T he attractiveness of a smile is an important compo- nent of oral health. The colour and arrangement of the teeth, and their relationship to the soft tissues and bones of the face, give the overall aesthetic value of the human face. Of these components, the shade of the teeth is the easiest to alter to gain a cosmetic improve- ment for the dental patient. Having said this, it must be remembered that the health of the gingival tissues can greatly affect the appearance of the smile. Thus, peri- odontal care is an important part of cosmetic dentistry, and should be undertaken before laser-assisted tooth whitening. DIAGNOSTIC WORK-UP OF THE PATIENT Dentists are asked frequently to give an expert opinion regarding the likely causes for tooth discolouration. It is therefore essential to understand the interactions be- tween tooth development and the various agents that can influence enamel and dentine formation. When assessing the patient with discoloured teeth, it is essential to determine the nature of the problem, specifically whether the discolouration is due to inter- nal or external factors. With internal discolouration, in- trinsic stains such as pigments of various types have become incorporated into the enamel or dentine, ei- ther during its formation, or after eruption. In con- trast, with external staining, a superficial layer forms Tooth Discolouration and Its Treatment Using KTP Laser-assisted Tooth Whitening Laurence J Walsh a , Jackson Y. Liu b , Peter Verheyen c a Professor of Dental Science and Head of School of Dentistry, The University of Queensland, Brisbane, Australia. b Graduate Research Student, School of Dentistry, The University of Queensland, Brisbane, Australia. c Dentist in Private Practice, Gruitrode, Belgium. Summary: When confronted clinically with the problem of tooth discolouration, the basic strategy is to first iden- tify the aetiology of the discolouration, and then to apply the selected treatment, using the philosophy “as much as required, but as little as necessary.” For internal discolourations, green laser light from a KTP or argon laser is able to elicit photochemical reactions both within tooth structure and within a bleaching gel applied onto the labial surface. The unique optical and chemical interactions makes photochemical bleaching possible through promoting oxidation events in a controlled manner. This paper outlines a clinical approach to the diagnosis and management of patients with tooth discolouration, and summarises the technical and clinical aspects of the Smartbleach system for laser whitening. While extremely useful for routine in-surgery whitening treatments, the system is also able to treat severe tetracycline staining, to achieve pleasing improvements in appearance. A case is presented to illustrate the application of the Smartbleach system in these more challenging situations. A simple objective method for as- sessing tooth shade changes during laser whitening is also described. Key words: discolouration, whitening, KTP laser, argon laser, tetracycline. J Oral Laser Applications 2004; 4: 7-21. Vol 4, No 1, 2004 7 STATE OF THE ART