Six females and 2 males (average age 66.4 years, range 52–85 years) with upper (n = 7) or lower (n = 1) complete dentures participated in this study. Inclusion criteria were (1) an opposite jaw that included natural dentition at least to the second premolar on both sides, (2) a need for fixed rehabilitation, (3) no medical contraindication to the placement of implants, (4) no need for augmentation procedures, and (5) willingness to participate in this study. The only exclusion criterion was temporo-mandibular dysfunction, since it may interfere with chewing and biting patterns and abilities. In the mandible 5 and in the maxilla, 6 OsseoSpeed implants and Uni Abutments 20° (Astra Tech, Mölndal, Sweden) were used to provide support for fixed rehabilitation. All participants were treated at the Center for Periodontology and Implantology, Leuven, Belgium, by the same surgeon (BC). Informed written consent with regard to treatment and masticatory function and follow-up procedures was provided to each participant. The study was approved by the ethics committee of the Catholic University of Leuven (B322201319432).

The day after implant surgery, implants were loaded with screw-retained implant-supported acrylic resin provisional restoration (immediate loading) as previously described [37, 38]. All provisional bridges extended to the second premolar or first molar region.

Patient’s head was positioned with the Frankfort plane parallel to the floor. After opening the mouth, a pressure-sensitive sheet (Dental Prescale, 50H, type R, 97 μm thick, GC, Tokyo, Japan) was inserted on the occlusal plane. Patients were instructed to bite onto the test sheet as hard as possible for 3 s in the intercuspal position. This was repeated three times in each patient. The sheets were analyzed using special analytical equipment (Occluzer FPD-707, GC, Tokyo, Japan), namely, an analyzing device that could calculate bite force (N) and occlusal contact area (mm²) from the degree of discoloration of the pressure-sensitive sheets. Values from three sheets were averaged for each measurement, as described in a previous study [39]. In a pilot study, dentate patients (n = 14, mean age 58.4 ± 12.6 years) showed an occlusal contact area of 20.79 ± 8.10 mm² and a maximal bite force of 696.8 ± 237.5 N.