Original Article
Published on 15-10-2001
In
Italiano, per favore
En Español, por favor
A new method for the assessment of changes in molar inclination during RME
Metin ORHAN *, Serdar ÜSÜMEZ **
* DDS, MS,
PhD., Assoc. Prof., Clinical Instructor, Lecturer
** DDS, PhD., Assist.
Prof.
Selçuk University, Faculty of Dentistry, Department of Orthodontics,
Konya, TURKEY
Corresponding
author: Dr.Serdar
ÜSÜMEZ Selcuk University, Faculty
of Dentistry, Dept. of Orthodontics Campus, Konya 42079 TURKEY E-mail:
susumez@hotmail.com
Abstract
The authors show a simple technique
to evaluate the changes in molar inclination during rapid maxillary expansion.
1. Introduction
The contemporary trends in the practice
of orthodontics have moved toward the principles of dentofacial orthopedics
and non-extraction treatment modalities (1-4). The use of headgear and functional
appliances has demonstrated orthopedic effects mostly in the sagittal and vertical
dimensions. One of the most impressive orthopedic procedures is the transverse
separation of the maxilla through rapid palatal expansion. This procedure has
lately been the subject of renewed interest in orthodontic treatment mechanics
because of its potential for increasing arch perimeter to alleviate crowding
in the maxillary arch without adversely affecting facial profile. In addition,
it assists in the correction of disharmonies in the transverse plane between
the maxillary and the mandibular arches. (1, 5-8)
During RME, tipping of the anchorage teeth is usually realized along with the
skeletal changes. This undesirable side effect can take place due to a number
of factors including type of the appliance used, mode of activation, resistance
of the surrounding skeletal tissues, and degree of maturation. Precautions had
to be taken to overcome this undesirable effect. There is no consensus on these
precautions, however, more rigid devices said to hold the anchor teeth upright
can be used, mode of activation can be changed or resistance of the surrounding
bony tissues can be weakened with surgery.
Whichever method is used, it is always critical to be able to measure the amount
of dental tipping particularly for the PA cephalometric studies of RME. This
is needed for differentiating the amount of skeletal separation of the maxillae
from that of dental arches.
As it is a challenging experience trying to find the molar teeth contours on
the PA radiographs due to superimpositions of bony structures, different methods
have been advocated to measure the molar tipping occurred during RME. (9-12)
The aim of this presentation is to introduce a new auxillary and method of measurement
for the assessment of changes in molar torque value on PA radiographs.
2. Fabrication
Cr-Co casts onlays, which cover the occlusal surfaces of the left and right upper 1st molars are prepared by the dental laboratory on the pretreatment working models. This onlay has a vertical spur that is 0.9 mm thick and 10 mm long, which is prepared as vertical as possible to the occlusal surface of the molar tooth. Occlusal onlays also have eyelets that will be used for tying with dental floss during oral application to avoid accidental swallowing or aspiration (Figures 1-3). Note on Figure 1 that presence of a molar band to not inhibit the placement of the auxillary.
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Fig. 1a -
1b
Schematic drawing of the occlusal
onlay. Please note that onlay does not interfere with the molar band. |
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Fig. 2
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Fig. 3
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Occlusal cast
onlays.
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Onlays are being tried-in on the dental cast. | ||
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Please note that the two onlays are tied to each other with a piece of dental floss. |
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Immediately after delivery from the dental laboratory, inner faces of the onlays are inspected carefully with a magnifying glass to find out if there are any metallic bubbles, which can adversely affect the adaptation of the cast to the tooth. Any formation of that kind is ground away with hand-piece to make sure perfect fit of the onlay to occlusal surface and this is followed by the disinfectioning of the onlay.
3. Oral Application
Before try-in, casts are tied with dental floss and then cemented temporarily
on the occlusal surfaces of the corresponding molar tooth using polycarboxylate
luting cement (Figure 4) and the patient is taken to radiology. Patient is instructed
not to bite down until the PA cephalograms are taken. Following positioning
in the cephalostat the film is exposed.
After the exposure, the onlays are removed from occlusal by little force from
the occlusal surface, possible cement remnants are removed and the onlays are
kept with patient's dental models until RME is completed. When the RME procedure
is completed, stored onlays are recemented to repeat the above procedure is
repeated with or without removing the RME device if using a Hyrax type expander.
However the appliance should be removed first if the orthodontist is using a
cap type expander.
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Fig.4
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| Onlays are cemented to the molars. Please note that the onlays are tied with a dental floss during oral application to avoid accidental swallowing or aspiration. |
4. Radiographic Evaluation
The radio-opaque image of the vertical spur is clearly visible on the pre and post-RME posteroanterior radiographs, occlusal to the molar region (Figures 5A and 5B). This image represents the long axis of the molar tooth and its inclination changes with the tipping of the molar tooth that itis cemented on. Thus, changes in the inclination of this image can be used to assess the treatment changes in the tipping of upper molar tooth.
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Fig. 5a
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Fig. 5b
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Posteroanterior
x-ray taken with the onlays in place before RME treatment. Note that images
of the spurs are clearly visible on the film.
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Posteroanterior
x-ray taken with the onlays in place after RME procedure is completed.
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Fig. 6a
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Fig. 6b
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Dotted lines
are constructed using the images of the spurs and provides a baseline
to assess the inclination changes.
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The difference
between the angles A-C and B-D correspond to the change in the inclination
of molar teeth.
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Lines supposed to represent the molar
long axis can easily be constructed using the clear images of the spurs on the
cephalometric tracings. The changes in the relation of these two lines to any
reference line of the individual orthodontist's choice can be measured easily
and reflect the changes in molar torque value. In figures 6A and 6B, dotted
lines are constructed using radiographic images of the vertical spurs.
In this presentation, ZL-ZR line (the line constructed between the left and
right intersections of the orbits with the zygomatico-frontal sutures) is used
for demonstration (Figure 6 A and B). Angular changes can easily be calculated
and evaluated by measuring the angles of A, B, C and D seen on Figures 6A and
6B.
5. Conclusion
This simple and easy to use technique
was originally developed for our RME study. For the posteroanterior cephalometric
studies of rapid maxillary expansion and any other orthodontic mechanics, which
may cause tipping of teeth, this technique is very useful and precise. The clear
radio-opaque image of the metal spur will be visible even on the most superimposed
area allowing more sensitive tracing or digitizing thus producing more accurate
and reliable results. If needed, the dental technician can easily construct
same kind of a capped onlay for any other tooth that needs to be studied. Furthermore,
the technique can be used on lateral cephalograms to evaluate the mesiodistal
tipping of teeth.
The main drawbacks of the procedure can be considered as extra laboratory work
and need for an extra PA radiograph.
References
To cite this article please write: A new method for the assessment of changes in molar inclination during RME. M. ORHAN, S. ÜSÜMEZ. Virtual Journal of Orthodontics [serial online] 2001 Oct 15; 4(2): Available from URL:http://www.vjo.it/042/molar.htm
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