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How to…. Mechanically erupt a palatal canine.
Authors
* PS Fleming, B Dent Sc. (Hons.), MSc., MFDS RCS, MFD RCS, MOrth RCS.
** P K Sharma BDS (Hons.), MSc, MFDS RCS, FDS (Orth) RCS, M Orth RCS.
*** A T DiBiase BDS (Hons.), MSc, FDS (Orth) RCS, M Orth RCS.
* Senior Registrar in Orthodontics
** Locum Senior Clinical Lecturer / Honorary Consultant in Orthodontics
*** Consultant in Orthodontics
*The Royal London Dental Institute and Maxillofacial Unit, Kent and Canterbury
Hospital,
Canterbury
** The Royal London Dental Institute
*** Maxillofacial Unit, Kent and Canterbury Hospital, Canterbury
Address for correspondence
Dr Padhraig Fleming
Senior Registrar in Orthodontics
Maxillofacial Unit
Kent and Canterbury Hospital
Ethelbert Road
Canterbury
CT1 3NG
Email: [email protected]
Abstract
Management of ectopic permanent maxillary canines represents one of the greatest
challenges to orthodontists. This paper outlines a variety of techniques and mechanics
which may facilitate expedient and safe eruption of palatal canines. While each
method may be useful in isolation, the varying presentations of palatal canines ensure
that the ability to apply an array of techniques is essential if successful outcomes are
to be consistently achieved.
Key words
Canine, impacted, fixed appliances, removable appliances.
Introduction
With the exception of the third molars, maxillary canines are the most frequently
impacted tooth1 with the vast majority lying palatal to the line of the arch2. There are
many approaches to the possible management of palatal canines, ranging from
interceptive techniques to removal of the impacted tooth3. Treatment decisions are
governed by a variety of factors including: position of the canine, the dictates of the
associated malocclusion, patient compliance and any relevant medical history. Where
interceptive measures are inappropriate, the preferred approach involves mechanical
eruption of the involved tooth.
Mechanical eruption of impacted canines may lead to prolonged treatment duration
which is thought to increase further with greater vertical and mesial displacement,
increased angulation of the canine and increasing age4-8. Deleterious effects of
prolonged orthodontic treatment are well-documented and include the propensity for
greater root resorption9 and poor patient compliance. Additionally, root resorption of
teeth neighbouring the impacted tooth is thought to be accelerated if mechanical
eruption is undertaken10. Consequently, there is a high premium on efficient
management of impacted maxillary canines. This paper highlights and appraises a
variety of mechanics at our disposal to successfully and safely mechanically erupt
impacted palatal canines.
Surgical exposure
Considerable research and debate has surrounded the merits of open and closed
eruption techniques11 (Table 1). Overall, there appears to be little difference between
the approaches in relation to overall treatment duration and periodontal health15,
although careless surgery with exposure of the cemento-enamel junction will have
deleterious periodontal consequence. Therefore, exposure type is often based on
individual preference, although open exposures have the obvious advantage of
allowing complete visualization of the crown permitting accurate bond placement.
Careless placement of attachments in closed techniques may be undetected until the
canine has been erupted; in such instances, prolonged treatment and unwanted
rotations invariably develop. With closed eruption techniques gold chains may,
however, permit directional control and assessment of progress. In general, the
authors favour open surgical exposure where permissible; this technique enhances
control and may allow spontaneous improvement without resort to active forces
(Figure 1). The latter approach is particularly beneficial where overbite is reduced but
may be contra-indicated if the canine is particularly high or where open exposure may
lead to periodontal damage or compromise adjacent teeth.
Mechanics for eruption of palatal canines:
While many of the mechanical approaches outlined below are applicable throughout
treatment, they are often used sequentially with more than one technique often
necessary prior to integration with a complete fixed appliance (Table 2). Initial
eruption can be achieved in many ways; however, to align the canine sufficient space
must be available within the arch.
It is inadvisable to apply buccally directed forces to the impacted canine where the
tooth is intimately related to the roots of the lateral incisors; such forces may induce
unwanted rotations, resorption of the incisor, and mechanical obstruction will cause
retardation of tooth movement. Therefore, judicious mechanics with precise
directional control are required to guarantee predictable tooth movement (Figure 2).
Typically, eruption may be commenced with an auxiliary e.g. TMA ‘fishing-rod’,
prior to placement of a complete fixed appliance. Concurrently or later in treatment
space, may be generated to fully align the canine within the arch by distal molar
movement, extraction of permanent teeth, use of comprehensive fixed appliances to
consolidate space in the incisor region or by advancement of the upper labial segment
using ‘push-pull’ mechanics.
Early treatment: Auxiliary appliances.
(i) Trans-palatal arch (TPA) with stainless steel auxiliary.
The use of auxiliary stainless steel projections (0.6-0.7mm stainless steel) connected
to a TPA has been described previuosly16. Typically, it is used early in treatment
where a high aesthetic premium exists and also may be integrated with comprehensive
fixed appliance therapy (Figure 3).
Advantages
 Excellent aesthetics; hidden from view
 The TPA reinforces vertical anchorage and may limit mesial tipping and rotation of
first permanent molars
 Versatile; may be adjusted to permit posterior, occlusal or buccal movements as
required
 Little impediment to oral cleansing
 A ‘lingual appliance’; consequently, no risk of visible decalcification
Disadvantages
 Prone to breakage
 Speech impediment
 Soft tissue irritation e.g. tongue ulceration
(ii) Titanium Molybdenum Alloy (TMA) ‘fishing-rod’
This approach offers similar properties as outlined above and may be used in
conjunction with a TPA. It may be equally discreet pending on the location, although
they typically lie buccal to the arch. TMA (0.017 X 0.025”) is favoured for this design
as it has inherent flexibility and is formable while being of sufficient resilience to
resist deformation 17(Figure 4). Particular advantages of this method include18:
 Minimal requirement for compliance
 Patient comfort
 Favourable range of action irrespective of canine position
 Good three-dimensional control
(iii)Removable appliances
Removable appliances may be used in either the upper19 or lower20 arch to apply
traction to the palatal canine. The principal advantages of this method include:
 Excellent anchorage, resisting unwanted reciprocal forces;
 Ability to achieve other tooth movements concurrently e.g. overbite reduction, class
II correction (Figure 5) or space redistribution;
 Incorporation of an anterior bite plane that eliminates occlusal interferences that
impedes lateral movement of the canine.
While upper removable appliances are retentive, they may not offer sufficient
flexibility in directional force application. Lower removable appliances are less
retentive as extrusive forces may unseat the appliance; however, force vectors are
ideal for canine eruption being inferiorly directed and distally directed if required20.
Additionally, all removable appliances may be complex in design; are relatively
costly; rely on technical assistance and depend on excellent patient compliance. Safe,
simple and secure attachment of elastics relying on little patient dexterity can be
assured using attachments that may be preformed 21 e.g. monkey hooks TM or
fabricated at the chairside.
(iv) Magnets (Figure 6)
Magnets are rarely used in orthodontics but have application in management of
impacted teeth particularly in conjunction with removable appliances22-23. Advantages
include versatility; minimal wire manipulation; the application of a low continuous
force increasing over time and the facility for directional control. However, magnets
are relatively expensive and are also subject to the limitations associated with
removable appliances.
(ii) Temporary anchorage devices (TADs) .
TADs have gained widespread popularity over the past decade being used to produce
a variety of tooth movements24-25; however, their application to address impacted
canines has received little attention. Giancotti et al.26 have reported a case
incorporating an osseointegrated mid-palatal implant to erupt bilaterally impacted
canines using the implant for indirect anchorage. The obvious advantage of TADs is
absolute anchorage which is particularly useful in a compromised dentition with little
facility to retain fixed or removable appliances (Figure 7). TADs are also versatile and
may be useful to achieve separate occlusal objectives. Limitations of this approach,
however, include:
 Cost
 Necessity for surgical intervention
 Potential for fracture or loss of the implant.
Mid-treatment. Mechanics in conjunction with pre-adjusted appliances.
Following initial movement, space creation to allow alignment of the canine is
typically necessary. Pre-adjusted edgewise appliances are preferred with space
redistribution usually performed on a 0.018” stainless steel archwire. This base wire
may also afford sufficient anchorage to permit simultaneous application of active
eruptive force to the misplaced canine.
1. Elastomeric traction to fixed appliance.
Elastomeric traction is useful to initiate eruption in conjunction with fixed appliances
and stainless steel archwires. Rigid stainless steel base archwires, e.g. 0.018” or 0.019
X 0.025” SSW, are desirable to minimise reactionary forces reinforcing vertical
anchorage in particular27.
Limitations of elastomeric materials are well-documented28-29. Applied forces decay
rapidly with force loss of up to 50% developing within 24 hours necessitating regular
re-activation. Precise directional control is often difficult but may be improved with
archwire adjustments or auxiliaries to centre force application e.g. passive coil-spring
(Figure 8b).
2. Piggyback NiTi archwires.
Auxiliary NiTi archwires provide inherent flexibility to continue the eruptive
process30, 31. Again rigid stainless steel base archwires with significantly higher elastic
modulus, e.g. 0.018” or 0.019 X 0.025” SSW, are preferred to limit unwanted effects
on anchor units (Figure 8c-d). NiTi wires are considered ideal as they provide a
relatively constant, light force with high flexibility and range17 allowing engagement
of significantly displaced teeth.
Disadvantages of piggyback wires include:
 Inability to apply a precise directional force
 Complexity
 Poor aesthetics
 Oral hygiene
3. Stainless steel archwire auxiliary.
The application of buccal auxiliary wires for correction of palatal canine position has
been championed by Becker et al. 32. The auxiliary spring is formed in 0.014” or
0.016” SSW with a vertical loop having a helix at its extremity (Figure 9). In the
passive position the loop points vertically downward towards the mandibular
dentition; the loop is activated by ligating the helix to an attachment on the canine
with a steel ligature generating an extrusive force. Particular advantages of this
approach include:
 Directional force; wire may be fashioned to produce precise movements
 Long range of activation
 Allow vertical movement which may not be achievable with nickel-titanium
auxiliary wires following initial vertical movements
 Avoid laboratory procedures
 Forces are controlled and measurable.
Limitations of this method, however, include relative complexity, oral hygiene
considerations and the risk of appliance breakages.
4. Nickel-titanium auxiliaries.
A variety of alternatives to elastomeric traction have been developed to eliminate the
problem of force degradation of elastomeric materials. They are ligated to the canine
in a similar fashion to elastomerics; most of these are nickel-titanium based with
excellent shape memory and may be capable of exerting continuous light forces33-35.
However, research confirming the value of such alternatives is lacking; additionally,
they are more costly and complex to use than elastomeric chains.
Final detailing of canine position
While mid-treatment mechanics greatly improve canine position, final detailing of
tooth position is invariably reliant on integration into a fixed orthodontic appliance to
correct vertical position of the canine and to apply correct angulation, inclination and
rotational control. A mandibular pre-adjusted appliance may be necessary to address
separate occlusal problems, to facilitate overbite reduction or to intrude opposing
teeth encroaching on the canine position (Figure 10).
Addition of sufficient buccal root torque is necessary to maximize aesthetics, gingival
position and enhance stability. Selective use of Andrew’s prescription (-7o torque) is
preferred to achieve this; buccal root torque may also be enhanced with arch wire
bends, e.g. in rectangular SSW or TMA, or with auxiliaries during the finishing stages
to correct root position.
Conclusion
Successful and predictable correction of impacted canines carries significant aesthetic,
functional and dental health importance. Initial movement may often involve distal
and occlusal movement prior to bringing the tooth buccally. This approach limits the
risk of deleterious consequences and stagnation of treatment. Impacted palatal canines
present with many variations; consequently, a ‘one size fits all’ approach will not
produce successful results on a consistent basis.
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Legends for illustrations
Figure 1 (a, b). Open surgical exposure may allow spontaneous progression without
orthodontic appliances.
Figure 2 a-c. Injudicious movement of the canine while intimately related to the
lateral incisor root may introduce moments leading to unwanted rotation of the
maxillary canine. Correct directional control with buccal movement only commencing
following initial posterior and inferior movement of the canine away from the root of
the incisor results in favourable translation of the canine.
Figure 3 a. Dental panoramic tomograph of ectopic maxillary canines in an adult
patient; UL3 is severely displaced.
Figure 3 b. Transpalatal arch used to initiate movement of the canine prior to
placement of the complete fixed appliance; removal of the primary canines was
postponed until initial movement of the canine was confirmed.
Figure 3 c. Mechanical eruption is continued with piggyback archwires.
Figure 3 d-f. Case following removal of appliances
Figure 4 a, b. TMA ‘fishing rods’ to start mechanical eruption of UR3; completed
result (Figure 4c).
Figure 5 (a-d). Inter-arch traction to erupt a maxillary canine combined with class II
correction using a Modified Twin Block appliance.
Figure 6. Magnets were used in conjunction with an upper removable appliance to
mechanically erupt palatal canines; reciprocal forces on the already compromised
dentition with generalized root shortening were kept to a minimum.
Figure 7 a-c. Temporary anchorage device in the mandibular parasymphysis used to
apply elastomeric traction to a maxillary canine in a compromised maxillary arch
subsequent to hemi-maxillectomy. Both buccal and palatal attachments were placed to
maintain correct canine inclination.
Figure 8a. Maxillary occlusal view of impacted UR3.
Figure 8b. Movement was initiated with elastomeric traction before ‘piggyback’ NiTi
archwires were used to erupt the displaced canine (Figure 8c).
Figure 8d. Eruption progressed successfully with ideal canine positioning following
integration into a complete pre-adjusted appliance.
Figure 9 a-c. A 0.014” SSW auxiliary used to continue vertical movement of UL3;
the 0.018” stainless steel base archwire minimized reciprocal effects.
Figure 10 a, b. Over-eruption of a mandibular canine opposing the unerupted
maxillary right canine; this was addressed with a lower fixed appliance permitting
ideal vertical positioning of both maxillary and mandibular canines. Placement of the
passive open coil spring ensured directional control during eruption of the canine with
elastomeric traction.
Table 1. The influence of exposure type on treatment duration.
Paper
Treatment duration (months)
Open
Closed
Wisth (1976)12
18
22
Pearson et al.
25.7
21.8
28.8
28.8
(1997) 13
Iramaneerat &
Cunningham
(1999) 14
Table 2. Properties of selected appliance mechanics.
Mechanics
Anchorage Aesthetics Appropriate
Dependence Cost/complexity Versatility/
stage of
on
ability to
treatment
compliance
control force
vector
TMA ‘fishing-rod’
Moderate
Moderate
Early
Low
Moderate
Excellent
Trans-palatal arch
Moderate
Excellent
Early
Low
Moderate
Excellent
Good
Moderate
Early
High
Moderate
Good
Magnet
Good
Good
Early-mid
High
High
Moderate
Temporary
Good
Good
Any
Low
Mod-high
Good
Fair –Poor
Poor
Early
Low
Low
Moderate
Moderate
Poor
Mid
Low
Low
Low
Moderate
Poor
Mid-late
Low
Moderate
Good
with whip spring
Removable
appliance
anchorage device
Elastomeric traction
to fixed appliance
(depends
on position
of canine
and type of
base
archwire
used)
Piggyback wire
(NiTi)
Stainless steel
archwire auxiliary