***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: The etiologic factors associated with  crestal bone loss  have not been comprehensively clarified . Several theories exist as to the reason for the observed changes in crestal bone height following implant restoration . In the 1990s , the wide-diameter implants were commercially introduced . Initially , the implants were restored with st and ard-diameter abutments because of lack of matching prosthetic components . Long-term radiographic follow-up of these ' platform-switched ' restored wide-diameter dental implants has demonstrated a smaller-than-expected vertical change in the crestal bone height around these implants that is typically observed around implants restored conventionally with prosthetic components of matching diameters . The aim of this r and omised controlled study was to assess radiographically marginal bone level alterations in implants restored according to the platform-switching concept compared with traditionally restored implants . Fifty-four subjects to participate in this r and omised controlled study were selected . Two groups were assigned at r and om : control group ( 56 implants were restored with st and ard matching-diameter abutments ) and test group ( 58 implants were restored with medialised abutments ) . X-ray explorations were taken for peri-implant bone level at the minute the last cementing of the prosthesis and at 1-year follow-up . NHI Image was used to digitally process and manipulate the radiographic images and perform the measurements . Mean of bone loss with platform-switching implants was -0·01 mm , and the mean of bone loss with st and ard platform implant was 0·42 mm . Outcomes of this study indicated that the platform-switching design could preserve the crestal bone levels to 1-year follow-up . There was a statistically significant difference in marginal bone loss The purpose of this study was to evaluate  crestal bone loss around 282 two-piece implants with straight ( n = 193 ) and platform-switched ( n = 89 ) abutment connections after placement at various crestal levels .  Implants were assigned into two groups according to straight and platform-switched abutment connections . Each group was further subdivided into three groups depending on the location ( supracrestal , crestal , or subcrestal ) of the implant cervical platform . Linear measurements of bone resorption were made from the implant 's platform to the first point of bone-to-implant contact at the time of implant placement and 2 years postrestoration . Data were statistically analyzed . Statistically significant differences were found between subgroups in both straight and platform-switched categories . The only nonstatistically significant difference ( P = .341 ) arose when comparing the supra- and subcrestal locations in the straight abutment connection group . The platform-switched group exhibited significantly less bone loss ( P = .046 ) only in subcrestal locations . The platform-switched concept was not beneficial during the overall comparison , but it was for the subcrestal location of the abutment connection . Crestal placement of the implant-abutment connection result ed in higher marginal bone resorption in both straight and platform-switched abutments AIM The temporal pattern of bone-level alterations in conventionally restored implants is dependent upon healing mode ( open or submerged ) . This study examined the influence of healing on marginal bone levels at implants with a medium-rough surface including the implant collar and a clearance-fit implant-abutment connection restored according to a platform-switching concept . MATERIAL AND METHODS  Two implants were placed in the posterior m and ible of 21 test subjects , r and omly assigned to open ( OH ) or submerged ( SH ) healing . St and ardized radiographs were obtained after implant surgery , before re-entry , after crown mounting , 1 and 2 years after implant surgery , and evaluated for implant-bone-level alterations ( ΔIBL ) . Bacterial sample s of the implants ' inner cavities were analysed by cultivation . STATISTICS Brunner-Langer Model , equivalence testings by Wilcoxon 's ( equivalence range ±0.4 mm ) . RESULTS After 2 years , ΔIBL were -0.47±0.46 mm ( OH ) and -0.54±0.38 mm ( SH ) . At the 1-year follow-up , all implants were contaminated with bacteria . ΔIBL ( p<0.001 ) and the amount of bacterial contamination ( p<0.001 ) significantly depended on time , but not on healing mode . ΔIBL of OH and SH were equivalent at all time points ( all p0.044 ) . CONCLUSIONS Platform-switched implants showed very limited peri-implant bone-level alterations . The healing-mode neither affected the total amount nor the temporal patterns of ΔIBL . Thus , the results for the tested implants with a non-rigid implant-abutment connection were similar to results reported previously for implants with a rigid implant-abutment connection PURPOSE The aim of this study was to evaluate the short-term bone level response around immediately placed and provisionally restored implants using a platform switching concept . MATERIAL S AND METHODS Twenty-two implants with a platform diameter of 5.5 mm were immediately placed in healthy maxillary sites in 22 patients . Result ant circumimplant spaces were filled with a mixture of bovine bone matrix and collagen . The implants were r and omly divided into two equal groups : 11 implants connected with 3.8-mm-diameter abutments ( test group ) and 11 with 5.5-mm-diameter ones ( control ) . Provisional crowns were adapted and adjusted for nonfunctional immediate placement on each implant and the final crowns were constructed 2 months later . Posttreatment assessment s were carried out by an independent trained observer at the time of implant placement ( baseline ) , at definitive prosthesis insertion , and every 6 months thereafter . These assessment s included periapical radiographs , pocket probing depths ( PPD ) , bleeding on probing ( BOP ) , and modified Plaque Index ( mPII ) on both implants and first proximal teeth . An image analysis software application was used to compare the bone crestal heights at the mesial and distal aspects of the implants . RESULTS The mean follow-up observation period was 25 months and all implants were judged to be successfully osseointegrated . In the test group , radiographic analysis showed an average bone reduction level of 0.30 mm ( SD = 0.16 mm ) . This mean value was statistically significantly different ( P < or = .005 ) from the average reduction in the control group ( mean = 1.19 mm , SD = 0.35 mm ) . No differences between the two groups in PPD , BOP , or mPII were found . CONCLUSION This preliminary study suggests that immediate single implant restorations in specific maxillary sites with subsequent platform switching may provide peri-implant alveolar bone-level stability PURPOSE To evaluate whether platform switching could preserve marginal bone around implants up to 6 months after loading . MATERIAL S AND METHODS 15 patients were selected for a r and omised controlled trial . Each patient received one customised wide body implant , with the external hex connection located eccentrically , allowing an extra 1 mm switch on one side . The hex was positioned at r and om at the mesial or distal side and the implant was loaded after 6 months of non-submerged healing . Patients were examined at 3 , 6 and 12 months after surgery , during which a radiograph was taken to evaluate bone levels . At 12 months , the mucosal thickness was measured using a perio-probe . RESULTS All implants survived and the mean overall bone loss , calculated from both the switched and non-switched side , was 0.39 mm ( SD 0.33 , range 0.00 - 1.45 ) , 0.85 mm ( SD 0.59 , range 0.10 - 2.50 ) and 0.80 mm ( SD 0.46 , 0.26 - 1.89 ) after 3 , 6 and 12 months , respectively . The bone loss continued up to 6 months but stabilised thereafter ( P = 0.615 ) . Significantly more bone loss was observed at the non-switched side compared to the switched side at 3 months ( 0.51 mm versus 0.28 mm , P = 0.019 ) , 6 months ( 1.05 mm versus 0.64 mm , P = 0.002 ) and 12 months ( 0.94 mm versus 0.66 mm , P = 0.002 ) . The mean mucosal thickness was 4.22 mm ( SD 1.45 ; range 1.50 - 7.00 ) , and was not significantly different between the switched and non-switched sides ( P = 0.882 ) . However , using a post-hoc analysis with the mean thickness as a threshold , the mean bone loss was only significantly different between switched and non-switched sides when the mucosa was thicker than 4.22 mm ( P = 0.036 ) . CONCLUSIONS The outcome of this r and omised trial is in accordance with earlier studies suggesting that that platform switching decreases bone loss by 30 % . Although the sample size was limited , it seems that the creation of a biologic width affects peri-implant bone loss to a significant extent and that platform switching is only effective when the mucosal thickness allows the establishment of a biologic width PURPOSE This prospect i ve r and omized matched-pair controlled trial aim ed to evaluate marginal bone levels and soft tissue alterations at implants restored according to the platform-switching concept with a new inward-inclined platform and compare them with external-hexagon implants . MATERIAL S AND METHODS Traditional external-hexagon ( control group ) implants and inward-inclined platform implants ( test group ) , all with the same implant body geometry and 13 mm in length , were inserted in a st and ardized manner in the posterior maxillae of 40 patients .  Radiographic bone levels were measured by two independent examiners after 6 , 12 , and 18 months of prosthetic loading . Buccal soft tissue height was measured at the time of abutment connection and 18 months later . RESULTS After 18 months of loading , all 80 implants were clinical ly osseointegrated in the 40 participating patients . Radiographic evaluation showed mean bone losses of 0.5 ± 0.1 mm ( range , 0.3 to 0.7 mm ) and 1.6 ± 0.3 mm ( range , 1.1 to 2.2 mm ) for test and control implants , respectively . Soft tissue height showed a significant mean decrease of 2.4 mm in the control group , compared to 0.6 mm around the test implants . CONCLUSIONS After 18 months , significantly greater bone loss was observed at implants restored according to the conventional external-hexagon protocol compared to the platform-switching concept . In addition , decreased soft tissue height was associated with the external-hexagon implants versus the platform-switched implants OBJECTIVES This r and omized-controlled trial aim ed to evaluate marginal bone level alterations at implants restored according to the platform-switching concept , using different implant/abutment mismatching . MATERIAL AND METHODS Eighty implants  were divided according to the platform diameter in four groups : 3.8 mm ( control ) , 4.3 mm ( test group(1 ) ) , 4.8 mm ( test group(2 ) ) and 5.5 mm ( test group(3 ) ) , and r and omly placed in the posterior maxilla of 31 patients . After 3 months , implants were connected to a 3.8-mm-diameter abutment and final restorations were performed . Radiographic bone height was measured by two independent examiners at the time of implant placement ( baseline ) , and after 9 , 15 , 21 and 33 months . RESULTS After 21 months , all 80 implants were clinical ly osseointegrated in the 31 patients treated . A total of 69 implants were available for analysis , as 11 implants had to be excluded from the study due to early unintentional cover screw exposure . Radiographic evaluation showed a mean bone loss of 0.99 mm ( SD = 0.42 mm ) for test group(1 ) , 0.82 mm ( SD = 0.36 mm ) for test group(2 ) and 0.56 mm ( SD = 0.31 mm ) for test group(3 ) . These values were statistically significantly lower ( P<0.005 ) compared with control ( 1.49 mm , SD = 0.54 mm ) . After 33 months , five patients were lost to follow-up . Evaluation of the remaining 60 implants showed no difference compared with 21 months data except for test group(2 ) ( 0.87 mm ) and test group(3 ) ( 0.64 mm ) . There was an inverse correlation between the extent of mismatching and the amount of bone loss . CONCLUSIONS This study suggested that marginal bone level alterations could be related to the extent of implant/abutment mismatching . Marginal bone levels were better maintained at implants restored according to the platform-switching concept OBJECTIVE The concept of platform switching has been introduced to implant dentistry based on observations of reduced peri-implant bone loss . However , r and omized clinical trials are still lacking . This study aim ed to test the hypothesis that platform switching has a positive impact on crestal bone-level changes . MATERIAL AND METHODS Two implants with diameters of 4 mm were inserted epicrestally into one side of the posterior m and ibles of 25 subjects . After 3 months of submerged healing , the reentry surgery was performed . On the r and omly placed test implant , an abutment 3.3 mm in diameter was mounted , result ing in a horizontal circular step of 0.35 mm ( platform switching ) . The control implant was straight , with an abutment 
    Output:
    
3D-Implant positioning , width of alveolar ridge and control of micromotion at the implant-abutment interface are the more critical factors that influence crestal bone levels than PS