Impact of the lower third molar presence and position on the risk of fracture in the regions of mandibular angle and condyle

Abstract

Previous clinically-epidemiological studies suggested that the presence of a lower third molar (wisdom tooth), especially unerupted, increases the risk of mandibular angle fracture. However, in the case of absent third molar, a greater frequency of condylar fractures is noted, the treatment of which is more complicated. Since previous studies have not considered other risk factors besides the the wisdoom tooth, the interest was to analyse the impact of the lower third molar parallel with the impacts of other risk factors (patient gender and age, trauma etiology, site od action of the traumatic force) on mandibular angle and condylar fractures, and to show possible predictors of these fractures. Given that the impact of the wisdom tooth on the distribution of the stress (important for fracture development) in the mandibular angle and condylar regions is not familiar, it was meaningful to analyze the stress distribution in the terms of the presence, position, eruption status of the wisdom tooth, and of the site of action of the impact force. The aim of the study was to investigate the influence of the lower third molar presence, position and number of the roots, on the risk of mandibular angle and condylar fractures. The aim was also to estimate the influence of trauma factors (trauma etiology and site of action of the impact force) on these fractures. The study consisted of two separate units: clinical-epidemiological study and Finite Element Analysis (FEA) of the computational models of the lower jaw. In the clinical-epidemiological study, collected data were based on the patient history, anamnesis, clinical examination and radiographs: the ortopantomorgraph and frontal radiograph of the lower jaw. Primary independent variables were: properties of the wisdom tooth (presence, eruption status, vertical and horizontal position classified by Pell and Gregory, angulation, relation to the inferior border of the mandible, number of roots), patient gender and age, trauma etiology and site of action of the impact force. The main outcome variables were the mandibular angle and condylar fractures. In the second part of the study computer models of the lower jaw were analysed by means of Finite element Analysis- FEA. The models were created on the basis of the CT scans of the mandible belonging to an adult male person with full dental arch and erupted third molars...

Dosadašnje kliničko-epidemiološke studije su pokazale da prisustvo donjeg trećeg molara (umnjaka), naročito neizniklog, povećava rizik za nastanak preloma donjeviličnog ugla. Međutim, u slučaju odsustva umnjaka, zapažena je veća učestalost preloma zglobnog nastavka donje vilice, koji u odnosu na prelom vličnog ugla iziskuje komplikovaniji hirurški tretman. Kako dosadašnje studije, pored umnjaka, nisu razmatrale i druge faktore rizika za nastanak preloma donjeviličnog ugla i zglobnog nastavka, od značaja je bilo analizirati uticaj umnjaka uporedno sa uticajem drugih faktora rizika (pol i starost pacijenata, etiologija povrede, mesto dejstva traumatske sile) i izdvojiti moguće prediktore ovih preloma. Obzirom na to da nije poznat uticaj umnjaka na distribuciju napona značajnog za nastanak preloma u regionu donjeviličnog ugla i zlobnog nastavka, od značaja je takođe bilo analizirati i distribuciju napona u zavisnosti od prisustva, položaja i stepena izniklosti umnjaka, kao i od mesta dejstva traumatske sile. Cilj rada je bio da se ispita uticaj prisustva, položaja i broja korenova donjeg umnjaka na rizik za nastanak preloma u regionu donjeviličnog ugla i zglobnog nastavka. Takođe, cilj je bio i da se proceni uticaj faktora traume (etiologije povrede i mesta dejstva traumatske sile) na ove prelome. Studija se sastojala iz dva zasebna dela: kliničko-epidemiološke studije i analize kompjuterskih modela donje vilice primenom metode konačnih elemenata. U kliničko-epidemiološkom delu studije, prikupljeni podaci su bili bazirani na istorijama bolesti, anamnezi, kliničkom pregledu i načinjenim radiogramima: ortopantomogramu i postero-anteriornom radiogramu donje vilice. Primarne nezavisne varijable su bile: svojstva donjeg umnjaka (prisustvo, stepen izniklosti, vertikalni i horizontalni položaj klasifikovan po Pell-u i Gregory-ju, nagib, odnos prema donjoj ivici donje viice, broj korenova), pol, starost, etiologija povrede i mesto dejstva traumatske sile. Glavne ishodne varijable su bili prelomi donjeviličnih uglova i zglobnih nastavaka. U drugom delu studije analizirani su kompjuterski modeli donje vilice primenom “metode konačnih elemenata” (Finite element Analysis-FEA). Modeli su kreirani na osnovu kompjuterizovano-tomografskih (Computerised Tomography- CT) snimaka donje vilice odrasle muške osobe, sa punim zubnim nizom i izniklim umnjacima...