Can previous acid etching increase the bond strength of a self-etching primer adhesive to enamel?

The contribution of chemical bonding to the short- and long-term enamel bond strengths

OBJECTIVES

MDP (10-methacryloyloxydecyl dihydrogenphosphate) has been proven to possess chemical bonding ability to tooth hard tissues, but its contribution to the enamel bond strength has not been recognized. The aim of this study was to investigate the contribution of chemical bonding to the short- and long-term bovine enamel micro-tensile bond strengths (μTBS).

METHODS

The acid-etched enamel surfaces were treated without any primer (control) or with one of three MDP-containing primers (containing different ratio of MDP/HEMA/Bis-GMA, Kuraray Co.) for 5s, water-sprayed and air-dried. Subsequently, the pretreated enamel surfaces were applied with an etch-and-rinse adhesive Durafill Bond (Heraeus Kulzer) and placed with composite resin Durafill VS (Heraeus Kulzer). The specimens were prepared for μTBS tests after 24-h or 1-yr water storage. The etched enamel surfaces treated with or without MDP-containing primers were analyzed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS).

RESULTS

The acid-etched enamel treated with the MDP-primers for a very short time could produce the greater enamel μTBS than the control did (p<0.05), and change enamel micromorphology. No significant different μTBS were found between 24-h and 1-yr water storage (p>0.05). The chemical bonding of MDP on the enamel surfaces was re-confirmed by XPS.

SIGNIFICANCE

The additional chemical bonding of MDP around the enamel crystallites of the etched enamel substrate could significantly increase the short- and long-term enamel μTBS, and their μTBS surpass those of the etch-and-rinse adhesive alone.

Morphology of the dentin on primary molars after the application of phosphoric acid under different conditions

The aim of this study was to evaluate changes in the superficial dentin pattern of primary teeth after applying different phosphoric acid concentrations and conditioning times. Twenty-four dentin surfaces were divided in 4 groups with 10 teeth each: GI -no treatment; GII to GIV -phosphoric acid at 37%, 32%, and 10% respectively. The samples were divided into two halves: one treated for 7 seconds (T1) and the other one for 15 seconds (T2). They were submitted to scanning electronic microscopy (SEM). A reticule was superimposed upon the images to randomly select dentinal tubules measured in µm². The conditioning times did not cause significant differences in the mean diameter values of the dentin tubules within each test group: GII (T1= 4.86; T2= 4.70); GIII (T1 = 3.83; T2= 3.08); GIV (T1= 5.04; T2= 5.23). Comparing different groups, there were no differences in T1. The same results were observed in T2, except for GIV which presented higher mean diameter values than GIII. The extent of acid conditioning did not influence tubule opening within groups. When different types of acids where compared, only the 10% phosphoric acid showed upper tubule opening than 32% phosphoric acid. The dentin pattern varied according to the type of acid used for conditioning.