Zum initialen Einfluss des anterioren Führungswinkels von Oberkiefer-Äquilibrierungsschienen auf die mandibuläre Ruhelage und den minimalen inzisalen Sprechabstand

The design of anterior tooth guidance is of great importance for dental restaurations, as it defines the individual interincisal free space, in which the mandibular rest position and the closest speaking space are usually located. In this space, the lower jaw can move freely without tooth collision. All sub-disciplines of dentistry can influence the shaping and limitation of the interincisal space. When bite splints are inserted as part of the pre-therapy of craniomandibular dysfunctions, the equilibration splint with anterior canine guidance is considered the gold standard. Depending on the length, curvature and steepness of the selected anterior guide, the interincisal space can be significantly influenced. Generally accepted guidelines regarding the length, inclination and spatial shape of the anterior guidance of bite splints and the anterior guidance in general are still lacking. Changes in the anterior guidance path and thus in the individual interincisal space inevitably lead to a changed cranial border guidance of the mandible. This has a biomechanical effect. The neuromuscular influence of changes in the anterior relation on non-tooth-guided mandibular postures and movements has not been sufficiently investigated. This is especially true for the mandibular rest position and the closest speeking space. The following hypotheses were part of the present study: • Restriction of the interincisal space by artificially dividing of the anterior guidance results in a dorsocaudal shift of the mandibular rest position. • Increasing the occlusal vertical dimension caused by the bite splint leads to a initial change in the mandibular rest position after inserting the bite splint. • Restriction of the interincisal space by artificially dividing of the anterior guidance leeds to a dorsocaudal shift of the closest speeking space. • Occlusal contacts initially occur during phonation after inserting the bite splint. In this study, 13 female and 8 male subjects with an average age of 25 years were involved. To participate in the study, they had to be fully dentate and have a stable occlusion with class I occlusion. Furthermore, they had to have anterior guidance with posterior tooth disclusion for dynamic occlusion and no disturbance of masticatory muscle and temporomandibular joint function. To test the hypotheses, two bite splints were fabricated for each of the 21 test subjects, which were almost identical except for the steepness of the anterior guidance path. Variant S0 contains the patient-specific steepness of the anterior guidance, variant S2 a steeper one by 15°. As components of the mandibular movement, the parameters of rest position and its adaptation as well as, from a phonetic point of view, the adaptation of the closest speaking space during the first hour of wearing the test splint were examined on the mandible. The movements of the lower jaw were determined at defined points in time using the K7 method, which works according to the magnetic kinesiographic principle. For this, only a small magnet (weight 2 g, dimensions 4 x 5 x 2 mm) had to be reversibly attached to the labial surfaces of the lower incisors; the lip closure remains almost unaffected by this magnet. The measurements were taken with the help of a sensor array that was placed on the subject's head. Changes in the mandibular positions were observed in the sagittal plane and checked for deviations in the vertical (y-axis) and anterior-posterior axis (x-axis). Due to its system, K7 magnetic kinesiography only allows the recording of one measuring point and therefore cannot track the spatial position of the mandibular body in the three spatial axes and thus the movement of the condyles. However, by recording in the area of the lower incisal point, conclusions can be drawn about the displacement of the condyles in the joints in the sagittal and vertical planes, as these points are coupled by the mandibular bone. The closer the registered mandibular position is to the retrally forced opening path, the lower the translational component of the mandibula. Mandibular positions posterior to the habitual opening path are associated with increased retractor activity. Their increased recruitment would cause a dorsocranially directed force vector. A power of 80% and a significance level of 5% were used for the statistical evaluation. If the investigated target variables did not correspond to a normal distribution, the WILCOXON test for pair differences was used as a non-parametric test. Based on the data analyses, the hypothesis that a dorsocaudal shift of the mandibular rest position occurs when the interincisal space is restricted by artificial steepening of the anterior guidance must be rejected. The assumed resting position with test splint S0 (patient-specific steepness of the anterior guide) and test splint S2 (15° offset of the anterior guide) was in the immediate vicinity of the habitual opening path during one hour of wear. Increased activity of the retractors and resulting dorsocranially directed force vectors in the temporomandibular joint can be excluded. In the present study, a mean vertical rest position of 0.81 mm for test splint S0 and 1.00 mm for test splint S2 was achieved immediately after insertion for both splint variants with a vertical elevation of 4.5 mm. None of the test subjects had tooth contact. Thus, the hypothesis that the blocking of the occlusal vertical dimension caused by the bite slint initially by insertion oft he bite splint leads to a change of the mandibular rest position can be accepted. The hypothesis that a change in the minimum speaking distance in dorsocaudal relation is caused by a restriction of the interincisal space due to an artificial division of the anterior guide path must be rejected. On average, there was no significant deviation from the habitual opening path at any point in time; the average positions for the speaking distance were in the vicinity of the habitual opening path at all points in time. When the S2 splint was worn, a minimally more anterior position was assumed on average. In the course of this study, no tooth contact was detected at any time when the closest speaking space was adopted, not even initially after the splints were inserted for the first time or at any other time with the splints in situ. Therefore, the hypothesis that occlusal contacts during phonation occur initially with the insertion of the bite splint must be rejected.