Cross bites- Classification, Possible causes, and management
A cross bite is defined in laypersons’ terms as a type of malocclusion where the upper teeth fit inside of lower teeth which is exactly opposite as they fit in the normal occlusion. According to Graber, however, cross bite is a condition where one or more teeth may be abnormally malposed buccally, lingually or labially with reference to opposing teeth. Another common term is under bite, which differs from cross bite by including the full arch of both anterior and posterior teeth.
Cross bites can be classified broadly as anterior and posterior cross bites. Furthermore, each can be sub-classified as being true or functional cross bites. A true anterior cross bite is defined as being present in both centric relation and centric occlusion without much noticeable change. On the other hand, a functional anterior cross bite would be present with the patient biting in centric occlusion only with the ability to bring the anterior teeth to an edge to edge relationship when guided to bite in centric relation. Another term for functional anterior cross bite is pseudo class III. As for the posterior cross bite, the same true and functional sub-classifications can be applied. However, in case of functional posterior cross bite there would be a lateral rather the anterior jump manifesting clinically as unilateral posterior cross bite on one side and normal horizontal posterior bite on the opposite side with an associated lower midline shift to the affected side. Other classifications, based mainly on etiology, have been advocated such as dental vs. skeletal, acquired vs. developmental and so on.
Generally speaking, cross bites are not very common in North America. However, the prevalence of posterior cross bites is higher than the anterior counterparts.
What causes cross bites is usually more than a single clear-cut factor; rather this problem is usually multi-factorial regarding the cause. Depending on the nature of a particular cross bite, etiology can be predicted with the help of thorough medical and dental history recording, clinical and radiographic examination as well as familial and heredity analysis. For dental cross bites, both anterior or posterior, some of the most common causes are history of traumatic injury, prolonged retention of primary teeth, ectopic eruption of permanent teeth, prolonged habits, supernumerary teeth, cleft lip/palate, as well as arch length discrepancy. On the other hand, skeletal cross bites mostly have a genetic factor. For anterior skeletal cross bite, there could be deficiency in anterior maxillary growth, excessive anterior mandibular growth, or a combination of both. Regarding posterior skeletal cross bites, there could be a deficiency in horizontal maxillary sutural growth, excessive horizontal mandibular growth it could be a combination of two. As for the functional cross bites, they are usually caused by any combination of the aforementioned factors leading to premature occlusal interferences which eventually lead the patient to develop a more comfortable “shifted” position of mandible. Sucking habits also contribute to development of posterior functional crossbites.
Though the main motivation for patients/parents to seek the orthodontic treatment is usually compromised esthetics, it is prudent to explain the consequences of failure, or even delay, in the treatment of such conditions and the possible detrimental effects they might have on the developing occlusion. Such as, tooth decay, periodontal diseases, stress on facial and masticatory muscles, grinding of teeth as well as abnormal growth patterns and psychological effects, to name a few.
The timing of orthodontic intervention for the treatment of cross bite has been a topic of constant debate. However, there is a consensus on the importance of early treatment of anterior dental cross bite as well as any type of malocclusion associated with a functional shift from centric relation; both anterior and posterior. On the other hand, posterior cross bite can be either treated in early mixed dentition or delayed after the eruption of premolars as long as there are no obvious functional discrepancies or associated shifts. For an anterior under bite with true Class III skeletal malocclusion, the treatment is either carried out in early mixed dentition for mild to moderate cases or should be delayed until completion of skeletal growth in more severe cases.
Treatment modalities for cross bites differ according to the age of the patient, etiology, and severity of the disease. In dental anterior cross bites, for instance, treatment may vary from the periodic use of a simple tongue blade, removable orthodontic appliance with springs, removable bite plane, to a more complex fixed appliances or full mouth braces. As for the posterior cross bites, maxillary dental and/or skeletal expanders are used to correct the horizontal deficiency usually associated with these types of malocclusions. For mild to moderate functional cross bites, a simple elimination of the premature contact by grinding or extraction of the offending primary tooth with or without functional appliance would solve the problem. For the treatment of a more complexed anterior cross bite associated with true class III skeletal malocclusions, different treatment options are there. These options will be discussed in another article soon as they are beyond the scope of this article.
After the completion of cross bite treatment, retention is usually not needed for simple anterior dental cross bites if sufficient overbite is present. On the other hand, posterior cross bites corrected by maxillary expansion usually need prolonged retention of full arch with removable appliances. There would be chances of relapse specially if there is a history of prolonged thumbsucking.
*Dr. El-Rass is full time Orthodontics Practitioner in Jeddah, KSA