Acrylic Model Research Articles

Retention force of all-zirconia, all-polyetheretherketone, and zirconia-polyetheretherketone telescopic attachments for implant-retained overdentures: In vitro comparative study

Aim: The aim was to evaluate and compare retention forces of all-zirconia (ZrO2), all-polyetheretherketone (PEEK), and ZrO2-PEEK Computer-Aided-Designing computer-Aided -Manufacturing (CAD-CAM) telescopic attachments for two implant-retained mandibular overdentures. Materials and Methods: Fifteen identical acrylic resin models of the edentulous mandibular arch without alveolar undercuts were fabricated. Two implants were inserted in the canine region of each model. According to the material of telescopic attachment, models were divided into three groups: all ZrO2 (ZZ): primary and secondary crowns were made of ZrO2, all PEEK (PP): primary and secondary crowns were made of PEEK, and ZrO2-PEEK (ZP): primary crowns were made of ZrO2 and secondary ones were made of PEEK. Identical experimental overdentures were constructed for all models. For measuring the retention force, a universal testing machine was used to apply a pull-off test in presence of artificial saliva between the crowns. The achieved maximum values of retention force were recorded at the beginning of the study (initial retention) and after 540 cycles of insertion and removal simulating 6 months of the clinical service (final retention). Results were statistically analyzed, analysis of variance (P Results: ZP group reported the highest initial force values for all groups. The final retention values of PP and ZP groups were significantly decreased than initial values, while the insignificant loss of retention was observed with ZZ group (P = 0.06). Independent samples test showed a significant difference in both initial and final retentions between each two groups. Conclusion: Within the limitations of this study, ZrO2 is more preferred as a secondary telescopic crown against a primary ZrO2 one. Despite the loss of retention by time, PEEK can still be used as a secondary telescopic crown against ZrO2 or PEEK primary crowns regarding the acceptable initial and final retention values.

Assessment of the Flexion Force of TMA and Elgiloy Intrusion Arches to Different Lengths of Activation. An In Vitro Study

The present study analyzed the utilitary arch of Ricketts made with TMA and Elgiloy alloys, evaluating the forces that each one presented at different activation lengths. METHODS: A total of 30 arches (15 per alloy) 17x25 caliber were assessed. An acrylic model that simulated the jaw was used with tubes welded to the bands located on the first molars where the arches were attached and brackets were bonded to the lower incisors. The Ricketts arches had a total length of 100 mm and were activated in their distal branch, obtaining the lengths of 5, 10 and 15 mm measured from the slot of the anterior brackets in the midline. A Digital Universal Testing Machine CMT-5L was used to measure the bending force and the statistical analysis was carried out with the Student's T and Mann-Whitney U test. RESULTS: The TMA alloys had a significantly lower strength in each of the activations 5, 10, 15 mm (13,53; 31,61 and 42,01grams respectively) compared to Elgiloy (31.41; 62,61 y 93,00 grams respectively). While increasing the activation length, the flexural forces increased significantly for both alloys. CONCLUSION: The suggested forces for the intrusion of lower incisors were reached by the Elgiloy arches.

Comparison of three dimensional accuracy of two implant level impression techniques; using three different elastomeric impression materials-an in vitro study

Aim: To compare 3-Dimensional accuracy of open and closed impression technique using three elastomeric impression materials to transfer the intraoral position of implant fixture to the working cast. Objective: To compare 3-Dimensional accuracy of open and closed tray impression technique by using addition silicone, condensation silicone and polyether impression materials for making implant level impressions. Materials and Methods: Experiments was conducted to find the three dimensional accuracy of casts made with three impression materials for implant impressions by open and closed tray impression techniques. Five implant analogs were placed on a maxillary acrylic model; impression posts were screwed to implant analogs. 30 stock trays and 30 open window custom trays were prepared. These 30 stock trays and 30 open window custom trays were again divided into three subgroups by using three impression materials. Then the impressions were poured using die stone according to manufacturer’s instructions. Specific dimensions of resultant cast was measured. The dimensional changes were measured using White light laser scanner and data analysis was done by XOV Rapidform Software. Comparison between materials was done by ANOVA test followed by Tukey’smultiple comparison test. Comparison between two techniques was done by unpaired‘t’ test. Results: The data was subjected to statistical analysis which was done by ANOVA test followed by Tukey’s multiple comparison test and Comparison between two techniques was done by unpaired‘t’ test. Statistical analysis shows significantly less difference in open tray technique when compared to closed tray impression technique. Conclusion: Within the limitation of this study;1. Open tray impression technique is more accurate than the closed tray impression technique for making implant impression; 2. Polyether and Addition silicone elastomeric impression materials were there commended materials for implant impressions. Keywords:

FLOW INVESTIGATIONS WITHIN A CONCENTRIC CYLINDERS OF GAS SENSOR MODULE FOR I.C. ENGINES

For the global warming issues such as the reduction of greenhouse gas emissions, the exhaust gas from the internal combustion engines must be strictly controlled and purified by means of the catalytic convertor. The present investigation deal with the optical visualization of the flow field around the Zirconium sensors that is protected with concentric double cylinders with opening apertures. The commercial gas sensor modules were used for the monitoring of the Oxygen concentration before and after the catalytic convertor in passenger vehicles. In the experiment, a transparent acrylic model was used in conjunction with the particle image velocimetry as the velocimetry. The experimental result demonstrated that the magnitude of velocity in the vicinity of the sensor rod was significantly lower than that of the external main flow. The higher velocity fluctuation through the opening apertures contributes to the better mass transfer between the inside and outside of the protectors and enhances the response of the sensing module.

Validated model of platelet slip at stenosis and device surfaces

Platelets are central to thrombosis. However, it is unknown whether platelets slip at vascular or device surfaces. The presence of platelet slip at a surface would interrupt physical contact between the platelet and that surface, and therefore diminish adhesion and thrombosis. Unfortunately, no existing technology can directly measure platelet slip in a biological environment. The objective of this study was to explore whether microspheres–modeling platelets–slip at different vascular and device surfaces in an acrylic scaled-up model coronary artery. The microspheres (3.12 µm diameter) were suspended in a transparent glycerol/water experimental fluid, which flowed continuously at Reynolds numbers typical of coronary flow (200–400) through the model artery. We placed a series of axisymmetric acrylic stenoses (cross-sectional area reduction [CSAr], 20–90%) into the model artery, both without and with a central cylinder present (modeling a percutaneous interventional guide wire, and with a scaled-up Doppler catheter mounted upstream). We used laser Doppler velocimetry (LDV) to measure microsphere velocities within, proximal and distal to each stenosis, and compared to computer simulations of fluid flow with no-slip. For validation, we replaced the acrylic with paraffin stenoses (more biologically relevant from a surface roughness perspective) and then analyzed the signal recorded by the scaled-up Doppler catheter. Using the LDV, we identified progressive microsphere slip proportional to CSAr inside entrances for stenoses ≥60% and ≥40% without and with cylinder present, respectively. Additionally, microsphere slip occurred universally along the cylinder surface. Computer simulations indicated increased fluid shear rates (velocity gradients) at these particular locations, and logistic regression analysis comparing microsphere slip with fluid shear rate resulted in a c-index of 0.989 at a cut-point fluid shear rate of (10.61 [cm−1]×mean velocity [cm×sec−1]). Moreover, the presence of the cylinder caused disordering of microsphere shear rates distal to higher grade stenoses, indicating a disturbance in their flow. Finally, despite lower precision, the signal recorded by the scaled-up Doppler catheter nonetheless indicated slip at the entry into and at most locations distal to the 90% stenosis. Our validated model establishes proof of concept for platelet slip, and platelet slip explains several important basic and clinical observations. If technological advances allow confirmation in a true biologic environment, then our results will likely influence the development of shear-dependent antiplatelet drugs. Also, adding shear rate information, our results provide a direct experimental fluid dynamic foundation for antiplatelet-focused antithrombotic therapy during coronary interventions directed towards higher grade atherosclerotic stenoses.

The Effect of using different locator attachments with a different retention value on the bone height changes in Implant Supported class I removable Mandibular partial Overdenture, A Radiographic Evaluation

Purpose: The aim of this study was to evaluate the effect of using different locator attachments with a different retention value and ball and socket attachment on the bone height changes in Implant Supported class I removable Mandibular partial Overdenture.Introduction: The use of osseointegrate dental implants is one of the most successful treatment options to solve the problem of distal extension cases. A critical factor affecting the success of an implant is the manner in which mechanical stresses are transferred from the implant to the bone. One of the factors which affect the amount of force transmitted to the implant is the choice of the attachment. The Locator attachment system is a self-aligning and has dual retention, supplied in different colors; with a different retention value (white, orange and blue). The white housing has light retention, the orange housing has standard retention, and the blue has high retention while the ball and socket attachments consist of a titanium male unit and an easily replaceable rubber ring female unit that is retained in a metal retainer ring. The question is which of the various Locator attachment system used to retain mandibular partial overdenture affect the magnitude of stresses transmitted to the implants thus affecting the bone height changes around the implants.Material and methods: Twelve class I mandibular partially edentulous patients with opposing full dentate maxillary arch were selected from the from the Outpatient clinic, Prosthodontic Department, Faculty of Dentistry, Ain shams University. For all the patients extra and intraoral examinations were done associated with the proper laboratory investigations. Acrylic temporary partial denture was made for all the patients, the partial denture was duplicated into clear acrylic resin model then the model was scanned using CBCT machine and the DICOM data was processed to obtain STL file for the model. The digital image was performed and the virtual implant was placed in the most optimal position at the first molar area according to the surgical and prosthetic design. Conventional implant fixture were surgically inserted so that the top level of fixture needs to be located 0.5mm below the marginal crestal bone level, After three month from implant insertion, each patient was recalled For the insertion of super structure. The selected cases were randomly divided into three equal groups; Group I received an implant Supported class I removable Mandibular partial Overdenture with white locator attachment Group II received a Implant Supported class I removable Mandibular partial Overdenture with an orange locator attachment and Group III received an implant Supported class I removable Mandibular partial Overdenture with a ball and socket attachment.CBCT was used to evaluate the bone height changes around each implant at time of partial over denture insertion, 6months and 12 months from partial over denture insertion.Results: The results show that in all groups the bone loss appeared to be within acceptable limits in the groups during follow up period(less than1 mm during first year) but with significant differences in the bone height changes around the implant between both locator attachments and ball and socket attachment while the results show no significant difference between white and orange locator but the orange locator show higher bone resorption than the white locator.Conclusion: The current study concluded that locator attachments with different retention value provides better preservation of crestal bone than ball and socket stud attachment , where the white locator attachment show transmits less stress to the abutment resulting in reducing the amount of bone loss around the implants than orange locator when used in implant supported class I mandibular partial over denture

Types of Intermaxillary Fixation and Their Interaction With Palatine Fracture Reduction

To compare 3 types of intermaxillary fixation (IMF) and their behavior when subjected to tension forces in 3 study models with a palatine fracture feature. An experimental study of 3 identical acrylic models was performed. All had the same palatine fracture pattern on the maxillary midline. All were reduced with different IMF methods (ie, direct interdental wiring, Erich arch bars, and self-tapping screws). Tension forces were applied to the study models to observe the fracture line behavior. IMF with direct interdental wiring did not cause significant separation of the fracture feature in the anterior or posterior sector. IMF with the Erich arch bars caused a 2-mm separation in the anterior sector and 0mm in the posterior sector. The IMF with self-tapping screws caused a 3-mm separation in the anterior sector and 1mm in the posterior sector. IMF using self-tapping screws resulted in the greatest separation of the fracture compared with the results with Erich arch bars and direct interdental wiring. IMF with self-tapping screws tended to displace the fracture lines by application of the vector furthest from the center of resistance.

Dislodgement force analysis of an overdenture attachment system

Statement of problemThe performance of a recently introduced overdenture attachment system after cyclic dislodgement is not known. PurposeThe purpose of this in vitro study was to compare a conventional attachment system and a recently introduced attachment system for their dislodgement forces before and after cyclic dislodgement. Material and methodsThree acrylic resin models were fabricated with 2 implant analogs (4.1 mm; Zimmer Dental) in different angulations; parallel in the first, divergent by 30 degrees in the second, and divergent by 60 degrees in the third model. Six acrylic resin blocks containing 2 metal housings of 2 different LOCATOR attachments (LOCATOR Legacy [LL], R-Tx, n=3; Zest Dental Solutions) were also fabricated. LOCATOR abutment pairs (LL and R-Tx) were placed onto the analogs. Seven specimens for LL and R-Tx with pink attachments were tested for dislodgement forces, and the values were recorded before and after 1440 times (simulated 1-year use) of cyclic dislodgement using an occlusal loading simulator machine. A 3-way ANOVA was used for dislodgement force comparison before and after cyclic dislodgement for different angulations and for 2 different LOCATOR attachments. Any significant differences were identified with the Tukey HSD test (α=.05). The percentage decrease in the dislodgement force was also calculated. ResultsA significant 3-way interaction was found for the LOCATOR type, implant angle, and time (P<.001). LOCATOR type made a difference for only parallel and 60 degree–divergent implants before cyclic dislodgement (P≤.022). After cyclic dislodgement, a significant effect of the LOCATOR type on dislodgement force was found for only parallel implants (P=.034). In both LOCATOR systems, the dislodgement force was different (P<.001) among different implant angulations, except for parallel to 30-degree comparison, before and after cyclic dislodgement. For both LL and R-Tx, significant differences (P≤.022) were found between before and after cyclic dislodgement for all angulations except LL in parallel (P=.214). ConclusionsWhen implants were parallel, initially, the dislodgement force of R-Tx was higher than that of LL; however, the forces were similar after cyclic dislodgement. When implants were divergent by 30 degrees, there were no differences between the dislodgement forces of the LOCATOR systems before and after cyclic dislodgement. When implants were divergent by 60 degrees, initially, the dislodgement force of LL was higher than that of R-Tx; however, the forces were similar after cyclic dislodgement. Before and after cyclic dislodgement, in each system, dislodgement forces were greater when implants were divergent by 60 degrees than when parallel and 30 degrees. After cyclic dislodgement, dislodgement forces decreased for both systems, except for LL when the implants were parallel.

Full arch digital scanning systems performances for implant-supported fixed dental prostheses: a comparative study of 8 intraoral scanners

PurposeCompare the accuracy of intraoral digital impression in full-arch implant-supported fixed dental prosthesis acquired with eight different intraoral scanner (Ios). MethodsA polymethyl methacrylate acrylic model of an edentulous mandible with six scan-abutment was used as a master model and its dimensions measured with a coordinate measuring machine. Eight different Ios were used to generate digital impression: True Definition, Trios, Cerec Omnicam, 3D progress, CS3500, CS3600, Planmeca Emelard and Dental Wings. Fifteen digital impressions were made. A software called “Scan-abut” was developed to analyse and compare the digital impression with the master model, obtaining the scanning accuracy. The three-dimensional (3D) position and distance analysis were performed. ResultsMean value of the 3D position analysis showed that the True Definition (31 μm ± 8 μm) and Trios (32 μm ± 5 μm) have the best performance of the group. The Cerec Omnicam (71 μm ± 55 μm), CS3600 (61 μm ± 14 μm) have an average performance. The CS3500 (107 μm ± 28 μm) and Planmeca Emelard (101 μm ± 38 μm) present a middle-low performance, while the 3D progress (344 μm ± 121 μm) and Dental Wings (148 μm ± 64 μm) show the low performance. The 3D distance analysis showed a good linear relationship between the errors and scan-abutment distance only with the True Definition and CS3600. ConclusionsNot all scanners are suitable for digital impression in full-arch implant-supported fixed dental prosthesis and the weight of the output files is independent from the accuracy of the Ios.

Materializing Convection

This essay uses a physical modeling technique from mechanical engineering, the filling box, as a speculative architectural design tool. In the filling box, dyed salt water is injected into acrylic models submerged within a tank of fresh water, simulating the introduction of cold air into a warm environment or, when mirrored, the introduction of warm air into a cooler environment. The models make complex and beautiful convective thermodynamic processes visible, revealing insights about environmental processes taking place within and around buildings. Mirror images of model studies are accompanied by writing that draws on the science of thermodynamics to explore the atmospheric milieu of architecture, aligning an increasingly ubiquitous concept in architectural design discourse – thermal variability – with a design technique that foregrounds this concern.

Development of a hybrid method for improved accuracy of mould filling computational models for castings

ABSTRACT Computational modelling of mould filling is a component of paramount importance for the design of gating systems of castings. The main methods are the body-fitted grid system and the Cartesian grid system. While the former comes with high accuracy but high calculation times, the latter is fast but less accurate. A hybrid method combining a three-dimensional Cartesian cut-cell method and a porous media approach has been further developed. The calculated filling patterns compared favourably with high-speed video images of sand mould filling during pouring of ductile iron, and with visual images recorded through an acrylic glass-water model device simulating the gravity die casting process. In addition, numerical experiments were conducted to demonstrate the improved filling accuracy of the developed hybrid method. To this goal, three different symmetry tests with and without sub-mesh were designed and evaluated. All tests convincingly demonstrated the computational time and accuracy advantages of the developed method.

Implant impression accuracy of parallel and non-parallel implants: a comparative in-vitro analysis of open and closed tray techniques

BackgroundThe outcome of the evaluation of impression techniques accuracy may improve the selection criteria for an ideal technique. The aim was to evaluate the accuracy of the open and closed tray techniques for implant impressions, in a partially edentulous maxilla, replaced with a three-unit fixed partial denture, as well as to assess the effect of implants parallelism on accuracy.Material and methodsThis is an experimental in vitro study to evaluate impressions accuracy of a simulated area restored with an implant retained FPD, using the open and closed tray implant impression techniques. The effect of implant position angulation, parallelism, and implant systems (Straumann, SIC Invent, Osstem) was also evaluated. Three custom-made acrylic resin test models were prepared with two parallel and two non-parallel implants, on either side of a maxillary arch. One hundred and ninety-two impressions were made using monophase VPS impression material. Their master casts were obtained and evaluated for the horizontal and vertical discrepancy. The casts were scanned using a model scanner. The distances between the two reference points were measured.ResultsThe Straumann and SIC Invent implants showed no statistically significant differences (Mann-Whitney U test), regarding accuracy for both the open and closed tray impression techniques (P = 0.667 and P = 0.472). There were no significant differences for the parallel and non-parallel implants (P = 0.323 and P = 0.814), respectively, while the Osstem system showed statistically significant differences for both the open and closed tray impression techniques (P = 0.035) and between the parallel and non-parallel implants (P = 0.045). For the vertical discrepancies, significant differences were detected (chi-square test) between the open and closed tray impression techniques (P = 0.037).ConclusionsWithin the limitations of this study, there were generally no significant differences between open and closed, although better results were obtained for the open tray techniques. On the use of the non-parallel implants, the open tray technique provided a better result than the closed tray technique.

Effect of Labial Implant Inclination on the Retention and Stability of Different Resilient Stud Attachments for Mandibular Implant Overdentures: An In vitro Study.

This study evaluated the influence of labial implant inclination on the retention and stability of different resilient stud attachments for mandibular implant overdentures. Four identical mandibular edentulous acrylic resin models were fabricated. For each model, two implants were inserted at the canine areas with different degrees of labial inclination: 0, 10, 20, and 30 degrees. Four experimental overdentures were fabricated over the models and fitted to the implants using resilient stud attachments. Regular retentive inserts (extra-light, light, and medium retention) were used for all implant inclinations, and extended-range inserts (extra-light and medium retention) were used for 30-degree inclination only. Vertical (retention) and oblique (stability) dislodging forces (lateral, anterior, and posterior) were evaluated initially (initial retention) and after overdenture insertion and removal (final retention). After repeated insertions and removals, inclination of 30 degrees recorded the highest retention and lateral stability, and 0 degrees recorded the highest posterior stability; 20 degrees showed the lowest retention, and 30 degrees recorded the lowest posterior stability. The highest stability and retention values were recorded with light and medium regular inserts, and the lowest values were noted with extra-light regular inserts. Within the limits of this study, moderate labial implant inclination (10 degrees and 20 degrees) was shown to negatively affect retention and anterior/lateral stability, and excessive implant inclination (30 degrees) to negatively affect posterior stability. When implants are inclined labially, it is recommended to use light and medium regular stud attachments to obtain high levels of retention and stability for two-implant-retained overdentures.

Volumetric measurement of dentoalveolar defects by means of intraoral 3D scanner and gravimetric model

The aim of this study was to evaluate the accuracy in volumetric measurements obtained on an experimental model using an intraoral scanner and a gravimetric method. Three identical partial dentate maxillary acrylic models with three fabricated alveolar defects, in anterior and posterior regions, were scanned using an intraoral scanner (20 scans/defects). The defects differed in terms of size and distance of neighbouring teeth. As references, replicas of each defect were created using a dimensional stable silicone impression material. After measuring the mass of each replica, the volume was calculated by dividing the mass of each replica by the density of the impression material. The defects had a volume, according to the gravimetric method, ranging from 40.5 to 143.7 mm3. The scans were imported to metrology software for analyses. Accuracy was determined in terms of trueness and precision. The mean trueness for all defect types was 0.168 mm3 (SD 0.691, range 2.82). There was no statistical significant difference between the mean trueness for all defects measured (p = 0.910). The mean precision for all defect types was 0.147 mm3 (SD 0.524, range 2.86). There were no statistical significant differences between the dental models in regard to mean precision (p = 0.401), however, there were statistical significant differences between defects in position 1 and 2 (p = 0.002) and 1 and 3 (p = 0.001). Based on the findings of this study, the intraoral scanner utilized in the current study presented an acceptable level of accuracy when measuring volume of defects.

Ultra-Low-Dose versus Normal-Dose Scan Protocol of Planmeca ProMax 3 D Mid CBCT machine in Detection of Second Mesi buccal Root Canal in Maxillary Molars: An ex vivo study

Objective: The aim of this study was to compare the ability of Normal and Ultra-Low-Dose protocols of Planmeca Promax 3 D Mid CBCT unit with different voxel sizes in detection of MB2 canal.Materials and Methods: This study was conducted on 36 extracted human maxillary first and second molars. Six acrylic models were prepared and six molars were embedded in each model using Inlay wax. Each acrylic model was then placed in a plastic container filled with water. CBCT imaging of the acrylic models containing the extracted molars was taken by Planmeca ProMax 3D Mid machine (Helsinky, Finland). Each model was scanned with three different voxel sizes (0.075, 0.1, 0.2 mm) and two different exposure protocols, namely the Normal-Dose (ND) and the Ultra-Low-Dose (ULD) protocol. Assessment of the number of MB canals was carried out by two Oral and Maxillofacial Radiologists. To verify the number of root canals of the mesiobuccal root, these roots were sectioned and visually inspected. The data obtained were tabulated and subjected to statistical analysis.Results: Transverse sections showed that 22 molars had two mesiobuccal root canals and 14 molars had only one mesiobuccal root canal. The results showed that the sensitivity and accuracy of CBCT images increase as the voxel size decrease. However, the results revealed no significant difference (p>0.05) between the (ND) and (ULD) protocol of the same voxel size used. Both intra and inter-observer reliability showed very good agreement (0.81–1).Conclusions: ULD CBCT protocol can be applied for the detection of MB2 of maxillary molars. The smaller the voxel size, the higher the image resolution and image quality. The 0.075 mm voxel size of both protocols is accurate enough to be used as a gold standard in laboratory studies instead of the standard root sectioning technique.

Biomechanical development and evaluation of a new framework for all-on-four rehabilitation

Abstract Introduction For complete rehabilitation of fully edentulous mandibles, the option for immediate loading determines the use of temporary prostheses that splint the installed implants. Although temporary prostheses with reinforcement provide rehabilitations with biomechanical benefits, the non-adoption of this recommendation coexists in different studies on immediate restorations. Objective This study evaluates a type of prosthesis to restore jaws by the all-on-four concept. Material and method: The mechanical behavior of prostheses with the modified framework was evaluated in vitro, under a cantilever mechanical unilateral bending test. Two representative groups were included in the all-on-four concept, with a G1 test group (n = 10) containing modified frameworks and a G2 control group (n = 10) that included full acrylic prostheses. The samples were submitted to thermal cycling with 500 cycles (5° ± 2 °C for 30 s, and 55° ± 2° for 30 s) and to the mechanical bending test on the cantilever. Result The Mann-Whitney test revealed a significant difference between G1 and G2 (p &lt;0.001). In the descriptive evaluation, G1 averaged 830.50 N until the initial resin fracture, while the control group presented a mean of 403.58N. The maximum resistance until complete fracture was recorded in G1, with a mean of 903.03N, while in G2, a mean of 435.20N was recorded. The linear vertical component of the flexion was 0.68 mm and 0.39 mm until the initial fracture of the bar, respectively for G1 and G2. Conclusion The modified framework for the all-on-four protocol determined better mechanical performance when compared to the same full acrylic prosthesis model.

Comparison between all zirconia, all PEEK, and zirconia-PEEK telescopic attachments for two implants retained mandibular complete overdentures: In vitro stress analysis study

Aim: This in vitro study was performed to evaluate and compare stresses applied to the implants retaining mandibular complete overdenture with telescopic attachments of different materials. Materials and Methods: Three identical clear acrylic resin models of completely edentulous mandibular arch were selected for this study. One implant was installed in each canine region of each model. The models were scanned to design telescopic attachment using computer-aided design/computer-aided manufacturing technology. According to material used for telescopic attachments fabrication, models were categorized as follows: All Zirconia (ZrO2) telescopic group (zz): Primary and secondary crowns were made of ZrO2, all polyetheretherketone (PEEK) telescopic group (pp): Primary and secondary crowns were made of PEEK, and Zirconia-PEEK telescopic group (zp): Primary crown was made of ZrO2, and secondary one was made of PEEK. Three identical mandibular complete overdentures were constructed. The secondary telescopic crowns were picked up within the intaglio surface of each overdenture. Four strain gauges were installed parallel to each implant. Bilateral and unilateral loads were applied, and strain values were recorded. Results: Comparison of recorded stresses values revealed a significant difference between groups where the highest stresses were recorded with all-PEEK group, followed by all-zircon group and the lowest stresses were noted with Zirconia-PEEK group for both bilateral and unilateral loading tests. Conclusion: Within the limitation of this in vitro study, it could be concluded that: telescopic attachments that fabricated from ZrO2 primary crown and PEEK secondary crown is a promising attachment regarding reductions of stresses transmitted to the implants retaining mandibular complete overdenture.

Effect of Different Bar Designs on Axial and Nonaxial Retention Forces of Implant-Retained Maxillary Overdentures: An In Vitro Study

This in vitro study aimed to evaluate and compare the effect of different bar designs on the retention forces of implant-retained maxillary overdentures. A maxillary edentulous acrylic resin model without alveolar undercut was fabricated. Four implant analogs were placed in the canine and second premolar regions. Overdentures were made and attached to the analogs with Dolder bar, Hader bar, and milled bar attachments. A universal testing machine was used to measure axial (resistance to vertical displacement) and nonaxial (resistance to anterior, posterior, and lateral displacement) retention forces (in Newtons). Measurements were made at the start of the experiment (initial retention) and after 540 cycles of denture insertion and removal to simulate 6 months of clinical function (final retention). Hader bar had the highest retention after insertions and removals, and Dolder bar had the lowest retention. Vertical displacement showed the highest retention for Dolder and milled bars, and posterior displacement showed the highest retention for Hader bar. Lateral displacement recorded the lowest retention for all bar designs. No significant difference in axial retention loss was observed between different bar designs. Dolder bar showed the highest nonaxial retention loss, and milled bar showed the lowest retention loss. Hader bar is recommended to retain maxillary implant overdentures, as it was associated with higher axial and nonaxial retention compared with Dolder and milled bars after 6 months of simulated denture wear.

Comparison of the accuracy of open-tray and snap-on impression techniques of implants with different angulations

A precise transfer of the position of an implant to the working cast is particularly important to achieve an optimal fit of the final restoration. Different variables affect the accuracy of implant impression. The purpose of the present study is to compare the accuracy of open-tray and snap-on impression techniques in implants with different angulations. In this experimental study: A reference acrylic resin model of the mandible was fabricated. Four implants were positioned with the angles of 0°, 10°, 15°, and 25° in the model. Ten impressions were prepared with open-tray technique and ten impressions were made using snap-on technique. All impressions were made from vinyl polysiloxane impression material. Linear (Δx, Δy, and Δr) and angular displacements (Δθ) of implants were evaluated using a coordinate measuring machine. Measured data were then analyzed using two-way analysis of variance and Tukey's test (α = 0.05). The results showed that the accuracy of open-tray impression technique is significantly different from snap-on technique in Δx (P = 0.003), Δy (P = 0.000), Δr (P = 0.000), and Δθ (P = 0.000). Implants with 25° angulation are significantly less accurate than 0°, 10°, and 15° implants in Δx, Δy, Δr, and Δθ. Fifteen-degree implants are less accurate than 0° and 10° ones in Δθ. Regarding the findings of this study, it can be concluded that snap-on technique is less accurate than open-tray technique, and the accuracy of 25° implant is less than that of 0°, 10°, and 15° implants.

Adhesive remedies for dentures. Myths and reality (laboratory research)

The research shows force-separation relation between layer thickness of Corega adhesive denture cream applied on lower jaw's models and denture basis itself. Four high strength die stone models with different wax isolation layers (0 mm; 0.3 mm; 0.5 mm; 1 mm) were prepared for further production of acrylic denture. Isolation thicknesses were verified by measuring light body c-silicone thickness, applied under each basis. Humidity and temperature of oral cavity were imitated during experiments. Mandible acrylic model with applied cream and denture was mounted on a tripod. A plastic 5-liter bottle was rigidly attached to denture basis with nylon straps. While experiment, bottle was filling with water until denture disassemble from jaw model. Results show that separation force increases with decreasing cream's thickness.