Patients often prioritise facial aesthetics, the primary motive for seeking an orthodontic consult. However, due to skeletal, dental and soft tissue abnormalities, orthodontic treatment alone may not suffice in many clinical situations. Patients with significant dentofacial deformities often need a combination of fixed orthodontic treatment and orthognathic surgery to attain properly aligned dental arches, optimal functional occlusion and harmonious balance between the skeletal structure and facial soft tissues.

A successful approach to treating skeletal dysplasia depends significantly on accurate diagnosis and comprehensive treatment planning for orthognathic surgery. Despite the availability of 3D planning in major cities and large institutions, the reliability and importance of 2D cephalometric analysis cannot be overstated. It remains the primary tool in diagnosing skeletal and dental problems. The diagnostic process begins with identifying the nature of the dental and skeletal dysplasia and their severity. The patients indicated for orthognathic surgery have facial bones and tooth positions requiring orthodontic and surgical treatment modification. Several cephalometric analyses are used to predict and harmonise the dental outcomes within the existing skeletal structure, which may not be appropriate for diagnosing the skeletal discrepancy in patients requiring orthognathic surgery.

A cephalometric evaluation system focusing on severe skeletal dysplasia was developed as cephalometrics for orthognathic surgery (COGS) at the University of Connecticut in 1978 by Charles J. Burstone and co-workers.

This system is based on the cephalometric analysis methodology initially established at Indiana University. Later, in 1980, Legan and Burstone developed soft tissue cephalometric analysis for orthognathic surgery.

This was important, as considering only skeletal analysis concerning the facial form and proportions of the patient would have resulted in incomplete information.

The initial normative values for hard tissue COGS were derived from a sample of 16 females and 14 males of Caucasian descent from the Child Research Council at the University of Colorado School of Medicine.

The normative values for soft tissue analysis were obtained from 40 white adults (20 men and 20 women) aged between 20 and 30. These individuals had not undergone orthodontic treatment, and they had class I occlusions with normal vertical proportions (N-ANS/ANS-Me = 0.75 and 0.85).

Keeping racial differences in mind, ethnic-specific norms studies in India were conducted to develop norms in different population groups.

A constant coordinate system describes the position (horizontal and vertical) of the facial bones. Linear and angular measurements represent the size of jaw bones and define their relative orientation in space, respectively. The distinctive characteristics that make COGS adaptable to evaluate the surgical orthognathic problem are that various surgical procedures, including facial bones and a cranial base reference plane, can alter chosen landmarks and measurements. The mock surgery can be conducted based on measurements obtained from COGS. The critical facial skeletal components are evaluated and compared with standards. The standards are available for variation in age and sex from age 5 to 20 years, and a systematised approach to measurement can be computerised.

COGS appraisal describes skeletal, dental and soft tissue variations. ^,

Landmarks and reference planes used in hard tissue and soft tissue COGS are depicted in Fig. 31.1 .

• •

  Horizontal plane (HP)—constructed 7° to SN plane (surrogate Frankfurt plane).

• •

  Mandibular plane (MP)—Me (Menton) to Go (Gonion) plane.

• •

  Nasal floor (NF)—ANS (anterior nasal spine) to PNS (posterior nasal spine) plane.

Landmarks for hard and soft tissue COGS.

Hard tissue is evaluated as a cranial base, horizontal skeletal, vertical skeletal and dental, maxilla and mandible, and dental parameters.

Cranial base ( Fig. 31.2 )

The cranial base is considered a reference to correlate measurements of the maxilla and mandible and there is no absolute value. The cranial base is relatively stable and is influenced by Lefort II and III osteotomies. Autorotation of the mandible may alter this slightly during mandibular surgery as ‘articulare’ might move closer to nasion. The cranial base is divided as follows:

• 1.

  Ar-PTM—posterior cranial base (||HP) (mm)

• 2.

  PTM-N—anterior cranial base (||HP) (mm)

Hard tissue COGS—cranial base measurements.

Horizontal skeletal profile measurements ( Fig. 31.3 )

• 1.

  N-A-Pg (degree)—facial skeletal convexity. A clockwise angle is positive (+) and represents a convex face; and a counterclockwise angle is negative angle (−) and represents a concave profile. It does not specify which jaw is at fault.

• 2.

  N-A (||HP) (mm)—maxillary protrusion. This value represents the relative position of the maxilla in reference to nasion. A positive (+) value represents maxillary protrusion and a negative (−) value indicates maxillary retrusion. This helps in determining the treatment planning of maxillary horizontal advancement or reduction.

• 3.

  N-B (||HP) (mm)—mandibular protrusion: This value represents the relative position of the mandible to the nasion. A positive (+) value indicates mandibular protrusion, a negative (−) value indicates mandibular retrusion. This quantifies the degree of mandibular dysplasia antero-posteriorly. This helps determine the treatment plan for mandibular horizontal advancement or reduction.

• 4.

  N-Pg (||HP) (mm)—chin protrusion. This parameter indicates the prominence of the chin. It is often correlated with N-B and B-Pg values to determine where the problem lies, that is proper alveolar process region, chin region or mandibular region. This helps in planning the genioplasty.

Hard tissue COGS—horizontal skeletal profile measurements.

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