The Effects Of Air Blowing Pressure On The Stability Of Bonded Interface Of Resin And Dentin

Dentin structure was the principal determinant of dental adhesion. Although significant development in understanding of adhesive theory greatly improved the bond strength, it was difficult to achieve stability of dental adhesion during long time. Adhesive resin monomers infiltrated into demineralized dentin and encapsulated the exposed collagen matrix. After polymerization with light, the hybrid layer including adhesive, collagen and part of mineral formed. Durable and effective dental bonding depended on the uniform and compact hybrid layer.Recently, no matter what kind of adhesive system or adhesive material was used, the creation of hybrid layer was not perfect. Hydrophilic property of adhesive system, resin monomer insufficient impregnation of dentin matrix, phase separation of adhesive, low rate of polymerization of resin monomer, endogenous enzymes, bacterial enzymes and presence of water may lead to degradation of hybrid layer, affecting the longevity of bonded interface of adhesive resin and dentin.The present study evaluated the effects of pressure on the bonding of resin and dentin, in the hope of improving the quality and stability of hybrid layer by adjusting the pressure of air-dry stream after adhesive application. From the infiltration of resin and encapsulation of collagen fibril, the study investigates the effects of air blowing pressure on the depth of resin monomer infiltration, the degradation of type I collagen, the immediate and aged bonding of total-etch adhesive and biological safey. The study provided theoretical basis and optimal parameter to the future research and clinical application.Major results and conclusions of the research are as follows:1. The presence of smear layer may affect the infiltration of adhesive resin monomers. Air blowing pressure may promote the resin diffuse into the demineralized dentin matrix without smear layer. With the pressure increased, the depth of resin monomer infiltration was deeper. CLSM showed the more uniform infiltration of resin monomer with the pressure of 0.2 MPa and 0.3 MPa than 0.4 MPa. The variety in infiltrate depth and fluorescence intensity in the same dentinal tubule were significant with the pressure of 0.4 MPa. Similar, FEISEM indicated the higher pressure(0.3 MPa) created thinner adhesive layer, more uniform and longer resin tags than ordinary pressure(0.1 MPa), without fracture of resin tags.2. Air blowing pressure may affect the immediate and aged bond strength. With the increased pressure, bond strength became stronger. Aging treatment may decrease the bond strength. Control groups(0.1 MPa) had the weakest immediate and aged bond strength. 0.3 MPa 5 s showed the highest immediate and aged bond strength, which were 55.19±6.44 MPa and 46.53±5.77 MPa, respectively. The application time of different pressure did not affect the bond strength significantly.3. The failure modes differed from each other with different pressure application. The majority were mixed failure. With the increased pressure, the proportion of mixed failure increased, except 0.4 MPa with 84% and 66% mixed failure in immediate and aged groups. Contrasting to other groups, the proportion of mixed failure in immediate and aged groups were 89% and 81% in 0.3 MPa, which was higher than other groups,and the proportion of adhesive failure were 11% in aged groups, which was lower than other groups.4. Air blowing pressure may affect the microscopic morphology of resin tags. With the increased pressure, the structure of resin tags were more compact and the length were more uniform. However, the highest pressure(0.4 MPa) lead to the dramatic variation in length and significant fracture. The hybrid layer became much more compact and the quantity and length of lateral branch of resin tags increased with the higher pressure application, but the overhigh may lead to a reverse result. Aging may induce the degradation of hybrid layer and fracture of resin tags. However, 0.3 MPa showed no difference within aged groups and immediate groups.5. The microscopic morphology of hybrid layer varied with pressure and application time. With the increased pressure, thinner and more compact hybrid layer with longer resin tags and lateral branch were observed. However, overhigh pressure may lead to ununiform infiltration of resin monomers. Aging treatment may to some extent degrade the hybrid layer. 0.3 MPa 5 s created the uniform thickness and compact without obvious drawbacks hybrid layer, and a large number of lateral branch were observed on the surface of rasin tags. Although aged phenomenon could be found, hybrid layer did not show obvious deteriorate proof. Therefore, uniform and compact hybrid layer may to some extent resist aging treatment, which was of great significance to improve the long-term stability of dental adhesion.6. Air blowing pressure may affect the pattern and distribution of silver tracer depositon. With the increased pressure, in contrast to the widely distribution in negative control groups and a small amount of silver depositon in control groups(0.1 MPa), 0.3 MPa showed spotted patterns of silver deposion with uniform distribution. A relative large amount of silver depositon could be found in the highest pressure(0.4 MPa). Aging treatment may to different extent enlarge the silver depositon, represented numerous reticular mode. However, 0.3 MPa 3 s and 5 s expressed only a little spotted deposition in aged groups.7. Air blowing pressure may affect the immediate and aged collagen degradation. With the increased pressure, collagen degradation became less. However, the collagen degradation of the highest pressure(0.4 MPa) and control groups(0.1 MPa) were more than other groups, with no statistic difference with each other. Aging treatment may increase the collagen degradation with the similar tendency of the immediate groups. 0.3 MPa had the least collagen degradation, which were 0.1226±0.01 mg/g and 0.1323±0.01 mg/g in immediate and aged groups.8. There was nagetive correlation between the bond strength of dental adhesion and the collagen degradation of bonded interface(r=- 0.58, P=0.000). The collagen degradation may interpret 33.7% of the variations of bond strength.9. Air blowing pressure may affect the histologic reaction of pulp-dentin complex. The mechanical stimuli during cavity preparation may mildly affect the pulp-dentin complex, with the separation of odontoblast cell layer and predentin layer. With the increased pressure, the morphology of odontoblast cells changed, disorder arranged, vacuolar degenerated, but, only few inflammatory cells infiltration could be observed in the highest pressure(0.4 MPa). After 3 w, while the morphology of odontoblast cells in 0.2 MPa and 0.3 MPa became as normal as control groups(0.1 MPa), 0.4 MPa revealed serious pulp inflammation. The control groups(0.1 MPa) and higher pressure groups(0.2 MPa and 0.3 MPa) represented biological safety.To conclude, pressure may significantly affect the bonding of resin and dentin, may increase the infiltration of adhesive resin monomers, and better encapsulate the exposed collagen fibrils, improve bond strength, creat compact and uniform hybrid lay, decrease nanoleakage, with no pulp inflammation, and enhance the resist aging ability of dental adhesion. 0.3 MPa 5 s is recommended.