Acrylic Model Research Articles

An unconventional impression method using implant mount: an alternative to open-and closed-tray impression technique

Background:Various impression techniques have been proposed for making implant prostheses. Impressions are made at implant level –closed and open tray impressions, as well as abutment level impressions. Closed and open tray copings are used to make the impressions. The limitations associated with the implant impression copings, including expensive ones, pose a significant challenge in limited mouth-opening cases, and customization of copings is not feasible.Aim: This study aimed to compare the dimensional accuracy of four impression methods, open-tray, closed-tray, disposable mount as coping and splinted mount as coping.Materials and methods:An ideal maxillary edentulous acrylic model was used with windows created at the canine and molar regions. Four analogues were implanted in the canine and molar areas to represent implants. The analogues were parallel to one other and were orientated at 0 degrees using the surveyor's assistance. Four groups were made: closed-tray, open-tray, implant mount as coping and splinted mount as coping. The custom trays were fabricated, accordingly. The implant-level impressions were made in all the groups using polyether impression material. The impressions were fitted with their respective impression copings with the analogues. The impressions were poured using die stone type-IV, and the casts were made. The resulting casts were 3D scanned, and a virtual model (.stl File) was created. Each .stl file was subjected to Geomagic software to evaluate the three-dimensional accuracy of conventional implant copings and implant mount as copings. Results:The Open-tray and the closed-tray groups exhibited the mean dimensional accuracy of 0.011±0.0016 μm and 0.018±0.0012 μm, respectively. The mount as coping and splinted mount displayed a mean dimensional accuracy of 0.017±0.0008 μm and 0.013±0.0020μm, respectively.Conclusions:This pilot study concludes that the implant mountcan be used as implant impression coping and an alternative to the conventional impression coping.

Preliminary Experiment on Reservoir Sediment Flushing

Prediction of reservoir sediment flushing requires a large amount of sample data obtained from long-term field measurements. Before running the complete laboratory experiments to understand the flushing mechanism, preliminary experiments using an acrylic tank and a simple piping system were carried out. The acrylic model consists of a constant head tank and a reservoir model. The constant head tank is a model that ensures a continuous and consistent flow rate contribution to the next model component, namely the reservoir model. The Reservoir model is a component for modeling the sediment flushing process, where the sediment deposits have been prepared. The reservoir sediment flushing experiment used a bottom outlet with a circular hole connected by a pipe to a valve to release sediment. The valve is assumed to be a sluice gate that can be opened and closed for sediment flushing. Preliminary experiments show that the model can simulate the flow of reservoir sediment flushing through the bottom outlet with stable reservoir water depth, operation of sluice gates, and the presence of scour cones in the sediment.

Digital versus radiographic accuracy evaluation of guided implant surgery: an in vitro study

BackgroundCone-beam computed tomography (CBCT) is the most widely used method for postsurgical evaluation of the accuracy of guided implant surgery. However, the disadvantages of CBCT include radiation exposure, artifacts caused by metal implants, and high cost. Few studies have introduced a digital registration method to replace CBCT for evaluating the accuracy of guided surgery. The purpose of this study was to compare digital registration to conventional CBCT in terms of the capacity to evaluate the implant positioning accuracy of guided surgery.Materials and methodsThis in vitro study included 40 acrylic resin models with posterior single mandibular tooth loss. Guided surgery software was used to determine the optimal implant position; 40 tooth-supported fully guided drilling templates were designed and milled accordingly. After the guided surgery, the accuracies of the surgical templates were evaluated by conventional CBCT and digital registration. For evaluation by conventional CBCT, postsurgical CBCT scans of the resin models were performed. The CBCT data were reconstructed and superimposed on the implant planning data. For digital registration, we constructed a virtual registration unit that consisted of an implant replica and a scan body. Next, we obtained postsurgical optical scans of resin models with the scan body. The postsurgical implant position was identified by superimposition of the registration unit and optical scan data. The implant planning data and postsurgical implant position data were superimposed; deviations were reported in terms of distance for implant entry/apex point and in terms of angle for the implant axis. Interclass correlation coefficients (ICCs) and Bland–Altman plots were used to analyze the agreement between the two evaluation methods.ResultsThe ICCs between the two methods were 0.986, 0.993, and 0.968 for the entry point, apex point, and angle, respectively; all were significantly greater than 0.75 (p < 0.001). Bland–Altman plots showed that the 95% limits of agreement of the differences were − 0.144 to + 0.081 mm, − 0.135 to + 0.147 mm, and − 0.451° to + 0.729° for the entry point, apex point, and angle, respectively; all values were within the maximum tolerated difference.ConclusionConventional CBCT and digital registration showed good agreement in terms of evaluating the accuracy of implant positioning using tooth-supported surgical templates.

Evaluation of the accuracy of light polymerizing tray material for splinting in open tray implant impressions: An In-vitro 3D Spatial Analysis.

Aims and objective: Precise reproduction of the intra-oral spatial relationship of implants with an impression becomes the first step in achieving an accurate, passively fitting prosthesis. This in vitro study aims to compare the dimensional accuracy of dental implants in casts obtained from open tray splinted implant impression techniques using two different splinting materials.&#x0D; Methods and Material: A mandibular acrylic model with four implant analogues was used as a reference model. Open tray impression copings were attached to the implant analogues and were splinted using two different materials. Group I-splinted with pattern resin, sectioned and re-joined and Group II- splinted with light cure tray material. Eight polyether impressions were made for each group and poured in type IV dental stone. The casts retrieved from each group were three-dimensionally analysed using coordinate measuring machine with 0.001 mm accuracy. A one-way ANOVA and post hoc test was done to calculate the statistically significant difference between the groups.&#x0D; Results: The present study revealed no significant difference in the inter-implant distances obtained from pattern resin splinted group, whereas, significant difference in z-axis was found in light polymerising tray resin splinted group when compared to the values obtained from the reference model.&#x0D; Conclusions: Casts obtained from splinting the impression copings using pattern resin before making implant impression were found to be more accurate than splinting with light cure tray material.

Improvement of Gas–Liquid Separation Performance of Engine Oil Using Swirling

The purpose of this study is to improve the gas–liquid separation performance of an oil tank and to establish a design method to enable gas–liquid separation only in an oil tank. Since it is difficult for conventional oil tanks to completely remove bubbles remaining in the hydraulic oil, it is essential to introduce a technology to actively separate and remove bubbles from the oil. Therefore, the bubble removal performance was improved even under the condition of added lateral acceleration by appropriately generating a swirl flow. First, an acrylic model of an oil tank was used to verify the accuracy by performing numerical analysis using various turbulence models. Then, the parameters of the bubble remover, such as the size of the oil tank, were studied. In addition, the bubble removal performance under the condition of added lateral acceleration was examined.

Vertical Deviation Caused by Tightening Torque on Implant Scan Body: An In Vitro Study.

This study evaluated the effects of manipulator level (ML) on implant scan body (ISB) seating. It also investigated ISB vertical deviation with various levels of tightening torque. In total, 10 standard acrylic resin models were prepared with the implant on the first molar site. ISBs were placed on the models by six operators with three MLs, manually and with a torque of 15 Ncm using an electronic torque driver. Digital scans were completed with an intraoral scan device. After superimposition in the software, ISB vertical deviation was compared between the 15 Ncm torque level and manual operation. One experienced operator then placed the ISB with different torque levels (20, 25, 30, and 35 Ncm) using an electronic torque driver. The ISB vertical deviation was also compared among torque levels. Vertical deviations within ML were analyzed using one-way analysis of variance (ANOVA). One-way repeated measures ANOVA was used to analyze the differences between torque levels (α = .05). ISB vertical deviations differed among MLs (P < .01). Significant vertical deviations were observed between 20 and 30 Ncm (P < .01), 20 and 35 Ncm (P < .05), and 25 and 35 Ncm (P < .05). The largest estimated marginal mean was 13.5 ± 4.11 μm with a torque of 35 Ncm. Significant differences in ISB vertical deviation were observed according to MLs and tightening torque levels. The amounts of those deviations did not exceed the previously described occlusal threshold.

Internal and Marginal Fit Accuracy of Pre-sintered CAD/CAM Implant-Supported Frameworks Before and After Porcelain Layering.

Internal and marginal fit accuracy of an implant-supported fixed partial denture (I-FPD) along with passive fit are required for long-term clinical success. This study compared the fit accuracy of three-unit CAD/CAM-fabricated cementretained I-FPDs milled from pre-sintered cobalt-chromium (Co-Cr) and zirconia (Zr) and evaluated the effect of applying porcelain. Two implant analogs were positioned parallel at first premolar and first molar sites in an acrylic model. Their corresponding abutments were tightened with 25-Ncm torque force. Four groups were designed: two groups of I-FPD frameworks with pre-sintered Zr (ZrF) and soft millable Co-Cr alloy (SF) blocks, and two groups by applying porcelain to the Co-Cr (SP) and Zr (ZrP) frameworks (n = 4 in each group). Absolute marginal gap (AMG), marginal gap (MG), and internal discrepancies were measured. Kolmogorov-Smirnov, Levene, one-way analysis of variance (ANOVA), and Scheffe tests were used for statistical analysis using SPSS software version 22 at a significance level of .05. All measured criteria were significantly different from each other (all P values < .001). The rankings from the lowest gap to the highest gap for the main criteria were as follows: MG: SF < SP < ZrF < ZrP; AMG and internal discrepancies: SF < SP < ZrP < ZrF. Comparing molars and premolars, molars had smaller MGs, larger internal discrepancies, and smaller AMG in ZrP but larger AMG in SP. All three-unit CAD/CAM-fabricated cement-retained I-FPDs were in the clinically acceptable range of fit accuracy. The lowest and highest misfit values were observed in the SF and ZrF groups, respectively.

The Accuracy of Open-Tray vs. Snap on Impression Techniques in A 6-Implant Model: An In Vitro 3D Study.

To compare the three-dimensional accuracy of an open-tray and two snap on impression techniques (with and without connecting the plastic caps of the snap on impression transfers) in a full arch 6-implant model, a reference acrylic resin model of the maxilla with six implants was fabricated. Prominent geometrical triangles, in the palate area, served as reference points for a digital overlap between scans. Three impression transfer techniques were evaluated and compared: open-tray direct impression (DI), snap on impression (SpO), and connected snap on impression (SpOC). Polyether impression material was used to make 30 impressions (n = 10), and the master model and all casts were digitally scanned with a laboratory optical scanner. The obtained 3D data were converted and recorded as STL files, which were imported to a 3D inspection software program. Angular deviations (buccal, occlusal and interproximal planes) between the study casts and the reference model were measured. Data were analyzed using one-way analysis of variance (ANOVA) and Tukey post hoc test, with 0.05 used as the level of significance. The 3D angular deviations from the master model revealed no significant differences between the DI and SpO impression groups, but there were significant differences in the SpOC impression group, particularly in the buccal and occlusal planes. In all groups, the 3D angular deviation between the most distal scan abutments on each side of the model was significantly different from all other areas when compared to the master model. Within the limits of this study, it is possible to conclude that the indirect closed tray snap on impression technique with unconnected plastic caps exhibited the same three-dimensional accuracies as the direct open tray technique. The indirect closed tray snap on impression technique with connected plastic caps was less accurate than either the indirect closed tray snap on impression technique with unconnected plastic caps or the direct open tray technique. In the case of full arch implant supported prostheses, inaccuracies may be expected in the most distal implants for all the three impression techniques evaluated in this study. Further in vitro and in vivo research is required.

Effect of Framework's Manufacturing Technique on Screw's Preload of Implant Supported Prosthesis

Implant supported prosthesis is a common treatment modality. Nowadays, new manufacturing techniques are available to fabricate them. To evaluate the effect of different manufacturing techniques of implant supported frameworks (ISF) on the preload of abutment's screws. A mandibular edentulous acrylic model with four dental implants temporarily stabilized in the interforaminal area was used. One ISF was fabricated using the conventional technique; implants were removed from the model and reassembled into the framework; this framework served as the passively fitting framework (PF). Three additional frameworks were constructed: conventional cast framework (CF), milled framework (MF) and 3D-printed framework (3D-PF). The gap between the frameworks and the neck of the implants were recorded in microns using a digital microscope. A tightening torque (TT) of 35 N·cm was applied to all the four abutments' screws and the screw's preload was recorded using two methods, by strain gauges (SGs) that were attached to the neck of each implant and fed into a stain book in microstrain (μɛ) and by removal torque (RT) using a digital torque meter. The frameworks' gap means from the lowest to the highest were PF, CF, 3D-PF, and MF. The RT was significantly lower than the TT in all frameworks (P ≤ 0.05). One-way analysis of variance (ANOVA) revealed that the PF had the lowest RT, while the CF and the 3DPF both had the highest RT, and those differences were found to be statistically significantly (P ≤ 0.05). When preload of the frameworks was recorded by SGs, one-way ANOVA revealed that PF had the highest preload value, while both 3D-PF and MF had the lowest preload values, those differences were also found to be statistically significant (P ≤ 0.05). The fabrication of implant-supported frameworks using milling or selective laser melting computer aided design/computer-aided manufacturing technologies did not necessarily enhance the screw's preload. This lack of enhancement could be attributed to the great amount of marginal gap in the frameworks fabricated by both techniques.

An In vitro Assessment of Retention Force of ZrO2, Polyether Ether Ketone, and ZrO2-Polyether Ether Ketone Telescopic Attachment for Mandibular Overdentures.

Objectives:The objective of this study was to compare ZrO2, polyether ether ketone (PEEK), and ZrO2-PEEK telescopic attachments in terms of retention of overdenture.Methodology:Forty-five acrylic resin models of the lower arch were divided into 3 groups of 15 each. In Group I, primary and secondary crowns were constructed from all zirconia (ZrO2), whereas all PEEK was used for Group II and Group III was made up of ZrO2 PEEK.Results:The mean retention value in Group I was 14.12 ± 3.4 N, in Group II was 15.86 ± 5.1, and in Group III was 22.40 ± 10.3 N. The mean final initial retention value in Group I was 14.50 ± 6.1 N, in Group II was 14.97 ± 8.2, and in Group III was 17.21 ± 9.3 N. A significant difference was observed in intergroup comparison (P < 0.05).Conclusion:Zirconia resulted in maximum retention as compared to other telescopic crown materials.

Effect of dental implant angulation on the dimensional accuracy of master casts.

Making accurate impressions of dental implants and transferring their three-dimensional (3D) position to master casts is critical for the passive fit of prosthetic frameworks. This study aimed to assess the effect of dental implant angulation on the dimensional accuracy of master casts. An acrylic model with 2 external hexagonal implants was used in this in vitro experimental study. The impressions of the model were made in 42 positions, with different angulation of the 2 implants, ranging from +15° to -15°, by means of the open-tray and closed-tray impression techniques, using a polyvinyl siloxane impression material. The spatial coordinates of the implants were measured on the X, Y and Z axes. The dimensional accuracy of the impressions made at different positions (parallel, convergent and divergent) and different angulation of the implants were determined. The data was analyzed using the one-way analysis of variance (ANOVA), Student's t test and Tukey's test. Casts with the lowest accuracy were obtained when the 2 implants were divergent by 25° (R = 1.1336). However, the position of the 2 implants had no significant effect on the dimensional accuracy of the master casts. The error rate was 0.4181 in the open-tray technique and 0.5095 in the closed-tray technique, with no significant difference between them (p > 0.05). The angulation of the 2 implants had a significant effect on the dimensional accuracy of the master casts (p = 0.0001). Considering the significant effect of implant angulation in the range from +15° to -15° relative to the longitudinal axis on the dimensional accuracy of master casts, further studies are required to reach a final conclusion in this respect.

The influence of crown coverage on the accuracy of static guided implant surgery in partially edentulous models: An in vitro study

ObjectiveTo evaluate the influence of crown coverage of surgical guides on the accuracy of static computer-assisted implant surgeries (sCAISs) in different partially edentulous situations. MethodsAcrylic models with five types of partially edentulous situations were fabricated in this study. In coDiagnostiX software (Dental Wings, Montreal, Canada), surgical templates were designed and fabricated with reduced crown coverage (RCC), standard crown coverage (SCC) and extended crown coverage (ECC). Then, fully guided implant placement into the acrylic models was performed by dental surgeons with more than 10 years of experience. In total, 120 models and 120 guides were manufactured, and 168 bone-level Straumann replica implants (4.1 × 10 mm, Institut Straumann AG, Basel, Switzerland) were inserted. Postoperative implant positions were scanned (Trios 3, 3 shape, Copenhagen, Denmark) and compared with the preplanned virtual positions via coDiagnostiX (Dental Wings, Montreal, Canada). The angular, coronal and apical deviations were measured and analyzed to evaluate the accuracy of implant insertion. Statistical analysis was performed using one-way ANOVA and Tukey's test. ResultsFor single tooth missing situations, the RCC group was similar to the SCC group and ECC group in anterior sites. In premolar or molar sites, the SCC and ECC groups had no statistically significant difference (p > .05), while the RCC group had more coronal and apical deviation (p < .05). For multiple teeth missing situations, there was no difference among the RCC, SCC and ECC groups (p > .05). No difference was found among the five edentulous situations with different CCs (p > .05). ConclusionThe CC of templates can significantly affect the accuracy of guided surgeries when implants are inserted in a single gap at posterior sites. Templates with CC extended to the undercut line may be an optimal choice for static guided surgeries. Clinical significanceThe accuracy of static guided implant surgery can be influenced by the CC of templates, and proper CC with the guide covering extending to the undercut line may contribute to improved accuracy. CC should be taken into consideration when designing surgical templates.

Comparison of the Accuracy of Fixture-Level Implant Impression Making with Different Splinting Techniques.

Objectives The impression-taking technique is one of the most critical factors that not only prevents the shrinkage caused by polymerization but also enhances the accuracy of implant impressions. Also, choosing the right time of taking impressions after splinting implants is one of the important criteria that affects the impression-taking technique. Accordingly, the present study aimed to evaluate the accuracy of different splint methods for implant impressions made at different times. Methods In this in vitro study, a two-piece metallic index was prepared, and the patient's jaw was simulated by placing self-cured acrylic resin in the lower part of the index. Then, two holes were made in the acrylic resin at a specific distance from each other, and the analogs were placed in these holes. Splinting of impression copings was carried out with autopolymerized acrylic resin (GC Pattern resin LS, GC America Inc., USA), and an open tray impression approach was performed. Thirty-six casts in three groups (n = 12) were fabricated from the acrylic model. After scanning the casts, the impression accuracy was compared between the three study groups by measuring the distance between the outer portions of the scan bodies screw-retained on implant analogs inside the cast using the Exocad software (2015.07 version). Group 1: splinting impression copings with autopolymerized acrylic resin and impression making immediately after the setting time (4 minutes); group 2: splinting and impression procedure after 17 minutes with splint sectioning and reconnection; group 3: splinting and impression procedure after 24 hours with splint sectioning and reconnection. The data were analyzed using SPSS 17 using the Kruskal–Wallis test. Results The mean distance measured in group 1 was 19.14 ± 0.029 mm, which was significantly lower than the main model. The distances were 19.15 ± 0.039 and 19.159 ± 0.33 mm in groups 2 and 3, respectively. These two groups were not significantly different from the main model. Moreover, the mean distance measured in the three impression techniques was similar. Conclusions There was no significant difference in the measurements between group 2, group 3, and the main model. Therefore, dentists can make an impression after 17 minutes to reduce chair time.

A Novel Digital Technique for Measuring the Accuracy of an Indirect Bonding Technique Using Fixed Buccal Multibracket Appliances.

The aim of this study was to analyze the accuracy and predictability of the indirect bonding technique of fixed buccal multibracket appliances using a customized iterative closest point algorithm. Materials and Methods: A total of 340 fixed buccal multibracket appliances were virtually planned and bonded on 34 experimental anatomically based acrylic resin models by using orthodontic templates designed and manufactured to indirectly bond the fixed buccal multibracket appliances. Afterwards, the models were submitted to a three-dimensional impression technique by an intraoral scanner, and the standard tessellation language digital files from the virtual planning and the digital impression were aligned, segmented, and realigned using morphometric software. Linear positioning deviations (mm) of the fixed buccal multibracket appliances were quantified at mesio-distal, bucco-lingual/palatal, and gingival/occlusal (vertical) planes, and angular deviations (°) were also recorded by analyzing the torque, tip, and rotation using a customized iterative closest point algorithm, the script for which allowed for an accuracy measurement procedure by comparing the tessellation network positioning of both standard tessellation language digital files. Results: The mean mesio-distal deviation was −0.065 ± 0.081 mm, the mean bucco-lingual/palatal deviation was 0.129 ± 0.06 m, the mean vertical deviation was −0.094 ± 0.147 mm, the mean torque deviation was −0.826 ± 1.721°, the mean tip deviation was −0.271 ± 0.920°, and the mean rotation deviation was −0.707 ± 0.648°. Conclusion: The indirect bonding technique provides accurate and predictable positioning of fixed buccal multibracket appliances.

A Comparative Evaluation of the Positional Accuracy of Multiple Implants by Open Tray Impression Technique using Three Different Splinting Materials: An in vitro study

&#x0D; Aim: To comparatively evaluate the positional accuracy of multiple implants by open tray impression technique using three different splinting materials namely self-cure acrylic resin, pattern resin and flowable composite.&#x0D; Materials and Methods: An edentulous maxillary model was fabricated with heat-cure acrylic resin. Four dummy implants were placed bilaterally at canine and second premolar positions in the acrylic model, perpendicular to the horizontal plane and parallel to each other. Open tray impression copings were attached to dummy implants. The copings were splinted with dental floss onto which self-cure acrylic resin was added, which was sectioned and rejoined (for Group A). Similarly, pattern resin (for Group B) and flowable composite (for Group C) were used as splinting materials after sectioning and rejoining as previously described for Group A. Open tray impressions were made using polyvinylsiloxane impression material to obtain 10 casts for each group categorized according to the splinting material used. Interimplant distances were measured between implants on the master model and between the implant analogs in the retrieved casts in three different groups using a Coordinate measuring machine and a comparative evaluation of positional accuracy was done.&#x0D; Results: Splinting with materials of all three Groups showed minimal variation in positions of multiple implants and within clinical limits. Group B (pattern resin) had more accurate values similar to master model compared to Group A (self-cure acrylic resin) and Group C (flowable composite), although statistically insignificant. The results with Groups A and C were similar. No statistically significant difference was derived between the three different groups.&#x0D; Conclusion: It was concluded that all the three splinting materials evaluated in the study can be recommended as splinting material of choice for multiple implants using open tray impression technique.

A New Method to Evaluate Trueness and Precision of Digital and Conventional Impression Techniques for Complete Dental Arch

Purpose: The aim of this study was to present a new method to analyze the three-dimensional accuracy of complete-arch dental impressions and verify the reliability of the method. Additionally, the accuracies of conventional and intraoral digital impressions were compared using the new method. Methods: A master model was fabricated using 14 milled polyetheretherketone cylinders and a maxillary acrylic model. Each cylinder was positioned and named according to its corresponding tooth position. Twenty-five definitive stone casts were fabricated using conventional impressions of the master model. An intraoral scanner was used to scan the master model 25 times to fabricate 25 digital models. A coordinate measuring machine was used to physically probe each cylinder in the master model and definitive casts. An inspection software was used to probe cylinders of digital models. A three-dimensional part coordinate system was defined and used to compute the centroid coordinate of each cylinder. Intraclass correlation coefficient (ICC) was evaluated to examine the reliability of the new method. Independent two sample t-test was performed to compare the trueness and precision of conventional and intraoral digital impressions (α = 0.05). Results: ICC results showed that, the new method had almost perfect reliability for the measurements of the master model, conventional and digital impression. Conventional impression showed more accurate absolute trueness and precision than intraoral digital impression for most of the tooth positions (p &lt; 0.05). Conclusions: The new method was reliable to analyze the three-dimensional deviation of complete-arch impressions. Conventional impression was still more accurate than digital intraoral impression for complete arches.

In Vitro Assessment of the Effect of Implant Position on Biomechanical Behaviors of Implant-Supported Removable Partial Dentures in Kennedy Class II Condition.

The purpose of this study was to investigate the effects of implant position and loading position on biomechanical behaviors using implant-supported removable partial denture (ISRPD) models in a simulated Kennedy class Ⅱ partially edentulous mandible. Three types of Kennedy class Ⅱ mandibular acrylic resin models (a conventional RPD without support by an implant—CRPD; models with an implant placed at first molar (#46)—MP-ISRPD— and second molar (#47)—DP-ISRPD) were used to measure vertical displacement of the RPD, mesio-distal displacement of the abutment tooth, and bending moment of the abutment tooth and implant under one-point loading. The variables at three respective loading points (#45, #46 and #47) were compared statistically. Vertical displacement was suppressed in ISRPDs compared to the CRPD, and significant effects were identified under loading at the implant position. The largest meiso-distal displacement was observed in MP-ISRPD under #47 loading. Bending moments of the abutment tooth and implant were significantly higher in MP-ISRPD than in DP-ISPRD. In MP-ISRPD, a higher bending moment of the abutment tooth under #45 and #47 loading was detected, although the bending moment in DP-ISRPD was almost zero. The results of this study suggested that MP-ISRPD shows the specific biomechanical behaviors, although DP-ISRPD might provide biomechanical benefits under all one-point loading conditions.

An in vitro Study to Assess the Positional Accuracy in Multiple Implants using Different Splinting Materials in Open-Tray Impression Technique

Context: Numerous implant techniques have been suggested in the literature to obtain an accurate master cast. One of those is to splint the impression copings; however, many controversies exist in type of splinting materials used. Aim: The aim of this study is to evaluate and compare the positional accuracy in multiple implants using different splinting materials in open-tray impression technique. Settings and Design: The study design involves an in vitro study. Materials and Methods: An acrylic resin model of a mandibular edentulous arch was used as a reference model in which four 3.75 mm × 10 mm implant analogs were placed and sequentially numbered as 1, 2, 3, and 4 from left to right. Open tray impression copings were attached to each of them and were then splinted by three different materials and divided into three Groups as Group I, Group II, and Group III splinted with pattern resin, composite resin, and titanium wire, respectively. Five implant level impressions were made from each group and poured in Type IV dental stone. The implant analogs were transferred to the casts and inter-implant distances were compared to the reference model using the Coordinate Measuring Machine. Statistical Analysis Used: One-way ANOVA test was used as a test of significance. Results: The present study revealed that all the three splinting materials can be used for the accurate reproduction of spatial relationship. There was no significant difference between the centroids of implant analogs 1 and 2, 1 and 3, 1 and 4, 2 and 3, 3 and 4, and 2 and 4 of reference model with the master models. Conclusion: Clinically acceptable accuracy in transferring the position of implants to the master cast could be obtained from all the three splinting materials used. However, splinting of impression copings with titanium wire showed greatest accuracy.

In vitro Study of the Effect of Internal Relief Space on the Color of Ceramic Laminate Veneer

BACKGROUND: Ceramic laminate veneer restoring is considered a challenging modality in solving various esthetic dental problems. AIM: The purpose of this study was to investigate the effect of digital internal relief space on the color of ceramic laminate veneer. MATERIALS AND METHODS: An acrylic central incisor model was prepared for ceramic laminate veneer with standard measures. The prepared acrylic resin dentotype model was scanned with intraoral computer-aided design/computer-aided manufacturing (CAD/CAM) optical scanner (CEREC Omnicam|Dentsply Sirona). The laminate veneer design was planned on the optically scanned preparation on CAD/CAM system software (CEREC software|Dentsply Sirona). Thirty ceramic laminate veneer specimens were machined from zirconia-reinforced lithium silicate (Celtra Duo blocks, Dentsply/Sirona) according to standard design by CAD/CAM system with the change of the digital internal relief space settings. The specimens were divided into three groups according to their digital internal relief settings (IRS) (20, 60, and 100 μm) (n = 10). Thirty epoxy dies were duplicated from the prepared acrylic model. The ceramic laminate veneer specimens were cemented to epoxy dies with total etch resin cement system according to the manufacture instructions. The color change (ΔE) of the cemented ceramic laminate veneer specimens was measured by spectrophotometer (Vita Easy shade, Ivoclar Vivadent AG, Schaan, Liechtenstein) using the CIELAB scale and L*, a*, b*. Each specimen was measured two times (before and after cementation). The value of color difference (ΔE) was calculated according to the formula: ΔE = [(L*2 - L*1)2 + (a*2 - a*1)2 + (b*2- b*1) 2]½. RESULTS: The highest mean value of ΔE was recorded in G100 group (1.91 ± 0.33), followed by G60 group (1.83 ± 0.09), with the least value recorded in G20 group (1.49 ± 0.49). Analysis of variance test revealed a statistically significant difference between groups (p = 0.024). CONCLUSION: The change of the digital IRS affects the color of ceramic laminate veneers.

Model Elde Etme Süresinin Polivinil Siloksan Ölçü Malzemelerinin Boyutsal Doğruluğu Üzerine Etkisi

Objective: The aim of this study was to evaluate of the dimensional accuracy of Polyvinylsiloxane (PVS) impression materials (Spirias, Imicryl, Konya, Turkey and Variotime, Heraeus, Hanau, Germany) by using stone models after different pouring time (1 hour and 24 hours). Methods: A standard maxillary dentulous acrylic model was selected as master model. Two linear measurements were selected on each sample for the evaluation of the models (x: 13-23 distance, y: 13-26 distance). A total of 40 samples were divided into 4 groups according to the impression brands and pouring time (n=10). All of measurements were made with CEREC SW 4.2.3 software (Sirona Dental System, GmbH, Bensheim, Germany) using “distance” tools of the programme. Statistical analysis was performed by using the IBM SPSS Statistics, Version 25 (IBM SPSS Statistics for Windows, IBM Corporation, Armonk, NY). A value of p&amp;lt;0.05 was considered statistically significant. Results: The relationship between different pouring times (1 hour and 24 hours) was not statistically significant (p&amp;gt;0.05). When the paired relations with the master model are evaluated, t test and p values show that there is statistically significant difference (p&amp;lt;0.05). Conclusion: When compared with the main model, PVS materials for both brands show dimensional distortion. For PVS impression materials, the pouring of the impressions does not make any difference.