Holdaway Ratio and how much can we procline?

Perhaps, one of the most primal human instincts is to seek beauty and balance in all forms around us, irrespective of sentience. Often, however, challenges from societal norms and verdicts can tether on or even encroach on lines so delicately crafted by personal human beliefs. These “esthetic canons” have long been sought after, often discussed, and frequently theorized in many principles of knowledge.

Something that has fascinated professionals from all disciplines of practice including but not limited to scholars and anatomists, scientists and even artists, have been the proportion of the human face. The face is the most expressive part of the human body, one that is responsible for visual evaluation and recognition. In his book “De Divina Proportione”, Luca Pacioli demonstrates the first canons on the proportions of the human face. He makes references to the golden section, a concept that has been accredited for imputing absolute harmony and balance between different parts of the human body.

While beauty is subjective and the conversation around it can be chalked up to differing conjectures, the appeal and intrigue around the face has far but died down, instead extending well beyond the neoclassical era and overspilled into much of the medical literature. In fact, sectors of medicine including dentistry have expressed great interest in facial symmetry and how it is a good candidate to assess dental (especially orthodontic) treatment.

The significance of facial esthetics

Traditionally, orthodontic treatment planning and dentistry, in general, have been predominantly focused on providing superior and “ideal” dental occlusion with little to no regard for facial esthetics and proportions. Hard and soft tissue analysis of the face is a good medium to evaluate dentofacial orthopaedic cases: a concept that gave rise to cephalometrics – a well-accepted method for soft tissue measurements and therefore, orthodontic diagnosis.

Angle, first emphasized the importance of these soft tissue relations to the overall orthodontic treatment plan as early as 1907. About eight decades later, in 1983, Reed Holdaway, an American orthodontist further stressed the importance of incorporating soft tissue analysis during the process of diagnosis with the help of facial lines. One of the principles popularized by Holdaway was the Holdaway Ratio.

Holdaway Ratio (Ll-NB/Pg-NB)

The Holdaway Ratio is a measurement introduced by Holdaway to evaluate the relative prominence of the mandibular incisors, as compared to the size of the bony chin. According to him, the linear distance from the labial surface (Ll) of the mandibular incisor to the nasion-basion (N-B) line and the distance from the pogonion (Pg) or the chin prominence to the N-B line should be equal.

If the ratio is 2:1, it means that the lower incisors are more proclined as compared to the chin prominence.  If the discrepancy is:

• 2 mm = acceptable
• 3 mm = less desirable
• 4 mm = correction indicated

What is the acceptable Holdaway ratio?

Several cephalometric analyses have been proposed to evaluate as well as quantify the soft tissue profile. Holdaway emphasized greatly the main profile characteristics of the lower and facial structures but many of his studies were limited by the patient pool (typically Caucasian). Due to this, many other studies then went on to utilize his principle to report cephalometric soft tissue findings of diverse ethnicities and compared them to the original Holdaway established norms.

• One study examined the Chinese population and compared them with the White norms. They found that the Chinese group had a less prominent nose, less obtuse nasolabial angle, and less chin thickness with both the upper and lower lips being more protrusive.
• Another study was able to measure the soft tissue cephalometric norms using the Holdaway analysis in Japanese adults. Upon analysing the cephalometric radiographs of 211 Japanese normal adults and comparing the soft tissue measurements with those of an esthetically pleasant Japanese subgroup and white adult sample, they made startling discoveries.

They found statistically significant differences between the Japanese and White samples. The Japanese normal group had:

• A longer distance from subnasale to a line tangent to the soft-tissue chin and the vermillion border of the upper lip (Harmony or H line).
• A less convex skeletal profile and larger upper lip strain.
• A more obtuse H angle with the lower lip.

• A third study compared the soft tissue values of Anatolian Turkish adults and found them to be generally similar to the established Holdaway soft tissue norms.

Saudis were shown to have a more skeletal convex profile with an increased H angle. The upper lip, lower lip, and nose were also found to be more protruded and prominent. Additionally, they found that the Saudi males demonstrated more prominent upper lips and noses as compared to the Saudi females.

As can be discerned, the acceptable Holdaway ratio varies from population to population. Having population-specific values of nasal soft tissue measurements and chin position by Holdaway ratio could greatly assist us in orthodontic and orthognathic surgical treatment planning.