Notes on Radiographic Interpretation of Dental Caries

Objectives and Overview

Topic: Radiographic Interpretation of Dental Caries
Presenter: Dr. V Pannu, Assistant Professor, Department of Restorative Sciences, The Dental College of Georgia
Focus areas: Radiation biology; ADA recommendations; role of radiology in detecting dental caries; ALARA principle; radiographic appearance of caries; types of caries; imaging modalities for caries detection; radiographic interpretation.

Radiation Dose and Population Context

In the US population (2006): percent contributions of sources to the total effective dose; total average effective dose around $6.2\,\text{mSv}$.
Dental radiographs account for a small fraction: 0.26\% of the total effective dose, equivalent to about 0.007\,\text{mSv}.

Radiation Doses for Common Examinations

Full-mouth survey, round collimation, D-speed film: 388\ \mu\text{Sv}
Full-mouth survey, round collimation, PSP: 171\ \mu\text{Sv}
Full-mouth survey, rectangular collimation, PSP: 35\ \mu\text{Sv}
Bitewings, rectangular collimation, PSP: 5\ \mu\text{Sv}
Panoramic: 9-24\ \mu\text{Sv}
Skull, plain film: 70\ \mu\text{Sv}
Chest, plain film: 20\ \mu\text{Sv}

Position and Distance for Radiation Protection

Rule: Maintain appropriate distance from the source.
Common guidance shown as: 6 feet distance from the source/personnel; typical operator positioning angles include 90° and 135° orientations relative to the patient and beam path.
Diagrammatic summary: 6 feet distance; angles 90° and 135°; indicates protection zoning around patient and operator.

Reducing Radiation Exposure: Best Practices

Use the fastest image receptor available (F-speed film or digital).
Collimate the beam to the size of the receptor; rectangular collimation reduces exposure by about 5-fold.
Use protective aprons and thyroid collars when appropriate.
Limit the number of images to the minimum necessary to obtain essential diagnostic information.

Radiation Protection: Core Principles

Take radiographs only when needed.
Use the lowest radiation dose that yields the necessary information (justification and optimization).
Do it right the first time to avoid repeat exposures.
Process and mount radiographs correctly to preserve interpretability.
Interpret radiographs completely and accurately for clinical decision-making.

ADA Recommendations for Prescribing Dental Radiographs

Frequency and justification context:
- New Patients:
- Initial radiographs as needed, based on clinical judgment.
- Full-mouth series may be considered to establish baseline.
- Justification: Establish baseline; Evaluate dental condition.
- Recall Patients: (Age-based guidance varies by risk and eruption patterns)
- Children:
  - Bitewing radiographs every 6-18\text{ months}, depending on caries risk and history.
  - Panoramic radiograph every 3-5\text{ years}.
  - Monitor caries progression; Evaluate changes in oral structures.
- Adolescents:
  - Bitewings every 6-12\text{ months}, depending on caries risk and eruption patterns.
  - Panoramic by age 7 or when necessary for treatment planning.
  - Monitor caries progression; Assess development and eruption of permanent teeth.
- Adults:
  - Bitewings every 6-18\text{ months}, depending on caries risk and eruption patterns.
  - Panoramic by age 12-16, or when necessary for treatment planning.
  - Monitor caries progression; Assess development and eruption of permanent teeth.
- Other recall intervals (general guidance):
  - Bitewings every 18-36\text{ months}, depending on caries risk and periodontal status.
  - Panoramic every 5-10\text{ years}, depending on clinical indication.
  - Monitor caries progression; Evaluate changes in oral structures.
Overall emphasis: Regular radiographs are justified by caries risk assessment, eruption/development monitoring, and progression assessment.

Radiographic Appearance of Dental Caries

Mineralization concepts:
- More mineralization => greater x-ray absorption => radiopaque and considered sound tooth structure.
- Less mineralization => less absorption => radiolucent and considered unsound structure.
Radiographic shades of grey reflect mineral density and structural integrity.

Radiographic Appearance Categories for Caries

Proximal Caries: Radiolucency just cervical to the proximal contact.
Occlusal or Incisal Caries: A radiolucent zone beneath a pit or fissure.
Buccal/Lingual Caries: Well-defined circular radiolucency that appears to extend through the tooth.

Proximal and Buccal/Lingual Caries (Illustrative Concepts)

Proximal Caries: typically seen on bitewing or periapical views as radiolucent bands near contact areas.
Buccal/Lingual Caries: may require carefully angled radiographs to detect because lesions can be through-and-through in those directions.

Recurrent or Secondary Caries

Definition: Caries occurring adjacent to or underneath previous restorations.
Radiographic signs include radiolucent zones at restoration margins, progressing lesions under or around existing fillings.

Caries and Cervical Burnout: Diagnostic Consideration

Cervical burnout: radiolucent appearance at the cervical area that may mimic caries.
Important to differentiate from true caries by considering morphology, clinical findings, and whether radiolucency extends beyond typical burnout zones.

Root Caries

Location and appearance: Caries occurring at or near the cementoenamel junction on root surfaces; may appear as shallow or extensive radiolucencies along root surfaces.

Radiographic Classification of Caries on the Approximal Surface

Key classifications (E-level and D-level, with additional RA/RB/RC codes):
- E0*** or R0#: No radiolucency observed.
- E1 or RA1 or E2 or RA2 or D1 or RA3: Radiolucency may extend to the dentinoenamel junction or outer one-third of the dentin.
- D2 or RB4 and D3 or RC5: Radiolucency extends into the middle one-third and inner one-third of the dentin, respectively.
Note: Radiographs are not reliable for mild occlusal lesions; clinical correlation is essential.

Radiographic Caries Classification: Healthy to Advanced

Healthy (no radiolucency).
E1, E2: Early enamel/dentin involvement.
D1, D2, D3: Increasing depth into dentin (outer to inner thirds).
MMM: (Interpretive placeholder in slides; refer to full manual classification for exact mapping in your course materials).

Types of Images for Caries Detection

Common radiographic modalities used for caries detection:
- Bitewing radiographs (for proximal surfaces and early interproximal caries).
- Periapical radiographs (for detailed root and proximal information).
- Panoramic radiographs (broad survey; less sensitivity for small proximal lesions but useful for baseline and eruption monitoring).
- Occlusal radiographs (limited use; sometimes helpful for buccal/lingual caries or gross pathology).
Selection depends on caries risk, eruption patterns, and need to monitor progression.

Practical and Clinical Implications

ALARA in practice: Always balance diagnostic yield with dose reduction; prioritize patient safety and minimize unnecessary exposure.
Interpretation involves integrating radiographic findings with clinical examination (visual/t tactile) and patient history.
Recognize imaging limitations: radiographs cannot reliably detect very mild occlusal lesions or early cervical burnout; correlate with clinical signs.
Ethical considerations: Justification of radiographs, patient consent, and documentation of rationale.

References and Further Reading

ADA press releases and recommendations on radiography safety: https://www.ada.org/about/press-releases/ada-releases-updated-recommendations-to-enhance-radiography-safety-in-dentistry
Caries classification systems: https://www.atsu.edu/faculty/chamberlain/mosdoh/cariesclassificationsystem.htm
ADA resources on x-rays and radiographs: https://www.ada.org/resources/ada-library/oral-health-topics/x-rays-radiographs
White, S. C., & Pharoah, M. J. (2014). Oral radiology: Principles and interpretation (7th ed.). Elsevier.
Radiographs from The Dental College of Georgia and University of Nebraska Medical Center College of Dentistry Dept

Concluding Note

The presentation emphasizes minimizing radiation exposure while maintaining diagnostic efficacy, understanding radiographic appearances of caries, and applying standardized classification systems to consistently interpret and communicate findings.

Appendix: Quick Reference Doses (for study)

Full-mouth survey, round collimation, D-speed film: 388\ \,\mu\text{Sv}
Full-mouth survey, round collimation, PSP: 171\ \,\mu\text{Sv}
Full-mouth survey, rectangular collimation, PSP: 35\ \,\mu\text{Sv}
Bitewings, rectangular collimation, PSP: 5\ \,\mu\text{Sv}
Panoramic: 9-24\ \,\mu\text{Sv}
Skull (plain): 70\ \,\mu\text{Sv}
Chest (plain): 20\ \,\mu\text{Sv}