The purpose of this meta-analysis was to compare implant survival, marginal bone loss, and complications between immediate and conventional loading of single implants installed in the posterior mandible. An extensive electronic search was performed of PubMed, Web of Science, and the Cochrane Central Register of Controlled Trials to identify relevant articles published up to January 2015. After the selection process, five studies met the eligibility criteria and were included. The results of the meta-analysis were expressed in terms of the odds ratio (OR) or standardized mean difference (SMD), with a confidence interval (CI) of 95%. Results were pooled according to heterogeneity using the fixed- or random-effects model. There was no statistically significant difference between the two techniques (immediate loading vs. conventional loading) with regard to implant survival (OR 1.71, 95% CI 0.40 to 7.36; P = 0.47). There was no statistically significant difference in marginal bone loss (SMD −0.58, 95% CI −1.55 to 0.38; P = 0.24). The reported mechanical and biological complications were common to both types of intervention, with the exception of probing depth, which was greater following the immediate loading technique (SMD 0.13, 95% CI −0.19 to 0.44), although this was not statistically significant ( P = 0.43).
The replacement of teeth by means of single implants is a predictable treatment with a high success rate. Historically, the recommended implant installation protocol has been a two-stage surgery, with the sinking of the implants followed by a healing period free of mechanical load of 3 months for the mandible and 6 months for the maxilla. However, with the growing demand for less invasive and faster procedures that optimize aesthetic requirements, single-stage surgery with immediate prosthetic loading (immediate loading) has been adopted.
Immediate loading can be defined as the installation of the prosthetic crown on the implant within 1 week of surgery. The single-stage installation of implants can also be classified as functional or non-functional, depending on the occlusal contact with the opposite arch. The first immediate loading protocol was performed to treat edentulous patients through four splinted implants placed in the mandible. The advantages of single-stage implant installation and the constant development of the implants and surgical techniques have encouraged further research into immediate loading of single implants in various regions of the mouth, with high rates of success and survival.
The main criterion for performing immediate loading of single implants is primary stability. The parameters used to evaluate the initial stability of the implant are usually insertion torque, measured in Newton-centimetres (N cm), and the implant stability quotient (ISQ), measured by resonance frequency analysis (RFA). A low initial stability necessitates long-term osteogenesis and therefore a greater healing period. Moreover, a lack of contact between the bone and the implant increases the risk of micro-movements, which decreases success rates. The incidence of high masticatory forces in the posterior mandible discourages many clinicians from conducting immediate prosthetic loading in this region. Additionally, few clinical trials have evaluated the performance of a single posterior implant after immediate prosthetic loading.
Thus, the purpose of this meta-analysis was to compare implant survival, marginal bone loss, and complications in immediate and conventional loading of single implants installed in the posterior mandible.
Materials and methods
The methodology of this study was adapted from the PRISMA statement (Preferred Reporting Items for Systematic Reviews and Meta-Analyses). Clinical questions were broken down and organized using the PICO strategy, as proposed by evidence-based practice.
The purpose of the present review was to test the null hypothesis of no difference in the implant survival rate, marginal bone loss, and complications in subjects who have received immediate or conventional loading of single implants installed in the posterior mandible.
What are the clinical outcomes of single implants placed in the partially edentulous posterior mandible between subjects who have received an immediate restoration and those who have received a late restoration in relation to the implant survival rate, marginal bone loss, and frequency of complications?
An extensive electronic search, with no date or language restriction, was performed in PubMed, Web of Science, and the Cochrane Central Register of Controlled Trials, up to January 2015. The search strategy and the PICO tool are shown in Table 1 . In addition, reference lists of potential studies for inclusion in the meta-analysis were explored for more studies.
|Population||#1||(partially edentulous mandible[MeSH] OR partially edentulous implant[MeSH] OR edentulous mandible[MeSH] OR edentulous posterior mandible[MeSH])|
|Intervention||#2||(implant*[all fields] OR dental implant surgery[MeSH] OR mandibular implant[MeSH] OR single implant[MeSH] OR single implant crown[MeSH] OR submerged implant[MeSH] OR non-submerged implants[MeSH] OR immediate loading[MeSH] OR immediate single implant[MeSH] OR immediate loading single tooth[MeSH] OR delayed load implants[MeSH] OR conventional loading implants[MeSH])|
|Comparisons||#3||(immediate loading single implants[MeSH] OR conventional loading single implants[MeSH])|
|Outcomes||#4||(survival*[all fields] OR implant survival[MeSH] OR dental implant survival[MeSH] OR marginal bone loss[MeSH] OR implant bone resorption[MeSH] OR dental implant bone loss[MeSH] OR complication*[all fields] dental implant complication[MeSH] OR postoperative complications[MeSH] OR randomized controlled trial[MeSH])|
|Search combination||#1 AND #2 AND #3 AND #4|
|Electronic databases||MEDLINE/PubMed, Web of Science, and Cochrane Central Register of Controlled Trials|
This review sought randomized controlled trials (RCTs). Clinical studies in humans with at least 12 months of follow-up data, studies involving single implants placed in the posterior mandible, and studies comparing immediate versus conventional prosthetic loading were included. Studies involving animals, patients with decompensated metabolic diseases that could affect bone turnover, periodontal patients without prior treatment, and non-randomized clinical studies were excluded.
Both authors/reviewers (V.M.F. and E.P.B.) performed the search and selection process. First, titles and abstracts were analyzed. Next, full papers were read carefully and analyzed according to the eligibility criteria (inclusion/exclusion) for data extraction. Differences between the reviewers were resolved through detailed discussion. Concordance between the two reviewers in relation to the search was assessed by Cohen’s kappa test ( κ ). The authors of the studies were contacted by e-mail for any clarification when necessary.
The quality analysis was performed independently by both authors/reviewers using the Cochrane Collaboration tool for assessing risk of bias in RCTs. The quality analysis of each study was based on four criteria: sequence generation (random selection in the population), allocation concealment (steps must be taken for strict implementation of the schedule of random assignments by preventing foreknowledge of the forthcoming allocations), incomplete outcome data (clear explanation of withdrawals and exclusions), and blinding (measures to blind study participants and personnel from knowledge of which intervention a participant received). In addition, an analysis of conflicts of interest was performed by reviewing the acknowledgments and disclosures of each study, as proposed by Friedman and Richter.
The following parameters were extracted from the studies: loading protocol, follow-up period, number of subjects, gender of subjects, age of subjects, intraoral region, number of drop-outs, number of implants placed, implant system, implant length and diameter, healing period, number of smokers, primary stability of implants, type of occlusal contact, implant survival, mean marginal bone loss, and implants placed in fresh extraction sockets.
For this meta-analysis, the prosthetic loading protocol for the implants was classified as follows : (1) immediate loading: prostheses connected to the implant within 1 week of implant installation; (2) conventional loading: prostheses connected to the implant more than 2 months after implant installation.
Binary and continuous variables of the RCTs were analyzed by meta-analysis when at least two studies evaluated the same data type. For binary outcomes (e.g. implant survival), the estimation of the intervention effect was expressed as the odds ratio (OR) with a confidence interval (CI) of 95%. For continuous outcomes (e.g. marginal bone loss), the mean and standard deviation (SD) were used to calculate the standardized mean difference (SMD) with a 95% CI. The results were pooled using the fixed-effects model (Mantel–Haenszel–Peto test) or the random-effects model (DerSimonian–Laird test). The I 2 statistical test was used to express the heterogeneity of the studies as a percentage value. Values up to 25% were classified as indicating low heterogeneity, values of 50% as indicating medium heterogeneity, and values of ≥70% as indicating high heterogeneity. When significant heterogeneity was found ( P < 0.10), the random-effects model was used. For a low heterogeneity value, the fixed-effects model was used. The level of statistical significance was set at P < 0.05.
Publication bias was explored graphically through a funnel plot. Asymmetry of the funnel plot may indicate possible publication bias.
The data were analyzed using the statistical software Review Manager version 5.2.8 (The Nordic Cochrane Centre, The Cochrane Collaboration, Copenhagen, Denmark; 2014).
The initial search yielded 1282 titles in Medline/PubMed, 70 in the Cochrane Central Register of Controlled Trials, and 381 in Web of Science. After the initial evaluation, 32 studies were selected. After careful reading, 27 studies were excluded because they did not fit the eligibility criteria of this review. Thus, five studies published between 2008 and 2014 were included in this review. The selection process and the reasons for the exclusion of studies are presented in Fig. 1 .
The κ agreement coefficient between the reviewers for the inclusion of potential studies (titles and abstracts) was 0.97 and for study selection was 0.85. This demonstrates ‘almost perfect’ agreement according to the criteria proposed by Landis and Koch.
The characteristics of the studies included are shown in Table 2 . In the five RCTs selected for the meta-analysis, a total of 286 implants were installed. The number of participants in the studies ranged from 12 to 71, and totalled 177. The age range of the participants was 20–75 years. Only two studies reported the number of smokers. The follow-up period in the studies ranged from 12 to 60 months, with a mean of 31.2 months.
|Authors (year)||Loading protocol||Follow-up period, months||No. of subjects||Gender||Age range (mean age), years||Region||No. of drop-outs||No. of implants
|Implant size (diameter × length, mm)|
|Güncü et al. (2008)||Conventional||12||12||4 M/8 F||30–55 (41)||Molar||0||12||4 × 11.5|
|Schincaglia et al. (2008)||Conventional||12||15||5 M/10 F||35–68 (49.2)||Molar||0||15||5 × 8.5, 10, 11.5|
|Immediate||15||4 M/11 F||31–75 (51.8)||Molar||0||15|
|Prosper et al. (2010)||Conventional||60||71||35 M/36 F||26–72 (58.3)||Molar||0||60||6.5, 7.5 × 9, 11, 13|
|Meloni et al. (2012)||Conventional||12||20||8 M/12 F||28–70 (46)||Molar||0||20||4.3, 5 × 8, 10|
|Kokovic et al. (2014)||Conventional||60||12||3 M/9 F||20–62 (49)||Molar, premolar||0||36||4.1, 4.8 × 8, 10|
|Healing period (delayed group)||Smokers||Primary stability||Occlusal contact (immediate group)||Implant survival rate (No. of failures)||Marginal bone loss, mm (mean ± SD)||Fresh extraction sockets|
|Insertion torque, N cm||ISQ|
|3 months||0||NR||≥65||Yes||100% (0)||0.68 ± 0.3||No|
|0||≥65||91.7% (1)||0.45 ± 0.39|
|3–4 months||2||≥20||NR||Yes||100% (0)||1.2 ± 0.55||No|
|1||≥20||93.3% (1)||0.77 ± 0.38|
|3 months||NR||NR||NR||Yes||96.6% (2)||1.01 ± 0.59||Yes|
|NR||NR||NR||96.6% (2)||1.31 ± 0.44|
|3–5 months||NR||≥35||NR||No||100% (0)||0.86 ± 0.16||No|
|NR||≥35||NR||100% (0)||0.83 ± 0.16|
|6 weeks||NR||NR||≥60||Yes||100% (0)||0.8 ± 0.19||No|
|NR||NR||≥60||100% (0)||0.4 ± 0.24|