Different Undercut Depths Influence on Fatigue Behavior and Retentive Force of Removable Partial Denture Clasp Materials: A Systematic Review

Abstract

Purpose To perform a systematic review that provides an overview of the current literature on fatigue behavior of removable partial denture (RPD) clasp materials based on different retentive areas. Materials and methods The review followed the Preferred Reporting Items for Systematic Review and Meta‐Analyses (PRISMA) guidelines. Electronic searches were done via PubMed, Scopus, and OVID for studies reporting on RPD clasps and the fatigue failure of clasp materials. Inclusion criteria were English language with full text and in vitro studies only. Exclusion criteria were studies that did not assess the fatigue of RPD clasp materials. A quality assessment and selection of full‐text articles were performed according to Consolidated Standards of Reporting Trials criteria. Results A total of 182 articles were initially identified and screened. After applying inclusion and exclusion criteria, 15 articles were selected for the final analysis. Seven of the included studies utilized a vertical insertion/removal testing approach. Ten studies used the constant deflection test. Three studies used untapered specimens, and 12 studies used tapered specimens. Ten studies performed post‐test analysis. Conclusions Cobalt‐chromium (CoCr) is the strongest material in terms of fatigue in relation to the undercut depth and the modern, digitally manufactured RPD clasp materials also exhibit comparable fatigue behavior. Recent RPD clasp materials such as polyetheretherketone (PEEK) or laser sintered CoCr, however, require further study in terms of their fatigue behavior. In order to improve the quality of future studies, a standardized and calibrated fatigue testing method is needed with standardized specimen size and shape, which will reduce the risk of bias and enable meta‐analysis for bulk comparison between studies.

Fatigue behavior of removable partial denture cast and laser‐sintered cobalt‐chromium (CoCr) and polyetheretherketone (PEEK) clasp materials

“…The stage was adjusted to one of the three different deflections, 0.25, 0.50, and 0.75 mm for the specific test. The rotational speed was set to 540 rpm and the test was terminated when the specimen fractured or when 30,000 cycles, equivalent to 21 years, (Zheng et al, 2021) were completed.…”

“…A systematic review by Zheng et al (2021) highlighted the lack of research available on the fatigue behaviors of the RPD clasps made with PEEK, cast, and laser-sintered CoCr alloys. There was also a lack of standardized testing methods in the previous studies used to evaluate the fatigue life of the RPD clasps, which were mostly vertical insertion/removal methods and constant deflection tests.…”

Clinical Applications of Polyetheretherketone in Removable Dental Prostheses: Accuracy, Characteristics, and Performance

“…One significant quality of clasps is their retention force, which will resist the removable prosthesis’ dislodging force during masticatory function and muscle movement [ 63 ]. When determining the fit of a clasp material to the retentive area, the clasp shape (length, width), flexibility, and undercut engagement should be considered [ 64 ].…”

“…However, the lowest acceptable retentive force for one clasp was determined to be approximately 1.6 N [ 64 ]. Therefore, the retentive force provided by PEEK may be clinically acceptable [ 63 , 65 , 66 , 70 ]. A clinical report [ 71 ] demonstrated that PEEK clasps with an undercut of 0.5 mm could provide an adequate retention force.…”

“…An essential element affecting the clinical durability of removable prosthesis clasps is fatigue resistance [ 63 ]. Clasps undergo repeated bending caused by mastication and by the insertion and removal of the removable prosthesis, which may cause fatigue failure during long-term use [ 68 ].…”