Severe posterior maxillary atrophy remains one of the most demanding scenarios in implant surgery. When residual bone height drops to 4 mm or less, lateral window sinus augmentation becomes not just an option but a necessity — and the choice of grafting material directly influences the quality and quantity of the regenerated bone.

This prospective histomorphometric study from a Vietnamese cohort addressed a straightforward but clinically critical question: what kind of bone does a composite graft made of corticocancellous allograft, synthetic β-TCP/HA substitute (30/70 ratio, Osteon II), and autologous platelet-rich fibrin actually produce after six months of healing?

Sixty biopsy specimens were harvested at implant placement from sinus augmentation sites with a mean residual bone height of just 2.31 ± 0.93 mm. Histomorphometric analysis was performed on three non-consecutive histological sections per specimen using ImageJ, providing a standardized and reproducible quantitative framework.

The results are reassuring. Newly formed bone averaged 31.28% (95% CI: 26.70–35.85%), with residual graft material accounting for 15.48% — a proportion suggesting meaningful resorption and active substitution rather than passive scaffold persistence. Connective tissue represented 53.23%, a figure consistent with the intermediate remodeling phase typical at six months. Critically, no inflammatory infiltrates or necrotic tissue were observed. The histological architecture was well-organized: lamellar bone with Haversian canals and osteocytes housed within lacunae, alongside active osteoblastic and osteoclastic fronts at the graft periphery — the hallmarks of ongoing, healthy remodeling.

From a clinical stability standpoint, primary implant stability (ISQ1) averaged 58.20 ± 6.47 and rose substantially to 74.85 ± 7.68 at six months (ISQ2). The correlation analyses are particularly informative: ISQ1 correlated strongly with residual bone height (r = 0.626) and inversely with connective tissue proportion (r = −0.627), and moderately with newly formed bone (r = 0.405). In practical terms, this confirms what experienced clinicians already suspect — the native bone still present at surgery is the primary mechanical anchor, while the quality of bone regeneration progressively takes over as the determinant of long-term stability.

The take-home message for the implant surgeon is clear: this composite protocol delivers histologically mature, biocompatible bone in severely atrophic sinuses, with a resorption-substitution dynamic that supports implant osseointegration. The PRF component likely contributes growth factor enrichment and improved scaffold handling, though its isolated effect cannot be quantified in the absence of a control group — a limitation the authors openly acknowledge.

This is a single-arm descriptive study. It does not tell us whether this graft combination outperforms alternatives. What it does tell us, with histological precision and a clinically relevant sample size, is that the regenerated environment is biologically sound and functionally adequate for implant placement in one of the most challenging anatomical conditions we routinely face.