الفهرس 
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Abstract
The Inferior Alveolar Nerve Block (IANB) is the most common & frequent technique used for local anesthesia of mandibular posterior teeth to perform any dental surgical procedure or dental restoration in the mandible.6,72
The clinical studies reported high failure rate in (IANB) some studies report as high as 10-39%,other studies reported 30-80% failure rate for IANB in patients with symptomatic irreversible pulpitis.45,72
Failure of (IANB) have several causes such as improper anesthetic techniques, anatomical variation of inferior alveolar nerve, or anatomical variation of Mandibular Foramen which is the most common cause of failure as practitioners have to inject nerve before entering MF, So, MF is critical landmark for success of IANB.6,15
These failures lead to complications that patients suffer from; including hematoma due to damage of blood vessels in area of anesthesia, trismus due to tearing of mucosa during insertion or withdrawal of needle, and also facial paralysis when needle inserted more posterior toward the posterior border of the mandible which lead to deposition of anesthetic solution in parotid gland, Other reported complications include ptosis and extraocular muscles paralysis, aphonia, necrosis of the skin of the chin, diplopia, and abducent nerve palsy.
Some rare complications include a reduction in visual acuity and atrophy of the optic nerve. It has been also reported recently that inferior alveolar nerve block could be a factor in third molar agenesis.
Mandibular Foramen location is related to mandibular ramus height & anterior posterior dimension (width) of mandibular ramus & relation between MF & occlusal plane these dimensions are influenced by age change. 15,6
Thangavelu et al. have shown that the position of the mandibular foramen is not at the center in the anterior-posterior dimension of the ramus, but it is around 2.75 mm posterior to the midpoint of the width of the ramus.6
They have also shown that the foramen is located at a distance of 19 mm from the coronoid notch and is either level with or below the occlusal plane. The foramen is also located 3 mm above the midpoint of an imaginary line running from the sigmoid notch to the inferior border of the mandible.15
Other studies have shown that the foramen can be at the center of anterior-posterior width of the ramus, 2.08-2.56 mm behind the midpoint of anterior-posterior dimension or on the posterior third quarter of the anterior-posterior width. 15
There are several (variation) anesthetic techniques used in (IANB) such as Gow Gates technique which has several advantages (require one injection for anesthetizing of IAN, lingual nerve & long buccal nerve, High success rate reach (52%). 73
It needs minimum aspiration rate due to fewer blood vessels in these level, cause few postoperative complication rate, provide successful anesthetic rate when bifid IAN & bifid mandibular canal are present.
It also has disadvantages (The time to onset of anesthesia is somewhat longer (5 to 7 min) when compared to inferior nerve block due to the larger diameter of nerve trunk and the distance from site of injection (1cm).
This technique needs wide mouth opening, lingual & lower lips anesthesia is uncomfortable for many patients & may be dangerous for some individuals, clinical experiences is needed in Gow Gates technique, after the operator withdraws needle, the patient has to keep mouth open for 20 to 30 seconds to allow bathing of nerve trunk that has been anaesthetized).
The second technique is vazirani-Akinosi closed mouth mandibular nerve block, its advantages (can be used with limited mouth opening patients, and patient with trismus), high success rate reach (41%).73
It Can be used with patients have strong gag reflex, relatively atraumatic, less pain (tissue are relaxed), less threatening to patient, suitable for patient with macroglossia.
The Disadvantage of closed mouth technique are(visualization of path & depth of insertion is difficult, no bony contact, painful if needle touch periosteum and difficult with patient have widely flaring ramus or pronounced zygomatic buttress or internal oblique ridge.
Third technique which is the most popular and common one is (The conventional Inferior Alveolar Nerve block TECHNIQUE).
The subject was immobilized in the seated position so that the mandibular occlusal plane was parallel with the floor when the mouth was opened maximally. A 27 Gauge, 21 mm dental disposable syringe needle was inserted 1 cm above the mandibular occlusal plane, in the depression between the internal oblique line and the pterygomandibular fold. The needle was inserted to a depth of 20 mm from the opposing first premolar, with the bevel facing the bone. 74
This technique has the advantages of: practitioner acceptance, faster onset than the others, bony landmark).
The disadvantages are (the success rate is the least as it is just (36%), unlikely to anaesthetize long buccal nerve & accessory nerves, area of injection is vascular, 10 -15% chance of positive aspiration and difficulty to see landmark in some patients like macroglossia)
So, we conclude that although different technique are available, the failure rate still high & that could be related to anatomic variation of landmarks like mandibular foramen which is the most critical landmark for success of IANB.
These variations are not only due to individual difference but there are also significant racial & ethnic variation 615.
So, lack of accurate information about MF accurate location in Egyptian population was the main target of this study.
Other studies are performed on different population which confirmed that MF location differ from population to another.6
As reported from previous studies on other populations there is no significant difference from in MF location between right & left mandibular sides. In our study we will determine accurate location of MF in Egyptian population compare anatomic variation between the following: (male & female, adult & old age, dentate & edentate).
Aim of the Study
Is to determine the accurate location of MF in a sample of Egyptian population & compare variations between males & females, adult & old age, dentate & edentate of same population in order to give obtain an information about MF location to increase rate of IANB success using CBCT (i-CAT vision¬).
Material and Method
This study is retrospective study based on CBCT data collected from department of Oral and Maxillofacial radiology of (Ain Shams University, Canadian University in Cairo and 3D dental radiology center in Mansoura) .
273 CBCT scans will be included in the study, which is equally distributed male & female, all of them are above 18 years old.
Inclusion criteria
1. Patient age above 18 years old
2. Patients are equally distributed male & female
3. Patients are dentate & edentate
Exclusion criteria
1. Patient under age 18 years old due to incomplete development of mandible.
2. Patients with syndromic craniofacial deformity
3. Patients with mandibular fracture
4. CBCt with artifact
CBCT Protocol
The machine used is I-CAT Next Generation machine (Imaging Sciences International, Hatfield, Pennsylvania, USA), the scan parameters were 120kv, 36.12ma/s, scanning time 26.9 sec, field of view is maxilla & mandible, voxel size is 5mm)
Image analysis
Software used is ICAT vision, the scan will be assessed through the axial, saggittal & coronal (MPR screen) & 3D reconstructed images.
Measurements will be assessed in these study is Aiming to relate the MF with the anterior ramus border (AB), posterior ramus border (PB), mandibular notch (MN) and point of greatest convexity of inferior ramus border (IB), apex of retromolar trigone (ATRM) lingula tip that covers depressed V shaped mandibular foramen fossa (MF fossa) limited by anterior margin (AM) & clear posterior margin (PM) that converge inferiorly forming entering point of MF.
A CBCT was used to obtain the following distances:
Distance from midpoint of the AM of the MF fossa to the nearest point of the anterior ramus border (AB-MF)
Distance from the midpoint of the PM of MF fossa to the nearest point of the posterior ramus border (PB-MF)
Distance from the lowest point of the mandibular notch to the entering point of MF fossa (MN-MF)
Distance from entering point of MF fossa to the point of the greatest convexity of the inferior ramus border (IB-MF)
Minimum distance between anterior & posterior ramus border passing by midpoint of the MF fossa (ramus width) (RW)
minimum distance between mandibular notch & inferior ramus border passing by entering point of MF fossa (ramus height)(RH)
Thickness of the ramus plate which forms MF fossa depression, from the point beyond the lingula tip on the inner plate surface to symmetrical point on the extrenal plate surface (ramus thickness)(RT)
Distance from the apex of retromolar trigone to the lingula tip in dentate mandible (ATRM-MF).
Mandibular foramen & mandibular lingula with occlusal plane
Assessment of measurements will be performed twice by two radiologists, one of them of two years experience & the other is of ten years experience to provide interobserver & intraobserver reliability, data will be monitored & statistically analyzed.
Results
In the present study, statistically significant differences in the location of the MF were found in relation with sex, age and dental status. Therefore, we reached the following recommendations for successful IANB and mandibular osteotomy.
Conclusion
According to sex, no changes in needle insertion position during IANB, while during MSSO care should be taken with females mandible.
According to different age categories, needle insertion position changes recommended to be taken in extremes of age.
According to dental status, needle insertion position at a lower level in edentate patients were recommended.