Comparison of Digital and Conventional Impressions Based on the 3D Fit of Crowns

PURPOSE

To evaluate intraoral scanners, scannable impression materials, and conventional methods for impression-taking with regard to precision and accuracy.

MATERIALS AND METHODS

Ten impressions per technique were initially taken from a cobalt-chromium (Co-Cr) master model (chamfer preparation for the maxillary right first molar) for fabricating Co-Cr crown copings. The test specimens, their respective metal master model, and the plaster casts from the conventional impressions were then digitized with the light-optical Atos Triple Scanner. The fit of the dental crown copings was measured in two and three dimensions using computer-aided design software. Global differences between the methods were determined using Kruskal-Wallis test, and pairwise comparisons were performed with Mann-Whitney U test. The significance level was set at .05.

RESULTS

The 2D analysis showed that the average absolute marginal distance of the crown copings was 0.026 mm when fabricated with the digital impression method and 0.038 mm when fabricated with the conventional method (P = .028). However, the 3D analysis revealed that the conventional group had a smaller marginal gap (0.028 mm) compared to the digital group (0.06 mm; P = .015).

CONCLUSION

This study showed that, in the field of single-crown prosthetics, digital impressions and the use of scannable impression material could serve as alternatives to conventional methods in the future.

Evaluation of a novel 3D-printed custom tray for the impressions of edentulous jaws

PURPOSE

The purpose of this study was to evaluate a novel 3D-printed custom tray for impressions of edentulous jaws, and to compare it with conventional impression trays.

METHODS

Fifteen edentulous patients were enroled to evaluate the accuracy and border extension of a novel custom tray in the shape of a complete denture. Four impressions were made for each patient. Impressions made using novel custom trays were considered the experimental group, impressions made using conventional custom trays were considered the control group, and impressions made using final dentures and non-pressure custom trays were considered the reference groups. The experimental and control groups were compared with the reference groups using three-dimensional (3D) comparison analysis, and the impressions were further divided into regions. The root mean square (RMS) value was calculated to analyse the differences in impression morphology. Additionally, the experimental and control groups were compared to analyse border extension at standard locations.

RESULTS

Compared to the final denture impression as a reference, the diagnostic denture impression (RMS:0.146 ± 0.024 mm) was closer to the reference than the conventional impression (RMS:0.176 ± 0.047 mm), with a significant difference only in the secondary stress-bearing area. The border extension of the diagnostic denture impression was slightly longer than the conventional impression; however, the difference was not statistically significant.

CONCLUSIONS

The impressions made using the novel custom tray were similar to those made with a definitive complete denture. However, no significant differences were noted when compared with the conventional impressions.

A newly developed patient fixation system using a dedicated mouthpiece and dental impression materials for head and neck radiotherapy: a preliminary study

We evaluated the basic characteristics and efficacy of our newly developed patient fixation system for head and neck radiotherapy that uses a dedicated mouthpiece and dental impression materials. The present investigation demonstrated that with this system, the changes in the absorbed dose to water depending on the material of the mouthpiece were small, with a maximum of 0.32% for a 10-MV photon beam. For the dental impression material, we selected a silicone material with the lowest Hounsfield unit (HU) value that had little effect on the generation of artifacts and the quality of the X-ray beam. Multiphase magnetic resonance imaging (MRI) revealed that the head-up and -down motions in the thermoplastic shell without the mouthpiece were 5.76 ± 1.54 mm, whereas the motion with the mouthpiece decreased significantly to 1.72 ± 0.92 mm (P = 0.006). Similarly, the head-left and -right motion displacement decreased from 6.32 ± 1.86 mm without the mouthpiece to 1.80 ± 0.42 mm with the mouthpiece (P = 0.003). Regarding the tongue depressor function of the mouthpiece, the median distance from the hard palate to the surface of the tongue was 28.42 mm. The present results indicate that the new immobilization device developed herein that uses a mouthpiece and a thermoplastic shell is useful for suppressing patients' head motions and tongue positions.

Accuracy of Impression Techniques for Dental Implants Placed in Five Different Orientations

PURPOSE

The purpose of this study was to evaluate the impression accuracy of two implants placed in different orientations and compare the impression accuracy obtained with the dual-arch impression technique using hybrid impression copings and the conventional open-tray impression technique.

MATERIALS AND METHODS

Five mandibular dentiform models were prepared by placing implants in the second premolar and second molar regions in the following different orientations: parallel to each other; 15-degree mesiodistal angulation; 30-degree mesiodistal angulation; 15-degree buccolingual angulation; and 30-degree buccolingual angulation. After making 10 impressions for each model with the open-tray impression technique and dual-arch impression technique with hybrid impression copings, cast models were fabricated for each impression (n = 10). Scan bodies were mounted on the five dentiform models and the fabricated 100 cast models were scanned using a desktop scanner. The three-dimensional deviation of the scan bodies on the cast models was calculated and compared to the reference data from the dentiform models. A two-way analysis of variance was conducted (α = .05).

RESULTS

The root mean square deviation values obtained from the implants placed with 30-degree mesiodistal angulation were 93.05 ± 6.21 μm with the open-tray impression technique and 104.01 ± 8.89 μm with the dual-arch impression technique, which were the largest deviation values for both techniques (P < .001). Compared to the open-tray impression technique, the dual-arch impression technique with the hybrid impression copings showed significantly lower accuracy when the angulation between the implants was 15 degrees mesiodistally (P < .001), 30 degrees mesiodistally (P = .016), or 30 degrees buccolingually (P < .001). However, there was no significant difference between the accuracy of the two impression techniques for parallel implants (P = .74).

CONCLUSION

When the two implants were inclined 30 degrees mesiodistally, both implant impression techniques showed the largest deviation and the dual-arch impression technique showed lower accuracy compared to the conventional open-tray impression technique. Parallel placement of implants may improve impression accuracy and enable use of the dual-arch impression technique.

The Influence of a Flexible Model on the Marginal Adaptation of Inlay Composite Restorations: A MicroCT Analysis

The aim of this study was to evaluate the influence of flexible models on the marginal adaptation of indirect resin composite restorations. Thirty-six cavity preparations were made for class II restorations in permanent molar teeth. Three groups (n=12) were defined following three impressions/model material combinations: G(STONE), polyvinylsiloxane, and type IV stone model, as a control group; G(IMPRESSIONPVS), alginate and flexible polyvinylsiloxane; G(MODELPVS), alginate and flexible polyvinylsiloxane for models. All restorations were positioned on their respective teeth and evaluated by micro-computed tomography. Absolute marginal discrepancies were measured digitally (ImageJ). The results were compared using one-way ANOVA (p⟨ 0.05). The mean ± SD absolute marginal discrepancy of indirect resin composite restorations made from flexible and rigid stone models was as follows: G(STONE), 206 (±79.95) μm; G(IMPRESSIONPVS), 221.50 (±61.73) μm; G(MODELPVS), 203.25 (±65.93) μm. Absolute marginal discrepancies were not significantly influenced by the flexible and rigid stone models (p=0.78). The flexible or rigid stone model did not influence the marginal adaptation of the indirect resin composite restorations.

Does Splinting the Direct Copings Increase the Impression Accuracy of Two-Unit Nonparallel Implant Restorations? A Systematic Review and Meta-analysis

PURPOSE

The purpose of this systematic review and meta-analysis was to evaluate the effects of splinting impression copings on the accuracy of conventional impressions for two-unit nonparallel implant restorations.

MATERIALS AND METHODS

MEDLINE via PubMed, Embase, and Web of Science databases were searched with no publication year or language limits, and studies comparing the accuracy of conventional impressions for two-unit nonparallel implant restorations made using splinted impression copings and nonsplinted impression copings were identified. A meta-analysis was performed using Review Manager software. The mean difference (MD) with 95% confidence interval (95% CI) for the framework strain and marginal gap of the implant-framework connection between impressions using splinted and nonsplinted copings were statistically analyzed (α = .05).

RESULTS

Initially, 142 articles were identified after the removal of duplicates. Five in vitro studies were included in the systematic review, and four in vitro studies were included in the meta-analysis. All the included studies were focused on internal-connection implants and implant-level impressions. The implant angulation in the included studies ranged from 8 to 30 degrees. Impressions using splinted impression copings exhibited significantly smaller marginal gaps than those using nonsplinted impression copings (P = .02; mean difference [MD] = -13.34; 95% CI = -24.31 to -2.36). Moreover, with respect to the framework strain, no significant differences were found between impressions using splinted impression copings and nonsplinted impression copings (P = .47; MD = -12.64; 95% CI = -47.32 to 22.03).

CONCLUSIONS

Significantly larger marginal gaps were found in the impressions using splinted impression copings, but the clinical significance was low. Based on the limited number of studies included, splinting copings is unnecessary when making conventional impressions for two-unit nonparallel implant restorations.

Splinting Open Tray Impression Copings Using Long Shank Carbide Burs during Definitive Impression: A Dental Technique

AIM

To splint implant impression copings using long shank carbide burs for definitive implant impressions.

BACKGROUND

The accurate transfer of the orientation recorded by impression copings to a definitive cast is a challenging step in implant prosthodontics. For achieving a passive fit from the mouth to the cast may include some discrepancies. Traditional methods of splinting can be time-consuming and troublesome to handle.

TECHNIQUE

This article describes a technique by using long shank carbide burs for splinting implant impression copings.

CONCLUSION

The favored implant splinting, evidence was inconclusive, and the data supporting splint pickup was the better performing technique, especially with an increased number of implants.

CLINICAL SIGNIFICANCE

This technique causes minimal discomfort and is straightforward when compared to other techniques.

Keys to Predictable Digital Impressions

Conventional impressions are the benchmark for any new replication technique due to the demonstrated accuracy of PVS and polyether impression materials.1 However, it is well known that throughout the impression process there are potential risks to final accuracy, including setting of the impression material, removal of the impression, and fabrication of the stone model.2-4 Despite the documented accuracy of PVS and polyether impressions, studies have repeatedly shown that most impressions sent to dental laboratories have some sort of deficiency. One study evaluated 193 FPD impressions made by 41 dentists immediately after they arrived at 11 dental laboratories and reported that 50.7 percent of all the impressions had voids or tears in the finish line area, 40.4 percent had air bubbles at the margin line, and 26.9 percent had both.5 Thus, although impression material has documented accuracy, making an accurate impression involves more than just the precision of the material.

[Application evaluation of prefabricated rigid connecting bar in implants immediate impression preparation of edentulous jaw]

OBJECTIVE

To compare the operation complexity and accuracy of traditional splint impression technique and impression technique with prefabricated rigid connecting bar system for full-arch implants-supported fixed protheses in vitro.

METHODS

Standard mandibular edentulous model with six implant analogs was prepared. The implants were placed at the bone level and multiunit abutments screwed into the implants. Two impression techniques were performed: the traditional splint impression technique was used in the control group, and the rigid connecting bar system was used in the test group. In the control group, impression copings were screwed into the multiunit abutments and connected with autopolymerizing acrylic resin. Open tray impression was fabricated with custom tray and polyether. In the test group, cylinders were screwed into the multiunit abutments. Prefabricated rigid bars with suitable length were selected and connected to the cylinders with small amount of autopolymerizing acrylic resin, and open tray impression was obtained. Impression procedures were repeated 6 times in each group. The working time of the two impression methods were recorded and compared. Analogs were screws into the impressions and gypsum casts were poured. The gypsum casts and the standard model were transferred to stereolithography (STL) files with model scanner. Comparative analysis of the STL files of the gypsum casts and the standard model was carried out and the root mean square (RMS) error value of the gypsum casts of the control and test groups compared with the standard model was recorded. The trueness of the two impression techniques was compared.

RESULTS

The work time in the test group was significantly lower than that in the control group and the difference was statistically significant [(984.5±63.3) s vs. (1 478.3±156.2) s, P < 0.05]. Compared with the standard model, the RMS error value of the implant abutments in the test group was (16.9±5.5) μm. The RMS value in the control group was (20.2±8.0) μm. The difference between the two groups was not significant (P>0.05).

CONCLUSION

The prefabricated rigid connecting bar can save the chair-side work time in implants immediate loading of edentulous jaw and simplify the impression process. The impression accuracy is not significantly different from the traditional impression technology. The impression technique with prefabricated rigid connecting bar system is worthy of clinical application.

[Accuracy of photogrammetry and conventional impression techniques for complete-arch implant rehabilitation: an in vitro comparative study]

Objective: To compare the accuracy of photogrammetry and conventional impression techniques for complete-arch implant rehabilitation. Methods: An edentulous maxillary stone cast containing 8 screw-retained implant abutment replicas was derived from a 74-year-old male patient who visited the Department of Dental Implant Center, Capital Medical University School of Stomatology in September 2019. The stone cast was copied through the open-tray splinted impression, and the copied cast was used as the master cast for this study. The abutment-level impressions of master cast were made by photogrammetry (PG) and the conventional impression technique (CNV) by one attending doctor. Group PG: after which scan bodies were connected to each implant replica, a photogrammetry system was used to obtain digital impressions of the master cast (n=10); Group CNV: conventional open-tray splinted impression technique was performed to fabricate conventional definitive casts (n=10). After connecting the scan bodies onto each implant replicas, the master cast and the 10 definitive casts from group CNV were digitized with a laboratory reference scanner. All data of group PG, group CNV and mater cast were saved as ".stl" files. For all test scans and reference scan, the three-dimensional information of scan bodies were converted to implant abutment replicas using a computer aided design software (Exocad). The data of the group PG and the group CNV were respectively registered with the reference data (trueness analysis) and pairwise within group (precision analysis) for accuracy evaluation in a three-dimensional analysis software (Geomagic Control X). Results: The trueness and precision of group PG [(17.33±0.34) and (2.50±0.79) μm ] were significantly statistically better than those of group CNV [(24.30±4.16) and (26.12±4.54) μm] respectively (t=-5.29 and -34.35, P<0.001). Conclusions: For complete-arch implant abutment-level impression, photogrammetry produces significantly better accuracy than conventional impression technique.

Comparative assessment of complete-coverage, fixed tooth-supported prostheses fabricated from digital scans or conventional impressions: A systematic review and meta-analysis

STATEMENT OF PROBLEM

Intraoral scanners have significantly improved over the last decade. Nevertheless, data comparing intraoral digital scans with conventional impressions are sparse.

PURPOSE

The purpose of this systematic review and meta-analysis was to determine the impact of impression technique (digital scans versus conventional impressions) on the clinical time, patient comfort, and marginal fit of tooth-supported prostheses.

MATERIAL AND METHODS

The authors conducted a literature search based on the Population, Intervention, Comparison, and Outcome (PICO) framework in 3 databases to identify clinical trials with no language or date restrictions. The mean clinical time, patient comfort, and marginal fit values of each study were independently extracted by 2 review authors and categorized according to the scanning or impression method. The authors assessed the study-level risk of bias.

RESULTS

A total of 16 clinical studies met the inclusion criteria. The mean clinical time was statistically similar for digital scan procedures (784 ±252 seconds) and for conventional impression methods (1125 ±159 seconds) (P>.05). The digital scan techniques were more comfortable for patients than conventional impressions; the mean visual analog scale score was 67.8 ±21.7 for digital scans and 39.6 ±9.3 for conventional impressions (P<.05). The mean marginal fit was 80.9 ±31.9 μm and 92.1 ±35.4 μm for digital scan and conventional impressions, respectively, with no statistically significant difference (P>.05).

CONCLUSIONS

Digital scan techniques are comparable with conventional impressions in terms of clinical time and marginal fit but are more comfortable for patients than conventional impression techniques.

Three-dimensional Change of Elastomeric Impression Materials During the First 24 Hours: A Pilot Study

OBJECTIVES

To evaluate the three-dimensional (3D) changes of three elastomeric impression materials using a novel measurement method for the first 24 hours after preparation.

METHODS AND MATERIALS

Three impression materials consisting of a low-viscosity polyvinyl siloxane (PVS) (Aquasil LV, Dentsply Sirona, Charlotte, NC, USA) and two vinyl polyether silicone (VPES) materials consisting of a light body (EXA'lence LB, GC America, Alsip, IL, USA) and monophase (EXA'lence Monophase, GC America) materials were used in this study. All materials were prepared following manufacturer's recommendations with approximately 1-2 millimeters of material placed on the measurement pedestal of a calibrated noncontact, video imaging based, volumetric change measuring device (AcuVol ver 2.5.9, Bisco, Schaumburg, IL, USA). Data collection was initiated immediately, with measurements made every 30 seconds for 24 hours. Each material was evaluated 10 times (n=10). Evaluated parameters included were 24-hour mean shrinkage, mean shrinkage at time of recommended first pour, mean shrinkage between recommended first pour and 24 hours, mean maximum shrinkage, and the time of maximum shrinkage. Mean data, both within and between each group, was evaluated using Kruskal-Wallis/Dunn's tests at a 95% level of confidence (α=0.05).

RESULTS

All three materials were found to have significant differences (p<0.001) in volumetric shrinkage over 24 hours. Aquasil LV and EXA'lence LB polymerization shrinkage rates were statistically similar all through the 24-hour evaluation (p=0.92). All three materials demonstrated similar (p=0.19) shrinkage between 10 and 15 minutes after preparation, while between 5 and 16 hours both EXA'lence Monophase and low-viscosity materials demonstrated similar polymerization shrinkage values (p=0.22). EXA'lence Monophase demonstrated significantly greater 24-hour mean shrinkage (p<0.008) as well as shrinkage between recommended first pour time and 24 hours (p=0.003) than Aquasil LV and EXA'lence LB. EXA'lence Monophase demonstrated significantly greater (p=0.002) shrinkage at the recommended time of first pour as compared to Aquasil LV and EXA'lence LB that displayed similar shrinkage (p=0.89). Furthermore, all materials demonstrated increasing polymerization shrinkage values that reached a maximum between 16 for Aquasil LV and 20 hours for EXA'lence LB, after which some relaxation behavior was observed. However, EXA'lence Monophase did not display any relaxation behavior over the 24-hour evaluation.

CONCLUSIONS

Under the conditions of this study, volumetric polymerization shrinkage was observed for one polyvinyl siloxane (PVS) and two vinyl polyether silicone (VPES) materials for up to 24 hours. All impression materials exhibited fast early volumetric shrinkage that continued past the manufacturer's recommended removal time. Dimensional change behavior was not uniform within or between groups; resultant volume change between the manufacturer recommended pouring time and 24 hours might represent up to from 20% to 30% of the total material shrinkage. It may be prudent to pour elastomeric impressions at the earliest time possible following the manufacturer's recommendations.

Design parameters of polylactic acid custom trays manufactured by fused deposition modeling for partial edentulism: Consideration of the accuracy of the definitive cast

STATEMENT OF PROBLEM

The effects of design parameters of polylactic acid (PLA) custom trays manufactured by fused deposition modeling (FDM) on the accuracy of partially edentulous definitive casts have not been thoroughly explored.

PURPOSE

The purpose of this in vitro study was to explore the effects of the impression gap and base thickness of FDM-printed PLA custom trays on the accuracy of maxillary and mandibular definitive casts with Kennedy class II, modification I partial edentulism and to optimize these 2 design parameters.

MATERIAL AND METHODS

Custom trays with a 1-mm, 2-mm, or 3-mm impression gap and 1-mm, 1.5-mm, or 2-mm base thickness were designed on a pair of maxillary and mandibular resin casts and printed with PLA materials by using an FDM printer. Two-step silicone impressions were made by using these custom trays or stock metal trays on resin casts. Digital scans of definitive casts from these impressions were aligned one by one with those of resin casts. Three-dimensional deviations of the tooth area, mucosal area, and overall area were analyzed by using root mean square (RMS) as a metric. Two-way and 1-way analyses of variance with the RMSs as the dependent variable were carried out (α=.05).

RESULTS

The accuracy of definitive casts from custom trays with a 2.0-mm or 3.0-mm impression gap and 1.5-mm or 2.0-mm base thickness was significantly better than that of definitive casts from custom trays with a 1.0-mm impression gap or 1.0-mm base thickness and was not significantly different from that of definitive casts from stock metal trays.

CONCLUSIONS

Considering the accuracy of definitive casts, the optimal base thickness of FDM-printed PLA custom trays was 1.5 mm or 2.0 mm and the optimal impression gap was 2.0 mm or 3.0 mm for Kennedy class II, modification I partial edentulism.

Effect of Arch Size and Implant Angulations on the Accuracy of Implant Impressions

PURPOSE

To evaluate the effects of arch size and implant angulation on the accuracy of implant impressions.

MATERIALS AND METHODS

Four different resin models (small and large) of edentulous maxilla were fabricated and four implants were inserted (Blossom®, ø 4.75 × 10 mm) in each model. Implants were either parallel or angled 25° buccally. Forty working casts (small parallel, small angled, large parallel, and large angled) were fabricated in dental stone (n=10). For each implant, linear and angular displacements were measured using a coordinate-measuring machine (CMM) and mean values were analyzed by univariate analysis (α = 0.05).

RESULTS

Arch size did not affect the linear or angular displacement (P ⟩ .05). However, the implant angulation had a marked influence on the linear displacement (P ⟨ .05). The largest linear displacement occurred in implant no. 4 of angled small groups.

CONCLUSION

Regardless of arch size, linear and angular accuracy of implant impression varied with the implant angulation.

Selecting the Right Intraoral Scanner to Transform Your Practice

In recent years digital technology has transformed the practice of modern dentistry, with intraoral scanners (IOSs) being among the most significant materializations of this digital boom. IOSs eliminate the need for traditional impression materials and allow for the immediate digital capture of a 3-dimentional (3D) object being scanned.4 When assessing the "most ideal" IOS for a dental practice, key considerations include the types of procedures being performed, practice demands, and patient demographics. Only after an initial practice assessment has been made can advantages and disadvantages of various IOSs be compared against practice needs.

Trueness and Precision Achieved With Conventional and Digital Implant Impressions: A Comparative Investigation of Stone Versus 3-D Printed Master Casts

OBJECTIVE

To analyze implant casts obtained from intraoral optical scanning and conventional impressions.

MATERIALS AND METHODS

Ten optical scans (test) and ten conventional polyether impressions (control) were obtained from a two-implant reference model. Ten casts each were manufactured additively or from stone. All casts were digitized and virtually superimposed to the digital reference (trueness) applying a best-fit algorithm, and secondary analysis for intra-group comparisons (precision). The signed nearest neighbor distance of each surface point (FDI:24/26) was computed and deviations of the three-dimensional vectors (X,Y,Z) analyzed. The groups were compared with the Wilcoxon's rank sum test.

RESULTS

The printed casts had mean deviations of 106.0μm and the stone casts 187.9μm compared to the reference. Controls had significantly higher deviations and dispersion (p⟨0.001). The printed casts showed mean intra-group deviations of 149.8μm and the stone casts 181.2μm without significant differences (p=0.162). There was no statistically significant difference in any of the vector analyses (X:p=0.105, Y:p=0.089, Z:p=0.123).

CONCLUSION

Optical scanning seems to be an alternative to conventional impressions in terms of trueness and precision of implant master casts, simulating the scenario of a three-unit implant-supported fixed dental prosthesis. Digitally manufactured master casts might serve as reliable reference for the final restorations.

Evaluation of reliability of face scanning using a new depth camera

AIM

3D face impression techniques have been defined to eliminate the disadvantages of conventional impression methods. The aim of the present study was to evaluate and compare the accuracy of a digital technique using a novel 3D camera in relation to a conventional impression technique.

MATERIALS AND METHODS

Ten prefabricated polystyrene head molds each containing 10 predetermined anatomical landmarks were used. The 3D data of each head mold included in the study were generated through the use of the Intel RealSense D415 camera. Ten stone casts of head molds were also fabricated using conventional silicone impressions through a putty-wash impression technique. The reliability of the 3D data (Group 1) was directly compared with that of the stone casts (Group 2) and prefabricated polystyrene head molds (Group 3) by measuring the distances between 10 anatomical landmarks, including 45 distance measurements. Differences and consistencies were determined using the intraclass correlation coefficient (ICC).

RESULTS

Significant consistencies were found among the groups in terms of the overall mean values of the 45 distance measurements (ICC = 0.978, P = 0.001). Paired comparisons indicated significant correlations between Groups 1 and 2 (ICC = 0.970, P = 0.001), Groups 1 and 3 (ICC = 0.967, P = 0.001), and Groups 2 and 3 (ICC = 0.998, P = 0.001).

CONCLUSION

The distance measurement accuracy of the 3D camera was consistent with the reference values. Digital impressions obtained with 3D cameras can be an effective alternative to conventional impressions for craniofacial defects or deficiencies.

Evaluation of Effectiveness of Three New Gingival Retraction Systems: A Comparative Study

AIM

To analyze the clinical effectiveness of three new gingival retraction systems: knitted retraction cord, expanding polyvinyl siloxane, and aluminium chloride containing paste.

MATERIALS AND METHODS

Twenty patients were enrolled with age-group of more than 18 years and who required fixed prosthesis with minimum of two abutments. A preliminary impression of the arch was made with a stock metal tray and irreversible hydrocolloid impression material. Group WR-impression without retraction, Group A-impression after retraction with gingival retraction cord, Group B-impression after retraction with expanding polyvinyl siloxane, and Group C-impression after retraction with aluminium chloride containing paste. A total of four impressions were made for each abutment tooth. Each impression was given a label 1WR, 1A, 1B, 1C-20WR, 20A, 20B, 20C: where 1 denoted the sample number. Comparison of the stereomicroscopic images was done using image analysis software. Time required from start of placement of gingival displacement agents till completion was recorded in seconds with the help of a stop clock.

RESULTS

The mean gingival retraction was found to be the highest for subjects of Group C followed by Group A, Group B, and Group WR. This difference was found to be statistically significant. Highly significant mean difference in time of placement was observed between Group A and Group B, between Group B and Group C, and between Group C and Group A.

CONCLUSION

The aluminium chloride containing paste was found effective in almost all the variables considered.

CLINICAL SIGNIFICANCE

The choice of particular gingival retraction system/technique is dependent upon the clinical variables and on operator's preference.

Accuracy of Impression Techniques with Maxillary Angled Implants Using Trays and Multifunctional Guides

PURPOSE

The purpose of this study was to evaluate in vitro the accuracy of different splinting techniques using transfers combined with different tray types.

MATERIALS AND METHODS

The research group fabricated a maxillary master cast with four implants and a passive metallic bar on this master cast. For the impression techniques, 48 casts were used with six different impression techniques: (1) metal tray with resin splinted transfers, (2) metal tray with metal and resin splinted transfers, (3) plastic tray with resin splinted transfers, (4) plastic tray with metal and resin splinted transfers, (5) multifunctional guide with resin splinted transfers, and (6) multifunctional guide with metal and resin splinted transfers (n = 8) using polyvinyl siloxane impression material. This study used a passive metallic bar to measure the malalignment between the framework and the analogs (A, B, C, and D) in 2D and 3D. The master and experimental casts were scanned with a contact scanner to compare the accuracy in 3D impression techniques. Discrepancies between the analogs were measured in three x-, y-, and z-axes.

RESULTS

There was no statistically significant difference (P > .05) between the groups in vertical malalignments (2D). In the 3D evaluation, for the z-axis and combination of xz-axis, plastic tray with metal, and resin splinted transfers (z = 487 μm; xz = 888 μm), there was a statistically significant difference compared with the multifunctional guide and resin splinted transfers (z = 772 μm; xz = 1,380 μm). When analyzing by analog, in C, the multifunctional guide with metal and resin splinted transfers (302 μm) presented a statistically significant difference compared with the multifunctional guide and resin splinted transfers (492 μm).

CONCLUSION

The evaluation methods for the accuracy impression technique presented different results between them. There was no difference in vertical malalignments (2D), but in 3D, the bonding with metal and acrylic resin presented better results than the bond with only acrylic resin when using the plastic tray and multifunctional guide, respectively, in the z-axis and the combination between the xz-axes. The bonding technique of the transfers with metal and acrylic resin presents better results in the 3D analysis for the multifunctional guide impressions.

Do different methods of digital data analysis lead to different results?

AIM

Dental research involves variations between actual and reference datasets of master models to determine the metric accuracy through transfer accuracy tests. Various methods of measurement are used to analyze the results, which are often subjected to direct comparisons. Hence, the aim of the present study was to analyze the influence and effect on results of different methods of digital data analysis, being coordinate-based analysis (CBA) and best-fit superimposition analysis.

MATERIALS AND METHODS

A model with four implants and a reference cuboid was digitized through computed tomography (CT), which served as the master model. Ten implant impressions were made using a Trios (3Shape) intraoral scanner, and three different scan bodies (nt-trading, Kulzer, and Medentika) were used. The deviations between the master model and the digital impressions were analyzed using CBA and best-fit superimposition analysis. Statistical analysis was performed using SPSS 25.

RESULTS

The deviations in the CBA and best-fit superimposition analysis ranged from 0.088 ± 0.012 mm (mean ± SE; Medentika, 14) to 0.199 ± 0.021 mm (Kulzer, 26), and from 0.042 ± 0.010 mm (Medentika, 16) to 0.074 ± 0.006 mm (Kulzer, 16), respectively. Significant differences were observed between the implant positions in the CBA and the digital measurements at each implant position, whereas the best-fit analysis showed no significant difference between the scan bodies and implant positions.

CONCLUSION

CBA displays an advantage over best-fit superimposition analysis in the detection of possible influencing factors for primarily scientific purposes. However, a global analysis and visualization of angles and torsions is difficult, for which a best-fit evaluation is needed. However, a best-fit analysis better represents the clinical try-in. It is associated with the risk that possible disturbing factors and resulting errors might be leveled out and their identification camouflaged.

Efficacy of Different Gingival Displacement Materials in the Management of Gingival Sulcus Width: A Comparative Study

AIM

The aim of this study was to assess the effectiveness of different gingival displacement materials in the management of the width of the gingival sulcus.

MATERIALS AND METHODS

Totally, 60 participants who were aged 18 years and more were chosen for this study. The eligible participants were those who required fixed prosthesis with at least one abutment. A modified sectional tray was used to make impressions with elastomeric materials along with additional polysilicon using the double mix single impression technique. All participants were divided randomly into three experimental groups with each group having 20 participants as follows: group I-Expasyl, group II-Magic Foam Cord, and group III-Traxodent. Soon after retraction, impressions were made and assessed in a comparable manner to pre-retraction impressions. Image analysis software was used to measure the quantity of displacement of the gingiva, marked as the distance from the tooth to the gingival crest in the horizontal level under stereomicroscope.

RESULTS

The highest mean sulcular gingival width (0.644 ± 0.22) was found in Traxodent group followed by Expasyl group (0.590 ± 0.11) and Magic Foam Cord group (0.528 ± 0.01). A statistically significant difference (p<0.001) was found between the groups. Intergroup comparisons between the gingival displacement materials showed a statistically significant difference (p<0.05) between group II and group III.

CONCLUSION

The present study concluded that all three gingival displacement materials lead to gingival displacement, which is needed for impression making. Slightly more retraction was seen in the Traxodent group when compared to the Expasyl group and Magic Foam Cord group.

CLINICAL SIGNIFICANCE

The success of fixed prosthodontic treatment depends upon precision and accuracy in every step involved in the procedure.One of the most vital stepsis making precise impressions in relation to dimensional accuracy, tear strength, etc. It is essential to have an adequate thickness of the impression material along the margins to avoid distortion. This objective can be achieved by acceptable gingival retraction.

The Influence of Using Different Types of Scan Bodies on the Transfer Accuracy of Implant Position: An In Vitro Study

PURPOSE

To assess the absolute linear distances of three different intraoral scan bodies (ISBs) using an intraoral scanner compared to a conventional impression in a common clinical model setup with a gap and a free-end situation in the maxilla.

MATERIALS AND METHODS

An implant master model with a reference cube was digitized using x-ray computed tomography and served as the reference file. Digital impressions (TRIOS, 3Shape) were taken using three different ISB manufacturers: NT Trading, Kulzer, and Medentika (n = 10 per group). Conventional implant impressions were taken for comparison (n = 10). The conventional models were digitized, and all models (digital and conventional) were superimposed with the reference file to obtain the 3D deviations for the implant-abutment-interface points (IAIPs). Results for linear deviation (trueness and precision) were analyzed using pairwise comparisons (P < .05; SPSS version 25). For precision, a two-way factorial mixed ANOVA was used.

RESULTS

The deviations for trueness (mean) ± precision (SD) of the IAIPs ranged as follows: FDI region 14 = 0.106 ± 0.050 mm (Medentika) to 0.134 ± .026 mm (NT Trading); region 16 = 0.108 ± 0.046 mm (conventional) to 0.164 ± 0.032 mm (NT Trading); region 24 = 0.111 ± 0.050 mm (conventional) to 0.191 ± 0.052 mm (Medentika); region 26 = 0.086 ± 0.040 mm (conventional) to 0.199 ± 0.066 mm (Kulzer). There were significant differences for trueness between all digital and conventional impression techniques. For precision, only two significant differences in two implant regions (14, 24) were observed.

CONCLUSION

Longer scanning paths resulted in higher deviations of the implant position in digital impressions. Due to algorithms implemented in the software, errors resulting from the different scan bodies may be reduced during the alignment process of the IOS in clinical practice.

Assessment of Effect of Implant Angulation and Implant Number on the Dimensional Accuracy of Definitive Casts

AIM

To analyze the impact of implant angulation and implant number on the dimensional accuracy of definitive casts.

MATERIALS AND METHODS

Seven definitive casts with implant analogs placed in a triangular pattern were made from dental stone. The groups were as follows: group 1 (control group) all implant analogs perpendicular to the plane of the cast; the center implant analog (implant 2) being at 90° to the plane of the cast in all groups and implant analogs number 1 and 3 arranged in 5°, 10°, or 15° divergence from or convergence to the center implant (implant number 2). Three open-tray impressions of definitive casts were made in each group. Impressions were poured in type IV dental stone. Coordinates in the three planes were measured at the implant analog top surface and the base of the cast using a fine tip measuring stylus. The data were aligned and the angular differences between implant analog vectors from definitive and duplicate casts were calculated in degrees.

RESULTS

The impact of implant number on the dimensional accuracy of definitive casts was significant whereas for implant angulation it was nonsignificant. The correlation of angulation and the number of the implant did not show an interpretable pattern. The precision of duplicate casts (compared to definitive casts) is not affected by the combined interaction of implant number and implant angulation.

CONCLUSION

The close proximity of implant angulation toward a right-angled direction results in higher precision of implant. In the impression, there is direct picking from the impression copings which decreases the discrepancies in implant angulation on impression and master cast. The interaction of implant angulation and the number shows a noninterpretable pattern.

CLINICAL SIGNIFICANCE

Dimensionally accurate implant impressions can be made by using an open tray technique for three implants angled up to 15°.

Comparison of Tensile Bond Strength of Addition Silicone with Different Custom Tray Materials Using Different Retentive Methods

AIM

To compare the bond strength of addition silicone with different commonly used custom tray materials by means of different retentive methods (mechanical, chemical, and a combination of chemical and mechanical methods).

MATERIALS AND METHODS

Fabrications of 90 samples of different tray resin materials were done using an aluminum mold. They were divided into three main groups. Perforations, adhesive application, and a combination of both were done according to the grouping of samples. Polyvinyl siloxane material (medium body) was loaded over the samples. A universal testing machine with a crosshead speed of 5 mm/minute was used to determine the tensile bond strength of tray resin samples to medium body impression material. Based on these values, Student's-test, group statistics, and ANOVA test were used for statistical analysis.

RESULTS

Visible light cure (VLC) resin showed the highest bond strength in chemicomechanical methods. This was followed by repair resin material. Tray resin material showed poor bond strength in all three retentive methods. The mechanical method was the least retentive in all three resin materials.

CLINICAL SIGNIFICANCE

VLC tray resin material can be used with chemical and mechanical retention in clinical situations to make predictably accurate elastomeric impressions.

CONCLUSION

It was concluded that VLC tray resin shows good bond strength with polyvinyl siloxane impression material when both mechanical perforations and adhesive applications were done.

Comparison of Dimensional Accuracy of Three Different Impression Materials Using Three Different Techniques for Implant Impressions: An In Vitro Study

AIM

To compare the dimensional accuracy of polyether, polyvinyl siloxane, and polyether polyvinyl siloxane hybrid impression materials using closed tray, open tray splinted, and open tray nonsplinted coping impression techniques and to find out the best suitable impression material and technique combination for implant impressions.

MATERIALS AND METHODS

The sample size of the study was 45. The combinations of materials and techniques were divided into nine groups, namely polyvinyl siloxane with closed tray, polyvinyl siloxane with open tray nonsplinted copings, polyvinyl siloxane with open tray splinted copings, polyether with closed tray, polyether with open tray nonsplinted copings, polyether with open tray splinted copings, polyvinyl siloxane-polyether hybrid with closed tray, polyvinyl siloxane-polyether hybrid with open tray nonsplinted copings, and polyvinyl siloxanepolyether hybrid with open tray splinted copings. Five samples of each group were evaluated. A total of 45 impressions were taken. A stainless steel master metal framework with three internal hex implants was fabricated and used to generate the samples. A common condensation silicone putty spacer was applied over the impression copings attached to the implants, which was then duplicated. All trays were fabricated on this duplicated silicone die using light cure acrylic resin. Trays to be used for open tray techniques had their top removed for gaining access to screws of the impression copings. Splinting of coping for OS group was done using pattern resin. Impressions were poured, and master cast was generated. Interimplant distance was measured using stereomicroscope and an image analyzing software.

RESULTS

Open nonsplinted technique resulted in significantly better replication of implant positions compared to open splinted and closed techniques. Hybrid impression material depicted significantly better dimensional accuracy than polyether and polyvinyl siloxane. Hybrid open nonsplinted depicted least mean difference in interimplant distance, followed by hybrid open splinted and polyether open splinted groups. Polyvinyl siloxane closed tray showed maximum difference in interimplant distance in comparison with other groups.

CONCLUSION

Polyvinyl siloxane-polyether hybrid impression material and open nonsplinted technique gave best replication of implant positions on the master cast.

CLINICAL SIGNIFICANCE

Accuracy of impressions and casts is of great importance for the fabrication and long-term clinical success of precisely fitting implant-retained prostheses.