Smile attractiveness in patients treated with or without 4 premolar extractions: A 36-year follow-up

Introduction

This study aimed to assess the smile attractiveness in patients treated with or without 4 premolar extractions at a 36-year follow-up.

Methods

The sample comprised 52 patients with Class I and II malocclusion divided into 2 groups. Group 1 consisted of 15 patients treated without extractions (10 females and 5 males), with a mean pretreatment, posttreatment, and long-term posttreatment (T3) age of 13.2, 15.1, and 49.8 years, respectively. The mean treatment time was 1.9 years, and the mean long-term follow-up period was 34.7 years. Group 2 consisted of 37 patients (25 females and 12 males) treated with 4 premolar extractions, with a mean pretreatment, posttreatment, and long-term posttreatment age of 13.3, 15.7, and 53.6 years, respectively. The mean treatment time was 2.3 years, and the mean long-term follow-up period was 37.9 years. The mean retention time was 2 years for both groups. Frontal smiling photographs were obtained at long-term follow-up. Smile attractiveness was evaluated in an online questionnaire in which the evaluator could rate the smiling photographs with a 10-point scale. The randomly selected evaluator sample consisted of 62 laypeople, 33 dentists, and 89 orthodontists. Independent t tests, 1-way analysis of variance, and Tukey tests were used for intergroup comparisons at P <0.05.

Results

The smile attractiveness on the long term was similar in the groups treated with 4 premolar extractions (4.70 ± 1.35) or without extractions (4.51 ± 1.46). Women and orthodontists were more critical in assessing smile attractiveness than men, dentists, and laypeople.

Conclusions

After long-term posttreatment, the smile attractiveness was similar in patients treated with 4 premolar extractions or without extractions.

Highlights

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Smile attractiveness was compared in patients treated with or without 4 premolar extractions.
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Long-term smile attractiveness was assessed at 36 years.
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Orthodontists, dentists, and laypeople evaluated the smile attractiveness on the long term.
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Smile attractiveness was similar in patients treated with or without 4 premolar extractions.
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Women and orthodontists were more critical in smile attractiveness assessment.

Beauty directly interferes with how people perceive themselves and how they are perceived by others. Although beauty perception is subjective, the construction of the attractiveness of the face is very well related to the harmony among the dentofacial structures. ^, The smile is part of a set of characteristics that are related to overall attractiveness and can be a powerful tool capable of influencing interpersonal relationships through esthetic judgment. A beautiful smile increases the chances of selection in a job interview; it can be seen as a sign of intelligence, dominance, self-confidence, and kindness and has positive influences on self-esteem. The smile attractiveness is not restricted to the teeth, and the integration among symmetry, gingival exposure, size of the buccal corridor, the thickness of the lips, the shape of the teeth, the severity of malocclusion, and familiarity are some aspects that may influence the determination of esthetic sense. ^,

There is a long debate in orthodontics between the type of treatment, with or without tooth extractions, and whether they could influence the esthetics of the face and smile. Edward Angle believed that treatment with extractions characterized mutilations and would disturb the natural harmony of the occlusion, bringing negative consequences for the beauty of the face. In contrast, his student Tweed, after observing that >80% of his patients treated without extractions presented relapse and compromised facial esthetics, suggested that the success of orthodontic treatment would only be achieved with extractions. Although studies reported that extractions could impoverish esthetics because of lower lip support after retraction mechanics and could be related to facial aging, ^, the choice of orthodontic treatment with or without extraction of premolars does not seem to negatively affect smile esthetics and facial attractiveness as long as they are well indicated, after evaluation of posttreatment photographs by orthodontists and laypeople. ^, Decisions between one protocol and another may depend on the clinical experience of the orthodontist and the severity of the malocclusion, and in patients with a borderline relationship, esthetics is a factor that must be considered when making a decision. ^,

It is essential to be aware of changes in occlusion over the years. It is challenging to differentiate physiological changes caused by occlusion maturation from those inherent to orthodontic treatment. From adolescence to adulthood, normal occlusion changes typical of aging, which involves an increase in the clinical crown in posterior teeth; crowding of the anterior sector; decreases of intercanine width and arch length and perimeter; overbite; and curve of Spee. Regarding the long-term changes in people with Class I and II malocclusions after undergoing orthodontic treatment treated with and without 4 premolar extractions, it is observed the increase of anterior incisor irregularity, overjet, and overbite; the decrease of intermolar width, arch length, and perimeter; and the tendency of relapse to the pretreatment situation. ^, This study showed the consequence of aging in occlusion in orthodontically treated and nontreated subjects with >40 years of follow-up. They demonstrated that maturational changes in patients with normal occlusion occur in a smaller proportion than in orthodontically treated patients.

The current literature provides a solid foundation for understanding how treatments, with or without extractions, impact smile esthetics. ^, ^, There is anecdotal knowledge in orthodontics that treatments involving premolar extractions can worsen the esthetics of the patient’s smile. However, according to our understanding, there are no studies on how aging interferes with the smile esthetics of patients treated with different orthodontic protocols. Knowing whether or not there is a difference in smile attractiveness over time could end once and for all the debate about extracting or not extracting, being able to base the orthodontist’s decision on his diagnosis. The knowledge of the long-term results of our treatments through evidence-based information allows us to build an excellent patient-professional relationship, increasing the chances of treatment success. Therefore, this study aimed to test the null hypothesis that there was no difference in smile attractiveness between patients treated with and without premolar extractions 36 years after treatment.

Material and methods

The Ethics Research Committee at Bauru Dental School, University of São Paulo approved this retrospective study. Written consent was obtained from all subjects.

The sample size calculation was based on an α significance level of 5% and a β of 20% to achieve a test power of 80% and to detect a minimum difference of 1 point in smile attractiveness, with a standard deviation of 0.96. Therefore, the sample size calculation indicated the need for at least 15 participants per group. The number of evaluators was similarly calculated and was found to be at least 20 evaluators per group of dentists, orthodontists, and laypeople.

The sample was obtained from retrospective files of the Orthodontic Department of Bauru Dental School, University of São Paulo. All records of patients treated orthodontically between the years of 1970 and 1980 were analyzed according to the inclusion criteria that were as follows: (1) Class I or II malocclusion at the beginning of orthodontic treatment (T1), (2) treatment protocol without extraction or extraction of 4 first premolars, (3) complete maxillary and mandibular orthodontic treatment with edgewise fixed appliance (0.022 × 0.028-in slot), (4) presence of all permanent teeth up to the first molars, (5) absence of dental anomalies or agenesis, and (6) use of a removable maxillary retainer (Hawley plate) and fixed mandibular retainer from canine to canine for a minimum of 1 year and a maximum of 3 years posttreatment, with no retention present at the time of follow-up.

The exclusion criteria were (1) lack of complete records from initial and final treatment stages, (2) history of orthodontic treatment during the long-term follow-up (retreatment), (3) the impossibility of contact during long-term follow-up, or (4) the patient’s unwillingness to participate in the study.

The sample consisted of 52 patients with Class I and II malocclusion divided into 2 groups according to the treatment protocol with 4 first premolars extractions or without extractions. Extraoral smile photographs were evaluated in the long-term follow-up to compare smile attractiveness among the groups. Group 1 consisted of 15 patients (10 females and 5 males) treated without extractions. Class I malocclusion was present in 5 patients, and 10 had Class II malocclusion. The mean age at T1 was 13.20 ± 0.85 years, the mean treatment time was 1.90 ± 0.84 years, and the mean posttreatment time was 34.70 ± 6.30 years. Group 2 consisted of 37 patients (25 females and 12 males) treated with 4 first premolar extractions. Class I malocclusion was present in 21 patients, whereas Class II malocclusion was present in 16 patients. The mean age at pretreatment was 13.30 ± 2.02 years, the mean treatment time was 2.34 ± 0.60 years, and the mean posttreatment time was 37.90 ± 4.24 years.

Orthodontic mechanics in both groups included extraoral headgear as anchorage in patients with Class I malocclusion and correction of anteroposterior molar relationship in patients with Class II malocclusion. Class II elastics were used when necessary, and an elastic chain was used to close spaces in patients treated with extractions.

The groups should have similar occlusal characteristics at T1, posttreatment (T2), and long-term follow-up (T3) and be comparable regarding age, sex distribution, type of malocclusion, time of treatment, retention time, and time of posttreatment evaluation. The occlusal evaluation was performed by dental model measurements using the peer assessment rating (PAR) index, objective grading system (OGS), and Little’s irregularity index (LII). The dental models were obtained at 3 different stages: T1, T2, and T3 (mean follow-up period was 35 years postretention). All dental models were digitized using a 3-dimensional scanner (R700; 3Shape, Copenhagen, Denmark), and the measurements were performed using the OrthoAnalyzer 3-dimensional software (3Shape). All measurements were performed in both maxillary and mandibular arches by a single calibrated examiner. The research measurements were performed only after proper calibration with an experienced professor (K.M.S.F.).

The smile attractiveness was evaluated through reproducible posed smile photographs obtained through the orthodontic files of patients in T3, a mean of 36 years after treatment. The photographs were imported to Adobe Photoshop CS6 (version 22.3.1; Adobe, San Jose, Calif) with measurements of 18 × 13 cm, restricting only the smile area. The images were converted to black and white, and facial structures that might interfere with confounding factors, such as the chin, cheeks, and nose, were eliminated. All images had 300 dpi resolution and were saved in TIFF format ( Fig 1 ).

A questionnaire generated in Google Forms was created exclusively for this study and was available for 3 months. The link was sent via WhatsApp messenger to the evaluators recruited from groups of dentists, postgraduate students in orthodontics, and social networks. The questionnaire had a series of 54 photographs of a posed smile 36 years after the end of treatment. By clicking on the link, participants were automatically redirected to the home page containing information about the research with an informed consent form with content regarding the confidentiality of their data and the possibility of withdrawing from participating in the study. All the evaluators were aged >18 years. The images were randomly ordered to assess smile attractiveness, and values were assigned on a numerical scale from 1 to 10 points, with 1 being the less attractive and 10 being the most attractive smile ( Fig 2 ). The evaluators could observe the photographs for as long as they wished and change their answers if necessary.

The smile attractiveness was evaluated by 62 laypeople (41 females and 21 males) with a mean age of 48.18 years, 33 dentists (20 females and 13 males) with a mean age of 33.55 years, and 89 orthodontists (59 females and 30 males) with a mean age of 36.74 years.

To evaluate the reliability of the evaluators in rating smile attractiveness, 2 smile photographs were randomly repeated in the questionnaire, and the intraclass correlation coefficient (ICC) was used.

Statistical analyses

The normal distribution of the sample was verified by the Shapiro-Wilk test, and parametric comparison analysis was performed.

Intergroup comparability of the initial, final, and long-term posttreatment ages, the treatment time (T2 − T1), time of long-term posttreatment evaluation (T3 − T2), retention time, PAR index, OGS index, and maxillary and mandibular LII were performed with independent t tests. The intergroup comparability of age among the groups of evaluators (dentists, orthodontists, and laypeople) was performed with a 1-way analysis of variance and post-hoc Tukey test when necessary. For intergroup comparison of sex distribution and type of malocclusion, the χ ² test was used. The comparisons of scores of smile attractiveness given by the evaluators’ groups (orthodontists, dentists, and laypeople) were performed with a 1-way analysis of variance and post-hoc Tukey test when necessary. A comparison of the scores of smile attractiveness of extraction and nonextraction groups given by each group of evaluators was performed with independent t tests. Comparison of the score of smile attractiveness given by females and male raters and comparison of extraction and nonextraction scores of smile attractiveness given by females and males separately were performed with independent t tests. Intergroup comparisons of smile attractiveness were performed with independent t tests.

Data were analyzed using the Statistica software (version 12.0; StatSoft, Tulsa, Okla) at P <0.05.

Results

The ICC of the precision of the evaluators in rating the smile attractiveness was 0.95, indicating an excellent intrarater agreement.

The groups were comparable regarding pretreatment and posttreatment age, retention time, sex distribution, and type of malocclusion ( Table I ). The long-term posttreatment age was significantly higher in the extraction group, and the treatment time and long-term follow-up evaluation time were significantly longer in the extraction group when compared with the nonextraction group ( Table I ).

Table I

Intergroup comparability of the T1, T2, and T3 ages, treatment time, time of long-term posttreatment evaluation, retention time, sex distribution, and type of malocclusion

Variables	Nonextraction (n = 15)	Extraction (n = 37)	P value
Initial age (y)	13.20 ± 0.85	13.30 ± 2.02	0.790 ^†
Final age (y)	15.01 ± 1.20	15.70 ± 2.19	0.329 ^†
Long-term age (y)	49.80 ± 6.25	53.60 ± 5.26	0.029 ^∗^,^†
Treatment time (y)	1.90 ± 0.84	2.34 ± 0.60	0.036 ^∗^,^†
Long-term follow-up (y)	34.70 ± 6.30	37.90 ± 4.24	0.037 ^∗^,^†
Retention time (y)	2.28 ± 1.21	2.35 ± 1.30	0.848 ^†
Sex			χ ²= 0.31, df = 1, P = 0.950 ^‡
Females	10	25
Males	5	12
Type of malocclusion			χ ²= 4.34, df = 3, P = 0.227 ^‡
Class I	5	21
Class II	10	16

Note. Values are presented as mean ± standard deviation.

Df , degrees of freedom.

∗ Statistically significant for P < 0.05.

† Independent t test.

‡ χ ²test.

The groups were comparable regarding malocclusion severity (PAR index, OGS, and maxillary LII) at T1, T2, and T3 ( Table II ). The mandibular LII was comparable between the groups at T2 and T3. The mandibular LII was significantly higher in the extraction group at T1 than in the nonextraction group ( Table II ).

Table II

Intergroup comparability of the PAR index, OGS index, and Mx and Md LII at T1, T2, and T3 (independent t test)

Variables	Nonextraction (n = 15)	Extraction (n = 37)	P value
PAR index T1	26.73 ± 9.25	23.80 ± 8.21	0.272
PAR index T2	2.67 ± 2.44	3.00 ± 2.00	0.612
PAR index T3	9.54 ± 9.13	7.51 ± 4.48	0.300
OGS index T1	66.20 ± 17.50	60.90 ± 14.69	0.272
OGS index T2	32.30 ± 9.61	31.30 ± 5.69	0.645
OGS index T3	42.30 ± 21.32	34.10 ± 10.31	0.073
Mx LII T1 (mm)	8.60 ± 5.20	9.88 ± 4.20	0.356
Mx LII T2 (mm)	1.47 ± 1.09	1.31 ± 1.20	0.662
Mx LII T3 (mm)	3.89 ± 2.45	3.69 ± 2.33	0.782
Md LII T1 (mm)	3.78 ± 1.95	8.88 ± 4.18	<0.001 ^∗
Md LII T2 (mm)	1.11 ± 0.89	1.09 ± 0.94	0.945
Md LII T3 (mm)	3.56 ± 2.04	4.42 ± 2.92	0.318