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

Eur J Oral Implantol. Summer 2013;6(2):121-31.


Purpose: 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.

Materials and 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.

Publication types

  • Comparative Study
  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Alveolar Bone Loss / etiology
  • Biomechanical Phenomena
  • Dental Alloys / chemistry
  • Dental Implant-Abutment Design
  • Dental Implants*
  • Dental Prosthesis, Implant-Supported*
  • Dental Restoration Failure
  • Denture Design*
  • Denture Repair
  • Denture Retention
  • Denture, Complete, Lower
  • Female
  • Follow-Up Studies
  • Humans
  • Immediate Dental Implant Loading / methods*
  • Jaw, Edentulous / rehabilitation
  • Jaw, Edentulous / surgery
  • Male
  • Mandible / pathology
  • Mandible / surgery*
  • Middle Aged
  • Pilot Projects
  • Postoperative Complications
  • Surgical Flaps
  • Tooth, Artificial
  • Torque
  • Treatment Outcome


  • Dental Alloys
  • Dental Implants