Halloysite nanotube incorporation into adhesive systems—effect on bond strength to human dentin
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This study aimed to evaluate the effect of Halloysite® aluminosilicate clay nanotube (HNT) incorporation into a two-step etch-and-rinse (ER) and a one-step self-etch (SE) adhesive on human dentin shear bond strength (SBS).
Materials and methods
Ten groups (n = 12) were prepared according to the adhesive system (i.e., ER or SE) and amount of HNT incorporated (5–20 %, w/v), as follows: commercial control (i.e., the adhesive was used as purchased, 0 % HNT); experimental control (i.e., the adhesive was processed through mixing/stirring and sonication similarly to the HNT-incorporated experimental groups, but without HNT); and 5, 10, and 20 % HNT. SBS testing was performed after 24 h of storage in deionized water at 37 °C. Failure modes were examined using a stereomicroscope (×40). Scanning electron microscopy (SEM) of the resin–dentin interface of selected specimens was carried out.
Two-way ANOVA revealed that incorporation of HNT up to 20 % (w/v) in ER and up to 10 % (w/v) in SE demonstrated an increased SBS compared to their experimental controls. Compared to the commercial control, SBS of HNT-modified dentin adhesives was not significantly different for ER adhesives (p > 0.05) but was significantly higher with 5 % HNT in the SE adhesive (p < 0.05). Failure modes were predominantly adhesive and mixed failures. SEM micrographs of resin–dentin interfaces for ER-commercial control and ER-10 % showed a similar morphology. A thicker adhesive layer and the presence of agglomerated HNT on the resin tags were seen in ER-10 %. An increased number of short resin tags in SE-5 % compared with SE-commercial control were observed.
HNT addition up to 20 % in ER and up to 10 % in SE showed increased SBS to dentin compared with the experimental control.
HNT can be used not only to reinforce adhesive resins but also hold potential for the development of bioactive adhesives by the encapsulation of matrix metalloproteinase (MMP) inhibitors or anticariogenic agents.
KeywordsHalloysite Nanotube Adhesive Dentin Bond strength SEM
The authors thank Mr. Andre Zeitoun (Applied Minerals Inc., New York, NY, USA) for halloysite nanotubes donation. This study was conducted as part of the requirements for the MSD degree in Dental Materials at the Indiana University School of Dentistry. The authors gratefully acknowledge the valuable advice provided by the committee members (Drs. N. Blaine Cook, Tien-Min G. Chu, and Michael A. Cochran). There is a pending patent request (US 62/008,647) under the name of Indiana University–Purdue University Indianapolis that refers to the proposed innovation.
Conflict of interest
The authors declare that they have no conflict of interest.
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