Investigation of bracket bonding for orthodontic treatments using en- face optical coherence tomography Cosmin Sinescu a , Meda L.Negrutiu a , Michael Hughes b , Adrian Bradu b , Carmen Todea c , Roxana Rominu a , Dorin Dodenciu d , Phillippe L. Laissue e and Adrian Gh. Podoleanu b a Department of Prostheses Technology and Dental Materials, Faculty of Dental Medicine, University of Medicine and Pharmacy "Victor Babeş" Timişoara, Romania b Applied Optics Group, School of Physical Sciences, University of Kent, Canterbury, UK c Department of Oral Rehabilitation, Faculty of Dental Medicine, University of Medicine and Pharmacy "Victor Babeş" Timişoara, Romania d Biophysics Department, University of Medicine and Pharmacy "Victor Babeş" Timişoara, Romania e Kent Institute of Medical and Health Studies, University of Kent, Canterbury, UK ABSTRACT Despite good diagnosis and treatment planning, orthodontic treatment can fail if bonding fails. It is now common practice to address the aesthetic appearance of patients using aesthetic brackets instead of metal ones. Therefore, bonding aesthetic brackets has become an issue for orthodontists today. Orthodontic bonding is mainly achieved using composite resin but can also be performed with glass ionomer or resin cements. For improving the quality of bonding, the enamel is acid etched for 30 seconds with 38% phosphoric acid and then a bonding agent is applied. In our study we investigated and compared the quality of bonding between ceramic brackets, polymeric brackets and enamel, respectively using a new investigation method - OCT. The aim of our study was to evaluate the resin layer at the bracket base - tooth interface. Keywords: OCT, orthodontic bonding, non-invasive interface investigation 1. INTRODUCTION Over the last decade, adult orthodontics has dramatically increased in importance. Tooth coloured aesthetic appliances has become more frequent. The use of tooth-coloured brackets or lingual metallic brackets is common procedure. Orthodontic treatment can fail or last much longer depending on bonding quality. Orthodontic bonding is primarily achieved with composite resin but can also be performed using glass ionomer or resin cements. For this, enamel conditioning is required. Out of all types of acids (maleic, oxalic, ETDA, sulphuric acid) that were tested since 1955, phosphoric acid proved to be the most suitable one for bonding. In order to gain maximum bond strength, enamel is acid etched for 30 seconds with 38% phosphoric acid and then a bonding agent is applied. In our study we investigated the quality of bonding between ceramic brackets, polymeric brackets and enamel, respectively using an innovative, non-invasive investigation method – en-face optical coherence tomography (OCT). Up until now orthodontic bonding has mainly been investigated by invasive (destructive) investigation methods such as mechanical testing followed by microscopic evaluation [10,11,12]. The aim of our study was to evaluate the bracket base - tooth interface using OCT to improve bonding protocols. 2. MATERIALS AND METHOD An en-face OCT system as described in previous reports has been employed [1,2] operating at 1300 nm. The optical configuration [4] uses two single mode directional couplers with a superluminiscent diode as the source. The scanning Biophotonics: Photonic Solutions for Better Health Care, edited by Jürgen Popp, Wolfgang Drexler, Valery V. Tuchin, Dennis L. Matthews, Proc. of SPIE Vol. 6991, 69911M, (2008) · 1605-7422/08/$18 · doi: 10.1117/12.780701 Proc. of SPIE Vol. 6991 69911M-1 2008 SPIE Digital Library -- Subscriber Archive Copy