Purpose : This study was performed to investigate and compare the mechanical influence of attachment types on the implant and mucosal tissue under the posterior part of implant overdentures (IOD) with a combination of mechanical reaction analysis and structural analysis using the finite element method (FEM) .
Methods : Implant overdentures with ball attachments (B-IOD), implant overdentures with locator attachments (L-IOD), and complete dentures (CD) were established in the experiment model. A 50 N load was applied onto the right first molar position of the overdenture, and the bending moment on each implant and the overdenture displacement were measured. Additionally, the FEM model was prepared based on DICOM data of the in vitro model. The interface between the denture base and mucosal tissue was assumed to be a contact interface, not a continuous interface. Displacement data measured by the experiment model analysis were inputted into the FEM model, and the stress distribution in the mucosal tissue under the posterior part of the denture was evaluated.
Results : In the L-IOD, the bending moment in the loaded-side implant was greater than that in the nonloaded side. In the B-IOD, the stress on both the loaded and non-loaded sides was smaller and almost equal. Mucosal stress in the loaded posterior part using B-IOD was the highest among the B-IOD, L-OD, and CD. The mucosal stress in the L-IOD was lower than that in the B-IOD and CD on both the loaded and non-loaded sides.
Conclusion : Stress in the mucosal tissue under the denture base was able to be evaluated using a combination of mechanical reaction analysis and FEM analysis. Differences in the mucosal stress distribution were detected among the CD, B-IOD, and L-IOD. The highest mucosal stress value was shown in the B-IOD.
Diabetes mellitus is a risk factor for implant treatment, as it is difficult to acquire osseointegration compared with healthy subjects. The effect of diabetes mellitus on osseointegration capacity has not been addressed using appropriate animal models. The aim of this study was to investigate the number of attached cells and differentiation of osteoblastic cells using a Type 2 diabetes rat model and titanium. The cells were cultured in a low glucose environment similar to the state in which blood glucose level was controlled.
In this study, Spontaneously Diabetic Torii (SDT) rats, which develop Type 2 diabetes mellitus, with Sprague Dawley (SD) rats as controls were used. The bone marrow-derived osteoblastic cells of these rats were cultured in a low glucose environment on a titanium disc 4 weeks after surface treatment of the disc. This experiment used the following two groups : control group : using osteoblast-like cells of SD rats on the titanium disc and diabetic group : using osteoblast-like cells of SDT rats on the titanium disc. In addition, WST-1 Cell Counting Kit, alkaline phosphatase (ALP) activity and Alizarin red staining were used to evaluate attached cell number, differentiation and mineralization, respectively.
In the diabetic group, the number of attached cells was small compared with the control group. The ALP activity of the diabetic group was lower than that of the control group.
Collectively, our data suggested that the osteoblast-like cells derived from SDT rats on the acid-etched titanium disc differentiated to osteoblasts. It was considered that acid-etched titanium is a useful method for implant treatment in diabetic patients receiving blood glucose control. Further study is required to examine the differentiation of osteoblasts and expression of bone formation related genes in a high glucose environment, in addition to in vivo research of implants for diabetic rats.
Purpose : The aim of this study was to introduce a new digital workflow using an intraoral digital scanner and a computer-aided design/computer-aided manufacturing (CAD/CAM) technology to transfer the shape of the provisional restoration to the final restoration supported by a bone-anchored dental implant.
Explanation of the workflow and its trial : In this study, an actual oral plaster cast of a patient with bounded edentulism in the right mandibular premolar region was set as a virtual oral cavity. In this region, a bone-anchored dental implant was placed and a replica of the implant was installed in the plaster cast, where the adjusted provisional restoration was screwed. In the new digital workflow, three types of digital scanning, e.g., the plaster cast, the die with a titanium abutment cylinder being connected to the implant replica, and the die with the implant replica including the provisional restoration, were conducted using an intraoral scanner (Trios2®, 3Shape, Copenhagen, Denmark). The scanned images of the gingiva and the provisional restoration were superimposed on the working cast image utilizing the surface shape of the die with a titanium abutment cylinder and remaining teeth. The final restoration was designed using this three-dimensional digital data by CAD software (Dental Designer™, 3Shape) and was milled from a zirconia disk. The final restoration was adhered to the titanium abutment cylinder on the cast. The provisional restoration and the final restoration were scanned by a 3D scanner (D-810, 3Shape). The morphological discrepancies among the two restorations were calculated as the total volume discrepancy by adding concave and convex volumes using Boolean operations. In addition, the volume ratios of the discrepancies were calculated. When the new digital technique was utilized, the total volume discrepancy was 12.7mm3 (concave:4.6mm3;convex:8.0mm3). The volume ratio of the discrepancy was 3.7%.
Conclusions : A new digital workflow to transfer the shape of the provisional restoration to the final restoration using an intraoral digital scanner, CAD/CAM technology and a plaster cast used for production of provisional restorations was successfully developed and introduced.