Biological and Chemo-Physical Features of Denture Resins

Evaluation of rheological properties of soft lining materials with different composition under various temperatures

PURPOSE

The aim of this in vitro study was to evaluate the changes the rheological properties of some soft lining materials, to compare the rheological properties and viscoelastic behaviour at different temperatures.

MATERIALS AND METHODS

Five soft lining materials (acrylic and silicone based) were used. the storage modulus (G'), loss modulus (G"), tan delta (tan δ) and complex viscosity (η') were chosen and for each material, measurements were repeated at 23, 33 and 37  °C, using an oscillating rheometer. All data were statistically analyzed using the Mann Whitney U test, Kruskal Wallis test and Conover's Multiple Comparison test at the significance level of 0.05.

RESULTS

Soft lining materials had different viscoelastic properties and most of the materials showed different rheological behavior at 23, 33 and 37  °C. At the end of the test (t¹5), at all the temperatures, Sofreliner Tough M had the highest storage modulus values while Visco Gel had the highest loss Tan delta values.

CONCLUSIONS

There were significant changes in the rheological parameters of all the materials. Also temperature affected the initial rheological properties, and polymerization reaction of all the materials, depending on temperature increase.

CLINICAL IMPLICATIONS

Temperature affected the initial rheological properties, and polymerization reaction of soft denture liner materials, and clinical inferences should be drawn from such studies conducted. It can be recommended to utilize viscoelastic acrylic-based temporary soft lining materials with lower storage modulus, higher tan delta value, and high viscosity in situations where pain complaint persists and tissue stress is extremely significant, provided that they are replaced often.

Considerations about Cytotoxicity of Resin-Based Composite Dental Materials: A Systematic Review

The dental material industry is rapidly developing resin-based composites (RBCs), which find widespread use in a variety of clinical settings. As such, their biocompatibility has gained increasing interest. This literature review presents a summary of research into the cytotoxicity of methacrylate-based composites published from 2017 to 2023. Subject to analysis were 14 in vitro studies on human and murine cell lines. Cytotoxicity in the included studies was measured via MTT assay, LDH assay, and WST-1 assay. The QUIN Risk of Bias Tool was performed to validate the included studies. Included studies (based entirely on the results of in vitro studies) provide evidence of dose- and time-dependent cytotoxicity of dental resin-based composites. Oxidative stress and the depletion of cellular glutathione (GSH) were suggested as reasons for cytotoxicity. Induction of apoptosis by RBCs was indicated. While composites remain the golden standard of dental restorative materials, their potential cytotoxicity cannot be ignored due to direct long-term exposure. Further in vitro investigations and clinical trials are required to understand the molecular mechanism of cytotoxicity and produce novel materials with improved safety profiles.

Evaluation of polymethyl-methacrylate and acetal denture base resins processed by two different techniques before and after nano-chlorohexidine surface treatment

BACKGROUND

Flexible denture base polymers have gained popularity in modern dentistry however, their biofilm formation tendency, adversely affecting the oral tissue heath, remains a concern. Consequently, this study aimed to evaluate surface roughness and biofilm formation tendency of two types of denture base resins manufactured with two techniques before and after surface coating with chlorohexidine (CHX) NPs.

MATERIALS AND METHODS

Acetal (AC) and Polymethyl-methacrylate (PMMA) resins manufactured by conventional and CAD/CAM methods were shaped into disk (10 X 10 X 1 mm). They were dipped for 8 h and 24 h in colloidal suspension prepared by mixing aqueous solution of CHX digluconate and hexa-metaphosphate (0.01 M). Surface roughness, optical density (OD) of microbial growth media and biofilm formation tendency were evaluated directly after coating. Elutes concentrations of released CHX were evaluated for 19 days using spectrophotometer. Three-way ANOVA and Tukey's post-hoc statistical analysis were used to assess the outcomes.

RESULTS

AC CAD/CAM groups showed statistically significant higher roughness before and after coating (54.703 ± 4.32 and 77.58 ± 6.07 nm, respectively). All groups showed significant reduction in OD and biofilm formation tendency after surface coating even after 19 days of CHX NPs release.

CONCLUSIONS

Biofilm formation tendency was highly relevant to surface roughness of tested resins before coating. After CHX NPs coating all tested groups showed significant impact on microbial growth and reduction in biofilm formation tendency with no relation to surface roughness. Significant antimicrobial effect remained even after 19 days of NPs release and specimens storage.

Effect of Different Chemical Surface Treatments on the Shear Bond Strength of Acrylic Teeth With Different High-Impact Denture Base Resins

Introduction The debonding of acrylic teeth from the denture base, particularly in cases of prominent ridges, is a common problem faced by clinicians and patients. The present study was conducted to assess the effects of various chemical treatments on the shear bond strength (SBS) of acrylic teeth bonded to different high-impact denture base materials. Materials and methods The present in vitro study was conducted on 80 wax specimens with acrylic teeth bonded to two high-impact denture base materials (DPI Tuff (DPI Dental Products of India Ltd, Mumbai) and Trevalon HI (Trevalon HI, Dentsply, Karnataka)). The two main groups were further divided into four subgroups of 10 specimens each, depending on the chemical treatment at the ridge lap area of the tooth: control group without any chemical treatment, chemical surface treatment (CST) with dichloromethane and monomer mix, CST with ethyl acetate, and CST with acrylic adhesive cyanoacrylate. The SBS was tested using a universal testing machine (UTM). Analysis of variance (ANOVA) and post-hoc Tukey tests were used for statistical analyses. Results The mean SBS of Group A (DPI Tuff) was 111.75 N as compared to 118 N in Group B (Trevalon HI). The differences were statistically significant (p<0.05). ANOVA and post-hoc Tukey's tests revealed significant differences between subgroups. The highest mean SBS was noted with a dichloromethane and monomer mix (1:1 volume), followed by the ethyl acetate, control, and cyanoacrylate subgroups. Conclusion The cross-linked acrylic teeth treated with a dichloromethane and monomer mixture (1:1 by volume), processed with Trevalon HI high-impact denture base resin had the highest SBS and thus were indicated for bonding teeth with the suggested denture base.

Evaluation of the Effect of Different Construction Techniques of CAD-CAM Milled, 3D-Printed, and Polyamide Denture Base Resins on Flexural Strength: An In Vitro Comparative Study

PURPOSE

To compare the flexural strength of computer-aided design and computer-aided manufacturing (CAD-CAM) milled denture base resin (DBR), 3D-printed DBR, polyamide, and conventional compression-molded DBR.

MATERIALS AND METHODS

Six denture base resins were used, one conventional heat-polymerized (Vertex), two milled CAD-CAM (AvaDent and Polident), two 3D-printed (Harz and NextDent), and one flexible polyamide (Polyamide). According to ISO 20795-1:2013, 60 specimens (65×10×3 mm) were constructed and divided into six groups (n = 10), according to DBR type. The flexural strength was measured using a universal testing machine and three-point loading test. Data were collected and analyzed using one-way ANOVA and Tukey's pair-wise post hoc tests (α = 0.05).

RESULTS

One-way ANOVA results showed significant differences in flexural strengths between the tested DBRs (p˂0.001). Milled denture base resins (AvaDent and Polident) had significantly higher flexural strength values than the other groups (p˂0.001) and were followed by Vertex and NextDent, while Polyamide and Harz had the lowest values. Polyamide and Harz denture base resins had significantly lower flexural strength values than conventional denture base resin (p˂0.001).

CONCLUSION

CAD-CAM milled DBRs showed the highest flexural strength when compared with conventional compression-molded or 3D-printed DBRs, while 3D-printed DBRs and polyamide showed the lowest flexural strengths.

Influence of Denture Cleansers on the Retention Loss of Attachment Systems Retained Implant Overdenture

Background

This study aimed to evaluate the effects of different denture cleansing solutions (DCSs) on the retention of Locator and Locator R-Tx attachment systems of implant retained overdentures (IRO).

Methods

Two part acrylic resin blocks were fabricated, upper part contained metal housing and plastic inserts and lower part contained implant analogs and abutments. Eighty pink plastic inserts (40/attachment, 10/solution) were immersed in Corega, Fittydent, sodium hypochlorite, and water for a time simulating upto 1-year of clinical usage. Acrylic blocks were held on a universal testing machine for a pull-out test to record the dislodgement force. Measurements were conducted after 6 months (T1) and 12 months (T2). One-way ANOVA followed by Tukey's HSD test was used to analyze the results (α = 0.05).

Results

For both attachments, retention significantly decreased after immersion in different solutions at T2 (P < 0.001). Locator R-Tx attachment in NaOCl showed a significant decrease in retention compared with other solutions at T1. At T2, there was a significant decrease in retention for all DCS compared with water (P < 0.001). Locator R-TX showed higher retention values per solution compared to Locator attachment (P < 0.001). In terms of retention loss %, NaOCl recorded the highest (61.87%) loss, followed by Corega (55.54%) and Fittydent (43.13%), whereas water demonstrated the best retention (16.13%) in both groups.

Conclusion

Locator R-TX has better retention with different DCS immersion. The loss of retention varied with different types of DCS and NaOCl recorded the highest retention loss. Therefore, denture cleanser selection must be guided by the type of IRO attachment.

Effects of incorporation of nanoparticles into dental acrylic resins on antimicrobial and physico-mechanical properties: A meta-analysis of in vitro studies

Background

A meta-analysis study was conducted to determine whether the incorporation of nanoparticles into the dental acrylic resins influence the physico-mechanical properties and whether there are the appropriate nanoparticles exhibiting excellent antimicrobial activity against cariogenic bacteria along with acceptable physico-mechanical properties.

Methods

We systematically searched the various databases up to December 2021. The review was performed based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and the Consolidated Standards of Reporting Trials (CONSORT) guidelines. A meta-analysis of physico-mechanical properties was performed by a random-effects model at a 95% confidence interval and the antimicrobial effects were analyzed descriptively.

Results

27 studies were included for the final analysis. There was no statistically significant difference in flexural strength (0.553, [95% confidence interval (CI) 0.501-0.604]), microhardness (0.509, [95% CI 0.278-0.736]), surface roughness (0.753, [95% CI 0.315-0.953]), impact strength (0.90, [95% CI 0.188-0.997]), and elastic modulus (0.848, [95% CI 0.514-0.967]), with nanoparticles addition compared with the control group. Forest plots were not generated for the thermal conductivity, tensile strength, and translucency because of the lack of comparison. Although the articles showed high heterogeneity without the high risk of bias, the finding showed the nanoparticles at low concentrations into dental acrylic resins could improve the antimicrobial activities without adverse effects on their physico-mechanical properties.

Conclusion

Adding the low concentration of nanoparticles such as 0.5% Ag, ≤0.25% TiO₂, and ≤0.25% SiO₂ as the most abundant antimicrobial nanoparticles do not influence their physico-mechanical properties and can be effective in the elimination of cariogenic pathogens.

Impact of Surface Changes and Microbial Adhesion on Mucosal Surface Finishing of Resin Denture Bases by Shot Blast Polishing Using Viscoelastic Media

Surface changes and microbiological effects following shot blast polishing with viscoelastic media of the mucosal surface of resin denture bases were examined. Average surface roughness (Ra) and the depth of surface removal of specimens were measured over time, and the clinical number of microbial adhesions on the mucosal surface of dentures was clinically assessed. The results obtained showed no changes in Ra after 20 s of polishing, Ra of <0.2 µm, and a depth of surface removal < 20 µm. This method of finishing did not affect the fit of the mucosal surface of the dentures. Furthermore, the adhesion of microorganisms to the mucosal surface of dentures was significantly suppressed. Shot blast polishing with viscoelastic media is useful for finishing the mucosal surface of resin denture bases.

Effect of Different Surface Modifications of Acrylic Teeth and Thermocycling on Shear Bond Strength to Polycarbonate Denture Base Material

During prosthodontic clinical practice, the most commonly reported type of failure is the debonding of teeth to the denture base. Incompatible surface conditions at the tooth/denture base interface result in a lack of bonding. This study aimed to study the influence of different surface modifications of acrylic teeth and thermocycling on shear bond strength to polycarbonate denture base material. Eighty cylinder-shaped samples were fabricated. The tested samples were divided into 4 groups (n = 20). Group A represents the control group, group B represents the mechanical modification of the tooth, while group C and group D represent the chemical treatment of the tooth with ethyl acetate and bonding agent, respectively. Each group was further subdivided into 2 categories depending on the thermocycling procedure (N = 10). All samples were tested for shear bond strength tests. A computer-controlled universal testing machine performed the shear bond test at a 0.5 mm/min crosshead speed. Three-way ANOVA (P=0.05) was used for the statistical analysis of the data. Results show that shear bond strength was significantly affected by the surface treatment, whether it is mechanical or chemical (P ≤ 0.01) (B > D > C) compared with a control group (A). However, thermocycling has a nonsignificant decrease in the bond strength values in all experimental groups (P > 0.05) (B > D > C > A). The mechanical treatment by creating retentive holes (B) provides better results than the chemical surface treatment with a bonding agent and ethyl acetate (D and C, respectively). This study concluded that various surface conditioning methods affect the bonding strength of acrylic teeth and polycarbonate denture base material with no effect of thermocycling.

Zirconia vs. stainless steel pediatric crowns: a literature review

The aim of this review was to assess efficacy and acceptance of aesthetic zirconia crowns (ZCs) compared to the traditionally employed stainless steel crowns (SSCs) for primary teeth restoration. A comprehensive literature search was completed for the relevant keywords in Scopus and Medline databases. Resulting article abstracts and full texts were screened to determine final inclusion. Eighteen articles were included from the initial search. There is still little evidence to support the use of one type of crowns over another for primary teeth, in particularly for ZCs, lately introduced in pediatric restoration. The gold standard for restoring decayed primary teeth is still represented by SSCs, despite the growing importance of the aesthetic issue related to their use. Aesthetic ZCs resulted in having adequate properties to be employed for the treatment of decayed primary teeth, such as mechanical resistance, limited plaque adhesion, wear behavior and natural appearance. There is still a paucity of literature clinically evaluating the efficacy of ZCs for primary teeth restoration, but they can be considered a promising alternative to SSCs. This field of research has to be more deeply explored to improve dental care in children affected by early childhood caries.