Interventions for replacing missing teeth: 1- versus 2-stage implant placement

Dental implants can be successful either if placed through the oral mucosa, sticking through the gums (1-stage procedure) or if completely buried under the soft tissues (2-stage procedure) to heal load-free for a few months. However, one additional minor surgical intervention is needed, if a 2-stage procedure is used, to allow the connection of the buried implants with the transgingival component which will hold the prosthesis in place.
The review found some evidence from five studies with 239 patients that 1- or 2-stage implant placement may have similar outcomes, though in patients with no teeth trends suggested more implant failures for those implants sticking through the gum. More research is needed to answer this question in a definitive way, but it appears possible to place dental implants following a 1-stage procedure (i.e. the implants are sticking through the gums during the bone healing period). The advantages of the 1-stage procedure are: (1) one minor surgical intervention can be avoided, and (2) the treatment time can be shortened, since it is not needed to wait for the healing/stabilization of the soft tissues after the second surgical intervention. Nevertheless there are situations when a 2-stage procedure could be preferable, for instance when a not optimal implant stability is achieved at implant placement or when there is the risk that the provisional denture transmits excessive forces to the portion of the implants sticking through the gums.

Authors' conclusions: 

The number of patients included in the trials was too small to draw definitive conclusions. The 1-stage approach might be preferable in partially edentulous patients since it avoids one surgical intervention and shortens treatment times, while a 2-stage submerged approach could be indicated when an implant has not obtained an optimal primary stability or when barriers are used for guided tissue regeneration, or when it is expected that removable temporary prostheses could transmit excessive forces on the penetrating abutments especially in fully edentulous patients.

Read the full abstract...

Implants may be placed penetrating the oral mucosa (1-stage procedure) or can be completely buried under the oral mucosa (2-stage procedure) during the healing phase of the bone at the implant surface. With a 2-stage procedure the risk of having unwanted loading onto the implants is minimized, but a second minor surgical intervention is needed to connect the healing abutments and more time is needed prior to start the prosthetic phase because of the wound-healing period required in relation to the second surgical intervention.


To evaluate whether a 1-stage implant placement procedure is as effective as a 2-stage procedure.

Search strategy: 

The Cochrane Oral Health Group's Trials Register, CENTRAL, MEDLINE and EMBASE were searched. Handsearching included several dental journals. Authors of all identified trials, an Internet discussion group and 55 dental implant manufacturers were contacted to find unpublished randomised controlled trials (RCTs). The last electronic search was conducted on 21 January 2009.

Selection criteria: 

All RCTs of osseointegrated dental implants comparing the same dental implants placed according to 1- versus 2-stage procedures with a minimum follow up of 6 months after loading. Outcome measures were: prosthesis failures, implant failures, marginal bone level changes on intraoral radiographs, patient preference including aesthetics, aesthetics evaluated by dentists, and complications.

Data collection and analysis: 

Screening of eligible studies, assessment of the methodological quality of the trials and data extraction were conducted in duplicate and independently by two review authors. Authors were contacted for missing information. Results were expressed as random-effects models using mean differences for continuous outcomes and risk ratios for dichotomous outcomes with 95% confidence intervals.

Main results: 

Five RCTs were identified and included reporting data on 239 patients in total. On a patient, rather than per implant basis, the meta-analyses showed no statistically significant differences for prosthesis and implant failures, though trends, especially in fully edentulous patients, favoured 2-stage (submerged) implants.