The Practical And New Method For The Fusion Of 3D CBCT Reconstructive Model And Laser-Scanned STL Dental Model

Objectives:The study is based on the CBCT data and the laser-scanned STL dental models to construct a novel and highly accurate three-dimensional model containing information of bone,teeth and occlusion at the same time.The study can supply orthodontic clinic with valid and reliable method to evaluate the treatment outcome especially the outcome of Invisalign treatment,as well as to acquire the patients' occlusion precisely for maxillofacial surgeons.Materials and Methods:The study included 9 patients seeking Invisalign(Align Technology,Santa Clara,CA,USA)treatment from 2015 to 2016.Their permanent teeth were fully erupted without any craniofacial pathology.The three-dimensional image data were acquired using NewTom 5 G(QR,Verona Italy)cone-beam computed tomography(CBCT)machine by the same investigator.And the data were stored in DICOM format,which then were into Mimics 17.0,In Mimics,threshold was selected.Mandible and maxilla together with the respective dentition were reconstructed separately into 3D digital models with the relative position unmodified.We use two-step method with Silagum Putty and Light to get the dental impression with high accuracy.Then we poured the impression with Type IV dental stone to make dental models of the upper and lower dentition.The fine stone models were scanned using Activity 888(Smart OpticsGnbH,Bochum,Germany).The digital models then can be exported in STL files.The STL files were also imported into Mimics 17.0.Point registration was performed based on structures easily identifiable on the occlusal surface.Finally,all of the clinical crown portion of the dentition is used to locally register the scanned STL models to the CBCT model.After the registration,the result was saved as MSC file.We used 3-matic 9.0 to open the MCS file.Firstly,the clinical crown portion of the scanned dental model is identified.Then,the RMS value between the CBCT model and the scanned dental was calculated.If the RMS was below 0.3 mm,the registration accuracy is deemed to be good and the error is not significant.When the registration accuracy is confirmed,the previous saved MCS file was opened in Mimics,the clinical crown portion of the CBCT model was eliminated and the CBCT model and the scanned dental model were merged to make the final model.Results:1.Scaled color map analysisSeen from the scaled color map,most area of the clinical crown is coated with the color green,indicating the distances between the two models are almost 0.2.Quantitative analysis of the distance between CBCT model and the scanned dental modelThe RMS value can be calculated from the output data.All of the RMSs are below 0.3 mm.3.The accurate reconstruction of the patient's occlusionPerfect occlusal relationship can be observed in the finished digital model.Conclusions:1.The accuracy of local registration method between the two digital models can be quantitatively evaluated by calculating the root mean square value.2.Highly accurate scanned dental model can be locally registered to the CBCT reconstructive model to create 3D digital model with dentition of high resolution,perfect reflection of occlusal relationship,the shape of the gingival margin and bony structure of the skeletal region.