الفهرس 
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Abstract
Statement of problem: Restoring a missing tooth, especially if the inter-occlusal distance is limited, with an implant-supported crown cemented extraorally onto a titanium (Ti) base abutment is beneficial, to remove the excess cement. Longer-term clinical trials with success data are required to validate the current design options of Ti base (inserts) (hybrid abutment) as a viable alternative to the Ti or ceramic abutment. Objective: The aim of this in vivo research was to investigate the influence of abutment design: (1) the hybrid (new prefabricated bonding base) titanium abutment (Variobase), (2) the (Dess Ti Base) non-segmented zirconia implant crowns, on the clinical, radiographic, and esthetic outcome of screw- and cement-retained, implant-supported monolithic zirconia crowns. Material and methods: A total of 28 patients with missing 30 single maxillary premolar areas indicated for single implants were implanted with RC bone level tapered implants (4.1x12mm) (Institut Straumann AG, Basel, Switzerland). The thirty implants were random classified for comparative evaluation into 3 equal groups (n =10) according to the design of Ti base abutment, and the retention type of zirconia crown as follows: group (A) (VC): patients receiving hybrid (prefabricated bonding bases) Ti abutments (Variobase, Straumann, Switzerland) with cement-retained monolithic zirconia crowns, group (B) (VS): patients receiving hybrid (prefabricated bonding bases) Ti abutments (Variobase) with screw-retained monolithic zirconia crowns, group (C) (DS): patients receiving non-segmented screw-retained monolithic zirconia crowns, cemented onto Dess Ti Base. The monolithic zirconia crowns were fabricated by CAD/CAM scanning, designing, milling, sintering, finishing and polishing, try-in, staining, and glazing. The crowns of each group were cemented to the respective Ti bases (abutments) according to the manufacturer’s instructions. The implant-supported crowns were evaluated at baseline, 3, 6, 12 and 18 months clinically, radiographically and esthetically. All data were collected and statistically analyzed. Results: 1- All 30 implants remained stable and reached osseointegration (100% cumulative success rate ⁅CSR⁆). The highest mean average crestal bone level (BL) measured 1.23+0.72mm (median: 1.40mm, range: 0.00-2.25mm) (P=0.09 NS) in group (C) (DS), and the least mean BL measured 1.00+0.55mm (median: 1.10mm, range: 0.00-2.00mm) and (median: 1.00mm, range: 0.10-1.90mm) (P=0.83 NS) and (P=0.52 NS) in the groups (B and A) (VS and VC) respectively. 2- Two patients had mucositis and 1 patient had periimplantitis in group (C). Insignificant changes in the biological parameters, except that a significant increase in GI, BoP, and MBI values in group (B), and a significant increase in PPD values in group (C) were documented. 3- The highest mean total of pink and white esthetic scores (PES/WES) (16.42+1.91) and (16.34+2.21) were recorded in the groups (C) and (B) respectively, and the least mean score (13.92+1.52) was recorded in group (A). There was a statistically non-significant difference between group (C) and (B). But there was a statistically significant difference between the groups (C and B) and group (A). 4- All 28 patients were entirely satisfied with their implant-supported restorations during 18-months follow up appointments. The highest mean value (1.41) was recorded in group (A) (VC), followed by (1.31) in group (B) (VS), and the least mean value (1.19) was recorded in group (C) (DS). Conclusions: Under the conditions of this study, using a prefabricated Ti base (Variobase or Dess Ti base) as an abutment for an implant-supported cement- or screw-retained zirconia crown is an alternative procedure for implant-supported restorations. It promotes healthy and stable hard and soft tissues, and achieves good esthetic results. Very few mechanical complications have been observed using these abutments during 18 months follow up. While these developments and concepts appear to be quite promising, nevertheless, longer term clinical studies are needed to confirm these results and to validate their performance. KEYWORDS: Variobase, Ti base, abutment design, clinical, esthetic evaluation, PES/WES index, CAD-CAM, monolithic zirconia, cement-retained, screw-retained, dental implants, bone loss.