What type of dentin is formed before a tooth erupts?

Primary dentin is the type of dentin that is formed before a tooth erupts. It constitutes the bulk of the tooth structure and is laid down during the development of the tooth. This dentin forms in a regular pattern and provides the primary structure and support needed for the tooth after it has emerged into the oral cavity.

Secondary dentin, on the other hand, is formed after the tooth has erupted and continues to grow throughout the life of the tooth, adding additional layers as the tooth ages. Tertiary dentin, also known as reparative or reactive dentin, is formed in response to stimuli such as trauma or caries and serves a protective function.

Enamel, while crucial for tooth protection and formed earlier in tooth development, is not a type of dentin but rather the outermost layer covering the tooth. Thus, primary dentin is the correct focus when discussing dentin formation prior to tooth eruption.