“The cemento-enamel junction (CEJ) represents the anatomic limit between the crown and root surface and is defined as the area of union of the cementum and enamel.” The article notes classical descriptions of three relationships between enamel and cementum at the CEJ: “(1) cementum overlapping enamel; (2) edge-to-edge adaptation of cementum and enamel; and (3) a gap between cementum and enamel exposing dentin.” These variations “may occur at different locations on the same tooth.”

In human teeth, the cementoenamel junction (CEJ) can have different morphologies, known as Choquet cases or types: in type 1, the cementum overlaps the enamel; in type 2, the enamel overlaps the cementum; in type 3, the relationship between the cementum and enamel is edge-to-edge; and in type 4, there is a gap between the enamel and the cementum, with exposed dentin. The teeth evaluated showed the 4 CEJ types.

“The cementoenamel junction (CEJ) represents the anatomic limit between the crown and root surface.” It is described as “a unique place on the dental surface where the three hard tissues, i.e., enamel, dentin and cementum, exist in union.” The paper reiterates that “traditionally, three types of CEJ have been reported. These include: (1) overlap, in which cementum overlaps enamel… (2) abutment, cementum butts with enamel; and (3) gap, a finite space between cementum and enamel, exposing cervical dentin.” The authors report that “in 10% of the cases, cementum does not meet enamel… in 30%… enamel meets cementum in a head-to-head ratio; while in the remaining 60% cases, cementum covers the enamel.”

At the cemento-enamel junction (CEJ), the text describes three patterns: “Pattern I: The cementum overlaps the enamel (42–60 %)… Pattern II: Edge-to-edge interrelationship between cementum and enamel (situation seen in 30–41 % of the teeth). Pattern III: There is a gap between root cementum with exposed dentin (10–12 %).” Earlier, it summarizes: “In the cemento-enamel junction, the cementum is overlapping enamel (a). In (b) cement and enamel are continuous, forming an edge-to-edge structure. In (c), gaps are obvious between root cementum and exposed dentin.”

Cementoenamel Junction (CEJ). The cementoenamel junction is the specific line where the enamel, which covers the tooth’s crown, meets the cementum, which covers the tooth root. In most cases, the cementum overlaps the enamel around the tooth.

The cervical part of the tooth is described as "the narrow area between the crown and the root." It is "the transition zone where the enamel ends and the cementum (the substance covering the root) begins." The text notes that this area is usually covered by gingiva and that sensitivity and caries are more likely when it is exposed.

The tooth is divided anatomically into crown, neck, and root. Structurally it consists of enamel, dentin, cementum, and pulp. Enamel is described as the hardest tissue, covering the outer surface during development and then having no cells or capacity for repair. Cementum is described as "a very thin white covering on the outside of the root" whose function is to serve as the attachment structure for the periodontal membrane, indicating that cementum normally covers the root surface, not the crown.

The tooth can be divided into three main parts: a crown coated by enamel, a root covered by cementum and the cervical margin or neck where these two regions meet. The cervical line or neck of the tooth is a slim, irregular margin that constitutes the boundary between the enamel covering the crown and the cementum covering the root. At this line the cementum usually overlaps the enamel slightly, although they can meet end on occasionally.

The page describes: “The cementum then connects to the enamel and forms the cementoenamel junction (CEJ). This is called the cervical line.” It explains that “the cementum is a specialized calcified substance covering the root of a tooth” and that the CEJ is where this tissue joins the overlying enamel of the crown, emphasizing the junction as a boundary rather than a region broadly covered by both tissues.

The article explains that every tooth has crown, neck, and root. It states that "enamel is the outermost layer of the tooth structure and covers the crown" whereas "cementum is part of the periodontal tissues, surrounding the root and the neck." By differentiating that enamel covers the crown and cementum surrounds the root/neck as part of periodontal support, it implies different coverage regions of the tooth surface.

This popular science article notes that the tooth is composed of crown and root, which join at the cervical region. "The outermost layer of the crown is enamel." It then describes cementum as covering the root, with thickness greatest at the apex (about 150–200 μm) and thinnest at the cementum–enamel junction (about 20–50 μm). The phrase "cementum–enamel junction" indicates a line where enamel and cementum meet at the cervical region, rather than an extended area of simultaneous coverage.

The glossary defines: “The cervical line, also known as the cementoenamel junction (CEJ), is the anatomical boundary that separates the crown of the tooth from the root. It marks the point where the enamel covering the crown meets the cementum covering the root surface.” It adds that this line “encircles the tooth and varies in curvature depending on the surface,” reinforcing the concept of a line or junction where enamel and cementum meet rather than a broad region covered by both simultaneously.

The booklet explains tooth structure by stating that the exposed part above the gingiva is the crown, the part in the jaw is the root, and the part between them is the neck, usually covered by gingiva. It describes dentin as lying beneath enamel in the crown and beneath cementum in the root. It defines cementum as "covering the outer side of root dentin" and emphasizes that its role is to attach periodontal fibers to the root, thus associating cementum with root surfaces rather than the enamel-covered crown.

Cementoenamel junction. The cementum attaches to the enamel to form the cementoenamel junction (CEJ) which is called the cervical line. There are three possible relationships found at this junction: cementum overlapping enamel, enamel meeting cementum in an edge-to-edge butt joint, or a gap between them exposing dentin.

Standard dental histology textbooks describe three classical relationships between enamel and cementum at the cemento-enamel junction in permanent teeth: (1) cementum overlapping enamel in the majority of teeth (often cited around 60–65%); (2) edge-to-edge contact where enamel and cementum meet in a butt joint; and (3) a gap between enamel and cementum exposing underlying dentin. In all three patterns, the cervical *line* is considered the boundary where enamel of the crown and cementum of the root meet; it is not generally described as a wide cervical “region” that is simultaneously covered by both tissues throughout.

An exam item covering oral anatomy and tooth morphology refers to the cervical ridge, crown, root, and primary molar root thickness. While the snippet does not directly define enamel–cementum distribution, the context shows that professional dental exams treat the crown, cervical region, and root as distinct anatomical zones with different coverings (enamel on crown, cementum on root), consistent with standard dental anatomy teaching.

The document on tooth structure notes that alveolar bone surrounds the roots and that gingiva covers the alveolar bone. It describes enamel as the hard tissue on the top (crown) responsible for protection and mastication, and describes cementum as the tissue covering the root dentin, to which periodontal fibers attach. The cervical part is implied as the junction between these regions, covered by gingiva, with enamel limited to the crown and cementum to the root.

In describing the neck of the tooth, the narrator states that it is “also called the cemento enamel junction or cervical line” and that it “represents the area where the crown's enamel layer meets the cementum layer covering the tooth's root” (around 1:05). The neck is thus identified as the junction where enamel and cementum come into contact, not as an area extensively overlapped by both tissues across a region.

The instructor explains: "There are three different types of cemento-enamel junction: overlap, edge to edge and gap junction. Overlap is seen in 60% of the teeth... Cementum will overlap enamel for a short distance." The video emphasizes that at the cervical portion of the tooth the junction is variable and may show cementum overlapping enamel, a simple meeting line, or a gap between them.