Effects of Streptococcus mutans and its fluoride resistant strains on the adhesion of CAD/CAM ceramics to teeth and resin.

Abstract

The similar elastic modulus of resin-matrix ceramics to dentin has resulted in their recent widespread application clinically. Nevertheless, the bacterial environment of oral cavity can degrade the resin composite. The objective was to analyse the effect of S. mutans and its fluoride-resistant strains on the adhesion of three CAD/CAM ceramics. S. mutans UA159 (UA) was identified, and its fluoride-resistant strain (FR) was induced. For crack observation, three kinds of CAD/CAM ceramics (IPS Empress, Lava Ultimate and Vita Enamic) were bonded with tooth complex (enamel, dentin and flowable resin) through adhesive. For micro-tensile test, ceramics were bonded with flowable resin, and cut into strip test pieces. Then specimens were immersed into the UA, FR and the control solution (BHI) separately for 14 d. Ceramic-adhesive interface and adhesive-tooth complex interface were observed and analyzed through electron microscope and stereomicroscope. Micro-tensile test was conducted. Specimens in bacterial solutions had more cracks and comparatively weaker micro-tensile strength than those in BHI. In ceramic-adhesive interface, Lava Ultimate produced the most cracks. In adhesive-tooth complex interface, adhesive-dentin produced the most cracks. Meanwhile, IPS Empress had the strongest micro-tensile strength when bonded with resin. S. mutans and its fluoride resistant strain can cause cracks in the bonding of ceramics and dental tissue, especially resin-matrix ceramic and dentin, and weaken the bonding strength between ceramics and resin.