# Caries Detection Devices

> Caries detection for BDS Operative Dentistry — DIAGNOdent laser fluorescence, QLF, ICDAS criteria, bitewing limits and fibre-optic transillumination.

- Canonical URL: https://prepelephant.com/topics/bds/operative-dentistry/caries-detection-devices
- Exam / course: BDS · Subject: Operative Dentistry
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-02
- Last updated: 2026-10-02
- How to cite: "Caries Detection Devices", PrepElephant, https://prepelephant.com/topics/bds/operative-dentistry/caries-detection-devices

## Direct answer

Visual inspection with ICDAS remains the reference standard against which every caries detection device is judged — a plain-mirror-and-explorer judgement made on clean, dried teeth, scored from 0 (sound) to 6 (frank cavity) — because radiographs systematically under-detect early lesions and over-call healed ones. The adjuncts earn their place on that weakness: a bitewing radiograph shows occlusal dentine caries only once demineralisation is substantial (roughly half the mineral must be lost before a radiolucency appears), laser fluorescence devices such as DIAGNOdent read bacterial porphyrin fluorescence at 655 nanometres as a numeric proxy for lesion depth, quantitative light-induced fluorescence and camera systems map mineral loss, fibre-optic transillumination shows proximal shadows, and electrical conductance detects dentine lesions by conductivity. Each adjunct adds a number or an image; none replaces the drying, lighting and probe that visual diagnosis depends on.

## What you must remember

- **ICDAS foundation:** the International Caries Detection and Assessment System scores cleaned, dried teeth 0 to 6 — from sound enamel through distinct visual change to extensive cavity — and remains the validated reference for lesion detection.
- **Radiographic ceiling:** bitewings detect occlusal lesions late — a substantial proportion of mineral (commonly cited around 40 to 50 per cent) must be lost before the lesion is radiographically visible, and proximal lesions are visible only once they are well established.
- **DIAGNOdent principle:** a 655-nanometre diode laser; bacterial porphyrins fluoresce and the device reads intensity as a numeric score used as a proxy for caries extent, with manufacturer thresholds separating enamel from dentine involvement.
- **DIAGNOdent caveats:** stains, calculus, plaque and restorative materials raise scores falsely; a clean, dried, calibrated probe on a controlled site is the usable method, and readings track a site over time better than they diagnose once.
- **QLF and fluorescence cameras:** ultraviolet or blue light excitation with filtered capture maps demineralisation as fluorescence loss, quantifiable and imageable for monitoring.
- **FOTI:** fibre-optic transillumination shows proximal lesions as dark shadows against transmitted light — quick, radiation-free, operator-dependent.
- **Electrical conductance:** demineralised dentine conducts current where sound enamel insulates; devices using this measure dentine involvement specifically.
- **Clinical grammar:** adjuncts detect and monitor — ICDAS with radiographs diagnoses; a positive adjunct reading without visual corroboration is a recheck, not a cavity preparation.

## Monitoring a stained fissure over two years

A 17-year-old's tooth 16 has a stained central fissure, ICDAS code 2 (distinct visual change after drying, no cavity), and a bitewing with no occlusal radiolucency. The fissure is cleaned, dried and scored; DIAGNOdent readings at the site are compared with a healthy reference surface on the same tooth — a low reading confirms the visual judgement and the fissure is sealed. At six-month recall the site is re-read: fluorescence numbers drifting upward, or an ICDAS code climbing to 3 with localised breakdown, move the plan toward restoration; stable readings justify leaving the sealed surface alone. The device's honest role emerges: not a red-green verdict but a reproducible measurement that makes monitoring a decision rather than a memory. A brown, sticky fissure with a cavitated spot — ICDAS 4 — justifies restoration on its own, adjuncts academic: devices extend the clinician's eyes for hidden lesions and surveillance, they do not outrank them.

## How examiners set the question

Papers ask "adjuncts to caries diagnosis" and reward a structured answer: visual systems (ICDAS), radiography with its limits, fluorescence (laser and QLF), transillumination and electrical methods. The two most examinable numbers are the DIAGNOdent wavelength — 655 nanometres — and the radiographic threshold, that roughly 40 to 50 per cent mineral loss must precede a visible radiolucency, both favourite discriminators in MCQ formats. The viva trap is overclaiming: candidates who present fluorescence scores as diagnosis are asked about stains, calculus and hypomineralisation all fluorescing falsely — the false-positive list is the follow-up. A second trap is the sensitivity-versus-specificity framing: radiography is specific but insensitive for early occlusal lesions, while fluorescence is sensitive but plagued by false positives — a sentence that summarises the whole topic. Ending on monitoring rather than one-off diagnosis signals current understanding.

## Frequently asked questions

### What does ICDAS score and why does it matter?

It scores visually assessed caries on clean, dried teeth from 0 (sound) to 6 (extensive cavity), providing the validated reference standard for detection and lesion severity.

### Why do bitewing radiographs miss early occlusal caries?

A substantial fraction of mineral — commonly cited around 40 to 50 per cent — must be lost before a radiolucency becomes visible, so radiographs detect occlusal dentine caries late.

### On what principle does DIAGNOdent work?

A 655-nanometre diode laser excites fluorescence from bacterial porphyrins in carious lesions, and the measured intensity provides a numeric proxy for lesion extent.

### What causes false-positive fluorescence readings?

Extrinsic stains, calculus, plaque, and some restorative or hypomineralised tissues fluoresce, inflating scores — hence readings are taken on clean, dried, calibrated sites.

### What is fibre-optic transillumination used for?

Detecting proximal caries as dark shadows where demineralised tissue scatters transmitted light — a rapid, radiation-free, operator-dependent adjunct.