During the dental crown lengthening procedure, excess gum and bone tissue is reshaped to expose more of the natural tooth. This can be done to one tooth, to even your gum line, or to several teeth to expose a natural, broad smile. Crown lengthening is necessary when a dentist identifies decay in the tooth they cannot easily access. This decay is usually hidden deep beneath the gums, and no matter what methods they use, they cannot properly access the decay without performing a crown lengthening procedure.