| ObjectiveThis study was designed to evaluate the effect of materials and designs on fracture strength of the computer aided design/computer aided manufacturing(CAD/CAM)three-unit implant-supported dentures and to observe the parts and modes of porcelain fatigue damage.Providing reference for improving the success rate of implant-supported denture.Materials and Methods1.32 models of epoxy resin were prepared to simulate the mandibular defect of 35 to 37,and 64 one-stage soft tissue implants were implanted at positions 35 and 37.CAD/CAM system was used to produce 4 groups(n=8)of three-unit implant-supported dentures with different materials and designs.Group A:zirconia basal implant-supported fixed prostheses with regular marginal design.Group B:zirconia basal implant-supported fixed prostheses with full circumferential zirconia-collar.Group C:titanium basal implant-supported fixed prostheses with regular marginal design.Group D:titanium basal implant-supported fixed prostheses with full circumferential titanium-collar.All crowns were cemented on implant abutment with adhesive resin cement.All steps in production were equivalent to clinical situations.2.The specimens were tested under compressive cyclic loading using a fatigue testing machine.Fatigue load was delivered with a spherical tungsten carbide indenter(3.18 mm radius)on the center of the occlusal surface using r-ratio fatigue with a loading frequency of 1 Hz.The maximum compressive load was increased as the number of cycle increased(120,000 cycles at 20～250 N,40,000 cycles at 20～400 N,40,000 cycles at 20～600 N and 40,000 cycles at 20～800 N)until completion of 240,000 cycles or failure.The specimens were inspected after each loading sequence for initial failures such as cracks,porcelain chipping or basal crown fracture.After 2.4×105 loads,the specimens were tested for fracture resistance using a universal testing machine at the rate of 0.5mm/min until the specimens failed.3.Final failure was considered as any loss of material and the test ended automatically and the number of the loading force was recorded.Fractographic analysis of the fractured specimens was performed with scanning electron microscopy(SEM).The data were analyzed using SPSS 22.0.Results1.All specimens detected no cracks or damage after cyclic loading.The mean fracture strength values(N)of group A,group B,group C and group D were 1518.29±208.05,1727.40±134.52,1543.73±177.39,1753.39±141.08,respectively.Analysis of variance(ANOVA)results indicated that there was significant difference between the fracture loading force of the four groups(P<0.05).After using LSD-t multiple comparison,the results showed that there was a statistically significant difference between groups A and B,groups C and D(P<0.05),no significant difference between group A and C,group B and D(P>0.05).2.The types of fracture were porcelain chipping and basal crown exposure,no basal crown fracture.The difference of fracture types were not statistically significant(P>0.05).3.Scanning electron microscope observation showed that cracks started at the loading zone and wake hackle,twist hackle and arrest line were observed in the section.Conclusion1.The basal crown designed with full circumferential collar can increase fracture resistance of three-unit implant-supported fixed prostheses.2.The basal crown designed with full circumferential collar plays an important role in inhibiting crack propagation both in titanium basal implant-supported fixed prostheses and zirconia basal implant-supported fixed prostheses.3.The CAD/CAM three-unit implant-supported dentures made of zirconia based double-layer crown and pure Titanium based PFM crown have considerable flexural strength,which can meet the needs of clinical application. |
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