Cantilever Lengths and Anterior-Posterior Spreads of Interim, Acrylic Resin, Full-Arch Screw-Retained Prostheses and Their Relationship to Prosthetic Complications.

PURPOSE: To retrospectively record the distal cantilever lengths (CL) of full-arch interim, all-acrylic resin prostheses used in an immediate occlusal loading protocol. Anterior/posterior (A/P) spreads were measured on master casts associated with the interim prostheses. Ratios were calculated (CL/AP). Prosthetic complications were recorded. The ratios and prosthetic complications were statistically compared and analyzed for statistical and clinical significance.

MATERIALS AND METHODS: One hundred twenty-eight patients with 192 edentulous arches (109 maxillary; 83 mandibular; 190 arches were restored with 4 implants; 2 maxillary arches were restored with 5 implants) were treated. Seven hundred seventy implants (Brånemark System) from September 1, 2011, until August 31, 2013 were included in this report. Patients were treated and followed in a single private practice for up to 40 months. Implants had to have at least 35 Ncm of insertion torque to be immediately loaded. All implants were immediately loaded with full functional occlusions on the day the implants were placed. Interim, full-arch, all-acrylic resin prostheses were fabricated and placed into full functional occlusion following an All-on-Four protocol. Measurements of the distal cantilevered segments were made on the prostheses prior to insertion. A/P spreads were measured on the master casts made from abutment level impressions made on the day of surgery. Prosthetic complications (denture base fracture, cohesive/adhesive denture tooth fractures) were recorded in the charts as they occurred. All charts were reviewed for this report; no patients were lost to follow-up. Interim prosthetic repairs were analyzed by type (tooth or denture base), arch, gender, and location within the edentulous arches.

RESULTS: One patient experienced complete maxillary implant failure; the overall implant survival rate (SR) was 99.5% (766 of 770). Four hundred thirty of 434 maxillary implants and 336 of 336 mandibular implants survived for SRs of 99.1 and 100%, respectively. Thirty four of the 192 interim prostheses (17.7%) warranted at least one repair during treatment. The average cantilevered segments for the interim maxillary prostheses without prosthetic complications were 9.7 mm (right) and 9.5 mm (left). The average cantilevered segments for the repaired maxillary prostheses were 10.1 mm (right); 9.9 mm (left). The average cantilevered segments for the interim mandibular prostheses without prosthetic complications were 9.2 mm (right) and 9.3 mm (left). The average cantilevered segments for the repaired mandibular prostheses were 9.87 mm (right) and 9.18 mm (left). The average maxillary A/P spread was 18.4 mm; the average mandibular A/P spread was 17.3 mm. The average maxillary CL/AP spread ratios were 0.55 (right) and 0.53 (left); the average mandibular CL/AP spread ratios were 0.61 (right) and 0.57 (left). There were no statistical correlations between the CL/AP ratios and the frequency or type of prosthetic repairs recorded in this study. The ratios were statistically significant (p = 0.041) for mandibular prostheses with prosthetic complications: slightly greater CL/A-P ratios were noted.

CONCLUSIONS: The results from this 2-year clinical retrospective analysis indicated that CL/AP ratios in the range of 0.5 to 0.6 generally resulted in successful interim prostheses during the time the interim prostheses were in function. The results of this investigation also revealed that 1 of 129 patients experienced implant failures; implants placed and restored on the same day with full-arch, screw-retained prostheses resulted in high clinical survival rates for implants and prostheses. The All-on-Four treatment protocol used in this study was a viable alternative to other implant loading/placement protocols for rehabilitating edentulous patients and resulted in minimal prosthetic complications.