Comparison of the marginal fit of lithium disilicate crowns fabricated with CAD/CAM technology by using conventional impressions and two intraoral digital scanners

BackgroundSeveral impression techniques, especially in combination with computer-aided design and computer-aided manufacturing (CAD/CAM), are used in increasing the accuracy of dental implantology and decreasing patient discomfort. The study was designed to examine the accuracy of the digital impression (DI) of multiple implants with an intraoral scanner (IOS) and compared with that of a conventional impression (CI).Material and MethodsFour dental implants were placed in teeth area #33, #36, #43 and 46# of the mandibular full-arch model. The implanted model was replicated by IOS and CI after fitting of scannable abutments over the implant screws. Then, a small hole was made on the scan region (as a reference point). Two types of CI techniques were used; dual-phase (DP) and monophase (MP). Stone casts were produced through a conventional close tray impression technique using die stone. The casts were scanned with a laboratory scanner. DI was attained by scanning the implanted model with the IOS. The control sample was accomplished by scanning the implanted model directly with a laboratory scanner. Dimensional accuracy was calculated by measuring the distances between the reference points of four measuring parameters as follows; A-B, B-C, C-D, and A-D using CAD software. ResultsThe mean values and standard deviation between the four parameters of different impression techniques (CI and DI) and the control group showed convergent value. One-way ANOVA test showed all CI techniques, except IOS, showed a significant differences from the control group.ConclusionsCompared with CI, the IOS was more accurate because no differences were observed between its measurements and those of the control model. CI is simple and reduces patient discomfort when used in fabricating multiple implants and allowing communication with dental technicians. Key words:Dimension accuracy, conventional impressions, digital impressions, multiple implants.

Fit of lithium disilicate crowns fabricated from conventional and digital impressions assessed with micro-CT

The accuracy of digital impressions is still controversial for complete arch implant cases. The aim of this study is to compare the accuracy of different intraoral scanners with the conventional technique in terms of trueness and precision in a complete arch implant model. Eight implants were inserted asymmetrically in a polyurethane edentulous mandibular model with different angulations. A 3-dimensional (3D) reference model was obtained by scanning this polyurethane model with an optical scanner. First, digital impressions were made by using 3 different intraoral scanners: Carestream 3500 (DC), Cerec Omnicam (DO) and 3Shape Trios 3 (DT). Subsequently, a nonsplinted open tray impression technique was used for conventional impression group (C) and then the master casts were digitalized with a lab scanner. Each 10 STL files belonging to 4 different impression groups were imported to a reverse engineering program, to measure distance and angle deviations from the reference model. All statistical analyses were performed after taking absolute values of the data. After comparing the impression groups with one-way ANOVA, the trueness and precision values were analyzed by Tukey post hoc test and 0.05 was used as the level of significance. The mean trueness of distance was 123.06 ± 89.83 µm for DC, 229.72 ± 121.34 µm for DO, 209.75± 47.07 µm for DT, and 345.32 ± 75.12 µm for C group (p < 0.0001). While DC showed significantly lower deviation compared to DO and C, no significant difference was found between DC and DT. C showed the highest distance deviation significantly in all groups; and no significant difference was found between DO and DT groups. In angle measurements; the trueness was 0.26° ± 0.07° for DC, 0.53° ± 0.42° for DO, 0.33° ± 0.30° for DT, and 0.74° ± 0.65° for C group. There was no significant difference between the groups in terms of angular trueness (p = 0.074). In terms of the precision for distance, the results of DC 80.43 ± 29.69µm, DO 94.06 ± 69.96 µm, DT 35.55 ± 28.46 µm and C 66.97 ± 36.69 µm were determined (p = 0.036). The significant difference was found only between DT and DO among all groups. Finally, angular precision was determined to be 0.19° ± 0.11° for DC, 0.30° ± 0.28° for DO, 0.22° ± 0.19° for DT, and 0.50° ± 0.38° for Group C. No significant difference was found between the groups, in terms of angular precision (p = 0.053). All digital impression groups yielded superior data compared to conventional technique in terms of trueness. DC formed the impression group with the highest trueness in both distance and angular measurements. The results of this in vitro study suggest the use of intraoral scanners compared to the conventional impression techniques in complete arch implant cases with high angulations.

Micro-computed tomography evaluation of marginal fit of lithium disilicate crowns fabricated by using chairside CAD/CAM systems or the heat-pressing technique

This study aimed to compare the accuracy of implant-level conventional and digital impressions for atrophied maxillary ridges. Twelve participants with atrophied edentulous maxillary ridges received six implants. Six months later and after soft tissue maturation around healing abutments, a control cast was constructed using the final passive restoration for each patient. Two types of implant-level impression techniques were carried out for each patient: (1) conventional (splinted open-tray) impression technique and (2) digital impression technique. For both techniques, scan bodies were labeled from the most distal implant on the left side (A, B, C, D, E, and F) and scanning was made. Accuracy of both techniques was measured using in vitro (two-dimensional and three-dimensional) and in vivo (clinical) methods. Two-dimensional methods include measurement of the difference in linear distances AB, AC AD, AE, and AF. Geomagic software was used to assess the three-dimensional deviation between the two impression techniques using the superimposition of standard tessellation language files. The incidence and percentage of nonpassive frameworks and framework misfits of final restorations for both types of impression techniques were assessed using the single screw test. For all distances, digital impressions recorded significantly higher deviation from control measurements than conventional impressions. The highest two-dimensional linear deviation was noted for AF distance and the lowest difference was noted for AB distance. For all scan bodies, digital impressions recorded significantly higher three-dimensional deviation than conventional impressions. The highest three-dimensional deviation was noted with scan bodies C and D. Digital impressions recorded a significantly higher incidence of nonpassive frameworks and framework misfits than conventional impressions. [Correction added on 11 June 2024, after first online publication: In the preceding sentence, "digital impressions" was changed to "conventional impressions" in this version.] CONCLUSION: Within the limitations of this study, it could be concluded that the conventional implant-level impression technique showed greater in vitro and in vivo accuracy than the digital impression technique when used for full-arch maxillary fixed restorations on inclined implants.

PurposeThe aim of this study was to evaluate and compare the inter-operator reproducibility of three-dimensional (3D) images of teeth captured by a digital impression technique to a conventional impression technique in vivo.Materials and methodsTwelve participants with complete natural dentition were included in this study. A digital impression of the mandibular molars of these participants was made by two operators with different levels of clinical experience, 3 or 16 years, using an intra-oral scanner (Lava COS, 3M ESPE). A silicone impression also was made by the same operators using the double mix impression technique (Imprint3, 3M ESPE). Stereolithography (STL) data were directly exported from the Lava COS system, while STL data of a plaster model made from silicone impression were captured by a three-dimensional (3D) laboratory scanner (D810, 3shape). The STL datasets recorded by two different operators were compared using 3D evaluation software and superimposed using the best-fit-algorithm method (least-squares method, PolyWorks, InnovMetric Software) for each impression technique. Inter-operator reproducibility as evaluated by average discrepancies of corresponding 3D data was compared between the two techniques (Wilcoxon signed-rank test).ResultsThe visual inspection of superimposed datasets revealed that discrepancies between repeated digital impression were smaller than observed with silicone impression. Confirmation was forthcoming from statistical analysis revealing significantly smaller average inter-operator reproducibility using a digital impression technique (0.014± 0.02 mm) than when using a conventional impression technique (0.023 ± 0.01 mm).ConclusionThe results of this in vivo study suggest that inter-operator reproducibility with a digital impression technique may be better than that of a conventional impression technique and is independent of the clinical experience of the operator.

An evaluation of student and clinician perception of digital and conventional implant impressions

With the current surge into digital dentistry, several options are available for clinicians, for example, when providing indirect restorations. There is a need for evidence on the quality of fixed dental prostheses (FDPs) fabricated using either digital or conventional impressions. This study aimed to evaluate the marginal fit of single-crown and three-unit FDP frameworks fabricated from digital and conventional impressions. Crown preparations were made on a maxillary typodont model (KaVo Dental GmbH, Biberach, Germany) on the right central incisor for a single-crown framework and the right first premolar and first molar for a three-unit framework to replace the second premolar. Four scanners (Dental Wings (DW, Straumann Group, Montreal, Canada), Carestream 3600 (CS, Carestream Dental, Atlanta, GA, USA), Medit i700 (M700, MEDIT Corp., Seoul, Republic of Korea), and Medit i500 (M500, MEDIT Corp.)) were used to record digital impressions of the preparations. Conventional impressions using polyether monophase impression material were also made, and stone casts were fabricated using high-strength stone and scanned using a laboratory scanner (Dental Wings, Straumann Group). Stereolithography files and computer-aided design and computer-aided manufacturing (CAD-CAM) were used to produce 50 zirconia FDPs (25 each of single crowns and three-unit frameworks). The marginal fit of the prostheses was determined by marginal gap measurements while seated on the typodont, a gap of ≤150µm being deemed acceptable. Results were summarized as means, standard deviations, medians, and interquartile ranges (IQRs). The independent t-test and one-way ANOVA followed by Tukey's post hoc test for means and Kruskal-Wallis test followed by Dunn's post hoc test for medians were performed for hypothesis testing at α<0.05. The respective marginal gap measurements for single-crown and three-unit FDPs were 151.3±60.1µm and 153.9±50.1µm (polyether), 185.0±63.7µm and 224.2±81.7µm (DW), 177.1±81.3µm and 146.4±44.9µm (CS), 158.0±48.7µm and 184.3±86.2µm (M700), and 195.9±61.7µm and 202.8±71.1µm (M500). The marginal gap measurements of single crowns were significantly different among the five impression methods (F = 2.54, p = 0.042; χ2 = 14.68, p = 0.005) but not among the four digital methods (F = 1.83, p = 0.146), with the specific differences being between polyether and DW (p<0.01) and between polyether and M500 (p<0.001). The marginal gap measurements of the three-unit prostheses were significantly different among all five impression methods (F = 13.52, χ2 = 46.64, p<0.001) and the four digital methods (F = 12.32, p<0.001). The specific differences were between polyether and DW (p<0.001), M700 (p=0.02), and M500 (p<0.001), respectively; between CS and the other three digital methods (DW, p<0.001; M700, p=0.024; M500, p<0.001); and between DW and M700 (p=0.016). Considering the means and standard deviations, all five impression techniques produced FDPs with acceptable marginal gap measurements. Significant differences were observed between conventional and digital impression techniques, with polyether and CS producing single-crown and three-unit FDPs having the least marginal gaps, respectively.

Context:Marginal fit being the prime concern of indirect restorations. Inlays can be either fabricated by conventional technique or computer-aided design and computer-aided manufacturing (CAD/CAM) techniques. CAD/CAM is the most evolving digital technique with faster, quicker, and precise results.Aims:The aim of this study is to evaluate and compare the marginal fit of MOD inlays fabricated with two different CAD/CAM methods and conventional fabrication methods.Settings and Design:Mesio-occlusal-distal preparation was done on a maxillary premolar typhodont tooth and divided into the following groups. Group A: 30 inlays were fabricated through the conventional impression technique. Group B: Preparation was scanning using an intraoral scanner followed by subtractive milling (Group B1) and subtractive milling of wax patterns (Group B2). Similarly, subgrouping was carried out for Group C except that an extraoral scanner was used. Occlusal and the cervical marginal fit were assessed using the replica technique and stereomicroscope. One-way ANOVA followed by Tukey honestly significant difference post hoc test for determining differences at a 95% level of confidence (P = 0.05).Results:Group A had the highest marginal discrepancy in comparison to Group B and Group C at occlusal and cervical edges, whereas subtractive milling showed comparatively better results than subtractive milling of wax patterns at cervical edges and similar results at occlusal edges.Conclusions:Ceramic inlays fabricated by subtractive milling yielded better results.

Comparison of marginal and internal fit of 3-unit ceramic fixed dental prostheses made with either a conventional or digital impression

Digital impression techniques are advertised as an alternative to conventional impressioning. The purpose of this in vitro study was to compare the accuracy of full ceramic crowns obtained from intraoral scans with Lava C.O.S. (3M ESPE), CEREC (Sirona), and iTero (Straumann) with conventional impression techniques. A model of a simplified molar was fabricated. Ten 2-step and 10 single-step putty-wash impressions were taken using silicone impression material and poured with type IV plaster. For both techniques 10 crowns were made of two materials (Lava zirconia, Cera E cast crowns). Then, 10 digital impressions (Lava C.O.S.) were taken and Lava zirconia crowns manufactured, 10 full ceramic crowns were fabricated with CEREC (Empress CAD) and 10 full ceramic crowns were made with iTero (Copran Zr-i). The accessible marginal inaccuracy (AMI) and the internal fit (IF) were measured. For AMI, the following results were obtained (mean ± SD): overall groups, 44 ± 26 μm; single-step putty-wash impression (Lava zirconia), 33 ± 19 μm; single-step putty-wash impression (Cera-E), 38 ± 25 μm; two-step putty-wash impression (Lava zirconia), 60 ± 30 μm; two-step putty-wash impression (Cera-E), 68 ± 29 μm; Lava C.O.S., 48 ± 25 μm; CEREC, 30 ± 17 μm; and iTero, 41 ± 16 μm. With regard to IF, errors were assessed as follows (mean ± SD): overall groups, 49 ± 25 μm; single-step putty-wash impression (Lava zirconia), 36 ± 5 μm; single-step putty-wash impression (Cera-E), 44 ± 22 μm; two-step putty-wash impression (Lava zirconia), 35 ± 7 μm; two-step putty-wash impression (Cera-E), 56 ± 36 μm; Lava C.O.S., 29 ± 7 μm; CEREC, 88 ± 20 μm; and iTero, 50 ± 2 μm. Within the limitations of this in vitro study, it can be stated that digital impression systems allow the fabrication of fixed prosthetic restorations with similar accuracy as conventional impression methods. Digital impression techniques can be regarded as a clinical alternative to conventional impressions for fixed dental restorations.

PURPOSEThe purpose of this in vitro study was to evaluate the marginal misfits of three-unit frameworks fabricated with conventional and digital impressions techniques.MATERIALS AND METHODSThirty brass canine and second premolar abutment preparations were fabricated by using a computer numerical control machine and were randomly divided into 3 groups (n=10) as follows: conventional impression group (Group Ci), Cerec Omnicam (Group Cdi), and 3shape TRIOS-3 (Group Tdi) digital impression groups. The laser-sintered metal frameworks were designed and fabricated with conventional and digital impressions. The marginal adaptation was assessed with a stereomicroscope at ×30 magnification. The data were analyzed with 1-way analysis of variances (ANOVAs) and the independent simple t tests.RESULTSA statistically significant difference was found between the frameworks fabricated by conventional methods and those fabricated by digital impression methods. Multiple comparison results revealed that the frameworks in Group Ci (average, 98.8 ± 16.43 µm; canine, 93.59 ± 16.82 µm; premolar, 104.10 ± 15.02 µm) had larger marginal misfit values than those in Group Cdi (average, 63.78 ± 14.05 µm; canine, 62.73 ± 13.71 µm; premolar, 64.84 ± 15.06 µm) and Group Tdi (average, 65.14 ± 18.05 µm; canine, 70.64 ± 19.02 µm; premolar, 59.64 ± 16.10 µm) (P=.000 for average; P=.001 for canine; P<.001 for premolar). No statistical difference was found between the marginal misfits of canine and premolar abutment teeth within the same groups (P>.05).CONCLUSIONThe three-unit frameworks fabricated with digital impression techniques showed better marginal fit compared to conventional impression techniques. All marginal misfit values were clinically acceptable.

Background: The success and maintenance of indirect dental restorations is closely related to the marginal accuracy, which is affected by many factors like preparation design, using of different fabrication techniques, and the time of taking final impression and pouring it. The purpose of this in vitro study was to evaluate the effect of different pouring time of conventional impression on the vertical marginal gap of full contour zirconia crowns in comparison with digital impression technique. Materials and Methods: Forty sound recently extracted human permanent maxillary first premolar teeth of comparable size and shape were collected. Standardized preparation of all teeth samples were carried out to receive full contour zirconia crown restoration with deep chamfer finishing line all around the tooth with (1mm) depth, axial length (4mm) and convergence angle (6 degree). The specimens separated into two groups; Group A; eight specimens were scanned digitally by using Omnicam scanner; Group B; conventional impressions were taken for the remaining thirty two specimens and further subdivided to four groups according to the time of impression pouring; Group B1: PVS were poured after 30 minutes; Group B2: PVS were poured after 24 hours; Group B3: PVS were poured after 7 days; Group B4:PVS were poured after 14 days. Marginal discrepancy was measured at four points at each tooth surface. Sixteen points per tooth were measured using digital microscope at (180X) magnification. One-way ANOVA test and LSD test were carried out to see if there was any significant difference among the means of the conventional impression groups. Independent samples t-test was carried out to examine if there is any significant difference between digital and conventional impression technique. Results: group B2 had the least mean of marginal gap with statistically significant difference when compared to group B1 and statistically highly significant difference when compared to group B3 and B4. There was a statistically highly significant difference in the vertical marginal gap between digital impression technique and conventional impression. Conclusions: the pouring of conventional impression after 24 hours provides better marginal fit than other pouring time. The digital impression provides better marginal fit than conventional impression.

Background: The success and maintenance of indirect dental restorations is closely related to the marginal accuracy, which is affected by many factors like preparation design, using of different fabrication techniques, and the time of taking final impression and pouring it. The purpose of this in vitro study was to evaluate the effect of different pouring time of conventional impression on the vertical marginal gap of full contour zirconia crowns in comparison with digital impression technique. Materials and Methods: Forty sound recently extracted human permanent maxillary first premolar teeth of comparable size and shape were collected. Standardized preparation of all teeth samples were carried out to receive full contour zirconia crown restoration with deep chamfer finishing line all around the tooth with (1mm) depth, axial length (4mm) and convergence angle (6 degree). The specimens separated into two groups; Group A; eight specimens were scanned digitally by using Omnicam scanner; Group B; conventional impressions were taken for the remaining thirty two specimens and further subdivided to four groups according to the time of impression pouring; Group B1: PVS were poured after 30 minutes; Group B2: PVS were poured after 24 hours; Group B3: PVS were poured after 7 days; Group B4:PVS were poured after 14 days. Marginal discrepancy was measured at four points at each tooth surface. Sixteen points per tooth were measured using digital microscope at (180X) magnification. One-way ANOVA test and LSD test were carried out to see if there was any significant difference among the means of the conventional impression groups. Independent samples t-test was carried out to examine if there is any significant difference between digital and conventional impression technique. Results: group B2 had the least mean of marginal gap with statistically significant difference when compared to group B1 and statistically highly significant difference when compared to group B3 and B4. There was a statistically highly significant difference in the vertical marginal gap between digital impression technique and conventional impression. Conclusions: the pouring of conventional impression after 24 hours provides better marginal fit than other pouring time. The digital impression provides better marginal fit than conventional impression.

To conduct a systematic review to evaluate the evidence of possible benefits and accuracy of digital impression techniques vs. conventional impression techniques. Reports of digital impression techniques versus conventional impression techniques were systematically searched for in the following databases: Cochrane Central Register of Controlled Trials, PubMed, and Web of Science. A combination of controlled vocabulary, free-text words, and well-defined inclusion and exclusion criteria guided the search. Digital impression accuracy is at the same level as conventional impression methods in fabrication of crowns and short fixed dental prostheses (FDPs). For fabrication of implant-supported crowns and FDPs, digital impression accuracy is clinically acceptable. In full-arch impressions, conventional impression methods resulted in better accuracy compared to digital impressions. Digital impression techniques are a clinically acceptable alternative to conventional impression methods in fabrication of crowns and short FDPs. For fabrication of implant-supported crowns and FDPs, digital impression systems also result in clinically acceptable fit. Digital impression techniques are faster and can shorten the operation time. Based on this study, the conventional impression technique is still recommended for full-arch impressions.