Assessment of the relationship between impacted mandibular third molars’ angulation pattern and crowding severity: A cross-sectional study

Abstract

Mandibular crowding is the most common type of dental crowding among adolescents.

Aims

To investigate the relationship between the angulation pattern of impacted mandibular third molars and the severity of mandibular anterior crowding.

Methodology

A total of 69 participants with impacted mandibular third molars were included in the study, and their records were analysed.

Results

There was no significant association between impacted mandibular third molars’ angulation pattern and mandibular anterior crowding severity, as well as no correlation between gender and either impacted mandibular third molars’ angulation pattern or mandibular anterior crowding severity.

Conclusion

Our findings suggest that the angulation pattern of impacted mandibular third molars is not a significant contributing factor to the severity of mandibular anterior crowding. However, further studies with larger sample sizes are necessary to validate these results.

1. Introduction

Dental crowding is considered to be the most frequent type of malocclusion (Lombardi, 1982). Mandibular anterior crowding (MAC) is more commonly observed than maxillary crowding (Al-Shahrani, 2016). Dental crowding can be influenced by several factors such as impacted mandibular third molars (IM3M), jaw–tooth size discrepancy, dental arch shape, and retroclination of lower anterior teeth. Other factors such as skeletal and soft tissue growth patterns, mesial drifting of posterior teeth, gender, forces exerted by periodontal fibres, and natural ageing process are considered to be risk factors (Haider et al., 2023).

Impaction refers to a situation in which a tooth fails to erupt completely into the dental arch and becomes partially or completely impacted (Erikson, 1938). Several factors can contribute to impaction, including abnormal tooth orientation of adjacent teeth, dense overlying bone, excessive soft tissue, and genetic abnormality preventing its eruption (Barakat and Nofal, 2019, Alling III and Catone, 1993).

The most commonly impacted teeth are the mandibular and maxillary third molars because they are the last teeth to erupt in the dental arch (Wei et al., 2019). Another explanation for their high incidence of impaction is insufficient development of the retromolar space (Behbehani et al., 2006).

The role of IM3M in MAC and its potential impact on the dental arch have been the subject of constant debate (Antanas and Giedre, 2006). Extensive investigations have been conducted to assess this impact, yet it remains a topic of controversy (Haider et al., 2023).

In addition, the angulation of IM3M and the severity of MAC are also investigated in literature (Cherian and Ravi, 2016, Sood et al., 2018). A study conducted by Merin Cherian and M. S. Ravi in 2020 aimed to evaluate the third molar space and angulation in individuals with MAC and compare it to those without crowding. The study revealed significant differences in the third molar space between the study group and the control group. However, there was no significant difference in third molar angulation between the two groups (Cherian and Ravi, 2016). In a similar study conducted by Ambika Sood et al. in 2018, the relationship between third molar angulation, eruption space, eruption level, and mandibular anterior crowding was evaluated. The study reported that there was no significant correlation between the variables studied and mandibular anterior crowding (Sood et al., 2018).

In Saudi Arabia, studies have been conducted on both MAC and IM3M (Al-Shahrani, 2016, Bin Rubaia’an et al., 2023). They have found an increase in the occurrence of malocclusion in the Saudi population, with crowding being the most common type of malocclusion, primarily affecting the anterior teeth (Al-Shahrani, 2016). Regarding IM3M, a study conducted by Muslat A. Bin Rubaia’an et al. in 2023 aimed to assess the condition of third molars in relation to various facial types in the Saudi population. The study revealed a notable prevalence of third molar impaction, with the most common angulation pattern for IM3M being mesioangular (Bin Rubaia’an et al., 2023).

The purpose of this study is to evaluate the relationship between the angulation pattern of IM3M and the severity of MAC. The study will give insight into early recognition of the angulation pattern of IM3M in cases with MAC as well as planning for early management of third molars. The study’s null hypothesis is that the severity of crowding does not worsen with the changes in angulation of IM3M.

2. Materials and methods

Data collection for this cross-sectional multi-centre study was carried out between November 2021 and December 2022. The participants’ records were obtained from individuals seeking orthodontic treatment at various governmental and private dental clinics in the Makkah region. Pretreatment records were gathered for each participant, encompassing the following: good-quality conventional study casts, digital study models created from.stl files on the dentition obtained from various intraoral scanners, and digital OPG.

From a sample of 104 individuals, 69 patients were eligible for analysis. The Raosoft sample size calculator estimated the need for a sample of 65 participants to achieve a margin of error of 5 % with a confidence level of 95 %. This calculation was based on the current visitors of the clinics at any point during the year typically ranges from 900 to 1000. The sample size was increased to 69 to increase the sample power.

Participants aged above 15 years who had not undergone prior orthodontic treatment were included in the study. Moreover, the inclusion criteria encompassed participants’ records with well-erupted permanent dentition in the lower jaw permitting proper measurements of crown dimensions and the lower arch perimeter, along with IM3M. Participants who had systemic conditions affecting the growth and development of the lower jaw, dentofacial deformities, significant facial asymmetries, syndromes, tumours, unerupted or missing third molars, casts or scans indicating any developmental tooth disorders, missing, extra or decayed permanent teeth, worn-out dentition, or large coronal restorations were excluded from the study.

Four dental students in their internship year participated in the study. Prior to the analysis, 20 study casts, 10 digital study models, and 10 OPG were randomly selected for calibration by the examiners. The examiners received instructions and training from an assistant professor from the Oral and Maxillofacial Surgery Department at the Faculty of Dentistry at Umm Al-Qura University, who guided them in both scoring MAC and assessing the angulation of IM3M. The calibration process was carried out individually, and comprehensive analysis of the sample took place over four weeks to detect any potential errors in measurements and interpretations. The kappa test for the calibration was 95 %.

3. Study procedure

3.1. MAC (mandibular anterior crowding) scoring

The severity of crowding in the anterior segment of the mandibular arch was assessed by calculating the numerical difference between the available space and the space needed in accordance with the anterior space analysis method (Harris et al., 1987). This measurement was obtained either directly from the mandibular study cast using a physical Boley gauge caliper or virtually on mandibular scans using a digital caliper from the software OrthoCAD®. The calipers were positioned to measure the greatest distance between the contact points on the buccal surfaces (as shown in Fig. 1). Research has shown that digital measurement software provides high levels of accuracy, reproducibility, and time efficiency (Tunca et al., 2021).

Fig. 1.

Measurement of the greatest distance between the contact points on the buccal surfaces.

3.2. Space analysis

The available space was measured using segmental arch analysis, which was conducted in four segments. For the posterior segments, the measurement was taken from the mesial aspect of the first molars to the mesial aspect of the canines on both sides. For the anterior segment, the measurement was taken between the mesial aspects of the canines to the midline on both sides.

The space required was calculated by adding together the maximum mesiodistal widths of the erupted lower permanent incisors, canines and premolars on both sides.

After calculating the space available and the space required, the participants were then distributed into three groups based on the severity of crowding (Fig. 2 A and B).

Fig. 2.

Schematic figure of the measurement process (2A available space, 2B space required).

Severity of crowding was categorised as mild (2–3.9 mm), moderate (4–5.9 mm) and severe (>6 mm) (Fig. 3A–C).

Fig. 3.

Intraoral clinical photos and conventional casts showing the three categories of MAC severity. 3A mild, 3B moderate and 3C severe.

3.3. Radiographic interpretation of IM3M

OPG obtained before orthodontic treatment were examined to assess the presence and angulation pattern of IM3M. If at least one mandibular third molar was found to be impacted on the OPG, its angulation pattern was assessed via tracing OPG using a digital protractor by the angle formed between intersected longitudinal axes of the second molar and the third molar. Impacted third molar categorization was done following Winter’s classification (Winter, 1926) (Table 1, Fig. 4A–C).

Table 1.

Third molar angulation pattern (Winter’s classification).

IM3M Angulation Pattern	Description
Vertical	parallel to the long axis of the second molar (from 10° to 10°)
Mesioangular	tilted toward the second molar in a mesial direction (from 11° to 79°)
Horizontal	long axis of the third molar is horizontal (from 80° to 100°)
Distoangular	tilted toward the ramus of the mandible in a distal direction (from −11° to −80°)

Fig. 4.

OPGs for different MAC severity showing IM3M in different angulation pattern.

4. Statistical analysis

SPSS® software (IBM Corp., Armonk, NY, version 20.0) was employed for data analysis. An analysis of covariance (ANCOVA) test statistic was utilized to assess whether a significant difference existed in the angulation of MAC and IM3M. Statistical significance was evaluated at the 0.05 level (P < 0.05).

5. Ethical considerations

This study received ethical approval from the University of Umm Al-Qura Research Ethics Board (HAPO-02-K-012-2021-11-859).

Data confidentiality will be maintained, and data will not be disclosed. Furthermore, the data will be permanently erased and will not be used under any circumstances.

6. Results

A total of 69 participants fulfilled the inclusion criteria and were considered to be eligible for analysis. The sample included records of individuals ranging in age from 16 to 24 years. Among these participants, there were 38 females and 31 males. The mean crowding scores for females and males were 4.897 mm and 4.953 mm, respectively. The severity of crowding among participants was stratified by gender, and the total number of participants in each severity category was as follows: mild (30), moderate (18) and severe (21). The total mean of crowding was 4.926 (Table 2).

Table 2.

Distribution of the crowding severity according to the sample gender.

Gender	Severity
	Mild	Moderate	Severe	Mean ± SD	Min - Max
M	16	5	10	4.897 ± 3.198	0.3–13.9
F	14	13	11	4.953 ± 2.866	0.1–12.3
Total	30	18	21	4.926 ± 2.768	0.1–13.9

Regarding the results of the linear regression testing the relationship between MAC and the pattern of IM3M, there is no statistically significant relationship observed between the numerical score of MAC and the pattern of IM3M angulation (p = 0.721). The study included 69 patients in the analysis (Table 3).

Table 3.

The linear regression testing the relationship between MAC and the pattern of IM3M.

	Model	Sum of Squares	Adjusted R2	Mean Square	F	P-value
H1	Regression	25.949	−0.016	5.19	0.573	0.721
	Residual	1195.606
	Total	1221.555

The contingency (chi-squared) table presents the distribution of severity of MAC as mild, moderate and severe according to the pattern of all IM3M (vertical, mesioangular, horizontal, distoangular and buccolingual), stratified by gender (male and female) (Table 4).

Table 4.

The distribution of impaction types based on gender and the severity of crowding.

Gender	Severity	Angulation
		Buccal	Disto-angular	Horizon-tal	Mesio-angular	Vertical	Total
F	mild	2	0	3	12	9	26
	moderate	1	2	6	11	8	28
	severe	0	3	5	8	6	22
	Total	3	5	14	31	23	76
X2 (p value)		7.158 (0.71)
M	mild	1	2	5	17	4	29
	moderate	1	1	1	7	2	12
	severe	2	2	4	8	5	21
	Total	4	5	10	32	11	62
X2 (p value)		6.099 (0.813)
Total	mild	3	2	8	29	13	55
	moderate	2	3	7	18	10	40
	severe	2	5	9	16	11	43
	Total	7	10	24	63	34	138
X2 (p value)		6.156 (0.802)

Chi-squared tests were employed to determine the presence of a significant association between the two variables. The chi-squared test for gender revealed no statistically significant results (χ² = 7.158, p = 0.710). Similarly, the chi-squared test for the angulation pattern of IM3M also revealed no statistically significant results (χ² = 6.156, p = 0.802). Overall, the results of the chi-squared tests suggest that there is no clinically significant association between the severity of MAC and either gender or the angulation pattern of IM3M (Table 4).

7. Discussion

The role of IM3M in exerting forces that can lead to MAC has been a controversial subject among dentists from various dental specialties, particularly oral surgeons and orthodontists, for numerous years (Alnamlah et al., 2021, Gökçe et al., 2021). A study conducted in Saudi Arabia aimed to compare the perspectives of Saudi oral surgeons and orthodontists regarding the prophylactic extraction of IM3M to prevent MAC. The findings revealed that the majority (61.1 %) of participants disagreed or strongly disagreed with the idea of a cause–effect relationship between third molar eruption and MAC. Additionally, 76.4 % of the sample did not recommend prophylactic IM3M extraction to prevent MAC (Alnamlah et al., 2021).

MAC is widely recognised as a significant concern that affects both oral hygiene and aesthetics in the general population. Several factors have been identified as potential causes of MAC (Gökçe et al., 2021). One of these factors is the availability of space for the eruption of the lower third molar, which was investigated in 2005 (Niedzielska, 2005). This research concluded that if there is sufficient space for the third molar to erupt, it will do so without causing any issues to the anterior teeth. When there is insufficient space, however, eruption of the third molars can potentially worsen existing crowding in the anterior region. It is worth noting that the precise role of IM3M as an aetiological factor of MAC remains unclear (Gökçe et al., 2021). However, an earlier study conducted by Marielle Blake and Bibby in 1998 emphasised the factors contributing to posttreatment crowding and concluded that if IM3M is involved in the development of late MAC, their impact is likely to be minimal (Blake and Bibby, 1998).

A review conducted by Konstantinia Almpani and Olga-Elpis Kolokitha reviewed the existing literature regarding IM3M and their relationship with preventing or relieving MAC. The study highlighted that those earlier studies indicated a stronger correlation between the presence of third molars and crowding in the lower jaw (Almpani and Kolokitha, 2015). However, more recent studies have contradicted this association and considered preventative extraction of third molars to be unnecessary.

In the present study, the samples were categorised based on the severity of anterior crowding into mild, moderate and severe groups. Additionally, the pattern of lower third molar impaction was classified using Winter’s classification, including vertical, mesioangular, horizontal, distoangular, buccolingual and inverted angulation. The results confirmed that there was no significant association between the angulation pattern of IM3M and the severity of MAC. Similar studies have supported this finding, with a study conducted by Gökçe, G. et al. in 2021 demonstrating no correlation between IM3M and MAC (Gökçe et al., 2021). Another study evaluated the influence of IM3M on the relapse of MAC in orthodontically treated patients and reached the conclusion that the presence or absence of mandibular third molars does not affect the relapse of MAC (Cotrin et al., 2020).

Moreover, a systematic review conducted by Lyros et al. in 2023 (Lyros et al., 2023) on the same topic supported these findings and concluded that a definitive relation between IM3M and MAC has not been established.

An example of a study that found a relationship between IM3M and MAC was a study conducted by Emad H. Abdulla et al. in 2014 (Abdulla et al., 2014). The study assessed the association between IM3M and MAC and categorised the sample into three groups: impacted third molars, erupted third molars, and missing third molars. It identified the potential role of IM3M in MAC, as the crowded group reported a higher percentage of IM3M while the lowest percentage of third molar agenesis. Another study investigated the prevalence of IM3M in patients with mandibular anterior teeth malocclusion. The study found that the most common angulation observed for impacted third molars in the entire sample was mesioangular, accounting for 68.5 %. The percentages of crowding associated with each impaction angulation were as follows: mesioangular (83.78 %), vertical (90.48 %), horizontal, distoangular and buccolingual positions (100 %). However, no assessment of the correlation between crowding and angulation was conducted in this study (Wei et al., 2019).

In the present study, the relationship between gender, the severity of crowding, and the angulation pattern of third molar impaction was investigated. However, the findings did not provide sufficient evidence to confirm any association between either the angulation pattern of third molar impaction or the severity of MAC.

A similar study was conducted to investigate the relationship between mandibular third molars and lower anterior teeth crowding following orthodontic treatment. The study found that retained mandibular third molars did not exhibit significant differences in crowding when compared between males and females (Azzaldeen, 2021).

Our study has notable limitations. The sample size was relatively small, and a larger sample size would provide more accurate and more robust results. The small sample size may be attributed to technical issues related to limited storage capacity in some hospitals, which resulted in the dental casts not being kept for the intended timeframe. Additionally, we encountered a challenge in our data collection process due to patients undergoing orthodontic treatment at a young age for aesthetic reasons, even before the completion of root formation in their third molars. This unfortunate circumstance potentially impacted the overall completeness of the data and affected our ability to collect comprehensive data.

It is important to note that this study is among the early efforts made to assess the relationship between the angulation pattern of IM3M and the severity of MAC. Therefore, we recommend conducting further studies to address the limitation of the present study and obtain more comprehensive insights into this subject matter.

8. Conclusion

Based on the findings of this study, it can be concluded that there is no significant relationship between the pattern of third molar impaction and the severity of MAC in the study sample. Furthermore, no association was observed between gender and either the pattern of third molar impaction or the severity of MAC.

9. Declaration

The Authors declare that the work described in this paper was not influenced by any conflicting interests or personal relationships. This research did not receive any funding. This study adhered to the ethical standards set by the Biomedical Research Ethics Committee at Umm Al-Qura University and received approval by the same committee.

10. Availability of data and materials

All materials are available from the corresponding author on request.

11. Ethics statement

The Biomedical Research Ethics Committee at Umm Al-Qura University approved this study, and all procedures followed ethical standards.

12. Financial support

This research did not receive any specific funding.

CRediT authorship contribution statement

Abrar K. Demyati: Conceptualization, Project administration, Methodology, Supervision, Writing – original draft. Fatima A. Badgaish: Project administration. Rawan A. Alzahrani: Project administration. Rawan O. Alsehli: Project administration. Sara A. Alnuayri: Project administration. Alaa W. Alqutub: Supervision, Formal analysis. Abdalmalik O. Ghandourah: Writing – review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.