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Dental arch dimensions in oligodontia patients
ORIGINAL ARTICLE
Dental arch dimensions in oligodontia patients Xianghhong Bu,a Khaled Khalaf,b and Ross S. Hobsonc Yanan, China, and Newcastle upon Tyne, United Kingdom Introducton: The aim of this study was to compare the dental arch sizes in a group of oligodontia patients with a group of age- and sex-matched untreated Class I control patients. Methods: Dental casts were measured of 50 oligodontia patients and 50 untreated Class I patients between 8 and 16 years old. For each subject, dental arch length and width parameters were measured in the maxillary and mandibular arches with digital calipers. The various dental arch parameters were compared between the 2 groups by using ANOVA. Results: The mean age of the subjects was 12.5 years. The average number of teeth missing in the oligodontia group was 11. The mean maxillary and mandibular arch lengths in the oligodontia group were reduced by 4.40 and 2.80 mm, respectively, when compared with the control group. The intercanine widths were reduced in the oligodontia group compared with the control group by 2.82 mm in the maxillary arch and 2.70 mm in the mandibular arch. The intermolar widths of the maxillary and mandibular arches in the oligodontia group were reduced by 3.40 and 1.80 mm, respectively, compared with the control group. These differences were statistically significant (P ⬍0.01). Conclusions: The findings indicate that arch length and width are reduced in oligodontia patients; this should be taken into account when planning orthodontic treatment. (Am J Orthod Dentofacial Orthop 2008;134:768-72)
H
ypodontia is the developmental absence of at least 1 tooth; when 6 or more teeth are congenitally absent, it is called oligodontia.1,2 The prevalence of hypodontia has been estimated between 2.3% and 10.1% in the permanent dentition.3-5 The prevalence of severe hypodontia is less than that of moderate hypodontia, which in turn is less than that of mild hypodontia. Sarnas and Rune6 estimated the prevalence of advanced hypodontia (congenital absence of 4 or more permanent teeth) at 0.25% in a Swedish population. The prevalence was reported to be as low as 0.084% for 6 or more congenitally missing teeth (oligodontia) in a Norwegian population.2 Patients seek orthodontic care because of an unesthetic and socially unacceptable malocclusion when teeth are missing. The absence of teeth can affect social interaction and masticatory function.7 Comprehensive management of hypodontia is best undertaken in multidisciplinary clinics, and these have been established in some centers for diagnosis, treatment planning, and coordination of treatment.8-14 a Lecturer in orthodontics, Department of Orthodontics, Yanan Municipal Hospital, Yanan, China. b Clinical lecturer and FTTA in orthodontics, School of Dental Sciences, Newcastle upon Tyne, United Kingdom. c Senior lecturer and honorary consultant in orthodontics, School of Dental Sciences, Newcastle upon Tyne, United Kingdom. Reprint requests to: Ross S. Hobson, School of Dental Sciences, Framlington Place, Newcastle upon Tyne NE2 4BW, United Kingdom; e-mail, R.S.Hobson@ ncl.ac.uk. Submitted, September 2005; revised and accepted, March 2007. 0889-5406/$34.00 Copyright © 2008 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2007.03.029
768
The etiology of oligodontia is not yet known. However, various genetic and environmental factors have been implicated in the etiology of congenitally missing teeth. Brook15 suggested a multi-factorial model with an underlying scale of continuous variation related to tooth number and size. Environmental influences such as trauma, infections (eg, rubella), ionizing radiation, drugs, and hormonal influences have been suggested as possible insults that might have impinged on tooth formation during the embryologic stages of dental development.15,16 Various homeobox genes— eg, Msx-1, Msx-2, Dlx-1, Dlx-2, Barx-1, Parx-9, and Pitx-2— have been found to be expressed in various regions of future tooth development in mice.17 Further studies have shown that oligodontia is most likely a genetic trait, and various gene defects have been proposed as the cause.18-25 Although several studies have investigated dental arch dimensions in hypodontia patients, there are no similar reports in oligodontia patients.26-29 Our aim in this study was to compare dental arch lengths and widths in a group of oligodontia patients with those in an age- and sex-matched control group. MATERIAL AND METHODS
Fifty oligodontia patients were selected randomly from the database of the hypodontia clinic at Newcastle upon Tyne in the United Kingdom. This database contain the records of more than 400 patients who have attended the multidisciplinary hypodontia clinic. The patients’ records were obtained and their radiographs examined to confirm the absence of teeth.
Bu, Khalaf, and Hobson 769
American Journal of Orthodontics and Dentofacial Orthopedics Volume 134, Number 6
A B
3
40
D
1 4
4 C
Upper
60
E 2
Frequency
3
80
20 0
1
2
3
4
5
6
7
20 40 60
Lower
80
Fig 1. Dimensions recorded: 1, intercanine width (cusp tip to cusp tip); 2, intermolar width (mesiobuccal cusp tip to mesiobuccal cusp tip); 3, anterior right and left lengths (A-B and A-D); 4, posterior right and left lengths (B-C and D-E); 5, total arch length ⫽ AB ⫹ BC ⫹ AD ⫹ DE.
The study group consisted of 25 girls and 25 boys with a mean age of 12.5 years (SD, 2.1 years; range, 8-16 years). Details recorded were age, sex, site and number of missing teeth (excluding third molars), family history, and any known syndrome. To allow comparison with other dental arch dimension studies, patients had to have the permanent canines and the first molar in at least the maxilla or the mandible. If the central incisors were absent, the frenal attachment was used as the midpoint of the dental arch. A control group of 50 subjects, 25 girls and 25 boys, matched by age and sex to the study group, were identified from Newcastle Dental Hospital records. Each subject had a clinically acceptable occlusion: Class I molar and canine relationship, anterior crowding of less than 2 mm at the eruption of the second permanent molars, and Class I skeletal pattern. No subject had congenitally missing teeth or previous extractions, or had undergone orthodontic treatment. The study models were collected for both groups, and the dimensions of the maxillary and mandibular dental arches were measured by an investigator (X.B.) using a digital Vernier caliper to the nearest 0.1 mm. Figure 1 shows the dimensions measured; they are the same as those described by Bishara et al,30 including the following. 1. Arch length measurements of the right and left sides: anterior arch length, the distance between the contact point of the central incisors and the contact point between the canine and the first premolar; posterior arch length, the distance between the contact point of
Fig 2. Frequency of missing teeth by tooth type: 1, central incisor; 2, lateral incisor; 3, canine; 4, first premolar; 5, second premolar; 6, first molar; 7, second molar.
the canine and the first premolar and the contact point between the second premolar and the first permanent molar; and total arch length, the sum of the anterior and posterior arch lengths. 2. Arch width measurements: intercanine width, the distance between the cusp tips of the canines; and intermolar width, the distance between the mesiobuccal cusp tips of the first permanent molars. Statistical analysis
The dental arch parameters were analyzed by using 1-way analysis of variance (ANOVA) and post-hoc Tukey tests. The magnitude of the error of measurement was calculated from double recordings of 20 randomly selected sets of dental casts from both groups not less than 4 weeks apart. A t test found no significant difference between the 2 sets of measurements (P ⬎0.05). RESULTS
The subjects’ mean age was 12.5 years. Figure 2 shows the distribution of the missing teeth. The average number of missing teeth was 11 (range, 6-20). Although any permanent tooth can be congenitally absent, the second premolars were most commonly missing. Dental arch dimensions for the oligodontia and control groups are given in the Table. The mean maxillary and mandibular arch lengths were reduced by 4.40 and 2.80 mm, respectively, in the oligodontia group compared with the control group. The intercanine widths in the oligodontia group were reduced by 2.82 and 2.70 mm in the maxillary and mandibular arches, respectively. The intermolar widths in the olig-
770 Bu, Khalaf, and Hobson
Table.
American Journal of Orthodontics and Dentofacial Orthopedics December 2008
Mean arch dimensions for the study and control groups (SD in parentheses) Maxilla
Group Class I Oligodontia
Mandible
Intercanine width (mm)
Intermolar width (mm)
Arch length (mm)
Intercanine width (mm)
Intermolar width (mm)
Arch length (mm)
31.4 (2.8) 28.6 (3.5)
47.9 (2.9) 44.5 (3.6)
71.2 (5.8) 66.8 (6.4)
24.2 (2.5) 21.5 (3.1)
42.4 (3.0) 40.6 (3.1)
63.1 (4.9) 60.3 (5.4)
odontia group were reduced by 3.40 and 1.80 mm in the maxillary and mandibular arches, respectively. These differences were statistically significant (P ⬍0.01). DISCUSSION
The study sample was taken from the database of the hypodontia clinic at Newcastle upon Tyne. This clinic has a multidisciplinary clinical and research team that takes patient referrals from northern England. These patients tend to have the greatest treatment need and complexity and do not represent the general population. The study compared the dental arch dimensions in a group of oligodontia patients with an age- and sex-matched control group. In all arch length studies, some approximations are necessary because the dental arch is a complex curve and does not lend itself readily to straight-line measurements. In this study, the total dental arch length was measured as a series of shorter straight-line measurements as described by Bishara et al.30 Arch widths were measured between the mesiobuccal cusp tips of the molars and between the cusp tips of the canines. An inclusion criterion in the study group was the presence of the canines and the first molars in at least 1 dental arch. This was to enable comparisons with other studies of arch dimensions in patients with complete dentitions and studies of hypodontia (⬍6 congenitally missing teeth). However, this criterion excluded some potentially severe cases of oligodontia. We found that all arch dimensions, both length and width, were statistically significantly reduced in the oligodontia patients compared with the controls. The arch lengths were 4.40 mm shorter in the maxilla and 2.80 mm shorter in the mandible. The intermolar arch widths were reduced by 3.40 mm in the maxilla and 1.80 mm in the mandible. This suggests a greater tendency toward posterior crossbite in the oligodontia patients, although this was not found when the occlusion was examined. Such a small difference in the oligodontia patients between the maxillary and mandibular arch widths compared with the controls is probably not sufficient to cause a clinically evident crossbite. Furthermore, the differential mesial movement of the molars in the opposing quadrants of the
dental arches that might have resulted in the differential reduction in arch length measurements in the oligodontia group might have altered the transverse and anteroposterior relationships of the molars. Moreover, the mandibular molars roll lingually as they move mesially to a greater extent than their opposing molars. Intercanine width reductions were similar in both dental arches. This suggests the importance of the canine in maintaining anterior dentoalveolar width. Le Bot and Salmon28 reported decreased arch widths and lengths in a large French male group with missing and small maxillary lateral incisors. However, the arch dimensions they used were slightly different from those in this study: arch length was extended to the distal surfaces of the second molars, interpremolar width was measured instead of intercanine width, and an extra intersecond molar width was also measured. Also, Le Bot and Salmon measured arch dimensions in the maxilla only. More importantly, the comparison with our study might not be valid due to differences in the inclusion criteria of the study and control groups. Other studies found few differences in dental arch dimensions between patients with congenitally missing teeth and the controls.26,27,29 However, no study investigated arch dimensions in oligodontia patients. Thus, it could be postulated that patients with oligodontia have greater reductions in their arch dimensions than those with hypodontia. The smaller dental arch dimensions in the oligodontia patients in our study when compared with an ageand sex-matched control group might be attributed to a combination of missing teeth and microdontia of the remaining teeth.31,32 The presence of teeth might stimulate the formation of the housing dentoalveolar bone; thus, the severe absence of teeth might render the dentoalveolar bone deficient, and this in turn results in small dental arches. Some evidence supporting the relationship between absence of teeth and small dental arches has come from studies of dental arches in patients with cleft lip and palate.33-36 We did not examine tooth form, although clinical observations support the findings of previous studies of the association between oligodontia and microdontia. A correla-
American Journal of Orthodontics and Dentofacial Orthopedics Volume 134, Number 6
tion study between the 2 warrants further investigation in this complex area. Changes in the size and shape of the dental arches as well as the dental anomalies associated with oligodontia could have considerable implications in orthodontic diagnosis and treatment planning, affecting the space available, dental esthetics, and the stability of the dentition. Occlusal features such as dental alignment, buccal interdigitation, normal overjet and overbite, and centerline coincidence require a subtle harmony among the teeth, dental arch dimensions, and the jaws. CONCLUSIONS
This study was the first to examine the dental arch dimensions in a group of oligodontia patients. From our findings, it can be concluded that arch length and width were reduced in oligodontia patients compared with a normal group with the full complement of teeth. Oligodontia patients also seem to differ from hypodontia patients in the impact on dental arch dimension measurements, with the former having smaller dimensions than the latter.
REFERENCES 1. Goodman JR, Jones SP, Hobkirk JA, King PA. Hypodontia: 1. Clinical features and the management of mild to moderate hypodontia. Dent Update 1994;21:381-4. 2. Nordgarden H, Jensen JL, Storhaug K. Reported prevalence of congenitally missing teeth in two Norwegian counties. Community Dent Health 2002;19:258-61. 3. Werther R, Rothenberg F. Anodontia: a review of its etiology with presentation of a case. Am J Orthod 1939;25:61-81. 4. Hunstadbraten K. Hypodontia in the permanent dentition. J Dent Child 1973;40:115-7. 5. Brook AH. Dental anomalies of number, form and size: their prevalence in British schoolchildren. J Int Assoc Dent Child 1974;5:37-53. 6. Sarnas KV, Rune B. The facial profile in advanced hypodontia: a mixed longitudinal study of 141 children. Eur J Orthod 1983; 5:133-43. 7. Slater DR. The impact of hypodontia on affected children and adolescents in the north east of England [dissertation]. Newcastle upon Tyne, United Kingdom: University of Newcastle upon Tyne; 2003. 8. Hobkirk JA, Brook AH. The management of patients with severe hypodontia. J Oral Rehabil 1980;7:289-98. 9. Hobkirk JA, Goodman JR, Jones SP. Presenting complaints and findings in a group of patients attending a hypodontia clinic. Br Dent J 1994;77:337-9. 10. Nunn JH, Carter NE, Gillgrass TJ, Hobson RS, Jepson NJ, Meechan JG, et al. The interdisciplinary management of hypodontia: background and role of paediatric dentistry. Br Dent J 2003;194:245-51. 11. Jepson NJ, Nohl FS, Carter NE, Gillgrass TJ, Meechan JG, Hobson RS, et al. The interdisciplinary management of hypodontia: restorative dentistry. Br Dent J 2003;194:299-304.
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12. Carter NE, Gillgrass TJ, Hobson RS, Jepson N, Eechan JG, Nohl FS, et al. The interdisciplinary management of hypodontia: orthodontics. Br Dent J 2003;194:361-6. 13. Meechan JG, Carter NE, Gillgrass TJ, Hobson RS, Jepson NJ, Nohl FS, et al. Interdisciplinary management of hypodontia: oral surgery. Br Dent J 2003;194:423-7. 14. Hobson RS, Carter NE, Gillgrass TJ, Jepson NJ, Meechan JG, Nohl F, et al. The interdisciplinary management of hypodontia: the relationship between an interdisciplinary team and the general dental practitioner. Br Dent J 2003;194:479-82. 15. Brook AH. A unifying aetiological explanation for anomalies of human tooth number and size. Arch Oral Biol 1984;29:373-8. 16. Arya BS, Savara BS. Familial partial anodontia: report of a case. ASDC J Dent Child 1974;41:47-54. 17. Cobourne MT. The genetic control of early odontogenesis. Br J Orthod 1999;26:21-8. 18. Lammi L, Halonen K, Pirinen S, Thesleff I, Arte S, Nieminen PA. A missense mutation in PAX9 in a family with distinct phenotype of oligodontia. Eur J Hum Genet 2003;11:866-71. 19. Nieminen P, Kotilainen J, Aalto Y, Knuutila S, Pirinen S, Thesleff I. MSX1 gene is deleted in Wolf-Hirschhorn syndrome patients with oligodontia. J Dent Res 2003;82:1013-7. 20. Jumlongras D, Lin JY, Chapra A, Seidman CE, Seidman JG, Maas RL, et al. A novel missense mutation in the paired domain of PAX9 causes non-syndromic oligodontia. Hum Genet 2004; 114:242-9. 21. Klein ML, Nieminen P, Lammi L, Niebuhr E, Kreiborg S. Novel mutation of the initiation codon of PAX9 causes oligodontia. J Dent Res 2005;84:43-7. 22. Kist R, Watson M, Wang X, Cairns P, Miles C, Reid DJ, et al. Reduction of Pax9 gene dosage in an allelic series of mouse mutants causes hypodontia and oligodontia. Hum Mol Genet 2005;14:3605-17. 23. Kim JW, Simmer JP, Lin BP, Hu JC. Novel MSX1 frameshift causes autosomal-dominant oligodontia. J Dent Res 2006;85: 267-71. 24. Gerits A, Nieminen P, De Muynck S, Carels C. Exclusion of coding region mutations in MSX1, PAX9 and AXIN2 in eight patients with severe oligodontia phenotype. Orthod Craniofac Res 2006;9:129-36. 25. Chishti MS, Muhammad D, Haider M, Ahmad W. A novel missense mutation in MSX1 underlies autosomal recessive oligodontia with associated dental anomalies in Pakistani families. J Hum Genet 2006;51:872-8. 26. Bailit HL, Thomson LA, Niswander JD. Dental eruption and hypodontia. J Dent Res 1968;47:669. 27. Wisth PJ, Thunold K, Boe OE. Frequency of hypodontia in relation to tooth size and dental arch width. Acta Odontol Scand 1974;32:201-6. 28. Le Bot P, Salmon D. Congenital defects of the upper lateral incisors (ULI): condition and measurements of the other teeth, measurements of the superior arch, head and face. Am J Phys Anthropol 1977;46:231-43. 29. Woodworth DA, Sinclair PM, Alexander RG. Bilateral congenital absence of maxillary lateral incisors: a craniofacial and dental cast analysis. Am J Orthod 1985;87:280-93. 30. Bishara SE, Bayati P, Jakobsen JR. Longitudinal comparisons of dental arch changes in normal and untreated Class II, Division 1 subjects and their clinical implications. Am J Orthod Dentofacial Orthop 1996;110:483-9. 31. Schalk-van der weide Y, Steen WHA, Bosman F. Distribution of missing teeth and tooth morphology in patients with oligodontia. J Dent Child 1992;59:133-40.
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32. McKeown HF, Robinson DL, Elcock C, al-Sharood M, Brook AH. Tooth dimensions in hypodontia patients, their unaffected relatives and a control group measured by a new image analysis system. Eur J Orthod 2002;24:131-41. 33. McCance AM, Roberts-Harry D, Sherriff M, Mars M, Houston WJ. A study model analysis of adult unoperated Sri Lankans with unilateral cleft lip and palate. Cleft Palate J 1990;27:146-54. 34. Laitinen SH. Sizes of dental arches in children with the Pierre Robin syndrome and isolated cleft palate aged from 0.2 to six
American Journal of Orthodontics and Dentofacial Orthopedics December 2008
years. Scand J Plast Reconstr Surg Hand Surg 1993;27: 285-90. 35. Heidbuchel KL, Kuijpers-Jagtman AM. Maxillary and mandibular dental-arch dimensions and occlusion in bilateral cleft lip and palate patients from 3 to 17 years of age. Cleft Palate Craniofac J 1997;34:21-6. 36. Laitinen SH, Ranta R. Sizes of dental arches in young adult patients with Pierre Robin sequence and isolated cleft palate. Acta Odontol Scand 1998;56:85-9.
Dental arch dimensions in oligodontia patients Xianghhong Bu,a Khaled Khalaf,b and Ross S. Hobsonc Yanan, China, and Newcastle upon Tyne, United Kingdom Introducton: The aim of this study was to compare the dental arch sizes in a group of oligodontia patients with a group of age- and sex-matched untreated Class I control patients. Methods: Dental casts were measured of 50 oligodontia patients and 50 untreated Class I patients between 8 and 16 years old. For each subject, dental arch length and width parameters were measured in the maxillary and mandibular arches with digital calipers. The various dental arch parameters were compared between the 2 groups by using ANOVA. Results: The mean age of the subjects was 12.5 years. The average number of teeth missing in the oligodontia group was 11. The mean maxillary and mandibular arch lengths in the oligodontia group were reduced by 4.40 and 2.80 mm, respectively, when compared with the control group. The intercanine widths were reduced in the oligodontia group compared with the control group by 2.82 mm in the maxillary arch and 2.70 mm in the mandibular arch. The intermolar widths of the maxillary and mandibular arches in the oligodontia group were reduced by 3.40 and 1.80 mm, respectively, compared with the control group. These differences were statistically significant (P ⬍0.01). Conclusions: The findings indicate that arch length and width are reduced in oligodontia patients; this should be taken into account when planning orthodontic treatment. (Am J Orthod Dentofacial Orthop 2008;134:768-72)
H
ypodontia is the developmental absence of at least 1 tooth; when 6 or more teeth are congenitally absent, it is called oligodontia.1,2 The prevalence of hypodontia has been estimated between 2.3% and 10.1% in the permanent dentition.3-5 The prevalence of severe hypodontia is less than that of moderate hypodontia, which in turn is less than that of mild hypodontia. Sarnas and Rune6 estimated the prevalence of advanced hypodontia (congenital absence of 4 or more permanent teeth) at 0.25% in a Swedish population. The prevalence was reported to be as low as 0.084% for 6 or more congenitally missing teeth (oligodontia) in a Norwegian population.2 Patients seek orthodontic care because of an unesthetic and socially unacceptable malocclusion when teeth are missing. The absence of teeth can affect social interaction and masticatory function.7 Comprehensive management of hypodontia is best undertaken in multidisciplinary clinics, and these have been established in some centers for diagnosis, treatment planning, and coordination of treatment.8-14 a Lecturer in orthodontics, Department of Orthodontics, Yanan Municipal Hospital, Yanan, China. b Clinical lecturer and FTTA in orthodontics, School of Dental Sciences, Newcastle upon Tyne, United Kingdom. c Senior lecturer and honorary consultant in orthodontics, School of Dental Sciences, Newcastle upon Tyne, United Kingdom. Reprint requests to: Ross S. Hobson, School of Dental Sciences, Framlington Place, Newcastle upon Tyne NE2 4BW, United Kingdom; e-mail, R.S.Hobson@ ncl.ac.uk. Submitted, September 2005; revised and accepted, March 2007. 0889-5406/$34.00 Copyright © 2008 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2007.03.029
768
The etiology of oligodontia is not yet known. However, various genetic and environmental factors have been implicated in the etiology of congenitally missing teeth. Brook15 suggested a multi-factorial model with an underlying scale of continuous variation related to tooth number and size. Environmental influences such as trauma, infections (eg, rubella), ionizing radiation, drugs, and hormonal influences have been suggested as possible insults that might have impinged on tooth formation during the embryologic stages of dental development.15,16 Various homeobox genes— eg, Msx-1, Msx-2, Dlx-1, Dlx-2, Barx-1, Parx-9, and Pitx-2— have been found to be expressed in various regions of future tooth development in mice.17 Further studies have shown that oligodontia is most likely a genetic trait, and various gene defects have been proposed as the cause.18-25 Although several studies have investigated dental arch dimensions in hypodontia patients, there are no similar reports in oligodontia patients.26-29 Our aim in this study was to compare dental arch lengths and widths in a group of oligodontia patients with those in an age- and sex-matched control group. MATERIAL AND METHODS
Fifty oligodontia patients were selected randomly from the database of the hypodontia clinic at Newcastle upon Tyne in the United Kingdom. This database contain the records of more than 400 patients who have attended the multidisciplinary hypodontia clinic. The patients’ records were obtained and their radiographs examined to confirm the absence of teeth.
Bu, Khalaf, and Hobson 769
American Journal of Orthodontics and Dentofacial Orthopedics Volume 134, Number 6
A B
3
40
D
1 4
4 C
Upper
60
E 2
Frequency
3
80
20 0
1
2
3
4
5
6
7
20 40 60
Lower
80
Fig 1. Dimensions recorded: 1, intercanine width (cusp tip to cusp tip); 2, intermolar width (mesiobuccal cusp tip to mesiobuccal cusp tip); 3, anterior right and left lengths (A-B and A-D); 4, posterior right and left lengths (B-C and D-E); 5, total arch length ⫽ AB ⫹ BC ⫹ AD ⫹ DE.
The study group consisted of 25 girls and 25 boys with a mean age of 12.5 years (SD, 2.1 years; range, 8-16 years). Details recorded were age, sex, site and number of missing teeth (excluding third molars), family history, and any known syndrome. To allow comparison with other dental arch dimension studies, patients had to have the permanent canines and the first molar in at least the maxilla or the mandible. If the central incisors were absent, the frenal attachment was used as the midpoint of the dental arch. A control group of 50 subjects, 25 girls and 25 boys, matched by age and sex to the study group, were identified from Newcastle Dental Hospital records. Each subject had a clinically acceptable occlusion: Class I molar and canine relationship, anterior crowding of less than 2 mm at the eruption of the second permanent molars, and Class I skeletal pattern. No subject had congenitally missing teeth or previous extractions, or had undergone orthodontic treatment. The study models were collected for both groups, and the dimensions of the maxillary and mandibular dental arches were measured by an investigator (X.B.) using a digital Vernier caliper to the nearest 0.1 mm. Figure 1 shows the dimensions measured; they are the same as those described by Bishara et al,30 including the following. 1. Arch length measurements of the right and left sides: anterior arch length, the distance between the contact point of the central incisors and the contact point between the canine and the first premolar; posterior arch length, the distance between the contact point of
Fig 2. Frequency of missing teeth by tooth type: 1, central incisor; 2, lateral incisor; 3, canine; 4, first premolar; 5, second premolar; 6, first molar; 7, second molar.
the canine and the first premolar and the contact point between the second premolar and the first permanent molar; and total arch length, the sum of the anterior and posterior arch lengths. 2. Arch width measurements: intercanine width, the distance between the cusp tips of the canines; and intermolar width, the distance between the mesiobuccal cusp tips of the first permanent molars. Statistical analysis
The dental arch parameters were analyzed by using 1-way analysis of variance (ANOVA) and post-hoc Tukey tests. The magnitude of the error of measurement was calculated from double recordings of 20 randomly selected sets of dental casts from both groups not less than 4 weeks apart. A t test found no significant difference between the 2 sets of measurements (P ⬎0.05). RESULTS
The subjects’ mean age was 12.5 years. Figure 2 shows the distribution of the missing teeth. The average number of missing teeth was 11 (range, 6-20). Although any permanent tooth can be congenitally absent, the second premolars were most commonly missing. Dental arch dimensions for the oligodontia and control groups are given in the Table. The mean maxillary and mandibular arch lengths were reduced by 4.40 and 2.80 mm, respectively, in the oligodontia group compared with the control group. The intercanine widths in the oligodontia group were reduced by 2.82 and 2.70 mm in the maxillary and mandibular arches, respectively. The intermolar widths in the olig-
770 Bu, Khalaf, and Hobson
Table.
American Journal of Orthodontics and Dentofacial Orthopedics December 2008
Mean arch dimensions for the study and control groups (SD in parentheses) Maxilla
Group Class I Oligodontia
Mandible
Intercanine width (mm)
Intermolar width (mm)
Arch length (mm)
Intercanine width (mm)
Intermolar width (mm)
Arch length (mm)
31.4 (2.8) 28.6 (3.5)
47.9 (2.9) 44.5 (3.6)
71.2 (5.8) 66.8 (6.4)
24.2 (2.5) 21.5 (3.1)
42.4 (3.0) 40.6 (3.1)
63.1 (4.9) 60.3 (5.4)
odontia group were reduced by 3.40 and 1.80 mm in the maxillary and mandibular arches, respectively. These differences were statistically significant (P ⬍0.01). DISCUSSION
The study sample was taken from the database of the hypodontia clinic at Newcastle upon Tyne. This clinic has a multidisciplinary clinical and research team that takes patient referrals from northern England. These patients tend to have the greatest treatment need and complexity and do not represent the general population. The study compared the dental arch dimensions in a group of oligodontia patients with an age- and sex-matched control group. In all arch length studies, some approximations are necessary because the dental arch is a complex curve and does not lend itself readily to straight-line measurements. In this study, the total dental arch length was measured as a series of shorter straight-line measurements as described by Bishara et al.30 Arch widths were measured between the mesiobuccal cusp tips of the molars and between the cusp tips of the canines. An inclusion criterion in the study group was the presence of the canines and the first molars in at least 1 dental arch. This was to enable comparisons with other studies of arch dimensions in patients with complete dentitions and studies of hypodontia (⬍6 congenitally missing teeth). However, this criterion excluded some potentially severe cases of oligodontia. We found that all arch dimensions, both length and width, were statistically significantly reduced in the oligodontia patients compared with the controls. The arch lengths were 4.40 mm shorter in the maxilla and 2.80 mm shorter in the mandible. The intermolar arch widths were reduced by 3.40 mm in the maxilla and 1.80 mm in the mandible. This suggests a greater tendency toward posterior crossbite in the oligodontia patients, although this was not found when the occlusion was examined. Such a small difference in the oligodontia patients between the maxillary and mandibular arch widths compared with the controls is probably not sufficient to cause a clinically evident crossbite. Furthermore, the differential mesial movement of the molars in the opposing quadrants of the
dental arches that might have resulted in the differential reduction in arch length measurements in the oligodontia group might have altered the transverse and anteroposterior relationships of the molars. Moreover, the mandibular molars roll lingually as they move mesially to a greater extent than their opposing molars. Intercanine width reductions were similar in both dental arches. This suggests the importance of the canine in maintaining anterior dentoalveolar width. Le Bot and Salmon28 reported decreased arch widths and lengths in a large French male group with missing and small maxillary lateral incisors. However, the arch dimensions they used were slightly different from those in this study: arch length was extended to the distal surfaces of the second molars, interpremolar width was measured instead of intercanine width, and an extra intersecond molar width was also measured. Also, Le Bot and Salmon measured arch dimensions in the maxilla only. More importantly, the comparison with our study might not be valid due to differences in the inclusion criteria of the study and control groups. Other studies found few differences in dental arch dimensions between patients with congenitally missing teeth and the controls.26,27,29 However, no study investigated arch dimensions in oligodontia patients. Thus, it could be postulated that patients with oligodontia have greater reductions in their arch dimensions than those with hypodontia. The smaller dental arch dimensions in the oligodontia patients in our study when compared with an ageand sex-matched control group might be attributed to a combination of missing teeth and microdontia of the remaining teeth.31,32 The presence of teeth might stimulate the formation of the housing dentoalveolar bone; thus, the severe absence of teeth might render the dentoalveolar bone deficient, and this in turn results in small dental arches. Some evidence supporting the relationship between absence of teeth and small dental arches has come from studies of dental arches in patients with cleft lip and palate.33-36 We did not examine tooth form, although clinical observations support the findings of previous studies of the association between oligodontia and microdontia. A correla-
American Journal of Orthodontics and Dentofacial Orthopedics Volume 134, Number 6
tion study between the 2 warrants further investigation in this complex area. Changes in the size and shape of the dental arches as well as the dental anomalies associated with oligodontia could have considerable implications in orthodontic diagnosis and treatment planning, affecting the space available, dental esthetics, and the stability of the dentition. Occlusal features such as dental alignment, buccal interdigitation, normal overjet and overbite, and centerline coincidence require a subtle harmony among the teeth, dental arch dimensions, and the jaws. CONCLUSIONS
This study was the first to examine the dental arch dimensions in a group of oligodontia patients. From our findings, it can be concluded that arch length and width were reduced in oligodontia patients compared with a normal group with the full complement of teeth. Oligodontia patients also seem to differ from hypodontia patients in the impact on dental arch dimension measurements, with the former having smaller dimensions than the latter.
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