***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: PURPOSE The literature reports that flapless compared with traditional implant surgery can be associated with several advantages , including the maintenance of peri-implant hard tissues . This study investigated vertical bone resorption during long-term follow-up after implant placement with flapless versus traditional surgery . MATERIAL AND METHODS In this prospect i ve , r and omized controlled clinical trial , 40 patients underwent implant placement at the Maxillofacial Department Surgery of the Istituto Stomatologico Italiano Hospital in Milan , Italy . Patients were r and omly assigned to the control or experimental group . The control group had implants placed with open flap surgery ( traditional surgery ) , whereas the experimental group had implants placed with flapless surgery . The distance between the first implant thread and the marginal crestal bone level was measured at the basal , loading , and long-term control points . The basal recording was performed just after implant placement . The loading measurement was recorded at the time of implant loading , after 2 months of healing for the lower jaw and after 3 months of healing for the upper jaw , and the long-term control record was registered 36 months after implant placement . Statistical analysis was performed using mean values and st and ard deviations based on bone resorption in the 2 groups . To detect statistical differences , the Student t test was applied . Differences were considered significant if P values were less than .05 . RESULTS The control group ( open flap surgery ) was comprised of 19 patients , and the experimental group ( flapless surgery ) was comprised of 21 patients . No statistical differences were found in peri-implant bone resorption between the 2 groups at the basal , implant loading , and 3-year control recordings . CONCLUSION According to this study , the approach to implant surgery does not seem to influence peri-implant bone resorption in humans , at least for the period measured in this study PURPOSE To compare the efficacy of immediate functionally loaded implants placed with a flapless procedure ( test group ) versus implants placed after flap elevation and conventional load-free healing ( control group ) in partially edentulous patients . MATERIAL S AND METHODS Forty patients were r and omized : 20 to the flapless immediately loaded group and 20 to the conventional group . To be immediately loaded , implants had to be inserted with a minimum torque > 45 Ncm . Implants in the immediately loaded group were provided with full acrylic resin temporary restorations the same day . Implants in the conventional group were submerged ( anterior region ) or left unsubmerged ( posterior region ) and were left load-free for 3 months ( m and ibles ) or 4 months ( maxillae ) . Provisional restorations were replaced with definitive single metal-ceramic crowns 1 month postloading . Outcome measures were prosthesis and implant failures , biological and prosthetic complications , postoperative edema , pain , and use of analgesics . Independent sample chi2 tests , Mann-Whitney tests , t tests , and paired t tests were used with a significance level of .05 . RESULTS Fifty-two implants were placed in the flapless group and 56 in the conventionally loaded group . In the flapless group , 1 flap had to be raised to control the direction of the bur and 1 implant did not reach the planned primary stability and was treated as belonging to the conventional group . After 3 years no dropouts or failures occurred . There was no statistically significant difference for complications ; however , patients in the conventional group had significantly more postoperative edema and pain and consumed more analgesics than those in the flapless group . Osstell values were significantly higher at baseline in the flapless group ( P = .033 ) . When comparing baseline data with years 1 , 2 , and 3 within each group , mean Osstell values of the flapless group did not increase , whereas there were statistically significant increases in the Periotest values . CONCLUSIONS Implants can be successfully placed flapless and loaded immediately without compromising success rates ; the procedure decreases treatment time and patient discomfort PURPOSE The purpose of this 2-year r and omized controlled clinical trial was to assess the differences in implant survival rates , soft tissue preservation , patient centered outcome and crestal bone changes applying the minimally invasive ( MI ) flapless approach for single implant placement compared to flapped implant surgery ( FS ) . MATERIAL S AND METHODS Subjects eligible for this study were r and omly assigned into two groups : MI or FS . Items of evaluation were the following : implant installation position , soft tissue healing , post-surgical pain , soft tissue outcome , marginal bone loss ( MBL ) , and implant survival rate . RESULTS Forty subjects ( 14 women and 26 men , 20 in MI group and 20 in FS group with a mean of 39 ± 13.2 years old ) were included in the study . None of the implants demonstrated dehiscence or loss during the follow-up . Subjects in MI group showed significantly lower post-surgical pain and significantly less wound healing index scores at 1-week follow-up . The width of keratinized mucosa decreased from a mean of 4.2 ± 1.6 mm pre-surgically to 3.7 ± 1.1 mm at crown delivery but remained stable at 2-year follow-up in MI group . At every appointment in the study , no statistical significant difference of PD and MBL was found between the two groups . CONCLUSION Compared with FS , single implants placed applying the MI technique in selected subjects showed advantages in improving patient comfort and decreasing post-implant placement soft tissue reaction . Meanwhile , implants with MI approach have the same level of MBL and high success rates as FS procedure at 2-year follow-up . The deduction of keratinized mucosa is very limited and the width of KM remained stable with MI approach at 2-year follow-up PURPOSE The aim of this prospect i ve clinical study was to evaluate the 3-year outcome of fixed partial prostheses supported by implants with immediate provisionalization without occlusal contacts inserted in predominantly soft bone with flap and flapless protocol s. MATERIAL S AND METHODS Forty-one patients partially rehabilitated with 72 NobelSpeedy implants ( 51 maxillary ; 21 m and ibular ) were consecutively included and treated with a flapless surgical protocol ( n = 20 patients ; 32 implants ) and flapped surgical protocol ( n = 21 patients ; 40 implants ) . Primary outcome measure was implant survival ; secondary outcome measures were marginal bone resorption ( comparing the bone levels at 1 and 3 years with baseline ) and the incidence of biological , mechanical , and esthetic complications . Survival was computed through life tables ; descriptive statistics were applied to the remaining variables of interest . RESULTS Eight patients with eight implants dropped out of the study . One implant failed in one patient ( flapless group ) giving an overall cumulative survival rate ( CSR ) of 98.6 % . No failures were noted with the flapped protocol ( CSR 100 % ) , while for the implants placed with the flapless surgical technique , a 96.9 % CSR was registered . The overall average marginal bone resorption at 3 years was 1.37 mm ( SD = 0.94 mm ) , with 1.14 mm ( SD = 0.49 mm ) and 1.60 mm ( SD = 1.22 mm ) for the flap and flapless groups , respectively . Mechanical complications occurred in nine patients ( n = 5 patients in the flapless group ; n = 4 patients in the flap group ) . Implant infection was registered in three implants and three patients ( flapless group ) , who exhibited inadequate oral hygiene levels . CONCLUSIONS Partial edentulism rehabilitation through immediate provisionalization fixed prosthesis supported by dental implants inserted through flap or flapless surgical techniques in areas of predominantly soft bone was viable at 3 years of follow-up . The limitations and risks of the " free-h and " method in flapless surgery should be considered when planning implant-supported fixed prosthetic reconstructions In this issue , we answer three questions with respect to loss to follow-up in a clinical trial : How important is loss to follow-up ? How is loss to follow-up calculated ? How many patients can be lost to follow-up without mistrusting the results ? 1 . How important is loss to follow-up ? The simple answer to this question is “ very important ” because loss to follow-up can severely compromise a study 's validity . Incomplete follow-up biases the results when either : The dropout rates are different between study groups ; or The patients who drop out are different from those who do not drop out . Why do these situations make a difference ? Because in each situation , those lost to follow-up often have a different prognosis than those who complete the study . For example , patients who receive treatment for cervical myelopathy may not return for follow-up because they became asymptomatic and felt no need to return to see the surgeon . Conversely , some patients may not return because they had a particularly bad outcome ( worse pain or function ) or complication , or because they died . In either case , bias can affect the validity of the inferences drawn from the study . 2 . How is loss to follow-up calculated ? There is much confusion about how to determine the proportion of patients lost to follow-up . In order to correctly calculate the follow-up rate , one needs to know the denominator . In a r and omized controlled trial ( RCT ) , the denominator for each group is the number of patients who were r and omized , not the number who received the treatment . For example , suppose we have an RCT comparing two treatment groups , Group A and Group B. The investigators evaluate 178 patients and r and omize 120 ; 61 to Group A and 59 to Group B ( Fig 1 ) . Following the figure , we note that 49 patients received treatment A and 52 received treatment B. At the final follow-up 40 were analyzed in Group A and 41 in Group B. How many were considered lost to follow-up ? Many would consider the loss to follow-up rate to be 9 ( 18 % ) of 49 in treatment A and 11 ( 21 % ) of 52 in treatment B using as the denominator only those that were treated . However , the real proportion lost to follow-up must consider those who were r and omly assigned , even if they did not receive treatment . In the present example , this is calculated as 21 ( 34 % ) of 61 for treatment A and 18 ( 31 % ) of 59 for treatment B. Fig 1 Hypothetical example of patients lost to follow-up in a r and omized controlled trial . When calculating loss to follow-up in a retrospective cohort study , all individuals receiving treatment during the study period should be used as the denominator , not just those with complete data . For example , let 's say you want to compare decompression plus lumbar fusion with decompression alone in disc herniation and the data available are all patients receiving either treatment in the last 5 years ( N = 275 ) . However , the data base from which the data are obtained is incomplete and only 190 have the necessary data available . Since the investigators stated as part of the inclusion criteria that only those patients with complete data are included , they consider the follow-up to be 100 % ( 190/190 ) . This conclusion is wrong . The denominator should include all patients who underwent the surgery irrespective of completeness of data . The follow-up rate for this example is 69 % ( 190/275 ) . 3 . How many patients can be lost to follow-up without mistrusting the results ? Some have suggested that 20 % poses serious threats to validity 1 . This may be a good rule of thumb , but keep in mind that even small proportions of patients lost to follow-up can cause significant bias 2 . One way to determine if loss to follow-up can seriously affect results is to assume a worst-case scenario with the missing data and look to see if the results would change . Here is an example : Let 's assume a multicenter study enrolled 500 patients into each arm of a study comparing artificial disc replacement ( ADR ) with fusion , and the end point is adjacent segment disease ( ASD ) . The trial numbers are found in Fig 2 . Fig 2 Hypothetical example of the effect of loss to follow-up considering a worst-case scenario . ADR indicates artificial disc replacement ; ASD , adjacent segment disease . The proportion of patients with ASD in the ADR group is half as much versus the fusion group , 25 % ( 100/400 ) compared with 50 % ( 200/400 ) . If we assume that the 100 lost to follow-up in the ADR group had ASD and the 100 lost to follow-up in the fusion group did not , then the rate of ASD in each group would be 40 % ( 200/500 ) . In this case , adopting the worst-case scenario for the intervention group with respect to those lost to follow-up causes the results to change significantly from half the rate of ASD with ADR to the same rate . When this happens , loss to follow-up can threaten the internal validity of the trial . Only when the worst case does not change the inferences derived from the results is lost to follow-up not a problem PURPOSE To compare outcomes for immediately loaded one-piece implants ( OPI ) , placed flapless , and conventionally loaded two-piece implants ( TPI ) , placed after two-stage flapped surgery . MATERIAL S AND METHODS Thirty-eight participants were r and omised to receive either one OPI ( 19 participants , OPI group ) or one TPI ( 19 participants , TPI group ) inserted in the posterior m and ible with a torque of at least 35 Ncm according to a parallel group design . OPI were immediately loaded with non-occluding temporary crowns . After 3 months , TPI were exposed and implants in both groups were occlusally loaded with zirconia crowns . Outcome measures were implant failure , prosthesis failure , any complication and changes of probing pocket depth ( PPD ) , plaque index ( PI ) , gingiva index ( GI ) , and peri-implant marginal bone level , recorded by unblinded assessors . 
    Output:
    
The flapless surgery and conventional approach had comparable clinical performance over three years or more .
The guided or free-h and technique does not significantly affect the long-term outcomes of flapless surgery