The Anterior Ratio: The Missing Link between Orthodontics and Aesthetic Dentistry

There is an increase in the number of dentists using orthodontic treatment for anterior tooth alignment. This is either combined with additive bonding or interproximal reduction; knowing “when to” and “how much” requires an understanding of the anterior ratio. This case report explains how to use the anterior ratio to help provide optimal aesthetics and function for the ortho-restorative patient. The anterior ratio is an important diagnostic tool required for both disciplines of orthodontics and restorative dentistry which is often overlooked. The case report demonstrates the use of the Invisalign orthodontic appliance and the corresponding ClinCheck software to help achieve the proposed treatment goals. 1. Introduction For all orthodontic-restorative cases, the use of the Bolton analysis is an invaluable diagnostic tool which helps to mathematically define a tooth size discrepancy (TSD). A tooth-size discrepancy (TSD) is defined as a disproportion among the sizes of individual teeth. If a tooth size discrepancy does exist with the anterior teeth and is corrected to ideal proportions, the aesthetic smile can be significantly improved [1]. Additionally, correcting a significant TSD can allow for ideal tooth alignment and occlusion in relation to overjet and overbite [2]. In 1958, Bolton [3] developed a method for estimating a TSD by measuring the summed mesiodistal widths of the mandibular to the maxillary anterior teeth from canine to canine; this was defined as the anterior ratio. The ideal value for the anterior ratio is 0.772 or 77.2% when described as a percentage. This is illustrated in (Figure 1). Figure 1: Showing anterior teeth and values required to calculate anterior ratio. The anterior ratio is calculated by the following equation: where is the sum of the mesiodistal widths of the lower anterior six teeth, where is the sum of the mesiodistal widths of the upper anterior six teeth: Bolton demonstrated that the deviation from the ideal value of any measured ratio would indicate the size of the discrepancy. Therefore as a general rule, an increased anterior ratio value could be due to small upper teeth or large lower teeth or a combination of the two factors. And a decreased anterior ratio could be due to large upper teeth or small lower teeth or a combination of the two factors. The solution to correcting the anterior ratio is by making an adjustment in the upper arch or in the lower arch or in both arches. The mesiodistal widths of teeth can be increased with composites or indirect restorations and decreased by interproximal reduction and