Investigation into the nature of dentin resin tags: a scanning electron microscopic morphological analysis of demineralized bonded dentin.

Statement Of Problem: While the formation of the dentin/adhesive hybrid layer has been generally established, the infiltration and flow of the adhesive resin inside the acid treated dentinal tubules remains controversial.

Purpose: The aim of the present study was to investigate and review the current interpretation of resin tags by means of scanning electron microscopic (SEM) observation.

Material And Methods: Eight noncarious, human third molars were cut transversally and then longitudinally to obtain 8 middle-to-deep dentinal surfaces. The dentin was etched with 37% phosphoric acid (H 3 PO 4 ) gel for 10 seconds and then rinsed with water for 20 seconds. The dentin was kept moist by removing the excess water with a damp cotton pellet. The conditioned dentin was treated with a dentin bonding agent (Single Bond) and was light-polymerized for 20 seconds. A 0.2- to 0.5-mm layer of flowable composite (Tetric Flow) was then applied to the bonded dentin followed by 2 layers (2 mm each) of composite (Z 250). Each composite was light-polymerized for 40 seconds. Subsequently, the specimens were cut lengthwise into 2 halves and randomly divided into 4 groups (n=4), according to the surface preparation modality of the sectioned surface: Group EA: ethylenediamine tetraacetic acid, Group PA3: H 3 PO 4, Group PA120: H 3 PO 4 + NaOCl, and Group CA: HCl + NaOCl. Two additional teeth (Group N) were cut lengthwise into 2 halves and served as the control. The sectioned surfaces were treated with HCl and NaOCl. All specimens were processed for SEM observation.

Results: Specimens from Groups EA, PA3, PA120, CA, and N showed filamentous structures that were tens of microns long. Some filaments presented split-ends with hollow structures and very thin walls. Others made sharp hairpin turns indicating they were soft and compliant.

Conclusions: Conventional SEM techniques, which are currently used to detect resin tags, actually identified filamentous organic structures, supposedly glycosaminoglycans, which were resistant to conventional specimen preparation techniques. The organic component showed a strong resemblance to the lamina limitans contained within the dentinal tubules. Over-reliance on SEM morphology has led to much confusion about the depth of penetration of resin tags.