Biocompatibility of dental materials

In silico assessment of biocompatibility and toxicity: molecular docking and dynamics simulation of PMMA-based dental materials for interim prosthetic restorations

AIM

This study aimed to comprehensively assess the biocompatibility and toxicity profiles of poly(methyl methacrylate) (PMMA) and its monomeric unit, methyl methacrylate (MMA), crucial components in dental materials for interim prosthetic restorations.

METHODOLOGY

Molecular docking was employed to predict the binding affinities, energetics, and steric features of MMA and PMMA with selected receptors involved in bone metabolism and tissue development, including RANKL, Fibronectin, BMP9, NOTCH2, and other related receptors. The HADDOCK standalone version was utilized for docking calculations, employing a Lamarckian genetic algorithm to explore the conformational space of ligand-receptor interactions. Furthermore, molecular dynamics (MD) simulations over 100 nanoseconds were conducted using the GROMACS package to evaluate dynamic actions and structural stability. The LigandScout was utilized for pharmacophore modeling, which employs a shape-based screening approach to identify potential ligand binding sites on protein targets.

RESULTS

The molecular docking studies elucidated promising interactions between PMMA and MMA with key biomolecular targets relevant to dental applications. MD simulation results provided strong evidence supporting the structural stability of PMMA complexes over time. Pharmacophore modeling highlighted the significance of carbonyl and hydroxyl groups as pharmacophoric features, indicating compounds with favorable biocompatibility profiles.

CONCLUSION

This study underscores the potential of PMMA in dental applications, emphasizing its structural stability, molecular interactions, and safety considerations. These findings lay a foundation for future advancements in dental biomaterials, guiding the design and optimization of materials for enhanced biocompatibility. Future directions include experimental validation of computational findings and the development of PMMA-based dental materials with improved biocompatibility and clinical performance.

Resin cement selection for different types of fixed partial coverage restorations: A narrative systematic review

OBJECTIVE

The aim of this study was to review the selection criteria of resin cements for different types of partial coverage restorations (PCRs) and investigate if the type of restorations or restorative materials affect the type of selected resin cement.

MATERIALS AND METHODS

An electronic search (1991-2023) was performed in PubMed, Medline, Scopus, and Google Scholar databases by combinations of related keywords.

RESULTS

A total of 68 articles were included to review the selection criteria based on the advantages, disadvantages, indications, and performance of resin cements for different types of PCRs.

CONCLUSIONS

The survival and success of PCRs are largely affected by appropriate cement selection. Self-curing and dual-curing resin cements have been recommended for the cementation of metallic PCRs. The PCRs fabricated from thin, translucent, and low-strength ceramics could be adhesively bonded by light-cure conventional resin cements. Self-etching and self-adhesive cements, especially dual-cure types, are not generally indicated for laminate veneers.

Biological effects of gamma-ray sterilization on 3 mol% yttria-stabilized tetragonal zirconia polycrystal: An in vitro study

STATEMENT OF PROBLEM

Selecting the sterilization method is important because sterilization can alter the surface chemistry of implant materials, including zirconia, and influence their cellular biocompatibility. Studies on the biological effects of sterilization on implant materials are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate the biocompatibility of gamma-ray irradiated 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) compared with unirradiated titanium, 3Y-TZP, and pure gold.

MATERIAL AND METHODS

Disk-shaped specimens each of commercially pure grade 4 titanium, 3Y-TZP, gamma-rayed 3Y-TZP, and pure gold were prepared and evaluated for osteogenic potential by using a clonal murine cell line of immature osteoblasts derived from mice (MC3T3-E1 cells). The surface topography (n=3), chemical analysis of the disks (n=3), and cell morphology cultured on these surfaces were examined using scanning electron microscopy, confocal laser scanning microscopy, and energy dispersive spectroscopy. Cellular biocompatibility was analyzed for 1 and 3 days after seeding. Cell adhesion and spreading were evaluated using confocal laser scanning microscopy (n=3). Cell proliferation was evaluated using methyl thiazolyl tetrazolium assay (n=3). Kruskal-Wallis and Bonferroni corrections were used to evaluate the statistical significance of the intergroup differences (α=.05).

RESULTS

Gamma-ray sterilization of 3Y-TZP showed significantly higher surface roughness compared with titanium and gold (P<.002). On day 1, the proliferation and adhesion of MC3T3-E1 cells cultured on gamma-rayed 3Y-TZP were significantly higher than those cultured on gold (P<.05); however, cell spreading was significantly lower than that of titanium on days 1 and 3 (P<.05). On day 3, cell proliferation of gamma-rayed 3Y-TZP was significantly lower than that of unirradiated 3Y-TZP (P<.05). Cell adhesion of gamma-rayed 3Y-TZP was slightly lower than that of zirconia and titanium but without significant difference (P>.05).

CONCLUSIONS

Gamma-rayed zirconia exhibited increased surface roughness compared with titanium and significantly decreased bioactivity compared with titanium and zirconia. The use of gamma-ray sterilization on zirconia is not promising regarding biocompatibility, and the effect of this sterilization method on implant materials warrants further investigation.

Apatite-coated outer layer eggshell membrane: A novel osteoinductive biohybrid composite for guided bone/tissue regeneration

Hybrid biomimetic materials aim to replicate the organic-inorganic constructs of mineralized tissues. During eggshell formation, the outer surface of the eggshell membrane (ESM) promotes calcium carbonate nucleation, while the inner one prevents mineralization toward the egg white and yolk. In the current study, the outer surface of the ESM acted as a heteronucleant in calcium phosphate precipitation by the vapor diffusion sitting drop method, while the inner one remained unmineralized. The aim was to fabricate a 2D biomaterial with dual functions, osteoinductive on one side and protective against cell invasion on the other side. The microstructural, physicochemical, morphological, and mechanical properties of the mineralized ESM were characterized by XRD, TGA, XPS, FTIR/Raman, HR-SEM, and mechanical testing techniques. The cytocompatibility and osteoinductive ability were assessed by biological assays of cell viability, proliferation, and osteogenic differentiation on human mesenchymal stromal cells (hMSCs). Results indicate that the outer surface of the ESM induces the heterogeneous precipitation of carbonate-apatite phase depicting biomimetic features. In addition, the apatite/ESM shows a much higher cytocompatibility than the pristine ESM and promotes the osteogenic differentiation of hMSCs more efficiently. Overall, the apatite/ESM composite exhibits compositional, crystalline, mechanical, and biological properties that resemble those of mineralized tissues, rendering it an approachable and novel material especially useful in guided tissue/bone regeneration.

Biocompatibility Testing for Implants: A Novel Tool for Selection and Characterization

This review article dives into the complex world of biocompatibility testing: chemical, mechanical, and biological characterization, including many elements of biocompatibility, such as definitions, descriptive examples, and the practical settings. The focus extends to evaluating standard documents obtained from reliable organizations; with a particular focus on open-source information, including FDA-USA, ISO 10933 series, and TÜV SÜD. We found a significant gap in this field: biomaterial scientists and those involved in the realm of medical device development in general, and implants in particular, lack access to a tool that reorganizes the process of selecting the appropriate biocompatibility test for the implant being examined. This work progressed through two key phases that aimed to provide a solution to this gap. A straightforward "yes or no" flowchart was initially developed to guide biocompatibility testing decisions based on the previously accumulated information. Subsequently, the Python code was employed, generating a framework through targeted questions. This work reshapes biocompatibility evaluation, bridging theory and practical implementation. An integrated approach via a flowchart and the Python code empowers stakeholders to navigate biocompatibility testing effortlessly. To conclude, researchers are now better equipped for a safer, more effective implant development, propelling the field towards improved patient care and innovative progress.

Advances of plant and biomass extracted zirconium nanoparticles in dental implant application

Nanoparticles are minimal materials with unique physicochemical features that set them apart from bulk materials of the same composition. These properties make nanoparticles highly desirable for use in commercial and medical research. The primary intention for the development of nanotechnology is to achieve overarching social objectives like bettering our understanding of nature, boosting productivity, improving healthcare, and extending the bounds of sustainable development and human potential. Keeping this as a motivation, Zirconia nanoparticles are becoming the preferred nanostructure for modern biomedical applications. This nanotechnology is exceptionally versatile and has several potential uses in dental research. This review paper concentrated on the various benefits of zirconium nanoparticles in dentistry and how they provide superior strength and flexibility compared to their counterparts. Moreover, the popularity of zirconium nanoparticles is also growing as it has strong biocompatibility potency. Zirconium nanoparticles can be used to develop or address the major difficulty in dentistry. Therefore, this review paper aims to provide a summary of the fundamental research and applications of zirconium nanoparticles in dental implants.

Preventing Peri-implantitis: The Quest for a Next Generation of Titanium Dental Implants

Titanium and its alloys are frequently the biomaterial of choice for dental implant applications. Although titanium dental implants have been utilized for decades, there are yet unresolved issues pertaining to implant failure. Dental implant failure can arise either through wear and fatigue of the implant itself or peri-implant disease and subsequent host inflammation. In the present report, we provide a comprehensive review of titanium and its alloys in the context of dental implant material, and how surface properties influence the rate of bacterial colonization and peri-implant disease. Details are provided on the various periodontal pathogens implicated in peri-implantitis, their adhesive behavior, and how this relationship is governed by the implant surface properties. Issues of osteointegration and immunomodulation are also discussed in relation to titanium dental implants. Some impediments in the commercial translation for a novel titanium-based dental implant from "bench to bedside" are discussed. Numerous in vitro studies on novel materials, processing techniques, and methodologies performed on dental implants have been highlighted. The present report review that comprehensively compares the in vitro, in vivo, and clinical studies of titanium and its alloys for dental implants.

Aspects and Principles of Material Connections in Restorative Dentistry-A Comprehensive Review

The combination of two dissimilar materials has always been a serious problem in dentistry. In order to meet this challenge, it is necessary to combine both chemical methods (treatment with silanes, (meth)acrylic functional monomers) and the development of the surface of the joined material in a physical way, e.g., by sandblasting with alumina, alumina with silica, acid etching, the use of lasers and other means. The purpose of this literature review is to present all methods of joining dental composites with other materials such as ceramics, metal, another composite material. This review covers articles published within the period 2012-2022 in journals indexed in the PubMed database, written in English and describing joining different dental materials to each other. All the critical steps of new joint preparation have been addressed, including proper cleaning of the joint surface, the application of appropriate primers capable of forming a chemical bond between ceramics, zirconium oxide or metals and alloys, and finally, the application of new composite materials.

Cytotoxic assessment of 3D printed photoinitiated prosthodontic resins versus heat polymerized acrylic resin (In-Vitro Study).. [DOI: 10.21203/rs.3.rs-1948364/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Background: Although 3D printed photoinitiated resins are among the many materials utilized in prosthetic appliances today, biocompatibility for photocuring 3D printing materials for direct and long-term contacting with living body remain scarce. The purpose of this in vitro study was to evaluate the cell viability of human gingival fibroblasts after the exposure to two different 3D printed photoinitiated resins and compare it to the traditionally used heat polymerized acrylic resin for up to 7 days.Methods: This comparative in vitro study of sample size (n= 96), where the 3D printed resin disc samples (n= 64), were divided into two test groups, test group 1 (TG1) for NextDent Base resin (n= 32) and test group 2 (TG2) for Dental LT clear resin (n= 32), to be compared to Heat polymerized acrylic resin samples (Reference group (RG)) (n= 32). Human gingival fibroblasts were extracted from attached keratinized gingival tissues collected from healthy patient undergoing clinical crown lengthening procedure, cellular viability using MTT assay in response to TG1, TG2 and RG samples was assessed throughout four-time intervals (24, 48, 72 and 168 hours). The One-Way ANOVA test followed by Tukey’s post hoc test and Repeated Measures ANOVA test were used for statistical analyses, statistically significant different at P value ≤ 0.05Results: Throughout time intervals, there was a decrease in cell viability of all groups but with favorable cell viability which was more that 90% denoting non cytotoxicity. It was found to be significant among RG (P< 0.0001). The highest cell viability was found after 24 hours among all groups; however, the least viability was found after 48 hours among TG1 and RG, and among TG2 after 72 hours. After 168 hours, there was a non-statistical significant change in cell viability between groups (P= 0.526). there was significant increase in optical density for all groups throughout time intervals (P< 0.0001).Conclusion: Photoinitiated resins are comparable to traditionally used heat polymerized acrylic resin with equivalent cytotoxic effect for long term use. 3D printed photoinitiated resins are biocompatible and suggested for long term intraoral use.

Biosafety evaluation of Li2Si2O5 whisker-reinforced glass-ceramics

Lithium disilicate (Li2Si2O5) glass-ceramic is a commonly used dental ceramic material. In this study, Li2Si2O5 whiskers were prepared by the hydrothermal method, mixed with Li2Si2O5 glass powders, and Li2Si2O5 whisker-reinforced glass-ceramics were prepared by reaction sintering. The biosafety of the new Li2Si2O5 glass-ceramics were evaluated by in vitro cytotoxicity, hemolysis, oral mucosal irritation, acute systemic toxicity, and subacute systemic toxicity (oral route) tests according to ISO 7405/ISO 10993 standards. The cytotoxicity test results showed that the cell growth of the experimental group was good, and the cell number and morphology were not significantly different from those of the blank group (P > 0.05). The toxicity grading for both experimental and blank control groups were 0. The hemolysis rate of the material was 1.25%, which indicated that it did not cause hemolytic reaction. The material was non-irritating to the oral mucosa. In acute systemic toxicity test, animals in the experimental group showed increased body weight, moved freely, with no signs of poisoning. The food utilization rate and relative growth rate (change of the weight) of rats in the subacute systemic toxicity test were not statistically different from those of the control group (P > 0.05). Preliminary evaluation of the biosafety of the Li2Si2O5 whisker-reinforced glass-ceramics showed that it met the existing regulatory standards, and further biosafety experiments can be conducted, following which the material may be expected to be applied in clinical practice.

Application of Antimicrobial Polymers in the Development of Dental Resin Composite

Dental resin composites have been widely used in a variety of direct and indirect dental restorations due to their aesthetic properties compared to amalgams and similar metals. Despite the fact that dental resin composites can contribute similar mechanical properties, they are more likely to have microbial accumulations leading to secondary caries. Therefore, the effective and long-lasting antimicrobial properties of dental resin composites are of great significance to their clinical applications. The approaches of ascribing antimicrobial properties to the resin composites may be divided into two types: The filler-type and the resin-type. In this review, the resin-type approaches were highlighted. Focusing on the antimicrobial polymers used in dental resin composites, their chemical structures, mechanical properties, antimicrobial effectiveness, releasing profile, and biocompatibility were included, and challenges, as well as future perspectives, were also discussed.

Wettability and pre-osteoblastic behavior evaluations of a dense bovine hydroxyapatite ceramics

In this study, the wettability, cell viability, and roughness of an experimental dense bovine hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂] ceramic block were evaluated so that, in the future, it could be used as a base material for dental implants. The results to commercial zirconia and a commercially pure titanium (Ti) alloy were compared. The surface roughness and contact angles were measured. An in vitro evaluation was conducted by means of tests in which pre-osteoblastic MC3T3-E1 cells were placed in indirect and direct contact with these materials. For cell viability, a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and crystal violet test were conducted. A qualitative analysis was conducted using variable pressure scanning electron microscopy (SEM). No statistically significant differences were observed in wettability and roughness tests among the groups. In both the MTT assay and crystal violet test, all groups demonstrated satisfactory results without cytotoxicity. SEM showed cell adhesion and cell proliferation results on the material surfaces after 24 h and 48 h. In conclusion, this dense Ca₁₀ (PO₄)₆(OH)₂ ceramic can be considered as a potential biocompatible material.

Production and Characterization of Porous Polymeric Membranes of PLA/PCL Blends with the Addition of Hydroxyapatite

Polymer membranes have been widely used in guided tissue regeneration (GTR) and guided bone regeneration (GBR). The literature recognizes that poly (lactic acid) (PLA)/poly (ε-caprolactone) (PCL) blends have better physicochemical properties and that a porous polymer surface facilitates cell adhesion and proliferation. In addition, hydroxyapatite (HAp) incorporated into the polymer matrix promotes osteoinduction properties and osteoconduction to the polymer-ceramic biocomposite. Therefore, polymer membranes of PLA/PCL blend with the addition of HAp could be an alternative to be used in GBR. HAp was obtained by precipitation using the mixture of solutions of tetrahydrate calcium nitrate and monobasic ammonium phosphate salts. The porous membranes of the PLA/PCL (80/20) blend with the addition of HAp were obtained by solvent casting with a controlled humidity method, with the dispersion of HAp in chloroform and subsequent solubilization with the components of the blend. The solution was poured into molds for solvent evaporation under a controlled humidity atmosphere. The membranes showed the formation of pores on their surface, together with dispersed HAp particles. The results showed an increase in the surface porosity and improved bioactivity properties with the addition of HAp. Moreover, in biological studies with cell culture, it was possible to observe that the membranes with HAp have no cytotoxic effect on MC3T3 cells. These results indicate a promising use of the new biomaterial for GBR.

Evaluation and comparison of shear bond strength of porcelain to a beryllium-free alloy of nickel-chromium, nickel and beryllium free alloy of cobalt-chromium, and titanium: An in vitro study

Aims:

The aim of this study was to evaluate and compare the shear bond strength of porcelain to the alloys of nickel-chromium (Ni-Cr), cobalt-chromium (Co-Cr), and titanium.

Materials and Methods:

A total of 40 samples (25 mm × 3 mm × 0.5 mm) were fabricated using smooth casting wax and cast using Ni-Cr, Co-Cr, and titanium alloys followed by porcelain buildup. The samples were divided into four groups with each group containing 10 samples (Group A1–10: sandblasted Ni-Cr alloy, Group B1–10: sandblasted Co-Cr alloy, Group C1–10: nonsandblasted titanium alloy, and Group D1–10: sandblasted titanium alloy). Shear bond strength was measured using a Universal Testing Machine.

Statistical Analysis Used:

ANOVA test and Tukey's honestly significance difference post hoc test for multiple comparisons.

Results:

The mean shear bond strength values for these groups were 22.8960, 27.4400, 13.2560, and 25.3440 MPa, respectively, with sandblasted Co-Cr alloy having the highest and nonsandblasted titanium alloy having the lowest value.

Conclusion:

It could be concluded that newer nickel and beryllium free Co-Cr alloys and titanium alloys with improved strength to weight ratio could prove to be good alternatives to the conventional nickel-based alloys when biocompatibility was a concern.

Oxidative Stress Evaluation in Patients Treated with Orthodontic Self-ligating Multibracket Appliances: An in Vivo Case-Control Study

OBJECTIVE

Oxidative stress is a pathologic event induced by a prevalence of oxidant agents on the antioxidant ones, with a consequent alteration of oxide-reducing balance.

INTRODUCTION

Freeradicals produce damages both in cellular and extra-cellular components; phospholipid membranes, proteins, mitochondrial and nuclear DNA, are the target of the oxidative stress, that can finally cause cellular death due to apoptosis.

MATERIALS & METHODS

Orthodontic appliances such as brackets, wires, resins and soldering have some components that can be considered as potential allergen, carcinogenic, cytotoxic and gene mutation factors. The primary aim of this research is to evaluate oxidative stress in the saliva of patients treated with multibracket self-ligating vestibular orthodontic appliances; the secondary purpose is to investigate the influence of orthodontic multibracket therapy on oral hygiene and the consequent effect on oxidative stress. Salivary specimens has been collected in a sample of 23 patients were enrolled (12 Female, 11 Male) between 12 and 16 years of age (mean age 14.2). For each patient has been collected a salivary specimen at the following time points; before orthodontic bonding (T1), five weeks (T2) and ten weeks (T3) after orthodontic appliance bonding.

RESULTS

Samples has been analysed with a photometer due to SAT Test (Salivary Antioxidant Test). Data obtained show a mean of 2971 mEq/l of anti-oxidant agents before orthodontic treatment, and after five weeks from the bonding the mean was decreased to 2909 mEq/l, instead at ten weeks was increased to 3332 mEq/l. Repeated measures ANOVA did not reveal statistically significant differences between the time points (P = 0.1697). The study did not reveal any correlation between the level of dental hygiene and that of oxidative stress (Pearson Correlation Coefficient R = 0).

CONCLUSION

Orthodontic treatment with multibrackets vestibular metallic appliance seems to be not able to affect oxidative stress during the first ten weeks of therapy.

Dentin on the nanoscale: Hierarchical organization, mechanical behavior and bioinspired engineering

OBJECTIVE

Knowledge of the structural organization and mechanical properties of dentin has expanded considerably during the past two decades, especially on a nanometer scale. In this paper, we review the recent literature on the nanostructural and nanomechanical properties of dentin, with special emphasis in its hierarchical organization.

METHODS

We give particular attention to the recent literature concerning the structural and mechanical influence of collagen intrafibrillar and extrafibrillar mineral in healthy and remineralized tissues. The multilevel hierarchical structure of collagen, and the participation of non-collagenous proteins and proteoglycans in healthy and diseased dentin are also discussed. Furthermore, we provide a forward-looking perspective of emerging topics in biomaterials sciences, such as bioinspired materials design and fabrication, 3D bioprinting and microfabrication, and briefly discuss recent developments on the emerging field of organs-on-a-chip.

RESULTS

The existing literature suggests that both the inorganic and organic nanostructural components of the dentin matrix play a critical role in various mechanisms that influence tissue properties.

SIGNIFICANCE

An in-depth understanding of such nanostructural and nanomechanical mechanisms can have a direct impact in our ability to evaluate and predict the efficacy of dental materials. This knowledge will pave the way for the development of improved dental materials and treatment strategies.

CONCLUSIONS

Development of future dental materials should take into consideration the intricate hierarchical organization of dentin, and pay particular attention to their complex interaction with the dentin matrix on a nanometer scale.

Determination of homologous distributions of bisEMA dimethacrylates in bulk-fill resin-composites by GC-MS

OBJECTIVES

Ethoxylated bisphenol A dimethacrylate (bisEMA) is a basis monomer in several dental resin composites. It was the aim of the present study to develop a method allowing detection of bisEMA and its different degrees of ethoxylation eluted from polymerized resin composites.

METHODS

High-temperature gas chromatography/mass spectrometry (HT-GC/MS) by direct on-column injection was used to identify ethoxylated bisEMA in ethanol/water (3:1) eluates from polymerized specimen of four bulk-fill resin composites - Venus(®) bulk fill, Surefil(®) SDR™ flow, Filtek™ Bulk Fill and Sonic Fill™. Additionally, the unpolymerised pastes were analysed.

RESULTS

The developed method allowed identification of a homologous series of bisEMA up to twelve ethoxy groups in the unpolymerised materials. The molecular masses of the homologous bisEMA varied between 452 g/mol and 892 g/mol and were detected for retention times from 9.43 min to 13.36 min. Analysis of eluates from polymerised materials identified bisEMA monomers with less than 6 ethoxy groups. Chromatograms showed larger peak areas for the lower volatile bisEMA with 4-6 ethoxy groups compared with higher volatile bisEMA with 2 or 3 ethoxy groups, thus indicating that the amounts of these homologues in the pastes were higher.

SIGNIFICANCE

Ethoxylated bisEMA with up to twelve ethoxy groups can be identified by HT-GC/MS. In all eluates bisEMA was found. The higher the number of ethoxy groups the lower are the peak areas from bisEMA in the gas chromatogram. These findings may be significant for toxicological analysis of resin-composites incorporating bis-EMA.

Comparison of the osteogenic potential of titanium- and modified zirconia-based bioceramics

Zirconia is now favored over titanium for use in dental implant materials because of its superior aesthetic qualities. However, zirconia is susceptible to degradation at lower temperatures. In order to address this issue, we have developed modified zirconia implants that contain tantalum oxide or niobium oxide. Cells attached as efficiently to the zirconia implants as to titanium-based materials, irrespective of surface roughness. Cell proliferation on the polished surface was higher than that on the rough surfaces, but the converse was true for the osteogenic response. Cells on yttrium oxide (Y₂O₃)/tantalum oxide (Ta₂O₅)- and yttrium oxide (Y₂O₃)/niobium oxide (Nb₂O₅)-containing tetragonal zirconia polycrystals (TZP) discs ((Y, Ta)-TZP and (Y, Nb)-TZP, respectively) had a similar proliferative potential as those grown on anodized titanium. The osteogenic potential of MC3T3-E1 pre-osteoblast cells on (Y, Ta)-TZP and (Y, Nb)-TZP was similar to that of cells grown on rough-surface titanium. These data demonstrate that improved zirconia implants, which are resistant to temperature-induced degradation, retain the desirable clinical properties of structural stability and support of an osteogenic response.

Human brain mercury levels related to exposure to amalgam fillings

The safety of dental amalgam as the primary material in dental restoration treatments has been debated since its introduction. It is widely accepted that amalgam restorations continuously release elemental mercury (Hg) vapor, which is inhaled and absorbed by the body and distributed to tissues, including the brain. The aim of the present study was to investigate whether the presence of amalgam fillings is correlated with brain Hg level. The Hg levels in the parietal lobes of the brains of 32 cadavers were analyzed with an atomic absorption spectrometer with the mercury hydride system. A total of 32 brain samples were tested; of these, 10 were from cadavers with amalgam fillings, while 22 of them were amalgam free. Hg was detected in 60.0% (6 of 10) of the samples in the amalgam group and in 36.3% (8 of 22) in the amalgam-free group. The average Hg level of the amalgam group was 0.97 ± 0.83 µg/g (minimum: 0.3 µg/g and maximum: 2.34 µg/g), and in the amalgam-free group, it was 1.06 ± 0.57 µg/g (minimum: 0.17 µg/g and maximum: 1.76 µg/g). The results of the present study showed no correlation between the presence of amalgam fillings and brain Hg level.

Efficacy of composite versus ceramic inlays and onlays: study protocol for the CECOIA randomized controlled trial

Background

Dental caries is a common disease and affects many adults worldwide. Inlay or onlay restoration is widely used to treat the resulting tooth substance loss. Two esthetic materials can be used to manufacture an inlay/onlay restoration of the tooth: ceramic or composite. Here, we present the protocol of a multicenter randomized controlled trial (RCT) comparing the clinical efficacy of both materials for tooth restoration. Other objectives are analysis of overall quality, wear, restoration survival and prognosis.

Methods

The CEramic and COmposite Inlays Assessment (CECOIA) trial is an open-label, parallel-group, multicenter RCT involving two hospitals and five private practices. In all, 400 patients will be included. Inclusion criteria are adults who need an inlay/onlay restoration for one tooth (that can be isolated with use of a dental dam and has at least one intact cusp), can tolerate restorative procedures and do not have severe bruxism, periodontal or carious disease or poor oral hygiene. The decayed tissue will be evicted, the cavity will be prepared for receiving an inlay/onlay and the patient will be randomized by use of a centralized web-based interface to receive: 1) a ceramic or 2) composite inlay or onlay. Treatment allocation will be balanced (1:1). The inlay/onlay will be adhesively luted. Follow-up will be for 2 years and may be extended; two independent examiners will perform the evaluations. The primary outcome measure will be the score obtained with use of the consensus instrument of the Fédération Dentaire Internationale (FDI) World Dental Federation. Secondary outcomes include this instrument’s items, inlay/onlay wear, overall quality and survival of the inlay/onlay. Data will be analyzed by a statistician blinded to treatments and an adjusted ordinal logistic regression model will be used to compare the efficacy of both materials.

Discussion

For clinicians, the CECOIA trial results may help with evidence-based recommendations concerning the choice of materials for inlay/onlay restoration. For patients, the results may lead to improvement in long-term restoration. For researchers, the results may provide ideas for further research concerning inlay/onlay materials and prognosis.

This trial is funded by a grant from the French Ministry of Health.

Trial registration

ClinicalTrials.gov Identifier: NCT01724827

Surface treatment of dental porcelain: CO2 laser as an alternative to oven glaze

This work tested continuous CO2 laser as a surface treatment to dental porcelain and compared it to oven glaze (auto-glaze) by means of roughness and color parameters. Three commercial veneering porcelains with different crystalline content were tested: VM7, VM9, and VM13. Porcelain discs (3.5 × 2.0 mm, diameter × height) were sintered and had one side ground by a diamond bur (45 μm) simulating a chairside adjustment in a clinical office. Specimens (n = 7) were divided into the following groups: C--control (no treatment), G--auto-glaze (oven), and L--surface continuous irradiation with CO2 laser (Gem Laser, Coherent; λ = 10.6 μm). Laser was tested in three exposure times (3, 4, or 5 min) and two irradiances (45 and 50 W/cm(2)). Roughness parameters (Ra, Rz, and Rpm/Rz) were measured using a rugosimeter (Surftest 301, Mitutoyo). Color differences (ΔE) between the G and L groups were calculated (VITA Easyshade); ΔE values up to 3.3 were considered as not perceivable. A surface analysis was conducted by stereomicroscopy (Olympus SZ61) and SEM (Stereoscan 440, LEO). Crystalline content of specimens from groups C and L (50 W/cm(2), 5 min) was assessed by X-ray diffraction and then compared. Surface roughness (Ra and Rz) observed for laser-irradiated groups was similar to G for all studied porcelains. Rpm/Rz ratios were near 1.0 for all groups that indicated a sharp ridge profile for all specimens. Only one laser condition studied (50 W/cm(2), 3 min) from VM7 porcelain resulted in color difference (ΔE = 3.5) to G. Specimens irradiated with 50 W/cm(2) for 5 min presented the smoother surface observed by SEM, comparable to G. X-ray diffraction data revealed an increase in leucite crystallite size for VM9 and VM13 porcelains after laser treatment. Regarding roughness, continuous CO2 laser applied on porcelain surface was as effective as conventional oven auto-glaze.

Risk aspects of dental restoratives: From amalgam to tooth-colored materials

Dental materials’ choice of patients has considerably changed. Whereas cast gold and amalgam have been the predominant biomaterials for decades, today tooth-colored materials like resin-based composites and ceramics are more and more successful. However, are we going to replace a good but biologically questionable material (amalgam) with an equal material (resin composite) being more esthetic but also biologically questionable For amalgam, long-term clinical studies reported some significant hints that in single cases amalgam may be a health hazard for patients, finally Norway banned amalgam completely. The main advantage of a resin-based composite over amalgam is its tooth-like appearance and more or less absence of extensive preparation rules. For many years it was believed that resin-based composites may cause pulpal injury. However, pulpal injury associated with the use of resin-based composites is not correlated with their cytotoxic properties. Nevertheless, resin-based composites and other dental materials require rigorous safety evaluation and continuous monitoring to prevent adverse events similar like with amalgam. Because of non-biocompatible pulp responses to resin-based composites and amalgam, they should not be placed in direct contact with the dental pulp. The less dentin remaining in the floor of preparations between resin-based composites or other dental materials is more likely to cause pulpitis. Percentage of patients and dental practitioners who display allergic reactions is between 0.7% and 2%. The release of cytotoxic monomers from resin-based materials is highest after polymerization and much lower after 1 wk. Substances released from resin-based composites have been shown to be toxic in cytotoxicity tests. Nevertheless, in vitro cytotoxicity assays have shown that amalgam has greater toxic effects than resin-based composites, sometime 100-700-fold higher. Altogether, the risk of side-effects is low, but not zero, especially for dental personnel.

Reaction of rat subcutaneous connective tissue to resin composites polymerized with different light curing units and different lightening methods

The aim of the study was to determine and compare the reaction of rat subcutaneous connective tissue to resin composites polymerized with different lights curing and lightening methods. In this in vivo study, 20 mature Wister Albino rats were used. The composite discs, 4 mm in diameter and 2 mm thick, were cured by QTH or LED light curing units with 4 different lightning methods (full power QTH, full power LED, pulse LED, and ramp LED). Five resin composite discs were implanted in each rat, so that 4 of 5 discs for implantation of cured composite discs differently and central one as control without implantation. After sacrificing at 7, 14, 30, and 60 days the inflammatory grade, fibrosis, and necrosis were determined. Freedman and Cochran tests were used to analyze the data using SPSS software ver. 15. The results of the study showed significant differences in inflammation grade and fibrosis among control group and 4 experimental groups at day 14 (P < 0.05). In necrosis, there was no significant difference among 4 groups in different times (P > 0.05). In conclusion, neither the type of light curing units (LED or QTH) nor the lightening methods can affect the grade of inflammatory reaction.

Predicting clinical biological responses to dental materials

OBJECTIVES

Methods used to measure and predict clinical biological responses to dental materials remain controversial, confusing, and to some extent, unsuccessful. The current paper reviews significant issues surrounding how we assess the biological safety of materials, with a historical summary and critical look at the biocompatibility literature. The review frames these issues from a U.S. perspective to some degree, but emphasizes their global nature and universal importance.

METHODS

The PubMed database and information from the U.S. Food and Drug Administration, International Standards Organization, and American National Standards Institute were searched for prominent literature addressing the definition of biocompatibility, types of biological tests employed, regulatory and standardization issues, and how biological tests are used together to establish the biological safety of materials. The search encompassed articles published in English from approximately 1965-2011. The review does not comprehensively review the literature, but highlights significant issues that confront the field.

RESULTS

Years ago, tests for biological safety sought to establish material inertness as the measure of safety, a criterion that is now deemed naive; the definition of biocompatibility has broadened along with the roles for materials in patient oral health care. Controversies persist about how in vitro or animal tests should be used to evaluate the biological safety of materials for clinical use. Controlled clinical trials remain the single best measure of the clinical response to materials, but even these tests have significant limitations and are less useful to identify mechanisms that shape material performance. Practice-based research networks and practitioner databases are emerging as important supplements to controlled clinical trials, but their final utility remains to be determined.

SIGNIFICANCE

Today we ask materials to play increasingly sophisticated structural and therapeutic roles in patient treatment. To accommodate these roles, strategies to assess, predict, and monitor material safety need to evolve. This evolution will be driven not only by researchers and manufacturers, but also by patients and practitioners, who want to use novel materials in new ways to treat oral disease.

Histopathologic study of rat connective tissue responses to maxillofacial silicone elastomers

The aim of this histopathologic study was to assess and compare the subcutaneous connective tissue reaction to three different maxillofacial silicone elastomers (Cosmesil, Multisil, Episil). The test materials were directly inserted subcutaneously into the dorsal subcutaneous tissue of Wistar albino rats. Histopathological examinations were done at 7, 30, and 90 days after the implantation procedure. The presence of inflammation, presence of inflammatory giant cells, and the thickness of fibrous connective tissue adjacent to each inserted sample were recorded. Data was evaluated by analysis of variance, Wilcoxon signed ranks test and Kruskal Wallis test. Cosmesil, Multisil and Episil silicone elastomers at 7 days elicited a severe inflammatory reaction. However, these reactions decreased by the 30 and 90 days. All silicone elastomers elicited a moderate inflammatory reaction at 30 and 90 days. There were no significant differences in tissue reaction between the materials at 7, 30, and 90 days (P > 0.05). All the maxillofacial silicone elastomers evaluated can not be assigned a favorable biocompatibility level based on this study's histologic findings.

GEPIs-HA hybrid: a novel biomaterial for tooth repair

Dental caries are slowly progressive and infectious disease, which result in localized dissolution and destruction of the calcified tissues. In routine clinical treatments, microleakage following with secondary caries usually occurs due to the discrepancy in physico-chemical property between filled materials and tooth. Ideal filling materials for tooth defect should be similar to the structure and chemical composition of natural tooth. Recently, molecular biomimetics developed a novel nanotechnology through biology, which fabricate materials based on molecular recognition between genetically engineered peptides for inorganics (GEPIs) and inorganic crystal. Since GEPIs can be used in the assembly of functional nanostructures, we hypothesis that an analogue of dental hard tissue, hybrid of GEPIs and HA crystal, might be engineered using the recognition properties between GEPIs and HA crystal.