Ferrule effect

FERRULE EFFECT
Dr. Rutuja Gawarle
2

Introduction
◦ Successful clinical outcome of an endodontically treated tooth depends not
only on adequate root canal treatment but also on an adequate restorative
treatment which is performed afterwards.
◦ A RC treated tooth is inherently compromised because of the loss of firm
coronal dentin, instrumented canals and hence increased flexure in response to
occlusal forces.
◦ When a tooth has suffered signiﬁcant structure loss, the restorative options may
include restoring the tooth with various involved procedures or extracting the
tooth.
3

◦ The longevity of endodontically treated tooth is directed related to the amount
of remaining sound tooth structure.
◦ When restoring these cases, the restoration’s ability to brace solid sound tooth
structure is the key for long-term success.
◦ Successful restoration of a root filled tooth should provide:
◦ 1. Effective coronal seal
◦ 2. Protection of remaining tooth structure
◦ 3. Restored function
◦ 4. Acceptable aesthetics
◦ And to fulfil all these requirements, a post retained crown is usually indicated.
◦ At one time dowel was thought to strengthen the remaining tooth structure
and was referred to as Intra-coronal Crutch by Rosen.
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◦ However, root fracture is one of the most common modes of failure of these
restorations.
◦ Fractured post, cores or roots of further crowned endodontically treated teeth
are disappointing clinical outcomes.
◦ Hence, for an attempt to reduce the failure when restoring such teeth,
incorporating certain designing features during the tooth preparation is
important. Ferrule is one of them.
◦ The incorporation of the long standing concept of ‘ferrule’ or ‘the ferrule
effect’ has been accepted as one of the foundations of the restoration of the
endodontically treated tooth that has suffered advanced structure loss.
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MEANING OFTHETERM
Comes from Latin
•FERRUM means “Iron”
•VIRIOLA means “Bracelet”
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What is Ferrule?
(Brown1993)

A ferrule, in respect to
teeth, is a band that
encircles the external
dimension of residual
tooth structure.
A dental ferrule is an
encircling band of cast
metal around the coronal
surface of the tooth.
(Galen WW, Mueller KI: Restoration of the Endodontically Treated Tooth. In Cohen, S. Burns, RC, editors: Pathways of the
Pulp, 10th Edition.) 7

◦ Extending a preparation apically
creates a ferrule and helps
prevents fracture of an
endodontically treated tooth
during function.
◦ A Prepared with a ferrule
(arrows).
◦ B Prepared without a ferrule.
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•The role of a dental ferrule, is embracement of the hard tissue by
crown restoration of a certain height which is mandatory for a post-
endodontic reconstruction of severely damaged teeth.
•A dental ferrule preparation combines a shoulder preparation with
parallel coronal dentin walls.
•The tooth tissue is enclosed by the crown improving the overall
resistance of the restoration
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DEFINITION
The ferrule effect can be defined as ‘‘a 360
metal collar of the crown surrounding the
parallel walls of the dentine extending coronal
to the shoulder of the preparation”.
(Sorensen & Engelman)
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MISINTERPRETED AS..
• The remaining amount of sound dentine above the finish line.
• It is in fact not the remaining tooth structure that is the ‘ferrule’ but rather the actual
bracing of the complete crown over the tooth structure that constitutes the ferrule
effect, i.e. the protection of the remaining tooth structure against fracture.
Jotkowitz A:Rethinking Ferrule:a new
approach to an old dillemma.British
Dental Journal,2010;209(1):25-33 11

FERRULE ADVANTAGES:
There are four advantages of this effect:
1:Promotes embracing actionofartificialcrownagainstdentin,
2:Preventstheshatteringoftheroot,
3:Reducesthewedgingeffectofatapered dowel,and
4:Resistsfunctionalleverforcesandthelateral forcesexertedduring
dowelinsertion.
RosenH:Operativeproceduresonmutilatedendodonticallytreatedteeth.JProsthet Dent1961;11:973-986.
 SorensenJA,EngelmanMJ:Ferruledesignandfractureresistanceof
endodonticallytreatedteeth.JProsthetDent1990;63:529-536
14

•The use of a ferrule as part of the core or artificial crown may be of benefit in
reinforcing root-filled teeth.
•A protective ‘ferrule effect’ could occur owing to the ferrule resisting
stresses such as
•functional lever forces,
•the wedging effect of tapered posts and
•the lateral forces exerted during the post insertion.
(Sorensen & Engelman1990).
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CROWN FERRULE: Ferrules created by the
overlying crown engaging tooth structure.
CORE FERRULE: Ferrules that are part of a
cast metal.
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FACTORS AFFECTING
FUNCTIONALITY OF
FERRULE
Trushkowsky RD:Restoration of endodontically treated teeth:
Criteria and technique considerations. Quintessence Int 2014;45:557–67
17

Four direct factors inﬂuencing the ferrule as well as two additional indirect
factors that may inﬂuence the functionality of the ferrule:
◦ a) Ferrule height
◦ b) Ferrule width
◦ c) Number of walls and ferrule location
◦ d) Type of tooth and the extent of lateral loads
◦ e) Type of post
◦ f) Type of core material.
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•1.Ferrule height
Greater the height of remaining tooth structure
better the fracture resistance.
Ferrule height of 1.5 to 2 mm of vertical tooth
structure would be the most beneficial.
The crown should encompass at least 2 mm past
the tooth core connection to achieve the most
protective ferrule effect.
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• Sorensen & Engelman (1990) advised that as much coronal tooth as
possible should be preserved, and a butt-joint margin between the core
and tooth be used, i.e. minimal taper.
• Every effort should be made to save as much of the coronal tooth structure
as possible, because this helps reduce stress concentrations at the gingival
margin." The amount of remaining tooth structure is probably the single
most important predictor of clinical success.
• The presence of a 1.5- to 2-mm ferrule has a positive effect on fracture
resistance of endodontically treated teeth.
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2. Ferrule width
Esthetic restorations often
require fairly aggressive
preparations at the gingival
margin and sometimes buccal
defects such as abfraction may
compromise the buccal dentin
wall.
It has been accepted that the
walls are considered too thin
if they are less than 1 mm in
thickness, and would negate
the ferrule effect.
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3. No of walls and ferrule location
A circumferential ferrule would be optimal but caries may
affect the interproximal areas and abrasion or erosion the
buccal walls.
A crown preparation will further reduce the wall thickness
and only a partial ferrule will remain.
Ng et al said that good palatal ferrule is as effective as
having a complete “all around” ferrule.
Al-Wahadni and Gutteridge found having a 3 mm ferrule on
the buccal aspect was better than having no ferrule at all.
23

4.Type of tooth and extent of lateral load
Anterior teeth are loaded non-axially.
Posterior teeth are loaded occluso-gingivally.
Anterior teeth with a deep overbite and parafunction are at a higher
risk of failure.
Teeth that are in group function with long maxillary buccal cusps
produce higher lateral forces than if there was canine guidance.
24

5. Type of post
Cast posts have been used for many years for the support of the final restoration.
However, in recent years this type of restoration has been progressively
replaced by composite cores with a glass fiber post or metal post.
Fiber-reinforced posts have shown positive results as compared to metal
posts.
25

6. Core materials
Composite resin with dentin bonding agent has frequently been
implicated as material that can strengthen the tooth and
reinforced cusps as compared to amalgam.
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•Repairable fractures: above cemento-enamel junction (CEJ),
horizontal cervical fracture, core-tooth fracture.
•Non-repairable oblique fracture: entirely below CEJ, fracture in
the middle or apical third of the root, vertical root fracture.
Non repairable fractures are more common with cast dowel
post and 2mm ferrule
Reparable fractures are seen with fiber-reinforced posts
and 2mm ferrule.
Aggarwal, et al:Effect of ferrule on fracture resistance. Journal ofConservative
Dentistry ,2014;17(2):183-7
28

HOW TO CREATE FERRULE IN A
NO FERRULE CASE????
There are two methods:
1.Crown lengthening
2.Orthodontic extrusion
29

Effect of apical preparation on crown-to-root ratio.
A Schematic of extensively damaged premolar tooth. Apical extension of the gingival margin would encroach on the
biologic width.This preparation has no ferrule.
B Creating a ferrule with orthodontic extrusion reduces root length (R) while crown length (C) remains unchanged.
C Surgical crown lengthening also reduces root length (R) but increases crown length (C). This results in a much less
favorable crown-to-root ratio, which may not in fact strengthen the restoration.
Dr. A.G. Gegauff.
30

CLASSIFICATION OF FERRULE
Jotkowitz A:Rethinking Ferrule:a new approach to an old
dillemma.British Dental Journal,2010;209(1):25-33
31
Although current literature does not
present a uniform description and
design of the ideal ferrule, a
classification that is based on the
remaining tooth structure would be of
value.

Category A : No anticipatedrisk
Category B : Low risk
Category C : Medium risk
Category D : High risk
Category X : No ferrule
32

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Category A : No anticipatedrisk
Sound dentine walls remaining all aroundthe tooth, with height greater than 2mm and
with a minimum thickness of 1mm.
Such teeth do not present an anticipated risk for structural or mechanical failure
Category B : Low risk
Compromised or no ferrule present on either proximal surface. (ie less than 2mm height
and/or 1 mm thickness) OR two compromised proximal walls on a tooth that undergoes
light lateral loads.
Such teeth present low risk for structural or mechanical failure.
Category C : Medium risk
Two compromised proximal walls on a tooth that undergoes heavy lateral loads OR a
compromised buccal or lingual wall on a tooth that undergoes light lateral loads. Such
teeth present medium risk for structural or mechanical failure.

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Category D : High risk
A compromised buccal or lingual wall on a tooth that undergoes heavy lateral loads OR a
compromised buccal, and lingual wall on any tooth OR a tooth that has only two adjacent
walls or only a single wall remaining. Such teeth present high risk for structural or
mechanical failure and alternate treatment modalities should be considered and may be
more appropriate.
Category X : No ferrule
No ferrule can be established, such that the tooth is non-restorable. Actual treatment
rendered will be determined based on considering the entire dentition and attachment
apparatus, as well as individual patient risk factors and expectations.

Summary and Conclusion
◦ Based on the evidence from in vitro and in vivo studies reviewed, the presence
of ferrule has a positive effect on fracture resistance of endodontically treated
teeth.
◦ More successful prognosis could be expected if healthy dentin extending 1.5 to
2 mm coronal to the margin of the crown is provided circumferentially.
◦ If the clinical situation does not permit a 360 circumferential ferrule because of
extensive caries lesions, previous restorations, or fractures, an incomplete
ferrule is still considered a better option than complete absence of a ferrule.
◦ Moreover, including a ferrule in the preparation design could possibly lead to
more favourable fracture patters.
37

◦ With regard to the effect of different restorative procedures on tooth resistance,
literature data are often controversial, probably because of the different
methodologies and study designs used.
◦ However, it could be generally concluded providing an adequate ferrule lowers
the impact of the post and core system, luting agents, and the final restoration
on the performance of endodontically restored teeth.
◦ When it comes to severely damaged teeth with no coronal structure, in order to
provide space for a ferrule, orthodontic extrusion should be considered rather
than surgical crown lengthening.
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◦ This approach preserves more tooth structure and ensures more favourable
biomechanical behaviour.
◦ If neither of the alternative methods for providing a ferrule can be performed,
currently available evidence suggests that poor treatment outcome is very
likely.
◦ Therefore, clinicians may take in consideration tooth extraction followed by
appropriate surgical and/or prosthetic rehabilitation.
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References
◦ (Galen WW, Mueller KI: Restoration of the Endodontically Treated Tooth.
◦ In Cohen, S. Burns, RC, editors: Pathways of the Pulp, 10th Edition.)
◦ Jotkowitz A:Rethinking Ferrule:a new approach to an old dillemma.British Dental
Journal,2010;209(1):25-33
◦ RosenH:Operativeproceduresonmutilatedendodonticallytreatedteeth.J Prosthet Dent1961;11:973-986.
◦ SorensenJA,EngelmanMJ:Ferruledesignandfractureresistanceof endodonticallytreatedteeth.JProsthetDent
1990;63:529-536
◦ Trushkowsky RD:Restoration of endodontically treated teeth: Criteria and technique considerations.
Quintessence Int 2014;45:557–67
◦ Aggarwal,etal:Effectofferruleonfractureresistance.JournalofConservative Dentistry ,2014;17(2):183-7
◦ Jelena Juloski et al Ferrule Effect: A Literature Review JOE — Volume 38, Number 1, January 2012
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