Incisor and mandibular movement during retrusion

Human mastication, respiration, speech, swallowing and suckling are directed by the jaw muscle activites, the temporo-mandibular joints, the ligaments and by the occlusal dental contacts. Mastication is usually assessed by border movements of the mandibular incisors. While the border movements of opening, protrusion and lateratrusion are often used to determine the mandibular functions, the movement of retrusion is rarely considered in the study of the human oro-facial functions. Our purpose was to evaluate the mandibular movement of retrusion in a population that did not present any symptoms nor clinical signs of temporo-mandibular disorders. The study was performed on 117 males and 121 females (age range: 17.7-65.2 years; mean age: 31.1 years) using electrognathographic registrations (Sirognatograph^*, Siemens, Benshein, Germany). Every patient was instructed and trained before recording. The measurements were calculated on the sagittal plane registrations. The results showed that the mandibular movement of retrusion was present in 233 out of the 238 studied subjects (97.9%) whatever was the dental class, the age or the sex. The width range was between 0.3 and 5.4 mm and the mean value was 1.75 ± 0.91 mm. The inferential analysis performed by a 3-way ANOVA model demonstrated no significant difference in retrusion value by dental class, gender or age. The most frequent numerical value was 1.5 mm, observed in 16 subjects (6.7% of the studied population). These results suggest that, in order to respect the physiological characteristics, more attention is needed in performing dental treatments.