Background. Screw-retained
restorations are favored in some clinical situations such as limited
inter-occlusal spaces. This study was designed to compare stresses developed
in the peri-implant bone in two different types of screw-retained restorations
(segmented vs. non-segmented abutment) using a finite element model.
Methods.
An implant, 4.1 mm in diameter and 10 mm in length,
was placed in the first molar site of a mandibular model with 1 mm of
cortical bone on the buccal and lingual sides. Segmented and non-segmented
screw abutments with their crowns were placed on the simulated implant in
each model. After loading (100 N, axial and 45° non-axial), von Mises stress
was recorded using ANSYS software, version 12.0.1.
Results.
The maximum stresses in the non-segmented abutment
screw were less than those of segmented abutment (87 vs. 100, and 375 vs. 430
MPa under axial and non-axial loading, respectively). The maximum stresses in
the peri-implant bone for the model with segmented abutment were less than
those of non-segmented ones (21 vs. 24 MPa, and 31 vs. 126 MPa under vertical
and angular loading, respectively). In addition, the micro-strain of
peri-implant bone for the segmented abutment restoration was less than that
of non-segmented abutment.
Conclusion.
Under
axial and non-axial loadings, non-segmented abutment showed less stress
concentration in the screw, while there was less stress and strain in the
peri-implant bone in the segmented abutment.
Objective:The objective of this study was to evaluate the stress distribution in bone-surrounding implants placed in different levels in a mandibular overdenture. Material and Methods: A Computerized Tomography (CT) scan of an edentulous mandible was used to generate the models. Two implants with an internal connection were placed perpendicular to the occlusal plane in the Canine sites of the mandible. The implant in the left side was placed 1mm higher than the other side. Dolder bar and ball attachments were designed. Loading was performed by clenching the teeth with reconstruction of the muscles. In the anterior loading condition, force was applied to the central incisors and in the posterior loading conditions, it was applied to the molars and premolars. Then the Maximum Principal Stresses in the peri implant bone was evaluated with finite element analysis. Results: In both models, the highest stress values were recorded in the cortical bone surrounding the higher implant except in the ball model with unilateral load application on the right side (64.7 MPa). In almost all loading conditions the stress value differences in models with bar and ball attachments were low. Only in the anterior loading condition, the stress magnitude was higher in two implants of the ball model (60.5 MPa in the left side and 21 MPa in the right side) compared to the bar model (54.5 MPa in the left side and 17.5 MPa in the right side). Conclusion: The stress concentration did not affected considerably by the attachment system. High stress values were found adjacent the implant with a higher level. To reduce the amount of stress, bilateral balance occlusion should be considered.
Background
The present study compared the effect of post space preparation time on the apical seal of two different sealers.
Methods
In the in vitro study, 94 central incisors were used. After the samples’ root canal preparation, they were randomly assigned to four experimental groups (n = 21). The samples in groups 1 and 2 were obturated with AH Plus sealer, gutta-percha, and in groups 3 and 4 with Endoseal MTA bioceramic sealer and single cone technique. The post spaces in groups 1 and 3 were prepared immediately and in groups 2 and 4 with a delay. The samples were evaluated at 7-, 30-, and 90-day intervals for apical microleakage using the fluid filtration technique. The data were analyzed with SPSS 25, using three-way ANOVA and independent t-test.
Results
The apical microleakage in groups 3 and 4, obturated with Endoseal MTA bioceramic sealer and prepared immediately and after a delay, respectively, was not significantly different between the interval times. In group 2, obturated with AH Plus sealer and prepared for post space with a delay, the apical microleakage was significantly less than all the other groups. Group 1, obturated with AH Plus sealer and prepared for post space immediately, exhibited the least microleakage after seven days, but its microleakage increased over time to reach the level of groups 3 and 4.
Conclusion
According to the results, the apical microleakage in the AH + sealer group and the delayed post-space preparation method, was significantly less than all the other groups over time.
Background: Hygiene and maintenance of removable prostheses are very important for the oral health. Elderly patients are not capable of this affair since they might have diseases in addition to being old; thus, they require new alternative methods. Objectives: The purpose of this study was to compare the disinfecting effects of three substances, water, normal saline and denture cleaning tablets Corega that patients commonly use as denture cleaning, against oral bacterial infections. Patients and Methods: In this study, complete maxillary dentures of 138 elderly individuals living in a nursing home (46 females and 92 males) with a mean age of 9 ± 75 years were studied. Their prostheses were soaked for 15 minutes randomly into one of the following substances: water, normal saline, or a solution containing denture cleaning tablets (Corega). Before and after this operation, samples were obtained by a third person using microbiological studies swabs. The samples were cultured and the colony forming units (CFU) were obtained. Data were evaluated by one-way ANOVA test. Results: Statistically, Corega reduced bacterial infections significantly more than water and normal saline (P = 0.0001). Water and normal saline had equal effects on reducing CFU. Conclusions: Denture cleaning tablet, Corega, is recommended for cleaning the prostheses, but using water or saline alone is not recommended.
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