Evidence about biological and technical complications regarding tilted versus straight implants supporting fixed dental prostheses

MEDLINE, Embase, and Web of Science for English studies published until December 2017 using a controlled vocabulary (MeSH, Emtree) with no time restrictions were searched. The system for

information on Grey literature in Europe (SIGLE), a manual search of all issues since 2000 of several implant-related journals, and reference list of all included studies were additionally

surveyed by two reviewers in duplicate.

Two reviewers assessed papers for eligibility by title and abstract and then by full text in duplicate. Disagreements were solved by a discussion with a third reviewer where agreement was

almost perfect (κ = 0.91). Randomized (RCTs) and non-randomized clinical studies with a minimum follow-up of 3 years and minimum sample size of 20 patients reporting on biological,

prosthetic complications, and patient-related outcome measures (PROMs) were eligible. The primary outcome was the biological complication of implant failure and the main secondary outcome

was peri-implant marginal bone loss (MBL).

No RCTs were found and eligible Non RCTs were assessed for risk of bias using ROBINS-I Tool. Implant failure and peri-implant MBL measured radiographically in mm were assessed between the

two groups using relative risk and mean difference respectively with 95% confidence interval. Meta-analysis was conducted using a random effects model with Paule-Mandle estimator as wide

variation of true effects was expected. Additional subgroup and sensitivity analyses were performed as well as rating the quality of meta-evidence using GRADE approach.

17 non-randomized studies (8 prospective and 9 retrospective) including a total of 7568 implants were included. Meta-analysis showed no difference in implant failure in 8 studies (RR = 0.95;

95% CI = 0.7 to 1.28; p = 0.74). Also, no significant difference was found in MBL in 16 studies (MD = 0.03 mm; 95% CI = −0.03 to 0.10 mm; p = 0.32).

Considering the serious risk of bias of included studies, heterogeneity, and lack of randomized controlled clinical studies, the placement of tilted implants showed no added risk of failure

or increased MBL compared to straight implants.

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