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I 31 special _ transparent teeth I roots4_2010 The clearing process consists of three basic steps: demineralisation, dehydration and clearing of the root structure.14–15 Samplepreparation _Store extracted teeth in 10% formal saline until use.11 _Scalecalculusandanyremainsofperiodontaltissue. _Decoronate samples and negotiate canals with a #10 file (this will enhance acid penetration). _Store samples in 4.2% NaOCl solution (the organic tissue removal can be enhanced by placing the solution with the samples in the Ultrasonic Cleaner for 20 minutes). _Wash under running water and dry. _Indianinkcanbedrawnthroughtheroot-canalsys- tembyapplyingnegativepressuretotheapicalend. Demineralisation _Store samples in 5% nitric acid (HNO3) for three days. _Change solution every eight hours. _Manual or mechanical agitation promotes even demineralisation of the root. _Washsamplesunderrunningwaterforfourhours16 to clean. Dehydration _Dehydrate samples by using ascending grades of alcohol: 60% ethanol for eight hours, 80% ethanol for four hours, and 96.6% ethanol for two hours. _Dry samples with paper towels. Clearing _Thesampleshouldbeplacedinxylenefortwohours to harden prior to placing the samples in methyl salicylate to render them transparent.16 (This step is essentialifsamplesaregoingtobeusedforpractis- ing instrumentation or obturation techniques.) _Store samples in methyl salicylate in order to pre- serve their transparency. Please note: Always use proper protection when handling these dangerous solutions. Disposal of the used solutions should be done according to country regulations. _Educational tool Successfulroot-canaltreatmentdependsonade- quate cleaning, shaping and filling of the root-canal system. However, in order to achieve this goal, it is imperative that the operator has a detailed know- ledgeoftheroot-canalmorphologyofeachindividual tooth that is treated. Demineralised and cleared teeth may become a very valuable aid in the teaching ofendodontictechniques.HasselgrenandTronstad17 used cleared teeth to teach and practise instrumen- tation and obturation procedures in a preclinical course at Lund University, Sweden. At the end of the course,thestudentswereaskedtogivetheiropinions regarding the use of the transparent teeth in the learning process. The reaction was very favourable andencouragedtheheadofthedepartmenttoextend the use of cleared teeth in following courses.17 Dipping the samples in xylene for two hours, as suggested by Robertson in 1980, prior to placing theminmethylsalicylatewillreturndentinehardness to values slightly lower than those found in normal dentine.16 This yields new possibilities for dentists eager to learn, who wish to practise new techniques, procedures and protocols, from rotary instrumen- tation with NiTi files to thermoplastic obturation with warm gutta-percha. Dentists are able to see what is actually happening with much greater detail, whichisasignificantimprovementtoworkingwitha simulated canal in plastic blocks. Additionally, the tactile feeling experienced is very similar to the real clinical situation. In summary, this simple and inexpensive tech- nique will enable dentists to visualise the root-canal morphology in detail while allowing them to practise almost every endodontic procedure desired._ Editorial note: A list of references is available from the publisher. DrSergioRoslergradu- atedfromtheUniversityof BuenosAires,Argentina,in 1996,andhadbecomea specialistinEndodonticsby 2005.Hehasbeenaspe- cialistinOralImplantology since2009andworksin privatepracticeinBuenos Aires.Hecanbecontacted atsarosler@hotmail.com.ar. _contact roots Fig. 4 Fig. 5