Effect of Immediate Dentin Sealing on the Bond Strength of Monolithic Zirconia to Human Dentin.

OBJECTIVE: This study evaluated the shear bond strength (SBS) of pretreated monolithic zirconia surfaces bonded to human dentin following immediate dentin sealing (IDS) using two different self-adhesive resin luting agents. METHODS AND MATERIALS: Sixty intact human third molars were collected, stored, sectioned appropriately, and molded according to ISO 29022:2013, resulting in 120 dentin specimens. Ceramic cylindrical specimens were fabricated using CAD/CAM technology and sintered as recommended (final bonding area A=2.56 mm2). Specimens were randomly assigned to eight groups (15≥n≥14) depending on dentin conditioning method (IDS or delayed dentin sealing [DDS]), zirconia surface pretreatment (airborne particle abrasion [APA] with 50 µm Al2O3 particles at 3 bar for 10 seconds or tribochemical silica coating [TBC] with 30 µm CoJet particles at 2.8 bar for 10 seconds), and adhesive luting agent type (Panavia F2.0 [PAN] or PermaCem Dual Smartmix [PER]). Bonded specimens were water-stored (37°C, 24 hours) and subjected to SBS testing (50-kgF load cell, 1 mm/min). Fracture type was evaluated with stereomicroscopy. Data (MPa) were statistically analyzed using three-way analysis of variance (α=0.05). RESULTS: All factors significantly affected SBS values (p<0.001). Dentin conditioning method presented the greatest effect. Mean SBS values ranged from 12.603 MPa (PER-APA-DDS) to 40.704 MPa (PER-TBC-IDS). Based on the fracture type, adhesive failures at the luting agent-zirconia interface were the least common. CONCLUSION: Bonding strategies for monolithic zirconia restorations could potentially benefit from IDS, regardless of the adhesive luting agent system used.

Aging of 3Y-TZP dental zirconia and yttrium depletion.

OBJECTIVE: Yttrium-stabilized zirconia is susceptible to low temperature degradation after interaction with water. Various mechanisms by which water molecules destabilize the tetragonal phase have been proposed, while the concept of yttrium depletion by the incorporation of hydroxyl ions in the crystalline structure either through the formation of YOH/ZrOH bonds or small α-Y(OH)3 crystallites, is prevailing. The present study was performed to investigate the surface alterations on a 3Y-TZP dental ceramic during the process of in-vitro aging and to further explore the yttrium depletion mechanism that occurs upon interaction with water. METHODS: Surface structural changes of zirconia specimens where investigated before and after in-vitro aging with X-ray diffraction analysis, Fourier-transformed infrared spectroscopy, X-ray photoelectron spectroscopy, fluorescence microscopy and scanning electron microscopy. RESULTS: High luminescence generated from the non-aged specimen was explained by the high amount of oxygen vacancies. The phase transformation from the t-ZrO2 to the m-ZrO2 phase after aging was accompanied by a significant loss of yttrium, a clear decrease of oxygen vacancies and a profound decrease of luminescence. Surface oxygen vacancies either migrated into the inner of the specimens or/and/engaged oxygen from the ZrO2 and formed the metallic phase of Y2O3 on the surface after aging. SIGNIFICANCE: An "ideal" amount of oxygen vacancies that could stabilize the tetragonal phase in Y-TZP zirconia ceramics, without compromising esthetics and LTD resistance, is still a matter of further research and different susceptibilities to LTD among various dental zirconia ceramics are based on the amount of oxygen vacancies that can be annihilated by water molecules.

Attachment and proliferation of human periodontal ligament fibroblasts on bioactive glass modified ceramics.

In this study, six groups of modified ceramic specimens were constructed and were studied comparatively with dental porcelain (P:control) for their ability to support human periodontal ligament fibroblasts attachment and proliferation. The dental porcelain was initially coated with bioactive glass (PCB) or with a mixture of porcelain and bioactive glass (PCBP) and then calcium-phosphate rich (Ca-P) or hydroxy-carbonate apatite (HCAp) layers were bio-mimetically developed on both surfaces (PCB and PCBP) after immersion in simulated body fluid. The development and characterization of Ca-P and HCAp layers on PCBCa-P, PCBHCAp, PCBPCa-P, PCBPHCAp specimens' surfaces were evaluated by Scanning Electron Microscopy (SEM) and further confirmed by Fourier Transform Infrared Spectroscopy (FTIR). The modified ceramics differed from their controls concerning their surface morphology as evaluated by SEM, and their surface chemical composition (Al, P, Si, Ca, Na and K) as evaluated by Energy Dispersive Spectroscopy (EDS). Almost all modified specimens supported cell attachment, spreading and proliferation at higher extent than the control porcelain specimens. The additional layers of Ca-P or HCAp on PCBP and PCB specimens were found to positively affect cell attachment and proliferation. The highest cell population, of all specimens tested, was observed on PCBPCa-P and PCBPHCAp. The Ca-P particles present on all Ca-P and HCAp coated specimens seemed to be involved in cell adhesion.

Teeth and gingival display in the premolar area during smiling in relation to gender and age.

There is limited knowledge concerning tooth and gingival display in the maxillary premolar area during smiling. The purpose of this study was to investigate maxillary premolar and associated gingival display during smiling, and to reveal possible differences related to gender and age. The study consisted of 90 males and 113 females (mean age 38 years, s.d. = 13.83) receiving regular dental care. Two pictures of each subject, one with lips in maximum smile, and the other a retracted frontal view, were made. Clinical crown length, tooth and gingival display were measured for the left maxillary premolars. Central incisors and canines were used as controls. anova with Bonferroni post hoc multiple comparisons tests was used to assess any statistically significant impact of gender and age on tooth and gingival display, and determine differences among gender and age groups (at 5% significance level). Premolars were partially visible in more than 80% of the smiles, and displayed more than 65% of their clinical crown length during smiling. The least display (P < 0.001) was recorded for first and the greatest for second premolars. Tooth display was greater in females, but statistically significant only in central incisors (P < 0.05). No significant differences were revealed between age subgroups. Gingival display was greater for premolars compared with both central incisors (P < 0.001) and canines (P < 0.05). Displayed gingiva was found in first and second premolars in 44 and 49% of subjects, respectively. More gingival display was recorded in females and in younger subjects.

Apatite formation on dental ceramics modified by a bioactive glass.

Restorative dental materials are considered biocompatible without exhibiting any bioactive behaviour. The aim of this study was the investigation of surface structure changes on conventional dental ceramics used in metal-ceramic restorations modified by a bioactive glass, after immersion in SBF for various time periods. Bioactive glass powder was mixed with porcelain powder with three different weight ratios: 1:1, 1:2, and 2:1. The two powders were mixed with porcelain modelling liquid and the mixture was transferred and spread on the surface of pre-fabricated ceramic disks. Coated ceramic specimens after being exposed to a specific thermal cycle as it is recommended for dental ceramics were soaked in Simulated Body Fluid (SBF) at 37 degrees C for various periods of time. After soaking, specimens were studied using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). Results revealed the development of a non-stoichiometric, biological apatite layer on their surface after exposure in SBF for several time periods. The onset of apatite-layer formation is directly dependent on the amount of bioglass in the coating and its thickness reduces within the specimens of the same bioactive glass-porcelain proportion with time, reaching an average thickness of 15 microm at the longest immersion time, for all the specimens.