Overview
The All-on-4 concept revolutionized dental full arch rehabilitation by maximizing bone utilization with angled posterior implants. However, this efficiency creates unique impression challenges: tilted implants require angulated dental abutments, multi-unit connections add potential error points, and the four-implant configuration means each fixture carries significant dental prosthetic load—making positional accuracy even more critical than in conventional cases.
What You'll Need
- Multi-unit impression copings compatible with your dental implant system
- Open-tray custom impression tray with adequate clearance
- Splinting material (resin or dental implant verification jig)
- Polyvinyl siloxane (PVS) or polyether impression material
- Torque wrench with appropriate hex drivers
- Multi-unit analogs for dental master cast fabrication
Step-by-Step
Assess Multi-Unit dental abutment Status
With the dental prosthesis removed, examine each multi-unit dental abutment for damage, debris, or loosening. Verify dental abutment torque before proceeding—loose dental abutments shift during impression, corrupting positional data. Clean all dental abutment interfaces with chlorhexidine and dry thoroughly.
Select Appropriate Impression Copings
Use impression copings designed for your specific multi-unit dental abutment system. These copings must engage the anti-rotational feature and seat completely flush. Verify compatibility—mismatched components create apparent positional errors.
Seat Impression Copings
Thread copings onto all four multi-unit dental abutments. Hand-tighten, then apply recommended torque (typically 10-15 Ncm). Verify seating by probing the coping-dental abutment junction—zero gap should be detectable.
Establish Rigid Splinting
Connect all four copings with rigid splinting material. For resin splinting, apply pattern resin with floss scaffold, allow complete cure, then section and relute between each coping pair. For metal splinting, assemble dental verification jig links between copings per manufacturer protocol.
Evaluate Splint Configuration
The splint must resist torsion and flexion during impression removal. All-on-4 configurations stress splints differently than conventional parallel implant setups—the angled posterior implants create rotational forces during unscrewing.
Prepare Custom Open Tray
Try-in your custom tray over the splinted assembly. Verify clearance around each coping access hole (minimum 2mm). The tray must not contact the splint or copings. Apply tray adhesive and allow to dry completely.
Take the Impression
Syringe light-body material around each coping, ensuring complete coverage of the coping-dental abutment interface. Load the tray with heavy-body material. Seat with even pressure and maintain stability throughout setting.
Remove Impression Carefully
Unscrew each coping through the tray access holes using appropriate hex drivers. Break torque smoothly to avoid rotating copings within the impression material. Remove the tray in the path of draw. All four copings should remain embedded and rigidly connected.
Inspect and Attach Analogs
Examine the impression for defects, particularly around coping bases. Thread multi-unit analogs onto each coping and torque to specification. Verify analog seating—gaps here directly transfer to the dental master cast.
Tips & Best Practices
- Use multi-unit level impression when possible; implant-level impressions through angled multi-units add complexity
- Allow extra cure time for impression material near angled posterior copings where material thickness varies
- Photograph the clinical setup for dental laboratory reference on angulation and emergence
- Communicate posterior implant angles to the dental laboratory for optimal dental framework design
Common Mistakes to Avoid
Using closed-tray technique
All-on-4 cases require open-tray pickup to maintain spatial accuracy. Closed-tray cannot accommodate angulated copings accurately.
Insufficient splint rigidity
The rotational forces from angled implants stress splints significantly. Inadequate rigidity allows coping movement during removal.
Ignoring multi-unit dental abutment torque
Loose dental abutments shift during impression, creating apparent implant positional error. Verify torque before every impression.