# Laser Use in Creating Orthodontic Adhesion to Ceramic Surfaces
## 1 Introduction  
Introduction of lasers in dentistry was announced in 1960, by [PERSON] [1] and its use was continuously extended and researched. There are hard lasers, such as, carbon dioxide (CO\({}_{2}\)), neodymium yttrium aluminium garnet (Nd:YAG), erbium-doped yttrium aluminium garnet laser (Er:YAG) and cold or soft lasers which are known as low-level laser therapy or 'biostimulation' [2]. In order to ensure laser efficacity on a certain surface, an adequate intensity on the surface must be obtained. Also, it should couple as high a fraction of incident power into the material as possible. Laser beam properties, that may influence these characteristics, are: wavelength, responsible for the focusability and absorptivity of the beam; power and achievable spot diameter, which determine the intensity in the interaction zone; beam quality, being a measure of the available focused spot diameter and beam divergence angle product; finally, the polarisation of the beam, which has a considerable influence on the absorptivity for large angles of incidence [3]. Lasers may be used for most of the common dental procedures, such as frenectomies, crown lengthening, composite curing, and control of haemorrhage disorders, caries detection and removal, reduction of pain and treatments of hypersensitivity, gingivectomy, gingivoplasty, soft-tissue lesions and aphthous ulcers [4]. A short presentation of lasers used in dentistry facilitates understanding of this review [5]. The CO\({}_{2}\) laser wavelength has a very high affinity for water, resulting in rapid soft tissue removal and haemostasis with a very shallow depth of penetration. Its disadvantages are its large size and high cost and destructive interactions with hard tissue. The Nd:YAG wavelength is an effective surgical laser for cutting and coagulating dental soft tissues, with good haemostasis, that has also been used in periodontal treatments. The erbium lasers have two distinct wavelengths, Er Cr:YSGG (yttrium scandium gallium garnet) lasers and Er:YAG (yttrium aluminium garnet) lasers, with a high affinity for hydroxyapatite and the highest absorption of water in any dental laser wavelengths, thus being used for the treatment of dental hard tissues [6]. Erbium lasers can also be used for soft tissue ablation [7]. The diode laser has an active medium made of aluminium, gallium, arsenide and indium. It is mostly used for aesthetic gingival re-contouring, soft tissue crown lengthening, exposure of soft tissue impacted teeth, removal of inflamed and hypertrophic tissue, frenectomies and photostimulation of the apthous and herpetic lesions [8]. One of the diode laser types that is also used in dentistry is titanium-doped sapphire. It is a widelyused gain medium, with an active ion which has a large bandwidth in a host crystal that is hard and has high thermal conductivity [9]. A femtosecond laser emits optical pulses with a duration in the domain of femtoseconds--1 ps. It is included in the category of ultrafast or ultrashort pulse lasers. Femtosecond pulsation may be obtained by various diode-pumped lasers, such as neodymium-doped or ytterbium-doped gain media. Diode lasers and titanium-sapphire lasers are also suitable for pulse durations below 10 fs [3]. Other classifications of lasers are presented in Table 1.  
In orthodontic practice, lasers have many common applications, including acceleration of tooth movement, bone remodelling, enamel etching prior to bonding, debonding of ceramic brackets and pain reduction after orthodontic force and prevention of enamel demineralisation or soft tissue modelling [10]. At times, orthodontists must bond attachments to ceramic crowns, as they are commonly used in prosthodonic procedures. This type of bonding may cause some concerns, as there are several types of surface preparations that may be used. Surface roughness is needed for creating microretention for the adhesive layer used to bond brackets. Traditionally, surface roughness was gained by sandblasting or acid etching with hydrofluoric (HF) acid.