10.59987/ads/2012.3-4.123-131
There is a debate in the literature about the need for Computed Tomagraphy (CT) before removing third molars, even if positive radiographic signs are present. In few cases, the third molar is so close to the inferior alveolar nerve that its extraction might expose patients to the risk of post-operative neuro-sensitive alterations of the skin and the mucosa of the homolateral lower lip and chin. Thus, the injury of the inferior alveolar nerve may represent a serious, though infrequent, neurologic complication in the surgery of the third molars rendering necessary a careful pre-operative evaluation of their anatomical relationship with the inferior alveolar nerve by means of radiographic imaging techniques. This contribution presents two case reports showing positive radiographic signs, which are the hallmarks of a possible close relationship between the inferior alveolar nerve and the third molars. We aim at better defining the relationship between third molars and the mandibular canal using Dental CT Scan, DICOM image acquisition and 3D reconstruction with a dedicated software. By our study we deduce that 3D images are not indispensable, but they can provide a very agreeable assistance in the most complicated cases.
application/pdf
1971-1441
154
3-4
en
A. Cicconetti 
https://creativecommons.org/licenses/by-nc-nd/4.0
Annali di stomatologia
3D reconstruction
3D imaging reconstruction and impacted third molars: case reports
Text.Serial.Journal
https://www.annalidistomatologia.eu/ads
3
Case Report
2022-08-17
2022-08-17
2012-12-01
2023-12-04
123-131
Ann Stomatol (Roma)
A. Cicconetti 
2012
10.59987/ads/2012.3-4.123-131
123
1971-1441
3-4
3D reconstruction
en
131
3D imaging reconstruction and impacted third molars: case reports
https://www.annalidistomatologia.eu/ads/article/download/154/137
3
                                                                                                                         Case report


3D imaging reconstruction and impacted
third molars: case reports




                                                                                                            li
                                                                                                         na
Andrea Tuzi, DDS                                                            reconstruction with a dedicated software. By our study
Roberto Di Bari, DDS                                                        we deduce that 3D images are not indispensable, but
                                                                            they can provide a very agreeable assistance in the most




                                                                                                      io
Andrea Cicconetti, MD
                                                                            complicated cases.

Department of Oral and Maxillofacial Sciences, School                       Key words: IAN Inferior Alveolar Nerve, 3M third molar,




                                                                                                   az
of Dentistry, Sapienza University of Rome, Italy                            CBCT Cone-Beam Computed Tomography, Dental CT
                                                                            Scan, DICOM image, 3D reconstruction.


Corresponding author:




                                                                                    n
Andrea Cicconetti, MD                                                       Introduction
Department of Oral and Maxillofacial Sciences, School of




                                                                                 er
Dentistry, Sapienza University of Rome, Italy                               Extraction of lower third molars, both impacted and not,
Via Caserta, 6 Italy                                                        has become a standard procedure in the clinical dental
00161 Rome, Italy                                                           practice. In most cases, this surgical treatment implies lit-
Phone: +39 06 49976633


Summary
                                                nt                          tle or no risk for the adjacent anatomic structures that
                                                                            comprise first of all the inferior alveolar nerve (IAN), and
                                                                            the lingual nerve. However, in very few cases, the third
                                                                            molar is so close to the IAN that its extraction might ex-
                                              iI
There is a debate in the literature about the need for                      pose patients to the risk, more or less relevant, of post-
Computed Tomagraphy (CT) before removing third mo-                          operative neuro sensitive alterations of the skin and the
lars, even if positive radiographic signs are present. In                   mucosa of the homolateral lower lip and chin.
                                            on

few cases, the third molar is so close to the inferior
                                                                            Moreover, extraction of the third molar is the primary
alveolar nerve that its extraction might expose patients
                                                                            cause of the permanent neurologic deficit of the inferior
to the risk of post-operative neuro-sensitive alterations
                                                                            alveolar nerve, being even more important than implant
of the skin and the mucosa of the homolateral lower lip
                                                                            and orthognathic surgery (1,2). Other less frequent
and chin. Thus, the injury of the inferior alveolar nerve
                                  i


                                                                            causes of IAN injury reported in literature are: loco-re-
                               iz


may represent a serious, though infrequent, neurologic
complication in the surgery of the third molars rendering                   gional injection of anaesthetic for IAN block, endodontic
necessary a careful pre-operative evaluation of their                       treatment of lower premolar and molar after overfilling,
                                                                            malignant expansive lesions, metastases, mandibular
               Ed




anatomical relationship with the inferior alveolar nerve
by means of radiographic imaging techniques. This con-                      fractures, local infections(osteomyelitis) and pre-pros-
tribution presents two case reports showing positive                        thetic surgery (3,4). The incidence of temporary (re-
radiographic signs, which are the hallmarks of a possi-                     versible) injuries ranges from 3,3% to 13.0% and repre-
ble close relationship between the inferior alveolar nerve                  sents the third most common complication after alveolitis
and the third molars. We aim at better defining the rela-                   and post-operative infections; the incidence of permanent
tionship between third molars and the mandibular canal                      (irreversible) lesions of the IAN ranges from 0,2% to 9%
 IC




using Dental CT Scan, DICOM image acquisition and 3D                        (Tab.1) (5). Thus, the injury of the inferior alveolar nerve
C




                                                            Temporary IAN Injury                    Permanent IAN Injury

Brann CR et al., 1999                                                13.0%                                   1.0%
Carmichael FA, McGowan DA, 1992                                       3.9%                                   9.0%
©




Gülicher D, Gerlach KL, 2000                                          3.6%                                   9.0%
Kipp DP et al., 1980                                                  4.5%                                   1.0%
Smith AC et al., 1997                                                 5.2%                                   0.2%
Strietzel FP, Reichart PA, 2002                                       3.6%                                   0.9%
Wofford DT, Miller RI, 1987                                           3.3%

Table 1. Incidence of IAN injury after extraction of the third molar (5).


Annali di Stomatologia 2012; III (3/4): 123-131                                                                                      123
A. Tuzi et al.


represents a serious but infrequent neurologic complica-             tween the IAN and the mesiolingual and distolingual
tion in the surgery of the third molars, which is usually due        roots of the right third molar, and between the IAN and
to the close anatomic relationship between IAN and third             the mesial root of the left third molar. Moreover we can
molars. Therefore, this anatomical relationship must be in-          evaluate the mandibular canal on its axial view (Figs. 2,
vestigated pre-operatively by means of the radiographic              9). Using the three scholding tools of the software we are




                                                                                                        li
imaging techniques currently available (1). In this study            able to obtain a 3D recostraction of the 3M teeth. We
clinical cases are presented where the Orthopanoramic




                                                                                                     na
radiography shows positive radiographic signs, which
are the hallmarks of a possible close relationship be-
tween the IAN and the third molars. This paper aims at
better defining the relationship between third molars and




                                                                                                  io
the mandibular canal using Dental CT Scan, DICOM im-
age acquisition and 3D reconstruction with a dedicated
software Simplant (Materialise, Ann Arbor, MI 1997).




                                                                                               az
Cases reports

Case 1




                                                                              n
A patient (female, age 35) was referred for the removal of
both lower third molars. The panoramic radiography




                                                                           er
showed a darkening of the roots of the right third molar
and a deviation of the canal of the left third molar. These          Figure 2. Axial view passing through the tooth roots and show-
                                                                     ing the canal traced at the level of the left and right third molars
are telltale signs of a close relationship with the mandibu-
                                                                     (Case 1 - Right third molar).


                                               nt
lar canal. In order to confidently proceed to surgery, the
patient underwent a Dental CT Scan to better evaluate the
relationship between the canal and the roots of the third
molar as this was not sufficiently clear on the first-level bi-
                                             iI
dimensional examination (orthopanoramic radiography).
After an accurate analysis of the CT, axial, paraxial and
panoramic slices, given the close relationship between the
                                           on

roots and the IAN and the complex anatomic morphology
of the examined third molars, we decided to proceed to
the 3-D reconstruction of the surgical area by means of
a dedicated software (Simplant).
                                 i


First step was to obtain the panoramic reconstruction
                              iz


carried out on the basis of the CT data (Fig. 1). On this
image we traced the right and left mandibular canal by
means of a dedicated tool (“nerve tool”) and the software
                 Ed




automatically traced it also on the axial and paraxial sec-
tions. Then we have studied the right and left mandibu-
lar canal, highlighted by the software, on the paraxial              Figure 3. Paraxial (coronal) views of the area of the right third mo-
sections (Figs. 3, 10). In both cases, we can appreciate             lar highlighting the canal (Case 1 - Right third molar).
IAN’s lingual position to the roots as well as the area of
contact (interruption of the cortical wall of the canal) be-
 IC




                                                                     can decide to visualize only the tooth, the mandibular
                                                                     canal or all the anatomical structures (also in trans-
                                                                     parency modality). 3D reconstructions help the surgeon
                                                                     in analysing the relationship between the canal and the
C




                                                                     roots of the third molar from different perspectives (Figs.
                                                                     4, 5, 6, 11, 12). For the right molar the buccal and
                                                                     mesiobuccal views providing information on both the
                                                                     morphology and crown-root angulation with respect to
©




                                                                     the canal pathway. Notice the apical hook-like shape of
                                                                     mesiolingual root, which was not clearly detectable on
                                                                     the CTs (Figs. 4, 5). The bottom view providing accurate
                                                                     information on the number and diameter of the tooth
                                                                     roots, 2 mesial and 2 distal roots- all separated, and on
                                                                     which root is in contact with the canal (Fig. 6). After the
Figure 1. CT image of a panoramic reconstruction showing the         extraction we take some photos of the tooth: notice the
impacted third molars and the right and left mandibular canal par-   correspondence between real anatomical details and 3D
tially traced in Simplant (Case 1 - Right third molar).              reconstruction (Figs. 7, 8).

124                                                                                     Annali di Stomatologia 2012; III (3/4): 123-131
3D imaging reconstruction and impacted third molars: case reports




                                                                                                      li
                                                                                                   na
                                                                                                io
                                                                                             az
Figure 4. 3D reconstruction buccal views showing the anteropos-




                                                                             n
terior pathway of the IAN. The other teeth are not shown (Case 1
- Right third molar).




                                                                          er
                                              nt                    Figure 7. Buccal View - extracted right molar (Case 1 - Right third
                                                                    molar).
                                            iI
                                 i        on
                              iz
              Ed




Figure 5. 3D reconstruction mesiobuccal views showing the an-
teroposterior pathway of the IAN. The other teeth are not shown
(Case 1 - Right third molar).
 IC
C
©




Figure 6. 3D reconstruction bottom view showing the contact be-     Figure 8. Bottom view - extracted right molar (Case 1 - Right third
tween the IAN and the mesiolingual and distolingual roots (Case 1   molar).
- Right third molar).


Annali di Stomatologia 2012; III (3/4): 123-131                                                                                   125
A. Tuzi et al.




                                                                                                         li
                                                                                                      na
                                                                                                   io
Figure 9. Axial view left molar (Case 1 - Left third molar).




                                                                                n               az
                                                                             er
                                                                       Figure 12. 3D reconstructions from different perspectives confirm-
                                                                       ing what was already highlighted on the paraxial views, i.e. the



                                                nt                     IAN’s lingual position and its contact with the third upper portion
                                                                       of the mesial root (Case 1 - Left third molar).

                                                                       Also for the left 3M molar a photo-analysis of the extracted
                                              iI
                                                                       tooth confirm the quality of 3D reconstruction (Fig. 13).
Figure 10. CT image of paraxial (coronal) views of the area of the
left third molar showing the mandibular canal, in Simplant, pass-
ing lingually to the roots and in close contact with the mesial root
                                            on

(Case 1 - Left third molar).

For the left molar, lingual and distal views indicate the
presence of two separate roots, a distal and a mesial one
                                  i


respectively; the mesial root is in contact with the IAN
                               iz


while the distal root has no relationship with the canal
(Figs. 11, 12).
                 Ed
 IC
C
©




Figure 11. 3D reconstructions from different perspectives confirm-
ing what was already highlighted on the paraxial views, i.e. the
IAN’s lingual position and its contact with the third upper portion
of the mesial root (Case 1 - Left third molar).                        Figure 13. The extracted Tooth (Case 1 - Left third molar).


126                                                                                      Annali di Stomatologia 2012; III (3/4): 123-131
3D imaging reconstruction and impacted third molars: case reports


Case 2
The patient (female, 30 years) had to remove both lower
third molars and a supernumerary tooth in the right mo-
lar region. The first-level panoramic X-ray showed posi-
tive radiographic signs, including interruption of the cor-




                                                                                                       li
tical bone of the roof of the canal and darkening of the
roots of the left lower third molar; darkening of the roots




                                                                                                    na
and deviation of the canal when passing nearby the left
lower third molar. These signs indicated the presence of
a close relationship between the IAN and the roots of the
third molars. This was an indication to proceed to the sec-




                                                                                                 io
ond-level examination, i.e. Dental CT Scan and 3D analy-
sis using the dedicated Simplant software. We started with
a panoramic reconstruction (Fig. 14) tracing the mandibu-             Figure 16. Paraxial slices (coronal) of the region of the right
                                                                      third molar with highlighted canal (Case 2 - Right third molar).




                                                                               n              az
                                                                            er
                                               nt
                                             iI
Figure 14. CT image of panoramic reconstruction showing im-
pacted third molars and the right and left mandibular canal traced    Figure 17. 3D reconstruction with the mandible in transparent
in Simplant (Case 2 - Right third molar).                             mode: we can appreciate the tooth roots and the pathway of the
                                           on

                                                                      mandibular canal (Case 2 - Right third molar).

lar canal that is also traced on the paraxial and sagittal
sections (Figs. 15, 16, 19). Furthermore, in both cases the
IAN is lingual to the roots and seems to be in contact with
                                  i


them. The 3-D reconstrucions confirmed the information
                               iz


provided by CT images, and in particular gave us the pos-
sibility to appreciate an array of anatomical details that
were not easily detectable on the CTs: the presence of a
               Ed




mesio-lingual root, with a 90° curvature in the distal direc-
tion, lying on the canal roof (Figs. 17, 18); the IAN partially
entrapped between the buccal and lingual roots (Fig.
18); the direct contact between the distal root and the IAN
 IC
C
©




                                                                      Figure 18. 3D reconstruction with different views showing the re-
                                                                      lationship between the third molar and the IAN which is partially
Figure 15. Axial slice showing the canal traced at the level of the   entrapped between the buccal and lingual roots (Case 2 - Right
third molars (Case 2 - Right third molar).                            third molar).


Annali di Stomatologia 2012; III (3/4): 123-131                                                                                   127
A. Tuzi et al.




                                                                                                          li
                                                                                                       na
                                                                                                    io
Figure 19. Images of paraxial (coronal) slices showing the
mandibular canal, traced in Simplant, lingual to and in contact with




                                                                                                 az
the roots of the third molar (Case 2 - Left third molar).


and the IAN’s close relationship with the mesial root (Fig.
20); the contact between the IAN and the disto-buccal root




                                                                                n
of the left third molar that showed a depression on the lin-
gual surface due to the direct contact with the IAN (Fig.




                                                                             er
21) and an intimate relationship (but no direct contact)
with the mesio-buccal root. The software can zoom-in the
relevant area highlighting anatomic details that help the
                                                                       Figure 21. 3D reconstructions, distal views, respectively, confirm-
and in planning the operation (Figs. 20, 21).
                                                 nt
surgeon both in assessing the risk of damaging the IAN
                                                                       ing the contact between roots and mandibular canal that creates
                                                                       a depression on the lingual surface of the distal root (Case 2 - Left
                                                                       third molar).
                                               iI
                                                                       In fact, it has many major limitations linked to superim-
                                                                       position, and thus to improper visualization of all anatom-
                                             on

                                                                       ical structures, as well as to the operator’s difficulty in ap-
                                                                       propriately positioning the film without causing major
                                                                       discomfort to the patient (2). Currently in oral surgery,
                                                                       panoramic radiography is the first-level imaging of choice
                                    i


                                                                       in the pre-operative evaluation of the third molar (6).
                                 iz


                                                                       Rood e Shehab (1990) described a series of radiographic
                                                                       signs, detectable on the OPT, that indicate the presence
                                                                       of a close relationship between the IAN and the lower
                  Ed




                                                                       third molar (Tab. 2) (7,8). There is no consensus in the
                                                                       literature about which of these 9 signs, detected on the
                                                                       panoramic radiography, is the most useful one in order
                                                                       to predict exposure of the IAN or clinical complications,
                                                                       such as paraesthesia, after the removal of a third molar
                                                                       (10). Some studies report that darkening of the roots, in-
 IC




                                                                       terruption of the cortex of the roof of the canal, and
                                                                       canal deviation are the radiographic signs, detected pre-
                                                                       operatively, that are most often associated with IAN’s ex-
                                                                       posure and injury (1,6,8,10). Sedaghatfar et al. found an
C




                                                                       association even between root narrowing and increased
                                                                       possibility of visualizing the IAN after removal of the
    Figure 20. 3D reconstruction, disto-buccal view, showing both
                                                                       third molars (10). Instead, Bell reported, a close relation-
                                                                       ship between the third molar and the inferior alveolar
©




    the buccal roots fused, with distal curvature extending apically
    beyond the IAN and partially enveloping it (Case 2 - Left third    nerve in 51% of cases where the panoramic radiography
    molar).                                                            showed a darkening of the roots, and only in 11% of
                                                                       cases where the OPT detected an interruption of the cor-
                                                                       tical bone of the roof of the canal (8). De Melo Albert et
Discussion                                                             al. report that root darkening, detected on the OPT, co-
                                                                       incides in 92% of cases with a direct relationship between
Despite its wide use in the dental clinical practice, peri-            the IAN and the roots of the third molar, detected on the
apical endoral radiography is not the ideal imaging tech-              CT (13). A review of literature indicates that most authors
nique to study impacted and non impacted third molars.                 agree that root deviation, bifid apex and canal narrowing

128                                                                                       Annali di Stomatologia 2012; III (3/4): 123-131
3D imaging reconstruction and impacted third molars: case reports



1. Radiotrasparent band darkening the root of the third molar due to its reduction in density caused
   by the mandibular canal crossing the area.

2. Interruption of the white line making up the cortical bone of the roof and ceiling of the canal due to the root
   of the third molar crossing it.




                                                                                                      li
3. Deviation of the mandibular canal: abrupt change of direction of the canal at the point




                                                                                                   na
   in which it is superimposed on or in contact with the roots of the third molar.

4. Narrowing of the canal: narrowing of the mandibular canal at the point where it superimposes
   on or comes in contact with the roots of the third molar.




                                                                                                io
5. Deviation of the root: abrupt deviation (dilaceration) of the roots of the third molar at the point
   where they superimpose on or come in contact with the mandibular canal.




                                                                                             az
6. Narrowing of the root: index of an area of root depression at the point in which they are crossed by the IAN.

7. Bifid apex with root darkening of the third molar at the point where they are crossed by the IAN.

8. Superimposition: superimposition involving the roots of the third molar and the mandibular canal.




                                                                              n
9. Contact with the mandibular canal: the roots of the third molar are in contact with the roof of the mandibular canal.




                                                                           er
Table 2. Radiographic signs, detectable on the OPT, that indicate the presence of a close relationship between the IAN and the lower
third molar (7,9).



posure and injury.                            nt
may have a lower predictive value in terms of IAN’s ex-

We can thus deduce that for pre-operative diagnostic
                                                                     Tomography (CBCT). These methods will provide a bet-
                                                                     ter way to evaluate the relationship between the third mo-
                                                                     lar’s roots and the IAN (2,9,10,16). As OPT is a bi-dimen-
                                            iI
purposes, the absence of positive radiographic signs on              sional examination, it does not provide information on the
the panoramic radiography is preferable to their presence.           depth of the anatomical structures studied. Indeed, it lo-
Without positive radiographic signs the risk of IAN injury           cates the mandibular canal only in the vertical and not in
                                          on

is considered very low, while the presence of one or                 the horizontal plane (2,6). Furthermore, the evaluation of
more signs is not a good predictor of IAN injury, although           the position of the mandibular canal in the vertical plane
it indicates a high probability of intra-operative exposure          is not always reliable due to magnification variables- 20-
of the vascular nervous bundle. This probability, in turn,           30% difference. Moreover, there may be other confound-
                                 i


increases with an increase in the number of positive ra-             ing sources of variation, e.g. the position of patient’s
                              iz


diographic signs detected on the OPT (9,10,15). In a                 head on the pantograph, and also the area of interest
study by Susarla and Dodson, the authors conclude that               given that the amplification might not be homogeneous
the specificity of orthopanoramic radiography to predict             across the whole image (5,19). Other challenges with
              Ed




IAN injury ranges between 96% and 98% (ability to ex-                OPT are the superimposition of air shadows and soft tis-
clude a direct IAN/M3 relationship); while its sensitivity           sues as well as phantom images (20). Furthermore, the
ranges between 24% and 38% (6,16) (ability to identify a             OPT does not detect either the buccolingual width or the
direct IAN/M3 relationship). This means that, in the ab-             atrophy of the alveolar crest (20). A positive feature of bi-
sence of positive radiographic signs, the OPT enables us             dimensional images, in standard radiological techniques,
to detect with almost 100% accuracy- the cases of third              is the high resolution and contrast of anatomical details
 IC




molars that are not in direct relationship with the IAN              which is not provided by CT images (8). It is important to
(high negative predictive value), whose extraction is thus           notice that the anatomical structures that are out of the
not associated with the risk of damaging the IAN. How-               centre of rotation of the source/detector are blurred and
ever, given its low sensitivity, in the presence of positive         distorted. Impacted or ectopic third molars are frequently
C




radiographic signs, OPT does not allow to detect- with               out of the centre of rotation and thus cannot be properly
equal accuracy- the cases where third molars are in direct           visualized. Hence it is often difficult to make a diagnosis
relationship with the IAN (low positive predictive value),           based only on OPT. Neugebauer et al. (5) compared the
and whose extraction entails the risk of injuring the IAN            diagnostic accuracy of OPT vs CBCT in detecting the po-
©




(6,17). In fact, it has been shown that relying only on the          sition of the root apex of third molars with respect to the
positive radiographic signs to make a pre-operatory diag-            IAN. There were no significant differences in diagnostic in-
nosis, can lead to an overestimate of the actual possibil-           formation between the two radiographic techniques with
ity of contact between the IAN and third molars, thus er-            respect to the vertical plane. In fact, both provide the cli-
roneously classifying a situation as a high risk one (false          nician with the same type of information. Conversely,
positive) (18). Therefore, the presence of positive radi-            there was a significant difference between the two tech-
ographic signs on the OPT should be regarded just an in-             niques with respect to the horizontal plane, and the diag-
dication to proceed to second-level instrumental investi-            nostic information provided by CBCT was clearly prefer-
gations with CT Dental Scan or Cone-Beam Computed                    able (5). The latter is a 3-D exam, which enables us to:

Annali di Stomatologia 2012; III (3/4): 123-131                                                                                129
A. Tuzi et al.


-    evaluate the buccolingual relationship between the          highlight the single components (bone, teeth, canal, im-
     IAN and the roots of the third molar, so as to avoid im-    plants, etc.) in different combinations (9).
     pacting the tooth with movements that can cause a
     impingement of the nerve’s root; plan the appropriate
     interradicular section if it is evident that the IAN        Conclusions




                                                                                                 li
     crosses the roots (21);
- identify the presence or the partial/total absence of          There is currently debate in literature about the need for




                                                                                              na
     cortical bone around the IAN (21);                          CTs before removing third molars, even if one or more
- visualize the number of roots and the exact root               positive radiographic signs, as mentioned before, are
     anatomy of the third molar; define the inclination of the   present on the panoramic radiography. Indeed, there are
     tooth and the position of the crown with respect to the     oral and maxillofacial surgeons who disagree about the




                                                                                           io
     buccal or lingual surface of the mandible (21).             need to resort to CTs, as they consider the panoramic ra-
To conclude, most authors in the literature agree that           diography as the first choice examination for the pre-op-
Dental CT Scan and CBCT are the most effective imag-             erative evaluation of impacted and non impacted third mo-
ing techniques to detect both the localization of the canal      lars. These surgeons infact underline both the high cost




                                                                                        az
in relation to its superior/inferior and bucco/lingual di-       of CT and the high dose of radiation patients are exposed
mensions, and the exact crown-root morphology of third           to. So, unlike OPT, CTs are not seen by these surgeons
molars (5). In the last decade, 3-D reconstruction soft-         as a routine examination for the evaluation of third molars.
wares- designed for the study of the jaws have been in-          However, CT evaluation should not be excluded a priori




                                                                         n
troduced to help clinicians both in the diagnosis and in the     as a potential diagnostic tool for clinicians (9). Indeed, it
treatment plan.                                                  should be used only for those patients whose first-level




                                                                      er
These softwares, initially introduced in implantology, rep-      OPT shows one or more of the nine radiographic signs in-
resent an excellent tool for the study of the relationship       dicating a close relationship between the IAN and the
between mandibular canal and third molars. They are              tooth root, and when this relationship cannot be defined


                                            nt
useful especially in challenging diagnostic cases, where
the 3-D visualization of the IAN/M3 relationship enables
clinicians both to decide the appropriate planning of the
surgical step, and to avoid jeopardising the integrity of the
                                                                 sufficiently using conventional radiology (2,9,10,16). In
                                                                 particular, Jhamb et al. (18) deem that a CT examination
                                                                 is absolutely necessary when the OPT detects one or
                                                                 more of the following radiographic signs: darkening of the
                                          iI
mandibular canal (9). One of the first softwares to be mar-      roots; interruption of the white line with narrowing of the
keted is SimPlant (Materialise, Ann Arbor, MI 1997). This        canal and superimposition of the roots and the mandibu-
software accepts images in DICOM format (Digital Imag-           lar canal. Moreover, CT examination is recommendable
                                        on

ing and Communications in Medicine), i.e. the first stan-        in all those instances in which it may have a direct impact
dard format for the distribution and viewing of any type of      on the planning of the surgical steps, and on the evalua-
medical image. Simplant is able to recognize DICOM im-           tion of sequelae, outcome and morbidity.
ages from many different types of CTs and CBCTs.                 It should also be stressed that the advent of CBCT in the
                                i


So to pass from a Digital CT or CBCT to a 3D reconstruc-         early 2000s has reduced the cost for patients, and mostly
                             iz


tion we have to import DICOM files in Simplant. A 3d re-         it has improved the risk-benefit profile by reducing the
construction doesn’t need an higher dose of radiation to         dose of radiations for patients if compared to conventional
patient; it allows to optimize the information contained in      CT scans (10). Moreover, in those cases where the root
                 Ed




CT or CBCT files.                                                of the third molars shows a complex morphology, and it
Once imported in SimPlant, the images show maxillary             is located in contact with the mandibular canal, the new
sections on the axial, paraxial (coronal) and sagittal           3D reconstruction softwares supporting CTs provide sur-
planes (panoramic reconstructions). These images are             geons with an additional planning tool that offers:
realistic representations of the maxilla (1:1 scale), allow-     • immediate and neat visualization of the noble struc-
ing accurate measurements of anatomical structures.                   tures that have to be respected and their localization
 IC




Importantly, SimPlant enables surgeons to trace the                   in the three spatial planes;
path of the mandibular canal. It can be traced either on         • the exact morphology of the relevant root apex;
the paraxial sections (coronal) or on the sagittal sec-          • a 360° view of the relationship between the IAN and
tions (panorex); usually it is easier to use than the                 the third molar;
C




panoramic images as the IAN can be more easily iden-             • the exact point in which the root is in relationship
tified and the software automatically detects it also on              with the canal.
the paraxial views. The buccolingual position of the             The complete anatomical image’s details and the friendly
IAN (in the horizontal plane) is detected on the parax-          and dynamic approach to them can influence the surgical
©




ial views, while the position in the vertical plane can be       approach: single or multiple odontotomy, depth of os-
assessed both in the panoramic and on the paraxial im-           teotomy or direct of luxation can be programmed more ac-
ages. The great advantage of SimPlant, and similar               curately.
softwares, is the possibility to have virtual 3-D recon-         To conclude, we can state that although 3D images are
structions of the bones, of the teeth, of the mandibular         not essential for the pre-operative evaluation of third mo-
canal as well as of other structure of the face.                 lars, they definitely enhance the information provided by
The most interesting feature of the software is its capa-        CT scans, and thus represent an added value in the
bility to rotate images, thus providing clinicians with a 360°   choice of the therapy to adopt in order to minimize pos-
view of the anatomic structures. Moreover it can hide or         sible injuries of the IAN.

130                                                                               Annali di Stomatologia 2012; III (3/4): 123-131
3D imaging reconstruction and impacted third molars: case reports


References                                                               12. Savi A, Manfredi M, Pizzi S, Vescovi P, Ferrari S. Inferior alve-
                                                                             olar nerve injury related to surgery for an erupted third mo-
1.  Dodson TB. Role of computerized tomography in manage-                    lar. Oral Med Oral Pathol Oral Radiol Endod 2007; 103:
    ment of impacted mandibular third molars. N Y State Dent J,              e7-e9.
    November 2005.                                                       13. Guimaraes D, de Melo ADG, Gomes ACA, do Egito Vascon-
2. Flygare L, Ohman A. Preoperative imaging procedures for                   celos BC, de Oliveira e Silva ED, Holanda GZ. Comparison




                                                                                                            li
    lower wisdom teeth removal. Review. Clin Oral Invest 2008;               of ortho-pantomographs and conventional tomography im-
    12:291-302.                                                              ages for assessing the relationship between impacted lower




                                                                                                         na
3. Jerjes W, Upile T, Shah P, Nhembe F et al. Risk factors as-               third molars and the mandibular canal. J Oral Maxillofac
    sociated with injury to the inferior alveolar and lingual nerves         Surg 2006; 64:1030-1037.
    following third molar surgery. Oral Surg Oral Med Oral Pathol        14. Tantanapornkul W, Okouchi K, Fujiwara Y, Yamashiro M,
    Oral Radiol Endod 2010; 109:335-345.                                     Maruoka Y, Ohbayashi N, Kurabayashi T. A comparative
                                                                             study of cone-beam computed tomography and conven-




                                                                                                      io
4. Tolstunov L, Pogrel MA. Delayed paresthesia of inferior alve-
    olar nerve after extraction of mandibular third molar: case re-          tional panoramic radiography in assessing the topographic
    port and possible etiology. J Oral Maxillofac Surg 2009;                 relationship between the mandibular canal and impacted
    67:1764-1766.                                                            third molars. Oral Surg Oral Med Oral Pathol Oral Radiol




                                                                                                   az
5. Neugebauer J, Shirani R, Mischkowski RA, Ritter L, Scheer                 Edod 2007; 103:253-9.
    M, Keeve E, Zoller JE. Comparison of cone beam volumet-              15. Jozsef S, Lempel E, Jeges S, Szabò G, Olasz L. The prog-
    ric imaging and combined plain radiographs for localization              nostic value of panoramic radiography of inferior alveolar
    of the mandibular canal before removal of impacted lower                 nerve damage after mandibular third molar removal: retro-
                                                                             spective study of 400 cases. Oral Surg Oral Med Oral Pathol




                                                                                  n
    third molars. Oral Surg Oral Med Oral Pathol Oral Radiol End
    2008; 105:633-42.                                                        Oral Radiol Endod 2010;109:294-302.
6. Atieh MA. Diagnostic accuracy of panoramic radiography in             16. Susarla SM, Dodson TB. Preoperative computed tomogra-




                                                                               er
    determining relationship between inferior alveolar nerve and             phy imaging in the management of impacted mandibular
    mandibular third molar. J Oral Maxillofac Surg 2010; 68:74-82.           third molars. J Oral Maxillofac Surg 2007; 65:83-88.
7. Koong B, Pharoah MJ, Bulsara M, Tennant M. Methods of                 17. Susarla SM, Sidhu HK, Avery LL, Dodson TB. Does com-
    determining the relationship of the mandibular canal and                 puted tomographic assessment of inferior alveolar canal

    geons. Aust Dent J 2006; 51: 64-68.
                                                 nt
    third molars: a survey of Australian oral maxillofacial sur-

8. Bell GW. Use of dental panoramic tomographs to predict the
                                                                             cortical integrity predict nerve exposure during third molar
                                                                             surgery? J Oral Maxillofac Surg 2010; 68:1296-1303.
                                                                         18. Jhamb A, Dolas R, Pandiwar PK, Mohanty S. Comparative
                                                                             efficacy of spiral computed tomography and orthopantomog-
                                               iI
    relation between mandibular third molar teeth and the infe-
    rior alveolar nerve. Radiological and surgical findings, and             raphy in preoperative detection of relation of inferior alveo-
    clinical outcome. Brit J Oral Maxillofac Surg 2004; 42: 21-27.           lar neurovascolar bundle to the impacted mandibular third
9. Friedland B, Donoff B, Dodson TB. The use of 3-dimen-                     molar. J Oral Maxillofac Surg 2009; 67:58-66.
                                             on

    sional reconstruction to evaluate the anatomic relationship of       19. Angelopoulos C, Thomas S, Hechler S, Parissis N, Hlavacek
    the mandibular canal and impacted mandibular third molars.               M. Comparison Between Digital Panoramic Radiography
    J Oral Maxillofac Surg 2008; 66:1678-1685.                               and Cone-Beam Computed Tomography for the Identification
10. Sedaghatfar M, August MA, Dodson TB. Panoramic radi-                     of the Mandibular Canal as Part of Presurgical Dental Implant
    ographic findings as predictors of inferior alveolar nerve ex-           Assessment. J Oral Maxillofac Surg 2008; 66:2130-2135.
                                   i


    posure following third molar extraction. J Oral Maxillofac           20. Liu T, Xia B, Gu Z. Inferior alveolar canal course: a radi-
                                iz


    Surg 2005; 63:3-7.                                                       ographic study. Clin Oral Implants Res 2009; 20:1212-1218.
11. Hillerup S. Iatrogenic injury to the inferior alveolar nerve: eti-   21. Pippi R. A case of inferior alveolar entrapment in the roots of
    ology, signs and symptoms, and observations on recovery.                 a partially erupted mandibular third molar. J Oral Maxillofac
               Ed




    J Oral Maxillofac Surg, 2008; 37:704-709.                                Surg 2010; 68:1170-1173.
 IC
C
©




Annali di Stomatologia 2012; III (3/4): 123-131                                                                                          131
