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Fundamental Concept Of Pulp Protection By: Dr. Rehab Alwakeb Operative Dentistry Division Refrence Art and science of operative dentistry, 6th edition, Biomaterials chapter 18. ILOs: Describe: biological influences, characteristics, Indications & contraindications. and manipulatio...

Fundamental Concept Of Pulp Protection By: Dr. Rehab Alwakeb Operative Dentistry Division Refrence Art and science of operative dentistry, 6th edition, Biomaterials chapter 18. ILOs: Describe: biological influences, characteristics, Indications & contraindications. and manipulation techniques of liners and bases. Outline of lecture Objectives of pulp protection Terminology and classifications of pulp protecting materials: Liners Bases Clinical considerations (case-based discussion) Introduction: There are certain materials which are placed in deep cavities between dentin (sometimes pulp) and the restoration for pulpal protection or pulpal response. 1. Objectives of pulpal protection To understand the actions of these agents, it is necessary to recall the anatomy and physiology of dentin. Normal coronal dentin includes: 1. Dentinal tubules that contain cellular extensions that are surrounded by dentinal fluid (odontoblastic processes) of the cells (odontoblasts) 2. Odontoblasts are columnar cells remain as a layer along the periphery of the dental pulp, partially embedded in poorly mineralized dentin (predentin).  If the insult produces fluid flow, in or out of the dentinal tubules: the pressure change is sensed by mechanoreceptors within the pulp (A delta fibers), and the patient experiences sensitivity. If leakage of chemical irritants from biomaterials or bacteria occurs, the pulp complex can become inflamed. Therefore, To protect against these events, it is paramount to seal the outer ends of the tubules along the dentinal tooth preparation wall. N.B: Tooth preparation with rotary instruments generates cutting debris, which is compacted into a layer on the cut surface called smear layer & smear plugs. The dentinal smear layer produces some degree of dentinal tubule sealing, although it is 25% to 30% porous.  Normal Dentin-pulp organ defense mechanisms to insult: Sclerotic dentin: Forms in response to stimuli such as aging or mild irritation as slow advancing caries. When responding to initial caries, demineralization events, crystalline material precipitates in intratubular and intertubular dentin. Sclerotic dentin walls off a lesion by blocking (sealing) the dentinal tubules. Clinically, sclerotic dentin is dark and harder than normal dentin. Tertiary dentin (reparative or reactive dentin): Forms in response to stimuli eg: acute caries, and operative procedures. Usually appears as a localized dentin deposit on the wall of the pulp space immediately subjacent to the area of the tooth that has received the injury. CCC: It is less mineralized than primary and secondary dentin, and contains irregular dentinal tubules. -Clinically, tertiary dentin is not as hard as primary dentin. 2. Terminology and classification I. Liners liners are relatively thin layers of material indicated in deep cavities beneath metallic restorations (direct or indirect) Action: 1. Prevent passage of chemicals (residual reactants leaking from restoration or from oral fluids). 2. Pulpal treatment  Classification depending on film thickness: Thin film liners (1-50 µm) Thick liners (0.2-1mm) Solution liner Suspension Cement liners used primarily for (varnish) liner pulpal medication or thermal 2-5 µm protection (e.g: Portland 20-25 µm cement=MTA) ingredients are based on water dissolved in a and volatile non- constituents aqueous suspended solvent dries to instead of generate a thin dissolved film are intended to protects provide against thermal chemical protection and irritation need to be thicker in dimension. Varnish Copal or other resin dissolved in a volatile solvent. Varnishes contains 10% copal resin in a combination of ether, alcohol, and acetone. The resin content is kept intentionally low to produce a thin film on drying. Thin films work best because they are flexible and dry rapidly. Most solvent loss occurs in 8 to 10 seconds and does not require forced air assistance. A single coat effectively covers only 55% of the surface. A second thin layer is recommended to produce sealing of 80% to 85% of the surface.  Suspension liners Dry more slowly and produce thicker films. The typical film thickness is 20 to 25 μm, in contrast to the 2- to 5- μm film produced by solution liners (varnishes). The primary purpose of the liners is: 1. Provides a protective seal on the exposed dentinal surface. 2. Provides a means of electrically isolating metallic restorations from external electrical circuits with restorations in the adjacent teeth (Galvanism) 3. Provides thermal insulation.  a. ZnoE These liners were used in the past in sites where tooth preparations were moderately deep. Eugenol is used to alleviate discomfort (sedative) resulting from mild-to-moderate pulpal inflammation as it produces palliative or obtundent actions on the pulp when used in very low concentrations.  b. CaoH In the deepest portions of the preparation or when a microscopic pulp exposure is suspected It is extremely caustic (pH >11). They are formulated to undergo a chemical setting reaction allowing minor amounts of calcium hydroxide to be released from the liner surface to produce the desired effect as it stimulates the formation of reparative dentin & encourage dentinal bridging  These liners may degrade severely over long periods. It is recommended that a calcium hydroxide liner be overlaid with RMGI base. II. Cavity bases (cement bases 1-2mm) Base used in thick dimensions beneath restorations. Generated by mixing dental cements at higher-than- normal powder-to-liquid ratios to increase the final compressive strength and to reduce the concentration of potentially irritating liquids. Action: 1. Provide mechanical support of restoration by distributing local stresses from restoration to dentin so prevent disruption of thin D bridge overlying the pulp during amalgam condensation, or cementation of indirect metallic restoration. 2. Thermal protection of the pulp beneath metallic restorations.  Base materials Zinc phosphate Zinc oxide-eugenol Zinc poly-carboxylate Glass ionomer Requirements of ideal dental cements Nontoxic, nonirritant Insoluble in fluids. Antibacterial effect. Obtunding effect (relief of pain). Adhere chemically to tooth Low film thickness when used as luting agent. Their coefficient of thermal expansion should match that of tooth structure. Dimensional stable on setting. Zinc Phosphate Cement Composition 1. Powder: Zn O (90%): main ingredient. 2. Liquid : H3PO4 (50%): main ingredient. Al2(PO4) 3 and ZnPO4:- -They reduce the reaction rate (retarder). -They stabilize the pH of the acid. Zinc Polycaroxylate Cement Composition Powder: Zinc Oxide Liquid : Poly-acrylic acid or acrylic acid copolymer. Forms a. Conventional type: powder and liquid in two separate bottles. b. Water settable type: powder + freeze-dried powder of the poly-acid in one bottle mixed with distilled water.  Biocompatibility pH of polycarboxylate cement (1.7) is higher than that of a zinc phosphate cement (2) but polycarboxylate cement is more compatible due to :- 1. Lower intrinsic toxicity. 2. The rapid rise of the cement pH toward neutrality (few minutes for ZPC but 24 hours for ZNPO. 3. Has bigger molecular size that blocks dentinal tubules. 4. The minimal movement of fluid in the dentinal tubules in response to the cement. Bonding to tooth structure Smear layer removal by conditioning tooth surface with 10% polya crylic acid for 10 seconds, will increase the bond strength. Bonds chemically to E & D as it reacts via COOH groups with calcium of hydroxyapatite forming chemical bonding (1ry bond). Hydrogen bonding (2ry bonding) is formed between hydrogen of the organic constituents of the enamel and dentine. Remark: Usually, a RMGI is used for “base” needs. These material effectively bond to tooth structure, release fluoride, and have sufficient strength. These materials are excellent for use under amalgam, gold, ceramic, and composite restorations. Remember always to consider the remaining thickness of the final restoration Clinical considerations  Clinical judgments about the need for specific liners and bases are linked to: the amount of remaining dentin thickness (RDT), considerations of adhesive materials. and the type of restorative material being used.  1. In a shallow tooth excavation ( ≥1.5-2 mm of RDT) The pulpal chemical protection, is needed. For an amalgam restoration, preparation is coated with 1. Two thin coats of a varnish, or 2. Single coat of a dentin sealer, or 3. Dentin bonding system, (in bonded amalgam) and then restored.  For a composite restoration: the preparation is treated with a bonding system 2. In a moderately deep tooth excavation For amalgam: so that a region includes less than ideal dentin protection. It may be judicious to apply a liner only at that site using ZOE or calcium hydroxide. Either one may provide pulpal medication, but the effects would be different. ZOE cement releases minor quantities of eugenol to behave as an obtundent toward the pulp. It also provides thermal insulation.  In composite: Zno Eugenol is contraindicated as it has the potential to inhibit polymerization of layers of bonding agent or composite in contact with it. 3. Deep cavities2hs). 3. Forms uniform and 2. High cost thicker dentin bridge 3. Potential of 4. Radio-opaque (Bismuth discoloration oxide) TheraCal LC is a light-cured, resin-modified calcium silicate. Its unique apatite stimulating ability makes it ideal for direct and indirect pulp capping and as a protective liner. Calcium release stimulates hydroxyapatite and secondary dentin bridge formation Alkaline pH promotes healing and apatite formation Protects and insulates the pulp Moisture tolerant and radiopaque – can be placed under restorative materials and cements Thank You