of teeth with four walls (965.7 ± 37.7 N) was significantly higher from teeth with three walls (P<.001). The mean failure load of specimens without a labial wall (675.1 ± 38.9), was near that of teeth without a palatal wall(692.7 ± 36.3), and the mean failure loads of both groups were lower than those of teeth without a mesial wall (713.4 ± 35.7).. The mode of failure in the control group was a horizontal root fracture, whereas that of the test groups was either vertical or oblique fracture. The mode of failure in the control group was a horizontal root fracture, whereas that of the test groups was either vertical or oblique fracture.
Conclusions. Maxillary central incisors with four walls of remaining coronal tooth structure had significantly higher fracture resistance than teeth with only three walls. The site of the missing coronal wall did not influence the fracture resistance of endodontically treated teeth.
Clinical implications. Presence of remaining coronal tooth structure may be an important prognostic factor for endodontically treated maxillary incisors.