Interceptive Maxillary Expansion to Relief Anterior Crowding in the Mixed Dentition

The study will be conducted on consecutively included subjects referred to the centers and then randomized into either an experimental group or a control group.

To be able to evaluate the amount of anterior crowding before the lateral incisors have erupted, low-dose Cone Beam Computed Tomography-scans are used to measure the width of the unerupted laterals. The anterior crowding is calculated by comparing the width of the laterals with measurements of the distance between the mesial surfaces of the deciduous upper canines on study casts. The eligible subjects are then randomized to either experimental och control group.

The subjects in the experimental group will be treated with a maxillary expansion appliance with bands on the second deciduous molars and arms to the deciduous canines. A small preparation on the palatal surface of the deciduous canines is performed to facilitate bonding of the arms. The screw gives a expansion of 0,20 millimeter per activation. The arms are bonded to the deciduous canines with light curing composite and the bands are cemented on the etched second deciduous molar with glassionomer cement.

Then the subject and the parents are instructed to activate the appliance once a day (1/4 turn) for 2 weeks and thereafter every second day until adequate space for the lateral incisors is obtained and the first permanent molars are approaching scissor-bite.

The expansion can be paused for 7-8 months after 25-30 activations if the lateral incisors are not yet erupted and the permanent molars are going in scissor-bite to allow for their spontaneous correction. The expansion is then continued until adequate space for the lateral permanent incisors is achieved.

During the expansion the subjects will be asked to complete a questionnaire on pain and discomfort.

When enough space is available for the crowding to be resolved the expander is blocked with light curing composite or a stainless steel ligature wire. The appliances is kept as a retainer until the laterals are fully erupted.

After the follow-up period the treatment effects will be evaluated by measuring of the study models. All measurements will be made digitally with the 3Shape OrthoAnalyzer Differences in palatal volume, transversal width of the maxillary and mandibular dentition between the start of the trial and at the end of the follow-up period will be measured. The questionnaires regarding pain and discomfort and PIDAQ will be analyzed.

The last part of the study is to perform a cost-effectiveness analysis for early treatment with maxillary expansion and a cost-effectiveness analysis for treatment in the permanent dentition and then compare them. The direct cost for both experiment and control group will be calculated by adding up material cost and chair-time cost. The indirect cost is defined as the cost for the parents regarding loss of income for the duration of the visits and the trips to and from the clinic. Due to the fact that there are substantial differences in traveling time and income for parents, the indirect costs of treatment will not be taken into account because the randomization will equalize the effect of the differences.

Inclusion criteria

• Healthy subjects without sucking habits
• Permanent maxillary central incisors and first permanent molars fully erupted. DS1M1.
• No severe crowding or protrusion in the lower arch considering the Leeway space and normal development of the arch.
• Permanent first molar in normal transversal relation.
• Crowding of the maxillary incisors with the lateral incisor just erupting ectopically or not yet emerged through the gingiva.
• Crowding greater than or equal to 6 millimeters between the upper deciduous canines.

Exclusion criteria

• Skeletal asymmetries, anomalies and syndromes.
• Previous orthodontic treatment