An in vitro study evaluating the effect of ferrule length on fracture resistance of endodontically treated teeth restored with fiber-reinforced and zirconia dowel systems

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Abstract

Statement of problem

There are few published studies analyzing the effects of different ferrule lengths of endodontically treated teeth in relationship to newly developed fiber-reinforced and zirconia dowel systems.

Purpose

This in vitro study compared the effect of 3 different ferrule lengths on the fracture resistance and fracture patterns of crowned endodontically treated teeth restored with 4 different esthetic dowel systems.

Material and methods

The crowns of 123 human maxillary canines were removed at the cementoenamel junction and the roots were endodontically treated. Three master tooth models were prepared to ferrule lengths of 1.0 mm, 1.5 mm, and 2.0 mm to produce 3 master analogs. Each root was embedded in autopolymerizing resin with a 0.2-mm layer of silicone impression material to simulate the periodontal ligament. Forty analogs of each master tooth, with ferrule lengths of 1.0 mm, 1.5 mm, and 2.0 mm were produced with copy-milling (Celay system). Each group was further subdivided into 4 groups of 10 specimens each and restored with 4 different esthetic dowel systems (quartz fiber, glass fiber, glass fiber plus zirconia, and zirconia). All dowels were luted with adhesive resin cement (RelyX ARC), restored with composite cores (Valux Plus), and Ni-Cr alloy (Wiron 99) complete crowns. All specimens were loaded at 130 degrees to the long axes in a universal testing machine at a crosshead speed of 1 mm/min until fracture. Fracture patterns were classified as failures above or below the incisal third of the roots. The data were analyzed with 2-way ANOVA and Tukey HSD tests (α=.05). A Fisher exact test was conducted for evaluation of the mode of failure (α=.05).

Results

Mean failure loads (kg) for quartz fiber, glass fiber, glass fiber plus zirconia, and zirconia groups, respectively, with the 3 ferrule lengths were: 1.0-mm ferrule specimens: 98.09 ± 2.90, 85.36 ± 2.82, 80.24 ± 1.88, 70.11 ± 2.48; 1.5-mm ferrule specimens: 101.0 ± 2.88, 87.58 ± 2.83, 89.8 ± 2.09, 82.71 ± 2.14; 2.0-mm ferrule specimens: 119.5±1.78, 99.84±1.23, 98.6 ± 1.64, 95.42 ± 1.02. Teeth prepared with 2.0-mm ferrules demonstrated significantly higher fracture thresholds (P<.001). There were no significant differences in fracture patterns.

Conclusion

Increasing the ferrule length of the endodontically treated teeth from 1 mm to 1.5 mm in specimens restored with quartz-fiber and glass-fiber dowels did not produce significant increases in the failure loads (P=.084, P=.119, respectively). No significant difference was detected between glass-fiber and glass-fiber plus zirconia dowels with 1.5-mm and 2.0-mm ferrules (P=.218, P=.244, respectively). However, fracture thresholds were higher for all 4 dowel systems when the specimens were prepared with a 2.0-mm ferrule length (P<.001).

Section snippets

Material and methods

One hundred twenty-three freshly extracted canines free of cracks, caries, fractures, and restorations were selected for the study. All external debris was removed with an ultrasonic scaler (Mini Piezon; EMS Piezon Systems, Nyon, Switzerland), and the teeth were stored in saline solution until testing. The anatomic crowns of all teeth were removed perpendicular to the long axis of the tooth, from the most incisal point of the approximal cementoenamel junction (CEJ), with the use of a

Results

Mean failure loads were calculated for all groups (Table II). Two-way ANOVA was performed to test the 2 main effects, dowels, and ferrule lengths on the fracture strength. The result of the analysis revealed a significant difference in both the main effect dowel (P<.0001) and ferrule length (P<.0001). Significant dowel by ferrule-length interaction was also encountered (P<.0001) (Table II).

Further analysis with the Tukey HSD test indicated that the within-group differences for all dowel

Discussion

In the present study, 2-way ANOVA was used to test the 2 main effects on the fracture resistance of endodontically treated teeth restored with 4 esthetic dowel systems and 3 different ferrule lengths. Significant within-group differences were observed for all subgroups except for the quartz-fiber groups with 1.0-mm and 1.5-mm ferrule lengths (P=.084) and glass-fiber groups with 1.0-mm and 1.5-mm ferrule lengths (P=.119). The low elastic modulus of quartz- and glass-reinforced dowels, which

Conclusions

Within the limitations of this in vitro study, the following conclusions were drawn.

  • 1.

    There was a significant difference in the mean fracture loads of endodontically treated teeth prepared to 2.0-mm ferrule length compared with 1.0-mm and 1.5-mm ferrule lengths regardless of the dowel system tested (P<.001).

  • 2.

    Among the 1.0-mm, 1.5-mm, and 2.0-mm ferrule-length specimens, significantly higher fracture loads were observed in teeth restored with quartz-fiber dowels compared with teeth restored with

Acknowledgements

The author acknowledges RTD, Brasseler-Komet, Dentsply-Maillefer, Ivoclar Vivadent, and 3M for generous support in the form of donated materials. The author thanks Professor M. Babur Caniklioglu for his expertise, Dr Gunay Can for statistical analysis of the data, and Dr Atakan Elter for assistance with the illustrations.

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