Abstract
Objective: To evaluate the effects of unilateral loss of the lower first permanent molar (L6) on the position and development of the lower third molar (L8) . Material and Methods: Fifty-four panoramic radiographs of subjects with unilateral loss of L6 were examined. The L8 on the side of the L6 loss was compared with the L8 in the hemiarch without L6 loss (contralateral). The effect of L6 loss on the positioning of L8 was examined in all the samples (n=54), whereas the effect on the development of the third molar was examined in 38 patients with L8 with incomplete root formation. The Signs statistical test was used to evaluate the comparison between loss and contralateral hemiarches. Results: In 20 (37%) of 54 subjects, the L8 was better positioned in the hemiarch with loss of the lower first molar (p<0.001) compared with the control side. In the remaining 34 subjects, no difference was found. When only the L8 considered as impacted on the control side was examined (n=30), the cases with better positioning on the side with L6 loss increased to 66.6% (p<0.001) . Conclusion: The loss of lower first molars improves the position of the lower third molar during its active eruption, mainly when the lower third molar is impacted. However, L6 loss does not affect the root development of lower third molars.
Highlights
The loss of lower first permanent molars is regarded as the most prevalent tooth loss because these are the permanent teeth most likely to decay and to have developmental defects [1]
The comparison of the degree of root development of the third molars in the 38 cases that presented third molar development indicated that in 33 (86.9%) cases, the third molars on both sides were considered to be at the same stage of root development; only in 5 (13.1%) cases were the third molars on the loss side considered to be in a more advanced stage (Figure 4)
The statistical analysis showed no difference in the degree of dental development of the lower third molars between the side with lower first molar loss and the control side (p=0.07)
Summary
The loss of lower first permanent molars is regarded as the most prevalent tooth loss because these are the permanent teeth most likely to decay and to have developmental defects [1]. Studies have reported that the extraction of first molars causes a lingual inclination of the lower incisors [4,5,6,7,8,9], enabling the migration of the adjacent teeth into the extraction side and increasing the eruption space of third molars [2,10,11] All these can justify the need for orthodontic treatment and rehabilitation due to the occlusal changes' complexity [3]. Recent studies have shown that before the age of 12 years, the loss of permanent first molars might have an accelerating effect on the development of the third molars on the extraction side compared with the contralateral teeth [5] Because these are the last teeth to complete their development and eruption process [8,9], there is sometimes not enough space for a normal eruption, leading to a total or partial impaction. A major issue in clinical practice is the diagnosis of the need for either preservation or surgical removal of third molars [6], which are the teeth most likely to remain retained [7,8], especially in the lower dental arch [9]
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