Therefore, in order to ‘harmonize with geometry’, EDD and IDD are now used widely.Vertical and Horizontal Mandibular Excess:
Simply put, excessive vertical growth is the term used for when the mandible is considered ‘too far down. Whereas in excessive horizontal growth the opposite applies, where the mandible is growing in a more horizontal pattern, in relation to the maxilla. The primary cause of the above two abnormalities in adolescents is due to accelerated and slow mandibular growth. Resulting in either a longer lower face height appearance (vertical growth) or a shorter one (horizontal growth). The length between the columella (base of the nose) and menton (base of the chin) is the variable measurement. This is in relation to the length between the glabella (between eyebrows) and the columella. In a normal case, these lengths would be equal or without a major discrepancy. However, in excess vertical and horizontal growth, the proportions vary and do not equal. The development of the mandible is such that it ossifies in two primary ways; endochondrally and intramembranously. Almost the entire mandible is formed via intramembranous ossification, with just the condyle ossifying endochondrally. This allows the condyle to resist forces exerted on it.
Because this syndrome can be acquired or occur at random and has spontaneous resolution, Brown hypothesized one major truth for this disorder — that the short tendon sheath was due to a complete separation, congenital paresis, of the ipsilateral (on the same side) inferior oblique muscle and secondary to a permanent shortening.After further research, he redefined the sheath syndrome into the following divisions: true sheath syndrome, which categorized only the cases that had a congenital short anterior sheath of the superior oblique tendon, and simulated sheath syndrome, which characterized all cases in which the clinical features of a sheath syndrome caused by something different other than a congenital short anterior sheath of the tendon. The clinical features of the two categories are correct but true sheath syndrome is always congenital. However, in 1970 it was discovered that a tight sheath tendon was not the cause of Browns Syndrome. The real cause was a tight or short superior oblique tendon; studies have confirmed this and have labeled the tendon inelastic. Causes
Browns syndrome can be divided in two categories based on the restriction of movement on the eye itself and how it affects the eye excluding the movement:
Congenital (present at birth) Browns syndrome results from structural anomalies other than a short tendon sheath but other fibrous adhesions may be present around the trochlear area. Acquired cases arise from trauma, surgery, sinusitis and inflammation of the superior oblique tendon sheath in rheumatoid arthritis.