From: 3DLab*. School of Dentistry, Department of Paediatric Dentistry, University of Copenhagen, Department of Mathematical Modelling, Technical University of Denmark. Nørre Alle 20, DK-2200 Copenhagen, Denmark.
Correspondence: sven@odont.ku.dk


Cases #1-#5.


1. Introduction

A number of craniofacial anomalies or syndromes involve severe disturbances of tooth formation and eruption (e.g. Apert syndrome, Crouzon syndrome, Tricho-Dento-Osseous Syndrome, cleidocranial dysplasia, and cleft lip and palate). So far, studies of these dental problems have been limited to 2-dimensional analysis from orthopantomograms, intra-oral X-rays or cephalometric radiographs. Recently, a method for visualization of developing teeth in three dimensions based on CT-scans of the jaws has been developed [2].

The purpose of the present study was to apply this new visulazation method to the analysis of the complex dental problems found in some of the syndromes listed above.

2. Method

High quality CT-scans were available on a number of syndrome cases treated and followed by the Craniofacial Team at The National University Hospital of Denmark and School of Dentistry, University of Copenhagen. CT-scanning of the craniofacial region was carried out in connection with diagnosis, planning of craniofacial surgery and follow-up.

All scannings were carried out at Department of Radiology in a Siemens CT-scanner, using the same protocol with a slice thickness of 2 mm.

3D reconstruction of the craniofacial region was performed on a powerfull graphic computer at the 3D-Lab. for clinical purposes. Afterwards, the raw data were made available for the 3D-Lab. for research and development purposes.

In the present study, the dentitions of selected cases were segmented using a combination of manual editing, threshold selection, and iso-surfaces [1] generated by an algorithm similar to the Marching Cubes algorithm [3, 4], and subsequently rendered on a Silicon Graphics workstation. All the tools have been implemented in the software package Mvox [1]. The method allows us to interactively pick out individual elements such as the teeth and change their properties.

In the present study 3D reconstruction of the craniofacial skeleton was carried out. The jaw bones were made transparent and the teeth of both the primary and permanent dentition were made opaque and specific teeth were colour coded, i.e. all primary teeth were given a white colour, the first permanent molars were assigned the colour red, the second permanent molars blue, and all permanent teeth mesial to the first molars green.

3. Material

CT-data from children with Apert syndrome, Crouzon syndrome, Tricho-Dento-Osseous Syndrome, and cleft lip and palate are included in the study. In several cases 2 or 3 CT datasets of the craniofacial region obtained during growth were available:

Case #1: Girl with Apert syndrome; CT-scans from 9 months, 21 months, and 7 years of age, respectively (Fig. 1).


Fig 1.

Case #2: Boy with Apert syndrome; CT-scans from 1 month, 8 months and 4 years of age, respectively (Fig. 2).


Fig 2.

Case #3: Boy with Crouzon syndrome; CT-scans from 10 months and 7 years of age respectively (Fig. 3).


Fig 3.

Case #4: Girl with Tricho-Dento-Osseous Syndrome; CT-scans from 15 years of age (Fig. 4).


Fig 4.

Case #5: Girl with cleft lip and palate and Frontonasal Dysplasia; CT-scans from 2 months, 10 months and 5 years of age, respectively (Fig. 5).


Fig 5.

Results

All twelve 3D datasets were visualized on the computer screen in the lateral, frontal, oblique lateral, and axial views. Images visualizing both the skeleton and the teeth as well as images visualizing the teeth seperately were produced and were printed on a colour printer in size 1:1.

As an example Fig. 1 and Fig. 2 illustrate two cases with Apert syndrome. The analysis revealed new relevant information concerning ectopic position and hindered eruption of the permanent maxillary molars and premolars, which could be directly related to a maxillary growth disturbance with early fusion of the sutures of the maxillary complex [5]. Similar problems was observed in Case #3 who suffered from Crouzon syndrome. (Fig. 3).The patient was treated with extraction of the maxillary primary second molars which caused the maxillary permanent first molars to erupt just distal to the maxillary primary first molars with total lack of space for the second premolars. In addition, this case showed disturbances in the eruption of the permanent maxillary incisors (Fig. 3).

Case # 4 showed severe malposition of unerupted permanent teeth in the maxillary premolar regions, delayed eruption and tooth malfomations as part of the skeletal dysplasia seen in the Tricho-Dento-Osseous Syndrome (Fig. 4) and Case #5 showed asymmetric deviations in both tooth formation and eruption in the maxillary incisor region in relation to complete cleft of the lip, alveolous and palate on the left side.

Discussion

In all five cases examined the 3D analysis of the formation, position, and eruption of permanent teeth revealed new relevant information which described the clinical problem more accurately with spatial information which is impossible to obtain from standard 2D methods (orthopantomograms, intra-oral X-rays or cephalometric radiographs).

The 3D method will undoubtedly lead to improved understanding of the often very complex dental problems found in patients with severe craniofacial anomalies and will, hopefully, also give a spin-off of new information on the general biological mechanisms involved in tooth eruption.

Acknowledgements

The authors are grateful to Dr. Aase Wagner and Dr. Karen-Lisbet Dirksen, Department of Radiology, The National University Hospital of Denmark for providing us with the CT- data, and to the clinical co-ordinator of the Craniofacial Team at this hospital, Dr. Flemming Skovby, Department of Pediatrics. Fig 1. 3D reconstruction of the craniofacial skeleton and the tooth crowns in a girl with Apert syndrome at 21 months of age. Fig. 2 Same patient as shown in Fig. 1; now 7 years of age. Note the numerous developing permanent teeth.

References

[1] Bro-Nielsen M. Mvox: 2-4D medical image and graphics visualization. Proceedings CAR '96. Paris, June 1996; pp. 335-338.
[2] Bro-Nielsen M, Larsen P, Kreiborg S. Virtual teeth. A 3D method for editing and visualizing small structures in CT scans. Proceedings CAR '96, Paris, June 1996; pp. 921-924.
[3] Lorensen WE, Cline H. Marching cubes: A high resolution 3D surface construction algorithm. Computer Graphics 1987; 21: 163-169.
[4] Liversage M, Bathia G, Vannier, M. Marching cubes: Algorithmic improvements. Automedica 1992; 14: 297-310.
[5] Kreiborg S, Bro-Nielsen M, Larsen P, Darvann T, Dirksen K-L, Skovby F. En ny metode til 3-dimensional analyse af tanddannelse og -eruption. Tandlægebladet 1996;100: 57-58.

*3DLab.
is the Research and Development Laboratory for
3D Image Processing and Reconstruction at the
National University Hospital of Denmark,
School of Dentistry, University of Copenhagen, and
Department of Mathematical Modelling, Technical University of Denmark.