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Studiu Occurrence of Malocclusion and need of orthodontic treatment in early mixed dentition

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1. ORIGINAL ARTICLE Occurrence of malocclusion and need of orthodontic treatment in early mixed dentition Katri Keski-Nisula, DDS, a Raija Lehto, DDS, b Vuokko Lusa, DDS, c Leo Keski-Nisula, MD, PhD, d and Juha Varrela, DDS, PhD e Vaasa, Jalasja ̈ rvi, Kurikka, Tampere, and Turku, Finland This study analyzed the occlusions of 489 children at the onset of the mixed dentition period (mean age 5.1 years, range 4.0-7.8 years). These children participate in an ongoing clinical trial that is investigating the effects of orthodontic intervention in the early mixed dentition. The aim was to report the occlusal findings at the baseline. The frequencies of mesial step, flush terminal plane, and distal step were 19.1%, 47.8%, and 33.1%, respectively. The canine relationship was Class I in 46.1%, Class II in 52.4%, and Class III in 1.5% of the sides examined. An asymmetrical canine relationship was found in 30.1% of the children, significantly more often on the right side than on the left ( P  .001). Overjet ranged from  2to  10 mm with a mean of 2.9 mm. Overbite ranged from  5to  8 mm with a mean of 2.8 mm. Excessive (  4 mm) overjet was found in 26.7% and overbite in 33.8% of the children; in 15.5% of the children, both variables were 4 mm or more. Anterior crowding was detected in the maxillary arch in 11.6% and in the mandibular arch in 38.9% of the children. Girls showed mandibular crowding more often than boys ( P  .01). A posterior crossbite was found in 7.5% of the children, unilaterally in 6.4% and bilaterally in 1.1%. Scissors-bite was detected in 1.1% and an anterior crossbite in 2.2% of the children. The mean maximal opening was 40.3 mm. Joint sounds were registered in 5.2% of the children. The prevalence of malocclusion was between 67.7% and 92.7%, depending on the values of unacceptable parameters used for each occlusal characteristic. (Am J Orthod Dentofacial Orthop 2003;124:631-8) T he workshop discussions on early orthodontic treatment, held by the American Board of Orthodontics in 1997, indicated that most par- ticipants considered early intervention as a viable option in many malocclusion cases, 1 but the optimal timing of such treatment remains controversial. 2 Al- though early treatment is suggested to bring about many benefits including better use of the patient’s growth potential, reduced need of extractions and orthognathic surgery, lesser risk for adverse iatrogenic effects, better patient compliance, and better and more stable results, 1,3-4 many clinicians express skepticism and point out that the effectiveness of early treatment is not corroborated by hard scientific evidence. 5-8 There are only a few well-controlled studies in which the timing of orthodontic treatment has been studied. During the 1990s, 3 large randomized clinical trials were carried out in the United States to study the effectiveness of early Class II treatment. 9-11 Because the results failed to show any major advantage to 2-stage treatment, these studies are frequently cited as evidence favoring 1-stage treatment of Class II patients in the early permanent dentition. However, even if these trials were designed to meet strict scientific standards, generalization of the findings is limited by other factors such as the type of malocclusion under study, selection and activation of the appliances tested, inclusion criteria, and ages of the patients. Further studies are needed before there is a full understanding of the advantages and disadvantages of early treatment in orthodontics. Many treatment modalities can be applied in the early stages of occlusal development, but they have not been sufficiently studied to date. In addition, important questions related to diagnostics in the deciduous and early mixed dentition must be addressed. In Finland, the health care system provides free dental care up to 18 years of age. This gives a rather unique opportunity, on a population basis, to monitor a Chief orthodontist, Vaasa Central Hospital, Vaasa, Finland. b General practitioner, Jalasja ̈rvi Health Center, Jalasja ̈rvi, Finland. c Chief dental officer, Kurikka Health Center, Kurikka, Finland. d Assistant chief of radiology, Tampere University Hospital, Tampere, Finland. e Professor and chair, Department of Oral Development and Orthodontics, Director, Postgraduate School of Oral Sciences, Institute of Dentistry, Univer- sity of Turku, Turku, Finland. This study was supported by the Finnish Dental Society Apollonia, the Medical Research Fund of Turku University Central Hospital, the Medical Research Fund of Vaasa Hospital District, and Plandent Oyj. Reprint requests to: Dr Juha Varrela, Department of Oral Development and Orthodontics, Institute Dentistry, University of Turku, Lemminka ̈isenkatu 2, FIN-20520 Turku, Finland; e-mail, juha.varrela@utu.fi. Submitted, November 2002; revised and accepted, February 2003. Copyright © 2003 by the American Association of Orthodontists. 0889-5406/2003/$30.00  0 doi:10.1016/j.adodo.2003.02.001 631

8. stomathognathic system in 5, 10 and 15 year old children in southwestern Finland. Proc Finn Dent Soc 1986;82:3-8. 20. Mylla ̈ rniemi S. Malocclusion in Finnish rural children [disserta- tion]. Proc Finn Dent Soc 1970;66:219-61. 21. Heikinheimo K, Salmi K. Need for orthodontic intervention in fi ve-year-old Finnish children. Proc Finn Dent Soc 1987;83:165-7. 22. Paunio P, Rautava P, Sillanpa ̈ a ̈ M. The Finnish Family Compe- tence Study: the effects of living conditions on sucking habits in 3-year-old Finnish children and the association between these habits and dental occlusion. Acta Odont Scand 1993;51:23-9. 23. Modeer T, Odenrick L, Lindner A. Sucking habits and their relation to posterior cross-bite in 4-year-old children. Scan J Dent Res 1982;90:323-8. 24. Larsson E. The effect of dummy-sucking on the occlusion: a review. Eur J Orthod 1986;8:127-30. 25. Lindner A, Modeer T. Relation between sucking habits and dental characteristics in preschool children with unilateral cross- bite. Scand J Dent Res 1989;97:278-83. 26. Heikinheimo K, Salmi K, Mylla ̈ rniemi S. Long-term evaluation of orthodontic diagnoses made at the ages of 7 and 10 years. Eur J Orthod 1987;9:151-9. 27. Fro ̈ lich FJ. A longitudinal study of untreated Class II type malocclusions. Trans Eur Orthod Soc 1961;37:139-59. 28. Fro ̈ lich FJ. Changes in untreated Class II type malocclusion. Angle Orthod 1962;32:167-79. 29. Arya BS, Savara BS, Thomas DR. Prediction of fi rst molar occlusion. Am J Orthod 1973;63:610-22. 30. Baccetti T, Franchi L, McNamara JA Jr, Tollaro I. Early dentaofacial features of Class II malocclusion: a longitudinal study from the deciduous through the mixed dentition. Am J Orthod Dentofacial Orthop 2000;111:502-9. 31. Varrela J. Development of distal occlusion: a follow-up study in the early mixed dentition. J Dent Res 1997;76:18. 32. Leighton BC. The early signs of malocclusion. Trans Eur Orthod Soc 1969;45:353-68. 33. Leighton BC. The value of prophecy in orthodontics. Dent Pract Dent Rec 1971;21:359-72. 34. Leighton BC. The early development of normal occlusion. Trans Eur Orthod Soc 1975;47:67-77. 35. Bergersen EO. A longitudinal study of anterior vertical overbite from eight to twenty years of age. Angle Orthod 1988;58:237-56. 36. Bjo ̈ rk A. Variability and changes in overjet and overbite. Am J Orthod 1953;39:779-801. 37. Leighton BC. The early development of cross-bites. Dent Pract Dent Rec 1966;17:145-52. 38. Heikinheimo K, Salmi K, Mylla ̈ rniemi S. Identi fi cation of cases requiring orthodontic treatment: a longitudinal study. Swed Dent J 1982;15:71-7. 39. Thilander B, Wahlund S, Lennartson B. The effect of early interceptive treatment in children with posterior crossbite. Eur J Orthod 1984;6:25-34. 40. Pirttiniemi P. Associations of mandibulofacial asymmetries, with special reference to glenoid fossa remodeling [dissertation]. Oulu, Finland: University of Oulu; 1992. 41. Popovich F, Thompson GW. Evaluation of preventive and interceptive treatment between three and eighteen years of age. In: Cook JT, editor. Transactions of the Third Orthodontic Congress; London 1973. London: Crosby, Lockwood and Sta- ples; 1975. p. 260-81. 42. Ko ̈ hler L, Holst K. Malocclusion and sucking habits in four-year- old children. Acta Paediat Scand 1973;62:373-9. RECEIVE THE JOURNAL’S TABLE OF CONTENTS EACH MONTH BY E-MAIL To receive the tables of contents by e-mail, send an e-mail message to majordomo@mosby.com Leave the subject line blank and type the following as the body of your message: Subscribe ajodo_toc You may sign up through our website at http://www.mosby.com/ajodo. You will receive an e-mail message con fi rming that you have been added to the mailing list. Note that TOC e-mails will be sent when a new issue is posted to the website. American Journal of Orthodontics and Dentofacial Orthopedics December 2003 638 Keski-Nisula et al

6. Foster and Hamilton, 18 for example, when both unilat - eral and bilateral cases were taken into account, the frequency of distal step was 38.8% and that of a Class II type canine relationship was 59.0%. The respective values in the present sample were 43.3% and 68.1%. Findings regarding the incisor relationship also show similarity. Foster and Hamilton 18 reported that 37% of the children lacked a contact between the maxillary and mandibular incisors, while in 20% the mandibular incisors were biting into the palatal gingiva. In the current sample, the frequencies were 39.1% and 32%, respectively. The percentages of children with overjet exceeding 2 mm were also similar (72% and 60.35%). Maximal opening in this sample was very close to what has been reported for 5-year-old children in Finland, whereas joint sounds were somewhat more prevalent (5.2%) than reported previously (3.2%). 19 In Finland, the prevalence of posterior crossbite in the deciduous dentition increased from 3% in the 1950s to 16% in the 1980s and decreased to 8.3% in the 1990s. 20-22 The prevalence of 7.5% in the present sample is in line with a decreasing trend. A strong association has been shown between paci fi er sucking and posterior crossbite. 23-25 It is therefore plausible that the changes in the occurrence of posterior crossbite might re fl ect alterations in the children ’ s paci fi er use and sucking habits. The use of paci fi ers increased dramatically in the 1960s, and habitual users, up to the age of 5 years, were not uncommon. 22 Presently, however, dental professionals are recommending that children should stop using paci fi ers much earlier. Prev- alence of anterior crossbite, on the other hand, has remained stable, about 2%, during the last 40 or 50 years for which records are available. 20,21 Orthodontic diagnostics in the deciduous or early mixed dentition are often considered to suffer from elements of uncertainty. The main reason for this seems to be that both positive and negative changes are possible in the occlusion during growth. 15, 26 Subtle - ness of the signs of malocclusion in the deciduous dentition could be another factor. As a result, the clinical signi fi cance of the occlusal variation in the deciduous dentition has not been fully explored. When considering early treatment, differentiation between patients with high and low capacities for self-correction would seem important. However, the longitudinal anal- ysis of Heikinheimo et al 26 indicated that in many children a positive development in 1 deviating charac- teristic was often followed by an adverse change in another. Consequently, most of the children who orig- inally were classi fi ed as having a de fi nite need of treatment remained in that category, albeit often for a different reason. This seems to suggest that the occlu- sion develops as a unit, and the deviant characteristics are but signs of an underlying disturbance in the development as a whole. Longitudinal studies have shown that a distal step in the deciduous dentition invariably leads to a Class II molar relationship in the permanent dentition. 16,27-30 Similarly, a mesial step seldom turns into a distal bite. In both cases, the relationship of the deciduous molars seems to give a fairly reliable prediction of the future permanent molar relationship. Children with fl ush ter- minal planes are more problematic because up to 44% seem to progress to a Class II occlusion. 16,29 The present analysis indicates (Table III), that, although there is a strong association between a distal step and a Class II canine relationship on the one hand and a mesial step and a Class I on the other, children with fl ush terminal planes are almost equally divided be- tween Class I and Class II canine relationships (55% vs. 45%). On the basis of the fi ndings that a canine relationship can be a diagnostic aid to predict changes in molar relationship, 31 it can be assumed that the combination of a fl ush terminal plane and a Class II canine relationship indicates a higher risk to develop a distal occlusion. It is therefore possible that, if both the molar and canine relationships are taken into consider- ation, a reliable prediction of the intermaxillary rela- tionship in the permanent dentition can be made in most cases, including those starting off with a fl ush terminal plane. The analyses by Leighton 32,33 indicated that, in his sample, crowding in the deciduous dentition always resulted in crowding of the permanent dentition. Only with spacing of more than 6 mm in the deciduous arches did the risk of subsequent crowding become zero. Crowding in the deciduous dentition can therefore be considered as an indicator of treatment need. In the present sample, 11.6% of the children had crowding in the maxillary arch, 38.9% in the mandibular arch, and 8% in both arches. Overbite and overjet usually increase when the permanent incisors erupt. 15,32,34,35 Thereafter, both tend to become smaller, although the decrease is less than 1 mm on average. 35,36 On an individual level, however, large changes in both directions have been reported. 35,36 It is possible that this variation re fl ects dentoalveolar compensations that take place in re- sponse to facial growth and functional changes as well as to the exfoliation and eruption of teeth. Presently, no data indicate a de fi nitive threshold value for overbite or overjet that could be applied in early diagnostics, although the fi ndings of Bergersen 35 regarding the development of overbite can be useful in the clinical decision making. American Journal of Orthodontics and Dentofacial Orthopedics December 2003 636 Keski-Nisula et al

2. occlusal development and provide treatment at any time during the entire postnatal growth period. Financial pressures and a desire to treat all children in need have encouraged orthodontists to develop novel solu- tions, 12,13 including treatment with orthopedic and functional appliances in the early mixed dentition. Recently, eruption guidance appliances have gained popularity. 14 Good results are reported from districts that have shifted to early treatment, but few scienti fi c studies have been published to date. A clinical trial was begun in 1998 to investigate the results obtained through an early orthodontic interven- tion in 2 municipalities, Jalasja ̈ rvi and Kurikka, in western Finland. Because the study is carried out in health centers with established early treatment proto- cols, it was not possible to assign the children to treatment and control groups. A neighboring town, Seina ̈ joki, where no treatment is normally given in the early mixed dentition, agreed to provide the control subjects for the study. In addition to the effectiveness and ef fi ciency of early orthodontic treatment, the study aims to analyze the direction and amount of spontane- ous occlusal changes during the early stages of the mixed dentition period to better establish the accuracy of a diagnosis based on the deciduous occlusion. Furthermore, the study will include a long-term fol- low-up of the children. Children from 2 age groups were clinically exam- ined in the deciduous dentition. These groups consisted of children born in 1992 or 1993. All children went through a second examination at the beginning of the mixed dentition period. At this point, radiographic records and dental impressions were taken, and the treatment was started in children who quali fi ed. The aim of the present study was to describe occlusal characteristics, investigate the occurrence of malocclu- sions, and assess the need of treatment at the baseline, ie, when the children were entering the mixed dentition stage. MATERIAL AND METHODS The study sample is derived from 3 rural munici- palities in western Finland, Jalasja ̈ rvi, Kurikka, and Seina ̈ joki, with a combined population of about 50,000 inhabitants. To eliminate selection bias and to increase the comparability of the study and control groups, whole age cohorts (Jalasja ̈ rvi and Kurikka) and a randomized sample from the same cohorts (Seina ̈ joki) were used. Consequently, the 137 children born in 1992 in Kurikka (population 11,000), the 253 born in 1992 and 1993 in Jalasja ̈ rvi (population 9,000), and 205 born in 1992 or 1993 in Seina ̈ joki (population 30,000) — a total of 595 children — were called in for a clinical examination. Twenty-six children in Kurikka, 21 in Jalasja ̈ rvi, and 3 in Seina ̈ joki were excluded from the study because of dif fi culties in cooperation or because their ethnic background was not Finnish. In addition, expansion treatment had already been started in 11 children with posterior crossbites (9 in Jalasja ̈ rvi and 2 in Kurikka). All available pretreatment information from these 11 children was used. Consequently, 534 children, 268 girls and 266 boys, all ethnically Finnish, were clinically examined between their fourth and fi fth birthdays. The health service authorities in each munic- ipality approved the study protocol. At any point, the children and their parents were free not to participate. To control the variation caused by individual dif- ferences in the rate of development, the timing of examinations and interventions was based on the stage of dental development rather than on chronological age. Therefore, all 534 children were recalled at the begin- ning of the mixed dentition period when the radio- graphic records and occlusal impressions were taken. At the same time, the treatment was initiated in the children in the treatment group. To ensure that the second appointment would take place near the onset of the mixed dentition stage, the parents were requested to make an appointment immediately after the fi rst decid- uous incisor was exfoliated. The mean age of the children at the second examination was 5.1 years (SD 2.6, range 4.0-7.8 years). Dental casts were collected from 486 children, 244 girls and 242 boys. The bite was registered in centric relation, and the casts were trimmed accordingly. Forty-eight (9.0%) of the 534 children either refused to cooperate or did not want to participate in the study. Of them, only the information collected at the fi rst examination was used in the present analysis. The data on overjet and overbite of these 48 children indicated that their occlusal charac- teristics were not different from those of the 486 who participated in the second examination. The fi rst examination, performed by 2 experienced orthodontists, included measuring overbite, overjet, gummy smile, and maximal opening, and recording crossbite, scissors-bite, and joint sounds during re- peated opening and closing movements. The 2 exam- iners were calibrated to carry out the measurements in a similar manner. Overbite and overjet were measured between the fi rst maxillary and mandibular deciduous incisors on the right side, as suggested by Moorrees, 15 by using a metal ruler with an accuracy of 0.1 mm. The values obtained for overbite were not corrected for incisal wear. The gummy smile was measured from the gingival margin of the right maxillary central incisor to the lower border of the upper lip as the child was smiling, by using a metal ruler with an accuracy of 1 American Journal of Orthodontics and Dentofacial Orthopedics December 2003 632 Keski-Nisula et al

7. Posterior crossbite of the deciduous dentition has been reported to occasionally self-correct during the eruption of the permanent teeth but only in a few patients. 37-39 Nevertheless, the risk of children with posterior crossbite to develop facial asymmetries in- cluding the condylar process and glenoid fossa 40 is a factor that favors early intervention. The number of children in the present sample who show at least 1 deviating occlusal characteristic varies between 67.7% and 92.7%, depending the initial threshold values used. Even the most conservative estimate (67.7%) appears high, but similar fi gures have been reported for Canadian and Swedish children — 66.5% and 66.4%, respectively. 41,42 An earlier Finnish study 21 that analyzed the occlusions of 5-year-olds found a prevalence of 60.7%. All these studies were based on unselected samples from the general popula- tion. Estimates of treatment need, on the other hand, show much wider variation, from 10.7% to 66.5%, 21,41,42 obviously re fl ecting the authors ’ differ - ent opinions concerning the clinical management of the detected malocclusions. Although a prediction of occlusal development can often be made with a reasonable degree of accuracy, the question of whether orthodontic treatment is warranted in the deciduous or the early mixed dentition remains. The problem is complex and cannot be answered on the basis of the information presently available. In addition to early diagnostics, other factors such as organization of the orthodontic care, cooperation of the children, risks involved if treatment is postponed, risk of relapse, and direct and indirect costs are important and should be considered along with the timing of treatment. The rationale of early treatment is based on the assumption that occlusal development can effectively be corrected by intervention in the early stages. The aim of the ongoing clinical study is to test this assumption and follow up the changes in the occlusion and the need of treatment as the children mature. CONCLUSIONS The present results, based on an analysis of a large unselected sample from the general population, indicate that signs of malocclusion are common fi ndings at the onset of the mixed dentition period. In particular, deviations towards a Class II molar or canine relation- ship, increased overjet and overbite, lack of adequate space in the dental arches, and crossbites are frequently seen in children at this age. In many cases, the deviation is severe enough to reliably indicate need of treatment at some point in the occlusal development, but, in others, where the changes are subtler, a de fi nitive prediction of future development might be either im- possible or beyond the knowledge presently available. Further longitudinal studies are necessary to establish the potential and limitations of a clinical approach relying on early orthodontic diagnostics and interven- tion. We thank the staff, the patients, and their parents at the health centers of Jalasja ̈ rvi, Kurikka, and Seina ̈ joki for their cooperation and assistance. We also thank Dr E. O. Bergersen for his help in the initial phase of the study. REFERENCES 1. Bishara SE, Justus R, Graber TM. Proceedings of the workshop discussions on early treatment. Am J Orthod Dentofacial Orthop 1998;113:5-6. 2. Graber TM. Foreword. Am J Orthod Dentofacial Orthop 1998; 113:1-4. 3. Dugoni SA. Comprehensive mixed dentition treatment. Am J Orthod Dentofacial Orthop 1998;113:75-84. 4. Hamilton DC. The emancipation of dentofacial orthopedics. Am J Orthod Dentofacial Orthop 1998;113:7-10. 5. Gianelly AA. Crowding: timing of treatment. Angle Orthod 1994;64:415-7. 6. Gianelly AA. One-phase versus two-phase treatment. Am J Orthod Dentofacial Orthop 1995;108:556-9. 7. Nelson G. Phase I treatment. Am J Orthod Dentofacial Orthop 1997;111:239-40. 8. Bowman SJ. One-stage versus two-stage treatment: are two really necessary? Am J Orthod Dentofacial Orthop 1998;113: 111-6. 9. Gafari J, Shofer FS, Jacobsson-Hunt U, Markowitz DL, Laster LL. Headgear versus function regulator in the early treatment of Class II, Division 1 malocclusion: a randomized clinical trial. Am J Orthod Dentofacial Orthop 1998;113:51-61. 10. Keeling SD, Wheeler TT, King GJ, Garvan CW, Cohen DA, Cabassa S, et al. Anteroposterior dental and skeletal changes after early Class II treatment with bionators and headgear. Am J Orthod Dentofacial Orthop 1998;113:40-50. 11. Tulloch JFC, Phillips C, Prof fi t WR. Bene fi t of early Class II treatment: progress report of a two-phase randomized clinical trial. Am J Orthod Dentofacial Orthop 1998;113:62-72. 12. Pulkkinen E, Pulli H. Oikomishoito Kajaanin terveyskeskuk- sessa. Suomen Hammasla ̈ a ̈ ka ̈ rilehti 1991;38:802-5. 13. Pietila ̈ T. Orthodontic care in Finnish health centers [disserta- tion]. Ann Univ Turkuensis 1998, Ser D:300. 14. Kangaspeska M, Keski-Nisula K, Varrela J. Ortopedisen niska- vedon ja purennanohjaimen yhteiska ̈ yto ̈ sta ̈ . Suomen Hammas- la ̈ a ̈ ka ̈ rilehti 2001;VIII(n.s.):742-7. 15. Moorrees CFS. The dentition of the growing child. Cambridge (Mass): Harvard University Press; 1959. 16. Bishara SE, Hoppens BJ, Jacobsen JR, Kohout FJ. Changes in the molar relationship between the deciduous and permanent dentitions: a longitudinal study. Am J Orthod Dentofacial Orthop 1988;93:19-28. 17. Dahlberg G. Statistical methods for medical and biological students. London: George Allen and Unwin Ltd; 1948. 18. Foster TD, Hamilton M. Occlusion in the primary dentition. Study of children at 2.5 to 3 years of life. Brit Dent J 1969;126:76-9. 19. Kirverskari P, Alanen P, Ja ̈ msa ̈ T. Functional state of the American Journal of Orthodontics and Dentofacial Orthopedics Volume 124, Number 6 Keski-Nisula et al 637

3. mm. Maximal opening was measured as the vertical distance between the incisal edges of the maxillary and mandibular right central incisors with an accuracy of 1 mm. When the right central incisors were missing, the left central incisors were used for all measurements. From the dental casts, crowding or spacing in the anterior segment was assessed qualitatively by regis- tering overlapping teeth or interdental spaces. In addi- tion, the terminal plane relationship and the sagittal relationship of the maxillary and mandibular canines were measured. The terminal plane relationship was measured between perpendicular projections, on the occlusal plane, from the distal surfaces of the maxillary and mandibular molars as suggested by Bishara et al. 16 A child was considered to have a fl ush terminal plane if the distance was less than 1 mm in either direction. If the difference was 1 mm or more, the child was classi fi ed as having a distal step or a mesial step, depending of the direction of the deviation. The sagittal relationship of the canines was measured between perpendicular projections, on the occlusal plane, from the tip of the maxillary deciduous canine and the contact point of the mandibular deciduous canine and fi rst molar. In case of wear of the tip of the canine, the midpoint of the facet was used as the reference point. Similarly, the midpoint between the mandibular canine and the fi rst molar was used if an interproximal space was present. The canine relationship was denoted as Class I if the tip of the maxillary canine deviated less than 1 mm from the ideal position in either direction. A deviation of 1 mm or more to the mesial or distal was classi fi ed as Class II or Class III, respectively. All assessments and measurements from the dental casts were performed by the fi rst author (K.K-N). All intermaxillary measurements were obtained from the casts with the mandible in centric relation. The mea- surements were taken with a digital caliper to the nearest 0.01 mm. Method error for the measurements, assessed by means of the standard error of a single determination 17 on repeated measurements of 30 ran - domly selected subjects, was 0.14 mm. In the statistical assessment, the chi-square test (lateral differences, sex differences of malocclusion traits) and the t test (sex differences in overbite and overjet) were used. Any P values smaller than .05 were interpreted as statistically signi fi cant. RESULTS Based on the combined values of the right and left sides, the frequencies of distal step, fl ush terminal plane, and mesial step were 33.1%, 47.8%, and 19.1%, respectively (Table I). Although in most children (69.5%) the terminal relationship was symmetrical, a considerable number (30.5%) indicated asymmetry. This asymmetry was, however, nondirectional; the right and left sides showed almost equal numbers of mesial, fl ush, and distal terminal planes. In 137 of the 145 asymmetrical subjects, a fl ush terminal plane was combined with either a distal step (61.4%) or a mesial step (32.4%). Only 8 children had a combination of a mesial step on one side and a distal step on the other. Altogether, 43.3% of the children had a distal step on at least 1 side. No statistical difference was found be- tween boys and girls in the frequency of distal step. The frequencies of Class I, Class II, and Class III canine relationships were 46.1%, 52.4%, and 1.5%, respectively, when pooling the right and left sides (Table II). The number of children with an asymmet- rical canine relationship (33.1%) was similar to that with an asymmetrical terminal plane (30.5%) but with a higher amount of directional asymmetry. The major- ity, 78.4%, showed a Class II relationship on the right side and only 21.6% on the left. The difference between the right and left sides was statistically signi fi cant ( P  .001). A Class I/Class II canine relationship was found in 93.2% of the children with asymmetry, a Class I/Class III combination was found in 5.0% and a Class II/Class III combination was found in 1.9%. The percentage of children with a Class II canine relation- ship on at least 1 side was 68.1%. More boys than girls had a unilateral or bilateral Class II canine relationship Table I. Terminal plane relationship; analysis is based on 476 casts where both sides were observable; for asymmetry, fi gures indicate combined frequencies of right and left sides Right side (N  476) Left side (N  476) Right and left sides combined (N  952) Symmetrical (N  331) Asymmetrical (N  145) Distal step (  1 mm) 156 (32.8%) 159 (33.4%) 315 (33.1%) 109 (32.9%) 97 (33.4%) Flush terminal plane (  1 mm) 235 (49.4%) 220 (46.2%) 455 (47.8%) 159 (48.0%) 137 (47.2%) Mesial step (  1 mm) 85 (17.9%) 97 (20.4%) 182 (19.1%) 63 (19.0%) 56 (19.3%) Total 476 (100%) 476 (100%) 952 (100%) 331 (100%) 290 (100%) Differences between right and left sides were statistically nonsigni fi cant. American Journal of Orthodontics and Dentofacial Orthopedics Volume 124, Number 6 Keski-Nisula et al 633

4. (173 vs 158), but the difference was of marginal signi fi cance only ( P  .05). The interrelation of terminal plane and canine relationship was analyzed on the right and left sides separately, and the combined frequencies are shown in Table III. A distal step was predominantly accompa- nied by a Class II relationship (88.3%) and a mesial step with a Class I canine relationship (85.6%). A fl ush terminal plane was associated almost equally with a Class I (54.3%) or a Class II (45.3%) canine relation- ship. With a very few exceptions, a Class II canine relationship was associated with either a distal step (56.3%) or a fl ush plane (41.2%). Subjects with a Class I canine relationship most frequently exhibited a fl ush plane (56.2%) or a mesial step (35.4%). In most children with a Class III canine relationship, that same side had a mesial step. The relationship of the incisors was recorded in 524 of the 534 children who took part in the fi rst clinical examination. The results showed that, with the jaws in centric relation, the maxillary and mandibular incisors were in contact in 28.2% of the children. The mandib- ular incisors were in contact with the palatal gingiva in 32.6% of the children. In 39.1% of the children, the bite was open, with no contact either between the maxillary and mandibular incisors or between the mandibular incisors and the palatal gingiva. The distributions of overjet and overbite measurements are shown in Fig- ures 1 and 2. Overjet ranged from  2 to 10 mm with a mean of 2.9 mm (SD 1.6). In 26.7% of the children, the overjet was 4 mm or more, and in 6.3% children it was 6 mm or more; negative overjet (anterior crossbite) was found in 1.0%. Overbite ranged from  5 (openbite) to 8 mm with a mean of 2.8 mm (SD 1.9). In 33.8% of the children, the overbite was 4 mm or more, and in 5.0% it was 6 mm or more, and an openbite was found in 4.6%; and 11.19% of the children had both overbite and overjet of 4 mm or more. No statistically signi fi cant Table II. Relationship of deciduous canines; analysis is based on 486 casts where both sides were observable; for asymmetry, fi gures indicate combined frequencies of right and left sides Right side (N  486) Left side (N  486) Right and left sides combined (N  972) Symmetrical (N  325) Asymmetrical (N  161) Class II (  1 mm) 298 (61.3%)* 211 (43.4%) 509 (52.4%) 178 (54.8%) 153 (47.5%) Class I (  1 mm) 182 (37.4%)* 266 (54.7%) 448 (46.1%) 145 (44.6%) 158 (49.1%) Class III (  1 mm) 6 (1.2%) 9 (1.9%) 15 (1.5%) 2 (0.6%) 11 (3.4%) Total 486 (100%) 486 (100%) 972 (100%) 325 (100%) 322 (100%) * P  .001 (difference between right and left sides). Table III. Interrelationship between terminal plane and canine relationship; right and left sides were analyzed separately, and combined frequencies are given (number of children  479; number of sides  958) Terminal plane Canine relationship Total Class II (  1 mm) Class I (  1 mm) Class III (  1 mm) Distal step (  1 mm) 280 36 0 316 Flush terminal plane (  1 mm) 205 252 1 458 Mesial step (  1 mm) 13 158 13 184 Total 498 446 14 958 Fig 1. Distribution of overjet (N  521). Fig 2. Distribution of overbite (N  521). American Journal of Orthodontics and Dentofacial Orthopedics December 2003 634 Keski-Nisula et al

5. difference was found between boys and girls in the frequency of excessive (  4 mm) overbite or overjet. Of 526 children, 126 (24.0%) had a gummy smile of 5 mm or more; 58% were girls, and 42% were boys, with no signi fi cant difference between the 2 groups. In an analysis of 486 casts of children with a mean age of 5.1 years, it was found that 11.6% had crowding in the maxillary anterior arch, and 38.9% had crowding in the mandibular arch. The percentages of children with closed anterior contacts were 41.2% in the max- illary arch and 32.5% in the mandibular arch. Of signi fi cance is the fi nding that only 47.1% of the children showed spacing in the maxillary arch and 28.6% in the mandibular arch. Although there were no sex differences in the maxillary arch, girls had signif- icantly more crowding in the mandible than boys ( P  .01). Only 8.0% of the subjects had simultaneous crowding in both arches. Data on crossbite were collected from 545 children from both the clinical examination and the assessment of the casts. A posterior crossbite was found in 7.5% of the children, unilaterally in 6.4% and bilaterally in 1.1%. A unilateral crossbite was on the right side in 20 and on the left side in 15 subjects. A scissors-bite was detected in 1.1% of the 545 children; 4 cases were on the right side, 1 was on the left, and both sides were involved in another case. An anterior crossbite was registered in 2.2% of the 545 children, and, in 1.7%, the deciduous incisors were in an edge-to-edge relationship. One child had a cross- bite in both the anterior and the left lateral segments. There was no statistically signi fi cant difference in the occurrence of crossbite or scissors-bite between the sexes. Simultaneous occurrence of the deviating occlusal characteristics was analyzed by cross-tabulation of their frequencies (Table IV). Children with distal steps also had a signi fi cantly higher frequency of deep bite and increased overjet. Similarly, those with a Class II canine relationship had more often a distal step and an increased overjet. Deep bite and increased overbite both showed a strong association with a Class II relationship (molar and canine) but occurred indepen- dently. Maxillary and mandibular crowding were seen in 8% of the same children, nearly twice the frequency expected by change alone, but showed no association with the other characteristics. In children with posterior crossbite, the frequencies of other deviating character- istics were signi fi cantly lower than in the whole sam- ple. The number of children with unilateral or bilateral distal step (  1 mm) and Class II canine relationship (  1 mm), deep bite (  4 mm), increased overjet (  4 mm), maxillary and mandibular crowding, posterior crossbite, anterior crossbite, and Class III relationship was 92.7%. If only bilateral cases of distal step and Class II canine relationship were included, the number of affected children dropped to 78.8%. By using a threshold value of 6 mm or more for deep bite and increased overjet, the number of children was further decreased to 67.7%. The mean maximal opening, measured in 532 children, was 40.3 mm (SD 3.9). Joint sounds, charac- terized as clickings, occurred in 5.2% of 533 children. DISCUSSION Both the methods of assessment and the de fi nitions of malocclusions vary in different studies, and their fi ndings should therefore be compared with caution. Allowing for the methodological differences, the present results do not seem to signi fi cantly differ from those reported earlier. In the British sample studied by Table IV. Interrelations of distal step, Class II canine relationship, overbite, overjet, upper and lower crowding, and posterior crossbite; table gives only frequencies that are signi fi cantly higher or lower than could be expected on basis of frequencies in whole sample Overall frequency Distal step  1mm (33%) Class II canine  1mm (52%) Overbite  4mm (34%) Overjet  4mm (27%) Crowding Posterior crossbite (8%) maxillary (12%) mandibular (39%) Distal step (  1 mm; N  206) 92%*** 43%** 41%*** 1%** Class II canine (  1 mm; N  331) 58%** 35%** 3%* Overbite (  4 mm; N  176) 52%*** 69%*** 0%*** Overjet (  4 mm; N  139) 62%*** 84%*** 1%** Maxillary crowding (N  56) 77%*** 69%*** Mandibular crowding (N  189) 69%*** 21%** Posterior crossbite (N  32) 9%** 0%*** 3%** 19%* * P  .05, ** P  .01, *** P  .001. American Journal of Orthodontics and Dentofacial Orthopedics Volume 124, Number 6 Keski-Nisula et al 635

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