Esthetic Dental Proportions

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Introduction

Mankind’s search for translating natural beauty into reproducible numbers has been well documented throughout history. Examples include ancient Egyptians sculpting a figure of their queen Nefertiti into perfect symmetrical facial proportions, or ancient greeks buildings of their glorious city Parthenon on the concept of golden proportions (Fig 1), or Leonardo Da vinci’s impressive human and facial anatomy studies that explain proportions and relations (Fig 2). This need for a scientific approach was necessary in order to obtain predictable aesthetic outcomes and to eliminate operator dependancy or discrepancy [6] (Naini et al, 2008).

Nowadays, surgeons rely on many proven measurements in their surgeries. The rule of thirds divide the face into three equal portions. Another rule suggests that the ideal incisor width is 1/16 of the inter-zygomatic width [2] (Ward, 2001).

The golden proportion

Definition. The golden proportion is the relation between multiple objects, where each object is exactly 0.618 in dimensions of the previous object (Approximately 62%) [2] (Ward, 2001). For example, if a line is to be divided according to the golden ratio by the point C (Fig 3), the relation between the bigger part (A to C) and smaller part (C to B) should be equal to the relation of the whole line (A to B) to the bigger part (A to C). It was first described by Leonardo De pisa when he was developing this mathematical sequence ,it’s also described as “the divine proportion” and is represented by the greek letter Φ (Phi) [3] (PRESTON, 1993), [4] (Levin, 1978).

Early Dental Application. Lombardi mentioned the importance of Composition and unity and how the parts of a sum contribute to the total appearance. In his comprehensive paper published on 1973, he mentioned the concept of golden proportions and anticipated its future use in dentistry [1] (Lombardi, 1973). Five years later, Levine Advised its use when he stated that the anterior teeth in pleasing smiles are perceived to be in golden proportions when viewed from the front. Meaning that a canine’s (perceived) width is 0.618 of the lateral incisor, and a central incisor’s is 1.618 of the lateral incisor [3] (PRESTON, 1993), [4] (Levin, 1978).

Measurement Tools. Shoemaker Advocated the use of a special calliper that only open on golden proportions [3] (PRESTON, 1993). Levin used it on butterfly wings, tree leaves and attractive car models to find the natural relationships of beautiful things. He suggested that it would be more practical in dentistry if we used a piece of paper marked according to the golden proportions and positioned under the examined anterior teeth [3] (PRESTON, 1993). However, with the advent of advanced and accessible technology and digital photography, we have the ability to do this task on computers (more on that later).

Subsequent Studies. Modern studies proved that Golden proportions are found in only 17% of natural attractive smiles, and although it can produce attractive smiles, it’s not a perquisite of every attractive smile [3] (PRESTON, 1993). A better understanding of the natural relations between teeth led to similar but more flexible concepts.

Repeated ratios

Instead of being obligated to follow a single proportion for teeth, the concept of recurring proportions follows a more realistic approach by finding out the proportions that are already established between the width of the central incisor and the lateral and use it for the rest of the teeth moving distally, this gives the smile a sense of continuity and harmony, a characteristic of pleasing looking smiles [1] (Lombardi, 1973) , [2] (Ward, 2001).

The repeated proportions was first described by Lombardi in his comprehensive aesthetic paper, it produces valid guidelines and natural results especially when only some of the teeth in a smile need aesthetic restorations. It also allows the dentist to follow the natural curve of the dental arch. It also allows the dentist to discover a culprit tooth in an otherwise attractive and harmonious smile [1] (Lombardi, 1973).

Recurring Esthetic Dental (RED) Proportions

The freedom of not being restricted by the 62% ratio have opened up the concept of Recurring Esthetic Dental (RED) Proportions. Practitioners don’t have to use the golden proportions or the predefined relation of the laterals and centrals. Instead, they can create an appropriate recurring proportion to use it for the whole dentition. [2] (Ward, 2001).
This concept is far more flexible and customisable to each patient’s facial and oral features. For instance, if a patient’s smile is too wide for a 70% proportion, it would be more suitable to use a greater ratio like 80% to produce an attractive and a natural looking smile [2] (Ward, 2001).

Width to Height Ratio Of The Central Incisor

This is an important factor that should be considered when deciding between teeth proportions. A width to height ratio of 78% was the most aesthetically satisfying according to (Ward, 2001). Taller patients can tolerate taller teeth while shorter patients can tolerate shorter teeth. The width/height ratio has an important impact on the smile, it is related to the study of the patient’s RED Proportions because the ideal width/height ratio is ideally determined when deciding on a RED proportion for the patient’s new prosthesis or veneers [2] (Ward, 2001).

Role of technology in determining Dental Proportions

It is impractical and inaccurate to make measurements on a patient’s mouth or his dental cast due to changed viewing angles, a well positioned photograph with an accurate calibration can solve this problem and make the measurement more precise and easier to compare [3] (PRESTON, 1993). This is made possible by using technology and digital Photography, using softwares like Adobe Photoshop or Apple Keynote to visualise the final outcome of the treatment and manipulating it for the most pleasing results (Fig 4 and 5). [2] (Ward, 2001)

What relevance does the golden proportions have today?

Preston found that golden proportion between the maxillary centrals and laterals were found in only 17% of the total casts he studied. He concluded that the golden proportions do not exist between teeth as a rule of attractive smiles, his findings clearly contradicted Levin’s findings. Furthermore, he stated that papers published based on Levin’s theory need to be revisited [3] (PRESTON, 1993).

In addition, it was reported that teeth exhibiting golden proportion produced Narrow arch form and a rapid curvature in the dental arch. It also produced an exaggerated central incisor dominance and very narrow laterals and canines that are not sufficiently prevalent [2] (Ward, 2001), [5] (Snow, 1999).

It is clear from the literature above that even if the golden ratio is not a requirement for every pleasing smile, its use is unquestionably helpful in measuring the relative proportions of individual teeth in a smile. And it certainly opened the door for more realistic concepts of teeth proportions, such as repeated ratios [4] (Levin, 1978).

When Preston re-evaluated the golden proportions theory in 1993, not only did he find out that the golden proportion was not observed in the 58 cases he studied, he also suggested that a re- evaluation of the previous studies that were built on the golden proportions theory has to be done [3] (PRESTON, 1993), [7] (Burke et al., 2011). The golden proportion was investigated by Bukhary and his colleagues as well, their results agree with preston’s and they clearly contradict the gold proportions theory. Williams advocated that the use of golden proportions produced aesthetically pleasing results, However, these proportions were rarely found in natural teeth [3] (PRESTON, 1993).

Levin used irrelevant analogies in his paper; like cars models, trees leaves, butterflies wings and music notes or irrelevant facial proportions when establishing the golden proportions for teeth. Granted, golden proportion is indeed an established aesthetic concept in nature, but its application in dental proportions wasn’t supported by true evidence according to Preston [3] (PRESTON, 1993).

To Conclude, the golden proportion theory was historically important because it was a cornerstone to a better understanding of the relation between aesthetics and harmonious proportions, and even if its use today is outdated by more practical and true concepts, it’s still considered as an important theory in the history of dental aesthetics. Nowadays, its use is indicated only for patients with suitable facial characteristics and a relatively narrow arch form. All patients need to be treated individually with his unique and ideal dental proportions in order to reach a successful aesthetic outcome [3] (PRESTON, 1993)

References:

1. Lombardi, R, (1973) The Principles Of Visual Perception And Their Clinical Application To Denture Esthetics, from The journal of prosthetic dentistry (April) pp.358-360, St Louis, Mosby: Academy of Denture Prosthetics and other prosthetic dentistry societies.
   
2. Ward, D, (2001) "Proportional smile design using the recurring esthetic dental(Red) proportion" from Dental clinics of North America pp.143-155, Philadelphia: Philadelphia, Pa. : Elsevier Health Sciences Division ©
   
3. PRESTON, J. (1993). The Golden Proportion Revisited. J Esthet Restor Dent, 5(6), pp. 247-251.
   
4. Levin,E,(1978)"DentalEstheticsAndTheGoldenProportion"fromThejournalofprosthetic dentistry 40 (3) pp.244-252, St Louis, Mosby: Academy of Denture Prosthetics and other prosthetic dentistry societies. ©
   
5. Snow, S. R., (1999) "Esthetic Smile Analysis Of Maxillary Anterior Tooth Width: The golden percentage" from Journal of esthetic and restorative dentistry 11 (4) pp.649-661, Malden Mass: Blackwell ©
   
6. B Naini, F. and S Gill, D. (2008). Facial Aesthetics: 1. Concepts and Canons.
   
7. Burke, F., Kelleher, M., Wilson, N. and Bishop, K. (2011). Introducing the Concept of Pragmatic Esthetics, with Special Reference to the Treatment of Tooth Wear. Journal of Esthetic and Restorative Dentistry, 23(5), pp.277-293.
   
8. Wikipedia, (2015). Nefertiti. [online] Available at: https://en.wikipedia.org/wiki/ Nefertiti#/media/File:Nofretete_Neues_Museum.jpg [Accessed 29 Jun. 2015].
   
9. Flickr, (2015). The Parthenon Athens. [online] Available at: https://www.flickr.com/ photos/68686051@N00/2416778389 [Accessed 29 Jun. 2015].