Liners and Bases PDF

Liners and bases Dr. Omar Abdelaziz Ismail Lecturer of Operative Dentistry Hours University in Egypt 0  Liners and bases Introduction -The crown is exposed to numer...

Liners and bases Dr. Omar Abdelaziz Ismail Lecturer of Operative Dentistry Hours University in Egypt 0  Liners and bases Introduction -The crown is exposed to numerous biomechanical insults during function, which include thermal changes, pH changes, bacterial attacks, masticatory and wear forces, etc. -The dentin-pulp organ could not tolerate such insults without suffering from pain, excessive wear and ultimate pulp degeneration. -The non-porous, non-vital enamel provides the necessary protection for the vital dentin-pulp organ to accommodate the challenges present in the oral environment without suffering from any pathological changes. Protective Functions of Enamel and Dentin: 1. Enamel effectively seals the dentinal tubules against chemical and biological insults. 2. Enamel is an effective thermal and electric insulator. 3. Dentin is a good thermal insulator that can effectively protect the pulp from thermal shocks. 4. Dentin is a dynamic biological barrier that can respond to biological insults by a variety of mechanisms that can block the passage of such irritants to the pulp. 5. The dentin core is designed to distribute the forces falling on the tooth surface along a wide area, where it could be elastically absorbed. 6. The perceived vital color of the tooth structure is a combination of the optical characteristics of both enamel and dentin tissues. -The thermal, chemical, biological and mechanical protective functions of dentin are dependent upon the thickness and the type of the bridge of dentin overlaying the pulp. -So, any loss in enamel or dentin by a lesion or by cavity preparation deprives the tooth from some of such protection; the amount 1  Liners and bases of protection lost is relative to the amount of destruction in the hard tooth structures. Problems Associated with Loss of Enamel and Dentin: 1. The communication with the oral environment will expose the dentin- pulp system to thermal, osmotic, tactile, evaporative, bacterial, electric and chemical irritations. The patient may experience pain and may suffer from pathological dentin-pulp conditions as dental caries and reversible or irreversible pulpitis. 2. Enamel loss also exposes the dentin to the action of chromogenic bacteria and food stains. This may cause dentin discoloration. 3. Lesions involving the dentin are often irregular in shape, the removal of which leaves the dentin with an irregular shape. This leads to unfavorable resolution of forces falling on the tooth and may result in stress concentration that ultimately leads to mechanical failure. -In most instances, the material used as a permanent restoration, may not be sufficient by itself, to restore all of the lost protective functions of enamel and dentin. Therefore, several lining materials are used to line the prepared cavities underneath permanent restorations, to provide thermal, chemical, electric, mechanical and biological protection of the dentin- pulp organ as well as to medicate the pulp or to compensate for the lost esthetics. 2  Liners and bases Required Properties for Lining and Cement Materials: 1. It should be compatible with the tooth substrate. 2. It should be compatible with the restorative material. 3. It should be easy in application. 4. It should be able to seal the dentinal tubules. 5. It should be having adequate working time. 6. It should be having short setting time so as to be directly followed by the final restoration or by temporary filling procedures. 7. It should withstand the manipulative procedures involved in the placement of the final restoration and the forces applied during function. 8. It should enhance the repair capacity of the pulp by reversing inflammation and stimulating the deposition of reactionary dentin. 9. It should not be degradable by the dentinal or oral fluids. 10. Lining materials used under metallic restoration should be good thermal insulators. 11. Lining materials used under tooth-colored restoration should have similar optical properties to dentin. 3  Liners and bases Classification of intermediately Protective materials (Intermediately Protective Materials) liners and Cement bases A) Liners I. Thin film liners a. Solution liners (varnishes, 2-5 µm) b. Suspension liners ii. Thick liners (Cement liners) a. Hard setting Calcium Hydroxide Cement b. Light-Cured Calcium Hydroxide Cement c. Low Viscosity Zinc Oxide Eugenol (ZOE) Cement d. Resin-Modified Glass Ionomer (RMGI)) Cement B) Base a. Zinc Phosphate Cement b. Resin-Reinforced ZOE Cement c. Polycarboxylate Cement d. Glass Ionomer (GI) Cement e. RMGI Cement 4  Liners and bases Liners -Liners are thin layers of material used primarily to provide a barrier to protect dentin from residual reactants diffusing out of a restoration or from oral fluids that may penetrate leaky tooth restoration. -They also provide initial electrical insulation, thermal protection and pulpal treatment. Liners can be classified on the basis of film thickness into:- i. Thin film liners (1-50 µm), which can be subdivided into: a. Solution liners (varnishes, 2-5 µm) b. Suspension liners (Typically 20-25 µm) ii. Thick liners (called Cement liners of 200-1000 µm = 0.2- 1 mm), which can be subdivided into: a. Hard setting Calcium Hydroxide Cement b. Light-Cured Calcium Hydroxide Cement c. Low Viscosity Zinc Oxide Eugenol (ZOE) Cement d. Resin-Modified Glass Ionomer (RMGI)) Cement 5  Liners and bases i. Thin liners: 1- Solution liners (varnishes, 2-5 µm) Definition Any liner based on non aqueous solvents that rely on evaporation for hardening is designed as a solution liner (or varnish). Composition Copal or other resin dissolved in a volatile solvent. Copalite contain 10% copal resin in a combination of ether, alcohol, and acetone. Concept Liner ingredients are dissolved in a volatile non aqueous solvent. The solution is applied to the prepared cavity surfaces and dries to generate a thin film. Clinical Notes A thin coat of varnish is applied to the cavity walls using a micro brush. The solvent evaporates in 10 sec’s leaving behind a thin film of 2-5 μm over the smear layer. Since the dentin surface is always moist and the varnish is hydrophobic, a single coat of the varnish covers nearly 50% only of the dentin surface. A second coat is usually required and this produces over 80 - 85 %coverage. 6  Liners and bases Indications 1-Under amalgam restorations, the liner may be extended to the enamel margin to initially seal the cavity margins and to provide electric insulation from galvanic currents. 2-When zinc phosphate cement is used as a base or luting material, cavity varnishes can help to prevent the cement acidity from harming the pulp. Contraindications Varnishes are not used with adhesive restorations (resin composite, glass ionomer, and indirect esthetic restorations) as it interfere with bonding mechanism. 2- Suspension liners (20-25 µm) Definition Liners based on water have many of the constituents suspended instead of dissolved. Concept Suspension liners dry more slowly and produce thicker films. The typical film thickness is 20-25 µm, in contrast to the 2-5 µm film produced by solution liners (varnishes). 7  Liners and bases ii. Thick Liner (Cement liner 200-100 µm) Definition Thicker liners that are selected primarily for pulpal medication and thermal protection are sometimes identified as cement liners. Their film thickness varies between 200-1000 µm =0.2 -1 mm. Types 1. Hard Setting Calcium Hydroxide Cement Advantages -It has no irritating constituents. -It is applied with no pressure and sets without the evolution of heat. -It adapts well to dentin and seals the dentinal tubules and prevent the passage of irritants to the pulp giving it a break to repair. -It has a pharmacological effect. -It is favorable for the deposition of reactionary dentin and stimulates dentinal bridging. -It has bactericidal properties. -It is a good thermal insulator. Disadvantages -It lacks sufficient strength to be placed in sections that are thicker than 1mm. 8  Liners and bases Indications -To line the extremely deep locations in the prepared cavities where the remaining dentin bridge may be less than 0.5-mm. Form -Two-paste system, a base that contains calcium hydroxide particles and a catalyst that contains a phenolic compound. Setting reaction -By the reaction between calcium hydroxide particles and phenolic compounds. -Calcium hydroxide in excess than that required to complete the reaction is usually present in the mix to remain as a source for (Ca) and (OH) ions after setting. -As the cement dissolves, the ions are released to reach the pulp through direct contact or through diffusion in the dentinal fluid of short and wide dentinal tubules. 9  Liners and bases Clinical notes -Before insertion, the cavity has to be dry without being desiccated. A cotton pelt could be used for this purpose. -Two small equal portions of the base and the catalyst are dispensed close to but without touching each other on a dry slap. -The cement is mixed in an uni-directional rotational motion to decrease the introduction of air bubbles in the mix. -The cement is applied on the desired location using a calcium hydroxide applicator that looks like a tiny rounded burnisher. Or, a small excavator, rounded-ended probe and small rounded burnisher could be used. -The cement sets very quickly when exposed to moisture. Since the dentin surface is always moist, therefore, the cement tends to set as soon as it contacts the dentin surface. The cement could be trimmed with a sharp excavator or an explorer to the desired shape. -Care should be exercised to remove all cement excess on the cavity margin. -At least a 1mm cement free zone should be present between the cement and the cavity margin to be covered later on by the permanent restoration. 2. Light- 10  Liners and bases 2.Light Cured Calcium Hydroxide Cement Form -This is a one-paste system that contains the calcium hydroxide particles together with a photo-polymerizable resin in one tube. Setting reaction -It hardens by light polymerization of the resin component and the calcium hydroxide particles remains dispersed in between the polymerized resin network. Importance of resin component 1-It extends the working time. 2-It ensures reliable chemical bonding with resin composites. 3-It provides insolubility in oral fluids. 4-It ensures sufficient strength properties for the liner to be applied in thick sections. Disadvantage -The insolubility of the liner, as the calcium hydroxide is not leachable any more to give the desirable pharmacological effects of the (Ca) and (OH) ions on pulp medication. 11  Liners and bases 3.Mineral Trioxide Aggregate (MTA) In the 1990s, Torabinejad and White introduced, mineral trioxide aggregate (MTA) is basically a hydraulic Portland cement, the unset MTA is primarily calcium oxide in the form of tricalcium silicate, dicalcium silicate, tricalcium aluminate and Bismuth oxide is added for radiopacity and it releases calcium hydroxide slowly while setting. MTA can be described as a calcium-hydroxide releasing material and, therefore, is expected to present various properties similar to those for calcium hydroxide. Its antibacterial and biocompatibility properties High pH Radiopacity Its ability to aid in the release of bioactive dentin matrix proteins. MTA is suggested to be superior to calcium hydroxide due to: Its more uniform and thicker dentin bridge formation Less inflammatory response Less necrosis of pulpal tissue Its improved sealing ability Limitations of MTA: The presence of iron in the grey MTA formulation may darken the tooth Prolonged setting time of approximately 2 hours and 45 minutes The handling characteristics of the powder/liquid MTA are very different from the typical paste/paste formulations of calcium hydroxide MTA is very expensive 12  Liners and bases 4. Biodentine Contains tricalcium silicate, calcium carbonate and oxide and zirconium oxide (radiopacifier) in the powder and Calcium chloride solution containing modified polycarboxylate instead of water. Both substances in the liquid contribute to shortened setting times (from 10 to 12 min) The manufacturer claims that it has increased the physico-chemical properties: Setting time is much shorter than MTA (12 min compared to 2 h 45 min). High mechanical strength, which is similar to Glass ionomers. It is encapsulated, and thus easier to handle Leakage resistance and mechanical strength will improve over the first weeks after placement 5. Theracal LC A resin-modified calcium silicate cement, thus it sets by using a light curing unit. Setting starts with the contact of the material and water and TheraCal LC does not include water for material hydration so it depends on the water taken up from the environment and its diffusion within the material. 13  Liners and bases Hence, the manufacturer instructions implement placing the material on moist dentin The cytotoxicity of the resin component is still of question although the manufacturer claims it is bioactive. Studies comparing its cytotoxicity to MTA or other calcium silicates were in favor for MTA 6. Low Viscosity Zinc Oxide Eugenol (ZOE) Cement Advantages 1-Eugenol in very small concentrations has an antiseptic, an anti- inflammatory, anti-irritant and a sedative action. 2-It has palliative effect on the mildly or moderately inflamed pulp. 3-It has excellent initial sealing ability to be used as a temporary filling in between visits. 4-It adapts well to dentin and has an effective sealing to dentinal tubules. 5-It is an effective thermal insulator. Disadvantages 1-It sets very slowly. 2-It has low initial strength properties. 3-Eugenol in high concentrations can severely irritate the pulp. Indications -To medicate the inflamed pulp in moderately deep cavities. 14  Liners and bases Contraindications 1-Under amalgam restorations without an overlying base. 2-Under resin composites because the eugenol ring prevents polymerization of resin materials. Eugenol is a strong chelator for (Ca) ions; therefore, both materials could not be used together. Setting reaction -Similar to CaOH, moisture is needed for the setting of the cement and it sets faster in presence of water. 7. Resin-Modified Glass Ionomer (RMGI)) Cement It will be discussed in Glass Ionomer chapter Self-Cured, Glass Ionomer Lining Cement, GC America GC Fuji LINING™ LC (Paste Pak) Radiopaque Lining Material 15  Liners and bases Bases -Bases (cement bases, typically 1-2 mm) are used to provide thermal protection for the pulp and to supplement mechanical support for the restoration by distributing local stresses from the restoration across the underlying dentinal surface. 1. Zinc Phosphate Cement Form The powder is zinc oxide and the liquid are phosphoric acid. Advantages 1-It has sufficient compressive strength to be used as a base under metallic restorations. 2-It is a good thermal insulator under metallic restorations. 3-It can be used to level up any irregular dentin walls to provide for mechanical resistance. 4-It can be mixed in a thin film to be used for luting metallic inlays. 5-It can be used as a long-term temporary dressing. 16  Liners and bases Disadvantages 1-It has high initial acidity, therefore, chemical pulp protection is indicated. 2-It does not bond to tooth structure or to resin or ceramic restorations. 3-It is extremely opaque; therefore, it is not used under tooth colored restoratives or for luting non-metallic inlays. Clinical notes -Before mixing the cement the cavity should be cleaned from all debris, dried but never desiccated then isolated properly. -A cavity varnish should be used under it for chemical pulp protection. -A cool glass slap is preferred for mixing because the reaction is exothermic. -The powder is divided into two equal halves. -Each half is further divided into two equal quarters then one of these quarters is divided into two equal eighths. -Each of these parts is added to the liquid separately and mixed for 10- sec. -The one-eighth portion is added first followed by the other one- eighth, then the quarter and finally the half portion. 17  Liners and bases -Mixing is carried on a large area with a long bladed spatula to dissipate the heat of the reaction. -The base consistency is heavy putty like and would not stick easily to the instruments. -The cement is placed on the dentin with a condenser. -Any excess cement could be removed with a sharp excavator before setting. 2.Resin-Reinforced ZOE Cement Form -The ZOE cement has been reinforced by the incorporation of resins, ethoxybenzoic acid or alumina. -Also, it was modified by using smaller powder particles, which besides increasing the strength of the cement it accelerated the setting time as well. Indications 1-It is used as a base under metallic restorations for chemical and thermal protection and to medicate the hyperemic pulp as well. 2-It is used as a long-term temporary filling. 18  Liners and bases 3.Polycarboxylate Cement Form The powder is zinc oxide and the liquid is a polyacrylic acid co-polymer. Advantages 1-It has high strength properties. 2-It is good thermal insulator. 3-It is characterized by its adhesive potentials. 4-It is characterized by fluoride release. 4.Glass Ionomer (GI) Cement Setting reaction -An acid-base reaction between a basic alumino-silicate glass and polyalkenoic or poly (acrylic) acid. In the initial stages of the setting reaction, divalent calcium ions are rapidly released and form primarily calcium salt bridges. At this stage, both water uptake and water loss can occur, with the clinical problems of water contamination and dehydration. 19  Liners and bases The restoration must therefore be protected from excess water gain and loss by covering with resin immediately after placement. In later stages of the setting reaction, cross-linking by trivalent aluminium ions gives greater stability to the matrix structure. 5.RMGI Cement Advantages 1-It is good thermal insulator. 2-It has very high strength.. 3-It is very resistant to dissolution. 4-It has an extended working time. 5-It has controlled setting time. 6-It has sufficient translucency to be used under tooth-colored restoratives. 7-It bonds chemically to resin composites and to the tooth structure. 8-It is biologically very compatible, it does not irritate the pulp. 9-It releases fluorides. 10-It has very good sealing properties. Indications The cement can be safely applied in deep cavities. 20