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Background <p>The mesiobuccal roots of maxillary first molars frequently contain a second mesiobuccal (MB2) canal, where limited dentin thickness near the furcation may compromise root strength during instrumentation. This study evaluated the effects of MB2 preparation taper and sealer type on fracture resistance in these roots.</p> Methods <p>Sixty extracted maxillary first molars with an MB2 canal in the mesiobuccal root were identified using cone-beam computed tomography (CBCT). Teeth with two canals in the mesiobuccal root, either separate or merging within the apical 1–2&#xa0;mm, were included. Mesiobuccal roots were sectioned at the furcation level and remaining root length from the cut surface to the apex was standardized to 9 ± 1&#xa0;mm. The specimens were allocated into four experimental groups (<i>n</i> = 10 each) according to MB2 taper (25/0.04 or 25/0.06) and sealer type (bioceramic or epoxy resin–based). Two control groups (<i>n</i> = 10 each) were included: negative control, with no preparation or obturation, and positive control, with MB1 and MB2 canals prepared to 25/0.06 without obturation. Dentin thickness in the danger zone was measured before and after preparation at 8&#xa0;mm from the apex using CBCT. Fracture resistance was evaluated by vertical loading using a universal testing machine.</p> Results <p>No significant differences were found among the groups in terms of initial dentin thickness. Dentin removal in the danger zone did not differ significantly between the 25/0.04 and 25/0.06 taper groups (<i>p</i> = 0.921). Preparation taper significantly affected fracture resistance (<i>p</i> &lt; 0.001), whereas sealer type (<i>p</i> = 0.295) and the taper-sealer interaction (<i>p</i> = 0.559) were not significant. Mean fracture resistance values for the 0.04 taper groups ranged from 583.9 to 600.4&#xa0;N, whereas those for the 0.06 taper groups ranged from 426.6 to 484.1&#xa0;N. The negative control group exhibited the highest fracture resistance value (638.2&#xa0;N), whereas the positive control group showed the lowest fracture resistance value (385.2&#xa0;N).</p> Conclusions <p>Within the limitations of this study, MB2 preparation taper had a greater influence on fracture resistance than sealer type. Increasing taper reduced fracture resistance despite similar dentin removal at the danger-zone level, suggesting that overall root geometry and stress distribution may play an important role.</p>

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Effect of preparation taper and sealer type on fracture resistance of mesiobuccal roots with MB2 canals in maxillary first molars: an in vitro study

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月10日

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  • Evren Sarıyılmaz,
  • Öznur Sarıyılmaz,
  • Emek Bayındır,
  • Rüya Sessi̇z,
  • Esra Ercan

摘要

Background

The mesiobuccal roots of maxillary first molars frequently contain a second mesiobuccal (MB2) canal, where limited dentin thickness near the furcation may compromise root strength during instrumentation. This study evaluated the effects of MB2 preparation taper and sealer type on fracture resistance in these roots.

Methods

Sixty extracted maxillary first molars with an MB2 canal in the mesiobuccal root were identified using cone-beam computed tomography (CBCT). Teeth with two canals in the mesiobuccal root, either separate or merging within the apical 1–2 mm, were included. Mesiobuccal roots were sectioned at the furcation level and remaining root length from the cut surface to the apex was standardized to 9 ± 1 mm. The specimens were allocated into four experimental groups (n = 10 each) according to MB2 taper (25/0.04 or 25/0.06) and sealer type (bioceramic or epoxy resin–based). Two control groups (n = 10 each) were included: negative control, with no preparation or obturation, and positive control, with MB1 and MB2 canals prepared to 25/0.06 without obturation. Dentin thickness in the danger zone was measured before and after preparation at 8 mm from the apex using CBCT. Fracture resistance was evaluated by vertical loading using a universal testing machine.

Results

No significant differences were found among the groups in terms of initial dentin thickness. Dentin removal in the danger zone did not differ significantly between the 25/0.04 and 25/0.06 taper groups (p = 0.921). Preparation taper significantly affected fracture resistance (p < 0.001), whereas sealer type (p = 0.295) and the taper-sealer interaction (p = 0.559) were not significant. Mean fracture resistance values for the 0.04 taper groups ranged from 583.9 to 600.4 N, whereas those for the 0.06 taper groups ranged from 426.6 to 484.1 N. The negative control group exhibited the highest fracture resistance value (638.2 N), whereas the positive control group showed the lowest fracture resistance value (385.2 N).

Conclusions

Within the limitations of this study, MB2 preparation taper had a greater influence on fracture resistance than sealer type. Increasing taper reduced fracture resistance despite similar dentin removal at the danger-zone level, suggesting that overall root geometry and stress distribution may play an important role.