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11 • Orthodontics III: Appliances and Tooth Movement
287
Anterior bite plane. An anterior bite plane is required
when overbite reduction is necessary or when removal of
an occlusal interference is required to allow tooth movement. Three essential elements must be addressed:
n
The bite plane should be flat: if inclined, it may procline
or retrocline the lower incisors.
n
It must have sufficient extension posteriorly to contact
the lower incisors; to ensure this, a measurement of the
overjet (13 mm) should be forwarded to the laboratory
at the time of appliance fabrication.
n
It should separate the molar teeth by about 2 mm; it will
be necessary, in most cases, to add cold-cure acrylic to
the flat anterior bite plane during treatment to continue
overbite reduction.
Posterior bite planes. Posterior bite planes are required
to remove occlusal interferences and facilitate tooth movement when overbite reduction is unnecessary. This is commonly the case when correcting a unilateral buccal crossbite
with mandibular displacement or an incisor crossbite. The
acrylic coverage should be just sufficient to disengage the occlusion but must be adjusted to give even contact of the
posterior teeth. The bite planes should be removed when the
malocclusion is corrected, and the appliance should then
be worn as a retainer while the posterior occlusion settles.
COMMON TOOTH MOVEMENTS REQUIRED
Table 11.1 summarises some common desired tooth
movements and the active components to achieve these.
Box 11.1 describes the steps involved in fitting a remov-
able appliance.
MANAGING PROBLEMS DURING TREATMENT
Problems that arise commonly during treatment are listed
in Table 11.2 together with the most likely causes and
necessary treatment.
CLEAR ALIGNER THERAPY
This form of treatment involves creating a series of aligners
(clear vacuum-formed thermoplastic appliances). Scanned
dental casts or impressions are used to create digital models, which are then related using the bite registration. Alternatively, the teeth and bite registration may be scanned and
transferred to the manufacturer. Following the clinicians
prescription, the technician moves the teeth small amounts
(0.25 mm for incisors and canines; 0.33 mm for premolars
and molars), incorporating any adjunctive treatments
(interproximal reduction, placement of attachments and
inter-arch elastics) until all treatment objectives have been
achieved. The full series of movements should be reviewed
using a three-dimensional (3D) visualisation software and
any changes made before finalising the plan for the manufacturer to produce the sequence of aligners. Although
there are differences between aligner systems with regard
to types of tooth movement possible, these appliances perform well, particularly in adults, where tipping movements
are required for relief of mild-to-moderate crowding. This
treatment is combined with interproximal stripping and/or
expansion. Clear aligners have also achieved success with
lower incisor extraction for severe crowding, closure of
mild-to-moderate spacing, posterior dental expansion and
where intrusion of one or two teeth is required. With choice
of an apt sophisticated aligner system in conjunction with
attachments to allow suitable force application and an experienced operator, it is possible to extend their use to more
complex cases, such as alignment of very ectopic teeth,
molar uprighting, molar translation, closure of anterior
open bite and extraction space closure.
The initial aligner is fitted active to be worn a minimum
of 22 hours/day and is likely to produce discomfort that
may require relief with mild analgesics. The patient must
be told how to assess change in tooth position so timely
progress can be made to the next aligner in the sequence.
Depending on the tooth movements required, attachments may need to be added during treatment.
The clinician should review treatment progress regularly
by comparing the anticipated with the actual movement.
On completion of treatment, retainers must be fitted (see
Section 11.4).
11.2 Fixed Appliances
LEARNING OBJECTIVES
You should:
• be aware of the components of a fixed appliance
• know the indications for a fixed appliance
• be aware of how management of fixed and removable
appliances differ
• be aware of different fixed appliance types.
A fixed appliance is attached to the teeth.
Table 11.1 Common Tooth Movements and Related Active Components.
Tooth Movement Required Component and Wire Diameter Activation
Upper arch expansion Two or more teeth: screw Instruct the patient to turn screw once or twice per week
Distal movement of upper
first permanent molar (FPM)
Proclination of incisor(s) Z-spring 0.5 mm
0.6 mm palatal finger springs to retract
banded FPMs
Double cantilever springs 0.6/0.7 mm
Screw appliance
1–2 mm activation of springs, with headgear worn
12–16 hours/day with a force 200–250 g per side
Must fit with two safety mechanisms (e.g. ‘Ni Tom’
facebow and ‘Snap-away’ headcap)
Pull the spring 1–2 mm away from the base plate at
,45° angle to direction of wanted movement
As for Z-spring
Instruct patient to turn screw one or two turns per week
288
Master Dentistry
Box 11.1 Fitting a Removable Appliance.
1. Check that the working model and appliance are those of the
patient, and that the appliance has been well made to your design.
2. Check the fitting surface for roughness and any sharp edges of
wire tags. These should be smoothed off with an acrylic bur or
green stone, respectively.
3. Try the appliance in the patient’s mouth. If any teeth have
been lost or extracted since the impression was taken, some
adjustment is likely to be required to get the appliance to fit well.
4. Adjust the posterior, and then the anterior retention until
satisfactory.
5. Trim any anterior or posterior bite plane to the correct height.
6. If extractions are required to provide space for the tooth movements required, leave all springs passive for the first 2 weeks
until the patient has adapted to wearing the appliance. Otherwise, gentle activation of the springs may be undertaken.
7. Show the patient in a mirror how to insert and remove the
appliance, stressing that it is important not to damage any springs.
Let the patient practise this several times under your supervision.
8. Instruct the patient and parent or guardian in wear and care of
the appliance, emphasising the following:
n
full-time wear, including mealtimes, is essential; it will take a
few days to get used to eating with the appliance in, but
you must persevere
n
sticky and hard foods, particularly toffees and chewing gum,
must not be eaten. Fizzy drinks are also to be avoided
n
the appliance must be taken out after meals for cleaning
and for contact sports (when it should be stored in the
strong plastic container provided)
n
speech is likely to be affected for the first week but will
recover thereafter
n
mild localised discomfort is to be expected if the appliance
is gently activated on one or two teeth. An analgesic,
usually that taken for headache, may be taken for relief
as required
n
if the appliance cannot be worn as instructed or breaks or
discomfort other than mild ensues, the clinic must be
contacted immediately. A list of written instructions
should be issued and a note to this effect made in the patient’s file.
9. Explain that any extractions will be requested once there is
evidence of full-time wear.
10. Make a review appointment for 4 weeks if the appliance is
active, otherwise for 2–3 weeks to review wear and request
any extractions necessary.
Subsequent Visits
1. Check that the appliance is being worn full time; if so:
n
speech should be clear with no lisp
n
the patient should be able to remove and insert the appliance
unaided by a mirror
n
the base plate should have lost its shine
n
if there is an anterior or posterior bite plane on the
appliance, there should be occlusal markings from the
opposing teeth
n
mild gingival erythema and a slight mark across the posterior
extent of the appliance on the palate should also be present.
2. If full-time wear is not apparent, the patient should be questioned
as to why and informed that treatment will be terminated unless
total compliance is forthcoming.
3. Check oral hygiene.
4. Check for anchorage loss by recording the buccal segment
relationship and the overjet. If headgear is being worn, ask if
there have been any problems. These must be documented, and
if none are apparent, this should be noted. Check for evidence of
headgear wear and for how long it is worn by assessing the time
sheet. Check the headgear safety mechanisms.
5. Assess the intended tooth movement; record the changes in
the patient’s case records.
6. Adjust the retention of the appliance if necessary.
7. Check the base plate so that there is no impediment to the
intended tooth movement, and/or that its height is satisfactory
for overbite reduction or to prevent occlusal interference.
8. Adjust the active component(s) if necessary.
9. Indicate in the patient’s records the action plan for the next visit.
COMPONENTS
The appliance is composed of three elements: the attachments (brackets/bonded molar tubes/bands), the archwires
and the accessories.
Brackets, Bonded Molar Tubes and Bands
It is becoming increasingly popular to bond all teeth, including molars. Bonding of brackets or molar tubes, which
mainly have a mesh base, is primarily undertaken using
composite resin following acid-etching of the enamel, although self-etching primers (SEPs, which combine etchant
and primer to avoid the need to wash the etchant away)
may also be used. Resin-modified glass ionomer cements,
which release and uptake fluoride in an attempt to prevent
enamel demineralisation, are an alternative. These newer
systems, however, are not as popular as the two-stage etch
and prime system. Adhesive precoated brackets are also
available; these are claimed to reduce excess composite or to
absorb it internally, save on clean-up time and give a more
consistent bond.
The bonded brackets and molar tubes allow the teeth to be
directed by the active components comprising the archwire
and/or accessories. Brackets may be made from stainless steel,
titanium, polycarbonate, ceramic or a combination of polycarbonate/ceramic. Molar tubes are made from stainless steel
or titanium. Ceramic brackets are more aesthetic than metal
but have disadvantages. They are hard and brittle so may
wear the opposing teeth, increase friction with the archwire
and can cause enamel fracture at debond due to the strong
bond to the adhesive (common with the early-marketed
types). The problems with friction and enamel fracture have
now been overcome by a polycarbonate base on a ceramicfaced bracket with a metal insert in the bracket slot.
Despite the trend to use bonded tubes instead of bands
on molars, bands are particularly indicated for the upper
molars especially if headgear, a palatal arch or rapid
maxillary expansion is being used. Other indications include teeth with short clinical crowns, as placement of
bonded attachments is difficult, and teeth with repeated
bond failure or those that are heavily restored. Bands are
usually cemented using a glass ionomer cement. Separation of the teeth, commonly with elastomeric rings, is
required for up to 1 week to facilitate band placement and
guarantee best fit.
11 • Orthodontics III: Appliances and Tooth Movement
Table 11.2 Problems During Treatment.
Problem Cause Management
Base plate fracture Existing crack
Base plate too thin
Damage by patient out of the mouth
Clicking habit Discourage habit
Eating sticky/hard foods Reinstruct the patient regarding avoidance of
Wire fracture Work hardened from repeated bends or oc-
clusal loading
Damaged while trimming base plate
Clicking habit Discourage habit
Eating sticky/hard foods Dissuade from eating inappropriate foods
Rapid deterioration in retention Clicking habit Discourage
Palatal hyperplasia Failure to trim base plate to allow tooth
movement
Poor oral hygiene Oral hygiene instruction, but if marked, additional four
Slow progress Lack of full-time wear Caution the patient and encourage to wear the appliance
Active component not adjusted as instructed
or spring overactivated/passive/distorted
Incorrect positioning of springs by patient Reinstruct in appliance insertion and removal
Acrylic, wire or the opposing occlusion preventing movement
Retained root fragment/ankyloses Consider removal of root fragment; if tooth ankylosed,
Lack of overbite reduction Appliance not worn at meals Caution and reinforce importance of full-time wear
Marked tipping of tooth Incorrect spring positioning Relocate spring to just above gingival margin
Excess force Reduce force
Anchorage loss Appliance not being worn full time Reinforce importance of full-time wear
Anchorage demands exceed those required Reassess anchorage need carefully; consider revised treat-
Check co-operation; caution the patient if necessary
If small fracture, cold-cure acrylic repair; if large fracture, consider remake with heat-cured acrylic
inappropriate foods
If arrowhead fracture on Adams’ clasp, use solder; otherwise replace component; ensure component is not
loaded by the occlusion
Ensure base plate trimmed appropriately
times a day application of antifungal agent (e.g. Nystatin)
to the fitting surface
full time
Reinstruct or adjust/reposition spring correctly
Remove acrylic/adjust wire/increase height of any bite
plane
reassess and consider other treatment options
ment plan, appliance design, anchorage reinforcement
289
Archwires
Archwires may be round or rectangular.
With its easy formability, good stiffness and reasonable
cost, stainless steel is the most popular archwire material;
however, nickel–titanium, cobalt–chromium and beta–
titanium – all with greater flexibility than stainless
steel – may also be used at different stages of treatment.
Nickel–titanium has two unique properties – shape memory and superelasticity – that relate to phase transitions
between the martensitic and austenitic alloy forms. Even
with a large deflection, a relatively constant low force is
applied, making these archwires an excellent choice for
initial alignment. They are, however, more expensive than
stainless steel archwires, which because of the properties
given above are especially suitable later in treatment.
Cobalt–chromium alloy (Elgiloy) may be shaped while in
a soft state, and then hardened by heat treatment and may
be used for a quadhelix or a utility arch for incisor intrusion. Titanium molybdenum (TMA) has excellent strength
and springiness, mid-way between nickel–titanium and
stainless steel, making it ideal for intermediate and finishing stages of treatment.
Accessories
Elastics, elastomeric modules/chain/thread, wire lig-
atures. Latex elastics produced for orthodontic pur-
poses may be used for intra- or intermaxillary traction.
A range of sizes is available. Elastomeric modules are
used to maintain an archwire in an edgewise bracket
slot (see later), while elastomeric chain or thread may
be used to move teeth along an archwire, or for derotation. Stainless steel wire ligatures continue to be used
particularly when maximum contact is desired between the wire and the bracket slot or to maintain
space closure.
Springs. Uprighting or rotation of teeth may be carried out
by auxiliary springs, while space opening or closure may
be undertaken by coil springs.
290
Master Dentistry
INDICATIONS FOR FIXED APPLIANCES
Indications include:
n
bodily movement of incisors to correct mild-to-moderate
skeletal discrepancies
n
overbite reduction by incisor intrusion
n
correction of rotations
n
alignment of grossly misplaced teeth, particularly those
requiring extrusion
n
closure of spaces
n
multiple movements required in either one or both arches.
Tooth Movement
As with a removable appliance, a fixed appliance may also
tip teeth but has the additional possibilities of producing
bodily movement (crown and root apex move in the same
direction), uprighting, torqueing, rotation, intrusion and
extrusion of teeth. Torquing is a complex movement involving apical bucco-lingual movement in addition to no or
negligible crown movement in the equivalent direction.
ANCHORAGE CONTROL
Because the palate is not covered by a base plate, anchorage
control is more critical with a fixed than with a removable
appliance. In addition, bodily rather than tipping movement places greater strain on anchorage.
Anchorage may be reinforced by:
n
increasing the anchorage unit by bonding more teeth
and ligating them together.
n
preventing forward tipping of the molars by anchor
bends in the archwire (placed between premolar and
molar at 30° to the occlusal plane).
n
placing torque in the archwire ensuring that the anchor
teeth can only move bodily, thereby increasing resistance
to unwanted movement; a twist is placed in the plane of
the wire so that on insertion in a rectangular bracket
slot, it exerts a bucco-lingual force on the root apex.
n
palatal and/or lingual arches: these link molar teeth
across the arch, which increases RSA of the anchor unit
to resist mesial drift and molar tipping.
n
intermaxillary traction (see Section 11.1): as well as reinforcing anchorage, the incisor relationship may be
corrected, the direction of the elastic traction depending
on the malocclusion: class II traction pulls backward on
the upper labial segment and forward on the lower buccal segment; class III traction pulls forward on the upper
molars and backward on the lower labial segment.
n
placement of a Temporary Anchorage Device (TAD); may
be an implant, mini-plate attached with screws to maxillary or mandibular basal bone or a mini-screw (usually
6–12 mm long and 1.2–2 mm wide) in the alveolus. Miniscrews are the most popular and as not osseointegrated,
they do not provide absolute anchorage.
n
extraoral means, including reverse headgear (see Sections
10.4 and 11.1).
APPLIANCE TYPES
Preadjusted Appliances
The preadjusted edgewise appliance uses an individual
bracket with a rectangular slot for each tooth to give it
‘average’ tip, torque and bucco-lingual position and to allow the placement of flat archwires; some individual adjustment bends, however, are often required to the wire to
compensate for these ‘average’ values. 0.018 and 0.022
systems (which describes the bracket slot height in inches)
exist and bracket prescriptions by Andrews, Roth and MBT
are available. Round flexible wires are used for initial alignment, and rectangular wires are required for precise apical
control. Clinical time is saved and good occlusal results are
achieved consistently with these appliances.
Tip-Edge appliance. This system was developed from the
Begg appliance to overcome some of its deficiencies and
uses brackets with rectangular slots. The Begg appliance
uses a bracket with a vertical slot and round wires exclusively held in place loosely with brass pins. Tipping
movement is facilitated, but auxiliaries are necessary for
rotational and apical movement. With the Tip-Edge appliance, although round wire is used for most of the
treatment as with the Begg technique, the facility exists
to place rectangular wire in the final stages, affording
greater control of tooth positions without the need for
additional springs, which the latter required.
Lingual appliance. Brackets are bonded, usually indi-
rectly, to the lingual or palatal surfaces of the teeth. With
the Incognito system, brackets are fully customised to be
low profile and are supplemented with individualised
archwires fabricated by a robot. More expensive than
conventional labial appliances, chairside time is also increased due to difficulty with adjustment. In addition,
there is interference with speech and tongue irritation.
Self-ligating appliances. These remove the need for elas-
tomeric or stainless steel wire ligation of the archwire to
the bracket. Available systems include Damon, Speed and
SmartClip. Because the archwire is not pressed firmly
against the base of the bracket, as is the case with use of
an elastomeric module or wire ligature, friction is reduced. Claims that the need for extractions is reduced,
and that overall treatment time is significantly shorter
than with conventional preadjusted edgewise appliances
have not been upheld, although there is some evidence of
reduced chairside time.
Fully Customised Appliances
Aside from fully customised lingual appliances, similar
labial appliances (Insignia) have been developed but are
costly. These have not been shown to shorten treatment
time or to improve treatment quality compared to noncustomised self-ligating designs.
Appliance Management
An excellent standard of oral hygiene is essential prior to and
during fixed appliance treatment. All patients must be instructed specifically in relation to diet and optimal oral hygiene
practices following placement of the appliance to minimise the
risk of enamel demineralisation. Mucosal ulceration is common in the early stages of treatment, and it is wise to give the
patient some soft ribbon wax to place over any components
that are causing minor trauma. Adjustment visits are usually
at intervals of 4–10 weeks. Repairing fixed appliances occupies more chairside time than does removable appliances.
Some discomfort is to be expected for a few days following
adjustment and is usually overcome by mild analgesics.
11 • Orthodontics III: Appliances and Tooth Movement
291
11.3 Functional Appliances
LEARNING OBJECTIVES
You should:
• have an appreciation of how functional appliances
work
• know the indications for functional appliance therapy
• be familiar with the practical management of a patient
with a functional appliance
• be aware of differences between functional appliance
types
• know the skeletal and dental effects of functional
appliance therapy.
Functional appliances correct malocclusion by using, removing or modifying the forces generated by the orofacial
musculature, tooth eruption and dentofacial growth.
MECHANISM OF ACTION
How functional appliances work is not completely understood. They are not efficient at managing malaligned teeth
or addressing asymmetry between upper and lower arches.
Instead, they operate by applying (through stretching) or
eliminating forces that are generated via the facial and
masticatory musculature and by harnessing those that occur through natural growth processes. They are, therefore,
only effective in growing children, preferably just prior to
their pubertal growth spurt.
The specific force system set up by any appliance will depend on its particular design. Essentially, forces are developed by posturing the mandible – either downward and
forward in class II or downward and backward in class III.
This applies intermaxillary traction between the arches, as
can be produced by elastics with fixed appliances. As the
scope for posturing the mandible backward is far less than
for posturing it forward, functional appliances are more
successful in, and are indicated almost exclusively for, class
II malocclusion. For this reason, the possible mechanisms
of action will only be considered for class II malocclusion.
In these cases, the result is a forward tipping of the lower
incisors and the entire mandibular dentition, with acceleration of mandibular growth, as well as a backward tipping
of the upper incisors and restraint of maxillary growth.
Overall mandibular growth is modified – the total amount
is unaffected, but the expression of growth is altered.
INDICATIONS
Where used for correction of class II malocclusion, the
following should ideally be present:
In most cases, a further phase of fixed appliances is
required to detail the occlusion. In moderate class II malocclusion with crowding, this may involve extractions also
(see Section 10.1). In more severe cases, the prospect of
successful correction of the malocclusion by functional
appliance therapy alone is limited; if this is undertaken, the
likely need for subsequent extractions and fixed appliances
or even combined surgical–orthodontic treatment should
be explained.
PRACTICAL MANAGEMENT OF PATIENTS WITH A FUNCTIONAL APPLIANCE
Box 11.2 outlines the general steps involved in using a func-
tional appliance. The orthodontist must be confident about
the ability of the appliance to work and relay this enthusiastically to both the patient and parent as compliance with
wear is critical to success.
Types of Functional Appliance
The following account describes some standard functional
appliances. Current thinking, however, regarding design is
to ‘pick and mix’ the components that are necessary for the
specific correction of a particular malocclusion. Such a
‘components approach’ to design requires considerable
insight into the working of these appliances, which necessitates specialist knowledge and expertise. Functional appliances may be removable or fixed, tooth borne or tissue
borne.
Twin-Block Appliance
The Twin-block appliance consists of upper and lower
appliances incorporating buccal blocks, with interfacing
inclined planes at 70° that posture the mandible forward on
closure. Although a labial bow was incorporated in the upper appliance with the original design, this has now been
shown not to be necessary (Fig. 11.1). Full-time wear is facilitated by the two-part design. Where the mandible needs
to be postured further forward during treatment to reactivate, acrylic may be added to the inclined bite planes. When
the overjet is corrected, trimming of the upper buccal
blocks or a modified retainer with a steep anterior inclined
plane is required to close the lateral open bites that develop,
especially evident where the overbite is deep to start with.
Variants for treatment of class II division 2 and class III
malocclusions also exist.
Herbst Appliance
This fixed-functional appliance consists of splints cemented
to the upper and lower buccal segment teeth connected by
a rigid arm to posture the mandible forward. Although
costly and subject to breakages, speaking and eating are
reported to be easier than with the Twin-block.
n
Patient should be actively growing, preferably just
prepubertal.
n
Mild-to-moderate skeletal class II owing to mandibular
retrusion.
n
Average or reduced FMPA.
n
Uncrowded arches.
n
Lower incisors upright or slightly retroclined; proclined
lower incisors usually contraindicates functional appliance therapy.
Bionator
A labial bow is extended back to hold the cheeks out of contact with the buccal segment teeth and allow arch expansion,
while a thick palatal loop takes the place of acrylic. Full-time
wear is advisable except for meals.
Medium Opening Activator
Particularly useful where deep overbite correction is
required, this appliance has molar clasping, a palatal base
292
Master Dentistry
Box 11.2 Management Technique for a Patient With a Functional Appliance.
1. Ensure that the patient is keen for treatment and is growing.
2. A lateral cephalometric film, in addition to the usual diagnostic
records, is essential before treatment starts. Staging of skeletal
maturity may be assessed from the cervical vertebrae with
specific changes in shape of C3 and C4 coinciding with peak
mandibular growth.
3. In some patients, a preliminary phase of arch expansion and/
or alignment is necessary before proceeding to functional
appliance treatment. The upper incisors will need to be proclined
and aligned in class II division 2 malocclusion to allow forward
posturing of the mandible to obtain the construction bite;
the appliance used for the first stage of treatment may then
be worn as a retainer at all times when the functional
appliance is out of the mouth. (Alternatively, if a Twin-block
appliance is used, the design can be modified to incorporate
these movements simultaneously with anteroposterior
correction of the buccal segments.)
4. Obtain well-extended upper and lower impressions and a
construction bite, the specifics of which depend on the functional
appliance chosen. Generally, the construction bite is taken with the
mandible postured forward, ideally to an edge-to-edge incisor relationship and in the case of a Twin-block appliance open 2–3 mm
(some operators recommend 5–6 mm). Where the overjet is
markedly increased, it may be necessary for patient comfort to
reduce the initial advancement by 25% of the maximal possible,
and then to reactivate the appliance as treatment progresses.
5. Record the patient’s standing height at the appointment when
the appliance is fitted. Recording height over several visits will
give an indication of the rate of growth. Greatest growth in the
maxilla and mandible corresponds with a period of maximum
increase in height.
6. The Herbst and other fixed class II correctors can be worn full
time. For other appliances, the number of hours of prescribed
wear is appliance-dependent, but a minimum is likely to be
evenings and bedtime. While prescribed wear of the Twinblock appliance has usually been full time, apart from sports
and appliance hygiene after meals, it appears from the results
of a recent clinical trial that prescribed wear for a minimum of
probably 8–12 hours/day may suffice. Although a time
sheet could be used to record the number of hours of wear and
should be brought along for inspection at each review visit, this
is subject to overestimation. Compliance with prescribed wear
is better assessed with microsensors (TheraMon) embedded in
the acrylic, but this incurs an additional cost and makes the
appliance bulkier. Granting that patients appear not to comply
with prescribed full-time or part-time wear of the Twin-block
appliance, the latter has proved as effective at overjet reduction
as the former.
7. Warn the patient that minor discomfort is common initially,
particularly muscular and temporomandibular joint tenderness,
but this usually subsides after 1–2 weeks. Mild analgesics may
be taken as required. If an area of mucosal ulceration develops,
the patient must return for appliance adjustment.
8. Review 1–2 weeks after appliance fitting to check appliance wear, to
make any necessary adjustments and, most importantly, to assess
and encourage compliance. Then recall at intervals of 6–8 weeks.
9. Measure the overjet and check the buccal segment relationships at each recall visit, ensuring that the patient’s mandible
is retruded maximally – otherwise, a false indication of any
progress will arise. Check the time sheet or microsensor
(TheraMon) data at each visit and encourage if progress is
good; about 1 mm of overjet reduction per month is usual in
co-operative, growing individuals. If the appliance is not being
worn as instructed, careful counselling, highlighting that this
form of treatment is only effective for a finite time while the
patient is growing, may improve co-operation.
10. Depending on the initial construction bite, at 4–6 months in
treatment, reactivation of the appliance (or a new appliance)
may be necessary, with further posturing of the mandible to
achieve the desired incisor relationship.
11. If there is no discernible progress in 6 months, stop treatment
and reassess.
12. Slight overcorrection of the occlusion is advisable, and then the
appliance should be worn as a retainer at nights until growth
reduces to adult levels or until a second phase of treatment
(possibly with extractions and fixed appliances) gets underway.
It may be necessary to make a new appliance for this purpose.
In the case of treatment with a Twin-block appliance, in order to
facilitate closure of the lateral open bites that are created,
acrylic may be trimmed away from the occlusal surfaces of the
upper block or an upper retainer with a steep anterior inclined
bite plane may be fitted.
A B
Fig. 11.1 The Twin-block appliance. (A) Upper occlusal view. (B) Lower occlusal view. The design is modified from the original developed by Clark.
(Reprinted with permission from Millett D, Day P, Clinical Problem Solving in Orthodontics and Paediatric Dentistry. 3rd ed. © 2017 Elsevier Ltd. All rights
reserved. ISBN: 9780702058363.)
plate, acrylic extensions lingual to the lower incisors and no
buccal capping; acrylic struts link the upper to the lower,
and the lower buccal segment teeth have scope to erupt.
Full-time wear with the usual exceptions is possible.
Frankel Appliance
Originally termed a ‘function regulator’, this may have particular use in the management of atypical soft tissue pattern, for example, hyperactive mentalis muscle. The only
soft tissue–borne functional appliance, buccal shields hold
the cheeks away from the teeth and stretch the mucoperiosteum at the sulcus depth, intending to expand the arches
and widen the alveolar processes. There are three types: FR
1 for class I and class II division 1 malocclusions; FR 2 for
class II division 2 malocclusion and FR 3 for class III malocclusion. Wear is built up over the first weeks until full time,
apart from sports and while eating. Frankel appliances are
complex in design, expensive to make and repair and easy
to damage and distort. They can, however, be reactivated by
sectioning the buccal shields and repositioning them
forward.
Headgear Addition to Functional Appliances
In cases where maximal anteroposterior and vertical maxillary restraint is desirable, usually in association with considerable upper incisor and gingival display, occipital-pull
headgear may be added to tubes incorporated in the acrylic
or soldered to the clasp bridges. Forces of about 500 g
should be used for 14–16 hours/day, and the usual headgear safety precautions and instructions should be followed
(see Section 11.1). If the FMPA is increased, molar capping
is essential to promote a closing rotation of the mandible
and prevent molar eruption, thereby facilitating an increase in overbite. The addition of high-pull headgear to the
appliance will facilitate this process.
Effects of Functional Appliances
For class II malocclusion with deep overbite, these are:
Dentoalveolar
n
Retroclination of the upper incisors and proclination of
the lower incisors are usual, although the latter is not
found consistently and is best minimised by placing
acrylic capping on the lower anterior teeth.
n
Inhibition of lower incisor eruption and promotion of
eruption of the posterior teeth lead to levelling of the
curve of Spee. This process is facilitated by lower incisor
capping on the appliance.
n
Guidance of eruption of the lower posterior teeth in an
upward and forward direction while preventing eruption
and forward movement of the upper posterior teeth
encourages correction of a class II buccal relationship.
n
Arch expansion is intended through the buccal shields
of the Frankel appliance, the buccal wire of the Bionator
or by adjustment of the midline screw of the Twin-block.
Skeletal
n
Enhancement of mandibular growth is brought about
by movement of the mandibular condyle out of the
fossa, promoting growth of the condylar cartilage and
forward migration of the glenoid fossa. This effect is very
variable.
n
Restraint of forward maxillary growth.
11 • Orthodontics III: Appliances and Tooth Movement
n
An increase in lower facial height is mediated by the
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alterations in the eruption of the posterior teeth, as
described above.
The skeletal effects (1–2 mm mostly) only account for a
small portion of the treatment effects even when efforts are
made to limit the amount of tooth movement. Treatment is
successful in about 70–80% of cases. Treatment process or
outcome was no better with incremental (2 mm advancement initially and 2 mm at 6-week intervals) than with
maximum bite advancement (edge-to-edge) during Twinblock treatment. Again with the Twin-block appliance,
treatment undertaken in the early mixed dentition before
10 years of age has been shown to be no more effective
than treatment undertaken in the late mixed dentition in
terms of overjet reduction, skeletal change, occlusal improvement or extraction need. Furthermore, early treatment increases the overall treatment duration and taxes
co-operation. Despite this, as self-esteem is improved temporarily and the trauma risk to the incisors reduced by
maximally 40%, early treatment is indicated if a child is being teased or bullied because of dentofacial appearance (see
Sections 9.4 and 10.1) or where the incisors are deemed to
be at serious risk of trauma.
The limited indications, use and effects of functional appliances in class III malocclusion are dealt with in Section 10.4.
11.4 Orthodontic Tooth Movement and Retention
LEARNING OBJECTIVES
You should:
• know the histological response in areas of pressure and
tension with orthodontic tooth movement, and how
tipping differs from bodily movement
• be able to give the range of force required for each type
of tooth movement
• know the undesirable sequelae of orthodontic forces
• understand the rationale for retention and factors to be
considered in planning retention.
ORTHODONTIC TOOTH MOVEMENT
The biological response to a sustained force is determined
mainly by the force magnitude and duration, which generate zones of pressure and tension within the periodontal
ligament, their extent and location depending on the intended movement. It is the cells of the periodontal ligament
which detect, instigate and coordinate the process of bone
remodelling and tooth movement.
Pressure Zones
The cellular response relates to whether a light or heavy
force is applied. With a light sustained force, movement occurs within a few seconds as periodontal ligament fluid is
squeezed out and the vascular supply is compressed, setting
off a complex biochemical response. Osteoclastic invasion
occurs within 2 days and frontal resorption follows.
When a heavy sustained force is applied, the periodontal
ligament is compressed to such a degree that the blood flow
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is cut off completely, producing an area of sterile necrosis
(hyalinisation). Small zones of hyalinisation are inevitable
even with light forces, but the area of hyalinisation is extended with forces of greater magnitude. Osteoclastic differentiation is impossible within the necrotic periodontal
ligament space but, after several days, osteoclasts appear
adjacent to and within the adjacent cancellous spaces.
From there, they invade the bone adjacent to the hyalinised
area, and tooth movement eventually occurs by undermining resorption, albeit delayed by 10–14 days.
Tension Zones
Following initial application of a light force, the blood vessels
vasodilate and the periodontal ligament fibres are stretched.
In response to escalation in extracellular kinase signalling
which stimulates release of a transcription factor (RUNX-2),
fibroblast and osteoblast proliferation occurs. The stretched
fibres become embedded in osteoid, which later mineralises.
The typical periodontal ligament width is eventually regained by simultaneous collagen fibre remodelling.
With heavy forces, rupture of blood vessels and severing
of the periodontal ligament fibres are likely, but these are
restored with the remodelling processes.
Mechanisms of Tooth Movement
Although the histological response to an applied orthodontic force has been investigated extensively, the mechanism
by which a mechanical stimulus effects a cellular response
is complex and at present unclarified. It is likely that vascular changes in the periodontal ligament in areas of pressure
and tension, electrical signals generated in response to flexing of alveolar bone following force application, cytokine
(bone morphogenetic proteins (BMPs); interleukin-1 (IL-1))
and prostaglandins (such as PGE-2) interact in the process.
B
A
Fig. 11.2 The effect of tipping movement. A 5 area of periodontal
ligament compression/alveolar bone resorption; B 5 area of periodontal ligament tension/alveolar bone deposition.
A
A
B
B
Types of Tooth Movement, Force Magnitude and Duration
Although it was previously thought that tipping of a singlerooted tooth (Fig. 11.2) occurred about a point almost midway along the root, rotation now appears to take place near
the apical third within an elliptically shaped area. Half of the
periodontal ligament is stressed, with maximum pressure created at the alveolar crest in the direction of movement and at
the diagonally opposite apical area. For bodily movement and
rotation, a force couple must be applied, loading uniformly
the whole of the periodontal ligament in the direction of
translation so both crown and root move in the same direction by equal amounts (Fig. 11.3). With extrusion, all of the
periodontal ligament is tensed, but when a tooth is intruded,
the force is concentrated at the apex. An element of tipping is
unavoidable with extrusion, intrusion and rotation.
For tooth movement to occur optimally, the force per unit
area within the periodontal ligament should ideally not occlude the vascular supply, yet be sufficient to induce a cellular
response. A force should, therefore, be as light as possible for
the movement intended, taking into account the root surface
area over which it is spread. Optimal force ranges for various
tooth movements are:
n
tipping: 50–75 g
n
extrusion: 50–100 g
Fig. 11.3 The effect of bodily movement. A 5 area of periodontal liga-
ment compression/alveolar bone resorption; B 5 area of periodontal
ligament tension/alveolar bone deposition.
n
bodily movement: 100–150 g
n
rotation: 35–60 g
n
uprighting: 75–125 g
n
intrusion: 15–25 g.
Although tooth movement can occur in response to
heavy forces, these should not be applied continuously;
intermittent application may be clinically acceptable. Not
only must a force be of sufficient magnitude to effect
the movement desired, but it must also be sustained for
sufficient time. For successful movement, a force must
be applied for about 6 out of 24 hours, and continuous
11 • Orthodontics III: Appliances and Tooth Movement
295
application of light forces is optimal. This is favoured,
because control of tooth movement and anchorage is facilitated, while the risks of pulpal and radicular damage
are minimised. Excessive mobility is avoided and movement is more efficient with less discomfort. Movement of
the order of 1 mm in a 4-week period is regarded as optimal, with faster progress recorded in children than in
adults. This is largely a consequence of the greater cellularity of the periodontal ligament, more cancellous alveolar bone and faster tissue turnover in a growing patient,
which ensure a more rapid response to an applied force.
Accelerated Tooth Movement
Various non-surgical and surgical means, which kindle
bone resorption/deposition or reduce the bony resistance
to tooth movement, respectively, have and are currently
being explored as means of promoting bone remodelling
and a faster rate of orthodontic tooth movement. Intraoral devices which apply supplementary vibrational
forces for around 20 minutes/day have been assessed
mostly as a non-surgical option, although pulsed
electromagnetic waves and localised laser radiation of
low energy have also been tested. Surgical adjuncts explored are primarily corticotomy/piezocision and microosteoperforation. Good quality evidence has not found supplementary vibrational forces to speed up tooth movement
and further high-quality evidence is required regarding
non-surgical methodologies.
Furthermore, pharmacological means of stimulating
tooth movement, some with local application, are being
considered but require further investigation.
Undesirable Sequelae of Orthodontic Force
Pulpal Damage
A mild pulpitis following initial force application is common, but has no effect long term. Where the apical blood
vessels are severed by the use of heavy continuous force or
by injudicious root movement through the alveolar plate,
pulp death is likely, although this is usually associated with
previous trauma.
Root Resorption
Areas of cementum resorbed during tooth movement are
usually repaired. Some permanent loss of root length is
found, however, on nearly all teeth following bodily movement over long distances. The maxillary incisors, then the
mandibular incisors and first permanent molars, are primarily affected. Fortunately, in most instances, loss of
0.5–1.0 mm of root length is of no long-term significance.
Suggested risk factors include: root resorption before
treatment, a history of previous trauma, roots that are
pipette-shaped, blunt or demonstrate a marked apical curvature, use of excessive forces and apical contact with
cortical bone. Genetic risk factors are also involved. Comprehensive orthodontic treatment increases the severity
and incidence, and that heavy forces produce most root
resorption.
Loss of Alveolar Bone Height
With fixed appliance treatment, 0.5–1 mm loss of crestal
alveolar height is common, with the greatest loss occurring
at extraction sites. In the presence of good oral hygiene, this
appears of little concern.
Pain and Mobility
Even with appropriate force magnitude, ischaemic areas
develop in the periodontal ligament after activation of an
orthodontic appliance, leading to mild discomfort and pressure sensitivity. These usually last for 2–4 days and return
when the appliance is reactivated. Some increase in mobility is common, as the periodontal ligament space widens
and the fibres reorganise in response to the applied force.
With heavy orthodontic forces, however, the likelihood of
almost immediate onset of pain and marked mobility is increased, as the periodontal ligament is crushed and further
undermining resorption occurs.
Retention
Following tooth movement, a period of retention is usually
required to hold the teeth passively, preventing them returning to their pre-treatment position while the periodontal fibres and alveolar bone adapt to their new locations. As
part of informed consent, the retention phase should be
planned and discussed fully with the patient before treatment starts. The following factors are likely to destabilise
the final result.
Forces From the Supporting Tissues
Reorganisation of the principal periodontal ligament fibres
and supporting alveolar bone occurs within 4–6 months,
but at least 7–8 months is required for the supracrestal fibres to reorganise because of the slow turnover of the free
gingival fibres. Rotational correction is, therefore, liable to
relapse, but this tendency may be reduced by surgical sectioning (pericision) of the supracrestal fibres. Overcorrection of the rotation early in treatment may help to minimise
relapse; however, irrespective of strategy, bonded retention
is required to guarantee alignment.
Where periodontal support is compromised, indefinite
retention will be necessary following orthodontic treatment. When the maxillary labial frenum is suspected in the
aetiology of a diastema (see Section 10.1), a fraenectomy
is recommended. This is best undertaken during space
closure so incisor approximation is aided by scar formation,
although indefinite retention is required.
Soft Tissues
Following appliance therapy, the teeth should be in a position of soft tissue balance. The original mandibular archform should remain unchanged, as markedly altering the
angulation of the lower incisors will promote relapse.
Limited proclination of the lower labial segment may be
stable, however, where the lower incisors have been retroclined by a digit-sucking habit, a lower lip trap or by retroclined upper incisors. In addition, some retroclination of
the lower incisors may be stable in class III correction
where the upper incisors have been proclined and, as a
result, the labiolingual position of the incisors is, in effect,
interchanged.
In class II division 1, a pre-treatment assessment of the
degree of lip incompetence and mechanism of achieving an
anterior oral seal should be made, followed by an estimate
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of the likely post-treatment coverage of the upper incisors
by the lower lip. One-third to one-half of the labial surface of the upper incisors should be covered to give the best
chance of stable overjet correction.
Occlusal Factors
A good buccal segment interdigitation, although unproven,
and an interincisal angulation of about 135° promote stability. In addition, following incisor proclination, a positive
overbite is necessary to prevent relapse.
Facial Growth
Continuing growth in the original pattern that contributed
to the malocclusion is particularly likely to occur posttreatment in class III, open bite and deep bite cases. Some
overcorrection of these incisor relationships is recommended, and retention should be continued until growth is
complete. To prevent facial growth impacting the development of late lower incisor crowding, permanent retention
to the lower labial segment is now widely advocated.
Retention Strategies
There are no specific rules as to the most appropriate retention strategy for each patient; this must be devised on an
individual basis. As it is impossible to predict which cases
will and which will not stay relatively stable, indefinite retention is advisable in all cases or until the patient decides
to cease retainer wear themselves. In advance of treatment,
the clinician must notify the patient of the post-treatment
need for retention, select the most suitable retainer type,
provide information on the manner by which any associated risks may be reduced and plan for their long-term upkeep. The patient must wear and maintain the retainers as
instructed as well as take responsibility for having them
inspected on a regular basis for as long as they are worn.
Selection of a Retention Regime
This requires consideration of the following:
Patient factors: starting malocclusion and growth pattern,
oral health, demands, likes, potential compliance
Occlusal factors: final occlusion and prospects of stability
Retainer factors: ease of care
Need for adjunctive procedures: pericision or interproximal
reduction
Retainers
These may be removable or fixed.
Removable. Aside from a positioner, which is con-
structed to teeth ideally repositioned on a working cast
and is therefore active when fitted initially to encourage
occlusal settling but subsequently worn as a retainer,
these appliances are devoid of active components. The two
most common removable retainers are the Hawley retainer and the clear plastic retainer; the latter looks better,
is cheaper and easier to make, has less impact on speech
and fractures less easily. The Hawley and clear plastic retainer are equally effective at maintaining upper arch
alignment, but the latter is superior in the lower arch.
Night-only wear of either retainer is sufficient.
The Hawley retainer may be modified to incorporate an
acrylated labial bow (useful following alignment of rotated
teeth), an anterior bite plane for maintenance of overbite
correction or an acrylic prosthetic tooth with metal stops
either side of a potential pontic space.
Carbonated beverages must not be consumed with the
either removable retainer in place, but especially with the
clear plastic retainer, as there is a serious rick of demineralisation of the tooth surfaces in prolonged contact with
any residual drinking solution. Furthermore, the clear plastic retainer should not be run under hot water, as it will
distort the fit. Neither should it be cleaned with toothpaste,
as this damages the surface; special cleaning solution
should be used instead. As retention is by engagement in
the undercut below the contact points, where the gingivae
are inflamed, an alternative design may be better to ensure
a good fit.
Fixed. Fixed bonded retainers are particularly indicated
where initially teeth are markedly rotated or severely
displaced, the dentition exhibits generalised spacing, a median diastema, root resorption or is periodontally compromised. Following treatment of cleft of lip and palate, where
treatment has considerably adjusted the intercanine width
or moved the lower incisors appreciably in a lingual or
labial direction or where lip competence is not present after
correction of an increased overjet, fixed retention is also
advisable.
Bonded passively to the inner surface of each of the labial segment teeth, stainless steel multistranded wire is
most frequently used with 0.0195 inch recommended. The
retainer may be bonded directly or indirectly using lightcured composite following acid-etching of the enamel. Alternatively, the retainer may be attached to the canine
teeth only. This, however, runs the risk of the incisors misaligning, but access for oral hygiene is enabled. Other types
of retainer include single strand rectangular titanium,
CAD/CAM nickle titanium (Memotain), flexible chain
(stainless steel or gold) or fibre-reinforced polymer bonded
to each tooth. Regular review is required to confirm periodontal and dental health are maintained and to ensure
the retainer is intact with no induced unwanted tooth
movement, although this is rare.
Fixed retainers make compliance with wear easier for the
patient as they are in situ, whereas removable retainers rely
entirely on patient compliance for wear but facilitate oral
hygiene.
Adjunctive Procedures
By severing the supracrestal fibres above the alveolar bone,
pericision reduces rotational relapse by 30%, is more successful in the maxilla than in the mandible and has no longterm periodontal consequences. Interproximal reduction
removes 0.25 mm of enamel from each proximal surface. It
is useful where teeth need to be reshaped to flatten the contact area which is thought to promote stability.