Intraoral low-temperature degradation of monolithic zirconia dental prostheses: 5-year results of a prospective clinical study with ex vivo monitoring.

OBJECTIVES: To investigate the 5-year intraoral evolution and kinetics of low-temperature degradation (LTD) of second-generation monolithic prostheses made of 3% molar yttrium-doped tetragonal zirconia polycrystal (3Y-TZP) and the influence of masticatory mechanical stresses and glaze layer on this evolution. METHODS: A total of 101 posterior tooth elements were included in this prospective clinical study, which comprised ex vivo LTD monitoring (at baseline, 6 months, 1 year, 2 years, 3 years, and 5 years) using Raman spectroscopy (n = 2640 monoclinic phase measurement points per evaluation time) and scanning electron microscopy (SEM). Four types of areas (1-2 mm2 surface, six on molars, and four on premolars) were analysed on each element surface: occlusal, axial, glazed, or unglazed. Raman mapping, high-resolution SEM, and focused ion beam-SEM were performed on selected samples. RESULTS: The dental prostheses developed a tetragonal-to-monoclinic transformation at the extreme surface of the material after six months in a buccal environment, and this process increased significantly over time. Over the five years of monitoring, the transformation developed nonuniformly with the presence of localised clusters of monoclinic grains. Tribological stresses generate grain pull-out from these clusters, which may raise questions regarding the release of 3Y-TZP nanoparticles into the body. The prosthesis fracture rate was 4.5% after 5 years. SIGNIFICANCE: LTD developed in vivo on the surfaces of 3Y-TZP dental prostheses and progressed slowly but significantly over time, up to 5 years investigation. However, the effects of aging on the failure rate recorded and of zirconia nanoparticles released into the body require further investigation.

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.

[Failure of zirconia-based prostheses on natural teeth and implants: focus on risk factors]. / Echecs des prothèses dentaires et implantaires en zircone : le point sur les facteurs de risqué.

Cohesive fracture of the veneering ceramic (chipping) is the first cause of failure of zirconia-based prostheses on natural teeth and implants. Besides risk factors related to the material (thermal stresses generated during the manufacturing process, framework inappropriate design), there are some clinical risk factors, which can influence the restoration prognosis. Indeed, unfavorable occlusal relationships and/or the presence of parafunctions such as bruxism and clenching, which are frequent pathologies, engender significant overloading. A retrospective study was performed at the University Hospital Center (CHU) of Liege on 147 dental and implants prostheses, placed between May 2003 and January 2012. This study highlighted a significant correlation between chipping and the absence of an occlusal nightguard (p = 0.0048), the presence of a ceramic restoration as an antagonist (p = 0.013), the presence of occlusal parafunctions (p = 0.018), and the presence of implants as support of the restorations (p = 0.026). These results underline the importance of external stress and occlusal risk factors diagnosis, as the need to perform an occlusal nightguard to patients with parafunctions.

Antibiotic prescribing in dental practice in Belgium.

AIM: To assess the types and frequency of antibiotic prescriptions by Belgian dentists, the indications for antibiotic prescription, and dentists' knowledge about recommended practice in antibiotic use. METHODOLOGY: In this cross-sectional survey, dental practitioners were asked to record information about all antibiotics prescribed to their patients during a 2-week period. The dental practitioners were also asked to complete a self-administered questionnaire regarding demographic data, prescribing practices, and knowledge about antibiotic use. A random sample of 268 Belgian dentists participated in the survey. RESULTS: During the 2-week period, 24 421 patient encounters were recorded; 1033 patients were prescribed an antibiotic (4.2%). The median number of prescriptions per dentist for the 2 weeks was 3. Broad spectrum antibiotics were most commonly prescribed: 82% of all prescriptions were for amoxycillin, amoxycillin-clavulanic acid and clindamycin. Antibiotics were often prescribed in the absence of fever (92.2%) and without any local treatment (54.2%). The most frequent diagnosis for which antibiotics were prescribed was periapical abscess (51.9%). Antibiotics were prescribed to 63.3% of patients with periapical abscess and 4.3% of patients with pulpitis. Patterns of prescriptions were confirmed by the data from the self-reported practice. CONCLUSIONS: Discrepancies between observed and recommended practice support the need for educational initiatives to promote rational use of antibiotics in dentistry in Belgium.

[Improvement of oral rehabilitation prosthetic techniques thanks to orthodontics]. / Optimalisation des techniques prothétiques de réhabilitation orale grace à l'orthodontie: analyse d'un cas clinique.

This clinical case underlines the importance of a multidisciplinary approach, prosthetic and orthodontic, for the achievement of an oral rehabilitation treatment plan. Preliminary orthodontic treatment has significantly improved, the position of some natural teeth, which can serve or not as a prosthetic abutment. This has produced a direct prosthetic benefit by limiting tissue reduction for preparation and by giving a better biomechanical and functional context to the restoration.Thus, after an orthodontic treatment step, lasting a year and a half, using both removable appliance and fixed appliance, prosthetic rehabilitation was possible. This included a fixed prosthesis and a removable prosthesis that gave a very satisfying an esthetic result and good masticatory function.

[Impression technics in implantology]. / Les techniques d'empreinte en implantologie.

The implant-borne prostheses have become an integral part of the oral rehabilitation procedures. The aim of this article is to describe the most current impression techniques for oral implant prosthetics used at the University of Liège, Belgium. Impression protocols adapted to various prosthetic procedures are described step-by-step through several clinical cases. Emphasis is put on the means necessary for achieving a precise adaptation and a passive fit of the final prosthetic suprastructure.

In vitro stimulation of human gingival epithelial cell attachment to dentin by surface conditioning.

BACKGROUND: Chemical root conditioning is widely used to improve the outcome of regenerative periodontal therapies by favoring the attachment of the regenerated periodontal structures. Although the effect of root conditioning on periodontal mesenchymal cells is well documented, very little is known about its potential effect on the re-formation of the junctional epithelium, a crucial event for the protection of the wound. The goal of the present study was to test in vitro the consequences of dentin conditioning with citric acid or minocycline on the attachment kinetics and morphology of human gingival keratinocytes (HGK). METHODS: The attachment kinetics of HGK to samples of powdered human dentin (particle size 44 to 76 microm) were examined by use of 3H-labeled cells. The morphology of attached epithelial cells was then determined by scanning electron microscopy (SEM). RESULTS: When the initial adhesion kinetics of cells on untreated dentin were tested, the percentage of attached HGK proved to be dependent on the number of plated cells and the time of incubation (from 0 to 12 hours). Conditioning the dentin by 3% citric acid or by minocycline-HCl (at 0.01, 0.1, or 2.5%) significantly increased (P <0.005) keratinocyte attachment beyond 6 hours, without notable differences between the 2 substances at any concentration. The attachment kinetics of HGK preincubated for 24 hours by 10 microg/ml minocyline-HCl on untreated dentin was found to be similar to that observed for non-preincubated cells. These results are in agreement with the SEM observations: indeed, the surface conditioning of dentin significantly modified the morphology of attached HGK, whereas the preincubation of these cells with minocyline-HCl did not. CONCLUSIONS: These results suggest that minocycline-HCl does not exert a direct effect on human gingival epithelial cells. In contrast, conditioning the dentin by citric acid or by minocycline stimulates the attachment of HGK, which could lead to a rapid periodontal healing by favoring the re-formation of a junctional epithelium.

The influence of cortical perforations and of space filling with peripheral blood on the kinetics of guided bone generation. A comparative histometric study in the rat.

The aim of the present study was to evaluate the influence of cortical perforations and of peripheral blood addition in guided bone generation beyond the skeletal envelope in rats. A total of 30 isogenic adult rats were divided into 3 equal groups. In each rat, two hollow parallelipipedic titanium chambers were placed bilaterally on the calvaria after a periosteal skin flap was raised. While on the right sides (controls) the osseous surface was left intact and the chambers were empty, the cortical bone under the left-side chambers (test sites) was perforated with nine 0.8 mm-diameter holes (group I), or left intact but with the chambers filled with a clot of peripheral blood (group II). In group III, both procedures were combined in the test sites. The healing was assessed at 4, 8 and 16 weeks after surgery by histologic and computer-assisted histometric analysis. The results demonstrated a substantial augmentation of on average 141% (SD 18) of the skull's thickness after 16 weeks in the controls, indicating that a predictable bone formation can be achieved beneath completely occlusive barriers over a non-injured cortical layer. In all test groups, a significantly larger bone augmentation was observed after 16 weeks compared to the control sites 172.8% (SD 41.7) in group I (P < 0.05), 172.0% (SD 18.4) in group II (P < 0.05) and 221.5% (SD 42.3) in group III (P < 0.001), demonstrating that stimulating blood supply and bone forming cells access by cortical perforations and/or blood clot addition enhances de novo bone formation in this experimental model.

In vitro modulation of human gingival epithelial cell attachment and migration by minocycline-HCL.

Although the influence of tetracyclines on periodontal connective tissue cells has been the topic of many in vitro and in vivo studies, data regarding their effects on gingival epithelial cells are scarce. The present in vitro study was designed to examine the influence of minocycline, a semi-synthetic analog of tetracycline, on human gingival keratinocyte (HGK) attachment and migration. Attachment tests were performed with HGK prelabeled by tritiated amino-acids. Increasing concentrations of minocycline (10, 50, 100 micrograms/ml) in the medium produced no significant modification of cell adhesion kinetics compared to control conditions, except for 100 micrograms/ml which statistically significantly (p < 0.05) reduced the number of attached cells beyond 6 h. A 24-h cell preincubation in 10 micrograms/ml of minocycline did not alter the kinetics of HGK attachment. Scanning electron microscopic observations of attached HGK showed that the presence of 10 micrograms/ml of minocycline in the "attachment medium" induced the production of multiple filopodial extensions. Migration tests in Boyden chambers for 40 h demonstrated that HGK preincubation for 24 h in a 10 micrograms/ml minocycline-HCl solution increased significantly (p < 0.005) cell migration towards a gradient of fetal calf serum. The presence of 10 micrograms/ml of minocycline in contact with the keratinocytes in the upper compartment of the migration chambers also produced a significant (p < 0.005) result. In contrast, the presence of minocycline in the lower compartments did not produce any chemoattractive effect. Within the limits of their significance, these results suggest that, at concentrations not beyond 50 micrograms/ml, minocycline could fasten the periodontal wound coverage by epithelial cells and allow the normal reformation of a junctional epithelium.