“I Want Teeth That Don't Come Out”

Correct answer: B. An implant-supported FIXED prosthesis

• A. An implant-RETAINED removable prosthesis still comes out, which is precisely what she has rejected. It is the compromise for a patient with inadequate bone, limited finances or poor dexterity — none of which apply.
• B. CORRECT. The chief complaint is explicit and it is the governing constraint: she wants a FIXED result. She has adequate bone, sound remaining teeth, good general health and the means to proceed — every prerequisite is satisfied. An implant-supported fixed prosthesis meets the stated goal, preserves the remaining teeth by avoiding their preparation, and maintains alveolar bone through functional loading.
• C. A better-made removable denture is still removable. Making a superior version of the appliance the patient has explicitly rejected does not address the complaint.
• D. The edentulous spans are extensive and multiple. Conventional bridgework across them would violate Ante's law, require preparation of sound teeth, and produce excessive leverage on the abutments.

Note: The teaching point of this item is that the CHIEF COMPLAINT frames the treatment plan. Where a patient states a clear goal and the clinical situation permits it, the plan that ignores the goal is wrong however technically sound it may be.

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.

Correct answer: B. About 6 degrees

• A. 20 degrees is a common real-world value but represents a substantial loss of retention compared with the ideal.
• B. CORRECT. Approximately 6 DEGREES of TOTAL convergence — that is, about 3 degrees per wall — is the classical ideal. Retention falls sharply as taper increases, because the resistance to displacement along the path of insertion depends on near-parallel opposing walls. Clinically achieved tapers are commonly 12–20 degrees; the accepted practical range is about 6–10 degrees.
• C. 2 degrees is too little. Walls that near-parallel risk UNDERCUTS, which prevent the restoration seating at all, and they trap hydraulic pressure during cementation.
• D. 30 degrees provides very poor retention and resistance form and would require auxiliary features such as grooves and boxes to compensate.

Note: Retention and resistance also depend on axial wall HEIGHT (more is better), the surface AREA of the preparation, surface roughness and the cement used. Where wall height is limited, add proximal grooves or boxes rather than accepting excessive taper.

Correct answer: D. Zinc

• A. Methylcellulose and carboxymethylcellulose are the standard adhesive polymers and are inert.
• B. Copper is the mineral that becomes DEFICIENT as a consequence — it is not an adhesive ingredient.
• C. Glycerin is a humectant and carrier with no neurotoxicity.
• D. CORRECT. ZINC. Some denture adhesives contained zinc salts to improve adhesion, and patients who used very large quantities daily over long periods absorbed enough zinc to cause the problem. Excess zinc interferes with COPPER absorption, and the resulting copper deficiency produces a MYELONEUROPATHY: sensory ataxia, paraesthesia, limb weakness and gait disturbance, sometimes with anaemia and neutropenia. Major manufacturers reformulated to zinc-free products after this was recognised.

Note: The clinical clue is a denture wearer using several tubes of adhesive per week with unexplained neurological symptoms. The underlying issue is nearly always an ill-fitting denture — the correct treatment is to reline or remake the prosthesis, not to switch adhesives.