Assuming that the centre of resistance in a tooth is in the
middle of the apical third of that tooth;
Explain the effect the following
lines of distal force will have on the position of the rotational centre and
the movement of the tooth, when applied to a maxillary molar by means of a face
bow.
(a) A line of
force passing through the centre of resistance.
(b) A line of
force apical to the centre of resistance.
(c) A line of
force further apically to the centre of resistance.
(d) A line of
force passing occlusally to the centre of resistance.
The results suggested that different heights of retraction forces could affect the direction
ReplyDeleteof anterior tooth movement. The higher the retraction force was applied, the lower the degree of rotation (crown-lingual tipping) would be. The tooth rotation was in the opposite direction (from crown-lingual to crown-labial) if the height of the force was raised above the level of the center of resistance.
(a): IF A SINGLE FORCE IS APPLIED TO THE CROWN OF A TOOTH, THE TOOTH WILL NOT ONLY TRANSLATE BUT ALSO ROTATE AROUND CR (I.E., THE CENTER OF ROTATION AND CENTER OF RESISTANCE ARE IDENTICAL)
(b): When a force is placed on the crown, and the crown goes in one direction, while the root goes in the other. In this case, the center of rotation is near, or apical to the center of resistance
(c): Almost the same as the force of the apical to the center of resistance but more tipping will take place.
(d): The tooth will tip.
(a)when a line of force passing through the centre of resistance it will tilt the tooth
ReplyDelete(b)when a line of force apical to the centre of resistance it will cause little tilting of the tooth compared to when the force is place farther away from the centre of resistance.
(c) A line of force further apically to the centre of resistance will have cause more tilting to the tooth since the force is further away from the centre of resistance
(d)A line of force passing occlusally to the centre of resistance will produce vertical movement of the tooth on its axes
(A) If a force is applied down the centre of resistance of the tooth, more bodily moment will be achieved, be the force great enough to do so.
ReplyDeleteb) the more apically the force is applied the more tilting will occur in that particular direction. This is the result of the force being further away from the fulcrum (CR), creating a greater levering effect in that part of the tooth. As Mauritz has mentioned the crown will tilt in one direction and the root will move in the opposite direction.
C) The effect described in (b), is increased the move apically the force is placed.
a) A force applied to the centre will create a bodily movement ( translation) of the tooth, this means that all the points on the tooth will move an equal distance in the same direction.
ReplyDeleteb) An apical force closest to the centre will create uncontrolled tipping. The crown will move in one direction while the root mopves in the opposite direction.
c) A line force further apical to the centre of resistance will create controlled tipping of a tooth, there will be lingual movement of the crown with little movement of the root.
d) A line force passing occlusally to the centre of resistance will cause torquing.
a) If the line of the force is passing through the resistant center of the tooth from the distal, the whole tooth will move mesial.
ReplyDeleteb) If the line of force is more to the apical of the resistance center, the tooth will rotate in the sense that the apical portion will rotate the most, thus the distal side will lower and the mesial will be lifted (so to speak, this is the best I can explain as I do not know which tooth it is)
c) More rotation will occur than that in (b), just more severe.
d) If the force is occlusally, the tooth will shorten or be embedded deeper into the bone and gingiva, thus less of the crown will become visible.
(a) A line of force passing through the centre of resistance will produce translation with very little or no tipping of the tooth.
ReplyDeleteThe force will move the whole tooth distally.
(b) A line of force apical to the centre of resistance creates a perpendicular moment arm. The created rotational centre is moved towards the edge of the crown of the tooth resulting in the tipping of the root in a distal direction.
(c) The line of force passing further apically to the centre of resistance results in the shifting of the created centre of rotation even closer to the centre of resistance resulting in a greater distal root tipping of the tooth.
(d) A line of distal force passing occlusally to the centre of resistance will shift the centre of rotation resulting in mesial tipping of the roots of the tooth.
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ReplyDelete