**4. Orthodontic preparation of the patient**

The initial consultation between the doctor and patient is important for successful treatment. The purpose of the consultation is to consider the options of surgical treatment, but also to acquaint the patient with the limits and complications of treatment.

The patient is acquainted with the reasons why TMJ reconstruction is planned. It is important to know the patient's expectations and the reasons why they decided to address their DFD. Of course, it is essential to temper any unrealistic expectations the patient may have (both in terms of correcting the DFD and eliminating TMJ problems).

An initial consultation at the authors' workplace is always held in the presence of orthodontist, orthognathic surgeon and TMJ surgeon. Orthodontic-surgical treatment of maxillary anomalies is a team effort, in which the specific approach in all phases is the result of joint decision-making and mutual consultation by individual experts.

Only after the patient has fully understood and consented to the procedure does planning the surgery begin.

The initial interview includes photo documentation of the patient, an X-ray and cone beam CT. Stone models of the upper and lower dental arch are also required to assess occlusal conditions.

In principle, the same rules apply for orthodontic preparation as when preparing patients for orthognathic surgery. Orthodontic pre-treatment is performed using fixed devices on the upper and lower arches. The main goals of orthodontic preoperative treatment are: decompensation of the defect and the creation of regular dental arches without the constriction, and rotation of the front teeth. Postoperative intercuspidation should create conditions for a stable overbite of the incisors, i.e., a suitable incisal overjet and bite depth, with normoocclusion of the canines. For lateral teeth, intercuspidation without a crossbite should be achieved postoperatively. The width of the dental arches must be proportional to each other, the shape of the arches must allow good postoperative intercuspidation [25].

In case of transverse narrowing of the upper jaw, orthodontic preparation includes expansion of the upper jaw depending on the patient's age, i.e., ossification of the *sutura palatina* (non-surgically in growing patients with a Hyrax palatal expander, or surgically in adult patients using the SARME method - surgically assisted rapid maxillary expansion).

If the patient has a biplanar occlusal plane of the upper jaw, it is important to maintain this and prepare the patient segmentally. Segments are typically formed by osteotomy between the Central incisors into segments 17–11 and 21–27 or between the lateral incisors and canines, whereby the dental arch is divided into three segments second molar to canine, incisors, canine to second molar [26–28].

In patients with congenital defects (e.g., hemifacial microsomia) or in patients who developed ankylosis in childhood, there is often severe hypoplasia of the affected branch and body of the lower jaw. In these cases, it is appropriate to use distraction osteogenesis to extend the ramus and body of the lower jaw. This technique has the advantages of providing superior amount of bone lengthening and allows simultaneos expansion of surrounding soft tissues. This elongated bone will then facilitate the movement of the jaw to the appropriate position, significantly improving the resulting esthetic effect.

Preoperative preparation includes the removal of retained teeth and introduction of dental implants. Knowledge of the patient's general condition is also required to prepare the patient for a procedure that takes several hours. Similarly, it is important to monitor levels of vitamin D and provide supplements, where necessary (low levels are associated with the risk of impaired healing of bone fragments).

The purpose of orthodontic preparation is to create ideal dental arches suitable for stable occlusion after repositioning one or both jaws. The length of orthodontic preparation depends on how complicated the condition of the dental arches is [29–31].

Depending on the condition of the dental arches, it is possible to prepare a patient for surgery in 4 ways [30]:


#### **4.1 Planning orthognathic surgery**

The actual planning of orthognathic surgery only begins after the completion of orthodontic preparation, when passive arches are deployed with orthodontic appliances. Planning consists of virtual surgical planning (VSP). The same CT is used for VSP as for planning joint replacement. A 3D virtual patient model is generated using a 3D planning program. This requires the aforementioned CT, as well as intraoral scans of dental arches, 3D photos and a clinical analysis of the patient. This virtual model then makes it possible to plan individual osteotomies and jaw repositioning [29, 32].

Clinical analysis of the patient involves a comprehensive examination of the patient's face before surgery. Exact measurements are made (with special attention given to the Central position of the Chin) of the mutual relationship of the lips when relaxed, the bilateral symmetry of the mandible angles, symmetry of the contour of the lower jaw line, symmetry of Chin contours and possible deviations in the soft tissues of the face. Also noted are the movement of the lips when smiling, the exposure of incisors and a possible gummy smile, the relationship and position of the dental center of the upper and lower dental arch to the center of the face, the inclination of the occlusal plane and a comparison of its inclination to the bipupillary plane [26, 33].

The virtual 3D model not only makes it possible to assess the bone structure of the facial skeleton, but also creates an image of soft tissues, which is important to get an idea of esthetic outcome and facial changes in a patient with DFD [32]. The use of modern planning technologies brings better and more predictable results [33].

The resulting position of the upper and lower jaws will enable the virtual production of surgical splints, which will be printed on a 3D printer before the surgery and will allow the jaws to be moved to the planned position during the procedure [29].

Note: An intraoral scan is clearly preferred for a scan of the dental arches rather than scanning the dental arches from the model. An intraoral scan eliminates minor deviations in the impression and plaster model.
