On failures and complications of tooth-supported fixed prostheses
Authors:   , Hawtan Mohammed 
Published: February 2023

Loss of tooth structure or loss of the tooth may affect masticatory function, phonetics, a person´s appearance, and might ultimately impair quality of life. Fixed prosthetic rehabilitation in the form of either fixed dental prosthesis (FDP)or single crown (SC) is a reliable treatment alternative to restore lost functions. Tooth-supported fixed prosthetic restorations (FDPs, SCs) are influenced by multiple combined general and local factors that may affect the risk of complication and failure. Recognizing risk factors is important in treatment planning, and will help the clinician optimize treatment outcomes. This will also be beneficial for both the patient and society from a cost-effective aspect, as a reduction in complications and failures reduces costs. Several factors have been suggested to impact the survival and failure rates of FDPs and SCs, but there is still limited evidence concerning the clinical outcomes of FDPs and SCs when subjected to a combination of multiple factors in a clinical setting. The aim of the present thesis was to evaluate whether the survival and failure rates of full-coverage tooth-supported fixed prosthetic restorations (FDPs, SC) are influenced by general and/or local factors. This thesis is based on a systematic review (Paper I) and three retrospective studies (Papers II, III, and IV). In Study I, PubMed, Web of Science and ScienceDirect databases were searched and manual searches were conducted to identify clinical human studies reporting on full-coverage tooth-supported FDPs and SCs. Cumulative survival rate (CSR) was calculated over the maximal period of follow-up reported, in a life-table survival analysis. Seventeen studies fulfilled the inclusion criteria. The highest 5-year survival rate was observed for all-ceramic and metal–ceramic SCs on vital teeth 97.8% (95%CI [97.1– 98.5%]), and all-ceramic SCs on non-vital teeth with fiber post 99.1% (95% CI [97.7– 100.4%]). Metal–ceramic SCs on vital teeth 97.5% (95% CI[96.8–98.3%]) showed a statistically significant higher estimated 5-year survival rate compared to metal–ceramic SCs with cast metal post 94.5% (95% CI [93.3–95.8%], p <0.001) and fiber post 95.1% (95% CI [93.4–96.6%], p <0.007), respectively. For FDPs, the 5-year survival rate was higher for metal–ceramic FDPs on vital abutments 96.9% (95% CI [95.5–98.4%]), compared to FDPs retained by non-vital abutment(s) with cast metal posts 94.3% (95% CI [89.3–99.3%]). The difference was not statistically significant. Tooth vitality is suggested to contribute positively to the survival of SCs. The results are, however, limited by the small number of studies and the presence of uncontrolled cofounding clinical variables. In the retrospective studies II, III, and IV, dental records archives and the digital journals of all patients at the Faculty of Odontology, Malmö University, Sweden were reviewed to identify patients rehabilitated with full-coverage toothsupported FDPs and SCs. Cox regression was used to evaluate the associations between clinical covariates and prosthesis failure. The CSR was similar for FDPs and SCs after 5 years of function. CSR was higher for SCs compared to FDPs after 10, 15, and 20 years of function. Smoking, type of prosthesis material, and bruxism significantly influenced the survival of FDPs, whereas abutment vitality, position of the non-vital abutment, or prosthesis length did not show any significant influence on the occurrence of FDP failure. The survival of SC was influenced by anterior placement, non-vital abutments, and bruxism, while the patient’s age and sex, the location of the crowns in relation to the jaws, the type of tooth, the presence of post and core, and the type of crown material, treatment providers, or smoking did not show significant effects on the survival of SC.In summary, within the limitations of the review and retrospective studies, bruxism, smoking, and type of prosthesis material are suggested to contribute toFDP failure. Anterior placement, non-vital abutments, and bruxism are factors increasing the rate of SC failure.