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Effects of different cusp coverage restorations on the fracture resistance of endodontically treated maxillary premolars

https://doi.org/10.1016/j.prosdent.2016.02.007Get rights and content

Abstract

Statement of problem

Cusp coverage restorations for the restoration of endodontically treated teeth represent a conservative approach in terms of function and esthetics. However, limited scientific data are available regarding the optimum reduction design and thicknesses.

Purpose

The purpose of this in vitro study was to evaluate the fracture resistance and fracture patterns of cusp coverage restorations with different cusp reduction designs and reduction thicknesses on endodontically treated maxillary premolars (ETMPs) with mesio-occluso-distal (MOD) cavities.

Material and methods

One hundred sixty-five extracted intact human maxillary premolars were divided into 11 groups: G1-10 (test groups) and G11 (intact group). In the test groups, all of the teeth were restored with composite resin after canal treatments with MOD cavities. However, the cusps of the G1-9 teeth were reduced with combinations of different thicknesses (1.5, 2.5, and 3.5 mm) and designs (beveled, horizontal, and anatomic). The specimens were subjected to 105 cycles of 50 N mechanical loading. Next, the specimens were subjected to a compressive load at a crosshead speed of 0.5 mm/min until fracture. The fractured specimens were analyzed to determine the fracture pattern. Two-way ANOVA followed by the Fisher least significant difference (LSD) test was used to analyze the interaction between groups.

Results

The fracture resistance values increased with increases in the cusp reductions. The fracture resistance values of the G6 (2.5 mm, anatomic) and G9 (3.5 mm, anatomic) groups were significantly greater than that of the MOD group. However, the G6, G8 (3.5 mm, horizontal), and G9 groups were comparable with G11. The highest restorable fracture rates were observed in G6 and G9.

Conclusions

Cusp reduction design and thickness influenced the fracture resistance and fracture patterns of cusp coverage restorations of ETMPs with MOD cavities. The teeth restored with anatomic cusp reduction designs with reduction thicknesses of at least 2.5 mm exhibited greater fracture resistance and more frequent restorable fractures.

Section snippets

Material and Methods

This study protocol was approved by the Ethical Research Committee (2014.144) of the Karadeniz Technical University. Caries-free human maxillary premolars with two roots and two canals (extracted for orthodontic reasons) were used. Teeth with cracks, fractures, or defects and internal-external resorption were excluded from the study. The mesiodistal and buccolingual tooth sizes were measured with digital calipers, and teeth with similar dimensions were selected. The selected teeth were assigned

Results

The data exhibited normal distributions according to the Shapiro-Wilk tests. Regarding the control and reduction groups, the 1-way ANOVA revealed significant differences (P<.001) among all groups. A Tamhane test revealed differences between the reduction groups and the control group (Table 1). All of the reduction groups exhibited higher fracture resistances than the MOD group. Significantly higher fracture resistance values were observed in 2 reduction groups (2.5-mm anatomic and 3.5-mm

Discussion

In the present study, the fracture resistances of ETMPs restored with various cusp coverage restorations were evaluated. Many factors may influence in vitro results; thus, in vitro experiments should represent the intraoral environment. Simulations of periodontal ligaments can influence not only the fracture load values but also the fracture patterns.35 For these reasons, the roots of the teeth were covered with latex liners.

Changes in the mechanical properties of a restoration under

Conclusions

Adhesive cusp coverage restorations increased the fracture resistances of ETMPs with MOD cavities to a level comparable with that of intact teeth. The cusp reduction designs and thicknesses influenced the fracture resistances and fracture patterns. Increases in cusp reduction thickness increased the mean fracture resistance values. The teeth restored with anatomic cusp reduction designs and reduction thicknesses of least 2.5 mm exhibited greater fracture resistances and greater proportions of

Acknowledgments

The authors thank Dr Tamer Tuzuner for support while preparing this study.

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      Such elements often require cusp coverage [17] or indirect reconstruction techniques (overlays, crowns), and direct restoration are indicated only in presence of well represented vestibular and palatal walls and at least one marginal ridge [18]. Kalay et al. [19] reported a very high percentage of cusp fractures in endodontically treated elements directly reconstructed without cusp coverage, with percentages of more than 70% in premolars presenting MOD cavities. From a functional point of view, premolars are subjected to more uniform lateral forces during mastication and present a smaller amount of tooth structure compared to molars [20].

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