 to OMFS lecture series. The topic for today's lecture is mandibular sub-apical osteotomy. Mandibular sub-apical osteotomy is performed to reposition the dendroalveolar segment and is done in the anterior posterior of the entire dendroalveolar segment of the mandible. Proclaim to anterior sub-apical osteotomy. First described in 1849 anterior sub-apical osteotomy was mainly indicated to correct the proclined lower anterior dendroalveolar segment. Other indications include closure of minimal anterior open bite and advancement of anterior teeth. It is also indicated in bimaxillary protrusion in combination with anterior maxillary osteotomy. Let's now see how the surgery is performed. Local anesthetic solution is infiltrated into lower labial vestibule. A sulcus incision is placed and a full thickness mucoperiostial flap is raised to expose the inferior border of anterior mandible and mental freman on either sides. As been already explained in the lecture on genioplasty, it is important to preserve the muscle attachment at the inferior border of anterior mandible. Next, a subperiostial tunneling is done on the lingual side. This is in order to facilitate a free movement of the dendroalveolar segment once it's sectioned. In case of dendroalveolar segment set back, extraction of first premolar is done on either sides. If the intended plan is to reposition the dendroalveolar segment superiorly, if this segment is to go up, then there is a gap that is left at the osteotomy site. This gap is later filled using bone grafts. As you can see in these photographs, this is the osteotomy performed following which the dendroalveolar segment can be repositioned as required. Once the osteotomy is complete and the segment repositioned, it is then stabilized and fixed using bone plates or lag screws or even wires. This is a photograph showing the subapical osteotomy being performed along with genioplasty. Here subapical osteotomy is performed in combination with genioplasty. Let's now move on to total subapical osteotomy of mandible. It was first described by Macintosh in the year 1942 and used to reposition the entire dendroalveolar segment. Make sure at least 10 mm of bone to be present below the abysses of teeth before performing the osteotomy cut. Like in any other mandibular ortho-nethic surgical procedures, here also the basic principle is to reflect the buccal myocopyriosteum down to the inferior border and taking care not to injure the mental nerve. Later, the lingual pediosteum is also elevated without any damage. The first step here is to remove the buccal cortical plate just behind the mental ferramen. That means if the mental ferramen is located here, you remove a certain amount of buccal cortical plate. Why is it done? This procedure is done to release the neurovascular bundle from within the bony enclosure. You have the inferior alveolar nerve bundle passing through the canal within the body of mandible. So in order to release the nerve bundle from within the bony enclosure, using a fissure burr, a window is created on the outer cortical plate. And then the cancellous bone around the nerve bundle is removed and the nerve is released using a nerve hook. So in this way you expose and preserve the inferior alveolar nerve bundle. What is the next step? Osteotomy is started here that is just behind the most posterior tooth present. If it's the second molar, you create an osteotomy cut just posterior to it using a reciprocating saw or an oscillating saw. The osteotomy cut is continued through the window towards the midline. From here the osteotomy cut follows through the window towards the midline. All this while the nerve is still preserved. As you can see in this diagram, this is the osteotomy cut and you have kept the nerve at a safe position using a nerve hook. The same procedure is repeated on the other side as well. So a 4 mm of bone should be still left below the teeth apices. That means this distance from the teeth apices till the osteotomy the distance should be at least 4 to 5 mm and the distance from the osteotomy cut till the inferior border should be at least 10 mm. Once the osteotomy is completed the dental alveolar segment is then mobilized and repositioned. Like you can see in this diagram. The neurovascular bundle is also repositioned and secured using pieces of bones. So this is how a total sub-apical osteotomy of mandible is performed. Repositioned dental alveolar segment is then stabilized and rigid internal fixation is performed. Postoperative sequelae includes edema and sensory disturbances which will subside in about two weeks time. The importance of good blood supply through the lingual pedicle is of at most important for the segment to survive. So this is regarding total sub-apical osteotomy of mandible. Thank you.