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Retrievability of implant-retained crowns following cementation.

OBJECTIVES
The purpose of this study was to assess the retrievability of cemented implant crowns using two different removal devices. The influence of five cement types and two cement application techniques was evaluated.


METHODS
Forty copings were cast from a CoCr alloy for 40 tapered titanium abutments (5 degrees taper, 4.3 mm diameter, 6 mm height, Camlog, Germany). Twenty copings were modeled as single crowns, whereas 20 copings were modeled with an extension to simulate fixed partial dentures (FPDs). Before cementation, the inner surfaces of the copings were air-abraded (50 mum Al(2)O(3) particles at 2.5 bars), while the abutments were used as delivered with machined surfaces. Copings were cemented with eugenol-free zinc oxide (Freegenol), zinc phosphate (Harvard), glass ionomer (Ketac Cem), polycarboxylate (Durelon) and so-called self-adhesive resin (RelyX Unicem) cement. Cement was applied in a thin film band of 1 or 3 mm to the cervical margin of the inner surface of the copings, respectively. After cementation, specimens were stored in saline solution for 24 h. The Coronaflex and a standardized custom-made removal device were used to remove the copings from the abutments.


RESULTS
Using the same cement, no statistically significant influence with regard to the type of restoration (crown/FDP), cement application mode and device was detected (P>0.05). Therefore, data of specimens cemented with the same cement were pooled. Median attempts to remove the copings were: zinc oxide: 3, self-adhesive resin: 3, zinc phosphate: 5, glass ionomer: 16 and polycarboxylate: 58. Four levels of significance (P<0.0001) were found: (1) zinc oxide/self-adhesive resin; (2) zinc phosphate; (3) glass ionomer; and (4) polycarboxylate.


CONCLUSIONS
Zinc phosphate and glass ionomer cement might be suitable for a so-called 'semipermanent' (=retrievable) cementation, while polycarboxylate seems to provide the most durable cementation.