Andréa Sasso STUANI
Mírian Aiko Nakane MATSUMOTO
Maria Bernadete Sasso STUANI
Disciplina de Ortodontia Preventiva, Faculdade de Odontologia de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brasil
Braz Dent J (2000) 11(1): 35-40 ISSN 0103-6440
Introduction | Material and Methods | Results and Discussion | Conclusions | Resumo | Acknowledgments | References
Cephalometric evaluations of the skeletal pattern of 30 patients with anterior open-bite malocclusion were compared to those of 30 individuals with a normal overbite. The posterior/anterior face height ratio (PFH/AFH) was the only skeletal characteristic statistically different in the two groups. The other cephalometric measurements were not found to be statistically different in the malocclusion and normal overbite groups (SN-GoGn, SN-PP, gonial angle, LFH/AFH ratio), indicating that there is no skeletal origin in the group with anterior open-bite in this study.
Key Words: open-bite, overbite, malocclusion, cephalometrics.
Diagnosis and orthodontic treatment of anterior open-bite has been frequently discussed in the literature in terms of the difficulty of obtaining ideal and stable results after orthodontic treatment.
The open-bite is considered to be a deviation in the vertical relationship of the dental arches and is characterized by the absence of contact of the incisal borders of the maxillary and mandibular teeth in the vertical plane (Graber, 1961; Sassouni and Nanda, 1964; Nanda, 1988, 1990). Subtelny and Sakuda (1964), Richardson (1969), Nemeth and Isaacson (1974) and Trouten (1983) reported that the etiological factors of the anterior open-bite may be abnormal morphological characteristics resulting from a disturbance in skeletal development, abnormal muscular growth or poor positioning of the anterior teeth caused by buccal habits. According to Bjork (1947), genetic and environmental factors which stimulate the vertical growth of the molar region, which are not compensated by condyle growth, result in an anterior open-bite. Similarly, forces that impede eruption in the incisal region also result in an anterior open-bite (Ngan and Fields, 1997).
Isaacson (1971), Nahoum (1975, 1977), Lieberman and Gazit (1978), Trouten (1983) and Cangialosi (1984) reported that it is important to distinguish between dental open-bite and skeletal open-bite. Diagnosis can be made with careful cephalometric evaluation.
The objective of this report is to evaluate the skeletal pattern of patients with anterior open-bite and compare them to individuals with normal overbite using cephalometric evaluation.
Material and Methods
A total of 60 children, 7-10 years of age, were divided into two groups: group 1 (N = 30) were patients with Class I malocclusion with anterior open-bite and group 2 (N = 30) were children with normal overbite. The two groups were chosen according to the following criteria: the children had Class I dental and skeletal malocclusion with mixed dentition such that the maxillary and mandibular permanent incisors had stage 8 root formation according to Nolla (1960). Panoramic radiographs were used to exclude cases with congenital absence of permanent teeth and supranumerary teeth and to determine the stage of root formation. Open-bite and normal overbite were measured in orthodontic study models according to the criteria of Graber (1961).
The following cephalometric tracings of landmarks and planes were made on the cephalometric radiographs: S (sella), N (nasion), Go (gonion), Gn (gnathion), ANS (anterior nasal spine), PNS (posterior nasal spine), A (subspinal) B (supramenton), M (menton) and Ar (articular).
Using these landmarks the following cephalometric measurements were made for both groups (Figure 1):
1.ANB: angle formed by the intersection of lines NA and NB, which measures
the anterior-posterior relation of the maxilla and the mandible.
2.SN-GoGn: angle measuring the inclination of the mandibular plane in relation to the anterior base of the cranium.
3.SN-PP: angle formed by the intersection of the sella nasion line and the palatal plane (ANS and PNS). This established the degree of inclination of the maxilla in relation to the anterior base of the cranium.
4.ArGo-GoMe (gonial angle): angle formed by the posterior border of the ramus of the mandible and the mandibular plane.
5.N-Me: linear measure corresponding to the total anterior face height (AFH).
6.N-ANS: linear measure which represents the superior anterior face height (UFH).
7.ANS-Me: linear measure which represents the anterior inferior face height (LFH).
8.S-Go: linear measure which represents the posterior face height (PFH).
From these linear cephalometric measurements, two indices were proposed: 1: PFH/AFH ratio obtained by the proportion between the posterior face height and the anterior face height (S-Go/N-Me). 2: LFH/AFH ratio obtained by the proportion between the inferior anterior face height and the total anterior face height (ANS-Me/N-Me).
The data were submitted to statistical analysis using the GMC program, 7.3 version. The Student-t test was used when data distribution errors were normal and the Mann-Whitney U test was used when samples were not normal. The level of significance was set at P<0.05.
Results and Discussion
T-test results indicated that the SN-GoGn angle and the LFH/AFH ratio of the open-bite and the normal overbite subjects were statistically similar. The t-test showed a significant difference for the PFH/AFH ratio of the two groups (P<0.05) (Table 1). According to the Mann-Whitney U test, the two groups were equal regarding the gonial angle (ArGo-GoMe) and the inclination of the palatal plane (SN-PP) (Table 2).
Statistical evaluation of the SN-GoGn angle did not show a significant difference between the two groups indicating that the inclination of the mandibular plane in relation to the anterior cranial base is similar, in agreement with Panico et al. (1991). Several authors observed an increased inclination of the mandibular plane in cases of anterior open-bite (Hapak, 1964; Sassouni and Nanda, 1964; Subtelny and Sakuda, 1964; Nahoum, 1971, 1977; Cangialosi, 1984; Lopes-Gavito, 1985; Jones, 1989) noting a downward growth of the mandible as an important factor in open-bite development. This discordance can be attributed to the fact that the sample used in this investigation was very young (7-10 years of age). These patients had still not reached the pubertal growth period and, therefore, did not show a defined mandibular morphology. Trouten (1983), Cangialosi (1984), Lopez-Gavito (1985) and Jones (1989) evaluated adults or patients who had already reached the maximum pubertal growth with well defined morphologic patterns.
The proportion between the anterior face height (N-Me) and the lower face height (ENA-Me), represented by the LFH/AFH ratio, confirms that the patients had similar dimensions of inferior face height indicating that there was no increase in this dimension in individuals with anterior open-bite. Nevertheless, some authors found anterior lower face height increased in cases of open-bite, where the anterior upper face height was not a predominant factor (Sassouni and Nanda, 1964; Richardson, 1969; Nahoum, 1971, 1975, 1977; Lopes-Gavito, 1985; Tsang et al., 1997, 1998). Richardson (1969), using a facial polygon in open-bite and deep overbite patients, reported that total anterior face height was longer in open-bite patients than in closed-bite patients. This increase was the result of an increase in lower face height. This evaluation was done with lateral cephalograms in individuals from 7 to 27 years of age which may justify the differences obtained in this study because, according to Bjork (1947), the face shape can change significantly during the period of adolescence.
The inclination of the palatal plane, in relation to the anterior cranial base, was statistically similar between the malocclusions with open-bite and normal overbite. These results are in agreement with those reported by Subtelny and Sakuda (1964) and Cangialosi (1984). The individuals with open-bite in this study did not show changes in the vertical position of the maxilla that was represented by the palatal plane, i.e., in this sample the anterior open-bite was not due to altered maxillary inclination. On the other hand, Nahoum (1971) and Lopez-Gavito (1985) reported smaller values for the SN-PP angle in malocclusions with anterior open-bite suggesting that the lower face height could be increased in these cases due to the anterior maxillary rotation. Tsang et al. (1998) also reported a trend to the anterior and upper rotation of the palatal plane in the anterior open-bite, where the anterior nasal spine was superiorly located.
No statistically significant difference was shown in the values of the gonial angle (ArGo.GoMe) between the open-bite and normal overbite groups. However, several authors have reported that the gonial angle was increased in cases of open-bite (Sassouni and Nando, 1964; Subtelny and Sakuda, 1964; Richardson, 1969; Nahoum, 1971, 1975, 1977; Trouten, 1983; Tsang, 1998). This lack of agreement was due to the fact that the individuals in the present study did not yet show a defined morphologic pattern.
Considering the ratio between the posterior (S-Go) and the anterior (N-Me) face height, in the anterior open-bite group, the PFH/AFH ratio was statistically (P<0.05) smaller than in the normal overbite group, indicating a smaller posterior face height in cases with anterior open-bite, confirming the results reported by Saussouni and Nanda (1964), Nahoum (1971) and Tsang et al. (1997).
1.There was no statistically significant difference in the inclination of the mandibular plane (SN-GoGn) and the palatal plane (SN-PP) among patients with an open-bite and patients with a normal overbite.
2.The value of the gonial angle (ArGo-GoMe) was statistically similar in both groups.
3.The proportion between the posterior and anterior face heights (PFH/AFH ratio) was statistically less in patients with an anterior open-bite suggesting that the posterior face height is less in these malocclusions.
4.The anterior open-bite in this study did not have a skeletal origin, and was probably due to the presence of buccal habits and the early age range of the patients.
Stuani AS, Matsumoto MAN, Stuani MBS: Avaliação cefalométrica do padrão esquelético de pacientes com mordida aberta anterior. Braz Dent J 11(1): 35-40, 2000.
Uma avaliação cefalométrica do padrão esquelético de pacientes portadores de maloclusões com mordida aberta anterior foi realizada neste estudo, comparando-os com indivíduos que apresentavam sobremordida normal. Os resultados obtidos permitiram concluir que a mordida aberta anterior que caracteriza a amostra estudada não tem origem esquelética, uma vez que a maioria das medidas cefalométricas consideradas neste trabalho não são estatisticamente diferentes nos grupos com maloclusão e sobremordida normal (SN.GoGn, SNPP, ângulo goníaco, iAFA). Apenas uma característica esquelética foi estatisticamente diferente nas duas amostras estudadas, a proporção entre altura facial posterior e anterior (iAF).
Unitermos: mordida aberta, sobremordida, maloclusão, cefalometria.
The authors would like to express their appreciation to Dr. Geraldo Maia Campos, retired Full Professor of the Faculty of Dentistry of Ribeirão Preto, USP, for performing the statistical analysis of this study.
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Correspondence: Professora Mírian Aiko Nakane Matsumoto, Disciplina de Ortodontia Preventiva, Faculdade de Odontologia de Ribeirão Preto, USP, 14040-904 Ribeirão Preto, SP, Brasil.
Accepted March 3, 2000
Eletronic publication July, 2000