ABSTRACT

Objective:

The aim of this study was to perform a systematic review on the morphological characteristics of the skull base (flexion, anterior length and posterior length) and the concomitant development of malocclusions, by comparing differences in dimorphism, ethnicity and age.

Methods:

The articles were selected by means of electronic search on BBO, MEDLINE and LILACS databases from 1966 to 2016. A qualitative evaluation of the methodologies used on the articles was also performed.

Results:

Although the literature on this topic is abundant, only 16 articles were selected for the present systematic review. The cranial base angle itself does not seem to play a significant role in the development of malocclusions. In fact, the cranial base angle is relatively stable at the ages of 5 to 15 years.

Conclusions:

A more obtuse angle at the skull base, in association or not with a greater anterior length of the cranial base, can contribute to the development of Class II division 1 malocclusions. On the other hand, a more acute angle at the skull base can contribute to a more anterior positioning of the mandible and to the development of Class III malocclusions.

Keywords:
Malocclusion; Cephalometry; Growth; Skull base

RESUMO

Objetivo:

o objetivo desse estudo foi realizar uma revisão sistemática sobre as características morfológicas da base do crânio (flexão, comprimento anterior e comprimento posterior) e o desenvolvimento concomitante da má oclusão, comparando as diferenças do dimorfismo, etnia e idade.

Métodos:

os artigos foram selecionados por meio de busca eletrônica nas bases de dados BBO, MEDLINE e LILACS, de 1966 a 2016. Uma avaliação qualitativa da metodologia dos artigos também foi executada.

Resultados:

ainda que a literatura seja abundante nesse assunto, somente 16 artigos foram selecionados para a presente revisão sistemática. O ângulo da base do crânio, por si só, não parece desempenhar papel significativo no desenvolvimento das más oclusões. De fato, o ângulo da base do crânio é relativamente estável dos 5 aos 15 anos.

Conclusões:

um ângulo mais obtuso na base do crânio, associado ou não a um comprimento maior, pode contribuir para o desenvolvimento da má oclusão de Classe II, divisão 1. Por outro lado, um ângulo mais agudo na base do crânio pode contribuir para um posicionamento mais anterior da mandíbula e para o desenvolvimento da má oclusão de Classe III.

Palavras-chave:
Má oclusão; Cefalometria; Crescimento; Base do crânio

INTRODUCTION

The skull base plays a key role in the craniofacial growth, thus helping to integrate different growth patterns both spatially and functionally, regarding several regions adjacent to the skull - such as brain components, nasal cavity, oral cavity and pharynx.¹ In this way, the skull base supports the brain and allows the neurocranium and viscerocranium to adapt and develop during growth.²2 Björk A. Cranial base development. Am J Orthod. 1955 Mar;41(3):198-255.^,33 Ford EHR. Growth of the human cranial base. Am J Orthod. 1958 July;44(7):498-506. It is reported that the first growth spurt of the skull base occurs between 14 and 32 weeks of intra-uterine life, and the second one occurs during the first year of life.⁴4 Scott JH. The cranial base. Am L Phys Anthropol. 1958 Apr;16(3):319-48.

The development of the skull base is closely related to both middle region of the face and mandibular positioning, with its anterior-posterior growth playing an important role in mandibular and nasomaxillary growth, thus directly contributing to the degree of facial prognathism.⁵5 Moyers RE. Ortodontia. 4ª ed. Rio de Janeiro: Guanabara Koogan; 1991. Based on geometrical relationships, it would be reasonable to say that any change in the skull base flexion might affect the positioning of maxilla and mandible, thus influencing skeletal pattern and occlusion as well.⁶6 Santos-Pinto A, Martins JCR, Uetanabaro T, Sakima T, Mendes AJD. Influência do grau de deflexão da base craniana no relacionamento ântero-posterior dos maxilares. Ortodontia. 1983;16:5-9.

The literature is abundant, but controversial, regarding the influence of the skull base flexion on the development of malocclusions.⁶6 Santos-Pinto A, Martins JCR, Uetanabaro T, Sakima T, Mendes AJD. Influência do grau de deflexão da base craniana no relacionamento ântero-posterior dos maxilares. Ortodontia. 1983;16:5-9. Although there are studies supporting that the skull base flexion is not a factor in the etiology of malocclusions, others suggest the contrary.²2 Björk A. Cranial base development. Am J Orthod. 1955 Mar;41(3):198-255.^,77 Björk A. The nature of facial prognathism and its relation to normal occlusion of the teeth. Am J Orthod. 1951 Feb;37(2):106-24. In fact, several authors²2 Björk A. Cranial base development. Am J Orthod. 1955 Mar;41(3):198-255.^,88 Björk A. The face in profile. An Anthropological X-ray Investigation on Swedish Children and Conscripts. Svensk Tandläkare-Tidskrift. 1947;40(5B Suppl):1-180.

9 Ricketts RM. A foundation for cephalometric communication. Am J Orthod. 1960 May;46(5):330-57.

10 Hopkin GB, Houston WJ, James GA,et al. The cranial base as an aetiological, factor in malocclusion. Angle Orthod. 1968 July;38(3):250-5.

11 Horowitz SL, Converse JM. Craniofacial relationships in mandibular prognathism. Arch Oral Biol. 1969 Jan;14(1):121-31.^-1212 Dibbets JMH. Morphological associations between the Angle classes. Eur J Orthod. 1996 Apr;18(2):111-8. showed evidence that the skull base has a considerable influence in the inter-maxillary relationships.

Ricketts⁹9 Ricketts RM. A foundation for cephalometric communication. Am J Orthod. 1960 May;46(5):330-57. reported that the skull base area has an important influence on total facial prognathism and development of anteroposterior relationship between maxilla and mandible. According to the same author, the Class II malocclusion worsens with age. To Hopkin et al,¹⁰10 Hopkin GB, Houston WJ, James GA,et al. The cranial base as an aetiological, factor in malocclusion. Angle Orthod. 1968 July;38(3):250-5. the skull base angle was lower in individuals with Class III malocclusions (males = 122.4^o and females = 122.2^o) and higher in those with Class II division 1 (males = 126.7^o and females = 128.8^o). By analyzing the craniofacial relationships in the mandibular prognathism and comparing them to Class I malocclusions, Horowitz and Converse¹¹11 Horowitz SL, Converse JM. Craniofacial relationships in mandibular prognathism. Arch Oral Biol. 1969 Jan;14(1):121-31. found mean values of 119.3^o for the BaSN angle in Class III malocclusions with horizontal growth pattern, 116.6^o in Class III malocclusions with vertical growth pattern, and 124.1^o in Class I malocclusions.

Among studies showing no influence of the skull base on malocclusions, Hildwein et al¹³13 Hildwein M, Bacon W, Turlot JC, Kuntz M. Spécificités et discriminants majeurs dans une population de Classe II division 1. Revue d'Orthopédie Dento-Faciale. 1986 June;20(2):197-208. found no significant difference in the BaSN angle in individuals with Class II and Class I malocclusions. Kasai et al¹⁴14 Kasai K, Moro T, Kanazawa E, Iwasawa T. Relationship between cranial base and maxillofacial morphology. Eur J Orthod. 1995 Oct;17(5):403-10. investigated the relationship between skull base and maxillofacial morphology in Japanese subjects and found no difference between Class I and Class II malocclusions. Similarly, Wilhelm et al¹⁵15 Wilhelm BM, Beck FM, Lidral AC, Vig KWL. A comparison of cranial base growth in Class I and Class II skeletal patterns. Am J Orthod Dentofacial Orthop. 2001 Apr;119(4):401-5. observed no difference in the measurements of the skull base regarding Class I and Class II malocclusions.¹1 Polat OO, Kaya B. Changes in cranial base morphology in difference malocclusions. Orthod Craniofac Res. 2007 Nov;10(4):216-21.

There are many studies corroborating the finding that skull base flexion has an influence on malocclusions, whereas others show no such evidence. Different factors can contribute to these divergent findings, such mixed samples - in terms of age and gender - as well as the use of chronological age instead of skeletal age. Other factors possibly contributing to these divergent findings include the following: lack of radiographic standardization, small sample size, and number of inter-group comparisons. In this way, the influence of the skull base flexion as an etiological factor influencing inter-maxillary relationships is still a matter of debate and investigation.¹⁶16 Rothstein T, Yoon-Tarlie C. Dental and facial skeletal characteristics and growth of males and females with Class II, division 1 malocclusion between the ages of 10 and 14 (revisited)-Part I: characteristics of size form, and position. Am J Orthod Dentofacial Orthop. 2000 Mar;117(3):320-32.

The objective of the present study was to perform a systematic review on the relationship between skull base (flexion, anterior length and posterior length) and the development of malocclusions, by comparing differences in gender dimorphism, ethnicity and age.

METHODS

Search strategy

The articles selected for this systematic review of the literature were found by means of electronic search on BBO, MEDLINE and LILACS databases, from 1966 to 2016. The keywords used for this bibliographic search were the following: skull base, cephalometry, malocclusion, Class I malocclusion, Class II malocclusion, Class III malocclusion.

Next, a manual search was also performed by analyzing the bibliographic references of the articles according to the systematic review.

Criteria for study selection

The inclusion criteria were the following:

The exclusion criteria were the following:

Article selection

Four researchers have independently examined titles, keywords and abstracts of the articles found in the databases, according to the inclusion and exclusion criteria aforementioned. The articles were consensually selected and integrally considered, and after reading them a final decision was made regarding their inclusion or not in the present study. The articles were classified according to the criteria summarized in Table 1.

RESULTS

A total of 315 articles were initially identified, 8 from BBO, 12 from LILACS and 295 from MEDLINE. After reading the abstracts, only 55 were selected: no article from BBO, 2 from LILACS and 53 from MEDLINE. These were fully considered and after applying the inclusion and exclusion criteria, 39 articles were excluded and 16 remained, all from the MEDLINE database (Table 2). Next, another article was excluded due to lack of the measurements considered for review.

A qualitative evaluation of the methodology used by these articles was performed according to previous studies.¹⁷17 Antczak AA, Tang J, Chalmers TC. Quality assessent of randomized control trials in dental research. I: Methods. J Periodontal Res. 1986 July;21(4):305-14.^,1818 Flores-Mir C, Major MP, Major PW. Search and selection methodology of systematic reviews in orthodontics. Am J Orthod Dentofacial Orthop. 2006 Aug;130(2):214-7. The variables being considered for review are listed in Table 1, including corresponding values. Table 2 shows the articles presenting more accurate methodologies.

Each article was given points according to the items evaluated, as can be seen in Table 1. Each item had a maximum score of 2 points if there was a consensus on it, otherwise 1 point was given. This procedure was applied to each article.

Therefore, each article could reach a maximum score of 20 points, thus allowing the study quality to be ranked as follows: ≤ 10 points = low score; > 10 and ≤15 = average score; > 15 and ≤ 18 = moderately high score; and > 18 points = high score.

Table 3 shows the sample characteristics, including the objective of each article, and Table 4 lists the epitomes. In this last table, a study²²22 Alexander AEZ, McNamara JA, Franchi L, Baccetti T. Semi longitudinal cephalometric study of craniofacial growth in untreated Class III malocclusion. Am J Orthod Dentofacial Orthop. 2009 June;135(6):701-14. was excluded because it did not present total measures, but rather growth increments.

Age

Seven studies have investigated the growth of the skull base by comparing the data obtained from different age groups¹⁶16 Rothstein T, Yoon-Tarlie C. Dental and facial skeletal characteristics and growth of males and females with Class II, division 1 malocclusion between the ages of 10 and 14 (revisited)-Part I: characteristics of size form, and position. Am J Orthod Dentofacial Orthop. 2000 Mar;117(3):320-32.^,2020 Andria LM, Leite LP, Prevatte TM, King LB. Correlation of the cranial base angle and its components with other dental /skeletal variables and treatment time. Angle Orthod. 2004 June;74(3):361-6.^,2222 Alexander AEZ, McNamara JA, Franchi L, Baccetti T. Semi longitudinal cephalometric study of craniofacial growth in untreated Class III malocclusion. Am J Orthod Dentofacial Orthop. 2009 June;135(6):701-14.^,2323 Ishii N, Deguchi T, Hunt N. Craniofacial morphology of Japanese girls with Class II division 1 malocclusion. J Orthod. 2001 Sept;28(3):211-5.^,2424 Singh GD, McNamara JA Jr, Lozanoff S. Morphometry of the cranial base in subjects with Class III malocclusion. J Dent Res. 1997 Feb;76(2):694-703.^,2828 Singh GD, McNamara JA Jr, Lozanoff S. Craniofacial heterogeneity of prepubertal Korean and European-American subjects with Class III malocclusions: procrustes, EDMA, and cephalometric analyses. Int J Adult Orthod Orthognath Surg. 1998 Jan;13(3):227-40.^,3737 Yoon SS, Chung CH. Comparison of craniofacial growth of untreated Class I and Class II girls from ages 9 to 18 years: a longitudinal study. Am J Orthod Dentofacial Orthop. 2015 Feb;147(2):190-6. with three²²22 Alexander AEZ, McNamara JA, Franchi L, Baccetti T. Semi longitudinal cephalometric study of craniofacial growth in untreated Class III malocclusion. Am J Orthod Dentofacial Orthop. 2009 June;135(6):701-14.^,2424 Singh GD, McNamara JA Jr, Lozanoff S. Morphometry of the cranial base in subjects with Class III malocclusion. J Dent Res. 1997 Feb;76(2):694-703.^,2828 Singh GD, McNamara JA Jr, Lozanoff S. Craniofacial heterogeneity of prepubertal Korean and European-American subjects with Class III malocclusions: procrustes, EDMA, and cephalometric analyses. Int J Adult Orthod Orthognath Surg. 1998 Jan;13(3):227-40. of them using samples of individuals with Class III malocclusion and whose age ranged from 5 to 18 years old. These individuals were found²²22 Alexander AEZ, McNamara JA, Franchi L, Baccetti T. Semi longitudinal cephalometric study of craniofacial growth in untreated Class III malocclusion. Am J Orthod Dentofacial Orthop. 2009 June;135(6):701-14. to have a yearly increment in the length of the anterior skull base in all age groups (6 to 18 years old), which was smaller than 1 mm for women and approximately equal to 1 mm for men, similar to the growth estimated for individuals with Class I malocclusion. In another study²⁴24 Singh GD, McNamara JA Jr, Lozanoff S. Morphometry of the cranial base in subjects with Class III malocclusion. J Dent Res. 1997 Feb;76(2):694-703. comparing Class III malocclusion to Class I malocclusion in individuals aged 5 to 11 years old, it was found that NSBa angle was more acute in the latter at ages of 5, 8, and 9 years old, and that NSAr angle had the same trend; but no statistically significant difference was found at 8 years old. Researchers²³23 Ishii N, Deguchi T, Hunt N. Craniofacial morphology of Japanese girls with Class II division 1 malocclusion. J Orthod. 2001 Sept;28(3):211-5. have reported that the skull base of Japanese individuals with Class II division 1 malocclusion had a significantly smaller anterior length at 10 years and 10 months to 15 years and 10 months old compared to other age groups, involving individuals with same malocclusion and race (Group 1: 7 years and 6 months to 13 years and 6 months old; and Group 2: 9 years and 1 month to 13 years and 6 months old). On the other hand, another study²⁹29 Zeng XL, Forsberg CM, Aronson SL. Craniofacial morphology in Chinese and Swedish children with Angle Class I and Class II occlusal relations. Australian Orthod J. 1998 Oct;15(3):168-76. compared individuals with Class II division 1 malocclusion to controls and found that the length of the anterior skull base was statistically greater in all six age groups studied (females aged 10, 12, 14 years old, and males aged 10, 12, 14 years old). Two studies²⁰20 Andria LM, Leite LP, Prevatte TM, King LB. Correlation of the cranial base angle and its components with other dental /skeletal variables and treatment time. Angle Orthod. 2004 June;74(3):361-6.^,2828 Singh GD, McNamara JA Jr, Lozanoff S. Craniofacial heterogeneity of prepubertal Korean and European-American subjects with Class III malocclusions: procrustes, EDMA, and cephalometric analyses. Int J Adult Orthod Orthognath Surg. 1998 Jan;13(3):227-40. had samples with different age groups, but it was not possible to use all data because the first study²⁰20 Andria LM, Leite LP, Prevatte TM, King LB. Correlation of the cranial base angle and its components with other dental /skeletal variables and treatment time. Angle Orthod. 2004 June;74(3):361-6. had compared age groups of 1 month, 2 years and 14 years old, whereas the second study²⁸28 Singh GD, McNamara JA Jr, Lozanoff S. Craniofacial heterogeneity of prepubertal Korean and European-American subjects with Class III malocclusions: procrustes, EDMA, and cephalometric analyses. Int J Adult Orthod Orthognath Surg. 1998 Jan;13(3):227-40. had assessed neither flexion nor the skull base length at different age groups. For Yoon and Chung,³⁷37 Yoon SS, Chung CH. Comparison of craniofacial growth of untreated Class I and Class II girls from ages 9 to 18 years: a longitudinal study. Am J Orthod Dentofacial Orthop. 2015 Feb;147(2):190-6. which compared Class I with Class II at three different ages (9, 14 and 18 years - all female), no difference was observed in the flexion or length of the anterior skull base.

Ethnic group

Three studies have assessed different ethnic groups,²⁶26 Ishii N, Deguchi T, Hunt NP. Morphological diferences in the craniofacial structure between Japanese and Caucasian girls with Class II division 1 malocclusion. Eur J Orthod. 2002 Feb;24(1):61-7.^,2828 Singh GD, McNamara JA Jr, Lozanoff S. Craniofacial heterogeneity of prepubertal Korean and European-American subjects with Class III malocclusions: procrustes, EDMA, and cephalometric analyses. Int J Adult Orthod Orthognath Surg. 1998 Jan;13(3):227-40.^,2929 Zeng XL, Forsberg CM, Aronson SL. Craniofacial morphology in Chinese and Swedish children with Angle Class I and Class II occlusal relations. Australian Orthod J. 1998 Oct;15(3):168-76. with Asian being compared to Caucasian individuals in most cases, and significant differences being found. The length of the anterior skull base was found to be greater for Japanese than for Caucasian females.²⁶26 Ishii N, Deguchi T, Hunt NP. Morphological diferences in the craniofacial structure between Japanese and Caucasian girls with Class II division 1 malocclusion. Eur J Orthod. 2002 Feb;24(1):61-7. However, a study²⁸28 Singh GD, McNamara JA Jr, Lozanoff S. Craniofacial heterogeneity of prepubertal Korean and European-American subjects with Class III malocclusions: procrustes, EDMA, and cephalometric analyses. Int J Adult Orthod Orthognath Surg. 1998 Jan;13(3):227-40. reported a greater anterior skull base as well as a more acute NSAr angle in European/American than in Korean individuals. Similarly, with regard to the length of the anterior skull base, a study²⁹29 Zeng XL, Forsberg CM, Aronson SL. Craniofacial morphology in Chinese and Swedish children with Angle Class I and Class II occlusal relations. Australian Orthod J. 1998 Oct;15(3):168-76. showed this measurement was smaller in Chinese than in Swedish individuals for both types of malocclusions (Class I and Class II), with the posterior length (S-Ba) being also smaller in Chinese individuals with Class II malocclusion. Another study²⁴24 Singh GD, McNamara JA Jr, Lozanoff S. Morphometry of the cranial base in subjects with Class III malocclusion. J Dent Res. 1997 Feb;76(2):694-703. evaluated two ethnic groups but no comparison was possible because of the lack of data on skull base structures regarding Caucasian individuals.

Dimorphism

Six studies have evaluated the relationship between sexual dimorphism and development of the skull base,²²22 Alexander AEZ, McNamara JA, Franchi L, Baccetti T. Semi longitudinal cephalometric study of craniofacial growth in untreated Class III malocclusion. Am J Orthod Dentofacial Orthop. 2009 June;135(6):701-14.^,2525 Johannsdottir B, Thordarson A, Magnusson TE. Craniofacial morphology in 6-year-old Icelandic children. Eur J Orthod. 1999 June;21(3):283-90.^,2727 Kapoor S, Kapoor DN, Jaiswal JN. Cephalometric evaluation of Class II malocclusion in transitional dentition. J Indian Soc Pedo Dent. 2001 Dec;19(4):127-33.^,3030 Lau JWP, Hagg U. Cephalometric morphology of Chinese with Class II division 1 malocclusion. Br Dental J. 1999 Feb;186(4):188-90.^,1616 Rothstein T, Yoon-Tarlie C. Dental and facial skeletal characteristics and growth of males and females with Class II, division 1 malocclusion between the ages of 10 and 14 (revisited)-Part I: characteristics of size form, and position. Am J Orthod Dentofacial Orthop. 2000 Mar;117(3):320-32.^,2929 Zeng XL, Forsberg CM, Aronson SL. Craniofacial morphology in Chinese and Swedish children with Angle Class I and Class II occlusal relations. Australian Orthod J. 1998 Oct;15(3):168-76. but no significant difference was found in the angular measurements. However, one study²⁵25 Johannsdottir B, Thordarson A, Magnusson TE. Craniofacial morphology in 6-year-old Icelandic children. Eur J Orthod. 1999 June;21(3):283-90. showed that linear measurements (S-N, S-Ar and S-Ba) were significantly greater in Icelander male children compared to female ones with Class I and Class II malocclusions.

Malocclusion differences

Of the 16 articles selected, only one has not compared flexion or length of the skull base to some type of malocclusion.²²22 Alexander AEZ, McNamara JA, Franchi L, Baccetti T. Semi longitudinal cephalometric study of craniofacial growth in untreated Class III malocclusion. Am J Orthod Dentofacial Orthop. 2009 June;135(6):701-14. Two studies¹1 Polat OO, Kaya B. Changes in cranial base morphology in difference malocclusions. Orthod Craniofac Res. 2007 Nov;10(4):216-21.^,1919 Dhoptkar A, Bhatia S, Rock P. An investigation into the relationship between the cranial base angle and malocclusion. Angle Orthodontist. 2002 Oct;72(5):456-63. compared flexion or length of the skull base in individuals with Class I, Class II and Class III malocclusions. One of these studies¹⁹19 Dhoptkar A, Bhatia S, Rock P. An investigation into the relationship between the cranial base angle and malocclusion. Angle Orthodontist. 2002 Oct;72(5):456-63. found greater angular measurements for the skull base in Class II division 1 malocclusion, compared to Class I malocclusion. In this same study, no difference was found between Class I malocclusion and other ones, regarding such angular measurements, whereas the length of the anterior and posterior skull base were greater in the cases of Class II malocclusion. However, the other study¹1 Polat OO, Kaya B. Changes in cranial base morphology in difference malocclusions. Orthod Craniofac Res. 2007 Nov;10(4):216-21. reported significant differences in the skull base length between the three types of malocclusion. Studies²¹21 Mouakeh M. Cephalometric evaluation of craniofacial pattern of Syrian children with Class III malocclusion. Am J Orthod Dentofacial Orthop. 2001 June;119(6):640-9.^,2424 Singh GD, McNamara JA Jr, Lozanoff S. Morphometry of the cranial base in subjects with Class III malocclusion. J Dent Res. 1997 Feb;76(2):694-703.^,3131 Chang HP, Hsieh SH, Tseng YC, Chou TM. Cranial-base morphology in children with Class III malocclusion. Kaohsiung J Med Sci. 2005 Apr;21(4):159-65. have also compared Class III malocclusion to normal occlusion, whereas another one²⁸28 Singh GD, McNamara JA Jr, Lozanoff S. Craniofacial heterogeneity of prepubertal Korean and European-American subjects with Class III malocclusions: procrustes, EDMA, and cephalometric analyses. Int J Adult Orthod Orthognath Surg. 1998 Jan;13(3):227-40. compared this condition between Caucasian and Korean individuals. All these studies found similar results, with the length of the anterior skull base being smaller in Korean individuals with Class III malocclusion and skull base flexion tending to be more acute in Caucasian individuals with the same condition.

Among these seven studies¹⁶16 Rothstein T, Yoon-Tarlie C. Dental and facial skeletal characteristics and growth of males and females with Class II, division 1 malocclusion between the ages of 10 and 14 (revisited)-Part I: characteristics of size form, and position. Am J Orthod Dentofacial Orthop. 2000 Mar;117(3):320-32.^,2020 Andria LM, Leite LP, Prevatte TM, King LB. Correlation of the cranial base angle and its components with other dental /skeletal variables and treatment time. Angle Orthod. 2004 June;74(3):361-6.^,2323 Ishii N, Deguchi T, Hunt N. Craniofacial morphology of Japanese girls with Class II division 1 malocclusion. J Orthod. 2001 Sept;28(3):211-5.^,2525 Johannsdottir B, Thordarson A, Magnusson TE. Craniofacial morphology in 6-year-old Icelandic children. Eur J Orthod. 1999 June;21(3):283-90.^,2727 Kapoor S, Kapoor DN, Jaiswal JN. Cephalometric evaluation of Class II malocclusion in transitional dentition. J Indian Soc Pedo Dent. 2001 Dec;19(4):127-33.^,3030 Lau JWP, Hagg U. Cephalometric morphology of Chinese with Class II division 1 malocclusion. Br Dental J. 1999 Feb;186(4):188-90.^,3737 Yoon SS, Chung CH. Comparison of craniofacial growth of untreated Class I and Class II girls from ages 9 to 18 years: a longitudinal study. Am J Orthod Dentofacial Orthop. 2015 Feb;147(2):190-6. comparing Class II malocclusion to Class I malocclusion, similar results have been reported. For example, individuals with Class II malocclusion had greater anterior and posterior lengths and more obtuse angular measurements regarding the skull base. However, one study²³23 Ishii N, Deguchi T, Hunt N. Craniofacial morphology of Japanese girls with Class II division 1 malocclusion. J Orthod. 2001 Sept;28(3):211-5. reported a smaller length of the skull base in Japanese girls with Class I malocclusion presenting permanent dentition, whereas another³⁰30 Lau JWP, Hagg U. Cephalometric morphology of Chinese with Class II division 1 malocclusion. Br Dental J. 1999 Feb;186(4):188-90. found no significant differences in the skull base flexion compared to normal occlusion. In the study, the compared groups (Class I and Class II) showed no differences in the length of the anterior skull base and flexion of the cranial base.

DISCUSSION

The skull base not only supports and protects the brain but also articulates the cranium with vertebral column, maxilla and mandible. One of its key functions has to do with adaptation and protection, including a shock-absorbing area between brain, face and pharyngeal region, whose growths occur differently. The growth of the skull base occurs by means of a complex balance between sutural growth, prolongation of synchondroses, extensive cortical sliding, and remodelling. This combination allows an increase in the differential growth between base and vault of the skull, expansion of the contours of the various endo-cranial fossae, maintenance of vessel and nerve pathways, and prolongation of the processes, such as hypophysis. Prolongation of the skull base occurs with the growth of synchondroses and direct cortical growth. The cortical sliding of the skull floor produces several degrees of growth movement at different regions, usually towards the ecto-cranial direction, with apposition proportional to the external surface.⁵5 Moyers RE. Ortodontia. 4ª ed. Rio de Janeiro: Guanabara Koogan; 1991.

Enlow³²32 Enlow DH. Crescimento facial. 3ª ed. Rio de Janeiro: Artes Médicas; 1993. has shown that maxilla growth is influenced by the skull base, which in turn, is influenced by the growth of the brain. The mandible, because of its distant positioning, acts more independently, despite being articulated with glenoid fossa, thus being a potential factor influencing the skull base.

To better understand the cephalometric aspects, the skull base is divided into anterior and posterior lengths, the former extending anteriorly from sella turcica (S) to nasofrontal suture (N), and the latter extending from sella turcica to the anterior edge of the foramen magnum, defined as Ba.²¹21 Mouakeh M. Cephalometric evaluation of craniofacial pattern of Syrian children with Class III malocclusion. Am J Orthod Dentofacial Orthop. 2001 June;119(6):640-9. There is a consensus that the length of the anterior skull base corresponds to the linear N-S distance, but the same cannot be said about the posterior region, which corresponds to either S-Ba or S-Ar linear distances.¹⁹19 Dhoptkar A, Bhatia S, Rock P. An investigation into the relationship between the cranial base angle and malocclusion. Angle Orthodontist. 2002 Oct;72(5):456-63.

Björk²2 Björk A. Cranial base development. Am J Orthod. 1955 Mar;41(3):198-255. supported the use of the latter, as it is more easily visualized, with most studies using this measurement. Verjanne and Koski³³33 Varjanne I, Koski K. Cranial base, sagittal jaw relationship and occlusion. A radiological: craniometric appraisal. Proc Finn Dent Soc. 1982 Jan;78(4):179-83. suggested the use of Ba to measure the skull base angle as they considered the S-Ar measurement too distant; Kerr and Adams³⁴34 Kerr WJS, Adams CP. Cranial base and jaw relationship. Am J Phys Anthropol. 1988 Oct;77(2):213-20. used Ba to measure the skull base angle. Bhatia and Leighton³⁵35 Bathia SN, Leighton BC. A manual of facial growth. Oxford: Oxford University Press; 1993. used N-S-Ba, N-S-Art as well as S-Ba and S-Art, and found similar measurements.

According to the other authors,¹⁹19 Dhoptkar A, Bhatia S, Rock P. An investigation into the relationship between the cranial base angle and malocclusion. Angle Orthodontist. 2002 Oct;72(5):456-63. the skull base follows a neural (anterior region) and somatic (posterior region) growth pattern despite its cartilaginous origin (chondrocranium). After birth, especially in the early childhood, the growth of the anterior portion occurs mainly due to the increase in frontal sinus and remodelling of the nasal region, whereas the growth of the posterior region is related to the interstitial growth occurring in the spheno-occipital synchondrosis.

The two segments of the base of the skull form an flexion of 130-135 degrees at the angle formed at the Sela point (center of the sella turcica). This angle (NSBa) has approximately 142 degrees at birth, but decreases to 130 degrees at 5 years old.¹⁹19 Dhoptkar A, Bhatia S, Rock P. An investigation into the relationship between the cranial base angle and malocclusion. Angle Orthodontist. 2002 Oct;72(5):456-63. From 5 to 15 years old, the skull base angle is relatively stable.²³23 Ishii N, Deguchi T, Hunt N. Craniofacial morphology of Japanese girls with Class II division 1 malocclusion. J Orthod. 2001 Sept;28(3):211-5. Other studies suggest that there are no differences in this angle of the skull base during childhood, puberty and adult phase.¹1 Polat OO, Kaya B. Changes in cranial base morphology in difference malocclusions. Orthod Craniofac Res. 2007 Nov;10(4):216-21.^,2323 Ishii N, Deguchi T, Hunt N. Craniofacial morphology of Japanese girls with Class II division 1 malocclusion. J Orthod. 2001 Sept;28(3):211-5.

There is evidence showing that the skull base angle (N-S-Ba) is greater in Class II division 1 malocclusion than in Class I malocclusion or normal occlusion, with this angle not differing between Class II division 2 and Class I malocclusions.¹⁹19 Dhoptkar A, Bhatia S, Rock P. An investigation into the relationship between the cranial base angle and malocclusion. Angle Orthodontist. 2002 Oct;72(5):456-63. In addition, studies comparing Class II malocclusions to normal occlusion or Class I malocclusion¹⁶16 Rothstein T, Yoon-Tarlie C. Dental and facial skeletal characteristics and growth of males and females with Class II, division 1 malocclusion between the ages of 10 and 14 (revisited)-Part I: characteristics of size form, and position. Am J Orthod Dentofacial Orthop. 2000 Mar;117(3):320-32.^,2020 Andria LM, Leite LP, Prevatte TM, King LB. Correlation of the cranial base angle and its components with other dental /skeletal variables and treatment time. Angle Orthod. 2004 June;74(3):361-6.^,2323 Ishii N, Deguchi T, Hunt N. Craniofacial morphology of Japanese girls with Class II division 1 malocclusion. J Orthod. 2001 Sept;28(3):211-5.^,2525 Johannsdottir B, Thordarson A, Magnusson TE. Craniofacial morphology in 6-year-old Icelandic children. Eur J Orthod. 1999 June;21(3):283-90.^,2727 Kapoor S, Kapoor DN, Jaiswal JN. Cephalometric evaluation of Class II malocclusion in transitional dentition. J Indian Soc Pedo Dent. 2001 Dec;19(4):127-33.^,3030 Lau JWP, Hagg U. Cephalometric morphology of Chinese with Class II division 1 malocclusion. Br Dental J. 1999 Feb;186(4):188-90.^,3737 Yoon SS, Chung CH. Comparison of craniofacial growth of untreated Class I and Class II girls from ages 9 to 18 years: a longitudinal study. Am J Orthod Dentofacial Orthop. 2015 Feb;147(2):190-6. found similar results.¹⁶16 Rothstein T, Yoon-Tarlie C. Dental and facial skeletal characteristics and growth of males and females with Class II, division 1 malocclusion between the ages of 10 and 14 (revisited)-Part I: characteristics of size form, and position. Am J Orthod Dentofacial Orthop. 2000 Mar;117(3):320-32.^,2525 Johannsdottir B, Thordarson A, Magnusson TE. Craniofacial morphology in 6-year-old Icelandic children. Eur J Orthod. 1999 June;21(3):283-90.^,2727 Kapoor S, Kapoor DN, Jaiswal JN. Cephalometric evaluation of Class II malocclusion in transitional dentition. J Indian Soc Pedo Dent. 2001 Dec;19(4):127-33. However, two studies³⁰30 Lau JWP, Hagg U. Cephalometric morphology of Chinese with Class II division 1 malocclusion. Br Dental J. 1999 Feb;186(4):188-90.^,3737 Yoon SS, Chung CH. Comparison of craniofacial growth of untreated Class I and Class II girls from ages 9 to 18 years: a longitudinal study. Am J Orthod Dentofacial Orthop. 2015 Feb;147(2):190-6. compared such malocclusions and reported a smaller flexion of the skull base in individuals with Class II malocclusion. This can be explained by the fact that the posterior region of the skull base (S-Ba) forming the S-N-Ba angle might be anteriorly or posteriorly inclined, whereas the anterior region (S-N) might also be inclined anteriorly upwards or downwards, thus causing a variation in either S or N points vertically.³⁶36 Kerr WJS. A method of superimposing serial lateral cephalometric films for the purpose of comparison: a preliminary report. Br J Orthod. 1978 Jan;5(1):51-3. Therefore, variable lengths of the anterior and posterior regions of the skull base can compensate any cranial flexion, that is, a posterior acute angle anteriorly positioned in relation to the mandible can neutralize the cranial flexion through the greater posterior length, thus positioning Ba and mandible posteriorly and vice-versa.²⁰20 Andria LM, Leite LP, Prevatte TM, King LB. Correlation of the cranial base angle and its components with other dental /skeletal variables and treatment time. Angle Orthod. 2004 June;74(3):361-6. However, the skull base length was not assessed.³⁰30 Lau JWP, Hagg U. Cephalometric morphology of Chinese with Class II division 1 malocclusion. Br Dental J. 1999 Feb;186(4):188-90. Despite these findings, the skull base flexion is thought to have no influence on malocclusions,¹1 Polat OO, Kaya B. Changes in cranial base morphology in difference malocclusions. Orthod Craniofac Res. 2007 Nov;10(4):216-21.^,1919 Dhoptkar A, Bhatia S, Rock P. An investigation into the relationship between the cranial base angle and malocclusion. Angle Orthodontist. 2002 Oct;72(5):456-63. whereas there is no consensus among other studies regarding this issue.²¹21 Mouakeh M. Cephalometric evaluation of craniofacial pattern of Syrian children with Class III malocclusion. Am J Orthod Dentofacial Orthop. 2001 June;119(6):640-9.^,2323 Ishii N, Deguchi T, Hunt N. Craniofacial morphology of Japanese girls with Class II division 1 malocclusion. J Orthod. 2001 Sept;28(3):211-5.

24 Singh GD, McNamara JA Jr, Lozanoff S. Morphometry of the cranial base in subjects with Class III malocclusion. J Dent Res. 1997 Feb;76(2):694-703.

25 Johannsdottir B, Thordarson A, Magnusson TE. Craniofacial morphology in 6-year-old Icelandic children. Eur J Orthod. 1999 June;21(3):283-90.

26 Ishii N, Deguchi T, Hunt NP. Morphological diferences in the craniofacial structure between Japanese and Caucasian girls with Class II division 1 malocclusion. Eur J Orthod. 2002 Feb;24(1):61-7.^-2727 Kapoor S, Kapoor DN, Jaiswal JN. Cephalometric evaluation of Class II malocclusion in transitional dentition. J Indian Soc Pedo Dent. 2001 Dec;19(4):127-33.^,3030 Lau JWP, Hagg U. Cephalometric morphology of Chinese with Class II division 1 malocclusion. Br Dental J. 1999 Feb;186(4):188-90.^-3131 Chang HP, Hsieh SH, Tseng YC, Chou TM. Cranial-base morphology in children with Class III malocclusion. Kaohsiung J Med Sci. 2005 Apr;21(4):159-65.

With regard to the Class III malocclusion, it has been reported that linear and angular measurements of the skull base are smaller when compared to other types of malocclusion.¹1 Polat OO, Kaya B. Changes in cranial base morphology in difference malocclusions. Orthod Craniofac Res. 2007 Nov;10(4):216-21. These findings are corroborated by some studies,²¹21 Mouakeh M. Cephalometric evaluation of craniofacial pattern of Syrian children with Class III malocclusion. Am J Orthod Dentofacial Orthop. 2001 June;119(6):640-9.^,3131 Chang HP, Hsieh SH, Tseng YC, Chou TM. Cranial-base morphology in children with Class III malocclusion. Kaohsiung J Med Sci. 2005 Apr;21(4):159-65. although one study¹1 Polat OO, Kaya B. Changes in cranial base morphology in difference malocclusions. Orthod Craniofac Res. 2007 Nov;10(4):216-21. had found smaller angular measurements for Class III malocclusions, despite not being significant.

Asian individuals present a smaller anterior length and a more obtuse angle of the skull base, compared to Caucasians, with this finding comprising the both ethnic and morphological characteristics, according to some authors.²³23 Ishii N, Deguchi T, Hunt N. Craniofacial morphology of Japanese girls with Class II division 1 malocclusion. J Orthod. 2001 Sept;28(3):211-5.^,2626 Ishii N, Deguchi T, Hunt NP. Morphological diferences in the craniofacial structure between Japanese and Caucasian girls with Class II division 1 malocclusion. Eur J Orthod. 2002 Feb;24(1):61-7.^,2828 Singh GD, McNamara JA Jr, Lozanoff S. Craniofacial heterogeneity of prepubertal Korean and European-American subjects with Class III malocclusions: procrustes, EDMA, and cephalometric analyses. Int J Adult Orthod Orthognath Surg. 1998 Jan;13(3):227-40.

CONCLUSIONS

After evaluating all these articles selected for the present systematic review, one can state the following:

REFERENCES

Publication Dates

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