Ante’s Law - Crown to Root Ratio

In the field of dentistry, the postulate known as Ante’s law was first offered in a 1926 thesis paper written by Irwin H. Ante, a Canadian dental health professional. Ante’s law addresses ideas about crown-to-root ratio and is unconfirmed by longer-term and recent clinical trials, though its concepts affected periodontology for decades. Ante’s law states that the amount of periodontal membrane available to the teeth immediately adjacent to a restoration, also known as the abutment teeth, must be equal to or greater than that of the teeth that are being replaced. Eventually, it also suggested specific measurements, stating that the length of the membrane attachment of an adjacent tooth must be one half to two thirds the length of its normal root attachment. Because of these concepts, which have not been clinically substantiated, many patients were deemed unsuitable for fixed partial dentures, instead undergoing double abutment procedures involving implants used as abutments, as opposed to the natural teeth serving as abutments.

Crown-to-root ratio is the measurement of the length of the part of a tooth that is visible above the alveolar bone compared to the measurement of what lies below the alveolar bone. In the diagnosis and treatment planning for tooth restorations, crown-to-root ratio is an essential consideration that should, ideally, guide the treatment plan to ensure appropriate results.

Every tooth is divided into two sections: the crown and the root. The line of demarcation between these two sections is called the cementoenamel junction, based on the enamel that covers the crown of the tooth and cementum that covers the tooth’s root. In a healthy periodontium, the roots of the teeth are entirely submerged in and surrounded by the alveolar bone of the jaw in which they rest; they are submerged up to the cementoenamel junction. The soft tissue of the gingiva lies on top of the bone; the gingiva averages about 1 mm of thickness. The crown, which is not surrounded by any bone at all, is partly obscured by the gingiva at this junction. The crown and the root can therefore be viewed as two discrete anatomical parts, and the crown-to-root ratio can be used as a helpful and effective tool to measure and note periodontal pathologies and other problems. Clinical terms used in reference to the crown-to-root ratio include relative crown and relative root, as well as effective crown height and effective root height; each of these terms can be used to indicate the recession or resorption of gum and bone tissue.

Crown-to-root ratio becomes important when determining what percentage of a tooth remains embedded in the alveolar bone. Root length is significantly longer than crown length, as the roots of the teeth reach farther into the bone than the crown emerges from the gums, providing stable support, facilitating the mechanical function of the teeth, and helping securely root the teeth in the mouth. The naturally occurring crown-to-root ratio in a healthy mouth contains a root system that can effectively support the tooth when exposed to normal stresses. If bone loss occurs, however, and more of the root becomes visible beyond the bone, this diminishes the efficacy of the root support and also increases the amount of tooth that is to be supported by the part of the root system that is still submerged in the bone. This means that for every millimeter of bone that is lost, a millimeter of supportive root is lost and a millimeter of supported crown is gained, which can clearly lead to serious problems over time and as the loss of bone progresses with advanced periodontal disease. Without a 1:1 crown-to-root ratio, the prognosis for the tooth and for any potential restorations is considerably diminished and will eventually lead to loss of the tooth.