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Objectives: To evaluate the effects of surface treatment, specimen thickness, and aging on the biaxial flexural strength (BFS) of two types of yttria-stabilized, tetragonal zirconia polycrystal (Y-TZP) ceramics.

Methods and Materials: Disc-shaped specimens, 0.4 and 1.3 mm thick, made from hot isostatic pressed (Denzir) and non–hot isostatic pressed (ZirPlus) Y-TZP, were sandblasted, heat treated, and autoclaved. The surface topography was assessed in accordance with European Standard 623-624:2004 and the BFS tests in accordance with International Organization for Standardization Standard 6872:2008. For statistical analyses, one-way Shapiro-Wilk test, analysis of variance (post hoc: least significant differences), Mann-Whitney U-test, and Pearson correlation tests (p<0.05) were used.

Results: As delivered, the BFS of the 0.4-mm ZirPlus was >1.3-mm ZirPlus (p<0.01), and the BFS of the 0.4-mm Denzir was >1.3-mm Denzir (p<0.001). Sandblasting with 0.2 MPa reduced the BFS of the ZirPlus and Denzir discs (p<0.01), whereas sandblasting with 0.6 MPa increased the BFS of the 0.4-mm Denzir (p<0.001) and reduced the BFS of the 0.4-mm ZirPlus (p<0.05). Heat treatment significantly reduced the BFS of all the groups except for the 0.6 MPa sandblasted 0.4-mm ZirPlus. Autoclaving reduced the BFS of the as-delivered ZirPlus and Denzir specimens (p<0.001), whereas autoclaving the 0.6 MPa sandblasted and heat-treated specimens had no effect (p>0.05) on the BFS. The 0.6 MPa sandblasted, heat-treated, and autoclaved 0.4-mm Denzir exhibited higher BFS than the 0.6 MPa sandblasted, heat-treated, and autoclaved 0.4-mm ZirPlus (p<0.05).

Conclusions: Thickness and surface treatment of Y-TZP–based ceramics should be considered since those factors could influence the BFS of the material.

Objectives: To evaluate the effect of specimen thickness, pretreatment and hydrothermal aging on the biaxial flexural strength (BFS) of lithium di-silicate glass (e.max Cad) and magnesia-stabilized zirconia (ZirMagnum) ceramic discs. Methods: The e.max Cad discs was studied: i) crystallized, ii) crystallized and glazed and iii) crystallized, glazed and unglazed side etched with hydrofluoric acid. The ZirMagnum discs were studied: i) as delivered, ii) after sandblasting and iii) after heat treatment similar to veneering. Hydrothermal aging was simulated by autoclave treatment. Results: The BFS of all the ZirMagnum specimens was superior (p < 0.001) to all the e.max Cad specimens. Glazing the 0.4 mm e.max Cad discs reduced (p < 0.05) their BFS compared with the unglazed 0.8 mm specimens, whereas glazing of 0.8 mm discs had no influence (p > 0.05) on the strength. Etching and autoclaving of e.max Cad did not affect (p > 0.05) the BFS. For ZirMagnum sandblasting with 0.2 MPa or 0.6 MPa did not influence the biaxial flexural strength (p > 0.05), whereas heat treatment reduced (p < 0.01) the BFS of 0.6 MPa sandblasted ZirMagnum. Autoclaving reduced the strength (p < 0.05) compared with ZirMagnum as delivered, whereas autoclaving of the 0.6 MPa sandblasted and heat treated specimens did not influence (p > 0.05) the BFS. Glazing, etching and sandblasting increased (p < 0.05) surface roughness. Conclusions: The effects of glazing, heat treatment, aging and mechanical treatment of the materials evaluated should be considered since their strength could be affected. Clinical significance: Mechanical properties of restorations made from prefabricated ceramic blocks could be affected of various treatments and could change over time.

Objectives: To evaluate zirconia-based fixed partial dentures (FPDs) after more than 8 years in clinical service.

Methods: Patients treated between 2000 and 2004 with zirconia FPDs were identified from the records of a manufacturer of FPD substructures. Of the 45 patients who met the inclusion criteria 30 attended the appointment and 33 FPDs were evaluated using modified California Dental Association (CDA) criteria. In addition, plaque and the bleeding index were registered. Patient satisfaction with the restorations was evaluated using a 10-point visual analog scale (VAS).

Results: All the FPDs were made using CAD/CAM and hot isostatic pressed yttria-tetragonal zirconia polycrystal (HIPed Y-TZP) ceramic (Denzir) and were placed within general practices. The mean observation period was 9.6 ± 1.6 years (range 3.0–13.1 years). The CDA rating was 90% satisfactory for the surface. Corresponding figures for anatomic form, color and margin integrity were 94%, 100% and 94%, respectively. Regarding surface three (9.7%) FPDs exhibited veneer chipping and were rated ‘not acceptable’. For margin integrity two (6.5%) were rated ‘not acceptable’ because of caries. For anatomic form two (6.1%) were rated ‘not acceptable’ due to two lost FPDs. No significant differences were seen between the FPDs and controls for plaque and bleeding. The Kaplan–Meier survival rate (still in clinical function) was 94%, the success rate (technical events accounted for) 91% and (biological events accounted for) 73%. Based on the VAS the mean value for patient satisfaction was 9.3 ± 1.2.

Significance: Ninety-four percent of the FPDs were still in clinical function. HIPed Y-TZP could serve as an alternative for FPD treatments similar to those in the current study.

Using a newly developed three-dimensional (3D) numerical modeling code, an analysis was performed of the fracture behavior in a three-unit ceramic-based fixed partial denture (FPD) framework subjected to oblique loading. All the materials in the study were treated heterogeneously; Weibull׳s distribution law was applied to the description of the heterogeneity. The Mohr-Coulomb failure criterion with tensile strength cut-off was utilized in judging whether the material was in an elastic or failed state. The simulated loading area was placed either on the buccal or the lingual cusp of a premolar-shaped pontic with the loading direction at 30°, 45°, 60°, 75° or 90° angles to the occlusal surface. The stress distribution, fracture initiation and propagation in the framework during the loading and fracture process were analyzed. This numerical simulation allowed the cause of the framework fracture to be identified as tensile stress failure. The decisive fracture was initiated in the gingival embrasure of the pontic, regardless of whether the buccal or lingual cusp of the pontic was loaded. The stress distribution and fracture propagation process of the framework could be followed step by step from beginning to end. The bearing capacity and the rigidity of the framework vary with the loading position and direction. The framework loaded with 90° towards the occlusal surface has the highest bearing capacity and the greatest rigidity. The framework loaded with 30° towards the occlusal surface has the least rigidity indicating that oblique loading has a major impact on the fracture of ceramic frameworks.

The present in vitro study concerns determination of the pre-cementation gap width of all-ceramic crowns made using an in-office digital-impression technique and subsequent computer-aided design/computer-aided manufacturing (CAD/CAM) production. Two chairside video camera systems were used: the Lava Oral scanner and Cadent's iTero scanner. Digital scans were made of a first molar typodont tooth that was suitably prepared for an all-ceramic crown. The digital impressions were sent via the Internet to commercial dental laboratories, where the crowns were made. Also, an impression of the typodont tooth was made, poured, and scanned in order to evaluate the pre-cementation gap of crowns produced from scanning stone dies. These methods and systems were evaluated by creating replicas of the intermediate space using an addition-cured silicone, and the gap widths were determined using a measuring microscope. Hot-pressed leucite-reinforced glass-ceramic crowns were selected as a reference. The mean value for the marginal measuring points of the control was 170 μm, and the values for all the evaluated crowns ranged from 107 to 128 μm. Corresponding figures for the internal measuring points were 141-210 μm and 115-237 μm, respectively. Based on the findings in the present study, an in-office digital-impression technique can be used to fabricate CAD/CAM ceramic single crowns with a marginal and internal accuracy that is on the same level as that of a conventional hot-pressed glass-ceramic crown. In the present study, however, slight differences could be seen between the two types of ceramic crowns studied with respect to the internal fit obtained.

The purpose of this study is to evaluate functionalized multiwalled carbon nanotubes (fMWCNTs) as a potential coating material for dental zirconia from a biological perspective: its effect on cell proliferation, viability, morphology, and the attachment of an osteoblast-like cell. Osteoblast-like (Saos-2) cells were seeded on uncoated and fMWCNT-coated zirconia discs and in culture dishes that served as controls. The seeding density was 10⁴ cells/cm², and the cells were cultured for 6 days. Cell viability, proliferation and attachment of the Saos-2 cells were studied. The results showed that Saos-2 cells were well attached to both the uncoated and the fMWCNT-coated zirconia discs. Cell viability and proliferation on the fMWCNT-coated zirconia discs were almost the same as for the control discs. Better cell attachment was seen on the fMWCNT-coated than on the uncoated zirconia discs. In conclusion, fMWCNTs seem to be a promising coating material for zirconia-based ceramic surfaces to increase the roughness and thereby enhance the osseointegration of zirconia implants.

In this study, a numerical approach to the fracture behavior in a three-unit zirconia-based fixed partial denture (FPD) framework was made under mechanical loading using a newly developed three-dimensional (3D) numerical modeling code. All the materials studied were treated heterogeneously and Weibull distribution law was applied to describe the heterogeneity. The Mohr-Coulomb failure criterion with tensile strength cut-off was utilized to judge whether the material was in an elastic or failed state. For validation, the fracture pattern obtained from the numerical modeling was compared with a laboratory test; they largely correlated with each other. Similar fracture initiation sites were detected both in the numerical simulation and in an earlier fractographic analysis. The numerical simulation applied in this study clearly described the stress distribution and fracture process of zirconia-based FPD frameworks, information that could not be gained from the laboratory tests alone. Thus, the newly developed 3D numerical modeling code seems to be an efficient tool for prediction of the fracture process in ceramic FPD frameworks.

 The purpose of this study was to evaluate the occurrence of superficial flaws after machining and to identify fracture initiation and propagation in three-unit heat-treated machined fixed partial dentures (FPDs) substructures made of hot isostatic pressed (HIPed) yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) after loaded to fracture. Four three-unit HIPed Y-TZP-based FPDs substructures were examined. To evaluate the occurrence of superficial flaws after machining, the surfaces were studied utilizing a fluorescent penetrant method. After static loading to fracture, characteristic fracture features on both mating halves of the fractured specimens were studied using a stereomicroscope and a scanning electron microscope. Grinding grooves were clearly visible on the surfaces of the machined FPDs substructures, but no other flaws could be seen with the fluorescent penetrant method. After loading to fracture, the characteristic fracture features of arrest lines, compression curl, fracture mirror, fracture origin, hackle and twist hackle were detected. These findings indicated that the decisive fracture was initiated at the gingival embrasure of the pontic in association with a grinding groove. Thus, in three-unit heat-treated machined HIPed Y-TZP FPDs substructures, with the shape studied in this study, the gingival embrasure of the pontic seems to be a weak area providing a location for tensile stresses when they are occlusally loaded. In this area, fracture initiation may be located to a grinding groove.