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Prediction of the occurrence and severity of mandibular incisor crowding in the early mixed dentition using craniofacial parameters
ORIGINAL ARTICLE
Prediction of the occurrence and severity of mandibular incisor crowding in the early mixed dentition using craniofacial parameters Ahmadreza Sardariana and Faezeh Ghaderib Shiraz, Iran
Introduction: With the recent interest in esthetics at an early age, prediction of mandibular incisor crowding is of significant importance. Since dental arch development is related to craniofacial growth, we conducted a cohort study to find a regression model for mandibular incisor crowding based on various craniofacial parameters in children. Methods: A total of 250 children, all in the early mixed dentition, were selected randomly by cluster sampling from primary schools. Craniofacial parameters were measured by a caliper bow, and intercanine widths were measured on dental casts. After a 12-month follow-up period, mandibular incisor crowding and intercanine width were assessed on each subject's dental cast. Discriminant and multiple regression analyses were performed separately for boys and girls. Results: Of 250 children, 148 returned for the 1-year follow-up and met the inclusion criteria. Regression analyses of patients with normal occlusion showed a statistically significant correlation between anterior dental crowding and facial height and bigonial width in both sexes. A significant inverse correlation was found between initial intercanine width and incisor crowding in girls. Furthermore, using the aforementioned parameters, the occurrence of mandibular incisor crowding could be predicted with an accuracy of 92.6%. Conclusions: We found that the occurrence and severity of mandibular incisor crowding in the early mixed dentition can be predicted accurately based on certain craniofacial parameters. (Am J Orthod Dentofacial Orthop 2018;153:701-7)
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rowding of the permanent teeth, especially in the anterior part of the mandible, is one of the most prevalent forms of malocclusion among children.1,2 For esthetic reasons, these patients comprise a significant portion of visits to a dental office.3 Mandibular anterior crowding is the result of a discrepancy between the sum of mesiodistal widths of 4 permanent incisors widths and the available space in the alveolar process. Several factors are related to the development of mandibular incisor crowding in the mixed dentition: arch dimensions, increased intercanine width, and mandibular growth pattern.4-8 The ability to predict the development of mandibular incisor crowding,
From the School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran. a Orthodontics Research Center, Department of Orthodontics. b Department of Pediatric Dentistry All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Address correspondence to: Faezeh Ghaderi, Department of Pediatric Dentistry, School of Dentistry, Ghasr-e-dasht Street, Shiraz, Iran; e-mail, ghaderi_fa@ sums.ac.ir. Submitted, December 2016; revised and accepted, August 2017. 0889-5406/$36.00 Ó 2018 by the American Association of Orthodontists. All rights reserved. https://doi.org/10.1016/j.ajodo.2017.08.025
especially in the early mixed dentition, has significant value to clinicians for decisions regarding the beginning of preventive therapy in the form of space management and preservation of the leeway space.9,10 In line with the reported correlations between facial and cranial parameters with dental arch changes in the literature,11-14 various authors have evaluated the relationship between dental crowding and craniofacial measurements.3,6-8,15 However, the results of these studies have yielded dissimilar and conflicting results.3,16-18 Since the current literature on this topic consists of cross-sectional studies evaluating a limited number of variants, the need for a well-designed cohort study to find a predictable regression model based on craniofacial parameters seems apparent. To the best of our knowledge, this study is the first cohort study investigating the relationship between incisor crowding and anthropometric parameters. Our aim was to determine whether mandibular incisor crowding can be predicted in the early mixed dentition stage using craniofacial measurements; this could provide a valuable tool for treatment planning. 701
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MATERIAL AND METHODS
The individuals enrolled in the study were selected based on a cluster sampling method. To this end, various districts in Shiraz, Iran, were selected as clusters, and the primary schools in each cluster were each given a number. Five schools in each cluster were selected randomly, yielding a total of 1700 white children aged 7 to 8 years. From this population, 250 subjects were selected randomly to take part in the study. The inclusion criteria for the study were children with a normal molar relationship defined as a flush terminal plane (1 mm deviation of the mandibular molars either mesial or distal from this position was deemed acceptable), an orthognathic growth pattern, erupted mandibular permanent central incisors, exfoliated or mobile mandibular deciduous lateral incisors, bilateral deciduous canines, no evidence of interproximal caries or cuspal wear in the mandibular deciduous canines, and erupted mandibular permanent first molars. The skeletal growth pattern was analyzed based on the positions of subnasale and pogonion relative to the true vertical line from the deepest point on the nasal bridge. Subjects with a history of previous orthodontic intervention and detected oral habits were excluded as were those who began orthodontic therapy during this study. Of the 250 children, 148 returned at the 1-year follow-up. There were many reasons for this drop in attendance. Some children changed schools, and others did not respond to the second visit call. Furthermore, some children were excluded due to loss or extraction of deciduous teeth or starting orthodontic treatment. After explaining the study procedure, written informed consent was obtained from the parents of all participants. Cranial and facial dimensions (height and width) of the sample population were measured on soft tissue landmarks by a caliper bow (ICS-Spreading CaliperSPCG01P, Industrial and Commercial Services, Telangana, India). The measurements and the landmarks are summarized in Table I. The measurements were performed 3 times, and an average was reported for each parameter. Some subjects (10% of the total sample population) were reassessed 2 days later to analyze the intraexaminer reliability using the intraclass correlation coefficient (ICC); this was determined to be 0.87. The mean error of the 2 measurements was 0.23 6 0.21 cm. Mandibular arch impressions of the children were taken at the first visit by mixing 52 g of alginate powder (Tropicalgin; Zhermack, Badio Polesine, Italy) and 40 mL of water for 15 seconds. The paste was immediately placed on a tray while the patient rinsed with warm water. Once the tray was seated on the dental arch, it was kept in place under finger pressure for
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Table I. Craniofacial measurements and definitions Measurement Facial height Facial width
Cranial height Cranial width Bigonial width
Definition From nasion* to mentony measured on the soft tissue Distance between the most prominent points of zygomatic bones in soft tissue from the frontal view Summit of glabellaz to furthest occipital point Widest measurement of the cranium at right angles to median plane Measurement from gonion§ to gonion on soft tissue
*The deepest point of the concavity between the forehead and the soft tissue contour of the nose in the midsagittal plane; yThe most inferior point of the soft tissue chin in the midsagittal plane; zThe most prominent point of the soft tissue drape of the forehead in the midsagittal plane; §The mandibular angle point projected most downward, backward, and outward identified by palpation.
90 seconds. The impressions were rinsed with cold water and disinfected using a glutaraldehide solution for 10 minutes. After a final rinse, the impressions were stored in a damp and cool environment for 1 hour and subsequently poured using type IV dental stone (GC Corporation, Tokyo, Japan) where 100 g of powder was hand-mixed with 30 mL of water. The impressions were subjected to vibration for 20 seconds and allowed to set for an hour at room temperature. Dental casts were used to obtain the mandibular intercanine width. The intercanine width was measured directly on the casts using a digital caliper (Shoka Gulf, Spain) in millimeters with an accuracy of 0.01 mm from the canine cusp tip of 1 side to the other. A secondary alginate impression was obtained at the 12-month follow up and used to acquire dental measurements including mandibular intercanine widths, incisor widths, and available space. The measurements were performed 3 times by a board-certified orthodontist (A.S.), and an average was used. Ten percent of the casts were remeasured, and the intraexaminer reliability was calculated as 0.88 using the ICC method. The mean error of the 2 measurements was 0.38 6 0.27 mm. Mandibular incisor crowding was measured on dental casts with a digital caliper. Incisor widths were measured as described by Hunter and Priest.19 The tips of the digital caliper were introduced from the labial side of the teeth and held incisally parallel to the occlusal plane, and the distances between the anatomic contact points of the teeth were measured. The available incisor space was measured between the mesial surfaces of the deciduous canines by allocating the dental arch into 2 straight-line segments (from the mesial contact point of the mandibular canine to the mesial contact point
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of the central incisor). To calculate the severity of crowding, the sum of incisor widths was subtracted from the available incisor space. For the prevalence of incisor crowding. the children were classified into 2 groups based on the amount of incisor crowding. Crowding greater than 2 mm was regarded as the threshold for clinical significance because of reports of spontaneous improvement of irregularities less than this amount.3 All measurements were performed 3 times by a boardcertified orthodontist, and an average was used. Ten percent of the casts were remeasured, and the intraexaminer reliability was calculated as 0.91 using the ICC method. The mean error of the 2 measurements was 0.12 6 0.23 mm. Statistical analysis
The Student t test was used to compare the values for the craniofacial parameters and the measurements from the dental casts between boys and girls. Both groups had a normal distribution. To compare the prevalence of mandibular incisor crowding between boys and girls, the chi-square test was applied. The increase in intercanine width was evaluated using the paired t test. To analyze the relationship between the initial intercanine width and the subsequent increase in intercanine width, the Pearson coefficient was used. A stepwise discriminant analysis was performed to render a quick tool for the prediction of patients who will have crowding (.2 mm) later. Stepwise multiple regression to analyze the potency of the craniofacial parameters in predicting the severity of mandibular incisor crowding was performed. For all statistical tests, P values less than 0.05 were considered significant. The tests were performed using the Statistical Package for the Social Sciences (version 18; SPSS, Chicago, Ill). RESULTS
Of the 250 children, 148—83 boys (56%) and 65 girls (44%),—with a mean gge of 7.4 6 0.48 years participated in the follow-up. This reduction of the sample was because some participants changed schools and were out of reach or refused to comply, and others were excluded because they began orthodontic treatment or had tooth extractions. Mandibular incisor crowding (.2 mm) was found in 36% of the sample population (boys, 28; girls, 25). Applying the chi-square test, we found no significant difference in the prevalence of crowding between boys and girls (P .0.05). The amounts of mean crowding of the mandibular incisors were 2.1 mm for girls and 2.7 mm for boys, with no statistically significant difference between them (P .0.05). Intercanine width
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measurements were significantly greater in boys at the initial measurement (Table II). There was also a significant inverse correlation between intercanine width at the first visit and the amount of increase in this parameter during the 1-year period. The Pearson coefficients demonstrating this correlation were –0.73 for girls and –0.65 for boys. Stronger correlations were present between the 2 parameters in subjects with crowding (Table III). The craniofacial parameters selected for this study had significantly greater values in boys (Table II). A stepwise discriminant analysis in girls provided a model in which bigonial width, facial height, and initial intercanine width could predict those who would develop mandibluar incisor crowding (.2 mm). The same model in boys included only bigonial width and facial height. The results of the discriminant analysis are shown in Table IV. As is apparent, excluding initial intercanine width, all variables remaining in the models for both sexes were significantly different between the crowding and noncrowding groups. Subsequently, a formula was derived for predicting whether a subject would develop crowding in the future (Table IV). The letter D stands for the threshold of the discriminant analysis where one can predict whether crowding will occur if the value obtained from the formula is more negative than the threshold. This threshold number has no units and only has a numeric value for a yes or no answer regarding crowding. The threshold values for the prediction of crowding were 0.396 for girls and 0.412 for boys. We then used the model to see whether it could accurately predict those in our sample who developed crowding. The result for girls was sensitivity of 88%, specificity of 95.3%, and total accuracy of 92.6%. The same analysis in boys resulted in sensitivity of 96.4%, specificity of 90.9%, and total accuracy of 92.8%. The subsequent stepwise multiple regression also excluded the same parameters as the discriminant analysis in both sexes and was based on the parameters deemed more influential in predicting the severity of crowding (Table V). The discriminant analysis singled out subjects who were likely to develop crowding of more than 2 mm, whereas the multiple regression specified the amount of crowding. The correlation coefficients of the models were 0.81 and 0.85 for boys and girls, respectively, yielding R2 values of 0.65 and 0.73. After use of the derived formulae for the estimation of mandibular incisor crowding in the 2 groups, we calculated the standard errors of the estimate. The calculated values for boys and girls were 0.69 6 0.54 mm and 0.62 6 0.57 mm, respectively. The percentage errors of the estimate were 7.39% 6 12.89% and 11.43% 6 18.29%, respectively.
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Table II. Craniofacial parameters and sum of mandibular incisor widths (means and standard deviations) Facial neight)cm) Facial width (cm) Height of head (cm) Width of head (cm) Bigonial width (cm) Tooth size (mm) Intercanine width (mm)
Boys 10.31 6 0.73 9.48 6 0.92 16.25 6 0.63 12.37 6 0.67 6.65 6 0.65 20.60 6 0.92 28.15 6 1.02
Girls 9.92 6 0.58 8.63 6 0.52 16.16 6 0.53 11.51 6 0.64 6.12 6 0.39 20.53 6 0.72 26.42 6 0.97
P value* \0.001 \0.001 0.28 \0.001 \0.001 0.59 \0.001
Crowding 10.55 6 0.64 8.75 6 0.78 16.3 6 0.54 11.83 6 0.79 5.89 6 0.33 20.69 6 0.74 28.03 6 1.52
No crowding 9.91 6 0.61 9.3 6 0.87 16.17 6 0.61 12.08 6 0.78 6.7 6 0.52 20.5 6 0.88 27.69 6 1.69
P value \0.001 \0.001 0.2 0.07 \0.001 0.18 0.15
*The P value pertains to the Student t test.
Table III. Pearson correlation between initial interca-
nine width and the increase in width after 1 year Boys 0.65 Crowding No crowding 0.78
Girls 0.73 Crowding No crowding
0.48
0.76
0.72
DISCUSSION
We aimed to evaluate the predictive potential of selected craniofacial parameters in determining mandibular incisor crowding at an early age. These parameters were based on the literature in a way that parameters linked with mandibular incisor crowding were selected. A stepwise discriminant analysis was performed that excluded parameters having no particular effect in our predictive model. The parameters that remained in the model were facial height and bigonial width in both sexes and initial intercanine width in girls. Multiple regression analysis showed that the correlation coefficients of the overall model in boys and girls are 0.81 and 0.85, respectively, demonstrating the strong predictive value of the model in both sexes. Measurement of crowding at the second visit showed that 36% of the subects had crowding of the mandibular incisors (.2 mm). The 2-mm cutoff point was chosen because it is believed that at mandibular incisor eruption there is a 1.6-mm discrepancy due to the difference between the width of the deciduous and permanent teeth termed “incisor liability.”20 This discrepancy is usually relieved by mechanisms such as labial positioning of the permanent incisors, a mild increase in intercanine width, and a slight distal positioning of the canines into the primate space.21,22 Thus, 2 mm of crowding is the amount that is expected to self-correct due to events related to normal development and not as a result of filling the leeway space. Although the leeway space could also help to alleviate any crowding in the mandible, it is usually reserved for the mesial migration of the molars leading to a Class I molar relationship. The
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prevalence of crowding observed in this study, considering the 2-mm threshold, is similar to previous reports by Keski-Nisula et al23 (38.9%) and BorzabadiFarahani et al24 (32.7%) in white populations, whereas studies of Brazilian and German children reported prevalences of 29% and 14.3%, respectively.25,26 The differences in the prevalence of crowding can be attributed to the 2-mm cutoff point selected in this study and the different ethnic groups in the studies. As a whole, the measured craniofacial parameters were significantly greater in boys compared with girls; the only exception was height of the head, which did not show a significant difference between the sexes. Tooth size was marginally greater in males, and the difference was insignificant. This is contradictory to the findings of Moorrees and Reed.27 and Niswander and Chong,28 who reported larger teeth in boys in white and Japanese populations, respectively, and also to the reports of Sampson and Richards29 in an American aboriginal population with larger incisors in girls, but it closely resembles a study on Dominican Americans that also found similar tooth sizes between the sexes.30 Regarding intercanine width, boys demonstrated significantly greater values. Moreover, the increase in intercanine width was significantly more pronounced in boys. By correlating the initial intercanine width with its subsequent increase, we found a negative relationship, meaning that subjets with a smaller intercanine width had a greater increase in this parameter during the 1-year period. This finding supports the reports of Sampson and Richads29 of a greater reduction in crowding in subjects with more crowding initially. The multiple regression model demonstrated that, in boys, intercanine width at the time of early mixed dentition was not significantly correlated with crowding and therefore lacks predictive value. However, in girls, this parameter remained in the stepwise multiple regression model (P \0.01). This could be because girls have significantly less growth in intercanine width compared with boys; therefore, the initial measurement of intercanine width was closer to the same measurement a year later.
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Table IV. Results of the stepwise discriminant analysis (means and standard deciations) Crowding Sex Female*
Maley
Parameter Bigonial width (cm) Facial height (cm) Initial intercanine width (mm) Bigonial width (cm) Facial height (cm)
Yes 5.75 6 0.22 10.3 6 0.61 26.6 6 1.43 5.99 6 0.35 10.75 6 0.6
No 6.34 6 0.3 9.7 6 0.44 26.75 6 1.1 6.99 6 0.48 10.07 6 0.68
P value \0.001 \0.001 0.628 \0.001 \0.001
Wilk's l 0.702 0.474 0.346 0.804 0.468
DCF 3.401 1.547 0.305 2.065 0.722
DCF, Discriminant function coefficient. *The discriminate formula for girls: D 5 –13.632 1.547 (facial height) 1 0.305 (initial intercanine width) 1 3.40 1 (bigonial width); yThe discriminate formula for boys: D 5 –6.298 0.722 (facial height) 1 2.065 (bigonial width).
Table V. Results of the stepwise multiple regression
analysis Sex Female*
Maley
Parameter Bigonial width (cm) Facial height (cm) Intercanine width (mm) Bigonial width (cm) Facial height (cm)
Beta 2.633 1.386 0.3 1.908 0.622
SE 0.285 0.203 0.095 0.189 0.167
*The formula for prediction of crowding severity in girls: X 5 11.559 1 1.386 (facial height) 0.3 (initial intercanine width) 2.633 (bigonial width); yThe formula for prediction of crowding severity in boys: X 5 7.451 1 0.622 (facial height) 1.908 (bigonial width).
The relationship between intercanine width and crowding has been previously demonstrated by Sayin and Turkkahraman,20 who reported smaller values in patients with crowding. To obtain a quick tool for categorizing patients into those who will develop crowding in the future and those who will not, we performed a discriminant analysis on the measured parameters. The resultant formulas were accurate (92.6% for girls; 92.8% for boys) in predicting who will have at least 2 mm of crowding in the 1-year period of this study. By opting for a stepwise discriminant analysis, we aimed to reduce the number of measurements required to predict crowding. For girls, 3 parameters remained in the final model: facial height, bigonial width, and intercanine width; for boys, only the first 2 made it to the final model. We compared the mean values of these parameters between subjects with and without crowding, and except for intercanine width in girls, all parameters significantly differed between the groups; facial height was higher, and bigonial width was narrower in subjects with crowding. According to the stepwise multiple regression, the same parameters also had a significant value in predicting the severity of crowding. Bigonial width had the most predictive value among the selected parameters, both in
prediction and severity of crowding; this was true for both sexes. We found no studies regarding the relationship between bigonial width and mandibular incisor crowding in the literature; however, the link between increased facial height and divergence has been previously reported in both treated and untreated subjects.31,32 Moreover, Sakuda et al16 reported positive correlations between mandibular incisor crowding and high mandibular planes, short mandibular body length, and reduced vertical dimension in the maxillary posterior segments.16 Our results give the clinician an accurate tool to predict whether a patient will develop crowding in the early mixed dentition based on craniofacial parameters that can readily be determined. Furthermore, the severity of the expected crowding can also be calculated based on the same parameters. The correlation coefficients for the prediction of the severity of mandibular incisor crowding using the multiple regression model were 0.81 for boys and 0.85 for girls; these are considerably higher than the figures for conventional mixed dentition analyses. A systematic review on the validity of mixed dentition space analysis methods reported correlation coefficient values about 0.6 when Tanaka-Johnston and Moyers methods are used.33 Another advantage of the present method is that it does not depend on the presence of permanent teeth for accurate prediction of crowding. Conventional techniques use the widths of the mandibular permanent incisors for prediction of crowding; this means that the clinician must wait until the permanent incisors have erupted; furthermore, alterations in the morphology of these teeth would add error to the calculations. The prediction of whether a person will develop crowding in the future together with the severity of the expected crowding can enable the clinician to better plan for future treatment and to provide valuable information to parents. Although crowding in the early mixed dentition may seem insignificant, a longitudinal study of 150 subjects showed that 89% of those with crowding in
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the early mixed dentition maintain this condition until all permanent teeth have erupted.4 It is tempting to use a singular model for the prediction of crowding, but individual variations from the norm should not be underestimated; whereas the sample size of this study was considerable, future studies verifying our results on larger populations seem necessary. Racial and ethnic diversity should also be taken into account in forthcoming studies due to previous reports emphasizing the effect they imply on incisor crowding. The measurement of incisor inclinations in the sample population would have added significant value to, and is therefore a limitation of, this study. Although one could argue that our findings enable clinicians to predict future crowding without needing to concern themselves with incisor inclination, it does not detract from the importance of the latter. Correcting excessive mandibular incisor inclination has been linked to improved mucogingival status.34 Furthermore, changing incisor inclination leads to changes in arch length, meaning that to correct an excessive incisor labial inclination, space will be required in the arch.35 We were unable to include incisor inclination measurement in our study since it would have required unnecessary radiation exposure of the subjects; this was ethically unacceptable. This study relied on measurements made with a caliper bow. Although a caliper bow would be hard to find in most orthodontic offices, the advent of 3-dimensional photography and advances in this field will enable clinicians to perform the measurements readily. Future studies should be performed on 3-dimensional photographs to investigate whether the same formulas will apply to them and make any adjustments necessary. In the end, these methods merely predict the occurrence and severity of future crowding and do not make any recommendations or assumptions regarding the treatment chosen by the clinician. CONCLUSIONS
The following conclusions can be drawn from our findings. 1.
2.
The occurrence and severity of mandibular incisor crowding can be predicted accurately at the start of the mixed dentition using just a few craniofacial parameters. Increases in intercanine width occur more often in subjects with mandibular incisor crowding. This emphasizes the need to refrain from the extraction or interproximal reduction of the deciduous canines before emergence of the lateral incisors when crowding is expected.
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REFERENCES 1. Hunter WS, Smith BR. Development of mandibular spacingcrowding from nine to 16 years of age. J Can Dent Assoc 1972; 38:178-85. 2. Doris JM, Bernard BW, Kuftinec MM, Stom D. A biometric study of tooth size and dental crowding. Am J Orthod 1981; 79:326-36. 3. Melo L, Ono Y, Takagi Y. Indicators of mandibular dental crowding in the mixed dentition. Pediatr Dent 2001;23:118-22. 4. Sanin C, Savara BS. Factors that affect the alignment of the mandibular incisors: a longitudinal study. Am J Orthod 1973;64: 248-57. 5. Perera PS. Rotational growth and incisor compensation. Angle Orthod 1987;57:39-49. 6. Turkkahraman H, Sayin MO. Relationship between mandibular anterior crowding and lateral dentofacial morphology in the early mixed dentition. Angle Orthod 2004;74:759-64. 7. Mucedero M, Rozzi M, Cardoni G, Ricchiuti MR, Cozza P. Dentoskeletal features in individuals with ectopic eruption of the permanent maxillary first molar. Korean J Orthod 2015;45:190-7. 8. Mucedero M, Ricchiuti MR, Cozza P, Baccetti T. Prevalence rate and dentoskeletal features associated with buccally displaced maxillary canines. Eur J Orthod 2013;35:305-9. 9. Hernandez-Sayago E, Espinar-Escalona E, Barrera-Mora JM, RuizNavarro MB, Llamas-Carreras JM, Solano-Reina E. Lower incisor position in different malocclusions and facial patterns. Med Oral Patol Oral Cir Bucal 2013;18:e343-50. 10. Sangwan S, Chawla HS, Goyal A, Gauba K, Mohanty U. Progressive changes in arch width from primary to early mixed dentition period: a longitudinal study. J Indian Soc Pedod Prev Dent 2011;29:14-9. 11. Nasby JA, Isaacson RJ, Worms FW, Speidel TM. Orthodontic extractions and the facial skeletal pattern. Angle Orthod 1972;42: 116-22. 12. Christie TE. Cephalometric patterns of adults with normal occlusion. Angle Orthod 1977;47:128-35. 13. Alvaran N, Roldan SI, Buschang PH. Maxillary and mandibular arch widths of Colombians. Am J Orthod Dentofacial Orthop 2009;135: 649-56. 14. Ghaderi F, Badakhsh S, Hekmatfar S. Investigation of the relationship between the increase in the intercanine width and the children's facial parameters; a 6-month follow-up study. J Dent (Shiraz) 2013;14:82-3. 15. Abdollahi-Fakhim S, Asghari Estiar M, Varghaei P, Alizadeh Sharafi M, Sakhinia M, Sakhinia E. Common mutations of the methylenetetrahydrofolate reductase (MTHFR) gene in nonsyndromic cleft lips and palates children in north-west of Iran. Iran J Otorhinolaryngol 2015;27:7-14. 16. Sakuda M, Kuroda Y, Wada K, Matsumoto M. Changes in crowding of the teeth during adolescence and their relation to growth of the facial skeleton. Trans Eur Orthod Soc (Spec ed) 1976;93-104. 17. Howe RP, McNamara JA Jr, O'Connor KA. An examination of dental crowding and its relationship to tooth size and arch dimension. Am J Orthod 1983;83:363-73. 18. Sinclair PM, Little RM. Maturation of untreated normal occlusions. Am J Orthod 1983;83:114-23. 19. Hunter WS, Priest WR. Errors and discrepancies in measurement of tooth size. J Dent Res 1960;39:405-14. 20. Sayin MO, T€ urkkahraman H. Factors contributing to mandibular anterior crowding in the early mixed dentition. Angle Orthod 2004;74:754-8.
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21. Proffit WR, Fields HW. Contemporary orthodontics. St Louis: C. V. Mosby; 1986. p. 72-4. 22. Moorrees CF, Chadha JM. Available space for the incisors during dental development—a growth study based on physiologic age. Angle Orthod 1965;35:12-22. 23. Keski-Nisula K, Lehto R, Lusa V, Keski-Nisula L, Varrela J. Occurrence of malocclusion and need of orthodontic treatment in early mixed dentition. Am J Orthod Dentofacial Orthop 2003;124: 631-8. 24. Borzabadi-Farahani A, Borzabadi-Farahani A, Eslamipour F. Malocclusion and occlusal traits in an urban Iranian population. An epidemiological study of 11- to 14-year-old children. Eur J Orthod 2009;31:477-84. 25. da Silva LP, Gleiser R. Occlusal development between primary and mixed dentitions: a 5-year longitudinal study. J Dent Child (Chic) 2008;75:287-94. 26. Tausche E, Luck O, Harzer W. Prevalence of malocclusions in the early mixed dentition and orthodontic treatment need. Eur J Orthod 2004;26:237-44. 27. Moorrees CF, Reed RB. Correlation among crown diameters of human teeth. Arch Oral Biol 1964;9:685-97.
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28. Niswander JD, Chung CS. The effects of inbreeding on tooth size in Japanese children. Am J Hum Genet 1965;17:390-8. 29. Sampson WJ, Richards LC. Prediction of mandibular incisor and canine crowding changes in the mixed dentition. Am J Orthod 1985;88:47-63. 30. Santoro M, Ayoub ME, Pardi VA, Cangialosi TJ. Mesiodistal crown dimensions and tooth size discrepancy of the permanent dentition of Dominican Americans. Angle Orthod 2000;70:303-7. 31. Goldberg AI, Behrents RG, Oliver DR, Buschang PH. Facial divergence and mandibular crowding in treated subjects. Angle Orthod 2013;83:381-8. 32. Leighton BC, Hunter WS. Relationship between lower arch spacing/ crowding and facial height and depth. Am J Orthod 1982;82:418-25. 33. Luu NS, Mandich MA, Tieu LD, Kaipatur N, Flores-Mir C. The validity and reliability of mixed-dentition analysis methods: a systematic review. J Am Dent Assoc 2011;142:1143-53. 34. Geiger AM. Mucogingival problems and the movement of mandibular incisors: a clinical review. Am J Orthod 1980;78:511-27. 35. Mutinelli S, Manfredi M, Cozzani M. A mathematic-geometric model to calculate variation in mandibular arch form. Eur J Orthod 2000;22:113-25.
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Prediction of the occurrence and severity of mandibular incisor crowding in the early mixed dentition using craniofacial parameters Ahmadreza Sardariana and Faezeh Ghaderib Shiraz, Iran
Introduction: With the recent interest in esthetics at an early age, prediction of mandibular incisor crowding is of significant importance. Since dental arch development is related to craniofacial growth, we conducted a cohort study to find a regression model for mandibular incisor crowding based on various craniofacial parameters in children. Methods: A total of 250 children, all in the early mixed dentition, were selected randomly by cluster sampling from primary schools. Craniofacial parameters were measured by a caliper bow, and intercanine widths were measured on dental casts. After a 12-month follow-up period, mandibular incisor crowding and intercanine width were assessed on each subject's dental cast. Discriminant and multiple regression analyses were performed separately for boys and girls. Results: Of 250 children, 148 returned for the 1-year follow-up and met the inclusion criteria. Regression analyses of patients with normal occlusion showed a statistically significant correlation between anterior dental crowding and facial height and bigonial width in both sexes. A significant inverse correlation was found between initial intercanine width and incisor crowding in girls. Furthermore, using the aforementioned parameters, the occurrence of mandibular incisor crowding could be predicted with an accuracy of 92.6%. Conclusions: We found that the occurrence and severity of mandibular incisor crowding in the early mixed dentition can be predicted accurately based on certain craniofacial parameters. (Am J Orthod Dentofacial Orthop 2018;153:701-7)
C
rowding of the permanent teeth, especially in the anterior part of the mandible, is one of the most prevalent forms of malocclusion among children.1,2 For esthetic reasons, these patients comprise a significant portion of visits to a dental office.3 Mandibular anterior crowding is the result of a discrepancy between the sum of mesiodistal widths of 4 permanent incisors widths and the available space in the alveolar process. Several factors are related to the development of mandibular incisor crowding in the mixed dentition: arch dimensions, increased intercanine width, and mandibular growth pattern.4-8 The ability to predict the development of mandibular incisor crowding,
From the School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran. a Orthodontics Research Center, Department of Orthodontics. b Department of Pediatric Dentistry All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Address correspondence to: Faezeh Ghaderi, Department of Pediatric Dentistry, School of Dentistry, Ghasr-e-dasht Street, Shiraz, Iran; e-mail, ghaderi_fa@ sums.ac.ir. Submitted, December 2016; revised and accepted, August 2017. 0889-5406/$36.00 Ó 2018 by the American Association of Orthodontists. All rights reserved. https://doi.org/10.1016/j.ajodo.2017.08.025
especially in the early mixed dentition, has significant value to clinicians for decisions regarding the beginning of preventive therapy in the form of space management and preservation of the leeway space.9,10 In line with the reported correlations between facial and cranial parameters with dental arch changes in the literature,11-14 various authors have evaluated the relationship between dental crowding and craniofacial measurements.3,6-8,15 However, the results of these studies have yielded dissimilar and conflicting results.3,16-18 Since the current literature on this topic consists of cross-sectional studies evaluating a limited number of variants, the need for a well-designed cohort study to find a predictable regression model based on craniofacial parameters seems apparent. To the best of our knowledge, this study is the first cohort study investigating the relationship between incisor crowding and anthropometric parameters. Our aim was to determine whether mandibular incisor crowding can be predicted in the early mixed dentition stage using craniofacial measurements; this could provide a valuable tool for treatment planning. 701
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MATERIAL AND METHODS
The individuals enrolled in the study were selected based on a cluster sampling method. To this end, various districts in Shiraz, Iran, were selected as clusters, and the primary schools in each cluster were each given a number. Five schools in each cluster were selected randomly, yielding a total of 1700 white children aged 7 to 8 years. From this population, 250 subjects were selected randomly to take part in the study. The inclusion criteria for the study were children with a normal molar relationship defined as a flush terminal plane (1 mm deviation of the mandibular molars either mesial or distal from this position was deemed acceptable), an orthognathic growth pattern, erupted mandibular permanent central incisors, exfoliated or mobile mandibular deciduous lateral incisors, bilateral deciduous canines, no evidence of interproximal caries or cuspal wear in the mandibular deciduous canines, and erupted mandibular permanent first molars. The skeletal growth pattern was analyzed based on the positions of subnasale and pogonion relative to the true vertical line from the deepest point on the nasal bridge. Subjects with a history of previous orthodontic intervention and detected oral habits were excluded as were those who began orthodontic therapy during this study. Of the 250 children, 148 returned at the 1-year follow-up. There were many reasons for this drop in attendance. Some children changed schools, and others did not respond to the second visit call. Furthermore, some children were excluded due to loss or extraction of deciduous teeth or starting orthodontic treatment. After explaining the study procedure, written informed consent was obtained from the parents of all participants. Cranial and facial dimensions (height and width) of the sample population were measured on soft tissue landmarks by a caliper bow (ICS-Spreading CaliperSPCG01P, Industrial and Commercial Services, Telangana, India). The measurements and the landmarks are summarized in Table I. The measurements were performed 3 times, and an average was reported for each parameter. Some subjects (10% of the total sample population) were reassessed 2 days later to analyze the intraexaminer reliability using the intraclass correlation coefficient (ICC); this was determined to be 0.87. The mean error of the 2 measurements was 0.23 6 0.21 cm. Mandibular arch impressions of the children were taken at the first visit by mixing 52 g of alginate powder (Tropicalgin; Zhermack, Badio Polesine, Italy) and 40 mL of water for 15 seconds. The paste was immediately placed on a tray while the patient rinsed with warm water. Once the tray was seated on the dental arch, it was kept in place under finger pressure for
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Table I. Craniofacial measurements and definitions Measurement Facial height Facial width
Cranial height Cranial width Bigonial width
Definition From nasion* to mentony measured on the soft tissue Distance between the most prominent points of zygomatic bones in soft tissue from the frontal view Summit of glabellaz to furthest occipital point Widest measurement of the cranium at right angles to median plane Measurement from gonion§ to gonion on soft tissue
*The deepest point of the concavity between the forehead and the soft tissue contour of the nose in the midsagittal plane; yThe most inferior point of the soft tissue chin in the midsagittal plane; zThe most prominent point of the soft tissue drape of the forehead in the midsagittal plane; §The mandibular angle point projected most downward, backward, and outward identified by palpation.
90 seconds. The impressions were rinsed with cold water and disinfected using a glutaraldehide solution for 10 minutes. After a final rinse, the impressions were stored in a damp and cool environment for 1 hour and subsequently poured using type IV dental stone (GC Corporation, Tokyo, Japan) where 100 g of powder was hand-mixed with 30 mL of water. The impressions were subjected to vibration for 20 seconds and allowed to set for an hour at room temperature. Dental casts were used to obtain the mandibular intercanine width. The intercanine width was measured directly on the casts using a digital caliper (Shoka Gulf, Spain) in millimeters with an accuracy of 0.01 mm from the canine cusp tip of 1 side to the other. A secondary alginate impression was obtained at the 12-month follow up and used to acquire dental measurements including mandibular intercanine widths, incisor widths, and available space. The measurements were performed 3 times by a board-certified orthodontist (A.S.), and an average was used. Ten percent of the casts were remeasured, and the intraexaminer reliability was calculated as 0.88 using the ICC method. The mean error of the 2 measurements was 0.38 6 0.27 mm. Mandibular incisor crowding was measured on dental casts with a digital caliper. Incisor widths were measured as described by Hunter and Priest.19 The tips of the digital caliper were introduced from the labial side of the teeth and held incisally parallel to the occlusal plane, and the distances between the anatomic contact points of the teeth were measured. The available incisor space was measured between the mesial surfaces of the deciduous canines by allocating the dental arch into 2 straight-line segments (from the mesial contact point of the mandibular canine to the mesial contact point
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of the central incisor). To calculate the severity of crowding, the sum of incisor widths was subtracted from the available incisor space. For the prevalence of incisor crowding. the children were classified into 2 groups based on the amount of incisor crowding. Crowding greater than 2 mm was regarded as the threshold for clinical significance because of reports of spontaneous improvement of irregularities less than this amount.3 All measurements were performed 3 times by a boardcertified orthodontist, and an average was used. Ten percent of the casts were remeasured, and the intraexaminer reliability was calculated as 0.91 using the ICC method. The mean error of the 2 measurements was 0.12 6 0.23 mm. Statistical analysis
The Student t test was used to compare the values for the craniofacial parameters and the measurements from the dental casts between boys and girls. Both groups had a normal distribution. To compare the prevalence of mandibular incisor crowding between boys and girls, the chi-square test was applied. The increase in intercanine width was evaluated using the paired t test. To analyze the relationship between the initial intercanine width and the subsequent increase in intercanine width, the Pearson coefficient was used. A stepwise discriminant analysis was performed to render a quick tool for the prediction of patients who will have crowding (.2 mm) later. Stepwise multiple regression to analyze the potency of the craniofacial parameters in predicting the severity of mandibular incisor crowding was performed. For all statistical tests, P values less than 0.05 were considered significant. The tests were performed using the Statistical Package for the Social Sciences (version 18; SPSS, Chicago, Ill). RESULTS
Of the 250 children, 148—83 boys (56%) and 65 girls (44%),—with a mean gge of 7.4 6 0.48 years participated in the follow-up. This reduction of the sample was because some participants changed schools and were out of reach or refused to comply, and others were excluded because they began orthodontic treatment or had tooth extractions. Mandibular incisor crowding (.2 mm) was found in 36% of the sample population (boys, 28; girls, 25). Applying the chi-square test, we found no significant difference in the prevalence of crowding between boys and girls (P .0.05). The amounts of mean crowding of the mandibular incisors were 2.1 mm for girls and 2.7 mm for boys, with no statistically significant difference between them (P .0.05). Intercanine width
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measurements were significantly greater in boys at the initial measurement (Table II). There was also a significant inverse correlation between intercanine width at the first visit and the amount of increase in this parameter during the 1-year period. The Pearson coefficients demonstrating this correlation were –0.73 for girls and –0.65 for boys. Stronger correlations were present between the 2 parameters in subjects with crowding (Table III). The craniofacial parameters selected for this study had significantly greater values in boys (Table II). A stepwise discriminant analysis in girls provided a model in which bigonial width, facial height, and initial intercanine width could predict those who would develop mandibluar incisor crowding (.2 mm). The same model in boys included only bigonial width and facial height. The results of the discriminant analysis are shown in Table IV. As is apparent, excluding initial intercanine width, all variables remaining in the models for both sexes were significantly different between the crowding and noncrowding groups. Subsequently, a formula was derived for predicting whether a subject would develop crowding in the future (Table IV). The letter D stands for the threshold of the discriminant analysis where one can predict whether crowding will occur if the value obtained from the formula is more negative than the threshold. This threshold number has no units and only has a numeric value for a yes or no answer regarding crowding. The threshold values for the prediction of crowding were 0.396 for girls and 0.412 for boys. We then used the model to see whether it could accurately predict those in our sample who developed crowding. The result for girls was sensitivity of 88%, specificity of 95.3%, and total accuracy of 92.6%. The same analysis in boys resulted in sensitivity of 96.4%, specificity of 90.9%, and total accuracy of 92.8%. The subsequent stepwise multiple regression also excluded the same parameters as the discriminant analysis in both sexes and was based on the parameters deemed more influential in predicting the severity of crowding (Table V). The discriminant analysis singled out subjects who were likely to develop crowding of more than 2 mm, whereas the multiple regression specified the amount of crowding. The correlation coefficients of the models were 0.81 and 0.85 for boys and girls, respectively, yielding R2 values of 0.65 and 0.73. After use of the derived formulae for the estimation of mandibular incisor crowding in the 2 groups, we calculated the standard errors of the estimate. The calculated values for boys and girls were 0.69 6 0.54 mm and 0.62 6 0.57 mm, respectively. The percentage errors of the estimate were 7.39% 6 12.89% and 11.43% 6 18.29%, respectively.
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Table II. Craniofacial parameters and sum of mandibular incisor widths (means and standard deviations) Facial neight)cm) Facial width (cm) Height of head (cm) Width of head (cm) Bigonial width (cm) Tooth size (mm) Intercanine width (mm)
Boys 10.31 6 0.73 9.48 6 0.92 16.25 6 0.63 12.37 6 0.67 6.65 6 0.65 20.60 6 0.92 28.15 6 1.02
Girls 9.92 6 0.58 8.63 6 0.52 16.16 6 0.53 11.51 6 0.64 6.12 6 0.39 20.53 6 0.72 26.42 6 0.97
P value* \0.001 \0.001 0.28 \0.001 \0.001 0.59 \0.001
Crowding 10.55 6 0.64 8.75 6 0.78 16.3 6 0.54 11.83 6 0.79 5.89 6 0.33 20.69 6 0.74 28.03 6 1.52
No crowding 9.91 6 0.61 9.3 6 0.87 16.17 6 0.61 12.08 6 0.78 6.7 6 0.52 20.5 6 0.88 27.69 6 1.69
P value \0.001 \0.001 0.2 0.07 \0.001 0.18 0.15
*The P value pertains to the Student t test.
Table III. Pearson correlation between initial interca-
nine width and the increase in width after 1 year Boys 0.65 Crowding No crowding 0.78
Girls 0.73 Crowding No crowding
0.48
0.76
0.72
DISCUSSION
We aimed to evaluate the predictive potential of selected craniofacial parameters in determining mandibular incisor crowding at an early age. These parameters were based on the literature in a way that parameters linked with mandibular incisor crowding were selected. A stepwise discriminant analysis was performed that excluded parameters having no particular effect in our predictive model. The parameters that remained in the model were facial height and bigonial width in both sexes and initial intercanine width in girls. Multiple regression analysis showed that the correlation coefficients of the overall model in boys and girls are 0.81 and 0.85, respectively, demonstrating the strong predictive value of the model in both sexes. Measurement of crowding at the second visit showed that 36% of the subects had crowding of the mandibular incisors (.2 mm). The 2-mm cutoff point was chosen because it is believed that at mandibular incisor eruption there is a 1.6-mm discrepancy due to the difference between the width of the deciduous and permanent teeth termed “incisor liability.”20 This discrepancy is usually relieved by mechanisms such as labial positioning of the permanent incisors, a mild increase in intercanine width, and a slight distal positioning of the canines into the primate space.21,22 Thus, 2 mm of crowding is the amount that is expected to self-correct due to events related to normal development and not as a result of filling the leeway space. Although the leeway space could also help to alleviate any crowding in the mandible, it is usually reserved for the mesial migration of the molars leading to a Class I molar relationship. The
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prevalence of crowding observed in this study, considering the 2-mm threshold, is similar to previous reports by Keski-Nisula et al23 (38.9%) and BorzabadiFarahani et al24 (32.7%) in white populations, whereas studies of Brazilian and German children reported prevalences of 29% and 14.3%, respectively.25,26 The differences in the prevalence of crowding can be attributed to the 2-mm cutoff point selected in this study and the different ethnic groups in the studies. As a whole, the measured craniofacial parameters were significantly greater in boys compared with girls; the only exception was height of the head, which did not show a significant difference between the sexes. Tooth size was marginally greater in males, and the difference was insignificant. This is contradictory to the findings of Moorrees and Reed.27 and Niswander and Chong,28 who reported larger teeth in boys in white and Japanese populations, respectively, and also to the reports of Sampson and Richards29 in an American aboriginal population with larger incisors in girls, but it closely resembles a study on Dominican Americans that also found similar tooth sizes between the sexes.30 Regarding intercanine width, boys demonstrated significantly greater values. Moreover, the increase in intercanine width was significantly more pronounced in boys. By correlating the initial intercanine width with its subsequent increase, we found a negative relationship, meaning that subjets with a smaller intercanine width had a greater increase in this parameter during the 1-year period. This finding supports the reports of Sampson and Richads29 of a greater reduction in crowding in subjects with more crowding initially. The multiple regression model demonstrated that, in boys, intercanine width at the time of early mixed dentition was not significantly correlated with crowding and therefore lacks predictive value. However, in girls, this parameter remained in the stepwise multiple regression model (P \0.01). This could be because girls have significantly less growth in intercanine width compared with boys; therefore, the initial measurement of intercanine width was closer to the same measurement a year later.
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Table IV. Results of the stepwise discriminant analysis (means and standard deciations) Crowding Sex Female*
Maley
Parameter Bigonial width (cm) Facial height (cm) Initial intercanine width (mm) Bigonial width (cm) Facial height (cm)
Yes 5.75 6 0.22 10.3 6 0.61 26.6 6 1.43 5.99 6 0.35 10.75 6 0.6
No 6.34 6 0.3 9.7 6 0.44 26.75 6 1.1 6.99 6 0.48 10.07 6 0.68
P value \0.001 \0.001 0.628 \0.001 \0.001
Wilk's l 0.702 0.474 0.346 0.804 0.468
DCF 3.401 1.547 0.305 2.065 0.722
DCF, Discriminant function coefficient. *The discriminate formula for girls: D 5 –13.632 1.547 (facial height) 1 0.305 (initial intercanine width) 1 3.40 1 (bigonial width); yThe discriminate formula for boys: D 5 –6.298 0.722 (facial height) 1 2.065 (bigonial width).
Table V. Results of the stepwise multiple regression
analysis Sex Female*
Maley
Parameter Bigonial width (cm) Facial height (cm) Intercanine width (mm) Bigonial width (cm) Facial height (cm)
Beta 2.633 1.386 0.3 1.908 0.622
SE 0.285 0.203 0.095 0.189 0.167
*The formula for prediction of crowding severity in girls: X 5 11.559 1 1.386 (facial height) 0.3 (initial intercanine width) 2.633 (bigonial width); yThe formula for prediction of crowding severity in boys: X 5 7.451 1 0.622 (facial height) 1.908 (bigonial width).
The relationship between intercanine width and crowding has been previously demonstrated by Sayin and Turkkahraman,20 who reported smaller values in patients with crowding. To obtain a quick tool for categorizing patients into those who will develop crowding in the future and those who will not, we performed a discriminant analysis on the measured parameters. The resultant formulas were accurate (92.6% for girls; 92.8% for boys) in predicting who will have at least 2 mm of crowding in the 1-year period of this study. By opting for a stepwise discriminant analysis, we aimed to reduce the number of measurements required to predict crowding. For girls, 3 parameters remained in the final model: facial height, bigonial width, and intercanine width; for boys, only the first 2 made it to the final model. We compared the mean values of these parameters between subjects with and without crowding, and except for intercanine width in girls, all parameters significantly differed between the groups; facial height was higher, and bigonial width was narrower in subjects with crowding. According to the stepwise multiple regression, the same parameters also had a significant value in predicting the severity of crowding. Bigonial width had the most predictive value among the selected parameters, both in
prediction and severity of crowding; this was true for both sexes. We found no studies regarding the relationship between bigonial width and mandibular incisor crowding in the literature; however, the link between increased facial height and divergence has been previously reported in both treated and untreated subjects.31,32 Moreover, Sakuda et al16 reported positive correlations between mandibular incisor crowding and high mandibular planes, short mandibular body length, and reduced vertical dimension in the maxillary posterior segments.16 Our results give the clinician an accurate tool to predict whether a patient will develop crowding in the early mixed dentition based on craniofacial parameters that can readily be determined. Furthermore, the severity of the expected crowding can also be calculated based on the same parameters. The correlation coefficients for the prediction of the severity of mandibular incisor crowding using the multiple regression model were 0.81 for boys and 0.85 for girls; these are considerably higher than the figures for conventional mixed dentition analyses. A systematic review on the validity of mixed dentition space analysis methods reported correlation coefficient values about 0.6 when Tanaka-Johnston and Moyers methods are used.33 Another advantage of the present method is that it does not depend on the presence of permanent teeth for accurate prediction of crowding. Conventional techniques use the widths of the mandibular permanent incisors for prediction of crowding; this means that the clinician must wait until the permanent incisors have erupted; furthermore, alterations in the morphology of these teeth would add error to the calculations. The prediction of whether a person will develop crowding in the future together with the severity of the expected crowding can enable the clinician to better plan for future treatment and to provide valuable information to parents. Although crowding in the early mixed dentition may seem insignificant, a longitudinal study of 150 subjects showed that 89% of those with crowding in
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the early mixed dentition maintain this condition until all permanent teeth have erupted.4 It is tempting to use a singular model for the prediction of crowding, but individual variations from the norm should not be underestimated; whereas the sample size of this study was considerable, future studies verifying our results on larger populations seem necessary. Racial and ethnic diversity should also be taken into account in forthcoming studies due to previous reports emphasizing the effect they imply on incisor crowding. The measurement of incisor inclinations in the sample population would have added significant value to, and is therefore a limitation of, this study. Although one could argue that our findings enable clinicians to predict future crowding without needing to concern themselves with incisor inclination, it does not detract from the importance of the latter. Correcting excessive mandibular incisor inclination has been linked to improved mucogingival status.34 Furthermore, changing incisor inclination leads to changes in arch length, meaning that to correct an excessive incisor labial inclination, space will be required in the arch.35 We were unable to include incisor inclination measurement in our study since it would have required unnecessary radiation exposure of the subjects; this was ethically unacceptable. This study relied on measurements made with a caliper bow. Although a caliper bow would be hard to find in most orthodontic offices, the advent of 3-dimensional photography and advances in this field will enable clinicians to perform the measurements readily. Future studies should be performed on 3-dimensional photographs to investigate whether the same formulas will apply to them and make any adjustments necessary. In the end, these methods merely predict the occurrence and severity of future crowding and do not make any recommendations or assumptions regarding the treatment chosen by the clinician. CONCLUSIONS
The following conclusions can be drawn from our findings. 1.
2.
The occurrence and severity of mandibular incisor crowding can be predicted accurately at the start of the mixed dentition using just a few craniofacial parameters. Increases in intercanine width occur more often in subjects with mandibular incisor crowding. This emphasizes the need to refrain from the extraction or interproximal reduction of the deciduous canines before emergence of the lateral incisors when crowding is expected.
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28. Niswander JD, Chung CS. The effects of inbreeding on tooth size in Japanese children. Am J Hum Genet 1965;17:390-8. 29. Sampson WJ, Richards LC. Prediction of mandibular incisor and canine crowding changes in the mixed dentition. Am J Orthod 1985;88:47-63. 30. Santoro M, Ayoub ME, Pardi VA, Cangialosi TJ. Mesiodistal crown dimensions and tooth size discrepancy of the permanent dentition of Dominican Americans. Angle Orthod 2000;70:303-7. 31. Goldberg AI, Behrents RG, Oliver DR, Buschang PH. Facial divergence and mandibular crowding in treated subjects. Angle Orthod 2013;83:381-8. 32. Leighton BC, Hunter WS. Relationship between lower arch spacing/ crowding and facial height and depth. Am J Orthod 1982;82:418-25. 33. Luu NS, Mandich MA, Tieu LD, Kaipatur N, Flores-Mir C. The validity and reliability of mixed-dentition analysis methods: a systematic review. J Am Dent Assoc 2011;142:1143-53. 34. Geiger AM. Mucogingival problems and the movement of mandibular incisors: a clinical review. Am J Orthod 1980;78:511-27. 35. Mutinelli S, Manfredi M, Cozzani M. A mathematic-geometric model to calculate variation in mandibular arch form. Eur J Orthod 2000;22:113-25.
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