Introduction
Malocclusions may cause social and health problems at any age (1). Several theories have been proposed on the formation of malocclusions. The most widely agreed upon theory is the functional matrix theory, which argues that bone develops in response to changes in functional matrices (2).
Moss reported that the coronoid process does not develop after the unilateral resection of the temporal muscle because it is dependent on the demands of the functional matrix (temporalis muscle) of the coronoid (skeletal unit) (2).
Face remodeling and growth are also linked to the development of neurocrania. Most of the maturation process of the brain occurs in the first 2 years of life. During this time, deviations in the maturation process may lead to abnormal skeletal patterns. Another theory associated with this condition is the osteopathic theory. The osteopathic theory specifies neuromuscular and joint dynamics for the primary movements of cranial respiration and the formation of surrounding facial structures (3).
In their study that was conducted with the participation of 1,250 children, Frymann (4) observed that osteopathic birth trauma created cranial dynamics that caused complications such as abnormal craniofacial shapes and abnormal neuromotor development in the future. In their study, it was shown that osteopathic disorders of the occipital condyle were observed quite frequently. This is because the 12th cranial nerve, which innervates the lingual muscles, is located in the condylar canal (5). It is assumed that birth trauma may cause orthodontic problems in two ways: the formation of irregular facial structures as a result of cranial growth and changes in sucking-swallowing patterns (4).
There are a few studies investigating the effects of birth trauma on dental malocclusions using the Angle classification. To better understand the links between the osteopathic theory and dental occlusion, Cattaneo et al. (3) reported that precise and more accurate evaluations are necessary. Schoenwetter (6) stated that there might be shape changes in the maxilla since premaxillary compression occurs in normal birth, and they believed that two children born by cesarean section had symmetrical narrow maxillae, and the pressure the fetus was exposed to before birth caused the deformity.
Irma et al. (7) found that birth by cesarean delivery seemed to be slightly protective against the risk of malocclusions.
While some studies have focused on dental occlusions, no studies exist on the cephalometric assessment of skeletal and soft tissue growth models and mandibular asymmetries. The aim of this study was to determine whether type of delivery influenced skeletal and soft tissue growth patterns and mandibular condylar asymmetry status.
Our null hypothesis was that there would be no difference in the asymmetry index between the two methods.
Methods
This study was approved by the Ethics Committee of the Bezmialem Vakıf University (12/2019). Informed consent was received from the patients for their orthodontic treatments.
For the study, 372 patients who were admitted to Bezmialem Vakıf University for orthodontic treatment were selected. The following inclusion and exclusion criteria were considered before the examinations of the radiographic images of patients.
Inclusion criteria: (1) Having been born via spontaneous vaginal delivery or cesarean delivery, (2) having good-quality radiographic records before orthodontic treatment, and (3) being in the 6th cervical vertebral maturation stage.
Exclusion criteria: (1) Having been born via forceps-assisted vaginal delivery, (2) having been born before 32 weeks of gestation, (3) being a cleft lip and palate patient, (4) history of orthognathic surgery, (5) systemic or metabolic diseases, and (6) history of facial trauma.
After applying the inclusion criteria, 108 patients (38 males, 70 females) were included in this study. The patients were divided into two groups as the normal delivery group (36 females, 18 males; mean age: 14.21±2.27 years) and the cesarean delivery group (34 females, 20 males; mean age: 14.16±2.19 years).
The mothers of the patients who were included in the study were asked to respond to questions on their childbirth experiences such as the gestational week of childbirth, duration of labor, the birth order of the child included in the study (first child vs. other), status of breastfeeding in the first 6 months, duration of breastfeeding, use of an infant bottle/pacifier, duration of using an infant bottle/pacifier, and timing and form of introduction to solid food (Table 1).
Cephalometric Analyses
Lateral cephalometric images were taken using the same device (Planmeca ProMax, Helsinki, Finland) and with the same standardized method. All measurements were performed by the same researcher (İ.E.M.) using the NemoCeph program (Nemotec, Madrid, Spain). Skeletal, vertical, dental, and soft tissue measurements were performed in this study. The included measurements are shown in (Figure 1).
Vertical Condylar Symmetry Evaluations
Digital panoramic radiographs (Planmeca Promax Digital Panoramic X-ray Unit, Planmeca Inc, Helsinki, Finland) taken before the orthodontic treatments of the patients were used for the condylar asymmetry measurements. The ImageJ software (ImageJ software, 1.37, National Institutes of Health, Bethesda, Maryland, USA) was used for the measurement of the distance between the Condylion (Co) and Sigmoid Notch (Sg) (condylar height), between the Sg and Gonion (Go) (ramal height), and between the Co and Go (total height) to evaluate condylar asymmetry (Figure 2). The scale settings were calibrated after importing the radiographic images, and the linear distances between the examined points were measured in pixels.
We calculated the asymmetry index with the formula (Asymmetry index = (right-left)/(right + left) x100) used by Lim et al. (8).
Statistical Analysis
The radiographic images of 25 patients were randomly selected after 2 weeks and re-analyzed to assess intra-examiner agreement. The intraclass correlation coefficient (ICC) was used to assess intra-observer reliability. The mean intra-observer ICC was 0.964 (0.932-0.996), which indicated a high level of agreement between the two measurements.
The SPSS package program (version 15.0; SPSS, Chicago, IL) was used for the statistical analyses. The data were tested for normal distribution by using the Shapiro-Wilk test. T-tests and the Mann-Whitney U test were performed to identify differences between groups. Pearson’s correlation tests were performed to analyze the relationships between the asymmetry index scores of the patients and their gestational week at birth and feeding and sucking patterns. The level of statistical significance was set at p<0.05.
Results
Table 1 presents the data on the demographic characteristics of the participants. There was no statistically significant difference between the normal delivery and cesarean delivery groups in terms of their demographic characteristics.
There was no statistically significant difference between the normal and cesarean delivery groups in terms of their sagittal, vertical, dental, and soft tissue measurements on cephalometric radiographs (Table 2 and p>0.05).
The intra-group comparison in the normal delivery group showed a statistically significant difference in the asymmetry index scores based on the Co-Sg length (p<0.05 and Table 3).
The intra-group comparisons in the cesarean delivery group showed a statistically significant difference in the asymmetry index scores based on the Sg-Go length values (p<0.05 and Table 3).
Total asymmetry index indicated a statistically significant difference for both groups (p<0.05 and Table 3).
The inter-group comparisons indicated no statistically significant differences in the asymmetry index scores between the groups based on their Co-Sg, Sg-Go, and Co-Go lengths (p>0.05 and Table 4).
A significant negative correlation was observed between the gestational weeks of the patients at birth and their total asymmetry index scores (p<0.05 and Table 5). On the other hand, no significant correlation was found between the total asymmetry index scores of the patients and other characteristics of them presented in Table 5 (p>0.05).
Discussion
Abnormal muscle tone may restrict the protective effect of the uterus on the head of the fetus during vaginal delivery, and the compression of the head by the pelvic bones of the mother may result in abnormal cranial development (9). Frymann (4) reported that in cases of vaginal delivery, the duration of the labor should be between 6 and 12 hours to consider the delivery as a normal delivery. The author classified longer or shorter vaginal deliveries as non-normal vaginal deliveries (slow and quick deliveries). This categorization was based fundamentally on the duration of labor as evidence of force applied on the cranium of the infant (4). A higher force on the baby’s skull in a non-normal delivery causes occipital condylar dysfunction, which negatively affects the function of the XII pair of the cranial nerves (hypoglossal nerves). The hypoglossal nerve functionally facilitates the motor innervation and posture of the tongue (3,4,10), and the function of the tongue affects the development of craniofacial structures, and accordingly, the formation of malocclusions (11). Another concern is the recent significant increase in the number of cesarean deliveries due to the preferences of mothers and healthcare practitioners. The worldwide cesarean section rate is about 15% in general, even reaching 35-45% in some countries, according to the World Health Organization (12-14). The Turkish Society of Obstetrics and Gynecology reported the cesarean section rate as 5.7% in 1988, 21% in 1998, and over 45% in 2010. Turkey is one of the countries with the highest cesarean section rates in the world, at a current rate of 53.2% (15,16).
It has been reported in the literature that there are some advantages and disadvantages of normal or cesarean deliveries for both the mother and the infant. Although each procedure carries its own risks for systemic condition and malocclusion development, both methods are routinely performed in clinical obstetrics. While genetic factors are highly effective in the development of malocclusions, it is also known that gestational week at birth, parental age, birth order, birth weight, characteristics of pregnancy, and type of delivery also play a critical role in the etiology of malocclusions (2). Therefore, the aim of this study was to compare cephalometric parameters and facial symmetry characteristics between individuals who were born via cesarean delivery and those born via normal delivery.
To eliminate the possible effects of differential jaw growth and occlusal changes from primary to permanent dentition on the results, patients who completed pubertal growth were included in this study (14,17-19). No statistically significant differences in sex and age were observed between the normal delivery and cesarean delivery groups.
Cattaneo et al. (3) and Zhou et al. (20) reported that children born via normal delivery had lower rates of malocclusions than those born via cesarean delivery. On the other hand, Irma et al. (9) reported that cesarean delivery had slightly protective effects against the risk of malocclusion development. In our study, no significant difference was found between the groups in terms of their cephalometric values. Cattaneo et al. (3) defined deliveries lasting 6-12 hours as normal deliveries in their study. On the other hand, Zhou et al. (20) did not define a specified duration of delivery considered natural. This difference in findings may be attributed to the fact that the births of the patients in the normal delivery group took shorter (4.8±1.9 hours) as the mothers of most of these patients were multiparous. Another possible explanation might be that patients with severe skeletal malocclusions requiring orthognathic surgery in which genetic factors were significantly effective were excluded from this study.
We used panoramic radiographs to examine Co-Sg, Sg-Go, Co-Go distances, and asymmetry index values. Many studies have reported that panoramic radiographs give reliable results in the measurement of condylar asymmetry and condylar height (21-23). No statistically significant differences in condylar asymmetry, ramal asymmetry, or total asymmetry index values were found between the groups in this study. On the other hand, we found a statistically significant difference between the right and left sides in terms of condylar height in the normal delivery group, as well as a significant difference in terms of ramus height in the cesarian delivery group. However, a statistically significant difference was observed in total asymmetry index for both groups. Therefore, the null hypothesis was rejected. A relationship between labor and delivery stress and orthodontic malocclusions was reported (3). This was because asymmetric mechanical forces could induce deviations in the craniofacial bones by the accumulation of stress in the mandibular condyles and the inability to tolerate this stress due to the articulation of the condyle with the skull base (3,4,25). Therefore, this condylar asymmetry could be attributed to the maxillofacial trauma caused by muscular and positional push and pull forces applied to the craniofacial structure during vaginal deliveries (24, 25).
The difference in the position of the mandible between normal and cesarean delivery depending on the way the head is delivered, the localization of the forces that the baby is exposed to during two different types of birth, and the difference in the extension and flexion of the head may have led to this finding.
The condylar asymmetry index values of both groups were similar when compared based on the 3% threshold value proposed by Habets et al. (26) However, to the best of our current knowledge, the present study is the first to investigate the relationship between mandibular asymmetry and type of delivery. It is difficult to compare our findings to those of previous studies evaluating condylar asymmetry, as there have been no studies investigating mandibular vertical asymmetry in cases of different type of delivery. Thus, further studies are needed in this field.
Zhou et al. (20) reported that breastfed children had lower risk levels in terms of malocclusion development. In this study, the majority of the patients in both groups had mixed breast and bottle feeding in the first 6 months. Moreover, the groups had similar results in terms of the duration of breastfeeding, the duration of using an infant bottle/pacifier, and the timing and type of introduction to solid food. Prolonged breastfeeding is one of the factors that prevent malocclusions by restricting bottle-feeding and non-nutritive habits (27,28). One of the possible explanations for the absence of a significant difference between the groups in terms of malocclusions may also be the similar feeding habits of the two groups.
Moreover, in this study while no significant correlations were found between the duration of breastfeeding, the duration of using an infant bottle/pacifier, and the timing of introduction to solid food in the groups and their mandibular asymmetry index scores, a significant negative correlation was identified between gestational week at birth and mandibular asymmetry index scores. It has been reported in the literature that the development of malocclusions is associated with preterm birth (15,29).
Pogliani et al. (30) stated that the risk of plagiocephaly was high in preterm children, and accordingly, the possibility of mandibular asymmetry development was high. On the other hand, the specific mechanism that can explain this association remains unclear (15).
Study Limitations
Finally, this study had several limitations. In this study, data were collected using retrospective questionnaires applied to the mothers of the patients who might not be able to remember every detail of their pregnancy and childbirth correctly (recall bias). Individual variations may also make it difficult to determine the relationship between the variables in prenatal and infantile periods and orthodontic malocclusions. Therefore, further prospective controlled studies with larger sample sizes are needed to determine whether perinatal and infantile variables may increase the risk of malocclusions.
Conclusion
Keeping in mind the limitations of this study, it was concluded that;
- Type of delivery had no significant effect on skeletal, dental, and soft tissue cephalometric parameters.
- The patients born via vaginal delivery tended to have a higher prevalence of condylar asymmetry, whereas those born via caesarean section tended to have a higher prevalence of ramal asymmetry.
- A statistically significant relationship was observed between preterm birth and mandibular asymmetry.
Ethics
Ethics Committee Approval: Ethical approval was obtained from the Research Ethics Committee of Bezmialem Vakıf University (protocol no: 54022451-050.05.04).
Informed Consent: The informed consent forms were obtained from individuals included.
Peer-review: Externally peer reviewed.
Authorship Contributions
Surgical and Medical Practices: İ.E.M., E.D.Ş., Concept: İ.E.M., E.D.Ş., Design: İ.E.M., E.D.Ş., Data Collection or Processing: İ.E.M., E.D.Ş., Analysis or Interpretation: İ.E.M., E.D.Ş., Literature Search: İ.E.M., E.D.Ş., Writing: İ.E.M.
Conflict of Interest: No conflict of interest was declared by the authors.
Financial Disclosure: The authors declared that this study received no financial support.