Received: 11 July 2017 | Revised: 30 August 2017 | Accepted: 6 September 2017

DOI: 10.1111/jerd.12341

RESEARCH ARTICLE

Prevalence of tooth forms and their gender correlation

Eduardo Mahn DDS, MS, PhD1 | Stephanie Walls DDS1 | Gilbert Jorquera DDS1 |

s DDS1 | Alejandra Val DDS1 | Camila S. Sampaio DDS, MS, PhD2
Ana María Valde

1
Department of Prosthetic Dentistry,
College of Dentistry, Universidad de los
Abstract
Andes, Av Monsen ~or Alvaro del Portillo,
Objective: This study evaluated different tooth shapes from female and male genders, matching
Santiago, 12455, Chile, Santiago, Chile
2
them with the firstly proposed pure basic forms, and proposed different hybrid shapes; it also
Department of Biomaterials, College of
Dentistry, Universidad de los Andes, Av evaluated the percentage of correct gender identification of lay people, dentists and dental
Monsen~or Alvaro del Portillo, Santiago, students.
12455, Chile, Santiago, Chile
Materials and Methods: Standardized digital photos were taken from 460 people and analyzed
Correspondence by 3 experts regarding genders and tooth forms: pure basic forms—oval (O), triangular (T), square
Camila Sobral Sampaio, Department of (S) and rectangular (R); and combined hybrid forms—oval-rectangular (OR), triangular-rectangular
Biomaterials, Universidad de los Andes,
(TR), triangular-oval (TO), square-oval with flat lateral incisors (SOF), and square-oval with scal-
College of Dentistry, Av Monsen ~or Alvaro
del Portillo, 12455, Santiago, Chile. loped lateral incisors (SOS). Then, correct gender identification (%) was evaluated among lay
Email: csampaio@miuandes.cl people, dentists and dental students (n 5 10).

Results: Pure forms showed less prevalence in the population studied (O:6.52%; S:3.48%;
T:3.26%; R:2.39%) than hybrid ones (TO:20.87%; SOS:20.65%; OR:19.57%; SOF:16.96%;TR:
6.30%). Tooth gender selection among different evaluators was not significantly different (50%
correct answers).

Conclusions: No correspondence exists between tooth shapes and patient genders. Pre-
standardized pure tooth forms appeared less than hybrid ones, while the most frequently found in
the population studied were TO, SOS, and OR forms, disregarding genders.

Clinical significance
Esthetic perception is an increasingly important criterion critical to satisfy patients. The correlation
of reported tooth shapes with specific genders was not reliably observed in natural smiles. Tooth
shapes should be selected according to the wishes of the patient rather than by previously
believed gender specific tooth shapes. Pure basic tooth forms should be complemented with the
addition of combination forms to more accurately portray forms found in nature.

KEYWORDS
forms perception, gender classification, tooth shapes

1 | INTRODUCTION Different aspects need to be taken into consideration when observing

an ideal smile, such as symmetric composition of teeth, color and tooth
It has been proposed that optimal esthetics is accomplished if face, shapes.1–10 It has been said that tooth forms might be determined by
1
arch and tooth forms are in harmony. When planning a treatment, sex gender,11–13 age,11 gingival arrangement,14 facial form,15 and even
dentists need to understand beauty, harmony, balance, and proportion, patient’s emotions,10,11,16 among others. Esthetic perception and
2,3
as perceived by the society; thus, smile components make a strong patients concerns are becoming an increasingly important issue, along
contribution in order to achieve an attractive face and pleasant smile. with the demand of patients wanting to esthetically change their teeth.

J Esthet Restor Dent. 2018;30:45–50. wileyonlinelibrary.com/journal/jerd V

C 2017 Wiley Periodicals, Inc. | 45
46 | MAHN ET AL.

When the upper anterior teeth need to be restored, natural denti- dentists and dental students throughout the photos. Hypotheses
tion clues can be used to help achieving individual and attractive resto- tested were that: (1) Pure basic forms do not correlate to the majority
rations, therefore, photographs or cast models are of great help.1 of the population studied; and (2) Percentage of correct gender identifi-
However, today, issues regarding dissatisfaction of patients with their cation by teeth photographs is showed to be different when evaluated
original smile seem to be increasing, and the search for a pleasant smile by lay people, dentists and dental students.
is a trend within healthy patients. Improvements in dental materials
made it possible to achieve tooth form and function using minimally
invasive approaches.10 Final results must meet patient’s esthetic 2 | MATERIALS AND METHODS
expectations regarding harmony of the smile design and tooth shapes,
frequently different than the ones they had originally. This study was performed according to protocols approved by Univer-
It has been suggested by some that tooth forms should be influ- sidad de los Andes, Chile, Institutional Review Board. Four hundred
enced by the emotional aspects of the patient, the “theory of tempera- and sixty students (285 female; 175 male) from the University of Los
ment,” which was characterized by temperaments such as sanguine or Andes, Chile were randomly selected; research details were explained
dynamic, choleric or strong, melancholic or sensitive, and phlegmatic or and each student signed a consent of agreement. Inclusion criteria
10,11 regarded students within 18–32 years which anterior teeth had not
peaceful. Williams suggested that the shape of the central incisor
is supposed to be the inverted frontal view of the face (characterized undergone restorative treatments.
as square, ovoid, and tapered), known as the “law of harmony” and Digital photos were taken by an iSight camera from iPhone 6
15 (Apple, Cupertino, CA) and a 60-mm Moment lens (Moment; Los
considered until today as the pure basic forms. Further studies pro-
posed additional combinations of the pure forms.8 Another theory is Angeles, CA), in artificial light calibrated into 5.500 Kelvin (IceLight; F.J.
correlated to sex genders, which is a theory based on stereotypes that Westcott, Toledo, OH). A total of 920 photographs were taken and
suggest that women presents more rounded, soft and delicate teeth evaluated by three calibrated operators, being two per patient, with
11,12 the camera positioned perpendicular to the floor at a standard distance
(tapering/ovoid), and men should have square, angular teeth. Many
dental schools instruct students to consider gender when arranging of 40 cm from the patient’s nose. Patients were instructed to stay with
11,12 their head upright, without rotating, and with the occlusal plane of
teeth and selecting tooth molds.
Among all those theories, innumerous papers cited that such corre- maxillary teeth parallel to the floor. For the first photo, a lip retractor
lations might not exist in nature.1,4,5,17,18 Different studies stated that was used and the patient was asked to open the mouth until a dark
it cannot be distinguished by photographs the patients’ gender just by space was seen between both superior and inferior arches. Second
1,18
looking at their teeth. Also, it’s been proved that inverted shape of photo was also taken with a lip retractor, from the superior arch with a
the face does not correspond to the teeth shapes.4 A research that dark contrast. Both photos were taken from the face of the patients,
observed differences in genders concluded that some photos are with a perfect observation of the teeth, which were separately ana-
1
wrongly identified as male, as well as the opposite. They stated that it lyzed after.
might happen because decisions are taken based on accepted assump- Photographs were evaluated in the Keynote software from a
tions regarding sex related differences of tooth forms, which might not Macbook Air 13-in. 2015 (Apple, Cupertino, CA) by three different
reflect the reality. Also, it was noted in nature that among pure forms, experts, and an agreement was obtained within them regarding the
oval are more frequent than other shapes, in both female and male shapes. In the software, photographs were superimposed in the four
genders.19 conventional prototyped pure basic tooth shapes and evaluated:
To visualize and study those different characteristics, digital soft- oval (O), triangular (T), square (S), and rectangular (R). While photo-
6,20
ware and digital cameras are tools that can be used. Digital tools graphs were evaluated, it was observed numerous patients that did
exist for the purpose of designing anatomically shaped tooth restora- not fit the scope of the prestandardized tooth biotypes, and five
20
tions, and digital cameras are the most common tool present in den- new hybrid combinations were purposed, according to the combina-
tal offices and laboratories, and can be used for communication tion of the previous biotypes: oval-rectangular (OR); triangular-
between, dentists, technicians and patients to accomplish a desirable rectangular (TR); and triangular-oval (TO), square-oval with flat lat-
treatment regarding forms and colors.6 eral incisors (SOF), square-oval with scalloped lateral incisors (SOS).
Contradictory results regarding tooth shapes among different stud- After the observation of the new tooth shapes, images of hybrid
ies might be related to the belief that diverse characteristics exist prototypes were created and the superimposition of the images to
between genders and tooth forms, and digital photographs might be of the photographs that did not match the first tooth shape criteria
great help in order to identify these characteristics. Thus, the aim of were performed again, with the new shapes. After that, a correlation
this study was to evaluate, throughout digital photos, the different between shapes and genders were performed.
tooth shapes found in different people regarding female and male gen- The same photos were used to evaluate the percentage of correct
ders, matching them with the firstly showed pure basic forms, and to responses of 10 dentists, 10 dental students and 10 lay persons regard-
propose different hybrid shapes according to the needs; and to evalu- ing the gender of the patient in the photo. Data were analyzed using a
ate the percentage of correct gender identification of lay people, one-way analysis of variance.
MAHN ET AL. | 47

TA BL E 1 Total prevalence of tooth shapes regarding genders tooth shapes and Figure 2 shows the combined hybrid ones, together
with photographs that corresponded to the correlated form.
Tooth shapes Total (%) % Female % Male
Tables 2 show the differences on tooth gender selection among lay
Oval (O) 6.52% 7.37% 5.14%
people, dentists and dental students. It was not observed a statistical sig-
Square (S) 3.48% 4.56% 1.71% nificant difference among lay people (51.37% of correct gender answers),
Triangular (T) 3.26% 1.75% 5.71% dentists (52.99%), or dental students (54.33%) (P > .05). Figure 3 shows
correctly and incorrectly identified photographs regarding genders.
Rectangular (R) 2.39% 1.05% 4.57%

Triangular-oval (TO) 20.87% 21.40% 20.00%

4 | DISCUSSION
Square-oval/scalloped (SOS) 20.65% 21.40% 19.43%

Oval-rectangular (OR) 19.57% 17.89% 22.29% Different aspects have been studied in order to correlate tooth shapes,
Square-oval/flat (SOF) 16.96% 20.00% 12.00% genders and facial structures.11,12,15 However it is difficult to routinely
correlate these factors with patient gender.1,4,5,17,18 This study aimed
Triangular-rectangular (TR) 6.30% 4.56% 9.14%
to evaluate different tooth shapes and propose hybrid shapes in order
Total 100% 100% 100%
to clarify the large amount of possibilities in which a clinician can
restore function and/or esthetic of a patient.
The first hypothesis was accepted, once it was observed a larger
3 | RESULTS percentage of teeth characterized by the combined hybrid tooth
shapes than the pure basic forms. Also, tooth forms are, in the wide
Table 1 shows the percentages of the nine evaluated tooth shapes, the majority of the cases, showed not to be correlated to gender. Tooth
basic and hybrid ones. It was observed a higher prevalence of com- forms with the most ranked percentages (TO—20.87%, SOS—20.65%,
bined tooth forms than pure basic forms. Pure basic forms corre- and OR—19.57%) showed to have similar percentages among female
sponded to: 6.52% (O); 3.48% (S); 3.26% (T); 2.39% (R); while and male genders. Regarding the basic forms, it was observed a slightly
combined hybrid tooth shapes corresponded to a total of: 20.87% higher prevalence of square form for female than male, and slightly
(TO); 20.65% (SOS); 19.57% (OR); 16.96% (SOF); and 6.30% (TR). Dif- higher percentages of triangular and rectangular shapes for male than
ference between female and male genders concerning each tooth female, going in accordance to previous studies.18,19 Oval form showed
shape is also distinguished in Table 1. Figure 1 shows the pure basic to be similar for both genders, and was the shape with the highest

FIGURE 1 Pure basic tooth shapes and their correspondent photographs

48 | MAHN ET AL.

FIGURE 2 Combined tooth shapes and their correspondent photographs

percentage among the pure basic forms, also in accordance to previous Identification of genders by anterior tooth segment photographs
4,8,18,19
studies. When evaluating the combined forms, TO, SOS and OR has been showed in the literature.1,14,18 An average of 53% was found
showed to have similar percentages within each other and when com- when correct answers were analyzed by dentists (54.33%), dental stu-
paring female and male genders, while SOF showed higher percentage dents (52.99%) and lay people (51.37%), and were not significantly dif-
for female gender and TR showed prevalence for male gender. The ferent among each other in total, rejecting the second hypothesis.
combined shapes showed a tendency when evaluated together with When evaluating correct answers when compared answers from male
the pure forms, as triangular and rectangular forms separately showed and female genders, it was observed that male gender was more easily
a tendency for male genders, and when the two forms were combined, detected than female (higher percentage of correct answers). A study
the same tendency was observed, although it was not dramatic. that evaluated experts’ answers from 60 digital photos showed that
On the contrary of what was believed at first about female show- around 53–58% were correct, depending on gender.1 Although the
11
ing a rounded form, oval shape and its combinations (TO, SOS, and mentioned study evaluated less photographs than the present study,
OR) were not showed as a characteristic of female gender only and percentages of correct answers showed to be similar.1 However, this
showed to be homogeneous among female and male genders, and was study evaluated different types of people, and they all showed the sta-
the most observed tooth shape in both hybrid and pure forms. This tistical same values. The high number of pictures analyzed in this study,
goes in accordance to previous studies.18,19 It was previously men- that showed no differences between lay people, dentists and dental
tioned that a truly accurate method to measure and compare shapes students (all close to 50%), means that results came closer to random
such as face and teeth probably does not exist;4 moreover, it has been (only two options were possible, male or female), showing the impossi-
previously observed that tooth shapes cannot be correlated to gen- bility to correlate tooth form and gender. No studies or background
ders,18 which was once again proved in this study. can help a person identify gender based on tooth form. These results
might also reflect the idea that not only experts believe that there is a
TA BL E 2 Correct answers among lay people, dental students and specific form for woman and man, but the society in general has also
dentists, regarding female and male genders
the same erroneous perception, which is not observed in reality, as
Lay-people Dental students Dentists seen in this study. Careful analysis of the pictures also showed that lay
Correct answers (%) 51.37% A 52.99% A 54.33% A people have a tendency to choose a “male” form when teeth have cer-
tain defects, misalignments, or just an undesirable appearance. Also, it
Correct female (%) 37.82% 48.11% 39.14%
was observed that, although a perception of rounded is characteristic
Correct male (%) 73.14% 67.14% 72.25%
for woman and square for man according to previous beliefs,11
MAHN ET AL. | 49

F I G U R E 3 Correctly and incorrectly identified photographs regarding to female and male genders. First row relates to male gender and
the second row relates to female gender. Note that a more square shape results in a higher percentage of correct answers for male and a
more rounded shape results in a higher percentage of correct answers for female for dentists and dental students. Lay people have the
tendency to choose a “male” form when teeth have certain defects, misalignments, or just an undesirable appearance.

contrary to what was seen in the present study, there is a different per- with the face and lips and show the patient a previous expected result
ception by people when dealing with what they think is more esthetic of the case, allowing options regarding shapes to be chosen.
or not.2,8 Schools should teach the students that gender and forms are
not always related, other than teaching the past doctrines and theo- 5 | CONCLUSIONS
ries.13 Until the date, there is no accepted rule or mathematical method
to define morphologic features,1 and most likely it will never exist, Results from this study confirm the evidence that there is no correspon-
since tooth form results are not specific for a certain gender. dence between tooth shapes and patient genders, as believed previ-
Obviously, the hybrid combinations cited in this study are not the ously. In addition, the pre-established four conventional tooth forms
only ones that exist and options must be given for patients to make a (oval, triangular, rectangular, and square) do appear in the population;
decision. Central incisors have been cited to be the key determinant however, it corresponds to a low percentage of people. It was observed
for judge’s esthetic preferences7 and the most dominant teeth dis- that the highest percentages of tooth shapes observed in the population
played during smile;8 also, ridges, grooves, lobes, cingulum, and surface studied was hybrid forms, such as TO (20.87% total; 21.4% female and
texture are easily detectable features recognized by the human 20% male), SOS (20.65% total; 21.4% female and 19.43% male) and OR
observer20 and should be taken into account when dealing with an (19.57% total; 17.89% female and 22.29% male), while within the pure
esthetic treatment. Although photographs are the most used method basic forms, the oval was the most prevalent (6.52% total; 7.37% female
to evaluate shapes and color,2,4,6,8,9,18 different diagnosis methodolo- and 5.15% male). Because of this, five new hybrid tooth shapes were
gies can also be used in the clinic to design the restorations according proposed, being them: TO (triangular-oval), SOS (square-oval with scal-
to patient’s needs, such as the digital smile design, based on drawings loped lateral incisors), OR (oval-rectangular), SOF (square-oval with flat
in the screen of a computer, the morphogenic design method, CAD/ lateral incisors), and TR (triangular-rectangular). Clinically, there is no
CAM software, wax up and mock up, which by their turn shows the such thing as correlation among tooth forms and genders, and when
final outcome of the treatment via a resin applied onto the teeth of the dealing with esthetic procedures, trials must be performed and patient’s
patient.10,20 Such details must be taken into consideration, since differ- suggestions must be taken into consideration, without considering only
ent shapes have been described to be more pleasant in a rank of order a specific tooth form, but the wide variety of it. Although not described
of attractiveness when evaluated by dentists, technicians or patients.8 in anatomy texts, combined hybrid forms should be primarily chosen,
Results from this study show evidence that tooth shapes should since their prevalence is much higher than classic pure forms, when wax
be evaluated separately and according to patients’ opinions, and not ups and mock ups, prosthesis teeth or final restorations are done. Also,
generalized according to genders or any pre-established parameters dental photographs are of good help in the dental practice and can help
and shapes. Moreover, not only the pure basic forms should be consid- to guide decisions of patients and clinicians. Further studies should be
ered, but also a combination of them (hybrid shapes), since the com- performed to study prevalence in bigger samples.
bined forms are much more prevalent than pure forms, as previously
shown. Even more, in order to achieve natural looking restorations, cli- DISCLOSURE STATEMENT
nician should rather think in combined forms as the first choice, since
the prevalence of the just four combinations (TO-OR-SOS, and SOF) is Author Eduardo Mahn declares that he has no conflict of interest.
roughly 80% compared to the four pure form together with<16% com- Author Stephanie Walls declares that she has no conflict of interest.
bined. Dentists and technicians should always consider several factors Author Gilbert Jorquera declares that he has no conflict of interest.
like recessions, alignment, gingival zeniths, gingival biotype, relation
s declares that she has no conflict of interest.
Author Ana María Valde
50 | MAHN ET AL.

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