Evaluation of zirconia crowns restoring endodontically treated posterior teeth with 2 finish line designs and 2 occlusal reduction schemes: A randomized clinical trial

Elsevier

Available online 15 November 2022

The Journal of Prosthetic DentistryAbstractStatement of problem

Preparation design has been linked to restoration survival, and the finish line geometry, such as a deep chamfer or shoulder, has been linked to marginal integrity. However, limited data are available for restoration success with the feather-edge finish line when used with monolithic zirconia crowns with different occlusal reduction schemes.

Purpose

The purpose of this randomized clinical trial was to evaluate the clinical performance of 2 finish line designs (feather-edge and rounded shoulder) in relation to 2 occlusal designs (flat and planar) in endodontically treated teeth restored with monolithic zirconia crowns.

Material and methods

Sixty-six complete-coverage monolithic zirconia crowns were provided for posterior endodontically treated teeth. The participants were divided into 3 groups based on the preparation design: the control group (PS) had a planar occlusal scheme with a rounded shoulder finish line; the first intervention group (FF) had a flat occlusal scheme with a feather-edge finish line; and the second intervention group (FS) had a flat occlusal scheme with a rounded shoulder finish line. The crowns were designed with the exocad software program and milled with a 5-axis machine. After cementation, clinical performance in terms of marginal adaptation, marginal discoloration, fracture, and secondary caries was evaluated by using the modified United States Public Health Service (USPHS) criteria. The gingival index score system was used to evaluate the gingival response. The scores were recorded immediately after cementation and at 3 subsequent follow-up visits every 3 months for 1 year. The chi-square test was used in all comparisons of outcomes and follow-up durations (α=.05).

Results

In terms of marginal adaptations, the control group (PS) demonstrated the best marginal adaptation scores during follow-up visits, followed by intervention 2 (FS), and lastly, intervention 1 (FF), which was scored mostly with Bravo. At the third follow-up visit, the intervention 1 (FF) group reported the most gingival responses of all groups. No significant difference among the groups was found in terms of marginal discoloration, fracture, or secondary caries at any of the follow-up visits. Each group received a perfect Alfa score of 100% on all 3 follow-up assessments.

Conclusions

In this 1-year randomized clinical trial, all evaluated preparation schemes and corresponding crowns were clinically successful. The clinical performance of monolithic zirconia crowns of the novel preparation design (FF) was successful in terms of marginal adaption, fracture, secondary caries, and marginal discoloration.

Section snippetsMaterial and methods

This research was conducted in the Department of Fixed Prosthodontics at Cairo University, with participants enrolled as clinic patients. The clinical trial was registered with the Clinical Trial Registry of the United States (NCT04052490) and had been approved by the faculty ethics committee (2872019-17966). Participants had severe tooth structure loss with a risk of fracture after endodontic treatment and were planned for complete-coverage restoration. Informed consent was acquired. Based on

Results

A comparison of different marginal adaptation scores in all groups was performed, which revealed a significant difference at all follow-ups (P<.05). The chi-square test showed that the PS group had the best scores (100% Alfa). The FS group scored 90.9% Alfa and 9.1% Bravo, while the FF group recorded the highest Bravo scores with 100% at different follow-ups (Table 1).

For the gingival response, a comparison of different gingival scores in all groups revealed a significant difference at all

Discussion

Despite extensive research, the optimal definitive restoration for endodontically treated teeth remains unclear.1 Depending on the tooth type and remaining tooth structure, it is not always possible to restore extensively damaged endodontically treated posterior teeth with endocrowns, and complete-coverage crowns have proven reliable over time.7,23 A complete-coverage restoration braces the residual structure, protects against tooth fracture, and prevents the cusps from deflecting.23 The

Conclusions

Based on the findings of this randomized clinical trial, the following conclusions were drawn:

1.

Over a 1-year period, the clinical performance of monolithic zirconia crowns with the novel flat occlusal scheme and feather-edge finish line preparation design (FF) was successful in terms of marginal adaption, fracture, secondary caries, and marginal discoloration.

2.

The flat occlusal scheme and feather-edge finish line (FF) preparation groups had clinically manageable gingival reactions. However, the

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