25.4 Gingival Retraction, Provisionals and Temporary Cements

1. Gingival Retraction and Soft Tissue Management

Accurate marginal reproduction requires displacing the gingival margin 0.2 mm laterally and exposing at least 0.5 mm of unprepared tooth structure apical to the finish line, while maintaining absolute haemostasis and controlling crevicular exudate.

Tissue Management Approaches
  ┌────────────────────────────────────────────────────────┐
  │               Gingival Retraction Methods              │
  └───────────────┬────────────────────────┬───────────────┘
                  │                        │
         Mechanical-Chemical            Surgical
         ┌────────┴────────┐      ┌────────┴────────┐
      Single-Cord     Dual-Cord  Electrosurgery  Diode Laser
      (Shallow)       (Deep/Ant) (Non-cardiac)   (Safe/Implants)

Mechanical Retraction Techniques

• Knitted vs Braided Cords: Knitted cords (sizes 000, 00, 0, 1, 2) expand upon wetting, exerting a continuous outward lateral force against the sulcular wall, making them superior to braided cords.
• Single-Cord Technique:
  • Indicated for shallow, healthy sulci where preparations have supragingival or equigingival margins.
  • A medium cord (size 0 or 1) soaked in astringent is gently packed circumferentially using a thin, non-serrated cord packer. It is left in place for 4 to 5 minutes and removed immediately prior to injecting light-body wash.
• Dual-Cord (Two-Cord) Technique:
  • The gold standard for subgingival margins, aesthetic anterior preparations, and impression taking in friable, hyperaemic tissue.
  • Step 1: A small first cord (size 000 or 00) is placed at the base of the sulcus to seal off apical fluid seepage and protect the junctional epithelium. This cord remains in place during impression taking.
  • Step 2: A larger second cord (size 1 or 2) is placed over the first cord to achieve lateral tissue deflection. It is left in situ for 3 to 5 minutes and removed immediately before injecting impression material.

Chemical Haemostatic Agents

Surgical Retraction Modalities

1. Electrosurgery:
   • Utilizes a high-frequency unipolar alternating radio-current (1.5–3.0 MHz) to vaporize intracellular fluid, cutting tissue cleanly while sealing capillaries.
   • Contraindications: Strictly contraindicated in patients wearing cardiac pacemakers or implantable cardioverter-defibrillators (ICDs). Must never touch titanium dental implants (causes electrical arcing and osseointegration failure) or contact alveolar bone (risks irreversible necrosis and sloughing).
2. Soft-Tissue Diode Laser (810–980 nm):
   • Highly absorbed by melanin and haemoglobin, providing precise soft tissue excision and simultaneous coagulation.
   • Advantages: Safe around dental implants and pacemakers; produces minimal thermal collateral damage (< 0.5 mm); causes virtually zero postoperative gingival recession compared to electrosurgery.

4. Provisional Restorations (Temporization)

Provisional restorations are an indispensable phase of fixed prosthodontic therapy, serving critical biological, mechanical, and diagnostic roles during the laboratory fabrication period.

Functions of Provisional Restorations
       Biological                     Mechanical                    Diagnostic
  ┌──────────────────┐           ┌──────────────────┐          ┌──────────────────┐
  │ Pulp protection  │           │ Maintain space   │          │ Aesthetic trial  │
  │ Prevent caries   │           │ Prevent drift    │          │ Phonetic check   │
  │ Gingival health  │           │ Prevent supra-er.│          │ OVD verification │
  └──────────────────┘           └──────────────────┘          └──────────────────┘

Primary Functions of Provisional Restorations

1. Biological Protection: Seals cut dentinal tubules against oral fluids, bacteria, and thermal extremes, preventing pulpal inflammation and necrosis; protects margins from secondary caries; preserves periodontal health by establishing correct emergence profiles and cleansable embrasures.
2. Mechanical Positional Stability: Maintains proximal contacts to prevent mesio-distal drift; maintains occlusal contacts to prevent supra-eruption of the prepared tooth or opposing dentition; resists occlusal forces without breaking.
3. Diagnostic Trial: Evaluates aesthetics, incisal edge position, smile line, lip support, and phonetics. Specifically, tests the 'F' and 'V' sounds (incisal edges of maxillary centrals should lightly contact the wet-dry line of the lower lip) and the 'S' sound (evaluates the closest speaking space, ensuring no tooth clatter at the proposed OVD).

Material Science: Bis-Acryl Composite vs PMMA

Temporary Luting Cements: The Eugenol Prohibition

• Zinc Oxide Eugenol (ZOE - e.g., Temp-Bond): Eugenol provides an obtundent, sedative effect on hyperaemic dental pulp by inhibiting prostaglandin synthesis.
• The Chemical Hazard: Eugenol contains a phenolic hydroxyl group that acts as an aggressive free-radical scavenger. If a provisional crown is cemented with ZOE, residual eugenol penetrates dentinal tubules and adsorbs to the preparation surface.
• When the definitive restoration is subsequently cemented using a resin-based composite cement (e.g., Panavia, RelyX Ultimate), the residual eugenol poisons the free-radical polymerization of the methacrylate monomers, leading to incomplete resin cure, drastically reduced bond strength, microleakage, and premature crown debonding.
• Clinical Rule: Whenever the definitive restoration is to be cemented with a resin cement or resin-modified glass ionomer, the provisional must be cemented exclusively with a Zinc Oxide Non-Eugenol (NE) cement (e.g., Temp-Bond NE).

6. Clinical Traps, Pitfalls, and Worked Scenarios

[!CAUTION] Clinical Trap: Cleaning Zirconia with Phosphoric Acid: After intraoral try-in of a zirconia crown, the clinician cleans the saliva-contaminated intaglio by applying 37% phosphoric acid etching gel for 30 seconds. This is a severe chemical error. The phosphate ions (PO₄³⁻) in the acid form irreversible ionic bonds with the reactive zirconium oxide sites on the ceramic surface. When the 10-MDP primer is subsequently applied, its dihydrogen phosphate groups cannot find free zirconium sites to bond with, destroying the chemical bond and causing premature crown debonding. Clean zirconia exclusively with 50 µm alumina sandblasting or an alkaline zirconia cleaner (Ivoclean).

[!WARNING] Clinical Trap: Luting a Feldspathic Porcelain Crown with RMGIC: A clinician places a delicate anterior feldspathic porcelain jacket crown using Resin-Modified Glass Ionomer (Fuji Plus) because of its simple mixing and fluoride release. Six months later, the patient returns with a longitudinal "half-moon" catastrophic fracture across the facial margin. RMGICs absorb oral moisture, undergoing delayed hygroscopic expansion. The radial tensile stress generated by this expansion exceeds the low tensile strength (70 MPa) of feldspathic porcelain. Glass-ceramics must be bonded exclusively with resin cements.

Worked Clinical SBA Scenario

Scenario: A 32-year-old female attends for definitive cementation of a single lithium disilicate crown on tooth 21. At the previous preparation appointment, a bis-acryl provisional crown was cemented. Following removal of the provisional, the clinician notices localized bleeding at the palatal sulcus. The clinician aims to achieve reliable haemostasis and execute an evidence-based cementation protocol with a dual-cure resin cement.

Question: What is the most appropriate management of the soft tissue and conditioning of the ceramic restoration prior to cementation?

Clinical Reasoning Formulation:

1. Haemostatic Selection: Ferric sulphate rapidly arrests bleeding but causes dark coagulum staining on tooth structure and leaves residual ferric ions that impair resin dentine hybridization and polymerization. Because a resin cement is planned in the aesthetic zone, aluminium chloride (15–25%) is mandatory to achieve haemostasis without staining or interfering with resin polymerization.
2. Provisional Cement Verification: The provisional must have been luted with zinc oxide non-eugenol cement; any residual eugenol would inhibit the polymerization of the dual-cure resin.
3. Glass-Ceramic Conditioning: Lithium disilicate is a glass-matrix ceramic. The intaglio must be treated with 4.5–5% hydrofluoric acid for 20 seconds, rinsed thoroughly, and dried. Subsequently, a silane coupling agent must be applied for 60 seconds to establish covalent siloxane bridges between the ceramic silica and the resin cement matrix.
4. Definitive Step: Dual-cure resin cement is loaded, the crown seated, excess tacked and removed, and final light curing completed under glycerin gel to prevent oxygen inhibition.