Primary Impression in Complete Dentures

Introduction

• A primary impression in complete dentures is a negative registration of the denture bearing areas.
• It is made of a material that sets in the mouth, capturing the denture bearing areas accurately.
• Objectives of a primary impression include preserving remaining structures, ensuring retention, stability, support, and esthetics.

Types of Impressions

• Mucostatic: Uses minimal pressure during impression making.
• Mucocompression: Applies pressure to record tissues in a functional state.
• Selective Pressure: Applies pressure selectively to specific areas.

Techniques for Impressions

• Open Mouth Technique: Patient keeps mouth open during impression.
• Closed Mouth Technique: Patient bites during impression to capture functional movements.
• Dynamic Impressions: Manipulation of tissues for functional movements.
• Trays: Use of stock or custom trays based on needs.

Materials Used

• Diagnostic Impressions: Alginate, impression compound, etc.
• Primary and Secondary Impressions: Materials like agar, silicone, thiokol rubber.

Principles of Impression Making

1. Ensure oral tissues are healthy.
2. Include basal seat within limits.
3. Borders should conform with anatomical and physiological limits.
4. Use selective pressure techniques.
5. Provide space in tray for impression material.
6. Guide mechanism for correct tray positioning.
7. Remove impression without damaging mucosa.
8. Ensure materials are dimensionally stable.
9. Impression shape should match external form of the denture.

Objectives of Impression Making

• Preservation: Maintain remaining natural structures.
• Retention: Ability of denture to resist displacement forces.
• Esthetics: Proper reproduction of sulcus dimensions.
• Stability: Denture should resist horizontal forces.
• Support: Provide resistance to vertical masticatory forces.

Factors Affecting Retention

• Anatomical: Size and quality of denture bearing area.
• Physiological: Saliva viscosity.
• Physical: Adhesion, cohesion, surface tension.
• Mechanical: Use of undercuts, springs, magnets.
• Muscular: Position in neutral zone.

Factors Affecting Stability

• Vertical height of ridge.
• Quality of soft tissue.
• Accurate and stable impression quality.
• Balanced occlusion in tooth arrangement.

Support in Dentures

• Achieved by maximizing area coverage.
• Helps distribute forces effectively like a snowshoe.

Esthetics in Denture Impressions

• Proper flange thickness.
• Accurate reproduction of sulcus.

Recording the Preliminary Impression

• Use of trays: Stock or custom, depending on patient needs.
• Tray materials should be well adapted and stable.
• Fabrication materials include shellac, self-cure resin, thermoplastics.

Conclusion

• The process of making an impression is critical for the success of complete dentures, influencing fit, comfort, and function.