Marginal and Internal Fit of Milled Zirconia Copings/FPD frameworks

Objective:

To evaluate marginal and internal fit of single copings and FPD frameworks fabricated from two zirconia brands and milling systems.

Method:

Two ivorine teeth were mounted in clear epoxy resin (Buehler) with space for a missing tooth, then prepared for an all-ceramic FPD and replicated 20 times. Ten ivorine teeth were prepared for all-ceramic crowns and replicated twice.

The “master models” were replicated with elastomeric impression material (Reprosil-Dentsply) and type IV stone generating 20 dies for FPDs and 20 dies for crowns.

Zirconia copings and FPD frameworks were milled for all dies using two CAD-CAM systems and materials: System-1: In-Ceram Zirconia (VITA) copings and frameworks milled by Cerec-inLab (Sirona); System-2: Aadva-Zr (GC) copings and frameworks milled by GM1000 (GC).

Restorations were seated on their respective “master models” and clamped with uniform force. Eight measurements per coping and 12 measurements per framework were performed at pre-established points, with a Metallurgical microscope (Zeiss) at 50X magnification. Each restoration was subsequently cemented (RelyX™Unicem-3M ESPE) on its corresponding stone die under 50-N load. Cemented specimens were embedded in epoxy resin, sectioned BL and MD. Eight measurements of cement space per section were performed.

Result:

Means and SD (microns) for marginal and internal fit are displayed below. Data were subjected to two-way ANOVA (α=0.05) for analysis.

 

Milling System	System-1		System-2
Restoration	Crown	FPD	Crown	FPD
Marginal Fit	35.2 (7.2)	38.9 (8.2)	19.9 (6.9)	20.8 (8.3)
Internal Fit	98.1 (11.7)	102.5 (13.4)	45.7 (8.0)	50.3 (11.4)

Conclusion:

A significant difference was found among the two systems for both marginal and internal fit (p<0.0001) with System-2 exhibiting significantly lower marginal and internal gaps. Within each system there was no significant difference between the fit of crowns and FPDs. Marginal gaps for all systems tested were clinically acceptable.