The following article was written by Dr. Davis for Facets, a magazine for dentists, published by the San Deigo County Dental Society.
Evaluation of patients for what is commonly called a Phase I orthodontic treatment in the mixed dentition has become the standard of care among orthodontic professionals. Indications for this type of treatment include severe dental and skeletal malocclusions, arch length deficiency, and harmful habits. In order to determine if a given patient would benefit from a Phase I treatment, the AAO recommends referral for an orthodontic screening exam by age 7. The decision of whether to provide this early treatment needs to be based on careful case selection and a thorough diagnosis and treatment plan. Patients and parents need to realize that Phase I does not obviate Phase II treatment. Patients who receive treatment in the mixed dentition commonly also require a second phase of treatment in the permanent dentition. Phase I treatment is best considered as a way of laying the groundwork for better results in Phase II.
One of the primary objectives of mixed dentition treatment is to obtain some degree of skeletal correction. The advantage in initiating some sort of treatment at this developmental stage is that an optimum orthopedic influence can be exerted during the rapid rate of bone growth that is occurring. Thus, somewhat of a “window of opportunity” presents itself for treatment directed at correcting the skeletal component of a Class II malocclusion, Class III malocclusion or bilateral crossbite. Fixed or removable appliance therapy, or some combination of both, may be chosen as treatment modalities.
Functional appliances such as Bionators, Frankels, or Twin Block appliances may be a consideration. They work by holding the mandible in a more ideal position in an attempt to orthopedically influence ramal growth in a more favorable direction. They may also increase arch development, expand arch length, and open or close the bite depending on the design. Patient cooperation may pose a problem with these appliances since 24 hour wear is recommended for optimum results.
Fixed appliance therapy in the mixed dentition has the advantage of increased patient compliance because the appliance is bonded and/or cemented in place. When the permanent first molars and anterior incisors are fully erupted, a “2 by 4” appliance can be placed. Bands are placed on the first molars and brackets on the incisors, connected together by an orthodontic wire, bypassing the remaining deciduous teeth. Quad helix or rapid palatal expanders can be cemented to correct posterior crossbites.
Extraoral appliances can be utilized to correct anterior-posterior discrepancies. For maxillary retraction cervical-pull headgear is available. However, for patients with an open bite tendency, high-pull headgear may be more appropriate. For correction of maxillary retrusion, forward-pull headgear can be used to achieve maxillary protraction.
Removable biteplates can be made to correct anterior deep bites or crossbites and can be combined with fixed appliance therapy. For example, a patient with maxillary protrusion and a deep anterior overbite can be treated with a maxillary anterior biteplate, a “2 by 4” appliance, and a cervical-pull headgear. The patient is requested to wear the headgear 14-16 hours per day, so compliance may be may be better than with the 24 hour functional appliance routine.
Issues of arch length deficiency can be addressed through some sort of expansion protocol or, in severe cases, a treatment involving serial extraction. Fixed or removable expanders can be used to gain arch length, although patient compliance is better with a fixed expander attached to first molar bands. If the degree of arch length deficiency is too severe, then there may be no other choice other than to proceed with a serial extraction regimen, eventually ending up with the extraction of first bicuspids in the permanent dentition.
Harmful habits, such as thumb sucking and tongue thrust can be successfully treated in the mixed dentition. This may involve a palatal appliance cemented to first molar bands. It can have little prongs to discourage thumb sucking. Or it can be like a little wire fence to hold the tongue back away from the teeth in an attempt to treat a tongue thrust. If these mechanical barriers don’t work, then some type of behavioral treatment involving a myofunctional therapist may be necessary.
Interception of other dental problems is often best timed in the mixed dentition. These include ankylosed deciduous teeth, impacted teeth, ectopic teeth, missing teeth, and supernumerary teeth.
Treatment of cranio-facial anomalies such as cleft palate and suture formation abnormalities may be initiated in the mixed dentition. However, diagnosis and treatment may begin much earlier, usually involving a panel of expert specialists associated with a children’s or university hospital.
In conclusion, many developmental problems can be diagnosed and successfully treated in the mixed dentition. As mentioned above, patients should be screened by age 7 to determine if they would benefit from early treatment or would be better off postponing treatment until the permanent dentition.