Peri-implant bone loss: abutment height matters in screw-retained cases

Clinical question. Studies on abutment height and peri-implant marginal bone loss (MBL) contradict each other. The authors propose that the contradiction is not in the biology but in the way the evidence has been pooled: trials with screw-retained and cement-retained restorations have been analysed together, when mechanically they are not the same situation.

Methodology. This is a critical review rather than new primary data. The authors reclassified the studies included in four recent systematic reviews according to retention type, and read the resulting picture against the mechanical behaviour of each configuration.

Findings. In screw-retained restorations, micromovement at the abutment-crown interface is mechanically unavoidable, and abutment height governs how close that mobile interface sits to the crestal bone. Once the studies are re-sorted, the familiar association holds specifically here: shorter abutments are linked to greater MBL, and taller abutments consistently show more favourable outcomes. In cement-retained restorations the abutment and crown are bonded into a single complex, interface micromovement is substantially reduced, and abutment height loses its mechanical relevance. What emerges as the primary determinant there is the geometry of the transmucosal profile — specifically the contour angle within the 2 mm zone adjacent to the bone crest. Profile angles below roughly 20°, with concave or straight contours, have been associated with favourable peri-implant outcomes; the authors present this figure as a pragmatic clinical target, not an absolute threshold.

Clinical relevance. The practical message is that prosthetic strategy should follow the retention type. Where the restoration is screw-retained, prioritise a taller abutment and keep the mobile interface away from the crest. Where it is cement-retained, abutment height is the wrong lever to pull: the attention belongs on the emergence contour in the first 2 mm, kept straight or concave and shallow. The limits of the design should stay in view — this is a post hoc reclassification of existing literature, not a trial designed to test the hypothesis, and the 20° figure is a target drawn from associations rather than a validated cut-off.