A Comparative Study Of Four Crown Materials And Enamel On The Wearing Ability In Vitro

Objective：To study the wear ability of the zirconia full-coverage crownand three kinds of clinical commonly used full crown repair materials（Cobaltchromium crown，CAD/CAM titanium crown，all-ceramic crown）andenamel,and to compare different materials volume loss with the natural toothin order to research the abrasion wear mechanism of enamel and otherrepairing materials,and to provide the experimental basis for choosing betterclinical repair material appropriately.Methods:1experimental conditions: The tests were conducted using Pin-on-platetwo-body wear machine.The testing machine,which was set to75r/min,underthe vertical loading force is40N,and the testing time was5hours and33.5minutes, totally25000rpm.During the tests the artificial saliva which was setto37℃was added to immerse the specimens evenly.Four kinds of dentalmaterials and fresh natural enamel were installed in the upper fixture ofPin-on-plate two-body wear machine respectively, and steatite porcelain wasinstalled in the lower fixture.Steatite specimens should be replaced by the endof each test.2Specimen preparationPMMA dies which were used as the post-core were prepared according tothe Pin-on-plate two-body wear machine.Four kinds of ceramic:The zirconiafull-coverage crown，Cobalt chromium crown，CAD/CAM titanium crown andall-ceramic crown which used as experimental group were fabricated intotwenty uniform specimens, and there were five specimens for eachmaterial.The occlusal area of each specimen was a square of5.0x5.0mm,andthe occlusal was parallel with the bottom of the die.3The preparation of Human tooth enamel which was used as control group Five recently extracted maxillary third molar of adults were selected asgroup E, each of them remaining5.0mm×5.0mm occlusal area of enamelwhich was parallel with the bottom of the die, and then the roots wereembedded in PMMA.4The choose of antagonist material： Due to steatite with stableperformance which is similar to wear resistance of enamel， andstandardization may be relatively easy to materialize，so we choose steatite asantagonist material to reduce experimental error.The steatite was processedinto25disc-shaped ceramic chips,45.0mm in diameter and6.0mm inthickness.5Volume measurement and data:Before the experiment, the specimens were treated with ethanol cleaningfor15minutes followed by distilled water cleaning for3times. Then, thespecimens were dried and weighed using the electronic balance (accurate to0.0001g).After the experiment,repeat the foregoing steps,then calculate theweight loss. The density of each was measured by water overflow method.Atlast,the volume loss of the specimen，enamel and opposing steatite werecalculated by the mass loss and density.6Statistical analysisSPSS13.0statistical software was used for statistical analysis.7Scanning electron microscope observationScanning electron microscope microscope was used to analyze themicrostructure of the wear surface of specimens and the wear mechanism wasdiscussed.8Hardness testOne specimen made of each material was randomly selected, and thehardness of the specimen at five loci was determined using the VickersHardness Tester.Results:1The volume loss of specimens from group A to group E was: group A0.09051.0416㎜3,group B12.55961.2609㎜3,group C0.04800.0160 ㎜3,group D2.07500.3685㎜3,group E14.69490.4558㎜3.The ranking ofthe volume loss of four specimens from the most to the least was: group E,group B, group D, group A, group C. Group E was the most,significantdifference was found between group E and all the other groups(P＜0.01).TheVolume loss of Natural enamel was significant more than the other testedspecimens. Group C was the least,significant difference was found betweengroup C and all the other groups (P＜0.01）. The volume loss of zirconia wassignificant less than the other tested specimens.Group A with the othergroups,group B with the other groups,Group D with the other groups wassignificant difference.The volume loss of the steatites caused by the specimens: group A4.14220.1016㎜3，group B3.97870.0783㎜3，group C4.74290.5273㎜3，group D2.37070.7729㎜3，group E1.78610.4271㎜3.The ranking of thevolume loss from the most to the least was: group C, group A, group B,group D, group E.Group C was the most,no significant difference betweengroup A and group C（P＞0.05）,difference was found between group B andgroup C（P＜0.05）,significant difference was found between group C andgroup D,E（P＜0.01）.There was no difference in volume of group A and groupC,but more than the other groups.Group E was the least,no difference wasfound between group E and group D（P＞0.05）, significant difference wasfound between group E and group A,B,C.The volume loss caused by ceramicand natural enamel was not difference,but less than the other groups.Group Aand group B were difference (P＜0.05).Significant difference was foundbetween group A and group D, between group B and group D（P＜0.01）.2The results of hardness tests was: Cobalt chromium44718HV,titanium1747HV,zirconia140954HV,ceramic73530HV, natural enamel36315HV.3The result of scanning electron micrograph(SEM):In goup A,the surface wasSmooth, and a few scars and small pits can be found on it. In group B,the scarswas very clear,and was wider and deeper than group A.Chunks of grindingspots can be seen on the wear surface.In group C，the surface showed fine grain of crystal sizes and homogeneous structure，you see there were someScattered scratches parallel to each other.In group D,the surface showed aloose structure,scars was wider and deeper than group C.In group E, thesurface showed clear uniform arrays of fine scratches,scars was not verydeep.Conclusion:1The four materials were more resistant to wear than natrualtooth,zirconia showed the most resistant to wear. The wear resistance oftitanium was the least.2Among the four tested materials,SHOFU ceramic caused the leastabrasion to natural tooth,and the other three groups all created excessiveabrasion to natural tooth.3The microstructure of the ceramic material was an important factor thatinfluence the wear properties. Attempt to improving the microstructure ofmaterial could reduce the excessive abrasion to natrual enamel.