***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 PURPOSE Several long-term clinical studies have shown a mean marginal bone loss around dental implants of 1.5 to 2 mm in the first year after prosthetic restoration . Currently , concepts to avoid bone remodeling around dental implants have been developed . The use of prosthetic abutments with reduced width in relation to the implant diameter ( platform switching ) seems to have the greatest potential to limit the crestal resorption . The purpose of this clinical trial was to show that crestal bone height around dental implants  could be influenced using a platform switch protocol and that the bone level would remain stable within 1 year after final prosthetic reconstruction . MATERIAL S AND METHODS Fifteen patients were treated with fixed implant retained prosthesis ; 14  wide-diameter implants were supplied with platform-switched abutments and served as the test group . Eight implants with regular diameter were reconstructed with traditional abutments and served as the control group . St and ardized digital radiographs were obtained for evaluation of the peri-implant bone levels at the time of installation of the final restoration and at 1-year follow-up . Marginal peri-implant bone levels were measured at the mesial and distal surfaces of each implant using digital image analysis . RESULTS The mean values of crestal bone height at baseline were -0.09 mm + /- 0.65 mm for the platform-switched implants and -1.73 mm + /- 0.46 mm for the nonplatform-switched implants . One year after final restoration , the mean value of crestal bone height was -0.22 mm + /- 0.53 mm for the test group and -2.02 mm + /- 0.49 mm for the control group . When tested with statistical means , the differences were significant for baseline and for follow-up ( P < /= .0001 ) . Mean bone level change from baseline to 1-year follow-up was -0.12 mm + /- 0.40 mm for the test group and -0.29 mm + /- 0.34 mm , respectively , for the control group . On analysis using ANCOVA , this difference was shown to be significant ( P < /= .0132 ) . CONCLUSION The concept of platform switching appears to limit crestal resorption and seems to preserve peri-implant bone levels . A certain amount of bone remodeling 1 year after final reconstruction occurs , but significant differences concerning the peri-implant bone height compared with the nonplatform-switched abutments are still evident 1 year after final restoration . The reduction of the abutment of 0.45 mm on each side ( 5 mm implant/4.1 mm abutment ) seems sufficient to avoid peri-implant bone loss PURPOSE The purpose of this clinical trial was to evaluate whether the crestal bone height around dental implants  could be influenced by the use of a platform-switching protocol . MATERIAL S AND METHODS All implants placed in the year 2006 in healed bone without any need for ridge augmentation were included in this study . The following groups were created : ( 1 ) wide-diameter implants were placed subcrestally and regular-diameter cover screws were connected ; ( 2 ) regular-diameter implants were placed at the crest and regular-diameter cover screws were connected . St and ardized radiographs were obtained after insertion of the definitive prosthesis and after 1 year . Calibrated measurements were conducted initiating from the mesial and distal bone peaks to the implant-abutment junction . The average value of the mean medial and mean distal values was calculated and analyzed with an unpaired two-tailed t test . P values < .05 were regarded as statistically significant . RESULTS In all , 89 dental implants in 36 patients were evaluated . The implants with a platform-switched configuration ( n = 75 ) exhibited statistically significantly less bone loss at time of insertion of the definitive prosthesis ( 0.30 + /- 0.07 mm versus 0.68 + /- 0.17 mm ; P < .05 ) and at 1 year ( 0.39 + /- 0.07 mm versus 1.00 + /- 0.22 mm , P < .01 ) when compared to the nonplatform-switched implants ( n = 14 ) . CONCLUSION Platform-switched implants seem to limit crestal bone remodeling 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 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 BACKGROUND This prospect i ve and controlled histologic study evaluates the impact of smoking on bone-to-implant contact , the bone density in the threaded area , and the bone density outside the threaded area around microimplants with anodized surface retrieved from human jaws . METHODS A total of 24 subjects ( mean age 51.32 + or - 7.5 years ) were divided in two groups : smokers ( n = 13 subjects ) and non-smokers ( n = 11 subjects ) . Each subject received one microimplant with oxidized surface during conventional m and ible or maxilla implant surgery . After 8 weeks , the microimplants and the surrounding tissue were removed and prepared for histomorphometric analysis . RESULTS Three microimplants placed in smokers showed no osseointegration . The newly formed bone showed early stages of maturation , mainly in the non-smokers . Marginal bone loss , gap , and fibrous tissue were present around implants retrieved from smokers . Histometric evaluation indicated that the mean bone-to-implant contact ranged between 25.97 % + or - 9.02 % and 40.01 % + or - 12.98 % for smokers and non-smokers , respectively ( P < 0.001 ) . Smokers presented 28.17 % + or - 10.32 % of bone density in the threaded area , whereas non-smokers showed 46.34 % + or - 19.12 % . The mean of bone density outside the threaded area ranged between 18.76 % and 25.11 % for smokers and non-smokers , respectively ( P > 0.05 ) . CONCLUSION The present data obtained in human subjects confirm that smoking has a detrimental effect on early bone tissue response around oxidized implant surfaces OBJECTIVES The aim of the present study was to investigate histomorphometrically the influence of platform switching on crestal bone changes at non-submerged wide-body titanium implants in a dog model . MATERIAL AND METHODS One-stage insertion of s and -blasted and acid-etched screw-type implants with either matching ( CAM ) or smaller-diameter healing abutments ( CPS ) were r and omly assigned to the lower jaws of nine beagle dogs . The animals were killed after 7 , 14 , and 28 days of non-submerged healing . Dissected blocks were processed for histomorphometrical analysis . Measurements were made between the implant shoulder ( IS ) and : --the apical extension of the long junctional epithelium ( aJE ) , --the most coronal level of bone in contact with the implant ( CLB ) , and --the level of the alveolar bone crest ( BC ) . RESULTS At 7 , 14 , and 28 days , the mean IS-aJE values were significantly the lowest at CPS implants . However , after 28 days of healing , both groups revealed significantly increased mean IS-BC values at the buccal aspect of the alveolar bone . The difference in IS-CLB and IS-BC between groups was not significant . CONCLUSIONS Within the limits of the present study , it was concluded that both CAM and CPS implants revealed crestal bone-level changes after 28 days of healing This clinical and radiographic prospect i ve study evaluated bone loss around two-piece implants  that were restored according to the platform-switching protocol . One hundred thirty-one implants were consecutively placed in 45 patients following a nonsubmerged surgical protocol . On 75 implants , a healing abutment 1 mm narrower than the implant platform was placed at the time of surgery . On the remaining implants , a healing abutment of the same diameter as the implant was inserted . All implants were positioned at the crestal level . Clinical and radiographic examinations were performed prior to surgery , at the end of surgery , 8 weeks after implant placement , at the time of provisional prosthesis insertion , at the time of definitive prosthesis insertion , and 12 months after loading . The data collected showed that vertical bone loss for the test cases varied between 0.6 mm and 1.2 mm ( mean : 0.95 + /- 0.32 mm ) , while for the control cases , bone loss was between 1.3 mm 
    Output:
    
The meta- analysis revealed a significantly less mean MBL change at implants with a PS compared to PM-implant-abutment configuration .
The qualitative analysis revealed a tendency favoring the PS technique to prevent or minimize peri-implant marginal bone loss compared with PM technique .