Dental Liners, Bases, and Bonding Systems Chapter 44 Dental Liners, Bases, and Bonding Systems

Introduction A variety of supplemental dental materials can be incorporated in a restorative and esthetic procedure for the health and well-being of the tooth that is being restored Dental liners, bases, varnishes and bonding systems Liners and bases can make a big difference in postoperative sensitivity and long-term pulpal prognosis when used appropriately. Liners and bases are even used in cavity preparations that are small in circumference but deep.

Supplementary Dental Materials and Application in Order of Use This table is a simplified guide to how some of the discussed materials may be used in clinical practice. Often the treatment plan changes once a tooth has actually been opened up and evaluated. As research in the field of restorative dentistry continues, the methods and materials used will change.

Prepared Tooth Structures Design of the cavity preparation: Provides strength within the tooth Helps determine how the tooth will hold the restoration in place This is different with amalgam, which relies primarily on retentive features such as removing enough tooth structure to cause the opposing walls to slant slightly inward. In general, the more natural tooth structure that remains, the stronger the tooth will be.

Pulpal Responses: Types of Stimulus Physical stimuli Example: Thermal, electrical Mechanical stimuli Example: Handpiece, traumatic Chemical stimuli Example: Acid from dental materials Biologic stimuli Example: Bacteria from saliva The pulp, found inside the tooth, contains the nerve and blood supply that keep the tooth alive and supplied with nutrients. As was mentioned in earlier chapters, if decay has progressed through the enamel and into the dentin, a patient may have greater sensitivity and discomfort even after placement of a permanent restoration. These are only a few of the stimuli that may trigger an unfavorable response, either reversible or irreversible, in the pulp. Irreversible trauma to the pulp requires endodontic treatment (a root canal) to save the tooth.

Dental Liners A thin layer of material placed at the deepest portion of the dental preparation to provide pulpal protection or dentinal regeneration Protects pulpal tissue from irritation caused by physical, mechanical, chemical, and biologic elements The health and condition of the tooth being restored determines what lining agent the dentist will select What do liners help prevent? (Liners help protect the pulp from irreversible irritation that may lead to endodontic therapy or an extraction.)

Calcium Hydroxide A frequently selected type of cavity liner because of its unique characteristics: Protects the pulp from chemical irritation through its sealing ability Stimulates the production of reparative or secondary dentin Is compatible with all types of restorative materials Calcium hydroxide’s capacity for stimulating the production of reparative dentin is unusual among dental materials.

Application Liners are supplied either as a two-paste system or as a light-cured material The material is placed prior to placement of the restorative material and with the use of a Dycal (calcium hydroxide) applicator Placed only on the deepest dentin surface of the preparation This material is not to be placed on enamel or in retentive grooves of the preparation Refer students to Procedure 44-1 (p. 758) for more information on applying calcium hydroxide. What would be an advantage of the light-cured calcium hydroxide material over the two-paste system? (The operator can control the time of set with the light-cured material.)

Placement of a Liner This drawing represents a cross section of a tooth with its various layers and the preparation in the middle. As shown, calcium hydroxide is placed over the deepest portion of the pulpal floor, and only on dentin. Modified from Heymann HO, Swift EJ, Ritter AV: Sturdevant’s art and science of operative dentistry, ed 6, St Louis, 2013, Mosby.

Varnish Varnish is a liquid consisting of one or more resins in an organic solvent This material is placed within the entire preparation If varnish is indicated, would it be placed before or after placement of calcium hydroxide? (After)

Varnish Application accomplishes the following: Seals dentinal tubules Reduces microleakage around a restoration Acts as a barrier to protect the tooth from highly acidic cements such as zinc phosphate One popular use is placement of a dental varnish, such as Copalite, throughout the preparation just before amalgam placement. Note: Dental varnish has a distinct noxious smell that evaporates quickly. Care should be taken to replace the lid as soon as possible after varnish is dispensed.

Application of Varnishes Applied with a small disposable applicator or with a cotton pellet held in sterile cotton pliers It is important to note that when a liner is placed, the varnish will be placed after the liner is applied Because dental varnish interferes with the bonding and setting reaction of composite resins and glass ionomer restorations, the use of varnish is contraindicated with these materials For the sake of efficiency, the dentist usually applies the varnish while the assistant carefully prepares the amalgam.

Location for Placement of Cavity Varnish This drawing reiterates that varnish or sealer is placed over the liner, which is applied first and allowed to set. As you will see later in the lesson, a base is also sometimes placed after the liner but before the sealer. Modified from Heymann HO, Swift EJ, Ritter AV: Sturdevant’s art and science of operative dentistry, ed 6, St Louis, 2013, Mosby.

Fluoride Varnish This gel-like substance is designed to release fluoride on enamel, root structure, and dentin structure Specific indications include: Professional topical fluoride application Treatment of hypersensitive cervical areas Orthodontic patients Cavity varnish Dentin sealant Fluoride varnish is a highly effective cavity varnish and desensitizer. This was used in Europe and Canada before being approved for use in the United States. Refer students to Procedure 44-2 (p. 759) for more information on applying varnishes.

Desensitizer Used to treat or prevent hypersensitivity that a patient may experience from a newly placed direct or indirect restoration Also referred to as a primer The material is designed to seal the dentinal tubules No surface layer of the preparation is prepared when a desensitizer is used; this makes the material ideal for use under all indirect restorations Dentin sealer is used under restorations as per the listed indications. Dentin sealer may also be used as a temporary and conservative desensitizer in areas that may not be readily or immediately restored (e.g., cervical abfraction or in areas of toothbrush abrasion) instead of a cervical/gingival composite.

Application of Desensitizer Most desensitizers contain hydroxyethyl methacrylate (HEMA) and glutaraldehyde This material is used sparingly Do not allow the material to contact soft tissue The desensitizer is relatively costly, but well worth it. Does a dental assistant apply desensitizers? (The EFDA [RDA] can place desensitizers if the function is legal in the state in which the assistant is practicing.) Refer students to Procedure 44-3 (p. 760).

Dental Bases When a tooth preparation becomes moderately deep to deep, the dentist will place a base under the permanent restoration A base is an additional layer to protect the pulp Bases provide different types of pulpal protection: Protective: Protects the pulp from a large restoration Insulating: Protects the tooth from thermal shock Sedative: Soothes pulp that has been damaged by decay or irritated by mechanical means Recall that for the reasons listed in this slide, a base would be applied over a liner (if a liner was indicated) or directly on a moderately deep dentinal floor. The varnish, sealer, or both would then be placed before the final restoration.

Types of Base Materials Zinc oxide-eugenol (ZOE) Could be selected for use as an insulating base and as a sedative base Cannot be used under composite resins, glass ionomers, or other resin restorations Zinc phosphate An excellent material because of its thermal insulation qualities Polycarboxylate Nonirritating to the pulp Common commercial examples of dental bases include: Intermediate restorative material (ZOE) Tenacin (zinc phosphate) Durelon (polycarboxylate) Vitrebond (glass ionomer). Glass ionomer is a popular option because it is compatible under composite resins and easy to manipulate and place.

Application of Base The base material resembles a putty-like consistency because it actually provides a buffer or layer between the pulp and the restoration The entire pulpal floor is covered with a base to thickness of 1 to 2 mm A material may be called a cavity varnish, liner, or base. According to one placement scheme, it is a liner if the layer is less than 0.5 mm, and a base if it is thicker than 0.5 mm. Refer students to Procedures 44-4, 44-45, and 44-6 (pp. 761-763) for more information.

Location for Placement of a Base This diagram shows the proper order of placement of the base over the liner. The varnish or sealer is placed over the base. A bonding agent is placed over the base (after etching) if composite resin is to be placed. Modified from Heymann HO, Swift EJ, Ritter AV: Sturdevant’s art and science of operative dentistry, ed 6, St Louis, 2013, Mosby.

Dental Etchant In preparation for the use of a bonding material, the tooth surface will need to be etched with an acidic tooth conditioner When you rinse and dry an etched surface, it will have a distinct “frosted” appearance The use of etchant is critical for both enamel and dentin surfaces of a cavity preparation to form a better mechanical bond between the tooth and the permanent restorative material What do bonding agents do? (Bonding agents allow for the removal of less tooth structure before definitive restoration placement because minimal retentive features are needed.) Direct bonding to the tooth is achieved by way of removal of the smear layer with etchant. The use of a light helps the operator control the set time of the material. Proper isolation of the teeth to be treated is necessary because contact with skin or soft tissues in the mouth will cause a burn, irritation, or both.

Application of Dental Etchant The etchant material is supplied either as a liquid or gel, with gel being packaged in a syringe-type applicator Syringe dispensing through pre-bent dispenser needles provides precise placement of the material on tooth Fifteen to twenty seconds is the most common recommended time The acid etchant is usually 35% phosphoric acid gel, colored (e.g., blue) to make it easier to see where it has been placed and whether it has been completely washed off. Refer students to Procedure 44-7 (p. 764) for more information on the application of dental etchant.

Dental Bonding The process of solid and/or liquid contact of one material with another at a single margin Retaining properties of bonding systems have been improved by the creation of micromechanical retention between the tooth structure and the restoration Preparing the tooth surface properly with the use of acid etchant for removal of the smear layer before bonding exposes more microscopic surface area, and thus micromechanical retention is also achieved. How is plaque removed before bonding? (Prophylaxis paste. Note: The fluoride usually found in prophylaxis paste may interfere with proper bonding.) The bonding agent is usually light-cured. Some practitioners, as well as manufacturers, advocate the application of multiple layers of bonding agent.

Dentin Bonding A major factor in the success of bonding to dentin is the removal of the smear layer, which is a very thin layer of debris composed of fluids and tooth components that remain on dentin after cavity preparation has been completed A slight amount of moisture must be maintained on the dentin so as not to desiccate or “dry out” the tooth Before dentin bonding, the smear layer must be removed through application of etchant and the tubules opened The smear layer interferes with the strength of the bond. Overdrying the tooth weakens the bond strength and increases the chance of tooth sensitivity.

Enamel Bonding Examples of enamel bonding: Sealants Bonding of orthodontic brackets Resin‑bonded bridges Resin-bonded veneers When sealant, resin cement, or restorative material is placed on an etched surface, it flows in and around the enamel tags The material hardens in this location to form a strong mechanical bond with enamel Sealant material is also held in place by occlusal developmental grooves. Bonded veneers are an example of an aesthetic option available to an individual who wishes to change the shape, size, and color of the teeth. A very small layer of the facial enamel is removed, followed by an impression that allows the dental laboratory to fabricate a new facial surface in porcelain, which is bonded permanently to the prepared teeth.

Application of Enamel Bonding Bonding applications are available as self- curing, dual-cured, and light-cured systems Some systems use a single application, whereas others require the mixing of two liquids Each bonding system is different, and the material from one system is not interchangeable with that of another It is essential that the manufacturer’s instructions be followed exactly with each product All of them will involve some variation of etch, prime, and bond. Some combine etching and priming in one step with a separate bonding step. Others have a separate etch step and combine the priming and bonding step. Refer students to Procedure 44-8 (p. 765) for more detailed information.

Application of Enamel Bonding The tooth surface receives the etchant material, which removes the smear layer The bonding component is allowed to flow into these small defects and into the partially opened tubules in dentin The material is allowed either to: Harden and act as a hybrid layer Remain in a liquid state while the restoration is being placed, to bond together the tooth and the dental material If a metal matrix band is used, why is it important that the bond is prepared with cavity varnish or wax before placement around the tooth? (It prevents the bonding resin from adhering to the surface.)

Guidelines for Clinical Application of Bonding Products Remove any plaque or debris before beginning the bonding process Avoid overdrying the teeth; these products work best on a slightly moist tooth surface Note that too much bonding material is better than too little; multiple layers work best Ensure that the bonding solution covers all surfaces Avoid any contamination with saliva, blood, or debris, which will require the entire procedure to be redone Allow as much time as possible for the bond to mature before completing the restoration Overdrying the tooth is called desiccation. What will overdrying the tooth do to the bond strength? (It will weaken the bond strength.)