the pyramid - shaped maxillary sinus ( or 
 antrum of highmore ) is the largest of the paranasal sinuses , and drains 
 into the middle meatus of the nose . the sinus is lined with 
 mucoperiosteum , with cilia that beat toward the ostia . this membrane is 
 also referred to as the  schneiderian membrane  , which is histologically 
 a bilaminar membrane with ciliated columnar epithelial cells on the 
 internal ( or cavernous ) side and periosteum on the osseous side . the 
 size of the sinuses varies in different skulls , and even on the two 
 sides of the same skull . as a result of long term edentulism a 
 decrease in the bone level of the alveolar process occurs due to 
 postextractional bone resorption and sinus pneumatisation . the aim 
 of sinus lift procedure is to compensate this bone loss by creating 
 increased bone volume in the maxillary sinus and thus enabling 
 installation of dental implants . initially , the most popular bone 
 grafting materials are autogenous bone grafts and other bone substitutes 
 . the disadvantages of such methods are high costs for grafting 
 material , time consuming and high morbidity , because harvesting of bone 
 grafts is needed . discuss that the key role of the sinus membrane , as the main carrier 
 of bone reformation after sinus lift procedures , as multiple 
 experimental studies suggested . thus the importance of minimal invasive 
 and rupture free sinuslift procedures is underlined and does not depend 
 on the type of grafting material used . the potential of new bone 
 formation without bone graft in the maxillary sinus was presented in a 
 variety of studies including radiological and histological evidence , and 
 recent studies indicate high success rates of such method [ 6 - 10 ] . because of the disadvantages of existing methods that was described 
 above and because of the recent studies regarding the potential of new 
 bone formation without bone graft , there is an importance in reviewing 
 the existing information in the literature . the aim of this paper is to 
 review the scientific data regarding to the natural bone formation in 
 the sinus , after membrane elevation procedure , without using any bone 
 substitutes . the review included any published 
 observational studies ( cross - sectional surveys , cohort and case - control 
 studies ) , clinical trials of treatment and case series . graft - free sinus augmentation definition graft - free sinus augmentation is a sinus 
 lift procedure using the lateral window approach by boyne , while no 
 bone graft or other substitute is being used for the bone gain beside 
 blood clot . studies with radiological and/or 
 histological diagnostics of newly formed bone in the sinus were 
 included . literature search strategy according to the prisma guidelines   an 
 electronic search was conducted using medline ( pubmed ) to locate 
 articles concerning graft - free sinus lifts . the search terms used were : 
  sinus lift  ,  sinus membrane elevation  ,  sinus augmentation  , sinus 
 lift without bone graft  and  implant placement without bone graft  . due 
 to the low number of relevant articles and to insure the sensitivity of 
 the systemic review the articles were searched from 1993 to 2013 . titles derived from this broad search were independently 
 screened by two authors based on the inclusion criteria . full reports were obtained for all the 
 studies that were deemed eligible for inclusion in this paper . inclusion and exclusion criteria inclusion criteria for the selection were : minimum one year patient follow - up ; radiological and/or histological 
 diagnostics of newly formed bone . exclusion criteria for the selection were : usage of bone graft or bone substitutes 
 has been made ; usage of osteotome has been made . article review and data extraction the search delivered 2205 search results 
 from which 86 abstracts were reviewed ( figure 1 ) . a total of 75 articles 
 were ultimately reviewed in full . preliminary exclusion was made by the 
 title and its relevancy , later by abstract and articles availability 
 online . finally , articles that did not meet the inclusion and exclusion 
 criteria , where filtered as followed : usage of bone graft or bone 
 substitutes has been made ( 8) , usage of osteotome has been made ( 32 ) and 
 no minimum one year follow - up was found ( 13 ) . the cochrane collaboration bias summary for 
 potential bias was used to assess the quality of studies and identify 
 papers with intrinsic flaws in method and design . 2 studies were related to sinus membrane s osteogenic potential , 
 3 studies were related to histological evidence of bone formation in 
 monkeys and humans , 12 studies were related to the outcome , implant 
 stability and radiologic evidence of bone gain after using the 
 graft - free augmentation , 2 studies were related to space - maintaining 
 management ( table 1 ) . description of studies included in the review scheidrian membrane s osteogenic 
 potential studies , reviewed in this paper presented 
 well a creation of new bone formation in the maxillary sinus by mucosal 
 membrane lifting without the use of any graft material . however , srouji 
 et al . , using both in vitro and in 
 vivo assays , attempted to 
 explore the bone formation beneath the sinus membrane on the maxillary 
 sinus floor . the aim was to test the osteogenic potential of human 
 maxillary sinus schneiderian membrane ( hmssm ) . flow cytometry analysis was 
 conducted on cultures by adopting mesenchymal progenitor cell markers . using relevant in vitro assays 
 the potential to osteogenic differentiation by the hmssm cells was 
 analyzed . it was seen that the cells are capable of inducing and 
 reviling different osteogenic markers such as osteonectin , osteopontin , 
 osteocalcin , alkaline phosphatase , bone morphogenic protein-2 , as well 
 as to induce their extracellular matrix mineralization . further , the 
 osteogenic potential of hmssm - derived cells was confirmed in 
 vivo experiments , where 
 cultured cells and a ceramic mix consisted from ha/-tcp were connected 
 into a fibrin clot and implanted under the skin of thymic mice . after 8 
 weeks of healing formation of histology - proven bone at ectopic sites 
 subsequent to transplantation of hmssm - derived cells where present . it 
 was deducted that genuine osteogenic potential is connected with the 
 hmssm and may be of great contribution to the development of successful 
 sinus augmentation techniques . in 2010 , srouji et al . tests whether 
 such osteogenic activity relies on inherent osteogenic capacity , that 
 existing in the sinus membrane using simulation in 
 vivo clinical condition 
 of sinus lifting in an animal model . human schneiderian membrane was 
 folded around a fibrin clot that was later transplanted subcutaneously 
 into mice . new bone formation was observed , as well as in the previous 
 experiment , illustrating the innate osteogenic potential within the 
 maxillary schneiderian sinus membrane and its importance of 
 understanding and potentially improving bone regeneration in sinus 
 lifting procedures in the future . histological evidence of bone formation the first histological evidence to verify 
 new bone formation was demonstrated in 2006 by palma et al .   on four 
 tufted capuchin primates that experienced maxillary sinus membrane 
 elevation surgery using a replaceable bone window technique . according 
 to palma et al . study , no differences on new bone formation , implant 
 stability and bone - implant contacts was demonstrated between two groups 
 with and without adjunctive autogenous bone graft , furthermore stronger 
 bone tissue response is seen in oxidized implants than the control 
 turned surface . an alike clinical studies with monkeys was already 
 described in 1993 by boyne   where maxillary sinus floor augmentation 
 on five monkeys was preformed , by simply elevating the maxillary sinus 
 membrane without the use of bone grafting . protruding implant in 
 the right antrum was placed with bone graft and in the contra - lateral 
 implant no bone grafts where used . radiologic evidence of new bone was 
 seen around the implant in which no bone graft was administered , though 
 unlike palma s et al . only 2 years afterwards a first histological evidence of new bone 
 formation in the maxillary sinus with membrane elevation only was 
 obtained on humans by sohn et al .   where 21 implants were placed , 
 with an average residual bone height of 5 mm after 6 months they where 
 evaluated . bone formation and new sinus floors were found in 
 both radiographic and histological evaluations . presented a case study 
 in 2003 on a patient that needed a removal of mucosal cyst of the 
 maxillary sinus and augmentation of the maxillary sinus in order to pace 
 an implant later on . an intra - sinus mucosal cyst was removed through a 
 prepared bony window in the lateral antral wall . after 3 months of healing , clear 
 radiographic signs of bone formation were observed . the space between 
 the replaced bony window and the lifted sinus membrane was filled with 
 newly formed bone . this was an unexpected healing pattern witch lead him 
 to conclude that the creation of a space between the bone surfaces and 
 the sinus mucosa in the combination of the surgical trauma result in 
 spontaneous bone formation in the maxillary sinus . since the 
 predictability of the technique presented above is yet unknown in 2004 
 lundgren et al . conducted a study in order to investigate the 
 possibility to perform sinus membrane elevation and facilitate implant 
 placement without any additional bone grafting material and whether it 
 is a valid technique . the study group consisted out of 10 patients in 
 whom a total of 12 maxillary sinus floor augmentations were performed 
 and 19 implants were installed . the bony window was dissected , elevated 
 superiorly , and sutured to the sinus wall to create and maintain a 
 compartment for blood clot formation . the implants were installed then 
 the bony window was replaced , and the flap was sutured into position . 
 during the study period all implants showed stability and clear signs of 
 bone formation , this clearly demonstrated great potential of bone 
 formation and regeneration capability in the maxillary sinus without the 
 use of additional bone grafts . lundgren et al .   concluded that in 
 general it is achieved by the principle of guided tissue regeneration , 
 but the precise mechanisms of this healing pattern are yet unknown . as a 
 result of previous studies that showed bone formation capability without 
 bone grafts , in 2010 sohn et al .   presented a study that 
 demonstrating new bone formation in the maxillary sinus using absorbable 
 gelatin only the study consisted of seven patients treated with sinus 
 augmentation with restorable gelatin sponge membrane and simultaneous 
 implant placement . the lateral bony window was formed and the sinus 
 membrane was elevated to make space . 18 implants were placed and the 
 absorbable gelatin sponge was inserted in the new compartment under the 
 elevated sinus membrane . after an average of 6 months given for the 
 implants to integrate , new bone formation in the maxillary sinus was 
 seen on radiographs . the study showed clearly that 
 implant placement with gelatin sponge can be a predictable procedure for 
 sinus augmentation without using bone graft . in 2007 , a study was 
 published by chen et al .   where maxillary sinus augmentation without 
 bone graft using only blood was preformed in 33 patients . the sinus mucosal membrane was 
 elevated with the bony window still attached to the membrane ( trap - door , 
 open - window method ) . increases in bone height ranged from 3 mm to 9 
 mm with an average of 4.5 mm bone gain thus it was concluded that the 
 survival rate was good . in 2007 , a case series was presented by hatano 
 et al .   of 6 patients that undergone a maxillary sinus floor 
 augmentation using peripheral venous blood alone . after the elevation of 
 a mucoperiosteal flap the lateral wall of sinus cavity was exposed . the 
 piezoelectric saw with thin blade connected to piezoelectric device was 
 used with copious saline irrigation to create the lateral window of the 
 maxillary sinus . the sinus membrane was carefully elevated from the sinus 
 floor walls with a manual elevator . the bone window was replaced with 
 medical tissue glue for closure of the potential gap in the bony window 
 of the osteotomy thus preventing blood leakage from the created 
 compartment in the maxillary sinus . one of the 14 implants failed but successful new bone 
 formation was found in all sinuses as seen from radiographs . in 2011 , published a similar study to the one presented above by 
 hatano et al . study results presenting with 
 similar conclusions thus giving further justification and strengthens 
 hatano s et al .   study results . in the study , fourteen patients were 
 consecutively treated and in total 17 sinus lifts had been made . in 
 hatano s the lateral 
 bony window was created using a piezoelectric saw , and the sinus 
 membrane was elevated to make space . the sinus cavity was filled with 
 venous blood and resorbable blast media - surfaced dental implants were 
 placed simultaneously . after 6.8 months , the sinus augmentations were 
 evaluated and new bone formation in the maxillary sinus was seen by both 
 radiographic and histological evaluation . overal , implant survival rate 
 was 93.5% and according to the histomorphometric data vital bone 
 formation was 38.7% . it was 
 mentioned in the study that all failures occurred when implants were 
 placed into the extraction socket . it was established that a maxillary 
 sinus floor augmentation using peripheral venous blood and simultaneous 
 placement of dental implants is a reliable procedure and this is in 
 coincidence with hatano et al . . in 2007 , thor   presented a 
 study , where 20 patients were treated with implant therapy . 44 astra 
 tech implants , in total , were placed in the maxillary sinus ( 27 sinuses 
 were lifted ) . implants were followed every year in the period of time 
 between november 2001 to june 2004 and all the implant installations 
 carried without graft material . the sinus membrane elevation preformed 
 in a matter where a bony window was removed from the maxillary anterior 
 sinus wall . implants were placed in the residual bone right after 
 elevation of the mucosal membrane . during the surgery , perforations of 
 the mucosal membrane was recorded together with the bone height . evaluation after an 
 average time of 27.5 months resulted in 97.7% of implants survival rate 
 and 6.51 mm was the average gain of bone at the maxillary sinus . although bone formation was successful few complications had occurred , 
 in 41% of operated sinuses observed perforations of the maxillary sinus 
 mucosal membrane and one implant was lost . marked bone gain was observed 
 around long implants as well as in the case when the residual bone below 
 the sinus was low . in 2010 , balleri et al . presented a study , where 
 fifteen patients were recruited for sinus augmentation in combination 
 with implant placement without biomaterials . a replaceable bone window was opened and the 
 membrane was dissected from the sinus walls . 28 of astra tech implants 
 were installed in the residual crest ( the implants were keeping the 
 membrane in the elevated position ) . after 1 year , the implants , where 
 evaluated and the average bone gain was 5.5 mm . it was established that the bone 
 gain was less than the average bone gain in membrane elevation which is 
 8.2 mm . bone regeneration was less at the distal aspect of the most 
 posterior - placed implant . the height of membrane lift was not correlated 
 with the amount of regenerated bone . in other words , the length of the 
 implants was not related to the amount of gained bone unlike in thor s 
  study from 2007 , where greater bone formation was observed around 
 the long implants . not only all of the 28 implants were stable during 
 the first year of loading and that no additional costs for biomaterials 
 were necessary , but also problems concerning bone harvesting as 
 morbidity were avoided . in 2011 , lin et al .   presented a 5-year 
 follow - up of 80 implants in 44 patients . the implants weere placed 
 immediately after the lateral trap - door window procedure to accomplish 
 maxillary sinus elevation without bone grafting . surgeries were carried 
 out with either local or general anesthesia and prophylactic antibiotics 
 were given . extreme care was taken to radically elevate the 
 sinus membrane from the trap - door window . the floor , lateral wall , and 
 posterior wall of the sinus membrane were detached and pushed upward and 
 medially to allow the placement of dental implants into the bone 
 chamber . , 3 mm of residual bone height was required for inclusion and 
 on average residual bone height was 5.1 mm . new bone formation in the 
 sinus was confirmed and the average gained bone height after five years 
 was 7.4 mm . presented a study were a total of 84 
 patients underwent 96 membrane elevation procedures and simultaneous 
 placement of 239 implants without adding any graft material . changes of 
 bone height in relation to the implants were measured using intraoral 
 radiographs taken at insertion . the implant follow - up period ranged 
 between 1 - 6 years after implants loading . all of the implants 
 demonstrated stability after 6 months of healing and a high implant 
 survival rate of 98.7% was seen through the follow - up . an average of 5.3 
  2.1 mm of intra - sinus new bone formation was observed on the 
 radiographs . resonance frequency analyses ( rfm ) , adequate primary 
 stability and small changes over time . the advantages of the graftless 
 technique as well as in other studies was presented stating that it 
 eliminates the costs of grafting materials and reduces the risks for 
 morbidity related to harvesting of bone grafts . presented a study in 1997 , where 24 periodontally compromised patients 
 were treated with implant therapy of which 38 included sinus lift 
 procedure . the patients , who where chosen for the study needed at least 
 2 implants each . in total , fenestration was prepared in the lateral sinus wall after that 
 the sinus membrane was lifted and the implants were inserted creating a 
 compartment filled with blood between themselves and the sinus membrane . the implants where loaded after 5 to 6 months . during an annual 
 follow - up , 35 out of 38 implants were successfully integrated . on a 
 follow - up radiographs it was seen that new bone formation accrued around 
 the part of the implants , which is protruding up into the sinus cavity . a follow - up of the study above was presented in 2006 by ellegaard et al 
 . were tested , all patients that was treated with implant therapy 
 between 1990 and 2002 out of 262 implants was placed in the maxillary 
 sinus . the results of the study had sown that similar success rate is 
 present in implants in periodontal compromised patients as well as in 
 ordinary implants . development of methods improving 
 space - maintaining management recently , two studies where published , one 
 by johansson et al .   and another by kaneko et al . both studies 
 already approve that sinus lifting without graft materials allows new 
 bone formation in the sinus and in their research they use this as a 
 fact , though both of the studies state that the amount of bone formation 
 varies . the papers aim into improving the amount of new bone by enabling 
 new methods for space - maintaining management . hollow hydroxyapatite 
 space - maintaining device was used in johansson s et al .   study and 
 titanium bone fixation device both studies concluded that predictable bone formation is 
 attained by space - maintaining devices . from the data that extracted from the 
 current literature we see clear radiological evidences to bone formation 
 in the sinus after using lateral window technique for the lift while 
 using blood clot alone for the bone formation [ 15 - 16 ] . the key role to 
 this bone formation lies in schneiderian membrane and the bone gain does 
 not depend much on the type of grafting material used . the leading 
 reason to the bone regeneration is the innate osteogenic potential of 
 the schneiderian membrane and the basic principle behind bone formation 
 is by guided tissue regeneration . while not all of the factors for this 
 verity are clear , as well as the exact bone formation mechanism , it is 
 possible that efficient space - maintaining management predicts an 
 increase in bone gaining [ 24 - 25 ] . in thor study it s been 
 observed that the amount of bone gain around long implants was greater , 
 this strengthens that the height of membrane lift is correlated with the 
 amount of regenerated bone . it can be beneficial if we could 
 identify how much bone formation we should expect since it is less 
 invasive and cost effective procedure . we suggest that in order to 
 achieve better results perhaps more research must be conducted 
 investigating the predictability of bone formation with focus on 
 individual patient s potential for this method . it is clearly shown in the review that the 
 potential of the maxillary sinus to heal and to form new bone without 
 bone grafts or substitutes is of high nature . the technique presented 
 proved to be reliable for bone augmentation of the maxillary sinus 
 floor . as the exact mechanisms of action on how the bone formation in 
 the sinus occurs , it is not fully cleared . more clinical studies need to 
 be carried out to clarify the bone formation mechanism and 
 predictability in the maxillary sinus after sinus lift without using any 
 bone graft materials .
abstractobjectivesthe restoration of edentulous posterior maxilla 
 with dental implants is challenging due to a deficient posterior 
 alveolar ridge . over the last decade 
 an advance in the graftless bone 
 augmentation procedures had occurred where the space left beneath the 
 schneiderian membrane is filled with blood clot in order to produce bone 
 formation . 
 the aim of present article is to review the scientific 
 literature with respect to bone formation in the sinus , after membrane 
 elevation procedure , without using any bone substitutes.material and methodsa comprehensive review of the current literature was 
 conducted according to the prisma guidelines by accessing the ncbi pubmed 
 database . 
 the articles were searched from 1993 to 2013 . 
 english language 
 articles with minimum one year patient follow - up and radiological and/or 
 histological diagnostics of newly formed bone were included . 
 articles were 
 excluded , if usage of bone graft or bone substitutes and/or usage of osteotome 
 has been made during sinus lift operation.resultsa total of 19 
 studies were included : 2 studies were related to the sinus membrane s osteogenic 
 potential , 3 to the histological evidence of bone formation in monkeys and 
 humans , 12 to the radiologic evidence of bone gain , and 2 to the 
 space - maintaining management . 
 100% of the reviewed articles presented with 
 increased bone formation and high implant survival rates resulting from the 
 graft - free technique.conclusionsit is clearly shown in the 
 review that the potential of the maxillary sinus to heal and to form new bone 
 without bone grafts or substitutes is of high nature .