A biometric approach to predictable treatment of clinical crown discrepancies


Stephen J. Chu, DMD, MSD, CDT*













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














Figure 10. Preoperative condition of a patient requiring RSM
for gingival recession, root hypersensitivity, and an unstable
occlusal scheme














Figure 11. Diagnostic cast analysis reveals 3 mm of buccolingual and
nearly 2 mm of mesiodistal space discrepancy














Figure 12. Diagnostic waxup showing correction of the BL/MD space
discrepancies, thereby restoring proper width and proportion














Figure 13. A silicone putty matrix was used to assess the proper
facial and proximal tooth reduction required to correct the
RSM discrepancies













Figure 14. Provisional restorations provide valuable information on the
projected aesthetic outcome from the case planning/waxup phase

Should crown lengthening be necessary to achieve this result, the alternating 1.5-mm/1-mm increments marked on the vertical axis of the gauge yield predictable requirements for the increased vertical height of the gingival architecture complex

 Utility
These gauges enable clinicians to diagnosis and correct tooth size discrepancies. The present armamentarium for such diagnosis consists of manual and digital calipers, Bouley gauges, millimeter rulers, and periodontal probes. The gauges are designed to replace the present techniques, allowing simple diagnosis of tooth width and/or length problems as well as gingival length discrepancies

 The color-coded marks on the horizontal axis (ie, width portion) of the T-bar tip are aligned to the corresponding color markings on the vertical axis (ie, length portion) of the instrument. The numbers on the horizontal axis are organized from inside (ie, 5.5 mm) to outside (ie, 10.5 mm) in 1-mm bilateral increments (Figure 5). The numbers on the vertical axis are organized from bottom (ie, 7 mm) to the top (ie, 13.5 mm).
The most common width/length numbers for the lateral (ie, blue), canine (ie, yellow), and central (ie, red) incisors are 6.5/8.5, 7.5/9.5, and 8.5/11 mm, respectively (Figure 7). The incisal edge position must be established before any gauges are used

The In-Line proportion tool measures the width and length of the lateral, canine and central incisors independently when crowding is present (Figures 8 and 9).
This instrument is color-coded similarly to the T-bar, with a preset width/length ratio of 78% and color-coded marks on the width portion aligned to the corresponding color markings on the length portion. The most common width/length numbers for the lateral (ie, blue), canine (ie, yellow), and central (ie, red) incisors are 6.5/8.5, 7.5/9.5, and 8.5/11 mm, respectively.
The width is measured first and then the correspond- ing color-coded length is noted. There is an incisal guide to help position and orient the instrument during measurement
Clinical Applications
Tooth size is a critical facet in aesthetics and has clinical relevance in restorative dentistry, orthodontics, periodontics, and implant dentistry. This is especially true and pertinent in the more complex restorative space management (RSM) case types, in which orthodontic therapy alone may be inadequate to address all the needs of the patient.12 These measurement gauges (ie, Chu’s Aesthetic Gauges, Hu-Friedy Inc, Chicago, IL) allow standardization of tooth size parameters













Figure 15. The aesthetic restorative outcome is achieved through
meticulous diagnosis, treatment planning, preparation matrices, laboratory
fabrication, and final insertion













 Figure 16. The T-Bar proportion gauge tip is used throughout treatment
to ensure the ITPs are optimized for a predictable aesthetic and
functional outcome













Figure 17. Preoperative appearance shows not only a high smile
line, but also mild crowding, disproportionate tooth size and gingival
harmony, and discoloration of the anterior dentition














 Figure 18. Measurement reveals a 10-mm–wide and 13-mm–long
maxillary central incisor. The exterior red markings indicate the
width/length of an average central incisor













Figure 19. Orthodontic treatment goals were to align the dental
arches and occlusal plane, retract the anterior teeth, close the gingival
black triangles, and erupt #10 to decrease clinical crown length














Figure 20. The proportion gauge is used during orthodontic therapy
to objectively evaluate and visualize the projected ITP in conjunction
with decreasing the interproximal gingival triangles

as well as objective communication between clinicians and auxiliaries involved in comprehensive patient care from diagnosis (Figure 10), indirect case planning (Figures 11 and 12), treatment provisional restorations, and verification of tooth size correction to the final aesthetic restorative outcome (Figures 13 through 16
 Orthodontic therapy involves managing space discrepancies such as excessive or insufficient space due to tooth size and/or arch size discrepancies. Frequently, residual spaces are purposely fashioned to allow the restorative dentist to create the proper tooth size and form. Conversely, excessive space and/or tooth stucture can be condensed to provide the correct  tooth size and proportion. Having measurement gauges that can guide the clinician in these RSM case types can lend to not only a stable occlusion, but also an aesthetically pleasing smile (Figures 17through 24  
Aesthetic periodontal therapy demands addition and/or subtraction procedures in an effort to restore the proper tooth size and form. These gauges facilitate easy and quick diagnosis for addition (eg, grafting) or subtraction (eg, crown reduction) procedures to correct tooth size discrepancies. Lastly, implant dentistry not only requires osseointegration for successful tooth replacement, but also edentulous ridge augmentation in order to provide enough hard and/or soft tissue to allow the proper tooth size to be established in the final aesthetic restorative outcome
Conclusion
Human dental anatomy has not changed significantly in hundreds of years. Although dental and dental laboratory students are taught human dental anatomy and morphology in preclinical curriculum, practitioners often see dental restorations that do not exhibit the proper
  proportions of natural teeth. When visually essential aspects of dental anatomy and composition are not accurately incorporated into aesthetic restorations, patients are not completely served and practitioners may be frustrated as well















Figure 21. The proportion gauge was used in laboratory fabrication
of restorations #7 through 11 within the preset 78% proportion ratio.
The final tooth size was average to large in dimension while maintaining
a pleasing ITP















Figure 23. The final width of 9 mm and final length of 12 mm
(ie, approximately 75%) was achieved using the proportion gauge
as an objective visual marker during treatment

The clinical examples depicted herein demonstrate the applicability of an aesthetic gauge system in maintaining anterior aesthetics for both standard and non-standard tooth sizes

    














Figure 22. View of the restorations one week following insertion and
cementation. The proportion gauge was used to visualize the final
restorative outcome from diagnosis to implementation of treatment















Figure 24. View of the aesthetic restorative outcome with a clear
vision of treatment objectives using innovative measurement gauges
and meeting the patient’s needs

When the tooth dimensions are maintained at 8.5 mm and 11 mm, a standardized length-to-width ratio can be developed. The aesthetic gauge can, however, be easily applied to non-standard tooth lengths (as demonstrated in the final clinical case), allowing the clinician to develop a harmonious proportion even when treating teeth with longer clinical crown lengths or widths. It is, therefore, the maintenanc
 of biometric proportions that will influence overall tooth harmony, particularly when treating teeth that fall outside of the traditional guidelines.
The creation and use of instruments such as these not only allows the restorative dentist to be an artist, giving expression to the restoration itself, but also provides the clinician with the opportunity to become an architect, incorporating numerical values of anatomic tooth
dimensions and proportions into aesthetically pleasing smile makeovers. Thus, the new generation of aesthetidentists will be architects and artists of the dentition.

Acknowledgment
The author expresses his gratitude to Adam Mieleszko, CDT, for the fabrication of the restorations depicted herein. The author is the inventor of Chu’s Aesthetic Gauges and serves as a consultant in the development of aesthetic instruments for the Hu-Friedy Co

References
1. Preston JD. The golden proportion revisited. J Esthet Dent 1993;
5(6):247-251.
2. Rosenstiel SF, Rashid RG. Public preferences for anterior tooth
variations: A web-based study. J. Esthet Restor Dent 2002;14(2):
97-106.
3. Rosenstiel SF, Ward DH, Rashid RG. Dentists’ preferences of
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2000;9(3):123-136.
4. Sterrett JD, Oliver T, Robinson F, et al. Width/length ratios of
normal clinical crowns of the maxillary anterior dentition in man.
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proportions and their relations to maxillary anterior
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6. Ward DH. Proportional smile design using the RED proportion.
Dent Clin North Am 2001;45(1):143-154.
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tooth width of the maxillary anterior dentition. Pract Proced Aesthet
Dent 2007;19(4):209-215.
8. Waerhaug J. The gingival pocket; anatomy, pathology, deepening
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9. Schroeder HE. Quantitative parameters of early human gingival
inflammation. Arch Oral Biol 1970;15:383-400.
10. Schroeder HE. Morphometric study of early gingivitis in man.
In: Eastoe JE, Picton DCA, Alexander AG, eds. The Prevention
of Periodontal Disease. London, UK: K. Kimpton Publ; 1971:
196-203.
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junctional epithelium in mild gingivitis. A retrospective study
[in German]. Schweiz Monatsschr Zahnmed 1989;99(10):
1131–1142.
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EXERCISE


. Which of the following is a potential disadvantage
to usage of the Golden Proportion?
a. It is only applicable to a confined segment of
the patient population.
b. Clinicians are often less satisfied with aesthetics
resulting from the Golden Proportion usage.
c. Patients report being less satisfied with
the results when clinicians apply the
Golden Proportion
d. All of the above.

2. What is the width-to-length proportion the
author applies to individual teeth?
a. 76%.
b. 77%.
c. 78%.
d. 79%.

3. According to the author, which of the following
is considered the foundation of smile design?
a. Periodontium structure.
b. Individual tooth size.
c. Dental arch structure.
d. Proportion of mandibular maxillary teeth.
4. Which of the following is a factor that affects
tooth proportion?
a. Developmental anomalies.
b. Age.
c. Gender.
d. All of the above.
5. The use of “nonstandard” proportions to treat
teeth with an abnormal size relative to
accepted width and height values often yields:
a. Aesthetically pleasing results.
b. Longer chairtime for the patient during treatment.
c. Unaesthetic, unnatural results.
d. b and c only

6. RSM refers to:
a. Restorative space management.
b. Restorative space movement.
c. Restrictive space management.
d. Restrictive space movement.
7. What are the most common width-to-length
measurements for canine incisors?
a. 8.5 mm to 11 mm.
b. 7.5 mm to 9.5 mm.
c. 6.5 mm to 8.5 mm.
d. 5.5 mm to 7.5 mm.
8. Why is tooth-size correction more difficult
in natural dentition than in removable
prosthodontics?
a. Teeth may exhibit width/length discrepancies.
b. Size correction can only be completed as
the last step in restorative treatment.
c. There are no standard measurement
gauges available.
d. Tooth-size correction is more difficult in removable
prosthodontics than in natural dentition.
9. Which of the following instruments have been
used as reference standards to diagnose and
correct tooth size discrepancies?
a. Calipers.
b. Periodontal probes.
c. Millimeter rulers.
d. All of the above.
10. Which of the following must be established
before any gauges are used?
a. Tooth length.
b. Tooth width.
c. Incisal edge.
d. The height of curvature.
 

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