This document discusses Class I malocclusions, which involve a normal anteroposterior relationship between the upper and lower jaws but have discrepancies within the arches. Common causes include tooth size-arch size discrepancies leading to crowding or spacing. Treatment depends on factors such as the severity of crowding, presence of other dental issues, and the patient's profile and preferences. For missing teeth, options are to close spaces or open them for prosthetics, considering the skeletal pattern, smile line, and other adjacent teeth. Bimaxillary proclination involves proclined upper and lower incisors, making treatment difficult as both arches need retroclining.

1. Orthodontics
Class I
By Cezar Edward

2. 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.

3. Aetiology
 Skeletal
 Soft tissues
 Dental factors

4. 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.

5. 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

6. 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.

7. Crowding
Crowding 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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;

15. 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.

16. 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.

17. 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.

18. 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

19. Serial extraction
The 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.

20. Autotransplantation
This 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

21. 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

22. 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.

23. 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.

24. 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.

25. Reference