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1. DOWN’S ANALYSIS
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2. INTRODUCTION
W.B. Down noted that generally the position of mandible can be used in
determining whether the faces are balanced or not
He recognized the facial profiles could be retrusive or protrusive yet still
be harmonious in proportion.
He reduced his observation in four basic facial types:-
- retrogathic (a recessive lower jaw)
- Mesognathic (an ideal or average lower jaw)
- Prognathic (a protrusive lower jaw)
- True prognathism (a pronounced protrusion of lower face)
He selected Frankfort Horizontal Plane as the reference plane
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3. DOWN’S NORMAL RANGES ARE
SKELETAL PATTERN DENTAL PATTREN
1. Facial angle 1. Cant of occlusal plane
2. Angle of convexity 2. Interincisal angle
3. A-B plane 3. Incisor occlusal plane
4. Mandibular plane angle 4. incisor mandibular plane
angle
5. Y(growth axis) 5. Protrusion of maxillary
incisors
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4. FACIAL ANGLE-
- This is an inferior inside angle used to measure the
degree of protrusion / retrusion of the lower jaw.
- Facial line (N-Pog) intersects with the FH line.
- Mean reading 87.8 with range 82 – 95.
- Prominent chin increases the angle while
retrusive chin gives smaller than average
angular reading.
- Indicates the degree of recession / protrusion of
mandible in relation to upper face.
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5. ANGLE OF CONVEXITY-
measures the extent of protrusion / retrusion of lower jaw, relation of jaw to each
other, convexity of maxilla & inclination of lower jaw.
- Formed by intersection of N-A to A-Pog
- Angle measures the degree of the maxillary basal
arch at its anterior limit (point A) relative to total
facial profile (N-Pog)
- Angle read as positive /negative, if A-Pog located
& extended anterior to N-A angle is positive
suggesting prominence of maxillary dental
base relative to mandible.
- Range extends from minimum –8.5 to
maximum +10 with mean of 0 .
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6. A-B PLANE-
- point A & B are joined by a line & angle
formed by line A-Pog
- It is a measure of the relation of the anterior
limit of the apical base to each other to the facial line
- As point B positioned behind point A this
angle is usually negative except in class III
or class I with prominence of mandible.
Large negative angle suggest class II
facial pattern.
- The reading extend from maximum of
0 to minimum of –9 with mean of –4.6
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7. MANDIBULAR PLANE ANGLE-
- mandibular plane is tangent to gonial angle & lowest point of sumphysis.
- Angle formed by relating MP with the FH plane.
- High mandibular plane occurs in retrusive & retrusive faces suggest hyperdivergent
facial pattern.
- Range is 17 – 28 with mean reading of 21.9
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8. Y- (GROWTH) AXIS-
- measures as an acute angle formed by the intersection of sellla tursica- gnathion
with the FH plane
- Angle is large in class II facial pattern than in class III
- This indicated the degree of downward, rearward & forward position of the chin in
relation to the upper face
- Decrease in angle suggest horizontal growth pattern while increase in angle suggest
vertical growth pattern.
- Range is 53 – 66 with mean of 59.4
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9. CANT OF OCCLUSAL PLANE-
- accordingly the occlusal plane is the line bisecting overlapping cusps of the 1st
molars & incisors overbite & if incisors mal aligned then bisecting line passing
through molars & premolars.
- It measures the slope of occlusal plane to FH plane
- If the anterior part of the plane is lower than the posterior, angle is positive
- Long ramus tends to decrease the angle
- Range is +1.5 - +14 with a mean of +9.3
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10. INTERINCISAL ANGLE-
- established by passing the line through incisal edge & apex of the root of the
maxillary & mandibular incisors
- Its relatively small in forwardly tipped incisors on the dental base
- Range from 130 – 150 with mean of 135.4
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11. INCISOR OCCLUSAP PLANE ANGLE-
- relates the lower incisors to their functioning surface at the occlusal plane
- Positive angle increases as the teeth inclines forward
- Range from +3.5 - +20 with a mean of 14.5
INCISOR MANDIBUALR PLANE ANGLE-
- formed by intersection of mandibilar plane with the line passing through the incisal
edge & apex of the lower central incisors
- Angle is positive when the incisors are tipped forward to the denture base
- Range is –8.5 to +7 with mean of 1.4
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12. UPPER INCISORS TO A-POG LINE-
- it is the distance between incisal edge of the
maxillary central incisor to the line from
point A-Pog
- Distance is positive if the incisal edge is
ahead of the A-Pog line indicating the
amount of the maxillary dental protrusion
- While negative if the incisal edge is
behind of A-Pog line suggest the
retruded position of maxillary incisors
- Range is –1 to +5 with a mean of +2.7mm.
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13. Thank you
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