the use of oral implants for the treatment of partially as well as totally edentulous 
 patients has increased incredibly . nowadays more imaging techniques have become 
 available for the preoperative planning of oral implant surgery , each with their 
 own strength and weaknesses and specific indications . in many 
 cases , the use of three - dimensional imaging may be beneficial as compared to two - dimensional 
 imaging and overcome its limitations . in particular , placement of dental implants in the posterior maxilla can be jeopardized 
 by several factors . the predominant problem is undoubtedly the lack of bone quantity . 
 considering that maxillary sinus floor elevation surgery may be indicated when dealing 
 with cases of insufficient bone below the maxillary sinus , a closer look to its 
 anatomical variations seems a necessity . it should be considered that the maxillary 
 sinus has a close relation to the roots of the maxillary molars and bicuspids . normally 
 tooth apices and the maxillary floor are separated by cortical bone , but some teeth 
 ( such as the first and second maxillary molar ) are only separated from the maxillary 
 sinus floor by a thin mucosal layer [ 4 - 6 ] . the volume of the maxillary 
 sinus has a natural tendency to increase during life . tooth loss in the posterior 
 maxilla can result a rapid alveolar bone resorption caused by inherent bone remodelling 
 of the alveolar bone . in addition , the maxillary sinus extends further by osteoclast 
 activity in the schneiderian membrane , causing pneumatisation of the sinus by resorbing 
 bone within a few months . because of the intimate relationship between teeth and maxillary sinus , periapical 
 infections might result in reactive mucosal response within the sinus . maxillary 
 sinus mucosal thickening is twice as common in patients with dental disease as in 
 the general population   and odontogenic sinusitis accounts 
 for approximately 10% to 12% of all cases of maxillary sinusitis . failure to recognize the tooth as a cause of sinus disease can result in incomplete 
 or inadequate therapy and mismanagement of these conditions . although surgical interventions involving the maxillary sinus are increasing , 
 the presurgical planning continues using two - dimensional radiographs for maxillary 
 sinus visualization [ 10 - 12 ] . considering the anatomical variability 
 related to the surgical site , including the maxillary sinus floor and its intimate 
 contact with the maxillary posterior teeth , observations on the three - dimensional 
 structure are most useful in relation to implant surgery and sinus grafting . yet therefore , the aim 
 of this study was to explore the maxillary sinus anatomy using spiral computed tomography 
 in order to obtain more accurate information on the morphology , variation , volume 
 and the amount of maxillary bone adjacent to the sinus . maxillary sinus computed tomography ( ct ) data of 101 consecutive patients ( edentulous 
 and partially dentate ) visiting the department of periodontology , university hospital , 
 catholic university of leuven , leuven , belgium were assessed . while 30 patients 
 ( 14 males , 16 females ; aged 20 to 70 years ; mean age = 53.8 years ) were edentulous , 
 71 were partially edentulous ( 36 males , 35 females ; aged 22 to 80 years ; mean age 
 = 52.8 years ) . they all gave informed consent to undergo maxillary spiral ct scans 
 as part of the clinical procedure for preoperative planning of implant placement 
 in the maxilla . spiral ct was carried out by somaton plus r ct scanner ( siemens , erlangen , germany ) 
 at 120 kv , 165 mas , 500 m reconstructed voxel size at the department of radiology 
 university hospital catholic university of leuven , leuven , belgium . the axial plan 
 was positioned parallel to the hard palate of the maxilla . for the computer - assisted 
 navigation system , a dual scanning procedure was used to allow the prosthetic model 
 to be visualized together with the jaw bone reconstruction . the latter included 
 a scanning of the patient with the scan prosthesis and some radio - opaque markers 
 included , followed by another scanning of the prosthesis only . this set - up allowed 
 identification of the respective edentulous sites with standardized linear measurements 
 of the bone height at the level of each tooth site . dimensional measurements below is an overview of the measurement of the patient 's spiral ct scans employed 
 for exploration of the maxillary sinus anatomy , its variation and volume . the minimum and maximum alveolar bone height was measured on cross - sectional 
 images between alveolar crest and maxillary sinus floor ( figure 1 ) , 
 as measured parallel to each tooth or scan prosthesis axis . cross - sectional image showing measurement of 
 the alveolar bone height below the sinus at the level of the respective 
 ( prosthetic ) tooth : the distance between the floor of the maxillary sinus 
 ( a ) and the alveolar crest ( b ) was considered to be the alveolar bone height 
 below the maxillary sinus floor . the size of the maxillary sinus according to anteroposterior ( ap ) and mediolateral 
 ( ml ) diameters of the sinus was measured ( figure 2 ) at 5 , 10 , 
 15 and 20 mm above the most apical level of the maxillary sinus floor . serial axial slice showing measurement of the 
 maxillary sinus dimensions : anteroposterior ( ap ) and mediolateral ( ml ) measures 
 were performed at 5 , 10 , 15 and 20 mm above the most apical level of the 
 maxillary sinus floor . 3 . mucosal thickening of the maxillary sinus was defined as the existence of 
 soft tissue structures thickness > 4 mm . all measures were done using an accurate measuring tool ( with an accuracy to 
 the nearest = 0.1 mm ) in the viewing software , by using a diagnostic screen ( sgi , 
 fremont , ca , usa ) . ( 1 oral 
 surgeon and 1 dentomaxillofacial radiologist ) , and 10% of the measures was repeated 
 to determine the intra- and inter - subject variability . the latter yielded a non - significant 
 variability , with a coefficient of variation below 4% for both intra- and inter - observer 
 measurements . morphologic assessments the maxillary sinus was also assessed morphologically , by determining the anterior 
 and posterior extends of the maxillary sinus , in relation to the respective teeth 
 or estimated tooth sites , in case of edentulism . this morphological rating was done 
 on axial , sagital and panoramic slices . at the same time this morphological assessment allowed 
 a general scoring on sinus morphology and the occurrence of any asymmetry ( which 
 was also confirmed dimensionally , see previous paragraph ) . , r.j . ) using the same 
 viewing software and the same diagnostic screen ( sgi , fremont , ca , usa ) . data and statistical analysis above mentioned data were pooled and averaged for further analysis . descriptive 
 variables included dental status , the number of septa in the maxillary sinus , the 
 respective location and morphologic variation of the sinus . statistical analysis 
 was performed using the statistical package of ncss 2000 ( kaysville , utah , usa ) . data were tested for normality which yielded a skewed data set necessitating non - parametric 
 analysis . the pearson 
 rank correlation was used to test the correlation between age and alveolar bone 
 height . differences were considered as statistically significant when p - values were 
 less than 0.05 . alveolar bone height under the maxillary sinus floor the outcome of the linear bone measurement in edentulous and partially dentate 
 patients is shown in tables 1 and 2 . further analysis indicated 
 that the mean values of the alveolar bone height were significantly higher in the 
 premolar region than in the molar region ( n = 46 ; p < 0.01 ) . besides , age showed 
 a negative relation to bone dimension ( r = - 0.32 , p = 0.04 ) . minimum alveolar bony height in edentulous 
 and partially dentate patient as measured in parallel to respective ( prosthetic ) 
 tooth axis alveolar bony height values in mm . maximum alveolar bony height in edentulous 
 and partially dentate patient as measured in parallel to respective ( prosthetic ) 
 tooth axis alveolar bony height values in mm . tested between the dentate and edentulous patients dimensions . size of the maxillary sinus in order to describe the size of the maxillary sinus , ap ( length ) and ml ( width ) 
 dimensions were determined and the mean values in partially dentate and edentulous 
 patients are shown in table 3 . the ap and ml dimensions of the 
 maxillary sinus were in the range of 38 ( sd 5.2 ) mm and 23.5 ( sd 5.1 ) mm respectively . there was no significant difference between both groups in ap and ml measurements 
 ( p > 0.05 ) . anteroposterior ( ap ) and mediolateral ( ml ) dimensions 
 of the sinus in partially dentate and edentulous patient in right and left 
 side anteroposterior and mediolateral dimensions expressed as mean values ( standard deviation ) in mm . location of the mucosal thickening in the maxillary sinus the data also showed that almost 2/3 of patients ( 66% ) showed major ( > 4 mm ) 
 mucosal thickening , mostly located on the maxillary sinus floor , with a complete 
 absence of swelling only found in 11% of the cases . furthermore , 11 cases of mucosal 
 retention cysts in the left ( n = 5 ) and right ( n = 6 ) side of the maxillary sinus 
 were observed . the extension of the maxillary sinus according to the present study , the anterior borders of the maxillary sinus were 
 located mostly at the level of the premolar region with first premolar being 44.7% 
 and 52.6% for right and left sides respectively . meanwhile 78.8% right sinus and 
 89.5% left sinus extended distally to the second molar region ( table 
 4 ) . patient left and right maxillary sinus anterior 
 and posterior border location in accordance to the tooth position 2 . symmetry of maxillary sinus the shape and size of the maxillary sinus could alter throughout the life . in 
 this study half of the patients ( 50% ) showed a somewhat symmetric morphology . one 
 third ( 33% ) of the patients had some differences at several levels while the remaining 
 patients ( 17% ) showed a predominant asymmetric morphology . 3 . septa in maxillary sinus the prevalence of one or more septa in overall study population was 47% . no correlation 
 was found between the number of septa and the sinus morphology . however , the statistical 
 analysis between the number of the septum and ap dimension showed that the ap dimension 
 was smaller in patients without septum as compared to patients with various sinus 
 septa , but only in left side ( p = 0.04)(table 5 ) . anteroposterior ( ap ) dimension of 
 the patients ' left and right sinus depending on sinus septa presence anteroposterior dimension expressed as mean values ( standard deviation ) in mm . tested between ap dimensions of maxillary sinus with and without septa . results of the present study demonstrated a considerable difference in mean values 
 of the alveolar bone height for the two groups of patients ( edentulous and partially 
 dentate ) . extreme differences were observed when contrasting the first molar region 
 in edentulous patients ( 4.9 [ sd 2.8 ] mm ; range 1.3 - 9 mm ) to the second premolar 
 region in dentate subjects ( 13.9 [ sd 4.8 ] mm ; range 5 - 20.2 mm ) . it is striking 
 that after tooth extraction such a drastic difference can exist between posterior 
 maxillae with and without teeth ( on average 9 mm difference ) . thus placement of 
 dental implants in these patients requires preprosthetic surgical procedures such 
 as alveolar ridge or sinus floor augmentation with bone grafting . although there is a wide range of maxillary sinus dimensions in different studies 
 that may reflect the influential effects like human variability and triggering of 
 pneumatisation [ 13 - 17 ] . analysis of maxillary sinus by application 
 of high - resolution ct in this study revealed ap and ml dimensions of maxillary sinus 
 in the range of 38 ( sd 5.2 ) mm and 23.5 ( sd 5.1 ) mm respectively . although sharan 
 et al .   has reported post extraction maxillary sinus pneumatisation , 
 but in this study there were no registered significant differences between ap and 
 ml dimensions in partially dentate and edentulous patients . . 
  also found no significant difference in maxillary sinus 
 volume in dentate and edentulous patients of the same age . yet , it should be considered that linear measures , as used in the current study , 
 do not fully reflect a three - dimensional volume of maxillary sinus . it is obvious that the use of volumetric measures of the sinus may be more precise 
 and could thus reveal distinct results . further studies are needed to study the 
 behaviour of the maxillary sinus in conjunction to tooth extraction , implant placement 
 and sinus grafting procedures . in such future studies , the current problem of an 
 unequal sample size ( 30 edentulous , 71 dentate ) significant mucosal thickening was observed in 66% of the study group and is 
 presumably related to periapical or periodontal diseases . others also found that 
 the presence of restorative dentistry and periapical infection can result in focal 
 mucosal thickening in the floor of the maxillary sinus . the extension of the maxillary sinus is variable in the population . in the present 
 study the anterior border was in the premolar region and posterior border located 
 mostly in second molar region , but in some studies the posterior border of the maxillary 
 sinus in third molar and tuberosity area was reported . in 83% of patients a symmetric morphology or small differences at some levels 
 in maxillary sinus was shown , while the remaining patients ( 17% ) showed a predominant 
 asymmetric morphology . some studies considered neighbouring cartilages or bony structures as an 
 influencing factor in shape and enlargement of the paranasal sinuses . mucosal retention cysts in the sinus are mostly found by accident as clinical 
 signs and symptoms are limited and majority of these cysts have spontaneous regression 
 . in the current study the right side showed a slight predominance 
 but because of insufficient quantity of this cyst in our study population we can not 
 draw a conclusion . the presence of anatomic variations within the maxillary sinus , such as septa , 
 can increase the risk of sinus membrane perforation during sinus elevation procedures 
 . the prevalence of the septa in our study population was 
 47% and ap length was larger in patients that had more than 1 septum as compared 
 to patients without septa . the incidence of antral septa varies from 16% to 69% in different studies [ 19,25 - 28 ] . this large variation may be related to a wide anatomical variation in the appearance 
 of the maxillary sinus in different study group populations and the ratio of edentulous 
 versus dentate patients can influence the outcome because etiologically , antral 
 septa constitute congenital ( primary ) and secondary septa formed in edentulous patients 
 . it seems obvious that there are lots of variations in the maxillary sinus anatomy 
 and a three - dimensional imaging yields much more information than plain film . in 
 this respect , ct is a valuable imaging modality for three - dimensional evaluations 
 of the anatomical structures but its major drawback remains the inherent costs and 
 the radiation concern . current low dose ct protocols may however enable low dose 
 imaging of the paranasal sinuses . alternatively , one may nowadays apply cone beam ct imaging as it offers a simple chair side technique , with low radiation burden and reduced costs . in the present study , higher mean values in alveolar bone height were 
 observed in the premolar region , while more bone loss occurred in older individuals . anterior and posterior border of the maxillary sinus were located in the first premolar 
 and second molar respectively . most of the patients ( 83% ) showed symmetric or small 
 differences sinus morphology in both sides , while almost half of the subjects showed 
 sinus septa . mucosal thickening was seen in 2/3 ( 66% ) of the patients mostly in 
 the sinus floor . we would like to acknowledge the immense amount of work put into the initial 
 project by professor johan van cleynenbreugel , oral imaging center , faculty of medicine , 
 catholic university of leuven , leuven , belgium , who passed away during the course 
 of this research .
abstractobjectivesthe purpose of the present study was to explore the maxillary sinus 
 anatomy , its variations and volume in patients with a need for maxillary implant 
 placement.material and methodsmaxillary sinus data of 101 consecutive 
 patients who underwent spiral computed tomography ( ct ) scans for preoperative implant 
 planning in the maxilla at the department of periodontology , university hospital , 
 catholic university of leuven , leuven , belgium were retrospectively evaluated . 
 the 
 alveolar bone height was measured on serial cross - sectional images between alveolar 
 crest and sinus floor , parallel to the tooth axis . in order to describe the size 
 of the maxillary sinus anteroposterior ( ap ) and mediolateral ( ml ) diameters of the 
 sinus 
 were measured.resultsthe results indicated that the alveolar bone height 
 was significantly higher in the premolar regions in comparison to the molar region 
 ( n = 46 , p < 0.01 ) 
 . the age showed negative relation to bone dimension ( r = - 0.32 , 
 p = 0.04).anterior and posterior border of the maxillary sinuses were mostly located in 
 the first premolar ( 49% ) and second molar ( 84% ) regions , respectively . 
 maxillary 
 sinus septa were indentified in 47% of the maxillary antra . 
 almost 2/3 ( 66% ) of 
 the patients showed major ( > 4 mm ) mucosal thickening mostly at the level of the 
 sinus floor . 
 the present sample did not allow revealing any significant difference 
 ( p > 0.05 ) in maxillary sinus dimensions for partially dentate and edentulous subjects.conclusionscross-sectional imaging can be used in order to 
 obtain more accurate information on the morphology , variation , and the amount of 
 maxillary bone adjacent to the maxillary sinus .