Ratios of Cantilever Lengths and Anterior-Posterior Spreads of Definitive Hybrid Full-Arch, Screw-Retained Prostheses: Results of a Clinical Study.

Purpose To record the distal cantilever lengths (CL) of full-arch, definitive hybrid prostheses fabricated for patients after treatment with an immediate occlusal loading protocol. Anterior/posterior (AP) spreads were measured on master casts of the definitive prostheses. CL/AP ratios were calculated for these 2 parameters. These measurements were then compared and evaluated for statistical and clinical significance; the CL/AP ratios were also compared between definitive and interim prostheses. Materials and Methods One hundred thirty patients with 193 edentulous arches (112 maxillary; 81 mandibular; 191 arches restored with 4 implants; 2 maxillary arches restored with 5 implants) were treated. Seven hundred seventy-four implants (Nobel Biocare Branemark System [Nobel Active]) were included in this report. All but 2 patients had 4 implants placed into each jaw: the anterior implants were relatively vertical; the posterior implants were tilted parallel to the anterior wall of the maxillary sinus and angled distally above the mental foramen. Patients were treated and followed in private practice by the author. Implants had to have at least 35 Ncm of insertion torque to be immediately loaded. All implants were immediately loaded with full functional occlusions via interim, full-arch, all-acrylic resin prostheses. Definitive full-arch, hybrid prostheses were fabricated approximately 6 to 9 months after implant placement with computer-aided design/computer-aided manufacturing (CAD/CAM) frameworks, denture bases, and acrylic resin denture teeth. Measurements of the distal cantilevered segments were made with a Boley gauge on the interim and definitive prostheses prior to insertion. AP spreads were measured on the master casts made from abutment level impressions approximately 4 months post-occlusal loading. Prosthetic complications such as denture base fractures and cohesive/adhesive denture tooth fractures were recorded in the charts as they occurred. All charts were reviewed for this report. Prosthetic repairs for the definitive prostheses were analyzed by type (tooth or denture base), arch, gender, and location within the edentulous arches. Results Patients were followed for up to 48 months post-immediate occlusal loading. One patient experienced maxillary implant failure; the overall implant survival rate (SR) was 99.5% (770 of 774). Four hundred forty-six of 450 maxillary implants and 324 of 324 mandibular implants survived for SRs of 99.1% and 100%, respectively. Thirty-three of the 193 interim prostheses (17.1%) warranted at least one repair during treatment. One of the 193 definitive prostheses demonstrated a posterior denture base fracture. The average cantilevered segments for the definitive maxillary prostheses were 15.6 mm (right) and 15.4 mm (left). The average cantilevered segments for the definitive mandibular prostheses were 15.5 mm (right) and 15.6 mm (left). The average maxillary AP spread was 18.4 mm; the average mandibular AP spread was 17.3 mm. Average maxillary CL/AP spread ratios were 0.85 (right) and 0.84 (left); average mandibular CL/AP spread ratios were 0.89 (right) and 0.90 (left). There were no statistically significant associations between the CL/AP ratios and the frequency or type of prosthetic repairs recorded in this study. Conclusions The results from this 4-year clinical retrospective analysis indicated that one of 130 patients experienced implant failures. The prosthetic complication rate for the definitive prostheses in this study was less than 1% (0.005). The author suggests that the parameters used in this study's framework designs for full-arch, titanium milled frameworks (CL/AP ratio <1), resulted in consistent, predictable results for rehabilitating edentulous patients.