# Effectiveness of Laser-Assisted Teeth Bleaching: A Systematic Review
## 4 Discussion
Studies show that increasing the laser irradiation time increases the bleaching effect. This effect can be said to increase proportionally, and with a twofold increase in time the effect doubles [35]. We must remember that during bleaching, the use of a laser only activates the chemical agent, which is crucial to the whole process. When using CP as a bleaching agent, both [PERSON] et al. [35] and [PERSON] et al. [46] proved that the effect was proportional to the CP's concentration and exposure time. There is no such relationship with HP [38; 48]. According to the studies of [PERSON] et al. [54], when bleaching teeth in patients, the use of 15% CPgives the same result as using 35 or 38% HP. Much better results, presented as \(\Delta\)E, were obtained using lasers with shorter wavelengths. Studies conducted by [PERSON] et al. [33] and [PERSON] et al. [37] compared the bleaching effect of diode lasers with different wavelengths--810, 940, and 980 nm. Analyzing these two studies, one can conclude that the bleaching effect increases with the decrease in the wavelength of the assisting laser, presented in both studies as \(\Delta\)E. The difference between the shortest and the longest wavelength is up to 7 units, which translates into a bleaching effect and enamel color change [37; 56]. Similar conclusions can be drawn by considering other studies, where examples with shorter wavelengths produced better bleaching effects than those with longer wavelengths [41]. Some studies combined the use of diode lasers and LED light [3; 9; 39]. The results of these studies show that LED light can additionally enhance the effect of the bleaching on enamel. For the purpose of this review, we can compare the study conducted by [PERSON] et al. [3], which used additional LED light, with the study by [PERSON] et al. [69], which only used a diode laser with the same wavelength of 808 nm. Despite slight differences in laser parameters and the use of different bleaching agents, a significantly better bleaching effect can be observed for the diode laser combined with LED light, where the \(\Delta\)E reaches up to 14 units [3]. Additionally, the use of LED light helps achieve a similar bleaching effect to that obtained at high concentrations even at low concentrations of the bleaching agent [9; 38]. However, the other factors, apart from the tooth color itself, which should be taken into account and were not included in most of the studies are intriguing. When looking for the positive effects of lasers, it is worth paying attention to the aforementioned hypersensitivity caused by whitening. [PERSON] et al. 's [70] study shows that as many as 77% of patients experience hypersensitivity within 2 weeks of teeth whitening, which indicates that this is a very important clinical aspect. [PERSON] et al. [71] and [PERSON] et al. [72] addressed this topic and both showed that laser activation does not reduce post-treatment hypersensitivity. In the literature on whitening dental materials, authors have discussed different aspects of the materials, making it difficult to directly compare their findings. [PERSON] and [PERSON] [4] analyzed color stability and concluded that as a result of whitening, the physical parameters of the composites change, causing their surface to become rough and increasing their water sorption, which makes them more susceptible to discoloration. The authors made an intriguing observation that changes in composite parameters are influenced by the amount of filler within the material. The bleaching of composites was also performed by [PERSON] et al. [8], and they concluded that it did not affect the color of resin-based restorations. Conversely, [PERSON] et al. [36], studying ceramics, concluded that these materials are susceptible to discoloration from specific substances used in their experiments, such as coffee and orange juice. However, samples soaked in distilled water after bleaching did not show any change in color compared to their initial state, indicating that bleaching does not alter the inherent color of the ceramics.