The study investigated the effects of different post and core material combinations on surface strain of zirconia fixed partial denture (FPD) margins. Artificial abutment teeth were restored with either resin composite cores with glass fiber posts or cast metal alloy posts and cores. Strain gauges measured surface strain on the zirconia frameworks and abutment roots under static loading. The results showed that restoring the premolar with a cast post and core and the molar with a resin composite core reduced stress concentration in both the frameworks and abutment teeth compared to the other combination. The study suggests considering post and core material properties and differences in abutment tooth morphology when selecting materials for zirconia FPD

1. The effects of post and core material combination on
the surface strain of the
4-unit zirconia fixed partial denture margins
Yoko ishikawa, Wataru komada, Tasuku inagaki, Reina nemoto,
Satoshi Omori and Hiroyuki miura
Dental Materials Journal 2017; 36(6): 798–808
Presented by,
Namitha.AP
III RD MDS
1

2. CONTENTS
 INTRODUCTION
 AIM
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSION
 REFERENCES
 RELATED ARTICLES
2

3. INTRODUCTION
 Endodontically treated teeth that show extensive damage to the coronal tooth
structure are usually restored with post and core systems for the final restoration.
CAST POST AND CORE
• traditional (high mechanical strength and desirable fit in the root canal)
• vertical root fractures( increased stress concentration at the apical region of the post and on the alveolar
bone ridge - difference in the Young’s modulus between dentin and metal)
COMPOSITE RESINS CORES WITH GLASS FIBER POSTS
• The Young’s modulus of composite resin is more comparable to that of dentin, resulting in decreased
stress concentration.
• superior esthetics and do not induce metal allergy.
3

4. Fixed partial dentures (FPDs)
• introduced as esthetic restorations several decades ago.
• good load-bearing capacity and exhibits high longevity
Metal ceramic FPDs
• good esthetics and biocompatible nature
• CAD/CAM) systems facilitated the use of yttria-stabilized tetragonal zirconia polycrystals (Y-
TZP) in both the anterior and posterior alveolar segments
• Remarkable strength
• relatively high Young’s modulus - prevents the flexural and radial fracture of the porcelain
veneer
All-ceramic restorations with zirconia frameworks
4

5. Stress distribution on endodontically
treated teeth
 cast post and core system played a role in limiting the magnitude of surface strain
on the framework.
Finite element
anaysis
Photoelastic
models
Strain gauges
attached to models fabricated from the actual materials - accurately
measure the magnitude of surface
strains. (closely simulates the
clinical situation)
Dentists should consider the stress distribution when each
abutment tooth is restored, as there are different types of
post and core materials that demonstrate different behaviors
in a clinical setting, resulting in a more complicated stress
distribution
5

6. Aim of the study
 to investigate the optimal combination of post and core materials for the 4-unit
zirconia FPD abutment teeth using the strain gauge method when each abutment
tooth is restored with different types of post and core materials.
 Hypothesis to be tested was that the premolar abutment tooth should be restored
with the cast post and core, and that the molar abutment tooth should be restored
with a composite resin core with glass fiber post.
 This strategy is expected to reduce the stress concentration on both the zirconia
framework and the abutment roots when each abutment tooth is restored with
different types of post and core materials.
6

7. Materials and methods
1.Root duplication of
abutment teeth
 Models of extracted human teeth, i.e.,
the mandibular right first premolars
and the mandibular right second
molars with prepared post spaces,
were used in this study.
 finish line shape had a rounded-
shoulder configuration
 Impressions - vinyl polysiloxane
impression material
 An automix resin composite into the
impression and light-cured
 The duplicated root models were
used as the experimental abutment
teeth
The experimental teeth were inclined at specific
angles relative to the vertical plane and were
temporarily fixed.
7

8. 2.Fabrication of posts and cores
POST AND CORE
SYSTEMS
RESIN COMPOSITE
CORE WITH GLASS
FIBER POST (RC)
CAST POST AND
CORE (MC)
EXPERIMENTAL
GROUPS (n= 10)
Group RM
PREMOLAR – RC
MOLAR-MC
GROUP MR
PREMOLAR – MC
MOLAR - RC
8

9. RC GROUP
 mold was made of vinyl polysiloxane impression
material
 The glass fiber posts were cut 3 mm above the
ferrule, etched with 40% phosphoric acid for 5 s,
rinsed with distilled water, air-dried, and then
applied with a ceramic primer.
 A resin composite core material was injected into
the post space of the stone cast and the glass fiber
post was inserted into the center of the canal.
 Following curing with a dental curing light from the
coronal sides for 20 s, the core was built up with the
same resin composite using the core mold and was
then light-cured from the lingual, coronal, mesial,
distal, and buccal sides for 20 s each.
 Following 10 min of chemical curing, the posts and
cores were then removed.
MC GROUP
 Impressions of the post spaces -
hydrophilic vinyl polysiloxane
impression materials
 Stone casts - improved dental stone.
 Post and core patterns - inlay wax
 For the MC, the post and core
patterns were invested with an
investment material and cast in
platinum gold alloy
9

10. 10
70-μm grain-sized aluminum
oxide particles at 0.4 MPa for
10 s from a distance of 10 mm
The posts and cores of both
systems were cemented to the
roots with a dual-curing resin
luting cement

11. 3.Fabrication of frameworks
 The abutment teeth inclined at specific angles, and set 18.0
mm apart from one another.
 The impressions of the abutment teeth were taken with
hydrophilic vinyl polysiloxane impression materials and
stone casts were fabricated with an improved dental stone.
 A CAD/CAM system was used to fabricate the 4-unit zirconia
bridge frameworks.
 The casts were scanned and the frameworks were designed.
 Thickness = 0.5 mm
 Cross sectional area of connector part were, from mesial to
distal, 9.0, 9.0, and 11.0 mm2, respectively shaped elliptically.
 Partially sintered zirconia blocks were milled and sintered.
11

12.  Each of the inner surfaces of the frameworks was sandblasted with 70-μm grain-
sized aluminum oxide particles at 0.2 MPa for 10 s from a distance of 10 mm,
ultrasonically cleaned in distilled water twice for 5 min each, and then applied with
a ceramic primer
 For the RC, the surfaces of the abutments were treated in the same manner as the
glass fiber post.
 For the MC, the surfaces of the abutments were applied with a metal primer
 The frameworks were then cemented onto the abutment with a dual-curing resin
luting cement
12

13. Measurement of strains
 Surface strain of the frameworks and the abutment roots was measured with strain
gauges.
 The gauges were placed accordingly at the mesiobuccal (FMB) and the
mesiolingual (FML) framework surfaces of the molar; the distobuccal (FPB) and
distolingual (FPL) framework surfaces of the premolar; the mesiobuccal (RMB) and
mesiolingual (RML) root surfaces of the molar abutment tooth and the distobuccal
(RPB) and distolingual (RPL) root surfaces of the premolar abutment tooth.
 The aforementioned surfaces of the frameworks and roots were sandblasted for 10
and 5 s, respectively, with 70-μm grain-sized aluminum oxide particles at 0.2 MPa
from a distance of 10 mm, and were then ultrasonically cleaned in distilled water
twice for 5 min each.
 Two kinds of rosette strain gauges were attached to the specimens with a strain
gauge cement under finger pressure for 1 min on a polyethylene film.
 These specimens were stored at room temperature for 24 h.
13

14.  All the specimens were embedded in an acrylic resin
 To simulate the periodontal ligament (approximately 0.25 mm), each root was
surrounded with a layer of vinyl polysiloxane material
 Using a universal testing machine the specimens were loaded on the occlusal
surfaces with a crosshead speed of 1.0 mm/min at up to 200 N through a small
load cell (φ2.5 mm).
14

15.  The outputs from the strain gauges were recorded with sensor interfaces
 The magnitudes of the maximum and minimum principal strain (εmax, εmin) were
calculated as follows:
 εa, εb and εc were the strains of each
gauge component.
 The rosette strain gauge was
composed of three linear gauges
placed at 0, 45, and 90-degree
positions.
Positive values -
tensile strain
Negative values –
compressive strain
Statistical analyses were performed using the Mann- Whitney U
test with Bonferroni correction at a significance level of
α=0.05/3=0.0167, α=0.05/6=0.0083 and α=0.05
15

16. Results
Comparison of the points of
loading For the consideration of
the two groups and the sum
total of the gauge positions, the
significant differences
between the two loading points
The magnitude of the maximum
principal strain of the framework
loading at CP was significantly lower
than those obtained with loading at CD
and CM
16

17. Comparison of groups
 At the surfaces of the molar frameworks and the molar roots (FMB, FML, RMB and
RML), Group MR had significantly higher magnitudes of principal strain than Group
RM.
 In contrast, at the surfaces of the premolar frameworks and the premolar roots
(FPL, FPB, RPL and RPB), Group RM had significantly higher magnitudes of principal
strain than Group MR.
 This indicated that the abutment tooth restored with the cast post and core system
resulted in significantly lower principal strains than those evident with resin
composite core with glass fiber posts.
17

18. Significant
differences
between the
two groups
were shown at
six gauge
positions
except for FML
and FMB
during loading
at CP
The magnitudes of the principal strain in the two groups (Group RM and MR) and in
the eight different gauge positions (FML, FMB, FPB, FPL, RML, RMB, RPB and RPL)
18

19. Significant
differences
between the two
groups were
shown at six
gauge positions
at all gauge
positions, during
loading at CD
19

20. 20

21. Comparison of gauge positions
 The surfaces of the premolar frameworks (FPB and FPL) showed significantly higher
magnitudes of principal strain than those of the molar frameworks (FML and FMB) in
both groups during loading at all points in the various gauge positions
 The surfaces of the premolar roots (RPB and RPL) also showed significantly higher
magnitudes of principal strain than those of the molar roots (RML and RMB) in both
groups during loading at all points in a large proportion of different gauge positions
 Group RM showed a greater number of statistical differences between the premolars
and the molars compared to Group MR for both the framework and the abutment root
 In particular, during loading at CM, the magnitude of the maximum principal strain of
the Group MR framework showed no statistical difference between the premolar and
the molar.
21

22. Discussion
 Pontic loading was characterized by high magnitudes of surface strains
 The loading at CM presented with the fewest statistical differences between the
premolar and the molar in a comparison of the three loading points
 Restoration of the premolar abutment tooth with the cast post and core, and the
molar abutment tooth with the composite resin core and glass fiber posts results in
reduced stress concentration in the zirconia frameworks and the abutment teeth.
 cast post and core limits and equally distributes surface strain when compared to
the resin composite core with glass fiber posts in both the framework and the
roots.
22

23.  The difference in the Young’s modulus between the Y-TZP
framework and the resin composite core with glass fiber post
was larger than that between the Y-TZP framework and the
cast post and core.
 stress concentration occurred at the interface between the
materials with differing Young’s modulus.
 framework and the roots may act as a rigid body owing to the
small differences between the elastic moduli of the restorative
materials.
23

24. High strain was observed during loading at
CD?!
 The FPD framework was fixed to the abutment teeth near the connectors;
therefore, when the center of the pontic was loaded, the FPD framework
caused a bending moment at the center of the pontic.
 In addition, the connectors were narrow.
 Hence, stress concentration is prone to occur at the connectors during
loading at the pontic.
 post and core materials should have a high Young’s modulus, similar to
that of the zirconia frameworks, in order to limit surface strains
 Young’s moduli of the post and core materials to be of a similar
magnitude to that of dentin, in order to avoid root fractures.
24

25. 25
RECURRENT
TREATMENTS
ROOTS WITH THIN
DENTIN WALLS
HIGH RISK OF
ROOT FRACTURE
resin composite core with glass fiber posts
is recommended for the reinforcement of
the residual dentin.
OPTIMAL
POST AND
CORE SYSTEM
AMOUNT OF
RESIDUAL
TOOTH
STRUCTURE
TYPE OF
ABUTMENT
TEETH
PATIENTS’S
OCCLUSION
SPAN OF FIXED
PROSTHESIS
PERIODONTAL
CONDITION

26.  The premolar surfaces showed significantly higher magnitudes of
principal strain compared to the molars for both the framework and
the roots at the various gauge positions, irrespective of the groups
and loading points.
 As the bulk of the molar is greater than that of the premolar, the
molar shows a lower magnitude of surface strain compared to the
premolar.
 The differences in root morphology are considered to affect the
stress distribution of the framework and abutment teeth.
 premolars have a greater tendency, compared to the molars, to
distort under loading conditions
26

27. Conclusions
 Within the limitations of this study, the following conclusions can be drawn for the use
of a 4-unit Y-TZP framework for the replacement of missing teeth (45 and 46):
1. The surface strain of the premolar abutment tooth was higher than that of the molar
abutment tooth, irrespective of the type of post and core material used when each
abutment tooth was restored with a different post and core material.
2. The cast post and core system limits the surface strain of the framework and the
abutment roots, in contrast to the resin composite core with glass fiber posts for the
same abutment tooth, when each abutment tooth was restored with a different post
and core material.
3. The stress concentration was reduced when the premolar abutment tooth was restored
with the cast post and core, and when the molar abutment tooth was restored with a
composite resin core with glass fiber posts, for the restoration of each abutment tooth
with different types of post and core materials
27

28. Influence of post and core materials on
distortion around 4-unit zirconia bridge
margins
 The purpose of this study was to evaluate the surface strain of zirconia fixed partial
denture frameworks and their abutment roots when restored with two types of
post and core materials.
Tasuku Inagaki, Wataru Komada, Reina Nemoto, Keiichi Yoshida and Hiroyuki
Miura
28

29. Artificial mandibular first premolars and second molars were used as the abutment teeth.
Posts and cores were of two types: resin composite with glass fiber posts (RC) and cast platinum
gold alloy (MC).
The cores and 4-unit zirconia frameworks were bonded to the specimens.
29

30. 30

31. Static loading was
applied to the
occlusal surfaces,
and the surface
strain of the
frameworks and
roots (distal
premolar and
mesial molar) was
measured by strain
gauge method
31

32. 32

33. Schematic illustrations of specimens and their magnitudes of principal strain (the left
illustrations indicate Group RC and the right illustrations indicate Group MC).
Static loading was applied at (A) CP, (B) CD and (C) CM. Rosette strain gauges were
placed at (a) FML, (b) FMB, (c) FPB, (d) FPL, (e) RML, (f) RMB, (g) RPB and (h) RPL.
33

34. 34

35. 35

36. 36

37. 37

38. Conclusions
 Within the limitations of this study, the following conclusions can be drawn:
1. In both abutment material groups, the high value of surface strain was concentrated
especially at the premolar abutment when the missing teeth (45 and 46) were replaced
by a 4-unit Y-TZP framework.
2. Cast post and core restrain the surface strain of the framework and the abutment
roots compared to resin composite core with glass fiber posts, when the missing teeth
were replaced by a 4-unit Y-TZP framework.
38

39. Effect of framework design on the surface strain
of zirconia fixed partial
dentures
Reina Nemoto, Kosuke Nozaki, Yuji Fukui, Kimihiro Yamashita
and Hiroyuki Miura
 The purpose of the study was to determine the optimal design of RBFPDs using
zirconia
 The influence of the thickness and the design of RBFPDs on the rigidity of zirconia
frameworks were examined by evaluating surface strain using simulation models.
 RBFPD metal frameworks that were designed according to the traditional standard
were used for comparison
39

40.  Three types of frameworks were fabricated as follows: 0.5-mm- and 0.8-mm-thick
zirconia frameworks with grooves and holes (0.5ZrG, 0.8ZrG) and 0.5-mm-thick
zirconia frameworks without grooves and holes (0.5Zr).
 The control group was designed as a 0.8-mm-thick metal framework with grooves
and holes (0.8MG).
40

41. Static loading was applied and the surface strain of the
retainers was measured with strain gages.
41

42. The magnitude of
the principal strain of
the
0.5ZrG framework
was significantly
lower than that of
the 0.8MG and the
0.5Zr frameworks.
42

43. CONCLUSIONS
 Within the limitations of this in vitro study, the RBFPDs using 0.5-mm-thick zirconia
framework is effective method for the anterior single missing tooth because of the
less amount of tooth reduction compared with that of using metal framework.
 Furthermore, when the RBFPDs are made of zirconia, the grooves and hole has
been purported to decrease the distortion on equality with the traditional metal.
 However, the effect of the reduction of framework thick on the mechanical strength
will also be examined using fracture test and the clinical evaluation will be further
investigated
43

44. Are Endodontically Treated Incisors Reliable
Abutments for Zirconia-based Fixed Partial
Dentures in the Esthetic Zone?
Rene Tunjan, Martin Rosentritt, Guido Sterzenbach, Arndt Happe, Roland
Frankenberger, Rainer Seemann, and Michael Naumann.
This ex vivo pilot study tested the influence of defect extension and quartz-fiber post
placement (QFP) on the ex vivo survival rate and fracture resistance of root-treated
upper central incisors served as abutments for zirconia 2-unit cantilever fixed partial
dentures (2U-FPDs) exposed to 10 years of simulated clinical function.
44

45.  Human maxillary central incisors were
endodontically treated and divided into the
following 5 groups (n = 8):
(1) access cavity filled with core buildup composite
(2) biproximal class III cavities filled as in group 1
(3) specimens restored as in group 2 with QFP placed
(4) specimens decoronated and core buildup as in
group 1
(5) specimens restored as in group 4 but with QFP as in
group 3.
On all specimens, 2U-FPDs were placed with dual-
curing resin cement.
In order to simulate 10 years of clinical function,
specimens were exposed to thermal cycling and
mechanical loading with subsequent loading to failure.
45

46.  For specimens only with an access cavity, it
was observed that 25% had catastrophic
tooth fractures and the lowest load-to
fracture values.
 In all other groups, chipping combined
with or without debonding occurred.
 Groups did not differ significantly
regarding the survival rate (P = .603) and
fracture patterns (P = .633), but they did
for fracture load including technical failures
(P = .017).
46

47. CONCLUSIONS
 In all groups, chipping within the ceramic material was mainly observed.
 Chipping of the veneering is a common type of clinical failure
 Because of the high strength of zirconia, no framework fracture occurred
 In accordance to clinical data , debonding may be explained by nonaxial and
torsion forces on the cement
 Neither defect size nor post placement appear to be predictors of the survival of
root-treated upper central incisors.
 Even severely damaged maxillary central incisors may be reliable abutments for
zirconia-framework 2U-FPDs to substitute lateral incisors.
47

48. The influence of the framework thickness on surface strain of
the 3-unit zirconia resin-bonded fixed dental prostheses under
the functional loading
Kyoshi Matsukawa, Reina Nemoto, Kosuke Nozaki, Mariko Kubo, Tasuku
Inagaki, Keiichi Yoshida, and Hiroyuki Miura
 The purpose of the present study was to optimize the form of a resin-bonded fixed
dental prosthesis (RBFDP) frame by preparing various framework designs using
ceria-stabilized tetragonal zirconia/alumina nano composite (Ce-TZP/Al) materials.
48

49.  Six types of frameworks were fabricated as follows: 0.8-mm-thick metal (0.8M), 0.8-
mm- and 0.5-mm-thick yttria-stabilized tetragonal zirconia polycrystal frameworks
(0.8Y, 0.5Y) and 0.8- mm-, 0.5 -mm- and 0.3-mm- thick Ce-TZP/Al frameworks
(0.8C, 0.5C, 0.3C).
49

50.  A load up to 200 N crosshead speed of 1.0 mm/min was applied to center of the
palatal surfaces of the pontic of the RBFDPs by a universal testing machine. The
strains of the RBFDPs during loading were measured and recorded by sensor
interfaces. Then, the magnitudes of the maximum and minimum principal strain
were calculated. A two-way analysis of variance (ANOVA) and a t-test with
Bonferroni correction were used for the statistical analysis of strain, with a
significance level at α = 0.05.
50

51.  In the canine, the magnitudes of the
maximum principal strain of 0.8M
were significantly higher than those
in group 0.8Y. There were no
significant differences among the
0.3C, 0.5Y, and 0.8M groups.
51

52. CONCLUSIONS
 This report suggested that Ce-TZP/Al can improve the long-term prognosis of resin
bonded fixed dental prostheses in the oral cavity due to its desirable mechanical
and hydrothermal degradation-resistant characteristics, enabling the design of a
resin bonded fixed dental prosthesis frame with a thickness of 0.3 mm.
52

53. REFERENCES
 Matsukawa K, Nemoto R, Nozaki K, Kubo M, Inagaki T, Yoshida K, Miura H. The
influence of the framework thickness on surface strain of the 3-unit zirconia resin-
bonded fixed dental prostheses under the functional loading. Asian Pac. J. Dent.
2017 Jan;17:1-7.
 Tunjan R, Rosentritt M, Sterzenbach G, Happe A, Frankenberger R, Seemann R,
Naumann M. Are endodontically treated incisors reliable abutments for zirconia-
based fixed partial dentures in the esthetic zone?. Journal of endodontics. 2012 Apr
1;38(4):519-22.
 Nemoto R, Nozaki K, Fukui Y, Yamashita K, Miura H. Effect of framework design on
the surface strain of zirconia fixed partial dentures. Dental materials journal. 2013
Mar 28;32(2):289-95.
 Inagaki T, Komada W, Nemoto R, Yoshida K, Miura H. Influence of post and core
materials on distortion around 4-unit zirconia bridge margins. Dental materials
journal. 2014 May 28:2013-306.
 Ishikawa Y, Komada W, Inagaki T, Nemoto R, Omori S, Miura H. The effects of post
and core material combination on the surface strain of the 4-unit zirconia fixed
partial denture margins. Dental Materials Journal. 2017 Nov 27;36(6):798-808.
53

54. 54