Final answer:
The formation of additional dentin on tooth #30 due to injury is known as tertiary dentin, which is a defensive response to protect the pulp cavity.
Step-by-step explanation:
Dentin Formation in Response to Injury:
The formation of additional dentin on tooth #30, as seen in a periapical radiograph taken by the dental hygienist, is a biological response to injury. This type of dentin is referred to as tertiary dentin, also known as reparative or reactive dentin. Unlike secondary dentin, which forms naturally as teeth age, tertiary dentin is produced by odontoblasts in the pulp in specific reactions to stimuli, such as caries or abrasion. The key purpose of dentin deposition is to protect the pulp from further injury or intrusion of pathogens.
Teeth are composed of several layers: the outer enamel, under which lies the dentin, and the innermost pulp cavity filled with blood vessels, connective tissue, and nerves. The crown is covered by enamel, which is the hardest body material, while both the crown and root contain the dentin, covered by cementum in the root, and encompass the pulp cavity. When the pulp is exposed to injury or decay, tertiary dentin is generated as a defensive measure.