Digital vs Analog Impression in Cases of All-on-4 - Prosthesis

The implants were considered surviving if they were clinically stable and functioning without any mobility. Failure was defined removal of implants due to loss of integration, pain, implant mobility, paraesthesia, neuropathies or psychological reasons. Calculation of the estimated failure rate was performed by dividing the number of implant failures by the total exposure time of the implant. The total exposure time is the interval of time the implants could be followed for the entire observation time or up to failure of the implants that were lost during the follow-up period.

Standardized periapical radiographs with long cone paralleling technique using film holders were used for the assessment of crestal bone loss. The loss of marginal bone relative to the implant shoulder at the mesial and distal of each implant was measured in mm and then the mean was calculated and statistically estimated. A digital intraoral imaging system was used (Digora phosphor plate reader, Soredex Tuusula, Finland). All the radiographs were scanned and then uploaded into the computer for assessing bone loss over time. The "ImageJ" software was used to take the measurements on the computer screen. Postoperative radiographs with the implants placed at the crest of the bone were compared with the 6,12 and 24 m radiographs.

During the follow-up period, prosthodontic (mechanical) complications for the four groups were registered and calculated according to the following events: number of screw loosening or screw fracture of the abutment, number of screw loosening or screw fracture of the prosthesis, number of framework fracture, fractured acrylic resin, number of prosthetic teeth fracture and loss of cover of access hole.