Effect of the attachments on clinical outcomes of mandibular distal extension implant-supported removable partial dentures: A systematic review

Healing abutments and attachments have been used for implant-supported removable partial dentures (ISRPDs). However, the effects of these abutments and attachments on the clinical outcomes of the implants and prostheses are elusive because of the lack of standardized research protocols.The purpose of this systematic review was to determine the clinical outcomes of mandibular distal extension ISRPDs with healing abutments and attachments by analyzing qualified studies.An electronic and manual literature search was conducted on PubMed, Web of Science, Scopus, Embase, and Cochrane Library databases including articles published in English from 1980 to 2020. Publications of clinical outcome studies on the mandibular distal extension ISRPDs with healing abutments or attachments were screened by inclusion and exclusion criteria. Clinical outcomes of removable partial dentures (RPDs) and ISRPDs with different types of abutments or attachments were compared by using patient-reported outcome measures, implant survival rate, masticatory performance, and implant- or prosthesis-related complications. Study designs and clinical outcome data were extracted and analyzed. The evidence of the selected studies and degree of recommendation were made according to the Oxford Centre for Evidence-based Medicine, and the risk of bias of the studies was assessed based on Newcastle-Ottawa criteria.Of 541 articles initially identified after removing duplicate records, 11 articles were selected by applying the inclusion and exclusion criteria, by inter-viewer agreement, and by hand searching. Nine prospective cohort studies, 1 retrospective cohort study, and 1 randomized controlled trial were included with evidence levels assessed at 1b, 2b, and 2c. The risk of bias varied from 5 to 8 out of 9. Patient overall satisfaction, oral health-related quality of life (OHRQoL) scores, and masticatory ability were significantly improved for ISRPDs with either healing abutments, ball, or LOCATOR attachments when compared with RPDs. The implant survival rate varied from 92% to 97% at 2 to 10 years for ball attachment and was 100% at 1 year for LOCATOR attachment-supported ISRPDs. Marginal bone loss (MBL) varied from 0 to 1 mm in all studies, although LOCATOR attachments had significantly less MBL compared with ball attachments. The maximal pocket depth and bleeding on probing index around implants at 1 year were 1.7 to 1.8 mm and 0.1 to 0.3. Loose healing caps were the main mechanical complication of implants. There were more prosthetic complications in ISRPDs with ball attachments than RPDs at 10-year follow-up, including gold matrix loosening, loss of retention, and denture base fractures. No direct comparisons were made of patient-reported outcomes or prosthetic complications between ball and LOCATOR attachment-supported ISRPDs.Healing abutments and attachments (ball or LOCATOR) improved patient-reported outcomes and the masticatory function of mandibular distal extension ISRPDs. However, insufficient evidence was found to determine the relative effectiveness of different attachment systems on the clinical outcomes of mandibular distal extension ISRPDs. Abutment loosening was the most frequent mechanical complication for healing abutments. More prosthetic complications were associated with ball attachment-supported ISRPDs than RPDs. The major weaknesses of this systematic review were the relatively moderate level of evidence and the publication language, since implant attachments are used in many non-English speaking countries.