# Biophotonics in Dentistry
## 2 Historical Events and Current Advancements  
Currently, different types of lasers with a wide range of wavelengths are widely utilised in medical applications, such as Ar (488-515 nm) [29], Er:YAG (2940 nm) [19; 30; 31], CO\({}_{2}\) (10,600 nm) [32] and Nd:YAG (1064 nm) [33]. In 1964, [PERSON] and [PERSON] began their laser studies on hard dental tissues using a ruby laser with a wavelength of 694 nm [34], which was followed by applying a CO\({}_{2}\) laser to cut bone tissue for the first time [35]. Although the CO\({}_{2}\) laser had shown promising results for successful soft tissue treatment [36; 37] and further studies suggested the use of Nd:YAG and CO\({}_{2}\) lasers considerably decreased severe irreversible damage to the pulp [38; 39], it was still not an appropriate candidate for cutting mineralised tissue due to its biological complications, such as severe carbonisation effects and a delayed bone healing [40; 41]. After research successes with short-pulsed infrared laser systems during the late 1980s and 1990s [42], the best results in ablation of bone and dental hard tissue were achieved by utilising a laser system operating at wavelengths of 2.9-3 \(\upmu\)m and 5.90-6.45 \(\upmu\)m [43]. As a result of this finding, the Er:YAG and the Er,Cr:YSGG lasers, with wavelengths of 2.94 \(\upmu\)m and 2.78 \(\upmu\)m, respectively, are promising candidates for laser surgery on hard and mineralised tissue [44; 45; 46; 47]. Figure 2 summarizes the classification of lasers according to their usage and their respective wavelengths [48]. Figure 1: Dental applications of laser in the modern era in according to specialty. Figure 3 illustrates a broad history of laser in relation to dentistry [48]. Other than laser applications in dentistry, carbon nanotubes (CNTs) have attracted attention in numerous medical applications, including as a biomaterial candidate for the purpose of tissue regeneration in dental implants, orthopaedic applications [49] and drug  
Figure 3: Timeline of lasers. Figure 2: Classification of laser according to its usage and wavelength. delivery [50], as well as applications in electronics [51], optical devices [9], and filtration [52] and sensing [53] applications. CNTs have unique optical, electrical, thermal and mechanical properties, as well as their functionalisation capability and biocompatibility, which enable an impressive capacity in medical applications, including for dental implants, drug delivery systems and as a scaffold for bone tissue engineering [54; 55]. CNTs constitute some of the strongest material in nature due to their mechanical properties; as a result, by adding single-wall carbon nanotubes (SWCNTs) to hydroxyapatite structures (HY-SWCNTs), which are mainly used in maxillofacial surgery, dental/orthopaedic implants become more resistant, achieving improved biocompatibility [56; 57]. In addition to enhanced biocompatibility and stronger implants, bone formation and bone-healing process are accelerated, which is specifically beneficial for diabetics who suffer from low rates bone growth [58; 59]. Clinical research on diabetic and non-diabetic rats revealed that HY-SWCNTs, compared to nanocomposites, improved bone repair of tooth sockets of rats with type I diabetes [59]. In addition, quantum dot (QDs), which are nanoscale semiconductors with three-dimensional quantum confinement of charge carriers, are another popular nanomaterial in biomedical applications [60; 61], particularly in florescence imaging and diagnostics [61; 62], in addition to their vast applications in optoelectronics [63; 64], such as solar cells [65], quantum cryptography [66], lasers [67] and LEDs [68], owing to their high quantum efficiency and unique optical and electrical properties (Figure 4). The first biomedical applications of QDs in biological detectors [69] and florescent biological labels [70] dates back to 1998, two decades after the invention of QDs by [PERSON] in 1981 [71; 72].