| Objective:By comparing the flexural strength of inner crown with different thickness of DOCERAM-Nacera full porcelain telescope denture,the experiment conclude the minimum thickness of the inner crown with zirconia porcelain crown to provide a basis for clinical treatment.Then load vertically and inclined loading to 30 degrees to the telescope denture to fracture with the outer crown of different materials and the inner crown with the same thickness,and compare the flexural strength,it provides a reference for choosing the material of the inner and outer crown in clinical cases,especially as patients with a smaller vertical distance.Methods:First: Moulds were made with a support base of 7 mm in diameter,5 mm in hight,and a mental abutment tooth generation type of 5 mm in diameter,6 mm in hight,1.0 mm wide in shoulder of 90 degrees.The moulds were randomly divided into six groups.Zirconia porcelain crowns were designed and product with thickness of 0.3 mm,0.4 mm,0.5 mm,0.6 mm,0.8 mm,1.0 mm using CAD/CAM system.Bond the crowns into the mental abutment tooth generation types using resin cement,50 n refers to the pressure in place.After preservated in normal temperature for 24 hours,all the samples were loaded vertically to fracture at a speed of 0.5mm per minute using a universal testing machine.For each sample,we recorded the force to fracture.Second: 45 mental abutment teeth were made with a support base of 7 mm in diameter,5 mm in height,and a shoulder of 90 degrees of 5 mm in diameter,6 mm in height,1.0 mm wide at the neck edge.The 45 samples were made as standard group.Another 45 mental abutment teeth were made with a support base of 7 mm in diameter,10 mm in height,60 degrees in gradient and a shoulder of 90 degrees of 5 mm in diameter,6 mm in height,1.0 mm wide at the neck edge.The 45 samples were made as gradient group.The samples in standard group were randomly divided into 3 groups.15 zirconia porcelain inner crowns were respectively designed and product with thickness of 0.3 mm,0.4mm and 0.5mm using CAD/CAM system.Then 15 casting co-cr alloy outer crowns,15 zirconia porcelain crowns and 15 thermosetting resin outer crowns were respectively made with no anatomical morphology of no buffer type telescope denture.The samples in gradient group were randomly divided into 3 groups.15 zirconia porcelain inner crowns were respectively designed and product with thickness of 0.3 mm,0.4mm and 0.5mm using CAD/CAM system.Then 15 casting co-cr alloy outer crowns,15 zirconia porcelain crowns and 15 thermosetting resin outer crowns were respectively made with no anatomical morphology of no buffer type telescope denture.Bond the 90 crowns into the mental abutment teeth using resin cement with 50 N position pressure.After preservated in normal temperature for 24 hours,all the samples were inserted and separated for 3000 times.Then all the samples with no inner crown fracturedwere loaded vertically and slantly for 30 degrees to fracture at a speed of 0.5mm per minute using a universal testing machine at a.For each sample,we recorded the force to fracture.Results:1.Part ? : the force to fracture of Group 0.03 mm is the smallest of(361.15±6.18)N,group 0.04 mm is(412.26±15.31)N,group 0.05 mm is(540.94±17.56)N,group 0.06 mm is(737.64±19.43)N,group 0.08 mm is(1169.33±47.19)N,the force to fracture of group 1.0mm is the largest of(1786.54±19.37)N.The force to fracture increased as the thickness of the inner crown increase.Among groups the force to fracture value sequentially,difference was statistically significant(?<0.05).Part?: For standard group,when the thickness of the inner crown is 0.3mm,the force to fracture of group thermosetting resin is(1053.39±63.53)N,group casting co-cr alloy is(1216.90±34.67)N,group zirconia porcelain is(432.95±19.86)N,when the thickness of the inner crown is 0.4mm,the force to fracture of group thermosetting resin is(1207.16±16.67)group casting co-cr alloy is(1302.50±18.37)N,group zirconia porcelain is(550.45±31.88)N,when the thickness of the inner crown is 0.5mm,the force to fracture of group thermosetting resin is(1337.54±22.06)N,group casting co-cr alloy is(1338.05±41.40)N.group zirconia porcelain is(761.78±16.71)N.With the same thickness,the force to fracture among groups thermosetting resin,casting co-cr alloy and zirconia porcelain was different,group casting co-cr alloy is the best,group zirconia porcelain is the last,difference was statistically significant(?<05).With the same outer crown material,the force to fracture among groups 0.3mm,0.4mm and 0.5mm was different,the force to fracture increased as the thickness of the inner crown increased,difference was statistically significant(?<0.05).For gradient group,when the thickness of the inner crown is 0.3mm,the force to fracture of group thermosetting resin is(789.81±20.71)N,group casting co-cr alloy is(462.18±16.61)N,group zirconia porcelain is(413.00±13.34)N,when the thickness of the inner crown is 0.4mm,the force to fracture of group thermosetting resin is(912.81±15.33)N,group casting co-cr alloy is(565.57±14.92)N,group zirconia porcelain is(506.23±14.43)N,when the thickness of the inner crown is 0.5mm,the force to fracture of group thermosetting resin is(1028.86±25.96)N,group casting co-cr alloy is(715.60±13.92)N,group zirconia porcelain is(652.79±23.74)N.With the same thickness,the force to fracture among groups thermosetting resin,casting co-cr alloy and zirconia porcelain was different,group thermosetting resin is the best,group zirconia porcelain is the last,difference was statistically significant(?<0.05).With the same outer crown material,the force to fracture among groups 0.3mm,0.4mm and 0.5mm was different,the force to fracture increased as the thickness of the inner crown increased,difference was statistically significant(?<0.05).Conclusion:1.Thickness has an influence on the fracture resistance of thezirconia crown.With the increase of thickness of zirconia crown,the fracture resistance of the zirconia crown also will increase.2.The force to fracture of the zirconia inner crowns with 0.3 mm thick were greater than 300 N according with clinical standards.So the thickness of 0.3mm satisfy the clinical requirements.3.The material of the outer crown has an influence on the fracture resistance of the porcelain telescope.With the same thickness of the inner crown,when loaded vertically,the fracture resistance of the outer crown with casting co-cr alloy is the best,then the thermosetting resin,and the zirconia porcelain is the last.When loaded slantly for 30 degrees,the fracture resistance of the outer crown with thermosetting resin is best,then the casting co-cr alloy and the zirconia porcelain is the last.4.When loaded vertically and slantly for 30 degrees The thickness of 0.3mm of the zirconia inner crown satisfy clinical requirements.When the thickness of the inner crown is larger then 0.3mm,the fracture resistance of the porcelain telescope with casting co-cr alloy,thermosetting resin,and zirconia porcelain all satisfy the clinical requirements,it can Provide a basis for clinical treatment to choose materials. |
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