Direct adhesive pulp capping: pulpal healing and ultra-morphology of the resin-pulp interface

To test the hypothesis that healing of adhesively capped pulps may depend on the type of adhesive system used and its specific application approach.

Buccal Class V cavities were prepared in 24 intact monkey teeth. After exposing the pulps, infiltration anesthesia (Xylocaine containing 1:80,000 epinephrine) was administered around the root apex. Two adhesives that make use of a different hybridization approach, Clearfil Liner Bond II (CLB-II) and Super-Bond D Liner II (SB-II) were directly applied to the exposed cavities. The pulpal response was histopathologically investigated using light microscopy at 3 and 90 days. In addition, the resin-pulp interface was characterized by transmission electron microscopy in an attempt to elucidate the underlying mechanisms of healing.

In the CLB-II capped pulps, little inflammation was detected at 3 days with the bonding resin intimately attached to the exposed pulpal tissue. At 90 days, a complete dentin bridge was formed in close adaptation to the resin cap. The ultra-structure of a thin intermediary layer at the bridge front resembled a so-called "reversal line". This layer typically appears during remodeling of bone to couple the newly formed to the old osseous tissue. In the SB-II capped pulps, an acute inflammation was in progress immediately beneath the bonding resin at 3 days. This tissue was resorbing the resin that had infiltrated relatively deeply into the pulp. Whereas healing of CLB-II capped pulps appeared to have been initiated promptly, healing of SB-II capped pulps was probably retarded. The formed soft-tissue hybrid layer had first to be resorbed before the formation of a dentin bridge could have been initiated. Hence, the dentin bridge was not completely finished at 90 days and no evidence of a "reversal line"-like layer could be detected. These results suggested that although both the adhesives tested appeared effective as pulp capping materials, the process and duration of healing substantially differed.