cosmetic dentistry_ beauty & science

I 13 special topic _ TouchWhite I cosmeticdentistry 1_2012 about safety owing to the unique way in which the Er:YAGlaserwavelengthinteractswiththebleach- ing gel. Before taking a closer look at the TouchWhite method, however, let’s first quickly review some of the basics of dental bleaching gels. _Bleaching gel effectiveness Bleaching gels consist mainly of water and a bleaching agent containing hydrogen perox- ide (H2O2). Water is the principal component of bleaching gels and commonly accounts for more than50%ofthegelbyweight.Thebleachingagent itself is present in an amount ranging from 3 to 50 % by weight. In a typical tooth-whitening process, the bleachinggelisappliedtotheteethandallowedto remain in contact for up to an hour. The intensity of the bleaching effect depends on both the dura- tionofcontactandtherateofactivationofthegel, whichcanbeincreasedbyraisingthetemperature. Heatservestoincreasetherateofactivationoffree radicals in H2O2, accelerating the speed at which whitening can be achieved.8, 9 Inparticular,highergeltemperaturesfacilitate: _faster generation and greater mobility of H2O2 in the bleaching gel; _decomposition of H2O2 into OH and O; _an enhanced diffusion rate into the tooth; and _an enhanced reaction time between the active peroxidespecies(radicalsofOHoratomicoxygen O)andthecompoundsoftheenamelanddentine. Typicaltemperatureincreasesinthegelthatare desirablefordentaltreatmentsarebetween10and 40 °C. _Light absorption The use of high-intensity light for increasing the temperature of H2O2 to enhance the chemical bleaching of teeth was first reported by Abbot in 1918.10 In modern dental offices, lasers are fre- quently used to deliver a controlled beam of high- intensity light to thermally activate the bleaching gel. Many manufacturers of laser- and light-based bleaching systems claim that there is improved light absorption, reduced tooth heating, and even photochemical activation of the bleaching gel following the addition of an activator, absorber or colourant to the gel.11, 12 In principle, this concept does improve the absorption efficiency, but not enough to alleviate all safety concerns. In a systematic review (conducted before the introduction of the TouchWhite method), Buchalla and Attin13 concluded that there was no real evidence to support a photochemical bleaching effect and that the en- hanced rate of bleaching with laser- or light-based treatments was the result of photothermal activa- tion. Additionally, they warnedthatactivationof bleaching agents by light or laser energy may have anadverseeffectonpul- pal tissue owing to an increase in intra-pulpal temperature exceed- ing the critical value of 5.6 °C. This is because most laser wave- lengths are not fully absorbed in the rela- tively thin layer of the gel that is de- posited on the tooth surface. As a result, the laser energy is transmitted directly into the dental tissue, possibly leading to pain and permanent damage. _The TouchWhite concept The TouchWhite method uses a very different approach, which eliminates these concerns by making optimum use of the unique properties of the Er:YAG laser wavelength, which is the laser wavelength that is most highly absorbed in water. Water is the major component of dental bleaching gels, and owing to the nearly instantaneous ab- sorption of the Er:YAG beam in water, the need for having special light-absorbing particles in the gel is removed entirely. All of the Er:YAG laser energy is used for direct heating of the bleaching gel, thus preventing any risk of thermal injury to the tooth. During the application of the Er:YAG laser dur- ingTouchWhite,thebeamoflightisfullyabsorbed in the first 10 to 50 µ of the gel, and deeper gel lay- ers are subsequently heated by means of thermal diffusionawayfromthelaser-heatedsurfacelayer.