**Restoration of Endodontically Treated Teeth** Compiled and Edited by: Dr. Marrwa Ibrahim, BDS, MD.Sc Lecturer, UWA Dental School  Compiled and Edited by: **Dr. Marrwa Ibrahim, BDS, MD.Sc** Lecturer, UWA Dental School Labelled diagram illustrating three types of posts used in the restoration of endodontically treated teeth. The image displays three vertical cross-sections of a tooth root within the jawbone. From left to right, the panels are labeled: 'Preformed post' (showing a threaded metal post), 'Esthetic post' (showing a smooth white post with a crown-like structure on top), and 'Cast post' (showing a solid silver-colored metallic post). Each panel depicts the post inserted into the prepared root canal space. The University of Western Australia | Oral Health Centre of Western Australia **Lecture 1: Introduction** The University of Western Australia | Oral Health Centre of Western Australia **Lecture 1: Introduction** <p><b>Learning Outcomes</b></p> <div class="image"></div> <p><b>By the end of this lecture, you should be able to:</b></p> <ol> <li>Understand the changes in the tooth structure after root canal treatment</li> <li>Discuss the factors that make endodontically treated tooth more susceptible to fracture</li> <li>Discuss restorative options for endo treated tooth (with and without a post)</li> <li>Discuss the function, indication, importance and clinical application of posts</li> <li>Understand and describe the concept of Ferrule and discuss the importance of the ferrule effect</li> <li>Understand the factors that affect the ferrule and the longevity of endodontically treated teeth</li> </ol> #### Learning Outcomes By the end of this lecture, you should be able to: 1. Understand the changes in the tooth structure after root canal treatment 2. Discuss the factors that make endodontically treated tooth more susceptible to fracture 3. Discuss restorative options for endo treated tooth (with and without a post) 4. Discuss the function, indication, importance and clinical application of posts 5. Understand and describe the concept of Ferrule and discuss the importance of the ferrule effect 6. Understand the factors that affect the ferrule and the longevity of endodontically treated teeth # What is Post and Core Restorations **Post (Definition & Purpose)** **A post** is typically made of **metal** or **fibre-reinforced composite** and is placed into a **prepared root canal** of a **natural tooth**. **Together with a core**, it provides **retention** (and some resistance form) for a **definitive coronal restoration** (e.g., crown). **Posts** may also support **attachment systems** and serve as a foundation for **overdenture post–copings** where indicated.  A post is typically made of **metal** or **fibre-reinforced composite** and is placed into a **prepared root canal** of a **natural tooth**. Together with a core, it provides **retention** (and some resistance form) for a **definitive coronal restoration** (e.g., crown). Posts may also support **attachment systems** and serve as a foundation for **overdenture post–copings** where indicated. Labelled diagram of a pre-fabricated post and core restoration in a natural tooth. The diagram shows a cross-section with labels pointing to: Crown (restoration on top), Gingiva (gum line), Bone (surrounding alveolar bone), Periodontal ligament (PDL) (between root and bone), Root (dentine) (tooth structure), Gutta-percha (root canal filling material below the post head), Post (vertical component inside root canal), Post head (top part of post above gingival level), and Core (filling material around post in crown area). The caption 'Pre-fabricated' is below the image. **What is Post and Core Restorations** Core (Definition & Role) A core is a **foundation restoration** that replaces missing coronal tooth structure. It **rebuilds coronal anatomy** to support the definitive restoration (e.g., crown/onlay) and helps establish **proper form**, **contour**, and **occlusion**. A core may be placed in **vital or endodontically treated teeth** and should provide **adequate retention** and **resistance form**, while preserving remaining tooth structure.  A core is a **foundation restoration** that replaces missing coronal tooth structure. It **rebuilds coronal anatomy** to support the definitive restoration (e.g., crown/onlay) and helps establish **proper form**, **contour**, and **occlusion**. A core may be placed in **vital or endodontically treated teeth** and should provide **adequate retention** and **resistance form**, while preserving remaining tooth structure. Labelled diagram of a 'Cast post and core' restoration. The image displays a cross-section of a tooth with the root embedded in bone (indicated by stippling). A dark central element represents the root canal filling, surrounded by a light grey structure labeled 'Cast post-core'. To the right, curly braces annotate the upper portion as 'Core' and the lower intraradicular portion as 'Post', visually correlating with the text definitions of foundation restoration and retention. The University of Western Australia **Treatment planning process** Findings from clinical and **r**adiographic assessment | Is the tooth predictably restorable? | | :--- | | **Yes** | No: <br> Arrangements should be made for extraction and **p**rosthetic replacement | | | **No** | | **Does the existing root canal treatment need to be revised prior to definitive restoration?** | | **Yes** | **No** | | | Either undertake in primary care, or consider referral to specialist endodontist | | | **Is the form of the existing tooth/restoration desirable for the definitive restoration?** | | | **Yes** | **No** | | | Take sectional silicone impression to create stent for manufacture of temporary crown (as required) | Diagnostic build-up either: <br> **directly** (**c**omposite added to tooth/ restoration to optimise form, then, as required, take sectional silicone impression f**o**r use as stent for manufacture of temporary crown), or <br> **indirectly** (laboratory made diagnostic wax-up) | | **Is a crown required?** <br> See section 2 | **No** | | **Yes** | Consider the use of minimally invasive techniques (see Paper 1) | | **Is a post required?** <br> See section 3 | | | **R. J. R. Smith et al**  #### Treatment Planning Process Findings from clinical and radiographic assessment determine the restorative path. 1. **Is the tooth predictably restorable?** - **No:** Arrangements should be made for extraction and prosthetic replacement. - **Yes:** Proceed to endodontic evaluation. 2. **Does the existing root canal treatment need to be revised?** - **Yes:** Undertake in primary care or refer to a specialist endodontist. - **No:** Proceed to form assessment. 3. **Is the form of the existing tooth/restoration desirable?** - **Yes:** Take sectional silicone impression for temporary crown stent. - **No:** Perform diagnostic build-up (direct composite or indirect laboratory wax-up) then take impression. 4. **Is a crown required?** - **No:** Consider minimally invasive techniques. - **Yes:** Determine if a post is required. Flowchart diagram illustrating the 'Treatment planning process'. The chart begins with a grey box labeled 'Findings from clinical and radiographic assessment' and proceeds downwards through a series of decision nodes and action boxes. Key steps include determining if the tooth is restorable, assessing the need for root canal revision, deciding on diagnostic build-up methods (directly or indirectly), evaluating crown requirements, and determining post needs. Arrows indicate the logical flow between these procedural steps. **Fundamental Concepts – Prognosis** • Properly treated, root-filled teeth can function long-term and serve as abutments • Restoration usually fails before the endodontic treatment fails • Survival is driven mainly by remaining tooth structure, presence of cuspal coverage, ferrule, occlusal loading and quality of restoration      - Properly treated, root-filled teeth can function long-term and serve as abutments. - Restoration usually fails before the endodontic treatment fails. - Survival is driven mainly by remaining tooth structure, presence of cuspal coverage, ferrule, occlusal loading, and quality of restoration. Periapical radiograph showing three mandibular incisors with root canal treatments. The central tooth exhibits a well-condensed root filling and intact periodontal ligament space, consistent with the text stating properly treated teeth can function long-term. Clinical photograph (labeled 'a') of posterior teeth demonstrating a failing restoration on the first molar. This visual supports the text point that restorations usually fail before endodontic treatment fails. Close-up clinical photograph (labeled 'b') of a tooth section revealing a large cavity preparation and compromised remaining tooth structure, illustrating factors affecting survival like remaining tooth structure. Clinical photograph (labeled 'c') showing a posterior tooth with significant structural loss and an open carious lesion, highlighting the importance of cuspal coverage and ferrule for prognosis. Periapical radiograph (labeled 'd') showing a molar with a root canal filling and a large radiopaque restoration, likely illustrating occlusal loading or quality of restoration factors mentioned in the text. **Endodontic Readiness – Biological Criteria** Before definitive restoration, confirm: • Adequate root canal filling and apical seal • No sinus tract, exudate or persistent swelling • No tenderness to percussion or palpation • Radiographic healing or stability of periapical area • No unresolved procedural errors compromising prognosis **THE UNIVERSITY OF WESTERN AUSTRALIA**  Before definitive restoration, confirm: - Adequate root canal filling and apical seal - No sinus tract, exudate, or persistent swelling - No tenderness to percussion or palpation - Radiographic healing or stability of periapical area - No unresolved procedural errors compromising prognosis Clinical radiograph (X-ray) of three posterior teeth demonstrating endodontic treatment. The central tooth shows a completed root canal filling with gutta-percha material extending to the apex, illustrating the 'Adequate root canal filling and apical seal' criterion mentioned in the text. **Periodontal & Structural Readiness** THE UNIVERSITY OF WESTERN AUSTRALIA * Evaluate periodontal support and crown-to-root ratio * Check for mobility and furcation involvement * Assess presence and height of potential ferrule * Consider need for crown lengthening or orthodontic extrusion * Decide early if the tooth is restorable or if extraction/implant is preferable **1A** **1B** Cusp tip CEJ Apex Apex AC    - Evaluate periodontal support and crown-to-root ratio - Check for mobility and furcation involvement - Assess presence and height of potential ferrule - Consider need for crown lengthening or orthodontic extrusion - Decide early if the tooth is restorable or if extraction/implant is preferable Clinical photograph showing two views of a molar tooth. Image (a) shows the clinical appearance of the tooth with visible gingival recession and exposed root surface. Image (b) shows the same tooth with a probe inserted into the periodontal sulcus to measure pocket depth or assess attachment loss. Composite figure demonstrating periodontal and structural assessment. Panel (a) is an intraoral photo of a fractured tooth with a green arrow pointing to the fracture line and blue arrows indicating furcation involvement. Panel (b) is a periapical radiograph showing the tooth structure with blue arrows highlighting furcation involvement and yellow arrows pointing to periapical pathology at the apex. Comparative radiographs labeled 1A and 1B showing crown-to-root ratio measurements. Both images show a molar tooth with labeled anatomical landmarks: Cusp tip, CEJ (Cemento-Enamel Junction), AC (Alveolar Crest), and Apex. Measurements are provided in millimeters for each landmark distance, illustrating the evaluation of periodontal support and structural integrity as mentioned in the slide title 'Periodontal & Structural Readiness'. **Role of Tooth Type and Position** * Anterior teeth: often less axial load, but high esthetic and guidance demands * Premolars: small cross-section, susceptible to fracture, especially maxillary premolars * Molars: larger roots and pulp chambers, often restored without posts using chamber retention * Teeth serving as abutments (FDP, RPD) face higher functional demands </img>  - **Anterior teeth:** Often less axial load, but high esthetic and guidance demands. - **Premolars:** Small cross-section, susceptible to fracture, especially maxillary premolars. - **Molars:** Larger roots and pulp chambers, often restored without posts using chamber retention. - **Abutments:** Teeth serving as abutments (FDP, RPD) face higher functional demands. University of Western Australia logo (visual element). The slide content is text-only and does not contain any diagrams, charts, or figures. # Remaining Tooth Structure – Key Predictor **MOST** The University of **WESTERN** **AUSTRALIA** • Height, thickness and number of residual walls strongly influence survival • Studies show that teeth with substantial dentin height perform significantly better, independent of post type or crown material • Once remaining wall height is <2 mm, failure risk increases steeply     - Height, thickness, and number of residual walls strongly influence survival. - Studies show that teeth with substantial dentin height perform significantly better, independent of post type or crown material. - Once remaining wall height is <2 mm, failure risk increases steeply. Clinical photo of a tooth with minimal remaining coronal structure, illustrating the concept of low residual wall height mentioned in the text. Clinical photo showing a molar with significant caries and loss of tooth structure, demonstrating substantial dentin height or lack thereof depending on interpretation. Clinical photo of a prepared tooth root showing the extent of remaining dentin walls, relevant to assessing structural integrity for restoration. Photo of extracted teeth or models showing cross-sections of roots, likely used to demonstrate measurement of residual wall height. # Peri-cervical Dentin – Why It Matters **THE UNIVERSITY OF WESTERN AUSTRALIA** ## Peri-cervical Dentin: A Critical Stress-Bearing Zone * The peri-cervical dentin (~4 mm above and 4 mm below the crestal bone) is key for resisting **bending and shear forces**. * **Over-flaring** and aggressive preparation in this region markedly reduce fracture resistance. * When preparing post space, **remove only what is necessary**—avoid unnecessary enlargement that sacrifices peri-cervical dentin.   #### Critical Stress-Bearing Zone - The peri-cervical dentin (~4 mm above and 4 mm below the crestal bone) is key for resisting **bending and shear forces**. - **Over-flaring** and aggressive preparation in this region markedly reduce fracture resistance. - When preparing post space, **remove only what is necessary**—avoid unnecessary enlargement that sacrifices peri-cervical dentin. Vertical anatomical diagram of a tooth showing the root canal space. The image labels three specific zones: 'Cervical', 'Middle', and 'Apical'. This visual demonstrates the location of the peri-cervical dentin (the cervical zone) which is described in the text as a critical stress-bearing area. Comparative figure illustrating two dental post preparations labeled 'A' and 'B'. Diagram A shows a wider preparation with dimensions '1.5mm' at the top and '2.0 mm' width indicated by brackets. Diagram B shows a narrower preparation with '0.5mm' at the top and '10mm' depth indicated on both sides. These visuals demonstrate the concept of over-flaring versus conservative preparation discussed in the text. **Mechanical Properties of Tooth Structure After Root Canal Treatment** - Common belief: endodontically treated teeth are weaker because dentin becomes ‘brittle’. - Many experimental studies show minimal change in dentin hardness/elastic modulus after RCT and dehydration. - Clinically, fracture risk rises mainly due to tooth structure loss (caries, restorations, access) and altered load paths. - Therefore: treat ETT as structurally compromised and restore to protect remaining dentin. - Common belief: endodontically treated teeth are weaker because dentin becomes ‘brittle’. - Many experimental studies show minimal change in dentin hardness/elastic modulus after RCT and dehydration. - Clinically, fracture risk rises mainly due to tooth structure loss (caries, restorations, access) and altered load paths. - **Conclusion:** Treat ETT as structurally compromised and restore to protect remaining dentin. **Why Dentin Properties Vary (Even Without RCT)** The University of Western Australia • Dentin is not uniform: tubule density and orientation (crown, cervical or root) affecting stiffness and toughness. • Age and sclerosis change dentin behaviour (often more mineralised and less compliant in some regions). • Moisture influences toughness; dehydration can reduce toughness, but impact is usually secondary to structural loss. • Procedures (instrumentation, irrigants, post preparation) can affect surfaces—preserve dentin and minimise over-preparation.  #### Variations in Dentin Behavior - **Non-uniformity:** Tubule density and orientation (crown, cervical, or root) affect stiffness and toughness. - **Age and Sclerosis:** Changes dentin behavior; it is often more mineralized and less compliant in some regions. - **Moisture:** Dehydration can reduce toughness, but the impact is usually secondary to structural loss. - **Procedural Impact:** Instrumentation, irrigants, and post preparation can affect surfaces; preserve dentin and minimize over-preparation. Composite diagram illustrating dentin structure and micro-architecture. Left panel shows a schematic cross-section of a tooth with labeled regions: enamel (top), dentin (yellow layer), pulp chamber (red area), and tubules radiating through the dentin. Right section contains four labeled panels (A–D) showing microscopic views: A depicts the dentino-enamel junction (DEJ); B shows deep dentin near the pulpal cavity; C illustrates Type I collagen fibrils; D displays hydroxyapatite crystals. All elements are consistent with the text discussing tubule density, orientation, and structural variation in dentin. **The Main Biomechanical Problem After Root Canal Treatment** THE UNIVERSITY OF WESTERN AUSTRALIA **Tooth Structural Loss is the Main Biomechanical Problem** * Major contributors: caries + existing restorations + access cavity + loss of marginal ridges/cusps. * Thin cusps and walls become stress concentrators $\rightarrow$ cracks initiate and propagate. * Goal of coronal restoration: redistribute forces and protect weakened tooth structure. * **Box 1 (Top):** Tooth tissue loss * Access + caries * + restorations * **Box 2 (Middle):** Stress concentration * Thin walls/cusps * marginal ridges * **Box 3 (Bottom):** Cracks / fracture * Catastrophic failure * or repairable  #### Biomechanical Progression of Failure 1. **Tooth Tissue Loss:** Caused by access cavity, caries, and existing restorations. 2. **Stress Concentration:** Resulting from thin walls, thin cusps, and loss of marginal ridges. 3. **Cracks / Fracture:** Leads to either repairable or catastrophic failure. **Goal of coronal restoration:** Redistribute forces and protect weakened tooth structure. A vertical flowchart diagram illustrating the progression of tooth structural failure. It consists of three stacked blue rounded rectangles connected by implied sequence. The top box is labeled 'Tooth tissue loss' with details 'Access + caries + restorations'. The middle box is labeled 'Stress concentration' with details 'Thin walls/cusps marginal ridges'. The bottom box is labeled 'Cracks / fracture' with outcomes 'Catastrophic failure or repairable'. # **Biomechanical Principles** ## **Predictors of Survival: Peri-cervical Dentin, Residual Walls & Ferrule:** * **Preserve peri-cervical dentin (~4 mm above and below the bone crest):** critical for resisting bending and shear. * **Remaining wall height/thickness/number** strongly predict survival — often independent of post type. * When remaining wall height is <2 mm, failure risk rises steeply. * **A circumferential ferrule** (often ~1.5–2 mm) improves fracture resistance and reduces catastrophic failures.  #### Predictors of Survival - **Preserve peri-cervical dentin:** Critical for resisting bending and shear (~4 mm above and below bone crest). - **Residual Walls:** Height, thickness, and number strongly predict survival, often independent of post type. - **Critical Threshold:** When remaining wall height is <2 mm, failure risk rises steeply. - **Ferrule:** A circumferential ferrule (~1.5–2 mm) improves fracture resistance and reduces catastrophic failures. University logo of The University of Western Australia featuring a shield with a swan and text. **Biomechanical Principles** **Stress Distribution:** * Finite element/photoelastic studies: cervical dentin often carries the highest stress under vertical loading. * Posts may shift some stress apically under vertical load; under oblique load they may not reduce overall stress and can increase apical stress. * Key principle: posts retain the core — they do not automatically ‘strengthen’ roots. * Prioritise ferrule, conservative post preparation, and occlusal risk management.   #### Stress Distribution and Post Function - **Cervical Dentin:** Often carries the highest stress under vertical loading according to finite element studies. - **Post Mechanics:** Posts may shift some stress apically under vertical load; under oblique load, they may increase apical stress rather than reducing overall stress. - **Key Principle:** Posts retain the core—they do not automatically ‘strengthen’ roots. - **Priorities:** Focus on ferrule, conservative post preparation, and occlusal risk management. Top row of Finite Element Analysis (FEA) stress distribution diagrams showing cervical tooth models under vertical loading. The image displays six variations labeled A through F: 'No Ferrule (NiCr)', 'No Ferrule (PEEK)', 'Buccal Ferrule', 'Lingual Ferrule', 'Buccolingual Ferrule', and 'Full Ferrule'. Each model includes a color-coded stress scale on the left, with blue indicating lower stress levels across all configurations. Bottom row of FEA stress distribution diagrams comparing two post materials ('No Ferrule PEEK' and 'No Ferrule NiCr') under oblique load conditions. These images highlight increased stress concentration in the apical region for both materials, as indicated by red/orange coloring near the root tip. Color scales are provided for reference. # FERRULE **General definition:** a ring or cap, typically a metal one, which strengthens the end of a handle, stick, or tube and prevents it from splitting or wearing Ferraletn  #### General Definition A ferrule is a ring or cap, typically metal, which strengthens the end of a handle, stick, or tube and prevents it from splitting or wearing. Visual demonstration of a ferrule's function. The image displays four panels: (1) A photograph of a wooden handle with a metal cap (ferrule) at the end; (2) A cartoon hammer striking a chisel held in wood without reinforcement, causing it to split ('CRAC'); (3) A cartoon hammer striking a reinforced handle where a tooth character holds the tool, preventing splitting; (4) A cartoon hammer striking a fully reinforced handle, showing successful use. This illustrates the definition provided in the text: 'a ring or cap... which strengthens the end of a handle... and prevents it from splitting'. **FERRULE** Parallel walls of dentin extending coronally from the crown margin provide ferrule Ferrule effect: a 360 metal collar of the crown surrounding the parallel walls of the dentine extending coronal to the shoulder of the preparation. Resistance form ↑ Stress within the tooth = TOOTH PROTECTION ↓ **Crown** **Core** **FERRULE** **Post** **Gutta-percha** **No Ferrule** JOE. Juloski et al. 2012 THE UNIVERSITY OF WESTERN AUSTRALIA | Oral Health Centre of Western Australia   #### The Ferrule Effect - **Definition:** A 360-degree metal collar of the crown surrounding the parallel walls of the dentine extending coronal to the shoulder of the preparation. - **Mechanical Benefit:** Increases resistance form and decreases stress within the tooth (Tooth Protection). - **Components:** Parallel walls of dentin extending coronally from the crown margin provide the ferrule. Labelled diagram of a tooth preparation showing the 'Ferrule' effect. The image displays a cross-section of a tooth with a crown and core, illustrating parallel walls of dentin extending coronally from the crown margin. Labels point to the Crown, Core, Ferrule (indicated by a bracket), Post, and Gutta-percha. An arrow points downwards indicating increased Resistance form and decreased Stress within the tooth. Diagram labeled 'No Ferrule' for comparison. It shows a tooth preparation where the metal collar does not surround the parallel walls of the dentine, demonstrating the absence of the ferrule effect compared to the main diagram. FERRULE Height * Minimum amount of ferrule: 1.5 – 2 mm * Determined by the amount of sound tooth structure above the gingival margin * At least 4 – 5 mm of tooth structure coronal to the bone crest (2 – 3 mm of biological width) The greater the height of remaining tooth structure above the margin of the preparation, the better fracture resistance provided Akkayan B 2014 JOE. Juloski et al. 2012, Jotkowitz et al. 2010  #### Ferrule Height Requirements - **Minimum Height:** 1.5 – 2 mm of sound tooth structure above the gingival margin. - **Biological Width:** Requires at least 4 – 5 mm of tooth structure coronal to the bone crest (accounting for 2 – 3 mm of biological width). - **Fracture Resistance:** The greater the height of remaining tooth structure above the preparation margin, the better the fracture resistance. Anatomical cross-section diagram of a tooth and surrounding bone illustrating the concept of a dental ferrule. The image shows the periodontal ligament space (yellow), alveolar bone (pinkish-brown with dark resorption spots), gingiva (pink), and tooth structure (orange/yellow). Two callouts with arrows indicate specific vertical measurements: '4 – 5 mm' pointing to the total height from the bone crest to the preparation margin, and '1.5 – 2 mm' pointing to the minimal ferrule height above the margin. **FERRULE** **Width** - Minimal thickness of remaining dentine: 1 - 2 mm - The axial reduction of the crown preparation and the width of the post preparation with determine the ferrule width (dentin thickness) Jotkowitz et al. 2010  #### Ferrule Width Requirements - **Minimum Thickness:** 1 – 2 mm of remaining dentine. - **Determining Factors:** Ferrule width (dentin thickness) is determined by the axial reduction of the crown preparation and the width of the post preparation. Labelled diagram of a dental tooth preparation showing the ferrule effect. The image displays a cross-section of a tooth with a crown and post structure. A callout arrow points to the remaining dentin thickness at the base of the preparation, labeled '1 - 2 mm'. The diagram illustrates the relationship between the axial reduction of the crown preparation, the width of the post preparation, and the resulting ferrule width (dentin thickness). # RULE **Location** * Circumferential ferrule is the ideal * This may not be possible due to: * - Caries * - Erosion and abrasion (more common on buccal wall) * - Over-reduction during tooth preparation An incomplete ferrule is a better option than a complete lack of ferrule Jotkowitz et al. 2010 #### Circumferential Requirements - **Ideal State:** A circumferential (360-degree) ferrule is the ideal. - **Barriers to Ideal Ferrule:** - Caries - Erosion and abrasion (common on buccal walls) - Over-reduction during tooth preparation - **Clinical Rule:** An incomplete ferrule is a better option than a complete lack of ferrule. FERRULE Location * Partial ferrule **Influence of remaining coronal tooth structure location on the fracture resistance of restored endodontically treated anterior teeth** Clarisse C. H. Ng, BDSc,$^a$ Herman B. Dumbrigue, DDM,$^b$ Manal I. Al-Bayat, BDS,$^c$ Jason A. Griggs, PhD,$^d$ and Charles W. Wakefield, DDS$^e$ **RESULTS**: - The location of the ferrule is important for the fracture resistance - **Maxillary incisors:** the palatal ferrule is the most important to provide longevity for the restoration  #### Partial Ferrule and Location Importance - The location of the ferrule is critical for fracture resistance. - **Maxillary Incisors:** The palatal ferrule is the most important for providing longevity to the restoration. A labeled diagram illustrating five different types of ferrule locations on a tooth cross-section. The visual shows a central black circle representing the tooth pulp, surrounded by concentric circles representing tooth structure and a restoration margin. Each panel is labeled below: 'Complete' (full circumferential ring), 'Palatal' (ferrule on the palatal side only), 'Labial' (ferrule on the labial side only), 'Proximal' (ferrule on the proximal side only), and 'Level' (no ferrule, just a flat margin). This figure demonstrates how varying the location of remaining coronal tooth structure affects the design. # **FERRULE** Providing an adequate ferrule lowers the impact of the post and core system, luting agents, and the final restoration on tooth performance Providing an adequate ferrule lowers the impact of the post and core system, luting agents, and the final restoration on tooth performance. What should you do when there is no tooth structure to create a ferrule? - Check the restorability of the tooth **If yes** Your need to expose tooth structure above the gingival margin - Crown lengthening – surgical procedure - Orthodontic extrusion  #### Strategies for Inadequate Structure If a tooth is deemed restorable but lacks structure for a ferrule, you must expose tooth structure above the gingival margin via: - **Crown lengthening:** A surgical procedure. - **Orthodontic extrusion.** A slide from a dental lecture at The University of Western Australia titled 'What should you do when there is no tooth structure to create a ferrule?'. It outlines a clinical decision-making process for restorability: first check if the tooth is restorable; if yes, expose tooth structure above the gingival margin via either 'Crown lengthening – surgical procedure' or 'Orthodontic extrusion'. What should you do when there is no tooth structure to create a ferrule? - A) No Ferrule - B) Crown lengthening – surgical procedure - C) Orthodontic extrusion **Crown lengthening vs Ortho extrusion** - Both reduce root length - Surgical crown lengthening reduces root length (R') and increases crown length (C'). - Time and cost may limit Orthodontic extrusion Contemporary Fixed Prosthodontics 4th ed  #### Comparison of Clinical Options 1. **No Ferrule** 2. **Crown Lengthening (Surgical):** Reduces root length (R') and increases crown length (C'). 3. **Orthodontic Extrusion:** Also reduces root length; may be limited by time and cost. Labelled diagram comparing three tooth treatment scenarios (A, B, C) with annotations for crown length (C/C') and root length (R/R'). Panel A shows initial state. Panel B illustrates surgical crown lengthening reducing root length to R' and increasing crown length to C'. Panel C shows orthodontic extrusion maintaining original crown length C but reducing exposed root length to R'. Diagrams include cross-sections of teeth within bone blocks. # OTHER FACTORS THAT AFFECT THE FERRULE * *Type of tooth and the extent of lateral load* ### Posteriors vs Anterior teeth | Anterior teeth | Postieror teeth | | :--- | :--- | | Deep bite | Group function | | Parafuntion | High cusps | | Dietary habits | | **MORE FERRULE** * Different sizes and direction of load Anterior: oblique forces Posterios: vertical forces along the axis > Non-desirable forces intronuced by the restoration (interferences, inadequate occlusal design) is probably more important for survival of structurally compromised endodontic treated teeth than is the post and core system Jotkowitz et al. 2010  #### Occlusal Loading by Tooth Type - **Anterior Teeth:** Subject to oblique forces; factors include deep bite and parafunction. - **Posterior Teeth:** Subject to vertical forces along the axis; factors include group function and high cusps. **Clinical Note:** Non-desirable forces (interferences, inadequate occlusal design) are likely more important for the survival of structurally compromised ETT than the specific post and core system used. Comparison table comparing Anterior teeth vs Posterior teeth. Columns: 'Anterior teeth' lists Deep bite, Parafuntion, Dietary habits; 'Postieror teeth' lists Group function, High cusps. Below the table is text 'MORE FERRULE'. # OTHER FACTORS THAT AFFECT THE FERRULE * **Type of post** **Different types available** Pre-fabricated | Cast post and core :--- Materials Mechanical properties Technique Cementation * No universal recommendations have been established. * **New literature seems to favor** bonded fiber reinforced post (pre-fabricated) as opposed to metal post (cast post and core). * Main reason is related to catastrophic failures. * *More favorable failure pattern* * *Less root fracture* * *Tooth fracture occur more occlusally* ### CAREFUL INTERPRETATION > **1.5-2 mm ferrule in sound tooth structure is more important in fracture resistance than the post design or type** Jotkowitz et al. 2010 THE UNIVERSITY OF **WESTERN AUSTRALIA** Oral Health Centre of Western Australia  #### Post Selection Considerations - **Types:** Pre-fabricated vs. Cast post and core. - **Current Trends:** Literature favors bonded fiber-reinforced posts (pre-fabricated) over metal posts due to more favorable failure patterns (less root fracture, more occlusal fractures). - **Critical Hierarchy:** A 1.5-2 mm ferrule in sound tooth structure is more important for fracture resistance than the specific post design or type. A schematic diagram illustrating the comparison between 'Pre-fabricated' and 'Cast post and core' types. The visual structure uses a bracketed list format with two columns: the left column lists 'Materials', 'Mechanical properties', 'Technique', and 'Cementation'; the right column contains corresponding explanatory text regarding catastrophic failures, favorable failure patterns, reduced root fracture, and occlusal tooth fractures. # OTHER FACTORS THAT AFFECT THE FERRULE ## Core materials (for pre-fabricated post) ### Amalgam: - **Advantage:** good for posterior teeth due to high compression strength - **Disadvantage:** - does not bond to tooth structure - require retentive features (undercuts) that may weaken the remaining walls ### Composite: - **Advantage:** bond to tooth structure (dentin bonding is less reliable), the modulus of elasticity more similar to dentin - **Disadvantage:** weak composite/tooth interface (technique sensitive) may compromise the final restoration **Controversy :** composite may reinforce residual tooth structure as it is bonded restoration Bryant et al 1986, Jotkowitz et al. 2010 #### Core Materials for Pre-fabricated Posts - **Amalgam:** - **Advantage:** High compressive strength; good for posterior teeth. - **Disadvantage:** No chemical bond; requires retentive undercuts that may weaken walls. - **Composite:** - **Advantage:** Bonds to tooth structure; modulus of elasticity similar to dentin; may reinforce residual structure. - **Disadvantage:** Technique sensitive; weak composite/tooth interface can compromise the restoration. **THE UNIVERSITY OF WESTERN AUSTRALIA | Oral Health Centre of Western Australia** *OTHER FACTORS THAT AFFECT THE FERRULE* * Core materials (for pre-fabricated post) * Amalgam * Composite * GIC: **block out undercuts** in the vertical walls (away from margins)   - **Amalgam and Composite:** Primary materials for pre-fabricated post cores. - **Glass Ionomer Cement (GIC):** Used to block out undercuts in vertical walls (away from margins). Clinical intraoral photograph showing a row of teeth with pre-fabricated metal posts and cores. The image demonstrates the placement of core materials (likely amalgam or composite) in the root canals to support a crown, illustrating the context for ferrule formation. Clinical intraoral photograph showing a red 'X' over a set of prepared teeth. This visual serves as a warning or negative example, likely indicating an incorrect preparation technique or poor ferrule design that compromises the restoration's retention. --- **An amalgam coronal-radicular dowel and core technique for endodontically treated posterior teeth** Arun Nayyar, B.D.S., D.M.D., M.S.,* Richard E. Walton, D.M.D., M.S.,** and Leon A. Leonard, D.D.S., M.S.*** Medical College of Georgia School of Dentistry, Augusta, Ga. --- **TECHNIQUE** - Remove the GP from the pulp chamber and 2 to 4 mm from the canal - Leave undercuts and divergence of canals - Remove unsupported tooth structures - Place matrix band - Condense the amalgam into the cavity starting from the root canal - Restore the tooth anatomy - Next session, crown preparation --- The natural divergence of the canals and the undercuts in the pulp chamber provide extra retention to the core. Natural coronal structure is still necessary for resistance form and ferrule effect   #### Amalgam Coronal-Radicular Technique 1. Remove Gutta-percha (GP) from the pulp chamber and 2 to 4 mm into the canal. 2. Maintain natural divergence of canals and undercuts in the pulp chamber for extra retention. 3. Remove unsupported tooth structures. 4. Place matrix band. 5. Condense amalgam into the cavity, starting from the root canal. 6. Restore tooth anatomy. 7. Proceed to crown preparation in the next session. **Note:** Natural coronal structure remains necessary for resistance form and the ferrule effect. A three-panel labeled diagram illustrating the 'amalgam coronal-radicular dowel and core technique'. It shows a cross-section of a tooth in three stages: Panel A displays an initial preparation with gutta percha; Panel B shows the removal of material leaving canals with divergence and undercuts; Panel C depicts the final restoration with amalgam filling the pulp chamber and root canal. A legend identifies Gold, Amalgam, and Gutta Percha. A clinical radiograph (X-ray) showing a posterior molar tooth restored with the described amalgam coronal-radicular dowel and core technique. The image visualizes the amalgam filling extending into the root canal space. # REFERENCES * Barnes, J., Patel, S. Contemporary endodontics – part 1. Br Dent J 211, 463–468 * Torabinejab and Walton. Endodontic Principles and Practice 4^th ed. * Sjbgren et al. Factors Affecting the Long-term Results of Endodontic Treatment. Journal Of Endodontics. 16 (10) 1990 * Rosenstiel et al. Contemporary Fixed Prosthodontics 4th ed * Heifer et al. Determination of the moisture content of vital and pulpless teeth Oral Surg Oral Med Oral Pathol. 1972 Oct;34(4):661-70 * Papa et al Moisture content of vital vs endodontically treated teeth. Endod Dent Traumatol. 1994 Apr;10(2):91-3. * Fusayama and Maeda. Effect of pulpectomy on dentin hardnessJ Dent Res. 1969 * Randow K, Glantz PO. On cantilever loading of vital and non-vital teeth. An experimental clinical study. Acta Odontol Scand 1986;44:271–7 * Lewinstein and Grajower Root dentin hardness of endodontically treated teeth JOURNAL OF ENDODONTICS I VOL 7, NO 9, SEPTEMBER 1981 * Huang et al. Effects of Mo. isture Content and Endodontic Treatment on Some Mechanical Properties of Human Dentin. Journal of Endodontics. 18(5), 1992. * Sedgley et al. Are Endodontically Treated Teeth more Brittle? Journal of Endodontics 18(7),1992 * Gutmann The dentin-root complex: Anatomic and biologic considerations in restoring endodontically treated teeth. J PROSTHET DENT 1992;67:468-67 * Glossary of Prosthodontic Terms 4^th ed * Goodacre et al. The Prosthodontic Management of Endodontically Treated Teeth: A Literature Review. Part I. Success and Failure Data, Treatment Concepts. J Prosthod 1994;3:243-250. * Tang et al. Identifying and Reducing Risks for Potential Fractures in Endodontically Treated Teeth. JOE — Volume 36, Number 4, April 2010 * Ko et al. Effects of post on dentin stress distribution in pulpless teeth J Prostret Dent 1992 * Juloski et al. Ferrule Effect: A Literature Review. Journal of Endodontics 38 (1)2012 (11-19) * Akkayan B. An in vitro study evaluating the effect of ferrule length on fracture resistance of endodonti- cally treated teeth restored with fiber-reinforced and zirconia dowel systems. J Prosthet Dent 2004; 92: 155-162. * Jotkowitz et al. Rethinking ferrule – a new approach to an old dilemma. British Dental Journal 2010; 209: 25–33 * Bryant et al. Modulus of elasticity in bending of composites and amalgams. Journal Of Prosthetic Dentistry 1986 * Ng et al Influence of remaining coronal tooth structure location on the fractureresistance of restored endodontically treated anterior teeth J Prosthet Dent 2006;95:290-6. * Nayyar et al. An amalgam coronal-radicular dowel and core technique for endodontically treated posterior teeth JOURNAL OF PROSTHETIC DENTISTRY 1980 - Akkayan B. An in vitro study evaluating the effect of ferrule length on fracture resistance of endodontically treated teeth restored with fiber-reinforced and zirconia dowel systems. J Prosthet Dent 2004; 92: 155-162. - Barnes, J., Patel, S. Contemporary endodontics – part 1. Br Dent J 211, 463–468 - Bryant et al. Modulus of elasticity in bending of composites and amalgams. Journal Of Prosthetic Dentistry 1986 - Fusayama and Maeda. Effect of pulpectomy on dentin hardness J Dent Res. 1969 - Glossary of Prosthodontic Terms 4th ed - Goodacre et al. The Prosthodontic Management of Endodontically Treated Teeth: A Literature Review. Part I. Success and Failure Data, Treatment Concepts. J Prosthod 1994;3:243-250. - Gutmann The dentin-root complex: Anatomic and biologic considerations in restoring endodontically treated teeth. J PROSTHET DENT 1992;67:468-67 - Heifer et al. Determination of the moisture content of vital and pulpless teeth Oral Surg Oral Med Oral Pathol. 1972 Oct;34(4):661-70 - Huang et al. Effects of Moisture Content and Endodontic Treatment on Some Mechanical Properties of Human Dentin. Journal of Endodontics. 18(5), 1992. - Jotkowitz et al. Rethinking ferrule – a new approach to an old dilemma. British Dental Journal 2010; 209: 25–33 - Juloski et al. Ferrule Effect: A Literature Review. Journal of Endodontics 38 (1) 2012 (11-19) - Ko et al. Effects of post on dentin stress distribution in pulpless teeth J Prosthet Dent 1992 - Lewinstein and Grajower Root dentin hardness of endodontically treated teeth JOURNAL OF ENDODONTICS VOL 7, NO 9, SEPTEMBER 1981 - Nayyar et al. An amalgam coronal-radicular dowel and core technique for endodontically treated posterior teeth JOURNAL OF PROSTHETIC DENTISTRY 1980 - Ng et al Influence of remaining coronal tooth structure location on the fracture resistance of restored endodontically treated anterior teeth J Prosthet Dent 2006;95:290-6. - Papa et al Moisture content of vital vs endodontically treated teeth. Endod Dent Traumatol. 1994 Apr;10(2):91-3. - Randow K, Glantz PO. On cantilever loading of vital and non-vital teeth. An experimental clinical study. Acta Odontol Scand 1986;44:271–7 - Rosenstiel et al. Contemporary Fixed Prosthodontics 4th ed - Sedgley et al. Are Endodontically Treated Teeth more Brittle? Journal of Endodontics 18(7), 1992 - Sjogren et al. Factors Affecting the Long-term Results of Endodontic Treatment. Journal Of Endodontics. 16 (10) 1990 - Tang et al. Identifying and Reducing Risks for Potential Fractures in Endodontically Treated Teeth. JOE — Volume 36, Number 4, April 2010 - Torabinejab and Walton. Endodontic Principles and Practice 4th ed. 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