***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 
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    ***EXAMPLES*** 
    Input: BACKGROUND The placement of different graft material s and /or the use of occlusive membranes to cover the extraction socket entrance are techniques aim ed at preserving/reducing alveolar ridge resorption . The use of grafting material s in fresh extraction sockets has , however , been question ed because particles of the grafted material have been found in alveolar sockets 6 - 9 months following their insertion . AIM The aims of the study were to ( i ) . evaluate whether alveolar ridge resorption following tooth extraction could be prevented or reduced by the application of a bioabsorbable polylactide-polyglycolide sponge used as a space filler , compared to natural healing by clot formation , and ( ii ) . evaluate histologically the amount and quality of bone tissue formed in the sockets , 6 months after the use of the bioabsorbable material . MATERIAL AND METHODS Thirty-six patients , undergoing periodontal therapy , participated in this study . All patients were scheduled for extraction of one or more compromised teeth . Following elevation of full-thickness flaps and extraction of teeth , measurements were taken to evaluate the distance between three l and marks ( mesio-buccal , mid-buccal , disto-buccal ) on individually prefabricated stents , and the alveolar crest . Twenty-six alveolar sockets ( test ) were filled with a bioabsorbable polylactide-polyglycolide acid sponge ( Fisiograft ) , while 13 sockets ( controls ) were allowed to heal without any filling material . The flaps were sutured with no attempt to achieve primary closure of the surgical wound . Re-entry for implant surgery was performed 6 months following the extraction s. Thirteen biopsies ( 10 test and three control sites ) were harvested from the sites scheduled for implant placement . RESULTS The clinical measurements at 6 months revealed , in the mesial-buccal site , a loss of bone height of 0.2 mm ( 1.4 SD ) in the test and 0.6 mm ( 1.1 SD ) in the controls ; in the mid-buccal portion a gain of 1.3 mm ( 1.9 SD ) in the test and a loss of 0.8 mm ( 1.6 SD ) in the controls ; and in the distal portion a loss of 0.1 mm ( 1.1 SD ) in the test and of 0.8 ( 1.5 SD ) mm in the controls . The biopsies harvested from the test sites revealed that the new bone formed at 6 months was mineralized , mature and well structured . Particles of the grafted material could not be identified in any of the 10 test biopsies . The bone formed in the control sites was also mature and well structured . CONCLUSION The results of this study indicate that alveolar bone resorption following tooth extraction may be prevented or reduced by the use of a bioabsorbable synthetic sponge of polylactide-polyglycolide acid . The quality of bone formed seemed to be optimal for dental implant insertion Using 14 meta-analyses that included both published ( n = 199 ) and unpublished ( n = 50 ) r and omized trials , we evaluated the utility of different analytical approaches to detect , assess robustness , and minimize publication bias in meta- analysis . The rank correlation and graphical tests indicated funnel plot asymmetry in 3 and 7 of the 14 meta-analyses , respectively . The file drawer number estimates using Iyengar-Greenhouse method were between 1.5 and 4.7 times smaller compared to Rosenthal ’s estimates . The median difference between the Trim and Fill estimates and the actual number of missing studies was 1 ( range -4 , 6 ) . Weighted estimation methods adjusted for publication bias and provided estimates of intervention effect close to the reference st and ard , on average . We showed there are differences in the conclusions one would reach clinical ly based on the different analytical approaches dealing with publication bias . Our results also suggest that the appropriate use of these methods improves the reliability and accuracy of meta- analysis Dimensional alterations of the facial bone wall following tooth extraction s in the esthetic zone have a profound effect on treatment outcomes . This prospect i ve study in 39 patients is the first to investigate three-dimensional ( 3D ) alterations of facial bone in the esthetic zone during the initial 8 wks following flapless tooth extraction .  A novel 3D analysis was carried out , based on 2 consecutive cone beam computed tomographies ( CBCTs ) . A risk zone for significant bone resorption was identified in central areas , whereas proximal areas yielded only minor changes . Correlation analysis identified a facial bone wall thickness of ≤ 1 mm as a critical factor associated with the extent of bone resorption . Thin-wall phenotypes displayed pronounced vertical bone resorption , with a median bone loss of 7.5 mm , as compared with thick-wall phenotypes , which decreased by only 1.1 mm . For the first time , 3D analysis has allowed for documentation of dimensional alterations of the facial bone wall in the esthetic zone of humans following extraction . It also characterized a risk zone prone to pronounced bone resorption in thin-wall phenotypes . Vertical bone loss was 3.5 times more severe than findings reported in the existing literature BACKGROUND Various material s have been used immediately following tooth extraction to fill and /or cover the socket in an attempt to limit or prevent ridge resorption . The purpose of the present pilot study was to establish a reliable model to investigate the effect of various bone graft and bone replacement material s on extraction socket healing . This study also compared healing extraction sockets 6 to 8 months postimplantation of a bioactive glass ( BG ) or demineralized freeze-dried bone allograft ( DFDBA ) to an unfilled socket control ( C ) . METHODS Following tooth extraction , a total of 30 sockets in 19 patients were r and omly divided into 3 treatment groups : 10 sockets received BG , 10 sockets DFDBA , and 10 sockets served as unfilled controls . Primary coverage was achieved by flap advancement over each socket . Six to 8 months post extraction at time of implant placement , histological cores of the treatment sites were obtained . These cores were processed , undecalcified sections prepared and stained with Stevenel blue/van Gieson 's picric fuchsin , and histomorphometrically analyzed . Vital bone , connective tissue and marrow , and residual graft particles were reported as a percentage of the total core . RESULTS A model system was described in humans and used to evaluate the healing response in the 3 treatment groups . Results concluded that mean vital bone present was 59.5 % for BG- , 34.7 % for DFDBA- , and 32.4 % for C-treated sites . These differences were not statistically significant . However , the residual implant material was significantly higher in DFDBA-treated ( 13.5 % ) versus BG-treated sockets ( 5.5 % ) . CONCLUSIONS Although the differences in percent vital bone were not statistically significant among the 3 treatment groups in this pilot study , BG material was observed to act as an osteoconductive material which had a positive effect on socket healing at 6 to 8 months post extraction . Further research following implant placement in treated and control sockets is warranted to determine if bone implant contact is improved in BG-filled versus unfilled sockets BACKGROUND Tooth extraction typically leads to loss of ridge width and height . The primary aim of this 6-month r and omized , controlled , blinded , clinical study was to determine whether ridge preservation would prevent post- extraction resorptive changes as assessed by clinical and histologic parameters . METHODS Twenty-four patients , 10 males and 14 females , aged 28 to 76 ( mean 51.5 + /- 13.6 ) , requiring a non-molar extraction and delayed implant placement were r and omly selected to receive either extraction alone ( EXT ) or ridge preservation ( RP ) using tetracycline hydrated freeze-dried bone allograft ( FDBA ) and a collagen membrane . A replaced flap , which did not completely cover the sockets , was used . Following extraction , horizontal and vertical ridge dimensions were determined using a modified digital caliper and an acrylic stent , respectively . Prior to implant placement , a 2.7 x 6.0 mm trephine core was obtained and preserved in formalin for histologic analysis . RESULTS The width of the RP group decreased from 9.2 + /- 1.2 mm to 8.0 + /- 1.4 mm ( P<0.05 ) , while the width of the EXT group decreased from 9.1 + /- 1.0 mm to 6.4 + /- 2.2 mm ( P<0.05 ) , a difference of 1.6 mm . Both the EXT and RP groups lost ridge width , although an improved result was obtained in the RP group . Most of the resorption occurred from the buccal ; maxillary sites lost more width than m and ibular sites . The vertical change for the RP group was a gain of 1.3 + /- 2.0 mm versus a loss of 0.9 + /- 1.6 mm for the EXT group ( P<0.05 ) , a height difference of 2.2 mm . Histologic analysis revealed more bone in the RP group : about 65 + /- 10 % versus 54 + /- 12 % in the EXT group . The RP group included both vital bone ( 28 % ) and non-vital ( 37 % ) FDBA fragments . CONCLUSIONS Ridge preservation using FDBA and a collagen membrane improved ridge height and width dimensions when compared to extraction alone . These dimensions may be more suitable for implant placement , especially in areas where loss of ridge height would compromise the esthetic result . The quantity of bone observed on histologic analysis was slightly greater in preservation sites , although these sites included both vital and non-vital bone . The most predictable maintenance of ridge width , height , and position was achieved when a ridge preservation procedure was employed After tooth extraction , varying amounts of bone resorption occur because of qualitative and quantitative changes at the edentulous site of the alveolar process . The aims of this r and omized controlled clinical trial were ( 1 ) to compare the post extraction changes in residual ridge dimensions during spontaneous healing with those during socket preservation , ( 2 ) to analyze the histologic and histomorphometric aspects of the grafted sockets , and ( 3 ) to compare probing procket depth ( PPD ) and clinical attachment level ( CAL ) changes at teeth adjacent to extraction sites . Forty-eight teeth were extracted from 41 patients referred for extraction of 1 or more maxillary or m and ibular premolars or molars . The edentulous sites were r and omly assigned to the control ( EXT , extraction alone ) or experimental groups ( SP , extraction and socket preservation ) . In the SP group , the sockets were filled with bovine bone mineral and covered with porcine collagen membrane . At baseline and after 4 months , PPD , gingival recession ( REC ) , and CAL were measured at teeth adjacent to the edentulous sites . The changes in ridge dimensions from baseline to 4 months were assessed on dental casts . At 4 months , bone was harvested from the grafted areas in the SP group and the edentulous areas in the EXT group . PPD , REC , and CAL were comparable between groups . However , from baseline to 4 months , the SP group showed significantly less reduction in ridge width ( 1.04 ± 1.08 mm vs 4.48 ± 0.65 mm , P < .001 ) and height ( 0.46 ± 0.46 mm vs 1.54 ± 0.33 mm , P < .001 ) . Histologically , the grafted sockets exhibited various stages of bone maturation and formation without inflammatory responses . No significant difference in the mineralized and nonmineralized fractions was noted between the groups . Socket preservation using bovine bone mineral and porcine collagen membrane considerably limits the amount of horizontal and vertical bone resorption when compared with extraction alone INTRODUCTION As a consequence of extraction , the height of the buccal wall tends to decrease and results in the disappearance of bundle bone . To modify bone remodelling after extraction , various ridge preservation techniques have been proposed . The present research was drawn up with the following considerations in mind : to evaluate and to compare changes of hard and soft tissues in post- extraction sockets which received a ridge preservation procedure , with post- extraction sockets which had healed naturally . MATERIAL S AND METHODS Each patient was r and omly allocated to a test or control group using a specific software package . After extraction , the sockets were carefully inspected and any granulation tissue was removed . The control sites received silk sutures to stabilize the clot without any grafting material . The test sites were grafted with corticocancellous porcine bone and a collagen membrane . All experimental sites had the membranes left exposed to the oral cavity with a secondary wound healing . The thickness of the buccal alveolar bone , if present , was carefully measured at the time of tooth extraction using a calliper at 1 mm from the edge of the wall . The following clinical parameters were evaluated at baseline and after 4 months at implant placement : vertical bone changes , horizontal bone changes and width of keratinized gingiva . The length , diameter and need for additional bone augmentation were assessed for both groups at the time of implant insertion . RESULTS The control group showed vertical bone resorption of 1 ± 0.7 mm , 2.1 ± 0.6 mm , 1 ± 0.8 mm and 2 ± 0.73 mm at the mesial , vestibular , distal and lingual sites respectively . Moreover , changes in horizontal dimension showed an average resorption of 3.6 ± 0.72 mm . The test sites showed a 
    Output:
    
Use of bone graft covered by a resorbable membrane can decrease the rate of alveolar ridge horizontal and vertical resorption after tooth extraction .