Aesthetics, preparation taper and post-endodontic restoration

Correct answer: C. Lithium disilicate

• A. Monolithic zirconia is very strong but comparatively opaque. Newer high-translucency formulations have narrowed the gap without closing it.
• B. Gold has excellent mechanical properties and biocompatibility but is obviously unacceptable aesthetically in the anterior region.
• C. Correct. Lithium disilicate combines high translucency with adequate strength for the anterior region, and its optical behaviour closely mimics natural enamel.
• D. Porcelain fused to metal is limited by the opaque metal substructure, which blocks light transmission and can produce a grey line at the margin as the gingiva recedes.

Correct answer: D. Aesthetics

• A. Retention falls sharply as taper increases; the near-parallel walls are what resist removal along the path of insertion.
• B. Resistance form also suffers. A tapered preparation offers less opposition to obliquely directed forces that would tip the restoration off.
• C. Excessive taper worsens marginal fit and increases the cement film thickness at the margin.
• D. Correct — this is the exception. Aesthetics is governed by the material, the margin design and the space available for porcelain, not by the convergence angle of the axial walls.

Note: The accepted optimum is about 6 to 10 degrees of total convergence. Too little taper risks undercuts and difficulty seating.

Correct answer: A. Core build-up and a full-coverage crown, without a post

• A. Correct. With the coronal walls intact, there is ample structure to retain a core. A post would only remove sound dentine and raise the risk of root fracture, while cuspal coverage protects a tooth that has lost its proprioceptive feedback and much of its moisture.
• B. A post is indicated only when insufficient coronal tooth structure remains to retain the core. It adds no strength to the root — it is purely a retentive device.
• C. An inlay does not provide cuspal coverage, so it leaves an endodontically treated posterior tooth vulnerable to fracture.
• D. Glass ionomer alone is far too weak to withstand occlusal load on a root-treated tooth in the long term.

Note: Anterior teeth with conservative access and intact walls can often be restored with composite alone — the crown-for-everything rule applies mainly to posterior teeth.