6.5 Pit & Fissure Sealants, Polishers & Biomaterial Biocompatibility

Pit & Fissure Sealants, Polishers & Biomaterial Biocompatibility

Pit & Fissure Sealants

Pit and fissure sealants are a highly effective evidence-based primary preventive intervention designed to prevent dental caries in the deep, narrow developmental pits and fissures of occlusal, buccal, and lingual tooth surfaces. Anatomical fissures provide ideal shelters for Streptococcus mutans biofilm accumulation while preventing entry of toothbrush bristles.

Enamel Acid Etching Mechanics

Resin sealants do not bond chemically to enamel; they rely entirely on micromechanical retention established via acid etching.

Enamel Acid Etching & Bonding Mechanics
├── Apply 37% Phosphoric Acid (15-30 seconds)
├── Dissolves Hydroxyapatite Crystals -> Microscopic Enamel Tags (Types I & II)
├── Increases Enamel Surface Area & Surface Free Energy
├── CRITICAL STEP: Isolate & Prevent Salivary Contamination
├── Liquid Resin Monomer (Bis-GMA/UDMA) Flows into Tags via Capillary Action
└── Light Polymerization (450-490 nm) -> Micromechanical Interlocking

• Etchant Agent: 37% Phosphoric Acid ($H_3PO_4$) in liquid or gel form.
• Etch Duration: 15 to 30 seconds for permanent enamel. Primary teeth or fluorosed teeth require longer etching times (up to 30-60 seconds) due to aprismatic enamel structure.
• Microscopic Effects: Phosphoric acid selectively dissolves hydroxyapatite crystals from enamel rods:
  • Type I Pattern: Preferential dissolution of enamel prism cores.
  • Type II Pattern: Preferential dissolution of enamel prism peripheries.
• Etching creates microscopic pores (10-40 $\mu m$ deep) and increases surface free energy, enabling the liquid resin monomer to wet the surface and penetrate enamel tags via capillary action.

Clinical Application Protocol

1. Surface Cleaning: Clean occlusal surface thoroughly with a slurry of plain flour of pumice and water using a prophy cup or bristle brush. Do not use pastes containing oils, glycerine, or fluoride, which leave a barrier film.
2. Isolation: Isolate tooth using a rubber dam (gold standard) or cotton rolls and dry angles. Moisture contamination by saliva is the single primary cause of sealant failure. Proteins in saliva immediately coat etched enamel, blocking resin tag formation.
3. Acid Etch Application: Apply 37% phosphoric acid gel to all pits and fissures for 15-30 seconds.
4. Rinse & Dry: Rinse for 15-20 seconds with water. Dry thoroughly with oil-free air. Etched enamel must display a frosty, chalky-white appearance. If saliva contacts etched enamel, re-etch for 10 seconds.
5. Sealant Placement: Apply flowable resin (Bis-GMA or UDMA matrix) sparingly into fissures.
6. Curing: Light cure for 20-40 seconds using an LED curing light (wavelength 450-490 nm).
7. Evaluation: Inspect retention with an explorer; check occlusion with articulating paper.

Sealant Material Options

• Filled Resins: Contain glass/silica particles to increase wear resistance. May require occlusal adjustment if high.
• Unfilled Resins: Clear or tinted resin without filler. Wears down naturally under masticatory forces.
• Glass Ionomer (GI) Sealants: Chemically bond to tooth structure via carboxylate groups and release fluoride. Ideal for partially erupted permanent molars where complete moisture control is impossible.

Polishing & Abrasive Hardness Principles

Selective Polishing Philosophy

Modern dental hygiene practice follows the principle of selective polishing. Polishing is not a routine mandatory component of every prophylaxis. Rubber-cup polishing with coarse abrasive paste removes 3 to 5 micrometers ($\mu m$) of the outer fluoride-rich layer of enamel. Polishing should be performed selectively only on tooth surfaces displaying remaining extrinsic stain after calculus removal.

Mohs Hardness Scale in Dentistry

To polish effectively without inflicting permanent scratch damage to tooth structures or restorative materials, the clinician must select an abrasive agent based on the Mohs Hardness Scale.

$\text{Rule of Abrasive Science: Abrasive Hardness } > \text{ Surface Hardness}$

Clinical Warning: Polishing exposed dentin (hardness 3-4) or cementum (hardness 2.5) with pumice (hardness 6.0) causes rapid structural loss and severe dentinal hypersensitivity.

Air-Powder Polishing (APP) Technologies

Air-powder polishing utilizes a pressurized mixture of compressed air, water, and specialized abrasive powders delivered through a handpiece nozzle.

Air-Powder Polishing Powders
├── Sodium Bicarbonate (Mohs 2.5, 74 microns): Supragingival Enamel ONLY
│   └── Contraindicated: Restorations, Roots, Sodium Diets, COPD/Asthma
└── Glycine & Erythritol (Mohs 2.0, 14-20 microns): Subgingival & Implants
    └── Safe for Root Surfaces, Pockets up to 9mm, Titanium Implants

Powder Comparisons and Clinical Applications

1. Sodium Bicarbonate ($NaHCO_3$):
   • Mohs Hardness: 2.5; particle size ~74 $\mu m$.
   • Clinical Indication: Heavy supragingival extrinsic stain and pit/fissure stain removal on intact enamel surfaces.
   • Contraindications:
     • Restorative materials (composite resins, porcelain, gold crowns, resin cements)
     • Exposed root surfaces (dentin/cementum)
     • Titanium dental implants
     • Patients on sodium-restricted diets or with hypertension
     • Severe respiratory conditions (asthma, COPD, cystic fibrosis)
     • Immunocompromised patients or active communicable diseases
2. Glycine Powder (Amino Acid):
   • Mohs Hardness: 2.0; particle size ~20 $\mu m$.
   • Clinical Indication: Safe for supragingival AND subgingival root surfaces, titanium implants, periodontally involved pockets up to 5 mm (or 9 mm with subgingival nozzle tips), and restorative materials.
3. Erythritol Powder (Sugar Alcohol):
   • Mohs Hardness: 2.0; particle size ~14 $\mu m$ (ultra-fine).
   • Clinical Indication: Subgingival biofilm removal, root surface debridement, and implant maintenance without surface roughness.

Biomaterial Biocompatibility & Safety

Biocompatibility is the ability of a material to perform with an appropriate host response in a specific application without causing toxic, allergenic, or mutagenic systemic or local adverse effects.

Biological Evaluation Standards (ISO 10993 / ISO 7405)

Dental biomaterials must undergo a strict 3-tier testing evaluation:

1. Initial (Tier 1) In-Vitro Tests: Cytotoxicity assays, hemolysis, and cell culture mutagenicity (Ames test).
2. Secondary (Tier 2) In-Vivo Tests: Subcutaneous implantation, contact hypersensitivity, and mucosal irritation tests in animal models.
3. Clinical (Tier 3) Pre-market Evaluation: Controlled clinical trials in humans to evaluate tissue compatibility.

Biocompatibility Profiles of Common Dental Materials

• Dental Amalgam & Mercury Safety: Solid set amalgam is insoluble and stable. Trace elemental mercury vapor ($Hg^0$) released during placement and removal is below OSHA threshold limits. Managed environmentally via EPA-mandated amalgam separators.
• Resin Monomer Leaching: Uncured composite resin monomer (Bis-DMA, TEGDMA) can leach into saliva. Salivary esterases can break Bis-DMA into trace Bisphenol A (BPA). Complete light curing and post-placement rinsing eliminate surface monomer.
• Nickel Hypersensitivity: Nickel is the most common metal allergen, causing Type IV cell-mediated delayed hypersensitivity (erythema, burning mucositis, lichenoid reactions) in 10-15% of females. Present in base-metal crown alloys (Ni-Cr) and stainless steel orthodontic wires.
• Zinc Oxide Eugenol (ZOE): Eugenol provides an obtundent (soothing) effect on dental pulp. However, Eugenol inhibits free-radical polymerization of composite resins. ZOE must never be used beneath resin composite restorations!