Resolution of crowding – diagnostic and treatment considerations

When considering whether or not to extract teeth, one question that needs to be asked is how will the patient’s hard tissue support be affected? For example, a hard tissue consideration might come into play when extracting either a partially erupted tooth, a buccally displaced ectopically erupted tooth, a tooth that is ankylosed, or excessive expansion of dental units anteriorly and/or laterally. Each of these clinical situations carries the consideration that the supporting alveolar bone may be compromised as a result of the procedure embarked upon. In many cases there may not be another viable treatment alternative but in those cases where choosing a different extraction pattern, changing the timing of certain aspects of treatment, or deciding not to position teeth off their supporting alveolar process is possible, those alternatives should be considered.

The same considerations apply to the supporting soft tissues. Both extraction and non-extraction therapy have the potential to affect the dentoalveolar soft tissue support. Soft tissue periodontal support, particularly in those patients whose biotype is thin or weak, may be acutely susceptible to iatrogenic compromise if taxed beyond their ability to positively withstand or respond to the treatment rendered.

Ultimately, the following considerations must be evaluated; (1) the esthetics associated with placing proclined versus upright incisors in the esthetic zone; (2) whether teeth have been placed in such a position as to jeopardize their long-term potential for relative stability due to an imbalance in the dynamic equilibrium of that patient; (3) whether or not the final positions of the teeth are such that their interdental relationships will adversely affect the functionality of the occlusal scheme; and (3) whether or not the positions of the teeth will contribute to periodontal compromise in any way. All of these “potential negative sequalae” must be pitted against the “value” of maintaining a full complement of teeth along with any “soft costs” related to extraction therapy such as temporal and financial considerations, or the risks and discomforts associated with exodontia.

Another consideration concerns the patient’s ability to cooperate with the treatment plan chosen. Today we have the ability to employ both intra and inter arch mechanics that can either necessitate the patient’s cooperation; or, in the alternative, be independent of patient participation save for showing up for their appointments and maintaining minimally acceptable oral hygiene practices. Once one is engaged in extraction therapy the question always exists as to whether the extraction of teeth in and of itself has provided a benefit to the patient; or, whether the practitioner, because teeth were extracted, has placed the patient in a worse position than before teeth were extracted? If cooperation will be needed, and if after consultation with the patient/parent it can be established that mechanotherpeutic cooperation or adequate home care will not be acceptable, one should question the decision to remove teeth; as it is somewhat more problematic to discontinue treatment or terminated the doctor patient relationship should the clinical situation dictate such action.

Another question to ask is whether or not any existing dental units have a poor or guarded prognosis? Any tooth is amenable for extraction under the appropriate set of clinical circumstances. This point will be discussed later. However, the consideration that needs to be addressed at this point in time is whether or not it is prudent to extract a tooth that has a poor prognosis or is potentially compromised as opposed to one that comports with more traditional extractions schemes. For example, an endodontically retreated second premolar with a continuously non-resolving periapical lesion should be considered for extraction as opposed to the desired first premolar. The question then becomes whether or not the practitioner has the clinical expertise to engage in an atypical or asymmetric extraction pattern as opposed to a typical symmetrical extraction pattern and if not, whether to change to an all second premolar extraction pattern? The potential for implant site development also needs to be considered when faced with a dental unit that has a poor or guarded prognosis as keeping the site viable for a future implant may once again necessitate changing the extraction scheme to one that was not originally considered.

Arch development is a somewhat controversial concept in clinical orthodontics. It is generally accepted that expanding the mandibular intercanine width, without concomitant long-term fixed retention, generally carries a guarded prognosis regarding stability and may also result in periodontal compromise. In addition, the same concerns attach to excessively flaring the lower anterior teeth. Maxillary expansion in order to facilitate lateral uprighting of the mandibular dentition may provide adequate space to relieve mandibular crowding; however, it too may result in some degree of periodontal compromise and instability as well as reducing the functionality of the Curve of Wilson. ^, Finally, it must be remembered that lower molar uprighting may be accomplished either posteriorly or laterally. If uprighting posteriorly, the following questions must be addressed. First, is there sufficient freeway space? Second, will any resulting clockwise mandibular rotation result in accentuating the height of the lower facial third? Next, will an open bite result from the uprighting? Finally, if uprighting laterally, is there sufficient transverse maxillary arch width to accommodate the expansion?

Resolving inter-arch discrepancies – Diagnostic and treatment considerations

Changing the size or shape of individual dental units is one useful method of resolving both inter and intra arch discrepancies that usually result from morphological and anatomical deviations in tooth size and shape. Interproximal reduction is an often utilized methodology to resolve minor to moderate amounts of crowding (up to 8 mm). ^, However, before undertaking any type of irreversible procedure, such as selective enamelplasty, practitioners should first address the clinical considerations associated with such procedures. When considering reproximation in either arch, to resolve lower anterior crowding for example, if there is no inter arch tooth size discrepancy initially, what will the resulting occlusion be after removing tooth structure in just one arch? Secondly, if reproximation is performed, will the health of the patient’s hard or soft tissues be compromised in any manner? Finally, reproximation to resolve crowding should generally not be performed if there is a possibility of requiring the extraction of dental units later on in treatment to address space requirements as the reproximation performed may now have created an inter and/or intra tooth size arch length discrepancy where none previously existed.

Inter arch mechanics is another means of addressing inter-arch occlusal discrepancies. Inter-arch mechanics effect the dentoalveolar structures in a number of different ways. For example, assume that the elastic traction extends from a mandibular first molar in one arch to the archwire in-between the lateral and the canine in the opposing arch; as opposed to being directly attached to the canine in the opposing arch. 4 premolars have been extracted, and, we are utilizing Cl II mechanics. It is well known that there is both a horizontal as well as a vertical component associated with Cl II elastic usage. Therefore, there is an extrusive component to the lower molar and an extrusive component to the anterior portion of the upper arch. The degree of clinical significance of these force components depends on the degree of angulation of the vertical vector and the amount of force being utilized. In other words, does the elastic run from the lower first or the lower second molar; or, is a “short Cl II” running off of the premolar? As one moves anteriorly, there is a greater extrusive effect on the lower “anchor’ tooth. There is a corresponding vertical component to the anterior portion of the upper arch that has the potential to cant the occlusal plane inferiorly when viewed from the posterior to the anterior. Extraction therapy may have the potential to negate some of the vertical component in those cases where the posterior teeth are being brought anteriorly into the extraction site. ^,

There is also an effect on the maxillary and mandibular teeth. Depending upon the wire construction relative to the use of, or absence of, molar stops, the maxillary anterior teeth may retrocline and the mandibular anterior teeth may procline in response to the horizontal component of Class II elastics. The mandibular posterior teeth will have a tendency to move in an anterior direction undergoing either tipping, bodily movement, and/or mesial rotation, depending upon the use of, or lack of various gabling techniques in the archwire. These resulting effects can be accentuated during closure of premolar extraction spaces.

One must be cognizant of the potential for periodontal effects secondary to any mandibular dental proclination that may result from using inter-arch elastic traction if treatment is undertaken on a non-extraction basis. Premolar extraction therapy provides the potential to offset labialization of the lower anterior teeth depending upon the intra-arch mechanics used.

Finally, there is the effect on the mandible itself. Being a movable bone subject to positional change, the mandible can respond in a number of ways. Depending upon mandibular anatomy, inter arch occlusal relationships, musculature, amount of elastic force used, and the resulting intra oral force vectors, mandibular postural changes can be directionally expected; however, the amount of change cannot be accurately predicted. These force vectors can be influenced by the presence or absence of specific premolar teeth.

In summary, if premolar extraction spaces have been created, one must be concerned with the potential overall effects regarding the patient’s skeletal, hard and/or soft tissues, occlusal relationships, and function. One more concern relates to those patients with fragile TM joints. Regardless of whether or not premolar extractions have been performed, should temporomandibular joint symptoms arise it may be wise to evaluate the use of inter-arch mechanics to assess whether the joint disturbance might be related, or not, in some way to their use.

Molar distalization mechanics using any number of extraoral or intraoral appliances is another means of resolving inter-arch discrepancies. The decision to employ any of these mechanotherpeutic treatment modalities may also influence one’s decision on whether or not to extract teeth. Studies by Sfondrini et al., Baek et al., and Singh et al. have addressed many of the following considerations regarding the use of maxillary distalization mechanics using a variety of appliances. Some specific considerations looked at were, what was the effect on the patient’s skeletal, dental, and/or occlusal relationships? If the molar is successfully distalized, will there be a reciprocal side effect of opening the vertical dimension and/or anterior anchorage loss depending on the mechanotherapy employed? Will the molars be excessively tipped as opposed to being moved bodily? Will the occlusal plane become canted? If successful, will there be an effect on the esthetic zone relating to the size of black triangles in the buccal corridors versus any effect that may be associated with extraction therapy? Will employing these mechanics have a negative effect on other hard tissues; for example, by impacting more posteriorly positioned molars? Will utilizing these mechanics as opposed to extraction mechanics have a negative effect on any soft tissues (will they result in palatal irritation, epuli of the buccal mucosa or cheek, etc.)? Finally, will the facial balance be negatively impacted by increasing the lower facial third resulting from a downward and backward mandibular rotation? If any of these questions are answered in the affirmative, some consideration to extraction therapy may be warranted. Sfondrini summed up the issue beautifully by noting:

Conventional molar distalization is not always indicated for Class II correction. It is contraindicated in open-bite patients and in the presence of a protrusive profile. In open-bite patients molar distalization would determine a clockwise mandibular rotation, thus increasing the lower face height and worsening the facial appearance. In the case of protrusive facial profile the anterior anchorage loss, which occurs during molar distalization, would worsen the inclination of the front teeth and, consequently, the profile itself. Molar distalization is recommended for the correction of Class II malocclusions in deep-bite patients and in the presence of a concave or normal facial profile. In borderline patients, the choice between whether to extract teeth or distalize molars must be made also taking into account the possibility of a longer treatment time of a non-extraction approach.

Lastly, as previously discussed, can the patient adequately comply with any necessary cooperation needed if non-compliance mechanics are not employed? If not than considering extraction therapy may be a viable alternative.