aging results in both bone density increasing and alterations on the biological behavior of the craniofacial complex sutures due to skeletal maturity . although the increasing of bone rigidity is variable among individuals , it offers greater resistance to the forces applied to midpalatal suture during maxillary expansion 
 . surgically assisted rapid maxillary expansion ( sarme ) or surgically assisted maxillary expansion ( same ) has been indicated both for patients reaching skeletal maturity and those previously submitted to rapid maxillary expansion ( rme ) whose treatment failed 


 . the literature emphasizes the indispensable role of post - expansion orthodontic retention of midpalatal suture 




 . within this retention period , both bone neoformation and suture remodeling takes place , decreasing the relapse possibilities 
 . in the studies on sarme mentioned in international literature , the mean age of the patients undergoing sarme varied from 19 to 29 . still , the biological behavior of midpalatal suture of adult patients submitted to sarme has not been fully clarified , especially regarding the time amount required to achieve bone neoformation / mineralization and the adequate retention period to achieve bone remodeling , thus assuring treatment stability 
 . cone beam computed tomography ( cbct ) is a useful tool to asses quantitatively the effects of maxillary expansion 
  and measure bone density at midpalatal suture area 
 . moreover , cbct provides tridimensional visualization of craniofacial structures and other advantages , such as : relatively low cost ; no anatomic structure superposition ; easy access ; and low radiation exposure compared to conventional multislice tomography 
 . the aim of this study was to evaluate the opening pattern and bone neoformation at the midpalatal suture area , immediately before and during orthodontic retention period , in patients submitted to surgically assisted rapid maxillary expansion through cone beam computed tomography . it was a prospective study and the sample comprised 56 digital volumetric tomographies of 14 adult patients ( four images per patient ) , both genders , presenting posterior cross bite due to transversal maxillary deficiency treated by surgically assisted rapid maxillary expansion ( sarme ) , no systemic disease that contraindicated the procedure . the tomography device used in this research was the i - cat ( imaging sciences international hatfield , pennsylvania , usa ) . patients wore either hyrax ( n=8 ) or haas ( n=6 ) appliances and did not have any contributory disease contraindicating the surgical procedure . this study was approved by the ethics in research committee protocol number 401.136 and all participants signed an informed consent agreement . all patients were subjected to modified subtotal le fort i with osteotomy of pterygoid pillars and midpalatal suture according to betts , et al . ( 1995 ) , but without osteotomy of the nasal septum ( figure 1 ) . the four tomographies were obtained at pre - operative and 15- , 60- , and 180-day post - operative periods for each patient . during the surgery , 1.0 g of cephalothin and 10 mg of intravenous dexamethasone were administered in addition to the drugs needed for the general anesthesia . cephalothin was maintained for 24 hours and during this period they were under nursing care . figure 1subtotal le fort i osteotomy with zygomatic pillar step 
  the following activation protocol was used : after a latency period of five days , the screws were turned 0.5 mm per day (  turn at the morning and  turn at night ) for 7 days followed by no activation for the next 7 days . the activation - latency cycles were interpolated until the palatal cusps of maxillary pre - molars and molars touched the buccal cusps of mandibular pre - molars and molars , achieving the desired expansion 
 . firstly irregular tool was used to mark an irregular line from posterior to anterior nasal spine , following the hard palate curvature at sagittal reformations ( figure 2 ) . this tracing enabled to obtain the axial reformation of the marked area and to analyze the opening pattern and bone neoformation density at the midpalatal suture area ( figure 3 ) . tool 
 
 figure 3new axial reformation obtained from hard palate demarcation 
  the midpalatal suture opening pattern classification was carried out in all 14 tomographic images at 60-day post - operative period , corresponding to the ending of the expansion period , through visual analysis of the images . ( 2010 ) , as follows : type i  opening from anterior to posterior nasal spine ; type ii  opening from anterior nasal spine to transversal palatal suture ( figure 4 ) . figure 4type i ( left ) and type ii ( right ) opening pattern 
  to measure the bone neoformation density , hu statistics tool was used by marking rectangles ( 1 mm 
 ) on all extension of the suture / disjunction of midpalatal suture at about 3 mm spacing among them through distance tool . once the rectangular area was marked , the software provided the mean expressed in housnfield units ( hu ) . approximately 15 rectangular marks were performed along with the midpalatal suture on 56 sample images , divided into the following areas : anterior ( from the anterior nasal spine to incisor foramen ) , median ( from incisor foramen to transversal palatal suture ) and posterior ( from transversal palatal suture to posterior transversal palatal suture ) ( figures 5 and 6 ) . figure 5density mean along with the area of interest 
 
 figure 6marked anterior , median and posterior areas 
  a single examiner assessed the images . the studied sample comprised 56 tomographies of 14 individuals ( 9 females and 5 males ) with mean age of 25.3 years ( sd=5.71 years ) . orthodontic appliances consisted of hyrax ( tooth born ) and haas ( tooth and mucosa born ) , respectively installed in 6 and 8 individuals . type i opening pattern of midpalatal suture was observed in 12 images , while type ii in 2 images ( figure 7 and 8) . figure 7gender , age , expander type and opening pattern of midpalatal suture 
 
 figure 8mean age for type i and ii opening patterns 
 
 table 1 displays the bone density mean of the three evaluated maxillary areas : anterior , median and posterior , at each studied period . the bone density at these 3 periods : 15-day post - operative ( po 15 ) , 60-day post - operative ( po 60 ) and 180-day post - operative ( po 180 ) was smaller than the initial period ( pre ) in the three regions studied . the period allowed the evaluation of bone density after that the total activation ( po 60 ) demonstrated the smallest density values . the density values found after six months retention ( po 180 ) were lower than the initial period ( pre ) . table 1density mean values ( hu ) of anterior , median , posterior areas of palate and percentage at the final period ( po 180 ) in relation to that of initial period ( pre)areaprepo 15po 60po 180%anterior334.117135.95365.85101.62530.4%median435.281264.155110.007188.63143.3%posterior424.916326.857151.497279.18865.7% 
 
 table 2 shows the density results at each studied period : pre - operative ( pre ) , 15-day post - operative ( po 15 ) , 60-day post - operative ( po 60 ) , and 180-day post - operative ( po 180 ) with the mean of each period and the percentage regarding to initial period and analyzed by anova . table 2anova comparative analysis of density variables before and after 15 , 60 , and 180 days in relation to the mean values and standard deviation ( sd ) of all areas . different letters show statistically significant differences among means by tukey testdensity variablesmeansdppre379.214c148.1930.000*po 15234.732b143.3930.000*po 60104.995a152.0920.000*po 180189.287ab100.9680.000 * * p<0.05 rapid maxillary expansion ( rme ) is considered a simple , highly efficient and stable treatment to correct even severe transversal maxillary discrepancies moreover , aging and the increasing of resistance against skeletal expansion is directly related because of cranial and face suture fusion 


 . accordingly , rme is a treatment with high predictability in children and teenagers , but not in adults , commonly resulting in treatment failure and complications like tooth tipping and reduction in buccal cortical bone thickness 
 . however , expansion in individuals reaching skeletal maturity is possible , but without predictable and stable outcomes . rme after the pubertal peak tends to show more relapse , hence it is important to plan a sufficient retention period with older patients 
 . usually , the orthopedic mechanics is capable of opening the midpalatal suture until 16 - 17 years old 
 . considering individuals achieving skeletal maturity , rme does not provide stable expansion of atresic maxilla whose deficiency was greater than 5 mm 
 . thus , currently , surgically assisted rapid expansion ( sarme ) has been the treatment of choice , well accepted by the literature , to overcome the bone resistance to expansion 


 . this treatment modality consists of associating surgical and orthodontic procedures aiming at providing space on tooth arch for tooth alignment 
 . a few studies demonstrated through finite element analysis the need of osteotomy of pterygoid pillars to decrease the stress concentration on this area , which was very high when the osteotomy was not performed 


 . moreover , this procedure prevents damage to sphenoid bone and results in a more uniform expansion of the maxillary posterior area . other authors concluded that sarme associated with pterygomaxillary disjunction should be chosen in patients aged above 20 years 
 . the aforementioned study was conducted through computed tomography aiming to compare pre- and post - operative periods of patients submitted to sarme with and without pterygoid pillar disjunction . sarme is considered a procedure with little risk of serious complications , although major complications are mentioned in literature , such as : life threatening epistaxis to a cerebrovascular accident , skull base fracture with reversible oculomotor nerve pareses and orbital compartment syndrome 
 . less serious complications reported are post - operative hemorrhage , pain , sinusitis , palatal tissue irritation / ulceration , asymmetrical expansion , nasal septum deviation , periodontal problems and relapse 
 . the mean age of this study s patients was 25.3 years ( figure 1 and 2 ) , which is in agreement with the literature which reports that patients submitted to sarme showed an age range from 19 - 29 years 
 . the mean age of patients exhibiting type i opening pattern was 23.9 years , while the mean age of those presenting type ii opening pattern was 33.5 years . this result corroborates the literature reporting the difficult in obtaining a greater and more parallel maxillary expansion in older individuals 
 . according to the findings of this study , age the rationale behind this affirmation is that all patients were submitted to a single surgical technique , but nevertheless exhibited different opening patterns of the midpalatal suture . thus , we can hypothesize that older individuals would show a tendency towards difficult in obtaining disjunction of the posterior area of maxilla , evidencing an opening pattern less parallel ( v shaped ) . also , the results of this study did not show statistically significant differences regarding the expander type . although hyrax and haas appliances show similar effects , maxillary expansion is obtained through different mechanisms : dental - alveolar expansion by the former and more orthopedic expansion by the latter 
 . in this study , regardless of the expander type , the desired expansion of maxillary expansion was achieved with both appliances and the opening pattern of the midpalatal suture seems to be more related to the patient s age and surgical technique than to the expander type used in the orthopedic mechanics , as aforementioned explained . it is worth emphasizing the indispensable role of post - expansion orthodontic retention of the midpalatal suture because at this period both bone neoformation and remodeling take place after disjunction , decreasing relapse possibilities 
 . according to a study which compared the stability between rapid and slow maxillary expansion , the dental arch transverse dimensions showed a more pronounced relapse maintaining approximately 40% of initial molar expansion with significant difference from control 
 . ( 2005 ) , reported 0.88 mm ( 12% ) , 1.01 mm ( 17.5% ) and 0.5 mm ( 55% ) of relapse , respectively , in a 12-month study period . they concluded that expansion obtained with sarpe is stable , but all their patients were still in orthodontic treatment . although a number of articles on the stability of surgically assisted rapid palatal expansion ( sarpe ) have been published , the reported stability varies considerably 




 . after midpalatal suture disjunction , bone repair of the area is required to reach treatment stability . however , literature has reached no consensus regarding to the retention period necessary for bone repair 
 . the midpalatal suture is the area in which the skeletal expansion is observed after rme or sarme and is commonly seen on conventional oclusal radiographs . on occlusal view , obtained through occlusal radiographs of the maxilla , midpalatal suture is visualized up to the middle of the palate . consequently , the proper view of the posterior area of palate is not possible because of the superposition of the cranial base structures . thus , the main advantage of computed tomography ( ct ) over oclusal radiograph of maxilla is the perfect visualization of the posterior area of midpalatal suture , without interference of the cranial structures 
 . in one study through cbct comprising 60 adult and 60 teenager patients , the authors concluded that bone density of adults was significantly higher than that of teenagers , but the density of the anterior palatal area of teenagers was similar to that of posterior palatal area of adults 
 . similarly , a ct study with teenagers showed the complete midpalatal suture ossification from anterior to posterior nasal spine after a mean retention period of 8 - 9 months 
 . nevertheless , in this present study , the complete bone neoformation of midpalatal suture did not take place within the studied period , that is , 180 days ( 6 months ) of retention . these findings were similar to those of the study conducted by petrick , et al . ( 2011 ) through ct , who evidenced different density values between pre - operative and 7-month post - operative periods 
 . the bone density of the anterior , median and posterior areas was 48% , 53% and 75% of their initial values , respectively . probably the difference in the retention periods between these studies occurred because the former employed children submitted to rme 


 . as shown by some studies 


 , rme tends to result in incomplete opening of posterior palatal area and consequently bone repair is faster together with the fact that bone neoformation takes place faster in children 



 . 
  in this study , similarly to that of petrick , et al . ( 2011 ) , the density values of the anterior area were significantly smaller than those of median and posterior areas of maxilla . the bone density of anterior , median , and posterior areas was 30.4% , 43.3% and 65.7% of the initial values , respectively . a study with a large number of patients , especially older individuals , is needed to conclude emphatically that the age affects the opening pattern and the bone neoformation . the importance of this study relies on the fact that the bone density at the ending of the retention period ( 180 days ) was smaller than that before sarme . accordingly , a retention period longer than 180 days is necessary to find similar density values between pre- and post - operative periods . based on the methodology employed and the results obtained , it can be concluded : 1 . the opening pattern of the palatal suture seems to be more related to patients age than to type of orthopedic mechanics employed . the bone density values after 180 days of retention were smaller than those of the pre - operative period , demonstrating that this retention period was not sufficient for the complete bone neoformation at the midpalatal suture area of the studied patients .
surgically assisted rapid maxillary expansion ( sarme ) is the treatment of choice to adult patients even with severe transversal maxillary discrepancies . 
 however , the adequate retention period to achieve the bone remodeling , thus assuring treatment stability , is controversial . objective to evaluate the opening pattern and 
 bone neoformation process at the midpalatal suture in patients submitted to surgically assisted ( sarme ) through cone beam computed tomography ( cbct).material and methods fourteen patients were submitted to sarme through subtotal le fort i osteotomy . 
 both the opening pattern and the mean bone density at midpalatal suture area to evaluate bone formation were assessed pre- and post - operatively ( 15 , 60 and 180 days ) through cbct.results type i opening pattern ( from anterior to posterior nasal spine ) occurred in 12 subjects while type ii opening pattern ( from anterior nasal spine to transverse palatine suture ) occurred in 2 individuals . 
 the 180-day postoperative mean ( po 180 ) of bone density value was 49.9% of the preoperative mean ( pre ) value.conclusions the opening pattern of midpalatal suture is more related to patients age ( 23.9 years in type i and 33.5 years in type ii ) and surgical technique . 
 it was not possible to observe complete bone formation at midpalatal suture area at the ending of the retention period studied ( 180 days ) .