The effect of increased overjet on the magnitude and reproducibility of smiling in adult females

1 of(2012) 6 European Journal of Orthodontics 34 640–645 doi:10.1093/ejo/cjr077 Advance Access Publication 26 July 2011 © The Author 2011. 2011. Published Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: The effect of increased overjet on the magnitude and reproducibility of smiling in adult females C.M. Campbell*, D.T. Millett*, A. O’Callaghan*, A. Marsh*, G.T. McIntyre** and M. Cronin*** *Postgraduate Orthodontic Unit, Oral Health and Development, Cork University Dental School and Hospital, University College Cork, Cork, Ireland, **Orthodontic Department, Dundee Dental Hospital and School, Dundee DD1 4HR, UK and ***Department of Statistics, Western Gateway, University College Cork, Cork, Ireland The objective of this study was to determine if increased overjet (greater than 6 mm) influences the magnitude and reproducibility of natural smile and maximal smile in Caucasian adult females. Twenty adult females with an increased overjet (6–10 mm) and 20 control adult females (overjet 2–4 mm) with no history of orthodontic treatment volunteered to participate. The mean age in the control group was 30.1 ± 6.4 years and the mean age in the test group was 31.9 ± 10.8 years. Three-dimensional stereophotogrammetric images were captured of each subject for three expressions: at rest, natural smile, and maximal smile. The images were recorded twice on two separate occasions, 6 weeks apart. Images were landmarked and a partial ordinary Procrustes superimposition was used to adjust for the differences in head posture between the same expressions. The magnitude of movement relative to the rest position, averaged over all the landmarks, was calculated and compared between the groups using analysis of variance (linear mixed-effects model); the intra- and inter-session reproducibility of both expressions was assessed. There was greater mean movement, averaged over all the landmarks, in the control group than in the increased overjet group for both natural smile and maximal smile (P = 0.0068). For these expressions, there were no statistically significant differences in reproducibility within sessions (P = 0.5403) or between sessions (P = 0.3665). Increased overjet had a statistically significant effect on the magnitude of smiling but did not influence the reproducibility of natural or maximal smile relative to controls. SUMMARY Introduction Smiling is a gesture unique to humans (Matthews, 1978). Associated with friendliness, agreement, contentment, and sociability (Tjan et al., 1984), smiling is pertinent in the evaluation of facial attractiveness (Kerns et al., 1997). As an aesthetic smile is a primary treatment goal in both orthodontic and surgical orthodontic treatment (Sarver, 2001), the interplay between the teeth and lips at rest, during function, and facial expression should be incorporated in diagnosis (Sarver and Ackerman, 2003; van der Geld et al., 2007). Smile aesthetics are a major impetus for seeking orthodontic treatment (Baldwin, 1980) with many patients qualifying for state funding as a consequence of increased overjet (Lindauer et al., 1988). This occlusal feature is a predictor of reduced facial attractiveness (O’Brien et al., 2009) and increased levels of low self-perception (Johnston et al., 2010). Although different types of smiles have been recognized (posed, strained, natural, spontaneous, open or closed, and half smiles), the natural (spontaneous) and maximal (posed) smiles have attracted most orthodontic interest (Ekman et al., 1990; Paletz et al., 1994; Peck and Peck, 1995). A variety of techniques have been used to assess smile aesthetics including photographs, video, model scanning, radiographs, stereophotogrammetry, and clinical assessment (Rigsbee et al., 1988; Ferrario et al., 1996; Wong et al., 2005; De Castro et al., 2006; Fudalej, 2008; Sforza et al., 2008). For quantitative assessment, landmarks are either placed onto the face before imaging (Johnston et al., 2003; Sawyer et al., 2009) or on the images (Strauss et al., 1997; Holberg et al., 2006). Variability has been noted in smile reproducibility (Ackerman et al., 1998; Frey et al., 1999) with the natural and maximal smile being less reproducible than rest position (Johnston et al., 2003), which has been shown to be the most reproducible (Johnston et al., 2003; Sawyer et al., 2009). Inter-session reproducibility has been noted to be lower than intra-session reproducibility (Trotman et al., 1998) although this may be subject specic. Open mouthed smile has been shown to have large inter-session variability (Sawyer et al., 2009). Inter-session reproducibility has greater relevance in orthodontics than intra-session reproducibility due to the need to make sequential assessments of smiling throughout orthodontic and surgical orthodontic management. Factors inuencing smiling include the maxillary and mandibular skeletal relationships (Trotman and Faraway, Correspondence to: Prof. D. T. Millett, Postgraduate Orthodontic Unit, Oral Health and Development, Cork University Dental School and Hospital, University College Cork, Cork, Ireland. E-mail: EFFECT 2 of 6 OF OJ ON SMILING IN FEMALES Materials and methods Ethical approval was obtained from the local medical ethics committee. Using the data from Johnston et al. (2003), a sample size of 30 subjects with 15 in each of the test and control groups would have a power of 80 per cent to detect differences of 0.5 mm between similar expressions between groups where P = 0.05. An additional ve subjects were recruited per group to allow for possible sample size attrition. Caucasian adult females of Irish origin greater than 18 years, with an overjet between 6 and 10 mm for the test group and between 2 and 4 mm for the control group, were invited to participate. Subjects who were non-Caucasian, male with congenital orofacial clefting or subjects with suspected or identiable syndromes, previous facial surgery, trauma, facial burns, muscular disorders, or palsy (including botulinum toxin injections and dermal llers) of the facial region, anterior open bite, and gross facial asymmetry were excluded. A stereophotogrammetric camera system (www.di3d.com; Ayoub et al., 1998), re-calibrated for each session, was connected to a Dell Dimension 8400 PC with images captured using diCapture™ software. This system has been shown to have an accuracy of 0.1 mm (Johnston et al., 2001). The cameras simultaneously recorded a pair of images corresponding to the left and right side of the face. A test shot was taken to familiarize the subject before the study images were captured. One operator, experienced in three-dimensional (3D) image capture, recorded the following facial expressions after giving each subject identical verbal and visual instructions (Zachrisson, 1998): 1. Rest position ○ Say ‘Mississippi’ then swallow and say ‘N’. 2. Natural smile ○ Bite teeth together gently and say (...truncated)