The aim of this systematic review was to investigate the influence of the presence and position of mandibular third molars in mandibular condyle fractures. An electronic search was conducted in PubMed, Scopus, Web of Science, Cochrane Library, and VHL, through January 2016. The eligibility criteria included observational studies. The search strategy resulted in 704 articles. Following the selection process, 13 studies were included in the systematic review and 11 in the meta-analysis. In terms of the risk of bias analysis, six studies presented ≤6 stars in the Newcastle–Ottawa scale assessment. The presence of a mandibular third molar decreased the probability of condylar fracture (cross-sectional and case–control studies: odds ratio (OR) 0.26, 95% confidence interval (CI) 0.17–0.40, I 2 = 87.8%; case–control studies: OR 0.30, 95% CI 0.16–0.58, I 2 = 91.6%). The third molar positions most favourable to condylar fracture according to the Pell and Gregory classification are class A (OR 1.32, 95% CI 1.09–1.61, I 2 = 0%) and class I (OR 1.37, 95% CI 1.05–1.77, I 2 = 32.8%). Class B (OR 0.69, 95% CI 0.49–0.97, I 2 = 56.0%) and class II (OR 0.71, 95% CI 0.57–0.87, I 2 = 0%) act as protective factors for condylar fracture. The results suggest that the presence of a mandibular third molar decreases the chance of condylar fracture and that the positions of the third molar most favourable for condylar fracture are classes A and I, with classes B and II acting as protective factors.
Mandibular fractures are common injuries and their prevalence is determined by factors such as sex, age, and socio-economic status . Among the mandibular fractures, condylar fractures are the most common, ranging from 29% to 56% . This high incidence of condylar fracture is attributed to the association of biomechanical factors such as bone density and anatomical structures that create weak areas . The join between the ramus of the mandible, which has a high rigidity, and the condyle, which has a lower rigidity, is responsible for indirectly transmitting impact forces and directing them to the condyle .
In addition to these factors, several authors have stated that the presence and position of the third molar are factors influencing the location at which mandibular fractures occur . It has been indicated that the presence of a mandibular third molar creates a weak area in the angle, which favours the incidence of fracture in this region . For this reason, the previously reported systematic review was performed to evaluate the influence of mandibular third molars on angle fractures . The results of the meta-analysis showed that the presence of a third molar increases the chance of fracture in the mandible angle by a factor of 3.27.
As well as their influence on angle fractures, epidemiological studies suggest that the absence of a third molar does not result in brittleness in the angle and would be responsible for transmitting the impact force to the condyle, thereby increasing the incidence of condylar fracture . In a study using finite element methods to assess the influence of the third molar on condylar fractures, it was demonstrated that when a third molar is present, the stress forces increase slightly in the angle region and simultaneously decrease in the condyle . In the model without a third molar, the stress forces were smaller in the angle region and increased in the condyle region. Moreover, it was possible to predict which region would have the largest stress according to the presence or absence of a third molar and the region of impact.
Some studies have even suggested the prophylactic removal of third molars in contact sport athletes, due to their influence in angle fractures . However, several other studies have shown that the incidence of condylar fracture is higher when the third molar is absent. Furthermore, condylar fractures are more difficult to treat because of issues with accessibility and the possibility of complications .
Therefore, the aim of this systematic review was to evaluate the scientific evidence regarding the influence of the presence and position of mandibular third molars in condylar fractures.
Materials and methods
This systematic review and meta-analysis was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. The PECO process was used to determine the clinical question (patient, problem, or population; exposure; comparison; outcomes). The population comprised patients with mandibular fractures; the exposure was the presence of the third molar and its different positions; the comparison was with other mandibular fractures; the outcome was a mandibular condyle fracture.
In terms of the study design, the inclusion criteria encompassed cross-sectional, case–control, and prospective or retrospective cohort studies that evaluated the influence of the presence of mandibular third molars on condyle fracture.
The exclusion criteria were: (1) case reports, case series, opinion articles, and review articles; (2) studies that reported mandibular fracture during the extraction of third molars; (3) studies that evaluated bad split fractures in orthognathic surgery due to the presence of the third molar; (4) studies including pathological mandibular fractures due to the presence of lesions associated with the presence of the third molar; (5) studies that included patients with diseases of bone metabolism (osteopenia and osteoporosis).
The electronic search was conducted in the PubMed, Scopus, Web of Science, Cochrane Library, and VHL (Virtual Health Library; BIREME (PAHO/WHO)) databases, and included publications through January 2016, without language restriction. A combination of medical subject heading (MeSH) terms was used for the search. The terms used in the databases were: (mandible fracture OR mandibular fracture) AND (third molar OR wisdom tooth OR wisdom teeth).
After searching the databases, the titles and abstracts of articles were read by two authors independently (ACVA and SGMF). Studies that could potentially meet the inclusion criteria for the review were identified at this stage. After independent reading, the authors compared the results of the studies that would pass to the next stage (article read in full), reaching an agreement on their inclusion or not. In the case of disagreement, a third author (ELG) was consulted to obtain a consensus. The studies selected after reading the title and summary were read in full. At this point, it was determined whether or not the study should be included in the systematic review.
The assessment of the quality of the studies was performed using the Newcastle–Ottawa scale (NOS) for case–control studies and a modified NOS for cross-sectional studies . The case–control studies were assessed for the following three components: selection, comparability, and exposure. The cross-sectional studies were assessed for the following three components: selection, comparability, and outcome. The NOS for both study types had a maximum possible score of 9 stars/points for each study.
The data extraction was performed in two stages. In the first stage, the following data were extracted: author, year of publication, study design, country where the research was performed, sample (male, female, and total), type of analysis (patients and fractures), mean age, and main cause of mandibular fracture ( Table 1 ). In the second stage, the following data were extracted: mandibular condyle fracture (present or absent), third molar (present or absent) ( Table 2 ), Pell and Gregory classification when a third molar was present, for the occlusal plane (A, B, C) and for the mandibular ramus (I, II, III), and the Winter classification (vertical V, mesioangular MA, horizontal H, distoangular DA) ( Table 3 ).
|Author||Year||Study design||Country||Sample||Analysis type||Age, years||Main cause of fracture|
|Choi et al.||2011||CS||South Korea||333||52||385||Patients||NR||Violence|
|Mah et al.||2015||CS||South Korea||348||92||440||Patients||NR||Violence|
|Duan and Zhang||2008||CS||China||563||137||700||Patients||NR||Traffic accident|
|Gaddipati et al.||2014||CS||India||95||15||110||Fractures||18–55||Traffic accident|
|Iida et al.||2004||CC||Japan||250||96||346||Patients and fractures||NR||Violence|
|Inaoka et al.||2009||CS||Brazil||38||5||43||Patients||26.35||NR|
|Oh et al.||2006||CC||South Korea||82||23||105||Fractures||35.8 ± 14.4 M||Traffic accident|
|36.9 ± 15.3 F|
|Revanth Kumar et al.||2015||CS||India||56||8||64||Patients and fractures||16–69||Traffic accident|
|Naghipur et al.||2014||CC||Canada||377||69||446||Patients||29.3 ± 11.3||Violence|
|Patil||2012||CS||India||164||26||190||Patients||21–30 (46%)||Traffic accident|
|Zhu et al.||2005||CC||South Korea||359||80||439||Fractures||28.5||Violence|
|Thangavelu et al.||2010||CC||India||345||115||460||Patients||31.2||Traffic accident|
|Lee et al.||2012||CS||South Korea||NR||NR||86||Patients||NR||Violence|
|Author||With condyle fracture||Without condyle fracture||P -value|
|With third molar||Without third molar||With third molar||Without third molar||Total|
|Choi et al.||47||87||145||182||461||0.067|
|Mah et al.||84||57||149||30||320||<0.001|
|Duan and Zhang||133||167||237||163||700||<0.001|
|Gaddipati et al.||6||41||60||11||118||<0.001|
|Iida et al.||78||97||111||60||346||NR|
|Inaoka et al.||39||52||NR||NR||91||<0.001|
|Oh et al.||42||32||234||103||411||<0.05|
|Revanth Kumar et al.||36||4||NR||NR||40||NS|
|Naghipur et al.||51||79||182||134||446||<0.001|
|Zhu et al.||38||108||136||34||316||<0.001|
|Thangavelu et al.||89||172||171||28||460||<0.001|
|Lee et al.||12||11||51||12||86||0.008|
|Author||Pell and Gregory classification||P -value||Pell and Gregory classification||P -value||Winter classification||P -value|
|With condyle fracture||Without condyle fracture||With condyle fracture||Without condyle fracture||With condyle fracture||Without condyle fracture|
|Mah et al.||40||29||15||60||61||28||<0.005||25||43||16||23||98||28||<0.005||33||28||7||1||42||64||23||7||<0.05|
|Duan and Zhang||194||79||31||462||269||63||0.003||164||75||65||361||247||186||0.003||NR||NR||NR||NR||NR||NR||NR||NR||NR|
|Iida et al.||76||133||NR||248||235||NR||0.0003||NR||NR||NR||NR||NR||NR||NR||NR||NR||NR||NR||NR||NR||NR||NR||NR|
|Inaoka et al.||65.4%||30.8%||NR||NR||NR||NR||NR||73.1%||NR||NR||NR||NR||NR||NR||75%||21.1%||NR||NR||NR||NR||NR||NR||NR|
|Naghipur et al.||38||25||6||234||162||74||0.301||32||27||10||188||206||76||0.603||20||42||6||1||119||311||34||6||0.859|
|Thangavelu et al.||51||23||27||167||174||78||<0.0001||50||33||27||184||155||71||<0.0001||75||83||29||64||76||167||6||11||<0.0002|
|Lee et al.||9||3||0||NR||NR||NR||0.042||7||5||0||NR||NR||NR||0.949||NR||NR||NR||NR||NR||NR||NR||NR||NR|