Objective:To investigate the three-dimensional accuracy of four impression materials for fixed denture:silicone(OX),hydrocolloid(HT) and two kinds of alginate impression(FC and ZS).Methods:Ten plaster replication models for each impression materials were made on the same metal master cast respectively, vertical and horizontal dimensions between landmarks on the masters and plaster casts were measured with an optical microscope. ANOVA was used to compare the measurements among the materials.Results:The difference between the masters and casts in horizontal distances measured on ZS produced models was bigger than that on other impression material produced ones (P<0.01) and beyond clinical requirment.The difference between the masters and casts in all measured dimensions on OX produced models was the smallest.Conclusion:Alginate paste is not accurate enough for denture model,while silicone is.The hydrocolloid material is relatively accurate.

Objective: To develop titanium posted keeper removable magnetic attachment and to decrease its influence on magnetic resonance imaging(MRI). Methods: Pre fabricated soft magnetic alloy pin cap keeper(PSAPK), casting non precious alloycoping keeper(CNPAK), casting precious alloy coping keeper(CPACK), titanium post keeper(TPK) and titanium post(TP) were prepared and applied on the maxilla of a volunteer, MRI was taken and measured. Results: ①The attachments producing artifacts in MRI from the biggest to the smallest were listed in following rank: PSAPK, CNPAK, CPACK, TPK and TP. ②After removing the keeper from titanium post keeper, the post had no artifact on MRI. ③The artifact was the smallest taken with SE sequence. Conclusion: Titanium post keeper is an effective way to solve the artifact problem and will bring benefits to the patients who need MRI examination of head.

Computer-Aided Design ; Craniofacial Abnormalities ; surgery ; Humans

Objective:To investigate the stress distribution of the edentulous maxilla with unilateral maxillary defect after implant rehabilitation under occlusal loads.Methods:Three dimensional finite element model of the edentulous maxilla with unilateral maxillary defect was build.The stress distribution of the edentulous maxilla under occlusal loads with computer simulated implant rehabilitation was investigated.Results:Regardless of load manner,the stress of the bone around 1 were high when just healthy side implanted,but the stress reduced after implantantion in health side combined with the implantation in zygoma in defect side.Conclusion:Implantation in health side combined with that in zygoma in defect side can reduce the stress of the bone around the implant.

Objective:To provide anatomic image data for ossointegrated implant for patients with nasal defect. Methods: 100 cases of (50 males, 50 females) 3D spiral CT images of normal bone of skull were measured with mimics 10.01 software. Results: The minimum distance between the root tips of central incisor and the anterior nasal floor was 13.03 in males and 11.06 in females. The minimum distance between the root tips of lateral incisor and the anterior nasal floor was 15.95 mm in males and 13.04 mm in females, the minimum thickness of palatine process 6mm inferior to piriform aperture was 9.96 mm, the minimum thickness of alveolus 6mm inferior to piriform aperture was 11.57 mm in males and 10.61 mm in females, the thickness of glabella adjoin to frontal sinus was 3.57mm. Conclusion: The lateral incisor region is an optimal one for nasal implants 4-8 mm in length. The inclined direction can either be forward or backward. When the vertical bone depth is not enough, horizontal placement of the implants in the inferior region of piriform should be considered. 4-8 mm implants is suitable in this region. The glabella region is not optimal but an alternative option for nasal implants.

Objective:To explore the method of the establishment of edentulous mandible All-on-4 implant photoelastic model with various distally tilted implants by computer-aided design(CAD).Methods:The edentulous mandible specimen was scanned by CT. Three-dimensional models of the mandible consisting of implant location were reconstructed and edited with Mimics and Geomagic Stu-dio software.Each of the four models had four implant sockets in the interforaminal area.In the first model,the bilateral distal im-plants were placed vertically.In the other models,the posterior implants were respectively inclined by 1 5°,30°and 45°distally.The four models were manufactured by RP and then the All-on-4 photoelastic models were made by traditional ways.Results:The ob-tained ethoxyline resin models featured bright surface,homogeneous structure,faintly yellowish,high optical sensibility,precision im-plants location and with no natural stress.The model offered a good experimental basis for the stress measurement.Conclusion:The method of fabricating ethoxyline resin models by CAD is reproducible,which simplifies the operating process.

Objective:To explore the differences of CBCT image gray value of commonly used dental materials.Methods:CBCT was used to scan 36 kinds of commonly dental material blocks,the tomographic image gray value was measured by Mimics software.Re-sults:CBCT image gray values of the materials were obtained.There were differences of the gray values of the materials not only among the different types,but also among the different varieties of the same materials.Conclusion:The discipline of CBCT image gray value differences of commonly used dental materials provided an objective basis for the establishment of 3D digital model including dental ma-terials.

Objective:To study the stress distribution of Magsoft (cushion type) and Magnedisk magnetic attachment. Methods: 2 overdentures were prepared on each of 5 edentulous jaw models. The overdentures were pared and retained with Magnedisk and Magsoft magnetic attachments respectively.Photoelastic analysis was used to study the stress distribution for the implanted complete overdentures. Results: Under the same load, around the implants, the stress under the overdentures retained with Magsoft was lower than that with Magnedisk. Compared with Magnedisk, the stress around the abutments under the overdenture retained with Magsoft were distributed in a more even manner. Conclusion: Magsoft magnetic attachment has better biomechanical characteristic than Magnedisk and can distribute stress more evenly throughout the whole supporting structure for its special cushioned design.

Both with the advantages of fixed and removable dentures,the attachment prostheses is an important component of prosthodontics.At present,the resin base for the removable part of attachment denture was majorly made with traditional methods such as cartoning,resin-filling,heat treatment.But the produced fixed part of attachment denture was easy to be deformed or broken off during such processes.Here a method were introduced to produce resin base with injection moulding,which could avoid the occurrence of the mistakes of traditional methods and simplify the process.

Objective:To evaluate of the feasibility of low-dose CT(LDCT)in the reconstruction of three-dimensional(3D)model of maxillofacial hard and soft tissues.Methods:Lightspeed 16-slice spiral CT scanner was used to scan one adult cadaveric head specimens with conventional parameters(280 mA)and low dose parameters(200,150,100,50,35,25,15 and 5 mA)respectively;the 3D model of the hard and soft tissues were reconstructed with Mimics 10.01 software,and 3D comparison were carried on with Geomagic 11.0 software.A comparison of the surface morphology of the hard and soft tissues of the 3D models with different scanning parameters was made.Results:With the reduction of the tube current,the model surface became rough gradually.Compared with the 280 mA scan results,the model surface produced by 35 mA scanning was still fairing,when the dose fell to less than 25 mA,the model surface became rough and the exact shape of the model could not be recognized.The same results of model surface were pro-duced after registration.Conclusion:The low-dose (35 mA)CT can be used to reconstruct 3D model of the maxillofacial hard and soft tissues.