Comparison of Conventional Impressions, Intraoral Scanners and Digital Photogrammetry for Full-arch Implant Prosthesis.

For each patient, 6 impressions were taken in the same order: 2 IOS, 2 photogrammetry, 2 conventional impressions. A satisfaction questionnaire in the form of a Visual Analogue Scale (VAS) was given after each group of impressions. The time required for each impression was also measured

Clinical and laboratory Protocol The conventional impression will taken in plaster using an open tray technique (Dr. Balzer® Special plaster, Siladent). The impression copings (Impression Coping Open Tray Multi-unit, NobelBiocare) will be screwed onto the transgingival abutments. The plaster wil then prepared with the 50:100 water/powder ratio recommended by the manufacturer. The resulting impression will then cast with low-extension plaster and digitized using a high-precision laboratory scanner. The entire procedure wil be conducted twice.

The IOS impression will obtained using an intraoral scanner (TRIOS4; 3Shape A/S) with implant scan bodies screwed at the multiunit abutment level (Elos Accurate Multi-Unit; Elos Medtech). The IOS device will be a wireless, powder-free scanner with a pen grip, based on confocal microscopy laser technology, and operated with software version 1.4.7.5, calibrated immediately before the impression. The scanning strategy will be consistent for all procedures, consisting of a first scan of the gingiva and implants, in accordance with the manufacturer's recommendations. The scanbodies will be then hand screwed and a second scan will be performed using the following scan path: from the last distal implant in a zigzag pattern[26]. The entire procedure will be conducted twice.

Photogrammetry will be carried out using an Imetric camera (ICam4D; Imetric4D Imaging Sàrl). The first step will be to use an intraoral scanner to scan the gingiva and optical markers screwed onto the transgingival abutments. In a second step, the scan bodies with superficial target points and titanium interfaces (ICamBody; Imetric4D Imaging Sàrl) will be hand screwed to the transgingival components. The ICamBodies will be placed with a visible edge in accordance with the manufacturer's recommendations. The operator will set up the photogrammetric camera (ICam4D; Imetric4D Imaging Sàrl) and directly capture the scan bodies from right to left at 10 cm to 15 cm from the lips. At least 2 sides of the scan body, with 3 target points on each side, will be captured according to the manufacturer's instructions. The scanbodies will be unscrewed and screwed back in random order and a second recording will be made after recalibrating the photogrammetry. The coordinates from the photogrammetry will be exported the to dedicated software to be merged with the STL file form the intraoral scanner. The entire procedure will be conducted twice.

Patient-reported outcome measures (PROMs) PROMs will be obtained using a Visual Analog Scale (VAS, [27]) immediately after the impression. For each impression technique, six domains will be used to evaluate which of the two was less unpleasant: (a) opinion on treatment length (1 = unsatisfactory to 10 = excellent), (b) comfort level during impression procedures (1 = unsatisfactory to 10 = excellent), (c) anxiety level before impression procedures (1 = high to 10 = low), (d) unpleasant taste during/after impression procedures (1 = bad taste to 10 = none), (e) nausea during the impression procedure (1 = severe to 10 = none), and (f) pain during impression procedures (1 = painful to 10 = none). For all Visual Analog Scales (VAS), higher scores indicated greater satisfaction with the procedure.