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Original Article
5 (
6
); 255-261
doi:
10.4103/2321-1407.169951

Skull bone thickness versus malocclusion

Department of Orthodontics and Dentofacial Orthopaedics, Yenepoya Dental College, Yenepoya University, Mangalore, Karnataka, India
Address for correspondence: Dr. Mahamad Iqbal D. K., Department of Orthodontics and Dentofacial Orthopaedics, Yenepoya Dental College, Yenepoya University, Mangalore, Karnataka, India. E-mail: driqbaldk@ hotmail.com
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This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-Share Alike 3.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.
How to cite this article: Mahamad Iqbal DK, Amin VB, Mascarenhas R, Husain A. Skull bone thickness versus malocclusion. APOS Trends Orthod 2015;5:255-61.

Abstract

Objective

The objectives of this study were to determine the thickness of skull bones, namely frontal, parietal, and occipital bones in Class I, Class II, and Class III patients.

Materials and Methods

Three hundred subjects who reported to the Department of Orthodontics requiring orthodontic treatment within the age group 17-35 were selected for the study. They were subdivided into three groups of 100 each according to the skeletal and dental relation. Profile radiographs were taken and the tracings were then scanned, and uploaded to the MATLAB 7.6.0 (R 2008a) software. The total surface areas of the individual bones were estimated by the software, which represented the thickness of each bone.

Result

Frontal bone was the thickest in Class III malocclusion group and the thinnest in Class II malocclusion group. But the parietal and occipital bone thickness were not significant. During gender differentiation in Class I, malocclusion group frontal bone thickness was more in males than females, In Class II, malocclusion parietal bone thickness was more in males than females. No statistically significant difference exists between genders, in Class III malocclusion group. During inter-comparison, the frontal bone thickness was significant when compared with Class I and Class II malocclusion groups and Class II and Class III malocclusion groups.

Conclusion

The differences in skull thickness in various malocclusions can be used as an adjunct in diagnosis and treatment planning for orthodontic patients. It was found that the new method (MATLAB 7.6.0 [R 2008a] software) of measuring skull thickness was easier, faster, precise, and accurate.

Keywords

Malocclusion
skull bone thickness
software

INTRODUCTION

Although orthodontics has progressed to a great extent, there are still some malocclusions which are difficult to treat. Such malocclusions many a times also have a skeletal component. A significant change in the skull thickness has been reported with age.[1] Few studies have also shown that there exists a relationship between the thickness of skull bones and dento-skeletal malocclusions.[2,3]

Jacobsen et al. found that the patients with deepbite have a general thickening of the skull[2] and they also found that there was reduced skull thickness in the occipital area and a thickening of the frontal bone in females with skeletal Class II when compared with Class I malocclusion.[1] Studies on sella turcica and cervical vertebrae revealed that there may be an association between the malocclusion and thickness of the bone in general.[4,5] Studies have also shown a connection between the thickness of the buccal cortical bone and the gonial angle[6] and have determined that the width of the ramus mandibulae varies in retrognathic and prognathic patients.[7]

Bjork observed that sturdily built children respond better to the orthodontic treatment, due to greater growth activity.[8] Skull thickness is considered to be important for orthodontic treatment planning, as it could be an indicator for the thickness of the bone which in turn could influence the treatment time.[2] Hence, skull thickness is important for the orthodontic treatment planning.

Different methods have been used to measure the human skull thickness. Anthropological material and biopsy samples from cadavers have been measured using a caliper.[9-11] Cephalometric analysis using radiographs has also been used in anthropologic and clinical studies. [3,9] Cephalometric measurement of the skull thickness has limitations and errors, which may be overcome by using the latest computer technology and software design.

In this study, we used a new method for measuring the skull thickness in skeletal Class I, Class II, and Class III subjects using computer software (MATLAB 7.6.0 [R 2008a], The Math works Inc., Massachusetts, USA).

MATERIALS AND METHODS

Three hundred subjects who reported to the Department of Orthodontics requiring orthodontic treatment within the age group 17-35 were selected for the study. They were subdivided into three groups of 100 each according to the skeletal and dental relation. The profile radiographs were recorded using cephalostat with a film-to-focus distance of 180 cm and a film-to-median plane distance of 10 cm. Profile radiograph [Figure 1] was used instead of lateral cephalogram so as to record the full orofacial skeleton. Each of the profile radiographs was traced[12] and following cephalometric reference points were marked.

Figure 1: Profile radiograph of the patient

Nasion (N)

The most anterior point on the fronto-nasal suture.

Bregma (br)

The intersection between the sagittal and coronal sutures on the surface of the cranial vault.

Lambda (l)

The intersection between the lambdoid and sagittal sutures on the surfaces of the cranial vault.

Opisthion (Op)

The midpoint of the posterior margin of foramen magnum situated above the floor of the posterior cranial fossa.[13,14]

These four points divide the skull to be measured into three different areas [Figure 2].

Figure 2: Outline of the profile radiograph. Four points: Nasion, bregma, lambda, and opisthion divide the skull into three areas to be measured

All the tracings were then scanned using a Scanner (Hewlett-Packard, F 2248, California, USA), decreasing the magnification to 50% of the original size. To determine the skull thickness in relation to parietal, occipital, and frontal bone, each of these bones was divided into three sections. The three sectioned areas in each bone constitute one inch wide area around the midpoint of each bone and one inch wide area on either end of the each bone. These selected areas were allotted different colors which are individually painted using Microsoft paint 2007 version. Frontal bone sections were painted with red color, parietal bone with black, and occipital with green [Figure 3]. After this, the images were uploaded to the MATLAB 7.6.0 (R 2008a, The Math works Inc., Masschusetts, USA) software. The total surface area of three sections in each bone was estimated by the number of pixels present in the colored areas, of which average was taken. This represents the thickness of each bone. The readings were recorded in the computer.

Figure 3: Colored areas representing the three different sections in bones of the skull

RESULTS

The normality distribution was assessed by the Shapiro-Wilks w-test. The thickness of the frontal, parietal, and occipital bones was normally distributed except for the frontal bone in Class II and parietal bone in Class III.

Differences in the medians of the thickness of the frontal, parietal, and occipital bones between the Class I, Class II, and Class III malocclusion groups were assessed by Kruskal-Wallis test. Difference between the skull thickness in Class I and Class II malocclusion group, Class II and Class III malocclusion group, and Class I and Class III malocclusion group was assessed by post hoc analysis, using Bonferroni’s correction. Differences in the medians of the thickness of the frontal, parietal, and occipital bones between genders were assessed by Mann-Whitney U-test. The statistical analysis was performed using PASW statistics 18 software, (IBM, Hong Kong).

Pixels in the frontal, parietal, and occipital bone in Class I, Class II, and Class III groups were measured using MATLAB 7.6.0 (R 2008a) software and tabulated. The median and interquartile range values were calculated [Table 1].

Table 1: Differences in the thickness of the frontal, parietal and occipital bones in Class I, Class II and Class III malocclusion groups with the median and interquartile range values
Parameters Categories N Min Max Median Interquartile range
Frontal (sq pixels) Class I 100 1723 3760 2691 753
Class II 100 1936 3204 2228 481
Class III 100 1985 4026 2741 826
Parietal (sq pixels) Class I 100 2510 4744 3564 926
Class II 100 2685 4179 3305 817
Class III 100 2010 4448 3263 701
Occipital (sq pixels) Class I 100 1580 3005 2322 660
Class II 100 1743 3200 2330 460
Class III 100 1577 2604 2097 415

Based on the median values obtained [Table 1], it was observed that the parietal bone was the thickest bone in all the three malocclusion groups. The thinnest bone in Class I and Class III malocclusion groups was occipital bone whereas in Class II group the frontal bone was the thinnest.

Gender differences in the measurement of the skull bones (frontal, parietal, and occipital bone) in all the three malocclusion groups were noted and the median values and the interquartile range were calculated for Class I [Table 2], Class II [Table 3], and Class III [Table 4].

Table 2: Gender differences for Class I malocclusion group
Parameters Categories N Min Max Median Interquartile range
Frontal (sq pixels) Male 50 2236 3760 2904 657
Female 50 1723 3153 2349 746
Parietal (sq pixels) Male 50 2510 4504 3564 586
Female 50 2689 4744 3353 1481
Occipital (sq pixels) Male 50 1755 3005 2333 666
Female 50 1580 2704 2089 767
Table 3: Gender differences for Class II malocclusion group
Parameters Categories N Min Max Median Interquartile range
Frontal (sq pixels) Male 50 1961 3204 2506 621
Female 50 1936 3077 2140 220
Parietal (sq pixels) Male 50 2685 4179 3701 565
Female 50 2696 3800 3254 519
Occipital (sq pixels) Male 50 1743 2898 2451 512
Female 50 1893 3200 2209 429
Table 4: Gender differences for Class III malocclusion group
Parameters Categories N Min Max Median Interquartile range
Frontal (sq pixels) Male 50 1985 4026 2960 1065
Female 50 2228 3816 2490 705
Parietal (sq pixels) Male 50 2154 4448 3470 281
Female 50 2010 3733 3256 1111
Occipital (sq pixels) Male 50 1910 2495 2123 530
Female 50 1577 2604 2086 460

It was observed that the parietal bone was the thickest bone in males as well as females in all the three malocclusion group. The thinnest bone in males in all the three malocclusion groups was occipital bone. Similarly, the occipital bone was the thinnest bone in females in Class I and Class III malocclusion group, whereas in Class II malocclusion frontal bone was the thinnest.

Results show that statistically significant differences exist between the three groups in the frontal bone thickness (the most significant being in Class III followed by Class I and Class II). But parietal and occipital bone thickness were not significant [Table 5].

Table 5: Kruskal-Wallis test
  Class N Median (25th, 75th) Minmum Maximum Mean Rank Chi square P value
Frontal bone measurement I 100 2508.0 1723.00 4026.00 34.35 12.107 0.002
II 100       18.90    
III 100       35.89    
Parietal bone measurement I 100 3408.0 2010.00 4744.00 34.30 3.508 0.173
II 100       29.63    
III 100       24.03    
Occipital bone measurement I 100 2215.0 1577.00 3200.00 31.98 5.345 0.069
II 100       33.83    
III 100       21.94    

Further statistical analysis (Post-hoc analysis) was done to find out whether the difference in the frontal bone thickness is between Class I and II malocclusion groups, or Class II and III malocclusion groups, or Class I and III malocclusion groups, using Bonferroni’s correction [Table 6].

Table 6: Post hoc Analysis
Compariso groups N Mean Rank Median Z P value
Class I 100 26.05 2691 −3.003 0.003
Class II 100 14.95 2228    
Class II 100 26.05 2228 −2.953 0.003
Class III 100 20.28 2741    
Class I 100 26.05 2691 −0.409 0.682
Class III 100 20.28 2741    

Differences in the medians of the thickness of the frontal, parietal, and occipital bones between the Class I, Class II, and Class III malocclusion groups were assessed by Kruskal-Wallis test [Table 5].

Results showed that the frontal bone thickness was statistically significant while comparing Class I and Class II malocclusion groups (the difference being 463 square pixels) and Class II and Class III malocclusion groups; (the difference being 513 square pixels) but there was no statistically significant difference between Class I and Class III malocclusion groups [Figures 4-6].

Figure 4: Graphical representation of the frontal bone thickness measurement in Class I, Class II, and Class III malocclusion groups with median value
Figure 5: Graphical representation of the parietal bone thickness measurement in Class I, Class II, and Class III malocclusion groups with median value
Figure 6: Graphical representation of the occipital bone thickness measurement in Class I, Class II, and Class III malocclusion groups with median value

The gender differences in thickness of the skull bones frontal, parietal, and occipital bone [Tables 2-4] in all the three malocclusion groups was evaluated based on median values. To see the statistical significance of these observations Mann-Whitney U-test was done [Tables 7-9].

Table 7: Statistical analysis for gender differences in Class I malocclusion group
Parameters Comparison groups N Mean rank Median Z P value
Frontal Male 50 12.21 2904 −1.979 0.048
Female 50 6.50 2349    
Parietal Male 50 10.79 3564 −0.33 0.741
Female 50 6.50 3353    
Occipital Male 50 11.86 2333 −1.567 0.117
Female 50 7.33 2089    
Table 8: Statistical analysis for gender differences in Class II malocclusion group
Parameters Comparison groups N Mean rank Median Z P value
Frontal Male 50 13.00 2506 −1.709 0.087
Female 50 8.45 2140    
Parietal Male 50 13.67 3701 −2.166 0.03
Female 50 7.91 3254    
Occipital Male 50 9.44 2451 −0.722 0.47
Female 50 11.36 2209    
Table 9: Statistical analysis for gender differences in Class III malocclusion group
Parameters Comparison groups N Mean rank Median Z P value
Frontal Male 50 11.86 2960 −1.494 0.135
Female 50 8.00 2490    
Parietal Male 50 12.21 3470 −1.723 0.085
Female 50 7.77 3256    
Occipital Male 50 10.86 2123 −0.86 0.39
Female 50 8.64 2086    

The statistical analysis showed [Tables 7-9]:

  • Frontal bone thickness was more in males than females and was statistically significant in Class I malocclusion group, (P = 0.048).

  • Parietal bone thickness was more in males than females and was statistically significant in Class II malocclusion group (P = 0.03).

  • No statistically significant difference exists between genders in Class III malocclusion group.

DISCUSSION

The skull thickness is considered important for orthodontic treatment planning. It could be an indicator of skeletal malocclusion and the thickness of other bones, in general, which in turn can be used to estimate the treatment time for the existing malocclusion. In 1954, Bjork found that men with skeletal sturdiness had a tendency to scissors bite and larger dental arches when compared with the slender built male patients.[8] These results suggest a connection between the thickness of the bone in general and malocclusions. In the same study, Bjork also found that sturdily built children respond better to the orthodontic treatment, explained by a greater growth activity.[8] These studies indicate that there may be an association between malocclusion, orthodontic treatment, and thickness of the bone in general.

This study evaluated the thickness of the skull in various skeletal and dental malocclusions, namely frontal, parietal, and occipital bones in Class I, Class II, and Class III patients. The bone which showed the most variation in different groups was determined.

There was a significant difference in the skull thickness among all the three classes of malocclusion. Based on the median values obtained [Table 1], it was observed that:

  • The parietal bone was the thickest bone in all the three malocclusion groups.

  • The thinnest bone in Class I and Class III malocclusion groups was occipital bone, whereas in Class II malocclusion group the frontal bone was the thinnest.

Statistical analysis of these results showed that frontal bone thickness was the most significant in Class III malocclusion group followed by Class I and Class II malocclusion group and hence, may be considered as an important factor in judging skull thickness, thus aiding in diagnosis [Table 5]. This is because, the parietal bone thickness showed more variation among all the malocclusion groups.

Inter-comparison of the frontal bone thickness in Class I, Class II, and Class III malocclusion groups showed that:

  • The frontal bone thickness was significant while comparing Class I with Class II and Class II with Class III malocclusion groups.

  • No statistically significant difference was seen between Class I and Class III malocclusion groups.

This implies that the frontal bone thickness can be used to differentiate between Class I and II malocclusion groups and Class II and III malocclusion groups, and not between Class III and I malocclusion groups. This is due to the negligible difference of the frontal bone thickness between Class I and III malocclusion group [Table 6].

Gender differences in the thickness of the skull bones showed that [Tables 2-4]:

  • The parietal bone was the thickest bone in males as well as females in all the three malocclusion group.

  • The thinnest bone in males in all the three malocclusion groups was occipital bone.

  • The thinnest bone in females in Class I and Class III malocclusion group was occipital bone.

  • The thinnest bone in females in Class II malocclusion was frontal bone.

Statistical analysis of these observations showed that [Tables 7-9]:

  • Frontal bone thickness showed statistically significant difference between males and females in Class I malocclusion group (thickness was more in males than females).

  • Parietal bone thickness showed statistically significant difference between males and females in Class II malocclusion group (thickness was more in males than females).

  • There was no statistically significant difference between genders in Class III malocclusion group.

From this, it can be concluded that deviations in the thickness of the skull are associated with the skeletal malocclusions. It can be hypothesized that the etiology of deviations in skull thickness is different. Other studies concluded that thickening in the frontal bone might be interrelated with a short nasal bone as both areas belong to the frontonasal developmental field.[14,15] The study also pointed out that skeletal Class III malocclusion subjects have a normal nasal bone length and a normal thickness of the frontal bone.[16]

Variations in skull bone thickness may also relate to variations in other skeletal structures. Differences between skeletal Class II and Class III malocclusion have also been found in the cervical spine. It was noticed that cervical spine of skeletal Class II patients had vertebral fusions localized more cranially than the fusions in skeletal Class III.[17] These differences might be interrelated with the differences in the frontal bone in the present study.

Until now, only two studies have correlated the skull thickness and malocclusion. The first study showed increased skull thickness in subjects with skeletal deepbite of all the three skull bones.[2] The second study[1] documented differences in skull thickness in all the three skeletal malocclusions and showed reduced skull thickness in the occipital area and thickening of the frontal bone in females with skeletal Class II malocclusion when compared with females with Class I.

This study also showed a similar association of skull thickness and malocclusion, but with few more additional findings. The frontal bone was the thickest in Class III malocclusion group and the thinnest in Class II malocclusion group. However, parietal and occipital bone thickness were not statistically significant. Frontal bone thickness was more in males than females in Class I, in Class II malocclusion parietal bone thickness was more in males than females. No statistically significant difference exists between genders, in Class III malocclusion group. The differences in findings in earlier studies and our study may be attributed to racial variation.[18-20]

The earlier studies used the conventional method of measuring the skull thickness using cephalometric radiographs. Direct cephalometric measurement of the skull thickness may have few limitations and errors, which were overcome by application of the latest computer technology. An outstanding feature of this was that a new method for measuring the skull thickness in Angle’s skeletal Class I, Class II, and Class III malocclusion using computer software (Mat Lab®) was used.

The advantage of this method is:

  • It is easier and faster to use.

  • More accurate.

  • Precise and reliable.

CONCLUSION

From this study, it can be concluded that there was a significant difference in the skull thickness between all the three classes of malocclusion. Frontal bone was the thickest in Class III malocclusion group and the thinnest in Class II malocclusion group. Frontal bone thickness was more in males than females in Class I malocclusion groups. Furthermore, the frontal bone thickness was statistically significant while comparing Class I and Class II malocclusion groups and Class II and Class III malocclusion groups.

The parietal bone showed more thickness in males than females in Class II malocclusion group. However, occipital bone thickness had no statistically significant correlation in any malocclusion group.

It can also be concluded that the new method (MATLAB 7.6.0 [R 2008a] software) of measuring skull thickness was easier, faster, and precise.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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