CONTINUING EDUCATION Congenitally missing mandibular premolars — treatment options for space closure Dr. Mark W. McDonough discusses recognition and treatment planning for congenitally missing second premolars Introduction The orthodontist often identifies missing Educational aims and objectives second premolars in the mixed dentition This article aims to direct the orthodontist through a diagnostic sequence of recognizing and treatment planning for congenitally missing second premolars. using routine panoramic radiographs. The early decisions that orthodontists make for Expected outcomes the congenitally missing teeth often have an Orthodontic Practice US subscribers can answer the CE questions on page 22 to impact on dental health for the rest of their earn 2 hours of CE from reading this article. Correctly answering the questions will demonstrate the reader can: patient’s life. Therefore, this finding should • Realize some diagnoses of missing mandibular premolars. result in a comprehensive set of diagnostic • Realize some treatment options for mandibular premolars. records in order to evaluate the patient in all three planes of space and establish a • Identify critical factors to consider to avoid complications. problem list and treatment alternatives. • Identify three different methods of space closure from the case studies presented. These records often need to be shared with the restorative dentist and other specialists in order to consider all viable alternatives and formulate a proper treatment plan. General concepts about missing more complex problem is if the patient would The clinician must make the proper deci- mandibular premolars not normally require extractions. Since the sion at the appropriate time regarding the Diagnosis of missing mandibular premolars introduction of temporary anchorage devices maintenance of the primary molar, the pros- Congenitally missing mandibular second (TADs), the unilateral space closure without thetic replacement of the missing second premolars are the second-most frequent other extractions has become more popular premolar, or the closure of the space from type of agenesis, after the third molar, with since the midline can be maintained while the the missing premolar. an incidence of 2.5% to 5% of the population space is closed. If the primary second molar The objectives of this review are to in the United States and Europe.1 Agenesis is to be maintained, the goal is to maintain direct the orthodontist through a diagnostic of the second premolars can usually be reli- the tooth with the alveolar bone for possible sequence of recognizing and treatment plan- ably diagnosed around age 9 on a panorex, future implant and prosthetic reconstruction. ning for congenitally missing second premo- but there have been reports in the literature lars. The emphasis of this article is the most of slow development of this tooth. Alexander- Critical factors to consider appropriate time and cost-effective way for Abt2 reported a case of a 12-year-old female 1. Dental and skeletal age of the patient closing the space for the missing premolar. whose panoramic radiographs revealed Treatment to close the space before or Three different methods of space closure will apparent agenesis of tooth No. 20. The prog- close to the peak of the pubertal growth be highlighted. ress panorex 13 months later revealed initial spurt will be more successful. Since crown formation of tooth No. 20. Unilateral definitive diagnosis of agenesis of the Mark W. McDonough, DMD, has a Bachelor of Science in Biology agenesis has been reported to consist in second premolar cannot be made until from Fordham University in New York, New York, and a Doctorate up to 60% of the agenesis cases.3 Missing the patient is 9 years old, the ques- of Dental Medicine from the University of Pennsylvania in Philadelphia. He completed his General Practice Residency at second premolars are more common in the tion arises, When is it too late to close Lenox Hill Hospital in New York and Postgraduate Orthodontic mandible than the maxilla. the space? It has been shown that if Training at Albert Einstein Medical Center in Philadelphia. He the primary molar is extracted prior to is a board-certified orthodontist with the American Board of Orthodontics (ABO) and has earned the esteemed designation Treatment options age 11, and the second molar has not of Diplomate of the ABO. He has been a clinical instructor at Upon the diagnosis of agenesis, two erupted, about 80% of the space will be Albert Einstein Medical Center in Philadelphia since 1995. He is main options are usually considered: extrac- closed through “driftodontics” within 4 also an active member of the following professional societies: Greater Philadelphia Society of Orthodontists (President 2016– tion of the primary second molar or its main- years, leaving a residual space of about 2017), Mercer Dental Society (President 2002–2003), Society tenance in the arch. If the primary second 2 mm.4 of Educators for the American Association of Orthodontists molar is extracted, the goal is usually to mesi- 2. Gender Female facial growth is gener- (2013–present), American Association of Orthodontists, Middle Atlantic Society of Orthodontists, Pennsylvania Association of alize the first permanent molar in conjunc- ally complete around age 17 and males Orthodontists, New Jersey Association of Orthodontists, American tion with the orthodontic treatment. If the not until around age 21.5 It is important Dental Association, and the New Jersey Dental Association. Dr. other three premolars can be extracted as to note that these ages are averages, McDonough also has authored articles and is on the educational advisory board of Orthodontic Practice US. well due to crowding or procumbent inci- and it is always best to confirm cessa- sors, the agenesis is a minor finding. The tion of vertical facial growth with annual Volume 8 Number 4 Orthodontic practice 23 CONTINUING EDUCATION serial cephalometric radiographs prior to there will be a more favorable bone for quadrant, which may be found in 48% of placement of implants. This is a critical the implant.6 This may result in longer patients.9 Usually, third molars have their role the orthodontist can provide to the orthodontic treatment time but a better initial calcification at age 9 and would be interdisciplinary team since orthodontists final result for the implant. considered missing only after age 14. are best able to evaluate cephalometric 5. Maintaining the primary second This also creates a treatment planning radiographs. These age differences molar Primary molars are shorter than dilemma in the mandibular arch since between male and female patients make permanent molar crowns, and therefore the decision to close the space may be prosthetic replacement more favorable in a marginal ridge discrepancy is to be made prior to definitive knowledge of the females since it can often be completed expected and is not an automatic indi- presence of the third molar. If the space prior to leaving for college or entering cation of ankylosis. If the primary molars is closed in the mandibular arch, the the workforce. For male patients who have healthy roots with no carious lesions maxillary second molar may not have a are away at college, it is often difficult to or large restorations and are not anky- vertical stop if the mandibular third molar coordinate implant placement and pros- losed, the decision may be made to is congenitally missing or does not erupt. thetic treatment. Many times, finances maintain these teeth into adulthood — 7. The overall malocclusion In general, are limited upon completion of college, many case reports of primary posterior patients with minimal crowding, deep and the patients are often no longer teeth surviving until the patient attains 40 overbites, retrusive incisors, decreased covered by their parents’ insurance, to 60 years of age.8 However, there is a lower facial heights, or flat mandib- further limiting the ability to have costly lack of long-term studies for the survival ular planes may be best managed by prosthetic replacement. rate of retained primary molars from nonextraction. These patients should 3. Ankylosis of the primary second molar adolescence to adulthood. Maintaining maintain the primary molars for as long Percussion of the primary second molar the primary molar can create an antero- as possible. Patients with significant is often used to diagnose ankylosis, but posterior arch-length discrepancy since crowding, dental protrusion, minimal it can be inaccurate. The most reliable the primary molars are 2 mm-3 mm larger overbites or open bites, and increased method to diagnose primary molar anky- than their permanent successor and facial heights often benefit from extrac- losis is to evaluate the interproximal bone results in an “end-on” molar relationship tion and space closure. levels on a bitewing radiograph. Flat bone when the canines are Class I. This has 8. Cost considerations Orthodontics to levels between the primary molar and the led to some clinicians to slenderize the close an edentulous premolar space is adjacent permanent teeth indicate the primary molar mesially and distally. The more cost-effective and is often more primary molar is erupting evenly with key is to remove sufficient tooth structure periodontally sound. When the space is the adjacent teeth. If there is an oblique to create space but not enough to cause closed, the patient incurs only the cost of angle, the primary tooth is ankylosed.6 pulpal necrosis. A bitewing radiograph is orthodontic treatment. When the space 4. The condition of the primary second useful to determine the width of the pulp is maintained, the patient incurs the cost molar Root resorption of the primary horns. In general, 2 mm per side can be of orthodontic treatment, possible pre- second molar or large restorations and/ removed resulting in a 7 mm-8mm-wide prosthetic bone grafting, implant place- or decay often lead to the decision to tooth. It is recommended that light-cured ment, and prosthetic restoration costs.