Eman A. Namankani,* BDS, MSc, Ortho Certificate
Mohammed T. Bukhary,** BDS, DOrth RCS, MOrthRCS, MDORCPS, PhD
*Riyadh Al Kharj Military Hospital, Riyadh, Saudi Arabia, ** College of Dentistry, King Saud University, Riyadh, Saudi Arabia

The purpose of this study was to investigate the morphologic characteristic of the craniofacial complex of Saudi adult females with Class III malocclusion. Lateral cephalometric radiographs of 30 Saudi adult females with Class III malocclusion (ages 18 to 28 years) were selected from the pretreatment orthodontic files of College of Dentistry of King Saud University. Cases were analyzed and compared with a Class I control group that was matched for age and sex. The Saudi females with Class III malocclusion exhibited a distinct craniofacial morphologic characteristic that was manifested in a combination of alterations in angular and linear measurements on the lateral cephalogram.  The anterior (S-N), posterior (S-Ar) and total cranial base (S-Ar) linear measurements were significantly shorter, and the cranial base angle (N-S-Ar and N-S-Ba) was significantly smaller in Class III than in control. Maxillary length (ANS-PNS) was significantly smaller, and the maxilla was more posteriorly positioned in the patients with Class III malocclusion. The mandible and chin position were prognathic, and there was increase in total mandibular length (Ar-Pog) accompanied by obtuse gonial (Ar-Go-Me) angle and steeper mandibular plane. Both the ramal height (Ar-Go) and the posterior facial height were significantly shorter in Class III malocclusion than in control. Dental compensation in the patients with Class III was manifested by protrusion of the maxillary incisors and retrusion of mandibular incisors. There was tendency to open bite in these Class III malocclusions. The soft tissue reflects the underlying skeletal pattern by retrusion of upper and lower lips to esthetic line, and smaller nasiolabial angle.

Class III malocclusions are considered one of the most complex and difficult orthodontic problems to diagnose and treat.^1-3 The prevalence of this type of malocclusion in Caucasians ranged from 0.8% to 4%,^4-6 but rises to as much as 12% among the Chinese,^{1, 7} whereas it ranged from 4% to 13% among the Japanese.^2,8  A relatively high prevalence of Class III malocclusion has been observed in some Mediterranean and Middle Eastern populations.  Toms⁹ investigated the observation reported by Jones¹⁰ and confirmed that the prevalence of Class III malocclusion in the Saudi Arabian population was higher than the Western sample with an incidence of 9.4%. Previous studies have found the prevalence of Class III malocclusion in Egyptians, Syrians and Lebanese to be 10.5%, 14% and 5.1% respectively.^11,12

Class III malocclusion is not described  by a single feature and in fact several authors^{1,4,6-9,13-20} found that Class III malocclusion was associated with a wide variety of underlying skeletal and dental patterns. The size and relative positions of the cranial base, the maxilla and the mandible in Class III malocclusion affected the position and the relationships of the teeth resulting in various facial appearances.

Sanborn¹³ concluded that the main difference between Class III malocclusion and the normal occlusion was in the mandible.  The role of the mandible in the production of Class III malocclusion was not only an overgrowth of the mandible, but it was an abnormal morphologic relation of the ramus and the body of the mandible in conjunction with poor relation to the cranium.

Dietrich¹⁴ divided a sample of patients who had negative ANB angles into three maturation levels based on tooth eruption.  Deciduous, mixed and permanent dentition Class III samples of patients were compared with Class I sample of patients with corresponding maturation levels.  The results showed that the incidence of pure mandibular prognathism increased from 23% in the primary dentition and 20% in the mixed dentition to 31% in the permanent dentition.  The corresponding figures for pure maxillary skeletal retrusion were 26%, 44% and 37%, respectively.

Dietrich¹⁴ further noted that mandibular prognathism was mainly due to positional deviation of the mandible relative to the cranial base, whereas maxillary retrognathism was caused primarily by inadequate length of the maxillary base.

Ellis and McNamara¹⁵ analyzed a sample of adult Class III individuals who were selected on the basis of molar relationship.  Their results indicated that 30.1% of the sample patients had a combination of maxillary skeletal retrusion and mandibular skeletal protrusion.   Pure maxillary retrusion and pure mandibular prognathism were found in 19.5% and 19.2% respectively, of the sample of patients. 

Numerous studies^{1,6,8,9,13-15,17,19} have been conducted to determine the morphologic variability of craniofacial complex in patients with Class III malocclusion.  These studies have shown that the term Class III malocclusion is not a single diagnostic entity but can result from numerous combinations of skeletal and dentoalveolar component.

Battagel¹⁷ carried out a cephalometric study to identify the aetiological features associated with Class III malocclusion. The sample of the study consisted of 495 cephalometric radiographs divided into Class III malocclusion group and control group. The Class III sample and the control group were further divided into four age groups.  In addition, males and females were examined separately so the total subgroups of the study were eight. The findings of the study confirmed the suggestion that the aetiology of Class III malocclusion was multifactorial.

Lew and Foong⁷ analyzed the cephalometric radiographs of adult Chinese patient with skeletal Class III malocclusion. The subjects were classified into one of six possible anteroposterior skeletal subtypes. The results indicated that majority of Class III malocclusion in males was due to prognathic mandible. On the other hand, most of females with true Class III malocclusion had normal mandible and hypoplastic maxillae.

Baik et al.¹⁹ analyzed the lateral cephalometric radiographs of Korean adult with Class III skeletal malocclusion planned for surgical correction of Class III skeletal relationship. The measurements were compared to the measurements of normal adult Korean.   They concluded that in Asians, Class III malocclusion was more likely to be due to mandibular prognathism and less likely as a result of maxillary deficiency compared to Caucasian counterparts.

There was a deficiency in the comprehensive description of Class III malocclusion of the Saudis in the literature. The lack of such study stimulated the interest to conduct the present study. The aim of this study was to identify the morphologic characteristics of craniofacial structures in a sample of Saudi adult females with Class III malocclusion and compare the results to control females with normal occlusion.

The study group consisted of 30 pretreatment lateral cephalometric radiographs of adult Saudi females with Class III malocclusion. The radiographs were derived from the files of patients diagnosed with skeletal Class III malocclusion at the Orthodontic Clinic in  College of Dentistry of King Saud University. The criteria for selection included (1) Adult Saudi ethnicity patients 18 years of age or above (2) Class III skeletal relationships [ANB > -1°] (3) Cross bite of anterior teeth [Overjet > -1 mm] (4) No previous orthodontic treatment (5) No trauma or jaw fracture (6) No cleft palate or craniofacial syndrome (7) No anterior mandibular shift from rest to occlusal position.

The control group was selected from the pool of cephalometric radiographs belonging to the undergraduate dental students of King Saud University. Out of 230 radiographs, 30 lateral cephalometric radiographs of adult Saudi females were selected as control group. The criteria for selection include (1) Adult Saudi ethnicity student 18 years of age or above (2) Normal skeletal relationship [ANB = 1°- 3°] (3) Normal overjet and overbite [2-4 mm] (4) No previous orthodontic treatment (5) No cleft palate or craniofacial syndrome.

The cephalographs of the study and the control group were traced by the investigator and cephalometric reference points were determined with the use of a hard 4H pencil on acetate tracing paper in predetermined order (Fig. 1).  For bilateral structures and double images, the midpoint was chosen by construction. Each radiograph was traced twice and the averages of the two measurements used in the subsequent analysis as recommended by Battagel.¹⁷

Landmarks were digitized into an X-Y coordinate system with the Jiffy Orthodontic Evaluation (JOE 32) computer program (Rocky Mountain Orthodontics). Although 23 anatomical landmarks were needed for analysis, each radiograph was digitized by the investigator using 138 points that was required by the software to complete the digitization. The errors of the measurements method was evaluated by repeated measurements of thirty cephalographs, retraced and redigitized, after six weeks interval.  Double determination method and coefficient of reliability were applied for the evaluation of the intra- and inter-examiner reliability.  The craniofacial structural relationships were divided into several categories for analysis: cranial base, maxillary, mandibular, dentoalveolar and soft tissue measurements (Figs. 2-6).

The resulting measures were added, the means, standard deviations for the Class III sample patients and the control group were calculated with the use of the SPSS version 10 statistical package.

Unpaired t-tests were performed to assess the differences between the Class III group and control subjects.  The significance of the difference was presented as one asterisk (*) to indicate significance difference at 5% level of confidence where P<0.05, (**) indicate high significant difference at 1% level of confidence where P<0.01, (***) indicate very high significant difference at 0.1% level of confidence where P<0.001, and (NS) indicating no significant difference.

Cephalometric Landmarks

The following anatomical landmarks were identified and located for digitization. The definition of each landmark was presented below. The definitions of landmarks were taken from Bhatia and Leighton, ²² and Riolo et al.²³

1.  (N)     Nasion, the most anterior point on the frontonasal suture, in adults the suture may be impossible to identify, the depth of the notch at the frontonasal junction is then used instead.

2.  (S)     Sella Turcica, the center of the pituitary fossa of the sphenoid bone determined by inspection.

3.  (Ba)   Basion, the lowest point on the anterior border of the foramen magnum. Radiographically, the tip of the triangular outline of the cortical plate of the basilar part of the occipital bone as it extended from the floor of the middle cranial fossa to the under surface of the cranial base.

4.  (Ar)    Articulare, the point of intersection between the posterior border of the mandibular condyle and the lower border of the cranial base.

5.  (Or)    Orbitale, the most inferior point on the lower border of the bony orbit.

6.  (Po)   Porion, the most superior point on the radiolucency of the external and internal auditory meati. It is located posterior to the mandibular condyle and posterior clivus.

7.  (ANS) Anterior nasal spine, the tip of the median, sharp bony process of the maxilla at the lower margin of the anterior nasal opening.

8.  (PNS) Posterior nasal spine, the most posterior point at the sagittal plane on the bony hard palate.

9.  (A)     A-Point, the deepest point on the concave outline of the upper labial alveolar process extending from the anterior nasal spine to prosthion.

10.(UIE)   Upper incisor edge, the tip of the most prominent upper incisor crown.

11.(UIA)  Upper incisor apex, the root apex of the most prominent upper incisors.

12.(Go)   Gonion, the midpoint at the angle of the mandibule.

13.(Me)   Menton, the lowest point on the lower border of the mandibular symphysis.

14.(Pog)  Pogonion, the most anterior point on the mandibular symphysis.

15.(B) B-point, the deepest point on the bony curvature between the crest of the alveolus (infradentale) and pogonion.

16.(LIE)   Lower incisor edge, the tip of the most prominent lower incisor crown.

17.(LIA)   Lower incisor apex, the root apex of the most prominent lower incisors.

18.(Pr)    Pronasale, the most prominent or anterior point of the nose tip.

19.(Cm)   Columella point, the most anterior point on the columella of the nose.

20.(Sn)    Subnasale, a point located at the junction between lower border of the nose and the beginning of the upper lip at the mid-sagittal plane.

21.(UL)    Laberale Superius, a point located at the maximum convexity of the vermilion border most prominent in mid-sagittal plane.

22.(LL)    Laberale inferius, the most prominent point on the vermilion border of the lower lip in the mid-sagittal plane.

23.(SPog) Soft tissue pogonion, the most prominent or anterior point on the soft tissue                chin in the mid-sagittal plane chin

The means and standard deviations of the linear and angular cephalometric variables of the Class III malocclusion and Class I normal occlusion groups are presented in Table 1 to 5.  The intra- and inter-examiner errors were found to be small and acceptable and the coefficient of reliability showed that they were highly correlated with each other.

Cranial Base Measurements

The anterior, posterior and total cranial base lengths, as determined by the measurements of S-N, S-Ar and N-Ar, and cranial base angle (N-S-Ar and N-S-Ba) were smaller for Class III Saudi females as compared to the control.  The mean differences were statistically significant at P<0.01 and P<0.001.

Maxillary Skeletal Measurements

The anteroposterior position of the maxilla relative to the cranial base (as indicated by S-A, Ar-A linear measurements and S-N-A angle) was significantly retrusive in the class III Saudi females as compared to the control. The convexity (A|N-Pog) and effective maxillary length (ANS-PNS) were also significantly smaller (P <0.001) than control group.

Mandibular Skeletal Measurements

The results showed that, the measurements of the mandibular skeletal relationship were larger for class III Saudi females as compared to the control except for S-Go, Ar-Go linear measurements and A-N-B angle which were smaller in Class IIII group. On the other hand, the means difference were significant for the measurements except for ANS-Me, N-Me, Go-Pog linear measurements and S-Ar-Go angle.

Dentoalveolar Relationship

The position of the maxillary and mandibular incisors was evaluated. Saudi females with Class III malocclusion showed protruded upper anterior teeth and retruded lower anterior teeth as compared to control. The interincisal angle was significantly more obtuse in patients with Class III malocclusion. The incisor overjet and overbite were significantly smaller (P<0.001) than control group.

Soft Tissue Relationship

The results showed that the upper and lower lips were retruded in Class III Saudi females as compared to the control Saudi females at a very high significant level of difference (P<0.001). The nasiolabial angle was smaller for Class III Saudi females as compared to control at a significant level of (P<0.01).

This retrospective comparative study was based on the measurements of the cephalometric radiographs of adult Saudi females with Class III skeletal malocclusion and control group with normal occlusion. The craniofacial structural relationships were divided into five craniofacial structures: the cranial base, the maxillary skeletal, the mandibular skeletal, the dentoalveolar, and the soft tissue. Similar divisions of the components of Class III malocclusion were used. ^8,15,17 In the present study, a total of 40 variables, 22 linear and 18 angular, were used for comparison between the Class III malocclusion and the control group of the Saudi females. Out of the 40 variables, 34 variables showed significant differences that represent 85% of the comparisons.

Cranial Base Relationship

The first components measured and compared was the cranial base. The anterior cranial base dimension (S-N) was significantly shorter in Saudi females with Class III malocclusion compared to the control group at 1% level of significance. This finding was in agreement with the results of Jacobson et al.⁶, Ishii et al.⁸, Sanborn¹³, Baik et al.¹⁹, Hayashi²³, Moukeh²⁴, Jarvinen²⁷, Bukhary and Al Namankani²⁸  but disagreed with Toms⁹ and Guyer et al.¹⁶ who found no significant difference between the Class III malocclusion and control group. The posterior cranial base measured from S to Ar also showed significant difference between Saudi females with Class III malfhocclusion and the control group at 1% level of significance. This was in the agreement with the findings of Ngan et al.¹, Björk⁴, Toms⁹, Baik et al.¹⁹, Bukhary and AlNamankani²⁸.  Other investigators measured the posterior cranial base dimension from different anatomical landmarks (S to Ba).  Their findings were conflicting. Battagel¹⁷ found significant difference whereas Jacobson et al.⁶ reported no significant difference between the Class III malocclusion and the control. The total cranial base measured from point N to Ar was also significantly shorter in Saudi females with Class III malocclusion compared to the control group at 1% level of significance. This finding was in agreement with the results of Baik et al.¹⁹ but disagreed with Ngan et al.¹ and Toms⁹ who found no significant difference between the Class III malocclusion and control group. The short total cranial base may have resulted from the short anterior and posterior cranial bases, but the angle between the anterior and the posterior cranial bases, known as the cranial base angle or the saddle angle has a major role to play regarding the dimension of the total cranial base which must be considered and evaluated. In this study, the cranial base angle or the saddle angle was measured by the angle N-S-Ar and N-S-Ba.  The two measurements indicated smaller cranial base angle for the Class III malocclusion compared to the control group for Saudi females.  This finding may support the role of this angle in producing Class III skeletal relationship as proposed by Björk⁴ and agreed with the findings of several investigators including Battagel^17, Moukeh²⁴, Jarvinen²⁷ and, Bukhary and AlNamankani.²⁸  The evaluation of the first component gives the picture that the sample of a Saudi females with Class III malocclusion had shorter cranial base and smaller cranial base angle compared to the control.

Maxillary Skeletal Measurements

The most significant differences between Saudi females with Class III malocclusion and control subjects were found in the anteroposterior position and length of the maxilla. All angular and linear measurements of the sagittal position of the upper jaw (S-A, Ar-A, A┴N-Pog linear measurements, and S-N-A angle) had smaller mean values which indicated a backward positioned maxilla in Saudi females with Class III malocclusion. The significantly shorter anterior cranial base in these patients contributed to a more retrusive position of the maxillary base. This was in agreement with Hayashi²³, and Kasai et al.²⁹  In addition, it was observed that the effective maxillary length measured from point ANS to point PNS was shorter in the Class III group as compared with the control subject which indicates smaller size of maxilla in Class III malocclusion. This result agreed with studies Ngan et al. ¹ Toms⁹, Dietrich¹⁴, Guyer et al. ¹⁶, Battagel¹⁷ and, Bukhary and Al Namankani²⁸ that reported similar results.  The evaluation of the second component showed that the sample of Saudi females with Class III malocclusion had short and smaller cranial base angle.  In addition, they have retruded and small size maxilla with normal vertical relation.

Mandibular Skeletal Measurements

Historically, Class III malocclusion was believed to result primarily through over development of the mandible. Several investigators^{1, 6, 13, 15,17,19,20} reported that the mandibles of patients with Class III malocclusion were protrusive. In the present study, the sagittal position of the mandibule and chin (S-B, S-N-B, S-Pog, and S-N-Pog) were protruded and located in a forward position relative to the cranial base in Saudi females with Class III malocclusion compared to the control group. The differences were statistically significant at 0.1% level of significance. The protruded position of the mandible resulted from forward positioning of the mandible or increased size of the mandible.  The short cranial base and small cranial base angle in Class III malocclusion reported earlier may contribute to the protrusive position of the mandible Sanborn¹³, Nojima et al.²⁰ and Hayashi.²³ However, the size of the mandible measured by the distance S-B demonstrated an increase in the size of the mandible. The result of the mandibular position found in the present study was in agreement with Ngan et al.¹, Jacobson et al.⁶, Sanborn¹³, Baik et al.¹⁹, Ellis and McNamara¹⁵, Battaggel¹⁷,  and Nojima et al.²⁰  In addition to evaluating the anteroposterior position of the mandible, the anteroposterior position of the chin was evaluated by measuring the distance of S-Pog and S-N-Pog angle. Similar to the mandible, the chin was also protruded and located in a forward position relative to the cranial base in females with Class III malocclusion compared to the control group. This was true at 0.1% level of significance for the two parameters. This result was in agreement with Sanborn¹³, Ellis and McNamara¹⁵, and Battaggel¹⁷.

The form of the mandible was evaluated by Ar-Go, Go-Pog, Ar-Pog and Ar-Go-Me angle. The ramus height (Ar-Go) was significantly shorter in the Class III group compared to the control. With respect to the body of the mandibule (Go-Pog), there was no significant difference between the Class III and the control indicated similar size of the body of the mandibule. Similar result was reported by Sanborn.¹³ However, the total size of the mandible measured from point Ar to point Pog demonstrated that females with Class III malocclusion had larger total mandibular length than the control. The difference was statistically significant at 0.1% level of significance. Investigating the gonial angle indicated that it had markedly increased in the Class III malocclusion compared to the control (P>0.001).  The marked increase in the gonial angle was observed and reported.^{6, 8, 9, 13, 14, 17, 19, 28}  The increase in the gonial angle might lead to an increase in the total length of the mandible in the Class III malocclusion. The ramus and the body of the mandible seemed to be bent away from each other and increased the distance between the anatomical landmark Ar and Pog.

The vertical position of the mandible was evaluated by measuring N-Me, S-Go, S-N/Go-Me angle and S-Ar-Go angle. The total posterior facial height (S-Go) was significantly reduced for patients with Class III malocclusion compared to the control group. That was true at 1% level of confidence. The mandibular plane angle to the anterior cranial base (S-N/Go-Me) in the Class III malocclusion was significantly increased compared to the control group. This might be related to the short posterior facial height and high position of point Go which was formed with point Me in the mandibular plane. This result was in agreement with Ellis and McNamara¹⁵, and Nojima et al.²⁰

The vertical relationship between the maxilla and the mandible was examined by the lower anterior facial height (ANS-Me) and maxillary mandibular plane angle (PP/Go-Me angle). There was no significant difference in the lower anterior facial height indicating the similarity in the lower face height between the Class III malocclusion and the control group. The findings reported previously on the total anterior facial height and the upper anterior facial height, in addition to the finding on the lower anterior facial height, indicated the similarity between the Class III malocclusion and the control regarding the anterior facial heights. The maxillary mandibular plane angle was significantly steeper in the Class III malocclusion compared to the control group. The significant increase in the maxillary mandibular plane angle in the Class III malocclusion might be related to the increase in the gonial angle and the short ramus height reported previously. This finding was in agreement with the results of Jacobson et al.⁶, Toms⁹, Sanborn¹³ and Baik et al.¹⁹In the light of the above findings, it can be said that there were significant differences in the form, position and size of the mandible between Class III malocclusion and the control. The Class III malocclusion had protruded and forwarded the position of the mandible and chin, short ramus, normal size of the body of mandible, increased total mandibular length, obtuse gonial angle, increased mandibular plane angle, and short posterior facial height. Evaluating the skeletal mandibular component completed the picture of the skeletal configuration of the Class III malocclusion.

Dentoalveolar Relationship

Compared to control subjects, the maxillary incisors were proclined and protruded and the mandibular incisors were retroclined and retruded in Saudi females with Class III malocclusion compared to the control. These dentoalveolar aberrations in adult skeletal Class III malocclusion are considered compensations for the underlying skeletal discrepancy. These findings were reported by Jacobson et al.⁶, Ishii et al.⁸, Toms⁹, Sanborn¹³, Ellis and McNamara¹⁵, Baik et al.¹⁹ and, Bukhary and AlNamankani²⁸.

The interincisal angle was significantly larger in the Class III malocclusion. This was due to the retroclination of the lower incisor. Several investigators^{6, 9, 16, 28} indicated that the increase in the interincisal angle in Class III malocclusion mainly resulted from the retroclination of the lower incisors. The degree of the lower incisor retroclination was usually more than the degree of the upper incisor proclination. This finding was in agreement with other studies.^{9, 15,18,25,28}

The occlusal relationship of the maxillary and mandibular incisors showed clearly the difference in the overjet and overbite between the two groups as expected. Significant difference was observed in the overjet (OJ) and overbite (OB) between Class III malocclusion and the control group in Saudi females. The difference in the overbite in Saudi females with Class III malocclusion indicated that the Class III malocclusion females tended to have open bite in the selected sample. There is no known study that specified the degree of overbite before starting the study.  However, Tsang et al.²⁶ indicated that the vertical incisor relationship did not correlate with the severity of Class III malocclusion.

Soft Tissue Relationship

The sample of Saudi adult females with Class III malocclusion had:

Table 1.  The mean and standard deviation of the cranial base measurements and the means difference, t-value, P-value and level of significance between Saudi females with Class III malocclusion and control.

Table 2. The mean and standard deviation of the maxillary skeletal measurements and the means difference, t-value, P-value and level of significance between Saudi females with Class III malocclusion and control.

Table 3. The mean and standard deviation of the mandibular skeletal measurements and the means difference, t-value, P-value and level of significance between Saudi females with Class III malocclusion and control.
SD = Standard deviation, Sig. Level = Level of significant difference presented as ْ٭P <0.05, ٭٭P <0.01,٭٭٭ P <0.001, or NS , mm = Millimeter, (° ) = Degrees

Table 4. The mean and standard deviation of the dentoalveolar measurements and the means difference, t-value, P-value and level of significance between Saudi females with Class III malocclusion and control

Table 5.  The mean and standard deviation of the soft tissue measurements and the means difference, t-value, P-value and level of significance between the Saudi females with Class III malocclusion and control

Figure 1. Anatomical landmarks

 Figure 2. Cranial base measurements

Figure 3. Maxillary skeletal measurements

Figure 4. Mandibualr skeletal measurements

Figure 5. Dentoalveolar measurements

Figure 6. Soft tissue measurements