Occlusal Factors and Restoration Failures

Occlusal Factors in Restoration Failure

Introduction

  • Occlusal factors can lead to restoration failures.
  • Possible issues include:
    • Fractured teeth and restorations
    • Increased mobility
    • Pain on biting
    • Loosening of crowns
  • These failures usually stem from:
    • Excessive forces
    • Forces applied in the wrong direction (laterally)
    • Premature contacts (interferences)
    • Lateral forces on posterior teeth
    • Strong forces on weak teeth

Preventing Failure

  • Conduct a thorough occlusal screening examination for every patient.
    • Assess ICP (Intercuspal Position).
    • Evaluate lateral guidance.
    • Consider other pertinent details.
  • Pay attention to indicators such as:
    • Repeated restoration failures
    • Protrusion on heavily restored anteriors
    • Wear facets on at-risk teeth
    • RCP-ICP slide when anterior wear is observed
    • Non-working side interferences, especially if palatal fractures are seen

ICP Examination

  • ICP Examination involves assessing the stability and health of the intercuspal position.
  • Possible assessment:
    • Stable and healthy
    • Damaging

Lateral Guidance

  • Canine Guidance:
    • Protects other teeth.
    • Requires a strong canine.
  • Group Function:
    • Normal as one ages.
    • Better if force is shared across many teeth and cusps are flatter.
  • Lateral guidance should never be on:
    • A post-crowned tooth
    • A bridge pontic

Repeated Anterior Failures

  • Guidance scheme expectations:
    • Consider restoring to either canine or group function.
  • Canine guidance considerations:
    • More likely in patients with Class III incisor relationship.
    • Should not be provided using a restored canine with a post crown.
    • Can exacerbate periodontitis around canines in smokers.
    • May complicate posterior teeth restoration.
  • Diagnostic wax-up:
    • Use an articulator, mounted in RCP (Retruded Contact Position).

Interferences

  • Definition: A heavy tooth-to-tooth contact that obstructs intended jaw movement.
  • Occur during any jaw movement:
    • ICP
    • RCP
    • Protrusive movements
    • Working side movements
    • Non-working side movements
  • ICP interferences:
    • Often feels "high" to the patient.
    • Can cause pain, mobility, increased tooth sensitivity, or restoration failure.
    • Should be addressed whenever placing any restoration.
    • Correct the occlusion before the patient leaves.

Working Side Interferences

  • Result from a lack of canine guidance to protect posterior teeth.
  • Importance of canine guidance in preventing these interferences.

Lateral Forces

  • Working side movements:
    • Affect buccal cusps of upper teeth and lingual cusps of lower teeth (BULL rule).
  • Non-working side interferences:
    • Occur when teeth clash on the non-working side during lateral movement.
    • Not common because the NWS condyle usually separates the teeth.
    • Affect palatal cusps of upper teeth and buccal cusps of lower teeth (PUBL rule).
    • Typically produce a semi-circular wear pattern on upper teeth.

Planning for Success

  • Incorporate occlusal examination into routine check-ups.
    • Assess ICP stability.
    • Check for weakening of teeth in lateral guidance.
  • Ensure the occlusion feels the same to the patient after treatment.
  • Select an articulator based on the risk of lateral forces:
    • Use an ICP record when conforming.
    • Use an RCP record when reorganizing or examining the occlusion.
  • When a patient presents with a broken tooth, investigate the cause.

Case Studies

Case 1

  • 47-year-old male.
  • Fractured lingual cusp on LL6.
  • Temporarily restored with RMGIC.
  • Symptoms of Cracked Tooth Syndrome.
  • Question: What type of interference caused this?
    • Non-working side interference.

Case 2

  • 54-year-old female.
  • Pain on biting on UL back tooth.
  • Mobile palatal cusp on UL7 upon examination.
  • Question: What kind of interference caused this?
    • Non-working side interference.
  • Occlusal splint used to protect other teeth.

Case 3

  • 67-year-old male receiving crowns, reports a "high" feeling.
  • Shimstock (8μm thick metal foil) used for evaluation.
  • Question: What type of interference is present?
    • ICP interference.
  • Correction methods:
    • High in ICP and lateral excursions: reduce cusp height (often a plunger cusp).
    • High in ICP but "free" in lateral excursions: deepen fossa.

Case 4

  • 36-year-old male with repeatedly fracturing composites on front teeth.
  • Question: What type of interference is likely?
    • Protrusive interference.

Case 4: Plan and Considerations

  • Build up canines to manage forces during protrusion and protect composites.
  • Reinstate canine guidance that has been lost due to wear.
  • Check the following before reinstating canine guidance:
    • Periodontal status
    • Pulp vitality
    • Periapical radiograph and status
    • Root length and angulation
    • Rule out RCT or post restorations on the canine
  • Use an articulated model and diagnostic wax-up to assess feasibility.
  • Plan includes:
    • Study models with RCP record
    • Mounting on an articulator
    • Diagnostic wax-up to determine canine build-up for incisor protection.
  • Articulator selection:
    • A semi-adjustable articulator is preferred.