A Quantitative Analysis of Lip Aesthetics: The Influence of Gender and Aging

Transcription

1 Aesth Plast Surg (2015) 39: DOI /s ORI GIN AL A RTI CLE NON-SURGICAL AESTHETIC A Quantitative Analysis of Lip Aesthetics: The Influence of Gender and Aging Daniele Gibelli 1,2 Marina Codari 1 Riccardo Rosati 1 Claudia Dolci 1 Gianluca Martino Tartaglia 1 Cristina Cattaneo 2 Chiarella Sforza 1 Received: 16 September 2014 / Accepted: 23 April 2015 / Published online: 7 May 2015 Springer Science+Business Media New York and International Society of Aesthetic Plastic Surgery 2015 Abstract Introduction The quantitative analysis of sexual dimorphism of facial structures may valuably support reconstructive and feminization surgery, thanks to the estimation of metrical thresholds useful for distinguishing male and female traits. This study aims at verifying the metrical characteristics of female and male lips, to provide indications for aesthetic surgery. Methods Thirty healthy Caucasian volunteers (20 men and 20 women) were divided into two groups according to age: years and years. Arches and the cutaneous (external) and mucosal (internal) labial surfaces were reproduced by stone models, and digitised using a computerised electromechanical instrument. Area, volume and thickness were measured separately for the upper and lower lips, and compared between sexes and ages by Student s t test, and multinomial logistic regression. Results All lip measurements were larger in males than in females; upper lip thickness best divided males from females, adopting a 9.5-mm threshold (percentage of correct diagnosis: 85 %). Young subjects always showed higher measurements than old subjects; lower lip thickness provided the highest percentage of correct age diagnosis (85 %, adopting a 13.8-mm threshold). & Daniele Gibelli daniele.gibelli@unimi.it 1 2 Dipartimento di Scienze Biomediche per la Salute, Università degli Studi di Milano, Via Mangiagalli 31, Milan, Italy Sezione di Medicina Legale, Dipartimento di Scienze Biomediche per la Salute, LABANOF, Laboratorio di Antropologia e Odontologia Forense, Milan, Italy Conclusion This study provides novel thresholds that may contribute to the assessment of adequate reconstruction of lips in aesthetic surgery. Level of Evidence III This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors Keywords Facial anatomy Lips Aesthetic surgery Feminization surgery Transsexualism Introduction In the last years, anatomical study of facial traits has grown in importance, as also shown by the increasing number of publications concerning the morphological features of the face according to different biological characteristics, first of all sex and age [1 10]. The improvement of studies concerning facial morphology has progressively expanded its fields of application, ranging from the identification of individuals in images taken from video surveillance systems [11 14], to age estimation of subjects represented in 2D images [15], to aesthetic surgery. Aesthetic surgery is extensively fostered by anatomical studies that provide metrical and morphological standards potentially useful for reconstructive surgery. Some examples are derived from the analysis of attractiveness in males, females and children [16 18]. In addition, metrical differences between males and females, and young and old subjects as well, have a practical importance in several areas of surgery, for example in reconstructive surgery, where the main task consists in reproducing the anatomical structures adequate to a specific biological profile [19].

2 772 Aesth Plast Surg (2015) 39: Another important field is facial surgery for male-tofemale and female-to-male transsexuals, where the face is artificially modified to match the aesthetic standards of the opposite sex [20 26]. Transsexualism is a recognised medical condition affecting individuals who believe themselves to have been born into a body of the wrong sex [21]. In Europe, the prevalence ranges between 1:8300 and 1:400,000 for male persons who consider themselves as females, and between 1:2900 and 1:100,000 for female individuals who consider themselves as males, with significant differences according to the geographic contexts [24]. These subjects are often affected by persistent psychological discomfort due to their anatomic sex and lack of appropriateness of their appearance with the gender they feel. Genital reassignment, although crucial, is not enough to guarantee the improvement of psychological conditions, because other body features, and especially the face, can prevent them from gaining social acceptance among the members of the same sex group [27]. In fact, facial appearance is of the utmost importance to reach a higher improvement of psychological conditions and comfort with the novel sex condition. After surgery involving facial traits, literature highlights an important impact on the overall perception of the patients [21]. Facial plastic surgery has, therefore, a key importance in the correct assessment of patients who aim at becoming members of the opposite sex. Standard measurements and morphological observations are therefore needed, but usually the indications for facial surgery are derived from ancient canons, often not based on scientific studies [23]. In fact, so far facial anatomical analysis has mainly focused on progressive modification of faces in different groups according to sex and age, but it actually lacks practical aspects appropriate for surgical fields, which usually consists of formulae and thresholds useful to distinguish males from females, and aged and young people. However, verifying the differences between different age and sex groups is the first step to modify the same parameters in patients accordingly [21 23]. The lips are among those facial structures usually involved in aesthetic surgery and which may take full advantage of anatomical studies; labial sexual dimorphism is well known in literature, as shown by several studies highlighting that labial dimensions change with sex and age [4, 5, 9, 10, 28, 29]. However, although the potentials for age and sex assessment have been analysed in depth, at the moment no specific statistical tools are available for verifying the differences between male and female lips, and between young and old subjects, to provide a more precise surgical reconstruction. This study aims at assessing age- and sex-specific characteristics of several measurements taken on the upper and lower lips. This will provide biological thresholds, which may be used for reconstructive surgery in transsexuals. Materials and Methods A group of 40 healthy volunteers (20 men and 20 women) were analysed in a previous study concerning the evaluation of metrical features of lips according to sex and age [30]. The subjects were divided into two groups according to age: years (men, mean age 26 years, SD 4 years; women, mean age 25 years, SD 4 years) and years (men, mean age 53 years, SD 4 years; women, mean age 54 years, SD 5 years). All subjects were Caucasians, and were selected according to strict inclusion criteria consisting of full permanent dentition including the first molars, bilateral angle Class I relationship, overjet and overbite ranging from 2 to 4 mm, no anterior cross-bite, no cast restoration or cuspal coverage, no previous or current orthodontic treatments, no previous craniofacial trauma or surgery. The dental profile and the cutaneous (external) and mucosal (internal) labial surfaces were reproduced using stone models. For each subject, a maxillary and mandibular dental reproduction was obtained by an irreversible hydrocolloid (Tropicalgin, Zhermack SpA, Badia Polesine, Italy) and cast with a type 3 model dental stone (Elite Model, Zhermack SpA, Badia Polesine, Italy); the models were set in maximal intercuspidation. The reproduction of the mucosal labial surface was performed by introducing an individual plastic mask within the oral vestibule; subsequently 3 ml of silicon impression material (President Plus, Coltene Whaledent, Altstatten, Switzerland) was put on the tray surface facing the mucosal labial area. The method used for the creation of soft-tissue casts and their 3D acquisition was previously validated [31]. In detail, the silicone impression material did not provide artefacts or air bubbles which may influence the results. The labial models were cast using a type 3 model dental stone (Elite Model, Zhermack SpA, Badia Polesine, RO, Italy); for each subject, the casts (lips plus dental models) were put in the correct anatomical position. A computerised 3D electromechanical digitizer (Microscribe G2X, Immersion, San José, CA, USA), with an accuracy of 0.23 mm ( was used to digitally reproduce the models [30]. A grid of standardised horizontal and vertical lines was drawn on each model, defining cutaneous labial surface, mucosal labial surface and maxillary and mandibular vestibular dental surface. Several points on these lines were digitised using the digitizer, and the files of the 3D coordinates were

3 Aesth Plast Surg (2015) 39: elaborated using a commercial software for 3D modelling (Rhinoceros 3.0, Robert McNeel & Associates, Seattle, WA, USA). The upper and lower vermilion lines, and the commissure line were used to identify the upper and lower lips (Fig. 1); area, volume and thickness were measured separately for the upper and lower lips [30, 31]. Unpaired Student s t-tests were used to compare metrical features of lips between sex and age groups. In addition, multinomial logistic regression was used to estimate the predictive odds for a correct diagnosis. A p value of 0.05 was set for statistical significance. Results All the metrical parameters were higher in males than in females; the difference was statistically significant for the lower lip area, upper and lower lip volume and upper lip thickness (Fig. 2). Among all the measurements, the multinomial logistic regression was applied to the four parameters whose differences between males and females showed the highest statistical significance (lower area, upper volume, lower volume and upper thickness), in order to find useful thresholds for distinguishing males from females. Results are shown in Table 1: the parameter with the best performances was the upper lip thickness, with a 85 % percentage of correct diagnosis. In addition, the negative predictive value was 100 %, i.e. the probability of being females with an upper lip thickness lower than 9.5 mm is 100 %. Concerning age, young subjects always showed higher measurements than older ones. Statistically, significant differences were found for the lower lip area and volume, and upper and lower lip thickness (Fig. 3). Also in this case, specific threshold values were estimated in order to provide a method for distinguishing among the two age groups. The parameter with the highest performance was Fig. 2 Above Two examples of a 3D model of female (a) and male (b) lips; below mean and standard deviation for each measurement performed in males and females the lower lip thickness, with 87.5 % of correct diagnosis, 75 % sensitivity and 100 % specificity (Table 2). The positive predictive value (the probability of being aged between 45 and 65 years with a lower lip thickness lower than 13.8 mm) was 100 %. Discussion Fig. 1 Detail of the labial surfaces calculated by the 3D image software (included within the white line) In the last 30 years, facial assessment has progressively increased both the technologies involved in morphological and metrical acquisition, and the fields of applications of the obtained data [1, 2]. The most important practical result obtained by anatomical studies consists in determining the biological standards of human faces according to different variables (sex, age, ancestry, etc.) [4 7, 9, 10, 13, 28, 29].

4 774 Aesth Plast Surg (2015) 39: Table 1 Estimated thresholds, sensibility (SE), specificity (SP), percentage of correct diagnosis of sex, positive (PPV) and negative predictive values (NPV) for each estimated threshold Threshold SE (%) SP (%) % Correct diagnosis PPV (%) NPV (%) Lower area mm Upper volume mm Lower volume mm Upper thickness 9.5 mm Fig. 3 Above Two examples of a 3D model of lips from a young (a) and an old (b) subject; below, mean and standard deviation for each measurement performed in young and old subjects In aesthetic surgery, the acquisition of standards has a key role, since they may help in reconstructing faces severed by traumatic causes according to the patient s original biological information. This is a novel and potentially very fertile field of application of anatomical data, that necessarily requires improvement of population-specific information to better define the ethnic influence, and therefore adequately reconstruct the facial appearance accordingly [4, 6, 7, 9, 10, 13, 28, 29]. Facial standards are even more useful in the case of surgery in transsexuals, where the novel face does not need to be reconstructed, but rather converted into a new appearance with different biological data [21 23]. Also in these cases, the knowledge of metrical standards for men and women may help in recreating a facial structure more similar to the specific sex group, and therefore more reliable and adequate for the patient. This is even more important considering the psychological consequences of surgery in cases of transsexuals, contributing to decreased psychological issues linked to the sex rectification, increasing the global quality of life [32, 33]. From this point of view, the anatomical data may help in recreating a more reliable face according to the novel biological information, and have therefore direct consequences on the psychological health of the patient [21]. In detail, in the last 50 years the global incidence of this type of surgery has significantly increased, especially among young adults and subjects over 30 years of age [24, 34], with a clear need for extending morphometric and aesthetic studies previously limited to young adults and to women [4, 6, 7, 9, 10, 16, 17, 31]. Indeed, even persons in their sixth or seventh decade of life are candidates for facial surgery for sex reassignment [24]. This clearly requires the development of specific standards according to the new sex and age of the patients. The technical protocol used for labial reproduction was developed to obtain 3D models of all lip structures, from skin to mucosa [30, 31]. In the current investigation, data obtained from the same reproductions were used to estimate predictive odds for a correct sex and age assignation that can be applied to surgical modifications of the labial area, usually included in several surgical procedures. For example, lip rejuvenation is a minimally invasive surgical operation, usually performed in old people, including the modification of perioral soft tissues and the increment of labial volume by dermal fillers [35]. When increasing lip volume, the application of specific

5 Aesth Plast Surg (2015) 39: Table 2 Estimated thresholds, sensibility (SE), specificity (SP), percentage of correct diagnosis of age, positive (PPV) and negative predictive values (NPV) for each estimated threshold Threshold SE (%) SP (%) % Correct diagnosis PPV (%) NPV (%) Lower area mm Lower volume mm Upper thickness 10.5 mm Lower thickness 13.8 mm anatomical thresholds may help in reaching the correct volume values, useful for enhancing the aesthetic effect. For example, a possible procedure may include, after the filling treatment, a 3D scan of lips with the evaluation of the acquired lip volume, thus gaining the chance of providing further adjustments if they are needed. In the current study, strict inclusion criteria were set in order to select healthy subjects without surgical, genetic or traumatic biases, thus providing valid data from the aesthetical point of view. Clearly, the current study is based on a limited number of patients. Further investigations are needed to increase the sample and provide more precise data concerning the differences according to sex and age. Subsequently, the next step is the assessment of population data in order to highlight similar anatomical thresholds in other ethnic groups, thereby improving aesthetic surgery also in other geographical contexts. This will contribute to the improvement of new standards for facial surgery and consequently of psychological conditions and quality of life of patients. Conflicts of interest The authors declare that they have no conflicts of interest to disclose. References 1. Farkas LG (1994) Anthropometry of the head and face, II edn. Raven Press, New York 2. Sforza C, de Menezes M, Ferrario V (2013) Soft- and hard-tissue facial anthropometry in three dimensions: what s new. 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