IMAGE-BASED 3D RECONSTRUCTION AND ANALYSIS FOR ORTHODONTIA
V. A. Knyaz *,
State Research Institute of Aviation Systems (GosNIIAS), 125319, 7, Victorenko str., Moscow, Russia -
knyaz@gosniias.ru
Commission V, WG V/4
KEY WORDS: Close-range Photogrammetry, Accuracy, Orthodontia, Visualization
ABSTRACT:
Among the main tasks of orthodontia are analysis of teeth arches and treatment planning for providing correct position for every
tooth. The treatment plan is based on measurement of teeth parameters and designing perfect teeth arch curve which teeth are to
create after treatment. The most common technique for teeth moving uses standard brackets which put on teeth and a wire of given
shape which is clamped by these brackets for producing necessary forces to every tooth for moving it in given direction. The
disadvantages of standard bracket technique are low accuracy of tooth dimensions measurements and problems with applying
standard approach for wide variety of complex orthodontic cases. The image-based technique for orthodontic planning, treatment
and documenting aimed at overcoming these disadvantages is proposed. The proposed approach provides performing accurate
measurements of teeth parameters needed for adequate planning, designing correct teeth position and monitoring treatment process.
The developed technique applies photogrammetric means for teeth arch 3D model generation, brackets position determination and
teeth shifting analysis.
1. INTRODUCTION
Being aimed for transforming patient’s teeth arches to a perfect
condition orthodontia needs accurate data of teeth dimensions,
shape, position and orientation relatively to a reference system
of coordinates. This information allows determining the perfect
teeth arches shape, which has to be the result of treatment. To
move teeth to the perfect position special techniques are used.
The most common one uses special brackets which put on teeth
and a wire of given shape which is clamped by these brackets
for producing necessary forces to every tooth for moving it in
given direction.
Most of existing techniques use orthodontic wires of standard
shape for treatment. Unfortunately it is an often case when
standard wire is not suit for individual person. So there is a
need for designing individual wire for every case. To solve this
problem the image based system for orthodontic treatment
planning and analysis is developed. It uses a plaster copy of
teeth arch for 3D reconstruction and measurements of required
teeth geometric parameters for orthodontic analysis of a given
case and for designing individual orthodontic wire. For 3D
reconstruction a photogrammetric technique is used. 3D
reconstruction system includes two high resolution CCD
cameras, structured light projector and rotation stage for
automatic whole 3D model reconstruction. It allows generating
of teeth arches 3D model in automatic mode and solving
occlusion registration problem (the problem of putting virtual
teeth arches in the mutual position according to a real case). For
this purpose plaster models are installed in given posture using
dental articulator or plaster form for setup. Then mutual
position of jaws is registered by the developed photogrammetric
system. Two methods of occlusion registration are developed
and tested. The first method uses a set of reference points on the
* Corresponding author.
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upper and lower teeth arches. Images of teeth arches are
captured by the photogrammetric system, and then 3D
coordinates of reference points are calculated for mutual jaws
position determination. When applying the second method the
surface of upper and lower teeth rows is scanned in given
position of teeth arches plaster models. Then the teeth arches
3D model mutual position is determined using a set of this
surface scans as a reference surface using iterative closest point
algorithm. The estimation of method accuracy and comparative
analysis of these two techniques for jaw 3D models translating
were performed.
For optimal orthodontic wire designing virtual bracket is placed
on virtual tooth in required position by expert. Then the
developed software allows designing perfect teeth arch for
given case using measured information about teeth and to
design optimal wire (or set of wires) for moving teeth to perfect
position.
Photogrammetric approach allows getting accurate and
convenient solution for concerned problems. Application of an
accurate teeth arch 3D model instead plaster mould gives to a
orthodontist new possibilities for occlusion analysis, treatment
planning and visualization of treatment forecast using patient’s
face 3D model.
Proposed photogrammetric system supports all necessary
functions for teeth arches occlusion analysis and treatment
planning. It uses specially designed hardware for generating a
teeth arch 3D model and face 3D model in automated mode and
original software for models setting up, occlusion analysis and
optimal wire design.
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