Immediate loading of 2(all-on-2) versus 4 (all-on-4) implants placed with a flapless technique supporting mandibular cross-arch fixed prostheses: 1-year results from a pilot randomised controlled trial.
OBJECTIVE
To evaluate the outcome of 2 versus 4 implants placed flapless in fully edentulous mandibles and immediately restored with metal-resin screw-retained cross-arch prostheses.


METHODS
Sixty patients from two different centres were randomised: 30 to the allon- 2 group and 30 to the all-on-4 group according to a parallel group design. To be immediately loaded, implants had to be inserted with a minimum torque of 40 Ncm. Outcome measures were prosthesis and implant failures, complications, and marginal bone level changes.


RESULTS
Flaps were raised in 18 patients. A total of 2 implants in 2 patients did not reach the planned insertion torque and were immediately replaced by larger diameter ones. One year after loading, no drop-out or implant failure occurred. Eight biomechanical complications occurred in the all-on-2 group versus 8 complications in the all-on-4 group. There were no statistically significant differences for complications between groups. There were no statistically significant differences for marginal peri-implant bone levels between the two groups (estimate of the difference = -0.16; 95%CI -0.40 to 0.08; P (ANCOVA) = 0.074), with both groups losing a statistically significant amount of marginal bone (0.74 mm for all-on-2 implants and 0.58 mm for all-on-4 implants). There were statistically significant differences between the two centres, with more bone being lost for the Bologna centre (0.26 mm versus 1.07 mm).


CONCLUSIONS
These preliminary results, up to 1 year after loading, suggest that immediately loaded mandibular cross-arch fixed prostheses can be supported by only 2 dental implants. Longer followups (approximately 10 years) are needed to properly evaluate this therapeutic option.
Department of Periodontology and Implantolgy, University of Bologna, Italy.
Gioacchino
G
Cannizzaro
Pietro
P
Felice
Elisa
E
Soardi
Vittorio
V
Ferri
Michele
M
Leone
Matteo
M
Lazzarini
Salvatore
S
Audino
Marco
M
Esposito
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016301:Alveolar Bone Loss / Q000209:etiology; D001696:Biomechanical Phenomena; D003722:Dental Alloys / Q000737:chemistry; D059605:Dental Implant-Abutment Design; D015921:Dental Implants; D019094:Dental Prosthesis, Implant-Supported; D019232:Dental Restoration Failure; D003779:Denture Design; D003780:Denture Repair; D003781:Denture Retention; D003826:Denture, Complete, Lower; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D057893:Immediate Dental Implant Loading / Q000379:methods*; D007575:Jaw, Edentulous / Q000534:rehabilitation / Q000601:surgery; D008297:Male; D008334:Mandible / Q000473:pathology / Q000601:surgery*; D008875:Middle Aged; D010865:Pilot Projects; D011183:Postoperative Complications; D013524:Surgical Flaps; D014093:Tooth, Artificial; D019415:Torque; D016896:Treatment Outcome
D003722:Dental Alloys; D015921:Dental Implants