Effects Of The Lubricating Condition And Loading On The Wear Resistance Of The Feldspathic And Fluorapatite Porcelain: An In Vitro Study

With the improvement of the living standards, people pay more attention to the esthetic result of dental prostheses. The use of veneering porcelain can meet the needs of patients and dentists. During the chewing process, veneering porcelain contact with the enamel directly in the oral environment. It is unavoidable that veneering porcelain and the enamel would undergo wear process simultaneously. Wear resistance of the ceramics will directly affect the service life of prostheses. In addition, excessive wear of natural teeth will cause a series of oral diseases, and even the body health. Therefore, it’s very important to choose the suitable porcelain materials, of which coefficient of thermal expansion is matching with the substrate material, and the wear properties is similar to the enamel. This research on the wear properties of porcelain materials can help the dentists choose the suitable ceramics for patients and help researchers develop the new dental porcelain which suitable to the oral environment.There are lots of reasons for the failure of the prostheses, for example: the low bond strength between the veneering porcelain and the substrate crown, the low mechanical properties of the veneering porcelain and so on. Many kinds of porcelain were developed to solve this problem. Dentists have paid lots of attention to the wear behavior of porcelain material. There are lots of factors influenced the wear properties of ceramic materials, such as: the microstructure and mechanical properties of the ceramics, the wear environments(chewing force, saliva, temperature, food), and other factors. Therefore, it is very important to evaluate the wear resistance of porcelain material and the enamel. Preliminary findings of my research group found that the wear process of dental ceramic materials have the time-dependent wear behavior. Therefore, this experiment intended to investigate the wear prosperities of the feldspathic and fluorapatite porcelain paired with the ball of steatite, under different lubricating conditions and loadings. AIM:To investigate the wear prosperities of the feldpathic and fluorapatite veneering porcelain and steatite which was paired with veneering porcelain under the water or drying environments, or suffering different loadings. To discover the law of the wear curve development and the relevance of the wear characteristics of porcelain material with its microstructure and physical properties. To provide a reference for choosing the dental ceramic more reasonable. METHODS:1. The microstructure and mechanical properties analysis of the feldspathic and fluorapatite veneering ceramics and the steatite which was paired with veneering ceramics in the wear test. Using the XRD diffraction to analysis the crystal phase, SEM to observe the crystal morphology of the ceramics after etched. Three-point bending test to obtain the flexural strength, Nanoindentation test to gain the hardness and elastic modulus.2. The effect of lubricating conditions on the wear behavior of the feldspathic and fluorapatite ceramics paired with the steatite: the wear tests was performed in CSM friction and wear testing machine under dry and water environment respectively, 10 N loads, the maximum wear cycle is 1.2 million cycles under water, and 0.6 million cycles under dry environment. Using 3D profile meter to measure the volume loss and surface roughness after every 10×104cycles, which can generate the wear curve; Using SEM to observe the surface topography after wear analyzing the change of the surface grinding morphology.3. The effect of loadings on the wear behavior of the feldspathic and fluorapatite ceramics paired with the steatite: 10 N water, 2 N water, 10 N drying, 2 N drying were chose respectively. In order to analysis the change of wear curves and the surface topography under dry and water environment of the small load, 0.6 million cycles were performed. Using 3D profile meter to measure the volume loss and surface roughness after every 20×104 cycles. Using SEM to observe the surface topography after wear analyzing the change of the surface grinding morphology. RESULTS:1. XRD analysis result: the feldspathic ceramic contained the leucite crystals; fluorapatite ceramic contained the fluorapatite crystals; steatite contained the original enstatite crystals. There was amorphous package in the veneering ceramics on the XRD graph. However, there was no amorphous package in the steatite. This phenomenon indicated that the two veneering ceramics were glass ceramics. Steatite was a crystalline ceramic without glass phase. SEM observation showed that there were significant differences in the microstructure of two veneering ceramic: the leucite crystal in feldspathic ceramic was in bulk size. However, the fluorapatite crystal in fluorapatite ceramic was in nanometer size. Although volume fraction of the crystals in feldspathic was higher than fluorapatite, but the flexural strength, hardness and elastic modulus were lower than fluorapatite. There were lots of voids in steatite which induced greater fluctuation in the nanoindentation hardness and elastic modulus values.2. The volume loss and surface roughness was lower significantly under water environment than under dry environment at load of 10 N. This phenomenon was consistent with the most tribological materials. Microstructure and mechanical properties of two veneering ceramics have an important impact on their wear resistance. The volume loss of fluorapatite ceramics was lower than feldspathic under dry environment, but higher under water, due to the different dominant mechanisms. Considering the ceramic and steatite as a whole, higher volume loss of the ceramics induced higher volume loss of the steatite under water and dry environment. In other words, the difference between the microstructure and mechanical properties of ceramics affected not only the wear characteristics of its own, but also the wear behavior of paired materials.3. Comparing the 10 N groups, the volume loss and surface roughness of the veneering ceramics in the 2 N groups were reduced significantly both in water and in dry environment. The load also had a significant effect on the wear properties of two veneering ceramics. The volume loss and surface roughness of the porcelain were higher in water than that in the dry environment. There was no significant difference between the two veneering ceramics due to the small amount of wear in the dry environment, 2 N loads. Feldspathic ceramic exhibited a better resistance than fluorapatite ceramic under water. Similarly, Considering the ceramic and steatite as a whole, higher volume loss of the fluorapatite ceramic induced higher volume loss of the steatite under water. When the load reduced from 10 N to 2 N, the difference between the microstructure and mechanical properties of ceramics also affected the wear characteristics of its own and paired materials. CONCLUSION:There is difference between feldspathic and fluorapatite veneering ceramics in microstructure and mechanical properties. The changing of the wear curves and the evolution of grinding morphology are different under different lubricating conditions. Load level also has an important impact on the wear curves and the grinding morphology evolution. Wear properties of two veneering have a close correlation with the microstructure and mechanical properties. At the same time, this relationship is affected by the lubricating conditions and loadings. The findings will help dentists choose the reasonable ceramic materials, and promote the development of a new type of veneering materials.