DOWN's Analysis / orthodontic courses by Indian dental academy

DOWN’S ANALYSIS

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INTRODUCTIONW.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


DOWN’S NORMAL RANGES ARE

SKELETAL PATTERN DENTAL PATTREN1. Facial angle 1. Cant of occlusal plane2. Angle of convexity 2. Interincisal angle3. A-B plane 3. Incisor occlusal plane4. Mandibular plane angle 4. incisor mandibular plane angle5. Y(growth axis) 5. Protrusion of maxillary incisors


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.


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°.


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°


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 °


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°


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°


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°


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°


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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DOWN's Analysis / orthodontic courses by Indian dental academy