Treatment modalities for subgingivally placed restorations and selection of restorative materials

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treatment modalities subgingivally placed restorations restorative material selection

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https://pmc.ncbi.nlm.nih.gov/articles/PMC4541299

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subgingival restoration margins periodontal biologic width

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PMID: 36295642

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PMID: 39628744

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subgingival restoration biologic width violation management crown lengthening deep margin elevation orthodontic extrusion restorative material choice

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Treatment Modalities for Subgingivally Placed Restorations and Selection of Restorative Materials

1. Understanding the Problem: Why Subgingival Margins Matter

A restoration is considered subgingivally placed when its cervical margin extends below the free gingival margin into the sulcus or deeper. Even a high-quality, well-adapted subgingival restoration:

Increases plaque accumulation compared to a supragingival margin
Elevates gingival fluid flow and triggers local inflammation
Risks violating the biologic width (supracrestal tissue attachment - STA), the combined dimension of junctional epithelium (~0.97 mm) and connective tissue attachment (~1.07 mm), totaling ~2 mm above the alveolar crest

Margins at the gingival crest produce less inflammation than truly subgingival margins; supragingival margins yield periodontal health almost comparable to unrestored surfaces. The goal of all treatment modalities is therefore to either: (a) relocate the margin coronally, or (b) relocate the tissues apically - so a biologically sound relationship is re-established.

2. Indications for Subgingival Margin Placement

Before intervening, it is worth recognizing the legitimate reasons margins may be placed subgingivally:

Indication	Rationale
Esthetics (anterior zone)	Conceal cervical preparation / discoloration
Retention and resistance	Increase crown height for adequate preparation
Subgingival caries	Caries extends below gingiva
Root fractures / perforations	Access requires subgingival entry
Root caries susceptibility	Patient at high risk; covering root surface
Existing subgingival restorations	Replacing defective margins

3. Margin Placement Rules (Gargiulo Guidelines)

Based on the sulcus depth at the time of preparation:

Sulcus ≤ 1.5 mm - Place margin 0.5 mm below the gingival crest (ensures it stays well above the STA)
Sulcus 1.5-2 mm - Place margin at half the depth of the sulcus below the crest
Sulcus > 2 mm - Surgical intervention (crown lengthening) to reduce sulcus depth to ~1.5 mm before following Rule 1; deep margin placement in a deep sulcus is biomechanically challenging and tissue stability is unpredictable

4. Treatment Modalities

4.1 Surgical Crown Lengthening (SCL)

The traditional standard of care for biologic width violation or deeply subgingival margins. It involves apical repositioning of gingival tissue with or without osseous resection, exposing sound tooth structure above the bone crest.

Technique options:

Gingivectomy only - when there is adequate keratinized tissue and no need for bone removal (e.g., pseudo-pockets)
Flap surgery + osseous resection - when bone must be recontoured to re-establish STA dimensions; most common approach for true biologic width violation

Indications:

STA violation requiring definitive re-establishment
Teeth requiring ferrule effect that cannot be achieved conservatively
Fractured teeth with subgingival margins
Long-term esthetic cases in the anterior zone

Waiting period after SCL: A minimum of 6-8 weeks is needed before impression / final restoration; 3-6 months is preferred in the esthetic zone to allow complete gingival stabilization.

Limitations:

Invasive (requires surgery + healing)
Risk of altered crown-to-root ratio
Adjacent teeth may be exposed inadvertently
Can compromise esthetics (longer clinical crowns, black triangles)

Per the Crown Lengthening Cureus 2024 review (PMID 39628744), the procedure is subdivided as functional (expose caries, fractures, re-establish biologic width) or esthetic (lengthen short anterior teeth, refine gingival contour), and technique selection hinges on patient-specific factors including bone architecture, keratinized tissue quantity, and remaining tooth structure.

4.2 Deep Margin Elevation (DME) / Cervical Margin Relocation (CMR)

Introduced by Dietschi and Spreafico in 1998. A minimally invasive restorative technique where a subgingival margin is relocated coronally using adhesive composite before placing the definitive indirect restoration (onlay, crown, endocrown).

Concept: An adhesive "step" of composite resin is placed at or slightly above the gingival margin, converting a subgingival preparation finish line into a supragingival one accessible for isolation, adhesive bonding, and impression/scanning.

Advantages:

Avoids surgery and bone manipulation
Preserves tooth structure
Preserves original periodontal attachment
Compatible with digital impressions and indirect adhesive restorations
Faster treatment timeline (no surgical healing phase)
Cost-effective

Contraindications:

True violation of STA that cannot be managed restoratively
Insufficient ferrule and structurally compromised teeth needing crown lengthening
Poor isolation is not achievable even transiently
Active periodontal disease

Periodontal compatibility: Per the Aldakheel et al. 2022 review (PMID 36295642), well-defined and polished subgingival DME restorations are compatible with periodontal health when biologic width is respected. DME is currently considered a minimally invasive alternative to SCL and orthodontic extrusion.

Adhesive protocol for DME:

Rubber dam or tissue retraction (cord, Expasyl, or retraction cap)
Selective or total etch depending on substrate
Place adhesive resin (ideally etch-and-rinse for enamel)
Increment flowable or bulk-fill composite to relocate margin 1-2 mm coronally
Light-cure and finish/polish meticulously
Proceed to indirect restoration workflow

4.3 Orthodontic Forced Eruption (OFE)

Used when a tooth has a deeply subgingival fracture or caries, and surgical crown lengthening would result in an unacceptable crown-to-root ratio or compromise adjacent teeth.

Principle: Controlled orthodontic forces move the tooth coronally, bringing the bone and gingiva with it, thereby extruding the fracture/caries line into a more accessible position.

With rapid extrusion (fibrotomy): Move tooth 4-6 weeks, perform circumferential fiberotomy to prevent bone from following the root; allows caries/fracture line to emerge without bone migration.

With slow extrusion: Bone and gingiva migrate coronally with the tooth; subsequent crown lengthening may still be needed to create adequate tooth structure above the gingival crest.

Ideal for: Single-rooted teeth with deep cervical fractures; avoids reducing adjacent bone support.

4.4 Proximal Box Elevation (PBE)

A specific DME application for posterior teeth where the proximal box of a Class II preparation extends subgingivally. A flowable composite or resin-modified glass ionomer (RMGI) is used to build up the gingival floor of the box to supragingival level before finalizing the preparation.

4.5 Do Nothing / Accept the Margin Position

Acceptable when:

Subgingival extension is shallow (< 0.5-1 mm)
Sulcus is adequate
Patient has excellent oral hygiene
Material properties and marginal fit are optimal

Monitoring is mandatory.

5. Selection of Restorative Materials for Subgingival Zones

Material choice is critical because the subgingival zone is a hostile environment (moisture, limited visibility, microbial colonization).

5.1 Composite Resin (for DME / PBE)

The most commonly used material for cervical margin relocation. Evidence (El-Ma'aita et al. 2024; Aziz et al. 2024) supports incremental layering under strict adhesive protocol.

Types:

Flowable composites - easy to adapt in confined subgingival spaces; lower viscosity aids wetting; adequate for DME step
Bulk-fill composites - reduce procedural time; adequate depth of cure; used in posterior PBE
Nanohybrid / microfill composites - excellent polishability; reduce surface roughness; important for plaque resistance in sulcular environment

Key brands referenced in literature: Filtek Z250 (3M), Tetric EvoCeram (Ivoclar), Estelite Sigma Quick (Tokuyama)

Advantages: Adhesive bonding, conservative, moisture-compatible if properly isolated, polishable, radiopaque, tooth-colored

Disadvantages: Technique-sensitive; requires meticulous isolation; polymerization shrinkage may affect marginal seal

5.2 Resin-Modified Glass Ionomer Cement (RMGI)

A viable alternative to composite for DME/PBE, particularly where isolation is challenging.

Advantages:

Chemical adhesion to tooth structure (no etching strictly required)
Fluoride release - anticariogenic benefit at high caries-risk cervical zones
Less technique-sensitive than composite
Coefficient of thermal expansion closer to tooth structure
Better moisture tolerance than conventional composites

Disadvantages:

Lower compressive strength and wear resistance
Less esthetic than composite
Not ideal as a final definitive restoration

Use case: Ideal as a base/liner under an indirect restoration, or as the CMR step in patients where rubber dam is not achievable

5.3 Glass Hybrid (e.g., EQUIA Forte - GC)

A next-generation glass ionomer with reinforced glass particles and surface resin coating. Has emerged as a material for CMR/DME due to:

Higher strength than conventional RMGI
Fluoride release
Adequate polishability
Good marginal integrity in subgingival environments

5.4 Amalgam

Historically used for subgingival margins (especially Class II boxes) due to its dimensional stability, biocompatibility, and ease of placement in wet environments.

Current status: Still used in some clinical scenarios (posterior, non-esthetic, high-caries-risk), though declining in use due to Minamata Convention restrictions. The Dental Update case report noted amalgam was preferred over composite for a subgingival distal margin in a posterior tooth where moisture control was limited.

Advantages: Moisture tolerant, self-sealing over time, well-documented longevity, affordable Disadvantages: No adhesion, requires mechanical retention, non-tooth-colored, mercury content

5.5 Gold Alloys / Cast Metal

For subgingival indirect restorations:

Excellent marginal fit (gap of ~20 µm achievable)
Biocompatibility
Non-corrosive in subgingival environment
High polishability

However, esthetic limitations restrict its use.

5.6 Ceramic (Zirconia, Lithium Disilicate)

For indirect restorations with subgingival margins:

Lithium disilicate (e.max): Adhesively bonded; excellent polishability; low plaque affinity
Zirconia: Strong but cemented conventionally; adequate polishability; suitable for subgingival margins when fit is excellent

Both ceramics, when properly finished and polished, show plaque affinity comparable to or lower than metals. The luting cement choice is equally important.

6. Factors Governing Treatment Modality Selection

Factor	Favors SCL	Favors DME/CMR	Favors OFE
Biologic width violation	Yes	No (if STA intact)	No
Crown-to-root ratio	Adequate	Adequate	Poor (deep fracture)
Ferrule requirement	Mandatory, not achievable	Adequate enamel remains	Margin too deep
Sulcus depth	Deep (> 2 mm)	Shallow sulcus	Any
Adjacent tooth involvement	Minimal	Minimal	Isolated tooth
Patient preference	Surgery acceptable	Minimally invasive	Orthodontic course
Oral hygiene	Adequate	Adequate	Adequate
Esthetic zone	Yes (with healing time)	Yes	Yes

7. Key Periodontal Considerations - Roughness and Marginal Fit

Per the PMC review on iatrogenic damage, the four main sources of roughness in the subgingival zone are:

Surface scratches on acrylic, porcelain, or gold restorations
Exposed rough prepared tooth surface at the margin-luting interface
Marginal gap between restoration and tooth (typically 20-40 µm in subgingival margins)
Dissolution and fragmentation of luting cement

All restorative materials used subgingivally must therefore be:

Finished and polished to the highest possible standard
Placed with attention to marginal integrity
Monitored radiographically and clinically

Summary

The management of subgingivally placed restorations requires a biology-first approach:

Assess sulcus depth and STA integrity before any restorative work
Choose the least invasive modality that respects biologic width
Deep Margin Elevation with composite resin or RMGI has emerged as the preferred minimally invasive option for most posterior subgingival situations, supported by recent systematic reviews (PMID 36295642; PMID 38481655)
Surgical Crown Lengthening remains the gold standard when true STA violation is present or ferrule cannot be achieved conservatively (PMID 39628744)
Orthodontic extrusion is reserved for deep isolated fractures/caries where surgery would impair crown-to-root ratio
Material selection must prioritize polishability, marginal fit, moisture compatibility, and low plaque affinity in the subgingival environment

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