Tem/SEM morphological analysis of dental tissue-resin bonding system in dry and wet conditions

The formation of a dental tissue-composite resin interface that is resistant to fracture, reducing degradation by microleakage and nanoleakage, is fundamental to almost all restorative adhesive dentistry. For quite long time, an alternative resin substitute for amalgam has been searched unfortunately without much success. The polymeric shrinkage generally observed on the tissue-resin restoration interface causes the failure by microleakage degradation. In this work the interface formed between one bond system and the dental tissue at different conditions was analyzed. Twelve erupted pre-molars, non-carious, not fractured were selected and extracted for orthodontics procedures. Duplicate teeth samples of both groups were acid etched (37% phosphoric acid) for different time intervals: 5s, 15s or 30s. Half of the samples were prepared for transmission electron microscopy (TEM) analysis and the other half for scanning electron microscopy (SEM) analysis. Teeth samples for SEM evaluation were prepared by restoration using Tetric Ceram Vivadent® resin. The specimens were stored in glularaldehyde solution (2.5% PBS/0.1M, pH=7.3). The characterization procedure was carried out by TEM and SEM coupled to EDX microprobe. All SEM samples were previously covered with a thin conductive film of Au-Pd before observation. Photomicrographs were collected and evaluated regarding to the dental tissue-composite resin interface and morphology. Resin-infiltrate hybrid layer was investigated depending on acid etching under wet or dry conditions. The results strongly suggested a significant positive relationship between wet substrate and hybrid layer formation. The use of phosphoric acid etching for 15 or 30 sec produced similar micromorphological patterns. The acid etching for 5 sec resulted on a worse hybrid layer formation compromising the adhesion of the dental tissue-resin interface.