An ideal smile model was selected [17] (Figure 1) with the purpose of making a template digitally manipulated in all its components. The selected picture was edited using Adobe Photoshop CS3 software (Adobe Systems, San Jose, CA, USA). Graphic components were carried out from the picture of the ideal smile: upper lip, lower lip, gingival tissue, and teeth. Each component was editable in position, size, and shape in order to simulate different clinical situations and treatment options.
Twelve treatment option simulations (Figure 2) with monolateral or bilateral missing lateral incisors were used in the study as follows:
–Simulation A is monolateral agenesis (2.2) with the permanent canine at the side of the agenesis and the deciduous canine (6.3) in the place of the permanent. The harmony of the smile was maintained, as well as the size of the connectors, and no diastemas were noticeable.
–Simulation B is bilateral agenesis (1.2 and 2.2) without deciduous canines (5.3 and 6.3) and diastemas between the front teeth.
–Simulation C is bilateral agenesis with persistence of the deciduous canines in the place of the permanent.
–Simulation D is monolateral agenesis (2.2) without deciduous canine (6.3). Diastemas, dental midline deviation, and tipping of the teeth are evident in this simulation due to teeth migration in the area of the missing lateral incisor.
–Simulation E is monolateral agenesis (2.2) without deciduous canine (6.3), with restoration of the front teeth and grinding of the canine (2.3) in order to eliminate spaces and diastemas. The midline is deviated to the agenesis side, and the restorations are oversized in order to fill diastemas.
–Simulation F is monolateral agenesis (2.2) with deciduous canine (6.3), with restoration of the frontal teeth and grinding of the canine (2.3) in order to eliminate spaces or diastemas. Due to the persistence of the deciduous canine, the midline is correct and the restoration is not oversized.
–Simulation G is bilateral agenesis (1.2 and 2.2) without deciduous canines, with simulation of anterior teeth esthetic restorations. These restorations are intended to correct diastemas, but they are oversized and do not fit correct smile proportions regarding crown size and gingival tissues.
–Simulation H is bilateral agenesis (1.2 and 2.2) with persistence of the deciduous canines and restorations of the front teeth and grinding of the cusps of the permanent canines.
–Simulation I is monolateral agenesis (2.2) and space closure treatment. The midline was shifted with no tipping, and gingival margins are maintained.
–Simulation L is bilateral agenesis (1.2 and 2.2) and space closure treatment. The midline is correct.
–Simulation M is bilateral agenesis (1.2 and 2.2) with space closure treatment and grinding of the canine cusps.
–Simulation N is bilateral agenesis (1.2 and 2.2) with space closure treatment and grinding of the canine cusps, with bleaching of the canine crowns and correction of the gingival levels.
All the simulations were collated on the second page of a two-page survey. Prints of the pictures were 2.4 × 3.1 in. in size and were produced with the same inkjet printer on photo-quality glossy paper, using the 1,400-dpi print mode. Subjects (160) belonging to the four categories of people were selected for the interview: 40 laypeople (N), 40 adult orthodontic patients (P), 40 general dentists (D), and 40 orthodontists (S). Orthodontic patients were recruited at the dental clinic of the University of Insubria (Varese, Italy), while general dentists and orthodontists were recruited among former/current undergraduate/postgraduate students and associates of the dental school. Finally, laypeople were recruited among those accompanying relatives to the dental clinic who were not undergoing orthodontic treatments. The age of the whole sample ranged between 25 and 60 years old and showed a similar socioeconomic status. Ethical approval for this study was obtained from the local ethical committee of the University of Insubria (no. 5184), and informed consent was obtained from the involved subjects.
The first page of the questionnaire was different depending on the category of the responder, collecting demographic data (age, sex, and income) for laypeople and also educational information for dentists and orthodontists. A visual analog scale (VAS) of 100 mm was drawn below each graphic simulation. Each respondent was asked to mark with a cross the value corresponding to each simulation. The distance from the most external left point of the line to the marked cross was measured with an Ultra-Cal Mark III (Fred V. Fowler, Newton, MA, USA) digital caliper by the same trained operator. The scale was divided into units ranging from 0 to 100. Numerical scale allowed easier collection and analysis of data. Moreover, each respondent was asked to rank in ascending order all the simulations presented, starting from the least attractive in his perception. This index allowed for descriptive analysis.
Sample size calculation
A sample size of at least 35 subjects from each group was set to detect an effect size coefficient [18] for the VAS score of 0.8 among them, with an alpha set at 0.05 and a power of 0.8 [19]. An effect size of at least 0.8 is regarded as a 'large effect’ [18].
Statistical analysis
The Statistical Package for Social Sciences Software release 13.0 (SPSS Inc., Chicago, IL, USA) was used for data analysis. After testing the normality of the data with the Shapiro-Wilk test and Q-Q normality plots and the equality of variance among the datasets using a Levene test, parametric methods were used for data analysis.
A one-way analysis of variance (ANOVA) was used to assess the significance of the differences in VAS scores among the groups for each simulation. When significant interactions were seen, an independent sample t test was employed for pairwise comparisons among all the possible combinations of the groups. In particular, each of the retrieved p values was multiplied for six. A p value less than 0.05 was used in the rejection of the null hypothesis.