Dissertation committee:
Τζούτζας Ι.,Καθηγητής, Ηλιάδης Γ.,Καθηγητής, Κοϊδης Π.,Καθηγητής
Summary:
In recent years zirconia ceramics hold a remarkable place in restorative
dentistry because of their advanced mechanical properties. One of their
drawbacks is the inferior bonding potential to dental cements compared to other
etchable ceramics. There is still no universally accepted protocol for adhesion
to zirconia.
Purpose: The aim of this study was to determine the influence of different
surface treatment and resin cements on shear bond strength in monolithic
zirconia surfaces in order to define the optimal adhesive combination.
Μaterial and Methods: One hundred eigthty monolithic zirconia ceramic disks
were fabricated and were boxed in plastic tubes. They were separated in three
main groups according to surface treatment. Control group (POL), sandblasting
group (AL) and tribochemical group (SJ).
The surface parameters of ten specimens from each group were
determined employing an optical interferometric profiler. Two amplitude (Sa,
Sz), one hybrid (Sdr) and one functional (Sci) parameters, were acquired. Two
specimens from each group were further analyzed by Raman microspectroscopy to
quantify the zirconia phase ratio of all treated surfaces.
Three different concept resin cements were used: Panavia 2.0 (PAN), Multilink
Automix (ML) and Permacem 2.0 (PC). A prehydrolyzed silane primer was applied
on the surface of SJ group. All specimens were stored for a week in deionized
water at 37 °C and half of them (N=90) underwent further water thermocycling
for 500 cycles (5 oC and 55 oC, with 10 s dwell time and 20 s immersion time).
All samples were loaded under shear testing in a universal testing machine
(Tensometer 10, Monsanto, USA) at a cross-head speed of 0.5 mm/min up to
fracture. The debonded zirconia surfaces were examined under a stereomicroscope
(M80, Leica, Weltzar, Germany) at 25 magnification to assess the failure
modes. Areas which were covered with zirconia primer in SJ group without resin
cement remnants were added in the remaining resin cement percentage. The
debonded areas were characterized with 5 different scores, based on the
percentage area covered by resin (1: 0-20%, 2: 20-40%, 3: 40-60%, 4: 60-80% and
5: 80-100%). Score 1 is considered as predominating adhesive, 2-4 as mixed and
5 as predominating cohesive.
In optical profilometry, one way ANOVA was used to evaluate
overall statistical significance (Wilk’s λ) and subsequent evaluations were
done using the standard univariate procedure. Individual comparisons were
carried out using the LSD method (Least Significant Difference). A 3-way ANOVA
was used in order to statistically evaluate the surface treatment, cement type
and immersion type combinations as measured by shear bond strength. Individual
comparisons were performed using the LSD statistic. For the statistical
evaluation of each resin cement type of fracture a 3X2 cross tabulation was
used. All two way tables were tested for statistical significance using the
Pearson-chi-square statistic. All analyses were performed using the STATISTICA
10 software from StatSoft Inc.
Results: Control group (POL) had significant lower roughness measurements in
all parameters than surface treatment groups AL and SJ. Groups AL and SJ had no
significant differences in three roughness parameters (Sa, Sz and Sdr). Sdr
ranged from 4,5 % in POL group to 23,5 % in AL and SJ group. Monoclinic
fraction was high (33-43 %) and was not influenced by surface treatment.
Thermocycling reduced shear bond strengths. Permacem 2.0 and Mutilink Automix
combined with tribochemical silica coating and primer Monobond plus had the
highest shear bond strengths (24,9 and 23,8 MPa respectively). Panavia F 2.0
had higher bond strength aftel AL treatment (15,7 MPa). Multilink Automix had
almost zero values in POL and AL treatments (0,4 and 2,4 MPa respectively). The
increase in shear strength values is followed by transition to a more cohesive
failure mode. The groups with low bond values had less residual cement (score 1
and 2), while groups with high values had significantly larger amounts of
cement (score 3,4 and 5).
Conclusion: Within the limitations of the current experiment, it can be
concluded that silica coating treatment in combination with chemical active
monomers is a promising luting concept for zirconia materials.
Keywords:
zirconia, resin cements, shear test, sandblast, adhesion