Which bone quality is LEAST favourable for implant placement?

Correct answer: A. Type IV

• A. CORRECT. TYPE IV bone — a thin cortical shell surrounding a core of very low-density trabecular bone — carries the highest failure rate. It provides poor primary stability at placement, which is the single strongest predictor of successful osseointegration. It is found most often in the POSTERIOR MAXILLA. It is managed with undersized osteotomy preparation, osteotome bone condensation, wider or roughened-surface implants, and a longer unloaded healing period.
• B. Type III has a thin cortex with dense trabecular bone and is also favourable, though slightly less so than Type II.
• C. Type II — a thick cortical layer around dense trabecular bone — is the IDEAL. It combines good stability with good blood supply.
• D. Type I is almost entirely dense homogeneous cortical bone, typical of the ANTERIOR MANDIBLE. It gives excellent primary stability but is poorly vascularised and prone to overheating during preparation, which risks necrosis. Copious irrigation and sharp drills are essential.

Note: The Lekholm and Zarb classification maps roughly onto anatomy: anterior mandible tends to Type I–II, posterior mandible Type II–III, anterior maxilla Type II–III, posterior maxilla Type III–IV. Which is why the posterior maxilla is the site most likely to need sinus augmentation and staged loading.