The absolute marginal gap (AMG) precementation and postcementation and the retention of zirconia crowns cemented to standardized molar preparations (4×10) by self-adhesive resin cements (SARCs) were evaluated. The following SARCs were used: RelyX U-200 (RXU200; 3M ESPE, Seefeld, Germany), SmartCem 2 (SC2; Dentsply, Milford, DE, USA), and G-Cem Automix (GCA; GC, Alsip, IL, USA). The control adhesive resin cement was Panavia 21 (PAN; Kuraray Dental Co Ltd, Osaka, Japan). Twenty measuring locations at a constant interval along the margins were marked, and the AMG was measured by an image analysis system connected to a stereomicroscope (20×). The cemented copings were aged 270 days at 100% humidity and 37°C and then underwent 10,000 thermal cycles, 5°C-55°C. After aging, the crowns were tested for retention, and the debonded surfaces were examined at 3× magnification. The mean marginal gaps precementation and postcementation were 34.8 ± 17.4 μm and 72.1 ± 31 μm, respectively, with no statistically significant differences between the cements. A significant difference ( p≤0.001) in retention between the cements was found. The highest values were obtained for SC2 and GCA (1385 Pa and 1229 Pa, respectively), but these presented no statistically significant differences. The lowest values were found for PAN and RXU200 (738 Pa and 489 Pa, respectively), but these showed no statistically significant differences. The predominant mode of failure in all of the groups was mixed, and no correlations were found between marginal gap and retention.

the objective of this in vivo study was to compare bone-to-implant contact (Bic) and bone area fraction occupancy (BAfo) values of a new implant, designed to be inserted without bone preparation, using two different preparation protocols: no site preparation and prior limited cortical perforation, versus the values of a control implant using a conventional drilling protocol. forty-one implants were inserted in 13 rabbits. Thirteen test implants with a new thread design were inserted using no bone preparation (NP), 14 test implants were inserted with limited cortical perforation (CP), and 14 conventional implants served as control. Five animals were sacrificed after 21 days and eight animals after 42 days. Histomorphometric analysis was performed and percentage of BIC and BAFO values were measured. AnoVA with tukey post hoc and Mann-Whitney nonparametric tests were calculated to compare between the groups. Statistical analysis showed no significant difference in the measured values between any of the groups, neither compered by implant nor by compered day. the results demonstrated that biological osseointegration parameters of implant that was inserted without any bone preparation was non-inferior compared to conventional preparation. the clinical relevance is that novel implant designs may not require bone preparation prior to placement. Various factors influence the long-term prognosis of dental implants and can affect osseointegration, such as surgical technique, host bed, implant surface, implant design, material biocompatibility, and loading conditions 1. Osseointegration is defined as a direct contact between living bone and the implant on light microscopic level 1. A wider definition considers bone quality, as well as stable support of a prosthesis and lack of motion of the implant under functional loads, apposition of new bone, that is identified as normal bone and marrow at microscopic levels, and in direct contact with the implant, without interposed connective tissue 2,3,4. Bone-to-implant contact (BIC) percentages is considered essential requisite for implant stability and an indication of successful osseointegration 5,6. The most common implant insertion technique is based on a conventional drilling technique, in which gradual expansion of the osteotomy site by sequential enlargement of the drill diameter is performed 8-10. Conversely, under-preparation of an implant site (also referred to as under-drilling) is defined as preparing the implant's bed narrower than the implant's inserted diameter 11-13 while over-preparation osteotomy refers to preparing an implant's bed wider than the implant's inserted diameter 13. Other available techniques for implant insertion are bone compaction, osteodistraction and piezo surgery 8. Implant placement without any site preparation is rarely mentioned in published literature; the exception is with regard to orthodontic mini implants which are self-drilling i.e., the implant is inserted without need of predrilling, or "drill free" placement 14. However, these orthodo...