European Journal of Orthodontics 36 (2014) 719–726 doi:10.1093/ejo/cjt102 Advance Access publication 7 February 2014

© The Author 2014. Published by Oxford University Press on behalf of the European Orthodontic Society. All rights reserved. For permissions, please email: [email protected]

Analysis of anterior dentoalveolar and perioral aesthetic characteristics and their impact on the decision to undergo a Phase II orthodontic treatment Carlos Flores-Mir*, Matthew M. Witt**, Giseon Heo*,*** and Paul W. Major* *School of Dentistry, University of Alberta, Canada, **Private Practice, Delta, BC, Canada, ***Department of Statistics, University of Alberta, Canada Correspondence to: Carlos Flores-Mir, School of Dentistry, University of Alberta, 5–528 Edmonton Clinic Health Academy, 11405–87 Ave NW, 5th Floor, Edmonton, Alberta, T6G 1C9, Canada. E-mail: [email protected] summary 

Introduction Previous studies (Johnston et al., 1999; Moore et al., 2005; Rosenstiel and Rashid, 2002; Parekh et al., 2006) have shown that the lay public is able to identify factors that detract from an aesthetic smile; however, they are far less critical than dental professionals with regards to some of those elements (Kokich et al., 1999, 2006; Martin et al., 2007). Tooth shape, tooth size and proportion, incisor position (including tooth angulation and presence of a diastema), midline deviation, gingival display and morphology, smile arc, buccal corridors are important factors for frontal dentofacial aesthetics from the layperson perspective as shown by two related systematic reviews (Witt and Flores-Mir, 2011a,b). Studies investigating these factors are typically survey based, with laypeople ranking or scoring a number of frontal photographs of smiling patients. In the majority of cases, photographs are either selected or modified such that only one parameter varies between the different photographs presented as survey

stimuli. Only a few studies (Hulsey, 1970; Parekh et  al., 2007; McNamara et  al., 2008) have attempted to analyze multiple factors simultaneously to determine their relative influence on the layperson’s perception of dental aesthetics. Moreover, there is limited research investigating how these various factors interact simultaneously and influence a patient’s decisions regarding orthodontic treatment. Phase I treatment with the Xbow may or may not be followed by a phase II treatment with conventional braces. The Xbow is a class  II fixed inter-arch corrector that supports the Forsus springs on a custom-made metallic framework attached to the upper and lower dentition (Flores-Mir et al., 2009). It appears that a number of patients and parents are satisfied with the occlusal and aesthetic results of the phase I  Xbow treatment and do not opt for phase II treatment despite a recommendation to continue with treatment. This recommendation is usually based on attaining final occlusal and aesthetic details. It can be hypothesized that patients

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Objectives: Researchers have conducted extensive studies regarding dentoalveolar factors that affect anterior dental aesthetics; however, there is no consensus regarding how these factors affect orthodontic treatment decisions. Only a few studies have included multiple factors simultaneously. Therefore, the objective was to investigate if there are identifiable dentofacial and perioral aesthetic factors that bias laypeople towards discontinuing treatment after a phase I treatment with this fixed class II corrector. Methods: An analysis of photos and dental casts of 60 children (23 males, 37 females) having received phase I orthodontic treatment with the Xbow appliance was conducted. Variables considered were incisor height and width measurements, incisor proportions, incisor angulations, vertical lip thickness, gingival/ incisal display, smile width per cent, diastema, midline deviation, smile arc, gender, and use of a 2 × 4. A principal component analysis and a logistic regression were used to determine which factors related to a patient’s likelihood of receiving further orthodontic treatment. Results: Only the angulation of the right maxillary incisors was significantly related to a patient’s likelihood (odds ratio 1.886 (1.004–3.466); P  =  0.049) to proceed to phase II orthodontic treatment following phase I orthodontic treatment with the Xbow appliance. The odds of proceeding to phase II treatment were 86.6% greater with a one standard deviation increase in the angulation of the right central and lateral incisors. Other factors demonstrated trends but were not statistically significant. Limitations: Sample in subgroups was small, excluded smiles that did not expose the upper incisor crowns significantly, smiles in real life are observed three-dimensionally, other factors outside the aesthetic measurements were not considered in the analysis. Conclusions: In this sample, the angulation of the maxillary right incisors was the most significant factor influencing the decision to undergo an orthodontic phase II.

720 that decide not to undergo a phase II orthodontic treatment may be completely satisfied with the final attained occlusion even though the treating orthodontist suggest otherwise. The objective of this study was to investigate if there are identifiable dentofacial and perioral aesthetic factors that bias laypeople towards discontinuing treatment after a phase I treatment with this fixed class II corrector. Materials and methods Ethics approval Ethical approval was granted by the appropriate committee at the University of Alberta. Study sample

Figure 1  Study sample details.

A total of 158 patients (38% male versus 62% female) had been treated with the Xbow appliance during the selected time frame. Unfortunately, only 60 of the 158 patients from this pool had the necessary T2 records available. The final sample included 30 patients that did undergo phase II orthodontic treatment and 30 that did not. Details of the study sample population are illustrated in Figure 1 (note that this is a description of the sample, not an allocation tree). Measurements The width of the patients’ maxillary right central incisors were measured on dental casts using a Max-Cal electronic digital caliper (Fowler Canada, Brantford, Ontario, Canada) for the calibration of measurements performed in the photographs. Patient photographs were cropped vertically (between the columella and the superior portion of the mental protuberance) and horizontally (between the inferior portions of the nasiolabial sulci) without distorting the proportions of the teeth and lips. Using Kodak Orthodontic Imaging Software (Carestream Dental LLC, Atlanta, Georgia, USA), a number of easily measured and previously reported aesthetically important (Witt and Flores-Mir, 2011a,b) dental and peri-dental factors were measured from both the T1 and T2 photographs of each patient. The width of each patient’s maxillary right central incisor was input into the software to calibrate the measurements. Measurements were recorded as a continuous variable in millimetres with two decimals. Height and width measurement.  Using the calibrated photographs, height (H) and width (W) measurements were taken for the upper right and left central and lateral incisors (Figure 2). These values are identified as ‘1.2 W’, ‘1.2 H’, ‘1.1 W’, ‘1.1 H’, ‘2.1 W’, ‘2.1 H’, ‘2.2 W’, and ‘2.2 H’. Tooth proportions.  Using the height and width (HW) measurements of the upper incisors (Figure 2), the width:height ratios were determined for each incisor. These values are identified as

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The treatment sample was obtained from the private practice and included all patients consecutively treated with the Xbow appliance between early 2006 and late 2010 that had dental casts, pre- (T1) and post-treatment (T2) digital frontal photographs of their smiles. Photographs were taken at f-stop 9.5 and ISO 200 using a Fuji Fine Pix S3 Pro (Fujifilm Canada, Mississauga, Ontario, Canada) equipped with a Nikon 60 mm lens and SU-800 Nikon Wireless Speedlight Commander (Nikon Canada, Mississauga, Ontario, Canada). Ideally, the patient photographs would be taken in maximum smile, but there was no way to retroactively determine if the smiles captured in the photographs were demonstrations of maximum smile, a natural smile, or a forced smile. Patients were excluded from the study if their smiling photographs depicted smiles that did not display the majority of the maxillary incisors because measurements of the teeth and gingiva would not be possible. For each patient, it was noted if a 2 × 4 fixed appliance was used during phase I, and if phase II treatment was administered, however, no information regarding age and phase I  treatment time was collected. The specific reason for not continuing treatment was not recorded in the clinical chart.

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‘1.2 HW’, ‘1.1 HW’, ‘2.1 HW’, and ‘2.2 HW’. Tooth width:width proportions between the central and ipsilateral lateral incisors were also determined. These values are identified as ‘1.2/1.1’ and ‘2.2/2.1’. Vertical lip thickness.  The vertical thicknesses of the upper and lower lip were measured in the facial midline (Figure 3). These values are identified as ‘U lip’ and ‘L lip’. Gingival display or incisal coverage.  The vertical height of the gingiva between the zenith of the gingival margin of the central incisors and the lower border of the upper lip was measured and recorded as a positive value (Figure 4). If the zenith of the gingival margin was covered by the lower border of the upper lip, an estimated negative value representing the distance covered was recorded. In cases where one central incisor was covered and the other was exposed, the positive value was recorded. Regardless of whether there was positive or negative gingival display, the value is identified as ‘gingiva’.

Figure 2  Width and height measurements for tooth 1.1.

Figure 3  Vertical thickness measurements for the upper and lower lips.

Diastema.  If present, the maxillary midline diastema was measured (Figure 6). This value is identified as ‘diast’ and was given a value of 0 if no diastema was present. Midline deviation.  The deviation of the midline was measured (Figure 7). The midline was determined by drawing a vertical line through the middle of the tip of the nose and through the middle of the philtrum of the lip. No indication of the direction (right or left) was given. This value is identified as ‘MLDev’. Incisor Angulations.  The angulations of the four upper incisors were measured with respect to the horizontal plane of the image (Figure 8). These values are identified as ‘1.2 A’, ‘1.1 A’, ‘2.1 A’, and ‘2.2 A’. Smile  arc.  As an approximate measure of the smile arc (i.e. the degree to which the incisal edges of the maxillary teeth follow the superior border of the lower lip), the vertical

Figure 4  Gingival display measurement.

Figure  5  Oral aperture width (top) and smile width (bottom) measurements.

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Smile width per cent.  The distance between the inner aspects of the commissures of the lip was measured to give the intercommissural width (ICW) as measured from the inner aspect of the buccal mucosa (Figure  5). The distance between the

buccal aspects of the most laterally situated teeth in the smile was measured to give the smile width, identified as ‘SmW’. The smile width per cent was obtained by dividing the SmW by ICW. This value was identified as ‘Sm%’ and is a measure of buccal corridor size.

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Figure 8  Measurement of the angulation of the maxillary incisors.

Figure 7  Measurement of midline deviation.

Figure 9  Measurement of distances between maxillary incisal edges and lower lip superior border.

distance between the incisal edges of the four upper incisors were measured (Figure 9). These values are identified as ‘1.2 E-L’, ‘1.1 E-L’, ‘2.1 E-L’, and ‘2.2 E-L’. It is important to recognize that an increase in these values indicates a decrease in the consonance of the smile arc with the contour of the lower lip.

(PC) while retaining most of the information in the original variables. The logistic regression analysis included the reduced variables as determined by the PCA with the dependent dichotomous final outcome as started or not a phase II orthodontic treatment. All statistical tests were performed using the Statistical Package for the Social Sciences 19.0 (International Business Machines Corp, Armonk, New York, USA).

Oral hygiene and gingival inflammation.  The level of oral hygiene/gingival inflammation was also considered in the analysis but was not included due to difficulty in assessing this factor on smiling photographs. Tooth shape was also initially considered; however, due to the degree of variation between patient photos, this factor could not be easily assessed and discarded for the final analysis. Statistical analysis The analysis of the data involved three elements: 1. reliability analysis (intraclass correlation), 2. principal component analysis (PCA), and 3. logistic regression. Due to the large number of variables measured and limited sample size, it was not considered appropriate to carry out a logistic regression analysis with all the variables included. Therefore, the number of variables was reduced using PCA, a statistical procedure that combines correlated variables into a set of variables called principal components

Results Reliability analysis As part of a reliability analysis, each measurement was repeated five times (at intervals of 1 week) by a one researcher for 10 randomly selected patients. Reliability testing suggested high intraclass  correlation coefficients, indicating strong intra-rater reliability and agreement for 1.2 H, U lip, L lip, gingiva, ICW, SmW, diast, 1.1 A, 2.1 A, and the E-L series of variables. The 1.2 W, 1.1 W, 1.1 H, 2.1 W, 2.1 H, 2.2 H, MLDev, 1.2 A, and 2.2 A variables demonstrated adequate reliability, though the lower limits for the confidence intervals on these variables were less than desirable. The variable 2.2 W had poor reliability (Table 1).

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Figure 6  Measurement of maxillary midline diastema.

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Table 1  Intra-rater reliability for variable measurements. Variable

ICC* 95% confidence interval

1.2 W 1.2 H 1.1 W 1.1 H 2.1 W 2.1 H 2.2 W 2.2 H U lip L lip Gingiva Intercommissural width SmW Diast MLDev 1.2 A 1.1 A 2.1 A 2.2 A 1.2 E-L 1.1 E-L 2.1 E-L 2.2 E-L

0.856 (0.683, 0.956) 0.879 (0.739, 0.963) 0.770 (0.554, 0.925) 0.844 (0.674, 0.951) 0.847 (0.668, 0.953) 0.838 (0.666, 0.949) 0.362 (0.110, 0.710) 0.756 (0.534, 0.919) 0.966 (0.909, 0.990) 0.959 (0.874, 0.989) 0.949 (0.881, 0.985) 0.965 (0.915, 0.990) 0.941 (0.863, 0.983) 0.982 (0.956, 0.995) 0.810 (0.618, 0.939) 0.821 (0.633, 0.943) 0.916 (0.793, 0.976) 0.893 (0.764, 0.968) 0.802 (0.598, 0.937) 0.985 (0.964, 0.996) 0.992 (0.980, 0.998) 0.980 (0.952, 0.994) 0.988 (0.971, 0.997)

Table 2  Correlation between PC and each variable based on varimax rotation (with outliers). Variable

PC1

PC2

PC3

PC4

PC5

1.2 E-L 1.1 E-L 2.1 E-L 2.2 E-L 1.2 WH 1.1 WH 2.1 WH 2.2 WH 1.2/1.1 2.2/2.1 1.2 A 1.1 A U lip L lip Gingiva Sm% MLDev 2.2 A 2.1 A

0.926 0.934 0.942 0.867 0.253 0.208 0.008 −0.028 0.201 −0.064 −0.084 0.125 0.190 0.141 0.177 0.224 0.054 −0.018 0.053

0.109 −0.046 0.048 0.175 0.625 0.880 0.926 0.789 −0.046 −0.049 −0.110 0.044 −0.041 0.061 −0.004 0.203 0.060 −0.113 −0.092

−0.015 0.105 0.115 0.098 0.566 −0.188 −0.133 0.412 0.826 0.821 −0.048 0.249 −0.133 0.060 −0.225 0.556 −0.042 0.429 −0.077

0.005 0.127 0.074 −0.203 0.152 −0.110 −0.082 −0.013 0.110 0.165 0.843 0.814 0.117 0.055 0.349 −0.392 −0.274 0.508 0.183

−0.071 0.141 0.141 0.067 0.163 0.089 −0.088 −0.024 0.139 −0.091 −0.003 0.053 0.812 0.832 −0.622 0.010 0.204 −0.188 −0.033

*ICC, intraclass correlation coefficient.

Principal component analysis Two sets of data were produced: one in which extreme values (i.e. outliers) were removed and one in which they were kept in the data set. Outliers were identified as starred values (*) on a boxplot graph designating a value further than three interquartile ranges from the nearer edge of the box. The PCA was conducted with and without these extreme values to determine the best theoretically fitted set of new variables to employ in a future logistic regression. Four PC analyses procedures were performed in attempt to find the best model: 1.  no rotation PCA with outliers, 2.  varimax rotation PCA with outliers, 3.  no rotation PCA without outliers, and 4. varimax rotation PCA without outliers. Of these four analyses, the varimax rotation PCA with the outliers produced the model with the most coherent results (Table 2). Due to the sample size limitations in this study, only those loading values (i.e. correlation between PC and each variable) that were greater than or equal to |0.600| were interpreted as significant, since components loadings above |0.600| are considered reliable regardless of a limited sample size (Velicer and Fava, 1998). A total of five s (PC1–PC5) were derived from the PCA. The remaining four variables (Sm%, MLDev, 2.2 A, and 2.1 A) did not interact significantly between themselves. It has to be noted that what would have been PC6 (2.2 A  alone) was not included for further analysis as 2.2 A had poor reliability as noted before. The total variance explained by each PC (i.e. the degree to which each component contributes to the description of the aesthetic smile) is shown in Table 3. Note that each

Table 3  Total variance of smile explained (rotation sums of squared loadings). Component

Component name

Eigenvalue

% of variance

Cumulative %

PC1 PC2 PC3 PC4 PC5

Smile arc Intratooth Intertooth Right angle Lips

4.461 2.812 2.530 1.930 1.637

22.303 14.058 12.652 9.652 8.187

22.303 36.361 49.013 58.665 66.852

subsequent factor is responsible for progressively less variation. Table  3 also lists the names given to the individual components. PC1 is dominated by four variables (1.2 E-L, 1.1 E-L, 2.1 E-L, and 2.2 E-L) and can be considered as the average of these four variables that represent the vertical distance between the incisal edges of the four upper incisors and the superior border of the lower lip and thus was labelled ‘smile arc’. PC2 is dominated by four variables (1.2 WH, 1.1 WH, 2.1 WH, and 2.2 WH) and can be considered as the average of these variables that represent the tooth width:height ratios (i.e. the proportionality within each tooth). This PC was labelled ‘intratooth’. PC3 is dominated by two variables (1.2/1.1, 2.2/2.1) and can be considered as the average of these variables representing the width:width ratios between the central and ipsilateral incisors (i.e. the proportionality between teeth). This PC was labelled ‘intertooth’.

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Bolded numbers are those values were the ones selected for the specific column (PC1 to PC5).

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PC4 is dominated by two variables (1.2 A and 1.1 A) and can be considered as the average of these variables representing the angulation of the right maxillary central incisor and the right maxillary lateral incisor with respect to a horizontal plane. This PC was labelled ‘right angle’. PC5 is dominated by three variables (U lip, L lip, and gingiva) and can be considered as the average of these variables representing the vertical dimension of the upper and lower lips. Gingiva display reacts accordingly. This PC was labelled ‘lips’. Independent t-tests were used to examine whether significant differences existed in any of the PC existed between 1. boys and girls and 2. those with and without 2 × 4. Results indicated that those with 2 × 4 were significantly lower in the right angle score than those without 2 × 4, (t(51)  =  2.572, P  =  0.013) (Table  4). No other significant differences for 2 × 4 or sex were revealed. Logistic regression

Discussion The goal of this study was to determine which aesthetic factors were related to a patient’s likelihood to proceed with phase II orthodontic treatment after receiving phase I Xbow orthodontic treatment. In this situation, the decision to continue to phase II treatment was viewed as an indicator of the aesthetic result following phase I treatment. Nine frontal Table 4  Independent samples t-test of 2 × 4 and the PCs* Component

T score

Degrees of freedom

P value**

Mean difference

Right angle Smile arc Intratooth Intertooth Lips

2.572 0.448 −0.038 −1.700 0.841

51 51 51 51 51

0.013 0.628 0.970 0.095 0.404

0.780 0.322 0.322 0.314 0.320

*Equal variances assumed. **2 tailed.

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First, an exploratory logistic regression was performed with the gender, 2 × 4, and diastema variables as covariates in order to test the hypothesis that these three variables are strong contributors to the decision to proceed to phase II treatment. None of the factors were significant. A  second exploratory logistic regression was run including the gender, 2 × 4, and diastema variable as covariates with the five PC. Only 2 × 4 and PC4 (right angle) were significant. Finally, through a forward stepwise logistic regression, only right angle barely reached significance (odds ratio 1.866 (1.004–3466); P = 0.049). Thus the odds of proceeding to phase II treatment were 86.6% greater with a one standard deviation increase in the value of right angle.

dentofacial aesthetic factors were chosen based on previous research (Witt and Flores-Mir, 2011a,b). The results of a PCA and logistic regression indicate that increased angulations of the maxillary right lateral and central incisor are related to increased odds (1.866) that a patient will proceed to phase II treatment. Previous studies have shown that laypeople are sensitive to changes in the angulation of the anterior dentition (either as an occlusal plane cant or as individual teeth; Kokich et al., 1999; Thomas et al., 2003; Wolfart et al., 2004; Geron and Atalia, 2005; Gul-e-Erum, 2008; Ker et al., 2008) However, none of these studies have determined how noticeable changes to the angulation of the anterior dentition are in the presence of other aesthetic defects. It is likely that seemingly separate aesthetic elements can influence each other’s contribution to smile aesthetics (Ker et al., 2008). Angulations of the left maxillary central and lateral incisors did not appear to be a significant contributor to the decision to proceed with phase II treatment. The variables representing the angulations of tooth 2.1 and 2.2 did not correlate well with any of the PC during dimension reduction (Table 3). Thus, they were not included in the logistic regression. The poor correlations of 2.1 and 2.2 angulations to the PC may be due to the lower reliability of these measurements (Table 1). To put this into a clinical perspective, however, during the intra-rater reliability testing the largest discrepancy between measurements of the angulation of tooth 2.1 was approximately 5 degrees (with the average discrepancy of approximately 3 degrees). The largest discrepancy between measurements of the angulation of tooth 2.2 was approximately 9 degrees (with the average discrepancy of approximately 4 degrees). One study (Rodrigues et al., 2009) has shown that laypeople are not sensitive to a 10 degree distal angulation of the lateral incisor. Thus, the discrepancy in measurements due to the decreased intra-rater reliability is probably not of significance to the layperson. A study (Geron and Atalia, 2005) demonstrated that laypeople are more sensitive to counter clockwise cants (versus clockwise cants), which in a sense result in the increase in angulation of the maxillary right incisors (and concurrent decrease in angulation of the maxillary left incisors). However, there is research that suggests that right-handed people are more sensitive to details in the right side of an asymmetric image (Mead and McLaughlin, 1992). A skeletal underlying cause should not be discarded in these scenarios. This would not explain the apparent increased sensitivity to increases in angulation of the maxillary right incisors, but may have been a factor during the measurement process and perhaps could explain increased variability on the left incisors as mentioned above. Interestingly, handedness appears to be neuropsychologically linked to right-versus-left aesthetic preferences, diminishing the effects of cultural cues (Strachan, 2000). It is important to keep in mind that people demonstrate an overall preference for symmetry over asymmetry (Hulsey, 1970; Strachan 2000; Wolfart et al., 2005).

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Limitations It is possible that the sample used for this study was a source of bias. The records used in this study came from a sample of 158 patients that was reduced due to a lack of T2 (post-phase I) records. Most of the patients that received only phase I treatment had T2 records, but the majority of the patients that received phase II treatment did not have T2 records. It is unclear why T2 records were taken for only some of the patients receiving phase II treatment. It is possible that these cases represented exceptional cases that made them desirable for documentation. There are two possible sources of bias related to the upper lip. Firstly, the sample of patients was further reduced because patients were excluded from this study if their smiling photographs depicted smiles that did not display the majority of the maxillary incisors. In most cases, it appears that poor display of the maxillary incisors was due to a poorly posed smile rather than anatomical limitations and could have been remedied by retaking the photograph. Secondly, for those cases in which the posed smile was adequate but the maxillary incisors were partially covered by the upper lip the degree of incisal coverage was estimated. Therefore, the measurements for gingival display are more accurate than those for incisal coverage. The degree of

estimation could have been reduced by taking incisogingival caliper measurements of the incisors on the patient models rather than just the mesiodistal measurements. An outstanding issue is the fact that 2D static photographs were considered when in real life the face is evaluated as a 3D fully expressive structure. In addition, patient’s data were not considered if their smiling photographs depicted smiles that did not display the majority of the maxillary incisors. This could in fact be a reason to be willing to continue orthodontic treatment for aesthetic reasons. The decision to consider only full smiling photos was to be able to properly complete the required measurements. Furthermore, there was a difference in the proportion of males to females in the sample (38% male, 62% female) versus the private practice from which the sample was taken (42% male, 58% female). Previous research (Huang et al., 2004) conducted in the neighbouring American state of Washington shows that there is a sex distribution of orthodontic patients (36% male, 64% female) that is more reflective of the ratio found in this study population. Still, it is unclear why the discrepancy exists between the gender ratio of the study population and the private practice from which it was obtained and thus indicates a possible source of bias. For this study, the decision regarding phase II orthodontic treatment is treated as a proxy for the patient’s (and likely their family’s) feelings about the aesthetic result of phase I treatment. Perhaps, the most obvious shortcoming of this approach is that it attempts to assign frontal dentofacial aesthetics as the single reason for family’s orthodontic treatment decisions, when these decisions are often made in a psycho-socio-economic context that includes the patient and caregiver burnout, peer pressures, and financial pressures. It was not possible to contact the patients in this study to find out the reasons they did or did not continue on to phase II treatment; even if it were possible, the actual truth may not be disclosed by the patient or their family (recall bias or fear to answer the truth). The individuals from whom the photos were taken were actual patients. Theoretically the decision to undergo further treatment was likely made by a combination of the actual patients but also their families. Hence, we use the term ‘laypersons’ as a more all-encompassing term to mean the non-professional aspect of the decision to undergo further treatment. A prospective study overcoming the above-stated limitations but using a similar statistical analysis should be conducted to confirm or not the current findings. Conclusions The angulations of the maxillary right central and lateral incisors were the most significant factor related to a patient’s likelihood of receiving phase II treatment following phase I  treatment with the Xbow appliance; a one standard unit increase in angulation of these teeth increases the odds of proceeding with phase II by 87%.

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It is interesting to note that incisor angulation was a significant factor but the use of orthodontic brackets on the incisors (2 × 4) was not, as the two should be intimately related. Sample size may have played a role in this regard. This indicates that although the two variables should be related, right angle is a more precise variable than 2 × 4 when predicting a patient’s likelihood of proceeding to phase II treatment. There are only two previous studies (Hulsey, 1970; McNamara et al., 2008) that are relatively similar in design to this study. In all three studies, buccal corridors appear to be of no significance. However, this study and the McNamara study (McNamara et  al., 2008) showed that smile arc was of no significance, which is in contradiction to the study by Hulsey (Hulsey, 1970). It is possible that these differences are due to the use of adult subjects or the changes in what is considered aesthetic over the decades since the 1970s. Unlike this study, most research on frontal dentofacial aesthetics assesses the importance of only one or two factors at a time (Witt and Flores-Mir, 2011a,b). The ability of this study to analyze multiple aesthetic factors simultaneously is both an advantage and disadvantage. Discerning the relative importance of multiple aesthetic factors is valuable, but the large number of factors needed to fully describe each photograph weakens the statistical analysis. It is tempting to include every imaginable aesthetic parameter for fear of excluding an important one. Even if a large number of factors were included, it is still possible that laypeople would be discriminating between photographs based on some unaccounted parameter.

726 References

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C. Flores-Mir et al.

Analysis of anterior dentoalveolar and perioral aesthetic characteristics and their impact on the decision to undergo a Phase II orthodontic treatment.

Researchers have conducted extensive studies regarding dentoalveolar factors that affect anterior dental aesthetics; however, there is no consensus re...
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