Why<unk>  form is unclear, but it may involve bruxism (tooth clenching and grinding), and genetic factors. Typically they first appear in early adulthood.
Buccal exostosis
Subungual exostosis
Hyperostosis frontalis interna
Melorheostosis
Achondroplasia
Osteoma cutis
Thanatophoric dysplasia
Omphalolith