Troubleshooting Impression Material Problems
Jim Hamilton, DDS
Welcome to the Course Home
Page of the Troubleshooting Impression Material Problems course. To view a
topic, just click its title from the index below. You can then return to this
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icon. For additional information on the course and for enrollment
information click here.
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Index:
A. Course and
Enrollment information
B. Background -
Why a course on "Troubleshooting Impression Material Problems"?
C. Troubleshooting
Impression Material Problems - What causes voids in crown and bridge
impressions?
- Voids on
buccal or lingual axial walls of the preparation
- Voids on the
distal axial wall of the preparation
- Voids at a
line angle
- Voids
throughout the impressions
- Voids in the
sulcus
- What causes
distortions in otherwise good looking impression?
- Single step
putty - wash technique
- Two step putty
- wash technique
This is the half way point in "Troubleshooting
Impression Material Problems". To view the rest of the course, or receive
credit or participate in the Question and Answer Forum, you will need to register for the course.
- Heavy body - light body
technique
- Triple tray technique
- What causes impression
materials to set too fast?
- Fast set due to
Temperature -- How can it happen?
- Mismatched base and
catalyst
- What causes impression
materials to set slowly?
- Shelf-life
- What causes positive, not
negative, spheres on this die?
- What class of impression
materials is the most popular in the United States and what causes them
not to set?
- Surface non set in the
sulcus
- Non set throughout the
material
- Test Questions
- Question and Answer Forum
Questions? Comments?
Questions or Comments relating to this CE course or activity can be e-mailed to Dr. Hamilton:
e-mail to: jchamilt@umich.edu
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© J.
Hamilton, University of Michigan, School of Dentistry, 1996
Voids on buccal or lingual
axial walls of the preparation
.
Figure 1
What causes voids on the
buccal or lingual axial walls of the crown and bridge impression (Figure1)? This
problem is often seen at the junction of the tray material and the injection
material. The most likely reason for this problem is that not enough wash
material was injected around the prep, so that when the tray material was
seated, there wasn't enough wash to flow up to the tray material.
Another possibility is
related to temperature. Higher temperatures lead to the wash material loosing
some of its ability to flow, and consequently, it did not flow up to meet the
tray material. The same may be true of the tray material, in that it is too far
along in its set to flow easily up to the wash.
This problem can be avoided
by covering the entire preparation with wash. My technique is to inject the
preparation, blow with air, and quickly inject again and seat the tray. This
will ensure that there will not be any voids on the axial surfaces.
You might ask why isn't
this problem seen on the mesial and distal surfaces of crown and bridge
preparations. The mesial and distal surfaces are usually confined by the
proximal surfaces of the adjacent teeth. These adjacent surfaces confine the
wash next to the mesial or distal surface of the prepared teeth. These adjacent
teeth also force the tray material to flow down next to these surfaces as the
tray is seated. On the buccal and lingual surfaces, as the tray material flows
down towards the sulcus, there are not the same confining surfaces, and the
tray material may not be forced up to the wash material.
On to the next session
Back to the
Course Index and Home Page
Questions? Comments?
Questions or Comments relating to this CE course or activity can be e-mailed to Dr. Hamilton:
e-mail to: jchamilt@umich.edu
© J.
Hamilton, University of Michigan, School of Dentistry, 1996
Voids on the distal axial
wall of the preparation
Figure 2, a void is
noted near the junction of the tray and injection material.
In Figure 2, a void is
noted at the junction of the tray and injection material. This special case is
due to the fact that there is no tooth distal to the prepared tooth to force or
confine the injections or tray material to that surface. In this instance, a
special effort needs to be made to forcibly inject material onto the distal
surface or confine the tray material with a custom tray. Another option with
the injection material is to blow it into the distal surface, if access allows,
which will ensure good apposition between the tooth surface and the impression
material.
On to the next session
Back to previous session
Back to the
Course Index and Home Page
Questions? Comments?
Questions or Comments relating to this CE course or activity can be e-mailed to Dr. Hamilton:
e-mail to: jchamilt@umich.edu
© J.
Hamilton, University of Michigan, School of Dentistry, 1996
Voids on the distal axial
wall of the preparation
Figure 2, a void is
noted near the junction of the tray and injection material.
In Figure 2, a void is
noted at the junction of the tray and injection material. This special case is
due to the fact that there is no tooth distal to the prepared tooth to force or
confine the injections or tray material to that surface. In this instance, a
special effort needs to be made to forcibly inject material onto the distal
surface or confine the tray material with a custom tray. Another option with
the injection material is to blow it into the distal surface, if access allows,
which will ensure good apposition between the tooth surface and the impression
material.
On to the next session
Back to previous session
Back to the
Course Index and Home Page
Questions? Comments?
Questions or Comments relating to this CE course or activity can be or e-mailed to Dr.
Hamilton:
e-mail to: jchamilt@umich.edu
© J.
Hamilton, University of Michigan, School of Dentistry, 1996
Voids on the distal axial
wall of the preparation
Figure 2, a void is
noted near the junction of the tray and injection material.
In Figure 2, a void is
noted at the junction of the tray and injection material. This special case is
due to the fact that there is no tooth distal to the prepared tooth to force or
confine the injections or tray material to that surface. In this instance, a
special effort needs to be made to forcibly inject material onto the distal
surface or confine the tray material with a custom tray. Another option with
the injection material is to blow it into the distal surface, if access allows,
which will ensure good apposition between the tooth surface and the impression
material.
On to the next session
Back to previous session
Back to the
Course Index and Home Page
Questions? Comments?
Questions or Comments relating to this CE course or activity can be or e-mailed to Dr.
Hamilton:
e-mail to: jchamilt@umich.edu
© J.
Hamilton, University of Michigan, School of Dentistry, 1996
Voids at a line angle
Figure 3
Figure 3 illustrates the
results of a void at the distal lingual line angle in an impression. This is
sometimes called a fin on the die. The most likely reason for this relates to
how the preparation was injected. Often the dentist will start injecting at a
line angle and go around the tooth, stopping at the same line angle. The
beginning and ending extrusions do not flow together. Why doesn't the beginning
and ending extrusions flow together? The material lost working time. This could
be due to room or mouth temperature (See what causes impression materials
to set too fast?)
or a timing issue. That is, it just took too long to inject the material.
The last possibility, and
least likely, is that the working time of the material was drifting. That means
that, due to problems in manufacturing, the working time was not stable, and
over time it got shorter or longer.
On to the next session
Back to previous session
Back to the
Course Index and Home Page
Questions? Comments?
Questions or Comments relating to this CE course or activity can be or e-mailed to Dr.
Hamilton:
e-mail to: jchamilt@umich.edu
© J.
Hamilton, University of Michigan, School of Dentistry, 1996
Voids on the distal axial
wall of the preparation
Figure 2, a void is
noted near the junction of the tray and injection material.
In Figure 2, a void is
noted at the junction of the tray and injection material. This special case is
due to the fact that there is no tooth distal to the prepared tooth to force or
confine the injections or tray material to that surface. In this instance, a
special effort needs to be made to forcibly inject material onto the distal
surface or confine the tray material with a custom tray. Another option with
the injection material is to blow it into the distal surface, if access allows,
which will ensure good apposition between the tooth surface and the impression
material.
On to the next session
Back to previous session
Back to the
Course Index and Home Page
Questions? Comments?
Questions or Comments relating to this CE course or activity can be or e-mailed to Dr.
Hamilton:
e-mail to: jchamilt@umich.edu
© J.
Hamilton, University of Michigan, School of Dentistry, 1996
Voids at a line angle
Figure 3
Figure 3 illustrates the
results of a void at the distal lingual line angle in an impression. This is
sometimes called a fin on the die. The most likely reason for this relates to
how the preparation was injected. Often the dentist will start injecting at a
line angle and go around the tooth, stopping at the same line angle. The
beginning and ending extrusions do not flow together. Why doesn't the beginning
and ending extrusions flow together? The material lost working time. This could
be due to room or mouth temperature (See what causes impression materials
to set too fast?)
or a timing issue. That is, it just took too long to inject the material.
The last possibility, and
least likely, is that the working time of the material was drifting. That means
that, due to problems in manufacturing, the working time was not stable, and
over time it got shorter or longer.
On to the next session
Back to previous session
Back to the
Course Index and Home Page
Questions? Comments?
Questions or Comments relating to this CE course or activity can be or e-mailed to Dr.
Hamilton:
e-mail to: jchamilt@umich.edu
© J.
Hamilton, University of Michigan, School of Dentistry, 1996
Voids on the distal axial
wall of the preparation
Figure 2, a void is
noted near the junction of the tray and injection material.
In Figure 2, a void is
noted at the junction of the tray and injection material. This special case is
due to the fact that there is no tooth distal to the prepared tooth to force or
confine the injections or tray material to that surface. In this instance, a
special effort needs to be made to forcibly inject material onto the distal
surface or confine the tray material with a custom tray. Another option with
the injection material is to blow it into the distal surface, if access allows,
which will ensure good apposition between the tooth surface and the impression
material.
On to the next session
Back to previous session
Back to the
Course Index and Home Page
Questions? Comments?
Questions or Comments relating to this CE course or activity can be or e-mailed to Dr.
Hamilton:
e-mail to: jchamilt@umich.edu
© J.
Hamilton, University of Michigan, School of Dentistry, 1996
Voids at a line angle
Figure 3
Figure 3 illustrates the
results of a void at the distal lingual line angle in an impression. This is
sometimes called a fin on the die. The most likely reason for this relates to
how the preparation was injected. Often the dentist will start injecting at a
line angle and go around the tooth, stopping at the same line angle. The
beginning and ending extrusions do not flow together. Why doesn't the beginning
and ending extrusions flow together? The material lost working time. This could
be due to room or mouth temperature (See what causes impression materials
to set too fast?)
or a timing issue. That is, it just took too long to inject the material.
The last possibility, and
least likely, is that the working time of the material was drifting. That means
that, due to problems in manufacturing, the working time was not stable, and
over time it got shorter or longer.
On to the next session
Back to previous session
Back to the
Course Index and Home Page
Questions? Comments?
Questions or Comments relating to this CE course or activity can be or e-mailed to Dr.
Hamilton:
e-mail to: jchamilt@umich.edu
© J.
Hamilton, University of Michigan, School of Dentistry, 1996
Voids throughout the
impression
Figure 4
Voids throughout the
impression material (Figure 4) are usually due to an error in mixing or loading
the tray or syringe. When loading a tray from an automix cartridge, always keep
the static mixing tip buried in the material. If you hold the mixing tip above
the tray and allow the material just to drop into the tray, it traps air and
leads to the problem seen in Figure 4. If an impression material syringe is
filled using a cartridge with a static mixing tip, the syringe should be filled
from the back to the front end with the piston already in position in the
syringe. This way, there will not be any air trapped in the cartridge between
the piston and material. This trapped air can become mixed with the material
and lead to an air voids in the impression. The air at the front of the
impression material syringe is expelled once the tip is screwed on prior to
injecting the material.
On to the next session
Back to previous session
Back to the
Course Index and Home Page
Questions? Comments?
Questions or Comments relating to this CE course or activity can be or e-mailed to Dr.
Hamilton:
e-mail to: jchamilt@umich.edu
© J.
Hamilton, University of Michigan, School of Dentistry, 1996
Voids in the sulcus
Figure 5
Voids in the sulcus (Figure
5) are a major concern. The most likely reason for a void at the gingival
margin is due to moisture contamination, or inability to deposit injection
impression material at this critical junction. In order to maintain a dry field
during injection, I use what is called a double cord technique. The tooth is
prepared down to, but not touching, the gingiva. A zero or double zero braided
retraction cord is packed to retract the gingiva. The preparation is then
dropped down to the braided cord. Now a number two cord is packed on top of the
double zero cord, pushing the double zero cord more apically. After waiting
five to ten minutes, only the number two cord is removed, leaving the smaller
retraction cord in the sulcus. The remaining smaller cord continues to maintain
pressure in the gingival sulcus and restricts the chance of hemorrhage into
this critical area. Now the hemostatic agent is rinsed and the area dried. The
margin should be fully visible, since the number two cord pushed the smaller
cord beyond the margin. The impression material is injected into the sulcus and
air from an air syringe is blown into the sulcus, blowing the material down to
the smaller cord. At the same time, the injection impression material is drawn
into a thin layer about the entire preparation. Another layer of impression
material is quickly deposited on to the prep, and the tray is seated. Most
often, when the impression material is set, and the tray is removed, the double
zero cord will come out in the impression. It's quite OK, since it is always
beyond the margin. If the smaller cord is not removed with the impression, pay
special attention to removing this cord prior to sending the patient home.
Voids at the gingival
margin can also be due to moisture contamination. The most likely area for
moisture contamination in the maxillary arch is the distal, buccal line angle
on the last tooth in the maxillary arch. In a mandibular impression, the most
likely area for moisture contamination is the distal lingual line angle of the
last mandibular tooth in the arch.
On to the next session
Back to previous session
Back to the
Course Index and Home Page
Questions? Comments?
Questions or Comments relating to this CE course or activity can be or e-mailed to Dr.
Hamilton:
e-mail to: jchamilt@umich.edu
© J.
Hamilton, University of Michigan, School of Dentistry, 1996
What causes distortion in
otherwise good looking impressions?
One of the most frustrating
problems associated with impression taking is the impression that looks
perfect, but is actually distorted. Much time is wasted in making the crown,
scheduling the patient, trying to seat the crown and retaking the impression. The
question immediately arises, why didn't it fit? Although there are many reasons
why a crown doesn't fit, most likely it is not the dental laboratory. Dental
labs couldn't stay in business if their crowns didn't fit a vast majority of
the time. The same goes for the impression material. Successful crowns and
bridges have been made with every major material. This is not to say that
dental laboratories and manufacturers don't have a bad day once in a while,
just that it is not as common as some dentists would like to believe.
I believe the most likely
reason for crowns that do not fit is rebound, or a change in the shape
of the preparation in the impression due to the springing back of the rubber
material that set under pressure. Shrinkage of an impression material, if the
tray is rigid and there is a bond between the tray and material, will most
likely lead to a larger die and crowns that go to place more easily on the
prepared tooth. The reason for this is that most preparations are extra
coronal. If the preparation is intra coronal, shrinkage will lead to a larger
unit and a restoration that will be more difficult to seat in the tooth.
How do we get rebound? There
are number of ways to create that unwanted rebound. In general terms, pressure
was generated in the impression material or placed on the tray during the
setting of the material while it was in the mouth. When the tray is removed
from the mouth, the pressure is released and the material springs into the
space left by both the teeth and preparation, leading to smaller dies and
crowns that are tight.
If the pressure to seat the
impression material flexed the tray, then the tray could also rebound, leading
to a distorted impression. Consequently, when an impression is seated, it
should be held with neutral pressure while setting.
On to the next session
Back to previous session
Back to the
Course Index and Home Page
Questions? Comments?
Questions or Comments relating to this CE course or activity can be or e-mailed to Dr.
Hamilton:
e-mail to: jchamilt@umich.edu
© J.
Hamilton, University of Michigan, School of Dentistry, 1996
Rebound - Single step
putty - wash technique
In the single step putty
wash technique, the current putties have shorter working times than the injection
materials. Consequently, it is quite possible that the putty could be seated
after it has started to gain memory and the injection material is still free
flowing. This leads to the putty setting under pressure and to rebound and
tight fitting crowns. With the single step technique, it is critical to
coordinate the mixing of the putty with the injection of the wash. That means
that if the dentist has a difficult prep to inject or multiple preps to inject,
the mixing of the putty will be delayed until after the start of injection. If
the injection of the preparation is relatively easy, the mixing of the putty
can start before the injection of the wash. The ideal case is when the putty is
mixed, placed in the tray, handed to the dentist and placed in the patient's
mouth, without any pauses in the sequence.
On to the next session
Back to previous session
Back to the
Course Index and Home Page
Questions? Comments?
Questions or Comments relating to this CE course or activity can be or e-mailed to Dr.
Hamilton:
e-mail to: jchamilt@umich.edu
© J.
Hamilton, University of Michigan, School of Dentistry, 1996
Rebound and two step putty
- wash technique
Figure 6.
In the two step putty wash
technique, the major problem is leaving room for the wash around the
preparation after the putty impression is taken. If a spacer is not used, or
the putty is not relieved, or the putty impression is held with too much
pressure, the putty will be in contact with the preparation. This will push all
the wash out of the area. This leads to the putty being under pressure when the
wash sets and rebound after the tray is removed from the mouth, leading to
smaller dies and crowns that are tight.
The easiest way to solve
this problem is to use a spacer when taking the putty impression. Figure 6
illustrates an area in which too much pressure was applied to the tray, or
there was not enough relief of the putty. The putty is showing through the wash
and had to be under pressure while the wash was setting. Consequently, when the
pressure was relieved as the tray was removed from the mouth, the putty
rebounded, leading to a smaller die and a crown that was tight.
On to the next session (requires course registration)
Back to previous session
Back to the
Course Index and Home Page
Questions? Comments?
Questions or Comments relating to this CE course or activity can be or e-mailed to Dr.
Hamilton:
e-mail to: jchamilt@umich.edu
© J.
Hamilton, University of Michigan, School of Dentistry, 1996