Linear dimensions of face and sassouni’s analysis

Introduction

The vertical proportions of the face are critical in determining its aesthetics and harmony.

Traditionally, orthodontists perceived malocclusion as an anteroposterior problem or tend to classify, record and treat it as sagittal dysplasia, that is, class I, II or III malocclusions. The role of the imbalance of vertical dimensions of the face in the aetiology of various anteroposterior problems was realised in the mid-20th century. The focus gradually shifted towards the three-dimensional evaluation of the face and malocclusion, the vertical dimensions reflecting the significant characteristics of facial types and their influence on occlusion phenotypes.

Wylie and Johnson, the pioneers of vertical analysis of face

As early as 1947, Wylie made some commendable attempts at devising a method to evaluate facial dysplasia in the vertical plane. He used the following linear dimensions in the anteroposterior plane to localise dysplasia of the maxilla and mandible on the lateral cephalogram using the Frankfort horizontal (FH) plane as a reference. He measured the following dimensions (mm) in the sagittal plane to discern facial dysmorphology ( Fig. 26.1 A and B):

1.
Glenoid fossa-Sella.
2.
Sella-pterygomaxillary point (Ptm).
3.
Ptm-maxillary first permanent molar (buccal groove).
4.
Ptm-anterior nasal spine (ANS) representing the maxillary length.
5.
Mandibular length: A vertical line drawn on the mandibular plane from the posterior condyle surface to the pogonion.

If the first four linear dimensions representing the maxilla and upper face are longer than average, then the upper face would be prognathic. The lower face will be prognathic if the mandibular length is larger than average.

These linear values should not be judged in an absolute sense but should be considered in proportionality. The relative proportions of some dimensions may vary but may show other compensatory balances that deviate in an appropriate direction. For example, a short cranial base can offset a large maxillary length.

In 1952, Wylie and Johnson used a vertical dimension approach to understand the anterior and posterior face proportions.

Anterior face height was divided into upper face height, Nasion (N) to anterior nasal spine (ANS), and lower face height, ANS to Menton (Me).

Posterior vertical height was measured from the summit of the condyle (Ar) to the gonial angle (Go).

Anterior facial height

Anterior face height can be divided into upper face height (N-ANS) and lower face height (ANS-Me). A ratio of 45:55 is considered normal. An increase in lower face height suggests downward and backward rotation of the mandible, anterior open bite, short ramus, large gonial angle or combinations of two or more of these features in varying degrees of severity ( Fig. 26.2 ).

Sassouni’s cephalometric analysis

Although several authors have tried to understand the role and importance of the vertical dimension and its effect on the anteroposterior dimensions of the face, Viken Sassouni’s work was the first to put great emphasis on it for orthodontic treatment planning.

Sassouni’s analysis was the first cephalometric method to categorise vertical and horizontal relationships and the interaction between the vertical and horizontal proportions of the face.

Sassouni constructed a series of planes, arcs and axes on a profile cephalogram. He was very inquisitive about studying the structural configuration of the skull for growth analysis and diagnosis and integrating this information into the treatment ( Fig. 26.3 .i and ii).

Planes

1.
Mandibular base plane (OG): The OG is tangent to the inferior border of the mandible.
2.
Occlusal plane (OP): The OP passes through the mesial cusps of the permanent first upper and lower molars and the incisal edges of the upper and lower central incisors.
3.
Palatal plane (ON): The ON is perpendicular to the mid-sagittal plane, passing through the anterior and posterior nasal spines (ANS-PNS).
4.
Anterior cranial base: The anterior cranial base is structurally the floor of the anterior cerebral fossa. In a lateral radiograph, there are two contours: the upper is the roof of the orbit, including the lesser wing of the sphenoid, and the lower is posteriorly the sphenoethmoid area and anteriorly the cribriform plate.
- Anterior cranial base plane or basal plane (OS): The basal plane is parallel to the axis of the upper contour of the anterior cranial base and tangent to the inferior border of the Sella turcica (S).
5.
Ramus plane (RX): The RX is tangent to the posterior border of the ascending ramus.

In a well-proportioned face, the following four planes meet at point O:

1.
The plane tangent to the Sella and parallel with the anterior cranial base (OS)
2.
Palatal plane (ON).
3.
Occlusal plane (OP)
4.
Mandibular plane (OG)

Based on the point of convergence of these planes, a face’s vertical proportionality can be appraised. The relation of the four planes to the common point ‘O’ is used as a reference guide to the classification of four facial types.

Facial types

There are four facial types according to Sassouni.

Type I	The anterior cranial base plane does not pass through O.
Type II	Palatal plane does not pass through O.
Type III	The occlusal plane does not pass through O.
	Mandibular base plane does not pass through O.

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Tags: Kharbanda's Orthodontics: Diagnosis and Management of Malocclusion and Dentofacial Deformities, OP Kharbanda

May 10, 2026 | Posted by drzezo in Orthodontics | 0 comments

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Linear dimensions of face and sassouni’s analysis

Introduction