Clinical Workflow for Partial Dentures
This document outlines the professional workflow for the fabrication of partial dentures, specifically focusing on Cobalt-Chrome (Co-Cr) frameworks. It details the steps from preliminary impressions to final framework construction, emphasizing the importance of mounting and occlusal management.
Phase 1: Preliminary Assessment and Planning
The initial phase focuses on gathering diagnostic information to design the denture framework before any irreversible changes are made to the patient’s dentition.
1.1 Preliminary Impressions
- Action: Take upper and lower preliminary impressions using alginate.
- Lab Requirement: Send impressions to the lab to fabricate study models and custom (special) trays.
1.2 Surveying and Design
- Timing: Surveying must be performed on the study models before mouth preparation.
- Purpose: Identify the path of insertion, location of clasps, and placement of occlusal rests.
- Mouth Preparation: Based on the survey, perform necessary mouth preparations (e.g., creating rest seats and guide planes) on the patient.
Phase 2: Master Impressions and Occlusal Registration
Once mouth preparation is complete, the focus shifts to capturing the final anatomy and the relationship between the arches.
2.1 Final Impressions
- Take master impressions using the custom trays.
- These models will be used for the actual fabrication of the metal framework.
2.2 Maxillo-Mandibular Relationship (MMR)
The timing of the MMR (bite registration) is critical, particularly in complex cases:
- Free-End Saddles: For posterior free-end saddles, an MMR must be taken using a base rim before the framework is fabricated to determine the available vertical space.
- Tight Occlusion: If the patient has a very tight bite or a Class II Division 2 relationship, the models must be mounted before sending them to the lab for the framework.
Phase 3: Framework Fabrication and Mounting
A common error in the workflow is failing to mount master models before framework construction.
3.1 The Importance of Pre-Framework Mounting
Mounting the master models with a base rim ensures the lab technician can visualize the occlusion. This prevents technical errors such as:
- Occlusal Interference: Rest seats being waxed too high, preventing the patient from biting down fully.
- Vertical Dimension Issues: Palatal plates being placed where lower teeth contact them, inadvertently increasing the patient’s vertical dimension.
3.2 Workflow Summary Table
| Step | Action | Key Consideration |
|---|---|---|
| 1 | Preliminary Alginate Impressions | Used for study models and custom trays. |
| 2 | Surveying & Design | Determine rest seat and clasp positions. |
| 3 | Mouth Preparation | Prepare rest seats and guide planes in the mouth. |
| 4 | Master Impressions | Use custom trays for high accuracy. |
| 5 | MMR / Mounting | Crucial step: Mount master models if occlusion is tight or free-end saddles exist. |
| 6 | Framework Fabrication | Lab constructs the Co-Cr frame on mounted models. |
| 7 | Framework Try-in | Check fit in the mouth using “Fit Checker” paste. |
Phase 4: Clinical Tips and Alternatives
4.1 Managing Occlusal Records
- Hand-Articulation: If the case is a simple Class III with sufficient stable occlusal stops, the lab may be able to hand-relate the models.
- Articulating Paper & Photography: If digital scanners are unavailable, use articulating paper in the mouth and take high-quality photographs of the occlusal contacts. This assists the lab in understanding the bite.
- Digital Scanning: While ideal for planning, ensure you capture videos of the bite from all angles and identify specific points of contact.
4.2 Framework Try-in
- When the framework returns, verify the fit using a silicone-based indicator (e.g., Fit Checker).
- If the MMR was taken correctly before the framework was made, you can proceed to setting teeth for an aesthetic try-in to confirm the bite is still accurate.
4.3 Articulators
- For most general cases, simple articulation (Mean Value) is sufficient.
- Semi-adjustable articulators and facebow transfers are ideal but often reserved for complex rehabilitations (DCD level) due to the labor-intensive nature and lab requirements.