Risk factors of tooth wear in permanent dentition: A scoping review.

BACKGROUND: Tooth wear (TW) prevalence is high and increasing and has important consequences on the patient's quality of life. Knowledge of risk factors is crucial to promote diagnosis, prevention strategies and timely interceptive treatment. Many studies have identified TW risk factors. OBJECTIVE: This scoping review aims to map and describe suspected available factors associated with TW in permanent dentition based on quantitative measurement. METHODS: The scoping review was conducted using the PRISMA extension of the Scoping Reviews checklist. The search was conducted in October 2022 from the Medline® (PubMed® interface) and Scopus® databases. Two independent reviewers selected and characterised the studies. RESULTS: 2702 articles were identified for assessment of titles and abstracts, and 273 articles were included in the review. The results show a need to standardise TW measurement indices and the study design. The included studies highlighted various factors, classified into nine domains: sociodemographic factors, medical history, drinking habits, eating habits, oral hygiene habits, dental factors, bruxism and temporomandibular disorders, behavioural factors, and stress. Results related to chemical TW (erosion) risk factors underline the importance of eating disorders, gastroesophageal reflux and lifestyle, particularly drinking and eating behaviours, which supports developing public health information campaigns and interventions. Besides chemical, this review identifies evidence of several mechanical TW risk factors, such as toothbrushing and bruxism; the influence of this last factor needs to be further explored. CONCLUSIONS: TW management and prevention require a multidisciplinary approach. Dentists are in the first line to detect associated diseases such as reflux or eating disorders. Consequently, practitioners' information and guideline diffusion should be promoted, and a TW risk factors checklist (the ToWeR checklist) is proposed to help diagnostic approaches.

An individualized approach for a one-abutment one-time protocol using fully guided implant surgery: a 4-year follow-up case series.

AIM: The objective of the present case series was to evaluate the 4-year outcomes of implants placed in the esthetic area using static computer-assisted implant surgery (s-CAIS) and restored with a one-abutment one-time (OAOT) protocol using custom-made zirconia abutments and cemented provisional crowns manufactured prior to surgery. Materials and methods: Ten consecutive implants were placed in the esthetic area. Based on a digital implant and prosthodontic planning, surgical guides were ordered and used for the preparation of definitive custom-made zirconia abutments and polymethylmethacrylate provisional crowns. Implants were placed using the s-CAIS guide, and prosthetic components were placed immediately. Implant outcomes were evaluated at the time of surgery, after 4 months, and after 4 years. RESULTS: All implants were successfully placed with s-CAIS and restored with final abutments and provisional crowns. No major prosthetic adverse events were observed. After 4 years, the implant survival rate was 100%, minor peri-implant bleeding on probing was reported, and very stable peri-implant bone levels were observed. The pink esthetic score showed that the prosthetic components were well integrated, and the peri-implant soft tissue was stable. CONCLUSIONS: Within the limitations of the present case series, these results suggest that emerging digital workflows allow the manufacture of final custom-made abutments and provisional crowns prior to surgery. This individualized OAOT procedure may reduce cement-related complications and improve esthetic outcomes by optimizing soft tissue healing with prosthetic components. However, such protocols have evolved toward fully digital workflows, and comparative clinical trials are needed.

Influence of High-Pressure Polymerization on Mechanical Properties of Denture Base Resins.

PURPOSE: The purpose of this study was to study the influence of high-pressure (HP) polymerization on the mechanical properties of denture base PMMA resins compared with conventional thermopolymerization and PMMA discs for digital dentures. MATERIALS AND METHODS: Three groups of blocks were prepared: Probase Hot (Ivoclar Vivadent, Lichtenstein) conventionally heat polymerized at 100°C, Probase Hot heat polymerized at 100°C under HP (200 MPa) and Ivobase CAD (Ivoclar Vivadent, Lichtenstein). Samples for mechanical/physical (n = 30) and samples for viscoelastic (n = 10) characterizations were cut from the blocks. Flexural strength (σf ), elastic modulus (Ef ), hardness, density (ρ), flexural deformation at maximal flexural stress, flexural load energy (Ur ) and viscoelastic properties (E', E'', Tanδ, Tg ) were analyzed using one-way ANOVA (α = 0.05), Scheffé multiple means comparisons (α = 0.05) and Weibull statistics (for σf ). SEM images of the fractured surfaces were obtained. RESULTS: Ef , E', E'' and density of HP polymerized Probase hot were significantly higher than conventional heat polymerized Probase Hot, whereas Tg was significantly lower and σf , Tanδ, hardness, flexural deformation at maximal flexural stress, Ur were not significantly different. The highest values for σf , flexural deformation at maximal flexural stress, Ur and Weibull modulus were obtained with Ivobase CAD. CONCLUSION: HP polymerization does not significantly increase the mechanical properties of denture base resins.

The One step-No prep technique: A straightforward and minimally invasive approach for full-mouth rehabilitation of worn dentition using polymer-infiltrated ceramic network (PICN) CAD-CAM prostheses.

OBJECTIVES: To introduce a novel approach for full-mouth rehabilitation of severely worn dentition using polymer-infiltrated ceramic network (PICN) computer-aided-design and manufacturing (CAD-CAM) restorations, without tooth tissue preparation and provisional phase. CLINICAL CONSIDERATIONS: Three patients with generalized tooth wear, suffering from dental pain, masticatory dysfunction, bruxism and neck and back pain, were selected and treated in collaboration with physiotherapists. Occlusal analyses were performed and full-mouth diagnostic wax-ups were designed on the basis of estimated tissue loss. Deficient direct restorations were replaced and low-thickness PICN (Vita Enamic) restorations (up to 0.2 mm) were CAD-CAM designed from wax-ups, milled, tried-in and then bonded within two consecutive days. To mask palatal veneers, either buccal direct composites or glass-ceramic veneers were later performed. An occlusal splint was realized. Clinical results were shown to be successful after a follow-up of 22, 18, and 13 months, respectively. The absence of provisional phase did not engender any inconveniences. Patient reported outcomes were very positive, showing a reduction in neck and back pain and a well-being increase. CONCLUSION: The proposed protocol is particularly minimally invasive and straightforward compared to classical techniques. PICNs exhibit several advantages compared to other materials. Preliminary results of this multidisciplinary approach are promising but deserve further clinical research. CLINICAL SIGNIFICANCE: The development of CAD-CAM technologies offers the possibility of improving treatment of severe worn dentition, reducing chairtime and need of tooth tissue preparation, and introducing a new class of composite materials (hybrid ceramics), which exhibit interesting properties for this indication. The influence of the proposed multidisciplinary approach, particularly the collaboration with physiotherapists, needs to be further explored with respect to treatment of associated symptoms, such as masticatory muscles hypertrophy and neck pain.

Orthodontic-assisted one step- no prep technique: A straightforward and minimally-invasive approach for localized tooth wear treatment using polymer-infiltrated ceramic network CAD-CAM prostheses.

OBJECTIVES: To introduce a minimally invasive and simple ortho-pros approach for localized tooth wear treatment. CLINICAL CONSIDERATIONS: Four patients with localized anterior and/or posterior tooth wear were treated. Occlusal analyses were performed, and localized wax-up or digital setup were designed based on estimated tissue loss. No-prep anterior and posterior partial-coverage polymer-infiltrated ceramic network (PICN, Vita Enamic) restorations (eg, palatal and occlusal veneers) were computer-aided designed and manufactured (CAD-CAM), tried in, and bonded in supraocclusion, creating a posterior open bite. Then, brief partial (three patients) or global (one patient, for anterior teeth alignment request) orthodontic treatment was performed to extrude the posterior teeth and re-establish posterior occlusal contacts. The orthodontic treatment duration was ~2 months for extrusion. Direct composites were performed to mask the labial finish line of palatal veneers. Clinical results were successful after a follow-up of 15, 21, 23, and 47 months, with 100% success rate of PICN anterior restorations and some minor chippings of borders of thin (0.2 mm) posterior occlusal veneers. Patient-reported outcomes were positive. CONCLUSION: Orthodontic-assisted one step-no prep technique is an advantageous and straightforward evolution of the Dahl concept. PICNs exhibit several advantages in this interdisciplinary approach. CLINICAL SIGNIFICANCE: New hybrid-ceramic CAD-CAM materials and a collaborative interdisciplinary approach support the evolution of the Dahl concept for conservative treatment of worn dentitions. The orthodontic-assisted one step-no prep technique is predictable, efficient, and well tolerated by patients and conserves tooth structure.

Intraoral wear of PICN CAD-CAM composite restorations used in severe tooth wear treatment: 5-year results of a prospective clinical study using 3D profilometry.

OBJECTIVES: To evaluate, in a prospective clinical study over 5 years with ex vivo 3D profilometry analyses, the intraoral wear of Polymer-Infiltrated Ceramic Network (PICN) CAD-CAM composite restorations used in severe tooth wear treatment with the One-Step No-Prep technique. METHODS: 192 PICN (Vita Enamic) restorations on molars and premolars were included in a prospective clinical study involving patients treated according to the One-step No-prep protocol (n = 7). All patients showed clinical signs of bruxism. Replicas of restorations on molars and premolars were realized at each evaluation time (baseline and then every year up to 5 years) and scanned to perform 3D profilometry. Baseline and recall scans were superimposed with Geomagic Control software. The mean material wear was calculated for the full occlusal area (FOA) and for the occlusal contact area (OCA), respectively. Clinical evaluation of restorations was performed at recall. RESULTS: At 5 years, the estimated mean material wear for FOA was inferior to the accuracy threshold of the profilometry measurement chain. For OCA, the estimated mean wear of the material was - 27.97 µm. This material wear was shown to be significantly influenced by time (p < 0.0001) and patient (p = 0.026), while the type of tooth (molar or premolar) had no influence. At 5 years, the survival and the success rates of restorations were 99.48% and 90.62%, respectively. SIGNIFICANCE: The PICN material exhibits a low wear process in the treatment of severe tooth wear despite the presence of clinical signs of bruxism, and it constitutes a suitable material for the One-step No-prep technique.

Interblock and intrablock homogeneity of CAD-CAM composites mechanical properties.

The purpose of this study was to characterize the homogeneity of the mechanical properties of commercial CAD-CAM composites between different blocks of the same material (interblock homogeneity) and within each block between the internal and external parts (intrablock homogeneity). Tetric CAD (TET); Katana Avencia (KAT); Cerasmart 270 (CER); Grandio (GRN) and Vita Enamic (ENA) were tested for flexural strength (σf), flexural modulus (Ef), flexural load energy (Ur) and hardness (HV). Results showed significant differences in interblock homogeneity of σf, Ef and Ur for TET, KAT, CER and ENA. In addition, significant differences in interblock homogeneity of HV for TET, CER and GRN were found. Moreover, significant differences in intrablock homogeneity of σf, Ef and Ur were found for KAT, CER, GRN and ENA, as well as for HV of all the tested materials except CER. Weibull modulus was highest for GRN, followed by ENA, KAT, TET then CER.

Bruxism as a new risk factor of musculo-skeletal disorders?

OBJECTIVES: Musculoskeletal disorders (MSDs), particularly neck and low back pain, constitute a major public health issue worldwide with a heavy morbidity and economic impact. However, the relationships between the stomatognathic system and MSDs are subjected to debate, data sorely lacking. The study objective was to investigate the association between bruxism (BR) and MSDs. Secondary objective includes the study of the association between tooth wear (TW) and MSDs. METHODS: This is a cross-sectional study on 425 participants frequenting a university dental clinic. The presence of MSDs was evaluated with the standardized Nordic questionnaire. The sleep and awake BR assessments were based on clinical examination and self-report. TW was measured with the BEWE index. Socio-demographic factors, medical history, life habits and stress were analyzed as potential confounding variables. RESULTS: 91% of patients reported at least one MSD during the preceding 12 months and 75.5% were diagnosed as bruxers. In multivariate analyses, BR was associated with a 5-fold increased risk of prevalent MSD (OR=5.88 (2.7-12.5), p<0.0001). Regarding TW, for a one-point increase in anterior BEWE score, the risk to present an MSD was increased by 53% (OR=1.53 (1.12-2.08), p = 0.0076). Moreover, BR was independently associated with neck, shoulder, upper back, low back, hip & thigh and knee MSDs. Anterior TW was independently associated with neck, low back and hip & thigh MSDs, and global TW with knee MSDs. CONCLUSIONS: BR and TW were shown to be associated with MSDs. The cause-and-effect relationships between those factors needs to be analyzed to optimize prevention and therapeutic care. CLINICAL SIGNIFICANCE: Results suggest that the body is a whole, a balanced muscular system, where every part constitutes a link of the chain. MSDs management and prevention may require a multidisciplinary team approach and future perspectives include defining the dentist's role in this context, particularly with respect to BR diagnostic and treatment.

Bonding properties of third-generation zirconia CAD-CAM blocks for monolithic restorations to composite and resin-modified glass-ionomer cements.

PURPOSE: To compare the interfacial fracture toughness (IFT) of two MDP-based composite cements and a resin-modified glass-ionomer cement (RMGIC) with third-generation zirconia CAD-CAM restorations using two different airborne-particle abrasion (AB) pressures. METHODS: Blocks were cut into prisms (n=60), split and sintered to the desired equilateral half prisms. Half-prisms were divided into two groups for AB at 0.5 or 2.5 bar with 50 µm Al2O3 particles. Each group was then further divided into 3 subgroups, and half-prisms were bonded to their counterparts with Panavia V5 (V5), Panavia Self Adhesive Cement Plus (SA), or RMGIC Fuji Plus (n=10/group). The IFT was determined using the Notchless Triangular Prism test in a water bath at 36°C after thermocycling (10,000 cycles). Surface roughness and SEM analyses were performed for representative zirconia samples after AB, and composite cements were tested for flexural strength and wettability. RESULTS: SA (2.5 bar) showed a significantly higher IFT. The 3 other groups with SA and V5 showed no significant difference in their IFT values regardless of the AB pressure (1-way ANOVA). Weibull analysis of SA was higher than V5. All RMGIC samples debonded while thermocycling, and were, therefore, not included in the statistical analysis. Surface roughness increased with increasing AB pressure, and both cements showed similar flexural strength values and good wettability. CONCLUSION: Contrary to RMGIC, composite cements show high performance with zirconia after AB. Increasing AB pressure enhances the micromechanical retention of composite cement. Future perspectives should include study of the effect of AB pressure on zirconia surface properties.

Fit of single tooth zirconia copings: comparison between various manufacturing processes.

STATEMENT OF PROBLEM: Various CAD/CAM processes are commercially available to manufacture zirconia copings. Comparative data on their performance in terms of fit are needed. PURPOSE: The purpose of this in vitro study was to compare the internal and marginal fit of single tooth zirconia copings manufactured with a CAD/CAM process (Procera; Nobel Biocare) and a mechanized manufacturing process (Ceramill; Amann Girrbach). MATERIAL AND METHODS: Abutments (n=20) prepared in vivo for ceramic crowns served as a template for manufacturing both Procera and Ceramill zirconia copings. Copings were manufactured and cemented (Clearfil Esthetic Cement; Kuraray) on epoxy replicas of stone cast abutments. Specimens were sectioned. Nine measurements were performed for each coping. Over- and under-extended margins were evaluated. Comparisons between the 2 processes were performed with a generalized linear mixed model (α=.05). RESULTS: Internal gap values between Procera and Ceramill groups were not significantly different (P=.13). The mean marginal gap (SD) for Procera copings (51(50) µm) was significantly smaller than for Ceramill (81(66) µm) (P<.005). The percentages of over- and under-extended margins were 43% and 57% for Procera respectively, and 71% and 29% for Ceramill. CONCLUSIONS: Within the limitations of this in vitro study, the marginal fit of Procera copings was significantly better than that of Ceramill copings. Furthermore, Procera copings showed a smaller percentage of over-extended margins than did Ceramill copings.

One-tooth one-time (1T1T), immediate loading of posterior single implants with the final crown: 2-year results of a case series.

Purpose: The purpose of this study was to evaluate the 2-year outcomes of the one-tooth onetime complete digital workflow, allowing the immediate loading of a single implant in the posterior region with a final CAD/CAM crown made of a polymer-infiltrated ceramic network. Materials and methods: A series of 10 implants were placed, and an intraoral scan was taken after surgery. A final screw-retained polymer-infiltrated ceramic network crown was manufactured chairside and placed the same day in full occlusion. Marginal peri-implant bone changes and soft tissue health were evaluated, and restoration performance was assessed using FDI World Dental Federation criteria and pink and white aesthetic scores. Patient-reported outcome measures and data on the time required to perform the procedures were collected. Results: After 2 years, the implant survival rate was 100%. The debonding of one crown from its titanium base led to prosthodontic survival rate of 90% and the remaining crowns were all considered successful. The mean marginal peri-implant bone changes yielded 0.87 mm (standard deviation 0.96 mm) and 0.55 mm (standard deviation 0.53 mm) after 1 and 2 years, respectively. Mild or no inflammation of peri-implant soft tissue was observed in most implants. The total treatment time was 175 minutes and patient-reported outcome measures displayed high patient satisfaction. Conclusions: This study constitutes the first report examining immediate loading of a single implant in the posterior region with a final crown in occlusion. In this case series, the 2-year outcomes of the one-tooth one-time protocol seem rather promising and fulfilled patient expectations. However, these preliminary results need to be confirmed by randomised controlled trials, and patient selection is likely to be a key factor in the success of this procedure.

Silane influence on bonding to CAD-CAM composites: An interfacial fracture toughness study.

OBJECTIVES: To evaluate silane influence on the interfacial fracture toughness (IFT) of composite cement, with the two sub-classes of CAD-CAM composites, polymer-infiltrated ceramic networks (PICN) and dispersed fillers (DF), after hydrofluoric acid etching (HF) or airborne-particle abrasion (AB). A secondary objective was to correlate results with developed interfacial area ratio (Sdr) and surface wettability. METHODS: Experimental PICN and DF blocks were cut into equilateral half-prisms, which were treated with HF or AB, then treated with an experimental silane or not and bonded to their counterparts with an experimental light-cure resin cement. After thermocycling, samples (n=30 per group) were tested for IFT using the notchless triangular prism test in a water bath at 36°C. Moreover, profilometry and contact angle measurement were performed on rectangular samples of each group. Finally, bonding interface was analysed by SEM. RESULTS: PICN-HF treated with silane showed the highest IFT significantly. Three-way ANOVA revealed the influence of silane, material class and surface pre-treatment (HF or AB) on IFT (p<0.05). When silane was used, IFT was correlated with Sdr, while surface wettability was increased. Silane application significantly increased IFT for PICN but not for DF, while PICN performed better with HF and DF with AB. SIGNIFICANCE: Silane increases IFT of composite cement with PICNs, but not with DF materials. Results suggest that silane increases the micromechanical bond by promoting resin cement spreading and penetration in surface roughness. This roughness is significantly higher for pre-treated PICNs than for DF due to their specific honeycomb microstructure when etched, which explains their better bonding properties.

Polymer-Infiltrated-Ceramic-Network, CAD/CAM Restorations for Oral Rehabilitation of Pediatric Patients with X-Linked Ectodermal Dysplasia.

Functional and esthetic oral rehabilitation of young patients affected by ectodermal dysplasia is traditionally performed with direct composite restorations, which encounter various limitations. However, recent advances in computer-aided design/computer-assisted manufacturing (CAD/CAM) composites have led to the introduction of high-performance materials. In the present case report, a 9-year-old patient was treated with 20 CAD/CAM partial and peripheral restorations in polymer-infiltrated-ceramic-network material to restore deciduous and permanent teeth. The restorations were minimally invasive, since they did not require any tooth tissue preparation. Appropriate occlusal relationships with increased vertical dimension of occlusion were obtained. Tooth anatomy and esthetics were significantly improved, and chairtime was reduced.

Biocompatibility of polymer-infiltrated-ceramic-network (PICN) materials with Human Gingival Keratinocytes (HGKs).

OBJECTIVE: Biocompatibility of polymer-infiltrated-ceramic-network (PICN) materials, a new class of CAD-CAM composites, is poorly explored in the literature, in particular, no data are available regarding Human Gingival Keratinocytes (HGK). The first objective of this study was to evaluate the in vitro biocompatibility of PICNs with HGKs in comparison with other materials typically used for implant prostheses. The second objective was to correlate results with PICN monomer release and indirect cytotoxicity. METHODS: HGK attachment, proliferation and spreading on PICN, grade V titanium (Ti), yttrium zirconia (Zi), lithium disilicate glass-ceramic (eM) and polytetrafluoroethylene (negative control) discs were evaluated using a specific insert-based culture system. For PICN and eM samples, monomer release in the culture medium was quantified by high performance liquid chromatography and indirect cytotoxicity tests were performed. RESULTS: Ti and Zi exhibited the best results regarding HGK viability, number and coverage. eM showed inferior results while PICN showed statistically similar results to eM but also to Ti regarding cell number and to Ti and Zi regarding cell viability. No monomer release from PICN discs was found, nor indirect cytotoxicity, as for eM. SIGNIFICANCE: The results confirmed the excellent behavior of Ti and Zi with gingival cells. Even if polymer based, PICN materials exhibited intermediate results between Ti-Zi and eM. These promising results could notably be explained by PICN high temperature-high pressure (HT-HP) innovative polymerization mode, as confirmed by the absence of monomer release and indirect cytotoxicity.

No post-no core approach to restore severely damaged posterior teeth: An up to 10-year retrospective study of documented endocrown cases.

OBJECTIVES: The objectives of the present study were to (1) retrospectively evaluate documented cases of ceramic and composite endocrowns performed using immediate dentin sealing (IDS); (2) correlate failures with clinical parameters such as tooth preparation characteristics and occlusal parameters. METHODS: 99 documented cases of endocrowns were evaluated after a mean observation period of 44.7±34.6months. A classification of restorations was established in function of the level of damage of residual tooth tissues after preparation, from 1 to 3. Evaluation was performed according to FDI criteria and endodontic outcomes were analyzed. Occlusal risk factors were examined and fractographic analysis was performed in case of fracture. RESULTS: 48.4% of patients were shown to present occlusal risk factors. 75.8% of restorations were Class 3 endocrowns. 56.6% were performed on molars, 41.4% on premolars and 2.0% on canines. 84.8% were performed in lithium-disilicate glass-ceramic and 12.1% in Polymer-Infiltrated Ceramic Network (PICN) material. The survival and success rates of endocrowns were 99.0% and 89.9% respectively, while the 10-year Kaplan-Meier estimated survival and success rates were 98.8% and 54.9% respectively. Ten failures were detected: periodontal disease (n=3), endocrown debonding (n=2), minor chipping (n=2), caries recurrence (n=2) and major fractures (n=1). Due to the reduced amount of failures, no statistical correlation could be established with clinical parameters. CONCLUSIONS: Endocrowns were shown to constitute a reliable approach to restore severely damaged molars and premolars, even in the presence of extensive coronal tissue loss or occlusal risk factors, such as bruxism or unfavorable occlusal relationships. CLINICAL SIGNIFICANCE: Practitioners should consider the endocrown instead of the post and core approach to restore severely damaged non-vital posterior teeth. This minimally invasive solution reduces the risk of catastrophic failures and is easily performed. The use of IDS procedure and lithium-disilicate glass-ceramic as prosthesis material gave very good results.

Biocompatibility of polymer-infiltrated-ceramic-network (PICN) materials with Human Gingival Fibroblasts (HGFs).

OBJECTIVES: Polymer-infiltrated-ceramic-network (PICN) materials constitute an innovative class of CAD-CAM materials offering promising perspectives in prosthodontics, but no data are available in the literature regarding their biological properties. The objective of the present study was to evaluate the in vitro biocompatibility of PICNs with human gingival fibroblasts (HGFs) in comparison with materials typically used for implant prostheses and abutments. METHODS: HGF attachment, proliferation and spreading on discs made of PICN, grade V titanium (Ti), yttrium zirconia (Zi), lithium disilicate glass-ceramic (eM) and polytetrafluoroethylene (negative control), were evaluated using a specific insert-based culture system (IBS-R). Sample surface properties were characterized by XPS, contact angle measurement, profilometry and SEM. RESULTS: Ti and Zi gave the best results regarding HGF viability, morphology, number and coverage increase with time in comparison with the negative control, while PICN and eM gave intermediate results, cell spreading being comparable for PICN, Ti, Zi and eM. Despite the presence of polymers and their related hydrophobicity, PICN exhibited comparable results to glass-ceramic materials, which could be explained by the mode of polymerization of the monomers. SIGNIFICANCE: The results of the present study confirm that the currently employed materials, i.e. Ti and Zi, can be considered to be the gold standard of materials in terms of HGF behavior, while PICN gave intermediate results comparable to eM. The impact of the present in vitro results needs to be further investigated clinically, particularly in the view of the utilization of PICNs for prostheses on bone-level implants.

A new method using insert-based systems (IBS) to improve cell behavior study on flexible and rigid biomaterials.

In vitro studies about biomaterials biological properties are essential screening tests. Yet cell cultures encounter difficulties related to cell retention on material surface or to the observation of both faces of permeable materials. The objective of the present study was to develop a reliable in vitro method to study cell behavior on rigid and flexible/permeable biomaterials elaborating two specific insert-based systems (IBS-R and IBS-F respectively). IBS-R was designed as a specific cylindrical polytetrafluoroethylene (PTFE) system to evaluate attachment, proliferation and morphology of human gingival fibroblasts (HGFs) on grade V titanium and lithium disilicate glass-ceramic discs characteristics of dental prostheses. The number of cells, their covering on discs and their morphology were determined from MTS assays and microscopic fluorescent images after 24, 48 and 72 h. IBS-F was developed as a two components system to study HGFs behavior on guided bone regeneration polyester membranes. The viability and the membrane barrier effect were evaluated by metabolic MTS assays and by scanning electron microscopy. IBS-R and IBS-F were shown to promote (1) easy and rapid handling; (2) cell retention on biomaterial surface; (3) accurate evaluation of the cellular proliferation, spreading and viability; (4) use of non-toxic material. Moreover IBS-F allowed the study of the cell migration through degradable membranes, with an access to both faces of the biomaterial and to the bottom of culture wells for medium changing.

Aging of monolithic zirconia dental prostheses: Protocol for a 5-year prospective clinical study using ex vivo analyses.

BACKGROUND: Recent introduction of computer-aided design/computer-aided manufacturing (CAD/CAM) monolithic zirconia dental prostheses raises the issue of material low thermal degradation (LTD), a well-known problem with zirconia hip prostheses. This phenomenon could be accentuated by masticatory mechanical stress. Until now zirconia LTD process has only been studied in vitro. This work introduces an original protocol to evaluate LTD process of monolithic zirconia prostheses in the oral environment and to study their general clinical behavior, notably in terms of wear. METHODS/DESIGN: 101 posterior monolithic zirconia tooth elements (molars and premolars) are included in a 5-year prospective clinical trial. On each element, several areas between 1 and 2 mm2 (6 on molars, 4 on premolars) are determined on restoration surface: areas submitted or non-submitted to mastication mechanical stress, glazed or non-glazed. Before prosthesis placement, ex vivo analyses regarding LTD and wear are performed using Raman spectroscopy, SEM imagery and 3D laser profilometry. After placement, restorations are clinically evaluated following criteria of the World Dental Federation (FDI), complemented by the analysis of fracture clinical risk factors. Two independent examiners perform the evaluations. Clinical evaluation and ex vivo analyses are carried out after 6 months and then each year for up to 5 years. DISCUSSION: For clinicians and patients, the results of this trial will justify the use of monolithic zirconia restorations in dental practice. For researchers, the originality of a clinical study including ex vivo analyses of material aging will provide important data regarding zirconia properties.Trial registration: ClinicalTrials.gov Identifier: NCT02150226.

Influence of thermal expansion mismatch on residual stress profile in veneering ceramic layered on zirconia: Measurement by hole-drilling.

OBJECTIVES: Mismatch in thermal expansion coefficient between core and veneering ceramic (Δα=αcore-αveneer, ppm/°C) is reported as a crucial parameter influencing veneer fractures with Yttria-tetragonal-zirconia-polycrystal (Y-TZP) prostheses, which still constitutes a misunderstood problem. However, the common positive Δα concept remains empirical. The objective of this study is to investigate the Δα dependence of residual stress profiles in veneering ceramic layered on Y-TZP frameworks. METHODS: The stress profile was measured with the hole-drilling method in bilayered disc samples of 20mm diameter with a 0.7mm thick Y-TZP framework and a 1.5mm thick veneer layer. 3 commercial and 4 experimental veneering ceramics (n=3 per group) were used to obtain different Δα varying from -1.3ppm/°C to +3.2ppm/°C, which were determined by dilatometric analyses. RESULTS: Veneer fractures were observed in samples with Δα≥+2.3 or ≤-0.3ppm/°C. Residual stress profiles measured in other groups showed compressive stresses in the surface, these stresses decreasing with depth and then becoming more compressive again near the interface. Small Δα variations were shown to induce significant changes in residual stress profiles. Compressive stress near the framework was found to decrease inversely to Δα. SIGNIFICANCE: Veneer CTE close to Y-TZP (+0.2ppm/°C Δα) gived the most favorable stress profile. Yet, near the framework, Δα-induced residual stress varied inversely to predictions. This could be explained by the hypothesis of structural changes occurrence within the Y-TZP surface. Consequently, the optimum Δα value cannot be determined before understanding Y-TZP's particular behavior when veneered.

Influence of firing time and framework thickness on veneered Y-TZP discs curvature.

OBJECTIVES: The objective of the present work was to study the curvature of very thinly, veneered Y-TZP discs of different framework thicknesses submitted to different firing times. METHODS: Fifteen 20-mm-wide Y-TZP discs were produced in three different thicknesses: 0.75, 1, 1.5mm. One disc from each group was left unveneered while the others were layered with a 0.1mm veneering ceramic layer. All discs underwent five firing cycles for a total cumulative firing time of 30 min, 1, 2, 5 and 10h at 900°C. The curvature profile was measured using a profilometer after the veneering process and after each firing cycle respectively. A fitted curve was then used to estimate the, curvature radius. The coefficient of thermal expansion (CTE) measurements were taken on veneering, ceramic and Y-TZP beam samples that underwent the same firing schedule. Those data were used to calculate the curvature generated by CTE variations over firing time. RESULTS: All bilayered samples exhibited a curvature that increased over firing time inversely to framework thickness. However non-veneered samples did not exhibit any curvature modification. SIGNIFICANCE: The results of the present study reveal that even a very thin veneer layer (0.1mm) can induce a significant curvature of Y-TZP discs. The dilatometric results showed that Tg and CTE, variations are not sufficient to explain this curvature. A chemical-induced zirconia volume, augmentation located at the framework sub-surface near the interface could explain the sample, curvature and its increase with firing time.