cone beam computed tomography ( cbct ) was introduced to the dental field to replace the cumbersome , expensive , and high - radiation  producing medical ct scans around a decade ago suomalainen et al .
the american association of oral and maxillofacial radiology has stated that cross - sectional views are recommended for planning dental implants , and this in combination with the easy accessibility , easy handling , and low - radiation dose of cbct imaging will lead to the widespread use of cbct imaging in implantology .
considering the dose of radiation from other image acquisition modalities such as multislice computed tomography ( msct , e.g. , maxmand ct scan : effective dose of 2100 according to the 1990 recommendations of the international commission on radiological protection ( icrp ) ) and panoramic radiography ( e.g. , panoramic orthophos plus : effective dose of 6.3 and 13.3 according to icrp 1990 and 2005 , respectively ) , cbct has lesser radiation than msct and 10 times more radiation than a panoramic x - ray . the dose of radiation should be reported in millisievert ( msv ) or microsievert ( sv ) to express the effective dose ( e ) .
as ludlow stated , the e of radiation has been recommended by the icrp as a means of comparing the detriment of different exposures to ionizing radiation to an equivalent detriment produced by a full - body dose of radiation .
the e should be calculated using the equation e = pwt_ht , where wt = weighting factor , ht = equivalent dose .
the ht should be calculated using the equation ht = pwr_dt , where wr = radiation weighting factor ( which is 1 in the case of x - ray radiation ) , dt = absorbed dose .
benefits of cbct are three - dimensional ( 3d ) dataset , real - size data , the potential for generating all 2d images ( e.g. , orthopantomogram , lateral cephalogram , imaging of the temporomandibular joint ( tmj ) ) , potential for vertical scanning in a natural seated position , isotropic voxel size , high - resolution ( e.g. , bone trabeculae , periodontal ligament ( pdl ) , root formation ) imaging , lower dose of radiation than msct , less disturbance from metal artifacts , reduced costs compared with msct , easier accessibility , in - office imaging , easier handling , small footprint , digital imaging and communications in medicine ( dicom ) compatiblity , user - friendly postprocessing and viewing software , and better saving of energy compared with msct .
limitations are low contrast range , limited detector size causing limited field of view and limited scanned volume , limited inner soft tissue information , increased noise from scatter radiation and concomitant loss of contrast resolution , movement of artifacts affecting the whole dataset , truncation artifacts ( caused by the fact that projections acquired with the region of interest selection do not contain the entire object ) , and that they can not be used for estimation of hounsfield units ( hus ) .
hus represent the relative density of body tissues according to a calibrated gray - level scale , based on normalized hu values for air ( 1000 hu ) , water ( 0 hu ) , and dense bone ( + 1000 hu ) .
hus are standard numbers originating from conventional msct imaging . despite the advantages of cbct compared with msct imaging , the latter
is still considered a better choice for the analysis of bone density using an hu scale .
the fan - shaped x - ray beam associated with less scattering and artifact production may explain the better accuracy of intensity values in an msct than in a cbct scanner which is a cone - shaped x - ray beam , and its higher amount of scattering and artifacts may explain the inaccuracies of their intensity values . in both technologies , the accuracy of intensity values can be affected by the beam - hardening phenomenon , which causes artifacts on the reconstructed images . in the posterior mandibular region ,
a deep lingual undercut is a common finding and can be difficult to manage , especially when a lingual plate perforation is suspected .
it is essential to check the angulations and positioning of the drills or implant fixtures via radiographs and clinical detection of a possible perforation in the osteotomy site . for preoperative implants
, cts are preferred because cross - sectional views bring a clearer visualization of the anatomy of the surgical site [ figure 1 ] .
the major potential risks of encountering a lingual plate perforation are massive hemorrhage of submental and sublingual arteries , airway obstruction , and a perforation above the mylohyoid ridge might injure the lingual nerve . if the extruded implant is left unattended , the infection might spread to the parapharyngeal and retropharyngeal space , leading to more severe complications , such as mediastinitis , mycotic aneurysm formation with possible subsequent rupture of the internal carotid artery , and internal jugular vein thrombosis with septic pulmonary embolism or upper airway obstruction .
the experimental site has to have sufficient vertical bone height ( 12 mm from the alveolar crest to the superior border of the inferior alveolar nerve canal ( ian ) ) to possibly place a 10 mm implant and a minimum gap of 2 mm between the tip of implant and mandibular canal .
mandibular cross - sectional imaging at the edentulous first molar region shows three types of morphologies .
the undercut ridge type ( type u , 66% ) is a ridge with a narrow base that expands bucco - lingually to a wider crest with a prominent point ( point p ) on the lingual plate , giving rise to a lingual undercut .
the parallel ridge type ( type p , 20.4% ) ridge generally has a more or less parallel ridge form ; no lingual undercut is seen .
the convergent ridge type ( type c , 13.6% ) ridge is one where the base of the ridge is wider than its crest ; no obvious undercut is seen [ figure 2 ] .
cone beam computed tomography image demonstrating the possibility of lingual plate perforation by an implant three types of cross - sectional posterior mandibular morphology : ( a ) c type , ( b ) p type , and ( c ) u type ; line a represented a reference line 2 mm coronal to the inferior alveolar nerve canal watanabe et al .
classified the cross - sectional mandibular morphology based on the outlines of the lingual and buccal plates , round on the buccal side and concave on the lingual side ( type a ) , concave on the buccal side and round on the lingual side ( type b ) , and round shape on both sides ( type c ) .
they reported that at the posterior region , type c ( round ) was the most commonly found ( 59 - 61% ) , followed by type a ( lingual concavity ) ( 36 - 39% ) .
the width of the mandible 5 - 20 mm from the inferior border of the mandible ranged from 10.5 to 15.8 mm , with no significant differences between genders .
panoramic radiographs have an inherent magnification ranging from 10 to 30% , with the horizontal magnification being more variable and thus less reliable .
marginal loss of bone and loss of bone - to - implant contact ( e.g. , by marsupuilization ) may indeed negatively influence success of the implant .
most of these studies suggest an acceptable average of marginal loss of bone ( bone loss of 2 mm after the first year ) and the absence of a peri - implant radiolucency as a criterion of radiological success .
the mandibular canal and mental foramen involve the inferior alveolar artery and inferior alveolar nerve . because images of the accessory mental foramina and bony canal to the accessory mental foramen overlap in various trabecular bone patterns .
it was reported that the presence of the bifid mandibular canal in the mandibular ramus region was observed more frequently with cbct images , in 65% of patients compared with rotational panoramic radiographs , with a range from 0.08 to 0.95% . the accessory mental nerve communicated with branches of the facial and buccal nerves .
so , it was indicated that surgical complications might be attributed to the existence of a mandibular incisive canal with a true neurovascular supply , and potential risks might also be related to the presence of the lingual foramen and anatomic variations , such as an anterior looping of the mental nerve [ figure 3 ] .
measurement between the accessory mental foramen and point of bifurcation from the mandibular canal : ( a ) two - dimensional cone beam computed tomography image of the accessory mental foramen and point of bifurcation from the mandibular canal ; ( b ) linear distance between the accessory mental foramen and point of bifurcation from the mandibular canal ; ( c ) schematic drawing of 2d cbct image ( a ) the nasopalatine canal is usually described as being located in the midline of the palate , posterior to the central maxillary incisors . the funnel - shaped oral opening of the canal in the midline of the anterior palate is known as the incisive foramen , and is usually located immediately below the incisive papilla .
the canal divides into two canaliculi on its way to the nasal cavity , and terminates at the nasal floor with an opening ( known as the foramina of stenson ) at either side of the septum .
the canal contains the nasopalatine ( incisive ) nerve and the terminal branch of the descending nasopalatine artery , as well as fibrous connective tissue , fat , and even small salivary glands .
contact of the implant with neural tissue may result in failure of osseointegration or lead to sensory dysfunction .
the anatomic variants of the canal are differentiated into three groups [ figures 4 and 5 ] .
classification of anatomic variations of the nasopalatine canal:(a ) a single canal ; ( b ) two parallel canals ; ( c ) variations of the y type of canal , with one oral / palatal opening (  incisive foramen ) and two or more nasal openings (  foramina of stenson ) type a nasopalatine canal ( a single canal ) type b nasopalatine canal ( two separate canals ) as evaluated in a coronal cone beam computed tomography image type c nasopalatine canal ( y configuration of canal ) with one oral / palatal opening and two nasal openings dimensional alterations occur on the alveolar process following tooth extraction .
after the healing process is completed , loss of bone at the facial aspect of the marginal one - third of the socket is more pronounced than in the palatal / lingual aspect .
this difference in the healing outcome maybe related to the fact that the buccal bone wall is thinner than its palatal counterpart .
the thinner the facial bone wall , the more extensive the loss of facial bone . following tooth removal / loss , the entire marginal ,
buccal bone plate be lost , but an additional 2 mm of the original socket dimension may disappear during the process of socket healing and site adaptation .
in the posterior mandibular region , a deep lingual undercut is a common finding and can be difficult to manage , especially when a lingual plate perforation is suspected .
it is essential to check the angulations and positioning of the drills or implant fixtures via radiographs and clinical detection of a possible perforation in the osteotomy site . for preoperative implants
, cts are preferred because cross - sectional views bring a clearer visualization of the anatomy of the surgical site [ figure 1 ] .
the major potential risks of encountering a lingual plate perforation are massive hemorrhage of submental and sublingual arteries , airway obstruction , and a perforation above the mylohyoid ridge might injure the lingual nerve .
if the extruded implant is left unattended , the infection might spread to the parapharyngeal and retropharyngeal space , leading to more severe complications , such as mediastinitis , mycotic aneurysm formation with possible subsequent rupture of the internal carotid artery , and internal jugular vein thrombosis with septic pulmonary embolism or upper airway obstruction .
the experimental site has to have sufficient vertical bone height ( 12 mm from the alveolar crest to the superior border of the inferior alveolar nerve canal ( ian ) ) to possibly place a 10 mm implant and a minimum gap of 2 mm between the tip of implant and mandibular canal .
mandibular cross - sectional imaging at the edentulous first molar region shows three types of morphologies .
the undercut ridge type ( type u , 66% ) is a ridge with a narrow base that expands bucco - lingually to a wider crest with a prominent point ( point p ) on the lingual plate , giving rise to a lingual undercut .
the parallel ridge type ( type p , 20.4% ) ridge generally has a more or less parallel ridge form ; no lingual undercut is seen . the convergent ridge type ( type c , 13.6% )
ridge is one where the base of the ridge is wider than its crest ; no obvious undercut is seen [ figure 2 ] .
cone beam computed tomography image demonstrating the possibility of lingual plate perforation by an implant three types of cross - sectional posterior mandibular morphology : ( a ) c type , ( b ) p type , and ( c ) u type ; line a represented a reference line 2 mm coronal to the inferior alveolar nerve canal watanabe et al . classified the cross - sectional mandibular morphology based on the outlines of the lingual and buccal plates , round on the buccal side and concave on the lingual side ( type a ) , concave on the buccal side and round on the lingual side ( type b ) , and round shape on both sides ( type c ) .
they reported that at the posterior region , type c ( round ) was the most commonly found ( 59 - 61% ) , followed by type a ( lingual concavity ) ( 36 - 39% ) .
the width of the mandible 5 - 20 mm from the inferior border of the mandible ranged from 10.5 to 15.8 mm , with no significant differences between genders .
panoramic radiographs have an inherent magnification ranging from 10 to 30% , with the horizontal magnification being more variable and thus less reliable
. marginal loss of bone and loss of bone - to - implant contact ( e.g. , by marsupuilization ) may indeed negatively influence success of the implant .
most of these studies suggest an acceptable average of marginal loss of bone ( bone loss of 2 mm after the first year ) and the absence of a peri - implant radiolucency as a criterion of radiological success .
the mandibular canal and mental foramen involve the inferior alveolar artery and inferior alveolar nerve . because images of the accessory mental foramina and bony canal to the accessory mental foramen overlap in various trabecular bone patterns .
it was reported that the presence of the bifid mandibular canal in the mandibular ramus region was observed more frequently with cbct images , in 65% of patients compared with rotational panoramic radiographs , with a range from 0.08 to 0.95% . the accessory mental nerve communicated with branches of the facial and buccal nerves .
so , it was indicated that surgical complications might be attributed to the existence of a mandibular incisive canal with a true neurovascular supply , and potential risks might also be related to the presence of the lingual foramen and anatomic variations , such as an anterior looping of the mental nerve [ figure 3 ] .
measurement between the accessory mental foramen and point of bifurcation from the mandibular canal : ( a ) two - dimensional cone beam computed tomography image of the accessory mental foramen and point of bifurcation from the mandibular canal ; ( b ) linear distance between the accessory mental foramen and point of bifurcation from the mandibular canal ; ( c ) schematic drawing of 2d cbct image ( a )
the nasopalatine canal is usually described as being located in the midline of the palate , posterior to the central maxillary incisors .
the funnel - shaped oral opening of the canal in the midline of the anterior palate is known as the incisive foramen , and is usually located immediately below the incisive papilla .
the canal divides into two canaliculi on its way to the nasal cavity , and terminates at the nasal floor with an opening ( known as the foramina of stenson ) at either side of the septum .
the canal contains the nasopalatine ( incisive ) nerve and the terminal branch of the descending nasopalatine artery , as well as fibrous connective tissue , fat , and even small salivary glands .
contact of the implant with neural tissue may result in failure of osseointegration or lead to sensory dysfunction .
the anatomic variants of the canal are differentiated into three groups [ figures 4 and 5 ] .
classification of anatomic variations of the nasopalatine canal:(a ) a single canal ; ( b ) two parallel canals ; ( c ) variations of the y type of canal , with one oral / palatal opening (  incisive foramen ) and two or more nasal openings (  foramina of stenson ) type a nasopalatine canal ( a single canal ) type b nasopalatine canal ( two separate canals ) as evaluated in a coronal cone beam computed tomography image type c nasopalatine canal ( y configuration of canal ) with one oral / palatal opening and two nasal openings
dimensional alterations occur on the alveolar process following tooth extraction . after the healing process is completed , loss of bone at the facial aspect of the marginal one - third of the socket is more pronounced than in the palatal / lingual aspect .
this difference in the healing outcome maybe related to the fact that the buccal bone wall is thinner than its palatal counterpart .
the thinner the facial bone wall , the more extensive the loss of facial bone . following tooth removal / loss , the entire marginal ,
buccal bone plate be lost , but an additional 2 mm of the original socket dimension may disappear during the process of socket healing and site adaptation .
 cone beam computed tomography ( cbct ) scanners for the oral and maxillofacial region were pioneered in the late 1990s independently by arai et al . in japan and mozzo et al . 
 cbct has a lower dose of radiation , minimal metal artifacts , reduced costs , easier accessibility , and easier handling than multislice computed tomography ( msct ) ; however , the latter is still considered a better choice for the analysis of bone density using a hounsfield unit ( hu ) scale . 
 oral implants require localized area of oral and maxillofacial area for radiation exposure ; so , cbct is an ideal choice . 
 cbct scans help in the planning of oral implants ; they enable measurement of the distance between the alveolar crest and mandibular canal to avoid impingement of inferior alveolar nerve , avoid perforation of the mandibular posterior lingual undercut , and assess the density and quality of bone , and help in planning of the oral implant in the maxilla with special attention to the nasopalatine canal and maxillary sinus . 
 hence , cbct reduces the overall exposure to radiation . 
I
Mandibular lingual undercut and inferior alveolar canal
Accessory mental foramen
Nasopalatine morphology
Alveolar process