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F. Beuer, K.J. Erdelt, R. Friedrich, K. Köbele-Bogai, M.
Eichberger, W. Gernet1
Retention and fracture resistance of acrylic denture teeth on
the denture base
This in vitro investigation is intended to show the influence of
preparation of denture teeth (macromechanical retention) and
conditioning of the base surface of the tooth (chemical bond) on
the failure of the acrylic-tooth bond. A total of 140 upper
incisors (2 different manufacturers, 3/ 4 different types of
preparation) were investigated with regard to their frac-ture
resistance and bond strength to the acrylic base. Half of all the
samples were artificially aged by thermocycling and all samples
were tested until failure in a universal testing ma-chine at an
angle of 45°.
All of the teeth fractured, though not at the interface be-tween
the denture base and tooth. Macromechanical reten-tion on the tooth
base and bonding agent were not necess-ary to ensure retention of
the acrylic teeth on the denture base. There were, however,
significant differences in the frac-ture resistance of the tooth
groups tested.
Keywords: denture teeth, acrylic tooth, bonding agent, fracture
resistance
1 Department of Dental Prosthetics, Ludwig Maximilian
University, Munich, Director: Prof. Dr. Dr. h.c. W. Gernet
1 Introduction
The use of acrylic denture teeth has be-come established both in
full denture prosthetics and partial denture pros-thetics since the
introduction of highly aesthetic teeth that are not prone to
dis-coloration [7]. They are superior to porcelain teeth
specifically due to the possibility of a chemical bond between the
denture teeth and denture base.
Suitable preparation of denture teeth proved to be a problem at
the De-partment of Prosthetics of the Ludwig Maximilian University,
Munich, Ger-many. In particular, anterior teeth that had come out
of dentures fabricated in the student course often had to be
re-paired and fixed in position again after a short time in situ.
Stricter monitoring of the students who fabricated these
resto-rations did not achieve any marked im-provement in the
complaints.
Technicians at the university ob-served, however, that there
were fre-quent fractures of the actual denture teeth, particularly
in the anterior region and mainly involving implant-borne,
removable restorations.
Both macroretention and micro-mechanical retention were options
for preparing the denture teeth for fixation in the denture base.
Manufacturers rec-
ommend roughening the areas that come into contact with the
acrylic and preparing grooves or a central hole in the base of the
tooth. Manufacturers also supply bonding agents, which are intended
to improve the bond between the tooth and base.
Due to their high filler content acrylic denture teeth now also
have im-proved abrasion properties compared with previous teeth,
which usually had a lower filler content. It is debatable whether
this higher filler content, which is subjectively associated with a
marked brittleness and difficulty dur-ing preparation, also
detrimentally af-fects the fracture properties of the teeth.
2 Materials and methods
Generally anterior teeth from two ma-nufacturers that have
different manu-facturing techniques should be tested. As identical
tooth ranges as possible we-re selected and therefore 80 teeth from
the Vitapan range (Vita Zahnfabrik/Bad Säckingen, Germany) and 60
teeth from the Mondial range (Heraeus Kulzer/Was-serburg, Germany)
were examined. All teeth were uniformly roughened on the base
section and cervical region using a
diamond rotary instrument with a 50 μm grit size. Then 20
samples from the Mondial group and 40 samples from the Vitapan
group were randomly selected and prepared basally using a channel
cutter. The macromechanical retention on all teeth of this group
was the same due to the defined channels. Twenty Mondial teeth and
20 Vitapan teeth from the group prepared with channels were wetted
with Palabond bonding agent (Heraeus-Kulzer), the remaining 20
Vitapan teeth were conditioned with Vitacoll (Vita Zahnfabrik).
This was to test the influence of the different bon-ding
agents.
A further 20 samples from the Mon-dial group and 20 samples from
the Vita-pan group were selected and a 3 mm deep drill hole
prepared in the centre using a round bur (diameter 3 mm). A mark on
the round bur ensured that all holes were drilled to the same
depth.
The Mondial group samples were conditioned with the bonding
agent (Palabond) recommended by the manu-facturer; the same
procedure was fol-lowed with the Vitapan samples and they were
wetted with Vitacoll.
In order to fabricate the same base for all samples, a positive
wax model was fabricated and an impression taken of it using
addition-curing silicone. This pro-
1
OffprintDZZ – Deutsche Zahnärzliche Zeitschrift
Volume 61, Issue 3 (2006) Page 147 – 150, 15.3.2006,
Postverlagsort Köln
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duced a negative that was used as a mould for all samples.
The prepared denture teeth were in-serted in this mould and the
base was fil-led with PalaXpress cold-curing acrylic (Heraeus
Kulzer/Hanau, Germany) and then polymerised in a pressure pot at 2
bar and 45° C for 30 minutes.
Ten samples from all the different sample groups of 20 were
randomly se-lected and artificially aged. The samples were aged
using 10000 thermocycles of 5°C to 55°C.
All samples were then tested in a universal testing machine
(Zwick/Ulm, Germany) with a feed rate of 0.5 mm/min. The force
application was the same as previously published and completed
studies at an angle of 45° [3], whereby the incisal edge was used
as the contact point for the indenter. Placement of polyethylene
foil between the indenter and denture tooth was intended to
dis-tribute the force uniformly (see Fig. 1).
3 Results
All samples tested fractured at the junction between the denture
base and acrylic tooth in the cervical area, i.e. the actual tooth
fractured and the interface between the cold-curing acrylic and
denture tooth withstood the loading. In order to check this fact, 3
samples with unprepared teeth were tested and in this case the
acrylic tooth loosened from the base with a load of approx. 60
N.
After preparation with a channel cutter and conditioning with
the bond-ing agent recommended by the manu-facturer, the Mondial
teeth exhibited an
initial mean fracture resistance of 570.12 N (± 46.47) and when
aged a mean fracture resistance of 378.10 N (± 60.84). This
corresponds to a loss of re-sistance of about 34%; the difference
was highly significant p = 0.000 (Mann-Whitney U test, significance
level p < 0.05). The Mondial teeth, which were provided with
hole retention and con-ditioned with Palabond, achieved a mean
fracture resistance of 515.10 N (± 27.80) [initial] and 376.60 N (±
45.40) [after artificial aging]. If these teeth were only roughened
and not prepared further, they achieved a mean fracture resistance
of 564.72 N (± 57.29) without aging and after artificial aging
397.79 N (± 39.97). Even with this type of prepara-tion the
differences in fracture resis-tance between the samples before and
after aging were statistically significant with p = 0.000 (hole
retention) and p = 0.000 (only roughened).
If the initial fracture resistance valu-es of the Mondial teeth
are compared with regard to the different methods of preparation,
the difference between the group with hole retention and the two
other groups is striking (see Fig. 2). This difference was
significantly different when compared with both the channel cut (p
= 0.009) and only roughening (p = 0.043).
With the channel retention and bonding agent Palabond the
Vitapan teeth exhibited a mean fracture strength of 471.49 N (±
61.17) [initial] and 363.53 N (± 56.65) [after artificial aging].
The fracture resistance after aging was 23% lower than the initial
value and was also statistically significant (p = 0.002). If the
conditioner Vitacoll recommended by
the manufacturer was used, mean frac-ture values of 480.66 N (±
38.99) [initial] and 373.40
N (± 46.61) [aged] were achieved. The bonding agent used did not
produce any significant difference with values of p = 0.684
[initial] and p = 0.529 [aged].
The type of preparation used with the Vitapan teeth did not have
any in-fluence on the initial resistance (see Fig. 3), whereby all
values were less than those achieved with the Mondial teeth. With
hole retention and Vitacoll con-ditioning they achieved a mean
fracture resistance of 457.73 N (± 35.47) [initial] and 353.72 N (±
29.77) [aged], while the samples that were only roughened achieved
459.12 N (± 52.54) [initial] and 345.93 N (± 50.11) [aged].
The Mondial teeth achieved signifi-cantly higher initial
fracture resistances than the Vitapan teeth when prepared with the
channel cutter and con-ditioned with Palabond bonding agent
(p=0.002) and with roughening only (p=0.000). After artificial
aging the frac-ture resistance of the Mondial teeth was also
significantly higher than that of the Vitapan teeth (p =
0.043).
4 Discussion
The fact that all samples fractured and no denture teeth
loosened from the acrylic base, suggests that conditioning does not
have any influence in the event of denture tooth breaking out of
the ba-se. If a denture tooth loosens from the base, therefore, it
has either been conta-minated or it was not prepared at all. This
is the only way a chemical bond
Figure 1 Test set up Figure 2 Fracture resistance of Mondial
teeth Illustration:
2F. Beuer et al.:Retention and fracture resistance of acrylic
denture teeth on the denture base
Channel + Cond. A Hole + Cond. A Without/WithoutConditioning
Frac
ture
fo
rce
650.00
600.00
550.00
500.00
450.00
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between the acrylic tooth and the den-ture base cannot be
produced.
There must therefore be another explanation for the general
differences in the mean fracture strengths. The first possibility
was the different di-mensions of the two different teeth. As
particular care was taken to ensure that the teeth had the same
dimensions and all fracture surfaces were measured after the test
and yet no differences were found, this was eliminated as a
possible explanation.
Another possible reason could be the different types of
manufacture of the denture teeth, though the so-called Incom
process (Heraeus Kulzer) should not be fundamentally different from
the press process (Vita-Zahnfa-brik).
The composition of the acrylic is the most likely explanation,
thus the Vita-pan tooth is characterised as a very brittle, highly
filled tooth, particularly in routine use. This is reflected in its
good abrasion properties, but also in a reduced fracture
resistance. The larger filler particles and their denser packing in
the Vitapan teeth can be clearly seen (Fig. 4) in comparison with
the Mondial teeth (Fig. 5), whose fracture surface comprises more
matrix and fewer filler particles. The values of the fracture
resis-tance of denture teeth may also not be fully achieved by
partial dentures, though the maximum strength values in other
studies achieved almost 300 N [8]. This leaves hardly any room for
safety margins, as the aged teeth have fracture resistances of
around 350 N.
5 Conclusion
The use of expensive bonding agents, which are offered by the
teeth manu-facturers, is not required to ensure an adequate bond of
acrylic teeth to the denture base. The bonding agent has a certain
cleaning effect at most and the-refore prevents contamination, e.g.
due to separating agent. The same success, however, can also be
achieved using mo-nomer.
Denture teeth lose a significant pro-portion of their initial
fracture resis-tance because of artificial aging. This remaining
fracture resistance is, how-ever, still sufficient to withstand any
masticatory loading that occurs in the anterior region of a full
denture. The maximum loading, which may occur with partial
dentures, is very close to the mean fracture values of aged Vita
teeth.
The publishing company retains all rights, including reprint,
the photo-mechanical reproduction of this off-print and the
translation.
This text is a translation of a contract from the original
German. The translators do not accept any liability for damages
that may arise from using the English text of the contract. The
original German text is definitive.
Figure 3 Fracture resistance of Vitapan teeth Illustration:
Figure 4 Fracture surface of a Vitapan tooth
Figure 5
Fracture surface
of a Mondial
tooth
Dr. Florian BeuerPoliklinik für zahnärztliche Prothetik der LMU
MünchenGoethestr. 7080336 MünchenGermanyTel.: +49 (0)
89/[email protected]
Contact address:
3F. Beuer et al.:Retention and fracture resistance of acrylic
denture teeth on the denture base
Frac
ture
fo
rce
Channel + Cond. A Hole + Cond. B Channel + Cond. B
Without/Without
Conditioning
600.000
550.00
500.00
450.00
400.00
350.00
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(Hrsg.): Kli-nische Materialkunde für Zahnärzte. Hanser, München
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8. Lauer H-Ch, Ottl P, Ficker E, Weigl P: Kaufkraftmessung an
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References
The publishing company retains all rights, including reprint,
the photomechanical reproduction of this offprint and the
translation.
This text is a translation of a contract from the original
German. The translators do not accept any liability for damages
thatmay arise from using the English text of the contract. The
original German text is definitive.
4F. Beuer et al.:Retention and fracture resistance of acrylic
denture teeth on the denture base
