Metal-ceramic fixed partial dentures (FPDs) have the highest long-term survival rates compared to other materials. Zirconia-ceramic FPDs have increased risks of framework fractures and chipping of veneering ceramic. According to a 10-year study, the survival rate of zirconia FPDs was only 67% due to ceramic fractures and framework failures. Lithium disilicate FPDs showed an 87.9% survival rate at 10 years but dropped dramatically to 48.6% at 15 years mostly due to catastrophic ceramic fractures. Proper tooth preparation and material selection are important for maximizing FPD durability over many years.

1. Structural durability of
bridges
prepared by: Ammar G. Salem
3rd year candidate KBMS
Supervised by: Assist.Prof.Dr. Raid Fahim

2. content
• Defining structural durability
• Preparation factors and durability.
• Some theories applied for force distribution.
• Framework design and durability.
• Articles related to durability of bridge.
• Conclusion

3. Structural Durability
• It is one of principles of tooth preparation.
• An adequate thickness (bulk) of restorative material should be
provided to withstand external forces.
• This thickness is variable according to type of material used.
• Geometrical design of preparation is also essential in stress
distribution.
• Those considerations should not be overlooked to provide longevity
for restorative material.
Shillingburg, Herbert T. Fundamentals of Fixed
Prosthodontics. Chicago: Quintessence Pub. Co, 1997.

4. Structural Durability
loading Geometry
Material
strength
manufacturing
• loading of occlusal forces
varies. i.e. between anterior
and posterior teeth.
• Material properties reflect
their different reaction to
loading forces. i.e.
brittleness and fracture
strength of material differ
when forces applied to cast
metal, lithium disilicate, or
zirconia.
• Geometrical design of
framework, and tooth
preparation design
contribute to stress
distribution over restorative
material.
• Laboratory manufacturing
of ceramic can leave
residual stress within
manufactured material
which affect its longevity.
Shillingburg, Herbert T. Fundamentals of Fixed
Prosthodontics. Chicago: Quintessence Pub. Co, 1997.

5. Structural Durability
• it depends on:
o Occlusal
reduction.
o Functional cusp
bevel.
o Axial reduction.
• Occlusal reduction include:
 Occlusal clearance.
 This clearance varies according to
the material used. i.e. cast metal
vs. all-ceramic.
 Planar (anatomical) occlusal reduction.
 Reflecting geometric inclined
planes provide adequate
thickness of material occlusally.
 A flat occlusal reduction lead to
thinning of material. i.e. metal
perforation.
 Avoid steep planes and occlusal
grooving which increases stress.
Shillingburg, Herbert T. Fundamentals of Fixed
Prosthodontics. Chicago: Quintessence Pub. Co, 1997.

6. Structural Durability
• Functional cusp bevel:
 Decreases stress over an
area of high occlusal
load.
 Avoid sharp line angles.
• Axial reduction:
 Inadequate reduction
may lead to fabrication of
over-contouring
restoration in lab.
 If lab fabricate a normal
contour it will produce a
thin thickness which with
some materials inability
to flex due to occlusal
loading can lead to crack
and fracture.
Shillingburg, Herbert T. Fundamentals of Fixed
Prosthodontics. Chicago: Quintessence Pub. Co, 1

7. beam theory
Deflection of a beam increases as the cube of its length and it is
inversely proportional to its width and is inversely proportional to
the cube of its height.
Shillingburg, Herbert T. Fundamentals of Fixed
Prosthodontics. Chicago: Quintessence Pub. Co, 1997.

8. Ante’s Law
• The root surface area of abutment teeth should equal or
surpasses that of teeth to be replaced.
Shillingburg, Herbert T. Fundamentals of Fixed
Prosthodontics. Chicago: Quintessence Pub. Co, 1997.

9. Framework design
The core substrucutre should provide an
even thickness for the veneering ceramic
material.
Cut back design should provide 90 or
greater degree angle joint between core
and ceramic.
In case of cut back design core is
preferred to be in the area of centric
stop.
Shillingburg, Herbert T. Fundamentals of Fixed
Prosthodontics. Chicago: Quintessence Pub. Co, 1997.

10. Framework design
Anterior bridges involving more than one pontic should
have the lingual strut of metal extended to the surface
where space is limited.
This will resist linguo-facial flexion.
Increasing the gingival embrasure radii results in better
distribution of stresses.
Increasing dimensions of the connector also result in
higher fracture load.
Shillingburg, Herbert T. Fundamentals of Fixed
Prosthodontics. Chicago: Quintessence Pub. Co, 1997.

11. Finite element analysis
• Highest stress concentrations exist in
the vicinity of the embrasure areas
between the inlay and pontic and at
the loading contact site.
Thompson, M. C., C. J. Field, and M. V. Swain. "The all‐ceramic, inlay supported fixed partial denture. Part 2.
Fixed partial denture design: a finite element analysis." Australian dental journal 56.3 (2011): 302-311.

12. Finite element analysis
• High tensile stress is evident at the gingival
aspect of the connectors.
Thompson, M. C., C. J. Field, and M. V. Swain. "The all‐ceramic, inlay supported fixed partial denture. Part 2.
Fixed partial denture design: a finite element analysis." Australian dental journal 56.3 (2011): 302-311.

13. Finite element analysis
• High compressive stress at the occlusal
aspect of the connectors.
Thompson, M. C., C. J. Field, and M. V. Swain. "The all‐ceramic, inlay supported fixed partial denture. Part 2.
Fixed partial denture design: a finite element analysis." Australian dental journal 56.3 (2011): 302-311.

14. • They concluded that increase age of patients should not be considered as a risk
factor for survival of fixed prostheses.
• Some evidnece that middle aged patients may present with higher failure rates.
• Limitations to the study were the lack of randomized clinical trial, and high rate of
drop out and some even didn’t report the drop out rate.
• Those evidence of middle aged patients high failure rate were explained by authors
that the need of prostheses in early ages showed an early onset of dental diseases
which were not favorble for the prognosis of the resotraton.

15. • 311 RBFPD from 226 patients were
evaluated.
• Framework designs were categorized into
two groups:
• RBFPDP retained with a wing (surface
retained).
• RBFPDP with a combination of wing
and full coverage crown.
• Failure parameters were:
• Partial or complete debonding of
framework.
• Fracture of the framework.

16. • Analyzed variables:
1. Gender.
2. Location (maxilla vs. mandible).
3. Location (posterior vs. anterior).
4. Number of missing teeth (1 vs. >1).
5. Number of abutment (2 vs. >2).
6. Framework structure.
7. Framework alloy.
8. Age.
9. Cement type.
10. Operators.
• Maximum observation period 28.8 years.
• Survival ratio of maximum observation
duration was 41.2%.
• Among 311 prostheses, 84 were evaluated
as failure.
• 6 framework fracture: (5) Si-Palladium-
Cu-gold alloy and (1) Co-Cr alloy.
• 78 failure were partial and complete
debonding, 13 of which were
rebonded.
• All of failures in combination were
attributed to debonding of the retainer
but no crown failures.

17. • Among all variables only age and operator
variable showed significant difference.
• Fracture on abutment tooth structure was
observed in 10 cases in older adult group,
they were not counted as failure since the
framework is not damaged.

18. • 51 RBFPDP evaluated over a
period of 13 years.
• Anterior design: slight lingual
reduction and vertical grooves
and proximal guide plane.
• Posterior design is wrap-around
desing with occlusal rests.
• Survival categorized to:
• Complete (no debonding).
• Functional (one
rebonding).
• Multiple (>1 rebonding)

19. • Significant difference in
complete survival time
between mandibular and
maxillary teeth: maxillary teeth
had a higher survival time.
• Risk according to etiology of
missing tooth: more risk at
patient with peridodontal
disease or after orthodontic
treatment.
• They discussed the cause behind this finding; they implied
the problem with mobile teeth which lead to inaccurate
impressions, fitting splints, and occlusa loading thus affect in
debonding. Thus they implied the importance of case
selection.

20. • Criteria was:
• Minimal follow up 5 years.
• Sufficient information about the
design of bridge.
• Clear definition about criteria of
failure.
• Present survival data.
• Of 33 studies only 7 were included in
the analysis. Between 1970-92
• Definition for failure was if the bridge were not in situ or
for any reason they required a remake.
• Data included 4118 conventional bridges with overall
survival rate 74+/-2.1% after 15 years.

21. • The limitation in the previous meta-analysis where
classification of failure was not systematically
detailed, this could either to overestimation or
underestimation of survival for FPDs.
• This meta-analysis categorized survival:
• Where failure defined narrowly (prosthesis
removed).
• Where failure defined more broadly
(technically failed necessitating replacement).
• Failure defined in catastrophic terms (lost
abutment).
• For the years 1966 through 1996.
• Inclusion criteria:
• Minimum follow up 3 years.
• Failure defined adequately to
allow categorization.
• Identify patient type, provider
type, and examiner status).
• FPD conventional
(predominantly <50% cantilever,
<25% nonfull coverage
retainers).

22. • Of 35 studies, 8 studies met the criteria.
• The results were:
• Failure as FPD removal 92% survival after 10
years, 75% after 15 yr.
• Failure as technical and needed replacement
were 87% survive after 10 yr, and 69% survive
after 15 yr.
• Survive for abutment tooth at 10 years 96%.
• Results are similar to previous meta-
analysis.
• The limitation is that the most
objective category of failure was
removal of FPD which overstates the
survival for there are many FPDs are
found in situ but in need for
replacement.

23. To compare the survival rates of
zirconia-ceramic, monolithic zirconia
implant-supported FPDs with metal-
ceramic FPDs.
Full analysis for 240 articles result in 19
studies on implant FPDs.
They reported 932 metal-ceramic and
175 zirconia-ceramic FPDs.
Estimated 5 years survival rate 98.7%
for metal-ceramic, 93% for zirconia-
ceramic.
13 studies include 781 metal-ceramic
with 11.6% showed fracture and
chipping of ceramic in 5 years
estimated rate.
4.1% of zirconia-ceramic FPDs lost due
to ceramic fractures compared to 0.2%
of metal-ceramic FPDs.

24. Metal-ceramic remain the gold
standard for implant-supported
multiple unit FPDs.
Monolithic zirconia is an interesting
alternative to zirconia-ceramic FPDs
due to pronounced risk of framework
fracture and chipping of veneering
ceramic.
Suggest more research on monolithic
zirconia in comparison to metal-
ceramic.
Limitation is the lack of medium and
long-term outcomes of monolithic
zirconia.
According to the review; metal-ceramic
stay the golden standard for implant
supported FPDs.

25. A prospective study to evaluate the
clinical long term outcome over 15 or
more years of FPDs made from lithium
disilicate.
Of 36 FPD, 30 were in posterior and 6
anterior.
5 year recall was done for 33 FPD, 8
year recall for 30 FPDs, 10 year recall
for 29 FPDs, and 15 year recall for 12
FPDs.
Survival rate after 10 years 87.9%, 3
losses due to catastrophic ceramic
fracture, after 15 years it dropped to
48.6%.
Total 6 ceramic catastrophic fractures,
and 6 biological failures.

28. • It is important to notice the dramatic
drop after 10 years to 48.6% and 30.9%
after 15 years.
• Common cause of failure in all-ceramic
monolithic lithium disilicate is the
fracture of the cermaic material.
• Molars are more affected which is
possibly due to higher loading forces.
• Age and sex have less or no influence.
• This study support the manufacturer’s
instructions that lithium disilicate should
be used only for replacement of anterior
teeth and no more than 1st premolar
replacement for posterior teeth.
• No significant difference between
conventional and adhesive cementation
on clinical outcome.
• It is also suggested that fatigue and crack
propagations caused by clinical aging and
loading might require substantial time.

29. • Metal-ceramic is still the gold standard
and material of choice for FPD longevity.

30. • Purpose is to clarify:
• Cumulative survival rate of 3 unit metal framed
2-retainer (wing-wing) RBFPDs compared to
conventional FPDs.
• Risk factors related to occurrence of non-
survival events in FPD.

31. • Data obtained:
• Treatment method (RBFPD/ FPD)
• Occlusal contact (normal, tight, hardly
touching).
• Lateral occlusion (group function/cuspid
guided occlusion).
• Adhesive material used.
• 306 prostheses were included in the analysis.
• No significant difference between RBFPD and full
crown FPD, although multiple previous reports that
RBFPDs is considerably lower than that of
conventional FPDs.
• Significant difference found in state of abutment
teeth for RBFPD/FPD. Balanced occlusion was
greater in difference also. While luting agents were
significantly different too.

33. • For assessment of 5 year survival of metal-ceramic
and all-ceramic FPDs.
• 40 studies reporting 1796 metal-ceramic and 1110
all-ceramic FPDs.
• Indicated that survival rate for metal-ceramic 94.4%
• For reinforced glass ceramic FPDs 89.1%
• For glass infiltrated alumina FPDs 86.2%
• For densely sintered zirconia FPDs 90.4%
• No significant difference in the first 5 years.
• Higher incidence of caries in abutment teeth for
densely sintered zirconia compared to metal ceramic.
• More framework fractures for reinforced glass
ceramic 8%, glass infiltrated alumina 12.9%,
compared to metal ceramic 0.6% and densely
sintered zirconia 1.9%.
• Incidence of ceramic fractures and loss of retention
significant for densely sintered zirconia compared to
all types.

34. • Survival was defined as FDP remaining in situ with or
without modifications and success was defined as
the FDPs remaining in situ free of all complications
over the entire observation period.
• Technical failure is frequently related to using
reinforced glass ceramic FDPs and glass-infiltrated
alumina FDPs in the posterior area and where the
diameter of the connectors was reduced below 4mm
× 4 mm.
• The high incidence of chipping by densely sintered
zirconia FDPs, may be due to the fact that the first
generation of zirconia FDPs was made before special
low-fusing ceramics with a thermal expansion
coefficient compatible with zirconia had been
developed

35. • Aim to monitor survival of zirconia ceramic and
metal ceramic posterior FPDs.
• 44 patients with 53 FPDs (29 ZC, 24 MC).
• Survival for ZC 91.3%, and 100% for MC.
• Minor chipping of veneering ceramic at ZC and MC.
• ZC demonstrated higher rate of framework
fracture, debonding, major fractures of veneering
ceramic and poor marginal adaptation.

37. Previous study is reporting on 10-year outcomes of
zirconia-ceramic FDPs. The survival rate of the zirconia
FDPs in that study was quite low with 67% at 10 years.
This study evaluated FDPs with zirconia frameworks
made with a prototype CAM procedure (Direct Ceramic
Machining, DCM, and at time of the study, clinical
guidelines for the preparation of the abutment teeth for
CAD/CAM reconstructions and the handling of the zirconia
frameworks were lacking.
Chipping of the veneering ceramic is a problem at metal-
ceramic FDPs , as well as at zirconia-ceramic FDPs, yet, the
extension of the zirconia veneering ceramic chipping was
larger.

38. Conclusion
• Metal-ceramic is still the gold-standard for conventional FPD.
• Current development in CAD/CAM zirconia materials and understanding of tooth
preparation design show close results with metal-ceramic and need long term
clinical study.
• The understanding of principles of tooth preparation and taking into account
framework design and the appropriate choice of material affect durbaility of
restoration.
• Patinet selection and the appropriate choice for abutment preparation design
affect the longevity of restoration.
• Despite the development in zirconia material, frequent chipping of veneering
ceramic is still encountered.