A biometric approach to predictable treatment of clinical crown discrepancies

Dental professionals have long been guided by mathematical principles when interpreting aesthetic andtooth proportions for their patients. While many acknowledge that such principles are merely launch points for a smile design or reconstructive procedure, their very existence appears to indicate practitioners’ desire for some predictable, objective, and reproducible means of achieving success in aesthetic dentistry.
The clinical reality, however, is that intra-arch tooth relationships used as guidelines for smile designs (eg, the Golden Proportion) are applicable to a confined segment of the patient population.1 In addition, dentists have been found to be less pleased with aesthetic outcomes with smiles designed using the Golden Proportion,2 and patients have been found to dislike such a proportion relationship. 3 Therefore the only tangible parameter in aesthetic dentistry is individual tooth size and proportion.4,5 Individual tooth size can be thought of as the building blocks of a smile design. Once the tooth size and proportion of the maxillary anterior teeth are corrected, they can then be arranged within the dental arch. Intra-arch tooth relationship proportions such as the recurring aesthetic dental proportion,6 which has been found to be amenable to patients and clinicians, can be used to arrange the teeth

Figure 1. Prototype proportion gauge; a Siamese twin instrument tip
with preset markings notched into the surface with measurements
indicating a predetermined 78% width to length proportion.

Figure 2. Surgical crown lengthening was provided additional
clinical crown exposure; the proportion gauge was used to
position the FGM of the soft tissue flap apicocoronally

Figure 3. Preoperative smile of patient requiring aesthetic
crown lengthening to restore proper individual tooth
dimensions/proportion and decrease gingival display

for a pleasing smile.6 This task is simplified in removable prosthodontics, in which selection of the proper tooth size and form is the primary step before their arrangement within
the dental arch or tooth setup. With the natural dentition, this task is infinitely more difficult, since the dilemma is such that existing teeth may exhibit altered width and/or length discrepancies due to developmental anomalies, changes resulting from the aging process, or prior restorative
procedures. Therefore, correction may require combination therapies such as orthodontics and/or periodontics prior to aesthetic restorative dentistry

In daily practice, the clinician’s use of “nonstandard” proportions to treat teeth with abnormal size relative to accepted width and height values can yield narrow or square teeth that are unnatural in size and shape and fail to achieve the aesthetic expectations of either the patient or clinician. This can be particularly challenging when performed with visual assessment only (ie, absent of clinical tools). Standardized individual tooth size and proportions fall within a given range around mean values, however, and gender differences exist between anterior tooth groups.7 Therefore, these parameters can be used to predictably diagnosis and correct discrepancies in tooth size
and individual tooth proportio

Figure 4. View of the smile after crown lengthening using
the prototype gauge to predict the proper clinical crown
length exposure

Figure 5. Diagram of T-Bar proportion gauge tip designed
for simultaneous width and length measurements of maxillary
anterior teeth within a range of small to extra large
tooth dimensions

Historical Background
Traditionally, dental instruments (eg, explorers, probes) have been used as reference standards to detect diseases such as caries and periodontitis. Periodontitis is detected, evaluated, and assessed using numerical values indicative of health or stage of disease.8-11 Instrumentation does not exist, however, to address aesthetic deformities from diagnosis to correction

Aesthetic tooth dimensions can be evaluated and treated by similar numerical analysis. To test the application of these concepts, the author created prototype instruments. Metal wire (ie, 0.036 gauge) was soldered to form a Siamese twin instrument tip with preset markings notched into the surface with measurements indicating a 78% width (W) to length (L), proportion
(Figure 1). Once the incisal edge position was established, the width of a tooth could be measured with the prototype instrument, and the notch on the short arm noted; then the corresponding notch on the long arm could be marked as the reference point for the new clinical crown length at a preset W/L ratio (Figures 2 through 4

Revolutionary Instrumentation
Aesthetic measurement gauges (ie, Chu’s Aesthetic Gauges, Hu-Friedy Inc, Chicago, IL), designed for diagnosis and correction of tooth size discrepancies and deformities, have been developed to eliminate the subjectivity associated with restorative care

Figure 6. Representation of In-Line proportion gauge tip; it is used to
measure widths and lengths of lateral incisors, canines, and central
incisors independently when crowding is present

Figure 7. T-Bar tip utility; numbers and color bars on the horizontal
axis correspond to those on the vertical axis, providing the clinician
with a visual representation of optimal ITP

These measurement tips include the Proportion Gauge (PG), which represents an objective mathematical appraisal of tooth size ranges. Through the use of such instrumentation, the clinician has a clearly visible means of applying aesthetic values to a patient chairside, directly or indirectly in the laboratory during projected treatment planning, and to objectively determine the intended treatment outcome

 The PG is designed as a double-ended instrument (ie, gauge) with a T-Bar and In-Line tip screwed into the handle at opposing ends. The T-Bar tip features an incisal edge position (ie, incisal stop); when a tooth is oriented with the tip accordingly, the practitioner can accurately evaluate its length (ie, vertical arm) and width (ie, horizontal arm) dimensions simultaneously. The width is indicated in equidistant 0.5-mm increments bilaterally, each with a vertical mark in a corresponding color (Figure 5).Thus, a central incisor with a “red” width of 8.5 mm will be in proper proportion if its height is also the “red” height (ie, 11 mm

The In-Line tip is analogous to the metal prototype used in the aforementioned case study; the most significant difference being that the latter is a color-coded,
plastic, disposable unit. The utility of the In-line gauge is identical to the T-Bar tip, except for the fact that the horizontal arm of the T-Bar is now the short arm of the In-Line tip; the vertical arm and long arm of the tips are also the same. The short arm, at 1-mm increments, measures
the tooth width, and the long arm measures the corresponding length at alternating 1.5-mm/1-mm increments, since the gauge is mathematically set at 78% W/L proportion. The black line at the base of the tip denotes the incisal guide, which is the starting point of measurement (Figure 6

Figure 8. In-Line tip width utility; the short arm is aligned with the
tip perpendicular to the long axis of the tooth to measure the width

Figure 9. In-Line tip length utility; the corresponding red band on the
long arm measures the clinical crown length. The outer blue bands
and the intermediate yellow bands measure the lateral incisors and
canines, respectively