1) The angle of wire entry into the bracket slot, known as the angle of entry, determines the moment of force and can have significant clinical implications. 2) A large angle of entry, such as from a distally tipped canine, can cause unwanted intrusion or extrusion of teeth due to the moment of the couple. 3) Bracket positioning can be used to compensate for unwanted moments and forces from the angle of entry, such as placing anterior brackets more gingivally to prevent bite opening.

1. Angle of Wire Entry
Implications in orthodontic
treatmment

2. A textbook reference

5. The farther the point of force application is from
the center of resistance the greater the
moment (rotational tendency) that is
produced.

10. Couple
• Two forces that are equal, parallel, and non-collinear
• Translational effects cancel each other out and
pure rotational forces remain

11. Couple
•The moments are in the same direction and
are additive

12. Rotation caused by a couple
• Center of resistance and
center of rotation are
the same

13. Commonly seen couple
• Wire contacts 2 of the 4 corners of the slot
• A couple can produce a….

14. Moment of a couple

15. “Moment of a Couple”
• Rotation resulting from the moment of the
couple is responsible for many tooth
movements
• This rotation can affect one tooth or a group
of teeth

18. Tom, age 13

19. Or Blake, age 13

23. Angle of Entry

24. Angle of entry can be affected by:
• Tip in the bracket (angle of bracket slot)
• Tipped teeth due to malocclusion
• Bend in the wire
• Combination of all three

25. Appliance Prescription-Tip

26. Concepts to remember
• Greatest angle of entry produces greatest
moment of couple
• The canine bracket, especially on the upper,
has the most tip built in. Therefore, greatest
angle of entry is most often at the canine
bracket.
• Large variations in canine position are often
present pretreatment. This can also result in
large angle of entry changes

28. Assume a fully bracketed maxillary arch
What effect does a straight wire have on the incisors in each of
these illustrations?
Remember Dr Prittinen’s angle of entry concept
R
R
L
L

29. R
R
L
L
The incisors intrude.
The incisors extrude.

30. Assume a fully bracketed maxillary arch
What effect does a straight wire have on the incisors in each of
these illustrations?
Remember Dr Prittinen’s angle of entry concept
R
R
L
L

31. R L
The incisors will cant running downhill right to left.
R
L
The incisors will cant running downhill left to right.

34. Normally positioned canine

35. Distally tipped canine

36. What happens?
• Combining the distal tipping of the tooth with the tip
built into the bracket produces a VERY LARGE angle
of wire entry.

37. Implications
• Extrusive force on the anteriors (expressed due to
small root surface area)
• Intrusive force on posteriors (not expressed due to
large root surface area, and because posterior
intrusion is tough to do)

38. Net effect
• Bite deepens and becomes very difficult to
open
• Intrusive and extrusive forces produced as a
result of the moment of the couple results in
tendencies for some teeth to flare and some
to roll in lingually

39. Intrusive/Extrusive force results
• Vertical forces
– Extrusive forces create the potential for LINGUAL
crown tipping
– Intrusive forces create the potential for BUCCAL
(or LABIAL) crown tipping

41. Axial inclination of canines.
Look at this example

42. Archwire at rest

43. Engaging wire produces these forces

44. Moment of couple on canine
(greatest angle of wire entry)
• Creates extrusive force
on the incisors
• Intrusive force on the
molars
• Distally inclined cuspid
crowns present a big
mechanical problem

45. Distally inclined canine crowns

51. Distally inclined canine crowns

55. Another solution
• When angle of entry will be a problem, start
the case by not bracketing the 4 anterior teeth
– 6543-----3456 are bracketed
• The angle of entry can’t affect anterior teeth if they are
not engaged
• Align the canines (this will take 3-4 months)
then after canine angulation is more ideal,
bracket and engage the anteriors.

56. What do you expect to happen here?

60. Does angle of entry make bite easier or
more difficult to open?

65. How can this be controlled?
• Brackets could be positioned to negate these
effects if desired.
• Horizontal, as well as vertical position of slot
could be altered.

66. Effect of vertical forces
• Remember the moment
• Extrusive forces result in lingual crown
movement
• Intrusive forces result in facial (or buccal)
crown movement

67. Another example
Q#1. Does the greatest angle of entry encourage an intrusive or
extrusive force on the upper anteriors?
Q#2 Would you expect flaring or de-torquing of those upper
anteriors?

68. Another example
Q#1. Does the greatest angle of entry encourage an intrusive or
extrusive force on the upper anteriors? (Intrusive)
Q#2 Would you expect flaring or de-torquing of those upper
anteriors? (Flaring due to moment of the intrusive force)

69. 3 months later
• Is what happened to the upper anteriors
predictable?

70. Yes!

71. Melanie, Age 28

74. Initial arch wires
after 2 mo (l) and 3 mo (r)

79. To summarize…
• The extrusive force
imparted to the incisors
because of the moment
(rotational tendency) of
the couple (angle of
entry on the canine
bracket) results in
lingual crown
movement.

89. If distally positioned canine crowns
result in bite deepening…
What happens with mesially inclined
canine crowns?

90. Mesially inclined canine crowns

91. Mesially inclined canine crowns

92. Would this case make you nervous?

93. • Open bite tendency
with mesially tipped
canine crowns
• This bite may open
excessively

94. Management
• Encourage mesial root
movement of cuspid
with mesio-gingival slot
angulation
• Discourage bite opening
by gingival bracket
placement in anteriors
(Question: Did I do
this?)

95. Would this case make you nervous?

96. • Open bite tendency
with mesially tipped
canine crowns
• Again, the bite could
open excessively
without modifications
to bracket positioning

97. Summary
• Positioning the slot to attain proper root
angulation may increase the already large
angle of entry
• If the greatest angle of entry is working
against you, change the inciso-gingival and/or
mesio-distal position to offset the angle of
entry effect, or consider modifications to
initial bracketing protocol

98. Summary, continued
• Use bite opening or bite closing techniques
after root alignment or
• If you expect angle of entry side effects to be
severe, do not bracket anteriors until after
canines are uprighted, or use spring system as
previously described

100. Bracketing Concept
• In the 1960’s, the best orthodontics was done
by the best wire benders. Today, the best
orthodontics is done by the best bracket
positioners.
• Vertical control by bracket positioning….

101. Anteriors; inciso-gingival placement
• Deep bite patients
– Position brackets 1 to 2 mm incisal to the center
of the tooth
• Open bite patients
– Position brackets 1 to 2 mm gingival to the center
of the tooth

102. Deep bite
Normal bite
Open bite

103. Premolars- inciso-gingival placement
• Deep bite cases
– Position brackets 1 to 2 mm gingival to the center
of the tooth
• Open bite cases
– Position brackets 1 to 2 mm occlusal to the center
of the tooth

104. Deep bite
Open bite

105. Concept
• Step 1-Identify greatest angle of entry
• Step 2-Vertically position brackets to
compensate for this, if necessary

107. Rule
• If I want the root to move to the distal, angle
the slot disto-gingivally.
• If I want the root to move toward the mesial,
angle the slot mesio-gingivally.

108. Hands-on demo
• Step 1- Outline 2nd bicuspid and “move” it (this
represents pre-treatment position)
• We now want root to move to distal, and crown to
mesial.

109. Another example

113. Bone Anatomy
• Thick cortical plate
around canines make
them the slowest
moving teeth
• Angle of entry is most
critical here
• Tip: palpate canine
eminence to determine
difficulty of movement

114. Bracket position modifications to this
case?

115. Management
• Encourage mesial root
movement of cuspid
with mesio-gingival slot
angulation
• Discourage bite opening
by gingival bracket
placement in anteriors

117. Mallory, age 12

118. Questions
• What will happen
during initial leveling
and aligning?
• What 2 things could you
do to prevent this?

119. If angle of entry issues are not recognized, excessive bite opening will occur. To
prevent this from happening, do not bracket the canines at the initial appointment.
Also, compensate for bite opening by placing the anterior brackets gingivally.

120. Month 2

129. Evaluation
• Ben has a tougher initial
level and align
• But angle of entry
makes bite opening
more difficult in Cory

130. After 6 months of treatment

134. Angle of entry
Case examples

145. Indiscriminate leveling and aligning will cause
occlusal plane canting. To prevent this, do not place brackets on
the upper incisors until after the canines are uprighted.

154. Chris, Age 14

155. Nicole, Age 15

156. Chris Nicole

157. Chris
• Excessive mesial
inclination of canines
could lead to excessive
bite opening.

158. 1st month of treatment-Chris

159. 2nd month of treatment- Chris

160. Questions
• Is this the expected
treatment response?
• Could anything have
been done to prevent
this? Explain.

161. Questions
• Is this the expected
treatment response?
• Could anything have
been done to prevent
this? Explain.
• This is the expected
response. Bracket
positioning and
bracketing scheme should
have been altered to
compensate for angle of
entry issues.

162. Nicole- Month 1

163. Nicole-Month 2

166. Nicole: initial aligning complete

167. Chris: initial aligning complete

168. Chris Nicole