Effects of nickel-titanium file systems on relationship between cleanliness and fracture resistance of long-oval root canals

doi:10.3969/j.issn.1674-8115.2026.04.003

Abstract

Abstract:

Objective ·To investigate the relationship between the cleanliness and fracture resistance of long-oval root canals using small field-of-view cone-beam CT (CBCT), computer-aided technologies, and a universal testing machine, and to explore the effects of commonly used nickel-titanium (NiTi) file systems on this relationship. Methods ·Mandibular premolars with single straight roots extracted for orthodontic reasons between April 2024 and April 2025 in the Department of Stomatology, Xinhua Hospital, Shanghai Jiao Tong University School of Medicine, were collected. CBCT was used to analyze canal morphology, and 40 teeth with long-oval canals were selected. The crowns were removed to prepare standardized root samples with a length of 13 mm. The samples were randomly and equally divided into Group A (X-GOLD, n=10), Group B (Reciproc Blue, n=10), Group C (ProTaper Universal, n=10), and a control group (n=10). Root canal preparation was performed in Groups A, B, and C using different NiTi file systems. All samples were scanned before and after preparation using CBCT, and three-dimensional models were reconstructed to calculate canal cleanliness by comparing pre- and post-preparation morphologies. The experimental groups were obturated using the single-cone technique, while the control group was left unobturated. All roots were embedded and subjected to static loading using a universal testing machine to determine fracture load. Data were analyzed to evaluate differences and trends in cleanliness and fracture resistance among the groups, and to assess their relationship. Results ·Group C showed significantly higher overall cleanliness compared to Groups A and B, and the differences were statistically significant (P<0.05), while no statistically significant difference was observed between Groups A and B (P>0.05). CBCT-based 3D reconstruction illustrated that long-oval canals tended to be over-prepared in the mesiodistal direction and under-prepared in the buccolingual direction. The control group demonstrated significantly higher fracture resistance than Groups A, B and C, and the differences were statistically significant (P<0.05). There was no statistically significant difference in the fracture load between Group A and Group B (P>0.05). Group C had significantly lower fracture resistance compared to Group A and the control group, and the difference were statistically significant (P<0.05). A significant negative correlation was found between canal cleanliness and fracture resistance in long-oval root canals (r=-0.379, P=0.039). Conclusion ·NiTi file systems affect the relationship between cleanliness and fracture resistance in long-oval root canals. In mandibular premolars with long-oval single straight canals, cleanliness is negatively correlated with fracture resistance. The ProTaper Universal NiTi file system achieves higher cleanliness while maintaining a certain level of fracture resistance in such cases.

Key words: long-oval root canal, computer-aided technology, root canal preparation, cleanliness, fracture resistance

CLC Number:

R781.05

Zhang Zhuoyang, Wang Yiwei, Chen Xiyao, Wang Ying, Sun Shuntao, Tang Zisheng. Effects of nickel-titanium file systems on relationship between cleanliness and fracture resistance of long-oval root canals[J]. Journal of Shanghai Jiao Tong University (Medical Science), 2026, 46(4): 434-441.

Figures/Tables 6

Fig 1 Embedded root specimens after root canal obturation

Fig 2 Compression testing of root specimens using a universal testing machine

Tab 1 Measured data of isolated root specimens in each group （n=10）

Group	Weight /g	Buccolingual diameter /mm	Mesiodistal diameter/mm
A	0.34±0.07	7.21±0.62	4.73±0.43
B	0.32±0.06	7.10±0.35	4.55±0.40
C	0.33±0.04	7.06±0.43	4.50±0.42
Control	0.35±0.05	7.41±0.57	4.67±0.78

Tab 2 Cleanliness of different regions of the root canals after preparation with three nickel-titanium file systems

Group	Coronal 1/3/%	Middle 1/3/%	Apical 1/3/%
A	74.70±10.73	62.51±12.97^①⑤	61.78±13.64^②
B	74.54±10.52^③	65.80±12.21^④⑥	55.06±11.74
C	82.97±9.37	83.75±9.81	70.27±19.02

Fig 3 Three-dimensional reconstruction of root canal preparation

Fig 4 Relationship between overall cleanliness and fracture load of long-oval root canal specimens prepared with different nickel-titanium file systems

TrendMD

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