Each crown was cemented to its corresponding implant-abutment assembly using temporary cement (Cavex Temporary Cement, Cavex, Holland).

Each implant received 4 strain gauges (Kowa strain gages, Japan) placed on the mesial, distal, buccal, and lingual surfaces of the epoxy resin adjacent to the implants. At these selected sites, the thickness of the epoxy resin surrounding each implant was reduced to approximately 1 mm and was adjusted to be parallel to the long axis of the implant abutment units using disc and diamond stones (Fig. 4). Electric strain gauges which were 1 mm in length, 2.09 ± 1.0%, and 119.6 ± 0.4 Ω were bonded to their corresponding sites using cyanoacrylate adhesive (Amir, Egypt).They were bonded in a vertical position parallel to the implant bodies and held in place for about 5 min using adhesive tape. The lead wire from each active strain gauge was connected to a multichannel strain meter to register the microstrains transmitted to each strain gauge.

Functional loads of 300 N were applied to the crowns using computerized testing machine (Lloyds LR5K Plus Advance Universal Testing System, Johnson Scale CO., Inc). The machine is computer controlled by the Nexegen ver 4.3 software which permits the collection of data.

Two types of static axial loads were applied with 0.5 mm/min speed. The first load was 300 N applied axially in the position of the centric fossa of each crown Fig. 5 while the second load was 300 N applied 3 mm off-axial distally Fig. 6. The B/L and M/D strains were recorded separately for each strain gauge. Records were repeated five times, allowing the strain indicator to recover to 0 strain before reloading. A fundamental parameter of the strain gauge is its sensitivity to strain, expressed quantitatively as the gauge factor (GF). Gauge factor is defined as the ratio of fractional change in electrical resistance to the fractional change in length (strain) [10]: