Computer Guided for Mandibular Distraction Osteogenesis
Condition: Hemifacial Microsomia
MeSH terms: Goldenhar Syndrome; Fetal Growth Retardation
Study type: Interventional

Summary: 
      Objectives: Distraction Osteogenesis is an integral part in management of mandibular defects
      associated with Hemifacial Microsomia (HFM) and post-ankylotic mandibular defects. The most
      difficult part in distraction osteogenesis is the prediction of distraction vector and risk
      of injury to vital structures as inferior alveolar. The current study aimed to present
      Three-Dimensionally Constructed Computer Guided Splints in Distraction Osteogenesis to get an
      ideal vector and minimal risk of vital structures injury.

      Methods: The study presents computer-guided distraction osteogenesis surgery using
      prefabricated splints.
    

Detailed description: 
      The current study was performed on a case control trial of patients complaining of hemifacial
      microsomia.. The research was reviewed by the ethical committee of the authors institute
      (approval number: 392, date: 30/12/2015). Written informed consent for the case to be
      published (incl. images, case history and data) was obtained from the patients for
      publication of this case report, including accompanying images In order to accurately analyse
      the patients' condition and formulate an optimal treatment plan, a pre-operative CBCT scan
      was performed using i-CAT CBCT scanner (Imaging Sciences International, Hatfield, PA, U.S.A).

      Each patient was positioned in the machine and imaged at the same manner according to the
      recommendations of CBCT manufacturer. The Frankfurt plane was positioned parallel to the
      horizontal plane and the midsagittal plane was perpendicular to the horizontal plane.

      The CBCT scan was required to fulfill the following criteria:

        -  Showing the full bony facial structures, extending from at least the inferior border of
           the mandible to the supraorbital ridge.

        -  CBCT scan should be free from any motion artifacts.

        -  Patient biting on cotton rolls in order to free the occlusion.

        -  A scan of optimum quality and resolution. (0.25 mm voxel size) IV. Virtual Treatment
           Planning

        -  The data from the CBCT scan were exported from the i-CAT Vision software in DICOM
           format, which was in turn imported into Mimics Medical 19.0 software (Materialise NV,
           Technologielaan 15, 3001 Leuven, Belgium) for virtual treatment planning.

        -  Using the "Thresholding" tool, the range of gray value sets is chosen to highlight the
           mineralized structures and separate them from the rest of soft tissue structures in the
           scan creating a new mask.

        -  Using the "Calculate 3D" tool on the new mask, a 3D rendering of the facial mineralized
           structures is created and is then refined using the "Smoothing" and "Wrap" tools.

        -  In order to properly orient the patient's head position, analyze the deficiencies, and
           standardize the planning process, the Frankfort Horizontal plane and the Midsagittal
           plan were constructed. Frankfort Horizontal Plane was defined by marking the right and
           left Orbitale, and the Porion of the non-affected side. The Midsagittal plane was
           defined by marking the Sella, the Nasion, and the Anterior Nasal Spine.

        -  Using the "Multiple Slice Edit" and "Region Growing" tools when needed, the jaws are
           separated and the mandible and maxilla are segmented separately.

        -  Using the "Distraction Wizard", an appropriate distraction type is selected. A
           distractor is selected and placed on the proposed site for distraction. The osteotomy
           and vector are visualized and the distractor is activated. This process is repeated
           until the final outcome is satisfactory. The ideal final outcome is when the canted
           occlusal plane is corrected and the mandibular midline is coincident with the facial
           midline simultaneously.

        -  Using the "Cylinder" tool in the "Medcad" menu, virtual distractor pins and osteotomy
           disk are drawn to match our selected custom-made distractor. The number of pins, their
           size, and orientation differed according to the vital structures in each distraction
           site. Hence, custom-made distractors were used. Guide fixation screws are also added to
           provide further retention for the guide when needed. The fixation screws, osteotomy and
           distractor pins are placed so as to avoid injury to any vital structures as the Inferior
           Alveolar Nerve, tooth buds, and dental roots .

        -  Using different Boolean operation, the body of the final guide is designed to fit over
           the bones and teeth and incorporate the different distractor components. It is then
           exported into STL format.

        -  The exported STL file is printed with Formlabs Form 2 stereolithography (SLA) 3D printer
           (Formlabs Inc. Somerville, MA 02143 USA) using Clear Photopolymer resin (FLGPCL02). The
           finished printed model is then checked for fit with the distractor.

        -  Prior to surgery, the guide is submerged in a basin containing 2.4% activated
           glutaraldehyde solution (Cidex) for 20 minutes for high level disinfection.

      Surgical Procedure

        -  The patient was placed in supine position. General anesthesia was administered through
           Naso-Tracheal intubation. A cannula was inserted in a peripheral vein (18G) and normal
           saline infusion was started at a rate of 6 ml/kg along with Ringer's solution.

        -  Anesthesia was induced with IV propofol 1.5-2 mg/kg, fentanyl 1.3 μ/kg and succinyl
           choline 1mg/kg to facilitate nasotracheal intubation using armored tube. Anesthesia was
           maintained with isoflurane in oxygen and atracurium in a dose of 0.3-0.6 mg/kg.

        -  The surgical sites were prepared with povidone iodine and then draped according to the
           standard oral and maxillofacial surgery operating room procedures.

        -  An Antibiotic dose of 1 gm Cefotaxime vial was administered followed by Dexamethasone
           phosphate (as sodium salt) 4 mg vial through peripheral IV route at the beginning of the
           procedure. A local anesthetic solution of Articaine 4% containing Epinephrine
           (1:200,000) was infiltrated along the proposed operative field for hemostasis.

        -  A three-line pyramidal incision was performed. The distal incision was carried buccally
           across the external oblique ridge, and then joined to a gingival incision running
           buccally around the necks of the teeth on which the guide rests. The releasing incision
           is carried in a curved manner inferiorly and anteriorly, keeping in mind not to extend
           to the area of the mental foramen. Reflection of the flap was done with a periosteal
           elevator beginning from under the periosteum of the anterior buccal incision, working
           parallel to the gingival margin to detach the papillae and push distally.

        -  Once the field of interest was exposed, the guide was introduced onto the bone and
           teeth, and moved until a tight fit was achieved throughout its fitting surface. When
           needed, the guide was secured to the underlying bones by 2.0 miniscrews placed through
           their preplanned guiding tubes.

        -  Via a small stab incision through the skin, a transbuccal trochar is introduced, through
           which the self-drilling extraoral distractor pins are passed. The pins are inserted into
           the mandible at their designated points of entry through the guide.

        -  Using a piezotome, the osteotomy line is marked and the osteotomy is initiated guided by
           the osteotomy slit in the guide. The fixating screws and the guide are then removed. The
           use of piezotome allowed the planning of the osteotomies through the path of the
           inferior alveolar nerve without fear of nerve injury.

        -  After guide removal, the osteotomy is completed. The distractor is connected to the
           extraoral distractor pins and is then activated to insure free mobility of the distal
           segment. Once confirmed, the distractor is returned to its zero position. The flap was
           then repositioned and closed using 4-0 Braided Polyglycolic Acid sutures.
    

Intervention name(s): 3D printed surgical guide constructed; free hand surgery
Intervention type(s): Other; Other
Intervention description(s): A printed surgical guide ( to direct through the surgery and make results predictable), the guide is designed by Mimics 19.0, Materialise NV,Belgium and printed with self cure resin; A control group in which patients are randomly assigned and surgeries are planned without surgical guides and performed free handed
Allocation: Randomized
Intervention model: Parallel Assignment
Intervention model description: Case control trial
Masking: Double (Participant, Care Provider)
Primary purpose: Other
Keywords: Computer guided surgery; Hemifacial Microsomia