UMEÅ UNIVERSITY ODONTOLOGICAL DISSERTATIONS No 84, ISSN 0345-7532, ISBN 91-7305-589-1 Calcium Aluminate Cement as Dental Restorative. Mechanical Properties and Clinical Durability Karin Sunnegårdh-Grönberg From the Department of Dental Hygienist Education, Faculty of Medicine, Umeå University, Sweden and Department of Dental Materials, Faculty of Health Sciences, Copenhagen University, Denmark 2004
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UMEÅ UNIVERSITY ODONTOLOGICAL DISSERTATIONS
No 84, ISSN 0345-7532, ISBN 91-7305-589-1
Calcium Aluminate Cement as Dental
Restorative. Mechanical Properties and
Clinical Durability
Karin Sunnegårdh-Grönberg
From the Department of Dental Hygienist Education, Faculty of Medicine, Umeå University, Sweden and Department
of Dental Materials, Faculty of Health Sciences, Copenhagen University, Denmark
Calcium Aluminate Cement as Dental Restorative. Mechanical Properties and Clinical Durability
Karin Sunnegårdh-Grönberg, Department of Dental Hygienist Education, Dental School, Umeå University, 901 87 Umeå, Sweden. In 1995, the Swedish government recommended the discontinuation of amalgam as restorative in paediatric dentistry. Because the mercury content in amalgam constitutes an environmental hazard, its use has declined. The use of resin composites is increasing, but the polymerisation shrinkage of the material is still undesirably high, and the handling of uncured resin can cause contact dermatitis. A new restorative material has recently been developed in Sweden as an alternative to amalgam and resin composite: a calcium aluminate cement (CAC). CAC has been marketed as a ceramic direct restorative for posterior restorations (class I, II) and for class V restorations. This thesis evaluates mechanical properties and clinical durability of the calcium aluminate cement when used for class II restorations. Hardness, in vitro wear, flexural strength, flexural modulus, and surface roughness were evaluated. A scanning electron replica method was used for evaluation of the interfacial adaptation to tooth structures in vivo. The durability was studied in a 2-year intra-individually clinical follow-up of class II restorations. Major results and conclusions from the studies are as follows:
• The CAC was a relatively hard material, harder than resin-modified glass ionomer cement but within the range of resin composites. The CAC wore less than resin-modified glass ionomer cement but more than resin composite.
• Flexural strength of CAC was in the same range as that of zinc phosphate cement and far below that of both resin composite and resin-modified glass ionomer cement. Flexural modulus of CAC was higher than both resin composite and resin-modified glass ionomer cement. The low flexural strength of CAC precludes its use in stress-bearing areas.
• Surface roughness of CAC could be decreased by several polishing techniques. • For CAC restorations, interfacial adaptation was higher to dentin but lower to
enamel compared with resin composite restorations. Fractures were found perpendicular to the boarders of all CAC restorations and may indicate expansion of the material.
• After 2 years of clinical service, the class II CAC restorations showed an unacceptably high failure rate. Material fractures and tooth fractures were the main reasons for failure.
DEX = Doxadent experimental, calcium aluminate cement. ANA = ANA 2000, amalgam. # = 15 500 rpm, *=27 000 rpm.
Interfacial adaptation (Paper IV) Eight sound and caries-free premolars scheduled for extraction were used in
the study, which was approved by the Ethics Committee of the University
of Umeå. In each tooth, a mesial and distal box-shaped class II cavity was
prepared with a cylindrical diamond bur in a high-speed hand-piece using
copious water-cooling. No bevels were prepared and all margins were
placed in enamel. The prepared cavities of each tooth were arbitrarily
assigned to one of the two experimental groups, Doxadent or Tetric
Ceram/Syntac Single-Component. All restorations were made by one
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operator. After 1 month functioning time, the premolars were extracted,
sectioned, and prepared for SEM analysis.
Scanning electron microscopy (SEM)
Sectioning of the restorations was performed in buccal-lingual direction
starting at the outermost part of the restoration and continuing with five
consecutive sections providing six different cross-sectional surfaces per
restoration. To remove the smear layer, the tooth sections were etched with
35% phosphoric acid for 5 seconds and thereafter rinsed with water for
20 seconds and gently dried. Immediately after etching, impressions were
made of each section with a polyvinylsiloxane impression material. Positive
replica models were fabricated for all sectioned restoration surfaces by
pouring epoxy resin into the negative impression. The models were
prepared for SEM by mounting on metal stubs and coating with gold by a
standard metal evaporation technique. The interface of each restoration to
enamel and dentin was evaluated at x275 and x1400 and supplemented
when necessary with other magnifications. The quality of the interfacial
marginal adaptation between the restorative material and enamel or dentin
was evaluated according to a five-point rating scale with increasing degree
of openings and breakdown. The scores 1–3 represent acceptable adaptation
(with an increase of irregularities at the interface) and scores 4 and 5
represent unacceptable adaptation with crack and gap formation (Table 3).
Two operators performed the scoring on microphotographs at a
magnification of x275. Quantitative data were obtained by measuring the
length of each evaluation score expressed as percentage of the total length
of the examined interface. Fractures in enamel or dentin were recorded as
well.
33
Table 3. Scores for interfacial adaptation.
1 No interfacial opening or deficiencies
2 Slight interfacial irregularities
3 Severe interfacial irregularities, no crack visible
4 Hairline crack, gap with bottom visible
5 Severe gap, bottom hardly or not visible
A two-year clinical evaluation (Paper V) Patients visiting the clinic for dental hygienists education in Umeå for their
yearly examination and which were in the need of at least one pair of
class II restorations were asked to participate in the study: 57 patients
attended and a total of 122 posterior restorations were placed. High caries
activity, periodontal condition, or para-functional habits were not exclusion
criteria. All restorations were replacements of class II amalgam restorations
because of secondary caries, fracture, or “non-amalgam” reasons. Each
patient received at least two class II restorations of the same size, one in the
experimental version of calcium aluminate cement and one in the resin
composite (Tetric Ceram/Excite). The resin composite was placed if
possible in the same type of tooth as the experimental version of Doxadent
in order to make an intra-individual comparison possible. One dentist
experienced with both materials placed all restorations according to the
instructions of the manufacturer. Fifty percent of the proximal cervical
margins were situated apical to the cement-enamel junction. No bevelling
of the cavity margins was performed. The experimental Doxadent
restorations were finished after at least two days in contrast to the resin
composite restorations, which were finished immediately.
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Evaluation
Each restoration was evaluated after final finishing (baseline) and after 6,
12, and 24 months. A slight modification of the USPHS (United States
Public Health Service) criteria was used to evaluate the quality of the
restorations by two calibrated observers (Table 4). Disagreement was
resolved by consensus. Bite-wing radiographs were taken of all restorations
and colour slides were made of selected cases. The evaluated characteristics
of the restorations were described by descriptive statistics, using frequency
distributions of the scores.
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Table 4. Clinical criteria for evaluation of restoration success. Unacceptable scores in italics. (modified USPHS criteria: van Dijken 1986, Pallesen and van Dijken 2000).
Category Score Criteria
Anatomical
form
0
1
2
3
Restoration contiguous with tooth anatomy
Slightly under- or over-contoured, contact slightly open
Under- contoured, dentin or base exposed, contact is faulty,
reduced occlusal height, occlusion affected
Restoration is missing partially or totally, tooth fracture,
restoration causes pain
Marginal
adaptation
0
1
2
3
4
Restoration contiguous with existing anatomic form,
explorer does not catch
Explorer catches, no crevice is visible into which explorer
will penetrate
Crevice at margin, enamel exposed
Obvious crevice, dentin or base exposed
Restoration mobile, fractured or missing
Colour match
0
1
2
3
4
Very good colour match
Good colour match
Slight mismatch in colour, shade or translucency
Obvious mismatch, outside the normal range
Gross mismatch
Marginal
discoloration
0
1
2
3
No discoloration evident
Slight staining can be polished away
Obvious staining can not be polished away
Gross staining
Surface
roughness
0
1
2
3
Smooth surface
Slightly rough or pitted
Rough, can not be refinished
Surface deeply pitted, irregular grooves
Caries
0
1
2
No evidence of caries contiguous to the restoration margin
Superficial caries, no operative treatment necessary
Caries adjacent to restoration, operative treatment
indicated
36
Statistical analysis
In paper I, the data were analysed by ANOVA, Newman-Keuls´ multiple
range test and regression analysis.
In paper II, the data were analysed by Kruskal-Wallis H tests and Mann-
Whitney U tests. For each material, the influence of storage time in water
was analysed using one-way ANOVA and Newman-Keuls´ multiple-range
tests or in the case of lack of homogeneity of the standard deviations, by
Kruskal-Wallis H tests.
In paper III, the data were analysed by general linear module, multivariate
analysis (ANOVA), and exact test (Montecarlo).
In paper IV, the data were analysed by Mann-Whitney U-test and exact
test (Montecarlo).
In paper V, the data were analysed by Friedman´s two-way analysis of
variance test.
In all studies, the level of significance was set at P<0.05.
37
Results
Hardness and in vitro wear (Paper I)
Hardness values varied between 7.1 and 11.7 µm for the investigated
materials. The four resin composites, all for posterior use, differed
significantly in hardness showing hardness values between 8.2 and
11.7 µm. Doxadent showed a hardness of 9.2 µm and zinc phosphate
cement 9.1 µm. The experimental version of Doxadent (7.1 µm) was
significantly harder than any of the other materials. The resin composites
and the polyacid-modified resin composite wore significantly less than the
other materials tested (20.5 – 40.3 µm). The wear values of Doxadent, the
experimental version of Doxadent, and the zinc phosphate cement were
52.9 – 59.5 µm. These materials wore significantly less than the glass
ionomer cements with values of 73.9 – 108.5 µm. No linear correlation was
found between wear and hardness.
Flexural strength and flexural modulus (Paper II) Mean values and standard deviations of flexural strength and flexural
modulus for each material and storage time are presented in Table 5.
Irrespective of storage time, the following general ranking was found
between the flexural strengths of the different types of materials with the
strongest material mentioned first: resin composite = polyacid-modified
Surface roughness (Paper III) The significantly smoothest surface of the experimental version of
Doxadent was obtained with the Sof-Lex system (Table 6, group 3). The
fine Sof-Lex disc gave a Ra value of 0.26 µm. Extra fine Sof-Lex disc re-
increased surface roughness to a Ra value of 0.44 µm. Diamond burs at
39
higher speed, points, and polisher (group 1, 4-7) gave statistically similar
Ra values between 0.58 - 0.72 µm. The phenomena with re-increased
surface roughness was also seen when the fine polisher Super Greenie was
used (group 5, 6). The diamond burs at lower speed (group 2) gave an
increased surface roughness compared to baseline, which could not be
reduced by any of the finer polishing steps.
Table 6. Mean and standard deviation of roughness average Ra (µm) for each polishing step. The lowest Ra-value for each polishing method is given in italics.
The two investigated materials differed in the aspect of cavity
preparation. Resin composite restorations are used with micro-mechanical
retention, whereas the instructions for the calcium aluminate cement
54
dictate moderate amalgam preparations with rather parallel cavity walls.
The adhesive property of resin composite allows a minimal preparation
technique, which spares sound tooth substance and reduces the
preparation trauma to the tooth. The term biocompatibility is often
described as “the ability of a material to perform with an appropriate host
response in a specific application”. Even if a material is considered as
non-toxic, it cannot be considered as highly biocompatible if the
application in itself requires destruction of sound human tissue.
One of the most influencing parameters on the clinical outcome of
a dental restorative is its handling characteristics. It is not insignificant
that the preparation of specimen is in accordance with the clinical
instruction for the respective material and that the test reflects the clinical
situation since the desire is to interpret the results from a clinical point of
view and not from a strictly physical point of view. Therefore, it is
justified to use specimens and methods reflecting the clinical reality. The
calcium aluminate cement has been used according to the manufacturer’s
instructions. Great effort was put into thoroughly familiarise with the
material and making specimens and restorations in the best way. It seems
unlikely that the material would be easier to use in a clinical situation than
in the laboratory. The material has a crumbly character and reminds one
of a somewhat too dry sand cake. To restore a convex tooth surface with
Doxadent is very difficult. Despite the measured hardness of the material
gross reduction of the calcium aluminate cement is observed during
polishing with low pressure. At the time of the study, three shades of
Doxadent were available, all very opaque, which is common for cements.
This can be considered a dramatic step back from modern adhesive and
aesthetic dentistry.
55
Over the years, several dental materials have been marketed that
turned out in clinical follow-ups not to fulfil their marketing claims (Hickel
et al. 1988, Smales et al. 1990, Krämer et al. 1994, Pilebro et al. 1999, van
Dijken 2002). At the time of CE marking of Doxadent little was known
about calcium aluminate cement functioning as a dental restorative. It can
be debated whether a clinical trial would have been appropriate or not
before CE marking. The Directive for medical devices mainly addresses
general requirements such as design, construction, and manufacturing of the
device but no direct clinical evaluation requirement is included. However,
the Directive does state that the manufacturers have a clinical responsibility
after obtaining the CE marking. It is prohibited to place medical devices on
the market if the devices are claimed to have a performance they do not
have. It is also prohibited to give a deceptive impression that application of
the given medical device is certain to be successful and/or that no harmful
effects result when the device is used as intended or used for a prolonged
period. Failure of dental restoratives will probably seldom influence general
health, but degeneration and fracture of material and tooth will compromise
dental health. However, dental health is not included in the Directive
requirements. The result of the clinical trial clearly indicates the necessity
to include clinical evaluation of new restoratives in the CE marking.
56
Conclusions
The high failure rate of calcium aluminate cement restorations in the
clinical trial clearly shows that the material is not suitable for class II
restorations. Based also on the results of the three-point bending test, it is
concluded that Doxadent does not possess sufficient strength for a class II
restorative. The enamel fractures seen around the in vivo calcium
aluminate cement restorations and the relatively high frequency of cusp
fracture may indicate an undesirably high expansion of the material. It
was also observed that the clinical handling of the calcium aluminate
cement required a long learning period. The aesthetics of the calcium
aluminate cements as a dental restorative is limited.
57
Acknowledgements
I wish to express my sincere gratitude to all colleagues and friends who have supported
me during this work with special thanks to the following people:
Professor Jan van Dijken, thank you for sharing your great knowledge and enthusiasm
with me and for giving me the opportunity to go through with this work. You have
introduced me to the world of research. Even if I was negative at the beginning, I have
come to like it very much. Your positive attitude and curiosity about research issues is
admirable.
Associate professor, Anne Peutzfeldt, my co-supervisor and co-author also deserves my
gratitude. Thank you so very much for all nice working days in Copenhagen, and the
concern you have shown. Your considerate help with my problems have been invaluable
to me. Your profound knowledge in material-science and your clarity of vision
concerning research is impressive!
Jörgen Paulander, thank you for helping me with all my statistical problems no matter
if it is on a Sunday or late at night. You have a very pleasant way of explaining tricky
things in different ways without making me feel stupid.
Assistant Vivi Rønne, thank you for all your invaluable and skilful laboratory help at
the Department of Dental Materials, University of Copenhagen.
Research engineer Per Hörstedt, at the Department of Medical Biosciences, thank you
for all your help and knowledge about scanning electron microscopy.
Laboratory engineer Rolf Olofsson and Eva Gruffman at the Department of Dental
Material Science at Umeå University thank you for your help and technical support.
Anders Lindberg, my co-author, it is always a joy to work with you; I appreciate your
comments, which always are careful.
58
Dental nurse Margareta Widman, thank you for your help with the clinical studies,
tracking me down when I was needed for evaluating restorations.
Professor Lars-Olov Öhman at the Department of Inorganic Chemistry Umeå
University, thank you for all your help concerning chemical issues.
Dr Ingrid Andersson-Wenckert, thank you for being a good friend and travelling
companion and always taking your time when I have needed help.
Katarina Konradsson, Elisabeth Johansson and Anitha Persson, also being Jan’s
girls, thanks for your good friendship and all serious discussions about research.
Margot Grönlund, Carin Sjöström, Staffan Sjöström, Rut Rönnqvist, and Inga
Hamberg also at the Department of Dental Hygienist Education: thank you for your
concern about me and my work and your companionship.
Doxa AB, thanks for fruitful discussions and financial support.
The Faculty of Medicine, the Swedish Dental Society and the County Council of
Västerbotten, thanks for the financial support.
59
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