Marginal Discrepancy Research Articles

Marginal Discrepancy and Internal Fit of Bi-Layered and Monolithic Zirconia Fixed Dental Prostheses: An In Vitro Study

This in vitro study evaluated the influence of restoration design (bi-layered vs. monolithic) and manufacturing technique on the marginal discrepancy and internal fit of 3-unit zirconia fixed dental prostheses (FDPs). Mandibular second premolars and second molars were prepared as abutments in a 3-unit zirconia bridge to develop four groups (n = 10 FDPs): MZ: Monolithic zirconia FDPs, ZL: zirconia framework veneered by the hand-layering technique, ZP: zirconia framework veneered by the heat-pressed technique, and CAD-on: zirconia framework veneered by CAD/CAM lithium-disilicate glass–ceramic. All the zirconia FDPs were cemented to their corresponding die replicas using dual-cure resin cement and were subjected to compressive cyclic loading at a load range for half a million cycles using a universal testing machine. FDPs were sectioned mesiodistally to measure the marginal gap and internal fit using scanning electron microscopy. The measurements were taken at pre-assigned points of each abutment. Data were statistically analyzed via a Kruskal–Wallis test (α = 0.05). No significant differences were found between the monolithic and bi-layered zirconia groups in terms of the marginal discrepancy. However, there was a significant difference in the marginal gap between the zirconia groups. The marginal gap between monolithic and bi-layered zirconia FDPs was within the clinically acceptable range (<100 μm). Comparable mean values of the marginal gaps of 3-unit monolithic and veneered zirconia FDPs were found. Therefore, the FDP design and veneering methods did not affect the marginal discrepancy. However, the mean internal gap varied among the experimental groups. As the current in vitro investigation demonstrated equivalent mean values of marginal gaps of both 3-unit monolithic and bi-layered zirconia FPDs, the use of monolithic 3-unit zirconia FPDs would be a viable alternative fabrication technique.

Marginal Fit Evaluation of Zirconia Substructure Computer-Aided Design and Manufacturing (CAD/CAM) by Scanning Electron Microscope

Purpose. This in vitro study compared the vertical marginal discrepancy (MD) and absolute marginal discrepancy (AMD) between the zirconia substructure and titanium (Ti)-base abutment before and after cementation. Material and methods. An intraoral scanner (CEREC Omnicam scanner; Dentsply Sirona) was used to scan the dental model of missing tooth 36 and obtain a three-dimensional virtual model. It was designed and milled for 25 zirconia superstructures (inCoris ZI meso F2 L, Dentsply Sirona). The samples were cemented to Ti bases. The MD and AMD were measured for each sample by using a scanning electron microscope (SEM) before and after cementation. Results. The overall mean values of MD measurements before and after cementation were 14.12 μm and 20.28 μm, respectively. The overall mean values of AMD measurements prior to and after substructure cementation on the Ti base were 54.85 μm and 116.0 μm, respectively. ANOVA revealed significant differences in MD (p = 0.001) and AMD (p < 0.001) before and after cementation. Conclusions. Significant differences were observed in MD and AMD values before and after cementation. The MD and AMD values were significantly lower before cementation than after cementation. The mean MD and AMD values were clinically acceptable.

Comparative in-vitro microscopic evaluation of vertical marginal discrepancy, microhardness, and surface roughness of nickel–chromium in new and recast alloy

Reusing of alloy has become a need of time due to the increasing demand, depletion of resources, and substantial increase in their price. The alloys used require a long-term stay in the oral cavity exposed to a wet environment, so they must have good wear resistance, biocompatibility, and mechanically good strength. In this study, the vertical marginal discrepancy, surface roughness, and microhardness of the new and recast nickel–chromium (base metal) alloys were evaluated. 125 wax patterns were fabricated from a customized stainless steel master die with a heavy chamfer cervical margin divided into 5 groups. Each group had 25 samples. Group A: 25 wax patterns were cast using 100% by weight of new alloy, Group B: the casting was done by using 75% new alloy and 25% alloy by weight, Group C: wax patterns were cast using 50% new alloy and 50% alloy, Group D: 25% new alloy and 75% alloy and Group E: 100% recast alloy. The vertical marginal discrepancy was measured by an analytical scanning microscope, microhardness was tested on a universal testing machine, and surface roughness was on a tester of surface roughness. Castings produced using new alloys were better than those obtained with reused alloys. Alloys can be reused till 50% by weight along with the new alloy and accelerated casting technique can be used to save the lab time to fabricate castings with acceptable vertical marginal discrepancy, microhardness, and surface roughness. This indicated that 50% recasting of (Ni–Cr) can be used as a good alternative for the new alloy from an economical point of view.

Marginal discrepancy of lithium disilicate crowns made with digital and conventional technologies

Digital technologies have brought different workflows to prosthetic rehabilitations, but analyses of the available processes and their influence on the marginal fit of complete crowns are lacking. The purpose of this in vitro study was to evaluate the marginal discrepancy of lithium disilicate complete crowns made with different workflows. Fifty lithium disilicate crowns were made with 5 different workflows (n=10): G1-Analog (control): conventional flow/pressed crown; G2-Hybrid: hybrid flow/milled crown; G3-Hybrid: hybrid flow/pressed crown; G4-Hybrid: hybrid flow/printed wax pattern/pressed crown; G5-Digital: digital flow/milled crown. The specimens were analyzed by scanning electron microscopy, and the data were analyzed for normality and submitted to analysis of variance (ANOVA). Multiple comparisons were made by using the Tukey HSD test (α=.05). G4H (18.1 ±6.6µm) had the lowest mean ±standard deviation marginal discrepancy values, statistically different from G2H (217.9 ±81.4µm), G5D (236.4 ±89µm), and G3H (661.8 ±61.9µm) (P<.05). G3H had the highest marginal discrepancy values and were statistically similar to each other (P>.05). G1A (163.2 ±10.9µm) had intermediate values, statistically similar to those of other groups (P>.05). The conventional method showed no statistical differences in marginal discrepancy compared with methods using digital technology (scanner, software, 3D printer, or milling machine).

Clinical marginal and internal adaptation of single metal-ceramic crowns fabricated by casting, milling, and milling/sintering methods.

To compare the adaptation of single metal-ceramic crowns (MCCs) fabricated by three different methods: lost-wax metal casting (LMC); milling of hard cobalt-chromium (HCC) blanks; and milling of soft presintered cobalt-chromium (SCC) blanks. In this double-blinded parallel randomized clinical trial, 60 single MCCs were fabricated using three different methods. The adaptation of copings was evaluated radiographically, visually, and microscopically. Data were compared among the three groups using Kruskal-Wallis test followed by Dunn post hoc test, one-way ANOVA, and paired t test (α = .05). Radiographic data showed that the frequency of crowns with no marginal discrepancy was significantly higher in the SCC group than the LMC group. Evaluation of marginal adaptation with an explorer revealed that crowns with excellent marginal adaptation had lower frequency in the LMC group than the HCC and SCC groups. In the silicone replica technique, the recorded data revealed no significant difference. Application of porcelain veneering did not affect the adaptation of copings. The SCC and HCC groups showed better clinical outcomes compared to the LMC group. However, all MCCs fabricated by the LMC method, milling of HCC blanks, and milling of SCC blanks had acceptable clinical adaptation.

Influence of thermal aging on the marginal integrity of computer aided design/computer aided manufacturing fabricated crowns

Background/purposeThe adaptation and marginal integrity of computer-aided designed and computer-aided manufactured (CAD/CAM) crowns after exposure to thermal aging need to be investigated. The present in-vitro study was designed to investigate the marginal integrity of CAD/CAM fabricated crowns cemented on extracted teeth after thermocycling aging. Materials and methodsTwenty-six newly extracted human premolars were prepared for full-coverage CAD/CAM crowns and were divided into two groups (leucite-reinforced glass-ceramics and lithium disilicate glass-ceramics). Both crowns’ groups were cemented using dual curing resin cement. All specimen margins were measured for marginal integrity using an imaging system 24 h post cementation; then after 1, 3, and 5 estimated clinical years (10,000, 30,000, and 50,000 thermocycles). Two-way ANOVA analysis were used to determine whether the mean value difference is significantly different (ɑ = 0.05). ResultsThe average margin gaps recorded for leucite-reinforced glass-ceramic crowns were: 82.61 μm initial, and 91.02 μm after 5 estimated clinical year). For the lithium disilicate glass-ceramic crowns, the average margin gaps recorded were: 100.01 μm initial, and 120.21 μm after 5 estimated clinical year. During all measuring intervals, the leucite-reinforced glass-ceramic crown group had a lower marginal discrepancy. No statistically significant difference between the two groups was recorded. ConclusionAfter being subjected to thermocycling, both CAD/CAM ceramic crowns, exhibited an increase in their marginal discrepancy; the difference was within the accepted clinical range.

Comparative Microscopic and Radiographic Evaluation of Proximal Marginal Integrity of CAD/CAM PMMA Crown and CAD/CAM Zirconia Monolithic Crown- An In-vitro Study

ABSTRACTS&#x0D; Aim: to evaluate and compare proximal marginal integrity radiographically and microscopically of CAD/CAM PMMA crown and CAD/CAM monolithic zirconia crown.&#x0D; Materials and methods: Fifteen maxillary or mandibular molar teeth with standardized anatomic preparation for provisional crown and monolithic zirconia crown were scanned with a 3-dimensional laboratory scanner. CAD/CAM crowns were designed 3-dimensionally using exocad software and then milled from presintered blocks in a milling machine. The proximal marginal integrity of CAD/CAM PMMA and monolithic zirconia crown were evaluated radiographically and microscopically. For radiographic evaluation, radiopaque dye is used to measured proximal marginal discrepancies on six reference points on PMMA crown. A digital microscope was used to measure the marginal discrepancies on six reference points on PMMA and zirconia crown. Photographs of the proximal marginal areas were captured at six reference lines at standardized orientation and placement of the samples. In all photographs margin was traced with the help of HiViewSetup software. The mean marginal discrepancies for each group were analysed using chi-square test and man whitney U test.&#x0D; Results: the test result shows there were no significant differences in radiographic and microscopic evaluation of CAD/CAM PMMA crown and CAD/CAM monolithic zirconia crown.&#x0D; Conclusion:&#x0D; It is found that radiographically, PMMA crown had greater marginal discrepancy as compared to the Zirconia crown. Microscopically, PMMA crown and the CAD/CAM monolithic zirconia crown had almost similar marginal discrepancy (statistically non- significant).

Impact of different CAD/CAM materials on internal and marginal adaptations and fracture resistance of endocrown restorations with: 3D finite element analysis

PurposeTo assess and compare the impact of various computers aided design/manufacturing (CAD/CAM) materials on internal and marginal discrepancies, fracture resistance and failure probability of Endocrown restorations with 3D Finite Element analysis.Material and methodsForty devitalized human maxillary first molars were collected. After endodontic treatment, they classified into 4 groups (n = 10) based on the materials used for endocrown fabrication. Group V (Vita-Enamic), Group N (Nacera Hybrid), Group T (Translucent Prettau Zirconia) and Group P (Pekkton ivory). All samples were exposed to artificial aging method simulating one year of clinical service. Silicone replica technique and stereomicroscope (25X) utilized to evaluate the marginal and internal gaps of endocrowns at different areas. Fracture resistance test used for cemented specimens followed by qualitative investigation utilizing Stereomicroscopy. Four models representing four endocrown systems used for restoration of severely-damaged endodontically treated upper first molar were generated for finite element analysis (FEA). Axially and centrally static occlusal compressive load was applied. Modified Von Mises and maximum principal stress values on the remaining tooth structure, cement lines and restorative materials were assessed independently. Resulted data were statistically analyzed at P-value ≤ 0.05.ResultsIn the current study, the highest mean values of internal and marginal discrepancies (μm) among studied groups were reported for Zirconia group (100.300 and 102.650) respectively, while the lowest mean value of internal discrepancy (μm) was observed for Nacera group (69.275) and the lowest mean value of marginal discrepancy (μm) was observed for PEKK group (78.4750). Regarding internal discrepancy, Vita-Enamic and PEKK groups did not exhibit any statistically significant differences (P = 0.293), however zirconia and the other tested groups exhibited statistically significant differences in the mean values of the marginal gap region (p 0.05).On the other hand, PEKK group showed the highest mean value of fracture resistance (1845.20 N) and the lowest value was observed for Vita-Enamic group (946.50 N). Regarding to stress distributions through 3D FEA, and according to modified von Mises (mvM) analysis, the greatest possible stress values were noticed in PEKK model in relation to tooth structure, cement line, and flowable composite as the following: (93.1, 64.5, 58.4 MPa) respectively, while Zirconia revealed lower maximum stress values (11.4, 13.6, 11.6 MPa) respectively.ConclusionsStatistically excellent marginal and internal fit was observed for PEKK in relation to other used endocrown materials. Also, PEKK material explained fracture resistance comparable to zirconia value while the lowest value was detected for Vita Enamic material.

Rethinking solutions for protracted refugee situation: A case study of the Buduburam refugee camp closure in Ghana

Despite the passage of three decades since their forced migration, many former Liberian refugees remain confined within the Buduburam refugee camp in Ghana. Recent tensions between the former refugees and the Ghanaian government have arisen due to the proposed closure of the camp. In light of these circumstances, this paper reexamines the preferred durable solution sought by the former refugees and demonstrates its relevance within their current protracted situation in Ghana. The study adopts a comprehensive approach that combines data from past interviews, a survey conducted amongst former refugees, and insights derived from a rapid scoping review of the existing literature. By synthesising these various sources of information, this paper sheds light on the nuanced perspectives and ideas expressed by the former refugees. Furthermore, it explores how the findings from these data sources have shaped the present state of affairs within the Buduburam refugee camp. The study reveals that a significant majority (∼77%) of the former refugees expressed a strong preference for resettlement in a third advanced country, driven not only by security concerns but also by their aspirations for improved economic wellbeing. This preference for resettlement stands in contrast to the available solutions offered by governing institutions, which have contributed to the protracted nature of their situation. Nonetheless, there were marginal discrepancies in the inclination towards durable solutions among individuals, contingent upon their educational attainment (x2 = 30.452; p = 0.002) and marital status (x2 = 23.746; p = 0.022). Drawing on the available evidence and insights gained from the former refugees, this paper advocates for a more comprehensive bottom-up, multifactorial approach to the implementation of durable solutions for refugees. It emphasises the need for a more holistic and concurrent application of all viable solutions, right from the beginning of refugee settlement in host countries, to break the cycle of protracted displacement. By taking into account the persistent preferences and needs of the affected individuals, policymakers and governing institutions can work towards implementing durable solutions that address both the immediate and long-term aspirations of refugees, aiming to bring an end to the protracted refugee cycle once and for all.

Marginal and internal discrepancies associated with carbon digital light synthesis additively manufactured interim crowns

Statement of problemThe carbon digital light synthesis (DLS) or continuous liquid interface production (CLIP) technology is an innovative additive manufacturing technology using oxygen-inhibited photopolymerization to create a continuous liquid interface of unpolymerized resin between the growing component and the exposure window. This interface eliminates the need for an incremental layer-by-layer approach, allowing for continuous creation and increased printing speed. However, the internal and marginal discrepancies associated with this new technology remain unclear. PurposeThe purpose of this in vitro study was to evaluate the marginal and internal discrepancies by using the silicone replica technique of interim crowns fabricated by 3 different manufacturing technologies: direct light processing (DLP), DLS, and milling. Material and methodsA mandibular first molar was prepared, and a crown was designed with a computer-aided design (CAD) software program. The standard tessellation language (STL) file was used to create 30 crowns from the DLP, DLS, milling technologies (n=10). The gap discrepancy was determined using the silicone replica approach, with 50 measurements made with a ×70 microscope for each specimen for the marginal and internal gaps. The data were analyzed using 1-way ANOVA, followed by the Tukey HSD post hoc test (α=.05). ResultsThe DLS group had the least marginal discrepancy compared with the DLP and milling groups (P<.001). The DLP group showed the highest internal discrepancy followed by the DLS and milling groups (P=.038). No significant difference was found between DLS and milling in terms of internal discrepancy (P>.05). ConclusionsThe manufacturing technique had a significant effect on both internal and marginal discrepancies. The DLS technology showed the smallest marginal discrepancies.

Fracture strength and three-dimensional marginal evaluation of biocompatible high-performance polymer versus pressed lithium disilicate crowns

Statement of problemDespite the acceptable physical properties of biocompatible high-performance polymer (BioHPP), little is known about the marginal accuracy and fracture strength of restorations made from this material. PurposeThis in vitro study assessed the marginal and internal adaptation and fracture strength of teeth restored with lithium disilicate (LD) ceramics and BioHPP monolithic crowns. Material and methodsTwenty-four extracted premolars were prepared for complete coverage crowns and divided into 2 groups to receive pressed IPS e.max LD, or computer-aided design and computer-aided manufacturing (CAD-CAM) BioHPP monolithic crowns. After adhesive cementation, the marginal and internal adaptations of the restorations were evaluated by microcomputed tomography at 18 points for each crown. Specimens were subjected to 6000 thermal cycles at 5 °C and 55 °C and 200 000 load cycles of 100 N at a frequency of 1.2 Hz. The fracture strength of the restorations was then measured in a universal testing machine at a crosshead speed of 0.5 mm/min. Data were analyzed via an independent-sample t-test (α=.05). ResultsThe mean ±standard deviation of marginal gap was 138.8 ±43.6 μm for LD and 242.1 ±70.7 μm for BioHPP groups (P=.001). The mean ±standard deviation value of absolute marginal discrepancy was 193.8 ±60.8 μm for LD and 263.5 ±97.6 μm for BioHPP groups (P=.06). The internal occlusal and axial gap measurements were 547.5 ±253.1 μm and 197.3 ±54.8 μm for LD (P=.03) and 360 ±62.9 μm and 152.8 ±44.8 μm for BioHPP (P=.04). The mean ±standard deviation of internal space volume was 15.3 ±11.8 μm³ for LD and 24.1 ±10.7 μm³ for BioHPP (P=.08). The mean ±standard deviation of fracture strength was 2509.8 ±680 N for BioHPP and 1090.4 ±454.2 MPa for LD groups (P<.05). ConclusionsThe marginal adaptation of pressed lithium disilicate crowns was better, while BioHPP crowns displayed greater fracture strength. Marginal gap width was not correlated with fracture strength in either group.

Comparative Effect of No Finish Line, Heavy Chamfer, and Shoulder Marginal Designs on the Fracture Resistance of Zirconia (Cercon) Ceramic Restoration: An In Vitro Study.

Background Because all-ceramic crowns are more aesthetic and biocompatible than metal-ceramic crowns, they have grown in popularity among patients and dentists. Poor finish line layout can result in restoration margin fracturing, hence, finish line arrangement is critical to maintaining the restoration's marginal integrity. The goal of this in-vitro study is to evaluate zirconia's resistance to fracture (Cercon) ceramic restorations with three marginal designs (no finish line, heavy chamfer, and shoulder). This study is important in contributing to the ongoing debate about the optimal finish line design for zirconia restorations. Methodology Three different finish lines, namely, biologically oriented preparation technique (BOPT) with a marginal width of less than 0.3 mm, heavy chamfer with a marginal width of up to 0.3 mm, and shoulder with a marginal width greater than 0.3 mm, were made on 10 extracted maxillary first premolar tooth to make 30 epoxy resin dies on which zirconia (Cercon) coping was done using CAD/CAM technology, and marginal discrepancies were measured using a three-dimensional scanner. All the copings were affixed to their respective dies using GIC luting cement, and fracture resistance was measured using a digital universal testing machine. Results The Kruskal-Wallis test revealed that the mean fracture resistance was more in the heavy chamfer finish line, followed by the no finish line (BOPT) and the shoulder finish line. No statistically significant difference was seen between the no finish line and the heavy chamfer finish line. There was a significant difference between the heavy chamfer and shoulder finish lines (p = 0.004). Conclusions To increase the biomechanical performance of posterior single zirconia restorations, heavy chamfer margins are indicated.

Dimensional accuracy and clinical adaptation of monolithic zirconia crowns fabricated with the nanoparticle jetting technique

Statement of problemThe nanoparticle jetting (NPJ) technique is a recently developed additive manufacturing method that may have useful dental applications. The manufacturing accuracy and clinical adaptation of zirconia monolithic crowns fabricated with NPJ are unknown. PurposeThe purpose of this in vitro study was to compare the dimensional accuracy and clinical adaptation of zirconia crowns fabricated with NPJ and those fabricated with subtractive manufacturing (SM) and digital light processing (DLP). Material and methodsFive standardized typodont right mandibular first molars were prepared for ceramic complete crowns, and 30 zirconia monolithic crowns were fabricated using SM, DLP, and NPJ (n=10) with a completely digital workflow. The dimensional accuracy at the external, intaglio, and marginal areas was determined by superimposing the scanned data and computer-aided design data of the crowns (n=10). Occlusal, axial, and marginal adaptations were evaluated by using a nondestructive silicone replica and dual scanning method. The 3-dimensional discrepancy was evaluated to determine clinical adaptation. Differences among test groups were analyzed by using a MANOVA and the post hoc least significant difference test for normally distributed data or the Kruskal-Wallis test with Bonferroni correction for nonnormally distributed data (α=.05). ResultsSignificant differences were found in the dimensional accuracy and clinical adaptation among the groups (P<.001). The NPJ group had a lower overall root mean square (RMS) value for dimensional accuracy (22.9 ±1.4 μm) than the SM (27.3 ±5.0 μm) and DLP (36.4 ±5.9 μm) groups (P<.001). The NPJ group had a lower external RMS value (23.0 ±3.0 μm) than the SM group (28.9 ±5.4 μm) (P<.001) and equivalent marginal and intaglio RMS values than the SM group. The DLP group had larger external (33.3 ±4.3 μm), intaglio (36.1 ±10.7 μm), and marginal (79.4 ±12.9 μm) deviations than the NPJ and SM groups (P<.001). With regard to clinical adaptation, the marginal discrepancy was smaller in the NPJ group (63.9 ±27.3 μm) than in the SM group (70.8 ±27.5 μm) (P<.001). No significant differences were found between the SM and NPJ groups in terms of the occlusal (87.2 ±25.5 and 80.5 ±24.2 μm, respectively) and axial (39.1 ±19.7 and 38.4 ±13.7 μm, respectively) discrepancies. The DLP group had larger occlusal (239.0 ±60.1 μm), axial (84.9 ±29.1 μm), and marginal (140.4 ±84.3 μm) discrepancies than the NPJ and SM groups (P<.001). ConclusionsMonolithic zirconia crowns fabricated using NPJ have higher dimensional accuracy and clinical adaptation than those fabricated using SM or DLP.

Fundamental Properties and Clinical Application of 3D-Printed Bioglass Porcelain Fused to Metal Dental Restoration.

The purpose of this study is to evaluate the mechanical properties and clinical fitness of 3D-printed bioglass porcelain fused to metal (PFM) dental crowns. To evaluate the mechanical properties, tensile strength, Vickers microhardness, shear bond strength, and surface roughness tests of the SLM printed Co-Cr alloy was conducted. A right mandibular 1st molar tooth was prepared for a single dental crown (n = 10). For a three-unit metal crown and bridge, the right mandibular first premolar and first molar were prepared. Bioglass porcelain was fired to fabricate PFM dental restorations. A clinical gap was observed and measured during each of the four times porcelain was fired. A statistical analysis was conducted. The SLM technique showed the largest statistically significant tensile strength and a 0.2% yield strength value. The milling technique had the lowest statistically significant compressive strength value. The shear bond strength and surface roughness showed no statistically significant difference between the fabricated method. There was a statistically significant change in marginal discrepancy according to the porcelain firing step. The casting technique showed the greatest statistically significant margin discrepancy value. The SLM method showed better fitness than the traditional casting method and showed better mechanical properties as a dental material.

Evaluation of marginal and internal fit of single crowns manufactured with an analog workflow and three CAD-CAM systems: A prospective clinical study.

This prospective clinical study evaluated and compared the marginal and internal fit of crowns fabricated with an analog workflow and three different computer-aided design and computer-aided manufacturing (CAD-CAM) systems. Twenty-five participants in need of a single complete-coverage molar or premolar crown were recruited in the study. Twenty-two completed the study, and three participants dropped out. Teeth were prepared according to a standardized protocol by one operator. For each participant, one final impression was made with polyether material (PP) and three intraoral scanners: CEREC Omnicam (C), Planmeca Planscan (PM), and True Definition (TR). For the PP group, crowns were fabricated with a pressable lithium disilicate ceramic, whereas for the other three groups (C, PM, and TR), crowns were designed and milled with dedicated CAD-CAM systems and materials. Marginal (vertical and horizontal) and internal discrepancies between the crowns and tooth preparation were measured at various locations with digital superimposition software. Data was analyzed for normality with Kolmogorov-Smirnov and Shapiro-Wilk tests and then compared with one-way ANOVA and Kruskal-Wallis tests. Mean vertical marginal gap values were 92.18±141.41μm (PP), 150.12±138.06μm (C), 129.07±109.96μm (PM), and 135.09±112.03μm (TR). PP group had statistically significantly smaller vertical marginal discrepancy (p=0.001) than all other groups, whereas no significant difference was detected among the three CAD-CAM systems (C, PM, and TR). Horizontal marginal discrepancies were 104.93±111.96μm (PP), 89.49±119.66μm (C), 113.36±128.49μm (PM), and 136.39±142.52μm (TR). A significant difference was detected only between C and TR (p<0.0001). Values for the internal fit were 128.40±49.31μm (PP), 190.70±69.79μm (C), 146.30±57.70μm (PM), and 168.20±86.67μm (TR). The PP group had a statistically significant smaller internal discrepancy than C (p<0.0001) and TR groups (p=0.001), whereas no significant difference was found compared to the PM group. Posterior crowns fabricated with CAD-CAM systems showed vertical margin discrepancy greater than 120μm. Only crowns fabricated with the conventional methodology had vertical margins below 100μm. Horizontal marginal discrepancy was different among all groups, and only CEREC CAD-CAM was below 100μm. Internal discrepancy was less for crowns fabricated with an analog workflow.

SEM Evaluation of the Marginal Accuracy of Zirconia, Lithium Disilicate, and Composite Single Crowns Created by CAD/CAM Method: Comparative Analysis of Different Materials.

(1) Background: The objective of this in vitro study is to evaluate the marginal accuracy of crowns created by CAD/CAM. (2) Methods: A customized chrome-cobalt (Cr-Co) implant abutment simulating a maxillary right first molar was fixed in a hemi-maxillary stone model and scanned. In total, 27 crowns were fabricated, including 9 lithium disilicate crowns, 9 composite crowns, and 9 zirconia crowns. The measurements were determined by scanning electron microscopy. Descriptive analysis was performed using the mean and standard deviation, while the Kruskal-Wallis test was performed to determine whether the marginal discrepancies were significantly different between each group (p < 0.05). (3) Results: The lowest marginal gap value was reported for zirconia (21.45 ± 12.58 µm), followed by composite (44.7 ± 24.96 µm) and lithium disilicate (62.28 ± 51.8 µm). The Kruskal-Wallis tests revealed a statistically significant difference (p-value < 0.05) in the mean marginal gaps between different materials. (4) Conclusions: The proposed digital workflow can be a viable alternative for fixed prosthetic rehabilitations. The best performance in terms of marginal gap was achieved by zirconia crowns, but all three materials demonstrate marginal closure below the clinically accepted threshold value (120 µm). Clinical significance: although significant differences were reported, the investigated CAD/CAM materials showed clinically acceptable marginal gaps.

Crystallization firing effect on the marginal discrepancy of the IPS. emax CAD crowns using two different CAD/CAM systems

Background: Marginal adaptation is critical for long – term success of crown and bridge restoration. Computer aided design / computer aided manufacture (CAD/ CAM) system is gaining more importance in the fabrication of dental restoration. Objective: The aim of this study is to evaluate the effect of crystallization firing on the vertical marginal gap of IPS. emax CAD crowns which fabricated with two different CAD/CAM systems .Materials and Methods: Twenty IPS e.max CAD crowns were fabricated. We had two major groups (A, B) (10 crowns for each group) according to the CAD/CAM system being used: Group A: fabricated with Imes - Icore CAD/CAM system; Group B: fabricated with In Lab Sirona CAD/CAM system. Each group was subdivided into two subgroups pre-crystallized (Group A1, B1) and crystallized crowns (Group A2, B2). At four points on each aspect of the crown, marginal gaps were assessed on the master metal die by using digital microscope at a magnification of (110X) and image- J program. The measurement was done twice for each crown; before and after crystallization process.Results: The lowest mean of marginal gap before and after crystallization was (29.387±2.774μm) and (70.108±5.569μm) respectively for Group A (Imes - Icore system) and the highest mean value before and after crystallization was (51.728 ±3.774μm) and (84.071 ±4.567μm) respectively for Group B (Sirona system). Paired sample t-test result showed a statistically highly significant difference in marginal gap between all groups.Conclusions: The crystallization process increases the vertical marginal gap. Imes - Icore system showed the lower marginal gap than Sirona system. The two systems have an acceptable marginal gap

Crystallization firing effect on the marginal discrepancy of the IPS. emax CAD crowns using two different CAD/CAM systems

Crystallization firing effect on the marginal discrepancy of the IPS. emax CAD crowns using two different CAD/CAM systems

Effect of a new support design on the marginal and internal gap of additively manufactured interim crowns using direct light deposition technology.

To investigate the design and location of supporting structures on the marginal and internal gap of interim restorations. A mandibular right first molar resin tooth was prepared for a full coverage crown and scanned using a laboratory scanner (3Shape D900). The scanned data were converted into standard tessellation language (STL) format and an indirect prosthesis was designed using computer-aided design (CAD) software (exocad DentalCAD). The STL file was used to fabricate a total of 60 crowns with a 3D printer (EnvisionTEC Vida HD). The crowns were printed using E-Dent C&B MH resin and divided into 4 groups based on four different support structure designs, including supports on the occlusal (0° group), buccal and occlusal (45° group), buccal (90° group), and a new design consisting of horizontal bars placed on all surfaces and line angles (Bar) (n=15). The silicone replica technique was used to determine the gap discrepancy. Fifty measurements were obtained for each specimen to examine the marginal and internal gaps by using a digital microscope (Olympus SZX16) at ×70 magnification. Additionally, the marginal discrepancy at different locations of the tested crowns, including buccal (B), lingual (L), mesial (M), and distal (D), as well as the maximum and minimum marginal gap intervals among groups, were analyzed. The collected data were analyzed using factorial ANOVA, followed by the Tukey HSD test for multiple comparisons (a=0.05). There was a significant difference in marginal and internal gaps among the groups (p<0.001). The buccal placement supports (90° group) had the least marginal and internal discrepancies (p<0.001). The new design group showed the highest marginal and internal gap. The marginal discrepancy in different locations of the tested crowns (B, L, M, D) was found to be significantly different among the groups (p<0.001). The mesial margin of the Bar group had the largest marginal gap, whereas the buccal margin of the 90° group had the lowest marginal gap. The new design had a significantly smaller difference between the maximum and minimum marginal gap intervals than other groups (p<0.001). The location and design of the supporting structures affected the marginal and internal gaps of an interim crown. The buccal placement of supporting bars (90° printing orientation) showed the smallest mean internal and marginal discrepancies.

Evaluation of Marginal and Internal Fit of Ceramic Laminate Veneers Fabricated with Five Intraoral Scanners and Indirect Digitization.

The long-term success of ceramic laminate veneers (CLVs) is influenced by the marginal and internal fit of the restorations. However, studies comparing the fit of CLVs using different intraoral scanners or the indirect digitization technique are lacking. The purpose of this study was therefore to assess the marginal and internal fit of CAD/CAM-milled CLVs using different intraoral scanners and the indirect digitalization technique. An ivorine typodont maxillary left-central incisor was prepared; the tooth and the neighboring teeth were scanned and used as a template to print ninety 3D partial models. Thereafter, ceramic laminate veneers (CLVs) (N = 90) were milled from IPS-Emax CAD blocks and divided into six equal groups (15 specimens each) according to the type of intraoral scanner (IOS), as follows: Omnicam IOS, SC3600 IOS, Trios 3 IOS, Emerald IOS, I500 IOS. Fifteen further CLVs were fabricated using the conventional indirect digitalization technique. After cementation on the resin dies and embedding in clear epoxy resin, specimens were sectioned inciso-gingivally and mesio-distally. At the incisal and cervical positions, the marginal discrepancy was measured and evaluated in addition to the internal gap at six locations using SEM (200×). Differences between gap measurements among the six groups were determined using ANOVA. Games-Howell multiple comparisons for homogenous variances and LSD multiple comparisons for non-homogenous variances were used with 95% confidence intervals. The significance level was set at 0.05. The lowest mean absolute marginal gap at the incisal margins (AMGI) was recorded for Omnicam group (203.28 ± 80.14) µm, while the highest mean absolute marginal gap at the cervical margins (AMGC) was recorded for Omnicam group (147.16 ± 59.78) µm. The mean AMGC was reported to be significantly different between the conventional technique (146.75 ± 38.43) µm and Trios 3 (91.86 ± (35.51) µm; p = 0.001) and between Emerald (112.37 ± (50.31) µm; p = 0.042) and I500 (86.95 ± (41.55) µm; p < 0.001). The mean MGI was found to be significantly different between the conventional technique (114.11 ± (43.45) µm and I500 group (186.99 ± (73.84) µm) only (p = 0.035). However, no significant differences were found in the mean MGI between all types of IOSs. The means of AMG and MG were significantly different at incisal or cervical areas between the conventional technique and IOSs and within the scanner groups (p > 0.05). Marginal gaps were higher in the incisal region compared to the cervical region with both the indirect digitization technique and the IOSs. Ceramic laminate veneers (CLVs) fabricated using IOSs produced overall internal and marginal fit adaptation results comparable to CLVs fabricated from the indirect digitalization method, and both techniques produced clinically acceptable results.