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Scientific Section |
Department of Child Dental Health, Newcastle Dental School, Framlington Place, Newcastle upon Tyne NE2 4BW, UK
R. S. Hobson.
Abstract
The objective of this investigation was to examine the dentofacial features of a group of patients with hypodontia, in particular assessing whether cephalometric analysis confirmed the clinical assumption of a reduced lower face height, and to determine the relationship of these facial features with different numbers of missing teeth. It took the form of a cephalometric study, undertaken in a dedicated Dental Hospital clinic for patients with hypodontia. The study group comprised 59 patients seen on the Hypodontia Clinic: 32 females, 27 males, mean age 13•1 ± 3•1 years (range 6–23 years). The average number of missing teeth was 7 (SD 5), ranging from 1 to 21. The mean SNA, SNB, and MMA angles were within normal limits, but there was a statistically significant reduction in the MMA when more than one tooth type was missing (P = 0•007) and the ANB angle decreased as the number of missing tooth types increased (P = 0•034). The mean values for the whole sample were within the normal range and did not demonstrate any feature specific to the group, but patients with more severe hypodontia showed tendencies to a Class III skeletal relationship and a reduced maxillary-mandibular planes angle.
Key words: Hypodontia, Cephalometric analysis.
Introduction
Hypodontia is the developmental absence of one or more teeth, excluding the third molars (Goodman et al., 1994
). The prevalence in the general population is between 3•5 and 6•5 per cent (Brook, 1974), whilst a survey of 6000 orthodontic patients gave a prevalence of 4•3 per cent, with the lower second premolar followed by the upper lateral incisor being the most frequently missing teeth (Rose, 1966). The absence of one or two teeth is relatively common, but severe hypodontia (six or more missing teeth) is rarer and may be associated with a syndrome such as ectodermal dysplasia (Hobkirk and Brook, 1980).
Previous cephalometric studies of these patients have shown a reduced lower face height and increased overbite (Woodworth et al., 1985; Dermaut et al., 1986), together with a number of other dentofacial features, some agreeing and some contradictory. Whilst Woodworth et al. (1985) found a reduced lower face height, Roald et al. (1982) found that the lower face height was normal. Direct comparisons between studies is complicated by the varying severity of hypodontia of the sample groups, in addition to the cephalometric analysis used (Sarnas and Rune, 1983; Woodworth et al., 1985;Yuksel and Ucem, 1997). A recent study (Yuksel and Ucem, 1997) subdivided their group of patients according to the location of the absent tooth and investigated the effect of the site of location of hypodontia on dentofacial features.
Comprehensive management of hypodontia is best undertaken in interdisciplinary clinics, and these have been established in a number of centres for diagnosis, treatment planning and co-ordination of treatment (Hobkirk et al., 1994). A dedicated clinic for patients with hypodontia has run for 5 years at Newcastle Dental Hospital, with over 150 new patients seen. The most significant presenting complaints were poor appearance and lack of function. On clinical examination, in addition to the expected reduction in tooth number and variations in tooth morphology, there was a clinical perception that patients had a reduced lower face height and increased overbite.
The objectives of the present study were thus to examine the dentofacial features of a group of patients with hypodontia, in particular whether cephalometric analysis confirmed the clinical perception of reduced lower face height and to determine the relationship of these facial features with different numbers of missing teeth.
Material and Methods
Patient Selection
Fifty-nine out of 150 patients seen on the Hypodontia clinic were included in the study, selection being based on the presence of a lateral cephalometric radiograph. The group consisted of 32 females and 27 males with a mean age of 13•1 ± 3•1years (range 6–23 years). Clinical details recorded from the Hypodontia database were age, sex, site, and number of missing teeth (excluding third molars), family history, and any known syndrome.
Cephalometric Analysis
All radiographs were digitized by one operator using GELA, a geometric digitizing program (Consultant Orthodontists Group, British Orthodontic Society). The landmarks used in this study are shown in Figure 1.
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The malocclusions were classified according to the British Standards Institute classification for incisors (BS4492, 1969). The skeletal pattern was recorded from the cephalometric radiographs and the Eastman standard values (Mills, 1983) were used as the norm for comparison. Eleven of the 59 radiographs were re-digitized and re-analysed 4 weeks after the first digitization to estimate the repeatability of the measurement technique. The mean differences between digitizations varied between measurements made. Analysis of the difference between the two assessments showed an acceptable degree of accuracy. The estimate between measurement SD for SNA was 1•0 degree, for SNB was 0•6 degrees, for MMA was 0•9 degrees, for LFH was 0•3 mm, for TFH was 0•6 mm, for FP was 0, for OJ was 0•3 mm, for OB was 0•3 mm, for UI–MAX was 1•1 degrees, for LI–MAND was 1•0 degrees, and for LI–APo was 0•5 mm.
In order to examine the effect of the severity of hypodontia on dentofacial features, the group was subdivided according to the number of missing tooth types (incisors, canines, premolars, and molars). Group A had only one tooth type missing, Group B had two tooth types missing (usually incisors and premolars), Group C had three tooth types missing, and Group D had at least one tooth of each type missing.
Statistical analysis was undertaken using ANOVA, with post-hoc Tukey tests to examine the data for the effect of missing teeth upon cephalometric values.
Results
The mean ages of the subgroups are shown in Table 1. Figure 2 shows the distribution of the numbers of missing teeth. The average number of missing teeth was seven (SD 5) and ranged from 1 to 21. The proportion of patients with the different tooth types (incisors, canines, premolars, and molars, both maxillary and mandibular teeth) missing, is shown in Figure 3. It can be seen that, although any of the permanent teeth has the potential to be congenitally absent, the second premolars and upper lateral incisors were most commonly missing. Thirty-seven per cent of patients had a family history of hypodontia and 7 per cent of young people with hypodontia had an associated syndrome. The distribution of malocclusions is shown in Table 2.
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shows the cephalometric measurements for the whole group. The mean SNA, SNB, and MMA angles were within the normal limits, but there was a wide variation in the size of these angles. The dento-alveolar findings demonstrated that the upper and lower incisors were slightly retroclined, at 105•6 and 86•9 degrees, respectively, in comparison with normal values. All other measurements were within normal limits in comparison with the Eastman values.
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. Statistical analysis of the subgroups revealed a statistically significant reduction in the MMA when more than one tooth type was missing (P = 0•007) and the ANB angle decreased as number of missing tooth types increased (P = 0•034). Both factors were independent of age.
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A wide range of results has been reported in previous cephalometric studies of the dentofacial structure of patients affected by hypodontia. Roald et al. (1982) found little effect on the growth pattern when following a group of patients with hypodontia between the ages of 9–16 years and other workers (Dermaut et al., 1986; Yuksel and Ucem, 1997) have reported predominantly Class I skeletal patterns in their groups of patients. However, other studies (Wisth et al., 1974; Sarnas and Rune, 1983; Woodworth et al., 1985) have shown results which indicate smaller and more retrognathic maxillae in children with hypodontia. The subjects in this study had a greater proportion of Class III skeletal patterns as measured by the ANB angle and this tendency was particularly significant as the severity of hypodontia increased (more than one tooth type missing). However, this study population is skewed because only those subjects who had had a lateral skull radiograph taken were included in the study. Thus, extrapolation to the wider population with hypodontia must be made with caution.
The mean MMA of the whole sample in this study was within the normal range (25•6 degrees), but there was a wide range from 15•2 to 36•6 degrees. When analyses were undertaken of the subgroups, there was a significant reduction in the MMA with increasing severity of hypodontia. This is in agreement with the findings of Woodworth et al. (1985) who found a similar relationship in their sample of patients with missing upper lateral incisors, as did Øgaard and Krogstad (1995) who looked at differences in the relationship between craniofacial features with increasing severity of hypodontia. The latter studies both found a reduction in anterior lower face height. However, in this study the difference in the lower face height or the facial proportions and increasing severity of hypodontia was not apparent.
One study (Yuksel and Ucem, 1997) reported a tendency towards bimaxillary protrusion, which is contrary to the tendency of bimaxillary retroclination found in this study. Although the mean upper and lower incisor inclinations were towards the lower limits of normal, there was no significant relationship found with increasing numbers of missing teeth. By contrast, the study by Øgaard and Krogstad (1995) reported a significant incisor retroclination with increasing severity of hypodontia. Dermaut et al. (1986) found more deep bite cases in their study, but overall this was not seen in the patients in the present study.
Conclusions
The mean cephalometric values for the sample as a whole were within the normal range and did not demonstrate any feature specific to the group. However, patients with more severe hypodontia demonstrated tendencies to a Class III skeletal relationship and a reduced maxillary-mandibular planes angle.
References
British Standard Classification of Incisors (1969)BS4492,British Standards Institute, London.
Brook, A. H. (1974) Dental anomalies of number, form and size: their prevalence in British schoolchildren, Journal of the International Association of Dentistry for Children, 5, 37–53.[Medline]
Dermaut, L.R., Goeffers, K.R. and De Smit, A.A. (1986) Prevalence of tooth agenesis correlated with jaw relationship and dental crowding, American Journal of Orthodontics and Dentofacial Orthopaedics, 90, 204–210.
Goodman, J. R., Jones, S. P., Hobkirk J. A. & King, P. A. (1994) Hypodontia: 1. Clinical features and the management of mild to moderate hypodontia, Dental Update, 21, 381–384.
Hobkirk J. A. and Brook A. H. (1980) The management of patients with severe hypodontia, Journal of Oral Rehabilitation, 7, 289–298.[Medline]
Hobkirk, J. A., Goodman, J. R. and Jones S. P. (1994) Presenting complaints and findings in a group of patients attending a hypodontia clinic, British Dental Journal, 177, 337–339.[Medline]
Mills, J. R. E. (1983)Principles and Practice of Orthodontics,Churchill Livingstone, London.
Øgaard, B. and Krogstad. O. (1995) Craniofacial structure and soft tissue profile in patients with severe hypodontia, American Journal of Orthodontics & Dentofacial Orthopedics, 108, 472–477.
Roald, K. L., Wisth, P. J. and Boe, O. E. (1982) Changes in cranio-facial morphology of individuals with hypodontia between the ages of 9 and 16, Acta Odontologica Scandinavica, 40, 65–74.[Medline]
Rose, J. S. (1966) A survey of congenitally missing teeth, excluding third molars, in 6000 orthodontic patients, Dental Practitioner & Dental Record, 17, 107–114.
Sarnas, K. V. and Rune, B. (1983) The facial profile in advanced hypodontia: a mixed longitudinal study of 141 children 6–19 years, European Journal of Orthodontics, 5, 133–143.
Wisth, P. J., Thunold, K. and Boe O. E. (1974) The craniofacial morphology of individuals with hypodontia, Acta Odontologica Scandinavica, 32, 282–290.
Woodworth, D. A. Sinclair, P. M. and Alexander R. G. (1985) Bilateral congenital absence of maxillary lateral incisors: a craniofacial and dental cast analysis, American Journal of Orthodontics, 87, 280–293.[Medline]
Yuksel, S. and Ucem, T. (1997) The effect of tooth agenesis on dentofacial structures, European Journal of Orthodontics, 19, 71–78.
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