# Biophotonics in Dentistry
## 3 Applications in Dentistry
### Quantum Dots  
Quantum dots are semiconductor nanocrystals with unique optoelectronic properties; when stimulated and excited, they release energy via single photons. The wavelength of the light emitted is dependent on the size, composition and shape, something which can be easily changed to produce a specific desired wavelength. As the size decreases, the wavelength emitted decreases, and hence, the photoluminescence colour tends towards the blue end of the spectrum. As the size increases, the wavelength emitted increases. The diagram below represents the applications of quantum dots in biomedical and biological application [151].  
The potential applications for quantum dots in both medical and non-medical fields are various, including fluorescent labels for biomedical imaging and cancer research, photonic devices, sensor materials, quantum communication networks, greater efficiency in LEDs and solar cells, quantum computing, drug delivery and engineered tissues [152]. Nanotechnology is expected to revolutionise science and technology, and dentistry is no exception to this. Improving understanding to a nanometre resolution allows for the development of novel dental materials, techniques and tools. A good example of this is how research on micro and nano-leakages of resin-based dental restorations has allowed dentists to work towards preventing secondary caries, as referred in Section 3.3.  
One application of quantum dots is the development of cosmetic dentistry. Natural teeth emit light at 440 nanometres when exposed to ultraviolet light and in daylight. In order for resin composites to closely resemble the colour and transparency of natural teeth, the optical properties of the resin composites must be considered, and emission under UV must occur at a similar wavelength. However, restorative materials tend to have very different luminescent characteristics, as discovered by [PERSON] and [PERSON] [152]. Luminophores inserted into dental resin can be used to alter optical properties, but the result still does not resemble natural teeth [73]. [PERSON] et al. investigated the use of core-shell quantum dots to alter the fluorescence and optical properties of dental resin composites. The authors proved that the incorporation of core-shell nano-structured CdSe/ZnS quantum dots into dental resins allows tailoring of fluorescence intensity to more closely resemble natural human teeth [73].  
The use of nanoparticles within adhesive resins causes clumping and agglomeration, making it structurally weak. [PERSON] et al. proposed the synthesis of zinc oxide quantum dots (ZnO) to an adhesive resin due to their non-agglomerated nature [153]. The findings suggested that this was a possible and reliable method to overcome the agglomeration concern associated with nanoparticles within fillers. The fluorescence properties of quantum dots were applied in vitro and in vivo by [PERSON] et al. to label bacterial cells [154]. This method was then compared to the conventional way of marking bacterial cells using fluorophores, and the use of quantum dots was shown to be more advantageous in achieving single-cell resolution with a standard epifluorescence microscope. This is significant because gaining insight into the interactions between various bacterial species allows for greater understanding of the development of biofilm.  
Applications of quantum dots in oral cancer research are also of particular interest, as they may be combined with antibodies to bind to specific proteins of tumour cells, thus acting as fluorescent markers for sensitive detection [155; 156].