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Prosthodontics & Occlusion · patient case with 3 questions

Bruxist requiring a posterior crown and a splint

Patient: Adult with established parafunction

Chief complaint: Requires a crown; already wears a hard occlusal splint.

Background: Long-standing bruxism. Wears a hard acrylic splint nightly.

Current findings: Generalised occlusal wear. The splint is presented for review.

Question 1

Which crown material is most appropriate for this patient?

  1. Feldspathic all-ceramic
  2. Lithium disilicate with a layered occlusal surface
  3. Porcelain fused to metal with a porcelain occlusal surface
  4. Monolithic zirconia
Show answer and explanation

Correct answer: D. Monolithic zirconia

  • A. Feldspathic porcelain is the weakest option (roughly 60–100 MPa) and is contraindicated in parafunction.
  • B. Layered lithium disilicate has the same weakness — the veneer chips. Monolithic lithium disilicate (around 400 MPa) is reasonable but still weaker than zirconia.
  • C. PFM with a porcelain occlusal surface leaves the vulnerable veneer bearing the load. PFM with a METAL occlusal surface would be a strong alternative, but the porcelain-occluding version is not.
  • D. MONOLITHIC ZIRCONIA offers the highest flexural strength (roughly 900–1200 MPa) with no weak veneering layer to chip. In a heavy bruxist, the failure mode that matters is cohesive fracture of veneering porcelain, and a monolithic restoration eliminates it entirely.

Note: Note the trade-off: monolithic zirconia is strong but abrasive to opposing enamel, and must be well polished after any adjustment.

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Question 2

What would you expect to observe on the hard splint of a bruxist?

  1. Staining without any surface change
  2. Softening and distortion of the acrylic
  3. Wear facets and crack lines in the acrylic
  4. No visible change
Show answer and explanation

Correct answer: C. Wear facets and crack lines in the acrylic

  • A. Staining alone does not account for the mechanical effect of parafunction.
  • B. Acrylic does not soften at oral temperatures.
  • C. CORRECT. The splint is designed to be the sacrificial surface. Parafunctional loading produces flat, polished WEAR FACETS corresponding to the excursive pathways, together with crack and craze lines in the acrylic. The pattern of wear is itself a diagnostic record of the patient's parafunctional movements.
  • D. An absence of wear in an established bruxist suggests the splint is not being worn.

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Question 3

What is the principal purpose of anterior guidance in an occlusal scheme?

  1. To disclude the posterior teeth in excursions, reducing the load on the muscles of mastication
  2. To cure temporomandibular joint disorders
  3. To restrict the border movements of the mandible
  4. To alter centric relation
Show answer and explanation

Correct answer: A. To disclude the posterior teeth in excursions, reducing the load on the muscles of mastication

  • A. Anterior guidance causes the posterior teeth to separate immediately in excursive movements. Because elevator muscle activity is reflexly reduced when posterior contacts are absent, the loads transmitted to teeth, joints and musculature all fall. This is the rationale behind both the anterior guidance concept and the anterior ramp on a splint.
  • B. It can relieve symptoms, but 'curing' a temporomandibular disorder overstates the case considerably.
  • C. Border movements are determined by joint and ligament anatomy, not by tooth guidance.
  • D. Centric relation is a bone-to-bone joint relationship and is not altered by anterior guidance.

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