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Objective: To compare the biomechanical characteristics of four-implants mandibular overdentures supported by Locator attachment or bar-clip attachment under different mechanical loads using three-dimensional finite element analysis method. Methods: Two different models of four-implants supported mandibular overdentures using Locator attachment and bar-clip attachment (hereinafter called Locator model and bar-clip model) were established. Each model was subjected to five different mechanical loading conditions: 100 N vertical loading in central incisor (vertical load of incisor), 100 N vertical loading or oblique loading in canine (vertical or oblique loads of canines), 100 N vertical or oblique loading in mandibular first molar (vertical or oblique loads of mandibular first molar). The stress distributions in implants, peri-implant bone and mucosa were recorded under the above five conditions to evaluate the effects of different attachments on the biomechanical properties of implant-supported mandibular overdentures. Results: Regardless of loading conditions and types of attachments, the stress concentration in implants were located at the neck of implants, and the stress concentration in peri-implant bone was located in the cortical bone. The stress values in mucosa were always much smaller than those in implants and cortical bone. Regardless of loading positions (on canine or on mandibular first molar), the maximum stress at the bone interface around the implant under lateral loading was much higher than that under vertical loading. Under various loading conditions, the stress in implants and cortical bone of the Locator model (the highest von Mise stress value was respectively 79.5 and 22.3 MPa) were lower than that of bar-clip model (the highest von Mise stress value was 110.3 and 28.7 MPa respectively) while the maximum compressive stress in mucosa (0.198 MPa) in Locator model was slightly higher than that in the bar-clip model (0.137 MPa). Conclusions: In clinical practice, the lateral force applied to the implant-retained overdenture should be minimized to avoid complications caused by pathological loads. Under the same loading condition, the stress distributions in overdenture using Locator attachment are more dispersed, which is more conducive to long-term stability of implants.

Objective: To evaluate the outcomes of attachments prosthesis in patients with complicated intraoral situation., Methods: Thirty-eight patients provided with fixed-removable partial denture were followed up for 1 to 5 years. A total of 51 attachments restoration supported by 139 abutments were included., Results: Good retention and stability of the restoration were achieved; masticatory function and esthetic effects were recovered satisfactorily., Conclusions: Fixed-removable partial denture is an effective method for patients with complicated intraoral situation.

Objective: To investigate effects of the static magnetic field (SMF) generated by dental magnetic attachment on osteoblastic morphology and surface ultrastructure., Methods: The in vitro cultured rat osteoblasts were exposed continuously to 12.5 mT, 125 mT, and 250 mT static magnetic fields for 1, 3, 5, and 7 days. After exposed in SMF, osteoblasts were observed under a phase contrast microscope, and then HE stained and observed under a light microscope. In addition, the cells were observed under a scanning electron microscope (SEM)., Results: By continuous exposure, the different intensities of SMF exposure did not change the vital osteoblast growth pattern or distribution. The SEM photos showed that there were certain changes in cellular microstructures for osteoblasts after exposed to 12.5 mT for 5 to 7 days, as well as 125 mT and 250 mT for 3 to 7 days. The more exposure time increased, the more microvesicles on the surfaces of cells were observed., Conclusions: Continuous SMF-stimulation could not affect the shape, distribution, and growth pattern of osteoblasts. The SMF of magnetic attachments could lead to certain changes in surface ultrastructures of osteoblasts in this study.

A 3D finite element model of bilateral distal-extension edentulous dentition, which includes mandible, incisors, canines and premolars, was established in the first place. Based on it, another model with extra-coronal attachments and dentures was also developed. Moreover, contact elements were applied to the regions between the denture and alveolar bone. The von Mises stress distributions of the abutments and their periodontal tissues, edentulous alveolar bone in the two models were compared. The results indicate that the stresses in the abutments and the alveolar sockets obviously increase at the buccal and lingual sides after reparation, and that the stresses on the edentulous alveolar bone also increase.

From alveolar bone and the complete dentition CT images, a three-dimensionalysis of nonlinear finite element model of mandibular unilateral distal-extension with extracoronal precision attachment was established. The contact elements were used between the denture and alveolar bone. The result shows that, the stress in the second premolar and periodontal tissue decreased obviously as the second abutment was added. However, the stress difference was unapparent as the third abutment was added. Considering various facts, the attachment with two abutments was suggested to be used. With the decrease of the periodontal tissue, the stress in the periodontal tissue increased, however the stress in the tooth changed slightly. Thestress in the periodontal tissue decreased effectively when the third abutment was added, as the tooth root was absorbed by 50%. In this situation, the extracoronal precision attachment can also be used.

Purpose: The purpose is to evaluate the effect of the stress distribution of support tissues when using the hinge extracoronal attachment for distal-extension prosthesis with different number of abutment., Methods: Hinge extracoronal attachment was used for retention in distal-extension prosthesis. The 3-D photoelastic models of attachment of the denture of single abutment with the first molar or double abutments with the first molar and the second premolar were fabricated. Photoelastic analysis was adopted to compare the stress patterns generated around the support tissues with different number of abutment., Results: Under central occlusion, most stress of the attachment of the denture with single abutment was concentrated at the edentulous ridge, the distal and mesial apex of the abutment. The results were similar with double abutments., Conclusions: In choosing attachment prostheses to restore the second molar distal-extension defects, we can choose only one tooth as abutment. The number of the abutment has no significant effect on the stress distribution in the supporting tissue under central occlusion,and there is an evenly stress distribution at the edentulous ridge and in the abutment. The attachment is suitable for cases with better alveolar membrane without high demand for abutment teeth. Supported by Development Fund of Science and Technology of Shanghai Municipality (Grant No. 004119075).

Purpose: To study the influence on the abutment movement with three kinds of precision attachments designed for distal-extension removable partial dentures (RPDs)., Methods: Snap attachment, Ceka attachment, Mini-SG attachment were used to retain RPDs. Then food chip was masticated between the upper and lower dentitions on the attachments side. Placement of abutment was measured by LB-72 high-sensitive-laser-traneferring-detector and the data were statistically analyzed for random block analysis of variance., Results: The displacement, inclination, and torsion of the abutment movements in the mesial-distal, bucco-lingual and occluso-gingival directions all had statistical significance (P<0.05). The largest mesial-distal inclination occurred with the Mini-SG attachment. The Ceka attachment produced more abutment displacement in mesial distal and apical directions. Occlusal displacement and anti-clockwise rotation were the least with the Snap attachment., Conclusion: The most equitable distribution of stresses on the supporting structures was achieved by Snap attachment with its resilent assemble, Ceka attachment transfers most of the loading forces to the abutments, Mini-SG attachment can not reduce the excessive torque applied to the abutments effectively.

Objective: To investigate the effects of Mini-SG F attachment on periodontal health of the abutment teeth in restoring free-end removable partial dentures (RPDs)., Methods: The periodontal status of the abutments in restoring free-end RPDs was longitudinally observed with periodontal indices commonly used in clinics, and a group comparison was made using a one-way analysis of variance (ANOVA)., Results: The stability and retention of free-end RPDs retained by Mini-SG F attachments were excellent during the whole observation course. Compared with the periodontal status of the first and the second abutments before restoration respectively, no significant differences in gingival indices, plaque indices, periodontal probing depth, alveolar bone resorption levels of those were shown 6 months after restoration. The mobility of the abutments was significantly reduced when they were splinted together., Conclusion: Mini-SG F attachments used in free-end RPDs have no evident adverse effect on periodontal health of the abutment teeth, and the way of splinting the abutments is advantageous to their long-term health and stability.

Objective: To measure and analyze the flux densities of static magnetic fields generated by two types of commonly used dental magnetic attachments and their retentive forces, and to provide guidance for the clinical application of magnetic attachments., Methods: A digital Gaussmeter was used to measure the flux densities of static magnetic fields generated by two types of magnetic attachments, under four circumstances: open-field circuit; closed-field circuit; keeper and magnet slid laterally for a certain distance; and existence of air gap between keeper and magnet. The retentive forces of the magnetic attachments in standard closed-field circuit, with the keeper and magnet sliding laterally for a certain distance or with a certain air gap between keeper and magnet were measured by a tensile testing machine., Results: There were flux leakages under both the open-field circuit and closed-field circuit of the two types of magnetic attachments. The flux densities on the surfaces of MAGNEDISC 800 (MD800) and MAGFIT EX600W (EX600) magnetic attachments under open-field circuit were 275.0 mT and 147.0 mT respectively. The flux leakages under closed-field circuit were smaller than those under open-field circuit. The respective flux densities on the surfaces of MD800 and EX600 magnetic attachments decreased to 11.4 mT and 4.5 mT under closed-field circuit. The flux density around the magnetic attachment decreased as the distance from the surface of the attachment increased. When keeper and magnet slid laterally for a certain distance or when air gap existed between keeper and magnet, the flux leakage increased in comparison with that under closed-field circuit. Under the standard closed-field circuit, the two types of magnetic attachments achieved the largest retentive forces. The retentive forces of MD800 and EX600 magnetic attachments under the standard closed-field circuit were 6.20 N and 4.80 N respectively. The retentive forces decreased with the sliding distance or with the increase of air gap between keeper and magnet., Conclusion: The magnetic attachments have flux leakages. When they are used in patients' oral cavities, if keeper and magnet are not attached accurately, the flux leakage will increase, and at the same time the retentive force will decrease. Therefore the keeper and magnet should be attached accurately in clinical application.

Purpose: The purpose is to discuss the clinical indications of hinge extracoronal attachment., Methods: In the experiment, the stress distribution in the periodontal support tissue of the abutment was analyzed under different numbers of abutments by EFA., Results: There was no significant effect on the stress distribution in the supporting tissue according to the different numbers of abutments at the central occlusion, and there was an evenly stress distribution in the abutment and alveolar membrane of the area around the missing teeth., Conclusions: When using the attachment prostheses to restore the type of the second molar distal-extension for the patient, we can use one teeth as abutment. The attachment is suitable for the cases with better condition of the alveolar membrane without high demand of the abutment teeth of the patient.

Objective: To evaluate the in vivo retentive forces of mandibular complete overdenture with Magfit attachments, as well as the relation between the location of magnetic attachments and the retentive forces of the denture., Methods: 5 patients were selected and treated with mandibular complete overdentures retained by Magfit EX600 and MD800 attachments. A strainometer was used to measure the retentive forces in anterior, central and posterior parts of the overdenture before and after magnets were set. The vertical and anterior-upper 60 degrees retentive forces of the overdenture were measured one month later., Results: The retentive forces of the overdentures after setting magnets were significantly greater than that before magnets were set (P < 0.05). There was no significant difference in retentive forces between the different parts (P > 0.05). The retentive force in vertical direction was greater than that in anterior-upper 60 degrees direction (P < 0.025)., Conclusion: Magnetic attachments can significantly improve the retention of mandibular complete overdenture. The location of magnetic attachments greatly influences the retentive force of the overdenture.

Objective: In order to compare the influence of casting and laser welding on magnetic retentive force, the magnetic retentive forces of laser-melted and cast post-keepers of the magnetic attachments were measured in vitro., Methods: 5 cast and 6 laser-melted post-keeper specimens (Magfit MD800) were formed, respectively. Using untreated keeper as control group, the vertical magnetic retentive forces were measured by a universal testing machine., Results: The average vertical magnetic retentive force of the laser-melted post-keeper group and the cast post-keeper group in vitro were (4.223 +/- 0.217,0)N, (3.792,9 +/- 0.296,4)N, respectively. Compared with the cast post-keeper group, the average vertical magnetic retentive force of the laser-melted post-keeper groups was much higher in vitro (P < 0.05)., Conclusion: Laser welding had less influence on the magnetic retentive force of the magnetic attachments than casting.

Objective: In order to introduce the laser welding technology into root-cap making, this study compared the surface characters and internal structures of laser-melted and cast post-keeper to provide experimental data for clinical application of the technique., Methods: Using untreated keeper as the control group, the surface characters and metallographic structures of the keepers were examined by stereomicroscope, metallographic microscope and SEM, and element analysis were conducted with EPMA., Results: The laser-melted post-keeper basically kept the original smooth and the internal structure of the keeper, the heat reaction zone was extremely small and elements diffused mutually around the fusion zone obviously. While in the cast post-keeper, the surface was rough and had an oxide-layer. The internal structure changed and a fusion band formed between the base alloy and the keeper, but element diffusion was limited to the fusion zone., Conclusion: Compared with casting, laser welding technique demonstrated less influence on the surface and internal structure of the keepers.

Objective: The aims of this study are to analyze the surface stress of the periodontal supporting bone of the bilateral distol extension removable partial denture which is retained by using intra-coronal or extra-coronal semi-precision attachment, and to characterize the biomechanics of these two designs by using a strain gauge., Methods: A fresh human mandible specimen with 76|67 missing and six bilateral partial removable denture retained with six semi-precision attachments were made, including three attachments with intra-coronal studs and three attachments with extra-coronal vertical bars. A total of six 45 degrees rosette strain gauges were bonded at six prepared points on the surface of the mandible to measure the surface stress, including the middle point between 76 of the buccal edentulous alveolar crest area under the denture base verge(point 1), the distal buccal cervix of 5 (point 2), the buccal apical area of 5 (point 3), the buccal middle area of 34 roots (point 4, 5), the lingual middle area of 5 root (point 6). The static loads of 14N, 28N and 42N were applied vertically, buccally 45 degrees, lingually 45 degrees at the middle point of the 6|6 occlusal surface. The micro-strain was recorded, and the maximal/minimal principle stresses were calculated for each RPD and each point. The stress characteristics of these two types of attachments were compared and analyzed., Results: In most situations, the stress of these two semi-precision attachments showed significant differences. The vertical load: The stress values of these intra-coronal and extra-coronal attachments at points 1, 2, 3, 4, 6 differed significantly(P < 0.05), including points 1, 2, (sigma intra < sigma extra) and points 3, 4, 6(sigma intra > sigma extra). Buccal loads: The stress values of these intra-coronal and extra-coronal attachments at points 1, 2, 3, 4, 5 differed significantly(P < 0.05), including points 1, 2(sigma intra < sigma extra) and points 3, 4, 5(sigma intra > sigma extra). Lingual loads: The stress values of these intra-coronal and extra-coronal attachments at points 2, 3, 4, 6 differed significantly (P < 0.05, sigma intra > sigma extra). The intra-coronal attachment generally produced higher stress at the site of the alveolar bone around the abutment than the extra-coronal attachment, but extra-coronal attachment produced higher stress at the edentulous alveolar crest and the distal cervical alveolar bone of the distal abutment than the intra-coronal attachment., Conclusion: The intra-coronal attachment is suggested to be applied in some cases that the periodontal condition of distal abutment was good, and the extra-coronal attachment is suggested to be used in some cases that the condition of the edentulous alveolar crest is fairly good, while the periodontal condition of the distal abutment was relatively weak.

Objective: The effect of the post diameter design of over dentures attachment on the strss distribution of pulpless dentine was investigated in this study., Methods: The optimal post diameter design was computed with a finite element method and analyzed with graphic method., Results: The changes between the dentine stress value and the post diameter was parabola relationship. The optimal diameter of attachment post was 1.55 mm for this study model. The dentine thickness which retained above apical foramen 4 mm was 0.83 mm., Conclusion: This investigation provides a series of valuable parameters for making a post diameter optimal design of over dentures attachment.

The authors introduced the fabrication of stud attachment and bar attachment used to increase the stability and retention of overdenture. During two years' periods, the results of the clinical practice indicated: the retention of overdenture was increased and patients' masticator function was improved when attachments were used, and then the fabrications of two kinds of attachments were simple and value of attachments is cheap. The technique was popularized and used easily.

The shape design of attachment post is crucial factors influencing post retention and stress distribution to the dentin. By means of CAD and FEA, the present study investigated the effects of the shape designs of attachment posts on the stress distribution in dentin. The results indicated that the taper post had wedging effects on the dentin and produced higher Von Misses stress than that of parallel side post and the Von Misses stress value of the dentin was about 1.1 times. The maximum Von Misses stress value that the design of the thread post produced was about 1.06 times the stress of the nonthread post did. However, the effects of post design on the dentin were minor compared with the bite force directions. In the same post design, the maximum Von Misses stress in dentin with 45 degree oblique force was about 2.1 times with vertical force. Therefore, reducing oblique force is the main method to prevent root fracture in clinic.

Thirty-two patients provided with the fixed-removable prosthes is were followed up 3 month to 2.5 years. A total of 52 abutments were included, 17 of which were telescopic retainer, 14 were bar attachment retainer, 4 were rod attachment, 12 were stud attachment and 5 were slide attachment. Few technical failures were recorded. All found the prosthesis satisfactory and well functioning.