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ePaper created 2016-09-20, 16:58:27 | version 1.38.0
Journal of Oral Science & Rehabilitation 28 Volume 2 | Issue 3/2016 F r a c t u r e r e s i s t a n c e o f p r o v i s i o n a l i m p l a n t - p r o s t h e t i c a b u t m e n t s position conditions in the alveolar ridge in the premaxilla,specimenswereplacedinthecylinder at an angle of30°tothe direction ofthe load.The abutments were screwed on to the implant– cylinder complex using a dynamometric torque wrench,applyingatorqueof30N,asrecommend- ed by the manufacturer. M e t h o d Before specimens underwent static loadtesting, they were subjected to dynamic loading. This fatiguing process was performed using a chew- ing simulator (CS-4, SD Mechatronik. Rosen- heim, Germany; Fig. 1). Loading was applied to the upper part of the abutment (angled at 30°) with an impact force of 80 N and a frequency of 2 Hz. Each specimen was subjected to 60,000 cycles at an application speed of 40 mm/s. They then underwent thermocycling (Thermocycler 2000, Heto-Holten A/S, Allerod, Denmark) for 6000cycleswithtemperaturechangesbetween 5°C and 55°C every 30 seconds. Static compression load testing was used to evaluatethe abutments’fracture resistance.The testing was performed using a static load test- ing machine (AG-X plus, Shimadzu, Kyoto, Japan). A load cell of 5,000 N was used at a crosshead speed of 0.5 mm/min (Fig. 2). Statistical analysis consisted of preliminary descriptive analysis of the force (fracture re- sistance) and deformation variables (mean, standard deviation, range and median). Com- parisons were made adopting a nonparametric approach. Significancewas set at 5% (p = 0.05). Results TheresultsobtainedregisteredtheforceinNew- tons (N) required to produce the fracture of each specimen(Tables2&3). Fracture ofthe prosthe- siswasunderstoodasthefirstmechanicalfailure that the specimen underwent, whether this was the maximum load that produced a clearly ob- served fracture or the maximum load before the test machine registered a decrease in load even if the fracture was not visibly obvious. Fracture resistance values for two specimens (not sub- jectedto fatiguing)were discarded owingto fail- ure to fulfill the study procedure. The same also occurred with two specimens subjected to fa- tiguing. Table 4 shows the descriptive data by group forfractureresistanceinspecimensnotsubjected tofatiguing.Thegroupthatpresentedthehighest resistance to fracture was the TD group and the group that showed the least resistance was the PP group, with mean values of 1,106.7 N and 329.4 N, respectively.The groupsthat presented the lowest resistance to fracture were CMP and PP, obtaining values of between 300 N and 400 N. Fracture resistance levels were hetero- geneous, as the Kruskal–Wallis test confirmed that there was no homogeneity in the distributi- onofresistanceacrossthefourgroups(p=0.006). When the Mann–Whitney test was applied to identify differences between pairs of groups, CMPshowedlowerresistancethanTP(p=0.032) and TD (p = 0.016), with the differences being statisticallysignificant. PPrestorations obtained lower resistance than the TP (p = 0.016) and TD Fig. 1 Cyclic loading of implant- supported abutments. Fig. 2 Static load testing of implant-supported abutments. Figs. 1 & 2