Abstract
Literature regarding the outcome of maxillary sinus floor elevation to create sufficient bone fraction to enable implant placement was systematically reviewed. Bone fraction and implant survival rate were assessed to determine whether grafting material or applied growth factor affected bone fraction. Trials where sinus floor elevations with autogenous bone (controls) were compared with autogenous bone combined with growth factors or bone substitutes, or solely with bone substitutes (test groups) were identified; 12 of 1124 fulfilled all inclusion criteria. Meta-analyses comparing the bone fraction after applying: autogenous bone; autologous bone with growth factors (platelet rich plasma); or autogenous bone and bone substitutes (bovine hydroxyapatite, bioactive glass, corticocancellous pig bone) revealed no significant differences in bone formation after 5 months. A significantly higher bone fraction was found in the autogenous bone group compared to the sole use of β-tricalciumphosphate ( P = 0.036). The one-year overall implant survival rate showed no significant difference between implants. Bone substitutes combined with autogenous bone provide a reliable alternative for autogenous bone as sole grafting material to reconstruct maxillary sinus bony deficiencies, for supporting dental implants after 5 months. Adding growth factors (platelet rich plasma) to grafting material and the sole use of β-tricalciumphosphate did not promote bone formation.
Application of dental implants to support prosthetic constructions has evolved into a viable alternative to conventional prosthetic procedures. Implant procedures in the posterior maxilla often pose a problem due to insufficient pre-existing bone fraction . This is not restricted to edentulous patients, but is also often observed in partially dentate patients needing an implant-based prosthodontic reconstruction in the posterior region of the maxilla. The problem of an insufficient level of bone to allow for reliable primary placement of implants can be solved by a maxillary sinus floor elevation procedure using autogenous bone, bone substitutes or a mixture of autogenous bone and bone substitutes as grafting materials. Augmentation of the maxillary sinus floor with an autogenous bone graft, introduced by B oyne & J ames and T atum , is a commonly used method for increasing vertical bone height for insertion of dental implants.
During the maxillary sinus floor elevation procedure, the space created between the residual maxillary ridge and the elevated Schneiderian membrane is usually filled with grafting material . In this way, a bone fraction is created that may allow for reliable implant placement, either simultaneously with the elevation procedure when the residual ridge allows for primary implant stability or as a second stage after healing of the grafted site .
For sinus floor augmentation, autogenous bone is the most commonly used material and is still considered the gold standard , although numerous alternative materials have been used with variable results. Recent studies have demonstrated that the mere lifting of the sinus mucosal lining and simultaneous placement of implants also can result in bone formation without the use of a grafting material . Currently, this technique only is applied for conditions allowing for sufficient primary stability of implants during placement and a sufficient width of the alveolar crest but not for reconstruction in horizontal and vertical directions.
Autogenous bone grafts are the most widely used . Autografts are popular because they have osteogenic, osteoinductive, osteoconductive properties, a high number of viable cells and are rich in growth factors. The viable cells consist of osteoblasts, undifferentiated mesenchymal cells, monocytes and osteoclast precursor cells. These cells participate in the remodelling and formation of the new bone . Alternatives such as bone substitutes do not provide the cellular elements necessary for osteogenesis and are only osteoconductive . These alternatives are synthetic or most organic material has been removed from the substitute material during the fabrication process.
Donor site morbidity is a problem associated with bone-harvesting techniques, which can be reduced or avoided when using bone substitutes . Whether autogenous bone should still be considered as the grafting material of choice can be questioned. Can autogenous bone be (partially) replaced by bone-substitutes? The length of healing time required before placing implants in a site grafted with a bone substitute remains unclear (usually a site reconstructed with a bone substitute requires longer before implant placement than a site reconstructed with autogenous bone). Also, whether a bone substitute can be applied solely or always has to be combined with autogenous bone remains unclear. Clinicians are keen to speed up healing, and the effect of using platelet rich plasma (PRP) has been studied for its presumed effect of speeding up bone regeneration. It has been speculated that growth factors that are present in PRP could enhance healing of the grafts and might counteract resorption after augmentation .
The effect of maxillary sinus floor elevation on the survival of endosseous dental implants has been reviewed systematically in general terms in the past , but a detailed analysis of the efficacy of using an autogenous bone graft compared with bone substitutes and bone growth factors on bone formation and implants was not carried out. The authors of the reviews discussed solely autogenous bone or only bone substitutes, but did not compare the treatment outcome of various grafting materials with autogenous bone serving as a control. Retrospective studies, case reports, prospective and cohort studies were included in the reviews mentioned above, so the conclusions of the reviews were not based on the most reliable type of clinical studies. The consensus of the sixth European workshop on periodontology emphasized the research need to answer comparative questions to establish the clinical benefit of bone augmentation with respect to alternative treatments and to compare different treatments in terms of, amongst others, effectiveness, adverse effects and morbidity. In a recent Cochrane review, E sposito et al. discussed the effectiveness of sinus lift procedures for dental implant rehabilitation. No statistically significant difference was observed for any of the interventions evaluated. Conclusions are based on a few trials, usually underpowered, with short follow-up periods, and often judged to be at high risk of bias, therefore they should be viewed as preliminary and interpreted with caution. Analysis of the efficacy of using an autogenous bone graft compared with bone substitutes and bone growth factors on bone formation and implant survival was not studied.
The aim of this study was systematically to review the literature regarding the treatment outcome of residual maxillary ridges needing maxillary sinus floor elevation surgery to create sufficient bone fraction for reliable implant placement in humans. The objectives of this systematic review were to assess the bone fraction and implant survival rate and to determine whether the bone fraction is affected by the grafting material or growth factor applied.
Material and methods
For this review, a thorough search of the literature was conducted in the electronic databases MEDLINE (1979–September 2010, via PUBMED) and EMBASE (1987–September 2010). Studies in which patients were treated with a maxillary sinus floor elevation with autogenous bone as a control group were searched. Three types of intervention were considered: solely bone substitutes; autogenous bone in combination with bone substitutes; and autogenous bone in combination with growth factors. Outcome measures were bone fraction after healing period and implant survival.
The search strategy used was a combination of MeSH terms and free text words; ‘Maxilllary sinus lift’[Mesh] OR (sinus augmentation) OR (sinus floor elevation) OR (maxillary sinus lift) OR (sinus graft) AND ‘Dental Prosthesis, Implant-Supported’[Mesh] OR ‘Implants, Experimental’[Mesh] OR ‘Prostheses and Implants’[Mesh] OR ‘Dental Implants’[Mesh] OR ‘Dental Implantation, Endosseous’[Mesh] OR ‘Dental Abutments’[Mesh] OR (alveolar atrophy) OR (implant*) OR (dental implant*) OR (oral implant*) AND (Humans[Mesh]). No language restrictions were applied.
The references of each relevant review and eligible study were checked. The titles and abstracts of the searches were assessed independently by two examiners. Full text documents were obtained for possibly relevant articles. Manual searches of the bibliographies of all full text articles and related reviews selected from the electronic search were also performed and completed the review.
Longitudinal studies (randomized controlled trials, cohort studies) were considered for evaluation. Patients with maxillary atrophy, who had undergone a maxillary sinus lift, were included. Only studies in which autogenous bone was used as a control group were chosen as autogenous bone is considered the gold standard and is considered to be accompanied by the highest level of bone growth, at least during the first months after grafting. Including an autogenous bone group as a control also better allows for comparison of the various studies. There were three types of intervention: solely bone substitutes; autogenous bone in combination with bone substitutes; autogenous bone in combination with growth-factors. Outcome measures were bone fraction after the healing period and implant survival after at least 1-year follow-up in patients with alveolar atrophy treated with a sinus lift procedure. This sinus lift was performed with autogenous bone alone (control group) compared to autogenous bone in combination with growth factors or bone substitutes, or solely with bone substitutes (test groups). Retrospective studies, studies with an inadequate study design, or an unclear intervention, case series, technical reports and reviews were excluded. Articles that were not topic related, with no full texts were excluded. Language was not restricted.
Two reviewers independently assessed the methodological quality using the forms ‘quality assessment of a cohort study’ and ‘quality assessment of a randomized clinical trial’ developed by the Dutch Cochrane Centre, a centre of the Cochrane Collaboration ( www.cochrane.nl ). These two validity tools consist of eight and nine items, respectively, which have to be scored with a plus, minus or a question mark. It was decided that studies scoring four or more plusses were considered methodologically acceptable. The two observers independently generated a score for the included articles. No blinding for author, institute or journal was performed. The main items of quality assessment were: Was the study randomized and the randomization procedure clearly stated? How good was the allocation concealment? Was a clear description of study group, inclusion and exclusion criteria, intervention and outcomes given? Was a clear description of withdrawals and drop outs given? Disagreements on validity assessment were resolved by discussion.
For each study the following data were extracted and recorded on a data sheet: study design (randomized controlled trial or prospective cohort study); treatment (control versus test); number of patients; type of patient (edentulous or not); details of type of intervention; number of sinus floor elevations and implants placed; details of the outcomes (new bone formation) and implant survival; follow-up time.
Statistical analysis
With respect to the quality assessment, agreement between the two reviewers regarding eligible studies was expressed using Cohen’s unweighted kappa. Failure rates were calculated by dividing the number of events (failures or complications) in the numerator by the total exposure time (implant time) in the denominator. The numerator was in all cases extracted directly from the publication or was provided by the authors of the original papers in cases in which only a part of the full sample was taken into consideration. The exposure time was extracted and calculated by multiplying the mean follow-up time by the number of implants available in the given statistical analysis. The mean follow-up was directly extracted from the articles. For each study, event rates for implants were calculated by dividing the total number of events by the implants’ exposure time in years.
A meta-analysis was carried out for evaluating bone fraction. Random effect models were created and a standardized weighted mean difference was used to evaluate bone fraction. Meta-analysis was performed using the statistical software package ‘Meta-analysis’ (Comprehensive Meta-analysis Version 2.2, Biostat, Englewood NJ, USA (2005), www.meta-analysis.com ).
Results
The search in MEDLINE and EMBASE provided 1124 articles reporting maxillary sinus floor elevation in combination with dental implant placement. Fig. 1 outlines the study selection procedure. Articles which were not topic related, with no full texts were excluded. Also studies with an improper study design or an unclear intervention, case series, technical reports and reviews were excluded ( n = 1085). The κ -value for inter-reviewer agreement on the methodological appraisal was 0.85. Disagreement was generally caused by slight differences in interpretation and was easily resolved in a consensus discussion.
39 articles were selected for full-text analysis. Of these, 27 further articles had to be excluded because they did not satisfy the inclusion criteria (see the appendix available online). These articles were excluded because of inadequate study design (not longitudinal, not prospective or unclear description of randomization), for not executing histomorphometric analysis or for not including autogenous bone as a control group (details of the excluded studies are given in the online appendix). Authors who did not describe randomization clearly were contacted via e-mail for additional information. When a proper randomization procedure was applied, these studies were added to the results .
The 12 articles that fulfilled the inclusion criteria were randomized clinical trials and had applied a split mouth design. There were considerable differences in the selected articles regarding the number of patients, residual bone height, graft materials used, whether implants were placed or not and follow-up. There were some differences in data reporting and in inclusion and exclusion criteria in the studies.
Description of studies
In all eligible maxillary sinus floor elevation studies autogenous bone was used as a control group. The three types of intervention were: solely bone substitutes; autogenous bone in combination with bone substitutes; autogenous bone in combination with growth-factors. Outcome measures were bone fraction after healing period and implant survival.
In the studies included, patients had been treated with autogenous bone, autogenous bone in combination with bone substitutes or PRP ( Table 1 ). In 5 of the 12 studies, the patients were edentulous, in the others edentulous and dentate patients were treated. In five publications the number of implants placed, the implant survival rate and follow-up was mentioned. To determine an overall survival rate, a comprehensive meta-analysis of these five studies was performed ( Table 2 ).
