All PhD Theses

O. van Vlijmen

Cone beam CT in orthodontics


A scientific essay in Medical Sciences

DOCTORAL THESIS defended in public on 11th of January 2013


For longitudinal studies it is essential to be able to compare records made at different points in time. About 15 years ago three dimensional (3D) cone beam computer tomography (CBCT) has been introduced into the field of orthodontics. CBCT has expanded the diagnostic possibilities for orthodontic patients and has changed the way diagnosis and treatment plans for certain patient categories are made. Nowadays, these patients will be documented in 3D. If longitudinal evaluation is indicated those 3D records need to be compared with older two dimensional (2D) records. For further application of CBCT technology within the field of orthodontics, it is important to develop evidence based guidelines. At first, it is important to know which evidence is currently available for the use of CBCT for orthodontic purposes. Therefore the aim of this thesis was to investigate the comparability of 2D and 3D images and to assess the level of evidence for the use of CBCT in orthodontics.

Chapter one explains the background of the thesis. The history of early attempts to make an orthodontic diagnosis in three dimensions is described as well as a brief history of cephalometrics in the orthodontic field. Also the introduction of CT and CBCT is described. The basic principles of CBCT are explained and possible indications for CBCT in the field of orthodontics are presented.

In chapters two to five of this thesis, four methodological studies performed on dry human skulls are worked out. The aim of these studies was to determine whether different 2D and 3D image x-ray modalities of the facial skeleton can be compared. The first two studies are concerned with lateral cephalometry and the latter are concerned with frontal cephalometry.

Chapter two describes a study in which measurements on conventional lateral cephalometric radiographs were compared to measurements on CBCTconstructed lateral cephalometric radiographs taken from human skulls.

In chapter three, measurements on conventional lateral cephalometric radiographs were compared to 3D measurements on 3D models of human skulls.

Chapter four describes a study in which measurements on conventional frontal radiographs are compared to measurements on CBCT-constructed frontal cephalometric radiographs.

Finally, in chapter five, measurements on conventional frontal radiographs were compared to measurements on 3D models of human skulls derived from CBCT scans. These four methodological studies proved that only a 2D lateral projection of the 3D volumetric data set can be compared to a conventional 2D lateral cephalometric radiograph. Comparison between conventional frontal radiographs and frontal projections of the 3D volumetric data and comparison of conventional 2D images and 3D models, is not accurate. This is crucial information for longitudinal research in cases where part of the records are in 2D and a another part of the records is in 3D.

Chapter six describes a study which investigated whether the used hardware influences the performed measurements. Images obtained from two different CBCT devices were compared. Thereto CBCT scans of 40 dry human skulls were made with both the i-CAT™ and the Iluma™ cone beam CT device. From the CBCT scans 3D models were constructed and cephalometric measurements were performed repeatedly. The results showed that hardware used for making a CBCT might influence the measurements. It was concluded that care should be taken when interpreting measurements made on CBCT 3D models derived from different CBCT devices.

In chapter seven a systematic review on the evidence for the use of CBCT in orthodontics is described. Articles were identified by searching the Cochrane library, PubMed, Medline, Embase, Scopus and CINHAL. Articles up to March 2010 were reviewed and the methodological quality was evaluated. From the systematic review of the literature it was concluded that only a few studies have quantified the assumed advantages of CBCT in orthodontics. Only for the analysis of airway volume scientific evidence was available, suggesting that CBCT provided added value. Future research is needed to elucidate the efficacy, efficiency and cost effectiveness of using CBCT in orthodontic diagnosis and treatment planning. Future studies should quantitatively evaluate the effects of CBCT on diagnostic and treatment procedures, progression and outcome.

Chapter eight is the general discussion. In this chapter the results of the studies performed for this thesis are discussed, concentrating on the aims set out in the first chapter. At the end of the chapter suggestions for future research are given and future perspectives of CBCT applications for the orthodontic specialty are explored.