Effect of cementation, cement type and vent holes on fit of zirconia copings

CAD-CAM and heat-press: Comparison of internal and marginal fit of lithium disilicate copings

The aim of this in vitro study is to compare the performance of digital and conventional methods in the manufacture of single copings in terms of the internal and marginal fit. Twenty-four prefabricated titanium Cone Morse Exact abutments of the lateral anatomical type were used to manufacture 24 lithium disilicate copings in the CAD-CAM Ceramill (n = 12) and heat-press (n = 12) systems. The copings were cemented using a self-adhesive resin cement (RelyX U-200; 3M ESPE) and then cut vertically. The cement line was photographed using an optical microscope at ×100 and ×200 magnification and then the internal and marginal regions were measured. The mean values of fits, for the CAD-CAM and heat-press techniques, respectively, were (μm): angular regions, 81.8 and 75.3; linear regions, 63.1 and 60.1; incisal regions, 171.1 and 114.7; marginal discrepancy, 74.1 and 75.2; and absolute marginal discrepancy, 99.5 and 96.2. MANOVA test showed that there is an effect of the techniques on the regions (p < .05). The effects of laboratories and the interaction between laboratories and techniques on the regions were not statistically significant (p > .05). The techniques evaluated presented clinically acceptable results for the marginal fit. However, the conventional method performed better for the internal fit. RESEARCH HIGHLIGHTS: Scientific evidence regarding the methods of making prosthesis can help the dental professional in decision-making. Digital and conventional methods is both good in the manufacture of single copings in terms of the internal and marginal fit.

Three Self-Adhesive Resin Cements and Their Influence on the Marginal Adaptation of Zirconia-Reinforced Lithium Silicate Single Crowns: An In Vitro Scanning Electron Microscope Evaluation

Background: In everyday dentistry, monolithic single crowns can be cemented with self-adhesive resin cements. The aim of this in vitro study was to evaluate how the marginal adaptation of full monolithic zirconia-reinforced lithium silicate (ZLS) single crowns is influenced by three different self-adhesive resin cements. Methods: Forty-five typodont teeth fully prepared for full monolithic crowns were divided into three groups (fifteen each) for the use of three different self-adhesive resin cements. A fourth control group (Temp-bond) was created by taking five teeth from each group before cementation with self-adhesive resin cements. All forty-five abutments were scanned using a Primescan intra-oral scanner (IOS), followed by computer-aided design (CAD) and computer-aided manufacturing (CAM) of zirconia-reinforced lithium silicate (ZLS) full crowns using a four-axis machine. Initially, the crowns of the control group were fixed to the abutments using Temp-bond, and the marginal gap was evaluated using a scanning electron microscope (SEM). After removing the control group crowns from the abutments, fifteen crowns in each group were cemented using a different self-adhesive resin cement and observed under SEM for evaluation of the marginal gap. A Kolmogorov-Smirnov test was performed, indicating no normal distribution (p < 0.05), followed by Mann-Whitney tests (α = 0.05). Results: The total mean marginal gap of the temp-bond control group was significantly lower compared to all three groups of self-adhesive resin cement (p < 0.0005). The total mean marginal gap of the G-cem ONE group was significantly lower compared to the TheraCem group (p < 0.026) and RelyX U200 group (p < 0.008). The total mean marginal gap of the TheraCem group was significantly higher than the G-cem ONE group (p < 0.026) but showed no significant difference with the RelyX U200 group (p > 0.110). Conclusions: All four groups showed a clinically acceptable marginal gap (<120 microns). Although all three groups of self-adhesive resin cement showed a significant increase in the marginal gap compared to the temp-bond control group, they were within the limits of clinical acceptability. Regarding the marginal gap, in everyday dentistry, it is acceptable to use all three self-adhesive resin cements, although the G-cem ONE group exhibited the lowest marginal gap for ZLS single crowns.

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

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

SEM Evaluation of the Marginal Gap of Zirconia-Reinforced Lithium Silicate Full Crowns and the Effect of Post Crystallization: An In Vitro Study

BACKGROUND

This study compared the influence of crystallization on marginal gap adaptation by using computer-aided design and manufacturing (CAD-CAM) for producing monolithic zirconia-reinforced lithium silicate (ZLS) ceramic crowns.

METHODS

A total of 25 plastic teeth were scanned using a Primescan intra-oral scanner (IOS), and ZLS crowns were ground. For each unit (abutment and crown), the marginal gap was evaluated pre crystallization and post crystallization at four regions of interest through the use of a scanning electron microscope (SEM). To compare the marginal gap between the two groups, a Kolmogorov-Smirnov test performed on the study variables indicated a normal distribution (p > 0.05) followed by paired samples T-tests (α = 0.0005).

RESULTS

After crystallization, there were significantly higher circumferential marginal gaps (CMGs) for all four surfaces (distal (p = 0.0005), mesial (p = 0.0005), palatal (p = 0.0005), and buccal (p = 0.0005)). The total mean marginal gap (MMG) revealed a significantly higher result for the post-crystallization group (79.82 ± 7.86 μm) compared to the pre-crystallization group (24.25 ± 5.49 μm).

CONCLUSIONS

The post-crystallization group showed a significantly higher marginal gap compared to the pre-crystallization group in all parameters, but both groups were in the clinically accepted threshold (<120 microns). In terms of the marginal gap, it is arguable whether to carry out post-crystallization for CELTRA® DUO crowns and achieve better mechanical properties but significantly increase the marginal gap.

Effect of three different preparation designs on the marginal adaptation of indirect overlay restoration fabricated from lithium disilicate ceramic material: An in-vitro comparative study

Objectives

Marginal adaptation is considered one of the key factors influencing the success of indirect restorations. This study aimed to estimate the marginal fit of lithium disilicate overlays with three distinct preparation designs before and after cementation.

Methods

Thirty maxillary first premolars were divided into the hollow chamfer design (HCD) group, butt-joint design (BJD) group, and conventional occlusal box design (COD) group (n = 10 each). The samples were scanned using an intra-oral scanner, and overlays were fabricated using computer-assisted design and milled on a computer-assisted machine. The finished restorations were luted using a self-adhesive resin RelyX Ultimate. The marginal gap was assessed using a digital microscope with 230X magnification power. Statistical analysis was conducted using analysis of variance and post hoc (Bonferroni correction) tests, assuming a significance level of 5%.

Results

The HCD and BJD groups recorded significantly lower marginal gap, (11.39 ± 0.72, 16.29 ± 0.75) and (11.59 ± 0.75, 16.93 ± 0.65) respectively, than the COD group (24.57 ± 1.18, 34.45 ± 1.09) both pre- and post-cementation.

Conclusion

This study demonstrated that modification of tooth preparation plays a significant role in the marginal adaptation of the lithium disilicate overlays. The gap was smaller with the HCD and BJD than with the COD, with a statistically significant difference.

Prosthodontic Applications of Polymethyl Methacrylate (PMMA): An Update

A wide range of polymers are commonly used for various applications in prosthodontics. Polymethyl methacrylate (PMMA) is commonly used for prosthetic dental applications, including the fabrication of artificial teeth, denture bases, dentures, obturators, orthodontic retainers, temporary or provisional crowns, and for the repair of dental prostheses. Additional dental applications of PMMA include occlusal splints, printed or milled casts, dies for treatment planning, and the embedding of tooth specimens for research purposes. The unique properties of PMMA, such as its low density, aesthetics, cost-effectiveness, ease of manipulation, and tailorable physical and mechanical properties, make it a suitable and popular biomaterial for these dental applications. To further improve the properties (thermal properties, water sorption, solubility, impact strength, flexural strength) of PMMA, several chemical modifications and mechanical reinforcement techniques using various types of fibers, nanoparticles, and nanotubes have been reported recently. The present article comprehensively reviews various aspects and properties of PMMA biomaterials, mainly for prosthodontic applications. In addition, recent updates and modifications to enhance the physical and mechanical properties of PMMA are also discussed.

Evaluation of Film Thickness of Crown Disclosing Agents and Their Comparison with Cement Film Thickness after Final Cementation

OBJECTIVE

 Verification of the accuracy of crown fit before final cementation is imperative. The aim of this in vitro study was to evaluate the film thickness of commonly used dental crown disclosing materials and their comparison with final cement thickness.

MATERIALS

AND METHODS: One hundred fifty provisional crowns (Protemp) were fabricated on standardized resin dies and divided into five groups (N = 150; n = 30) based on five disclosing agents: A = Fit-Checker auto-mix; B = Okklu-top; C = Express; D = Fit-Checker hand-mix; E = Coltene PSI, and Final cement = Relyx U200. Crowns were loaded with test materials, tried over dies under load (50N), and later cemented under same load. Film thickness (µm) was recorded between crown margin and the finish line of die after loading with test material and final cementation using a digital microscope.

STATISTICAL ANALYSIS

 Descriptive statistics, analysis of variance, Tukey's and paired t-test were used for statistical analysis (p < 0.05).

RESULTS

 Significant variations were found between the film thicknesses of the five disclosing agents (p = 0.019). Group-A showed the lowest (131.67 ± 101.10 μm), while group-B (295.00 ± 263.88 μm) showed the highest film thickness (p = 0.011). Film thicknesses after cementation were similar for groups (p = 0.957). Significant difference was observed for group-B disclosing agent versus final cement (p = 0.010). The lowest mean difference between the film thicknesses of the disclosing agent and final cementation of 13.1 μm was revealed for group-A.

CONCLUSIONS

 Variations in the film thicknesses of the tested disclosing agents were found. Fit-Checker auto-mix was found with minimal film thickness and satisfied the requirements as the disclosing agent, while Okklu-top aerosol spray did not.

An Advanced Fiber-Reinforced Composite Solution for Gingival Inflammation and Bone Loss Related to Restorative Crowns

Soaring gold prices have created an almost impossible void in the Dental Materials supply reserves for affordable patient posterior crowns. Fortunately, aerotech fiber-reinforced composite (FRC) materials in use for many diverse structural applications can be developed for dentistry to replace gold with computer-assisted design/computer-assisted manufacture (CAD/CAM) technology. Current dental ceramics or high-strength oxide ceramics like alumina and zirconia available for CAD/CAM have extremely poor fracture-toughness properties and can propagate microscopic cracks rapidly to sudden adverse brittle failure. As a highly promising alternative, exceptional FRC fracture toughness properties counteract brittle failure with high-strength fibers that act as major barriers to crack propagation. In addition, excellent rapid FRC CAD/CAM machining can offer one-patient appointments for single crowns. FRCs have high-strength fibers coupled into a polymer matrix with the ability to form strong covalent bonds with resin adhesives whereas ceramics do not bond well and oxide ceramics have non-reactive inert surfaces making resin bonding extremely difficult. Prominent adhesive free-radical covalent bonding by FRCs then provides a great opportunity to achieve a crown marginal reline directly on the patienťs clinical tooth for possible near zero-gap defect tolerances. To place crown gingival marginal defects in proper perspective, gaps between the tooth and crown expose luting cements that can wash out and provide space for microbial plaque growth. Bacterial toxins released from a crown-tooth interface can subsequently produce secondary decay, gingival inflammation and eventually under severe plaque environments breed periodontal disease with bone loss.