Quartz 4

L5 Digital Approach to RETT

9 min read

Restoration of Endodontically Treated Teeth12

Dr. Marrwa Ibrahim

Learning Outcomes3

By the end of this lecture, you should be able to:

  1. Identify drawback and limitation of traditional techniques for post and core fabrication
  2. Understand CAD/CAM workflows
  • Understand the full CAD/CAM workflow, including both semi-digital and fully digital approaches.
  1. Compare the digital approach with the traditional technique
  • Critically compare digital and conventional techniques regarding accuracy, efficiency, and outcomes.
  1. Apply clinical decision-making

Traditional Post and Core Techniques

Purpose of Post and Core

A post and core is required when there is excessive loss of coronal tooth structure following endodontic treatment. The post provides retention for the core, while the core replaces lost tooth structure and supports the final crown. Posts do not reinforce the tooth and may increase fracture risk if poorly designed.

Classification of Post and Core Systems4

  • Customized post and cores
    • These adapt better to irregular canals and are easier to remove during potential retreatment.
  • Prefabricated posts
    • These are simple to use but less adaptable to the canal.

Fabrication Techniques

  • Direct technique: Utilizes a resin pattern.
    • The clinician uses auto-polymerized acrylic resin to shape a pattern directly in the tooth, which is then sent to the lab for burnout and casting. This allows the clinician to physically assess the fit on the actual tooth before casting.
  • Indirect technique: Utilizes elastomeric impressions.
    • Uses impression material to capture the canal, which is replaced by gypsum in the laboratory, crafted into a wax pattern, and cast into a metal alloy.

The choice of technique relies on factors such as the tooth’s condition, the patient’s oral health, and the clinician’s proficiency.

Drawbacks and Limitations of Traditional Methods5

Traditional techniques for post and core fabrication are subject to several constraints:

  • Shrinkage
  • Distortion
  • Human error
  • Lab variability
  • Multiple visits
  • Technique sensitivity
  • Material mismatch

Introduction to Digital Dentistry and CAD/CAM6

Digital dentistry is reshaping the foundations of restorative procedures through three primary components:

  • Digital Scanning
  • CAD (Computer-Aided Design)
  • CAM (Computer-Aided Manufacturing)

Benefits of Digital Integration7

  • Improves reproducibility
  • Reduces operator dependency
  • Improves accuracy
  • Provides consistency through standardized production protocols
  • Standardization and better communication with the laboratory
  • Ability to simulate restorations before fabrication using software like Exocad or 3Shape
  • Pre-visualization, adjustment, and optimization before irreversible clinical steps

Modern dentistry integrates CAD (digital design) and CAM (manufacturing) to create a precision workflow. This digital workflow allows for the simulation and previsualization of outcomes.

  • CAD: Software modeling (e.g., Exocad, 3Shape)
  • CAM: Milling or printing systems

CAD/CAM Manufacturing Approaches

Additive Manufacturing8

Additive manufacturing, or 3D printing, builds structures layer upon layer. Each precise deposition contributes to the emergence of intricate forms.

  • Useful for complex geometries

  • Limitations: Material properties may be inferior to milled restorations in some cases

  • Efficient with high accuracy

  • Minimal waste

  • Materials used: Resin or metal printing

Subtractive Manufacturing9

Subtractive manufacturing revolves around material removal, sculpting the desired shape by chiseling away from a solid block.

  • Also known as milling

  • Excellent precision

  • Limitations: May have difficulty reproducing very fine internal geometries

  • High strength

  • Material waste

  • Materials used: Dense materials such as Zirconia or Cobalt-Chromium (Co-Cr)

Materials in CAD/CAM Restorations10

The choice of material significantly affects the fracture mode and long-term prognosis of the restoration. Common materials include:

Goal of Material Selection

The goal of material selection is to match the properties of dentin as closely as possible to reduce stress concentration and minimize fracture risk.

  • Zirconia
  • Hybrid ceramics
  • Fiber Reinforced Composite (FRC) materials

Zirconia Properties and Risks

Characteristics of Zirconia11

  • High strength
  • Aesthetic

Risks and Challenges

  • Stiffness: High stiffness carries a risk of catastrophic root fracture.
    • High elastic modulus (too stiff compared to dentin)
    • Stresses are transferred to the root, increasing the risk of catastrophic root fracture.
  • Bonding: Establishing a strong bond to acid-resistant zirconia can be challenging.
  • Retrievability: In the event of treatment failure, it may be extremely difficult to retrieve zirconia posts from root canals.

Hybrid Ceramic Materials12

Hybrid materials (such as Enamic) are created by blending ceramics with composite resin. This results in a material that combines the mechanical properties and color stability of ceramics with the elasticity and robustness of resin composites.

  • Elastic modulus close to dentin
  • Better fracture behavior
  • Improved stress distribution
  • Repairable failure patterns

Fiber Reinforced Composite Materials

Biomechanical Advantages13

  • Flexible with a modulus of elasticity closer to dentin.
  • Favorable biomechanical properties.
    • Distribute stress evenly and fail in a repairable way
  • Repairable fractures compared to the catastrophic failures associated with zirconia.

Clinical and Manufacturing Benefits

  • Excellent aesthetics.
  • Does not require sintering, reducing manufacturing time and cost.
  • Incorporation of heat-cured denture base acrylics enhances marginal strength.
    • Often considered the "gold standard" for post testing.

Digital Fabrication Workflows14

The digital workflow for fabricating post and cores follows a standard sequence:

  1. Scan: Intraoral or impression scanning.
  2. Design: CAD software modeling.
  3. Manufacture: CAM production.

Semi-Digital Indirect Workflow15

The semi-digital workflow combines traditional impressions or patterns with digital fabrication:

  • Scan: Scanning of the impression or a resin/wax pattern. Scanning the impression requires less chairside time and improves efficiency.
  • This approach is used when intraoral scanning is limited.
  • The workflow includes post space preparation, conventional impression or resin pattern, digitalization of the impression/pattern using a scanner, CAD design, CAM fabrication, and finally try-in and cementation.
  • Virtual Design: Created using Exocad or 3Shape software.
  • Fabrication: Post and core produced via milling or 3D printing.

Fully Digital Direct Workflow16

The digital workflow consists of the following steps:

  1. Post space preparation
  2. Digital impression
  3. CAD design
  4. CAM fabrication
  5. Clinical try-in and cementation

Direct Digital Process17

  • Direct Digital Impression: Using an intraoral scanner to scan the prepared post space.
  • Direct CAD Design: Utilizing Exocad or 3Shape software.
  • Fabrication: Production via milling or 3D printing.

Advantages and Limitations

  • Benefits: Reduces chairside time, simplifies laboratory procedures, and eliminates the risk of material distortion.
  • Limitations: Depending on the efficiency of the intraoral camera system, it may not be indicated for long and narrow post spaces.
  • Deep and narrow canals remain challenging to scan accurately.

CAD Design Principles and Advantages

Design Objectives18

  • Customize post length and taper
  • Optimize core contour
  • Preserve ferrule
  • Optimize post length and taper for retention.
  • Ensure proper core contour for crown support.
  • Preserve the ferrule effect for fracture resistance.

Benefits of Custom Digital Design19

  • Precise adaptation
  • Improved marginal fit
  • Reduced laboratory steps
  • Precision adaptation to canal morphology.
  • Improved retention and reduced cement thickness.
  • Reduction of laboratory steps and potential sources of error.

System Advantages20

  • Improved precision
  • Customization for specific canal morphology
  • Reduced treatment time
  • Enhanced communication with the laboratory
  • Improved precision and fit.
  • Customization to individual anatomy.
  • Better communication between clinician and technician.

Clinical Considerations and Limitations21

The implementation of digital systems involves certain constraints:

  • High cost of equipment
  • Learning curve for the clinician and staff
  • Technical limitations of the scanner
  • Evolving long-term evidence regarding clinical success rates.

CBCT Integration in Post Design

Anatomical Replication22

  • Provides 3D canal morphology.
  • Enables accurate post design.
  • CBCT allows for precise anatomical replication of the root canal.
  • Segmentation: Allows accurate extraction of canal morphology for post design, improving adaptation and reducing unnecessary dentin removal.
  • 3D Guidance: Provides controlled drill direction and depth, reducing the risk of deviation or perforation during post space preparation.

Clinical Take-Home Messages23

  • CAD/CAM represents the future of restorative dentistry.
  • Digital workflows lead to improved clinical outcomes.
  • A case-based approach is essential for selecting the appropriate technique.

Clinical Case Examples and Scanning Techniques2425

Final scan ready for CAD design

3Shape TRIOS Post & Core PVS Hybrid Scanning Technique

  • The lecture included a video demonstration of post and core design using the Three Shape system.

References26

  1. Ahmed RA, Aseri FA, Alammari AS, Asiri ZS, Al Matir FO, Al Shahrani SS, et al. CAD/CAM technologies in post and core restoration of endodontically treated teeth: current evidence, clinical applications, and interdisciplinary perspectives. J Clin Pract Med Res. 2025;1(3):178–189.

  2. Rosenstiel SF, Land MF, Fujimoto J. Restoration of the endodontically treated tooth. In: Contemporary Fixed Prosthodontics. Philadelphia: Elsevier; 2015. p. 278–280.

  3. al-Qarni FD. Customized post and cores fabricated with CAD/CAM technology: a literature review. Int J Gen Med. 2022;15:4771–4779.

  4. Abhishek G, Chakrabarty A, Kavlekar V, Singh Y, Mahajan S. Prosthetic rehabilitation of endodontically treated tooth by using CAD-CAM milled zirconia post and core system: a clinical report. Int J Sci Healthc Res. 2023;8(1):95–97.

  5. Lin P, Xu Z, Luo Y, Yin L. A digital technique for a prefabricated custom post-and-core restoration. J Prosthet Dent.

  6. Dimitrova M, Vlahova A, Kazakova R. Assessment of CAD/CAM fabrication technologies for post and core restorations—A narrative review. Medicina. 2024;60:748

  • The lecture concluded with a list of references and a second video demonstration.

Conclusion27

Thank You

Footnotes

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