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ePaper created 2016-09-20, 16:58:27 | version 1.38.0
Journal of Oral Science & Rehabilitation 48 Volume 2 | Issue 3/2016 A x i a l p l a n e i n c o m p u t e d t o m o g r a p h y usedtenrectangularacrylicblocks(preparedwith titanium–molybdenum alloy) as markers spaced from 1 to 10 mm, respectively.14 A plastic sphere was prepared with ten sets of titanium markers spacedatvariableintervalsof1–10mm.Eachob- ject was scanned three times at slice thicknesses of 3.0 mm and slice thicknesses of 1.5 mm with 0.5 mm overlap, positioned in the CT scanner in two different positions in relation to the scanning beam (perpendicular and parallel). The authors concluded that when CT was carried out with slicesevery3.0mm,iftheprocedurewasnotper- formed correctly, significant errors would occur, but ifthe sliceswere less than 1.5 mm, even ifthe CT procedure were performed erroneously to some extent, the results would not show much variation and would be more precise. In 2004, Hanazawaetal.compareddataobtainedbymeans of a modified CT system and a conventional CT devicewithrealmeasurementstakendirectlyfrom cadaver mandibles, finding discrepancies in 90% ofthe measurements taken with the modified CT system compared with the direct measurements and in 87.5% ofthose taken with the convention- alCTdevice,thediscrepanciesbeingapproximate- ly 1 mm.25 These radiographic discrepancies can leadto iatrogenic lesions during implant treatment, which are ofparticularconcern in posteriorman- dibular regions, where they can produce lesions of the mandibular canal. In this regard, Klinge et al., who studied sensitivity and accuracy in lo- cating the mandibular canal using cadaverous mandibles, observed that when the accuracy in determining mandibular canal position was evaluated,comparingtheextentoferrorwiththe true value, the error was up to 1 mm in 94% of the CT measurements, but 39% with tomog- raphy,17%withpanoramicradiographyand53% using intra-oral radiography.23 Similar discrep- ancies between mandibular canal positions de- termined radiographically using CT and mea- surements taken directly from the bone have been observed by other authors.15, 16, 26 Similarly, numerous authors have observed small variations between the precision of three-dimensionalpreoperative imaging andthe final surgical positions of the dental implants, with variations ranging between 0.7 mm and 1.0 mm,2, 27 due to the discrepancies between CT measurements and the real dimensions. In this way, the results of the present study, in which discrepancies varied between 0.03 mm and 1.47 mm, coincide with the discrepancies obser- ved by these authors. Acquiring a good CT scan is of primary impor- tanceforvisualizingthedifferentbonystructures, and the quality and accuracy of the scan are in- fluenced by various factors. The skill of the op- erator has a major influence.Adequate position- ing of the patient will minimize error, and the choice of the appropriate equipment settings is important for achieving good contrast. Discrep- ancies between radiographic and real measure- mentscanincreaseaccordingtopatientposition- ingforCTscanning.17, 18 However, although many authors have observed discrepancies between radiographic measurements using CT and real bone measurements,these authors used a single axial reference plane, which in many cases was not specified.28–31 Currently, there are very few articlesthat examinethe discrepancies obtained with various axial reference planes. Cucchiarelli et al.’s comparison ofthe discrepancies between radiographic measurements with CT and mea- surements taken directly from 15 edentulous maxillae showed distortions with regard to the real bone measurements.19 It was found that the use ofthe horizontalplane showed 19.20% mag- nification, as opposed to the use of the occlusal plane,whichshowed16.5%magnification.Inthis regard,Abrahams made a general studyofman- dibles using CT and concluded that the best ax- ial reference plane is the occlusal plane.32 Al- though the present study found discrepancies when boththe occlusalplane andthe basalplane were taken as the axial reference plane, the dis- crepancies were greater when the basal plane was used. Conclusion The present studyfound that there are slight dis- crepancies between radiographic measurements takenusingCTandrealbonemeasurement.These must be taken into consideration in order to per- formsatisfactoryimplanttreatments.Withregard topatientpositioningfortheCTprocedure,useof the occlusal plane as axial reference will produce the most accurate measurements. Competing interests Wewishtoconfirmthattherearenoknowncon- flicts of interest associated with this publication and there has been no significant financial sup- port for this work that may have influenced its outcome.