| Secondary caries occuring along the restoration margins or under therestoration materials over time is considered as one of the main causes for thefailure of restorations. Many reasons have been shown to be responsible forsecondary caries, including microleakadge. The contraction stress that occursduring the polymerization of the resin-based restorative materials may result inan early marginal breakdown, facilitating microleakadge. Acidic bacterialbyproducts may infiltrate not only the interface, but also the dentin tissue at theperiphery, creating a maginal demineralized zone, and thus rapidly promotecaries occurrence. In this regard, it's reasonable to conclude that an increasedresistance of the tooth-resin interface to acid may effevtively retard theprogression of secondary caries.In 2004, Tsuchiya et al. firstly observed a new structure under the hybridlayer of dentin-resin interface, when dentin was treated with a fluoride-free selfetchingadhesive system. It's characterized by a resistance to an acid and basechallenge, and essentially different from the concept of conventional hybridlayer and caries-inhibition zone (fluoride-releasing material). Therefore, it was named as“Acid-base Resistant Zone (ABRZ)”. It's supposed to play animportant role in the prevention of secondary caries, the sealing of restorationmargins and the promotion of restoration durability. The formation and propertyof ABRZ are influenced by many factors, including: (1) the conditions of thebonding tooth substrates; (2) bonding materials and techniques; (3) parametersrelated to the acid and base challenge during the sample preparation. Althoughthe formative mechanism is still unclear, it was speculated that the chemicalinteraction between adhesive acidic functional monomer and hydroxyapatite intooth tissue may at least partly contribute to the formaion of ABRZ. However, inorder to verify the aboving hypothesis, the exact effect of functional monomerson the morphology of ABRZ should been fully elucidated. Moreover, enamel isthe other important bonding substrate, different from dentin in both compositionand structure. It is meaningful to investigate the formation of ABRZ on enamel.Therefore, two aspects were included in this study. On one hand, themechanisms and relavent factors of dentin ABRZ were further investigatedaccording to the present dentin ABRZ sample preparation method; on the otherhand, a new experimental method was set up to explore the formation andcharacteristics of enamel ABRZ. SEM, TEM were used for the ultramorphologyobservation; microtensile and microshear tests were applied to evaluate thebonding performance.The present study could be divided into two parts. Part?is composed oftwo experiments, investigating the effects of different factors on the formation ofABRZ and bond strength to dentin. Part?is composed of five experiments. Thenew method of sample preparation was set up for the observation of enamelABRZ and the influences of adhesive functional monomers and pre-etchingtechnique on the enamel ABRZ and bonding performance were assessed.In experiment 1, the effects of four different curing modes on themorphology of ABRZ and bonding performance of two dual-cure core resinsystems to dentin were compared. The results indicated that:?curing modes had significant influence on bonding performance, regardless of materials. Butthe changing tendency of bond strength was different according to core systems;?The morphology of ABRZ was highly adhesive-material-dependent. Thereseemed to be no obvious influence of curing modes on the formation andproperty of ABRZ in a short time.In experiment 2, experimental two-step self-etching adhesive systemsdifferering from each other only in functional monomers were prepared. Theeffects of two functional monomers (MDP & Phenyl-P) contained in the primerand the bond on the morphology of ABRZ and bonding performance to dentinwere examined. The results indicated that:?The highest bond strength wasobtained when the functional monomers contained in the primer and the bondwere the same;?The formation and characteristics of ABRZ were intimatelyrelated to the adhesive funtional monomers.In experiment 3, the enamel bonding interfaces under different acid-basechallenge conditions were observed and analyzed. Based on these datas, optimalconditions for enamel ABRZ sample preparation were filtered. The existence ofenamel ABRZ was confirmed with this method.In experiment 4, effects of two functional monomers (MDP & Phenyl-P) onthe morphology of ABRZ and bonding performance of two-step self-etchingadhesive systems to dentin were examined. The results indicated that: both thebond strength and the ABRZ were influenced by functional monomers.In experiment 5, effects of pre-etching on the bond strength and ABRZ of atwo-step self-etching adhesive system to enamel were investigated. The resultsindicated that: Pre-etching on enamel promoted the bond strength and formationof ABRZ. After the enamel being pre-etched, whether applying the self-etchingprimer or not, there was no difference in both bond strength and ABRZmorphology for Clearfil SE Bond system.In experiment 6, effects of functional monomers and pre-etching techniqueon the bond strength and the ABRZ of intact enamel were evaluated. The results indicated that: when the intact enamel was treated with MDP-containingadhesive and pre-etching technique, both the bond strength and the quality ofABRZ were improved.In experiment 7, sample preparation and observation of enamel ABRZ withTEM and FIB-TEM were explored. The results indicated that:?EnamelABRZ could be successfully observed with conventional TEM, but the bondinginterface was easy to get fracture during the ultra-thin sectioning;?FIB-TEMis a reliable alternative to conventional ultramicrotomy for brittle enamel-resininterface, but the current embedding method over the ABRZ should be modified. |
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