Effect of cement type on vertical marginal discrepancy and residual excess cement in screwmentable and cementable implant-supported monolithic zirconia crowns

The purpose of this study was to investigate the vertical marginal discrepancy (VMD) and residual excess cement (REC) of cementable and screwmentable monolithic zirconia crowns cemented with different types of cement. Abutments were attached to 40 implant analogues. Crowns were created using computer-aided design/computer-aided manufacturing technology from monolithic zirconia blocks, either with or without a screw access hole (SAC). Crowns created both ways were split into two groups and cemented with resin and zinc polycarboxylate cement under a 5-kg weight. VMD and REC values were evaluated using an X20 zoom stereomicroscope. Data were analysed using two-way ANOVA and the Bonferroni test. According to the two-way ANOVA results, REC measurements differed significantly in the crown design and cement groups. However, whilst VMD values were significantly different in both crown design groups, there was no significant difference in the cement groups. According to the Bonferroni test results, the highest REC (157.241 ± 44.29 µm) and VMD (68.052 ± 16.19 µm) values were found in the crowns without SAC and cemented with zinc polycarboxylate. Screwmentable crowns are more effective than cementable crowns in reducing REC and VMD. Whilst polycarboxylate cement reduces VMD in screwmentable crowns, resin cement is more suitable for cementable crowns.

Immediate loading on two adjacent single dental implants with definitive nonsplinted restorations: A proof of concept in the posterior zone

OBJECTIVES

To evaluate clinical, clinician- and patient-reported outcomes (PROs) of two adjacent single posterior implants immediately loaded with definitive single crowns up to 1 year. Ten patients in need of two adjacent posterior single implants were included. All implants were placed applying a fully digital workflow. Definitive screw-retained single zirconia crowns were delivered within 72 h after implant placement. Clinical parameters, patient- and clinician-reported outcomes were assessed up to 1 year of follow-up.

CLINICAL CONSIDERATIONS

Clinical outcomes remained stable, with no implant failures or technical and biological complications throughout the observation period. Patient satisfaction was very high at baseline (crown delivery) and remained consistently high at 6 and 12 months of follow-up. Crown insertion 3 days after implant placement was rated as an easy procedure by clinicians.

CONCLUSIONS

Two adjacent single implants with immediate definitive restorations (<72 h) in the posterior region appear to be a viable and easy treatment option to shorten the overall treatment time and potentially enhancing patient satisfaction. However, randomized controlled trials are needed to confirm the advantages of this treatment protocol over a delayed loading approach.

CLINICAL SIGNIFICANCE

In selected cases, immediate implant loading with definitive restorations in the posterior region appears a valuable and straightforward option to shorten the overall treatment time.

Adaptation and uniformity of monolithic zirconia crowns fabricated by additive 3-dimensional gel deposition

STATEMENT OF PROBLEM

A novel monolithic zirconia restoration fabricated by additive 3-dimensional (3D) gel deposition, named as self-glazed zirconia (SGZ), has recently been developed. SGZ crowns exhibit reliable mechanical properties and esthetic appearance, but their adaptation and uniformity are unclear.

PURPOSE

The purpose of this in vitro study was to compare the adaptation and uniformity of monolithic zirconia crowns fabricated by additive 3D gel deposition with that of milled zirconia and lithium disilicate crowns.

MATERIAL AND METHODS

Ten identical resin abutments were made based on the scanning data of an extracted and prepared human mandibular first molar. Three types of monolithic crowns were then fabricated by using 2 different processes: 3D gel deposition zirconia (SGZ), milled zirconia (ZZ), and milled lithium disilicate (EMX) (n=10) through a completely digital workflow. The nondestructive direct-view technique and replica technique were used to measure the marginal and internal discrepancy values individually. The uniformity index was calculated to describe the uniformity of the internal space. The results were analyzed by using 1-way ANOVA and Kruskal-Wallis statistical tests (α=.05).

RESULTS

The marginal discrepancy of EMX exhibited the highest values among the 3 groups (P=.001). The 2 types of zirconia crowns had comparable marginal discrepancy values (P>.05). The internal discrepancy values of SGZ were significantly lower than those of EMX at the occlusal region and of ZZ at all measured locations (P<.05). All 3 types of monolithic crowns showed comparable good uniformity (P=.056).

CONCLUSIONS

The marginal and internal adaptations of novel monolithic zirconia crowns were within clinical requirements. Compared with the zirconia and lithium disilicate crowns fabricated by subtractive milling, monolithic zirconia crowns fabricated by additive 3D gel deposition had comparable uniformity and better internal adaptation.

Effect of cement space settings on the marginal and internal fit of 3D-printed definitive resin crowns

STATEMENT OF PROBLEM

The cement gap setting affects the marginal and internal fits depending on the crown material and manufacturing method (subtractive or additive manufacturing). However, information on the effects of cement space settings in the computer-aided design (CAD) software program, which is used to aid the manufacturing with 3-dimensional (3D) printing-type resin material, is lacking, and recommendations for optimal marginal and internal fit are needed.

PURPOSE

The purpose of this in vitro study was to evaluate how cement gap settings affect the marginal and internal fit of a 3D-printed definitive resin crown.

MATERIAL AND METHODS

After scanning a prepared typodont left maxillary first molar, a crown was designed with cement spaces of 35, 50, 70, and 100 μm by using a CAD software program. A total of 14 specimens per group were 3D printed from definitive 3D-printing resin. By using the replica technique, the intaglio surface of the crown was duplicated, and the duplicated specimen was sectioned in the buccolingual and mesiodistal directions. Statistical analyses were performed using the Kruskal-Wallis and the Mann-Whitney post hoc tests (α=.05).

RESULTS

Although the median values of the marginal gaps were within the clinically acceptable limit (<120 μm) for all the groups, the smallest marginal gaps were obtained with the 70-μm setting. For the axial gaps, there was no observed difference in the 35-, 50-, and 70-μm groups, and the 100-μm group showed the largest gap. The smallest axio-occlusal and occlusal gaps were obtained with the 70-μm setting.

CONCLUSIONS

Based on the findings of this in vitro study, a 70-μm cement gap setting is recommended for optimal marginal and internal fit of 3D-printed resin crowns.

Evaluation of the virtual cement gap parameter of different CAD software programs in designing a single crown restoration: An in vitro study

STATEMENT OF PROBLEM

The accuracy of different virtual cement gap parameters in designing a single crown in a computer-aided design (CAD) software program is still unclear.

PURPOSE

The purpose of this in vitro study was to evaluate and compare the virtual cement gap settings of 3 different CAD software programs used to design a single crown restoration.

MATERIAL AND METHODS

Three different CAD software programs (exocad, Dental System, and B4D) were evaluated for designing single crowns with similar virtual cement gap settings. Three experimental groups were created based on the CAD software program used (n=10). Three-dimensional analysis software program was used to assess the virtual cement gap in the CAD restoration. The Shapiro-Wilk test of normality was used. Comparisons were carried out by using 1-way ANOVA and the Scheffé post hoc test (α=.05).

RESULTS

The Dental System software program had the lowest statistical mean error values at both tooth margin (4.6 μm) and axial wall (1.5 μm), followed by B4D then exocad. At the occlusal surface, the lowest statistical mean error value of 5 μm was achieved by the Dental System followed by exocad then B4D.

CONCLUSIONS

Accuracy of the virtual cement gap parameter in single crown design varies based on the CAD software used. The highest accuracy was attained by the Dental System software program at all tooth surfaces, followed by B4D at the tooth margin and axial wall and by exocad at the occlusal surface.

Evaluation of marginal and internal fit of lithium disilicate and zirconia all-ceramic CAD-CAM crowns using digital impressions: A systematic review

PURPOSE

A range of materials for single-tooth computer-aided design and computer-aided manufacturing (CAD-CAM) restorations have been introduced that may affect CAM accuracy. This study aimed to review articles evaluating marginal and internal fit of lithium disilicate (LD) and zirconia (Z) crowns fabricated by CAD-CAM systems using intraoral optical scanners (IOS).

MATERIALS AND METHODS

Under the guidelines of Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA), a systematic review was performed along with an electronic article search in the Medline/Pubmed database. The articles were limited to those in the English language that were published within the past ten years.

RESULTS

The initial search resulted in 50 articles and of those, a total of 18 articles were selected for full-text review following abstract evaluation. Eight articles that did not meet the inclusion criteria were excluded and the remaining ten articles, which provided internal and marginal gap values, were used in this review. For LD crowns, marginal gap values ranged between 45µm and 190.2µm. For Z crowns, the values varied between 39µm and 126.4µm. For LD crowns, the internal gap values were between 57.8µm and 475.4µm, and for Z crowns, the values were between 79µm and 205.8µm.

CONCLUSION

The outcome of this review suggests that clinically acceptable marginal and internal fit can be attained with LD and Z all-ceramic CAD-CAM crowns using digital impressions. Additionally, it has been found that LD and Z ceramics provide similar marginal gap values, but LD material provides better internal fit than Z.

Trueness of full-arch dental models obtained by digital and conventional impression techniques: an in vivo study

The aim of this study was to compare the trueness of complete- and partial-arch impressions obtained using conventional impression materials and intraoral scanners in vivo. Full-arch impressions were taken using polyether and polyvinylsiloxane. Gypsum casts were digitized using a laboratory scanner (IM, AF). Casts obtained from polyether impressions were also scanned using an industrial blue light scanner to construct 3D reference models. Intraoral scanning was performed using CEREC Omnicam (CO) and Trios 3 (TR). Surface matching software (Atos Professional) enabled to determine the mean deviations (mean distances) from the reference casts. Statistically significant discrepancies were calculated using the Wilcoxon signed-rank test. The mean distance for trueness ranged from 0.005 mm (TR) to 0.023 mm (IM) for the full arch, from 0.001 mm (CO) to 0.068 mm (IM) for the anterior segment, and from 0.019 mm (AF) to 0.042 mm (IM) for the posterior segment. Comparing the anterior vs. the posterior segment, significantly less deviations were observed for anterior with CO (p < 0.001) and TR (p < 0.001). Full-arch comparisons revealed significant differences between AF vs. IM (p = 0.014), IM vs. CO (p = 0.002), and IM vs. TR (p = 0.001). Full-arch trueness was comparable when using Affinis and the two intraoral scanners CEREC Omnicam and Trios 3. The digital impression devices yielded higher local deviations within the complete arch. Digital impressions of the complete arch are a suitable and reliable alternative to conventional impressions. However, they should be used with caution in the posterior region.Trial registration: Registration number at the German Clinical Trial Register (04.02.2022): DRKS00027988 ( https://trialsearch.who.int/ ).

Effect of Abutment Geometry and Luting Agents on the Vertical Marginal Discrepancy of Cast Copings on Implant Abutments: An In Vitro Study

Aim

Vertical marginal discrepancy (VMD) influences the success of implant-supported restorations. However, there is little literature that has investigated the influence of geometry and cementing agent on changes in VMD of metal copings on implant abutments. The objective was to evaluate the effect of the geometry of the abutment and cementing agents on VMD.

Methods

Cast copings were cemented on implant abutments customized cylindrical (4, 5.5, and 7 mm) and on hexagonal implant abutments (4 mm) cemented or uncemented molded copings were placed (n = 4, totally 64 samples) with different luting agents. The VMD of the copings were measured in the coping-abutment interface at three reference points using a stereomicroscope. The independent Student's t test was used for comparison between the two different abutment walls. The post hoc statistical analysis was performed by the Tukey test.

Results

There was a significant VMD increase between noncemented and cemented cast copings using different luting agents. Abutment geometry and luting agents significantly influenced the VMD (p ≤ 0.05). Cylindrical abutment at 7 mm in height cemented with different luting agent tested showed significantly higher VMD values than cylindrical abutments of 4 mm (p=0.019). Hexagonal abutments with a 4 mm height showed significantly higher VMD values than cylindrical 4 mm abutments using zinc oxide noneugenol and glass ionomer cements (p=0.032).

Conclusions

Abutment geometry and luting agents influence the VMD of cast copings cemented on implant abutment. The higher the cylindrical abutment, the greater the VMD, and hexagonal wall abutments promote greater marginal gap.

Effect of cement space on marginal discrepancy and retention of CAD/CAM crown

This research aimed to evaluate the effect of cement space on the marginal discrepancy and retention of computer-aided design/computer-aided manufacturing (CAD/CAM) crowns. A total of 30 premolar Frasaco teeth were machined to receive crowns with cement spaces of 70, 90, and 110 μm. The marginal discrepancy measurements were done before and after cementation. Pull-off test was conducted using universal testing machine (UTM). Data was analyzed using two-way mixed ANOVA with post-hoc Bonferroni test and Kruskal-Wallis test. The crowns with cement space of 70 μm showed a significantly higher absolute marginal discrepancy than those with 90 and 110 μm. No significant effect on the crown retention was found. Within the limitations of this study, modifying cement space to 90 μm and 110 μm may improve the marginal adaptation of CAD/CAM crown, whereas adjusting cement space from 70 to 110 μm did not significantly affect the crown retention.

Effect of virtual cement gap settings on the marginal fit of cemented resin-ceramic crowns on implant abutments

STATEMENT OF PROBLEM

Agreement on the perfect virtual cement space value for computer-aided design and computer-aided manufacturing (CAD-CAM) implant-supported resin-ceramic crowns with the best marginal adaptation is lacking. The range of cement gap settings in some CAD design software programs is wide (0 to 200 μm), and manufacturer recommendations regarding the best cement gap setting for certain types of ceramics is not specific.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of virtual cement gap settings on the marginal fit of cemented resin-ceramic crowns on implant abutments.

MATERIAL AND METHODS

Thirty implant analogs and matching stock abutments were coupled and implanted into autopolymerizing acrylic resin blocks. Three groups (n=10) of resin-ceramic molar crowns with 3 different virtual cement space settings (40, 60, and 100 μm) were designed by using a CAD design software program. The crowns were cemented over their corresponding abutments under a static load by using a specially designed cementing device. A scanning electron microscope was used to measure the mean vertical marginal gap (MG) for each group, where a total of 120 measurements for each of the 3 groups (12 sites per crown and 10 crowns per group) were evaluated. One-way analysis of variance and the post hoc Tukey pairwise comparison tests were used to analyze the data (α=.05).

RESULTS

A significant difference (P<.001) was found between the MG values of the resin-ceramic implant-supported crowns fabricated by using the 3 cement space settings. The smallest MG was obtained with the 60-μm setting as compared with the 40-μm and 100-μm settings.

CONCLUSIONS

A limited inverse relation was found between the MGs of CAD-CAM-fabricated resin-ceramic implant-supported crowns and the cement gap settings in the exocad software program. The smallest MGs were obtained when a 60-μm cement space value was used (P<.001).

Effects of porcelain veneering methods on conformity of the marginal and internal fit of three-unit zirconia framework

The purpose of this study is to investigate the effects of porcelain veneering methods on the marginal and internal fit of a three-unit zirconia framework. A zirconia master model, in which the lower-left second premolar and the second left molar were used as the abutment, was obtained using an intraoral scanner. Based on the data, three-unit zirconia frameworks for fabricating all-ceramic bridges were designed and milled (FW group). Two types of all-ceramic bridge were fabricated by veneering porcelain onto these frameworks using the press-over technique (P group) and the layering technique (L group). The replica technique was used to measure the gap size between the abutments and the bridges. Measurements were taken in the marginal opening area (MO), chamfer area (CH), axial area (AX), and occlusal area (OC). Statistical analysis was performed using the Mann-Whitney U-test. There was no significant difference in MO and CH between the P and L groups. However, in AX, the L group had a significantly larger gap size than that of the P group (p = 0.003). In addition, compared with the FW group, the P group showed a significantly larger gap size in MO (p < 0.000), CH (p = 0.008), and OC (p < 0.000). These results indicate that the gap size increased after porcelain veneering using the press-over and layering techniques. In addition, the all-ceramic bridges fabricated using the press-over and layering techniques had approximately equal gap sizes in MO.

Influence of luting space of zirconia abutment on marginal discrepancy and tensile strength after dynamic loading

STATEMENT OF PROBLEM

Although luting space is related to the marginal fit of indirect restorations, information on its influence on the marginal fit and tensile strength of zirconia abutments bonded to titanium bases is lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the influence of luting space on the marginal discrepancy and tensile strength of zirconia abutments bonded to a titanium base after dynamic loading.

MATERIAL AND METHODS

Ninety implant replicas were embedded in resin blocks to attach 4-mm-high titanium luting bases. Zirconia abutments (Ceramill Zolid FX) were fabricated with different internal luting spaces: 25 μm (G25), 50 μm (G50), or 75 μm (G75). The zirconia abutments were cemented on the titanium bases by using a resin cement (Panavia F 2.0) under a constant load of 20 N. The marginal discrepancy and internal fit of 10 random specimens from each group were evaluated with a stereoscopic microscope at ×50 magnification. The remaining specimens were submitted to the tensile strength test in which half were evaluated after dynamic loading (1.2 million cycles of 200 N at 3.8 Hz) in a mechanical fatigue machine. The tensile strength test was performed using a pullout apparatus coupled to a universal testing machine at a crosshead speed of 0.5 mm/min. The mode of failure was determined by observation at ×50 magnification under a stereomicroscope and classified into adhesive or mixed. The groups were compared by using 2-way ANOVA and the Tukey HSD test (α=.05).

RESULTS

Increase in the luting space did not influence the marginal discrepancy (P>.05). All zirconia abutments exhibited lower pullout strength after fatigue simulation (P<.05). G75 demonstrated lower tensile strength than G25 and G50 before and after loading (P<.05). Most failures were adhesive at the zirconia-cement interface.

CONCLUSIONS

The increase of the luting space to 75 μm did not influence marginal discrepancy; however, it reduced the tensile strength of a zirconia abutment bonded to a titanium base.

Effect of Anti-Rotational Abutment Features and Novel Computerized Fabrication Techniques on the Marginal Fit of Implant-Supported Metal Copings

PURPOSE

An in vitro study to compare the marginal fit of cobalt-chromium (Co-Cr) metal copings fabricated with selective laser melting (SLM), computer-aided design and computer-aided manufacturing (CAD/CAM) milling, and lost-wax (LW) techniques, on abutments with two different antirotational features.

MATERIALS AND METHODS

A total of 60 stainless steel abutments with the same length and convergence angles were fabricated using a numerical control machining. Half of the abutments had one flat plane, while the other half had three grooves as an antirotation feature. Thirty abutments of each kind were then divided into three subgroups, and metal copings were fabricated with SLM, CAD/CAM milling, or the LW technique (n = 10). The metal copings were cemented with polycarboxylate cement. Marginal gap measurements were performed using a stereomicroscope at a magnification of × 45 and data were analyzed with two-way analysis of variance (ANOVA) tests.

RESULTS

The LW (p = 0.002) and CAD/CAM (p < 0.001) techniques exhibited increased marginal gaps on the abutments with a three groove antirotational feature; however, no significant difference was detected with the SLM technique (p = 0.259). The copings fabricated with the SLM technique demonstrated significantly lower gap values in both abutment types (p < 0.001).

CONCLUSION

While all marginal gap values were within the clinically acceptable range (<120 µm), abutments with more antirotational grooves exhibited wider marginal gaps with the LW and CAD/CAM techniques.

Influence of the CAD-CAM Systems on the Marginal Accuracy and Mechanical Properties of Dental Restorations

The aim of this study was to compare the quality of different computer-assisted-design and computer assisted manufacturing systems (CAD-CAM) generated by only one scanner, focusing on vertical fit discrepancies and the mechanical properties. A master model was obtained from a real clinical situation: the replacement of an absent (pontic) tooth, with the construction of a fixed partial denture on natural abutments with three elements. Nine scans were performed by each tested and 36 copies were designed using a dental CAD-CAM software (Exocad). The frameworks were manufactured using three-axis and five-axis, with the same batch of the chrome-cobalt (CrCo) alloy. The frameworks were not cemented. A focus ion beam-high resolution scanning electron microscope (FIB-HRSEM) allowed us to obtain the vertical gap measurements in five points for each specimen. Roughness parameters were measured using white light interferometry (WLI). The samples were mechanically characterized by means of flexural tests. A servo-hydraulic testing machine was used with a cross-head rate of 1 mm/min. One-way ANOVA statistical analysis was performed to determine whether the vertical discrepancies and mechanical properties were significantly different between each group (significance level p < 0.05). The overall mean marginal gap values ranged: from 92.38 ± 19.24 µm to 19.46 ± 10.20 µm, for the samples produced by three-axis and five-axis machines, respectively. Roughness was lower in the five-axis machine than the three-axis one, and as a consequence, the surface quality was better when the five-axis machine was used. These results revealed a statistically significant difference (p < 0.005) in the mean marginal gap between the CAD-CAM systems studied. The flexural strength for these restorations range from 6500 to 7000 N, and does not present any statistical differences’ significance between two CAD-CAM systems studied. This contribution suggests that the number of axes improves vertical fit and surface quality due to the lower roughness. These claims show some discrepancies with other studies.

Mechanical Properties of CoCr Dental-Prosthesis Restorations Made by Three Manufacturing Processes. Influence of the Microstructure and Topography

The aim of this study is to compare the mechanical properties of three different dental restorations’ manufacturing processes (CADCAM milling, casting and laser sintering) generated by only one laboratory scanner focusing on marginal fit analysis and their mechanical properties. A chrome-cobalt (Cr-Co) alloy from the same batch was used for three different methods to make an implant abutment. This simulates a maxillary right first molar that was fixed in a hemi-maxillary stone model. Five scans were performed by each tested framework. Nine frameworks were manufactured for each manufacture procedure. Field-Emission Scanning Electron Microscope (FE-SEM) direct vision was used to marginal gap measurement in five critical points for each specimen. In order to fix the samples in the microscope chamber, the restorations were submitted at a compression load of 50 N. The samples always have the same orientation and conditions. The resolution of the microscope is 4 nm and it is equipped by J image software. The microstructure of the samples was also determined with the FE-SEM equipped with EDS-microanalysis. Roughness parameters were measured using White Light Interferometry (WLI). The arithmetical mean for the Ra and Rq of each sample was calculated. The samples were mechanically characterized by means of microhardness and flexural testing. Servo-hydraulic testing machine was used with cross-head rate of 1 mm/min. Two-way ANOVA statistical analysis was performed to determine whether the marginal discrepancies and mechanical properties were significantly different between each group (significance level p < 0.05). The overall mean marginal gap values were: from 50.53 ± 10.30 µm for the samples produced by CADCAM to 85.76 ± 22.56 µm for the samples produced by the casting method. Laser sintering presents a marginal gap of 60.95 ± 20.66 µm. The results revealed a statistically significant difference (p-value < 0.005) in the mean marginal gap between the CADCAM systems studied. The higher flexure load to fracture for these restorations were for CADCAM restoration and the lower was for the casting samples. For these restorations, CADCAM Restoration yielded a higher flexure load to fracture and Casting ones yielded the lower. Porosity and microstructure play a very important role in the mechanical properties.

Ceramic Materials and Technologies Applied to Digital Works in Implant-Supported Restorative Dentistry

Computer-aided design and manufacturing technology has been closely associated with implant-supported restoration. The digital system employed for prosthodontic restorations comprises data acquisition, processing, and manufacturing using subtractive or additive methods. As digital implantology has developed, optical scanning, computer-based digital algorithms, fabricating techniques, and numerical control skills have all rapidly improved in terms of their accuracy, which has resulted in the development of new ceramic materials with advanced esthetics and durability for clinical application. This study reviews the application of digital technology in implant-supported dental restoration and explores two globally utilized ceramic restorative materials: Yttria-stabilized tetragonal zirconia polycrystalline and lithium disilicate glass ceramics.

Marginal fit of CAD-CAM monolithic zirconia crowns fabricated by using cone beam computed tomography scans

STATEMENT OF PROBLEM

Information regarding the precision of monolithic zirconia crowns fabricated by using a standard computer-aided design and computer-aided manufacturing (CAD-CAM) workflow is available. However, information on the effect of a modified workflow using 3D laboratory scanning and/or cone beam computed tomography (CBCT) for monolithic zirconia crown fabrication is lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the effect of different scans on the marginal fit of CAD-CAM monolithic zirconia crowns fabricated by 3D laboratory scanning and CBCT.

MATERIAL AND METHODS

An extracted maxillary left first molar was prepared and digitized by using a 3D laboratory scanner (D900; 3Shape A/S) (control group). The tooth was also scanned by CBCT (i-CAT; Imaging Sciences) to generate a second virtual 3D model (CBCTscan group). A tooth cast out of polyurethane (PU) (Zenotec Model; Wieland) was reproduced from the CBCT data by using a CAD software program (Dental System 2.6; 3Shape A/S) and milling machine (CORiTEC 550i; imes-icore) and further scanned by using the 3D laboratory scanner to generate a third virtual 3D model to represent a clinical scenario where a patient's cast is needed (PU3DLab group). A monolithic zirconia crown design (cement space: margin 40 μm, 1 mm above 70 μm) was used on the virtual models, and crowns were fabricated out of presintered zirconia blocks (ZenostarT4; Wieland) by using a 5-axis milling machine (CORiTEC 550i; imes-icore). The crowns were sintered (Sinterofen HT-S Speed; Mihm-Vogt), and the vertical marginal discrepancy (VMD) was measured by ×100-magnification microscopy. Measurements were made at 384 points in 3 groups of 16 specimens. The measurements for each specimen were averaged, and VMD mean values were calculated. The Kruskal-Wallis test was used for the statistical analysis (α=.05). The Mann-Whitney U test and Bonferroni adjustment were further used to compare the pairs (α=.017).

RESULTS

The mean VMD value was 41 μm (median: 38 μm) for the control group, 44 μm (median: 42 μm) for the CBCTscan, and 60 μm (median: 58 μm) for the PU3DLab. No significant difference was found between control and CBCTscan groups (P=.274). However, there was a significant difference between control and PU3DLab and CBCTscan and PU3DLab groups (P<.001).

CONCLUSIONS

Marginal fit of the crowns fabricated by using the 3D laboratory scanner and through the direct use of CBCT was better than that of the crowns fabricated by using the workflow that combined the use of CBCT, PU cast, and 3D laboratory scanner. All tested protocols enabled the fabrication of monolithic zirconia crowns with a marginal discrepancy smaller than 120 μm.

Influence of Intra-Oral Scanner (I.O.S.) on The Marginal Accuracy of CAD/CAM Single Crowns

The aim of this in vitro study was to compare the quality of digital workflows generated by different scanners (Intra-oral digital scanners (I.O.S.s)) focusing on marginal fit analysis. A customized chrome-cobalt (Cr-Co) implant abutment simulating a maxillary right first molar was fixed in hemi-maxillary stone model and scanned by eight different I.O.S.s: Omnicam^® (Denstply Sirona, Verona, Italy) CS3500^®, CS3600^®, (Carestream Dental, Atlanta, GA, USA), True Definition Scanner^® (3M, St. Paul, MN, USA), DWIO^® (Dental Wings, Montreal, Quebec, Canada), PlanScan^® (Planmeca Oy, Helsinki, Finland), 3D PROGRESS Plus^® (MHT, Verona, Italy), TRIOS 3^® (3Shape, Copenhagen, Denmark). Nine scans were performed by each tested I.O.S. and 72 copings were designed using a dental computer-assisted-design/computer-assisted-manufacturing (CAD/CAM) software (exocad GmbH, Darmstadt, Germany). According to CAD data, zirconium dioxide (ZrO₂) copings were digitally milled (Roland DWX-50, Irvine, CA, USA). Scanning electron microscope (SEM) direct vision allowed for marginal gap measurements in eight points for each specimen. Descriptive analysis was performed using mean, standard deviation, and median, while the Kruskal⁻Wallis test was performed to determine whether the marginal discrepancies were significantly different between each group (significance level p < 0.05). The overall mean marginal gap value and standard deviation were 53.45 ± 30.52 μm. The minimum mean value (40.04 ± 18.90 μm) was recorded by PlanScan^®, then 3D PROGRESS Plus^® (40.20 ± 21.91 μm), True Definition Scanner^® (40.82 ± 26.19 μm), CS3500^® (54.82 ± 28.86 μm) CS3600^® (59,67 ± 28.72 μm), Omnicam^® (61.57 ± 38.59 μm), DWIO^® (62.49 ± 31.54 μm), while the maximum mean value (67.95 ± 30.41 μm) was recorded by TRIOS 3^®. The Kruskal⁻Wallis tests revealed a statistically significant difference (p-value < 0.5) in the mean marginal gaps between copings produced by 3D PROGRESS Plus^®, PlanScan, True Definition Scanner, and the other evaluated I.O.S.s. The use of an I.O.S. for digital impressions may be a viable alternative to analog techniques. Although in this in vitro study PlanScan^®, 3D PROGRESS Plus^® and True Definition Scanner^® may have showed the best performances, all I.O.S.s tested could provide clinically encouraging results especially in terms of marginal accuracy, since mean marginal gap values were all within the clinically acceptable threshold of 120 μm.

Internal Adaptation of Implant-Supported, Polymer-Infused Ceramic Crowns Fabricated by Two CAD/CAM Systems

PURPOSE

The aim of this in vitro study was to compare the internal 3D adaptation of polymer-infused ceramic crowns fabricated using two CAD/CAM systems: CEREC inLab MC XL and Ceramill Motion 2 (5X).

MATERIALS AND METHODS

Twenty-five implant-supported metal-ceramic crowns were fabricated conventionally using the lost-wax technique, and the outer contour was scanned to serve as a guide for designing the polymer-infused ceramic CAD/CAM crowns. Twenty-five crowns were fabricated using CEREC, and 25 crowns were fabricated using Ceramill. The cement space was set to 20 μm. The Zeiss Accura Microsystem Coordinate Measuring Machine (CMM), Calypso, and Geomagic software were used to measure the 3D accuracy of fit of all crowns to their respective implant abutments. To test for the statistical significance between groups in terms of 3D total distortion, a one-way ANOVA was conducted. The Kolmogorov-Smirnov test was used to investigate the differences in the x, y, and z coordinates. A p-value of 0.05 or less was considered statistically significant at an alpha level of 0.05.

RESULTS

Comparing the 3D misfit of metal-ceramic crowns to those of CAD/CAM crowns fabricated using CEREC revealed no significant difference (88.20 ± 36.59 μm vs. 102.45 ± 36.58 μm, p = 0.161). Similarly, no significant difference in 3D total distortion was identified between metal-ceramic crowns and crowns fabricated using Ceramill (88.20 ± 36.59 μm vs. 78.40 ± 31.03 μm, p = 0.336); however, the 3D total distortion of polymer-infused crowns made by Ceramill was significantly reduced compared to that of crowns fabricated by CEREC (78.3 ± 31.0 μm vs. 102.4 ± 36.5 μm, p = 0.019).

CONCLUSIONS

Polymer-infused ceramic crowns fabricated using CEREC exhibited the least accurate 3D fit. All misfit values of the tested groups were within clinically acceptable levels.

Influence of Material Selection on the Marginal Accuracy of CAD/CAM-Fabricated Metal- and All-Ceramic Single Crown Copings

This study evaluated the marginal accuracy of CAD/CAM-fabricated crown copings from four different materials within the same processing route. Twenty stone replicas of a metallic master die (prepared upper premolar) were scanned and divided into two groups. Group 1 (n = 10) was used for a pilot test to determine the design parameters for best marginal accuracy. Group 2 (n = 10) was used to fabricate 10 specimens from the following materials with one identical CAD/CAM system (GAMMA 202, Wissner GmbH, Goettingen, Germany): A = commercially pure (cp) titanium, B = cobalt-chromium alloy, C = yttria-stabilized zirconia (YSZ), and D = leucite-reinforced glass-ceramics. Copings from group 2 were evaluated for the mean marginal gap size (MeanMG) and average maximum marginal gap size (AMaxMG) with a light microscope in the “as-machined” state. The effect of the material on the marginal accuracy was analyzed by multiple pairwise comparisons (Mann–Whitney, U-test, α = 0.05, adjusted by Bonferroni-Holmes method). MeanMG values were as follows: A: 46.92 ± 23.12 μm, B: 48.37 ± 29.72 μm, C: 68.25 ± 28.54 μm, and D: 58.73 ± 21.15 μm. The differences in the MeanMG values proved to be significant for groups A/C (p = 0.0024), A/D (p = 0.008), and B/C (p = 0.0332). AMaxMG values (A: 91.54 ± 23.39 μm, B: 96.86 ± 24.19 μm, C: 120.66 ± 32.75 μm, and D: 100.22 ± 10.83 μm) revealed no significant differences. The material had a significant impact on the marginal accuracy of CAD/CAM-fabricated copings.

Digital technology in fixed implant prosthodontics

Digital protocols are increasingly influencing prosthodontic treatment concepts. Implant-supported single-unit and short-span reconstructions will benefit mostly from the present digital trends. In these protocols, monolithic implant crowns connected to prefabricated titanium abutments, which are created based on data obtained from an intraoral scan followed by virtual design and production, without the need of a physical master cast, have to be considered in lieu of conventional manufacturing techniques for posterior implant restorations. No space for storage is needed in the complete digital workflow, and if a remake is required a replica of the original reconstruction can be produced quickly and inexpensively using rapid prototyping. The technological process is split into subtractive methods, such as milling or laser ablation, and additive processing, such as three-dimensional printing and selective laser melting. The dimensions of the supra-implant soft-tissue architecture can be calculated in advance of implant placement, according to the morphologic copy, and consequently are individualized for each patient. All these technologies have to be considered before implementing new digital dental workflows in daily routine. The correct indication and application are prerequisite and crucial for the success of the overall therapy, and, finally, for a satisfied patient. This includes a teamwork approach and equally affects the clinician, the dental assistant and the technician as well. The digitization process has the potential to change the entire dental profession. The major benefits will be reduced production costs, improvement in time efficiency and fulfilment of patients' perceptions of a modernized treatment concept.

Marginal Fit and Retention Strength of Zirconia Crowns Cemented by Self-adhesive Resin Cements

The absolute marginal gap (AMG) precementation and postcementation and the retention of zirconia crowns cemented to standardized molar preparations (4×10) by self-adhesive resin cements (SARCs) were evaluated. The following SARCs were used: RelyX U-200 (RXU200; 3M ESPE, Seefeld, Germany), SmartCem 2 (SC2; Dentsply, Milford, DE, USA), and G-Cem Automix (GCA; GC, Alsip, IL, USA). The control adhesive resin cement was Panavia 21 (PAN; Kuraray Dental Co Ltd, Osaka, Japan). Twenty measuring locations at a constant interval along the margins were marked, and the AMG was measured by an image analysis system connected to a stereomicroscope (20×). The cemented copings were aged 270 days at 100% humidity and 37°C and then underwent 10,000 thermal cycles, 5°C-55°C. After aging, the crowns were tested for retention, and the debonded surfaces were examined at 3× magnification. The mean marginal gaps precementation and postcementation were 34.8 ± 17.4 μm and 72.1 ± 31 μm, respectively, with no statistically significant differences between the cements. A significant difference ( p≤0.001) in retention between the cements was found. The highest values were obtained for SC2 and GCA (1385 Pa and 1229 Pa, respectively), but these presented no statistically significant differences. The lowest values were found for PAN and RXU200 (738 Pa and 489 Pa, respectively), but these showed no statistically significant differences. The predominant mode of failure in all of the groups was mixed, and no correlations were found between marginal gap and retention.

Fracture behavior, marginal gap width, and marginal quality of vented or pre-cemented CAD/CAM all-ceramic crowns luted on Y-TZP implants

OBJECTIVES

To investigate the fracture behavior and marginal gap region of CAD/CAM fabricated lithium disilicate (L) and zirconium dioxide (Z) crowns using palatal venting (PV), pre-cementation with custom analogs (CA), or conventional cementation technique (SP) with adhesive cement (A) or resin-modified glass ionomer cement (B).

MATERIAL AND METHODS

Twelve groups (n = 6) were set according to material (L, Z), cement (A, B), and technique (PV, CA, SP). Specimens were thermo-mechanical aged (TML), loaded until fracture (LF) and fracture patterns recorded. Marginal gap width and quality were assessed and compared to replicas obtained before and after TML.

RESULTS

Crown material significantly influenced LF with a mean of 1037.6 ± 282.4 N in L and 5356.3 ± 1207.0 N in Z groups (p < .001). Neither cement material nor cementation method affected the outcome. Fractures occurred along the mesial-distal central fissure in both materials. Gap width before TML was 22.04 ± 13.42 μm for L and 19.98 ± 12.72 μm for Z specimens, with overall no influence of crown material, cement type, or method. Marginal cleanliness just below the polished implant shoulder reached 66.7%-88.9% with A, and 91.7%-100% with B, and tended to increase in all groups during TML indicating a decrease in excess cement. Implant-crown junctions were cleaner with B compared to A (p ≤ .001) and along Z crown surfaces compared to L (p ≤ .007).

CONCLUSIONS

Crown venting of lithium disilicate and zirconium dioxide crowns did not affect the fracture load and patterns. Complete cement removal was rare, and the observed particle ablation requires further clinical attention, particularly with submucosal margins.

Monolithic implant-supported lithium disilicate (LS2) crowns in a complete digital workflow: A prospective clinical trial with a 2-year follow-up

BACKGROUND

The technical development of digital processing allows the production of anatomically full-contoured implant-supported restorations.

PURPOSE

The aim of this prospective clinical trial was to analyze the treatment concept of monolithic lithium disilicate (LS2) single-unit restorations in a complete digital workflow.

MATERIAL AND METHODS

Forty-four patients were restored with 50 screw-retained monolithic implant LS2 crowns bonded to pre-fabricated titanium abutments on soft tissue level implants (Institut Straumann AG, Basel, Switzerland) in premolar and molar sites. All implant restorations were digitally designed after intraoral optical scanning (IOS) and CAD/CAM-processing without physical model situations. Study participants were clinically and radiographically examined based on an annually performed follow-up. The "Functional Implant Prosthodontic Score" (FIPS) was applied for objective outcome assessment after 2 years of loading. Five variables were defined for FIPS evaluation, resulting in a maximum score of 10 per implant restoration. Descriptive statistics were calculated for mean scores standard deviations, medians, and Q₂₅ -Q₇₅ .

RESULTS

All patients could be successfully treated within two clinical appointments. No clinical modifications were necessary for the seating of the monolithic crowns, neither for interproximal nor occlusal sites. The implant LS2 restorations demonstrated survival rates of 100% without any technical or biological complications after 2 years. The mean total FIPS score was 7.7 ± 1.0, ranging from 6 to 10.

CONCLUSIONS

CAD/CAM-produced monolithic implant crowns out of LS2 in a complete digital workflow seem to be a feasible treatment concept for the rehabilitation of single-tooth gaps in posterior sites under mid-term observation.

Time-efficiency analysis of the treatment with monolithic implant crowns in a digital workflow: a randomized controlled trial

OBJECTIVES

The aim of the randomized controlled trial was to analyze time-efficiency of a treatment with implant crowns made of monolithic lithium disilicate (LS2) plus titanium base vs. porcelain fuse to zirconium dioxide (ZrO₂ ) in a digital workflow.

MATERIALS AND METHODS

Twenty study participants were included for single-tooth replacement in premolar and molar sites. Baseline was the start of the prosthetic treatment. All patients received transocclusal screw-retained implant reconstructions on a soft tissue level-type implant. The 3D implant position was captured with intraoral optical scanning (IOS). After randomization, ten patients were restored with CAD-/CAM-produced monolithic LS2-crowns bonded to prefabricated titanium abutments without any physical models (test), and ten patients with CAD-/CAM-fabricated ZrO₂ -suprastructures and hand-layered ceramic veneering with milled master models (control). Every single clinical and laboratory work step was timed in minutes and then analyzed for time-efficiency with Wilcoxon Rank Sum Tests. Direct costs were assessed for laboratory fees for first line production in Swiss Francs (CHF).

RESULTS

Two clinical appointments were necessary for IOS and seating of all implant crowns. The mean total production time, as the sum of clinical plus laboratory work steps, was significantly different, resulting in 75.3 min (SD ± 2.1) for test and 156.6 min (SD ± 4.6) for control [P = 0.0001]. Analysis for clinical treatment sessions showed a significantly shorter mean chair time for the complete digital workflow of 20.8 min (SD ± 0.3) compared to 24.1 min (SD ± 1.1) [P = 0.001]. Even more obvious were the results for the mean laboratory work time with a significant reduction of 54.5 min (SD ± 4.9) vs. 132.5 min (SD ± 8.7), respectively [P = 0.0001].

CONCLUSION

The test workflow was more time-efficient than the controls for implant-supported crowns; notably, laboratory fabrication steps could be effectively shortened with the digital process of monolithic LS2 plus titanium base resulting in more than 30% reduced overall treatment costs.