How common is it?

One of the most common presentations of a malocclusion in primary and mixed dentitions is that of posterior crossbites 4-17% (Lombardo 2020). The prevalence varies from primary to permanent dentition (Dimberge et. al., 2015):

·      Primary dentition: 2.4% – 18%

·      Mixed dentition: 5% – 18%

·      Permanent detention: 8.5% – 15%

From the above it is evident to see that a posterior crossbite in the primary dentition usually persists to secondary dentition and rarely self corrects from primary to permanent dentitions (Thilander 1984). Unilateral crossbites are commonly occurring when compared to bilateral crossbites at a ratio of 11:1 (Filho 2007).

Why is it a problem?

A crossbite is an expression of a transverse discrepancy, with a usual manifest of a unilateral crossbite with possible further asymmetries at other levels. The key consequences of a crossbite are detailed below.

1.   Functional crossbites and Temporomandibular Dysfunction (TMD)

Let’s address the debated issue of crossbites and TMD, whereby a mandibular shift occurs from initial tooth contact (RCP) to intercuspation occurs (ICP). The debate is evidenced in both directions, with a posterior crossbite and shift showing increased TMD (Egermark 1990), whilst other research (Ellabban 2018) pointing to a weak association. To skip to the end of the debate, (and avoid further heated discussions amongst the three of us)  it would appear more recent research concludes that there is a only a weak relationship between a functional crossbite and TMD (Gesch 2004; Iodice 2013; Thilander 2002; Thilander 2012).

2.   Growth and Development of an Asymmetry

A functional crossbite and shift combined with continued growth and development can lead to a facial asymmetry due to the asymmetry in forces experienced in the mandible (Pullinger 1991). This occurrence is explained through the Melvin Moss’ functional matrix theory, where growth responds to functional forces. The asymmetric forces on the mandibular structures result in differential growth, with greater relative growth on the non-crossbite side of the mandible, and it has been observed that the mandible is shorter in ramal height on the crossbite side (Schmid et al., 1991). 

Evidence of developing a skeletal asymmetry are numerous, however a systematic review summed up the evidence excellently (Iodice 2016) “to date this chain of events (research) represents only an undemonstrated hypothesis”.

3.   Functional Changes in Masticatory Muscles

Muscular changes can occur in the presence of a long term functional crossbite and mandibular shift. Proposed changes are reduced biting force and altered muscular activity. Research does support the reduction of biting forces for patients with a unilateral posterior crossbite Iodice 2016. Interestingly when assessing patients electromyographic (EMG) activity, there was an increase in activity of some masticatory muscles on the crossbite side, especially the lateral pterygoid Iodice 2016. These two findings suggest increased muscle activity but with a reduced biting force. However it must be remembered increased muscular activity is not pathology and it is possible to have asymmetric muscular activity which is physiological.  

When assessing the effect of a crossbite from the patient’s perspective, from the Oral Health Related Quality of Life it was found there was no significant difference when compared to patients without a crossbite (0.7 difference) Kallunki 2019.

4.   Functional Displacement and Condylar Position

The final point to discuss is changes of condylar position. Through a combination of differential occlusal and muscular forces from the crossbite and shift, the position of the condyles can also be affected. For a unilateral crossbite the side of the crossbite can have a reduced articular space, whereas on the non-crossbite side the condyle may not be fully seated in the articular fossa and be displaced forwards.

What are the methods of treatment?

Two methods of crossbite correction are detailed below, one involves no orthodontic treatment (yet still found its way into the blog) and the other maxillary expansion. The advantage of early treatment is it prevents the progression of crossbite from mixed dentition to permanent dentition, and should be a considered for all patients with crossbites  (Petren et. al., 2003). 

Equilibration of primary canines

Premature contacts in primary or mixed dentition can be the culprits of a mandibular shift. Primary canines seem to be frequently guilty of this and a simple non-orthodontic solution is at hand, termed ‘equilibration’. Equilibration is the selective grinding of the primary canine which eliminates the premature contact and hence resolve the displacement. The success rate of resolving the mandibular shift is 64% Kurol et.al

Expansion of the maxillary arch

 A variety of appliances both fixed (i.e. Quadhelix (QH), expansion archwire, multi bracketed appliances, RME, miniscrew assisted rapid palatal expansion MARPE) and removable appliances (expansion plate, aligners) can achieve maxillary expansion. However the reliability and quantity of expansion varies between fixed and removable appliances. Fixed appliances for crossbite correction are 20% more likely to correct the crossbite than removable appliances (RR 1.20; 95% CI 1.04 to 1.37) Angostino 2014. 

When comparing different fixed appliances there is no overall difference in intermolar distance or crossbite correction between Quadhelix, RME (Hyrax) and MARPE (miniscrew assisted) Ugolini 2021. Although the use of miniscrew assisted expansion has shown significant expansion possibilities, for the age group of primary dentition up to 11 years of age the results appear to be no difference between bone-borne and tooth borne appliances (Bazargani 2021).

Is it stable?

With fixed or removable  appliance, around 70% to 80% of the expansion can be maintained long term. Between removable and fixed appliances there is no statistical difference in relapse at 3 years, with relapse being small at 0.4-0.8mm Petren 2011. Crossbites can be self-retentive, if ideal interdigitation is achieved. Leaving the appliance in place for up to 6 months help improved stability. Overcorrection is important as the molars tend to upright by up to 8 degrees which is equivalent to 1.35 mm.

What does the evidence say?

A recent Cochrane review explored the topic and has been used in this blog, we recommend looking at this latest body of work. Click the link below to view the full paper:

Orthodontic treatment for posterior crossbites Ugolini 2021

References

Dimberg L, Lennartsson B, Arnrup K, Bondemark L. Prevalence and change of malocclusions from primary to early permanent dentition: a longitudinal study. Angle Orthod. 2015;85(5):728–34

Melsen B, Stensgaard K, Pedersen J. Sucking habits and their influence on swallowing pattern and prevalence of malocclusion. Eur J Orthod. 1979;1(4):271–80.

Bresolin D, Shapiro PA, Shapiro GG, Chapko MK, Dassel S. Mouth breathing in allergic children: its relationship to dentofacial development. Am J Orthod. 1983;83:334–40.

Subtelny JD. Oral respiration: facial maldevelopment and corrective dentofacial orthopedics. Angle Orthod. 1980;50:147–64

Iodice G, Danzi G, Cimino R, Paduano S, Michelotti A. Association between posterior crossbite, masticatory muscle pain, and disc displacement: a systematic review. Eur J Orthod. 2013;35(6):737–44

Talapaneni AK, Nuvvula S. The association between posterior unilateral crossbite and craniomandibular asymmetry: a systematic review. J Orthod. 2012;39:279–91

Kecik D, Kocadereli I, Saatci I. Evaluation of the treatment changes of functional posterior crossbite in the mixed dentition. Am J Orthod Dentofacial Orthop. 2007;131:202–15.

ANDRADE, A. S., GAMEIRO, G. H., DEROSSI, M. & GAVIÃO, M. B. D. 2009. Posterior crossbite and functional changes: a systematic review. The angle orthodontist, 79, 380-386.

SCHMID, W., MONGINI, F. & FELISIO, A. 1991. A computer-based assessment of structural and displacement asymmetries of the mandible. American Journal of Orthodontics and Dentofacial Orthopedics, 100, 19-34.

Contributions

• Contents by Kerolos AlHakeem 
• Contents by James Andrews 
• Edited and contents by Farooq Ahmed

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