Abstract : Statement of the problem. Assessing the effects on maxilla when using fixed vs. removable prosthesis on All-On-4® protocol. This in-vitro study was conducted to compare stresses induced on distal implants in the All-On-4® concept between digitally constructed removable overdenture and fixed bridge, using strain gauge analysis. Four dummy implants were placed in their designed locations according to the All-On-4® concept; in a 3D printed completely edentulous maxillary acrylic cast. Multiunit abutments were secured to the implants. Two groups were defined: Group A: The framework was cemented to the four titanium copings over the implants (Fixed bridge). Group B: The same framework was picked up after relief was done and then seated on the ball attachments (Removable overdenture). Stresses were measured using strain gauges installed in their designed sites in the 3D printed cast. Loads of 100N were applied in a vertical and oblique direction on the right molar area. Paired t-test was used to compare between two different load directions within the same group, and unpaired t-test was used to compare between different groups. P-value ≤ 0.05 was statistically significant. Group A with vertical loads (532±9.2) and oblique loads (464±40.3) showed significantly higher stresses on the supporting structures of the distal implants than group B with vertical loads (64 ±7.75) and oblique loads (41.5±2.42). Within group A, higher microstrains were recorded on the distal implants in the loaded side in case of applying vertical loads (532±9.2) than in the case of oblique loads (464±40.3). Also, lower microstrains were recorded in the unloaded side in the case of vertical loads (21.5±2.42) than in oblique loads (43±2.58). Within group B, higher microstrains were recorded in the loaded side in case of applying vertical loads (64±7.75), than in case of oblique loads (41.5±2.42). Also, lower microstrains were recorded in the unloaded side in case of vertical loads (10.5±1.58) than in case of oblique loads (18.5±2.42). Within the limitations of this study, it could be concluded that the distal implants in the fixed bridge suffered higher loads than the removable overdenture.

Keyword : All-on-4 protocol, digitally constructed prostheses, Polyetheretherketone and strain gauge.