ANDREWS STRAIGHT WIRE APPLIANCE

1. ANDREWS STRAIGHT
WIRE APPLIANCE
Presented by
Dr. Roshni Krishnan
Post Graduate Student
Second Year

2. Content (Part – 1)
✣ Introduction
✣ History
✣ Naturally occurring optimal occlusion
✣ Six keys to optimal occlusion
✣ Measurements
✣ Normality, abnormality, optimally
✣ Non programmed appliance
2

3. Content (Part – 2)
✣ Fully programmed standard brackets
✣ Fully programmed translation brackets
✣ Partially programmed appliances
✣ Andrews2 appliance
✣ Conclusion
✣ References
3

4. Introduction

5. Regardless of one’s expertise in other aspects of orthodontics,
fitting the teeth together as well as they can be is essential to
being a good orthodontist.
Bracket stand between the teeth and the orthodontist, which
one are prescribed play a large role in the quality of the results
and in treatment efficiency.
One must ask in matters of occlusion, whether there are clinical
limitations that prevents orthodontists from reaching goals
considered exemplary by others.
5

6. Initial attempt to assess the state of the art of orthodontics in
terms of post treatment static occlusion did not yield the
consistent and adequate data required for firm conclusions.
One implication, however was clear the paragon positions of
natural teeth could be found only by studying dentitions with
naturally optimal occlusion.
6

7. History

8.  Dr. Lawrence Fredrick Andrews
 Research spanning ten years led to the Six Keys
to Optimal Occlusion, quantifying the tooth
positions of naturally optimal dentitions, and
the Andrews Straight-Wire Appliance.
8

9. The collecting of over 120 casts of individuals with optimal occlusion that
have never had orthodontic treatment
The Six Keys to Optimal Occlusion
Finding and using the facial-axis of the clinical crown and the
facial-axis point for measuring tooth position, for designing brackets,
and for bracket siting
A tooth-position measurement study (angulation, inclination, and
prominence)
The Straight-Wire Appliance
“Straight-Wire, The Concept and Appliance” textbook (L.A. Wells, Inc.,
1989)
1962
1965
1965
1965
1970
1989
9

10. NATURALLY OCCURING
OPTIMAL OCCLUSION

11. • On the hypothesis of naturally occurring optimal occlusion
would be worthy of emulation, casts of such dentitions were
collected over a period of 4 year.
• Fifteen orthodontists and general dentists assisted in this
research among which Dr. A . G Brodie arranged to duplicate
a collection of casts with naturally good to excellent occlusion
at the university of Illinois orthodontic department.
11

12. • By 1984 the sample comprised 120 casts.
• These samples comprised of dentitions:
1. Have never been subjected to orthodontic treatment
2. Are well aligned and pleasing in appearance
3. Appear to have excellent occlusion
12

13. Six keys to optimal occlusion

14. • The most important step leading to the development of the
appliance was the discovery of six characteristics that were
consistently present in the collection of 120 casts of naturally
occurring optimal occlusion. These qualities are referred to
as “Six Keys to Optimal Occlusion”.
14

15. • They have special value for the orthodontist because
1. Complete set of indicators of optimal occlusion
2. Can be judged from tangible landmarks
3. Can be judged from facial and occlusal surfaces of
crowns reducing the need for a lingual view or for
articulating paper to confirm the occlusal interface.
15

16.  Andrews plane: The surface or plane on which the mid-
transverse plane of every crown in an arch will fall when the
teeth are optimally positioned.
16

17.  Clinical crown:
Normally the amount of crown that can be seen
intraorally or with a study cast.
17

18.  Crown angulation:
The angle formed by the facial axis of the clinical crown
and a line perpendicular to the occlusal plane.
18

19.  CROWN INCLINATION
Angle between a line perpendicular to the
occlusal plane and a line that is parallel and
tangent to the FACC at its mid-point ( FA point ).
19

20.  Facial Axis Of The Clinical Crown:
For all teeth except molars, the most prominent portion of the central
lobe on each crown’s facial surface while for molars the buccal groove
that separates the two large facial cusps.
20

21.  Facial Axis Point (FA point) :
The point on the facial axis that separates the gingival half of the
clinical crown from the occlusal half.
21

22. Mid sagittal plane
An imaginary line that separates
the crown mesio - distally at the
facial axis of the clinical crown
(FACC).
Mid transverse plane
An imaginary line that separates
occlusal half the crown from the
gingival half of the crown. 22

23. Key I : Interarch Relationship
• Pertains to the occlusion and the Interarch relationships of the
teeth.
23

24. This key consists of seven parts:
1. The mesiobuccal cusp of the permanent
maxillary first molar occludes in the
groove between the mesial and middle
buccal cusps of the permanent
mandibular first molar.
2. The distal marginal ridge of the
maxillary first molar occludes with the
mesial marginal ridge of the
mandibular second molar. 24

25. 3. The mesiolingual cusp of the maxillary first molar occludes in
the central fossa of the mandibular first molar.
4. The buccal cusps of the maxillary premolars have a cusp –
embrasure relationship with the mandibular premolars.
5. The lingual cusps of the maxillary premolars have a cusp – fossa
relationship with the mandibular premolars.
25

26. 6. The maxillary canine has a cusp – embrasure relationship
with the mandibular canine and first premolar. The tip of its
cusp is slightly mesial to the embrasure.
7. The maxillary incisors overlap the mandibular incisors and
the midlines of the arches match.
26

27. Molar relationship:
When Angle described about molar relationship he stated that the
mesiobuccal cusp of the upper first permanent molar should rest on
mesiobuccal groove of the lower first permanent molar. But non
orthodontic models consistently demonstrated that
“ Distal surface of the distobuccal cusp of the upper first molar
occluded with the mesial surface of the mesiobuccal cusp of the
lower second molar ”
27

28. 28

29. Key II : Crown Angulation
• Essentially all crowns in the sample have a positive angulation.
• All crowns of each tooth type are similar in the amount of
angulation.
29

30. Key III : Crown Inclination
• Most maxillary incisors have a positive inclination ; the centrals
have more positive than the laterals. Canines and premolars are
negative and quite similar. Molars are slightly negative but slightly
more negative than canine and premolars.
• Mandibular incisors have slightly negative inclination and are
progressively more negative from the incisors through the second
molars. 30

31. Key IV : Rotations
The fourth key to optimal occlusion is an absence of tooth rotations.
31

32. Key V : Tight Contacts
Contact points should abut unless a discrepancy exists in mesiodistal
crown diameter.
32

33. Key VI : Curve Of Spee
The depth of the curve of spee ranges from a flat plane to a slightly
concave surface.
33

34. Key VII : Tooth size
• In 1993 Bennet and McLaughlin gave 7th key of normal occlusion ;
the tooth size of upper and lower arch should be correctly
balanced.
• If not, there would be either spacing in one arch or crowding in
opposing arch.
• Tooth size is actually the 7th key of normal occlusion. Andrew’s non
orthodontic normal models had balanced tooth size.
John C. Benenett, Richard P. McLaughlin. Orthodontic management of the dentition with the
Pre-adjusted appliance. 1997;1:1-24
34

35. Measurements

36. The fourth study leading to the development of the first fully
programmed appliance involved thousands of measurements of the
crowns in the 120 cast sample.
The purpose was to learn the extent to which position and shape
were constant within each tooth type and how relative size was
consistent within an arch.
36

37. The measurements made were :
1. Bracket area of each tooth type
2. Vertical crown contour
3. Crown angulation
4. Crown inclination
37

38. 5. Maxillary molar offset
6. Horizontal crown contour
7. Facial prominence of each crown
8. Depth of curve of spee
38

39. • The facial axis of the clinical
crown (FACC) and the facial axis
point (FA Point) were marked on
the each crown of the dental casts.
• The FACC is the reference line
from which crown angulation and
inclination are measured.
39

40. • Duplicate casts of 120 casts were
made and the occlusal half of
each crown was trimmed away.
• A line was drawn on the
trimmed surfaces of the casts,
connecting the most facial
aspects of the contact areas. This
is called as the “embrasure line”.
40

41. • The maxillary molar offset and the most facially
prominent portion of each crown were measured from
embrasure line.
• Ultimately these data were used in bracket design to
eliminate the need for first order arch wire bends.
41

42.  Bracket area:
The smallest crowns of each normal tooth type determined the
occlusogingival height and mesiodistal width limits of each bracket
base
42

43.  Vertical Crown Contour
43

44.  Crown Angulation
44

45.  Crown Inclination
45

46.  Offset of Maxillary Molars
46

47.  Horizontal Crown Contour
47

48.  Crown Facial Prominence
48

49.  Depth Of Curve Of Spee
49

50. Findings of the experiment
• Crown inclination: ( Torque )
70 30 -70 -70 -70 -90 -90
U1 U2 U3 U4 U5 U6 U7
L1 L2 L3 L4 L5 L6 L7
-10 -10 -110 -170 -220 -300 -350
50

51. Findings of the experiment
• Crown Angulation: ( Tip )
50 90 110 20 20 50 50
U1 U2 U3 U4 U5 U6 U7
L1 L2 L3 L4 L5 L6 L7
20 20 50 20 20 20 20
51

52. Findings of the experiment
• Crown Prominence :
52

53. Findings of the experiment
• Offset of Maxillary Molars :
Maxillary molar offset averaged 100 relative to the
embrasure line while no offset is needed for
mandibular molars because the middle and
mesiobuccal cusps are equally prominent.
• Curve of Spee :
Ranged from flat to 2.5 mm deep
53

54. Normality , Abnormality, Optimally

55. • Abnormality : Individuals with abnormal jaws and teeth. Eg –
cleft palate, peg laterals etc. treatment for this group always
needs a multi disciplinary approach
• Naturally optimal : Group with normal teeth and jaws who
require no orthodontic treatment. 120 non orthodontic models
can be included in this group.
• Normal malocclusion : Group with malocclusion which can be
treated to optimal standards. 55

56.  Both the naturally optimal and the normal malocclusion fall under
a same category where they are differentiated only through 6 keys
of occlusion.
 It seemed feasible to design an appliance that could be readily
applied to normal teeth with normal malocclusions and direct them
to optimal goals.
 When correctly sited the brackets would be designed to provide the
guidance needed with few wire bends.
 The development of this appliance resulted partly from the 6 keys
of optimal occlusion and partly from detailed analysis of
limitations of edgewise appliance.
56

57. The Non Programmed Appliance

58. Slot
Stem
Slot base
Tie wings
Base point
Bracket base
Slot point
Tie wings
58

59. Non programmed appliance :
A set of brackets designed the same type for all tooth types
relying totally on wire bending to achieve the optimal position
for each individual tooth.
Partly programmed appliance :
A set of brackets designed with some built in features but that
always requires some wire bending
59

60. • The Angle designed edgewise brackets are “non programmed”
because of their bilaterally symmetrical design.
• Angle recognized some consistencies in the position of
optimally occluded teeth, as shown in his directive to complete
active treatment with an ideal archwire.
• However Angle did not incorporate these treatment objectives
into his appliance.
60

61. Design shortcomings:
• For tooth movement not involving translation, six factors cause the
slot of non programmed edgewise brackets to be sited in ways that
always require archwire bends.
1. Perpendicular bases
2. Bases not contoured occlusogingivally
3. Mesiodistal base contour
4. Slots not angulated
5. Stems of equal prominence
6. Maxillary molar offset not built-in
61

62. 1. Perpendicular bases:
The base of the non programmed bracket is perpendicular to
the stem.
This feature can cause problems for the slot inclination and
occluso gingival position.
62

63. • Each crown in an arch has its own optimal amount of
inclination.
• Therefore brackets having bases that are perpendicular to their
stem and sites base point of each crown will target their slots so
that many different inclination and occlusogingival levels, even
when the base point of the bracket is sited on the FA point of
the crowns occlusogingivally the slots are poorly aligned to the
Andrew’s plane.
63

64. 64

65. 2. Bases not contoured occlusogingivally
Occlusogingivally the bracket is flat but the facial surface of
crown is curved. So when such a bracket is being attached to
the crown it can unintentionally be rocked occlusally or
gingivally.
65

66. There will be irregular slot
sitting in each of the arch
caused by vertically flat based
brackets. Only a part of the
bracket will be touching the
crown.
66

67. 3. Mesiodistal base contour
Irregular mesiodistal slot sitting can occur when the
mesiodistal contour of the bracket base does not match that of
the crown.
67

68. 4. Slots not angulated :
• The bracket slots of the edgewise brackets are non angulated.
68

69. • When the vertical components of
the brackets are sited parallel to
FACC and base point sited at FA
point the angle of the slot vary to
many different angulation.
• Under these circumstances , the
inclination and occlusogingival
ranges for slot sitting are greater
than when the bracket is not
angulated.
69

70. 5. Stem of equal prominence:
• Distance between bracket base and center of slot is same in each
brackets.
70

71. • Therefore when the brackets are placed they become as
irregular in the facial prominence as the crown.
• So when the unbent archwire the facial surface of the each
crown becomes equidistant from the embrasure line, which
is undesirable.
71

72. 6. Maxillary offset not built – in:
• Since the maxillary molars offset is
not built in, the mid sagittal plane
of the slot is angular to the mid
sagittal plane of the crown. This will
lead to rotational effect of molars.
• So a first order bend must be
installed into archwire to
accommodate these differences.
72

73. Non programmed brackets are simple in design, easily
manufactured and inexpensive but difficult to use because
considerable wire bending is needed throughout the treatment.
There are three type of wire bending:
1. Primary wire bending
2. Secondary wire bending
3. Tertiary wire bending
73

74. 1. Primary wire bending:
Intended for the most direct movement of the teeth.
Consists of :
a) First order bend
b)Second order bend
c)Third order bend
74

75. a) First order bend
75

76. b) Second order bend
76

77. c) Third order bend
77

78. When the brackets are sited on a full complement of optimally
positioned teeth, the final “ideal” archwire will require 76 primary
wire bending if it is to be places passively into the slots. This number
includes 46 bends for angulation, inclination and offset and 30 bends
for prominence and occlusogingival slot position error..
78

79. 2. Secondary wire bending:
• Any bends which are for tooth guidance and that are not primary
bends
• Secondary bends are needed to compensate for slot sitting
irregularities caused by bracket design and unreliable bracket
sitting techniques, wire bending and wire forming side effects.
79

80. 3. Tertiary wire bending:
• Any bends that are placed for any reason other than guidance.
• Eg – omega loops for stops, loops for increasing wire flexibility
and loops for elastics.
80

81. ANDREWS STRAIGHT
WIRE APPLIANCE
Presented by
Dr. Roshni Krishnan
Post Graduate Student
Second Year

82. PART - II

83. Fully programmed appliance

84. 84
 The concept of programming tooth guidance into bracket rather
than into wire is based on the recognition that extensive
similarities prevail morphology of normal tooth types and their
positions when they are optimally occluded.
 A fully programmed appliance puts these similarities to work,
accomplishing all or nearly all tooth guidance with flexed but
unbent archwires.
 Fully programmed standard brackets
 Fully programmed translation brackets

85. Fully programmed standard brackets

86. 86
The simplest version of fully programmed appliance consists of
standard brackets designed to guide teeth that do not require
translation.
There is one standard bracket for each tooth type except for incisors
and maxillary molars; for incisors there are three while for maxillary
molars two.
To eliminate archwire bending, more slot siting features are required
than just the correct amount of slot angulation, inclination and facial
prominence.

87. 87
 Auxiliary feature: A design feature that contributes to the
biological aspect of treatment but is not involved in targeting the
slot.
 Convinence feature: A design feature that facilitates use by the
orthodontist or promotes comfort for the patient but does not
contribute to the biological aspects of treatment or to targeting the
slot.
 Fully programmed appliance: A set of brackets designed to guide
teeth directly to their goal positions with unbent archwires.

88. 88
 Inclined base: A bracket base that is angled more or less than 900 to
the midtransverse plane of the bracket stem.
 Inclined slot: A slot whose midtransverse plane is inclined relative
to the midtransverse plane of the bracket stem.
 Maxillary molar offset: the angle between the crown’s embrasure
line and a line connecting the buccal cusps of a maxillary molar. It
is measured along the crown’s midtransverse plane.

89. 89
 Mesiodistal base contour: the horizontal contour of
the brackets base.
 Occlusogingival base contour: The vertical contour of
the bracket base.

90. 90
Slot point
 Slot point: The junction of the midtransverse, midsagittal and
midfrontal planes of the bracket slot.
 Slot site: The area that the bracket slot must occupy if it is to
passively receive a fully size unbent archwire when a tooth is
optimally positioned.
Slot area

91. 91
 Standard bracket: A fully programmed bracket designed for teeth
that do not require translation.

92. 92
 Translation bracket: A fully programmed bracket for teeth that
require translation. It is designed to promote bodily movement
during mesial or distal movement.

93. 93
Mid transverse plane :-
 Feature 1: The midtransverse planes of the slot,
stem and crown must be the same.

94. 94
Mid transverse plane :-
 Feature 2: The base of the bracket for each tooth type must have
the same inclination as the facial plane of the crown at the FA
point.

95. 95
Mid transverse plane :-
 Feature 3: Each bracket’s inclined base must be
contour occlusogingivally to match the
curvature of the crown.

96. 96
Mid transverse plane :-

97. 97
Mid sagittal plane :-
 Feature 4: The midsagittal plane of the slot,
stem and crown must be the same.

98. 98
Mid sagittal plane :-
 Feature 5: The plane of the bracket base at its base point must
be identical to the facial plane of the crown at the FA point.

99. 99
Mid sagittal plane :-
 Feature 6: The base of each bracket
must be contoured to the match the
mesiodistal radius of the area of the
crown it is designed to fit.

100. 100
Mid sagittal plane :-
 Feature 7: In each fully programmed bracket, the vertical
components are designed to parallel one another. These components,
when the parallel and midpoint bracket siting technique is used.
The horizontal components of the bracket are the superior and
inferior sides of the bracket stem.

101. 101
Mid sagittal plane and mid transverse plane :-
• Eliminates requirement of first order bends.
• Eliminates requirement of second order bends for angulation
• Occlusogingival slot siting

102. 102
Mid frontal plane :-
 Feature 8: Within an arch, all slot points must have the same
distance between them and the embrasure’s line. It eliminates first
order wire bends to accommodate for varying crown prominence.

103. 103
• Convenience features: It do not play a role in slot siting, but they
make the appliance easier for the orthodontist to use and
sometimes more comfortable for patient.

104. 104

105. Fully programmed translation
brackets

106. 106
• A fully programmed appliance must offer more than one standard
or basic version. When teeth require bodily movement, translation
brackets have significant advantages over standard brackets.
• Translation brackets have all the qualities of standard brackets
plus a power arm and two additional slot siting features ‘counter –
mesio distal tip’ and ‘counter rotation’. Maxillary molar brackets
include a third feature ‘counter buccolingual tip’

107. 107
• These features along with the archwire and mesial or distal force,
provide counter moments for translation and the guidance needed
for overcorrection in all three planes of space.

108. 108
 Counter buccolingual tip: A slot siting feature for maxillary molars
that counteracts buccolingual tip during translation and then
overcorrects.
 Counter mesiodistal tip: A slot siting feature that counteracts
mesial or distal tipping during translation and then overcorrects.
 Counterrotation: A slot siting feature that counteracts rotation
during translation and then overcorrects.

109. 109

110. 110
 Maximum translation bracket: A translation bracket for posterior
teeth that require more than 4mm of translation.
 Medium translation bracket: A translation bracket for teeth that
require more than 2 mm but not more than 4mm of translation.
 Minimum translation bracket: A translation bracket for teeth that
require 2 mm or less of translation.

111. 111
 Counterrotation:

112. 112
 Counterrotation:

113. 113
 Counterrotation:
Slot rotation + mesiodistal slot length + archwire flex + mesial or
distal force

114. 114
 Counter mesiodistal tip:

115. 115
 Counter mesiodistal tip:

116. 116
 Counter buccolingual tip:

117. Partly programmed brackets

118. 118
• By definition, a partly programmed appliance lacks at least one slot
siting feature for this reason alone it would fail to fully direct each
slot to its tooth’s slot site
• In actuality the inadequacy in both quality and quantity of slot
siting feature makes wire bending necessary.

119. 119
• Its brackets have four slot siting features : Slot inclination,
Slot angulation , prominence and horizontal base curvature.
• This is in contrast to the non programmed appliance which has
none and fully programmed appliance which has eight for
standard brackets and eleven for translation brackets.

120. 120
 Slot inclination:
The amount of slot inclination for each bracket is the same as
the base inclination for each fully programmed standard bracket.
Non programmed brackets have no inclination while in fully
programmed brackets the inclination is built in base.

121. 121
 Slot inclination:

122. 122
 Slot angulation:

123. 123
 Slot prominence:
• Eliminates the need of first order bends.
• Several data indicated faciolingual prominence as thinner or
thicker than in non programmed brackets
• An amount of more than 0.5 mm from the amount in Straight wire
appliance can be considered clinically significant.

124. 124
 Horizontal base contour:
• Most partly programmed and some non programmed
brackets have horizontal base contour.
• They may or may not be same as for the straight wire
appliance.

125. 125
• If they are not, an appliance will not be reliably
locate the mid sagittal plane of the bracket stem
and slot on the crown’s mid sagittal plane.

126. 126
• Patent restrict translation slot siting features; that
means unless treated with combinations of wire
bending and possibly with auxiliary rotation devices,
none of the teeth requiring translation will translate.

127. Andrews2 Appliance

128. 128
• The Andrews2 Appliance is comprised of both standard and
translation brackets. Teeth that do not require translation are
assigned standard brackets. Teeth that need to be translated
mesially or distally are assigned translation brackets –
minimum (T1), medium (T2), or maximum (T3) depending on
the distance the teeth need to be translated.
• Andrews2 Brackets can be prescribed individually or by
prearranged set.

129. 129
• There are 11 sets for the maxillary arch and 10 for the
mandibular arch.
• Arch correction efficiency is maximized when the most
appropriate brackets are prescribed, properly sited, and the
most suitable archwires and forces are applied. When used as
such it becomes a fully-programmed appliance.

130. 130

131. 131

132. 132
The bracket sets are combinations of 5 different types of brackets
• S – Standard bracket
• T1 – Minimum translation bracket
• T2 – Medium translation bracket
• T3 – Maximum translation bracket
• T4 – Maxillary molar 7mm overjet bracket

133. Conclusion

134. 134
 The SWA is programmed to deliver treatment to optimum end
results with few archwire bends.
 This is possible, basically, because of the commonality of dental
morphology in our species.
 Andrew stressed on translation of the teeth utilizing sliding
mechanics with different series of brackets for extraction and non
extraction cases.
 But the problem of extensive inventory of brackets was a setback to
Andrews’s prescription.

135. References

136. 136
1. Andrews LF. The Six Keys to Normal Occlusion. American Journal of
Orthodontics, 1972;62:296-309.
2. Andrews LF. The straight wire appliance origin, controversy, commentary. J
Clin Orthod. 1976;10(2):99– 114.
3. Andrews LF. The straight wire appliance explained and compared. J Clin
Orthod. 1976;10(3):174–195.
4. Andrews LF. JCO interviews on the straight-wire appliance. J Clin Orthod.
1990;24:493-508.

137. 137
5. Andrews LF. The straight-wire appliance. Extraction series brackets. J Clin
Orthod. 1976;10(6):425-441.
6. Andrews LF. The straight-wire appliance. Extraction series brackets. J Clin
Orthod. 1976;10(7):507-529.
7. Andrews LF. Straight Wire: The Concept and the Appliance. 1989, San Diego, L
A Wells Co.
8. Andrews LF. Fully programmed translation brackets. In: Andrews LF, ed.
Straight wire: the concept and appliance. San Diego, CA: LA Wells;1989.

138. THANK YOU