| PurposeTo study the effection of the digital splint thickness and the position of splints to mandibular molar advancement.The biomechanical evaluation was performed on the digital splints moving mandibular molar phase,including the material properties of the splint,and the manner of force applied on the buccal and lingual side.MethodThe 3D geometric model of mandible bone and teeth with high geometric similarity and mechanical similarity were obtained by high-precision CBCT scans and Mimics 17.0.Individualized teeth were simulated by CAD software(Geomagic 2015,Solidworks 2010,3-matic 10.0)to simulate the mandibular dentition after aligning and leveling,as well as the creation of entity models such as lip appliance,arch wire,and personalized tongue buttons.Personalized designs of various types of front digital splints through 3-matic10.0 and Geomagic 2015 software include the left cuspid to the right cuspid lingual side splint(mandibular 3-3 splint),the left first premolar to the right first premolar lingual splint(mandibular 4-4 splint),the left cuspid to right cuspid side lingual splint with hook(mandibular 3-3 splint with hook),the left first premolar to the right first premolar lingual splint with hook(mandibular 4-4 splint with hook).After importing the three-dimensional finite element calculation software ANSYS Workbench16.0 to divide the grid and set the material properties,the three-dimensional finite element nonlinear models with digital splints to forward the molar were obtained,including the geometric model without the first premolars and the another model without the second premolars.On the basis of the model without the mandibular first premolars,the different thickness of digitized splints were established,including 0mm,0.3mm,0.5mm,0.7mm,0.9mm.The traction force of the buccal side is 100 g.Set up buccal force group:(1)extaction of the fisrt premolars without the splint;(2)extaction of the fisrt premolars with the 3-3 splint;(3)extaction of the second premolars without the splint;(4)extaction of the second premolars with the 3-3 splint;(5)extaction of the second premolars with the 4-4splint 。 Set up buccal-lingual force group:(6)extaction of the fisrt premolars without the splint;(7)extaction of the fisrt premolars with the 3-3 splint plusing hook;(8)extaction of the second premolars without the splint;(9)extaction of the second premolars with the 3-3 splint plusing hook;(10)extaction of the second premolars with the 4-4splint plusing hook。In the(1)-(5)groups,the buccal force system was established.The intra-mandibular traction force was applied between the buccal tube of the mandibular first molar and the traction hook using a spring unit.The traction force was 100 g.The(6)-(10)groups established a simultaneous force system on the buccal-lingual side,and the intra-mandibular traction force was applied between the buccal tube of the mandibular first molar and the traction hook using a spring unit.Another intra-maxillary traction force was applied between the molar lingual side and the mandibular cuspid lingual button or the hook of the splint.The traction force was 50 g respectively.The sagittal initial displacement of the anterior teeth and the hydrostatic pressure of the periodontal ligament were measured and analyzed.Result1.the three-dimensional finite element nonlinear models with digital splints to forward the molar were established.2.With the increase of the thickness of the splint,the sagittal initial displacement of the midpoint of the lower anterior tooth decreases gradually.When the thickness of the splint gradually increases to 0.7mm,the displacement of the lower anterior tooth tends to be stable.With the increase of the thickness of the splint,the maximum deformation and the minimum deformation of the splint gradually decrease.When the thickness of the splint is 0.7mm,it shows a steady state.The stress concentration area of the splint is located on the occlusal side of the splint and is evenly distributed on each teeth.3.Comparison of the sagittal initial displacement of the midpoint of the mandibular anterior teeth with the buccal force:(1)>(2);(3)>(4)>(5).Comparison of initial sagittal displacement at the midpoint of the mandibular incisor margin with the buccal-lingual force:(6)>(7);(8)>(9)>(10).4.At the same 100 g loading force,when the buccal force-applying system was used,the buccal cusp of the first molars showed a lingual rotation,and the lingual cusp showed a distal lingual rotation.When the buccal-lingual side force-applying system was applied,the buccal and lingual cusp of the first molar showed a near-medium movement.5.Under pure buccal force,if there is no splint,the brearing force of mandibular central incisor is obvious.If the splint exists,the brearing force of mandibular canine is obvious,and the hydrostatic pressure of mandibular anterior teeth is lower than the upper limit.Under the simultaneous application of force on the buccal and lingual sides,the mandibular canine was subjected to significant force.Only when there was no splint,the hydrostatic pressure of the mandibular canine exceeded the upper limit value.Conclusion1.Under 100 g intra-mandibular tractive force,the lingual tipping movement occurred at the incisal margin and apical point of the lower anterior tooth,and the initial displacement of the incisal margin was significantly greater than the initial displacement of the root tip.2.Under 100 g intra-mandibular traction,when the thickness of the splint is 0.7mm,the initial displacement of the lower anterior tooth and the deformation of the splint tend to be stable,and the thickness can reach the experimental and clinical requirements.This will have certain effect on the subsequent experiments and clinical design.3.Whether it is the buccal force or the simultaneous application of force on the buccal and lingual sides,the mandibular anterior splints enhance the anchorage of the mandibular anterior teeth,and the more the mandibular anterior teeth contact the mandibular anterior splint,the better the anchorage effect is.And it’s more conducive to the mandibular molars to move forward.When the mandibular anterior splint is present,the initial displacement of the mandibular anterior tooth is relatively uniform,so that the force of the teeth is evenly distributed,which is more conducive to the health of the teeth and periodontal. |
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