Periodontal Stress Distribution In Maxillary First Molar Distal Movement Three-dimensional Finite Element Analysis

Objective: The aim of this study was to analyse the stress distribution in the periodontium of the maxillary first molar and to grasp optimal loads pattern when distal movement to provide biomechanical basis for the clinical practice. Methods: By CT scanning,a three-dimensional finite element model of the maxillary first molar was established, and then four different load patterns was added, which include: (I) a unit distalizing force only, F=1N (2) a unit countertipping moment(Mt) , Mt1N mm; (3) a unit counterrotation moment(Mr), MrIN mm; (4)a unit distalizing force combined with different Mt and Mr Different forces were added to the molar to obtain the optimal load partern for molar bodily movement. Results: Stress patterns in the periodontium changes with different load patterns. (1) A distalizing force(1N) without any moments made a high concentration of compression (-O.0605N/mm2) at the cervical region of the distal-buccal root due to the tipping and rotation of the tooth. (2) Applying a countertipping moment(Mt=1N mm) , a high tensive stress(0.00494N/mm2) was observed at the cervical level of the periodontium of the distal-buccal root and a compressive stress (O.0029N/mm2 ) at the cervical level of the peripdontium of mesial (3)When a countez-rotation moment (Mr=IN mm) was applied , A lower tensive stress(about 0.001 89N/mm2 ) was found on mesial side of palatal root , distal side of the distal-buccal root and buccal side of mesial-buccal root.0(4) A distalizing force combined with a countertipping momt(Mt10N mm,Mt/F= 10) and a counterrotation moment (Mr N mm, Mr/F=6) can obtain a very lower stress distribution on the distal side of periodonflum, whereas a concentration of compressive stress was observed on the mesial side of the roots at the furcation level Conclusions: (1) A distalizing force combined with a countertipping moment (Mt/F=10) and a counterrotation moment(Mr/F6) can lead to a lower and uniform stress on the distal side of the periodontal ligament ,it implys a tendency of translation. (2) The shape and stiffliess of the root made the stress distribution vary significantly with different loads,espeeially around the furcation.High stress concentration on the root at the furcation level demonstrates that the shape of the root of the maxillary first molar made it less prone to apical stress concentration.