Wear analysis and topographical properties of monolithic zirconia and CoCr against human enamel after polishing and glazing procedures.

PURPOSE: Intraoral adjustments of monolithic zirconia (MZ) necessitate intraoral grinding and polishing procedures, causing surface topography changes. The effect of various polishing and glazing procedures on surface roughness, topographical and phase changes of CoCr compared to zirconia, and assessment of the wear of the opposing dentition has been evaluated in this study. MATERIALS AND METHODS: One group of square Cobaltchromium (CoCr) and four groups of sintered and polished zirconia specimens (12 × 12 × 1mm) were fabricated (N = 5, n = 8) using Cobaltchromium or yttria-stabilized zirconia (ZrO2, Y2O3) blocks (ZENTROSTAR Zr Translucent; Wieland Dental + Technik). Each of the four zirconia groups was treated differently, one group was glazed (G), one was left unglazed (UG), two groups were polished, one using silicon carbide polishers (BG) and one with diamond-impregnated ceramic polisher kit (CG). All specimens were thereafter subjected to chewing simulation using enamel cusps (1'200'000 cycles, 49N force and 1.67 Hz loading frequency). Topographical changes were evaluated considering (a) weight (digital scale), (b) volume loss (digital microscope), (c) vertical height loss (digital microscope), (d) surface roughness (Ra, profilometer), and (e) mean roughness depth (Rz, profilometer). In addition the volume loss (digital microscope) of the used corresponding enamel cusps was measured. The surface roughness, topographical changes and antagonist wear of enamel cusps were measured. Statistical analysis was performed using the statical software R and the kruskal-wallis rank sum test and posthoc pairwise comparisons (a = 0.05). RESULTS: The mean surface roughness (µm) difference (ΔRa) was lowest for UG (-0.014 ± 0.007) and the highest for CG (-0.806 ± 0.172) (UGa < CoCrb < BGc < Ga,d < CGe). UG showed the lowest surface peak roughness (µm) difference (ΔRz) -0.316 ± 0.084 and CG the highest (-3.691 ± 0.369) (UGa < CoCrb < BGc < Ga,d < CGe). Material weight loss (ΔW) ranged between -0.005 ± 0.0001 and -0.000 ± 0.000 g (CoCra < UGa,b < CGb < BGb < Gb) compared to baseline, while the volume loss (ΔV) was between -21 ± 52 × 106 and 58 ± 36 × 106 µm3 (CoCra < BGa < UGa < CGa < Ga). The vertical height loss (ΔVH) was highest for UG (-12.067 ± 11.624) and lowest for G -0.033 ± 0.034 µm (Ga < CoCra,b < CGc < BGa,c,d < UGa,b,d). As for the volume loss (ΔV) of the corresponding enamel cusps, no significant differences could be measured (BGa < UGa < Ga < CGa < CoCra), therefore surface treatment did not affect the wear of the enamel antagonist. CONCLUSION: CoCr and highly polished monolitic zirconia produced less surface roughness and similar antagonist wear compared to glazed or unglazed zirconia. CoCr and highly polished monolitic zirconia can be considered as a good choice regarding the mechanical wear behaviour of materials and their corresponding enamel antagonist.

Clinical and histologic evaluation of different approaches to gain keratinized tissue prior to implant placement in fully edentulous patients.

OBJECTIVES: This work aimed to investigate the effectiveness and predictability of different treatment modalities for gain of keratinized tissue (KT) in fully edentulous jaws prior to dental implant placement: apically positioned flap (APF), APF plus xenogeneic collagen matrix (XCM), and APF plus free gingival graft (FGG). MATERIALS AND METHODS: In fully edentulous patients with insufficient zones of KT at the prospective implant positions, four treatment modalities were performed in the lower jaw: APF, XCM, FGG, and an untreated control group (control). APF and XCM were applied in the first molar positions, FGG and control in the canine positions. Assessed outcomes up to 3 months post-surgery included changes in width of KT (over a 3-month period), histomorphometric analysis of harvested soft-tissue biopsies (at 3 months postoperatively), and patient-reported outcomes measures (PROMs). RESULTS: For the primary outcome, changes in KT width demonstrated an increase of 1.93 ± 1.6 mm (APF), whereas XCM and FGG showed an increase of 4.63 ± 1.25 mm and 3.64 ± 2.01, respectively. Histomorphometric analyses revealed a thickness of the epithelium ranging between 375 ± 122 µm (APF), 410 ± 116 µm (XCM), 336 ± 122 µm (FGG), and 413 ± 109 µm (control). All biopsies showed a regular muco-periosteal structure with a keratinized epithelium of comparable thickness in all groups. CONCLUSION: All three methods were suitable to increase the width of KT, although APF alone rendered roughly 50% less gain compared to XCM and FGG. CLINICAL RELEVANCE: The use of XCM in conjunction with an APF represents a valuable treatment option for the gain of keratinized tissue in edentulous sites.

Long-term stability of peri-implant tissues after bone or soft tissue augmentation. Effect of zirconia or titanium abutments on peri-implant soft tissues. Summary and consensus statements. The 4th EAO Consensus Conference 2015.

INTRODUCTION: Several surgical techniques and prosthetic devices have been developed in the last decades, aiming to improve aesthetic, hygienic and functional outcomes that may affect the peri-implant tissues, such as procedures of bone and soft tissue augmentation and the use of custom-made abutments of titanium and zirconium. MATERIALS AND METHODS: Three systematic reviews, based on randomized clinical trials and prospective studies covering the above reported topics were analysed, and the detected evidence was exposed to interactive experts' discussion during the group's and general assembly's meetings of the 4th EAO Consensus Conference. The results are reported using the following abbreviations: S-T: short-term evidence, M-T: medium-term evidence; L-T: long-term evidence; LE: limited evidence. RESULTS: Soft tissue augmentation procedures may be indicated for the increase of soft tissue thickness and keratinized tissue, the reduction of interproximal peri-implant bone loss, and the coverage of shallow peri-implant soft tissue recessions (S-T, LE), L-T is lacking. Guided bone regeneration approaches (GBR) showed efficacy when used for ridge reconstruction after the complete healing of the soft tissues (S-T & L-T), and the stability of the augmented bone may play a role in the maintenance of the soft tissue position and dimensions (LE). No significant differences were observed between titanium and zirconia abutments when evaluating probing pocket depth, bleeding on probing, marginal bone levels and mucosal recessions. Zirconia abutments were associated with more biological complications but demonstrated superiority in terms of achieving natural soft tissue colour (S-T).