Metallic and Metallic/ Oxide Nanoparticles in Restorative Dentistry

The use of metallic nanoparticle fillers has been suggested as an approach to target cariogenic species. Several metallic nanoparticle platforms such as bioactive glass, silver, zinc oxide, copper oxide, and diamond nanoparticles were found effective in the perspective of bacterial growth inhibition (Balhaddad et al. 2019b). Multiple studies have demonstrated the ability of bioactive glass to reduce the growth and activity of S. mutans (Khvostenko et al. 2016; Chatzistavrou et al. 2015; Tezvergil-Mutluay et al. 2017).

In one study, the amount of bacterial penetration in resin composite with bioactive glass was reduced by 40% compared to resin composite with no bioactive glass (Khvostenko et al. 2016). These results could be

Three cycles of calcium

Figure 8.3 Three cycles of calcium (a) and phosphate (b) ion recharge and re- release by the NACP resin composite. (Adapted from Al-Dulaijan et al. (2018a), with permission from © 2015 Elsevier.) elaborated to reduce the risk of secondary caries around resin composite restorations. The suggested mechanism of bioactive glass is that the release of calcium and phosphate ions could be bactericidal to the S. mutans biofilm, also helping in reducing the acidity and enhancing the remineralization of the surrounding tooth structure (Khvostenko et al. 2016). The combining effect of silver and bioactive glass can reduce S. mutans biofilm and increase the formation of the appetite layer (Chatzistavrou et al. 2015). The synergetic effect of fluoride ions and calcium phosphate ions released by bioactive glass demonstrates greater remineralization capability and

Agent

References

Concentration

Mechanical Properties

Remarks

ACP ZrOCI,-ACP TEOS-ACP

Skrtic et al. (1996)

40%

Biaxial flexure strength values were significantly lower compared to control samples

Sustained release of Ca and P04 ions that is able to induce remineralization

ACP reinforced with silica or zirconia

Skrtic et al. (2000)

40%

Nano DCPA

Xu et al. (2006)

60%

Mixed with nano silica fused whisker, flexural strength values were comparable to control samples and higher than previous CaP compounds

Comparable or higher amount of Ca and P04 ion release compared to previous CaP compounds

Nano DCPA

Xu et al. (2007)

Varied from 0% to 75%

Compared to control, nano DCPA demonstrated higher elastic modulus and hardness, but comparable flexural strength values

TTCP

Xu et al. (2009)

Varied from 0% to 75%

TTCP with whisker reinforcement demonstrated flexural strength values that were not significantly different compared to control hybrid resin composites. TTCP with whisker reinforcement demonstrated significantly high flexural strength compared to TTCP alone

Ca and P04 ion release increased by about 6-fold when the pH changed from 6 to 4. TTCP resin composites demonstrated higher amount of released ions compared to TTCP with whisker reinforcement

TTCP

Cheng et al. (2012b)

40%

No significant differences were found in flexural strength and elastic modulus between TTCP-QADM and control samples

TTCP-QADM resin composites demonstrated higher antibacterial action against S. mutans compared to control. CFU, metabolic activity, and lactic acid production were 50% lower in TTCP- QADM samples compared to control

Agent

References

Concentration

Mechanical Properties

Remarks

NACP

Xu et al. (2011)

10%, 15%, and 20%

No significant differences were found in flexural strength and elastic modulus between all NACP samples and control

Increasing NACP amount was associated with higher ion release

NACP

Moreau et al. (2011)

10%-40%

10%-30% NACP resin composite demonstrated comparable flexural strength and elastic modulus to hybrid resin composite control. 40% NACP resin composite demonstrated significantly low flexural strength and elastic modulus compared to control, but was similar to microfill resin composite control

NACP resin composites raised the pH and neutralized the acid, higher capability to raise the pH and neutralize the acid was observed and the NACP concentration increased. NACP resin composite demonstrated a significant ability to resist the adherence of S. mutans compared to control samples

NACP

Moreau et al. (2012)

10%, 15% and 20%

Flexural strength and elastic modulus were higher or matching that of control samples before and after thermal cycling. With water aging, the flexural strength of NACP samples decreased significantly, but they were higher than their control counterparts Increasing the NACP mass fraction significantly increased the amount of wear compared to control, but the values were lower than that of RMGI

(Continued)

Agent

References

Concentration

Mechanical Properties

Remarks

NACP

Melo et al. (2013)

40%

This in situ study demonstrated that biofilms collected from NACP restored samples had a higher amount of Ca and P04 ions compared to control. Biofilm CFU values of S. mutans, Lactobacillus and total Streptococcus were lower, but not significant, in NACP samples. Also, NACP samples demonstrated fewer subsurface enamel lesions compared to control

DCPD

Chiari et al. (2015)

Varied from 0% to 20%

Adding DCPD filler did not affect the degree of conversion of resin composites. Increasing the mass fraction of filler negatively compromised the material strength. However, the optimum mass friction of DCPD that demonstrated proper mechanical properties after water aging was 10%

10% Mass fraction of DCPD demonstrated a constant ion release for 28 days

NACP

Zhang et al. (2016)

20%

No significant differences were found in flexural strength and elastic modulus between PE-NACP and control samples

A novel rechargeable NACP resin composite was invented with sustainable and longterm ion release

NACP+TTCP

Weir et al. (2017)

40% NACP, 20% TTCP

NACP-TTCP resin composite was able to remineralize dentin and neutralizes pH. However, no significant differences were found in ion release and remineralization capability between NACP and NACP-TTCP

Agent

References

Concentration

Mechanical Properties

Remarks

NACP

Al-Dulaijan et al. (2018a)

20%

Flexural strength and elastic modulus were similar to control

No effect on the recharging capability and ion release after adding 3% of DMAHDM into the NACP mixture. The ion release was maintained as the number of recharging cycles increased. NACP-DMAHDM resin composite reduced the lactic acid, metabolic activities, and colony-forming units of S. mutans, total Streptococcus, and total microorganisms by around 3 log

NACP

Al-Dulaijan et al. (2018b)

20%

Flexural strength and elastic modulus were similar to control

NACP mixed with 3% of MPC demonstrated excellent rechargeability and ion release.

The ion release was maintained as the number of recharging cycles increased NACP-MPC resin composites reduced the lactic acid, metabolic activities, and colony-forming units ofS. mutans, total Streptococcus, and total microorganisms by 2 log. NACP-MPC resin composites

Source: Adapted from Balhaddad et al. (2019b), with permission from © 2019 Elsevier.

Ag, silver; DCPA, dicalcium phosphate anhydrate; DCPD, dicalcium phosphate dehydrate; DMAHDM, dimethylaminohexadecyl methacrylate; MPC, 2-methacryloyloxyethyl phosphorylcholine; NACP, nano amorphous calcium phosphate; PE-NACP, NACP mixed with pyromellitic glycerol dimethacrylate (PMGDM) and ethoxylated bisphenol A dimethacrylate (EBPADMA) at 1:1 ratio; QADM, quaternary ammonium dimethacrylate; TF.OS-ACP, tetraethoxysilane-modified AGP; TTCP, tetracalcium phosphate; ZrOCI2-ACP, zirconyl chloride-modified AGP.

degradation resistance compared to bioactive glass alone (Tezvergil- Mutluay et al. 2017). These results may indicate combining bioactive glass with another antibacterial or remineralizing particle to enhance the performance of such restoration.

Silver nanoparticles have been used in medicine for centuries due to its unique antibacterial effect and biocompatibility. Silver ions can interact with the cell membrane and DNA confirmation of many bacterial species (Balhaddad et al. 2019b). In restorative dentistry, silver-containing resin composite has demonstrated the ability to reduce the pathogenicity of caries-related pathogens. The incorporation of 0.028% of silver into resin composite was found effective to reduce the S. mutans biofilm by 75%, and decreasing the metabolic activities and lactic acid production of multispecies pathogens isolated from saliva by 50% and 60%, respectively. Increasing the silver weight in different fractions from 0.028% to 0.175% was associated with more bacterial inhibition, but less mechanical properties. The maximum bacterial inhibition with acceptable mechanical properties compared to the control was found with 0.088% of silver in resin composite (Cheng et al. 2012b). Silver ions released from resin composite are also effective in reducing the biofilm of Lactobacillus species, one of the main microorganisms of root caries (Kasraei et al. 2014).

Zinc oxide nanoparticles are effective in killing many oral species. The antibacterial activities of zinc oxide in resin composite were investigated first time in 2010. Compared to zinc oxide weights of 3% and 10% added to resin composites, 5% of zinc oxide demonstrates good antibacterial properties without compromising the mechanical properties. However, the antibacterial efficiency is reduced with aging (Niu et al. 2010). It is suggested that zinc oxide nanoparticles have the ability to produce reactive oxygen species, which then reduce the growth of bacterial species. In another study, the zinc oxide nanoparticles were incorporated in different weights: 1%, 5%, and 10%. While zinc oxide resin composites demonstrated higher antibacterial activities compared to unmodified resin composites, resin composites with incorporated silver nanoparticles demonstrated the highest antibacterial properties, which may indicate the superiority of silver over zinc oxide nanoparticles (Aydin Sevin$ and Hanley 2010).

Zinc oxide nanoparticles demonstrate the ability to reduce Lactobacillus growth, but the antibacterial activities were found less compared to silver- containing resin composites (Kasraei et al. 2014). The limitations associated with zinc oxide-containing resin composites are the reduced antibacterial efficiency with aging and against multispecies biofilm, and also the reduced depth of cure compared with resin composites without zinc oxide nanoparticles (Aydin Sevimj and Hanley 2010; Tavassoli Hojati et al. 2013).

The use of copper oxide nanoparticles has limited uses to target caries- related pathogens. The important use of copper oxide nanoparticles in restorative dentistry is to reduce the polymerization shrinkage of resin composites (Song et al. 2016). The construction of copper oxide-containing resin composite showed 1-2 log reduction of S. mutans biofilm and reduced luciferase activity (Zajdowicz et al. 2018). The suggested mechanism of antibacterial action referred to the ability of copper oxide nanoparticles to generate reactive hydroxyl radicals, thereby inhibiting the growth of many microorganisms (Balhaddad et al. 2019b).

In nanotechnology, the use of nanodiamonds in polymer engineering has improved the mechanical and antibacterial properties of several materials in the industrial and medical fields. Nanodiamonds are suggested to have the ability to manipulate the permeability of the bacterial cell walls causing bacterial death. Besides the abroad antibacterial properties, nanodiamonds present suitable biocompatibility and structural stability (Turcheniuk and Mochalin 2017). Adding nanodiamonds with silver nanoparticles into resin composite was achieved with different mass fractions between 0.1% and 1.5%. A significant increase in the microhardness and flexural strength was observed with decreased viability of S. mutans biofilm. Unfortunately, only nanodiamonds’ mass fractions of less than 1% revealed acceptable biocompatibility as concentrations of higher than 1% was associated with cytotoxicity (Cao et al. 2018). Table 8.3 outlines bioactive metallic nanoparticles used as reinforcing fillers in the resin composite system to target dental biofilms.

 
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