ORTHODONTIC DIALOGUE Orthodontic Dialogue, Summer 1997 Issue, Dr. Gerald Nelson, Berkeley, CA Orthodontic treatment in the The palatal midline suture closes back, increasing the lower facial mixed dentition at about the age of 13 in girls, height, measured from nose to chin. “I’d like my daughter’s braces 16 in boys. This response is appropriate for the done now so we don’t have to deal The fronto-palatal suture closes at patient who has an average or short with it at age 13.” Orthodontists, around age 2. lower face height, but not appropri- pediatric dentists, and general den- The mandible is a single bone (no ate for the patient with a long lower tists have all heard this before. sutures) after the age of one. face height. Orthodontic clinicians know, how- Growth rates peak for girls at age The retrusive maxilla can be ever, that most patients who receive 13, boys age 15. brought forward if appropriate orthodontic care in the mixed denti- forces are applied to the maxillary tion will need a second phase of dentition. An example of this is the treatment in the permanent denti- use of a fixed expansion device on tion. Whether to render treatment the upper buccal segments, with in the mixed dentition requires hooks to accept elastics from a for- careful case selection and a thorough ward-pull headgear. We know such diagnosis and treatment plan. appliances will slip the maxilla for- The mixed dentition is the ward on its sutures. This is best developmental period after the per- done at an early age, as more sutures manent first molars and incisors are open.9 have erupted, and before the The narrow maxilla is often remaining deciduous teeth are lost. An interesting feature of dental associated with a posterior cross- 10 Phase I treatment is usually done development is the leeway space3 bite (figure 1). You may see the early in this period. The American (extra space under the primary sec- mandible shift out of centric Association of Orthodontists ond molars). The primary second relation laterally toward the cross- recommends all children should see molars are often larger than the bite side. This problem may cause an orthodontist by age 7. A favor- underlying second bicuspids. enamel wear or stress on the TMJ ably developing occlusion at this During the transition to the perma- and facilitate asymmetrical growth. 1 stage has these characteristics : nent dentition, this space is liberat- The treatment is likely to involve ed. This may provide some extra expansion of the maxilla at the The molar relationship is usually space, however, in many patients it suture. Mandibular skeletal prob- end-on (slightly forward of Class I), is lost as the permanent first molars lems are complicated by the fact and typically transforms into a Class drift forward to take up the slack. that the mandible has no sutures. I during the transition from the Growth occurs at the condyle, and mixed to the permanent dentition. Treatment strategies by surface apposition. We do not I Nicely aligned permanent incisors, Mixed dentition treatment know how to make a short often still sporting their mammel- goals often focus on skeletal rather mandible grow significantly more. ons, with rather short clinical than dental correction. To design a Researchers have studied functional crowns, and a 1-3 mm overbite treatment plan, the clinician must appliances and overjet. understand the growth and develop- (activator, bionator, Frankel, Twin- There will often be a small space ment patterns, and the known block), and can demonstrate only either mesial or distal to the primary effects of the chosen treatment 1-2 mm more mandibular growth 11 canines. modality. than control groups. We do not Jaw growth Skeletal problems Jaw growth affects orthodontic Three common skeletal prob- treatment, usually favorably, but some- lems are the protrusive, retrusive, or times unfavorably. When and how very narrow maxilla.4,5 The protru- much growth will occur is completely sive maxilla and dentition can be unpredictable. However, we know some affected by distal forces placed on useful facts about jaw growth in the the upper teeth.6 An example of this 2 mixed dentition : is the use of bonded or banded attachments on the upper molars Between the ages of 5-10 years, and incisors along with a headgear. the inter-canine dimension may If the force levels are about one know if such effects are permanent. increase by 3 mm (on the average). pound per side, and the patient uses We also don’t know how to make a After the age of 10, there are no the appliance 10-12 hours per day, long mandible grow less, or how to width increases. two things will happen. The upper make an asymmetrical mandible The space in the maxillary arch teeth will be moved distally within straighten out. When such problems (from molar to molar, traced the maxilla, and the maxilla will be are severe, the clinician will often through the contact points) increas- shifted distally on its sutures.7,8 With delay treatment until growth is es by an average of 2 mm. The the neckband, the force vector is complete, and consider change in the mandible varies from down as well as back, so the upper surgical/orthodontic correction. a decrease of 2 mm to an increase of molars may also extrude. This can Since the mandible cannot be 4 mm. tip the upper occlusal plane down in widened through sutural expansion, our ability to create space is limited. Another dental condition that the dental alignment can improve There is no research to show that we deserves attention is TMD. dramatically. However, the timing of can expand the mandibular dental Symptoms appear in some patients, the extractions has a potent effect on arch more than 3-4 mm with perma- and can be diagnosed and treated as the amount of spontaneous improve- nent results.12 Therefore, treatment with older patients. ment, so the clinician must be famil- strategies for crowding in the mixed iar with the limits and indications of dentition focus on saving the leeway Anomalies this maneuver.19 In almost every case, space under the deciduous second Cranio-facial anomalies present the serial extraction procedure is fol- molars, mild expansion, or serial some challenging skeletal discrepan- lowed by comprehensive orthodontic extraction of first bicuspid teeth cies. Most patients with facial defor- treatment in the permanent dentition (figure 2). mities (cleft palate, suture formation with fixed appliances. abnormalities) should be supervised Dental problems by a cranio-facial panel of experts. Many dental development prob- These panels are typically associated lems can be headed off in the mixed with a children’s or university hospi- dentition; for example, anterior cross- tal and will include a psychologist, bites (figure 3). In-time removal of a plastic surgeon, oral surgeon, ortho- deciduous tooth could prevent a dontist, speech therapist, etc. crossbite, but once the permanent upper incisor is caught on the lingual The late mixed dentition of the lower incisors, treatment is The transition period when the needed. The anterior crossbite can deciduous molars and canines are cause tissue damage around the exfoliating is often called the late affected lower incisor. mixed dentition. This is the classic Removal of permanent teeth is Another example is the displaced period to place a lower lingual arch less controversial than expansion to lower midline as a result of the early to save extra space under the decidu- provide room because research that loss of a lower deciduous canine. ous second molars.13,14 Some clini- supports expansion of the dental arch Removal of the opposing canine may cians advocate starting comprehensive is lacking.12 cause spontaneous correction of the orthodontic treatment during this Early correction of the Class II midline. Delayed exfoliation can have period. It gives you a head start on maxillary protrusion can be valid in a negative effect as well. The succeda- Class II correction in girls. some cases. We know that very pro- neous tooth may become seriously Normalizing jaw relationship as the trusive teeth increase the risk of trau- teeth erupt may guide them into bet- matic injury. We can usually expect ter occlusion, thus simplifying the better cooperation with headgear treatment. The downside of starting appliances when the patient is in the treatment at this age is extended preteen years. Gender is also an issue. treatment time. With some patients, Many girls’ facial growth is slowing the final eruption of the second down as the permanent teeth erupt. molars may be a couple of years after This limits the clinician’s ability to the late mixed dentition. use growth as an ally to correct the problem. While most clinicians uti- Controversy lize the above principles in deciding The two areas that remain con- whether or not to undertake a Phase displaced or impacted. troversial in the orthodontic literature I treatment, there remains conflicting A panogram will reveal many are treatment of crowding and of evidence that treatment of mild-to- aberrations of dental development, Class II malocclusions in the mixed moderate Class II problems is worth- such as missing teeth, supernumerary dentition. Is there a benefit to early while.15 teeth, impactions and displaced teeth. treatment for these problems? This Ankylosis of primary molars is a question has yet to be fully answered Final thoughts common finding in the mixed denti- by research.15,16,17,18 The AAO recommendation to tion. If the tooth is moderately sub- In the case of crowding, the clin- provide orthodontic screening or merged, leave it to exfoliate on sched- ician should at least supervise the referral by age 7 is well-founded.