In the present study, the following materials were used: titanium root form endosseous implants of standard diameter and length (4-mm platform, 3.8-mm diameter,12-mm length, fixture bevel 0.2 mm, Super Line System, Dentium, USA), short-wide implant (7-mm platform, 5.8-mm diameter, 7-mm length, Super Line System, Dentium, Seoul, Korea) with 1.5-mm machined surface and 5.5-mm threaded surface that were fixed and tightened to the internally hexed implants, and 2 one-piece implant with square head mini implants (2.5-mm diameter × 12 mm, Slim Line System, Dentium, Seoul Korea), in addition to titanium implant abutments (straight abutments) with 5.5-mm height and matching width for short-wide and standard implants (5.5 mm and 4.5 mm, respectively) (Fig. 1).

Two epoxy resin casts were constructed using epoxy resin material (Transparent Epoxy, Kemapoxy 150, CMB International, Egypt). A dental milling machine (bredent GmbH & Co.KG, Weissenhorner Str. 2, 89250 Senden, Germany) was used to prepare the site for the implant fixtures insertion. The holes were filled with epoxy resin; then, using a dental surveyor (Ramses, Egypt), the implant-abutment units were placed in straight line configuration into the epoxy resin cast which is mounted on surveyor table at zero tilt. The two mini implants were prepared using tapered stone with round end to create a 0.5 chamfer finish line. A total of six crowns were constructed in this study, three full-metal crowns (Kera NH, Deutschland) (Fig. 2), and three hybrid-ceramic (Lava™ Ultimate Restorative, 3M™ ESPE™, Deutschland GmbH) crowns (Fig. 3). They were constructed with standardized dimensions 7-mm height, 7-mm bucco-lingual, and 8-mm mesio-distal width.

A split silicon index was constructed. The first full-metal crown was seated over its corresponding abutment using temporary cement. A duplicating addition silicon impression material was mixed according to the manufacturer’s instructions. The silicon index was split mesiodistally using sharp scalpel into two halves. The other wax patterns were adjusted using this index. The resin nano-ceramic crowns are milled by Computer Aided Design/Computer Aided Manufacturing (CAD/CAM) technology using CEREC inLAB MC XL (Cerec inLab, Sirona dental systems GmbH Fabrikstrasse, Bensheim, Deutschland) with inLab 3D software version 3.88. The restoration was modified to the required dimensions as the metal crowns (7 mm high, 7 mm bucco-lingual, and 8-mm mesio-distal width) by the help of the Cerec grade tool, and the occlusal table was shaped to be non-anatomical.