Dental liners, bases, and bonding systems

• Dental liners, bases, and bonding systems are dental materials that provide extra protection for the tooth being restored.

Prepared Tooth Structures

• The cavity preparation provides strength and determines how the tooth will hold the restoration.

Pulpal Responses

• Pulpal responses to stimuli can be physical, mechanical, chemical or biologic.
• Physical stimulus examples include thermal and electrical.
• Mechanical stimulus examples include traumatic occlusion and handpiece use.
• Chemical stimulus is acid from dental materials.
• Biologic stimulus is bacteria from saliva.

Dental Liners

• Dental liners create a barrier to protect the pulpal tissue from irritation caused by physical, mechanical, chemical, and biologic elements.

Calcium Hydroxide

• Calcium hydroxide protects the pulp from chemical irritation through its sealing ability.
• It encourages the production of reparative or secondary dentin.
• Calcium hydroxide is compatible with all restorative materials.
• Calcium Hydroxide is placed directly over the deepest portion of the preparation, and only on the dentin.

Varnish

• Varnish is a liquid with one or more resins in an organic solvent and is applied to the internal preparation structure.
• Varnish seals dentinal tubules and reduces leakage around a restoration.
• It acts as a barrier to protect the tooth from highly acidic cements like zinc phosphate.
• This material is not used under composite resins and glass ionomer restorations.
• Varnish is applied with a small disposable applicator or cotton pellet.
• A thin coating is placed on the internal walls, floor, and margin of a cavity preparation with a second application recommended.
• Varnish must be allowed to air dry.

Dentin Sealer

• Dentin sealer addresses or prevents hypersensitivity.
• It is applied instead of varnish and can seal dentinal tubules.
• In the case of indirect restorations, the sealer is ideal for use under them.
• It is applied sparingly, avoiding contact with soft tissues, and applied to all areas of exposed dentin with a cotton-tipped applicator.

Dental Bases

• Dental bases offer pulpal protection through protective, insulating, and sedative properties.
• Protective bases protect the pulp from a large restoration.
• Insulating protects the tooth from thermal shock.
• Sedative bases soothe pulp damaged by decay or mechanical means.

Types of Base Materials

• Zinc oxide-eugenol (ZOE) is a base material.
• Zinc phosphate is a base material.
• Polycarboxylate is a base material.
• Glass ionomer is a base material.

Dental Bonding

• Dental bonding helps retention by creating a micromechanical retention between the tooth structure and the restoration.

Enamel Bonding

• Enamel bonding is placed directly on the intact enamel surface.
• Sealants are an example of enamel bonding.
• Bonded orthodontic brackets are an example of enamel bonding.
• Resin-bonded bridges are an example of enamel bonding.
• Bonded veneers are an example of enamel bonding.

Dentin Bonding

• Dentin bonding is placed on the prepared dentin for the bonding of a restorative material to tooth structure.
• The smear layer is a thin layer of debris or "nature's bandage" of the prepared dentin.

Etching Systems

• Etching systems are used to remove the smear layer in preparation for bonding.
• Etching systems are available as a liquid/gel.
• Maleic acid is used in etching systems.
• Phosphoric acid is used in etching systems.

Clinical Application of the Etchant and Bonding Systems

• Plaque or debris is removed before the bonding process.
• Etchant removes the smear layer.
• The tooth structure is rinsed and dried, avoiding over-drying etched teeth.
• All surfaces are covered with bonding solution, applying more rather than less.
• Saliva contamination requires the entire procedure to be redone.
• The bonding material needs time to mature before completing the restoration.

Dental Cements

• Dental cements form a group of dental materials routinely used for placing indirect restorations.

Classification of Cements

• Type I cements are luting agents, including permanent and temporary options.
• Type II cements are restorative materials like glass ionomers.
• Type III cements are liners or bases placed within the cavity preparation.

Luting Agent

• Type I dental cements work as adhesives to hold castings and tooth structure together.
• Luting agents can be permanent or temporary.

Permanent Cement

• Permanent cement is used for long-term cementation of gold and ceramic restorations like inlays/onlays, crowns, bridges, veneers, and orthodontic appliances.

Temporary Cement

• Temporary cements are used for restorations needing potential removal due to sensitivity or other symptoms, as well as for provisional coverage.

Variables Affecting Cements

• Mixing Time: Follow the manufacturer's instructions.
• The powder and liquid should be measured according to intended use, and separated to make space for mixing.
• Incrementally divide the powder, incorporating smaller increments first if sizes vary.
• Thoroughly mix each powder increment into the liquid.
• Humidity: Premature exposure to warm temperatures or humidity can cause water loss from the liquid or moisture addition to the powder.
• Powder-to-Liquid Ratio: Consistency changes if the powder amount is off.
• Temperature: Some cements undergo an exothermic reaction.

Types of Cements

• Glass ionomer is a type of dental cement.
• Composite resin is a type of dental cement.
• Zinc oxide-eugenol is a type of dental cement.
• Polycarboxylate is a type of dental cement.
• Zinc phosphate is a type of dental cement.

Glass Ionomer Cements

• Liquid component: itaconic acid, tartaric acid, maleic acid, and water.
• Powder component: zinc oxide, aluminum oxide, and calcium.

Types of Glass Ionomer

• Type I glass ionomer is used for cementing metal restorations and direct-bonded orthodontic brackets.
• Type II glass ionomer is designed for restoring areas of erosion near the gingiva.
• Type III glass ionomer is used as liners and dentin-bonding agents.

Benefits of Glass Ionomer

• The powder is an acid-soluble calcium which releases fluoride, helping inhibit recurrent decay.
• Glass ionomer causes less trauma or shock to the pulp.
• It has a low solubility in the mouth and adheres to slightly moist tooth surfaces.
• It has a very thin film thickness, which is excellent for seating ease.

Supply of Glass Ionomer

• Type I can come as a powder/liquid mix.
• It should be manually mixed on a paper pad or cool, dry glass slab (the slab increases the working time of the cement.)
• Type I may be premeasured capsules.
• Premeasured capsules need to be triturated and expressed through a dispenser.

Composite Resin Cements

• Chemical construction is similar to composite resins.
• They feature a low film thickness, thinner than standard composite resins, and are insoluble in the mouth.

Uses of Composite Resin

• Ceramic or resin inlays and onlays can be cemented with composite resin.
• Ceramic veneers can be cemented with composite resin.
• Orthodontic bands can be cemented with composite resin.
• Direct bonding of orthodontic brackets can be done with composite resin.
• Composite resin can be used to cement all metal castings.

Supply of Composite Resin

• Composite resin may come as a powder and liquid mix.
• Syringe-type applicators may be used to apply composite resin.
• Some composite resins use a base and catalyst.
• Light-cure/dual-cure systems exist that need recommended portions on a paper pad mixed with a spatula.

ZOE Cements

• Liquid component: eugenol, H₂O, acetic acid, zinc acetate, and calcium chloride.
• Powder component: zinc oxide, magnesium oxide, and silica.

Types of ZOE

• Type I ZOE lacks strength and long-term durability and is used for temporary cementation of provisional coverage.
• Type II ZOE has reinforcing agents, used for permanent cementation of cast restorations or appliances.

Supply of ZOE

• Type I ZOE is supplied as a two paste system.
• The two pastes need to be dispensed in equal lengths on a paper pad and mixed.
• Type II ZOE is liquid/powder form.
• The two components are mixed on an oil resistant paper pad, should be mixed for 30 to 60 seconds, and has a setting time in the mouth of 3 to 5 minutes.

Polycarboxylate Cements

• Liquid component: polyacrylic acid, itaconic acid, maleic acid, tartaric acid, and water.
• Powder component: zinc oxide.

Use of Polycarboxylate

• Can be used as permanent cement for cast restorations, stainless-steel crowns, and orthodontic bands.
• Or a nonirritating base under both composite and amalgam restorations.
• Can also be an intermediate restoration.

Supply of Polycarboxylate

• Polycarboxylate can be a powder/liquid mix.
• Liquids are measured with a plastic squeeze bottle or calibrated syringe-type liquid dispenser.
• The liquid has a limited shelf life because it thickens as it evaporates.
• Mixing is carried out on a nonabsorbent paper pad.

Zinc Phosphate Cements

• Liquid component: phosphoric acid, aluminum phosphate, and water.
• Powder component: zinc oxide, magnesium oxide, and silica.

Types of Zinc Phosphate

• Type I (fine grain) is for the permanent cementation of castings like crowns, inlays, onlays, and bridges, which require a thin film layer.
• Type II (medium grain) is recommended as an insulating base for deep cavity preparations.

Supply of Zinc Phosphate

• Type I zinc phosphate is a powder/liquid mix
• The powder is divided into increments of varying sizes.
• Critically, the powder must be added to the liquid in very small increments.
• The cement must be spatulated slowly over an area of a cool, dry, thick glass slab to dissipate the heat.

Cement Removal

• The operator needs to be prepared and knowledgeable.
• Instruments needed include an explorer, mouth mirror, and excavator.
• Use a fulcrum during removal.
• Use dental floss in and around the embrasure areas.