Australasian Dentist Issue 89

Category AustrAlAsiAn Dentist 63 the most common measurements used are the AnB (A point, nasion and B point) angle. (Fig 3). and also the Wits appraisal (which factors in any rotation of the occlusal plane). (Fig 4) With regards to the Vertical analysis, the most common measurement used is the FMA (Frankfort Mandibular plane angle ) but i highly recommend using the Bjork Jarabak vertical analysis which provides the most detail in assessing the skeletal vertical surgery. (Fig 6) Over the years, the best method for detecting the true unstrained position of the mandible has been heavily debated with no universal consensus. 9,10,11 in certain situations, a functional shift cannot be detected without a period of muscular deprogramming with an occlusal splint. b. the lip/incisor relationships: the following measurements should be recorded during the clinical examination of a prospective candidate for orthognathic surgery: – incisal show at repose and at full smile. – length of upper lip: if a patient has an abnormally long or even short upper lip, it may be impossible to achieve an ideal lip/incisor relationship without surgical intervention to the upper lip. – sulcus depth: sulcular depths of more than 3 mm in a skeletally mature individual may represent a condition known as delayed or altered passive eruption. 12 in these situations, an excessive sulcular depth is associated with a short clinical crown. it is critical to factor in the additional incisor length that can and should be exposed by gingival recontouring. 5 c. temporomandibular joint (tMJ) function: this exam should include an assessment of any pain, crepitus, or popping in the joint, any pain in the associated masticatory musculature, an evaluation of the path of opening, along with measurements of maximum opening and excursive mandibular movements. 13 d. location of the facial midline: Although the facial midline can be assessed from a frontal photograph, (Fig 7) many subtleties can best be appreciated during a thorough clinical exam. 5 (Fig.8) Data from orthodontic records and the clinical evaluation should be organised in a manner that allows for easy interpretation. A useful framework found in the orthodontic literature is known as the 3D–3t (three- dimensional–three- tissue) analysis. (Fig 9) this organization allows for the interactions between each type of tissue and each dimension to be easily assessed. 5 Presurgical Orthodontics the goal of presurgical orthodontics is to decompensate the occlusion. if the teeth are not decompensated prior to orthognathic surgery, dental interferences may occur that prevent ideal positioning of the skeletal subunits. (Fig 10) Decompensation of the dentition can be accomplished in many different ways depending on the initial deformity. At times, extractions of permanent teeth may be required, in conjunction with fill braces or possibly even aligners. (Fig 11) to achieve anchorage control if required nance arches, transpalatal arches, or temporary anchorage devises maybe used. (Fig 12) With patient compliance, lInICal Fig 5a: The Frankfort Mandibular Plane angle (FMA) Sum of all angles Normal value: 396° Posterior (clockwise) grower: above 403° Anterior (counterclockwise) grower: below 394° Fig 5b: Bjork Jarabak vertical analysis iv. Although emphasis is made on obtaining perfect orthodontic records, the clinical examination often provides the most critical data. ideally, the clinical evaluation is performed in conjunction with the orthodontist and the surgeon. Much of the information gleaned from the clinical evaluation can be confirmed by other records collected, such as photographs, study models, and radiographs, but there are several critical data points that can only be accurately obtained during the clinical evaluation. Four of these points include: a. the presence of a mandibular functional shift: the most obvious discrepancy that initiates the desire of a patient to seek orthognathic Fig 6: The presence of a mandibular functional shift: The most obvious discrepancy that initiates the desire of a patient to seek orthognathic surgery Fig 7: Facial midline can be assessed from a frontal photograph using the philtrum of the upper lip as a reference. Fig 8: Many subtleties can best be appreciated during a clinical exam such as dystopia, malalignment of the ears, subtle soft tissue asymmetries, and natural head position Fig 9: The 3D–3T (three- dimensional–three- tissue) analysis is a useful framework that organizes data from orthodontic records and clinical evaluation in a manner that allows for easy interpretation