Topic 7 - Pulp Protection II - Zinc Oxide Based Cements PDF

Topic 7: Pulp Protection II - Zinc oxide based Cements Lecturer: Dr. Lamia A. T. Bin Yehia BDS, Clinical MSc in Pediatric Dentistry Clinical Importance of dental varnishes, liners and...

Topic 7: Pulp Protection II - Zinc oxide based Cements Lecturer: Dr. Lamia A. T. Bin Yehia BDS, Clinical MSc in Pediatric Dentistry Clinical Importance of dental varnishes, liners and bases: ❑ These materials have been used beneath restorative materials to protect the pulp from various injuries, e.g.…… Stimuli / insult type Examples Affecting Pulp Physical Thermal and electrical from dental procedures, food and drinks Mechanical Handpiece and traumatic occlusion Chemical Dental materials and caries Biological Bacteria from saliva Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. MSc. 2 1 ❑ These are substances are applied in a flowable state underneath a restoration (direct or indirect) and hardens to a solid state. ❑ They differ in composition, clinical manipulation, properties and functions. Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 3 MSc. Material Thickness Function 2–5 Insulator against microleakage and tooth discoloration Varnish microns under other cements and amalgam. approx. All are chemical insulators. Liner 0.5 mm Some have regenerative abilities. All provide thermal, electrical and mechanical > 0.5 – Base insulation. 0.75 mm Some provide palliative, sedative and medicating effect. Luting 25 or less Variations of Base materials used solely as adhesive to agent microns bind indirect restorations to tooth structures. Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 4 MSc. 2  Dental Cements They are viscous material that serve 2 functions: 1. Base underneath fillings (Thickness = 0.5 mm – 0.75 mm): For Thermal, mechanical and chemical insulators Some have therapeutic effect (e.g. ZOE) Used for bulk build-up and blocking undercuts 2. Luting agents (Thickness = 25 or less microns): Bind indirect restorations to tooth structures. Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 5 MSc. Cements are classified based on: I. Their chemical / setting reaction: 1. Acid – base reaction: A. Zinc phosphate C. (Exothermic) B. Zinc poly-carboxylate C. C. Zinc oxide-eugenol C. 3. Polymerization + acid – base reaction: D. Glass ionomer C ❑ Resin-modified glass ionomer 2. Polymerization reaction: A. Light cured (Resin cements) B. Chemical cured (Resin cements) Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 6 C. Dual cured (Resin cements) MSc. 3 II. Their adhesion to tooth: 1. Physical retention: A. Zinc phosphate C. 3. Chemical retention: B. Zinc oxide-eugenol C. A. Glass ionomer cement 2. Micro-mechanical retention: B. Polycarboxylate cement A. Light cured (Resin cements) B. Chemical cured (Resin cements) C. Dual cured (Resin cements) D. Resin modified glass ionomer (RMGIC) cements Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS.: 7 MSc. III. Their chemical nature: 1. Oil based: A. Zinc oxide-eugenol C. 2. Water based: A. Zinc phosphate C. B. Zinc poly-carboxylate C. C. Glass ionomer C 3. Resin based: A. Light cured (Resin cements) B. Chemical cured (Resin cements) C. Dual cured (Resin cements) Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 8 MSc. 4  Old cements (Zinc-oxide based): 1. Zinc Phosphate cement (Thermal, mechanical, chemical and electrical insulation) 2. Zinc Polycarboxylate cement (Thermal, mechanical, chemical and electrical insulation) 3. Zinc Oxide Eugenol cement (Thermal, chemical insulation and sedative function) Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 9 MSc. Setting Reaction: All set via Acid – base reaction Speed of reaction = ZPoC (fastest / minutes & exothermic) > ZPC (Most exothermic) > GIC (good working time) > ZOE (slowest / hours). Mechanical properties (strength) dependant on >>> Increase p:l ratio Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 10 MSc. 5  Zinc phosphate cement Powder: Liquid: 75% of zinc phosphoric acid (38% to oxide 59%) 13% of water (30% to 55%) magnesium oxide Uses: radiopaque aluminum phosphate (2% 1. Luting best under indirect powders to 3%) metallic restoration(thin mix) zinc phosphate (up to 2. Base under metallic 10%)Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. restoration (thick mix) 11 MSc. Zinc polycarboxylate cement Powder: Liquid: Zinc oxide Polyacrylic acid Magnesia Other carboxylic acids, such as itaconic acid Uses: Tin oxide Bismuth oxide, and/or 1. Luting best under indirect alumina metallic restoration(thin mix) Small amounts of stannous fluoride 2. Base under metallic restoration (thick mix) Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 12 MSc. 6  Zinc-oxide eugenol (ZOE) 1. Powder-liquid: the powder contains zinc oxide particles and the liquid is eugenol. 2. Two-paste system: the base paste contains zinc oxide powder and the accelerator / catalyst has the eugenol + water 3. One paste system (ready made temporary restorative material) Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 13 MSc. Types: 1. Conventional ZOE (lack good mechanical properties) 2. Zinc oxide non-eugenol cements (for pt. sensitive to eugenol & underneath ceramic restorations) 3. Improved ZOE (high compressive strength but still inferior to ZPC, ZPoC, GIC & resin cements) A. EBA- ZOE: substitutes part of eugenol with ortho-ethoxybenzoic acid (EBA) and includes alumina in the powder to improve the strength and abrasion resistance of ZOE cement for long-term luting. B. ZOE plus polymer: consists of liquid (eugenol + polystyrene) and powder (Zno surface treated with carboxylic acidMaterial. Year 1 (Term 1): Dental + 20 - 40% Dr. lamia fine A. T. Bin Yehia. BDS.polymer (PMMA)particles). 14 MSc. 7  ZOE Uses (the most versatile of the 3 zinc oxide based cements): 1. Dentin-substitute / base material: against thermal and chemical insults and has additional palliative / sedative effect. 2. Temporary cementation / luting agent: for luting provisional acrylic (temporary) crowns and temporary cementation of permanent crowns and bridges. 3. Temporary / intermediate fillings: (lasting for few weeks at most). 4. In endodontic: Root canal sealer b/w the gutta percha cones and radicular dentin. 5. In paediatric dent.: Root canal obturating material in pulpectomy and dressing over pulp in pulpotomy procedures. 6. ZOE cement is also used as a periodontal dressings. Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 15 MSc. Properties of zinc-oxide based cements: 1. Retention to tooth: ZPC & ZOE = Mechanical bond ZPoC = chemical bond (bond to enamel > 2. Retention to dental material: to dentin) Best retentive ability to metals >>> ZPC (lowest thickness = permanent cement under metallic indirect restoration) Least retentive ability under indirect restoration >>> ZOE (highest thickness = used as temporary cement) Contraindicated beneath composite resin >>> Inhibit resin polymerization. ZPoC is not a good lutingYearchoice = thick 1 (Term 1): Dental Material. Dr. mix MSc. lamia A. T.and Bin Yehia.has BDS. lowest flowability 16 8 3. Setting time: ZPC + ZPoC = Fast setting (mins) ZOE = slow setting (hours) 4. Heat generation during setting = ZPC & ZPoC (exothermic) 5. Best biocompatibility with pulp: ZOE (neutral PH) but ZPC + ZPoC (acidic) ALL are Good thermal insulators ZOE ✓ Least irritant to pulp (Neutral pH, sedative, antiseptic and anti-inflammatory) + eugenol has antimicrobial effect ✓ CTE closest to tooth: Good sealability of dentinal tubules against the ingress of oral fluids (good temporary restorative treatment). Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 17 MSc. 6. Ph and cytotoxiciy: ZPC = Acidic (2.5 – 3 PH) ZPoC = Acidic (PH 1.7) ZOE = Neutral (pH = 7) ❑ Cytotoxicity (Dycal used as an intermediate liner between the ZPoC or ZPC and pulp): ZPC [lowest molecular weight (able to penetrate dentinal tubules to reach pulp) and most acidic] > ZPoC [higher molecular weight than ZPC & neutralizes faster] > ZOE is neutral pH but cytotoxic [not applied directly on pulp but when placed on dentin, it provide sedative and palliative effect on pulp]. Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 18 MSc. 9 7. Solubility: All are soluble in fluids before they set (isolate the margins of indirect restorations with varnish). After setting; ZPC and ZPoC are more insoluble than ZOE. 8. Opacity: all are opaque (do not use underneath composite or ceramic r.). 9. Mechanical properties: ZPC = strongest against compressive forces [High compressive strength (104 Mpa) and an elastic modulus (13 Gpa)]. ZPoC < ZPC against tensile forces (5.5 MPa) ZOE = Moderate to low strength; compressive strengths (3 - 55 MPa) Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 19 MSc. CLINICAL MANIPULATION Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 20 MSc. 10 Clinical manipulation of Zinc phosphate cement First and oldest luting cement (Gold standard by which newer cements are compared). Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 21 MSc. Mixing tools: glass slab and metal spatula. Powder : liquid ratio & mixing time >> based on the manufacturer’s instructions Mixing technique: Powder mixed to acid in increments & mixing should be fast (within 1.5 to 2 minutes). Spread mixture over wide area of the mixing slab (to dissipate heat). For cementation under metallic restoration: A. Low viscosity >> A string of cement can be lifted 12 -19 mm from glass slab B. Excess cement should be allowed to set before removal C. A layer of varnish or bond should be applied to allow the cement more time to mature and become insoluble in oral fluid. Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 22 MSc. 11 Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 23 MSc. Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 24 MSc. 12  Zinc polycarboxylate cement Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 25 MSc. Clinical Manipulation of Polycarboxylate Cement: Apply 10% polyacrylic or maleic acid solution to the tooth for 10 to 15 seconds (conditioning of tooth surface), followed by rinsing with water. Proper isolation and air drying. This cement should be mixed on a glass slab quickly. Do not refrigerate the liquid component of polycarboxylate cement because it is viscous. The cement must be used before it loses its glossy appearance which indicates free carboxylic acid groups are still present for good bonding to the tooth. Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 26 MSc. 13 Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 27 MSc. Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 28 MSc. 14  ZOE Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 29 MSc. Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 30 MSc. 15 Year 1 (Term 1): Dental Material. Dr. lamia A. T. Bin Yehia. BDS. 31 MSc. 16