Identification and quantification of leachable substances from polymer-based orthodontic base-plate materials

Contact Dermatitis From Biomedical Devices, Implants, and Metals-Trouble From Within

Allergic contact dermatitis is characterized by its appearance of red, raised and infiltrated, scaling or scabbed skin and intense pruritus, and distinguished from irritant contact dermatitis by its specific immune process and histopathology. Many contact allergens are low-molecular- weight chemicals including metals such as nickel, cobalt, and chromium, preservatives, and adhesives. When such materials are used internally in biomedical devices, they are similarly capable of causing sensitization and an inflammatory response. Sometimes, the reaction remains internal, and presents as swelling, pain, stiffness, decreased range of motion, and internal itching around the implant. Such reactions may, in some cases, also extend to include a localized or, rarely, systemic contact dermatitis indicative of the same process. This review will present an overview of reported skin and local internal reactions to orthopedic implants, which are the largest category of implanted internal metal devices. Immune reactions to smaller categories of medical appliances include cardiac devices and vascular stents, neuromodulation devices, diabetic appliances, Nuss bar surgery for pectus excavatum, and dental and spinal implants. We will review the available diagnostic tools, the consensus on interpretation, and reported strategies for treatment.

Embryotoxicity and teratogenesis of orthodontic acrylic resin in zebrafish

Objectives

This study investigated the in vivo embryotoxicity, teratogenic potential, and additional effects of orthodontic acrylic resin as well as its components, utilizing zebrafish as a model organism. The research focused on morphological, cardiac, behavioral, and cognitive evaluations that were performed on embryos and larval-stage animals subjected to chronic exposure.

Materials and methods

Embryo and larval-stage zebrafish were categorized into five experimental groups, which were further subdivided into five subgroups. These subgroups included three specific doses for each tested substance, a control with the vehicle (0.1 % dimethyl sulfoxide in water), and an absolute control (water). Assessments were performed on day 5 post-fertilization, which included morphological, cardiac, behavioral, and cognitive evaluations. All experiments had a sample size of ten animals and were performed in triplicate. Survival and hatching rates were analyzed using the Kaplan-Meier test, while other measurements were assessed using one-way analysis of variance (ANOVA), followed by the Tukey post hoc test.

Results

Statistically significant differences were observed between the control and treatment groups across all the tested substances for heart rate, cognitive responsiveness, and cellular apoptosis. However, survival, hatching rate, and other parameters exhibited no significant variation, except for the highest dose in the dibutyl phthalate group, which demonstrated a notable difference in survival.

Conclusions

Chronic exposure to acrylic resin and its components may be associated with decreased cognitive ability and cardiac rhythm, as well as an increase in the level of cellular apoptosis in zebrafish.

Polymeric Denture Base Materials: A Review

An ideal denture base must have good physical and mechanical properties, biocompatibility, and esthetic properties. Various polymeric materials have been used to construct denture bases. Polymethyl methacrylate (PMMA) is the most used biomaterial for dentures fabrication due to its favorable properties, which include ease of processing and pigmenting, sufficient mechanical properties, economy, and low toxicity. This article aimed to comprehensively review the current knowledge about denture base materials (DBMs) types, properties, modifications, applications, and construction methods. We searched for articles about denture base materials in PubMed, Scopus, and Embase. Journals covering topics including dental materials, prosthodontics, and restorative dentistry were also combed through. Denture base material variations, types, qualities, applications, and fabrication research published in English were considered. Although PMMA has several benefits and gained popularity as a denture base material, it has certain limitations and cannot be classified as an ideal biomaterial for fabricating dental prostheses. Accordingly, several studies have been performed to enhance the physical and mechanical properties of PMMA by chemical modifications and mechanical reinforcement using fibers, nanofillers, and hybrid materials. This review aimed to update the current knowledge about DBMs' types, properties, applications, and recent developments. There is a need for specific research to improve their biological properties due to patient and dental staff adverse reactions to possibly harmful substances produced during their manufacturing and use.

Biological aspects of modern dental composites

Biological evaluation of resin-based dental composites has traditionally been based on in vitro endpoint tests with different methods to determine loss of cell viability and cell morphology changes after exposure to the material or monomer constituents. The data reveals a potential for biological effects, but clinical relevance of such data is limited. Positive allergy tests and allergic clinical reactions to dental monomers are observed in dental personnel and patients. The aim of this review is to address newer research on molecular events caused by exposure to resin-based composites to have a better understanding of the potential for clinical adverse effects. A more accurate understanding of the biological aspects of dental composite materials has been found after studying parameters like glutathione depletion, oxidative stress, genotoxicity, and immunomodulatory key effects in various cell culture models. Using omics-based approaches allow for a broader and non-specified search of changes caused by methacrylate exposure. Defense mechanisms and adaption are observed in cells exposed to monomer concentrations relevant to clinical exposure. The above-mentioned methods are the foundations for modified testing strategies. The clinical relevance of most available in vitro endpoint tests is of limited relevance for the patient. Research focusing on molecular mechanisms has given new insight into methacrylate toxicity in exposed cells. Using this knowledge from mechanistic studies to develop standardized in vitro biocompatibility tests will likely improve their clinical relevance.

Novel Tuning of PMMA Orthopedic Bone Cement Using TBB Initiator: Effect of Bone Cement Extracts on Bioactivity of Osteoblasts and Osteoclasts

Bone cement containing benzoyl peroxide (BPO) as a polymerization initiator are commonly used to fix orthopedic metal implants. However, toxic complications caused by bone cement are a clinically significant problem. Poly (methyl methacrylate) tri-n-butylborane (PMMA-TBB), a newly developed material containing TBB as a polymerization initiator, was found to be more biocompatible than conventional PMMA-BPO bone cements due to reduced free radical generation during polymerization. However, free radicals might not be the only determinant of cytotoxicity. Here, we evaluated the response and functional phenotypes of cells exposed to extracts derived from different bone cements. Bone cement extracts were prepared from two commercial PMMA-BPO cements and an experimental PMMA-TBB. Rat bone marrow-derived osteoblasts and osteoclasts were cultured in a medium supplemented with bone cement extracts. More osteoblasts survived and attached to the culture dish with PMMA-TBB extract than in the culture with PMMA-BPO extracts. Osteoblast proliferation and differentiation were higher in the culture with PMMA-TBB extract. The number of TRAP-positive multinucleated cells was significantly lower in the culture with PMMA-TBB extract. There was no difference in osteoclast-related gene expression in response to different bone cement extracts. In conclusion, PMMA-TBB extract was less toxic to osteoblasts than PMMA-BPO extracts. Although extracts from the different cement types did not affect osteoclast function, PMMA-TBB extract seemed to reduce osteoclastogenesis, a possible further advantage of PMMA-TBB cement. These implied that the reduced radical generation during polymerization is not the only determinant for the improved biocompatibility of PMMA-TBB and that the post-polymerization chemical elution may also be important.

Modification of Polymer Based Dentures on Biological Properties: Current Update, Status, and Findings

Polymers remain an integral part of denture fabrication materials, specifically polymethylmetacrylate (PMMA). PMMA has been extensively used, particularly in construction as a denture base material. Nonetheless, various challenges, including microbial threats in the form of candidiasis occurrence, still remain a biological challenge to denture wearers. The present article comprehensively reviews the biomodifications introduced to denture components, in particular denture base material, to improve the overall biological properties, together with physical, mechanical, structural integrity, and optical properties. In addition, fundamental information specifically to PMMA as a conventional denture base material and the causative aetiological microbial agents for biological threat to dentures are explored.

Oil-Incorporated Poly(Lactic Acid) as an Alternative Material for Orthodontic Base Plate: A 3D Printing Approach

Removable orthodontic appliances fabricated from poly (methyl methacrylate) (PMMA) have been routinely used for active orthodontic correction and as retention appliances. This article reports the use of a combination of biodegradable-grade poly (lactic acid) (PLA) and cooking-grade sesame oil as a biodegradable alternative for PMMA. The underlying purpose is to combat the environmental hazards due to nondegradable PMMA as well as to overcome its structural and mechanical drawbacks. The fabrication technique that has been used is fused deposition modeling-based 3D printing technology. Oil-dipping for 24 h was done to render the PLA hydrophobic and to reduce its brittleness. Incorporation of oil within the PLA base plate has been confirmed by FT-IR and FT-Raman spectroscopic techniques. The PLA-cooking oil material has exhibited satisfactory tensile, compressive and flexural strengths. The proposed material has demonstrated excellent attributes in terms of product precision, dimensional stability, density, hardness, and maximum load bearing capacity for the purpose of fabricating orthodontic appliances.

The Biological Effects of 3D Resins Used in Orthodontics: A Systematic Review

Three-dimensional (3D) resin medical-dental devices have been increasingly used in recent years after the emergence of digital technologies. In Orthodontics, therapies with aligners have gained popularity, mainly due to the aggressive promotion policies developed by the industry. However, their systemic effects are largely unknown, with few studies evaluating the systemic toxicity of these materials. The release of bisphenol A and other residual monomers have cytotoxic, genotoxic, and estrogenic effects. This systematic review aims to analyze the release of toxic substances from 3D resins used in Orthodontics and their toxic systemic effects systematically. The PICO question asked was, "Does the use of 3D resins in orthodontic devices induce cytotoxic effects or changes in estrogen levels?". The search was carried out in several databases and according to PRISMA guidelines. In vitro, in vivo, and clinical studies were included. The in vitro studies' risk of bias was assessed using the guidelines for the reporting of pre-clinical studies on dental materials by Faggion Jr. For the in vivo studies, the SYRCLE risk of bias tool was used, and for the clinical studies, the Cochrane tool. A total of 400 articles retrieved from the databases were initially scrutinized. Fourteen articles were included for qualitative analysis. The risk of bias was considered medium to high. Cytotoxic effects or estrogen levels cannot be confirmed based on the limited preliminary evidence given by in vitro studies. Evidence of the release of bisphenol A and other monomers from 3D resin devices, either in vitro or clinical studies, remains ambiguous. The few robust results in the current literature demonstrate the absolute need for further studies, especially given the possible implications for the young patient's fertility, which constitutes one of the largest groups of patients using these orthodontic devices.

Customizable 3D-Printed (Co-)Cultivation Systems for In Vitro Study of Angiogenesis

Due to the ever-increasing resolution of 3D printing technology, additive manufacturing is now even used to produce complex devices for laboratory applications. Personalized experimental devices or entire cultivation systems of almost unlimited complexity can potentially be manufactured within hours from start to finish-an enormous potential for experimental parallelization in a highly controllable environment. This study presents customized 3D-printed co-cultivation systems, which qualify for angiogenesis studies. In these systems, endothelial and mesenchymal stem cells (AD-MSC) were indirectly co-cultivated-that is, both cell types were physically separated through a rigid, 3D-printed barrier in the middle, while still sharing the same cell culture medium that allows for the exchange of signalling molecules. Biochemical-based cytotoxicity assays initially confirmed that the 3D printing material does not exert any negative effects on cells. Since the material also enables phase contrast and fluorescence microscopy, the behaviour of cells could be observed over the entire cultivation via both. Microscopic observations and subsequent quantitative analysis revealed that endothelial cells form tubular-like structures as angiogenic feature when indirectly co-cultured alongside AD-MSCs in the 3D-printed co-cultivation system. In addition, further 3D-printed devices are also introduced that address different issues and aspire to help in varying experimental setups. Our results mark an important step forward for the integration of customized 3D-printed systems as self-contained test systems or equipment in biomedical applications.

Real-Time Live-Cell Imaging Technology Enables High-Throughput Screening to Verify in Vitro Biocompatibility of 3D Printed Materials

With growing advances in three-dimensional (3D) printing technology, the availability and diversity of printing materials has rapidly increased over the last years. 3D printing has quickly become a useful tool for biomedical and various laboratory applications, offering a tremendous potential for efficiently fabricating complex devices in a short period of time. However, there still remains a lack of information regarding the impact of printing materials and post-processing techniques on cell behavior. This study introduces real-time live-cell imaging technology as a fast, user-friendly, and high-throughput screening strategy to verify the in vitro biocompatibility of 3D printed materials. Polyacrylate-based photopolymer material was printed using high-resolution 3D printing techniques, post-processed using three different procedures, and then analyzed with respect to its effects on cell viability, apoptosis, and necrosis of adipogenic mesenchymal stem cells (MSCs). When using ethanol for the post-processing procedure and disinfection, no significant effects on MSCs could be detected. For the analyses a novel image-based live-cell analysis system was compared against a biochemical-based standard plate reader assay and traditional flow cytometry. This comparison illustrates the superiority of using image-based detection of in vitro biocompatibility with respect to analysis time, usability, and scientific outcome.

Contact Sensitization to Formaldehyde in Veterinary Medicine - An Unexplored Field in Occupational Health

Background:

Veterinary staff and students could be exposed to formaldehyde – a ubiquitous agent, common cause of contact allergy.

Aim:

To evaluate the incidence of contact sensitization to formaldehyde in exposures in veterinary medicine.

Settings and Design:

A cross-sectional study was conducted during July–December 2017.

Materials and Methods:

A total of 206 individuals were included, patch tested with formaldehyde 1.0%/aq – 36 veterinary medicine students, 20 veterinarians, 47 students and 28 trainees of dental medicine, 41 dental professionals, and 35 non-occupationally exposed individuals.

Results:

The incidence of contact sensitization to formaldehyde among the whole studied population was 48.1%, highest being among the students of veterinary medicine (94.4%) and the veterinarians (85%). With very high significance, the sensitization incidence was higher in the groups of students of veterinary medicine and veterinarians, if compared to the control group (P < 0.001); (P = 0.004), dental professionals (P < 0.001); (P = 0.001), trainees of dental medicine (P < 0.001); (P = 0.005), and students of dental medicine three-fourth year of education (P < 0.001); (P = 0.001). Significantly, higher was the incidence of contact allergy in the control group if compared to those of dental professionals (P = 0.033) and dental students three-fourth year of education (P = 0.028).

Conclusions:

The exposure to formaldehyde during the education in veterinary medicine and practice could be an important risk factor for the onset of contact sensitization. Stricter preventive measures are needed to reduce veterinary student's and lecturer's exposures. Equipment of dissection tables with local exhaust ventilation system could reduce the concentration of formaldehyde in the gross anatomy laboratory.

Water sorption and solubility of polyamide denture base materials

Purpose: Some patients experience adverse reactions to poly(methyl methacrylate)-based (PMMA) dentures. Polyamide (PA) as an alternative to PMMA has, however, not been well documented with regard to water sorption and water solubility. The aim of this in vitro study was to measure water sorption and water solubility of two PA materials compared with PMMA, and to evaluate the major components released from the PA materials and the effect on hardness of the materials. Methods: Ten discs (40.0 mm diameter, 2.0 mm thick) of each material (PA: Valplast and Breflex; PMMA: SR Ivocap HIP) were prepared according to manufacturers' recommendations. The specimens were tested for water sorption and water solubility, according to a modification of ISO 20795-1:2008. Released substances were analysed by gas chromatography/mass spectrometry (GC/MS). Results: There were statistically significant differences among the materials regarding water sorption, water solubility and time to water saturation. Breflex had the highest water sorption (30.4 μg/mm³), followed by PMMA-material (25.8 μg/mm³) and Valplast (13.6 μg/mm³). Both PA materials had statistically significant lower water solubility than the PMMA. Both PA had a net increase in weight. Analysis by GC/MS identified release of the compound 12-aminododecanolactam from the material Valplast. No release was found from the Breflex material. Conclusions: The PA denture materials show differences in water sorption and solubility, but within the limits of the standard requirements. The PA showed a net increase in weight after long-term water sorption. The clinical implications of the findings are not elucidated.

The antifungal effects and mechanical properties of silver bromide/cationic polymer nano-composite-modified Poly-methyl methacrylate-based dental resin

Poly-methyl methacrylate (PMMA)-based dental resins with strong and long-lasting antifungal properties are critical for the prevention of denture stomatitis. This study evaluated the antifungal effects on Candida albicans ATCC90028, the cytotoxicity toward human dental pulp cells (HDPCs), and the mechanical properties of a silver bromide/cationic polymer nano-composite (AgBr/NPVP)-modified PMMA-based dental resin. AgBr/NPVP was added to the PMMA resin at 0.1, 0.2, and 0.3 wt%, and PMMA resin without AgBr/NPVP served as the control. Fungal growth was inhibited on the AgBr/NPVP-modified PMMA resin compared to the control (P < 0.05), and the antifungal activity increased as the incorporation of the AgBr/NPVP antimicrobial composite increased. Confocal laser scanning microscopy (CLSM) showed that the number of fungal cells attached to the modified PMMA resin was considerably lower than in the control. The relative growth rate of HDPCs of modified groups were higher than 75%. The flexural strength (FS) and flexural modulus (FM) were not significantly different (P > 0.05) between the experimental and control groups. These data indicate that the incorporation of AgBr/NPVP conferred strong and long-lasting antifungal effects against Candida albicans to the PMMA resin, and it has low toxicity toward HDPCs, and its mechanical properties were not significantly affected.

Allergic effects of the residual monomer used in denture base acrylic resins

Denture base resins are extensively used in dentistry for a variety of purposes. These materials can be classified as chemical, heat, light, and microwave polymerization materials depending upon the factor which starts the polymerization reaction. Their applications include use during denture base construction, relining existing dentures, and for fabrication of orthodontic removable appliances. There have been increased concerns regarding the safe clinical application of these materials as their biodegradation in the oral environment leads to harmful effects. Along with local side effects, the materials have certain occupational hazards, and numerous studies can be found in the literature mentioning those. The purpose of this article is to outline the cytotoxic consequences of denture base acrylic resins and clinical recommendations for their use.

The influences of N-acetyl cysteine (NAC) on the cytotoxicity and mechanical properties of Poly-methylmethacrylate (PMMA)-based dental resin

Objectives. This study aimed to investigate the influences of N-acetyl cysteine (NAC) on cytotoxicity and mechanical properties of Poly-methylmethacrylate (PMMA) dental resins.

Methods. Experimental PMMA resin was prepared by incorporating various concentrations of NAC (0, 0.15, 0.3, 0.6 and 0.9 wt.%). MTT assay was performed to investigate viability of human dental pulp cells after exposure to extract of PMMA resin with or without NAC. Cell adhesion on resin specimens was examined with scanning electron microscopy. Degree of conversion was studied with Fourier Transform Infrared Spectroscopy (FTIR). Flexural strength, microhardness and surface roughness was evaluated using a universal testing machine, microhardness tester and optical profilometer, respectively.

Results. Incorporation of NAC into PMMA resin significantly reduced its cytotoxicity and enhanced cell adhesion on its surface. NAC induced negative influences on the mechanical and physical properties of PMMA resin in a dose-dependent manner. The degree of conversion for all experimental PMMA resins reached as high as 72% after 24 h of polymerization. All the tested properties were maintained when the concentration of incorporated NAC was 0.15 wt.%.

Conclusion. The addition of 0.15 wt.% NAC remarkably improved biocompatibility of PMMA resin without exerting significant negative influence on its mechanical and physical properties.

A review of the effects of formaldehyde release from endodontic materials

Formaldehyde is present in most living cells and the environment. In dentistry, patients may be exposed to formaldehyde through the use of several endodontic materials (e.g. AH 26) and during formocresol pulpotomies. This review outlines how the human body reacts to formaldehyde exposure, how recent data has relooked at the issue of carcinogenicity and leukaemia associated with formaldehyde, and whether it is possible to quantify the amount of formaldehyde produced by endodontic cements. The review analyses the way formaldehyde is produced from epoxy resins and addresses the question of whether the amount of formaldehyde from endodontic cements is large enough to override the body's ability to deal with its own endogenous levels of formaldehyde and should the amount of formaldehyde produced be a concern.

Effect of light aging on silicone-resin bond strength in maxillofacial prostheses

PURPOSE

The aim of this study was to investigate the effect of accelerated light aging on bond strength of a silicone elastomer to three types of denture resin.

MATERIALS AND METHODS

A total of 60 single lap joint specimens were fabricated with auto-, heat-, and photopolymerized (n = 20) resins. An addition-type silicone elastomer (Episil-E) was bonded to resins treated with the same primer (A330-G). Thirty specimens served as controls and were tested after 24 hours, and the remaining were aged under accelerated exposure to daylight for 546 hours (irradiance 765 W/m(2) ). Lap shear joint tests were performed to evaluate bond strength at 50 mm/min crosshead speed. Two-way ANOVA and Tukey's test were carried out to detect statistical significance (p < 0.05).

RESULTS

ANOVA showed that the main effect of light aging was the most important factor determining the shear bond strength. The mean bond strength values ranged from 0.096 to 0.136 MPa. The highest values were recorded for auto- (0.131 MPa) and photopolymerized (0.136 MPa) resins after aging.

CONCLUSIONS

Accelerated light aging for 546 hours affects the bond strength of an addition-type silicone elastomer to three different denture resins. The bond strength significantly increased after aging for photo- and autopolymerized resins. All the bonds failed adhesively.

2-hydroxylethyl methacrylate (HEMA), a tooth restoration component, exerts its genotoxic effects in human gingival fibroblasts trough methacrylic acid, an immediate product of its degradation

HEMA (2-hydroxyethyl methacrylate), a methacrylate commonly used in dentistry, was reported to induce genotoxic effects, but their mechanism is not fully understood. HEMA may be degraded by the oral cavity esterases or through mechanical stress following the chewing process. Methacrylic acid (MAA) is the primary product of HEMA degradation. In the present work we compared cytotoxic and genotoxic effects induced by HEMA and MAA in human gingival fibroblasts (HGFs). A 6-h exposure to HEMA or MAA induced a weak decrease in the viability of HGFs. Neither HEMA nor MAA induced strand breaks in the isolated plasmid DNA, but both compounds evoked DNA damage in HGFs, as evaluated by the alkaline comet assay. Oxidative modifications to the DNA bases were monitored by the DNA repair enzymes Endo III and Fpg. DNA damage induced by HEMA and MAA was not persistent and was removed during a 120 min repair incubation. Results from the neutral comet assay indicated that both compounds induced DNA double strand breaks (DSBs) and they were confirmed by the γ-H2AX assay. Both compounds induced apoptosis and perturbed the cell cycle. Therefore, methacrylic acid, a product of HEMA degradation, may be involved in its cytotoxic and genotoxic action.