Ossification of the spheno-occipital synchondrosis. Literature review

Closure of the spheno-occipital synchondrosis is progressing in both sexes from the inside to the outside of the skull. Compared to other cranial base synchondroses, the spheno-occipital synchondrosis ossifies relatively late, and therefore it is of great importance for the growth of the facial skeleton.

Aim
The aim of this paper is to present data on ossification time of the spheno-occipital synchondrosis based on data obtained from macro-anatomical studies, CT and CBCT scans; to present information on sexual dimorphism, ethnic differences and clinical aspects, as well as to demonstrate the use of results of these studies in orthodontics.

Material and methods
Electronic databases (Scopus, ScienceDirect, Web of Science, BIOSIS, EMBASE and PubMed) were used in the search of literature from the period 1960–2019 and information on the ossification of the spheno-occipital synchondrosis was summarised. The following search criteria were used in English: spheno-occipital synchondrosis, ossification degree, synchondrosis closure time.

Results
172 publications with keywords of interest were identified, and a review of 38 papers from the years 1960–2019 was conducted. The spheno-occipital synchondrosis ossifies and closes about 1–2 years later in males. The stage of ossification of the spheno-occipital synchondrosis shows significant ethnic differences. The prolonged period of growth and ossification of the spheno-occipital synchondrosis until adolescence acts as a delaying mechanism which is necessary because the permanent dentition erupts relatively late.

Conclusions
When one knows the periods of ossification of the spheno-occipital synchondrosis and associated effects on the position of the maxilla, it allows better planning of orthodontic treatment, assessment of the effects of growth that is still present after treatment on the long-term stability of results obtained, and it also allows for correct interpretation of outcomes of orthodontic treatment. In addition, the assessment of the degree of fusion of the spheno-occipital synchondrosis can be used to assess skeletal maturation, and this evaluation has a significant impact on the time when orthodontic treatment of individual malocclusions is started.