First molar health status in different craniofacial relationships

Introduction

The health status of the molar region is under the pressure of multiple surrounding variables, including oral hygiene, biting forces, craniofacial morphology, as well as the dental malocclusion.^1–7 The permanent first molars, being the first permanent posterior teeth to erupt in the oral cavity, face high load and pressure for healthy survival until adulthood.

The correlation between dental caries on the posterior teeth and malocclusion had been investigated in the literature. Crowding was found to be strongly associated with high caries index, which was claimed to cause difficulty in brushing and maintaining good oral health,^6,8,9 especially in the mandibular anterior region.^2,3 In contrast, such correlation was negatively affected in the maxillary posterior region.^2,3 Singh et al⁵ also found a strong correlation between caries and severe malocclusions among school children.Other dental problems, including posterior crossbite and mandibular overjet, were also found to be significantly associated with dental caries in the mixed dentition.^10,11 However, Mtaya et al⁴ and Borzabadi-Farahani et al¹² found that the socioeconomic status played a major role in the association between malocclusion and dental caries.

The relationship between form and function, especially in the craniofacial skeleton, might have an added effect on the health status of posterior teeth.^13–16 Overbite and the biting forces on the posterior teeth were found to have a direct strong correlation.^1,17 Subjects with normal vertical dimension showed twice as great mean bite force in the molar region than those with long face anterior open bite.^16,18 In contrast, subjects with a short face and deep bite generated higher biting forces than those with a normal face.^16,18,19 Muscle activities and the musculoskeletal relationships were also found to correlate with facial morphology and thus have an effect on the biting forces.²⁰ For example, a square face was found to generate high biting forces by providing a higher mechanical advantage for muscles of mastication,²¹ while a face with a diverged mandibular plane angle showed a negative relationship with the muscle activity level.²² Tooth wear was also found to be more evident in subjects with stronger biting forces and decreased vertical skeletal relationships.⁷ Biting force was further found to be strongly correlated with the number of teeth in contact^19,23 and age.^24,25 However, other studies showed no significant correlations between biting force and the following occlusal relationships: functional occlusion, the presence of occlusal interferences,^14,24 as well as the sagittal molar relationships as defined by the Angle classification.^16,20 The correlation with sex showed varied results.^13,14,20

From the latter findings, it was hypothesized that the permanent first molar health status might be affected by the biting forces and thus might correlate differently with different craniofacial relationships. Thus, the aim of this study was to investigate the association between the health status of the permanent first molars and different craniofacial relationships in adolescents.

Materials and methods

Study design

This is a retrospective study with a sample comprising pretreatment records of patients at the outpatient clinic of the Department of Orthodontics, King Abdulaziz University, Jeddah, Saudi Arabia. The study was approved by the King Abdulaziz University, Faculty of Dentistry Ethical Committee as it involved the data of patients. However, due to the restrospective nature of the study the committee deemed patient consent unnecessary.

Sample

The selection of patients’ records included the following criteria: age range from 11 to 15 years; no history of orthodontic treatment; no severe craniofacial disorders such as cleft palate; and had pretreatment intraoral photographs, orthopantomograms, and lateral cephalometric radiographs. Records of 400 randomly selected patients’ files were then screened, of which 210 files fulfilled the selection criteria.

Data collection

Lateral cephalometric radiographs of the selected cases were traced and analyzed by a trained examiner to identify the underlying anteroposterior and vertical morphologies. The anteroposterior morphologies included the anteroposterior skeletal relationship, malocclusion classification, and the overjet. The vertical morphologies included the vertical growth pattern and the overbite.

The variables assessed were then defined and categorized as follows:

• The anteroposterior skeletal relationship was defined based on ANB angle as: Class I (ANB 2–4°), Class II (ANB >4°), and Class III (ANB <2°).
• The vertical growth pattern was defined based on Frankfort-Mandibular plane angle (FMA) as; normal (FMA 23°–27°), horizontal (FMA <23°), and vertical (FMA >27°) growth patterns.
• The overbite was measured on the cephalometric radiograph to the nearest 0.5 mm and defined as: average (2–4 mm), moderate deep bite (4–6 mm), severe deep bite (>6 mm), shallow bite (0–1 mm), moderate open bite (−1 to −3 mm), and severe open bite (less than −3 mm).
• The overjet was measured on the cephalometric radiograph to the nearest 0.5 mm and defined as: normal (2–4 mm), reduced (<2–0 mm), reverse overjet (<0 mm), moderately increased (>4–6 mm), and severely increased overjet (>6 mm).
• The malocclusion was classified on the intraoral photographs according to the Angle’s classification as: Class I, Class II division 1, Class II division 2, and Class III.

The health status of the first four permanent molars (upper right, upper left, lower left, lower right) was assessed on the orthopantomograms and confirmed by the intraoral photographs. The health status of each tooth was then scored as sound (S), decayed (D), missing (M), or filled (F) tooth. The DMF (decayed, missing, filled) scores were then given a collective score as not sound (NS). Thus, each tooth was finally scored as either S or NS. The number of S and NS teeth for each case was further recorded.

Statistical analysis

Before data collection, ten cases were randomly selected and the health status of the first permanent molars was recorded twice, 2 weeks apart, to calculate the intra-examiner reliability. The kappa statistics of intra-examiner consistency was 0.80 for the first four molar categories.

Descriptive statistics and group comparison were further calculated using the Pearson chi-square test, Mann–Whitney U-test, and Kruskal–Wallis test. The Pearson’s correlation coefficient was used to correlate the assessed craniofacial components with the health status of the permanent first molars. All statistical analyses were done by the SPSS 16.0 software (SPSS Inc. Chicago, USA). The significance level was set at P<0.05.

Results

A total of 210 records were evaluated with the following findings: 81 were male subjects and 129 were female subjects. The majority of subjects had the following categories of craniofacial morphologies: Class I (n=68) and Class II (n=91) skeletal relationships; normal (n=67) to moderate deep bite (n=72); normal (n=91), moderately increased (n=54), to severely increased (n=50) overjet; and Class I (n=106) and Class II division 1 (n=75) malocclusion (Table 1).

Table 1 Sample distribution by variables

The health status of the permanent first molars was found to differ significantly with regard to sex difference (P=0.034), vertical growth pattern (P=0.01), and overbite (P=0.047). In male subjects, 44.4% had all first molars S and only 12.3% had all first molars NS. On the other hand, in female subjects, 36.4% had all first molars S and 31.0% had all first molars NS. Others had between one and three molars as NS (Figure 1).

Figure 1 Health status of the permanent first molars distributed according to sex. Note: Using a Mann-Whitney U test, a significant difference in molar health status between sex was reported (P<0.004).

The health status of the permanent first molars was also found to differ significantly by changes in the vertical growth pattern (P=0.01). A total of 46% of the subjects with normal growth pattern had all their first molars S, while only 19% had all first molars NS. In subjects with horizontal growth pattern, 58.3% had all first molars S, while only 20.8% of those subjects had all first molars NS. In subjects with vertical growth pattern, 31.3% had all first molars S and 27.7% had all first molars NS (Figure 2).

Figure 2 Health status of the permanent first molars distributed according to vertical growth pattern. Note: Using a Kruskal-Wallis test, a significant difference in molar health status between the different growth pattern was reported (P<0.014). Abbrevation: FMA, Frankfort-Mandibular plane angle.

The health status was also found to differ significantly by changes in overbite (P=0.047). In subjects with normal overbite, 22.4% had all first molars S and 38.8% had all first molars NS. In subjects with moderate deep bite, 29.2% had all first molars S and 37.5% had all first molars NS. In subjects with severe deep bite, only 8.1% had all first molars S and 59.5% had all first molars NS. In subjects with shallow bite, 28.6% had all first molars S and 35.7% had all first molars NS. In subjects with moderate open bite, 41.7% had all first molars S and 33.3% had all first molars NS. In subjects with severe open bite, 25.0% had all first molars S, while 75.0% of the latter group had 1–3 first molars NS, but none of the subjects had all first molars NS (Figure 3).

Figure 3 Health status of the permanent first molars distributed according to overbite. Note: Using a Kruskal-Wallis test, a significant difference in molar health status between the different overbite was reported (P<0.047).

In contrast to the latter findings, no significant association was found between the health status of the permanent first molars and the following anteroposterior variables: skeletal relationship (P=0.503), malocclusion classification (P=0.849), and overjet (P=0.536).

The Pearson’s correlation coefficient revealed that the sex (P=0.036) and vertical growth pattern (P=0.004) had a significant impact on the first molar health status (Table 2).

Table 2 Results of the Pearson correlation coefficient analysis based on “health status of permanent first molars” Notes: Significant using the Pearson’s correlation test at *P<0.05, **P<0.01.

Data were further analyzed for significant association between the health status of each category of permanent first molars and the different craniofacial components assessed. Results showed a significant association between the health status of the upper left first molar and sex (P=0.019). Seventy-four percent of the male subjects had the upper left first molar recorded as S, while female subjects had equal percentages of upper left first molar recorded as S and NS. Results also showed a significant association between the health status of the lower right first molar and the vertical growth pattern (P=0.001). In total, 70.8% of the horizontal growers and 64.8% of the normal growers had their lower right first molars recorded as S, while almost 60% of the vertical growers had their lower right first molars recorded as NS.

Discussion

The health status of the permanent first molars seems to be affected by multiple factors. They are the first permanent teeth to erupt in the oral cavity and act as the first vertical, anteroposterior, and transverse stop for the permanent occlusion. Understanding the skeletal, functional, and dental components that affect the health status of the permanent first molars is thus a crucial step when planning for preserving them.

The current study showed a significant association between the health status of the permanent first molars and the vertical growth pattern. The more horizontal the growth, the more was the number of sound and healthy first molars recorded. Similar positive findings were reported when correlating the molar biting force with the vertical growth pattern.^16,18–20

The current study also showed a negative correlation between the health status of the permanent first molars and overbite. The more increase in overbite, the less was the number of sound and healthy first molars recorded. On the contrary, the relationship between the molar biting force and the overbite showed positive correlations in multiple studies.^{1,16–20,23,26}

No correlation between the anteroposterior craniofacial morphology and the health status of the permanent first molars was reported in this study, as well as with the biting force as reported in other studies.^16,18

The biting force and sex in most studies showed a strong correlation, as males exhibit stronger molar biting force than females.^13,14,16,20 The current findings also showed that sex difference had a significant impact on the health status of the first molars.

In comparison to findings related to the biting forces, the health status of the permanent first molars showed similar direct association with the vertical craniofacial dimensions, including vertical growth pattern and overbite; as well as with sex difference. Thus, a direct correlation between the biting force and the health status of the permanent first molars can be investigated in further research.

Limitations

Multiple studies reported a significant association between dental caries and crowding.⁶ Others found a significant correlation between the number of teeth in contact and the molar biting force.^{16–20,23,26} Alabdullah et al²⁷ also reported a positive correlation between the molar biting force and the axial inclination of upper and lower incisors. They found that the higher the number of proclined incisors, the more the molar biting force.²⁷ Transverse craniofacial relationships and crossbite also had a reported association with the biting force.^10,11 However, such factors, which might have a contributing effect on the health status of the permanent first molars, were not assessed in the current study. Other variables, such as the oral hygiene status, were also not evaluated. Further research is required to assess all the factors together for better conclusion. A direct assessment of the correlation between the biting force and the health status of the permanent first molars is also needed.

Conclusion

The health status of the permanent first molars was strongly affected by sex difference and vertical growth pattern. No significant association was found with the anteroposterior craniofacial relationships.

Disclosure

The author reports no other conflicts of interest in this work.

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