Orthodontics

Class I

By Cezar Edward

Introduction

‘the lower incisor edges occlude with or lie immediately

below the cingulum plateau of the upper central incisors’.

Therefore Class I malocclusions include those where the

anteroposterior occlusal relationship is normal and there is

a discrepancy either within the arches and/or in the

transverse or vertical relationship between the arches.

Aetiology

Skeletal

Soft tissues

Dental factors

Skeletal

Fig. 8.1 (a) Class I incisor relationship on

Class I skeletal pattern; (b) Class I incisor

relationship on a Class II skeletal pattern;

(c) Class I incisor relationship on a Class III

skeletal pattern.

In Class I malocclusions the skeletal pattern is usually Class I, but it can

also be Class II or Class III with the inclination of the incisors compensating

for the underlying skeletal discrepancy ( Fig. 8.1 ), i.e. dento-alveolar

compensation.

Soft tissues

In most Class I cases the soft tissue

environment is favourable (for example

resulting in dento-alveolar compensation)

and is not an aetiological Factor

Muscle tonisity =Normal

Dental factors

Dental factors are the main aetiological infl uences in Class I malocclusions.

The most common are tooth/arch size discrepancies, leading to

crowding or, less frequently, spacing.

Local factors also include displaced or impacted teeth, and anomalies

in the size, number, and form of the teeth, all of which can lead to

a localized malocclusion. However, it is important to remember that

these factors can also be found in association with Class II or Class III

malocclusions.

CrowdingCrowding occurs where there is a discrepancy between the size of the

teeth and the size of the arches. Approximately 60 per cent of Caucasian

children exhibit crowding to some degree.

In a crowded arch loss of a permanent or deciduous tooth will result in the remaining

teeth tilting or drifting into the space created. This tendency is greatest when the

adjacent teeth are erupting

* Spacing in deciduous teeth is indicator of normal permanent teeth

When planning treatment for crowding the following should be

considered:

• the position, presence, and prognosis of remaining permanent teeth

• the degree of crowding which is usually calculated in millimetres per

arch or quadrant

• the patient’s malocclusion and any orthodontic treatment planned,

including anchorage requirements

• the patient’s age and the likelihood of the crowding increasing or

reducing with growth

• the patient’s profile

Most spontaneous improvement occurs in the first 6 months after

the extractions. If alignment is not complete after 1 year, then further

improvement will require active tooth movement with appliances.

Dentists prefer to extract 4th or 5th

Late lower incisor crowding

In most individuals intercanine width increases up to

around 12 to 13 years of age

and this is followed by a very gradual diminution throughout

adult life. The rate of decrease is most noticeable during

the mid to late teens. This reduction in intercanine width

results in an increase of any pre-existing lower labial

crowding,

If pt has diastema it will close with age

Current opinion is that prophylactic removal

of lower third molars to prevent lower labial

segment crowding cannot be justified

Spacing

Generalized spacing is rare and is due to either hypodontia or small teeth

in well-developed arches.

there is usually a tendency for the spaces to re-open unless permanently

retained.

if the teeth are narrower than average, acid-etch composite additions or

porcelain veneers

1 Hypodontia

Mild: one to two teeth missing

Moderate: three to five teeth missing

Severe: more than six teeth missing

Features associated with hypodontia

• Familial tendency

• Association with syndromes (e.g. ectodermal dysplasia)

• Reduced lower facial height and increased overbite

• Small teeth

• Delayed dental development

• Retained deciduous teeth

2 Management of missing upper

incisorsUpper central incisors are rarely congenitally absent. They can be lost

as a result of trauma, or occasionally their extraction may be indicated

because of dilaceration.

Whatever the reason for their absence, there are two treatment options:

• closure of the space (and camouflage the adjacent teeth)

• opening of the space and placement of a fixed or removable prosthesis

Skeletal relationship: if the skeletal pattern is Class III, space closure

in the upper labial segment may compromise the incisor relationship;

conversely, for a Class II division 1 pattern space closure may be

preferable as it will aid overjet reduction.

• Smile line.

• Number and site of missing teeth. Are incisors missing unilateral or

bilaterally?

• Presence of crowding or spacing.

• Colour and form of adjacent teeth: if the permanent canines are much

darker than the incisors and/or particularly caniniform in shape, modifi

cation to make them resemble lateral incisors will be difficult;

Cont;

The inclination of adjacent teeth, as this will infl uence whether it is

easier to open or close the space.

• The desired buccal segment occlusion at the end of treatment; for

example if the lower arch is well aligned and the buccal segment

relationship is Class I, space opening is preferable.

• The patient’s wishes and ability to co-operate with complex treatment:

some patients have defi nite ideas about whether they are willing

to proceed with appliance treatment, and whether they wish to

have the space closed or opened for a prosthetic replacement.

• Long-term maintenance/ replacement of a prosthesis.

Trial (Kesling’s) set-up

To investigate the feasibility of different options a trial set-

up can be carried out using duplicate models. The teeth to

be moved are cut off the model and repositioned in the

desired place using wax

Trial (Kesling’s) set-up.

Space closure

(a) Patient with missing lateral

incisors treated by space closure and

modification of the upper canines. (b) Occlusal

view of same patient to show bonded retainer.

Requirements for the placement of implant to replace missing

upper incisor

• Growth rate slowed to adult levels

• Adequate bone height

• Adequate bone width

• Adequate space between roots of adjacent teeth

• Adequate space for crown between adjacent crowns and occlusally

Serial extractionThe deciduous canines are extracted at the age of 8–9 years to create space for

proper alignment of incisors, followed by extraction of deciduous first molars a year

later so that the eruption of first premolars is accelerated and lastly extraction of the

erupting first premolars to give space for the alignment of permanent canines. In

some cases a modified technique is followed in which the first premolars are

enucleated at the time of extraction of the deciduous first molar.

AutotransplantationThis is the surgical repositioning of a tooth into a surgically created socket

within the same patient. In recent years the success rate of this procedure has

improved in tandem with the understanding of the underlying biology – this is

good as autotransplantation has a number of a dvantages over other methods

of tooth replacement:

• Biological replacement – avoids the need for a prosthesis

• Creates alveolar bone

• Has a natural periodontal membrane and better gingival contour

• Can erupt in synchrony with adjacent teeth

• Can be moved orthodontically once healing complete

• Suitable for growing patient However, there are also disadvantages:

• Only feasible if there is a suitable tooth which is planned for extraction

• Increased burden of care + general anaesthetic required for procedure

• Requires skilled surgical technique

• Transplanted tooth may undergo resorption and/or ankylosis

Criteria for successful

autotransplantation• Root development of tooth to be transplanted – 2 / 3 to 3 / 4

complete

• Sufficient space in arch and occlusally to accommodate transplanted

tooth

• Careful preparation of donor site to ensure good root to bone

adaptation

• Careful surgical technique to avoid damage to root surface of

transplanted tooth

• Transplanted teeth positioned at same level as donor site and

splinted for 7–10 days

Median diastema

Rarely, the fraenal attachment appears to prevent the central incisors from

moving together.

A diastema is a normal physiological stage in the early mixed dentition when

the fraenal attachment passes between the upper central incisors to attach to

the incisive papilla.

In normal development, as the lateral incisors and canines erupt this gap

closes and the fraenal attachment migrates labially to the attached mucosa.

Before eruption of the permanent canines intervention is only

necessary if the diastema is greater than 3 mm and there is a

lack of space for the lateral incisors to erupt. Care is required not

to cause resorption of the incisor roots against the unerupted canines.

After eruption of the permanent canines space closure is usually

straightforward. Fixed appliances are required to achieve uprighting

of the incisors after space closure. Prolonged retention is usually

necessary as diastemas exhibit a great tendency to re-open,

particularly if there is a familial tendency, the upper arch is spaced

or the initial diastema was greater than 2 mm.

If it is thought that the fraenum is a contributory factor, then fraenectomy

should be considered.

Displaced teeth

Reasons

Retention of a deciduous predecessor: extraction of the retained

primary tooth should be carried out as soon as possible provided that

the permanent successor is not displaced.

Secondary to the presence of a supernumerary tooth or teeth ,management

involves extraction of the supernumerary

followed by tooth alignment, usually with fixed appliances. Displacements

due to supernumeraries have a tendency to relapse and prolonged

retention is required.

Abnormal position of the tooth germ

Crowding

Caused by a habit

Secondary to pathology, for example a dentigerous cyst. This is the

rarest cause.

Bimaxillary proclination

As the name suggests, bimaxillary proclination is the term used to

describe occlusions where both the upper and lower incisors are

proclined.

(a) Class I incisor relationship with normal axial

inclination (inter-incisal angle is 137°); (b) Class I

incisor relationship with bimaxillary inclination showing

increased overjet (inter-incisal angle is 107°).

Management is difficult because both

upper and lower incisors need to

be retroclined to reduce the overjet.

Retroclination of the lower labial segment

will encroach on tongue space and

therefore has a high likelihood

of relapse following removal of appliances.

Reference