| Because of its excellent biocompatibility and good performance dental ceramics waswidely used in clinical physicians. When dental ceramic restorations functioned in oral,the wear between restorations and enamels is widespread and inevitable. This behaviorwas harmful to both restorations and enamels. Clinical research results show that theexcessive wear of the teeth can produce a variety of oral diseases which would affect thewhole body health. Factors of basic chewing movement and night bruxism could causewear of dental ceramic restorations, thus would cause cracks of the ceramic restorations.So, the performance of dental ceramic materials and enamels needed to match each other.Therefore, understanding of the wear properties of dental ceramic materials and enamelcould help clinicians choose appropriate repair material for patients and help to developmore suitable dental restorative materials.in oral environment.Classic tribology theory of mechanical considered the wear process of friction pairwould show a wear curve consisted of three stages such as "running-in stage ","stable wear stage" and "severe wear stage". But in dental research, previous scholars studied thedental ceramic and natural teeth in a particular point of the time. Therefore, our researchgroup investgated the tribology characteristics of veneering porcelain of the co-cr alloyPFM crown. Results showed that superficial area of the worn co-cr alloy PFM crownshowed three stages: running-in ","stable wear " and "severe wear ". This researchinvestgated tribology characteristics of the friction pair such as dental feldspathicporcelain-enamel、lithium disilicate ceramic-enamel、dental feldspathic porcelain-ball、lithium disilicate ceramic-ball and enamel-ball from the dynamic chewing perspective andto explore the wear rules of the friction pair system.AIM:By simulating the oral environment under cyclic loading experiment in vitro, toinvestigate wear rules and macro、microstructure manifestation of the five friction pairs.To provide a reasonable evaluation of dental ceramic and enamel wear resistance from anew idea.METHOD:1. The study of tribology characteristics of dental feldspathic porcelain-enamel andlithium disilicate ceramic-enamel friction pairs in vitro：Wear tests were performed insimulated oral environment with enamel antagonists、dental feldspathic porcelain andlithium disilicate ceramic in the chewing simulator．There were6samples in each group.The tribological tests were carried out under artificial saliva lubrication condition、roomtemperature and a vertical load of10N for1.2×106cycles（f=2Hz，uniform circularmotion，revolving speed=120r/min）. The wear volumes of two ceramics and enamelwere measured by3D profiling every2×105cycles.2. The study of the two friction pairs’ macro and microstructure mechanism duringthree stages: The vickers hardness of enamel、dental feldspathic porcelain and lithiumdisilicate ceramic were measured by Automatic turret digital display microhardness tester.The parameters of the wear tests were the same as the first experiment. The surfaceroughness and the three-dimensional topography were measured by3D profiling and thesurface microscopic morphology were measured by scanning electron microscopy in the middle of each stages. There were3samples in each group.3. The study of tribology characteristics of dental feldspathic porcelainporcelain-enamel antagonist and lithium disilicate ceramic-enamel antagonist frictionpairs in vitro：Wear tests were performed in simulated oral environment with stainlesssteel ball antagonists、enamel、dental feldspathic porcelain and lithium disilicate ceramicin the chewing simulator．There were6samples in each group. The tribological tests werecarried out under artificial saliva lubrication condition、room temperature and a verticalload of10N for1.2×106cycles（f=2Hz，uniform circular motion，revolving speed=120r/min）. The wear volumes of two ceramics and enamel were measured by3D profilingevery2×105cycles.4. The study of the three friction pairs’ macro and microstructure mechanism duringthree stages: The surface roughness and the three-dimensional topography were measuredby3D profiling and the surface microscopic morphology were measured by scanningelectron microscopy in the middle of each stages. There were3samples in each group.The parameters of the wear tests were the same as the first experiment.RESULT:1. Under the simulated oral environment, in the dental feldspathic porcelain-enamelfriction pair the wear rates from2105to1.2106cycles of dental feldspathic porcelainwere （0.019090.00876）（0.019940.00511）,（0.052770.01612）,（0.008200.00258）,（0.061460.02677）and（0.031730.00419）(10-4mm3/cycles). The wear rates of enamel were（0.067590.03120）,（0.192140.05447）,（0.166360.04791）,（0.044140.006136）,（0.303990.17667）and（0.432760.25794）(10-4mm3/cycles). The differences between wearrate of the six point were statistically significant. The differences between6105cyclesand8105cycles,8105cycles and10105cycles were statistical significance. The wearcurve of dental feldspathic porcelain-enamel friction pairs presented three stages:running-in stage（0-6105cycles）, steady wear stage (6105-8105cycles)and severe wearstage(8105-1.2106cycles). Dental feldspathic porcelain and enamel went into steady wearstage together.Under the simulated oral environment, in the lithium disilicate ceramic-enamel antagonist friction pair the wear rates from2105to1.2106cycles oflithium disilicate ceramic were （0.095700.02193）,（0.124310.04226）,（0.134430.05023）,（0.339970.09603）（,0.094550.02678）and（0.779250.23597）(10-4mm3/cycles). The wear ratesof enamel were （0.055000.01828）（,0.038890.00841）（,0.082790.04619）（,0.061440.02785）,（0.008030.003333）and（0.385060.097667）(10-4mm3/cycles). The differences between wearrate of the six point were statistically significant. The differences between8105cyclesand1.0106cycles,1.0106cycles and1.2106cycles were statistical significance. Thewear curve of lithium disilicate ceramic-enamel antagonist friction pairs presented threestages: running-in stage（0-8105cycles）, stable wear stage (8105-1.0106cycles) and severewear stage(1.0106-1.2106cycles). Lithium disilicate ceramic and enamel went into steadywear stage together.In the dental feldspathic porcelain-enamel antagonist friction pair, the wear loss ofenamel was greater than dental feldspathic porcelain.While in the lithium disilicateceramic-enamel antagonist friction pair, the wear loss of lithium disilicate ceramic wasgreater than enamel. The total wear loss of lithium disilicate ceramic-enamel antagonist isgreater than dental feldspathic porcelain-enamel antagonist.2. The vickers hardness of enamel、dental feldspathic porcelain and lithium disilicateceramic were334.2±16.4Hv、540.7±19.8Hv、499.2±24.3Hv. The surface roughness ofdental feldspathic porcelain and lithium disilicate ceramic from running-in stage to severewear stage showed decreasing first then increasing. The surface roughness of lithiumdisilicate ceramic is bigger than dental feldspathic porcelain. The microstructure of dentalfeldspathic porcelain-enamel antagonist in running-in stage showed shallow and smallgrinding crack. The wear tracks fusioned in the steady wear stage and between the weartrack showed the smooth area. Severe wear stage showed large piece of debris peeling.The microstructure of lithium disilicate ceramic-enamel antagonist showed shallow weartrack in running-in stage. In steady wear stage, the narrow plow turned into wide plow.The area between the plow was flat. The enamel wear tracks changed deeper, butrelatively flat surface. In severe wear stage, lithium disilicate ceramic showed a flat surface under the effect of plowing. The enamel surface showed flake peeling. The macroand microstructure manifestation of dental feldspathic porcelain-enamel antagonist andlithium disilicate ceramic-enamel antagonist friction pairs were consistent withcharacterization of their wear curve during each wear stages.3. Under the simulated oral environment, the wear rates of dental feldspathicporcelain-ball antagonist friction pairs from2105to1.2106cycles were（0.001200.00018）,（0.000100.00003）,（0.000500.00005）,（0.000100.00002）,（0.004100.00038）and（0.019000.00353）(10-4mm3/cycles). The differences between wearrate of the six point were statistically significant. The differences between2105cyclesand4105cycles,8105cycles and1.0106cycles were statistical significance. The wearcurve of dental feldspathic porcelain-ball antagonist friction pairs presented three stages:running-in stage（0-2105cycles）, stable wear stage (2105-8105cycles) and severe wearstage(8105-1.2106cycles). Under the simulated oral environment, the wear rates of lithiumdisilicate ceramic-ball antagonist friction pairs from2105to1.2106cycles were（0.139500.03094）、（0.124400.03120）,（0.054800.00538）,（0.038800.00610）,（0.011100.00375）and（0.198900.04580）(10-4mm3/cycles). The differences between wearrate of the six point were statistically significant. The differences between4105cyclesand6105cycles,1.0106cycles and1.2106cycles were statistical significance. Thewear curve of lithium disilicate ceramic-ball antagonist friction pairs presented threestages: running-in stage（0-4105cycles）, stable wear stage (4105-1.0106cycles) and severewear stage(1.0106-1.2106cycles). Under the simulated oral environment, the wear rates ofenamel-ball antagonist friction pairs from2105to1.2106cycles were（0.001150.00022）,（0.001000.00042）,（0.001060.00021）,（0.000860.00019）,（0.001260.00060）and（0.001180.00096）(10-4mm3/cycles). The differences between wearrate of the six point had no statistically significant. The wear curve of this friction pairunder the condition had’t present three stages.The wear loss of lithium disilicate ceramic-ball antagonist was greater than dentalfeldspathic porcelain-ball antagonist. 4. The surface roughness of dental feldspathic porcelain-ball antagonist and lithiumdisilicate ceramic-ball antagonist from running-in stage to severe wear stage showeddecreasing first then increasing. The surface roughness of lithium disilicate ceramic wasgreater than dental feldspathic porcelain. While the surface roughness of enamel didn’tchange. The microstructure of dental feldspathic porcelain-ball antagonist in running-instage showed shallow tracks. The wear tracks fusioned in the steady wear stage andbetween the wear track showed the smooth area, While in severe wear stage showedplowing track. The microstructure of lithium disilicate ceramic-ball antagonist showedshallow and intensive wear track in running-in stage. In steady wear stage, the narrowplow turned into large area of stripped crack. In severe wear stage the surface showedplowing track. The enamel-ball antagonist showed uniform distribution of wear tracks.The macro and microstructure manifestation of veneer porcelain-ball antagonist andheat-pressed ceramic-ball antagonist friction pairs were consistent with characterizationof their wear curve during each wear stages. While the macro and microstructuremanifestation of enamel-ball antagonist friction pair suggested no obvious changes in theprocess of wear, thus was consistent with linear upward trend wear curve.By simulating the oral environment under cyclic loading experiment in vitro, thewear process of friction pairs such as veneer porcelain-enamel antagonist、heat-pressedceramic-enamel antagonist、veneer porcelain-ball antagonist and heat-pressed ceramic-ball antagonist demonstrated three stages：running-in stage，steady wear stage and severewear stage. The macro and microstructure manifestation of the four friction pairs wereconsistent with characterization of their wear curve during each wear stages. While thewear characteristic of enamel-ball antagonist friction pair hadn’t show the three wearstages under the condition of this experiment. The results helped the stomatologist tounderstand the wear mechanism, the prognosis of dental ceramic restorations as well as toreasonablely select proper restoration plan. |
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