The relationship between third molars and mandibular incisor crowding is one of the most debated and studied fields in orthodontics, and despite all, is still quite controversial. Late crowding is considered to have multifactorial etiology, whereas etiological factors may differ between individuals. Proposed etiological factors include differential growth of the jaws, functional and parafunctional pressure of the soft tissues, muscular imbalance and distribution of the anterior component of the occlusal force [1, 2]. Many studies have attempted to clarify and evaluate the third molars and incisor crowding interrelationship [3–8]. Mandibular incisor crowding is highly prevalent, as up to 40% of the general population has moderate to severe crowding [9]. Given the esthetic demands, maxillary incisor crowding is one of the most frequent reasons for seeking orthodontic treatment [10]. However, with aging, there is a gradual decrease of exposure of upper incisor, accompanied by an increase in lower incisor exposure [11], making the lower crowding more visible therefore compromising smile esthetics.
Skeletal maturation can be influenced by environmental and hereditary factors. On the other hand, teeth are much more reliable for age estimation because its tissues do not undergo continuous remodeling processes. During time, versatile dental age estimation methods have been developed. In 2006, Cameriere [12] presented a method based on a measurement of open apices of the teeth. The method was originally applied on Italians and then applied on different European and non-European subjects [13–16]. It was reported as very accurate, because it showed that variability between samples did not significantly influence the regression formula [17]. When applied to third molars, this method showed very high percentage of correctly classified cases in European subjects [18].
Crowding as an occlusal trait becomes more common during dentition development and aging, due to maturational, regressive and degenerative factors [1, 2, 19]. Incisor crowding most commonly manifests as tooth rotations and labiolingual displacement from the arch line, often followed by different amounts of mesiodistal overleap of contact points [20]. Late crowding is observed in mandibular incisors during late adolescence and it is considered to be a late expression of primary crowding [1, 19].
Increase in mandibular incisor crowding was reported to occur between 13 and 26 years, in the late adolescence and early adulthood [21, 22]. It often coincides with the eruption of mandibular third molars, which might imply their causal role. However, it seems that the role of mandibular third molars in anterior crowding cannot be categorically denied [23].
Late mandibular incisor crowding is observed in both treated and untreated subjects, and worsens with age, most evidently due to decrease in arch length and perimeter and mandibular dental arch becoming more square-shaped [21, 24–26].
Many literature reviews [27–29] attempted to affirm the relationship between third molars and crowding, however due to questionable methods, lack of standardization, various inclusion criteria and study designs definite conclusion on this interrelationship cannot be set [29]. Some authors attributed the incisor crowding to the mesial pressure exerted by the mandibular third molar [4], on the other hand others do not consider this pressure capable of causing anterior crowding [3]. Some research findings report that no strong relation exists between the third molar eruption level, space, and angulations to mandibular anterior crowding [6]. It seems that the only connection between crowding and eruption of the third molars is the concurrent occurrence of the two phenomena [30].
The aim of this study was to investigate presence and mandibular third molar development dynamics, i.e., rate; occurrence and amount of late mandibular incisor crowding and their possible interrelationship.
Hypotheses were that decelerated development and absence of eruption of mandibular third molars could influence the amount of mandibular incisor crowding.