The biosynthesis of HS takes place in the Golgi apparatus and endoplasmic reticulum, where glycosaminoglycans chains are maintained by type II glycosyltransferases encoded by EXOSTOSIN genes EXT1 and EXT2. Decreased levels of HS leads to mutations in EXT1 or EXT2 causing skeletal abnormality. The underlying mechanism for solitary and multiple osteochondromas have been associated with genetic alterations in EXT1 or EXT2 genes located on chromosomes 8 and 11. Approximately 65% of osteochondromas arise in the EXT1 gene loci on chromosome 8 and 35% arise in EXT2 gene loci on chromosome 11. About 70–75% of multiple osteochondromas are caused by point mutations, often involving deletion of single or multiple axons as found in 10% of all hereditary cases. In about 10–15% of all cases no genomic alterations are detected. The mechanism behind the formation of multiple osteochondroma is large genomic deletions of EXT1 and EXT2 genes. The identified mechanism behind solitary osteochondromas is the homozygous deletions of the EXT1 gene. However, the exact cause of osteochondroma is unknown. Additionally, the molecular basis of genetics and clinical variability of multiple osteochondroma as well as the underlying causes for the malignant transformation and the onset of osteochondroma in EXT negative patients is also currently unknown. Diagnosis
Osteochondromas are often asymptomatic and may not cause any kind of discomfort. They are often found accidentally when an X-ray is done for an unrelated reason. X-rays are the first tests performed that characterize a lesion.
Types
Supernumerary teeth can be classified by shape and by position. The shapes include the following:

Supplemental (where the tooth has a normal shape for the teeth in that series);
Tuberculate (also called barrel shaped);
Conical (also called peg shaped);
Compound odontoma (multiple small tooth-like forms);
Complex odontoma (a disorganized mass of dental tissue)When classified by position, a supernumerary tooth may be referred to as a mesiodens, a paramolar, or a distomolar. Occasionally, these teeth do not erupt into the oral cavity but manifest as a malocclusion.The most common supernumerary tooth is a mesiodens, which is a malformed, peg-like tooth that occurs between the maxillary central incisors. Fourth and fifth molars that form behind the third molars are another kind of supernumerary teeth. Treatment
Although these teeth are usually asymptomatic and pose no threat to the individual, they are often extracted for aesthetic reasons, to allow the eruption of other teeth, orthodontic reasons and/or suspected pathology. This is done particularly if the mesiodens is positioned in the maxillary central incisor region. The traditional method of removal is done by using bone chisels, although a more advanced technique has been found to be more beneficial, especially if surgery is required. Through the use of piezoelectricity, piezoelectric ultrasonic bone surgery may be more time-consuming than the traditional method but it seems to reduce the post-operative bleeding and associated complications quite significantly. Epidemiology
It is evident that hyperdontia is more common in the permanent dentition than in the primary.