Fracture-Resistant Endodontic & Restorative Preparations
Preserving dentine, respecting natural tooth anatomy and rethinking conventional cavity preparation.
Modern restorative and endodontic dentistry has access to sophisticated materials, instrumentation and imaging. Yet the fundamental question remains: how much healthy tooth structure should we remove to achieve treatment?
In this thought-provoking 2013 Dentistry Today article, Dr David Clark, Dr John Khademi and Dr Eric Herbranson challenge conventional preparation philosophies.
Their central argument is that retaining the natural structural integrity of a tooth should be considered alongside the technical objectives of restorative and endodontic treatment.
Clinical photograph from the existing Bioclear UK article.
Are We Weakening Teeth While Trying to Save Them?
The authors question whether long-established preparation designs sufficiently account for the biomechanical consequences of removing tooth structure.
Extensive Cavity Preparations
Long mesiodistal preparations can interrupt the natural continuity of the tooth and alter its resistance to bending and fracture.
Aggressive Endodontic Access
Excessive coronal enlargement can remove important pericervical dentine and compromise the remaining structural integrity.
Canal Over-Enlargement
Instrumenting non-round canals into larger circular shapes can create uneven wall thickness and localised areas of weakening.
Extensive Crown Preparation
Aggressive preparation for indirect restorations may remove additional healthy tissue from already compromised teeth.
The central question:
Can clinicians achieve the biological
and restorative objectives of treatment
while preserving more of the tooth's
original structural anatomy?
Three Clinical Perspectives. One Shared Philosophy.
The article brings together expertise in restorative dentistry, endodontic instrumentation and anatomical understanding.
Dr David Clark
Preserve the tooth before restoring it
Dr Clark explores the relationship between preparation geometry, stress concentration and the fracture resistance of posterior teeth.
He questions long continuous cavity preparations and discusses the advantages of disconnected preparations, conservative restorative design and cuspal protection.
Dr Eric Herbranson
Respect the anatomy that nature created
Dr Herbranson examines the relationship between external root anatomy and internal canal shape.
His discussion highlights why ovoid canals, root concavities and differences in dentine thickness matter when planning endodontic instrumentation.
Dr John Khademi
Rethink the objectives of canal shaping
Dr Khademi challenges conventional assumptions about access cavity preparation and continuous-taper shaping.
He introduces a framework comparing no shaping, intentional shaping and respectful shaping, emphasising the need to balance tooth, operator and restoration requirements.
The Principles of Fracture-Resistant Preparation
Rather than considering the restoration or endodontic procedure in isolation, the authors propose examining the tooth as a complete biomechanical structure.
Preserve Structural Continuity
Avoid unnecessary removal of the tooth structure that contributes to overall stiffness.
The authors particularly question long preparations that connect otherwise separate defects.
Respect Natural Root Anatomy
Recognise that many canals are not circular.
Instrumentation should account for differences in root dimensions, existing concavities and remaining dentine thickness.
Plan the Restoration Early
Restorative requirements should influence the endodontic plan rather than being considered only after root canal treatment is complete.
The authors particularly emphasise protecting weakened posterior cusps where appropriate.
A key distinction:
The paper challenges clinicians to
question whether preparation geometry
is dictated by biological necessity
or by conventional instrumentation
habits and restorative techniques.
Why the Shape of a Cavity Matters
Dr Clark argues that the effect of cavity preparation on tooth strength depends not simply on the volume of tissue removed, but on the geometry of the preparation itself.
Connected vs Interrupted Preparations
Traditional posterior preparations often connect occlusal and proximal defects into a single cavity.
However, continuous cuts can alter the remaining tooth's mechanical behaviour and create areas where stress is concentrated.
In the original article, Dr Clark discusses interrupted preparations that preserve tooth structure between separate defects.
The rationale is that maintaining structural continuity may better preserve the tooth's resistance to bending.
He also discusses rounded preparation shapes and the relationship between preparation length, curvature and stress concentration.
The Key Preparation Concepts
- Consider cavity length and geometry, not simply the total amount of tissue removed.
- Preserve sound tooth structure between separate defects where clinically possible.
- Avoid unnecessary connection of proximal, occlusal and endodontic preparations.
- Consider rounded preparation geometry and the effect of sharp transitions.
- Assess the remaining cusp structure and potential need for protective coverage.
Clinical perspective:
The argument for interrupted
preparations is based on
the authors' biomechanical
rationale. It should not be
used to justify retaining
caries, compromised tissue
or inaccessible areas that
require appropriate treatment.
Preserving Pericervical Dentine
One of the article's most important messages concerns conserving tooth structure around the cervical region during endodontic treatment.
Straight-Line Access and Canal Enlargement
Traditional access philosophies have often emphasised broad visibility and straight-line instrument access.
Similarly, some canal shaping techniques aim to create a continuously tapered preparation.
The authors question whether these objectives can lead to unnecessary removal of structurally important dentine.
Site-Specific Dentine Conservation
The paper proposes giving greater consideration to natural anatomy when designing endodontic access.
Dr Khademi discusses the potential role of magnification, smaller instruments and controlled access techniques.
The objective is to reduce unnecessary enlargement while still achieving the essential objectives of endodontic treatment.
Why this matters:
Pericervical dentine is an
important component of
the remaining tooth structure.
Conserving it may help
maintain structural integrity,
but adequate canal location,
cleaning, disinfection and
obturation must remain
central treatment objectives.
Root Anatomy: Why Round Is Not Always Right
Dr Herbranson's contribution highlights the relationship between external root form and the complex internal anatomy of root canals.
Understanding Ovoid Canals
Many natural roots have an ovoid rather than circular cross-section.
The internal pulp space often reflects the external root anatomy, although the relationship varies considerably between tooth types.
Premolars, anterior teeth and molars may also exhibit root concavities that influence internal canal shape.
These variations are particularly relevant when considering instrumentation within the coronal and middle portions of roots.
Enlarging an ovoid canal into a circular preparation may remove disproportionate amounts of dentine from particular walls.
Important Anatomical Considerations
- External root dimensions are rarely identical in all directions.
- Canal anatomy frequently differs substantially from a simple circular preparation.
- Root concavities can create areas of naturally reduced wall thickness.
- Excessive instrumentation may further weaken these areas.
- Knowledge of three-dimensional anatomy is important for safe access and instrumentation.
The anatomical message:
Endodontic preparation should
take account of the actual
tooth being treated rather
than assuming every canal
should be shaped into
an identical geometric form.
Three Approaches to Endodontic Shaping
Dr Khademi describes three different philosophies for managing root canal anatomy, each with different priorities and limitations.
No Shaping
A philosophy that prioritises preserving the natural canal dimensions without intentional enlargement.
The paper acknowledges that this approach is generally impractical with the instrumentation and treatment requirements discussed by the authors.
Intentional Shaping
Conventional shaping based on creating a planned continuous taper from the canal entrance towards the apex.
Dr Khademi questions the structural cost of imposing this geometry on canals that may naturally be ovoid or irregularly shaped.
Respectful Shaping
A more anatomy-led approach that avoids unnecessarily imposing a predefined geometric shape on the canal.
The objective is to balance effective endodontic treatment with preservation of the surrounding dentine.
Important clinical distinction:
These three categories are
taken from the authors'
2013 discussion. They
describe treatment philosophies
rather than a contemporary
evidence-based comparison
establishing one approach
as superior in every case.
Balancing Three Essential Needs
One of the strongest concepts in the paper is the need to balance the requirements of the tooth, the operator and the final restoration.
The Tooth's Needs
Preserve sufficient dentine and remaining structure to support long-term function wherever possible.
The Operator's Needs
Obtain access and instrumentation sufficient to undertake effective endodontic treatment.
The Restoration's Needs
Plan a definitive restoration capable of sealing and protecting the tooth, while considering its remaining structural anatomy.
Why this framework is valuable:
A technically successful
endodontic procedure
is only part of
the overall treatment
outcome. The tooth
must also remain
restorable and capable
of functioning.
The Importance of Cuspal Protection
The article discusses immediate restorative protection for compromised posterior teeth, including direct composite cuspal coverage.
Planning Beyond Root Canal Treatment
Following endodontic treatment, the remaining tooth may already be significantly compromised by caries, existing restorations or access preparation.
Dr Clark discusses the potential role of immediate direct composite cuspal coverage for posterior teeth.
In the original article, he describes a direct composite overlay technique incorporating approximately 2mm of cuspal coverage.
His rationale is that protecting compromised cusps should be considered at the time of endodontic treatment rather than routinely delaying restorative planning.
The paper includes clinical photographs demonstrating a direct composite onlay using the Bioclear Matrix System.
Restorative Considerations
- Assess remaining cusp thickness and the extent of previous tooth structure loss.
- Consider the presence and distribution of cracks.
- Evaluate the functional loading and occlusal circumstances.
- Determine whether direct or indirect cuspal protection is appropriate.
- Consider adhesive substrates, remaining dentine and restorability.
- Plan an effective definitive coronal seal and ongoing maintenance.
Clinical context:
The 2mm direct cuspal
coverage approach
represents Dr Clark's
described technique
in the 2013 article.
It should not be
interpreted as a
universal treatment
requirement or evidence
that all root-treated
posterior teeth can
be predictably restored
without indirect
cuspal coverage.
Posts, Ferrules and Remaining Tooth Structure
The authors also consider whether traditional restorative methods can compensate for structural tissue that has already been removed.
The paper distinguishes between the functions of cuspal protection, posts and the remaining natural tooth structure.
Cuspal coverage may provide protection for a compromised posterior tooth. A post may be useful in selected circumstances for retaining a core.
However, neither is a substitute for adequate remaining dentine.
The authors also discuss the importance of a three-dimensional ferrule, considering dentine height, dentine wall thickness and the overall preparation geometry.
The restorative principle:
Tooth structure that
has been unnecessarily
removed cannot simply
be replaced by adding
a post, core or crown.
Preservation of
restorable tooth
structure must remain
a central consideration.
Clinical Application of Conservative Restorative Dentistry
The publication includes clinical examples of compromised posterior teeth, endodontic access and direct composite cuspal protection.
Photograph currently featured in the Bioclear UK article. For the full illustrated cases, including preparation designs, endodontic radiographs, canal anatomy and direct composite cuspal coverage, refer to the original five-page publication.
Clinical Cases in the Original Paper
Case 1: The authors describe a posterior tooth that fractured following restorative and endodontic treatment, using the case to illustrate concerns about excessive structural removal.
Case 2: Dr Clark demonstrates direct composite cuspal coverage for a heavily compromised premolar, using the Bioclear Matrix System.
Additional figures illustrate canal anatomy, root cross-sections, access preparation, endodontic files and the effects of extensive coronal enlargement.
Five Questions for Clinical Decision-Making
The paper's central themes can be translated into five useful questions when assessing restorative and endodontic treatment.
Is This Preparation Necessary?
Identify the biological and technical reason for removing each area of tooth structure.
Can More Dentine Be Preserved?
Consider whether access and instrumentation can be achieved while conserving important tissue.
Does the Preparation Respect Anatomy?
Account for natural root morphology, canal shape and remaining wall thickness.
How Will the Tooth Be Restored?
Consider the restorative requirements before completing endodontic access and shaping.
Does the Tooth Need Cuspal Protection?
Assess the remaining cusps, structural defects and functional loading when planning treatment.
The bigger picture:
The paper encourages
clinicians to consider
tooth longevity,
rather than viewing
preparation, endodontic
treatment and the
final restoration as
separate procedures.
From Conservative Preparation to the Bioclear Method
The restorative philosophy discussed in this publication connects with the wider development of the Bioclear Method.
Conserving and Reconstructing Tooth Structure
Dr Clark's work increasingly explored restorative methods that combine contemporary cavity design with anatomical reconstruction.
The Bioclear Method uses a systematic approach incorporating surface cleaning, modern preparation, anatomically shaped matrices and composite injection moulding.
These principles are relevant to selected posterior restorations, including Class II cavities and direct overlays.
The underlying objective is to preserve healthy structure wherever appropriate while restoring anatomy and function.
The Five Pillars of Bioclear
-
Biofilm Removal
Thorough cleaning of the tooth surfaces before adhesive procedures. -
Modern Preparation Design
Conservative preparation principles appropriate for contemporary adhesive dentistry. -
Anatomical Matrices
Purpose-designed matrices for restorative contours and contacts. -
Heated Injection Moulding
Controlled placement of suitable warmed composite materials. -
Rockstar Polishing
Systematic finishing and polishing of restorative surfaces.
Publication context:
The 2013 article discusses
the Bioclear Matrix System
and direct composite
cuspal coverage.
This section also
explains how its
tooth-preservation
themes relate to
the broader Bioclear
Method taught today.
Read the Full Article
Fracture Resistant Endodontic and Restorative Preparations
Dr David Clark, Dr John Khademi
and Dr Eric Herbranson
Dentistry Today, February 2013
Five-page PDF
Includes the original discussions of tooth biomechanics, conservative endodontic access, ovoid root anatomy, canal shaping and clinical cases.
Frequently Asked Questions
Common clinical questions about fracture resistance, endodontic access and conservative restorative dentistry.
Why is preserving dentine important in endodontics?
Dentine contributes to the structural integrity of the tooth. Extensive removal during access and instrumentation can reduce the remaining wall thickness and influence the tooth's resistance to fracture. Preparation must balance conservation with effective endodontic treatment.
Are root-treated teeth naturally more brittle?
The authors challenge the traditional explanation that root-treated teeth become brittle primarily because they lose moisture. They emphasise instead the structural consequences of caries, previous restorations and treatment-related tooth tissue loss.
What is pericervical dentine?
Pericervical dentine refers to dentine around the cervical region of the tooth. It is an important component of the remaining structural tooth tissue and should be considered when planning endodontic access and definitive restoration.
Why can excessive canal enlargement weaken teeth?
Excessive instrumentation can reduce the thickness of the remaining root walls. This is particularly relevant where the natural root is ovoid or has concavities. The authors argue that imposing a large circular preparation on irregular anatomy may create unfavourable areas of structural weakness.
What is respectful endodontic shaping?
Respectful shaping is the term used by Dr Khademi in the 2013 paper for an anatomy-led instrumentation philosophy that avoids unnecessary enlargement simply to create a predefined continuous taper. Appropriate cleaning and treatment objectives must still be achieved.
Why does the shape of a cavity preparation matter?
Preparation geometry influences the distribution of stresses within the remaining tooth. Long continuous preparations may disrupt structural continuity differently from smaller, disconnected preparations. Dr Clark discusses these principles as part of his argument for more conservative restorative designs.
Do all root-treated posterior teeth need cuspal coverage?
The need for cuspal coverage depends on the amount and quality of remaining tooth structure, existing cracks, occlusion and other clinical factors. Dr Clark advocates immediate protection in the original article, but the specific restorative approach should be determined individually.
Can direct composite overlays protect compromised posterior teeth?
Direct composite cuspal coverage is an option for selected teeth. The 2013 paper illustrates this approach using a Bioclear Matrix. Suitability depends on remaining tooth structure, restorative design, material selection, occlusion and patient-specific circumstances.
Where can I learn contemporary Bioclear posterior techniques?
Bioclear Matrix UK provides hands-on education covering posterior composite dentistry, including Class II restorations, anatomical matrices, contemporary cavity design and injection moulding. More advanced courses also explore compromised teeth and complex restorative planning.
Continue Exploring Conservative Restorative Dentistry
Discover how the principles discussed in this publication connect with Dr Clark's subsequent work and modern posterior composite techniques.
Learn a More Conservative Approach to Posterior Restorations
Understanding preparation design, tooth anatomy and restorative biomechanics is central to managing compromised posterior teeth.
Bioclear Matrix UK provides hands-on education covering contemporary cavity preparations, anatomical matrix systems, Class II contacts, direct composite overlays and injection moulding.
Discover how the Bioclear Method can expand your restorative treatment options through structured clinical training.