Etiology – Definition

A malformation is a condition where some body part is not properly formed and usually has existed so from the birth, at least so to some degree. A synonym to malformation can be distortion or deformity. These descriptions do not include the etiology of the condition. Therefore, the etiology can be genetic, multifactorial, or due to external conditions for example during the intrauterine period.

When it comes to asymmetric growth of the face, or possible effects on occlusion, various malformations can cause disturbances in normal growth. Therefore, the proper diagnosis and the etiology of the condition are very important, also from the clinical point of view.

The following division does not include cleft lip or palate, or specific syndromes.

Craniosynostosis

Craniosynostosis is a congenital condition where one or several sutures between cranial bones have been prematurely closed. Craniosynostoses are the second most common craniofacial anomaly after the clefts.

Craniosynostosis can be linked to a specific syndrome or it can be separate, with different and often unknown origin. The condition causes abnormal cranial growth and facial dysmorphism. In some cases, the dental occlusion is affected, depending on the location of the premature fusion of the suture (Kreiborg and Björk 1981; Arvystas et al. 1985).

At the moment, about 85% of the craniosynostoses are not linked to any known syndrome. However, this number is continuously decreasing due to advances in genetics (McKusick 2017).

The fusion of craniofacial sutures or the existence of a functional suture is dependent on a group of cytokines, growth factor receptors, and transcription factors. Especially in syndromic craniosynostoses specific mutations in gene coding have been revealed. There are, however, some findings of nonsyndromic craniosynostoses with genetic background, usually with incomplete penetrance (Heuzé et al. 2014).

Single suture craniosynostosis is the most common involvement, being found in 85–90% in all craniosynostoses. Of the single suture craniosynostoses, the most common involvement is the sagittal suture. The next in prevalence are metopic and coronal sutures (Kolar 2011). Premature fusion of cranial suture, as a single suture fusion comprises about half of all single fusions. No asymmetric occlusal involvement has been reported with this type of craniosynostosis. Typically, asymmetric dentofacial growth when linked to nonsyndromic craniosynostosis, has been reported in association with unilateral fusion of coronal suture. In unilateral craniosynostosis of the coronal suture the midface often shifts to the affected side and the mandible does not shift to the same degree, the condition causing a midline shift in the occlusion. However, the dental midlines may be coinciding, due to compensatory mechanisms in the orofacial region, especially in the mandible. The functional occlusion is important in maintaining the symmetry, especially in the oral region (Kreiborg and Björk 1981; Arvystas et al. 1985; Pelo et al. 2011).

Plagiocephaly

The term plagiocephaly is used when there is flattening or bossing of the skull anteriorly or posteriorly. This can be either unilateral or bilateral. Plagiocephaly can be associated with craniosynostosis, or it can be caused by outer forces (Valkama et al. 2019), when it is called positional plagiocephaly. Anterior or frontal plagiocephaly, when linked to craniosynostosis, is usually linked to fusion of the coronal suture and posterior plagiocephaly linked to premature fusion of the lambdoid suture.

Pelo et al. (2011) examined the occlusion and craniofacial structures of 21 patients with unilateral coronal craniosynostosis. They found many craniofacial and dental alterations. The overbite and the overjet were increased in the craniosynostosis group and the lower midline deviation, when compared to the upper midline, was significant. However, as the authors state, the real asymmetry was difficult to measure, as nearly all the structures in the patient group were to some degree asymmetric and a clear reference line in cephalometry is difficult to find. Their conclusion was that the found mandibular asymmetry in the craniosynostosis group with the unilateral coronal synostosis would primarily be dependent on the altered position of the glenoid fossa on the affected side. Thus, the mandibular asymmetry is the consequence of the skull base asymmetry in these cases. Lebuis et al. (2015) did a study on a group of patients with scaphocephaly, where the premature fusion of the sagittal suture causes craniofacial alterations. They found an increase in the prevalence of Class II malocclusion. There was not any increase in asymmetry of the face or lateral malocclusions in these patients and the lateral cephalometric values were mostly within the limits of normal range, which finding could be related to the fact that the primary premature fusion of the suture in these cases was symmetric in the midsagittal plane and not affecting the symmetry of the developing skull or occlusion.