Dentin Permeability of a New Protective Coating on Smear-Layer Dentin

Objectives:  Compare the convective fluid movements across dentin covered with a smear layer after placement of an experimental coating material, EXM-713, versus an RMGI liner and a nanofilled adhesive control.  EXM-713 is a resin-modified glass ionomer coating material.

Methods:   Crown segments cut from extracted unerupted third molars were cemented onto plexiglass slabs penetrated by a stainless steel tube allowing filling of the pulp chamber with water under 140 cm H2O pressure. These were attached to a device that measured fluid movement through the dentin.  The dentin surface was etched with 37% phosphoric acid for 15 sec to permit measurement of the maximum permeability; three strokes on 320 grit paper yielded a controlled smear layer, which was coated with either 3M™ ESPE™ Vitrebond™ Plus Liner/Base (VBP)  or EXM-713.  Permeabilty was measured on the etched, smeared, and coated dentin for each sample. A control group, 3M™ ESPE™ Adper™ Single Bond Plus Adhesive (SBP) applied to etched dentin, was also measured.  Cross-sectional SEM was done on EXM-713 and VPB.  Data were analyzed via one-way ANOVA and Tukey's T-test (p<0.05). 

Results:  Permeability, in microliter/min @140cmH2O (stdev), is shown below.  Groups with the same superscript letter are not significantly different (p>0.05).

Material	n	Etched	Smear	Coated	% Reduction
EXM-713	6	14.6(13.1)a	3.7(2.4)b	0.25(0.32)c	96.5(6.0)%
VBP	6	10.7(7.4)a	3.2(1.9)b	0.17(0.25)c	98.9(1.1)%
SBP	10	13.8(5.6)a	n/a	0.9(1.3)c	93.3(8.0)%

Conclusions:   EXM-713 and VBP are effective at sealing smear-layer-covered dentin and reducing fluid flow through it; both are not statistically different from SBP in their ability to reduce fluid flow.  SEM of EXM-713 and VPB showed resin infiltration of the smear layer, resin tags on the etched dentin, and a resin-rich layer at the interface.