Routine Premolar extraction as part of orthodontic treatment may impact mandibular kinematics

The researchers showed that premolar extraction altered mandibular kinematics in at least 25% of the cases within the study sample, and the transversal discrepancy between retrusive and protrusive tracings was even predictive of group affiliation.

The practice of premolar extraction in orthodontics remains controversial owing to its potentially detrimental effects on the stomatognathic system. However, there is no proper understanding of how premolar extraction affects mandibular function. Alejandra Londoño, Department of Research in Occlusion Medicine, Vienna School of Interdisciplinary Dentistry — VieSID, Klosterneuburg, Austria, and colleagues, therefore, aimed to assess the impact of premolar extraction on mandibular kinematics by evaluating axiographic tracings.

For this purpose, the researchers compared forty-five orthodontically treated patients with premolar teeth extraction with 45 paired untreated controls, selected for the absence of malocclusions. Mandibular movements were recorded by systematic three-dimensional axiography for protrusive–retrusive movements and speech. The transversal deviations, length of the movements, and rotation angle were recorded for both sides during the speech.

The permutation test and Wilcoxon rank-sum test were used to analyze the differences between the axiographic variables. Linear regression was performed to test whether axiographic parameters predicted group affiliation. Dot plots were used to explore the distribution of each of the axiographic outcomes. Isometric principal component analysis was used to assess the differences between the cumulative effects of premolar extraction on jaw motion.

The study led to the following findings:

• The mandibular lateral translation in protrusion–retrusion and speech, the amount of rotation as well and the length of mandibular movements during speech were significantly higher in the treated subjects than in the controls, while retral stability did not differ.
• The linear regression yielded significant results for the mandibular lateral translation in protrusion–retrusion.
• The isometric principal component analysis showed higher values of the axiographic variables for 11 out of 45 individuals in the study sample compared with the control group.

"These results support the notion that the routine practice of premolar extraction as part of the orthodontic treatment should be discouraged," the researchers wrote.

Additionally, the team suggests recommending the evaluation of mandibular movements as an integral part of diagnostic and follow-up assessment of treatment outcomes.

"To assess whether a disrupted kinematics of the mandible is associated with temporomandibular disorders, it is compelling to perform further studies," they concluded.

Reference:

Londoño A, Assis M, Fornai C, Greven M. Premolar Extraction Affects Mandibular Kinematics. Eur J Dent. 2023 Jul;17(3):756-764. doi: 10.1055/s-0042-1755629. Epub 2022 Sep 27. PMID: 36167318; PMCID: PMC10569881.