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Questions and Answers
Why is axial reduction important in restoration design?
What is the primary focus in posterior restorations?
What is the purpose of reinforcing struts in restoration design?
Why is it important to consider treatment planning and smile analysis in esthetic restorations?
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What is the primary consideration in anterior restorations?
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What is the purpose of placing labial finish lines of PFM subgingivally?
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What is an important aspect of final restoration design?
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Why is enough axial reduction necessary in restoration design?
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What is important to consider in posterior restorations?
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What is the purpose of reinforcing struts in restoration design?
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Study Notes
Biomechanical Principles of Tooth Preparation
- Tooth preparation involves removing precise amounts of tooth and filling material to prepare for a dental crown.
- Goals of tooth preparation:
- Remove enough dental tissue to be replaced by the restoration.
- Eliminate undercuts to seat the crown in place.
Biologic Considerations
- Preservation of tooth structure:
- Conservation of tooth structure during preparation.
- Protection against tooth fracture.
- Adjacent teeth preservation.
- Preservation of periodontium:
- Avoidance of overcontouring.
- Location of the margins or finish lines.
- Preservation of the TMJ: Harmonious occlusion.
Preservation of Tooth Structure
- Conservation of tooth structure:
- Avoid injury to tooth pulp by not overheating.
- Use enough water cooling.
- Do not use old burs.
- Decrease pressure during cutting.
- Amount of reduction: as minimal as possible without interfering with other principles.
- Age and pulp size: as age increases, pulp size decreases.
- Chemical irritation: avoid opening dentinal tubules.
Protection Against Tooth Fracture
- Keep enough tooth structure to avoid fracture.
- Include parts of the tooth that could fracture during preparation.
Protection of Adjacent Teeth
- Use a metal matrix band around adjacent teeth.
- Leave an enamel lip between teeth during preparation.
Preservation of Periodontium
- Periodontal tissues are essential for oral health.
- General guidelines:
- Use biocompatible materials for restorations.
- Final restorations should be highly polished.
- Care should be taken during procedures to avoid harming periodontal tissues.
- Avoid overcontoured and overhanging restorations.
- Location of margins: supragingival > subgingival.
Biologic Width
- Fixed distance between the crest of alveolar bone and the gingival sulcus.
- Depth: 1.5-2 mm.
- If biologic width is not respected, it can lead to bone loss and recession.
Retention and Resistance
- Restoration material and luting material:
- Luting materials: zinc phosphate, zinc polycarboxylate, glass ionomer, resin cements.
- Cementation: zinc phosphate > glass ionomer > zinc polycarboxylate.
- Bonding/adhesion: resin cements are most retentive, especially with all-ceramic restorations.
Structural Durability
- Ability of the restoration to withstand forces of mastication without fracture or distortion.
- Factors to consider:
- Occlusal reduction.
- Axial reduction.
- Functional cusp bevel.
- Reinforcing struts.
Occlusal Reduction
- Enough bulk of material should be present on the occlusal surface to withstand forces of mastication.
- Gold: 1.5 mm functional cusp, 1 mm non-functional cusp.
- PFM: 1.5-2 mm functional cusp, 1-1.5 mm non-functional cusp.
- All Ceramic: 1.5 mm all occlusal surface.
Functional Cusp Bevel
- Provides bulk of restoration at an area of heavy occlusal contact.
Axial Reduction
- Enough axial reduction should be made to prevent thin restorations and overcontouring.
Reinforcing Struts
- Important in different designs of restorations.
- Made to provide bulk of material in weak areas or areas withstanding high occlusal load.
Esthetic Considerations
- Treatment planning and smile analysis are crucial for successful esthetics.
- In anterior restorations, esthetics take precedence.
- In posterior restorations, function is more important.
- General rules for esthetics:
- Color: enough reduction needed to hide opaque layer or tooth structure.
- Shape: final restoration must mimic normal tooth shape and emergence profiles.
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Description
Learn about the biomechanical principles of tooth preparation for a dental crown, including the importance of removing precise amounts of tooth and filling material and eliminating undercuts.
