Crown Retention After Long-Term Specimen Aging For Self-Adhesive Modified-Resin Cements

Objectives: � Evaluate crown retention for self-adhesive, modified resin (SAMR) cements using long-term aging to assess durability.�

 

 

Methods: � Extracted human molars prepared with a flat occlusal, 20-degree taper and 4mm axial length.  Preparation surface area determined and specimens distributed by areas equally into three groups (n=13). See J Am Dent Assn 2009;149;1125-1136.� �High noble alloy crowns (Special White, Ceramco) were cast. Non-eugenol temporary cement cleaned from preparations; teeth rinsed, dried, but not desiccated.  SAMR cements: 3M-ESPE RelyX Unicem Aplicap (RXU), RelyX Unicem 2 Automix (RXU2) and SDS/Kerr Maxcem Elite (MCE).� 20 Kg cementation force used.� Aging achieved by thermocycling between 5-55 �C for 5000 cycles and repeated monthly for 6 months (30,000 cycles).� Castings were removed at 0.5mm/min. Removal force and nature of cement failure recorded.�� Dislodgement stress calculated using surface area.�  

 

 

Results: � Mean crown removal stress with SD's given below.  One-way ANOVA with mean comparisons revealed significant differences (≠) of RXU and RXU2 from MCE (P=0.006). The mode of failure for 37 of 39 specimens was cement residing on the internal of the crowns with little on dentin.� Χ²=1.054,P=0.590.

 

	RXU		RXU2		MCE
Crown Removal Stress (MPa)	5.0 (1.6)	=	4.5 (1.0)	≠	3.4 (1.0)
Location of cement (%n)	92%-on crown; 8%-on crown & dentin	=	100%-on crown	=	92%-on crown; 8%-on crown & dentin

 

 

Conclusions: � (1) RXU and RXU2 achieved higher crown removal stresses than MCE, but (2) stresses for all three were greater than that shown for zinc phosphate (J Am Dent Assn 2009;149;1125-1136), thus clinically acceptable.� (3) Cement was uniformly found on the internal of the crown with very little on the dentin.� Although thought to be self-adhesive to dentin, the attachment of the SAMR cement is predominantly to the internal of the crown.� (4) Long-term aging of cemented crowns supports durability of crown retention.� Supported by 3M-ESPE.