Asian Journal of Dental Sciences

Horizontal resorption of the posterior alveolar ridge frequently reduces the bone width available for conventional implant placement, and the clinician must then choose between lateral bone augmentation with a standard-diameter implant and placement of a narrow-diameter implant in pristine bone. Posterior single crowns represent the least forgiving expression of this choice, because a solitary reduced-diameter fixture must carry masticatory loads without the mechanical redundancy conferred by splinting. This critical narrative review examines the contemporary evidence on marginal bone loss and implant survival for narrow- and standard-diameter implants supporting posterior single crowns, and evaluates whether the reassuring conclusions of earlier pooled analyses withstand scrutiny. Literature was identified through structured searching of biomedical and multidisciplinary scholarly sources, supplemented by backward and forward citation tracking, with a final search date of 13 July 2026. Evidence was appraised for design appropriateness, comparability of radiographic protocols, follow-up duration, and the fidelity between the populations actually studied and the posterior single-crown indication. The available evidence indicates that implants of 3.3 to 3.5 mm in diameter achieve short- and medium-term survival that is statistically indistinguishable from standard-diameter implants, and that differences in marginal bone loss between diameter groups are small, inconsistent in direction, and frequently below the resolution of intraoral radiography. Confidence in these conclusions is nevertheless constrained by the scarcity of randomised comparisons confined to posterior single crowns, by follow-up rarely exceeding three years in controlled designs, by the dilution of molar sites within premolar-dominated samples, and by a persistent signal of elevated technical complication and late fracture risk that pooled survival estimates conceal. Diameters below 3.0 mm remain inadequately documented for load-bearing posterior single-tooth replacement. The principal unresolved question is not whether narrow-diameter implants survive, but whether the mechanical reserve that remains after physiological bone remodelling is sufficient over the service life expected of a single posterior restoration.