Tooth Preparation and Pulp Protection

• Pulpal considerations include sealers, liners, and bases
• Steps in tooth preparation include initial and final tooth preparation

Initial Tooth Preparation

• Step 1: Initial depth and outline form
• Step 2: Primary resistance form
• Step 3: Primary retention form
• Step 4: Convenience form

Final Tooth Preparation

• Step 5: Removal of defective restoration or soft dentin
• Step 6: Pulp Protection
• Step 7: Secondary Resistance and retention forms
• Step 8: External wall finishing
• Step 9: Final debridement and inspection

Pulp Protection

• Pulp protection helps to finalize preparation for the final restorative material
• Pulp protection is needed to protect the pulp, seal the pulp, and reduce post-operative sensitivity

Interface Between Tooth and Restoration

• There are three options for interface between the tooth and the restoration: sealers, liners, and bases
• Sealers provide a protective coating for freshly cut tooth structure
• Liners placed with a minimal thickness of less than 0.5mm
• Liners offer fluoride release, dentinal seal through adhesion, and antibacterial action
• Bases are a dentin replacement material allowing for less bulk of restoration or blocking out undercuts for indirect restorations

Sealers

• Adhesive sealers providing bonding for retention and preventing leakage around enamel margins of restoration
• Bonding to enamel is a relatively simple process because etching increases surface energy
• Bonding to dentin presents a greater challenge because dentin adhesion relies primarily on the penetration of adhesive monomers into the network of collagen fibers
• Adhese Universal features an integrated desensitizing effect, eliminating the need for a separate desensitizing agent
• Adhese Universal forms a mechanical barrier and seals the dentin tubules

Dentin desensitizer sealers

• Occlude the dentinal tubules by precipitation of plasma proteins, limiting tubular fluid movement and resultant sensitivity
• Glutaraldehyde is a fixative that cross-links proteins
• Desensitizers like glutaraldehyde are effective disinfectants
• An example of desensitizer combination includes Gluma- 5% glutaraldehyde and 35% 2-hydroxyethyl-methacrylate (HEMA)

Deep Dentin

• Deep dentin is porous and susceptible to desiccation
• Thin dentin provides limited protection from heat generated by rotary instruments, noxious restorative material ingredients, thermal changes with restorative materials, transmitted forces, galvanic shock and microleakage of bacterial toxins
• Dentin permeability primarily depends on the remaining dentin thickness.
• Deep dentin is a less effective pulpal barrier compared with superficial dentin because the tubules are shorter, more numerous, and larger in diameter closer to the pulp
• 0.5 mm of remaining dentin thickness (RDT) reduces the effect of toxic substances by 75%
• 1 mm thickness by 90%
• 2 mm thickness has little or no pulpal reaction
• Remaining dentin thickness is the single most important factor in dentin permeability
• Deep dentin is a poor substrate for bonding procedures.
• Covering deep dentin can limit tubular fluid flow and create a protective thermal/physical barrier
• No liner is needed if RDT is greater than 2mm
• A liner can be considered if RDT is less than 2mm
• A liner is needed if RDT is less than 1mm

Sensitivity with composite restorations

• Postoperative sensitivity in resin composite restorations was not related to the absence of protective layers
• Postoperative sensitivity increased with the depth of cavities restored with the resin composite
• The type of dentine-bonding agents could also be responsible for postoperative sensitivity

Liners

• Reduce post-op sensitivity
• Seal dentin margins
• Protect the pulp
• RMGI Vitrebond and GC Fuji Lining LC are commonly used liners
• RMGI should not exceed layers thicker than 0.5mm

Benefits of RMGI

• Light activated
• Bond predictably to dentin with excellent seal
• Fluoride release
• Are compatible with pulp

Mineral Trioxide Aggregate (MTA) liners

• Liners are used with pulp exposure for vital pulp therapy
• MTA a silicate cement with primary reaction product with water as calcium hydroxide
• MTA liners are antibacterial/biocompatible and have a high Ph
• MTA liners are radiopaque and aid in the release of bioactive dentin matrix proteins
• MTA provides some seal to tooth structure
• MTA disadvantages are high solubility, prolonged setting time, liner needing to be covered, handling difficulties, and cost
• In the event of traumatic fracture and no pulp exposure- a liner can seal off the dentin immediately adjacent to the pulp in order to provide sedation and stimulate reparative dentin formation

Bases

• Block out undercuts under a restoration
• Act as a thermal or chemical barrier to the pulp
• Can be used a layer under composite in deep proximal boxes, when has no enamel remains
• These act as a base for metallic restorations or in deep proximal boxes with composite restorations
• The normal thickness for a base layer is greater than 0.5mm
• Examples include Fuji II LC, Fuji IX, Equia Forte.
• The most common base are glass ionomers or resin-modified glass ionomers

Workflow

• A 2mm bulk between the pulp and a metallic restorative material is desirable
• This bulk may include remaining dentin, liner, or base

Composite restorations workflow

• For deep and extensive preparations on a proximal surface, liner placement must be considered
• May need to consider liner and base placement
• Composite sandwich or bonded base technique can have a open or closed sandwich
• RMGI as a cavity liner under composite restorations create least microleakage unlike flowable composites
• When no enamel, consider amalgam or a bonded base technique
• Fuji II LC base is placed as first, in the box, and remains apical to the proximal contact because of decreased wear resistance
• The Fuji II LC should be 1-2mm and should impose a significant portion of the restoration

Composite Workflow

• Shallow Prep: Selective Etch on Enamel, Sealer Adhese Universal and Composite
• Deep prep: Liner over Pulp with RMGI and Fuji Lining LC, Selective Etch on enamel, Sealer Adhese Universal and Composite
• Deep Proximal Box with No Enamel: Consider using a Cavity Conditioner prior to the GI base of Fuji II LC or Equia Forte Selective Etch, Sealer Adhese universal and Composite

Cavity Conditioner

• Apply cavity conditioner for 10 seconds to remove the smear layer and lightly rinse taking care not to dessicate

Open Sandwich Technique

• The fluoride-releasing RMGI material is placed in the proximal box
• A wear-resistant composite is placed on the occlusal surface

Technique

• Ensure you follow manufacturer's instructions and remove any excess liner and base from preparation walls
• For metallic restorative material, a 2mm distance is desirable between pulp and restoration
• For composite, thermal insulators don't require as much material between restoration and pulp
• If excavation of caries extends to within 1.0mm of the pulp, a liner is selected to cover the deepest area of dentin
• If excavation in proximal is deep and no enamel remains, a bonded base with RMGI is considered
• With pulp exposure, perform vital pulp therapy after definite hemorrhage is stopped

Caries Removal Recommendations based on lesion severity

• Moderate lesion, selective carious tissue removal is needed
• If selective carious tissue removal is not fesible, non-selective carious tissue removal is recommended
• For advanced lesion, selective carious tissue removal
• If selective carious tissue removal is not feasible, step wise carious tissue removal is recommended
• Otherwise non-selective carious tissue removal