http://lbmd.coe.pku.edu.cn/PDF/2009biomaterials01.pdf

In vitro corrosion and biocompatibility of binary magnesium alloys

Calcium hydroxide has been included within several materials and antimicrobial formulations that are used in a number of treatment modalities in endodontics. These include, inter-appointment intracanal medicaments, pulp-capping agents and root canal sealers. Calcium hydroxide formulations are also used during treatment of root perforations, root fractures and root resorption and have a role in dental traumatology, for example, following tooth avulsion and luxation injuries. The purpose of this paper is to review the properties and clinical applications of calcium hydroxide in endodontics and dental traumatology including its antibacterial activity, antifungal activity, effect on bacterial biofilms, the synergism between calcium hydroxide and other agents, its effects on the properties of dentine, the diffusion of hydroxyl ions through dentine and its toxicity. Pure calcium hydroxide paste has a high pH (approximately 12.5-12.8) and is classified chemically as a strong base. Its main actions are achieved through the ionic dissociation of Ca2+ and OH- ions and their effect on vital tissues, the induction of hard-tissue deposition and the antibacterial properties. The lethal effects of calcium hydroxide on bacterial cells are probably due to protein denaturation and damage to DNA and cytoplasmic membranes. It has a wide range of antimicrobial activity against common endodontic pathogens but is less effective against Enterococcus faecalis and Candida albicans. Calcium hydroxide is also an effective anti-endotoxin agent. However, its effect on microbial biofilms is controversial.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2591.2011.01886.x

Properties and applications of calcium hydroxide in endodontics and dental traumatology.

Appropriate selection of the implant biomaterial is a key factor for long term success of implants. The biologic environment does not accept completely any material so to optimize biologic performance, implants should be selected to reduce the negative biologic response while maintaining adequate function. Every clinician should always gain a thorough knowledge about the different biomaterials used for the dental implants. This article makes an effort to summarize various dental bio-materials which were used in the past and as well as the latest material used now.

Implant biomaterials: A comprehensive review.

Monomers are released from dental resin materials, and thus cause adverse biological effects in mammalian cells. Cytotoxicity and genotoxicity of some of these methacrylates have been identified in a vast number of investigations during the last decade. It has been well-established that the co-monomer triethylene glycol dimethacrylate (TEGDMA) causes gene mutations in vitro. The formation of micronuclei is indicative of chromosomal damage and the induction of DNA strand breaks detected with monomers like TEGDMA and 2-hydroxyethyl methacrylate (HEMA). As a consequence of DNA damage, the mammalian cell cycle was delayed in both G1 and G2/M phases, depending on the concentrations of the monomers. Yet, the mechanisms underlying the genetic and cellular toxicology of resin monomers have remained obscure until recently. New findings indicate that increased oxidative stress results in an impairment of the cellular pro- and anti-oxidant redox balance caused by monomers. It has been demonstrated that monomers reduced the levels of the natural radical scavenger glutathione (GSH), which protects cell structures from damage caused by reactive oxygen species (ROS). Depletion of the intracellular GSH pool may then significantly contribute to cytotoxicity, because a related increase in ROS levels can activate pathways leading to apoptosis. Complementary, cytotoxic, and genotoxic effects of TEGDMA and HEMA are inhibited in the presence of ROS scavengers like N-acetylcysteine (NAC), ascorbate, and Trolox (vitamin E). Elevated intracellular levels of ROS can also activate a complex network of redox-responsive macromolecules, including redox-sensitive transcription factors like nuclear factor kappaB (NF-kappaB). It has been shown that NF-kappaB is activated probably to counteract HEMA-induced apoptosis. The induction of apoptosis by TEGDMA in human pulp cells has been associated with an inhibition of the phosphatidylinositol 3-kinase (PI3-K) cell-survival signaling pathway. Although the details of the mechanisms leading to cell death, genotoxicity, and cell-cycle delay are not completely understood, resin monomers may be able to alter the functions of the cells of the oral cavity. Pathways regulating cellular homeostasis, dentinogenesis, or tissue repair may be modified by monomers at concentrations well below those which cause acute cytotoxicity.

http://journals.sagepub.com/doi/pdf/10.1177/154405910608501001

Genetic and Cellular Toxicology of Dental Resin Monomers

A new look at biomedical Ti-based shape memory alloys

Most cast dental restorations are made from alloys or commercially pure titanium (cpTi). Many orthodontic appliances are also fabricated from metallic materials. It has been documented in vitro and in vivo that metallic dental devices release metal ions, mainly due to corrosion. Those metallic components may be locally and systemically distributed and could play a role in the etiology of oral and systemic pathological conditions. The quality and quantity of the released cations depend upon the type of alloy and various corrosion parameters. No general correlation has been observed between alloy nobility and corrosion. However, it has been documented that some Ni-based alloys, such as beryllium-containing Ni alloys, exhibit increased corrosion, specifically at low pH. Further, microparticles are abraded from metallic restorations due to wear. In sufficient quantities, released metal ions-particularly Cu, Ni, Be, and abraded microparticles-can also induce inflammation of the adjacent periodontal tissues and the oral mucosa. While there is also some in vitro evidence that the immune response can be altered by various metal ions, the role of these ions in oral inflammatory diseases such as gingivitis and periodontitis is unknown. Allergic reactions due to metallic dental restorations have been documented. Ni has especially been identified as being highly allergenic. Interestingly, from 34% to 65.5% of the patients who are allergic to Ni are also allergic to Pd. Further, Pd allergy always occurrs with Ni sensitivity. In contrast, no study has been published which supports the hypothesis that dental metallic materials are mutagenic/genotoxic or might be a carcinogenic hazard to man. Taken together, very contradictory data have been documented regarding the local and systemic effects of dental casting alloys and metallic ions released from them. Therefore, it is of critical importance to elucidate the release of cations from metallic dental restorations in the oral environment and to determine the biological interactions of released metal components with oral and systemic tissues.

https://journals.sagepub.com/doi/pdf/10.1177/154411130201300108

Biocompatibility of Dental Casting Alloys

Titanium is used for many dental applications and instruments, such as orthodontic wires, endodontic files, dental implants, and cast restorations. The popularity of titanium is primarily due to its good mechanical properties, its high corrosion resistance, and its excellent biocompatibility. A thorough review of the medical and dental literature reveals, however, that titanium can also cause chemical-biological interactions. Tissue discoloration and allergic reactions in patients who have come in contact with titanium have been reported. The biostability of titanium is becoming increasingly questioned. At the same time, new technologies and materials, such as high-performance ceramics, are emerging which could replace titanium in dentistry in the not-too-distant future.

Nonalloyed titanium as a bioinert metal--a review.

Previous studies revealed that primarily small and relatively hydrophilic comonomers, such as TEGDMA, leach out of resin-based restorative materials into aqueous media. Subsequently, these compounds may cause detrimental reactions with intracellular metabolic systems. The present experiments attempted to elucidate the interactions of TEGDMA with the important intracellular reducing agent glutathione (GSH). The influence of various concentrations of TEGDMA (0.5–7.5 mM) on viability and intracellular GSH concentration of primary human gingival fibroblasts was determined by means of a fluorescence assay (monobromobimane) performed in microtiter plates. Cells were treated with TEDGMA between 2 and 24 h. The incubation of fibroblasts with TEGDMA even at subtoxic concentrations quickly decreased the intracellular glutathione level to 30–50% of controls within the first 2–6 hours. However, no simultaneous adverse effect on cell viability was found. Longer incubation periods up to 24 h caused a regulatory reincrease at TEGDMA concentrations ≤ 2.5 mM, whereas higher concentrations resulted in a continuous depletion of glutathione concentration concomitant with a significant decrease of cell viability. Because glutathione plays an important role in protection and detoxification processes as well in the regulation of cell death, the early and extensive depletion of the intracellular glutathione pool due to TEGDMA may significantly contribute to the cytotoxic potency of this compound. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res (Appl Biomater) 63: 746–751, 2002

Effect of TEGDMA on the intracellular glutathione concentration of human gingival fibroblasts.

Long-term cytocompatibility of various endodontic sealers using a new root canal model.

Many morphologic, physical, and iatrogenic factors, such as deep grooves, pronounced intraoral temperature fluctuation, poor cavity preparation design, and wrong selection of restorative materials, may predispose posterior teeth to an incomplete fracture. The resulting cracked tooth syndrome is frequently associated with bizarre symptoms that may complicate diagnosis and can persist for many years. Epidemiologic data reveal that splits or fractures are the third most common cause of tooth loss in industrialized countries, primarily affecting maxillary molars and premolars and mandibular molars. This finding indicates that the cracked tooth syndrome is of high clinical importance. Thus, at-risk teeth should be reinforced early, for instance by castings with cusp coverage or by internal splinting with adhesive ceramic restorations.

W. Geurtsen

Papers

Biocompatibility of Dental Casting Alloys

Nonalloyed titanium as a bioinert metal--a review.

Effect of TEGDMA on the intracellular glutathione concentration of human gingival fibroblasts.

Long-term cytocompatibility of various endodontic sealers using a new root canal model.

Diagnosis, therapy, and prevention of the cracked tooth syndrome