Nanotechnology in dentistry: Benefits vs. risks

In simple terms, nanotechnology is the design and manufacture of extremely small devices and structures, those less than 100 nm. Applications of nanotechnology in dentistry are widely used in dental diagnostics, preventive dentistry, dental materials, prosthodontics, endodontics, conservative and esthetic dentistry, periodontics by use of the piezo, implantology, and regenerative dentistry.¹ Mouthwashes and bonding and teeth-sealing products commonly use nanomaterials.² Dental materials frequently use silver nanoparticles (SNPs) due to their antimicrobial properties. 

Although the use of nanomaterials has benefitted the dental field, research shows that nanoparticles (NPs) can be inhaled and can cross cell membranes and reach the liver, lymph nodes, spleen, and bone marrow.¹ NPs, including nanocarriers, can transport through the blood–brain barrier and locate in the central nervous system (CNS). Because nanoparticles are foreign to the body systems, they are usually redistributed and accumulated in some vital organs, which can produce toxic effects.³ This unpredictability of how bodies react to nanomaterials depends not only on size but also on how an immune system reacts to the nanoproduct, as studies have shown that nanoparticles could react differently in a cell culture than in an organism.¹

Silver leads to cell wall and cell membrane damage and to reaction with biomacromolecules within the cells.¹ Silver-based antimicrobials are demonstratively effective against microorganisms such as bacteria, viruses, and fungi or in the case of the oral cavity, caries, calculus, gingivitis, or periodontitis.⁴ However, metal cations such as silver in sufficient doses have a damaging effect to living cells. The antimicrobial action of these ions is based on cell wall and cell membrane damages, oxidation of proteins and lipids, and disruption of the hydrogen bond between DNA strands.²

Researchers state that nanoparticles have a high surface-to-volume ratio that contributes to their reactivity, allowing nanoparticles to pass through biological barriers, such as cell membranes, and rendering nanoparticles potentially biohazardous and cytotoxic.² Particles may be released and may enter the digestive system. 

The importance of the blood-brain barrier 

The blood-brain barrier (BBB) is a defensive, highly selective, and low permeable barrier that isolates the CNS, protecting and generating a stable environment for neurons.³ The use of transport mechanisms in the BBB allows the passage of essential molecules for the brain’s correct function and has been explored to deliver nanoparticles to the CNS.³

Very small nanoparticles are vulnerable to renal and kidney excretion and clearance from target tissues while bigger nanoparticles (≥ 20 nm) can pass through the BBB, but larger nanoparticles (> 200 nm) can be susceptible to uptake by other organs.³ Nanoparticle biodistribution and accumulation behavior may lead to an undesirable exposure to metal nanoparticles with potential toxic effects. SNPs exhibit a longer half-life in the brain than in other organs with possible neurotoxic effects such as inflammatory response and oxidative stress.³

Nanotechnology and dental hygiene 

Researchers developed a nano-toothbrush by incorporating nanogold or nanosilver colloidal particles between toothbrush bristles to assist with plaque removal and reduce periodontal disease.¹ Toothpaste and mouthwash solutions have also been nano-modified. Nano-calcium fluoride is added to mouthwash products to reduce caries activity, reduce dentine permeability, and increase labile fluoride concentration in oral fluid.¹ Toothpastes containing calcium carbonate nanoparticles and 3% nanosized sodium trimetaphosphate have been reported to promote remineralization of early carious lesions in comparison to a conventional toothpaste with no nano-additives.¹

In terms of periodontal disease, scientists were able to create a novel drug delivery system for the treatment of periodontal disease, through triclosan- or tetracycline-loaded nanoparticles.¹ Nanoparticles were uniformly dispersed, releasing loaded drugs in increments to provide a longer contact duration with the diseased site. 

Benefits vs. risks of nanotechnology in clinical practice 

The decision to use nanomaterials is dependent on the clinical setting. The unpredictability of nanomaterials creates an ethical dilemma for dentists when faced with a wide range of materials to choose from. Some have very long track records supporting their clinical use, such as hybrid or microfilled composite resins and the nanofilled composite resins.¹

Toxicity of SNPs is associated with the release of silver ions, which trigger biochemical alterations, abnormalities in behavior, and neurotoxic effects.² Studies have reported that even though the percentage of injected doses that reach the brain is relatively low, a high accumulation occurs in other vital organs, such as the liver and spleen.² Dentistry utilizes SNPs whereas gold nanoparticles (GNPs) ranging from 5nm to 100nm are less toxic than SNPs.³ 

Research on nanomaterials is new; researchers continue to discuss the future of nanotechnology as more efficient and cost-effective to diagnose the accuracy of new oral drug delivery systems to disrupt biofilm formation and reduce the incidence of caries and periodontal disease.¹ The science behind nanotechnology is innovative, but more long-term clinical evidence is needed to determine if the benefits outweigh the risks in clinical practice.

References 

1. Alkahtani R. The implications and applications of nanotechnology in dentistry: A review. The Saudi Dental Journal, 2018;.30(2), 107-116. doi:10.1016/j.sdentj.2018.01.002
2. Xiaoli F, Longquan, S. Emerging nanotechnologies in dentistry. Micro and Nano Technologies, 2018; 421-444. doi:10.1016/B978-0-12-812291-4.00020-0
3. Báez D, Gallardo-Toledo E, Paz Oyarzún M, Araya E, Kogan, M. The influence of size and chemical composition of silver and gold nanoparticles on in vivo toxicity with potential applications to central nervous system diseases. International Journal of Nanomedicine, 2021; 16, 2187-2201. doi:10.2147/IJN.S260375
4. Jandt K, Watts, D. Nanotechnology in dentistry: Present and future perspectives on dental nanomaterials. Dental Materials, 2020;36(11), 1365-1378. doi:10.1016/j.dental.2020.08.006