Intraoral low-temperature degradation of monolithic zirconia dental prostheses: Results of a prospective clinical study with ex vivo monitoring.

OBJECTIVE: To investigate the intraoral development and kinetics of low-temperature degradation (LTD) in second-generation 3 mol.% yttria-doped tetragonal zirconia polycrystal (3Y-TZP) monolithic prostheses, as well as the influence of masticatory mechanical stress and glaze layer on it. METHODS: A total of 101 posterior tooth elements were included in a prospective clinical study, which included ex vivo LTD monitoring (at baseline, 6 months, 1 year, and 2 years) using Raman spectroscopy (n = 2640 monoclinic phase measurement points per evaluation time) and SEM. Four types of areas (1-2 mm2 surface, 6 on molars, and 4 on premolars) were analyzed on each element surface: occlusal, axial, glazed, or unglazed. Raman depth mapping and high-resolution SEM were performed on the selected samples. RESULTS: LTD developed in 3Y-TZP monolithic restorations 6 months after intraoral placement and progressed with time. After two years, the tetragonal-to-monoclinic transformation was non-uniform, with the presence of localized clusters of transformed grains. In axial areas, the grain aspect was typical of the classical nucleation-growth process reported for LTD, which progresses from the surface to a depth of several tens of microns. However, in occlusal areas, tribological stress generated surface crushing and grain pull-out from the clusters, which induced an underestimation of the aging process when the evaluation was limited to monoclinic phase quantification. Glazing cannot be considered a protection against LTD. SIGNIFICANCE: If LTD occurs in dental prostheses in the same way as in orthopedic prostheses, its clinical impact is unknown and needs to be further studied.

The one-step no-prep approach for full-mouth rehabilitation of worn dentition using PICN CAD-CAM restorations: 2-yr results of a prospective clinical study.

OBJECTIVES: To prospectively evaluate the One-step No-prep treatment of full mouth-worn dentition, a minimally invasive and multidisciplinary approach using PICN CAD-CAM composite restorations without provisional phase. METHODS: Seven patients (n = 192 restorations) with severe tooth wear were included. Patient data were recorded, and an occlusal analysis and a tissue-guided wax-up were realized. After replacement of old fillings, no-prep Vita Enamic restorations (posterior restorations and palatal veneers) were bonded within 24 h. Direct composites were performed to mask the buccal joint on anterior teeth. Maxillo-facial physiotherapy was performed. Restorations were evaluated following World Dental Federation criteria. Treatment influence on Oral-Health-Impact-Profile-49 (OHIP-49) score was assessed. RESULTS: Tooth wear etiology was related to soft drink consumption and bruxism. Mean VDO increase was 5.09 ±â€¯0.85 mm on the incisal pin. The mean restoration thickness on molars was 0.55 ±â€¯0.21 mm, and the lowest was 0.11 mm. 2-year survival rate of restorations was 100 % and success rate was 93.5 %, with 11 minor chippings and one debonding. A significant improvement of the global OHIP-49 score was observed. CONCLUSIONS: In this clinical study on high risk patients, PICN restorations, applied in a minimally invasive way, showed high survival and success rates after two years, while minor chipping of very thin occlusal borders constituted the most frequent complication. Moreover, the patient acceptance was good according to OHIP-49 in this multidisciplinary approach. CLINICAL SIGNIFICANCE: The use of PICNs allows the development of no prep and simple treatment protocols of worn dentition. The absence of provisionals did not engender any problem, on the basis of the realization of an occlusal analysis, the support of a maxillo-facial physiotherapist, and the use of an easy-to-adjust restorative material.

Clinical behavior of second-generation zirconia monolithic posterior restorations: Two-year results of a prospective study with Ex vivo analyses including patients with clinical signs of bruxism.

OBJECTIVES: This study aimed to investigate (1) clinical outcomes of second-generation zirconia restorations, including patients with bruxism clinical signs, and (2) the material wear process. METHODS: A total of 95 posterior monolithic zirconia tooth-elements in 45 patients were evaluated, 85 on implants and 10 on natural teeth, and 20.3% of restorations being fixed partial dentures (FPDs). Occlusal contact point areas were determined and half of those areas were left unglazed and just polished. Restorations were clinically evaluated following criteria of the World Dental Federation and antagonistic teeth were examined at each evaluation time. Wear ex vivo analyses using SEM and 3D laser profilometry were performed at baseline and after 6 months, 1 year, and 2 years respectively, temporarily removing the prostheses. RESULTS: The Kaplan-Meier survival rate of restorations was 93.3% (100% for FPDs) and the success rate was 81.8%, with 4 abutment debondings, 3 tooth-supported crown debondings (provisional cement use), 1 restoration fracture, 1 minor chipping, 1 core fracture, 1 root fracture, and 2 implant losses. 80% of catastrophic failures occurred in patients with clinical signs of bruxism (61.7% of patients). Complications were also observed on antagonistic teeth (3 catastrophic failures). Clinical evaluation of the restorations showed good results from the aesthetic, functional, and biological perspective. Zirconia wear was inferior to 15 µm, while glaze wear was observed on all occlusal contact areas after 1 year. CONCLUSIONS: Monolithic zirconia FPDs are promising but the failure rate of single-unit restorations was not as high as expected in this sample including patients with bruxism clinical signs. CLINICAL SIGNIFICANCE: Within study limitations, FPDs showed excellent short-term results but further research is needed for single-unit restorations considering samples, which do not exclude bruxers. The weak link is the restoration support or the antagonist tooth, one hypothesis being that zirconia stiffness and lack of resilience do not promote occlusal stress damping.