The influence of pontic distribution on the marginal and internal gaps of CAD/CAM five-unit anterior zirconia framework

Background/purpose

Nowadays, zirconia-based framework has been used for longspan or full-arch fixed dental prostheses (FDPs). This study aimed to evaluate the effect of pontic distribution on marginal and internal gaps of five-unit anterior zirconiabased DPs.

Materials and methods

Right maxillary central incisor and second premolar were selected as terminal abutments and three different edentulous conditions with one nonterminal abutment were simulated. Marginal and internal gaps in each zirconia-based samples(n = 10) were examined by computer-aided replica technique. Five regions, including marginal gaps at mesial or distal finishing line, internal gaps at the mesial or distal axial wall, and occlusal surface, were statistically analyzed (α = .05).

Results

Most of marginal gaps and internal gaps at axial wall were clinically acceptable, but larger at occlusal surface. For the three experimental groups, clinically accepted percentage with qualified gaps were less than 30%.There were statistical differences at axial wall over pontic side and marginal gaps over non-pontic side between groups (P<0.05). For sum of gaps of all abutments in each group, statistical differences were found at marginal and axial wall (P < 0.05). As for those on terminal and non-terminal abutments, statistical differences were found on second premolar (P < 0.05).

Conclusion

Except for occlusal surface, the overall marginal gaps and internal gaps at axial wall of five-unit anterior zirconia-based FDPs with different pontic distribution were clinically acceptable. However, the percentage with qualified gaps were low (<30%). Greater gaps were noted when adjacent pontic existed. Different pontic size and distribution with curvature had an influence on the gaps.

The influence of different cement spaces on the marginal gap of lithium disilicate crowns constructed by two scanner and milling unit combinations

BACKGROUND

This study compared the marginal gaps of CAD/CAM lithium disilicate (LDS) crowns constructed using a contemporary and older scanner/milling unit combination at three different cement spaces.

METHODS

Twenty-four undergraduate students prepared a Columbia model lower left first molar for an LDS crown in a simulated environment. From each crown preparation, one LDS crown was constructed using an E4D scanner/E4D milling unit (E4DS/E4DM) and TRIOS 3 scanner/Sirona inLab MC X5 milling unit (TRIO/MCX5) at cement space settings of 50, 100 and 200 μm. Each LDS crown was positioned onto the original crown preparation, and then a stereomicroscope was used to make three vertical marginal gap measurements at four locations (mid-buccal, mid-lingual, mid-mesial and mid-distal). The mean marginal gap (MMG) was calculated for each crown and each individual tooth surface.

RESULTS

The MMGs of CAD/CAM LDS crowns constructed by TRIO/MCX5 were 72.31 at 50, 63.73 at 100 μm and 46.23 μm at 200 μm, which were smaller than E4DS/E4DM at each cement space.

CONCLUSIONS

Increasing the cement space decreased the MMG in both scanner/milling unit combinations. The smallest MMG was found using the newer scanner/milling unit at the 200 μm cement space. © 2024 Australian Dental Association.

Influence on marginal bone levels at implants equipped with blades aiming to control the lateral pressure on the cortical bone. An experimental study in dogs

BACKGROUND

To avoid cortical compression, several implant systems have included in the protocol dedicated drills aimed at widening the cortical region of osteotomy. However, the manual execution of this operation does not guarantee the necessary precision. Hence, the present study aimed to determine the optimal size of the recipient site at the level of the alveolar crest in relation to the size of the coronal region of the implant to achieve the best healing result.

MATERIALS AND METHODS

Blades of different diameters were incorporated into the coronal part of the implant to prepare the cortical region of the mandibular alveolar bone crest in different dimensions in relation to the collar of the implant. The differences in diameter of the blades in relation to the collar of the implant were as follows: one control group, -175 μm, and three test groups, 0 μm, + 50 μm, or + 200 μm.

RESULTS

The marginal bone loss (MBL) at the buccal aspect was 0.7 mm, 0.5 mm, 0.2 mm, and 0.7 mm in the - 175 μm, 0.0 μm, + 50 μm, + 200 μm groups, respectively. The differences were statistically significant between group + 50 μm and control group - 175 μm (p = 0.019), and between + 50 μm and + 200 μm (p < 0.01) groups. The level of osseointegration at the buccal aspect was more coronally located in the test groups than in the control group, whereas the bone-to-implant contact percentage was higher in the + 50 μm and + 200 μm groups. However, these differences were not statistically significant.

CONCLUSIONS

The lowest bone crest resorption and highest levels of osseointegration were observed in the 0.0 μm and + 50 μm groups. The cortical region where the blades had performed their cutting action showed regular healing with perfect hard and soft tissues sealing in all the groups. Cortical blades gathered bone particles, particularly in the + 200 μm group, which were incorporated into the newly formed bone. The results from the present experiment provide support to the use of blades that produce a marginal gap of 50 μm after implant insertion.

Application of the virtual-fit method for fixed complete denture cases designed on intraoral scans: Effect of cement spacing

OBJECTIVES

To validate the virtual-fit alignment, analyze the impact of cement spacing on internal/marginal gaps, and correlate results with conventional trueness measures.

METHODS

Four dental abutment models were scanned using an industrial reference scanner (one time each), Emerald S (three times each), and Medit i700 (three times each) intraoral scanners (IOS). On each IOS scan (n = 24), three complete-arch fixed frameworks were designed with 70 or 140 µm cement space with no marginal space (groups 70 and 140) and 70 µm with an additional 20 µm space, including the margin (group 70+20). Two types of alignment were performed by GOM Inspect software. The reference and IOS scans were aligned through a conventional iterative closest point algorithm (ICP) where the penetration of the two scans was permitted into each other (conventional trueness method). Second, the computer-aided designs were superimposed with the reference scan also using an ICP, but preventing the design from virtual penetration into the model (virtual-fit method). The virtual-fit algorithm was validated by non-penetration alignment of the designs with the IOS scans. Internal and marginal gap was measured between the design and the abutments. The difference between spacing groups was compared by Friedman's test. A statistical correlation (Spearman's Rho Test) was computed between the measured gaps and the conventional trueness method. A significant difference was accepted at p<0.05 after the Bonferroni correction.

RESULTS

The gaps deviated from the set cement space by 3-13 µm on IOS scans (validation of virtual-fit algorithm). The internal gap of the design on the reference scan was not affected by cement spacing (Emerald S, p = 0.779; Medit i700, p = 0.205). The marginal gap in groups 70 and 70+20 was significantly lower than in group 140 in Emerald S (p<0.05). In Medit i700, it was lower in the 70+20 group than in the group 70 (p<0.01) and in the group 140 (p<0.05). Some Medit i700 scans exhibited high marginal gaps within group 70 but not in groups 70 and 140. The measured gaps correlated significantly (r = 0.51-0.81, p<0.05-0.001) with the conventional trueness but were 2.6-4.6 times higher (p<0.001).

CONCLUSION

Virtual-fit alignment can simulate restoration seating. A 20 µm marginal and 90 µm internal spacing could compensate for scan errors up to several hundred micrometers. However, 140 µm internal spacing is counterproductive. The conventional trueness method could only partially predict framework misfit.

CLINICAL SIGNIFICANCE

The virtual-fit method can provide clinically interpretable data for intraoral scanners. Emerald S and Medit i700 intraoral scanners are suitable for fabricating complete-arch fixed tooth-supported prostheses. In addition, a slight elevation of spacing at the margin could compensate for moderate inaccuracies in a scan.

Marginal adaptation of different monolithic zirconia crowns with horizontal and vertical finish lines: A comparative in vitro study

Background

This study evaluated the influence of different tooth preparation techniques and zirconia materials on marginal adaptation.

Methods

Forty-eight healthy human maxillary first premolars were divided into two primary groups based on preparation design: group A (chamfer) and group B (vertical). Within each main group, there were three subgroups, comprising eight teeth each, distinguished by the type of zirconia material employed (Zircad LT, MT, and Prime by Ivoclar Vivadent). All the samples were prepared by the same operator using a dental surveyor. Intraoral scanning was performed on the prepared teeth. SironaInLab CAD 20.0 software was used to design crowns, which were subsequently generated using a 5-axis milling machine. The crowns were cemented to their respective teeth with self-adhesive resin cement. Marginal gap measurements were taken in micrometers (μm) before and after cementation at 16 sites per sample using a digital microscope at×230 magnification. The collected data were evaluated using statistical analysis using the independent t-test, paired t-test, and ANOVA at an 0.05 significance level.

Results

The vertical preparation group exhibited the smallest marginal gap, while the chamfer group displayed the largest. This disparity was statistically significant (P<0.05) for pre- and post-cementation measurements across all materials. There were no significant differences between the different monolithic zirconia crowns.

Conclusion

The vertical preparation design illustrated significantly better marginal adaptation than the chamfer preparation design. Comparisons between materials showed comparable marginal gaps. The mean values of the marginal gaps in all groups increased significantly after cementation.

Marginal gap and internal fit of 3D printed versus milled monolithic zirconia crowns

BACKGROUND

This study aimed to evaluate and compare the marginal gap using two different methods and the internal fit of 3D printed and zirconia crowns.

METHODS

3Y-TZP zirconia crowns (n = 20) were manufactured using subtractive milling (group M) and 3D printed (group P). The marginal gap was measured at 60 points using vertical marginal gap technique (VMGT). On the other hand, the silicone replica technique (SRT) was used to evaluate the internal fit and was divided into 4 groups: marginal gap, cervical gap, axial gap, and occlusal gap where the thickness of light impression was measured at 16 references. The numerical data was tested for normality using Shapiro-Wilk's test. They were found to be normally distributed and were analyzed using an independent t-test.

RESULTS

Using VMGT, group P had significantly higher mean marginal gap values of 80 ± 30 µm compared to group M = 60 ± 20 µm (p < 0.001). Also, with the SRT, the marginal gap of group P (100 ± 10 µm) had significantly higher values compared to group M (60 ± 10 µm). The internal fit showed significant difference between the tested groups except for Axial Gap.

CONCLUSIONS

Although milled crowns showed better results. The 3D printed zirconia crowns offer clinically acceptable results in terms of marginal adaptation and internal fit. Both VMGT and SRT are reliable methods for the assessment of the marginal gap.

Comparative evaluation of internal fit and marginal gap of endocrowns using lithium disilicate and polyether ether ketone materials - an in vitro study

BACKGROUND

The aim of the study was to investigate the effect of material and occlusal preparation design on the internal fit and marginal gap of endocrowns made of Polyether ether ketone (PEEK) and lithium disilicate.

METHODS

32 endocrowns were fabricated on prepared mandibular molars and divided into two groups (n = 16) according to the material. Group L: lithium disilicate and Group P: PEEK. Each group was further subdivided into two subgroups (n = 8) according to the occlusal preparation design: full occlusal coverage (LF and PF) and partial occlusal coverage (LP and PP). Samples were analyzed using microcomputed tomography (µCT) with a voxel size of 6 μm to evaluate internal fit, and an optical microscope was used to evaluate the marginal gap. Data were collected, tabulated, and statistically analyzed. Numerical data were described as mean and standard deviation and compared using the ANOVA test. The level of significance was set at α P ≤ 0.05.

RESULTS

All groups' internal fit and marginal gaps values were within the acceptable clinical range. However, the lithium disilicates group recorded statistically significantly higher mean internal gap values than the PEEK groups. Regardless of the material, the difference between the two occlusal designs was not statistically significant in both internal fit and marginal gap records.

CONCLUSION

Within the limitations of this study, PEEK endocrown restorations revealed better internal fit and marginal gap than lithium disilicate endocrown restorations. The marginal and internal fit of both lithium disilicate and PEEK endocrown restorations were within the clinically acceptable range. The occlusal preparation design had no influence on the internal fit and marginal gap of the endocrown restoration.

Effect of virtual cement space and restorative materials on the adaptation of CAD-CAM endocrowns

BACKGROUND

This study aimed to evaluate the effect of virtual cement space and restorative materials on the fit of computer-aided design and computer-aided manufacturing (CAD-CAM) endocrowns.

METHODS

A mandibular first molar tooth model received a butt joint margin endocrown preparation with a 2-mm occlusal thickness. Then, using a 3D-printing system, 120 copies of this prepared die were printed and assigned equally to three groups with different cement space settings (30, 60, and 120 μm) during the chairside CAD design. In the milling process, CAD-based models with a particular space setting were subdivided into four groups (n = 10) and fabricated from different CAD-CAM materials: Vita Suprinity (VS), Celtra Duo (CD), Lava Ultimate (LU), and Grandio blocs (GR). Finally, the endocrowns were stabilized over their corresponding models with siloxane and subjected to micro-computed tomography to measure the fit.

RESULTS

The cement space that was predesigned at 30 μm generated the largest marginal discrepancy (from 144.68 ± 22.43 μm to 174.36 ± 22.78 μm), which was significantly different from those at 60 μm and 120 μm (p < 0.001). The combination of VS or CD with a pre-setting cement space of 60 μm and the combination of LU or GR with a cement space of 120 μm showed better agreement between the predesigned and actual measured marginal gap widths. For internal adaptation, only the cement space set to 30 μm exceeded the clinically acceptable threshold (200 μm).

CONCLUSIONS

The setting of the cement space and restorative material significantly affected the marginal adaptation of CAD-CAM endocrown restorations. Considering the discrepancy between design and reality, different virtual cement spaces should be applied to ceramic and resin composite materials.

Marginal gap and fracture resistance of implant-supported 3D-printed definitive composite crowns: An in vitro study

OBJECTIVES

To compare the marginal gap and fracture resistance of implant-supported 3-dimensional (3D) printed definitive composite crowns with those fabricated by using 3 different millable materials.

MATERIAL AND METHODS

A prefabricated abutment was digitized by using a laboratory scanner (E4 Lab Scanner) and a complete-coverage maxillary first premolar crown was designed (Dental Designer). Forty crowns were fabricated either by 3D printing (Saremco Print Crowntec, SP) or milling (Brilliant Crios, BC; Vita Enamic, VE; Cerasmart 270, CS) (n = 10). Baseline marginal gap values were evaluated by measuring 60 predetermined points on an abutment (15 points for each side) with a stereomicroscope at ×40 magnification. Marginal gap values were reevaluated after adhesive cementation. Load-to-fracture test was performed by using a universal testing machine. Two-way analysis of variance (ANOVA) was used to evaluate the effect of material type and cementation on marginal gap values. While Tukey HSD tests were used to compare the materials' marginal gap values before and after cementation, the effect of cementation on marginal gap values within each material was analyzed by using paired samples t-tests. Fracture resistance data were analyzed by using 1-way ANOVA (α=0.05).

RESULTS

Material type and cementation significantly affected marginal gap values (P < .001). Regardless of cementation, SP had the lowest marginal gap values (P < .001), while the differences among milled crowns were nonsignificant (P ≥ .14). Cementation significantly increased the marginal gap values (P < .001). Material type did not affect fracture resistance values (F = 1.589, P = .209).

CONCLUSION

Implant-supported 3D-printed composite crowns showed higher marginal adaptation compared with the milled crowns before and after cementation. In addition, all crowns endured similar forces before fracture.

Assessment of the readiness of restorations manufactured by CAD/CAM in terms of marginal fit (Part I)

Background

The master cast is the gold standard for the control and eventual adjustment of restorations produced by conventional procedures. Some digital workflow bypasses the master cast and relies completely on the precision of the CAD/CAM restoration.

Aim

To examine the reproducibility of the margins of CAD/CAM restorations generated from a single digital scan. Also, to check the readiness of these restorations for delivery directly after fabrication without adjustment on a master cast and thereby eliminate the need for the master cast.

Methods

A total of 18 metal substructures made from cobalt chrome alloy were fabricated utilizing a single STL file. The circumference was divided into eight zones. The vertical marginal discrepancy (VMD) was measured at each zone of each metal substructure, with optical microscopy at ×200 magnification.

Results

Measurements of vertical marginal discrepancy were in a range of (-94: 300) with a mean of 62 ± 60 μm. A one-way ANOVA test revealed that the mean VMD is significantly different among the 18 substructures (F17, 1,134 = 63.948, p < 0.001).

Conclusion

Although all the received substructures were fabricated from the same scan file, they were not identical and varied widely, and they were going outside the acceptable range in some zones. Within the limitations of this study, the marginal fit can be improved by extraoral adjustments on the master cast. Thus, skipping the master cast deprives the dentist of delivering a restoration of higher quality.

Comparison of marginal and internal fit of three-unit implant-supported fixed prosthetic substructures fabricated using CAD/CAM systems

OBJECTIVE

This study compared the marginal and internal fit of implant-supported fixed dentures fabricated using CAD/CAM systems.

MATERIALS AND METHODS

A lower jaw model representing partial edentulism was produced. Two dental implants were inserted in the area of teeth 35 and 37, onto which cemented abutments were screwed. The model was scanned using a laboratory scanner and transferred to a design software program for substructure fabrication. Sixty substructures were fabricated out of each group for six substructure types (n = 10), cast Co-Cr (control), milling Co-Cr, laser sintering Co-Cr, titanium (Ti), zirconium, and polyetheretherketone (PEEK) substructures. The marginal and internal fit was evaluated using a silicone replica viewed under a stereomicroscope. The data were analyzed using the statistical package program for social sciences (SPSS, Chicago, IL, USA, v. 17) at a significance level of 0.05. Marginal and internal gaps were compared using the one-way ANOVA test and Tukey's post hoc test. The differences between abutment teeth were determined using the independent sample t-test.

RESULTS

There was a significant difference in the marginal gap between PEEK and Ti groups (p < 0.05) but no difference between other groups (p > 0.05). There was a significant difference in the internal gap between PEEK, laser sintering Co-Cr, and milling Co-Cr groups (p < 0.05) but no difference between other groups (p > 0.05). The PEEK group had a higher marginal gap than the Ti group and a higher internal gap than the DMLS Co-Cr group (p < 0.05).

CONCLUSION

All substructures have a marginal and internal fit within acceptable clinical limits.

CLINICAL RELEVANCE

This in vitro study suggests that materials and techniques used in CAD/CAM systems improve the fitting accuracy of implant-supported fixed restorations.

Marginal Integrity of CAD/CAM Ceramic Crowns Using Two Different Finish Line Designs

OBJECTIVE

Research on evaluation of crowns made by the latest contemporary dental computer-aided design/computer-aided manufacturing (CAD/CAM) systems for their marginal adaptation is scarce. The purpose of this in vitro study was to evaluate the marginal integrity of crowns fabricated by the latest Chairside Economical Restorations of Esthetic Ceramic (CEREC) system using 2 different finish line preparation designs: chamfer and shoulder.

MATERIALS AND METHODS

Typodont teeth were divided equally into 2 groups, A and B. The teeth were prepared for full coverage crowns with a shoulder (group A) and chamfer (group B) finish line design. An experienced prosthodontist prepared all crown preparations. Evaluation of 6 sites per sample was completed by 2 calibrated, experienced prosthodontists using the modified US Public Health Services (USPHS) criteria. The descriptive statistics and Z-test were used to evaluate the results.

RESULTS

A total of 180 teeth were included in the study (90 teeth in each group). Only 2 crowns in group A and 1 crown in group B were clinically unacceptable. There was no statistical significance (p = 0.282) between the 2 groups regarding finish line design.

CONCLUSIONS

The CEREC system provides clinically acceptable crowns and can safely be utilized in dental treatment. Therefore, CAD/CAM restorations could be considered as a safe treatment modality by dental professionals.

3D optical profilometer analysis of the marginal gap of Class II restorations made with different materials for vital pulp therapy procedures

We considered Class II dental cavities in critical tooth areas concerned with vital pulp therapy, and evaluated the marginal gap after treatment with Biodentine and Geristore, and one composite after either etching and adhesive (V2) and after use of a self-etching system (iBond Universal). We measured the surface morphology at the marginal gap by optical profilometry, and carried out analysis of the 3D data according to a new effective definition of marginal gap. The defined quantity was assessed for statistical significance of the apparent differences. The largest gaps appeared for Geristore (first) and Biodentine (not significantly lower), whereas the gaps of the composite controls were both lower, the lowest being the two-step self-etched system with respect to the three-steps etched and adhesive system, yet without statistical significance. Obviously, there is still room for improvement of the vital pulp therapy restorative materials, as compared to the use of standard composite systems.

Marginal and internal fit of full ceramic crowns milled using CADCAM systems on cadaver full arch scans

Background

Chairside systems are becoming more popular for fabricating full-ceramic single restorations, but there is very little knowledge about the effect of the entire workflow process on restoration fit. Therefore, this study aimed to compare the absolute marginal discrepancy (AMD) and the full internal fit (FULL) of all-ceramic crowns made by two chairside systems, Planmeca FIT and CEREC, with detailed and standard mill settings.

Methods

One upper molar was prepared for an all-ceramic crown in human cadaver maxilla. Full-arch scans were made by Emerald or Omnicam four times each. Twenty-four e.max crowns were designed and milled by the Planmill 30s or 40s or CEREC MCXL mills with either detailed or standard settings. The cadaver tooth was extracted, and each crown was fixed on it and scanned by a high-resolution microCT scanner. The AMD and FULL were measured digitally in mesio-distal and bucco-lingual 2D slices. The actual and predicted times of the milling were also registered.

Results

No differences were observed between detailed or standard settings in either system. The AMD was significantly higher with CEREC (132 ± 12 μm) than with either Planmill 30s (71 ± 6.9 μm) or 40s (78 ± 7.7 μm). In standard mode, the FULL was significantly higher with CEREC (224 ± 9.6 μm) than with either Planmill 30s (169 ± 8.1 μm) or 40s (178 ± 8.5 μm). There was no difference between actual and predicted time with the two Planmeca models, but with CEREC, the actual time was significantly higher than the predicted time. The 30s had significantly higher actual and predicted times compared to all other models. Across all models, the average milling time was 7.2 min less in standard mode than in detailed mode.

Conclusions

All fit parameters were in an acceptable range. No differences in fit between Planmeca models suggest no effect of spindle number on accuracy. The detailed setting has no improvement in the marginal or internal fit of the restoration, yet it increases milling time.

The influence of different cement spaces on the marginal gap of CAD/CAM all-ceramic crowns

BACKGROUND

The purpose of this study was to measure the marginal gaps of CAD/CAM all-ceramic crowns constructed using different cement spaces on crown preparations created by undergraduate students.

METHODS

Twenty-four Columbia model lower left first molars with assessed tapers and reduction volumes (RV) were recruited to receive complete coverage E.max crowns. Three E.max crowns were digitally designed and milled for each crown preparation using three different cement spaces: 50 μm (CS-50), 100 μm (CS-100), 200 μm (CS-200). Each crown was seated onto its original crown preparation and three vertical marginal gap measurements were taken at four locations (mid-buccal, mid-lingual, mid-mesial, mid-distal) using a stereomicroscope. The mean marginal gap (MMG) was calculated for each crown and each individual tooth surface.

RESULTS

The MMG was statistically significantly different for each of the three cement spaces (126 μm for CS-50, 89 μm for CS-100, and 75 μm for CS-200) (P < 0.0001). A taper of between 20 and 30° produced the smallest MMG. Insufficient RV caused significantly larger MMGs. The buccal margin had significantly smaller MMGs than all other measured surfaces.

CONCLUSIONS

The most accurate margins of digitally designed all-ceramic crowns constructed on simulation teeth prepared by undergraduate students were observed when using a 200 μm cement space.

Five-axis laser milling system that realizes more accurate zirconia CAD/CAM crowns by direct milling from fully sintered blocks

Directly milling zirconia computer-aided design (CAD)/computer-aided manufacturing (CAM) crowns from fully sintered zirconia blocks using a five-axis laser milling system, compared with three-axis milling and full sintering by heating milled semi-sintered crowns, was investigated. The mechanical characteristics of zirconia specimens were similar across groups. The order of the marginal gap was three-axis>conventional (lingual thickness of 1.5 mm>0.5 mm)>five-axis group (close to zero). The marginal shape was almost perfectly circular in all groups. The internal corner shape and gap were almost perfect for the five-axis milled crown but not for conventional and three-axis crowns. The roundness of the marginal and internal shapes was almost perfect in the five-axis milling group but not for the three-axis and conventional groups. These small distortions result in large marginal gaps. Results of the present study suggest the superiority of the five-axis milling system in creating a zirconia prosthesis.

Marginal adaptation of lithium disilicate ceramic crowns cemented with three different resin cements

OBJECTIVES

The cementation process and cementation materials have an influence on the marginal adaptation of restorations. The gap could be affected by thermal and mechanical loading (TCML). The computerized x-ray microtomography (μCT) method offers the possibility of measuring the marginal gap without destruction of the restoration. The aim of this study was to evaluate the marginal gap (MG) and the absolute marginal discrepancy (AMD) before and after TCML.

MATERIALS AND METHODS

Thirty-nine human premolars were prepared for full ceramic crowns made of lithium disilicate. The crowns were cemented by three different resins-Panavia F 2.0, Variolink II, and Relyx Unicem. The MG and AMD were evaluated by μCT before and after TCML.

RESULTS

Panavia F 2.0 had the lowest MG (before 118 μm-after TMCL 124 μm) and AMD (before 145 μm-after TMCL 154 μm), followed by Relyx Unicem (MG: before 164 μm-after TCML 155 μm; AMD: before 213 μm-after TMCL 209 μm) and Variolink II (MG: before 317 μm-after TMCL 320 μm; AMD: before 412 μm-after TMCL 406 μm). The differences were statistically significant before and after TCML. Rather than TCML, it appeared the resin cement was responsible for differences between the MG and AMD before and after TCML.

CONCLUSIONS

μCT is an accurate technique for assessing cemented restorations. Panavia F 2.0 has the lowest MG and AMD before and after TCML.

CLINICAL RELEVANCE

The resin material that features a three-step protocol (Variolink II) produced higher MG and AMG values than the Panavia or Relyx Unicem varieties with less or no intermediate steps at all.

In vitro Evaluation of the Marginal Fit and Internal Adaptation of Zirconia and Lithium Disilicate Single Crowns: Micro-CT Comparison Between Different Manufacturing Procedures

Background:

Prosthetic precision can be affected by several variables, such as restorative materials, manufacturing procedures, framework design, cementation techniques and aging. Marginal adaptation is critical for long-term longevity and clinical success of dental restorations. Marginal misfit may lead to cement exposure to oral fluids, resulting in microleakage and cement dissolution. As a consequence, marginal discrepancies enhance percolation of bacteria, food and oral debris, potentially causing secondary caries, endodontic inflammation and periodontal disease.

Objective:

The aim of the present in vitro study was to evaluate the marginal and internal adaptation of zirconia and lithium disilicate single crowns, produced with different manufacturing procedures.

Methods:

Forty-five intact human maxillary premolars were prepared for single crowns by means of standardized preparations. All-ceramic crowns were fabricated with either CAD-CAM or heat-pressing procedures (CAD-CAM zirconia, CAD-CAM lithium disilicate, heat-pressed lithium disilicate) and cemented onto the teeth with a universal resin cement. Non-destructive micro-CT scanning was used to achieve the marginal and internal gaps in the coronal and sagittal planes; then, precision of fit measurements were calculated in a dedicated software and the results were statistically analyzed.

Results:

The heat-pressed lithium disilicate crowns were significantly less accurate at the prosthetic margins (p<0.05) while they performed better at the occlusal surface (p<0.05). No significant differences were noticed between CAD-CAM zirconia and lithium disilicate crowns (p>0.05); nevertheless CAD-CAM zirconia copings presented the best marginal fit among the experimental groups. As to the thickness of the cement layer, reduced amounts of luting agent were noticed at the finishing line, whereas a thicker layer was reported at the occlusal level.

Conclusion:

Within the limitations of the present in vitro investigation, the following conclusions can be drawn: the recorded marginal gaps were within the clinical acceptability irrespective of both the restorative material and the manufacturing procedures; the CAD-CAM processing techniques for both zirconia and lithium disilicate produced more consistent marginal gaps than the heat-pressing procedures; the tested universal resin cement can be safely used with both restorative materials.

Evaluation of marginal and internal gap of three-unit metal framework according to subtractive manufacturing and additive manufacturing of CAD/CAM systems

PURPOSE

To evaluate the fit of a three-unit metal framework of fixed dental prostheses made by subtractive and additive manufacturing.

MATERIALS AND METHODS

One master model of metal was fabricated. Twenty silicone impressions were made on the master die, working die of 10 poured with Type 4 stone, and working die of 10 made of scannable stone. Ten three-unit wax frameworks were fabricated by wax-up from Type IV working die. Stereolithography files of 10 three-unit frameworks were obtained using a model scanner and three-dimensional design software on a scannable working die. The three-unit wax framework was fabricated using subtractive manufacturing (SM) by applying the prepared stereolithography file, and the resin framework was fabricated by additive manufacturing (AM); both used metal alloy castings for metal frameworks. Marginal and internal gap were measured using silicone replica technique and digital microscope. Measurement data were analyzed by Kruskal-Wallis H test and Mann-Whitney U-test (α=.05).

RESULTS

The lowest and highest gaps between premolar and molar margins were in the SM group and the AM group, respectively. There was a statistically significant difference in the marginal gap among the 3 groups (P<.001). In the marginal area where pontic was present, the largest gap was 149.39 ± 42.30 µm in the AM group, and the lowest gap was 24.40 ± 11.92 µm in the SM group.

CONCLUSION

Three-unit metal frameworks made by subtractive manufacturing are clinically applicable. However, additive manufacturing requires more research to be applied clinically.

Evaluation of marginal and internal gaps in single and three-unit metal frameworks made by micro-stereolithography

PURPOSE

The purpose of this study is to compare single and three-unit metal frameworks that are produced by micro-stereolithography.

MATERIALS AND METHODS

Silicone impressions of a selected molar and a premolar were used to make master abutments that were scanned into a stereolithography file. The file was processed with computer aided design software to create single and three-unit designs from which resin frameworks were created using micro-stereolithography. These resin frameworks were subjected to investment, burnout, and casting to fabricate single and three-unit metal ones that were measured under a digital microscope by using the silicone replica technique. The measurements were verified by means of the Mann-Whitney U test (α=.05).

RESULTS

The marginal gap was 101.9 ± 53.4 µm for SM group and 104.3 ± 62.9 µm for TUM group. The measurement of non-pontics in a single metal framework was 93.6 ± 43.9 µm, and that of non-pontics in a three-unit metal framework was 64.9 ± 46.5 µm. The dimension of pontics in a single metal framework was 110.2 ± 61.4 µm, and that of pontics in a three-unit metal framework was 143.7 ± 51.8 µm.

CONCLUSION

The marginal gap was smaller for the single metal framework than for the three-unit one, which requires further improvement before it can be used for clinical purposes.

Comparison and evaluation of marginal and internal gaps in cobalt-chromium alloy copings fabricated using subtractive and additive manufacturing

PURPOSE

To evaluate the marginal and internal gaps of cobalt-chromium (Co-Cr) alloy copings fabricated using subtractive and additive manufacturing.

METHODS

A study model of an abutment tooth 46 was prepared by a 2-step silicone impression with dental stone. Fifteen stereolithography files for Co-Cr alloy copings were compiled using a model scanner and dental CAD software. Using the lost wax (LW), wax block (WB), soft metal block (SMB), microstereolithography (μ-SLA), and selected laser melting (SLM) techniques, 15 Co-Cr alloy copings were fabricated per group. The marginal and internal gaps of these Co-Cr alloy copings were measured using a digital microscope (160×), and the data obtained were analyzed using the non-parametric Kruskal-Wallis H-test and post-hoc Mann-Whitney U-test with Bonferroni correction.

RESULTS

The mean values of the marginal, axial wall, and occlusal gaps were 91.8, 83.4, and 163μm in the LW group; 94.2, 77.5, and 122μm in the WB group; 60.0, 79.4, and 90.8μm in the SMB group; 154, 72.4, and 258μm in the μ-SLA group; and 239, 73.6, and 384μm in the SLM group, respectively. The differences in the marginal and occlusal gaps between the 5 groups were statistically significant (P<.05).

CONCLUSIONS

The marginal gaps of the LW, WB, and SMB groups were within the clinically acceptable limit, but further improvements in the μ-SLA and SLM approaches may be required prior to clinical implementation.

Evaluation of marginal and internal gaps of Ni-Cr and Co-Cr alloy copings manufactured by microstereolithography

PURPOSE

The purpose of this study was to evaluate the marginal and internal gaps of Ni-Cr and Co-Cr copings, fabricated using the dental µ-SLA system.

MATERIALS AND METHODS

Ten study dies were made using a two-step silicone impression with a dental stone (type IV) from the master die of a tooth. Ni-Cr (NC group) and Co-Cr (CC group) alloy copings were designed using a dental scanner, CAD software, resin coping, and casting process. In addition, 10 Ni-Cr alloy copings were manufactured using the lost-wax technique (LW group). The marginal and internal gaps in the 3 groups were measured using a digital microscope (160 ×) with the silicone replica technique, and the obtained data were analyzed using the non-parametric Kruskal-Wallis H test. Post-hoc comparisons were performed using Bonferroni-corrected Mann-Whitney U tests (α=.05).

RESULTS

The mean (±standard deviation) values of the marginal, chamfer, axial wall, and occlusal gaps in the 3 groups were as follows: 81.5±73.8, 98.1±76.1, 87.1±44.8, and 146.8±78.7 µm in the LW group; 76.8±48.0, 141.7±57.1, 80.7±47.5, and 194.69±63.8 µm in the NC group; and 124.2±52.0, 199.5±71.0, 67.1±37.6, and 244.5±58.9 µm in the CC group.

CONCLUSION

The marginal gap in the LW and NC groups were clinically acceptable. Further improvement is needed for CC group to be used clinical practice.

Comparison of marginal fit of cemented zirconia copings manufactured after digital impression with lava™ C.O.S and conventional impression technique

Background

Evaluation of the marginal fit of cemented zirconia copings manufactured after digital impression with Lava™ Chairside Oral Scanner in comparison to that of zirconia copings manufactured after conventional impressions with polyvinyl siloxane.

Methods

A prepared typodont tooth #36, was replicated 40 times with a vinyl silicone and precise model resin. The dies were randomly divided into two groups according to the impression taking technique. Digital impressions with Lava™ C.O.S. and conventional impressions were taken according to the group. Subsequently zirconia copings were manufactured and cemented on their respective dies with zinc oxide phosphate cement. After embedding in resin, mesio-distal section of each coping was performed with a diamond saw in order to obtain two slices. One half of the specimen was used for evaluation with an optical microscope (OM) and the other half for evaluation with a scanning electron microscope (SEM). Marginal gap (MG) and absolute marginal discrepancy (AMD) were measured mesial and distal on each slice.

Results

No significant difference of the marginal parameters between the digital and the conventional group was found. The mean values for MG in the digital group were 96.28 μm (+/−43.21 μm) measured with the OM and 99.26 μm (+/−48.73 μm) measured with the SEM, respectively. AMD mean values were 191.54 μm (+/−85.42 μm) measured with the optical microscope and 211.6 μm (+/−96.55 μm) with the SEM. For the conventional group the mean MG values were 94.84 μm (+/−50.77 μm) measured with the OM and 83.37 μm (+/−44.38 μm) measured with the SEM, respectively. AMD mean values were 158.60 μm (+/−69.14 μm) for the OM and 152.72 μm (+/−72.36) for the SEM.

Conclusions

Copings manufactured after digital impression with Lava™ C.O.S. show comparable marginal parameters with the copings manufactured after conventional impression with polyvinyl syloxane. The mean MG values of both groups fit in the clinically acceptable range.

Electronic supplementary material

The online version of this article (doi:10.1186/s12903-016-0323-8) contains supplementary material, which is available to authorized users.

Marginal and internal fit of nano-composite CAD/CAM restorations

Objectives

The purpose of this study was to compare the marginal and internal fit of nano-composite CAD-CAM restorations.

Materials and Methods

A full veneer crown and an mesio-occluso-distal (MOD) inlay cavity, which were prepared on extracted human molars, were used as templates of epoxy resin replicas. The prepared teeth were scanned and CAD-CAM restorations were milled using Lava Ultimate (LU) and experimental nano-composite CAD/CAM blocks (EB) under the same milling parameters. To assess the marginal and internal fit, the restorations were cemented to replicas and were embedded in an acrylic mold for sectioning at 0.5 mm intervals. The measured gap data were pooled according to the block types and measuring points for statistical analysis.

Results

Both the block type and measuring point significantly affected gap values, and their interaction was significant (p = 0.000). In crowns and inlays made from the two blocks, gap values were significantly larger in the occlusal area than in the axial area, while gap values in the marginal area were smallest (p < 0.001). Among the blocks, the restorations milled from EB had a significantly larger gap at all measuring points than those milled from LU (p = 0.000).

Conclusions

The marginal and internal gaps of the two nano-composite CAD/CAM blocks differed according to the measuring points. Among the internal area of the two nano-composite CAD/CAM restorations, occlusal gap data were significantly larger than axial gap data. The EB crowns and inlays had significantly larger gaps than LU restorations.

Bioactive glass fillers reduce bacterial penetration into marginal gaps for composite restorations

OBJECTIVE

Bioactive glass (BAG) is known to possess antimicrobial and remineralizing properties; however, the use of BAG as a filler for resin based composite restorations to slow recurrent caries has not been studied. Accordingly, the objective of this study was to investigate the effect of adding 15wt% BAG to a resin composite on bacterial biofilms penetrating into marginal gaps of simulated tooth fillings in vitro during cyclic mechanical loading.

METHODS

Human molars were machined into approximately 3mm thick disks of dentin and 1.5-2mm deep composite restorations were placed. A narrow 15-20 micrometer wide dentin-composite gap was allowed to form along half of the margin by not applying dental adhesive to that region. Two different 72wt% filled composites were used, one with 15wt% BAG filler (15BAG) and the balance silanated strontium glass and one filled with aerosol silica and silanated strontium glass without BAG (0BAG-control). Samples of both groups had Streptococcus mutans biofilms grown on the surface and were tested inside a bioreactor for two weeks while subjected to periods of cyclic mechanical loading. After post-test biofilm viability was confirmed, each specimen was fixed in glutaraldehyde, gram positive stained, mounted in resin and cross-sectioned to reveal the gap profile. Depth of biofilm penetration for 0BAG and 15BAG was quantified as the fraction of gap depth. The data were compared using a Student's t-test.

RESULTS

The average depth of bacterial penetration into the marginal gap for the 15BAG samples was significantly smaller (∼61%) in comparison to 0BAG, where 100% penetration was observed for all samples with the biofilm penetrating underneath of the restoration in some cases.

SIGNIFICANCE

BAG containing resin dental composites reduce biofilm penetration into marginal gaps of simulated tooth restorations. This suggests BAG containing composites may have the potential to slow the development and propagation of secondary tooth decay at restoration margins.

Comparison of prosthetic models produced by traditional and additive manufacturing methods

PURPOSE

The purpose of this study was to verify the clinical-feasibility of additive manufacturing by comparing the accuracy of four different manufacturing methods for metal coping: the conventional lost wax technique (CLWT); subtractive methods with wax blank milling (WBM); and two additive methods, multi jet modeling (MJM), and micro-stereolithography (Micro-SLA).

MATERIALS AND METHODS

Thirty study models were created using an acrylic model with the maxillary upper right canine, first premolar, and first molar teeth. Based on the scan files from a non-contact blue light scanner (Identica; Medit Co. Ltd., Seoul, Korea), thirty cores were produced using the WBM, MJM, and Micro-SLA methods, respectively, and another thirty frameworks were produced using the CLWT method. To measure the marginal and internal gap, the silicone replica method was adopted, and the silicone images obtained were evaluated using a digital microscope (KH-7700; Hirox, Tokyo, Japan) at 140X magnification. Analyses were performed using two-way analysis of variance (ANOVA) and Tukey post hoc test (α=.05).

RESULTS

The mean marginal gaps and internal gaps showed significant differences according to tooth type (P<.001 and P<.001, respectively) and manufacturing method (P<.037 and P<.001, respectively). Micro-SLA did not show any significant difference from CLWT regarding mean marginal gap compared to the WBM and MJM methods.

CONCLUSION

The mean values of gaps resulting from the four different manufacturing methods were within a clinically allowable range, and, thus, the clinical use of additive manufacturing methods is acceptable as an alternative to the traditional lost wax-technique and subtractive manufacturing.

Evaluation of marginal fit of 2 CAD-CAM anatomic contour zirconia crown systems and lithium disilicate glass-ceramic crown

PURPOSE

This study was to evaluate the marginal fit of two CAD-CAM anatomic contour zirconia crown systems compared to lithium disilicate glass-ceramic crowns.

MATERIALS AND METHODS

Shoulder and deep chamfer margin were formed on each acrylic resin tooth model of a maxillary first premolar. Two CAD-CAM systems (Prettau®Zirconia and ZENOSTAR®ZR translucent) and lithium disilicate glass ceramic (IPS e.max®press) crowns were made (n=16). Each crown was bonded to stone dies with resin cement (Rely X Unicem). Marginal gap and absolute marginal discrepancy of crowns were measured using a light microscope equipped with a digital camera (Leica DFC295) magnified by a factor of 100. Two-way analysis of variance (ANOVA) and post-hoc Tukey's HSD test were conducted to analyze the significance of crown marginal fit regarding the finish line configuration and the fabrication system.

RESULTS

The mean marginal gap of lithium disilicate glass ceramic crowns (IPS e.max®press) was significantly lower than that of the CAD-CAM anatomic contour zirconia crown system (Prettau®Zirconia) (P<.05). Both fabrication systems and finish line configurations significantly influenced the absolute marginal discrepancy (P<.05).

CONCLUSION

The lithium disilicate glass ceramic crown (IPS e.max®press) had significantly smaller marginal gap than the CAD-CAM anatomic contour zirconia crown system (Prettau®Zirconia). In terms of absolute marginal discrepancy, the CAD-CAM anatomic contour zirconia crown system (ZENOSTAR®ZR translucent) had under-extended margin, whereas the CAD-CAM anatomic contour zirconia crown system (Prettau®Zirconia) and lithium disilicate glass ceramic crowns (IPS e.max®press) had overextended margins.

Evaluation of fit and efficiency of CAD/CAM fabricated all-ceramic restorations based on direct and indirect digitalization: a double-blinded, randomized clinical trial

OBJECTIVES

The aim of this clinical trial was to evaluate the marginal and internal fit of CAD/CAM fabricated zirconia crowns and three-unit fixed dental prostheses (FDPs) resulting from direct versus indirect digitalization. The efficiency of both methods was analyzed.

MATERIALS AND METHODS

In 25 patients, 17 single crowns and eight three-unit FDPs were fabricated with all-ceramic zirconia using CAD/CAM technology. Each patient underwent two different impression methods; a computer-aided impression with Lava C.O.S. (CAI) and a conventional polyether impression with Impregum pent soft (CI). The working time for each group was recorded. Before insertion, the marginal and internal fit was recorded using silicone replicas of the frameworks. Each sample was cut into four sections and evaluated at four sites (marginal gap, mid-axial wall, axio-occlusal transition, centro-occlusal site) under ×64 magnification. The Mann-Whitney U test was used to detect significant differences between the two groups in terms of marginal and internal fit (α = 0.05).

RESULTS

The mean for the marginal gap was 61.08 μm (±24.77 μm) for CAI compared with 70.40 μm (±28.87 μm) for CI, which was a statistically significant difference. The other mean values for CAI and CI, respectively, were as follows in micrometers (± standard deviation): 88.27 (±41.49) and 92.13 (±49.87) at the mid-axial wall; 144.78 (±46.23) and 155.60 (±55.77) at the axio-occlusal transition; and 155.57 (49.85) and 171.51 (±60.98) at the centro-occlusal site. The CAI group showed significantly lower values of internal fit at the centro-occlusal site. A quadrant scan with a computer-aided impression was 5 min 6 s more time efficient when compared with a conventional impression, and a full-arch scan was 1 min 34 s more efficient.

CONCLUSIONS

Although both direct and indirect digitalization facilitate the fabrication of single crowns and three-unit FDPs with clinically acceptable marginal fit, a significantly better marginal fit was noted with direct digitalization. Digital impressions are also less time-consuming for the dental practitioner and the patient.

CLINICAL RELEVANCE

The results show that a direct, intraoral, digitalized impression technique is more accurate and efficient when compared with conventional impressions in fabricating single crowns and three-unit FDPs.

Cyclic mechanical loading promotes bacterial penetration along composite restoration marginal gaps

OBJECTIVES

Secondary caries is the most common reason for composite restoration replacement and usually forms between dentin and the filling. The objective of this study was to investigate the combined effect of cyclic loading and bacterial exposure on bacterial penetration into gaps at the interface between dentin and resin composite restorative material using a novel bioreactor system and test specimen design.

METHODS

Human molars were machined into 3mm thick disks with 2mm deep × 5 mm diameter cavity preparations into which composite restorations were placed. A ∼ 15-30 μm (small) or ∼ 300 μm wide (large) marginal gap was introduced along half of the interface between the dentin and restoration. Streptococcus mutans UA 159 biofilms were grown on each sample prior to testing each in a bioreactor both with and without cyclic loading. Both groups of samples were tested for 2 weeks and post-test biofilm viability was confirmed with a live-dead assay. Samples were fixed, mounted and cross-sectioned to reveal the gaps and observe the depth of bacterial penetration.

RESULTS

It was shown that for large gap samples the bacteria easily penetrated to the full depth of the gap independent of loading or non-loading conditions. The results for all cyclically loaded small gap samples show a consistently deep bacterial penetration down 100% of the gap while the average penetration depth was only 67% for the non-loaded samples with only two of six samples reaching 100%.

SIGNIFICANCE

A new bioreactor was developed that allows combining cyclic mechanical loading and bacterial exposure of restored teeth for bacterial biofilm and demineralization studies. Cyclic loading was shown to aid bacterial penetration into narrow marginal gaps, which could ultimately promote secondary caries formation.

Correlation between polymerization stress and interfacial integrity of composites restorations assessed by different in vitro tests

OBJECTIVE

to correlate polymerization stress data obtained under two compliance conditions with those from different interfacial quality tests.

METHODS

Six commercial composites were tested (Filtek Z250/3M ESPE, Heliomolar/Ivoclar Vivadent, Aelite LS Posterior/Bisco, Filtek Supreme/3M ESPE, ELS/Saremco and Venus Diamond/Heraeus Kulzer). Bond strength (BS) was evaluated by push-out test on slices of bovine dentin (2-mm thick) with tapered cavities. For microleakage (ML) and gap analysis, cylindrical cavities in bovine incisors (4-mm diameter and 1.5-mm height) were restored and epoxy replicas of the cavo-surface margins were prepared for analysis under scanning electron microscopy (200×). The same specimens were submitted to a microleakage protocol using AgNO3 as tracer. After sectioned twice perpendicularly, ML was determined under a stereomicroscope (60×). Polymerization stress (PS, n=5) was determined by the insertion of the composite (h=1.5mm) between poly(methyl methacrylate), PMMA, or glass rods (Ø=4 mm) attached to a universal testing machine. Data were analyzed using Kruskal-Wallis (ML and gaps), and ANOVA/Tukey (BS and PS, α=5%). Pearson's correlation test was used to verify correlations between stress and interfacial quality.

RESULTS

BS varied from 4.7 to 7.9 MPa. Average ML data ranged from 0.34 to 0.89 mm. Maximum ML varied from 0.61 to 1.34 mm. Gap incidence varied from 13 to 47%. PS ranged from 2.5 to 4.4 MPa in PMMA, and between 2.1 and 8.2 in glass. Statistically significant correlations were observed between stress and interfacial quality, except between BS and PS in glass. These correlations were stronger when PMMA was used as bonding substrate.

CONCLUSIONS

PS data obtained using a high compliance testing system showed a stronger correlation with "in vitro" interfacial integrity results, compared to data from a low compliance system.

Comparison of Marginal Gap and Microleakage in Copy-Milled and Cad-Milled Zirconia Copings Bonded Using Light Cure and Chemical Cure Resin Bonding Systems

This in vitro study assessed the marginal gap and marginal microleakage in zirconia copings fabricated using two computer aided techniques- CAD milling and Copy milling and cemented to respective tooth preparations using two resin bonding systems, light cure and self-cure resin bonding systems. 32 extracted premolars were prepared to receive zirconia copings fabricated using CAD/CAM and Copy milling techniques. Once the copings were fabricated, the samples were evaluated for marginal fit prior to cementation through microscopic observation. Evaluation of marginal gap was done again after cementation, in order to incorporate the influence of the resin bonding system on the marginal microgap. The specimens were evaluated under the stereomicroscope for micro-leakage using commercial software. A comparative statistical analysis was done following data collection using Mann-Whitney U test, Wilcoxon test and chi-square test. The data collected regarding marginal gap was well within 120 µ, which is in accordance with previous studies. However, Copy milled specimens showed statistically lesser marginal gap when compared to CAD milled specimens. While comparing microleakage, it was observed that the microleakage in Copy milled specimens bonded with light cure resin bonded cement was statistically lesser than that of specimens cemented with chemical cure resin cement.(P = 0.003). This in vitro study concluded that Copy milling technique fabricated zirconia restorations with lesser marginal gap and microleakage score in comparison to CAD milled samples. Light cure resin bonding system also proved to be more effective option compared to self cure resin bonding systems. However, the limitations of this study should be taken into concern and further research should be aimed at a larger sample size to validate the results.

Evaluation of different approaches for using a laser scanner in digitization of dental impressions

PURPOSE

This study aimed to investigate the potential clinical application of digitized silicone rubber impressions by comparing the accuracy of zirconia 3-unit fixed partial dentures (FPDs) fabricated from 2 types of data (working model and impression) obtained from a laser scanner.

MATERIALS AND METHODS

Ten working models and impressions were prepared with epoxy resin and vinyl polysiloxane, respectively. Based on the data obtained from the laser scanner (D-700; 3Shape A/S, Copenhagen, Denmark), a total of 20 zirconia frameworks were prepared using a dental CAD/CAM system (DentalDesigner; 3shape A/S, Copenhagen, Denmark / Ener-mill, Dentaim, Seoul, Korea). The silicone replicas were sectioned into four pieces to evaluate the framework fit. The replicas were imaged using a digital microscope, and the fit of the reference points (P1, P2, P3, P4, P5, P6, and P7) were measured using the program in the device. Measured discrepancies were divided into 5 categories of gaps (MG, CG, AWG, AOTG, OG). Data were analyzed with Student's t-test (α=0.05), repeated measures ANOVA and two-way ANOVA (α=0.05).

RESULTS

The mean gap of the zirconia framework prepared from the working models presented a narrower discrepancy than the frameworks fabricated from the impression bodies. The mean of the total gap in premolars (P=.003) and molars (P=.002) exhibited a statistical difference between two groups.

CONCLUSION

The mean gap dimensions of each category showed statistically significant difference. Nonetheless, the digitized impression bodies obtained with a laser scanner were applicable to clinical settings, considering the clinically acceptable marginal fit (120 µm).

Comparative Evaluation of Marginal and Internal Gap of Co-Cr Copings Fabricated from Conventional Wax Pattern, 3D Printed Resin Pattern and DMLS Tech: An In Vitro Study

Accuracy of the fit of the restoration has always remained as one of the primary factors in determining success of the restoration. A well fitting restoration needs to be accurate both along its margins and internal surface. This study was conducted to comparatively evaluate the marginal gap and internal gap of cobalt-chromium (Co-Cr) copings fabricated by conventional casting procedures and with direct metal laser sintering (DMLS) technique. Among the total of 30 test samples 10 cast copings were made from inlay casting wax and 10 from 3D printed resin pattern. 10 copings were obtained from DMLS technique. All the 30 test samples were then cemented sequentially on stainless steel model using pressure indicating paste and evaluated for vertical marginal gap in 8 predetermined reference areas. All copings were then removed and partially sectioned and cemented sequentially on same master model for evaluation of internal gap at 4 predetermined reference areas. Both marginal gap and internal gap were measured in microns using video measuring system (VMS2010F). The results obtained for both marginal and internal gap were statistically analyzed and the values fall within the clinically acceptable range. The DMLS technique had an edge over the other two techniques used, as it exhibited minimal gap in the marginal region which is an area of chief concern.

A comparison of marginal fit of glass infiltrated alumina copings fabricated using two different techniques and the effect of firing cycles over them

PURPOSE

This study evaluated marginal fit of glass infiltrated alumina cores fabricated using two techniques and their marginal stability after firing cycles of veneering porcelain.

MATERIALS AND METHODS

Fifteen standardized all-ceramic crowns were fabricated on a metal die using each technique: slip cast technique of VITA In-Ceram sprint Alumina (Group A as control) and plastic foil matrix technique of Turkom-Cera fused alumina core system (Group B). Copings were compared between groups and within groups at coping stage and after firing each layer of veneering porcelain. A device was used to standardize seating of copings on the metal die and positioning of the specimens under the microscope after each stage of fabrication. The specimens were not cemented and marginal gap was measured using an image analyzing software (Imagepro Express) on the photographs captured under an optical microscope. Two tailed unpaired 't test' was used to compare marginal gaps in two groups and one way ANOVA was used to analyze marginal distortion within each group at 95% confidence interval.

RESULTS

The marginal gap was smaller at the coping stage in group B (60 + 30 µm) than group A (81 + 21 µm) with statistical significance. After firing of veneering porcelain the difference was insignificant. At the final stage, both groups exhibited lower mean marginal gaps than at the initial coping stage with the difference of 11.75 µm for group A and 11.94 µm for group B, but it was statistically insignificant due to high value of standard deviation.

CONCLUSION

Within the limitations of this study, it was concluded that both techniques produced copings with comparable and acceptable marginal fit and marginal stability on firing veneering porcelain.