A finite element study on stress distribution of two different attachment designs under implant supported overdenture.

OBJECTIVE: This study aimed to evaluate stress patterns generated within implant-supported mandibular overdentures retained by two different attachment types: ball and socket and locator attachments. MATERIALS AND METHODS: Commercial CAD/CAM and finite element analysis software packages were utilized to construct two 3D finite element models for the two attachment types. Unilateral masticatory compressive loads of 50, 100, and 150 N were applied vertically to the overdentures, parallel to the longitudinal axes of the implants. Loads were directed toward the central fossa in the molar region of each overdenture, that linear static analysis was carried out to find the generated stresses and deformation on each part of the studied model. RESULTS: According to FEA results the ball attachment neck is highly stressed in comparison to the locator one. On the other hand mucosa and cortical bone received less stresses under ball and socket attachment. CONCLUSIONS: Locator and ball and socket attachments induce equivalent stresses on bone surrounding implants. Locator attachment performance was superior to that of the ball and socket attachment in the implants, nylon caps, and overdenture. Locator attachments are highly recommended and can increase the interval between successive maintenance sessions.

In Vitro Solubility and Wear Rates of Silorane and Dimethacrylate Resin Based Composite Restorative Materials under Different pH Conditions.

BACKGROUND: The purpose of this study was to evaluate the effect of different pH solutions on the solubility and wear resistance of Silorane and dimethacrylate resin based composite restorative materials. MATERIALS AND METHODS: Two different resin based restorative materials (Filtek Silorane P90 and hybrid composite Z100) were tested. Different pH solutions (2.5 and 5) also were used. A total of 60 samples of each type of selected composite were prepared. Specimens were immersed in each type of pH solutions (2.5 and 5) and distilled water as a control group for 24 h then the specimens was subjected to the required mechanical tests. RESULTS: Significant statistical differences were observed regarding water solubility and wear values in different pH solutions. Filtek Silorane presented the smallest values of water solubility and wear values. CONCLUSION: Under tested experimental conditions, the pH solutions used in this study showed pronounced effect on water solubility and wear values of both two restorative materials. Finally, within the limitation of this study we recommended to use Filtek Silorane (P90) instead of hybrid (Z100) due to its low solubility values under different pH solutions.

Two Years Retrospective Evaluation of Overdenture Retained by Symphyseal Single Implant Using Two Types of Attachments.

BACKGROUND: This study was aimed to evaluate complete mandibular overdentures retained by a symphyseal single implant using ball and magnet attachments in both clinical and radiographic evaluation. MATERIALS AND METHODS: Ten dental press fit titanium implants were installed in the lower jaws of completely edentulous patients according to two-stage surgical protocol. For each patient, one implant was installed in the symphyseal midline region, and left submerged and unloaded for 4 months. The patients were then divided into two equal groups. The first group received mandibular overdentures retained by ball and socket attachment. The second group received mandibular overdentures retained by magnet attachment. Both groups were supplied with conventional maxillary complete dentures. All patients were evaluated immediately after denture insertion, 6 months, and 12 months and after 24 months of overdenture insertion. RESULTS: The study showed insignificant difference regarding the clinical condition and the marginal bone height changes in both groups during the follow-up period. CONCLUSION: Single implant retained overdenture with ball and socket or magnetic attachments was easy in construction, required less home care to maintain gingival health and give satisfactory clinical results.

Implant Supported Distal Extension over Denture Retained by Two Types of Attachments. A Comparative Radiographic Study by Cone Beam Computed Tomography.

BACKGROUND: This study was conducted to compare and evaluate the effect of two different attachments (locator attachment and ball and socket [B&S] attachment) on implants and natural abutments supporting structures, in cases of limited inter-arch spaces in mandibular Kennedy Class I implant supported removable partial over dentures by measuring the bone height changes through the cone beam radiographic technology. MATERIALS AND METHODS: Two implants were positioned in the first or second molar area following the two-stage surgical protocol. Two equal groups were divided ten for each: Group I: Sides were the placed implants restored by the locator attachment. Group II: The other sides, implants were restored by B&S attachment. Evaluation of the implants and main abutments supporting structures of each group was done at the time of removable partial over denture insertion, 6, 12 and 18 months by measuring the bone height changes using cone beam computed tomography. RESULTS: Implants with locator attachment showed marginal bone height better effects on implants and main abutments supporting structures. CONCLUSION: Implants restored by locator attachment shows better effects on bone of both main natural abutments and implant than those restored with ball and socket.

A finite element study on the mechanical behavior of reciprocating endodontic files

To evaluate the mechanical behavior of reciprocating endodontic files, comparing nickel-titanium NiTi and stainless steel 316L St.St. 316L as manufacturing material for such instruments. METHODS: A three-dimensional finite element model was designed for this study. The simplified instrument model geometry was created on commercial CAD/CAM software. Real strain stress curves of St.St. 316L and NiTi were used in the analysis. Non-linear static analysis was performed to simulate the instrument inside root canal at an angle of 45° in the apical portion, and subjected to torsion of 0.3 N.cm. RESULTS: Non-linear NiTi material showed super elasticity and high functionality in such applications. Very high levels of stress appeared in the file at 3 mm from the tip close to yield point. CONCLUSIONS: St. St. 316L is not suitable for manufacturing reciprocating instruments. Modeling of the instrument with equivalent circular cross-sectional area did not affect results quality. Reciprocating instruments have short lifespan, thus manufacturers recommend using one file per tooth. Reciprocating instruments are recommended for less experienced dentist...