15.4 Infection Control in Dental Radiography & Digital Sensor Asepsis

15.4 Infection Control in Dental Radiography & Digital Sensor Asepsis

Radiographic procedures present complex infection control challenges in the dental operatory. During radiographic imaging, the dental assistant repeatedly moves their hands between the patient's saliva-coated oral cavity and dry operatory equipment—including the x-ray tubehead, collimator cylinder, exposure buttons, computer mice, keyboards, and darkroom hardware. Without meticulous adherence to aseptic technique, pathogens such as Mycobacterium tuberculosis, Hepatitis B virus (HBV), Hepatitis C virus (HCV), Herpes simplex virus (HSV), and Human Immunodeficiency Virus (HIV) can be cross-contaminated across clinical surfaces and transmitted to subsequent patients or dental personnel. The Centers for Disease Control and Prevention (CDC) Guidelines for Infection Control in Dental Health-Care Settings establish explicit protocols governing radiographic asepsis.

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The Spaulding Classification in Dental Radiography

In 1968, Dr. Earle Spaulding devised a medical classification system that categorizes patient-care instruments and environmental surfaces according to their inherent risk of transmitting infection. The CDC and ADA apply this classification to all dental radiographic equipment:

                    THE SPAULDING CLASSIFICATION IN RADIOGRAPHY
                                       │
         ┌─────────────────────────────┼─────────────────────────────┐
         ▼                             ▼                             ▼
┌─────────────────┐           ┌─────────────────┐           ┌─────────────────┐
│  CRITICAL ITEMS │           │  SEMI-CRITICAL  │           │   NON-CRITICAL  │
│ Penetrate soft  │           │ Contact mucous  │           │ Contact intact  │
│ tissue or bone  │           │ membranes; no   │           │ skin or clinical│
│                 │           │ penetration     │           │ surfaces        │
│ (None in normal │           │                 │           │                 │
│ dental x-rays)  │           │ - Digital CMOS  │           │ - Tubehead & PID│
│                 │           │ - PSP Plates    │           │ - Control Panel │
│ Must be Heat-   │           │ - XCP Aimers    │           │ - Lead Apron    │
│ Sterilized      │           │ - Film Packets  │           │ - Mouse/Keyboard│
└─────────────────┘           └─────────────────┘           └─────────────────┘

1. Critical Items

Instruments that penetrate oral soft tissue, enter the bloodstream, or contact alveolar bone. Critical items present the highest risk of disease transmission and must be heat-sterilized after every use. In routine diagnostic dental radiography, no critical items are employed (unless a surgical radiographic guide penetrates mucosa during implant surgery).

2. Semi-Critical Items

Instruments and devices that contact oral mucous membranes or non-intact skin but do not penetrate bone or soft tissue. In radiography, semi-critical items include:

• Digital intraoral sensors (CMOS and CCD)
• Photostimulable phosphor (PSP) storage plates
• Analog intraoral film packets
• Beam alignment devices and film holders (bite-blocks, indicator arms, and plastic collimator guide rings)

CDC Guidance: Semi-critical items should be heat-sterilized (or high-level disinfected) between patients. If an item cannot tolerate either (as with digital sensors and phosphor plates), at a minimum it is protected with an FDA-cleared barrier during use and then cleaned and disinfected with an EPA-registered hospital disinfectant with intermediate-level (tuberculocidal) activity between patients.

3. Non-Critical Items and Clinical Contact Surfaces

Devices and surfaces that contact only intact skin or do not directly contact the patient. In radiography, non-critical items and environmental contact surfaces include:

• X-ray tubehead, yoke, and position-indicating device (PID)
• Exposure control button, timer dials, and control panel console
• Lead apron and thyroid collar
• Operatory dental chair, headrest, and armrests
• Computer mouse, keyboard, and monitor housing

CDC Guidance: Non-critical items and clinical contact surfaces are barrier-protected or cleaned and disinfected between patients with an EPA-registered hospital disinfectant with low- to intermediate-level activity; use an intermediate-level (tuberculocidal) product when they are visibly contaminated with blood.

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Operatory Preparation and Surface Barrier Placement

To prevent the transfer of oral fluids to radiographic equipment, the operatory must be prepared prior to seating the patient. Dental assistants must perform hand hygiene, don clean examination gloves, and place disposable plastic barriers over all clinical contact surfaces that will be touched during the appointment:

1. X-Ray Tubehead and PID: Slide a large plastic sleeve over the tubehead positioning handles, the yoke, and the cylindrical rim of the PID. The PID rim is frequently touched when aligning the beam with intraoral aiming rings.
2. Control Panel and Exposure Switch: Cover the exposure button, timer dials, and activation switch with plastic wrap or form-fitting polyethylene sleeves. Because exposure buttons contain sensitive electronic relays, spraying liquid disinfectants directly onto the switch can induce internal corrosion, short circuits, or electrical malfunction.
3. Computer Hardware: Place clear plastic barrier covers over the computer mouse and keyboard. If a touch-screen monitor is utilized, apply an adhesive clear barrier film over the screen.
4. Operatory Chair: Cover the chair headrest with a plastic sheath, as the patient's hair and neck contact this surface.
5. Digital Sensor Cable: Slide a 3-to-6-foot plastic tube sheath over the sensor cord, as the cord routinely brushes against the patient's chest and the operator's gloved hands during positioning.

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Digital Intraoral Sensor Asepsis: CMOS/CCD and PSP Plates

Solid-state digital sensors (CMOS and CCD) represent a significant financial investment for the dental practice (typically costing $4,000 to $10,000 per sensor). They contain delicate silicon photodiodes, micro-circuitry boards, and fiber-optic scintillation plates hermetically sealed in ceramic or polymer casings.

Why Digital Sensors Cannot Be Autoclaved

Dental assistants must recognize that solid-state digital sensors CANNOT tolerate steam heat sterilization, dry heat, or chemical autoclaving. Subjecting a digital sensor to autoclave temperatures (121°C to 134°C / 250°F to 273°F) and extreme steam pressure melts the polymer housing, delaminates the fiber-optic faceplate, destroys delicate solder connections, and permanently ruins the microchip, voiding manufacturer warranties. Furthermore, sensors cannot be soaked in liquid chemical sterilants (such as 2.4% glutaraldehyde), because caustic liquids corrode the cable entry boot, seep into the internal circuitry, and destroy the electronics.

Barrier-Plus-Disinfection Protocol for Sensors

Because digital sensors are semi-critical items that cannot be heat-sterilized, CDC guidance calls for an FDA-cleared barrier plus intermediate-level disinfection between patients (always using a disinfectant the sensor manufacturer approves):

                     DIGITAL SENSOR ASEPSIS PROTOCOL
                                    │
1. PRE-EXPOSURE: Barrier Sheath Placement
   - Perform hand hygiene & don clean gloves
   - Insert bare sensor into FDA-cleared plastic sheath / finger cot
   - Ensure tight, smooth seal without wrinkles across active sensor face
   - Slide full-length plastic sleeve along entire sensor cord
                                    │
                                    ▼
2. INTRAORAL EXPOSURE: Patient Positioning
   - Assemble autoclaved XCP beam alignment holder over sheathed sensor
   - Position in patient's oral cavity & complete diagnostic exposure
                                    │
                                    ▼
3. POST-EXPOSURE: Aseptic Barrier Removal
   - Remove assembly from mouth; wipe saliva with 2x2 gauze
   - Invert plastic sheath inside-out away from sensor body
   - Release bare sensor onto clean, uncontaminated barrier surface
   - Discard saliva-contaminated plastic sheath in regular trash
                                    │
                                    ▼
4. DECONTAMINATION: Intermediate-Level Disinfection
   - Doff contaminated gloves, sanitize hands, don fresh gloves
   - Wipe entire sensor housing & cord with EPA-registered
     intermediate-level disinfectant wipe (tuberculocidal claim)
   - Maintain wet contact dwell time per manufacturer instructions (1-3 min)
   - Inspect casing and cable boot for microscopic cracks

Photostimulable Phosphor (PSP) Plate Asepsis

Phosphor storage plates (PSP plates) are cordless, flexible receptors that store latent x-ray energy in europium-doped barium fluorohalide crystals. Like digital sensors, PSP plates cannot be autoclaved, as high heat destroys the luminescent phosphor coating:

• Barrier Packaging: Prior to clinical use, each PSP plate is sealed inside an individual, fluid-proof, light-tight plastic barrier envelope. The active phosphor side must face the black exposure side of the envelope.
• Chairside Aseptic Removal: Following intraoral exposure, the assistant wipes saliva from the barrier envelope with a clean 2x2 gauze sponge. Using gloved hands, the assistant peels open the adhesive tear-strip of the envelope and carefully drops the bare phosphor plate directly into a clean transfer receptacle (or directly into the scanner loading chute) without touching the bare plate with saliva-contaminated gloves.
• Cleaning the Bare Plate: If a PSP plate becomes contaminated with saliva, it is cleaned only by the manufacturer's approved method, because water and many disinfectants can damage the phosphor coating. Manufacturers typically supply or name specific phosphor cleaning wipes (often alcohol-based).

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Chairside Handling and Darkroom Transfer of Analog Film

When exposing traditional analog film packets, oral saliva heavily contaminates the outer vinyl packet. Contaminated film packets transferred directly into a darkroom or daylight loader will contaminate darkroom counters, safelight switches, and processor transport rollers:

1. Chairside Decontamination: Upon removing the exposed film packet from the patient's mouth, the assistant immediately wipes all saliva and blood from the packet using a clean 2x2 gauze sponge. The wiped packet is dropped into a clean, disposable paper cup labeled with the patient's name.
2. Transfer to Darkroom: The assistant must never touch the outside of the clean paper cup with contaminated gloves. Once all exposures are completed, the assistant removes contaminated gloves, performs hand hygiene, and carries the clean paper cup to the darkroom.
3. Darkroom Processing Asepsis: Inside the darkroom under safelight illumination, the assistant dons clean examination gloves:
   • Carefully tear open the outer paper/vinyl packet flaps without touching the bare film emulsion inside.
   • Allow the bare film to drop freely onto a clean paper towel placed on the counter.
   • Discard the contaminated packet wrappers and black paper into the trash, and deposit the lead foil sheet into the scrap lead recycling container.
   • Doff gloves and wash hands before touching the automatic processor feed slot. Feeding bare films into the processor rollers with bare, clean hands prevents transferring microbial contaminants onto the internal processor rollers.
4. Daylight Loader Precautions: Automatic film processors equipped with daylight loaders feature flexible neoprene light-tight arm cuffs. Daylight loaders present an exceptionally high cross-contamination risk because operators frequently insert contaminated gloved hands through the cuffs. Dental assistants must never insert contaminated gloved hands into a daylight loader. Clean paper cups holding wiped packets, clean gloves, and clean paper barriers must be placed inside the daylight loader compartment before closing the access lid. The operator then inserts clean hands through the cuffs, dons the gloves inside the loader, unwraps the films, feeds them into the rollers, removes gloves inside, and withdraws clean hands.

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Beam Alignment Device Sterilization (XCP Assemblies)

Beam alignment assemblies—such as Rinn XCP (Extension Cone Paralleling) instruments—consist of plastic bite-blocks, colored plastic collimator guide rings, and stainless steel indicator arms. Because these devices are placed directly into the patient's oral cavity and contact mucous membranes, they are semi-critical instruments that must undergo heat sterilization between every patient:

• Disassembly: Immediately after patient dismissal, the assistant disassembles all bite-blocks, aiming rings, and metal arms. Leaving components assembled during processing traps saliva and cleaning chemicals in joint junctions.
• Ultrasonic Cleaning: Disassembled components are placed in an ultrasonic cleaning bath or automated instrument washer containing enzymatic detergent for 10 to 15 minutes to loosen and dissolve biological debris and dried saliva.
• Rinsing and Drying: Instruments are thoroughly rinsed with water and patted dry with lint-free paper towels.
• Packaging: Components are placed into FDA-cleared sterilization pouches equipped with internal and external chemical indicators. Color-coded components can be bagged as complete sets (e.g., anterior, posterior, bitewing).
• Heat Sterilization: Pouches are processed in a calibrated steam autoclave (typically at 121°C / 250°F for 30 minutes, or 132°C / 270°F for 4 to 10 minutes in a high-speed pre-vacuum sterilizer). Chemical cold immersion ("cold sterilization" in glutaraldehyde) is strictly unacceptable when heat-tolerant autoclavable plastics are utilized.

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Maintenance and Decontamination of the Lead Apron

The lead apron and thyroid collar are classified as non-critical patient-care items. However, because they are handled by gloved personnel during positioning and rest directly against patient clothing, necks, and skin, they are subjected to saliva spatter and microbial contamination.

Disinfection Protocol

Between every patient, the assistant must decontaminate the lead apron and thyroid collar:

• Don utility gloves or fresh examination gloves.
• Wipe all front surfaces, back surfaces, and hanging straps with an EPA-registered hospital disinfectant (many offices use the same tuberculocidal wipe they use on clinical contact surfaces; CDC calls for an intermediate-level product when blood is visible).
• Allow the surfaces to remain wet for the manufacturer's specified contact dwell time (typically 1 to 3 minutes).
• Allow the apron to air-dry completely before hanging or placing on a subsequent patient.

The Critical Storage Rule: Never Fold a Lead Apron

The protective core of a lead apron consists of a thin, flexible sheet of metallic lead or a lead-rubber composite matrix. When a lead apron is folded, severe mechanical stress is concentrated along the crease line. Repeated folding induces fatigue fracturing of the internal lead sheeting, creating microscopic and macroscopic cracks. These invisible fractures allow primary and scatter radiation to penetrate directly through the apron to the patient's underlying thyroid gland, gonads, and developing fetus, rendering the protective garment useless.

• Approved Storage: Lead aprons must always be stored hung flat on specialized heavy-duty lead apron wall racks, multi-arm pivoting apron hangers, or broad, rounded coat hangers designed to distribute weight without creasing.
• Quality Assurance Testing: Dental practices must periodically inspect lead aprons for internal shielding integrity. Aprons should be palpated manually every 3 months to detect lumps, tears, or thin spots, and imaged radiographically or under fluoroscopy annually to verify that no internal fractures exist.