20 2003 - Magne - Anatomic Crown Width Length
20 2003 - Magne - Anatomic Crown Width Length
20 2003 - Magne - Anatomic Crown Width Length
in white subjects
Pascal Magne, PD, Dr Med Dent,a German O. Gallucci, DMD,b and
Urs C. Belser, Prof, Dr Med Dentc
School of Dental Medicine, University of Geneva, Geneva, Switzerland
Statement of problem. Dimensions of teeth have been available for a century. Some significant and clinically
relevant aspects of dental esthetics, however, such as the crown width/length ratios, have not been presented in
tooth morphology sources until recently.
Purpose. The purpose of this study was to analyze the anatomic crowns of 4 tooth groups (central incisors,
lateral incisors, canines, and first premolars) of the maxillary dentition with respect to width, length and width/
length ratios and determine how these parameters are influenced by the incisal edge wear.
Material and methods. Standardized digital images of 146 extracted human maxillary anterior teeth from
white subjects (44 central incisors, 41 lateral incisors, 38 canines, 23 first premolars) were used to measure the
widest mesiodistal portion W (in millimeters) and the longest inciso-cervical/occluso-cervical distance L (in
millimeters). The width/length ratio R (%) was calculated for each tooth. A 1-way analysis of variance was used
to compare the mean values of W, L, and R for the different groups (unworn and worn subgroups, except
for premolars). Multiple least significant difference range tests (confidence level 95%) were then applied to
determine which means differed statistically from others.
Results. There was no influence of the incisal wear on the average value of W (width) within the same tooth
group. The widest crowns were those of central incisors (9.10 to 9.24 mm) canines (7.90 to 8.06 mm) lateral
incisors (7.07 to 7.38 mm). Premolars (7.84 mm) had similar width as canines and worn lateral incisors. The
L-value was logically influenced by incisal wear (worn teeth were shorter than unworn teeth) except for lateral
incisors. The longest crowns were those of unworn central incisors (11.69 mm) unworn canines (10.83 mm)
and worn central incisors (10.67 mm) worn canines (9.90), worn and unworn lateral incisors (9.34 to 9.55
mm), and premolars (9.33 mm). Width/length ratios also showed significant differences. The highest values were
found for worn central incisors (87%) and premolars (84%). The latter were also similar to worn canines (81%),
which constituted a homogeneous group with worn lateral incisors (79%) and unworn central incisors (78%). The
lowest ratios were found for unworn canines and unworn lateral incisors (both showing 73%).
Conclusions. Along with other specific and objective parameters related to dental esthetics, average values for
W (mesiodistal crown dimension), L (incisocervical crown dimension), and R (width/length ratio) given in this
study for white subjects may serve as guidelines for treatment planning in restorative dentistry and periodontal
surgery. (J Prosthet Dent 2003;89:453-61.)
CLINICAL IMPLICATIONS
This study provides maxillary tooth dimensions and proportions that may be adapted to individual patients relative to the amount of incisal wear. These numbers (widths, lengths, and
width/length ratios) may be useful guidelines for diagnosis and treatment planning (especially
periodontal surgery) in the maxillary dentition.
onsistent mastering of restorative dental procedures in the anterior dentition requires that both clinician and ceramist be intimately familiar with the basic
principles of natural oral esthetics. A checklist for esthetic restorative success was first presented in 19791
and recently updated.2 It encompasses the most objeca
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tive esthetic principles, including dental esthetics, gingival esthetics, but also the more subjective esthetic integration into the frame of the smile, face, and, more
generally, the individual (Fig. 1).
The relative dimensions of teeth seem to be among
the most objective dental criteria within the esthetic
checklist because they can be easily and physically controlled. The definition of ideal tooth dimensions, however, remains a difficult task due to individual variations
and proximal/incisal tooth wear. To provide magic
numbers for the clinician, mathematic theorems such
THE JOURNAL OF PROSTHETIC DENTISTRY 453
Fig. 1. New esthetic checklist. Reprinted with permission from Magne P, Belser U. Bonded porcelain restorations in the anterior
dentition: A biometric approach. Quintessence Publ. Co. Inc, Chicago 2002.
as the golden proportion3,4 and the golden percentage5 have been proposed, taking into account classic
elements of art and architecture. These rules were applied to the apparent size, as viewed directly from the
anterior. Lombardi,3 the first to mention golden numbers for anterior teeth, stated that strict application of
the golden proportion has proved to be too rigid for
dentistry. Measurements by Preston6 confirmed the unrealistic nature of the golden rule in this specific context.
Excessive narrowness of the maxillary arch and compression of lateral segments can be observed in situations of
strict adherence to the golden rule as illustrated in Figure 2. In addition, it appears that tooth height, crown
width/length ratios, transition line angles, and other
special effects of tooth form are likely to influence the
perception of symmetry, dominance, and proportion.
Among the aforementioned parameters, measurements
of width/length ratios of normal clinical crowns seem to
represent the most stable reference; a homogeneous ratio (81%) was found by Sterrett et al7 for the 3 anterior
maxillary tooth groups. Such measurements were carried out on clinical crowns of normal subjects with stone
casts derived from irreversible hydrocolloid impressions
and excluded teeth with incisal wear and premolars.
Data regarding natural tooth dimensions are accessible through a number of tooth morphology sources
(textbooks and journal articles).8-11 In spite of the fact
that mesiocervical and incisocervical dimensions of teeth
454
Fig. 4. Measurement technique. Longest apicocoronal distance (parallel to long axis, between most apical point of CEJ
and most incisal point of anatomical crown) and widest
mesiodistal portion (perpendicular to long axis) measured for
each specimen.
point of the anatomic crown) (Fig. 4). A special calibration tool built in Scion image was used to convert all
distances into millimeters.
The data were then transferred to a spreadsheet program for mathematical treatment, including the calculation of the width/length ratio R. Statistical analysis
was carried out to compare the 3 tooth groups. A 1-way
analysis of variance was used to compare the mean values
of W, L, and R for the 7 different subgroups. Multiple
least significant difference range tests (confidence level
95%) were then applied to determine which means differed statistically from others.
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455
Table I. The mean (mm) (in bold), followed by standard deviation (in parentheses) and range of the width, length and W/L
ratio of the 4 tooth types of the maxillary dentition
Table II. Result of statistical analysis for WIDTH (P .05, homogeneous groups determined by multiple range tests,
confidence level 95%)
RESULTS
The mean, standard deviation and range of the width,
length, and width/length ratio are presented in Table 1.
In each situation, analysis of variance outcomes required
multiple range tests to identify homogeneous groups
(Tables 2 through 4).
Within the same tooth group, there was no influence
of the incisal wear on the average crown width. The
456
Table III. Result of statistical analysis for LENGTH (P .05, homogeneous groups determined by multiple range tests,
confidence level 95%)
Table IV. Result of statistical analysis for W/L RATIO (P .05, homogeneous groups determined by multiple range tests,
confidence level 95%)
followed by unworn canines (10.83 mm) and worn central incisors (10.67 mm). The shortest crowns were
those of worn canines (9.90 mm), worn and unworn
lateral incisors (9.34 to 9.55 mm), and premolars (9.33
mm).
Width/length ratios also showed significant differences: highest values were found for worn central incisors (87%) and premolars (84%). The latter were also
similar to worn canines (81%), which constituted a homogeneous group with worn lateral incisors (79%) and
unworn central incisors (78%). The lowest ratios were
found for unworn canines and unworn lateral incisors
(both showing 73%).
DISCUSSION
Even though it would appear more relevant to measure clinical crowns, this experimental protocol intended to use extracted teeth and anatomic crown measurement instead. The reasons for this choice are
explained below.
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Width measurements of extracted teeth can be extremely precise because of the proximal clearance (absence of neighboring teeth); the precision of clinical
measurements (including those made on casts) can be
jeopardized, especially with overlapping teeth. This specific reason could explain why average widths in this
study are approximately 1 mm larger compared with
clinical measurements (from casts derived from irreversible hydrocolloid impressions) reported by Sterrett et
al.7
Length measurements were confined apically by the
CEJ, which normally sets the position and structure of
the soft tissues.12,13 However, the relationship between
CEJ and gingival level can show variations within and
above normal range,12 sometimes exposing part of the
root, sometimes covering enamel, an example of which
would be altered passive eruption. In this context, it
seems appropriate to use the CEJ (and not the gingival
level) as a reference for the establishment of natural
guidelines. Accordingly, average lengths in this study are
457
Fig. 7. A-C, Patient featuring reduced crown width/length ratios caused by erosion and wear. D-F, New situation (increased
ratios) after placement of bonded porcelain restorations.
Fig. 8. A, Diagnostic steps before treatment of reduced size teeth and diastemata. B, Directional coincidence of incisal edges
(also called smile line, dotted curve) and lower lip (white curve) provides cohesive forces to dentofacial composition; incisal
edges of central incisors have been positioned accordingly. C, Closing of space between central incisors generates width/length
ratio of 99%, which calls for gingival correction (black dotted line). D, Use of dimensions of central incisors as reference,
procedure can be extended to other teeth.
CONCLUSIONS
This work investigated the anatomic crown of the 4
anterior maxillary tooth groups of white subjects (cen460
3. Width/length ratios also showed significant differences: highest values were found for worn central
incisors (87%) and premolars (84%). The latter were
also similar to worn canines (81%), which constituted
a homogeneous group with worn lateral incisors
(79%) and unworn central incisors (78%). The lowest
ratios were found for unworn canines and unworn
lateral incisors (both showing 73%).
We express our gratitude to Dr Minos Stavridakis (research fellow, University of Geneva) for providing the extracted teeth and to
Dr Maria Cattani (Division of Dental Materials, University of Geneva) for computing of the statistical analyses presented in this study.
REFERENCES
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try-in. In: Scha rer P, Rinn LA, Kopp FR, editors. Esthetic guidelines for
restorative dentistry. Chicago: Quintessence; 1982. p. 188-92.
2. Magne P, Belser U. Natural oral esthetics. In: Magne P, Belser U, editors.
Bonded porcelain restorations in the anterior dentition: a biomimetic
approach. Chicago: Quintessence; 2002. p. 57-96.
3. Lombardi RE. The principles of visual perception and their clinical application to denture esthetics. J Prosthet Dent 1973;29:358-82.
4. Levin EI. Dental esthetics and the golden proportion. J Prosthet Dent
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5. Snow SR. Esthetic smile analysis of maxillary anterior tooth width: the
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