9.4 Dental Dam: Selection, Punching, Placement Errors & Removal

9.4 Dental Dam: Selection, Punching, Placement Errors & Removal

Quick Answer: Competency 5.6.4 covers the whole dental dam procedure:

• selecting and preparing the armamentarium for the patient's dentition and the planned procedure
• assisting with, and placing and removing, the dam
• finding and correcting placement and positioning errors
• checking how well the field is isolated
• giving pre- and post-operative instructions.

Punching errors are tested as matching items. Holes punched too large prevent inversion and leak. Holes punched too far apart leave excess, bunched material between teeth. Holes punched too close together stretch and tear the septa. An arch punched too flat bunches and stretches on the lingual. An arch punched too curved folds on the facial.

Dental Dam Isolation and Armamentarium

Complete dental dam isolation is the single most effective barrier against moisture, blood, and bacterial contamination. In endodontic therapy, dental dam isolation is the standard of care: treating canals without a dam exposes the patient to the risk of swallowing or aspirating endodontic files, reamers or irritating irrigants such as sodium hypochlorite ($NaOCl$).

Dental Dam Armamentarium

1. Dental Dam Material:

   • Composition: Natural rubber latex or synthetic elastomeric polymers (nitrile, polyisoprene) for latex-allergic patients and personnel.
   • Dimensions: 6 × 6 inch (15 × 15 cm) squares for adult posterior and anterior teeth; 5 × 5 inch (13 × 13 cm) squares for pediatric dentition.
   • Thickness (Gauge):
     • Light: Very flexible and easy to seat, but tears easily and provides poor soft tissue retraction.
     • Medium: Versatile, widely used for routine operative dentistry.
     • Heavy and Extra-Heavy: Strongly recommended for restorative and operative procedures; provides maximum tissue retraction, resists tearing when flossing through tight contacts, and easily maintains a stable inverted sulcular seal.

2. Dental Dam Punch and Hole Sizing: The standard Ainsworth punch features a rotating cutting wheel with five distinct hole sizes:

   • Hole 5 (Largest): Anchor tooth holding the clamp (typically second or third molars).
   • Hole 4: Molars (first and second molars without clamps).
   • Hole 3: Premolars (bicuspids) and canines (cuspids).
   • Hole 2: Maxillary incisors.
   • Hole 1 (Smallest): Mandibular central and lateral incisors.

3. Dental Dam Frames:

   • Young U-Shaped Metal Frame: Placed outside (facial to) the dam; durable and provides excellent lateral tension.
   • Plastic Radiolucent Frames (e.g., Nygaard-Ostby, Star Visi-Frame): Placed facial or lingual; radiolucent design allows dental assistants to take intermediate endodontic periapical radiographs without removing the frame or dam.

4. Lubricants:

   • A water-soluble lubricant (e.g., surgical lubricant, K-Y jelly) is applied sparingly to the tissue side of the dam around the punched holes to allow the rubber to slide effortlessly over interproximal contacts.
   • Absolute Contraindication: Petroleum jelly (Vaseline) must never be used on latex dams. Petroleum hydrocarbons cause rapid chemical breakdown, dissolution, and tearing of latex membranes.

Indications and Contraindications

Indications:

• Endodontic therapy (the standard of care)
• Moisture-sensitive bonding and composite restorations
• Amalgam placement or removal (keeps scrap and mercury vapour out of the throat)
• Pediatric restorative care
• Any procedure where small instruments could be aspirated.

Contraindications or modifications:

• A patient who cannot breathe through the nose (nasal obstruction, severe congestion). Cut a breathing opening or use another isolation method.
• Latex allergy (use a non-latex sheet)
• A tooth too partially erupted or broken down to hold a clamp (consider a different clamp, a ligature or a buildup first)
• A patient who refuses after the benefits are explained.

Planning Which Teeth to Isolate

• Posterior procedures: isolate at least one tooth distal to the tooth being treated (usually the clamped anchor tooth) forward to the canine or lateral incisor on the opposite side of the midline. This gives access and visibility.
• Anterior procedures: isolate from first premolar to first premolar so that the dam does not pull across the operative teeth.
• Endodontics: isolate the single tooth being treated.
• Mark the hole positions using a template or rubber stamp, following the patient's arch form. Adjust the marks for missing, malpositioned, crowded or widely spaced teeth.
• Place maxillary holes nearer the upper edge of the sheet and mandibular holes nearer the lower edge, so that the dam covers the mouth without covering the nose.
• Choose the punch-plate hole to match each tooth (the largest for the clamped anchor tooth, the smallest for mandibular incisors).

Dental Dam Clamps (Retainers)

Dental dam clamps anchor the sheet securely to the dentition and retract gingival tissues.

• Anatomy of a Clamp:

  • Bow: The arched spring steel loop connecting the two jaws, positioned toward the distal aspect of the tooth.
  • Jaws: The curved metal plates that encircle the tooth cervical contour; each jaw features two sharp prongs/points (four points total).
  • Forceps Holes: Circular holes in the jaws that receive the beaks of the dental dam clamp forceps.
  • Wings vs. Wingless: Winged clamps feature extra lateral metal projections designed to hold the dam sheet during one-step assembly; wingless clamps lack these projections and are designated by the letter "W" in their manufacturer model number (e.g., W7, W8A, W2).

• The Four-Point Contact Rule: For a clamp to remain stable and avoid popping off under rubber tension, all four prongs must firmly contact sound tooth structure below the height of contour at the cementoenamel junction (CEJ). Two-point or three-point contact causes rocking, tissue laceration, and clamp dislodgement.

• Standard Clinical Clamp Selection:

  • #7 / #W7: Universal flat-jawed clamp for mandibular molars.
  • #8 / #W8: Universal clamp with curved jaws for maxillary molars.
  • #W8A / #8A: Downward-canted, festooned subgingival jaws for partially erupted, small, or structurally compromised/broken-down molars.
  • #2 / #W2: Universal clamp for premolars (bicuspids).
  • #9 / #212: Double-bow butterfly clamps specifically contoured for anterior teeth and Class V cervical restorations.

• Mandatory Floss Safety Ligature: Before placing any clamp intraorally, an 18-inch length of dental floss must be securely tied through the hole or around the bow of the clamp. The loose tail of the ligature remains trailing outside the patient's mouth. If the tempered spring steel of the bow fractures under fatigue stress or slips off the anchor tooth, the assistant immediately grasps the safety ligature to retrieve the fragment, preventing aspiration into the trachea or ingestion into the esophagus.

Step-by-Step Clinical Placement and Inversion

1. Pre-Placement Preparation: Check contact tightness with floss; remove calculus or rough margins; apply topical anesthetic if the clamp prongs will impinge on inflamed gingival papillae.
2. Method Selection:
   • One-Step Method: The winged clamp is engaged in hole #5 of the lubricated dam sheet outside the mouth, mounted on the frame, and the entire assembly is carried to the anchor tooth with forceps and seated as a single unit.
   • Two-Step Method: The clamp (typically wingless, e.g., W7 or W8A) is seated directly on the anchor tooth and checked for four-point stability. The assistant stretches the lubricated dam hole over the clamp bow and jaws, followed by positioning the frame.
3. Interdental Flossing: Pull the dam sheet taut over adjacent teeth. Floss the interdental rubber septa through contacts using a single-thickness floss ligature. Never use double strands or sawing motions, which tear the septal rubber.
4. Dam Inversion Technique:
   • Inversion is the process of tucking the edge of each punched hole apically into the gingival crevice to create a positive hermetic seal against salivary microleakage.
   • The assistant directs a gentle, continuous stream of warm air from the air/water syringe to desiccate the tooth surface, while using a blunt instrument (e.g., spoon excavator, plastic filling instrument, or beavertail burnisher) to roll the rubber collar inward toward the root.
   • Anterior teeth can be stabilized with an interdental elastic stabilizing cord (Wedjets) or knotted floss ligatures.

Systematic Dental Dam Removal Protocol

Improper removal can cause gingival laceration or leave toxic foreign bodies behind in the periodontium:

1. Clear Debris: Evacuate all water, restorative amalgam scrap, or etched composite residue from the dam surface using HVE.
2. Remove Ligatures: Remove stabilizing Wedjets or cut floss ligatures.
3. Sever Interdental Septa: Place an index finger beneath the dam sheet to protect patient lips and buccal mucosa. Stretch each rubber septum facially, and use blunt-nosed curved crown and collar scissors to cut each interseptal bridge cleanly. Never cut toward gingival tissue.
4. Simultaneous Removal: Engage the clamp with dam forceps, expand the jaws, and lift the clamp, dam, and frame off the patient's teeth as a single cohesive unit.
5. Mandatory Post-Removal Dam Inspection: Immediately lay the removed dam flat across a white paper towel or light background. Align the cut septa and verify that every circular hole and interproximal segment is 100% accounted for.
   • Clinical Warning: If a triangular fragment of rubber is missing from an interdental septum, it has torn off and remains trapped subgingivally in the patient's interproximal contact. A retained fragment causes gingival inflammation and pain and can lead to a periodontal abscess. The assistant must immediately floss and explore the sulcus to retrieve any retained fragment.

Evaluating and Correcting Dental Dam Errors

Punching errors (competency 5.6.4.4)

Placement and isolation errors (competency 5.6.4.5)

• Clamp not stable (rocks or pops off): the four prongs are not contacting the tooth below the height of contour. Reseat it, or choose a better-fitting clamp, and always keep the floss ligature attached.
• Clamp impinging on the gingiva: the patient feels pain, or the tissue blanches and bleeds. Reposition the clamp more occlusally on sound tooth structure.
• Septa not through the contacts: use waxed floss to carry the septa gently through each contact, one at a time.
• Dam not inverted: saliva seeps around the cervical margins. Dry the tooth with air and tuck the edge into the sulcus with a blunt instrument. A floss ligature tied around the tooth can help.
• Small tear or leak: a little caulking material can seal it. A large tear means replacing the sheet.
• Dam covering the nose or eyes, or uneven tension: readjust the frame and the sheet so the patient can breathe comfortably.
• Isolation check: the operative field should stay dry with no saliva pooling on the dam surface (other than water spray, removed by HVE), and the patient should be comfortable.

Instructions to the patient

• Before placement: explain what the dam does and that it will feel snug. Ask the patient to breathe through the nose and to raise a hand for a break.
• During the procedure: check on comfort regularly.
• After removal: the gingiva may be slightly tender where the clamp sat for a day or two. Brush gently and rinse with warm salt water if needed. Call the office if pain or swelling increases.