Linear dimensional change, compressive strength and detail reproduction in type IV dental stone dried at room temperature and in a microwave oven

Evaluation of Intraoral Full-Arch Scan versus Conventional Preliminary Impression

An accurate impression is vital during prosthodontic rehabilitation. Digital scanning has become an alternative to conventional impressions. This study compares conventional preliminary impression techniques with digital scanning, evaluating the efficiency, treatment comfort, and trueness. Impressions of 28 patients were taken using conventional and digital techniques. The efficiency of both impression techniques was evaluated by measuring the mean working time. A visual analog scale questionnaire (1-10) was used to appreciate the participants' perceptions of discomfort. Morphometric measurements, which were carried out to determine the differences between the casts, were made on the buccolingual cross sections of teeth 11 and 31 and the distolingual and mesiobuccal cusp tips of each first molar. The total treatment time was 75.5 min for conventional and 12 min for digital impressions. The patients scored a mean discomfort assessment of 6.66 for conventional and 9.03 for digital scanning. No significant differences existed between the examined areas (p < 0.05, Wilcoxon and Mann-Whitney tests) of the digital casts obtained by both techniques. The intraoral scan can be considered as an alternative to conventional preliminary impressions for performing study model analysis during orthodontic treatment planning. The digital impression is more comfortable and accepted by the patients than the conventional impression and has a shorter working time.

Evaluating the accuracy of CAD/CAM optimized stones compared to conventional type IV stones

This study compared the accuracy (trueness and precision) of stone models fabricated using two brands of CAD/CAM optimized stones Cerec Stone (BC) and Elite Master (EM), and a conventional type IV stone Elite Rock Fast (ERF). 30 conventional Type IV and scannable stone complete-arch models were scanned with a blue LED extraoral scanner, and root mean square values were obtained. 6 abutments were used in complete-arch models. The digital models were compared with the master model to evaluate their trueness using model superimposition with Geomagic software. Precision was determined for each case by superimposing combinations of the 10 datasets in each group. The point cloud density of each model was calculated with MeshLab software. Kruskal-Wallis and Mann-Whitney non-parametric tests were used for the statistical analysis. The trueness of the stone models was 96 μm for the BC, 88.2 μm for the EM, and 87.6 μm for the ERF. There were no significant differences between the tested dental stones (p = .768). However, the EM models (35.6 μm) were more precise than the BC (46.9 μm) and ERF (56.4 μm) models (p = .001, p < .001). EM models also showed the highest point cloud density. There were significant differences in point cloud density (p = .003). The EM models showed significant differences in precision but no significant differences in terms of trueness. Although EM was more precise and had the highest point cloud density, all models were within the clinically acceptable limit.

The Effect of Different Additives on the Hydration and Gelation Properties of Composite Dental Gypsum

Dental mold gypsum materials require fine powder, appropriate liquidity, fast curing, and easy-to-perform clinical operations. They require low linear expansion coefficient and high strength, reflecting the master model and facilitating demolding. In this article, the suitable accelerators and reinforcing agents were selected as additives to modify dental gypsum. The main experimental methods used were to compare the trends of linear expansion coefficients of several commercially available dental gypsum products over 72 h and to observe the cross-sectional microstructure of cured bodies before and after dental gypsum modification using scanning electron microscopy. By adjusting the application of additives, the linear expansion coefficient of dental gypsum decreased from 0.26% to 0.06%, while the flexural strength increased from 6.7 MPa to 7.4 MPa at 2 h. Formulated samples showed good stability and gelation properties with linear expansion completed within 12 h. It is indicated that the performance of dental gypsum materials can be improved by adding additives and nanomaterials, which provided a good reference for clinical preparation of high-precision dental prosthesis.

Influence of preparation method on mechanical characteristics of plaster

Introduction: Plaster is widely used in dentistry for the production of master casts, as a binder in investment materials and as an auxiliary material in the laboratory stages of denture production. Due to its brittleness, there is a constant need to improve its mechanical properties. In this regard, in the research we started from the assumption that increasing the proportion of powder during the preparation of plaster improves its mechanical properties. The aim of this research wasto determine the significance of the change in the ratio of powder and liquid to the mechanical characteristics of plaster (compressive strength). Material and methods: Three types of plaster were used in the research: type 2, 3 and 4. For each type of plaster, three samples were made with different ratio of powder and amount of water (n = 9). After 24 hours, the samples were analyzed at the Faculty of Mechanical Engineering in Niš, on a universal testing machine. Results: Plaster type 2 showed the lowest values of compressive strength, and higher values of types 3 and 4, regardless of the ratio of plaster powder and water. As the powder content increased, the compressive strength of the samples increased. Conclusion: In order to improve the compressive strength, the proportion of powder in the liquid phase can be increased during the preparation of the material without visible changes in its structure.

Comparison of four cordless gingival displacement systems: A clinical study

STATEMENT OF PROBLEM

Although the conventional chemicomechanical cord technique is widely used, packing the cord into the sulcus may cause pain and bleeding. Cordless displacement techniques have been introduced, but a comparison of these systems is lacking.

PURPOSE

The purpose of this clinical study was to evaluate the efficiency and gingival response of 4 cordless gingival displacement systems.

MATERIAL AND METHODS

One hundred twenty teeth in 30 participants were allocated to 4 groups according to the material used: Tr (Traxodent; Premier Dental Products Co), Es (Expasyl; Acteon UK), Ez (Expazen; Acteon UK), and Mr (3M Retraction; 3M ESPE). Baseline measurements of periodontal indices and a digital scan were acquired. The cordless displacement pastes were applied according to the manufacturer's instructions. After removal, a second scan was acquired. Participants were recalled on the 2nd and 14th day to measure periodontal indices and for scans. Screenshots were superimposed to measure changes in the gingiva. Statistical differences among the different materials in achieving lingual and buccal vertical gingival displacement were tested using the related-samples Friedman 2-way ANOVA test by ranks at 3 time points such as immediate, at 2 days, and at 14 days (α=.05).

RESULTS

Immediate gingival displacement varied with the system used. For horizontal displacement, median values ranged between 150 μm (Tr) and 725 μm (Ez) for buccal displacement and between 93 μm (Tr) and 550 μm (Ez) for lingual displacement. Minimum and maximum displacements also varied and followed a similar trend, with Traxodent providing the lowest displacement. The plaque index and attachment level did not statistically differ before and after the treatment. The periodontal parameters were not statistically significant among the groups at all time intervals, except for the gingival index that increased for all the groups after 2 days.

CONCLUSIONS

Significant differences were found among the 4 tested systems in both vertical and horizontal gingival displacement. Expasyl, Expazen, and 3M Retraction exceeded the 200-μm requirements for horizontal displacement. Traxodent provided the least displacement in both vertical and horizontal dimensions.

The Effect of Microwave Oven Drying on the Compressive Strength of Type III and IV Dental Stones at Different Time Intervals

Background:

Dental stone cast needs 24 to 48 hours to evaporate excess water and acquire enough strength for manipulation. The microwave oven is used to save time by drying and disinfecting stone casts.

Objectives:

The aim of the present study is to evaluate the effect of microwave oven drying on the compressive strength of Type III and Type IV dental stone in three time intervals-3 hours, 5 hours and 24 hours after pouring.

Methods:

The study involved 120 samples: 60 samples for each type of dental stone. Thirty samples were subjected to air drying at 3, 5 and 24 hours) and 30 samples were dried in the microwave oven at 2450 MHZ -900 W for 150 seconds (at 3, 5 and 24 hours). The samples were tested by unconfined compression machine, with a 2000 kg proving ring at cross-head speed of 1 mm/min.

Results:

For the Type III dental stone drying at 3 hours, microwave radiation causes a significant increase in compressive strength and shows the highest score (mean 125 kg/cm); however, at 5 hours no significant difference was observed. However, at the 24 hour time interval, microwave drying causes significant reduction in the mean (100 kg/cm) p<0.01 .For the Type IV dental stone testing at all-time intervals (3,5, 24 hours), a significant reduction (p<0.05) in mean values was shown(80,85,87 respectively).

Conclusion:

Microwave oven drying increased the compressive strength of Type III dental stone at the 3 hour time interval from pouring, while microwave drying at the 5 hour interval had no significant effect; and at 24 hour the compressive strength of the dental stone was reduced. For the Type IV dental stone microwave drying had a detrimental effect on compressive strength at all-time intervals.

Disinfection effect of microwave radiation on Bacillus subtilis as indicator organism on contaminated dental stone casts under dry and wet conditions

Objective: The disinfection of dental stone casts using microwave radiation has been shown, but doubts remain regarding its efficacy under various conditions. The aim of the present study was to evaluate the efficacy of microwave disinfection on wet and dry dental stone casts contaminated by a resistant microorganism. Material and methods: In this in vitro study, 34 stone half-casts were prepared, contaminated with Bacillus subtilis and divided into two groups. After drying the specimens of one group for 15 minutes using 450 W microwave energy, all the wet and dry specimens were exposed to 900 W microwave energy for 5 minutes. Specimens were then individually transferred to nutrient broth culture medium and after 10 minutes, one milliliter from each tube was cultured in nutrient agar media for 24 hours, and the colonies were counted in CFU/mL. Data were analyzed using multifactorial ANOVA and Bonferroni tests. Results: Casts in both wet and dry groups were disinfected to a high level (6 log), with no statistically significant differences between them (P<0.05). Conclusion: According to the results, microwave irradiation can disinfect dental stone casts to a high degree, irrespective of moisture level. However, the result should be confirmed by exploring with other species of resistant microorganisms.

Effect of different energy levels of microwave on disinfection of dental stone casts

BACKGROUND AND AIMS

Current chemical methods may not efficiently disinfect dental stone casts. The aim of this study was to investigate if microwave irradiation is effective for disinfection of stone casts.

MATERIALS AND METHODS

In this laboratory study, three groups (n = 162) of prepared spherical stone beads as carriers with a diameter of 10 mm were inoculated by separately soaking in three broth culture media, each containing a study microorganism-Pseudomonas aeruginosa, Staphylococcus aureus or Candida albicans. Six inoculated carriers were used for every test, including irradiation in a household microwave oven at 300, 450, 600 or 900 W energy level, or soaking in 0.03%, 0.06%, 0.12%, 0.25% or 0.50% concentration of sodium hypochlorite solution, at 1, 2, or 3-minute test times. Positive and negative control groups were considered for each test. All treated carriers were then individually transferred to nutrient broth culture medium and one milliliter from each tube was cultured in nutrient agar media over night. Colony forming unit per milliliter (CFU/mL) was counted, and multi-factor ANOVA was used to analyze data (α = 0.05).

RESULTS

Microwave irradiation at 600 W resulted in high-level disinfection in 3 minutes. Immersion of the stone casts in hypochlorite solution at 0.06% concentration resulted in disinfection after 2 minutes.

CONCLUSION

According to the results, high level disinfection of the stone casts can be achieved by microwave irradiation at 600 W in 3 minutes, similar to a validated chemical method.