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Journal of Oral Science & Rehabilitation No. 4, 2016

Journal of Oral Science & Rehabilitation Volume 2 | Issue 4/2016 67 E f f e c t s o f i n s e r t i o n t o r q u e o n h a r d a n d s o f t t i s s u e a f t e r t w o y e a r s S t a t i s t i c a l a n a l y s i s Power analysis was employed to determine the sample size using a 0.05 significance level and a power of 80%, based on the results reported in a previous studyconcerning periimplant margin- al bone loss.15 Sample size estimates, ranging from 23to 168,were generated, comparing data on regular-IT and high-IT groups at the time of loading and aftertwoyears.Aprimarystatistical evaluation was performed with multiway analy- sis of variance and multiple regression analysis (DatabaseToolboxandStatisticsToolbox,MatLab 7.0.1, MathWorks, Natick, Mass., U.S.). Post-hoc comparisons were performed with a t-test and theconfidenceintervalwassetat95%(Statistics Toolbox). The level of statistical significance (p-value) was set at 0.05 for all analyses. Results One hundred and twenty implants were con- sidered eligible for this study. Four patients were excluded (two required bone augmenta- tion at the time of implant insertion; one re- fused to attend the recall visits; and one had excessive IT at the time of implant placement, so the osteotomy had to be widened with a countersink bur before implant insertion). The remaining 116 patients were allocated to two groups (58 to the regular-IT and 58 to the high- ITgroup), accordingto a randomization process. Each patient received one implant and the ex- perimental sites were followed for two years. The patients’ mean age at the time of the sur- gerywas 51.5 ± 8.2years inthe regular-ITgroup and 51.3 ± 8.2 years in the high-IT group. Im- plants were inserted both in the maxilla and in the mandible, showing a homogenous distri- bution between the lower and upper jaws. Most of the sites were located in the premolar area, both forthe regular-IT (29 implants) and forthe high-IT (36 implants). The mean IT registered at the time of implant insertion was 30.3 ± 7.5 N cm for the regular-IT group and 68.8 ± 9.0 N cm for the high-IT group. The im- plant distribution is shown in Table 1. After 24 months, one implant in the regu- lar-IT group and three implants in the high-IT group were considered failures, since it was necessary to remove and replace the implants. The survival rate recorded in the regular-IT group was 98.2%, while in the high-IT group it was 94.8%. Theimplantsuccessratewasestablishedaccord- ing to Buser et al.,14 considering a marginal bone loss > 1.5 mm at 12 months afailure criterion. On that basis, after two years, one implant in the regular-IT group could not be considered suc- cessful, and the cumulative success rate in this group was 98.2%. In the high-IT group, the cu- mulative success rate was significantly lower (93.1%), since four implants did not fulfil the success criteria. The MBL values were homogeneous at ba- seline between the two groups, as they depen- ded on the final position of the implants in the healed bone ridges decided by the surgeon. The MBLvalues at baseline (maxilla: 0.14 ± 0.47 mm in the high-IT group and 0.12 ± 0.39 mm in the regular-IT group; mandible: 0.10 ± 0.24 mm in the high-IT group and 0.06 ± 0.17 mm in the regular-IT group) attested that the fixture plat- formwas positioned at the bone crest level both in the maxilla and in the mandible (Figs. 2 & 3). Regarding the maxillary MBL values, after one year, the bone levels had decreased in both groups, showing a significant difference bet- weentheregular-andhigh-ITgroups(p=0.0045; Figs. 4 & 5). The difference between the two groups was still significant at the 24-month fol- low-up, being -0.79 ± 0.38 mm in the high-IT group and -0.55 ± 0.31 mm in the regular-IT group (p = 0.0056; Figs. 6 & 7). The ΔMBL emphasized the difference between the two groups after two years, being -0.93 ± 0.57 mm in the high-IT group and -0.67 ± 0.43 mm in the regular-IT group in the maxilla at the 24-month recall. In particular, the ΔMBL at 24 months in the high-ITgroup showed a slight increase inthe MBL compared with the 12-month time point, but the difference between the high- and regu- lar-IT groups was still significant (p = 0.0095). Differences inthe effects ofthe ITappeared even more evident inthe mandible.Afteroneyear,the MBL in the high-IT group was -1.23 ± 0.36 mm, and after 24 months, it was -1.21 ± 0.36 mm, showing that the MBL remained quite stable between the one- and the two-year recall visits. The MBL in the high-IT group had decreased to 1.31 ± 0.33 mm at the two-year follow-up; this value was similar to the ΔMBL at 12 months, attestingthattheboneridgearoundtheimplants in the high-IT group remained stable after a re- markable decrease inthefirstyear.The MBLand ΔMBLvalues in the regular-IT group were com- pletely dissimilar from the high-IT group values in the mandible. The MBL was -0.63 ± 0.31 mm atthe 12-monthfollow-up and -0.68 ± 0.30 mm Volume 2 | Issue 4/201667

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