Evaluation Of Craniomaxillofacial Effects During Miniscrew-assisted Rapid Palatal Expansion(MARPE):A Three-dimensional Finite Element Analysis

ObjectiveThe aim was to evaluate the effects of craniomaxillofacial structures after changing various parameters of the miniscrew-assisted rapid palatal expansion(MARPE)using the finite element method and to support clinical usage as a reference.MethodsThe FE model was created from tomography images of a young healthy male adult volunteer using Mimics(version 19.0),Geomagic wrap,and Hyper Mesh(version 14.0)software.The craniomaxillofacial complex,including their suture in the FE mesh were sectioned into 0.25-5 mm tetrahedrons and assumed to be isotropic,homogenous,and linearly elastic.The designs of miniscrew-assisted rapid palatal expansion(MARPE)were made under the following conditions: With the miniscrew inserted 3 mm and 6 mm lateral to the mid-palatal suture,each model was located in three anteroposterior positions: between the second premolar and first molar,first molar,and between the first and second molars.Then based on different designs of the anchorages,the MARPE models were further divided into three groups each:3mm group A,B,C,and 6mm group D,E,F.Expansion of 0.25 mm and 4 mm per side was applied,forming a total of 18 sets of MARPE model: A1,A2,A3,B1,B2,B3,C1,C2,C3,D1,D2,D3,E1,E2,E3,F1,F2,and F3,to analyze the Von Mises stress distribution and displacement during maxillary expansion.Result(1)The FE model of the craniomaxillofacial complex consisted of 4827430 nodes and 2346562 elements.There are 12 bones and their cancellous bones,including frontal bone,nasal bone,zygomatic bone,maxilla,sphenoid bone,jawbone,temporal bone,and occipital bone.And 13 sutures,including mid-palatal suture,zygomatic maxillary suture,zygomatic temporal suture,zygomatic frontal suture,nasomaxillary suture,nasofrontal suture,frontomaxillary suture,and pterygopalatine suture.The others are dentition,periodontal ligament,miniscrew with a diameter of 1.5mm and a length of 13.0mm,and 18 MARPE model sets.(2)Stress distribution of craniomaxillofacial bone after expansion: In all groups,the stress mainly concentrated in the middle and posterior segments of palatal suture and zygomatic bone,while in the anterior segment was lower and had a slightly difference in the frontomaxillary suture.(3)Stress distribution of the expander in the different positions: For all the expanders located between the zygomatic bones,the stress distribution in the palatal suture was more uniform than that in other groups,and the tendency of bilateral zygomatic rotation decreased,and the displacement was relatively parallel.(4)Stress distribution in different anchorage teeth: In the group of anchorage design methods,the stress distribution of type 1 and type 2 was similar and larger than that of type 3 except for pterygopalatine suture.(5)Stress distribution of different miniscrew distances: According to the results of the stress cloud diagram,the maximum stress appeared around the miniscrew.The stress distribution of Perimaxillary suture of the 6 mm group was greater than that of the 3 mm group.The 3 mm group was greater than that of the6 mm groups in the anterior part of mid-palatal suture,but the opposite in the posterior.Conclusions(1)By the helping of Mimics,Geomagic,Hyper Mesh,Solid Works software,a three-dimensional finite element model,with high biological similarity,of craniomaxillofacial bone complex perimaxillary suture and miniscrew-assisted rapid palatal expansion was established.The biomechanical effect of craniomaxillofacial complex was first time analyzed by the positioning of the device,the design of anchorage teeth and the insertion site of mini-screws,which can provide a reliable basis for the follow-up biomechanical research of miniscrew-assisted rapid maxillary expansion(2)The positioning of the expander is highly associated with the effect of expansion.The expander placed between the first molars can effectively resist the resistance structure such as zygomatic bone,achieve relatively parallel movement,and a reduction of stress distribution was found toward the surrounding tissues.It is more suitable than placing between the second premolar and the first molar,and between the first molar and the second molar.It is suggested that the surrounding tissue structure should be taken into consideration when setting the expander.(3)The design of anchorage teeth will influence the transmission of force.If the first premolar and the first molar were used as anchorage teeth,the second premolar should be added according to the demand.When the first molars were used,the effect of force was the smallest,but the palatal direction and position of the expander were similar to the other designs.The positioning of the expander should also be considered in anchorage designing.If the expander placed between the first molar and the second molar,which means behind the zygomatic bone,the anterior anchorage teeth should be added.(4)The stress produced by MARPE is concentrated around the miniscrews.The increase of the distance between the miniscrews is helpful to the expansion posteriorly of the mid-palatal suture,but it decreases the overall effect,which is not conducive to the expansion of the mid-palatal suture.The influence on the surrounding tissue is increased,so the effect of miniscrew implanted in the midpalatal suture 3mm is better than 6mm.