Clinical study evaluating the discrepancy of two different impression techniques of four implants in an edentulous jaw

Objectives

Precise implant-supported prosthodontics requires accurate impressions. Many in vitro studies comparing different implant impression techniques were performed. The purpose of this in vivo study was to compare the discrepancy of two different impression techniques of implants clinically.

Material and methods

Four implants were inserted nearly bilateral in ten edentulous jaws. From each jaw, two different impressions (A, transfer; B, splinted pick-up) were taken. Respectively two stone casts of each jaw were produced and scan bodies were mounted on the lab analogues to digitize the casts. One scan body of the digitized casts was each superimposed and the deviations of the remaining three scan bodies were measured three dimensionally. The fit of the suprareconstructions was evaluated clinically on both casts and in the mouth.

Results

The mean discrepancy of scan body 2 was 192 μm (±96), 282 μm (±97) for scan body 3, and 366 μm (±114) for scan body 4. The discrepancies between two scan bodies were statistically significant (p?≤?0.010; ANOVA test). Comparing the data with the span between the scan bodies, a linear regression line could be drawn to show the dependency between the misfit and the length of the span. Clinically, the fit on the cast produced by the splinted pick-up technique was favorable.

Conclusions

The discrepancy between the splinted pick-up impression technique and the transfer technique were in a range with clinical influence.

Clinical relevance

For better accuracy of implant-supported prosthodontics, the splinted pick-up technique should be used for impressions of four implants evenly spread in edentulous jaws.     

Two-body wear of occlusal splint materials

This study investigates the wear resistance of four different types of occlusal splint materials based on two-body wear simulations under wet and dry conditions. Twenty specimens of each splint material (Dentalon Plus, Orthoplast, Biocryl C, and Eclipse), each with a diameter of 16 mm and a thickness of 3 mm, were tested, half under wet and half under dry conditions. Each wear test was performed using a device called chewing simulator CS-4 (n=10; test load: 50 N; number of cycles: 10000, 20000, and 30000; continuous rinsing with 30°C water for wet conditions); the antagonists were simulated using steel balls. Wear was determined using a 3D laser scanner and a surface analysis program. To detect significant statistical differences, wear data after 10000; 20000; and 30000 cycles were compared using the Kruskal-Wallis test and the Mann-Whitney U-test. The level of significance was set at 5%. Significant differences were found between the groups of different materials tested under wet conditions (P<0.05), whereas no differences between them were found under dry conditions (P>0.05). No significant difference was found between the wet and dry conditions for all materials and cycles (P>0.05). For groups of different materials tested under wet conditions, the degree of volume loss generated in the Chewing Simulator CS-4 was found to differ significantly for different numbers of cycles. The presence of water had no effect on the volume loss in the different material groups that were tested.     

Fit of 4-unit FDPs made of zirconia and CoCr-alloy after chairside and labside digitalization – A laboratory study

Objectives

To analyse the marginal fit of 4-unit fixed dental prostheses (FDPs) and the accuracy of three-dimensional cast-datasets using both approaches to Computer Aided Design (CAD)/Computer Aided Manufacturing (CAM): direct and indirect digitalization.

Methods

A titanium model of a 4-unit FDP was digitized by an intraoral scanning device (iTero, Align Technology, Carlstadt, US; DD, n = 12). Additionally 12 conventional impressions were taken and referring master casts were digitized by a laboratory scanner (CS2, Straumann, Basel, Switzerland; ID, n = 12). Frameworks were fabricated (CARES CADCAM GmbH, Straumann, Markkleeberg, Germany) from base metal alloy (coron, Straumann; DD-C: n = 12; ID-C: n = 12) and zirconia (zerion, Straumann; DD-Z: n = 12; ID-Z: n = 12) from the same datasets. The marginal fit of the resulting frameworks and the accuracy of the underlying datasets from DD and ID were evaluated. Data were analyzed by unpaired two sample Student's t-test with Levene-test (p < 0.05).

Results

Frameworks from group DD-C showed significantly better marginal fit than ID-C (DD-C: 56.90 ± 27.37 μm, ID-C: 90.64 ± 90.81 μm). For zirconia frameworks no differences between both digitalization methods (DD-Z: 127.23 ± 66.87 μm, ID-Z: 141.08 ± 193.17 μm) could be observed. Base metal alloy frameworks exhibited significantly better marginal fit than zirconia frameworks (DD: p < 0.001; ID: p = 0.022). Regarding the accuracy group DD showed significantly higher “trueness” than ID.

Significance

Direct and indirect digitalization lead to clinically acceptable marginal fit of 4-unit FDPs from base metal alloy and zirconia. Higher accuracy of datasets from DD leads to better marginal fit of frameworks from base metal alloy but not for ones from zirconia.     

Residual monomer elution from different conventional and CAD/CAM dental polymers during artificial aging

Clinical Oral Investigations - Analyze and quantify the residual monomer elution of nine conventional and CAD/CAM (computer-aided design/computer-aided manufacturing) dental polymers during...     

Computable translucency as a function of thickness in a multi-layered zirconia

Statement of problem

Determining the relationship between variable thicknesses and the translucency of dental ceramics is essential for optimizing esthetics in different clinical situations.

Fracture behavior of straight or angulated zirconia implant abutments supporting anterior single crowns

The aim of the study was to evaluate the influence of artificial aging on the fracture behavior of straight and angulated zirconia implant abutments (ZirDesign?; Astra Tech, Mölndal, Sweden) supporting anterior single crowns (SCs). Four different test groups (n?=?8) representing anterior SCs were prepared. Groups 1 and 2 simulated a clinical situation with an ideal implant position (left central incisor) from a prosthetic point of view, which allows for the use of a straight, prefabricated zirconia abutment. Groups 3 and 4 simulated a situation with a compromised implant position, requiring an angulated (20°) abutment. OsseoSpeed? implants (Astra Tech) 4.5 mm in diameter and 13 mm in length were used to support the abutments. The SCs (chromium cobalt alloy) were cemented with glass ionomer cement. Groups 2 and 4 were thermomechanically loaded (TCML?=?1.2?×?10⁶; 10,000?×?5°/55°) and subjected to static loading until failure. Statistical analysis of force data at the fracture site was performed using nonparametric tests. All samples tested survived TCML. Artificial aging did not lead to a significant decrease in load-bearing capacity in either the groups with straight abutments or the groups with angulated abutments. The restorations that utilized angulated abutments exhibited higher fracture loads than the restorations with straight abutments (group 1, 280.25?±?30.45 N; group 2, 268.88?±?38.00 N; group 3, 355.00?±?24.71 N; group 4, 320.71?±?78.08 N). This difference in load-bearing performance between straight and angulated abutments was statistically significant (p?=?0.000) only when no artificial aging was employed. The vast majority of the abutments fractured below the implant shoulder.     

Fit of 4-unit FDPs from CoCr and zirconia after conventional and digital impressions

Objectives

To evaluate the marginal and internal fit of CAD/CAM-generated frameworks for 4-unit, fixed dental prostheses (FDPs) from zirconia (Z) and cobalt-chromium alloy (C) made with conventional (CI) and digital impressions (DI).

Materials and methods

A titanium model was digitized with an intraoral scanner (DI, LAVA? C.O.S.; 3M ESPE; Seefeld, Germany; n = 12). Additionally, 12 conventional impressions were taken, and referring plaster casts were digitized by a laboratory-scanner (CI, LAVA? Scan ST; 3M ESPE; n = 12). Frameworks were fabricated (3M ESPE) from cobalt-chromium (DI-C, n = 12; CI-C, n = 12) and zirconia (DI-Z, n = 12; CI-Z, n = 12) from the same datasets. A replica technique was applied to measure the accuracy. The Mann–Whitney U statistical test was applied to detect statistical differences between each material and methodology groups in terms of fit.

Results

Frameworks from DI-C (median 19.07 μm) showed significantly better marginal fit than CI-C (median 64.64 μm, p < 0.001). Frameworks from DI-Z (median 52.50 μm) showed significantly better marginal fit than CI-Z (median 72.94 μm, p = 0.001). Additionally, frameworks from DI-C showed a significantly better marginal fit than DI-Z (p < 0.001).

Conclusions

CI and DI led to a clinically acceptable marginal fit of 4-unit FDPs from cobalt-chromium and zirconia. DI leads to better marginal fit of the cobalt-chromium frameworks; however, no effect on zirconia was found.

Clinical relevance

The results indicate that DI is suitable for fabricating 4-unit, cobalt-chromium and zirconia frameworks with regard to fit requirements.

     

Evaluation of impression accuracy for a four-implant mandibular model--a digital approach

Implant-supported prosthodontics requires precise impressions to achieve a passive fit. Since the early 1990s, in vitro studies comparing different implant impression techniques were performed, capturing the data mostly mechanically. The purpose of this study was to evaluate the accuracy of three different impression techniques digitally. Dental implants were inserted bilaterally in ten polymer lower-arch models at the positions of the first molars and canines. From each original model, three different impressions (A, transfer; B, pick-up; and C, splinted pick-up) were taken. Scan-bodies were mounted on the implants of the polymer and on the lab analogues of the stone models and digitized. The scan-body in position 36 (FDI) of the digitized original and master casts were each superimposed, and the deviations of the remaining three scan-bodies were measured three-dimensionally. The systematic error of digitizing the models was 13 μm for the polymer and 5 μm for the stone model. The mean discrepancies of the original model to the stone casts were 124 μm (±34)?μm for the transfer technique, 116 (±46)?μm for the pick-up technique, and 80 (±25)?μm for the splinted pick-up technique. There were statistically significant discrepancies between the evaluated impression techniques (p ≤ 0.025; ANOVA test). The splinted pick-up impression showed the least deviation between original and stone model; transfer and pick-up techniques showed similar results. For better accuracy of implant-supported prosthodontics, the splinted pick-up technique should be used for impressions of four implants evenly spread in edentulous jaws.     

Full-arch prostheses from translucent zirconia: Accuracy of fit

Objectives

The aim of this study was to evaluate the marginal and internal fit of single crowns, compared to 14-unit frameworks made of translucent yttria-stabilized zirconia. We hypothesized that there is an influence of the type of restoration on the marginal and internal fit.

Methods

Eight teeth (FDI locations 17, 15, 13, 11, 21, 23, 25 and 27) of a typodont maxillary model were provided with a chamfer preparation to accommodate a 14-unit prosthesis or four single crowns (SCs). Ten 14-unit fixed dental prostheses (FDPs) and 40 single crowns were fabricated using a computer aided design (CAD)/computer aided manufacturing (CAM) system with pre-sintered translucent yttria-stabilized zirconia blanks. The restorations were cemented onto twenty master dies, which were sectioned into four pieces each. Then, the marginal and internal fits were examined using a binocular microscope. In order to detect the differences between the two types of restorations a non-parameteric test (Mann–Whitney-U) was carried out; to detect differences between the abutment teeth and the abutment surfaces non-parametric tests (Kruskal–Wallis) and pairwise post hoc analyses (Mann–Whitney-U) were performed after testing data for normal distribution (method according to Shapiro–Wilk). Level of significance was set at 5%.

Results

The mean (SD) marginal opening gap dimensions were 18 μm (14) for the single crowns and 29 μm (27) for the 14-unit FDPs (p < 0.001). Abutment 21 of the FDPs showed statistical differences concerning the location of the teeth in both marginal and internal fit (p < 0.001). The measured gaps (types I–IV) revealed statistical differences between all types, when comparing SCs to the FDPs (p < 0.001).

Significance

Single crowns showed significantly better accuracy of fit, compared to the 14-unit FDPs. However, both restorations showed clinically acceptable marginal and internal fit.