Orthodontic diagnosis and treatment in the mixed dentition
John Fricker, Om P Kharbanda and Julia Dando
The primary aim of orthodontic assessment in a growing child is to differentiate between a developing normal occlusion and a potential malocclusion, including any abnormal growth of the face and function of the stomatognathic system. It is essential to have a sound understanding of facial growth and dental development, and the ability to recognize the rate and direction of facial and dental growth. Many situations of apparent malocclusion in the mixed dentition are actually manifestation of the normal process of dental and facial development. Minor incisor irregularities, spacing and ectopic eruption of teeth, which may show up during the mixed dentition, could self-correct with growth and development.
Correction of dental arch irregularities, occlusal and jaw relation abnormalities and elimination of functional interferences may be classified as preventive or interceptive. The term ‘preventive orthodontics’ implies steps undertaken for elimination of factors that may lead to malocclusion in an otherwise normally developing dentition.
‘Interceptive orthodontics’ implies that corrective measures may be necessary to intercept a potential irregularity from progressing into a more severe malocclusion. Neither the appliances used nor the treatment itself should interfere with the often rapid changes in eruption of permanent teeth and the dynamic nature of occlusal adjustment. It is important to understand that even when such procedures are carried out, a majority of these children will go on to require some further treatment in the permanent dentition.
Orthodontic assessment of a child
An orthodontic assessment in common with other specialties, must include a good history, a thorough clinical examination and any relevant investigations. The information gathered leads to a diagnosis, which in turn allows treatment planning. This topic is covered in detail in Chapter 1. Additional points relevant to aid orthodontic diagnosis, however, will now be discussed.
The child should be assessed for skeletal and dental problems and abnormalities of functions of the stomatognathic system. Clinical assessment is performed in all the three dimensions of space, i.e. vertical, anteroposterior and transverse.
This describes the anteroposterior relationship between the maxilla and mandible relative to the cranial base:
Dental relationships are recorded with the teeth in occlusion. It describes the anteroposterior relationship of the upper and lower molars according to Angle’s classification and the anteroposterior incisor relationship according to the British Standards Institute classification (1983). Angle’s classification of malocclusion is based on the relationship of the upper and lower first permanent molars.
Molar relationship (Figure 14.1)
• Class II molar relationship implies disto-occlusion of the lower first permanent molar with the upper first permanent molar and is a reflection of a retrognathic skeletal pattern with increased over jet.
Figure 14.1 Orthodontic molar relationships: (A) Class I – normal occlusion. The mesio-buccal cusp of the upper first permanent molar occludes between the mesial and distal cusps of the lower first permanent molar. (B) Class II – disto-occlusion. The lower first permanent molar is distal to the upper tooth. (C) Class III – mesio-occlusion. The lower first permanent molar is mesial to the upper molar.
Incisor relationship (Figure 14.2)
Vertical assessment includes normal or abnormal vertical overlap of the incisors, i.e. normal, deep or open bite. Transverse assessment should include any cross-bite or scissors-bite of the buccal segments of the dental arches.
Figure 14.2 Orthodontic incisor relationships. (A) Class I – normal occlusion. The incisors. (B) Class II Division 1: The incisors are protruded and there is an excessive overjet. Class II Division 2: The upper central incisors are retroclined, while the upper lateral incisors are protruded. Furthermore, there is an excessive overbite. (C) Class III: An anterior cross-bite is present.
Complicating factors in any malocclusion
Intra-arch problems (Figure 14.3)
The physical status of the child should be included here, and if relevant, height and weight should be recorded on a standard growth chart. It is essential to determine if the face of the child is also growing normally. The face is examined with the child sitting upright. This is important because the mandibular rest position will change, if lying back.
• Symmetry – initial assessment from the front. Looking at the child from above and behind will confirm asymmetry. It is important to look at the position of the chin at rest and in occlusion. A deviation would suggest a functional shift is occurring rather than a true asymmetry.
• Facial proportions – viewed from the front, the face can be divided vertically into equal thirds. The height of the midface (supraorbital ridge to base of nose) should, therefore, equal that of the lower face (base of nose to chin). However, it may be increased or decreased.
Lateral view (Figure 14.4)
Figure 14.4 Evaluation of facial profile. (A) Child with retrognathic chin and convex face suggestive of skeletal – Class II pattern. (B) Normally growing chin – Class I pattern. (C) Prominent chin with concave profile, suggestive of Class III skeletal pattern.
A record should be made of:
It is important to identify any deviation of the mandible during opening and closing into full intercuspal occlusion. Often the underlying cause is interference from an erupting tooth leading to either functional forward or lateral shift that demands early treatment to restore the balance in the temporomandibular joint (TMJ).
These are determined by the findings at examination.
• Panoramic radiograph – will give an overall picture of the developing dentition and jaws. It is the standard radiograph used in orthodontic assessment. Additional films may be needed to allow a more detailed analysis of suspected pathology.
• Lateral cephalogram – this is useful to assess skeletal discrepancy when treatment is to be started. Tracing of the film and subsequent cephalometric analysis will aid diagnosis and treatment planning. This film can also be used as a baseline to monitor future growth.
• 3-dimensional CT may be required for evaluation of exact location of impacted or supernumerary teeth that are otherwise difficult to locate with standard 2D radiographs. Cone beam CT (CBCT) is becoming increasingly popular, since radiation doses are much less than CT (see Chapter 11).
Evaluation of crowding
In the permanent dentition, it is easy to assess the amount of crowding by taking measurements directly from study models. Treatment will depend on the severity of the problem and may involve arch lengthening or extractions. In the mixed dentition, however, a prediction of future crowding is necessary.
Mixed dentition analysis
The purpose of a mixed dentition analysis is to determine the space available in the dental arch for the permanent successors to erupt. To complete this analysis, it is necessary to first record the arch length and the mesiodistal widths of the mandibular permanent incisors.
Measurement of arch length
The conventional way to determine arch length is to measure directly from a set of study casts. Soft brass wire can be adapted from the mesial of the first permanent molar to follow the arch form around to the mesial of the contralateral first molar. The wire should be shaped to the ideal arch form and not follow any teeth out of alignment. Once the arch length has been determined, it is then necessary to estimate the space required for the permanent successors. Mesiodistal dimensions of erupted teeth up to second premolars can be obtained directly from a study cast. Unerupted teeth can be measured by one of two methods:
Both methods are based on the high correlation between the crown measurements of the permanent mandibular incisors and the combined sizes of two premolars and permanent canines. Thus, it is possible to forecast the amount of space required for the unerupted teeth and to plan interceptive and/or preventive space management requirements.
The difference in values between arch length and tooth size will indicate the amount of crowding or spacing present.
At the end of diagnosis, a clinician should have gathered the following information:
Crowding and space management in the mixed dentition
Space management can minimize the development of crowding in the permanent dentition. It essentially involves:
The best space maintenance treatment is the preservation of the primary molars until natural exfoliation. Although dental health education and improved caries prevention have lowered the number of children who develop malocclusion because of premature loss of primary teeth, it is still one of the most common controllable causes of malocclusion.
When a primary second molar is lost prematurely due to caries or to the ectopic eruption of the first permanent molar, the first permanent molar will drift mesially. This is most pronounced in the maxilla with a more rapid shift of the molar and causing a Class II malocclusion. The earlier the loss of the second primary molar and the less the root development of the permanent molar, the greater will be the amount of bodily mesial shift of the permanent molar.
Factors to consider for placement of space maintainers
Placement of a space maintainer requires care of the appliance and oral hygiene maintenance. A child with poor oral hygiene and high caries risk is not the ideal case for such appliance therapy. Before a decision is made to provide a space maintainer, it is often essential to critically evaluate its merits, the need and the benefit it would provide to the development of normal occlusion.
• Whenever a primary second molar is lost prematurely, whether before or after the eruption of the first permanent molar, there will be some loss of arch length caused by the mesial drift of the permanent molar.
Types of space maintainer
Removable space maintainers have shortcomings similar to all removable appliances:
A removable space maintainer that is only worn at night is often sufficient to hold space and prevent the mesial drift of permanent molars. Night-only wearing of the appliance also reduces the risk of loss or breakage by the patient. The appliance should be washed and inserted in place before going to bed, then removed, washed and placed in a safe place when not worn. Hawley’s appliance is a typical example.
Fixed space maintainers (Figure 14.6)
Figure 14.6 (A) A band and loop space maintainer. The placement of a space maintainer must not compromise the permanent tooth. Bands should be cemented with a luting glass ionomer as a protection against caries and the appliance reviewed regularly. As the premolar erupts, the appliance is removed when there is interference with normal emergence. (B) A distal shoe space maintainer is placed following early loss of the second primary molar prior to the eruption of the first permanent molar. It prevents mesial migration of the permanent tooth.
Utilization of the leeway space
Within an arch, space may need to be regained when migration of permanent teeth has already occurred following the loss of adjacent deciduous teeth (Figure 14.7). Furthermore, space maintenance would then be needed until the permanent successor erupted. In the maxilla, this would intercept a developing Class II, dental relationship secondary to mesial migration and rotation of the first permanent molar. In the mandible, it could prevent a mild dental Class III relationship by uprighting tipped lower first permanent molars. In individuals with a developing skeletal discrepancy, the dental correction would have no effect on the underlying skeletal problem.
Figure 14.7 The failure to place space maintainers following bilateral loss of primary second molars has resulted in forward movement of the first permanent molars thereby reducing the available space for the second premolars. (A) More space tends to be lost in the upper arch than in the lower arch following loss of the second primary molars (B).
In general, tooth movement is slower in cases with severe horizontal growth pattern (low FMPA). Conversely, it is rapid in vertical growers, and space loss can occur very quickly. Early fitting of a space maintainer will prevent space loss. If space is to be regained, it is essential that the mechanics should not extrude the teeth at all.
Radiographs and study models are essential aids in assessing space needs. It is important to note whether teeth have moved bodily or have tipped into the space. Tipping can be easier to resolve than bodily tooth movement. Radiographic examination should also locate the permanent second molars and establish space available for distalization of the first permanent molars.
Appliances used to regain space
An ACCO appliance (Figure 14.8) is comprised of a palatal acrylic plate with an anterior bite platform to disclude the posterior teeth, allowing the first permanent molar to move freely. Retention is obtained via Adams clasps on the first premolars or deciduous molars and a labial bow across the permanent incisors. The bow should be supported with a band of acrylic across the labial surfaces of the incisors to increase the anchorage for the finger springs against the mesial surface of the molars to be distalized. These are most successful in the maxillary arch, where there is a dental and skeletal Class I pattern with normal vertical proportions and the regaining of space is by way of uprighting the first permanent molar.
Figure 14.8 (A–C) The ACCO appliance is used for uprighting maxillary permanent molars to regain space. To maximize anchorage, acrylic is flowed over the labial arch wire and this limits the proclination of incisors as the molars are distalized.
Timed extraction of teeth to resolve intra-arch crowding
The total amount of arch length deficiency is the key to planning of timed extractions. For this to be beneficial, a cephalometric analysis should show the child to be growing within a normal pattern and that all the permanent teeth are present radiographically and in the normal order of eruption.
Extraction of deciduous canines
• Premature loss of a primary canine as the permanent lateral incisor erupts will result in a midline shift to the same side. Extraction of the contralateral deciduous canine will help prevent a shift occurring.
• As the permanent canines erupt, it may be necessary to reduce some part of crown at the mesial of the primary first molars and then, as the first premolars erupt, reduce the mesial of the second primary molars.
The purpose of serial extraction is to encourage the early eruption of the first premolars ahead of the permanent canines and should only be considered where there is an arch discrepancy of >4 mm. Serial extraction is usually limited to the upper arch as serial extractions in the lower arch usually results in lingual collapse of the lower anterior segment.
Serial extraction should not be performed in the following circumstances: