Ferrel Effects and Biologic Width in Dentistry

Introduction

• Presenter: Ryan
• Topics: Ferrel effects, biologic width, restore ability of teeth

What is a Ferrel?

• Definition: A ring or cap, typically metal, that strengthens and prevents splitting or wearing
• Origin: Latin words 'Ferrum' (iron) and 'Virilla' (bracelet)

Examples

• Iron bands on barrels
• Metal piece at the end of a paintbrush

Ferrel in Dentistry

• Dental Ferrel: A band that encircles the external dimension of tooth structure
• Includes axial walls and margin
• Purpose: Provides fracture resistance and lateral force resistance

Application in Prepared Teeth

• Crown prepared tooth: reduced coronal structure to fit crown material without bulkiness
• No decay, root canal treatment, or post and core required
• Ferrel provides resistance by engaging the axial wall of prepared tooth

Complex Cases

• Teeth with root canal treatment, core filling, and post
• Ideal design includes a ferrel for enhanced strength
• Non-ideal design lacks ferrel and offers no resistance to lateral forces
• Ferrel helps share force resistance with natural tooth structure and periodontal ligament (PDL)

Clinical Research

• Minimum ferrel length: 1.5mm for maxillary central incisor with post and core
• Widely accepted minimum for all teeth: 1.5mm
• 1.5mm refers to the crown’s contact with the natural tooth

Biologic Width

• Definition: Attachment of periodontium to the tooth above the bone
• Includes connective tissue attachment (~1mm) and epithelial attachment (~1mm)
• Total biologic width: ~2mm

Relevance in Dental Procedures

• Crowns/veneers must not impinge on biologic width
• Impingement causes inflammation, tissue recession, and potential bone loss

Guidelines

• Aim to stay supergingival (above the gingiva)
• Subgingival margin must not exceed 0.5mm below gingiva to avoid impingement
• Safe distance: 2.5mm from bone level to restorative margin

Application in Clinical Cases

• Example: Molar requiring crown due to extensive decay
• Required measures:
  • Achieve 1.5mm ferrel effect
  • Maintain 2.5mm distance from bone to avoid impinging biologic width
• Potential solutions for non-restorable teeth:
  • Clinical crown lengthening
  • Orthodontic extrusion

Final Notes

• Importance of determining restore-ability before treatment
• Overall aim: Doing what’s best for the patient

Conclusion

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