Treatment Modalities & Restorative Material Selection for Subgingivally Placed Restorations

Why Subgingival Margins Are Problematic

• Difficult isolation (moisture contamination compromises bonding)
• Inaccessibility for impression-taking and cementation
• Risk of violating the Supracrestal Tissue Attachment (STA) - formerly "biologic width" - leading to chronic inflammation, bone loss, and recession
• Bacterial biofilm accumulation causing periodontal breakdown

Key Rule: A minimum of 3 mm of sound tooth structure must exist between the alveolar crest and the final restoration margin to preserve the STA (junctional epithelium ~1 mm + connective tissue ~1 mm + sulcus ~1 mm).

Treatment Modalities

1. Deep Margin Elevation (DME) - Also Called Cervical Margin Relocation

• First described by Dietschi & Spreafico (1998); popularized by Magne & Spreafico (2012)
• Minimally invasive - no surgery, no bone removal
• Goal: relocate the adhesive interface to a dry, visible, accessible zone

• Subgingival caries or old restoration where isolation IS achievable
• Deep proximal boxes for onlays/inlays
• Reinforcing undermined cusps, sealing dentin, filling undercuts

1. Rubber dam isolation with appropriate clamp
2. Sectional matrix with wedge + Teflon tape for cervical seal (specialized matrices: Reel Matrix by Garrison)
3. Soft tissue retraction using cord, wedges, light-cured rubber dam, Teflon tape
4. Adhesive composite resin placed incrementally to elevate margin
5. Final preparation now with supragingival/equigingival finish line
6. Indirect restoration fabricated and cemented normally

2. Gingivectomy / Soft Tissue Ablation

• Scalpel/blade (traditional)
• Laser (diode, Nd:YAG, Er:YAG)
• Electrosurgery
• Soft tissue burs

• Cannot be used when bone removal is also needed
• Risk of STA violation if done too aggressively
• Contraindicated in thin biotype (recession risk)
• Wait 4-8 weeks post-surgery for tissue stabilization before final restoration

3. Surgical Crown Lengthening (SCL)

• When isolation for DME is not possible
• Contraindication to gingivectomy alone
• Subgingival crown fractures
• Increasing the ferrule effect (target: 1.5-2.0 mm of sound tooth structure above the finish line, 360 degrees)
• When DME would still violate STA

4. Orthodontic Extrusion (Forced Eruption)

• Subgingival fractures or deep caries where SCL would compromise crown-to-root ratio
• When preservation of bone is critical (esthetic zone)
• Where the extrusion margin migration avoids need for surgery

• Requires fibrotomy (fiberotomy) during extrusion to prevent soft tissue following the tooth
• May need retention period post-extrusion
• Time-consuming (weeks to months)
• Invasive in terms of treatment duration

Summary Comparison Table

Selection of Restorative Materials for Subgingival Restorations

A. Direct Restorations

1. Resin Composite (Material of Choice for DME)

• Preferred material for deep margin elevation
• Nanohybrid or bulk-fill composites (e.g., Filtek Z250, Tetric EvoCeram, Estelite Sigma Quick)
• Preheated composite improves flow and adaptation at deep margins
• Closed Sandwich Technique: thin RMGI liner/base over deep dentin (hydrophilic seal) + nanohybrid composite for margin elevation
• Requires strict adhesive protocol and rubber dam isolation
• Provides good marginal integrity, dentin sealing, cusp reinforcement
• High polish achievable - important as smooth margins reduce biofilm accumulation

2. Resin-Modified Glass Ionomer Cement (RMGI)

• Used as a liner/base in the closed sandwich technique
• Hydrophilic - tolerates slight moisture
• Chemical bond to dentin
• Good for deep, sclerotic dentin where adhesive bonding is less reliable
• Fluoride release - cariostatic benefit

3. Conventional Glass Ionomer Cement (GIC)

• Moisture-tolerant - can be used more easily in subgingival environments
• Suitable as a base or for temporary/interim restorations
• Used with indirect non-bonded restorations (conventional cementation approach)
• Less technique-sensitive than composites subgingivally
• Lower strength than composite; not ideal as a final esthetic restoration

B. Indirect Restorations (After Margin Management)

1. Ceramic Restorations (Lithium Disilicate, Zirconia)

• Preferred for posterior teeth requiring full/partial coverage
• Lithium disilicate (e.g., IPS e.max): good strength (400 MPa), excellent esthetics, can be adhesively cemented
• Zirconia: highest strength (>1000 MPa), ideal for high-load posterior areas, opaque
• Require dry, accessible margins for adhesive cementation - this is exactly why DME or SCL is done first

2. Metal-Ceramic (PFM) Restorations

• Suitable where esthetics is secondary and strength is needed
• Can be cemented with conventional cements (zinc phosphate, GIC) - more moisture-tolerant
• Less demanding of perfect subgingival isolation for cementation

3. Full-Metal Restorations (Cast Gold/Alloy)

• Most biologically inert and most tolerated by periodontal tissues
• Can be conventionally cemented
• Poor esthetics but excellent long-term durability
• Ideal for posterior teeth with subgingival margins where perfect isolation is difficult

Periodontal Response to Restorative Materials

Key principle: Surface smoothness and marginal fit are more important than material composition in determining the periodontal response to subgingival restorations.

Decision Algorithm

Deep subgingival margin identified
           |
    Can you isolate? (Rubber dam possible?)
    /              \
  YES               NO
   |                 |
  DME           Assess STA violation?
  (preferred)    /           \
           Violating STA    Not violating STA
                |                  |
         Need bone?           Gingivectomy
         /        \
        YES        NO
        |           |
       SCL       Gingivectomy
        
If poor crown-root ratio after SCL → consider Orthodontic Extrusion instead

Clinical Pearls

1. 0.5 mm subgingival margin is manageable; >1.5 mm creates major complications, especially for bonded cementation
2. Biologic width/STA = 3 mm from alveolar crest; NEVER violate this zone
3. For indirect bonded restorations (onlays, endocrowns), margin elevation is mandatory for predictable adhesion - you cannot bond with matrices and wedges in the way
4. Smooth, gap-free composite margins are tolerated without significant periodontal inflammation (supported by histological evidence)
5. After any surgical procedure (SCL or gingivectomy), wait 4-8 weeks for tissue stabilization before taking final impressions
6. After orthodontic extrusion, a retention/fibrotomy period is required before restoration