An evaluation of impression techniques for multiple internal connection implant prostheses

doi:10.1016/j.prosdent.2004.08.015

The Journal of Prosthetic Dentistry

Volume 92, Issue 5, November 2004, Pages 470-476

https://doi.org/10.1016/j.prosdent.2004.08.015 Get rights and content

Statement of problem

Movement of impression copings inside the impression material using an open-tray impression technique during clinical and laboratory phases may cause inaccuracy in transferring the 3-dimensional spatial orientation of implants intraorally to the definitive cast. Consequently the restoration may require corrective procedures.

Purpose

This in vitro study evaluated the accuracy of 3 different impression techniques using polyether impression material to obtain a precise definitive cast for a multi-unit implant restoration with multiple internal connection implants.

Material and methods

A reference acrylic resin model with 4 internal connection implants (3i Implant Innovations) was fabricated. Forty-five medium-consistency polyether impressions (Impregum Penta) of this model were made with square impression copings using an open-tray technique. Three groups of 15 specimens each were made with different impression techniques: in the first group, nonmodified square impression copings were used (NM group); in the second group, square impression copings were used and joined together with autopolymerizing acrylic resin before the impression procedure (R [resin] group); and in the third group, square impression copings previously airborne-particle abraded and coated with the manufacturer-recommended impression adhesive were used (M [modified] group). Matching implant replicas were screwed into the square impression copings in the impressions. Impressions were poured with ADA type IV stone (New Fujirock). A single calibrated examiner blinded to the nature of the impression technique used examined all definitive casts to evaluate the positional accuracy (μm) of the implant replica heads using a profile projector (at original magnification ×10). These measurements were compared to the measurements calculated on the reference resin model which served as control. Data were analyzed with a 1-way analysis of variance at α=.05, followed by the Student Newman-Keuls test (α=.05).

Results

The data obtained with the profile projector revealed significant differences within the 3 impression techniques (P<.001). The Student Newman-Keuls procedure disclosed significant differences between the groups, with group R casts being significantly more accurate than group NM and group M casts (P=.05). The mean distance (±SD) between the posterior implants compared to the reference acrylic resin model was 18.17 μm (± 6.4) greater for group R casts, 41.27 μm (± 8.4) greater for group M casts, and 46.21 μm (± 8.9) greater for group NM casts. Distances between the anterior implants were also greater than those recorded on the reference model. The distance was 15.23 μm (± 5.9) greater on group R casts, 38.17 μm (± 8.3) greater on group M casts, and 43.23 μm (± 8.7) greater on group NM casts.

Conclusion

Within the limitations of this study, improved accuracy of the definitive cast was achieved when the square impression copings joined together with autopolymerizing acrylic resin were used to make an impression of multiple internal connection implants.

Section snippets

Material and methods

An acrylic resin model (Blue Star Type E; Breitschmid, Kriens, Switzerland) of a maxillary arch with 4 internal connection 3.75 × 10-mm implants (IOSS310; 3i Implant Innovations, Inc) was fabricated (Fig. 1, A). The 4 implants in the acrylic resin model were sequentially numbered 1 through 4 from left to right (Fig. 1, B). Forty-five identical 2-mm–thick custom impression trays were made with light-polymerizing composite methacrylate resin (Palatray XL; Heraeus Kulzer, Hanau, Germany), prepared

Results

Relative to intraoperator variability, for each of the distances between posterior and anterior implants in the definitive casts selected from groups NM, R, and M, the range of standard deviations of the 10 repeated measurements was 3.2 to 3.4 μm, while the range of the intra-class correlation coefficients was 0.93 to 0.96. The small standard deviations and the high values of the intra-class correlation coefficients indicate the reliability of the measurement method.

With the use of the profile

Discussion

In implant prosthodontics, a successful result can be achieved only when passively fitting prostheses are fabricated.10., 11. The application of undue torque to screws during attachment of the superstructure to the abutments may jeopardize the outcome. If a clinically passive fit is not achieved and the metal supporting structure is unstable intraorally, the metal framework is usually sectioned, repositioned, and soldered. To eliminate discrepancies in fit, including those not visually

Conclusions

Within the limitations of this in vitro study, casts retrieved from transfer impressions with nonmodified implant impression copings and with airborne-particle–abraded, adhesive-coated copings were statistically less accurate than casts from square impression copings joined together with autopolymerizing acrylic resin prior to the impression procedure.

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The aim of this systematic review was to evaluate the in vitro accuracy of dental implant impressions taken using digitally coded healing abutments (CHAs) compared with impressions taken with conventional techniques (CI) and/or within the CHA group at varying degrees of angulations for multiple implant units. Two independent reviewers conducted a systematic electronic search in the MedLine, PubMed, Google Scholar, Cochrane Library, Web of Science, and Scopus databases. Some of the employed key terms, combined with the help of Boolean operators, were: “digitally coded healing abutments”, “encode healing abutment”, “dental implants”, “impression accuracy”, “digital impression”, and “conventional impression”. Publication dates ranged from January 2010 to November 2022. A total of 7 articles fulfilled the inclusion criteria: 6 studies compared the accuracy of CHA with conventional pick-up impression techniques, and one study only used CHAs at different angulations and heights to compare accuracy within the group. The results were divided into Group A (elastomeric impression of CHA) and Group B (CHA + Intraoral scanner). According to the results of this systematic review, elastomeric impression of CHA performed poorly when compared to CI for multiple implants, although an intraoral scan of CHA appears to be more accurate. Within the CHA group, the angulation and visible height of CHA play a significant role in impression accuracy. However, more studies are needed before CHA can be recommended for all non-parallel multiple implant-supported restorations.
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Despite the extensive studies on and comparisons of different implant impression techniques for completely edentulous patients, studies on novel techniques that combine conventional impression making with digital scanning are lacking.
The primary aim of this study was to compare the accuracy of the impression scan body technique with conventional impression making and digital scanning for a completely edentulous mandibular arch. The secondary aim was to assess the relationship between different implant angulations and interimplant distances in relation to the recording accuracy.
An edentulous mandibular definitive cast (control) was designed with 5 implants placed at different angles and interimplant distances. Three recording techniques were tested: a conventional impression with splinted copings (conventional) (n=15), an impression scan body technique where impression scan bodies were attached to the splinted impression copings in a conventional elastomeric impression and then digitally scanned with an extraoral scanner (n=15), and an intraoral digital scanning technique (digital) (n=15). For comparison, the definitive cast and the conventional impression stone casts were digitized into standard tessellation language (STL) datasets using the extraoral scanner. The 3-dimensional (3D) deviations between the 3 test groups and the control were calculated by superimposing the STL datasets. The 3D deviations from the control were compared by using the Kruskal-Wallis test followed by the Dunn post hoc test (α=.05). The Mann-Whitney test was used to investigate the effect of implant angulation and interimplant distance on impression accuracy (α=.05).
The conventional splinted-coping impression technique showed a mean 3D deviation of 0.408 mm. The impression scan body and intraoral digital scan showed similar mean 3D deviations, 0.219 mm and 0.257 mm, respectively (P=.334). Both techniques showed significantly lower 3D deviations than the conventional technique (P<.001). Implants at an angle of 5 degrees and 10 degrees showed a statistically significant difference (P=.010) with mean 3D deviations of 0.340 mm and 0.396 mm, respectively. Implants with 5-mm and 10-mm interimplant distance showed a significant difference (P<.001) with mean 3D deviations of 0.301 mm and 0.423 mm, respectively.
The impression scan body technique is comparable with intraoral digital scanning for a completely edentulous arch. Increased implant angulation and increased interimplant distance significantly reduced the accuracy of implant impression making or scanning.
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Although polyvinyl siloxane (PVS) materials and polyether (PE) materials have been the recommended materials for making impressions for implant-supported fixed complete dentures (IFCDs), a consensus regarding the optimal impression materials has yet to be established.
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The PubMed, Web of Science, and Embase databases were searched and supplemented via hand searches. Studies comparing the accuracy of conventional impressions for IFCDs by using PVS and PE materials with either direct (open-tray) or indirect (closed-tray) techniques were included. Linear distance deviations and angular deviations between adjacent implants were evaluated. The mean difference (MD) with a 95% confidence interval (CI) was calculated for continuous data. A subgroup analysis was conducted to evaluate the impact of implant angulation (α=.05).
Among the 597 publications identified, 27 in vitro studies were included for qualitative analysis, and 12 were included for quantitative analysis. The general analysis revealed no significant differences in linear distance and angular deviations between the 2 impression materials with the direct or indirect technique. The subgroup analysis found that a statistically significant difference in linear distance deviations was found when implants were placed at an angle greater than 15 degrees, favoring PE materials when using the direct technique (P=.010, MD: 32.54 µm; 95% CI: 6.83 to 58.24) and indirect technique (P=.020, MD: 138.15 µm, 95% CI: 19.17 to 257.13). However, only 2 relevant studies assessed the indirect technique.
When providing IFCDs, conventional impressions obtained by using PVS and PE materials were found to have similar accuracy in most scenarios. PE materials yielded better outcomes when implants were placed at an angle greater than 15 degrees.
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Classic ArticleAn evaluation of impression techniques for multiple internal connection implant prostheses

Statement of problem

Purpose

Material and methods

Results

Conclusion

Section snippets

Material and methods

Results

Discussion

Conclusions

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J Prosthet Dent

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J Prosthet Dent

Classic Article
An evaluation of impression techniques for multiple internal connection implant prostheses