Acrylic Model Research Articles

Investigation of the deviation during the information transfer from the prosthetic field to the laboratory scanners

The aim of this work is to investigate the deviations during the first stage of the information transfer from the prosthetic field to the dental laboratory scanners for CAD/CAM technology. The first upper left molar on an artificial acrylic resin dental model was prepared for full metal-ceramic crown according to the standard guidelines for step cut. The prepared prosthetic field was scanned by a high-precision industrial scanner with a 1-mm ruby ball stylus and a digital copy was made. With a standard tray, a two-phase two-stage silicon (A-silicone Zhermack hydrorise putty and light body) impression from the acrylic model was taken following the technology recommended by the manufacturer. The impression was powdered with dental stone type IV and a stone model was created 1 h after impression, the time delay taking place ordinarily in dental practice. Using the same measurement methods, the stone model’s surfaces were digitized. Both digital models were compared using the acrylic resin dental model as a reference. The results on the deviation during the transfer of information between the prosthetic field and the stone model represent the first level of inaccuracy in the CAD/CAM processing technology. The difference in the alteration of each dimension according to the reference and the stone model is not more than 20 μm in shrinkage or expansion direction. Thus, the widely used approach for information transfer using stone models from the prosthetic field to laboratory scanner for CAD/CAM technology could be considered as relevant with an accuracy of about ±10 μm. If the silicon impression is performed carefully, the stone models are sufficiently accurate representations of the prosthetic field and their digitalization in the dental laboratory is a reliable starting point for the CAD/CAM technology.

Effect of prosthetic framework material, cantilever length and opposing arch on peri-implant strain in an all-on-four implant prostheses.

To evaluate the effect of prosthetic framework material and cantilever length on peri-implant strain in mandibular all-on-four implant-supported prostheses with different types of arch antagonist forces. Models simulating a completely edentulous mandibular arch fabricated in heat-cured acrylic resin were used. On the acrylic models, four implants were placed at regions 34, 32, 42, and 44 simulating all-on-four implant placements. Implant-supported screw-retained fixed prosthesis frameworks were fabricated using three different materials (cobalt-chromium, zirconia, and polyetheretherketone) and with three different cantilever lengths (zero mm, 15 mm, and 25 mm). Strain gauges were attached on the model at the buccal and lingual positions of each implant. Forces simulating opposing natural dentition, conventional complete denture, and the parafunctional habit were applied to the models. The peri-implant strain in each strain gauge was recorded. Least peri-implant strains (67 microstrains) were observed when forces simulating conventional complete dentures were applied on the models and the highest peri-implant strains (9091 microstrains) were observed when forces simulating parafunctional habit were applied. One-way ANOVA test followed by Tukey's post hoc analysis was performed to compare the mean deformation scores between different materials at 50 N load. The level of significance [P-value] was set at P < 0.05. Tests showed significant differences between zero mm and the other types in all the different materials, and also between 1.5 x AP and 2.5 x AP for Zirconia and Peek material at P = 0.02 & P = .008, respectively. The results showed that the type of framework material, cantilever length, and occlusal forces from the opposing arch influence the peri-implant strain in the bone in all-on-four implant-supported prostheses. Rehabilitation of a single, completely edentulous arch with implant-supported prostheses should consider the situation of the opposing arch. The choice of framework material, as well as the cantilever length, should be altered based on the forces from the opposing arch.

Visualization of Continuous Fluid Behavior Using Acrylic Transparent Model

Visualization of Continuous Fluid Behavior Using Acrylic Transparent Model

Quantitative analysis of particulate matter release during orthodontic procedures: a pilot study.

Introduction Transmission of SARS-CoV-2 through aerosol has been suggested, particularly in the presence of highly concentrated aerosols in enclosed environments. It is accepted that aerosols are produced during a range of dental procedures, posing potential risks to both dental practitioners and patients. There has been little agreement concerning aerosol transmission associated with orthodontics and associated mitigation.Methods Orthodontic procedures were simulated in a closed side-surgery using a dental manikin on an acrylic model using composite-based adhesive. Adhesive removal representing debonding was undertaken using a 1:1 contra-angle handpiece (W&H Synea Vision WK-56 LT, Bürmoos, Austria) and fast handpiece with variation in air and water flow. The removal of acid etch was also simulated with the use of combined 3-in-1 air-water syringe. An optical particle sizer (OPS 3330, TSI Inc., Minnesota, USA) and a portable scanning mobility particle sizer (NanoScan SMPS Nanoparticle Sizer 3910, TSI Inc., Minnesota, USA) were both used to assess particulate matter ranging in dimension from 0.08 to 10 μm.Results Standard debonding procedure (involving air but no water) was associated with clear increase in the 'very small' and 'small' (0.26-0.9 μm) particles but only for a short period. Debonding procedures without supplementary air coolant appeared to produce similar levels of aerosol to standard debonding. Debonding in association with water tended to produce large increases in aerosol levels, producing particles of all sizes throughout the experiment. The use of water and a fast handpiece led to the most significant increase in particles. Combined use of the 3-in-1 air-water syringe did not result in any detectable increase in the aerosol levels.Conclusions Particulate matter was released during orthodontic debonding, although the concentration and volume was markedly less than that associated with the use of a fast handpiece. No increase in particulates was associated with prolonged use of a 3-in-1 air-water syringe. Particulate levels reduced to baseline levels over a short period (approximately five minutes). Further research within alternative, open environments and without air exchange systems is required.

The impact of impression coping geometrical design on accuracy of implant impressions: an experimental study

AimThis in vitro study aimed to evaluate the effect of implant impression coping geometrical designs on the accuracy of open and closed impression techniques and in the parallel and nonparallel implant positions.Material and methodsThree custom-made acrylic resin models of three tested implant systems (Straumann®, SIC Invent®, and Osstem®) with diverse coping geometrical designs were evaluated in simulated cases of two parallel and two nonparallel implants. The horizontal and vertical discrepancies were measured and analyzed.ResultsNo statistically significant differences between the two impression techniques in either parallel or nonparallel implants were observed. The high retentive design of the Osstem system showed a statistically significant difference.ConclusionThe geometrical design of the impression copings did not affect the accuracy for either the open and closed tray techniques. However, the high retentive coping design of the Osstem implant affected the accuracy in the open tray technique.

The effect of different storage times and storage conditions of two types of alginate impression on accuracy of master cast

The aims of this study were to determine the effect of using different storage time and storage media on the accuracy of two types of alginate impression material,Hydrogum soft and Hydrogum elastic. One hundred sixty impressions were recorded from a standard acrylic model using perforated trays. These impressions were divided into three main groups. In the first group,(48) impressions were stored at (3) times interval namely (15) minutes,(30) minutes,(60) minutes and left on the bench uncovered. In the second one,(48) impressions were stored in disposable plastic bags at the same time interval mentioned above. In the third one,(48) impressions were divided into (3) subgroups, the first one were only washed with tap water before pouring, the other two subgroups were immersed in Sodium Hypochiorite(0.5%) and ChlorhexidineGluconate(0.5%) disinfectant solutions for (30) minutes before pouring,(16) impression will be taken and poured immediately to be considered as a control for this study. A three dimensional measuring machine (3D) was used for measuring the dimensional change of stone casts, the results showed that there was no significant differences of casts accuracy produced from the two types of an alginate impression material. Storage of alginate impression material at (15) and (30) minutes on the bench or inside sealed plastic bags showed no significant differences in dimensional changes compared with control samples that poured immediately, Storage to (60) minutes showed a significant difference,washing alginate with tap water and immersion in chlorhexidine disinfectant solution (0.5%) for (30) minutes showed no significant difference Immersion in sodium hypochlorite (0.5%) for (30) minutes showed significant changes. It was concluded that alginate impression could be stored for (30) minutes inside bags without significant changes if the pouring of alginate impression will be delayed for any reason.

Comparison of Dental Stone Models and Their 3D Printed Acrylic Replicas for the Accuracy and Mechanical Properties.

This study was conducted to test possibilities of application of 3D printed dental models (DMs) in terms of their accuracy and physical properties. In this work, stone models of mandibles were cast from alginate impressions of 10 patients and scanned in order to obtain 3D printed acrylic replicas. The diagnostic value was tested as matching of model scans on three levels: peak of cusps, occlusal surface, and all teeth surfaces. The mechanical properties of acrylic and stone samples, specifically the impact strength, shore D hardness, and flexural and compressive strength were investigated according to ISO standards. The matching of models’ surfaces was the highest on the level of peaks of cusps (average lack of deviations, 0.21 mm) and the lowest on the level of all teeth surfaces (average lack of deviations, 0.64 mm). Acrylic samples subjected to mechanical testing, as expected, showed higher mechanical properties as compared to the specimens made of dental stone. In the present study we demonstrated that 3D printed acrylic models could be ideal representatives in the case of use as a diagnostic tool and as a part of medical records. The acrylic samples exhibited not only higher mechanical properties, but also showed better accuracy comparing to dental stone.

Accuracy of different impression techniques for multiunit implant restoration: A qualitative in vitro study

Statement of problemDisplacement of impression copings and/or implant replicas during impression making and dimensional changes that occur during clinical and laboratory phases of making multiunit implant prostheses may affect the accuracy and fit of the prostheses. PurposeThe purpose of this qualitative study was to investigate and compare 3 different impression techniques for osseointegrated dental implant transfer procedures. Material and methodsThree impression transfer approaches were evaluated and compared: closed-tray impression technique (CTT), impression with plastic snap-fit impression copings; open-tray impression technique (OTT), impression with independent square copings; and OTT joining the impression copings with a photo-polymerized resin (PPT). A reference acrylic resin model with 4 implants was fabricated. Polyvinyl siloxane with a stock tray was used to make 45 impressions (n=15 for each impression technique), and 45 die definitive stone casts. A computer-aided design and computer-aided manufacturing (CAD-CAM) titanium framework was fabricated on the reference model. Three blinded operators evaluated the fit of the CAD-CAM titanium framework on each model to find clinically acceptable fit. The Kappa test was used for the agreement between the examiners (α=.05). ResultsAgreement was found among the 3 examiners on 44 of 45 specimens (Kappa value= 0.939; P<.001). In the CTT group, 14 casts were found to be acceptable. In the OTT group, nearly half of the specimens produced unacceptable fitting casts, whereas in the PPT group, 13 casts were found acceptable. ConclusionsCTT and PPT produced more accurate casts than the OTT technique, which yielded inferior results.

The Influence of Implant Inclination on Retention and Peri-implant Stresses of Stud-Retained Implant Overdentures During Axial and Nonaxial Dislodgments: An In Vitro Study.

The purpose of this study was to evaluate the influence of implant inclination on retention and peri-implant stresses of stud-retained implant overdentures during axial and nonaxial dislodgments. Mandibular acrylic models (n = 4) received two implants in the canine areas with 0-, 5-, 10-, and 20-degree lingual inclinations. Dentures were attached to the implants with stud connectors. Four strain gauges were bonded at buccal, lingual, mesial, and distal surfaces of each implant to monitor strains around implants. Retention values (Newton) and peri-implant stresses (microstrains, μs) were recorded during axial (vertical) and nonaxial (anterior, posterior, and lateral) dislodging. A general linear model was used to compare retention forces and implant stresses between implant inclinations and dislodging direction. In addition, a linear regression model was used to test correlation of implant stresses with confounding factors. The highest retention and implant stresses were noted with 0 degrees, followed by 5 and 10 degrees (without difference), and the lowest values were noted with 20 degrees. Anterior dislodging was associated with the highest retention and implant stresses, followed by vertical dislodging, then lateral dislodging, and posterior dislodging. Peri-implant stresses significantly correlated with dislodging direction and retention forces. Every 1 N of increase in retention forces causes 19.17 μs increase in implant stresses. Anterior dislodging was associated with the highest predicted stress values (846.0 μs), and the lowest stress values (143.41 μs) were associated with posterior dislodging. Retention forces and peri-implant stresses decreased as lingual implant inclination increased during axial and nonaxial dislodging of stud-retained implant overdentures. Peri-implant stresses were significantly correlated with dislodging direction and retentive forces.

Cleaning Efficacy of Poly-ether-ether-ketone Tips in Eliminating Cement Remnants Around Implants With Different Abutment Heights.

The excess cement not removed after the cementation of fixed implant-supported restorations may cause loss of peri-implant attachment or adjacent bone. The aims of this study were to evaluate the amount of residual cement at different abutment-crown connection levels and to test the cleaning efficacy of poly-ether-ether-ketone (PEEK) ultrasonic tips after cementation. One implant was placed in an anterior central tooth position 5 mm below the gingival margin in an acrylic model, and 32 stone models were obtained with implant analogs. Abutment heights of 1-2 and 2.5-4 mm were used on the vestibular and lingual sides, respectively. Crowns were cemented and cleaned, and half of the samples were cleaned again using PEEK tips. The abutment-crown suprastructure was then disconnected, and cleaning efficacy was evaluated. Varying amounts of excess cement were found on all specimens except for the PEEK group with abutment-crown connections 1 mm below the gingival margin. An increase of undetected cement remnants was observed when the restoration margins were located deeper subgingivally. Various amounts of excess cement associated with margin location were detected on the abutment-restoration complex despite meticulous cleaning efforts. Ultrasonic PEEK tips were effective at cleaning the cement remnants around implants to a certain depth.

In Vitro Study Regarding the Biomechanical Behaviour of Bone, Fibre Reinforced Polymer and Wire Composite Perio-dontal Splints. Model Analysis

This paper is the second part of a study regarding the biomechanical behaviour of mandibular bone in the context of different periodontal splinting systems, occlusal forces and load distributions. Electric resistive tensometry method was used to measure the strains developed in mandibular bone replica. The tests were carried out on six mandibular acrylic models, each with 8 natural teeth. The experimental groups were defined corresponding to the bone condition and splint type: normal height bone; bone resorption without splint; bone resorption and wire-composite splint; bone resorption and polyethylene fiber-reinforced composite splint. Each sample was subjected to three similar loading cycles, the force being applied successively on four incisors, two central incisors and canines, and the specific deformation values were read for four loading forces: 30 N, 50 N, 100 N and 150 N. In case of bone loss, the bone deformations are up to 110%. Periodontal splinting redistribute forces, reducing incisors bone strains associated with a slight increase in canine bone strains.

THE EFFECT OF IMPLANT LOCATIONS ON THE STRESS TRANSMITTED TO IMPLANT-TOOTH-ASSISTED PARTIAL OVERDENTURE (IN VITRO STUDY)

Introduction: Posterior free end edentulous areas are more prevalent among population. Absence of posterior abutments to support and retain partial dentures affects the prognosis of prostheses. A problem of support, retention and stability is usually associated with distal extension removable partial dentures. Objectives: To evaluate and compare the effect of implant locations on the retention of the prostheses of implant tooth assisted partial overdenture for mandibular Kennedy class II with implant located in first premolar area and second molar area. Second objective was to evaluate the wear of female parts of the attachments attached to these implants. Materials and methods: The study was conducted on two parallel groups according to the different implant locations: Group (A) implant in first premolar area, Group (B) implant in second molar area. Two acrylic models with Kennedy class II were used in this study. Two implants with (2.3mm length and 3.6mm width), two positioner attachments were attached to implants and inserted in the previous locations for both groups. Each group had 9 sets of attachments with 3 different colored plastic matrices (27 matrices) with different retention force. A metallic overdenture with acrylic resin base and teeth was constructed for each group. By using the universal testing machine, vertical load dislodgment forces were measured at anterior of the saddle of the denture and posterior of the saddle of the denture for both groups at the beginning of the study (initial retention) and after 50,000 cyclic with load of 20 K at first molar area, the retention test was repeated and the mean value was recorded. All retention parts were imaged under stereomicroscope to study wear and attrition of internal components. All data from both groups in this in-vitro study was gathered, tabulated and statistically analyzed. Results:In vertical dislodging, Group (B) posterior of the saddle, recorded the highest retention force. In Group (B) anterior of the saddle recorded the lowest retention force. After 50,000 cyclic loading, Group (B) posterior of the saddle was higher than Group (A) in retention force. Dimensional changes and wear scratches appeared in the metal housing and plastic matrices in central and outer lines. Conclusions: The distal position of the implant with positioner attachment has great retention during vertical dislodgment compared with mesial implant location with positioner attachment.

Class II Kennedy implant assisted mandibular removable partial dentures with and without cross arch stabilization: A strain gauge in vitro study.

Introduction Dental implants and extracoronal attachments were used with Kennedy class II implant assisted removable partial dentures (IARPD) without a major connector. strain gauges were used to detect the microstrains generated around the abutments and dental implants. Materials and Methods Thirty acrylic resin models of a mandibular class II Kennedy received 3 RPD designs; a clasp retained RPD in group I, a unilateral clasp retained RPD without a major connector supported by a dental implant placed once at the first molar and once at the second molar position in group II, and in group III, a clasp free RPD, with extracoronal attachments, supported by a dental implants placed in similar positions to group II. Strain gauges were used to determine which design generated more significant loads, and recorded microstrains were statistically analyzed using the Kruskal-Wallis and Mann-Whitney tests. Results Significantly greater loads around abutment teeth were reported in group II and group III than in group I. The distal placement of the implants resulted in significantly greater microstrains more than the mesial placement in groups II and III, and both placements were of more intensity in group II than in group III. Conclusions A Kennedy class II IARPD can be effectively altered to a bounded space prosthesis by placement of a dental implant in the first rather than the second molar position, and together with an extracoronal attachment, the clasp and major connector can be omitted once the edentulous span is short, and the clinical situation is favorable.

Evaluation of the Accuracy of an Intraoral Scanner: An Update on the Omnicam

Computerized optical impression making is one of the most exciting topics in dentistry today. Therefore, it is very important to know how accurate these devices are. Purpose: To investigate the influence of a software update of an intraoral scanner. Materials and Methods: Accuracy was tested in terms of trueness and precision. An acrylic model was scanned with an industrial scanner. The dataset was used as reference for the evaluation of the CEREC AC Omnicam datasets and statistical analyses implemented. Results: Trueness and precision values very significantly smaller with the latest software version as opposed to the previous version. Conclusion: Within the limits of the present study, the investigated intraoral scanner meets the highest standards in terms of trueness and precision. The authors strongly recommend to not use software other than the proprietary workflows to export files to the open STL file format.

Nano-Hybrid Versus Micro-Hybrid Composite as Reinforced Resin for Ribbon Bar Attachment

Purpose: The goal of this study was to compare and evaluate stress transmitted to an overdenture abutment tooth supported by polyethylene ribbon bar reinforced composite resin of hybrid type, the hybrid type includes Nano-hybrid composite and Micro-hybrid composite. Methods: Edentulous educational acrylic model modified to receive two canine teeth and duplicated to ten models. Polyvinyl silicon impression material was packed to simulate mucosa covering the ridge. The canines prepared to receive a metal jacket and then infibra ribbon bar constructed on the abutments, mandibular overdenture constructed to each model over the bar, the ten models divided equally into two groups, Group I: Five models received mandibular overdenture supported by two canines splinted with ribbon fiber bar reinforced with Nano-hybrid composite. Group II: Five models received mandibular overdenture supported by two canines, splinted with ribbon fiber bar reinforced with Micro-hybrid composite. Installation of strain gauges around each surface of the abutment, Universal testing machine used to apply load to each model Unilateral (50 N) and bilateral (100 N) vertical static load applied at 1st molar area to measure µ-strains at buccal, lingual, mesial and distal surfaces of the abutment. the outcomes collected and statistically analyzed to compare between the two groups. Result: -Infibra ribbon bar reinforced by Nano-hybrid composite and infibra ribbon bar reinforced by micro-hybrid composite exhibits No significant difference of microstrain transmitted to overdenture abutment except the labial surface. - Under bilateral loading, Infibra ribbon bar reinforced with a Nano-hybrid composite bar transmit higher microstrain to all labial, lingual, and mesial surfaces of overdenture abutment than infibra ribbon bar reinforced with Micro-hybrid composite except the distal surface. Conclusion: -Infibra ribbon bar reinforced with hybrid type composite decrease stresses transmitted to mandibular overdenture abutment -Regarding stress distribution, Micro-hybrid composite is the material of choice to construct infibra ribbon bar over Nano-hybrid composite.

A comparative carbon footprint analysis of disposable and reusable vaginal specula

Healthcare systems in the United States have increasingly turned toward the use of disposable medical equipment in an attempt to save time, lower costs, and reduce the transmission of infections. However, the use of disposable instruments is associated with increased solid waste production and may have negative impacts on the environment, such as increased greenhouse gas emissions. The purpose of this study was to inform this discussion; we applied life cycle assessment methods to evaluate the carbon footprints of 3 vaginal specula: a single-use acrylic model and 2 reusable stainless steel models. The functional unit of the study was defined as the completion of 20 gynecologic examinations by either type of speculum. The greenhouse gas emissions (eg, carbon dioxide, methane, nitrous oxide) across all life cycle stages, which includes material production and manufacturing, transportation, use and reprocessing, and end-of-life, were analyzed with the use of SimaPro life cycle assessment software and converted into carbon dioxide equivalents. The reusable stainless steel grade 304 speculum was found to have a lesser carbon footprint over multiple model scenarios (different reprocessing techniques, autoclave loading/efficiency, and number of uses) than either the reusable stainless steel grade 316 or the disposable acrylic specula. The material production and manufacturing phase contributed most heavily to the total life cycle carbon footprint of the acrylic speculum, whereas the use and reprocessing phase contributed most to the carbon footprints of both stainless steel specula. The use of disposable vaginal specula is associated with increased greenhouse gas equivalents compared with reusable alternatives with no significant difference in clinical utility. These findings can be used to inform decision-making by healthcare systems, because they weigh a wide range of considerations in making final purchase decisions; similar analytic methods can and should be applied to other components of health systems' waste streams.

Micro-computed tomographic evaluation of a new system for root canal filling using calcium silicate-based root canal sealers.

ObjectivesThis study evaluated by using micro-computed tomography (micro-CT) the filling ability and sealer apical extrusion promoted by a new Sealer Injection System (SIS; Angelus) with side openings needle, in comparison with the conventional injection system, associated with a new ready-to-use calcium silicate-based sealer (Bio-C Sealer).Materials and MethodsAcrylic resin models containing a main curved artificial canal and 3 simulated lateral canals in apical, middle and cervical thirds were used. The main root canals were prepared using a rotary system up to size 35.05. The canals were filled with Bio-C sealer by using a single cone technique and the conventional delivery system or SIS. Samples were scanned in micro-CT. The percentage of voids throughout the entire extension of the main root canal and in each third of the lateral canals, besides the apical extrusion of the sealer was calculated. Data were submitted to t-test (p < 0.05).ResultsThere was no difference between both systems in the main root canals filling. Although the volume percentage of voids was similar in the apical and middle thirds of lateral canals, SIS had the greatest filling ability of the cervical third lateral canal. Moreover, the conventional system showed the highest apical extrusion of the sealer.ConclusionsThe conventional and SIS obturation systems had an appropriate filling ability of the main root canal. SIS had the best filling of the cervical third of the lateral canals, besides lower sealer apical extrusion, suggesting its clinical indication.

A comparative evaluation of accuracy of three impression techniques in parallel and angulated multiple implant impressions: An in vitro study

Introduction: Dental implants have become the treatment of choice in many situations where missing teeth require functional and esthetic replacements. The present study was conducted to evaluate and compare the accuracy of multiple implant impressions using different impression techniques such as open tray nonsplinted, open tray splinted, and closed tray in both parallel as well as angulated implants.Materials and Methods: Two acrylic models were fabricated with four implant analogs placed in each model. Three impression groups, Group 1 (open-tray nonsplinted technique), Group 2 (open -tray splinted technique), and Group 3 (closed tray technique) were formed for each model. The post hoc Tukey's test was used for multiple comparisons.Results: The results show that Group 3 is least accurate after that, Group 1 and Group 2 are most accurate techniques for impression making.Conclusions: These results indicate that the open-tray (pickup) impression technique is more accurate as compared to the closed tray (reposition) technique in both Model A (parallel analogs) and Model B (angulated analogs).

To evaluate and compare the accuracy of definitive casts using various splinting methods on implant level impressions in All-on-Four treatment: An in vitro study.

Aim:The aim of this study is to evaluate and compare the accuracy of master casts obtained by different splinting techniques for implant level impressions in All-on-Four implant treatment protocol using a coordinate measuring machine.Settings and Design:The study design involves an in vitro study.Materials and Methods:In this in vitro study, a reference clear acrylic resin (AR) model comprising four regular platform implant 3.6 mm × 10.0 mm (Dentium Implant India Pvt. Ltd, Bengaluru, India) which was placed following the All-on-Four implant protocol is prepared. Impressions were categorized into three different groups: Group 1 – impression copings were nonsplinted; Group 2 – impression copings were splinted using AR sectioned 17 min after setting and rewelded with the same resin; and Group 3 – impression copings were splinted by titanium bar using an intraoral welder. A total of 33 (n = 11 in each group) impressions were made to evaluate three different splinting techniques. Impressions were poured with Type 4 dental stone. A coordinate measuring machine was used to record the x, y, and z co-ordinates and angular displacement. The measurements were compared with those obtained from the reference model.Statistical Analysis Used:One-way ANOVA test was used as a test of significance.Results:There was less linear and rotational displacement for the metal-splinted group (P < 0.001) In the x-axis, nonsplinted group showed a statistically significant difference in straight implants (2 and 3 implants) (P = 0.001) of All-on-Four treatment protocol.Conclusion:The splinting methods have a direct effect on the accuracy of definitive casts. The metal-splinted direct technique produced the most accurate casts followed by AR-splinted direct technique and nonsplinted direct technique.

Impact of implants number and attachment type on the peri-implant stresses and retention of palateless implant-retained overdenture.

To evaluate the impact of implants number and attachments type on the peri-implant stresses and retention of maxillary palateless implant-supported overdenture. Four edentulous maxillary educational acrylic resin models were used. According to the implants number and type of attachment used, four groups were compared: Group I, 2-locator attachments in the canine area; Group II, 2- OT equator attachments in the canine area; Group III, 4-locator attachments in the canine, second premolar area and Group IV, 4-OT equator attachments in the canine, second premolar area. Implants retained palateless overdenture was constructed on each model. Four self-protected linear strain gauges were cemented on each implant. A digital loading device was used to apply compressive loads to measure the resulting peri-implant stresses. Forcemeter and Universal testing machines were used to test the retention of palateless overdenture. A significant difference between the same implant number and distribution with different attachments was found (P = 0.003, P = 0.020), respectively. Least stresses amount was found around the 4-implant locator palateless overdenture, while the highest was found around the 2-implant OT equator palateless overdenture. Nevertheless; the result was that 2-implant locator palateless overdenture recorded insignificant higher retentive forces than the 4-implant OT equator one. It can be concluded that the implant-retained palateless overdenture with four locator attachments is considered a promising treatment option regarding stress distribution. Using locator attachments, for implant-retained palateless overdenture with either two or four implants considering their superior retentive properties, is advantageous when compared to OT equator attachments.