An Interdisciplinary Study Regarding the Characteristics of Dental Resins Used for Temporary Bridges

Evaluation of the Milled and Three-Dimensional Digital Manufacturing, 10-Degree and 20-Degree Preparation Taper, Groove and Box Auxiliary Retentive Features, and Conventional and Resin-Based Provisional Cement Type on the Adhesive Failure Stress of 3 mm Short Provisional Crowns

BACKGROUND This study evaluated the effects of milling (CADCAM), 3D printing, preparation taper angles (10-degree and 20-degree), auxiliary retentive features (groove and box), and provisional cement types (conventional and resin-based) on the adhesive failure stress of 3-mm short provisional crowns (PC). The research was motivated by the need to understand how digital dentistry technologies impact the retention and durability of provisional crowns. MATERIAL AND METHODS A total of 160 working models (3D-printed) and PCs [80 milled (CopraTemp)/80 printed (Asiga)] were fabricated from two 10- and 20-degree typodont master models and two 20-degree 3D-printed master models (groove and box), simulating a 3 mm high all-ceramic short PC. After provisional cementation with conventional (Kerr TempBond) and resin-based (ProviTemp) cements, 16 subgroups (n=10 each) underwent thermocycling (10 000 cycles; 5-55°C) and pull-off tests on a universal testing machine. Statistical analysis was performed using one-way ANOVA and post hoc Tukey test. RESULTS Conventional cement failed at lower stress for milled (47.68 to 73.54) and printed (48.40 to 77.91) as compared to resin cement for milled (104.2 to 137.27) and printed (184.85 to 328.84), respectively, with significant differences. Increased taper and groove decreased failure load except for the printed PC/resin cement combination. Use of proximal box preparation increased retention significantly. Except for 20-degree taper cemented with conventional cement, the differences in auxiliary retentive features for milled and printed provisional crowns were statistically significant at P≤0.05. CONCLUSIONS 3D-printed PC, resin-based cement, 10-degree taper, and proximal box preparation were associated with higher retention than milled, conventional cements, 20-degree taper, and vertical groove.

Effect of smokeless tobacco on color stability and surface roughness of CAD/CAM milled, 3D printed, and conventional provisional crown and fixed dental prosthesis materials: An in vitro study

BACKGROUND

Provisional fixed dental prosthesis (FDP) plays an important role during fixed prosthodontic therapy till the definitive. Discoloration of materials used for provisional FDPs can cause patient dissatisfaction and may create doubt about the color stability of the definitive FDP. Surface roughness is the other major property to be taken into consideration for provisional FDP materials. Smokeless tobacco is reported to affect the color stability and surface roughness of different prosthetic materials.

OBJECTIVE

The aim of the current study was to evaluate the effect of two types of smokeless tobacco (black and white) on color stability and surface roughness of 3D printed, CAD/CAM milled, and conventional provisional FDP resin materials.

METHODS

A total of 144 disc-shaped specimens were fabricated using four techniques CAD/CAM subtractive technique (milling), CAD/CAM additive technique (3D Printing), and conventional technique using autopolymerized PMMA, and autopolymerized Bis-acrylic resins. Each group was subdivided into three subgroups of twelve specimens each, and were submerged into three solutions (artificial salivary substitute, black smokeless tobacco, white smokeless tobacco). The change in color and surface roughness was evaluated and the data collected were statistically analyzed.

RESULTS

It was observed that black smokeless tobacco caused the maximum color change and the effect was highest in autopolymerized PMMA resin specimens (ΔE = 9.343 ± 0.489), followed by 3D printed (ΔE = 7.187 ± 0.391), autopolymerized Bis-acryl (ΔE = 6.464 ± 0.453) and milled (ΔE = 4.978 ± 0.227). White smokeless tobacco was found to cause a maximum change in surface roughness and the effect was highest in autopolymerized Bis-acryl specimens (ΔRa = 0.321 ± 0.015 μm), followed by autopolymerized PMMA (ΔRa = 0.297± 0.015 μm), 3D printed (ΔRa = 0.191 ± 0.019 μm), and milled (ΔRa = 0.168 ± 0.014 μm). Statistically significant (p-value < 0.05) differences were observed among all techniques and solutions.

CONCLUSIONS

The change in color and surface roughness were maximum in the case of FDPs prepared using autopolymerizing resins, followed by 3D printed, and CAD/CAM milled reins.

The efficacy of reinforcement of glass fibers and ZrO2 nanoparticles on the mechanical properties of autopolymerizing provisional restorations (PMMA)

Objective

to investigate and compare the reinforcing effects of glass fibers (GFs) and ZrO2 nanoparticles at different ratios on the Flexural Strength (FS), Microhardness (MH), and Surface Roughness (SR) of autopolymerizing provisional PMMA.

Methods

A total of one hundred and twenty specimens of autopolymerizing PMMA were prepared for FS, MH, and SR tests and grouped as follows: no additives (control group), for the tested groups, different ratios of GFs and ZrO2 at 5% of autopolymerizing PMMA were incorporated. The ratios of GFs/ZrO2 nanoparticles were 0%-5%, 1%-4%, 2%-3%, 2.5%-2.5%, 3%-2%, 4%-1% and 5%-0% (n = 5). The FS was evaluated using the three-point bending test, MH was evaluated using the Vickers microhardness tester and SR was evaluated using a contact-type profilometer. Data were analyzed using ANOVA, Tukey's test, and Person correlation at 0.05 level of significance.

Results

The unreinforced group had the lowest FS, MH, and SR mean values followed by (0%GFs + 5% ZrO2), (1% GFs + 4% ZrO2), (2% GFs + 3% ZrO2), (2.5% GFs + 2.5% ZrO2), (3% GFs + 2% ZrO2), (4% GFs + 1% ZrO2) and (5% GFs + 0% ZrO2) which had the highest values.

Conclusion

Hybrid reinforcement with GFs, ZrO2 nanoparticles, or a combination of them effectively improved flexural strength and microhardness of autopolymerizing provisional PMMA that would create provisional restorations with extended clinical service. GFs demonstrated superior reinforcing effects compared to ZrO2 nanoparticles. However, reinforcement with 2.5-5% GFs increased the surface roughness for provisional restoration.

In Vitro Evaluation of Gastric Acid and Toothbrushing Effect on the Surface State of Different Types of Composite Resins

Background and Objectives: The aim of this in vitro study was to evaluate the effect of gastric acid associated with the effect of toothbrushing on the surface roughness of different types of composite resin used for direct restorations. Materials and Methods: The materials used in this study were two microhybrid (Filtek Z250, Herculite XRV) and two nanohybrid (Filtek Z550, Herculite XRV Ultra) composite resins. Two hundred and forty cylindrical samples with a height of 2 mm and a diameter of 6 mm were divided into four groups (groups A, B, C and D) corresponding to each tested material (n = 60). Each group was divided in two subgroups: subgroup I—the samples were submersed in hydrochloric acid and immediately submitted to toothbrushing; subgroup II—the samples were submitted only to toothbrushing. The simulation of the acid attack was performed by immersing the samples in a 0.01 M hydrochloric acid solution for 90 min. This procedure was followed immediately by toothbrushing simulation with 10,000 cycles. The acid attack and toothbrushing simulation were performed for two times. The surface roughness evaluation was performed with a Proscan 2100 profilometer. Repeated Measures ANOVA and Bonferroni post-hoc tests were used to perform the statistical analysis. Results: Simulation of one year of toothbrushing associated or not to hydrochloric acid exposure increases the surface roughness of microhybrid and nanohybrid composite resins. Six months of toothbrushing associated to six months of hydrochloric acid exposure increase the surface roughness of nanohybrid composite resins. Conclusions: Microhybrid composite resins surface becomes rougher after toothbrush and acid submersion when comparing to nanohybrid composite resins.

A Comparative Analysis of Dental Measurements in Physical and Digital Orthodontic Case Study Models

Background and Objectives: Study models are essential tools used in the dental teaching process. The aim of the present study was to compare the values obtained by manual and digital orthodontic measurements on physical and digital case study models. Materials and Methods: The physical experimental models were obtained by traditional pouring (improved stone-type IV gypsum products) and by additive manufacturing (resins). The digital experimental models were created by scanning the physical ones, using a white light-emitting diode (LED) source and an L-shaped dental scanner—Swing DOF (DOF, Seoul, Korea). The physical study models were first measured using a digital caliper, and then, they were scanned and evaluated using the DentalCad 3.0 Galway software (exocad GmbH, Darmstadt, Germany). The Pont, Linder−Harth, and Bolton indices, which are used in orthodontics for training students, were derived using the available data. Results: When comparing the linear measurement mean ranks taken on physical study models to those of digital models, no statistically significant differences (p > 0.05) were found. A similar result was also shown when the dentoalveolar growth indicators were analyzed. Conclusions: It can be concluded that dental study models made by direct light processing (DLP) and pouring type IV class gypsum are both acceptable for orthodontic teaching purposes.