Abstracts of the Academy of Dental Materials Annual ... - IsiRed

95
Evaluation of the mechanical behavior of ceramic systems
using fractographic analysis
M. Borba 1 , K.A. Fukushima 1 , H.N. Yoshimura 2 , P.F. Cesar 1 ,
J.A. Griggs 3 , A. Della Bona 4
1 University of São Paulo, Brazil
2 University of São Carlos, Brazil
3 University of Mississippi, USA
4 University of Passo Fundo, Brazil
Objectives: To evaluate the fracture strength ( f) and fracture
toughness (KIC) of ceramic systems used for fixed partial
dentures (FPDs).
Materials and methods: Five ceramic materials were used:
a yttria partially stabilized tetragonal zirconia polycrystal
(YZ – In-Ceram YZ, Vita), a glass-infiltrated alumina/zirconia
composite (IZ – In-Ceram Zirconia, Vita), a polycrystalline
alumina (AL – In-Ceram AL, Vita), and two feldspathic
ceramics (VM7 and VM9, Vita). Bar-shaped (BS) specimens
(2 mm × 4mm× 16 mm) were produced according to the manufacturer
instructions and polished to 1 �m (n = 30). Fixed
partial denture (FPD) frameworks were fabricated using CEREC
InLab and veneered with the recommended porcelain (n = 10).
BS specimens were tested in three-point flexure using a universal
testing machine at 1 MPa/s in 37 ◦ C artificial saliva.
FPDs were cemented in metal dies with zinc phosphate
cement and tested with the load being applied by a stainless
steel sphere in the center of the pontic with 1 MPa/s
stress rate until failure in a 37 ◦ C distilled water bath. Fracture
surfaces were analyzed under a stereomicroscope and
SEM. Fractography principles were used to determine the fracture
mode, to measure the critical flaw (c) and to calculate
KIC of the BS specimens, based on the following relation:
KIc = f·Y·c 1/2 , where f is the stress at fracture and Y is
the geometrical constant dependent on the flaw shape. For
FPDs, c values were also determined fractographically, and f
was estimated using the KIc values calculated for BS specimens,
using the same relation described above. Data were
statistically analyzed using Kruskal–Wallis and Tukey test
(˛ = 0.05).
Results: Considering the framework materials, the same
ranking of f observed for BS specimens was found for
FPDs. YZ had the highest f value (861 MPa) followed by
AL (474 MPa) and IZ (412 MPa). The porcelains showed the
lowest f results, approximately 65 MPa. The c values measured
for the framework materials were also similar in
both configurations (BS and FPD), varying from 35 to 45 �m.
Porcelain BS specimens showed c values from 75 to 86 �m.
KIC values were significantly different among the materials.
YZ showed the highest KIC value (6.5 MPa m 1/2 ). AL
and IZ presented intermediate KIC values (3.5 MPa m 1/2 ) followed
by the two porcelains (0.7 MPa m 1/2 ). The fracture
mode of FPDs was influenced by the framework material.
Conclusions: As the flaw population and mean f values
were similar for both specimen configurations (BS and FPDs),
the three-point flexural test is a reliable tool to predict the
mechanical behavior of FPDs. In addition, the material with
dental materials 26S (2010) e1–e84 e45
the best mechanical performance in both BS and FPD configuration
was YZ.
doi:10.1016/j.dental.2010.08.103
96
Clinical performance of posterior three-unit zirconia-based
fixed partial dentures: 63-Month prospective clinical study
B. Borelli, R. Sorrentino, G. De Simone, S. Tete’, F. Zarone
University of Naples “Federico II”, Italy
Objectives: This prospective clinical trial aimed at evaluating
the clinical performance of tooth-supported three-unit
posterior zirconia FPDs after 63 months of clinical function.
Materials and methods: Thirty-seven patients received
48 3-unit zirconia-based (Procera, NobelBiocare) FPDs. The
restorations replaced either a premolar or a molar. Specific
inclusion criteria were needed. Tooth preparation was standardized:
2 mm occlusal reduction, 1.5 mm axial reduction
and circumferential chamfer shoulder placed 0.5 mm subgingivally,
buccally and supragingivally lingually on sound tooth
structure; all internal angles were rounded. Impressions were
made with polyether (3M ESPE). CAD-CAM frameworks (Procera,
NobelBiocare) with 9 mm 2 connector and 0.6 mm retainer
were made. The restorations were luted with resin cement
(RelyXUnicem, 3M ESPE). The patients were recalled after 1, 6,
12, 24, 36, 48, 60 and 63 months. Survival and success of ceramics
and zirconia were evaluated. The technical and esthetic
outcomes were examined using USPHS criteria. The biologic
outcomes were analyzed at abutment and contralateral teeth.
Modified Ryge criteria were used to assess marginal adaptation
and discoloration. Descriptive statistics were performed
(Kaplan–Meier, Wilcoxon).
Results: All FPDs completed the study, resulting in 100%
cumulative survival rate and 93.75% cumulative success rate.
No losses of retention were recorded. 42 Restorations were
rated Alpha in all measured parameters. Minor chipping of
ceramics was detected in 3 restorations. 3 restorations were
rated Bravo for marginal integrity at 63 months. No significant
differences between the periodontal parameters of the test
and control teeth were observed. As to esthetics, 44 restorations
were rated Alpha and 4 were rated Bravo by both the
clinicians and the patients either at baseline and 63-month
follow-up.
Conclusions: 63-month clinical results proved that 3-unit
posterior zirconia-based FPDs were successful in the mediumterm.
This type of restoration may be considered reliable to
replace a missing tooth.
doi:10.1016/j.dental.2010.08.104