The correct answer is Dental follicle (ectomesenchyme).

- During tooth development, different embryonic tissues give rise to specific dental structures.
- Cementum, which is the calcified tissue covering the tooth root, is derived from the dental follicle, a specialized connective tissue called ectomesenchyme that surrounds the developing tooth germ.
- The dental follicle cells differentiate into cementoblasts, the cells responsible for producing cementum.

To clarify the roles of the other options:
- The oral epithelium contributes primarily to the formation of the enamel organ, which later forms enamel, not cementum.
- The dental papilla differentiates into the dentin and pulp of the tooth but does not contribute to cementum formation.
- The neural crest ectoderm is a broad term; neural crest cells give rise to ectomesenchyme, but specifically, it is the dental follicle (ectomesenchyme) derived from these cells that forms cementum.

Reference: Ten Cate's Oral Histology, 9th Edition, Chapter 5: Tooth Formation and Development, Page 98-102