Presurgical analysis and Planning
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PRE-SURGICAL PLANNING AND ANALYSIS

  1. Facial Proportions: The human face can be divided into three almost equal parts from the front.
    • Upper part or the forehead: From hairline to glabella.
    • Middle part or the midface: From glabella to subnasale.
    • Lower part or the lower face: From subnasale to menton.
                   

    In the side view (profile), the face can be convex, concave or straight type. To evaluate the horizontal relations of the soft tissues a line can be dropped perpendicular from the Frankfort horizontal plane through the root of the columella (subnasale). This perpendicular line passes through the upper vermilion border, 2 mm out to the lower vermilion border and 4mm (+/- 2 mm) anterior to the menton.

    Some salient features that tell about the harmony and balance of the face are:

    • Middle third is equal to Lower third of the face.
    • Subnasale to stomion is half that of stomion to menton.
    • Subnasale to lower lip vermilion border is equal to lower lip vermilion border to menton.
    • Interlabial distance is 0 - 3mm at rest.
    • The upper lip margin lies on the gingival margin while smiling.
    • Width of the nose is equal to or few mm wider than the inner intercanthal distance.
    • Position of the midline of the chin gives the face its symmetry.
    • Normal naso-labial angle ranges between 900 - 1100.
    • Labiomental fold gives a pleasant definition to the face.

  2. Cephalometric analysis: Lateral Cephalogram is traced to analyze the proportion of the various parts of the face. This will help to find out the areas of disproportion by marking out the various points, but should be correlated with clinical observations. Innumerable analyses have been proposed but great variations are seen in the "normal values" between different human races. More importance should be given for soft tissues measurements than skeletal analysis. The points, lines and angles marked are very arbitrary and different values can be obtained from different analysis of the same person. COGS analysis is the most commonly used and it describes the horizontal and vertical position of the facial bones by use of a constant coordinate system. Both the skeletal and soft tissue evaluation can be done by this analysis.

  3. Prediction tracing: This is a tracing on the facial profile to find out the outcome of surgery and gives a two dimensional assessment of the profile.
    Fig:1 – Pre operative profile tracing with vertical excess of maxilla marked.
    Fig:2 – Facial profile tracing after Le-Fort I osteotomy.
    Fig:3 – Anterior maxillary osteotomy traced.
    Fig:4 -- Profile tracing of the final surgical outcome.
    A cut and paste technique on the tracing paper is used for predicting the outcome.

    Computer prediction is now available due to the development of various software programs. This helps in visualizing the postoperative results better, but chances are, expectations become higher and the surgeon may have difficulty in producing the same results clinically.

  4. Model surgery: The plaster models are articulated on a anatomical articulator with face bow transfer. The area of the bone to be cut (site of osteotomy) is measured and marked on the plaster models and a mock surgery is done. This will help to
    • Get an idea about the extent of bone reduction required in the surgery.
    • Understand the post-operative relations of the jaws.
    • Understand the post-operative occlusion.
    • Helps in the fabrication of splints.
    • Decide about the post-surgical orthodontic treatment.

    Wafer thin occlusal splint should be fabricated to prevent the condyle from being unseated vertically, which can cause "condylar sag" post-surgically. The splint should allow the teeth to occlude properly in the preplanned occlusion.

  5. Presurgical Orthodontics: A good teamwork is necessary between the Orthodontist and the Maxillofacial Surgeon. The goal of pre-surgical orthodontia is to position the teeth in the arches to facilitate a good and stable occlusion post-surgically. Extraction of teeth for pre-surgical orthodontia is to be reviewed with cephalometric analysis, prediction tracing and model surgery. Commonly pre-surgical orthodontia is done to close any interdental space, derotation and proper alignment of all teeth.

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Prof. (Dr) Varghese Mani, Oral and Maxillofacial Surgeon.
Member Dental Council of India.
Past President Oral and Maxillofacial Surgeons of India.
Consultant:
Mani Specialty Clinic, MG Road, Trichur, Kerala 680004, India. Phone: 0091-0487-385996
Trichur Institute of Head and Neck Surgery (TIHANS), Saroja Hospital, Shornur Road, Trichur.

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copyright ©Aug 2001. No part of this website may be transmitted or reproduced in anyway. Every effort has been made to supply correct and accurate information, but I assume no responsibility for its use.


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updated Aug2002.