A JOURNAL CLUB PRESENTATION

1. JOURNAL CLUB
THE PROSTHODONTIC CONCEPT OF CROWN-TO-ROOT RATIO: A
REVIEW OF THE LITERATURE
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PRESENTED BY – DR. VAISHALI SHRIVASTAVA
2nd YEAR POST GRADUATE STUDENT
DEPT. OF PROSTHODONTICS, CROWN & BRIDGE
AND IMPLANTOLOGY

2. Grossmann Y, Sadan A. The prosthodontic concept of
crown-to-root ratio: a review of the literature. The Journal
of prosthetic dentistry. 2005 Jun 1;93(6):559-62.
2
SOURCE
AUTHORS- Yoav Grossmann,and Avishai Sadan
JOURNAL - . The Journal of prosthetic dentistry.
2005 Jun 1;93(6):559-62
TITLE- THE PROSTHODONTIC CONCEPT OF CROWN-
TO-ROOT RATIO: A REVIEW OF THE LITERATURE

3. The crown-to-root ratio (CRR) is one of the primary variables in the evaluation of the
suitability of a tooth as an abutment for a fixed or removable partial denture (FPD or
RPD).
.
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Abutment
longevity
Abutment
mobility
Alveolar bone
support
Root
configuration
Opposing
occlusion
Pulpal condition
Presence of
endodontic
treatment
Remaining tooth
structure
INTRODUCTION

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• The physical relationship between the portion of the tooth within the alveolar bone
compared with the portion not within the alveolar bone, as determined radiographically.’
• The fulcrum, or center of rotation, of the Class I lever is in the middle portion of the root
that is embedded in alveolar bone
DEFINITION OF CROWN-TO-ROOT RATIO

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• The CRR may increase over time, primarily as a result of loss of alveolar bone support;
the crown portion of the fulcrum (effort arm) would then increase, and the root portion
(resistance arm) would decrease.
• In addition, the center of rotation moves apically, and the tooth is more prone to the
harmful effect of lateral forces

6. • Since most roots have conical shape and the root length is only a 1-dimensional linear
measurement, other criteria should be used to evaluate the alveolar support of the
abutment.
• For example, it was found that if one half of the height of attachment to the root was lost
due to periodontal disease, a mean of 61.5% of the actual attachment area to the root
would be lost.
• Furthermore, if a mean of 5.72 mm of root attachment height is lost, or if a mean of
60.6% of the same root height remains, only one half of the total root attachment area
would remain to provide tooth support
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Radiographic evaluation has been the most widely used technique in clinical practice for
assessing bone level around teeth.
Pepelassi and Diamanti-Kipioti evaluated methods of conventional radiography for
detecting periodontal osseous destruction and suggested that periapical radiography is
more successful in assessing periodontal osseous destruction than panoramic
radiography

8. THE VALUE OF CRR
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CRR for an FPD
abutment of 1:2
to be ideal
Dykema et al suggested a ratio of 1:1.5
as an acceptable and desireable CRR
for abutments.
Shillingburg et al1 suggested a 1:1.5
CRR as optimum for an FPD abutment,
or a 1:1 ratio as a minimum ratio

9. CROWN-TO-ROOT RATIO IN CLINICAL PRACTICE
• Abutment preparation for overdentures has the most dramatic effect on the ratio,
reducing the crown to 1 to 2 mm above the free gingival margin,28 which can improve
the CRR from 1:1 to 1:2 or 1:3.
• any increase in the vertical dimension of occlusion (VDO) increases the CRR
• crown lengthening reestablishes the dentogingival junction at a more apical level on the
root to accommodate the junctional epithelium and the connective tissue attachment
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10. SPLINTING AND CROWN-TO-ROOT RATIO
Periodontal bone loss around abutments results in an increased CRR that is associated with
increased tooth mobility
Splinting abutments may enhance stability and may shift the center of rotation and transmit
less horizontal force to the abutment
when evaluating the need for splinting of periodontally compromised teeth, the clinician
should consider other predictive indices,
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indices
Presence of
increased
mobility
Initial probing
depth
Furcation
involvement
Ability to
maintain oral
hygiene
Presence of
parafunctional
habit

11. CROWN-TO-ROOT RATIO AS A PROGNOSTIC TOOL
• The primary objective in evaluating clinical criteria for abutments and periodontally
compromised teeth is to determine the best prognosis.
• McGuire and Nunn evaluated 100 periodontally treated patients (2,484 teeth) under
maintenance care for 5 years (with 38 of these patients followed for 8 years) to
determine the relationship of assigned prognosis to the clinical criteria commonly used
in the development of prognosis.
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• The total remaining periodontal bone support provides more accurate information than the
linear measurement of the ratio, which is limited even in the prediction of the prognosis of
nonabutment teeth.
• Therefore, indications other than the crown-to-root ratio should be used to determine
whether splinting of teeth is appropriate.
• long-term prospective clinical studies are required to identify the exact prognostic value of
each clinical requirement for abutments. Future research should concentrate on predictive
indices that will assist the clinician in deciding whether to preserve compromised teeth or
place implants.
Discussion

13. There is a lack of consensus and evidence-based research on the influence of
crown-to-root ratio on diagnosis and treatment planning for periodontally
compromised teeth.
It appears that multiple factors may play a role in determining the prognosis of
abutments considered for support of a fixed or removable prosthesis
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SUMMARY

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Covered many
studies regarding
CRR
Not explained
about how to
measure CRR
Not explained
about CIR

15. Crown-Implant Ratio versus Crown-Root Ratio – A
Review
Authors-*Dr. Rupal Jhanji 1 , Dr. Sumit Sethi 2 , Dr.
Sanjeev Mittal
IOSR Journal of Dental and Medical Sciences (IOSR-
JDMS) e-ISSN: 2279-0853, p-ISSN: 2279-0861.Volume
17, Issue 2 Ver. 5 February. (2018), PP 66-71
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Cross reference

16. In a crown to implant ratio (CIR), the crown height is measured from the most coronal
bone contact to the most coronal restoration surface and implant length is measured from
the most coronal bone contact to the apex
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Introduction

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According to Misch,the implant doesn’t rotate around a central two-third portion of the root as
in the crown root ratio. He also suggested that the length of the implant has no relation with
the implant mobility and resistance to the lateral forces.
Bidez and Misch conducted a research based on which it was concluded that an increase of 10-
20 mm in the height of a crown increases the force on an implant by 100% and an increase in
the angulation by 120 escalates the resultant forces by 20%.

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Reiger et al (1990) [16] observed increased stress levels
and high forces during bending movements around the
neck and apex of the implant fixture.
They concluded that increased C/I ratios produce more
stress thereby resulting in bone loss and implant failure.
Discussion

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Güngör H (2016) [44] studied the effects of C/I ratio using a 3-D finite element
analysis on stress distribution both in bone and implant under axial and oblique loads.
They found that the high C/I ratio affected both cortical and cancellous bone along
with the implant under oblique and axial load with more stress under oblique load
when compared to axial load.
Thus, in distal cantilever fixed dental prosthesis, increased C/I ratios should be
avoided due to increased stress concentration on bone and around implants. The data
also showed dynamic stress values under oblique load than axial in high C/I ratio
cases

22. review clearly explains that the crown implant ratio between 0.5 and 2 show a favorable
prognosis and can be maintained successfully if other prosthetic principles are equally
taken into consideration.
Increased CIR is not associated with bone loss or prosthetic failure if the forces are well
distributed and cannot be considered as risk factor for biological complications around
dental implants & implant failure
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SUMMARY

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Thankyou