Shalin Shah, DMD, MS
The goals of orthodontic treatment are well established for the sagittal and vertical dimensions in terms of how the teeth and jaws should relate, fit, and work together. Diagnostic and treatment strategies focusing on these dimensions are the topic of many orthodontic symposiums, conferences, and research papers. However, the transverse dimension is often missing from generally accepted and performed patient analyses and discussions. Additionally, well-defined criteria for determining if there is a need for correction based on objective means, instead of subjective, frequently are not used.
As there are treatment goals for the final tooth positions based on sagittal and vertical skeletal dimensions, there must be a set of defined goals for the transverse. For the posterior teeth, these would be to have them upright and centered in the alveolus in addition to being well-intercuspated with proper arch coordination, as shown in Figure 1.
When there is a skeletal transverse discrepancy, oftentimes this is recognized by a posterior dental crossbite. However, many times there is no posterior dental crossbite, but the maxillary posterior teeth are tipped buccally, and mandibular posterior teeth are inclined lingually to compensate for the skeletal disharmony. This compensated dental arrangement opens the patient to a higher likelihood for non-working interferences from plunging palatal cups, centric prematurities, and functional shifts, in addition to placing off-axis forces on the dentition. “Decompensation” which uprights and centers the teeth in the alveolus, then reveals the underlying “skeletal crossbite” and amount of skeletal correction required, as shown in Figure 2.
While it is possible to achieve good uprighting and intercuspation of the posterior teeth in the presence of a skeletal disharmony, a risk of doing so is potential compromise to the periodontium. In an attempt to upright and well-intercuspate the teeth in the presence of a discrepancy, the amount of soft tissue and bone overlying the roots becomes thinner (Figure 3) because the teeth will no longer be centered in the alveolus. In mild discrepancies, the effects of this dental positioning may not pose a concern. However, in severe transverse discrepancies, an attempt to normalize the posterior dentition inclination and intercuspation in light of the uncorrected skeletal disharmony risks root fenestration and clinically obvious attachment loss, as shown in Figure 4.
Moderate skeletal discrepancies are the most common missed situation using just clinical observation and not an objective analysis. However, a practitioner can gain an appreciation for where an underlying skeletal crossbite is present, in the absence of a dental one, by looking at the inclinations of the mandibular teeth (Figure 5).
In these scenarios the consequences of attempted tooth position normalization, without skeletal correction, and their effect on long-term periodontal viability may not be immediately realized clinically. On debond it may appear that the posterior teeth were corrected with just using brackets, cross-elastics, or expanded archwires. However, because no overt attachment loss was seen during treatment, the practitioner may wrongly assume that no harm was done to the patient or the periodontium is viable and resilient for the long term.
Over time and in a susceptible patient, as stated above, the gingival attachment may be less resilient to normal stresses placed on it due to the reduced bulk of tissue vs. the amount present in a non-compromised patient. There is now a higher risk for mechanically-induced periodontal tissue loss, especially for those patients who may have a thinner tissue biotype at baseline. Therefore, the negative sequelae of loss of attachment and recession may not appear until years or decades later, depending on the patient’s adaptability, periodontal biotype, and genetic makeup2.