STATEMENT OF PROBLEM: The mechanical effects of screw modifications, including coating and surface treatment, and the tightening conditions, including lubrication or contamination, on implant prosthetic screws remain unclear. PURPOSE: This systematic review and meta-analysis aimed to evaluate the effects on screw-related mechanical outcomes of screw modifications, including coating and surface treatment, and the tightening conditions, including lubrication or contamination. MATERIAL AND METHODS: A systematic search was conducted in the PubMed, Embase, Scopus, Web of Science, and Cochrane Library databases up to July 2025. In vitro studies assessing screw-related interventions were included. Outcomes were synthesized as weighted mean differences (WMDs) using random-effects meta-analysis. Heterogeneity (Cochrane Q, I²), subgroup and meta-regression analyses, publication bias (Egger, trim-and-fill), and risk of bias were assessed (α=.05). RESULTS: Twenty-six studies were included. Across screw-related interventions, detorque (WMD=0.997 Ncm; P=.011) and preload (WMD=16.072 N; P<.001) increased, while vertical gap and friction were unchanged. Screw coating increased detorque (WMD=1.73 Ncm; P<.001) and preload (WMD=78.59 N; P<.001) and reduced friction (P<.001) but did not affect vertical gap, fracture load, elastic modulus, or hardness. Surface treatment did not affect detorque. Contamination had no overall detorque effect, although blood with or without hemostatic agents reduced it. Lubrication increased preload (WMD=3.963 N; P=.001) without affecting detorque. Heterogeneity was substantial in most analyses. CONCLUSIONS: Selected screw coatings increased detorque and preload and reduced friction, whereas surface treatment had no significant effect. Contamination and lubrication showed protocol- and torque-dependent effects. Substantial heterogeneity limited certainty regarding effect magnitude.
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Khorasani et al. (2026) studied this question.