Winter 1999 Editorial:

Over the years, I have seen many children in the mixed dentition. Sometimes I have treated them, but many times I have waited. My partner and I have developed a list of premises for treatment in this age group. The list includes insights from our reading of dental literature, but not all of these assertions have a foundation in the literature. The list does not include cranio-facial disorders.

Most practitioners carry such lists in their heads as they consider treatment options for each patient. In our case, we decided to put it on paper. These premises not only guide our treatment decisions, but also help us inform patient families of the expectations and limitations of our recommendations. By the way, the Concise Oxford Dictionary offers the following definition of sine qua non: "An indispensable condition or qualification."

Treating the Mixed Dentition Patient: Considerations

Dento-alveolar change and orthopedics

• Dento-alveolar treatment changes are possible in the mixed dentition
• Sagittal orthopedic treatment changes are possible but limited to 5 mm or less in the maxilla and under 2 mm in the mandible.
• Upper dental protrusion beyond 8 mm is associated with an increased risk of dental injury.
• Class II cases typically have a maxillary dental arch that is too narrow to properly coordinate with the mandibular dental arch when in a Class I relationship.
• Girls’ peak growth velocity averages at 13 years, but many peak much earlier, so it may not be practical to delay headgear correction until the full eruption of the permanent dentition. It is not possible to predict the timing of maximum growth velocity.
• The mandible can be advanced 1-2 mm beyond normal development using bite-jumping appliances in some patients. One must expect to procline the lower incisors. The successful cases cannot be identified in advance of treatment.
• A bionator can have the following effects: Increase lower face height, retract the maxillary dentition on its base, protract the mandibular dentition on its base, and steepen the occlusal plane. These effects vary markedly from patient to patient, and success is not predictable. Case selection criteria include protruded upper dentition, retruded lower dentition, short lower face height, and a low occlusal plane angle.
• The maxilla can be advanced up to 5 mm with protraction mask therapy, but stability is unpredictable. Long term treatment with extended hours of wear may be necessary, ideally under the age of 11. One must expect proclination of the maxillary incisors.
• A splint headgear (maxillary plastic full coverage splint with a facebow imbedded, and attached to an occipital strap 12-plus hours a day) can reduce maxillary dental protrusion, reduce maxillary prognathia, while maintaining upper incisor torque during treatment. The upper molars will tip distally. Stability is variable. Growth pattern will profoundly affect the post-treatment molar relation and overjet.

Crossbites

• Correction of anterior crossbites can prevent enamel damage and soft tissue damage.
• Correction of posterior crossbites with a lateral CO/CR shift can avert enamel damage, TMJ stress, and asymmetrical growth.
• Posterior crossbites detected before the age of six may spontaneously correct, but it is not predictable.

Diastemas/missing teeth

• Stability of the end result is improved if a large diastema is closed before full eruption of the permanent dentition.
• Congenitally missing teeth want for early diagnosis and management. Sometimes early removal of deciduous teeth will induce spontaneous improvements as eruption progresses. (e.g. very early removal of lower deciduous second molar to let the six-year molar drift mesially into the space of a congenitally missing second premolar.)

Crowding/expansion

• Severe incisor crowding affects gingival contour (especially of the papilla) and the thickness of the band of attached gingiva. Such crowding should be relieved before the permanent dentition, if possible, to encourage ideal papilla and gingival formation.
• Serial extraction is valuable is selected cases.
• Correction of severe rotations is likely to be more stable if corrected early, or prevented from happening in the first place.
• Early loss of a deciduous canine on one side will induce a midline shift to the side of the tooth loss. Removing the opposite canine will typically correct the midline shift.
• Early removal of deciduous canines has not been shown to cause loss of archlength or induce overbite.
• Early extraction of selected primary teeth can avert impaction of the succedaneous teeth or shift the midline.
• Ectopic eruption of canines into the vestibule should be prevented, because the gingival tissue may form with inadequate attached gingiva.
• Clinically relevant orthopedic expansion of the maxilla is possible but prone to significant relapse, so overtreatment is prudent.
• Mandibular dental expansion of 2-3mm (beyond reserving E space) is possible, but long-term stability is not predictable. Case selection guidelines include profile considerations, lower incisor protrusive angle and relation to mandibular osseous anatomy, and lower incisor gingival quality.
• Ectopic eruption of a first molar into the root of a deciduous second molar can be corrected in many cases with interdental separators, and the primary molar retained.

Habits

• Digital habits can cause changes in alveolar dental and skeletal morphology. If the habit stops before the age of six, the changes may be self-correcting. After the age of six, spontaneous correction is less likely.
• Digital sucking typically narrows the maxilla, protrudes the maxillary anterior teeth, and tips the mandibular anterior teeth lingually.
• If the digital habit patient is given a maxillary removable appliance (24 hours), the habit will stop within one week in 90% of cases. The appliance should be used for at least 10 months after the habit stops to make sure it will not return.
• Anterior open bites spontaneously correct before the age of 10 in 75% of open bite cases.

Economics

• The Phase I patient family should expect a second phase of treatment in the permanent dentition.
• Two-phase treatment is more expensive to the patient family than one-phase treatment and will require more appointment time from the patient family.
• Mixed dentition treatment is less remunerative (at least in our practice) to the orthodontist than permanent dentition treatment (measured in dollars per appointment).

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