Vertical Cephalometric Characteristics in Class III Malocclusions

Abstract

The phenotypic variety of Angle Class III malocclusion requires in-depth investigation of the skeletal changes from a diagnostic, prognostic and therapeutic perspective alike. The aim of our study was to evaluate the particularities of vertical cephalometric parameters of patients with Class III malocclusions, according to gender and age group. Eight parameters were analyzed on lateral cephalograms of patients with Class III malocclusions and, comparatively, on lateral cephalograms of a group with Class I malocclusions. The results, grouped by gender and age, suggest that values of the gonial angle, values of the angles formed between the mandibular plane and the anterior cranial base, respectively the Frankfurt Horizontal plane were higher for patients with Class III malocclusions, differences being statistically significant especially after the pubertal growth period. Class III patients had lower values for the upper gonial angle and higher ones for the lower gonial angle. Furthermore, for patients with Class III malocclusions the Jaraback ratio decreased, based on the significantly higher values of the anterior facial height. No sexual dimorphism was associated with variation of the investigated parameters.

Introduction

Angle Class III malocclusion is one of the most severe dento-maxillary anomalies in terms of its complexity, variability of clinical expressiveness, aesthetic impairment, as well as its sometimes-reserved prognosis.

Under the umbrella of Angle's classification, the group of Class III malocclusion, which is characterized by a mesial relationship of the buccal groove of the lower first permanent molar to the mesiobuccal cusp of the upper first permanent molar, comprises a great clinical and etiological diversity, involving skeletal, dento-alveolar and facial soft tissues changes.

Starting from Angle’s classification, the notion of skeletal class was introduced [1, 2, 3]; this term describes the relative position of the maxillary and mandibular bases in the sagittal plane, which is established based on the interpretation of the lateral cephalogram.

Considering that the imbalances that interest the Class III malocclusion are not confined only in the antero-posterior direction but include all spatial reference planes, the study of vertical changes in patients with this type of malocclusions has a practical applicability for the orthodontist/maxillofacial surgeon from a diagnostic, prognostic and therapeutic perspective.

Aim

The study aims to highlight the vertical skeletal characteristics of patients with Class III malocclusion, in order to contribute to the knowledge of the specific features of this type of anomaly for the study group.

Materials and Methods

To achieve this goal, a cross-sectional descriptive study was conducted at the Orthodontic Dento-Facial Orthopedics Department of “Carol Davila” University of Medicine and Pharmacy, Bucharest, Romania, investigating several specific vertical cephalometric parameters in patients with Class III and Class I malocclusion, according to gender and age group.

The criteria for inclusion in the study group (group A) was represented by the diagnosis of Class III dental (based on study models) and skeletal (based on the angular cephalometric parameter ∡ANB on lateral cephalogram analysis) malocclusion.

Similarly, the control group (group B) was selected based on Class I dental and skeletal malocclusion diagnosis.

The inclusion and exclusion criteria in this study are shown in Table 1.

Table 1.

Selection criteria for the study and control group

Inclusion criteria	Exclusion criteria
Group A -Mesial first permanent molar occlusion -∡ANB < 2º Group B -Neutral first permanent molar occlusion -∡ANB 2º-4º	1. Previous orthodontic treatment 2. Genetic syndromes/ congenital malformations 3. Mesial drifting of posterior teeth 4. Extraction of permanent teeth 5. History of craniofacial trauma 6. Incomplete/poor quality medical records(lateral cephalograms, dental casts)

In the first stage, the subjects were selected according to the data from the clinical data sheet and the static occlusion analysis on the study model.

Afterwards, following the lateral cephalogram analysis, according to the value of the ∡ANB angle, the research groups were established.

For each subject, gender and age were recorded.

As a routine procedure, a signed informed consent for releasing diagnostic records for scientific purposes is always obtained from the patients or legal guardians of the patients prior to the beginning of treatment.

The present study was conducted in accordance with the Helsinki Declaration of 1975, revised in 2000 and it did not need ethic approval, as our research just used measurements performed on lateral cephalograms, not involving clinical activities on patients.

Based on the established criteria, 75 subjects were included in the research group, group A consisting of 45 subjects (66% female subjects/34% male subjects), and group B consisting of 30 subjects (60% female subjects/40% male subjects) (Figure 1)

Figure 1.

Gender distribution of subjects in the research groups

The ages of the patients included in the study varied between 8 and 20 years, with similar age ranges between the study and the control groups, respectively ages between 8 and 19 years for patients in group A and between 9 and 20 years for patients in group B.

In order to analyze the relationship between the changes in cephalometric parameters in the vertical plane and the chronological age of the patients, each research group was divided into two age groups (AG) according to whether or not they had reached the pubertal growth stage, ages chosen according to the data in other studies [4, 5, 6].

Thus, the first age group (AG1) included female subjects aged between 8 and 13 years and male subjects aged between 8 and 15 years.

The second age group (AG2) comprised female subjects over 14 years and male subjects over 16 years.

In both research groups, 60% of the subjects were included in AG1 and the rest in AG2.

Lateral cephalograms used in the study were made under standardized conditions, in the same radiology centre.

Interpretation of the cephalograms was carried out in the same time interval for all the selected subjects, by a single examiner, who used the technique of copying the contours on tracing paper, manually marking the anthropometric points of interest for the evaluation of the studied cephalometric parameters (Table 2).

Table 2.

Anthropometric points used in the study [].

Anthropometric point name (abbreviation)	Description
Nasion (N)	the most anterior point of the nasofrontal suture in the median plane
Sella (S)	constructed point in the median plane, midpoint of the hypophysial fossa
Point A, subspinale (A)	the deepest midline point in the curved bony outline of the maxilla
Point B, supramentale (B)	the most posterior point in the outer contour of the mandibular alveolar process/ mandible, in the median plane
Gnathion (Gn)	midline point, between the most anterior and the most inferior point of the bony chin
Menton (Me)	midline point, most caudal point in the outline of the symphysis, regarded as the lowest point of the mandible
Orbitale (Or)	lowermost point of the inferior border of the orbit
Porion (Po)	the point where the line starting from the Orbitale becomes tangent to the upper contour of the external auditory meatus
Articulare (Ar)	point of intersection of the posterior margin of the ascending ramus and the outer margin of the cranial base
Gonion (Go)	constructed point, the intersection of the line’s tangent to the posterior margin of the ascending ramus and the mandibular base

From these anthropometric points, it was possible to study a number of 8 cephalometric parameters (5 angular, 2 linear and 1 expressed as a percentage) (Figure 2), summarized in Table 3.

Figure 2.

(a) Lateral cephalogram and (b) analyzed cephalometric parameters (1.∡Ar-Go-Me, 2.∡Ar-Go-N, 3.∡N-Go-Me, 4.∡SN-GoGn, 5.∡FMA, 6. NGn, 7. SGo)

Table 3.

The cephalometric parameters studied and the normal variability for caucasian patients

Cephalometric parameter	Normal values
Gonial angle (∡Ar-Go-Me)	123-137 º [7]
Upper gonial angle (∡Ar-Go-N)	52-55º [7]
Lower gonial angle (∡N-Go-Me)	70-75º [7]
Angle between the mandibular plane and the anterior cranial base (∡SN-GoGn)	32º [8]
Angle between the mandibular plane and the Frankfurt horizontal plane (∡FMA/∡OrPo-GoMe)	22-28º [9]
Anterior facial height (NGn)
Posterior facial height (SGo)
Jarabak ratio-(SGo/NGn)x100	59-63% [7]

In order to highlight skeletal changes in the vertical plane as clearly as possible, cephalometric parameters were chosen from several lateral cephalogram analyses (Tweed analysis-∡FMA; Steiner analysis-∡SN-GoGn; Jaraback analysis-∡Ar-Go-Me, ∡Ar-Go-N, ∡N-Go-Me, anterior facial height, posterior facial height and Jarabak ratio between posterior and anterior facial height) and the limits of normal variability for Caucasian patients were set based on previously published data from the literature (Table 3).

Statistical data analysis

The collected data was centralized and statistically processed using the Microsoft Office Excel program (2019).

Quantitative variables were expressed as mean values (Mean) with standard deviations (SD), minimum values (Min) and maximum values (Max).

The values were tested for distribution using the Shapiro-Wilk test, the parametric distribution allowing the use of the T-Test for comparative analysis of the results.

The level of statistical significance (p) was set at a maximum of 0.05.

Results

The results show significant differences for all vertical parameters except posterior facial height (Table 4).

Table 4.

Comparison between the values of the cephalometric parameters obtained for the two study groups, analyzed by age group.

Age group	GROUP A				GROUP B				p
	Mean	SD	Min	Max	Mean	SD	Min	Max
	GONIAL ANGLE ∡ Ar-Go-Me (º)
AG1	127.80	5.36	116.58	139.89	124.48	1.54	122.38	128.65	0.102
AG2	129.24	1.65	125.12	130.68	120.30	6.35	112.16	127.71	0.047
	UPPER GONIAL ANGLE ∡ Ar-Go-N (º)
AG1	51.36	2.37	46.76	56.90	54.38	2.21	51.55	58.43	0.037
AG2	51.79	2.11	47.77	55.23	52.48	2.39	50.01	57.27	0.375
	LOWER GONIAL ANGLE ∡ N-Go-Me (º)
AG1	76.42	3.38	69.82	88.41	70.14	2.65	66.51	75.07	0.011
AG2	77.44	3.13	72.51	82.56	67.82	5.19	60.60	75.59	0.026
	∡ SN-GoGn (º) ANGLE
AG1	32.39111	3.145926	27.32	43.9	29.81	2.8	24.75	36.37	0.149
AG2	34.264	5.7888	26.45	44.43	25.37	4.35	18.76	32.43	0.043
	∡ FMA (º) ANGLE
AG1	24.86	3.91	19.89	30.11	22.73	2.38	18.33	29.88	0.217
AG2	26.34	2.26	23.02	33.89	18.82	4.71	10.30	25.73	0.008
	POSTERIOR FACIAL HEIGHT S-Go (mm)
AG1	69.05	4.65	60.88	78.05	67.04	7.53	58.70	79.12	0.321
AG2	75.54	2.20	72.56	79.07	75.87	1.56	73.83	78.73	0.420
	ANTERIOR FACIAL HEIGHT N-Me (mm)
AG1	107.62	9.31	92.51	131.22	101.82	9.15	91.53	115.96	0.181
AG2	122.58	5.68	116.22	136.80	106.58	4.87	101.7	113.94	0.006
	JARABAK RATIO (%)
AG1	64.43	2.89	56.36	69.77	65.78	3.08	60.27	70.81	0.264
AG2	61.94	2.48	57.80	66.72	71.42	4.71	64.80	77.41	0.008

The values of the gonial angle (∡Ar-Go-Me) were higher for study group A, although the mean values in both cases were within the normal range of variability according to the Jaraback analysis.

However, the differences between the two research groups for this angle were statistically significant only in the second age group (AG2).

Analysing the gonial angle by the two segments, respectively the upper and the lower portion of the gonial angle, significant differences were noted between the subjects in group A and group B.

Thus, for the subjects in group A the superior gonial angle (∡Ar-Go-Me) was significantly lower than for those in group B, the differences being statistically significant in the first age group (AG1), while the lower gonial angle (∡N-Go-Me) was significantly higher than for the subjects in group B.

For the latter parameter, the differences between the groups were the most important, statistically significant for both age groups.

Compared to the limits of normal variability established by Jarabak, the values recorded for the subjects in group A, both age groups, were discretely reduced for the upper gonial angle and slightly increased for the lower gonial.

The results of the statistical analysis revealed that subjects in group A had higher values of the ∡SN-GoGn and ∡FMA angles, the differences being statistically significant only for the second age group.

Regarding the posterior facial height, no differences were noted between the research groups for any age group, but when comparing the results obtained for the anterior facial height, statistically significant differences were highlighted for the second age group, in the sense of higher values for subjects in group A.

The Jaraback ratio, as the ratio between the posterior and anterior facial height expressed in percentages, revealed significantly lower values for subjects in group A compared to those in group B, but only in the second age group.

For group A, no statistically significant differences were noted for cephalometric parameters compared between the two genders (Table 5).

Table 5.

Comparison between the values of the cephalometric parameters obtained for group A, analyzed by gender.

Cephalometric parameter	Female		Male		p
	Mean	SD	Mean	SD
∡Ar-Go-Me (º)	127.60	4.44	130.12	2.38	0.206
∡Ar-Go-N (º)	50.99	2.15	52.64	1.81	0.147
∡N-Go-Me(º)	76.61	4.18	77.48	1.40	0.368
∡SN-GoGn (º)	33.66	5.20	32.57	1.65	0.365
∡FMA (º)	25.65	3.26	26.08	1.28	0.418
S-Go (mm)	72.08	4.15	70.93	5.63	0.364
N-Gn (mm)	114.16	10.43	117.68	7.87	0.424
S-Go/N-Gn (%)	63.54	3.25	63.19	2.02	0.434

Comparatively analyzing the results for each study group separately, we did not notice statistically significant differences between the values obtained for the two age groups.

Exceptions are the linear measurements for the posterior and anterior facial height, which in the case of group A revealed significantly increased values for the second age group.

Discussions

Class III malocclusion has a great phenotypic variety, of different severity, from discrete changes to severe disorders, with multiple complications and consequences on the patient's quality of life.

Therefore, in-depth knowledge of the characteristics of this anomaly, also highlighted by specific changes in some cephalometric parameters, allows not only a correct diagnosis but also guidance on the treatment plan.

In this study, the values of the gonial angle (∡Ar-Go-Me) were higher for patients with Class III malocclusion, suggesting the pattern of clockwise mandibular rotation.

The results of our research are in agreement with other studies [10], but the previousely published data didn’t reach a consensus regarding the specific variations of the gonial angle in patients with Class III malocclusion.

Al-Shamout R. et al. (2012) noted that the gonial angle and bigonial diameter increase with age, an expression of the change in mandibular morphology with time through continuous processes of bone remodelling.

The contour of the lower border of the horizontal ramus of the mandible, and especially the goniac angle, correlates with the form and function of the masticatory muscles [10].

The results of the aforementioned study indicated that male subjects had higher parameter values compared to female subjects.

Further research by Larrazabal-Moron C. and Sanchis-Gimeno J.A. (2018) [11] in the Caucasian Mediterranean population show that the gonial angle in men aged 16-21 years is significantly higher than that of women in the same age range, but there is no significant difference in the older age group (21-31 years old).

For the group analyzed in our study, there were no significant differences between the male and female gonial angles, a result in agreement with other studies such as those carried out by Park et al. (2017) [12] and Radhakrishnan et al. (2017) [13].

In a 1998 study, Singh, McNamara, and Lozano found that for a group of 73 subjects aged 5 to 11 years, gonial angle values were lower in subjects with Class III malocclusion compared to those of Class I malocclusion [14].

Riolo et al. (1974) observed a variation in mean values for this angle depending on age and gender [15].

Thus, for male subjects, a reduction in the average values of the gonial angle from 132º (6 years) to 124º (16 years) was noted.

Similarly, for female subjects the values ranged from 130º (6 years) to 123º (16 years).

According to Budipramana et al. (2021), the gonial angle is influenced by age, sex, bone cortical thickness, condylar growth and the strength of the mandibular masticatory muscles, which may represent an argument for the heterogeneous results in the specialized literature [16].

Regarding the differentiated analysis on the two segments of the gonial angle, namely the upper portion that provides information on the prognosis of mandibular growth in the horizontal plane and the lower portion that describes the direction of mandibular growth in the vertical plane [7,17], using Jarabak's method, in our study we observed an important variation of the two segments of the gonial angle, especially in its lower portion.

The values recorded for the upper gonial angle were significantly lower in subjects with Class III malocclusion compared to those with Class I malocclusion.

The results for the lower gonial angle were higher in patients with Class III malocclusion, regardless of age.

Also, comparing the values recorded for the group of patients with Class III malocclusion with those established by Jarabak as limits of normal variability, the gonial angle in its upper portion was somewhat reduced, while in its lower portion the gonial angle was slightly enlarged.

Thus, the variation of the two segments of the goniac angle suggests the existence of a predominantly vertical mandibular growth pattern in patients with Class III malocclusion, with a tendency to decrease overbite in the frontal area during growth.

Rubika J. et al., observed in the study carried out in 2015 that the upper gonial angle was the same regardless of facial pattern.

The same authors conclude that the gonial angle and the lower gonial angle can be used as indicators of the mandibular growth pattern [18].

Using the Björk-Jarabak cephalometric analysis, Rodriguez-Cardenas et al. (2014) noted that patients with skeletal Class III malocclusions had significantly higher gonial angle and upper gonial angle values compared to the other skeletal classes [19].

The authors of a study carried out on a population in Indonesia [16] conclude that the upper gonial angle varies with the position of the mandibular vertical ramus, while the lower portion of the gonial angle is influenced mostly by the anterior and posterior facial height, as well as mandibular size and rotation.

In agreement with the variation of the gonial angle, in our study statistically significant differences were noted between the two analyzed groups regarding the vertical position of the horizontal mandibular ramus relative to the anterior cranial base (expressed by ∡SN-GoGn) and relative to the Frankfurt horizontal plane (indicated by ∡FMA).

Values obtained for ∡SN-GoGn and ∡ FMA angles were higher in case of Class III malocclusion, the differences being statistically significant for subjects who have passed the puberty.

Schudy F.F. [20] introduced the term "facial divergence" in his 1965 article, dividing the study sample into three groups according to the values of the ∡SN-GoGn angle.

In a study with similar methodology, conducted on a group of Caucasian patients from Brazil [21] for patients with Class III malocclusion, the ∡SN-GoGn and ∡FMA angles were within the limits of normal variability, but the values were discretely lower compared to those registered for patients in the control group, without the differences being statistically significant.

On the other hand, there are also studies [22] that identified, similar to our study, significantly higher values of the ∡FMA angle for patients with Class III malocclusion.

For Jarabak's ratio, we recorded significantly lower values for patients with Class III malocclusion, suggesting that these patients generally present with posterior mandibular rotation and, by extrapolation, in some cases, a tendency toward skeletal open bite.

Most authors agree that a favorable outcome of an early treatment of Class III malocclusion is associated with a smaller gonial angle and facial hypodivergence, while an unfavorable outcome is related to a vertical growth pattern [23, 24].

However, the differences between the values of the Jarabak ratio were not due to the variation of the posterior facial height, which was similar for subjects with Class III and Class I malocclusion, but to the significantly higher values for the anterior facial height in the case of patients with Class III malocclusion who have passed the puberty stage.

Similar observations have been highlighted in other studies.

Nanda, cited by Ligthelm-Bakker et al. (1992) recommended that anterior facial height should be considered for cephalometric analysis because posterior facial height does not vary significantly between different facial types [25].

And in the case of anterior facial height, the specialized literature sometimes highlights contradictory results, the differences may be due to the lack of homogeneity of the research method, the study groups of different ages and ethnicity or the impressive phenotypic variability of this anomaly.

In evaluating vertical skeletal components in patients with Class III malocclusion, Ellis, and McNamara (1984), Guyer et al. (1986) and Ishii et al. (2002) reported an increase in anterior facial height, while the findings of Kao et al. (1995) and Mouakeh (2001) indicated decreased anterior facial height in subjects with this anomaly [1,2,26, 27, 28].

According to Rakosi (1993) there are two hypotheses regarding the relationship between the gonial angle and anterior facial height.

According to the first hypothesis, an increased gonial angle may be due to adaptive phenomena to the increase in anterior facial height.

However, adaptation can also occur in the posterior part of the facial skeleton due to the posterior rotation at the level of the temporomandibular joint, thus keeping the gonial angle unchanged.

The second hypothesis refers to an adaptation of the height of the alveolar processes to an increased gonial angle a priori (and not vice versa) thus resulting in an increase in the anterior facial height [7].

Regarding gender, in our study, there were no statistically significant differences in the investigated cephalometric parameters between female and male subjects.

However, there are specialized studies [5] that indicated that Class III malocclusion is associated with a significant degree of sexual dimorphism in terms of craniofacial parameters, especially after puberty.

In this context, the authors suggest that, within the studies carried out for this type of anomaly, male and female subjects should be investigated in separate groups.

Conclusions

The study revealed a series of cephalometric changes specific to the Class III malocclusion patients included in the study group.

Thus, we concluded that:

Values of the gonial angle were higher for subjects with Class III malocclusions compared to those with Class I malocclusions, differences becoming more emphasized after puberty.

Patients with Class III malocclusion presented reduced values of the upper gonial angle, respectively higher values of the lower gonial angle. These vertical changes suggest a previsional tendency of reduction of anterior overbite with growth, resulting in open bite; this occlusal feature, associated with Class III malocclusion is generally considered an unfavourable evolution.

Gonial angle values correlated with changes in anterior facial height, increased for patients with Class III malocclusions compared to those with Class I. Similar to the other results, statistically significant differences were highlighted for the group of patients over the age of puberty.

The angulation of the horizontal mandibular ramus relative to the anterior cranial base and the Frankfurt Horizontal plane varied significantly between the study and the control group, being steeper for subjects with Class III malocclusion.

Values of the investigated cephalometric parameters do not show sexual dimorphism.

Our research emphasizes the importance of studying the changes that appear in the vertical plane in patients with Class III malocclusion from a young age, as possible aggravating factors.

However, our results must be viewed in light of the associated limitations (small number of subjects included in the study and of selected cephalometric parameters).

Thus, in order to continue the research, it is necessary, on the one hand, to increase the number of subjects included in the study so that the population group is representative, and on the other hand, to correlate the results with other cephalometric parameters.

Conflict of interests

The authors have no conflict of interest to declare.