Dental Materials Applications and Manipulation Cairo University PDF

Cairo University Faculty of Oral and Dental Medicine Biomaterials Department Dental Materials Applications and Manipulation Name: Section: I.D. #: Contents: Chapter 1: Impression materials 1 - 17 Chapter 2: Model and die materials 1...

Cairo University Faculty of Oral and Dental Medicine Biomaterials Department Dental Materials Applications and Manipulation Name: Section: I.D. #: Contents: Chapter 1: Impression materials 1 - 17 Chapter 2: Model and die materials 19 - 24 Chapter 3: Investment materials 24 - Chapter 4: Dental waxes Chapter 5: Casting technology Chapter 6: Dental casting alloys Chapter 7: Wrought dental alloys Chapter 8: Joining of metals Chapter 9: Dental amalgam Chapter 10: Non-metallic denture base materials Chapter 11: Direct aesthetic restorative materials Chapter 12: Dental cements Chapter 13: Dental ceramics  Academic Calendar 2015/2016 Week Date 1st Lecture Date 2nd Lecture Section (Sunday) (Tuesday) Dental Casting Dental Casting Investment 1 14/02 Alloys 16/02 Alloys materials Prof. Dr. Nour Habib Prof. Dr. Nour Habib Dental Dental Casting Dental Casting Waxes + 2 21/02 Alloys 23/02 Alloys Casting Prof. Dr. Nour Habib Prof. Dr. Nour Habib Technology Dental Dental Cements Dental Cements 3 28/02 01/03 Casting Prof. Dr. Nour Habib Prof. Dr. Nour Habib Alloys Dental Cements Dental Cements Dental 4 06/03 08/03 Prof. Dr. Nour Habib Prof. Dr. Nour Habib Cements Dental Amalgam Dental Amalgam Dental 5 13/03 Prof. Dr. Taheya 15/03 Prof. Dr. Taheya Cements Moussa Moussa Dental Amalgam Composite 6 20/03 Prof. Dr. Taheya 22/03 Amalgam Prof. Dr. Gihan Aly Moussa Non- Composite Composite 7 27/03 29/03 metallic Prof. Dr. Gihan Aly Prof. Dr. Gihan Aly denture base Non-metallic Non-metallic 8 03/04 Denture Base 05/04 Denture Base Composite Prof. Dr. Gihan Aly Prof. Dr. Gihan Aly Introduction to Dental Ceramics dental ceramics Wrought 9 10/04 12/04 Prof. Dr. Azza Prof. Dr. Azza and Joining Hashem Hashem Dental Ceramics Dental Ceramics Dental 10 17/04 Prof. Dr. Azza 19/04 Prof. Dr. Azza Ceramics Hashem Hashem 11 24/04 Mid-term Ceramo-metallic Dental 12 01/05 Labor Day Holiday 03/05 Prof. Dr. Azza Hashem Ceramics  Weekly Quizzes Grades Quiz No. Quiz Grade (out of 10) 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. Total Mid-term exam  Chapter 1 Impression Materials  Impression Materials Figure 1. A) an upper impression (negative reproduction of the oral tissues) and B) a model or cast (positive reproduction of the oral tissues) Figure.2. Summary of the initial steps of constructing an indirect restoration Stock trays Acrylic special tray Figure 3. Types of Trays 2  Non-Elastic Impression Materials I. Plaster of Paris Presentation: Powder contained in large well sealed containers to be mixed with water (fig.4a). Application: Nowadays, its use is almost limited to making impressions for edentulous patients with multiple implants. Armamentarium: a. Plaster impression material b. Plastic measure for water c. Scoop for measuring the powder d. Rubber mixing bowl e. Stiff wide-blade steel or plastic spatula f. Acrylic resin special tray g. Disinfectant Manipulation: a. The proper volume of water is measured and poured in the rubber bowl. The powder (hemihydrate) is measured using the scoop according to the W/P ratio recommended by manufacturer. The aim of adding the powder to the water (and not the reverse) is to minimize the incorporation of air bubbles. b. Stir powder and water vigorously in the rubber bowl to wet the powder completely and produce a homogenous mix. (Fig.4B). c. The homogenous mix is then loaded in the special tray and inserted in patient’s mouth until setting is complete (the material becomes hard). Figure 4. (A) Plaster impression material in a well-sealed bag, (B) Mixing the plaster powder with water in a rubber bowl using a spatula d. The impression is then removed from the patient's mouth, washed with cold water to remove saliva or blood and is then disinfected. e. A separating medium (varnish or soap) should be used before pouring a plaster impression in plaster or stone to make a cast otherwise, the cast and the impression will be mechanically interlocked and become inseparable. f. After the cast is poured and allowed to harden, it is soaked in hot water where the starch (which is included as a constituent in the powder of the impression plaster) swells and the impression disintegrates to facilitate its separation from the cast. 3  II. Impression Compound Presentation and application: The material is supplied in the form of sheets (cakes) or sticks of different sizes and colors (Fig. 5). Figure 5. Impression compound sheets (left) and sticks (right) Armamentarium: a. Impression compound impression material b. Hot water bath (if compound sheets are used) or flame (if compound sticks are used) c. Stock tray (if the material is to be used for making primary impression) or acrylic resin special tray (if the material is to be used for border molding) Manipulation: a) Making an Impression (figure 6) : Figure 6. Steps of making a lower primary impression for an edentulous patient using impression compound: a. The compound sheets are softened in the hot water bath, b. The softened compound mass is kneaded outside the water, c. The softened compound is placed in the stock tray, d. The filled tray is placed again in the water bath to ensure adequate and uniform softening of the impression material, e. The tray is inserted in patient's mouth and allowed to harden, f. The final impression after removal from patient's mouth. 4  b) Border Molding: Figure 7. Using impression compound as a peripheral seal material (border molding). Note that the sticks are softened using a flame. III. Zinc Oxide-Eugenol Presentation: The material is supplied as a two-paste system in two metallic collapsible tubes (base and accelerator) (Fig.8). The two pastes have contrasting colors to allow the clinician to judge when proper homogenous mixing is accomplished. Figure 8. Representative zinc oxide-eugenol impression paste Application: Used for taking secondary impressions for edentulous patients Armamentarium: a. Zinc oxide-eugenol impression pastes b. Large oil-resistant mixing paper pad (or glass slab) c. Stiff, tapered-blade steel impression spatula d. Border-molded special tray (with peripheral seal impression compound) e. Disinfectant 5  Manipulation (figure 9): Figure 9. Manipulation of zinc oxide eugenol impression material: a. Dispensing equal lengths of the two pastes on an oil-resistant paper pad, b. Mixing until a homogenous mix is obtained, c. Placement of the final mix (2 - 3 mm thick) on the border-molded special tray, d. The final impression after removal from the mouth.  After removal of the impression from the patient's mouth, the impression is disinfected by immersion in 2% glutaraldehyde.  After pouring the cast, the zinc oxide eugenol impression is easily separated from the cast by softening in hot water at 60C. N.B: The lips of the patient should be coated with petroleum jelly (Vaseline) before making the impression?? to avoid adherence of the impression paste to patient's lips. B. Elastic Impression Materials These materials develop elasticity as they set so they can be used to record undercuts. I. Hydrocolloids 1. Reversible Hydrocolloids: Agar-agar Impression Material Presentation: The material is supplied as a gel in sealed containers (figure 10) to prevent evaporation of water. Tray material supplied in Large well-sealed jars for Syringe material supplied tubes to fill up the water- duplication purposes in cartridges cooled trays Figure 10. Presentation of Agar-agar impression material 6 Applications: a. Making secondary impressions for dentulous or edentulous patients. b. Duplication of casts Armamentarium: a. Agar hydrocolloid material b. Agar hydrocolloid conditioning unit c. Water-cooled tray d. Disinfectant and plastic bag Manipulation: The gel material is converted to sol by heating. After placement in the patient’s mouth, the material cools and converts back to gel. The steps of manipulation of agar can be summarized as follows: a. Liquefying and storage: The material is brought to the fluid state (sol) by heating the tube or syringe in boiling water for about 10 min (in the boiling compartment) and then the material is stored at 65C (in the storage compartment) (Fig.11). b. Loading of the tray: The sol material is extruded onto a metal tray (supplied for use with the agar particularly). The tray should have means of mechanical interlocking and a water cooling system (Fig. 12). The tray should allow a thickness not less than 4-6 mm for the agar material to overcome the material's low tear strength. c. Conditioning or tempering: Immediately before the impression is made, the filled tray is tempered at 46C ± 1C for a minimum of 2 min. (in the tempering compartment). Tempering is necessary to cool the material to a temperature that is compatible with the oral tissues. The thin layer of the material that has been in direct contact with water in the bath is removed with a suitable instrument before insertion in the mouth. d. Chilling (setting and gelation): The impression is seated against the oral tissues, allowed to cool and to convert into a gel in the mouth. Gelation is speeded by either spraying cold water on the tray, or preferably by using trays, which contain channels in which cold water is circulated at 20C until gelation occurs (Fig.12). The temperature of water should not be less than 13C. Figure 11. Conditioning unit for agar hydrocolloid impression materials. The three compartments are used for liquefying, storing and tempering the agar material. 7  Figure 12. Agar hydrocolloid impression material loaded in the water-cooled tray e. Removal of the impression: The tray should be removed with a sharp snap parallel to the long axis of the teeth to minimize the unavoidable viscous permanent deformation and to increase the tear strength. f. Disinfection: After the impression is thoroughly rinsed with water, the disinfectant (iodophor bleach or glutaraldehyde) is sprayed (not merged or soaked) on the impression surface. g. Pouring the impression: The impression should be cast as soon as possible (within 5-10 min). If casting is delayed, the impression should be stored in 100% humidity. h. Surface treatment of the impression: The impression may be dipped in 2% potassium sulfate solution (gypsum setting accelerator) before pouring the gypsum model material to avoid obtaining a cast with a soft surface. 2. Irreversible Hydrocolloids: Alginate Impression Material Presentation: a. Traditional alginate material: supplied as powder in large bags or containers to be mixed with water as seen in figure. 13. b. Modified alginate (less commonly used): available as two-component system in the form of two pastes, one containing the alginate sol and the second containing the calcium reactor. Application: Making primary impressions for both dentulous or edentulous patients Armamentarium: a. Alginate (bulk container or individual package) b. Plastic measure for water c. Special scoop for measuring the powder d. Rubber mixing bowl e. Wide-blade steel spatula f. Perforated plastic or metal stock tray g. Disinfectant and plastic bag 8 Figure 13. Alginate impression material and armamentarium needed for its manipulation Manipulation: a. The container of the powder should be shaken before use to get an even distribution of the constituents. b. The powder and water should be measured as directed by the manufacturer. The water is first placed in the rubber bowl then the powder is added to minimize the incorporation of air bubbles. c. Room-temperature water is usually used; slower or faster setting times can be achieved if required, by using cooler or warmer water respectively (18 C – 24 C). d. Mixing is performed using rubber bowl and plaster spatula (Fig.14a). Vigorous mixing should be done by spreading the material against the bowl side walls for the recommended time to eliminate air bubbles, and then the mixed material is loaded in the tray. e. Retention of the gel to the tray is achieved by using a perforated tray (Fig.14b). The thickness of the impression material should not be less than 4 mm to overcome its low tear strength. f. After setting, the alginate impression should be removed from the mouth by sharp snap removal. g. After removal from the mouth (Fig.14c), the impression should be:  Washed with cold water to remove saliva or blood.  Disinfected using the same procedure used for the agar impression.  Cast up as soon as possible (within 5-10 min). If casting is delayed, it should be stored in 100% humidity. h. After pouring the cast, gypsum should not be left for a long time after setting in contact with the impression. If left for too long, gypsum will absorb water from alginate leading to a poor surface quality of the cast. Figure 14. Manipulation of alginates: a) Vigorous mixing of alginate, b) Perforated stock trays used and c) The alginate impression after removal from the mouth. 9  II. Rubber Impression Materials Types and presentation: Rubber impression materials are available in four types: polysulfide, condensation silicone, addition silicone and polyether. They are supplied as two-component systems that have different consistencies: light, regular (medium), heavy and putty. Each of the former three consistencies (light, medium and heavy) is supplied as two tubes while the latter consistency (putty) is usually supplied in the form of two jars containing dough-like materials. Sometimes, the light, medium and heavy viscosities are supplied in the form of a cartridge to be used with a special mixing gun and mixing tip (Fig.15). B Figure 15. Presentation of rubber impression materials: a) Regular-body (two tubes), b) Putty addition silicone (two jars) c) light-body addition silicone supplied in cartridge used with a special mixing gun and mixing tip Application: Secondary impressions for dentulous or edentulous patients. Armamentarium: a. Base and catalyst of the impression material. b. Large, oil-resistant mixing paper pad and a stiff, tapered-blade steel impression spatula (needed only for mixing the light, medium and heavy consistencies if hand mixing is to be used whereas the putty consistency does not need a mixing pad). c. Special mixing gun for static automixing or a special motor-driven device for mechanical mixing. d. Special (custom) tray painted with the adhesive supplied by the manufacture and allowed to dry (only used for the light, medium and heavy consistencies while the putty type is used with a stock tray). e. Disinfectant Manipulation: One of the following mixing techniques is used: A. Hand mixing: Manipulation using hand mixing of the light, medium and heavy consistencies follows the steps shown in figure 16. 10  Figure 16. Manipulation of rubber impression materials using hand mixing: a. Equal lengths of the base and catalyst are dispensed onto oil-resistant paper pad, b. Initial mixing by circular motion using stainless steel spatula followed by: c. Wiping motion to obtain a homogenous mix free of air bubbles or color streaks, d. Loading the impression material (2-3 mm. to minimize polymerization shrinkage) in a special tray painted with adhesive using the syringe, e. Application of the impression material directly on the prepared teeth using the syringe before inserting the tray in the patient's mouth, f. The impression is allowed to set. Removal of the impression from patient’s mouth: Sharp snap removal parallel to the long axes of the teeth. Disinfection: The impression is immersed in the disinfectant solution for the time recommended by the manufacturer. For polyether, immersion time should not exceed 10 min. because of its hydrophilic nature. Pouring the cast: The impression is poured no later than one hour (time can be extended for many days when using addition silicon and polyether impression materials). Manipulating the putty consistency: equal number of scoops of both base and catalyst putties are kneaded with fingers until a uniform color is obtained. B. Static automixing (gun and cartridge system): The gun and cartridge system (figure 17) offers a very simple and effective way to mix and dispense impression materials. Figure 17. Assembled cartridge and gun: (a) special mixing gun, (b) cartridge formed of two cylinders containing the base and catalyst, (c) static mixing tip, (d) nozzle for direct injection of the material around the tooth preparation and (e) the series of helical mixers that are contained inside the static mixing tip. 11  The mixed material is injected into the adhesive-coated tray or a special nozzle is attached to the mixing tip to allow the clinician to inject the material in the mouth directly around the tooth preparation. C. Dynamic mechanical mixing: Polyether and addition silicon impression materials are available for mixing using this system. Dynamic mixing (figure 18) is an easy procedure that allows proper mixing especially for higher viscosity materials. However, the device is expensive and there is slightly more material retained in the mixing tip and wasted than with auto-mixing. Nevertheless, the wasted material with both systems is less than that wasted by hand mixing. Figure 18. Dynamic mixing of rubber impression material: a) Dynamic mechanical mixing device, b) cartridge containing the base and catalyst, c) Mixing tip with the motor-driven impeller inside, d) dispensing the mixed material in the adhesive coated tray and e) dispensing the mixed material directly inside the syringe. Impression techniques used with elastomeric impression materials 1. Multiple-mix technique: A light-body material is loaded in the syringe and injected around the prepared teeth while a heavy body material is used as a tray material. 2. Monophase technique (single viscosity technique): This technique is used with the medium-body addition silicone OR medium-body polyether. One mix of the material is made. Part of the material is loaded in the syringe and injected around the prepared teeth. As the material is sheared while extruded through the syringe tip, its viscosity decreases (due to its shear-thinning property) so it can record the fine details of the prepared teeth. The rest of the mix is loaded in the tray. 3. Putty-wash technique: This technique is used with both condensation and addition silicones. There are two ways to make a putty-wash impression, only the simpler one will be explained. The putty is used to make a preliminary impression in a perforated stock tray (fig. 19a). Since the putty cannot record the fine details of the oral structures, another impression is made on top of the putty impression using the light viscosity in order to record the fine details (fig.19b). The final putty wash impression is shown in figure 19c. 12  Figure 19. The putty-wash impression technique Manipulative Variables B I. While manipulating impression compound, what would happen if you do the following? Manipulative variable Result 1. Leave the impression compound sheet in the hot water bath for a long time 2. Knead the impression compound under water 3. Overheat the impression compound sticks on the flame II. While manipulating zinc oxide eugenol impression material, what would happen if you do the following? Manipulative variable Result 1. Use a higher base/catalyst ratio than that recommended by the manufacturer 2. Use a lower base/catalyst ratio than that recommended by the manufacturer 3. Mix the zinc oxide eugenol close to a flame III. While manipulating alginate impression material, what would happen if you do the following? Manipulative variable Result 1.Use a higher W/P ratio than that recommended by the manufacturer 2.Use a lower W/P ratio than that recommended by the manufacturer 3.Use a non-perforated tray 4.Use a tray that allows a thickness of 3 mm for the alginate 5.Mix the powder with cold water 6.Mix the powder with warm water 7.Leave the cast for a long time in contact with the alginate impression before cast separation 13 IV. While manipulating an elastomeric impression material, what would happen if you do the following? Manipulative variable Result 1. Use a higher base/catalyst ratio than that recommended by the manufacturer 2. Use a lower base/catalyst ratio than that recommended by the manufacturer 3. Use a tray that is not coated by an adhesive 4. Use a tray that allows a thickness of 6 mm for the elastomeric material 5. Knead the putty addition silicone while wearing latex gloves Study Questions I. Choose the single best answer: 1. Which of the following impression materials would you use for taking a secondary impression for a dentulous patient? a. Addition silicone b. Alginate c. Impression compound d. Zinc oxide eugenol 2. Which of the following impression materials can be used ONLY for edentulous patients? a. Alginate b. Condensation silicone c. Polysulfide d. Zinc oxide eugenol 3. What is loss of water from a hydrocolloid impression by evaporation called? a. Imbibition b. Hydrophobicity c. Hysteresis d. Synersis 4. Which of the following materials has the highest elastic recovery? a. Addition silicone b. Alginate c. Polysulfide d. Polyether 5. Which of the following materials is the most dimensionally stable? a. Addition silicone b. Alginate c. Condensation silicone d. Polyether 14  6. Which elastomeric impression material is the most difficult to remove from patient's mouth? a. Addition silicone b. Condensation silicone c. Polyether d. Polysulfide impression 7. Which of the following materials set through a reversible physical reaction? a. Agar b. Alginate c. Condensation silicone d. Zinc oxide eugenol 8. Which of the following is an undesirable property of the impression material? a. Dimensional stability b. High viscosity at the time of insertion in the mouth c. Minimal dimensional changes during setting d. Minimal permanent deformation upon removal from mouth 9. Which of the following impression materials is the most hydrophobic? a. Alginate b. Agar c. Condensation silicone d. Polyether II. Answer the following questions: 1. What impression material(s) would you use for making a primary impression and a secondary impression for the patient whose upper jaw is shown in the following figure? ------------------------------------------------------------------- ------------------------------------------------------------------- ------------------------------------------------------------------- ------------------------------------------------------------------- ------------------------------------------------------------------- ------------------------------------------------------------------- 2. What is the type of this cast (primary or secondary)? What is the type of this tray? Which impression material would be used to make an impression with this tray? ------------------------------------------------------------------- ------------------------------------------------------------------- ------------------------------------------------------------------- ------------------------------------------------------------------- ------------------------------------------------------------------- 15 3. Guess the type of impression material used. What is the name of the phenomenon shown in the following figure? What may have caused this phenomenon? How could it have been avoided? ------------------------------------------------ ------------------------------------------------ ------------------------------------------------ ------------------------------------------------ ------------------------------------------------ ----------------------------------------------- 4. What type of impression technique was used to make this impression? What type of impression materials do you think was used? ----------------------------------------------- ----------------------------------------------- ----------------------------------------------- ----------------------------------------------- ----------------------------------------------- 5. Which impression material(s) can you use to make primary and secondary impressions for your patient prior to construction of a prosthesis of the type shown in the following figure? Justify your selection. -------------------------------------------- -------------------------------------------- -------------------------------------------- -------------------------------------------- -------------------------------------------- 16  Quiz Answer Sheet Name: ID: 17  Chapter 2 Model and Die Materials  Model and Die Materials Manipulation:  Presentation: Supplied as powder to be mixed with water.  Armamentarium: Rubber bowl and stiff plastic spatula  Procedure: 1. Dispense the weighed powder into the 2. Vibrate or tap the rubber bowl. This premeasured water slowly (30 to 60 sec) to will remove air bubbles. allow the powder to sift into the water. N.B: Mechanical Mixers under vacuum produce gypsum with superior properties. 3. Mix the powder and water together 4. Visually inspect the final mix for vigorously along the sides of the bowl to help a glossy surface and a smooth and break-up any agglomerates. This will creamy consistency. enhance the wetting of the powder and will press the air bubbles out. 5. Pour the gypsum into the impression 6. After the cast has initially set (≈ 30 gradually and with slight vibration. This will min), carefully remove the impression help remove bubbles and will encourage flow tray from the plaster cast. into impression details. 20 Observation sheet for mixing dental plaster: Procedure Observation Comments 1. Mix 50 - 60 ml of water The mix is……………… with 100 gm powder …………………………… 2. Mix a high P/L The mix is……………… …………………………… 3. Mix a low P/L The mix is……………… …………………………… 4. What happens if: a. Water is added to the a. ……..………………… powder? ………..…… b. The powder is added b.………………………… at once to the water? …………… 5. Spatulate vigorously The mix sets ……… 6. Hand mixing will By using……………. incorporate air bubbles in the mix, how can you eliminate them? 7. How long does it take The time needed to obtain a to obtain a homogenous mix is homogenous mix? ………. min. 8. Describe the surface of: a. A freshly mixed  Freshly mixed material model material appears …………... b. Plaster mix after  Material after setting setting? appears ……………… 9. How long does it take to …… minutes after mixing pour the impression with the plaster mix? 10. Mix the powder with YES/ NO warm water. Is the setting time affected? 11. Is there a change in YES/ NO viscosity as the surface becomes dull? 12. At that stage, can you YES/ NO remove the cast from the impression? 13. Does the temperature YES/ NO of Plaster change as it undergoes setting? 21 14. Scratch the surface of Plaster using a pencil What can you observe?  5 minutes after After 5 min mixing. ……………………...  15 minutes after After 15 min mixing ……………………….  1 hour after mixing After 1 hour …………………………. 15. After hardening of YES/ NO Plaster, can you bend ………………………… or deform it? Why? ……………………… 16. Is there a change in YES/ NO the dimensions of the model material during setting? Study Questions I. Give reason(s) for: 1. Chemical additives decrease the setting expansion of gypsum products. 2. Water in excess is needed for mixing CaSO4. ½ H2O. 3. Mixing gypsum products with boiling water is contraindicated. 4. Addition of borax prolongs the setting time of gypsum products. II. Choose the single best answer: 1. Hydrocal and densite are two types of gypsum. What is the main difference between them related to? a. Chemical composition. b. Color of powder c. Particles' size and shape. d. Setting reaction. 2. What is the amount of water required to chemically react with 100 gm of improved stone powder? a. 18.6 ml. b. 22 ml. c. 30 ml. d. 55 ml. 3. What happens when the water/ powder ratio of gypsum products is increased? a. Flow is decreased. b. Setting expansion is increased. c. Setting time is increased. d. Strength is increased. 22  4. Which of the following is different among the various gypsum products and is therefore responsible for their different particles’ size and shape? a. Chemical formula. b. Method of manufacturing. c. Strength properties. d. Type of the modifiers. 5. Why does Plaster of Paris show higher setting expansion compared to dental stone? a. The powder particles of dental plaster are more porous. b. The powder particles of dental stone are more regular. c. Higher water/powder ratio is required for mixing dental stone. d. Plaster of Paris is prepared by calcination in an autoclave. 6. What is the plaster mix obtained by mixing 100 gm of powder with 22 ml water characterized by? a. Granular and friable. b. High Fluidity. c. Homogeneity. d. Prolonged setting. 7. What is the product obtained when heating gypsum at 120 °C in open air? a. Alpha hemihydrate. b. Anhydrous CaSO4 c. Beta hemihydrate. d. CaSO4 dihydrate. 8. What is the chemical formula of the dental stone powder? a. CaSO4 b. CaSO4. 2H2O. c. CaSO4. 3H2O. d. (CaSO4)2. H2O. III. State true or false and correct the false: 1. Plaster of Paris is the strongest gypsum product. 2. Densite shows the highest setting expansion. 3. The initial setting time of model plaster can be detected clinically by loss of gloss of the plaster mix. 23  Quiz Answer Sheet Name: ID: 24  Chapter 3 Investment Materials  Investment Materials Study Questions I. Give Reason(s) for: 1. The binder is considered to be one of the important components of investment material. 2. Cristobalite form is used for crown and bridge investment, while quartz form is used for soldering. 3. Investment materials should be porous. 4. The use of α-CaSO4.2H2O in investment materials rather than the β-form. 5. Gypsum bonded investment should not be used for the higher fusing dental alloys. 6. Investment materials should have sufficient expansion. 7. Venting of silicate bonded investment is a must. II. Choose the single best answer: 1. Which of the following investments is used for casting base metal alloys? a. Gypsum-bonded. b. Phosphate-bonded mixed with water. c. Silicate-bonded. 2. Which of the following is among the main requirements of an investment material? a. Friable b. Porous c. Weak. 3. Which type of expansion occurs when the investment is immersed in water? a. Hygroscopic. b. Setting c. Thermal 4. What is the ingredient added to dental investments to provide thermal expansion? a. Borax. b. Carbon. c. Cristobalite. 5. What is the role of silica in investment materials? a. Allow hygroscopic expansion of the mold. b. Allow thermal expansion of the mold. c. Provide mold contraction on heating. 6. Which type of investment needs venting? a. Gypsum-bonded. b. Phosphate-bonded. c. Silicate-bonded. 26  7. What is the role of the refractory material in investment materials? a. Decrease its strength. b. Increase its expansion. c. Produce porosity. III. State true or false and correct the false statement: 1. Investment materials should have high strength to withstand the driving force of the alloy during casting. 2. Phosphate bonded investment is suitable for casting both gold alloys and base metal alloys. 3. High thermal expansion of silicate bonded investment is due to the presence of large amount of silica. 4. Generally, investments are composed of refractory materials 65%, binder 30%, and 5% modifiers. 5. Dental plaster is used as a binder in gypsum bonded investment to provide strength. 6. A good amount of hygroscopic expansion occurs when silicate bonded investment is used. 7. A copper ring is used with silicate bonded investment. 27  Quiz Answer Sheet Name: ID: 28 Chapter 4 Waxes  Waxes Study Questions I. Give short account on: 1. Solid-solid transition temperature of dental wax (Definition and use) II. Give Reason(s) for: 1. Low thermal conductivity of dental waxes may increase the internal stresses and distortion after shaping. III. State true or false. Justify your answer: 1. Modelling waxes are used for the construction of metal castings and bases for dentures through lost wax technique. 2. Melting point is a characteristic of dental waxes. 3. Sticky wax is brittle and adhesive. IV. Choose the correct answer: 1. Inlay wax must be burnt out without any residue. It should have high thermal expansion and contraction. Which statement is true and which is false? a. The first statement is true, the second is false. b. The first statement is false, the second is true. c. Both statements are true. d. Both statements are false. 2. Which of the following waxes is used for boxing an impression before pouring gypsum? a. Baseplate wax b. Cording wax c. Sticky wax d. Pattern wax 30  Quiz Answer Sheet Name: ID: 31  Chapter 5 Casting Technology  Casting technology Procedure: 1. Formation of wax patterns: a) Direct technique b) Indirect technique c)Indirect and Direct technique 2. Spruing the pattern: a. Material: The sprue can be made of wax, plastic or metal. b. Attachment and direction: Sprue is attached to the thickest part of the wax pattern with a 45 angle to the proximal wall surface. c. Diameter (Thickness): Equal or slightly thicker than the thickest part of the wax pattern. d. Number: Single, double or multiple sprues e. Length: The length of the sprue is adjusted so that, when attached to the crucible former, keeps the wax pattern at about 6 - 8 mm from the end of the casting ring. 3. Casting ring and Liner: Metallic, split metallic or rubber ring Ring Liner 34 4. Investing wax pattern: Before investing wax pattern, the surface of the pattern should be painted by a wetting agent. There are two different methods of mixing the wax pattern: Hand-mixing and Vacuum-mixing. 5. Wax elimination Mould space 6. Casting A casting machine requires a heat source to melt the alloy. It also requires casting pressure to force the alloy inside the mold. 35 7. Devesting, finishing and polishing of the casting 36 What happens in case of….? 1. Improper handling of the wax pattern 2. Delayed investing of wax pattern 3. A short sprue is used 4. A long sprue is used 5. A thin sprue is used 6. A plastic sprue is used 7. Sprue is attached at 90° to the wax pattern 8. Improper use of wetting agent 9. Improper selection of the investment material 10. Improper vacuum investing 11. Incomplete wax elimination 12. Under-heating of the alloy 13. Insufficient casting pressure 14. Too rapid heating of the investment 15. Insufficient venting of the investment 37 Study Questions I. State true or false and correct the false: 1. Hand investing procedure is highly recommended to obtain casting with minimal surface defects. 2. The amount of expansion is a critical property in the investment materials to obtain an accurate casting. 3. Melting gold alloys is done by an oxyacetylene flame whereas melting base metal alloy is done by a blow pipe flame. 4. The length of the sprue should be adjusted so that the wax pattern is placed at about 6- 8 mm from the end of the casting ring. 5. An over-sized casting is obtained due to improper handling of the wax pattern. II. Give reason(s) for: 1. Wax sprues are preferred over plastic ones. 2. The use of wet ring liner during casting. III. Choose the single best answer: 1. What is the purpose of heating the investment? a. Hygroscopic expansion b. Melt the alloy c. Evaporate the water d. Expand the mold thermally 2. What is the cause of too small casting? a. Improper selection of the investment material b. Incomplete wax elimination c. Insufficient melting of the alloy d. Over-heating of the investment material 38  Quiz Answer Sheet Name: ID: 39  Chapter 6 Dental Casting Alloys  Dental Casting Alloys Dental applications: Casting alloys are used, in dental laboratories to produce indirect restorations such as those seen in figure 1. Inlays Onlays Crown Conventional all-metal bridge Ceramo-metallic restorations Resin bonded bridge Endodontic post and core Partial denture framework Figure 1. Indirect restorations 41 Comparison between Base Metal Alloys and types III and IV Gold Alloys Property/ Base Metal Gold Alloys Clinical Significance Co-Cr Ni-Cr Type III & IV Ti & Ti alloys I. Biocompatibility Resistance to tarnish and corrosion II. Physical Properties: a. Color b. Density c. Coefficient of thermal expansion and contraction d. Casting shrinkage e. Fusion temperature f. Sag resistance II. Mechanical properties  Cp Ti is similar in mechanical properties to gold alloys type III & IV.  While Ti alloys are similar in mechanical properties to Co/Cr &Ni/Cr base metal alloys. a) Modulus of elasticity 42 b) Yield strength c) Ultimate tensile strength d) % Elongation e) Hardness (VHN) IV. Casting a) Casting sensitivity b) Casting ring c) Investment material 43 d) Melting method e) Crucible f) Casting machine g) Cooling h) Finishing and polishing i) Recasting Study Questions I. Give reasons for: 1. Base metal alloys are difficult to be finished and polished. 2. Types III and IV gold alloys can be heat treated while types I and II cannot. 3. Nickel-chromium alloys are commonly used in crown and bridge work rather than cobalt-chromium alloys. 4. The percentage of chromium and carbon should be adjusted in base metal alloys. 44  5. Zinc is added in small quantities in gold alloys. 6. Base metal alloys are especially useful for construction of large and bulky maxillary dentures. 7. Types III and IV gold alloys have two values for their yield strength but Types I and II have only one value. II. Choose the single best answer: 1. What is the method of choice in polishing base metal alloys? a. Air abrasion. b. Electrolytic polishing. c. Electroplating. d. Pickling. 2. Which of the following contributes to the difficulty of casting of titanium alloys? a. High density. b. High reactivity at high temperature. c. Low melting temperature. d. Low corrosion resistance. 3. Compared with type IV gold alloys, which of the following is related to cobalt chromium alloys? a. About half as dense b. Easier to finish and polish c. Lower modulus of elasticity d. Use the same type of casting machine 4. A lab technician used silicate bonded investment material during casting a crown made of gold alloy. What is the suspected defect in the resultant crown? a. Broken margins. b. Oversized crown. c. Pitted crown surface. d. Rough surface. 5. Which of the following gold alloys is most suitable for fabrication of inlays? a. Type Ӏ b. Type II c. Type III d. Type IV 6. Addition of Aluminum to base metal alloys containing nickel will result in increased strength. What is the type of Nickel aluminide alloy responsible for this claimed strengthening effect? a. Eutectic b. interstitial solid solution c. Intermetallic compound. d. Substitutional solid solution. 45 Clinical Cases 1. During cementation of a gold crown on a lower right 2nd molar, you felt that the crown was a little bit loose. It was slightly oversized. What is the suspected error that occurred during the crown fabrication? How would the lab technician avoid such error? 2. To what extent is the use of Beryllium containing dental alloys is hazardous to both the dentists and the lab technicians? How to avoid such health hazards? 3. A patient represented to your clinic with several missing lower teeth as shown in this figure. He needed to restore these teeth with a suitable restoration. You decided to restore them with a removable partial denture. What is the alloy of choice to fabricate the framework of such a partial denture? Justify your answer. 4. A patient represented to your clinic with a discolored metallic part of his upper partial denture. The patient history revealed that he used to store his denture in a cup filled with diluted house hold bleach overnight. What is the cause of the denture discoloration? What will you advise your patient to do? 46 5. The two figures below show a type of prosthesis that is extensively used nowadays. a. What is the name of this prosthesis? b. What is the best suitable material for fabrication of this prosthesis? c. In your opinion, what was the method of shaping of this material? Is there any problem associated with shaping of this material? 6. The following two figures show two different materials that can be used for fabrication of dental crowns: a. Identify the two materials. b. Which of the two materials offer better adjustment of the crown margins? Justify your answer. c. What are the finishing and polishing methods that can be used with each of the 2 materials? 47  Quiz Answer Sheet Name: ID: 48  Chapter 7 Wrought Alloys  Wrought Alloys Study Questions I. Give Reason(s): 1. Weld decay phenomenon of stainless steel wire should be avoided. II. State true or false and correct the false statement: 1. Stainless steel wire has the lowest value of spring back action among other wrought base metal alloys. 2. β-titanium and nickel titanium alloys are used for fabrication of orthodontic wires. 3. Weld decay occurs at temperature higher than 800 °C in stainless steel wires. 4. Stabilized austenitic stainless steel has adequate tarnish and corrosion resistance. 5. Stabilized austenitic stainless steel is an alloy to which titanium is incorporated. III. Choose the single best answer: 1. What is the purpose of niobium addition to stainless steel alloy? a. Helps in formation of chromium carbides b. Stabilizes the alloy against weld decay c. Stabilizes the austenitic form at room temperature d. Stabilizes the martensitic form at room temperature 2. What should the chromium percentage in stainless steel alloy be higher than? a. 2.5% b. 13% c. 38% d. 52% 50  Quiz Answer Sheet Name: ID: 51  Chapter 8 Joining of Metals  Joining of Metals Soldering process includes: B A 1. Metals to be joined: A. Parent metals B. Solder alloy 2. Flux and antiflux: 3. Heat source: Gas-air or gas-oxygen torch: 53 I. Give reason(s) for: 1. The fineness of the gold solder should be slightly less than the fineness of the metallic parts being joined. 2. Laser welding is used for joining titanium components 3. Pure gold can be pressure welded at mouth temperature. 4. Gold solders are not preferred for joining base metal alloys. 5. Quartz-containing investment is used during soldering procedure. 6. Fluoride-containing flux should be used when soldering base metal alloys. 7. Flux must have a fusion temperature below that of the parent alloy that is being heated. II. Choose the correct answer: 1. Which of the following describes joining of two metals without using an intermediate third one? a. Casting. b. Sintering. c. Soldering. d. Welding. 2. Which of the following is the best method for joining two pieces of stainless steel? a. Spot welding for maximum time and current. b. Soldering using high fusing solder. c. Soldering using gold solder. d. Soldering using pressure welding. 3. Which of the following properties is high in gold alloys and therefore makes them not suitable for spot welding? a. Electrical conductivity. b. Melting range. c. Thermal conductivity. d. Thermal diffusivity. 4. Which type of antiflux is used for gold solders? a. Cryolite b. Graphite c. Silicon d. Titanium 5. Which of the following are joined by laser welding? a. Orthodontic appliances. b. Pure gold foil. c. Stainless steel wires. d. Titanium. 54  Quiz Answer Sheet Name: ID: 55  Chapter 9 Dental Amalgam  Dental Amalgam Dental amalgam is a mixture of special dental alloy (Powder) and highly pure mercury (Liquid) at room temperature (Figures 1, 2) to give plastic mass, which is packed into the prepared cavity where it hardens. Figure 1. Amalgam composition Powder Amalgam Capsule Figure 2. Amalgam presentation Manipulation of amalgam I. Selection of the alloy: The selection of an alloy involves a number of factors including particle size, particle shape, the presence or absence of zinc and composition. II. Proportioning (mercury: alloy ratio): Proportioning of mercury and alloy (figures 3 and 4) is the first important manipulative procedures in forming a suitable plastic mass of amalgam for placement into the prepared cavity. Proper proportioning must be maintained because: 1. Excess mercury will lead to the formation of more γ1 and γ2 on the expense of the stronger γ phase. This will lead to setting expansion, setting time, strength, tarnish and corrosion and creep. 2. Less mercury will lead to a friable mix with more voids (since not all the particles will be wetted by mercury), decreased strength and increased liability to tarnish and corrosion. Two techniques have been recommended for proportioning: 1. Wet technique: Which requires mercury slightly in excess of 1:1 mercury alloy ratio. 2. Minimal mercury (Eam’s) technique: Where the mercury: alloy ratio is less than 1:1. 57 Figure 3. Volumetric dispenser for alloy powder Figure 4. Volumetric dispenser for mercury III. Trituration: The mixing or trituration of amalgam may be carried out by hand, using mortar and pestle (figure 5) or mechanical with an electrically powered machine (amalgamator), which vibrates a capsule containing mercury and alloy (figure 6). Advantages of mechanical trituration: 1. More uniform and reproducible mix is produced. 2. Shorter trituration time can be used. 3. Low mercury alloy ratio can be used. 4. Less risk of exposure of mercury vapor. Figure 5. Mortar and pestle Figure 6. Amalgamator IV. Condensation: It is the packing of plastic amalgam mass inside the prepared cavity (figure 7). The objectives of condensation are to: 1. Yield a restoration with optimal adaptation to the cavity walls. 2. Reduce the mercury content of the condensed mass (express excess mercury to the surface). Thus improving mechanical properties. 3. The amount of mercury in the final restoration is determined in this stage. 4. Reduce the porosity content of the amalgam mass, thus producing structurally dense and strong restoration. 58  a. In class II cavities, matrix band and wedge is applied before condensation of amalgam b. Amalgam carrier to carry amalgam into c. Condensation of amalgam by the use of the prepared cavity amalgam condenser Figure 7. Condensation of amalgam V. Carving and Finishing: Carving: The restoration is carved to reproduce the proper tooth anatomy (figure 8). Figure 8. Carving of amalgam by amalgam carver Polishing: Polishing is carried out to achieve a lustrous surface having a more acceptable appearance and better corrosion resistance (figure 9). Conventional low-copper amalgams are polished not less than 24 hours after insertion. However, high-copper amalgams can be polished shortly after insertion since they gain their strengths rapidly. a. Unpolished amalgam b. Polished amalgam restoration Figure 9. Amalgam polishing 59 Observation Sheet Read the composition and manufacture’s instruction before use 1. What is the composition of the alloy you are using? 2. What is the shape of the particles you are using? ( ) ( ) ( ) 3. Properly triturate an amalgam capsule, over triturate another capsule and under triturate a third one and Match: Trituration Time Characteristics Figure Normal Triturated Amalgam Difficult to remove from capsule Over Triturated Amalgam Dry Mix Under Triturated Amalgam Homogenous Mass **NishaGarg and AmitGarg.Text of Operative Dentistry 2010. 4. Compare hand trituration of amalgam to the mechanical one and Record your observation regarding the “Hand Mixing”: ↑ ↓ Uniform and reproducible mix Trituration time Mercury alloy ratio Mercury vapor exposure risk 5. Properly condense the amalgam and choose your answer: o Do you express excess mercury to the surface? Yes or No ↑ ↓ Uniform and reproducible mix Trituration time 60  6. Condense partially set amalgam (Delayed condensation) and complete the following sentences: o The partially set mass will contain ….……mercury. o Reduction in the plasticity, which ………. the adaptation to the prepared cavity. 7. The cavity should be overfilled….Why? 8. If the direction of carving is from the restoration towards the tooth… what happens? 9. Notice the sound of the amalgam during carving (after 5 minutes). Study Questions I. Give reason(s) for: 1. When isolation of the prepared cavity is difficult, zinc-free amalgam should be used. 2. Spherical amalgam particles give superior amalgam properties than lathe-cut particles. 3. Creep occurs in dental amalgam. 4. Excess mercury in dental amalgam should be avoided. 5. Aging (annealing) of the irregular amalgam alloy powder particles is essential. 6. The importance of using the same rate of loading when comparing the compressive strengths of amalgam samples. 7. All types of dental amalgam undergo corrosion. 8. High-copper unicompositional amalgam is more preferred than high-copper admixed amalgam. 9. Dental amalgam restorations should be supported by bases with high modulus of elasticity. II. Choose the single best answer: 1. Which phase is eliminated in high-copper amalgam? a. Ag2 Hg3 (γ1 phase). b. Ag3 Sn (γ phase). c. Cu6Sn5 (η phase). d. Sn8 Hg (γ2 phase). 2. What is the role of Zinc added during the manufacturing of dental amalgam alloy? a. Grain refiner. b. Nucleating agent. c. Scavenger. d. Setting retarder. 3. What is the most common clinical application of dental amalgam? a. Anterior direct restoration. b. Crowns for posterior teeth. c. Partial denture framework. d. Posterior direct restoration. 61 III. State true or false and correct the false: 1. High-copper unicompositional amalgam has lower creep value than high-copper admixed amalgam. 2. Spherical amalgam alloy particles are exposed to homogenization process during manufacturing. 3. In dental amalgam, the mercury-containing phases represent the elastic portion. 4. γ1 is the weakest and most corrodible phase in low-copper amalgam. 5. The high-copper admixed amalgam exhibits higher strength than the high-copper unicompositional amalgam. 6. Fine-cut amalgam alloy particles produce amalgam with better properties than coarse- cut particles. 62  Quiz Answer Sheet Name: ID: 63  Chapter 10 Non-metallic denture base materials  Non-metallic denture base materials The material most commonly used for the fabrication of dentures is the acrylic resin, Poly Methyl Methacrylate (PMMA). Clinical and Laboratory Steps of Complete Denture construction: A. Primary Impressions  Pouring Impression  study cast B. Final Impressions Pouring Impression Master cast Bite block construction (occlusion wax rim, trial denture base) C. Recording Jaw Relationship (Jaw Registration) Mounting on Articulator, setting up teeth D. TRY-IN Procedures Flasking, Wax elimination and Denture fabrication E. Denture Delivery 65 Steps of mould preparation: A. Tooth arrangement prepared for B. Master cast embedded in dental stone flasking process C. Occlusal and incisal surfaces of D. Fully flasked Maxillary complete the artificial teeth exposed dentures E. Separation of flask segments F. Placement of separating medium during wax elimination process 66 Manipulation of Heat-Cured Acrylic Resin: A. Presentation (figure 1): Powder (polymethyl methacrylate) and liquid (methyl methacrylate) B. Proportioning: (P/L ratio) Powder/ Liquid ratio is 3:1 by volume or 2.5:1 by weight C. Mixing: Mixing is done with a stainless steel spatula in a sealed jar. The dough stage is the stage used for packing acrylic resin D. Separating medium: Before packing the dough, a separating medium should be applied (sodium alginate). All parts of the gypsum cast in the flask should be painted by separating medium except the necks (lower surface) of the teeth (figure 2). Figure 2. Painting the separating medium E. Packing:  The powder-liquid mixture should be packed in the dough stage (Figure 3a).  The mould should be over filled (figure 3 b) and sufficient pressure should be applied on the mould (figure 3 c). a b c Figure 3. a) Packing the acrylic resin dough b) in excess c) applying sufficient pressure 67  F. Processing:  Heat is applied to cure the polymer usually in water bath (Figure 4).  The temperature and time should be controlled. Curing Cycles: 1. Long Cycle: A satisfactory processing procedure is to cure the plastic in a constant temperature water bath at 74 °C for 8 hours. OR 2. Short cycle: To heat at 74 °C for one hour and half, then increasing the temperature of water bath to boiling for an additional hour. G. Deflasking and Finishing: After polymerization, the flask is removed from the water bath and allowed to cool to room temperature. After cooling, the denture is ejected from the flask, stone is removed. Figure 4. Processing acrylic resin followed by deflasking  Stone adhering to plastic is removed by shell blasting.  Denture is trimmed with acrylic burs to remove any excesses of acrylic. Figure 5. Finishing the acrylic resin denture 68  Polishing is performed by a wet polishing wheel and slurry of pumice in water. Figure 6. Unpolished complete denture Figure 7. Polished complete denture  After finishing and polishing, the denture should be stored in water. 69 N.B: Other uses of Acrylic Resin include: 1. Special tray 2. Trial denture base 3. Anterior restorations 4. Temporary crowns 5. Acrylic artificial teeth 6. Removable appliances and Mouth Guards 70 Observation sheet Procedure Observation Comments 1. Mix proper P/L ratio ( ) Describe the stages that the mix goes through. 2. Try to shape the mixed material at the different stages. 3. Increase P/L ratio 4. Decrease P/L ratio 5. Feel the temperature of the mixed dough as it sets 71 Study Questions I. Give reasons for: 1. Cross-linking agent is added in the formulation of acrylic resin. 2. Delayed packing of acrylic resin should be avoided. 3. The finished denture must be placed in a cup of water after processing. 4. Crazing may occur in acrylic complete denture. 5. Addition of butadiene styrene rubber inclusions to acrylic resin. II. State true or False and correct the false: 1. Polymer powder is mixed with MMA monomer with a ratio of 3:1 by weight to obtain an acrylic resin denture base. 2. The monomer of the heat-cured acrylic resin denture base material contains the activator. 3. Premature opening of the flask before cooling may cause warpage of the denture. 4. The rubbery stage is the desirable consistency for packing into the denture flask. 5. Fluid resin has chemical composition similar to that of heat-cured acrylic resin. 6. Denture base materials should be radiolucent. III. Choose the single best answer: 1. Which of the following can result in gaseous porosity in heat-cured acrylic resin? a. Insufficient packing of acrylic dough. b. Insufficient pressure on the mould. c. Mixing low powder/liquid ratio. d. Monomer boiling during polymerization. 2. What are the precautions that should be considered during packing of acrylic resin mix? a. Apply a separating medium on teeth surfaces b. Apply sufficient pressure on the mould c. Make sure the mould is not over-packed d. Pack the dough in the sandy stage. 3. What is the possible cause of contraction or shrinkage porosity (surface porosity)? a. Over packing. b. Packing at dough stage. c. Use of excessive monomer. d. Use of separating medium. 4. What will happen if the acrylic resin denture was cooled rapidly after polymerization? a. Change in strength. b. Increase monomer. c. Increase thermal stresses. d. Minimize porosity. 5. What does keeping the monomer in a tightly sealed dark bottle help avoid? a. Change in color of the polymer b. Crazing of the acrylic resin c. Porosity of finished denture d. Self-polymerization of the liquid on storage. 72  Quiz Answer Sheet Name: ID: 73  Chapter 11 Direct aesthetic restorative materials  Direct aesthetic restorative materials I. Presentation: Resin composite restorative materials are supplied as either: 1. Chemical-Cured Resin Composite: It is supplied as two pastes (base and catalyst paste). The kit contains etching liquid, a chemical cure bonding system (two bottles), a mixing pad and plastic spatula for mixing. Composite Mixing paper Bonding agent paste base pad and plastic and etching gel and catalyst spatula Chemically cured composite is mixed over mixing paper pad using plastic spatula Plastic spatula for mixing of chemical- cured resin composite 2. Light-Cured Resin Composite: It supplied as one paste, light proof syringe. It should be used in conjunction with a bonding system and etching gel. Etching gel Composite syringes Bonding agent 75  Gold plated instruments used for placement of light-cured composite 3. Dual-cured composite: Consist of two pastes, one containing benzoyl peroxide and the other containing an aromatic tertiary amine accelerator. They are formulated to set up very slowly when mixed via the self-cure mechanism. The cure is then accelerated on “command” via light-curing. Dual-cured composite. 76 II. Manipulation of light-cured composite: 1. Carious mandibular molars. 2. Field isolation with a rubber dam. 3. Class I cavity preparations. 4. Etching for 20 sec. with a 37% phosphoric acid gel, water rinsing and gentle air drying. 5. Application of light cure bonding 6. The bonding adhesive is light-cured 20 sec. agent 7. Application of the 1st increment of 8. Polymerization of each composite increment. composite 9. Completed occlusal anatomy 10. Finishing and polishing the final restoration. 77 III. Dental applications for resin-based composites: 1. Anterior Restorations: 2. Direct Posterior Restorations: 3. Laminate veneers in anterior teeth: 4. Pit and fissure sealant: 5. Core Build-Up Composites: 6. Resin Composite Inlay/Onlay: 78 IV. Light Curing Units: The traditional method for delivering the blue visible light required for ‘visible light activation’ involves the use of a quartz tungsten halogen (QTH) lamp. Other systems including plasma arc, laser and light emitting diode (LED) systems are also available now. Quartz-Tungsten-Halogen Light-Curing Units (QTH):  Halogen lamps are the most widely used and are relatively cheap. A QTH light source consists of a light bulb, several filters, a reflector, a fan, a power supply, and a light guide.  They produce a broad spectrum of light and require appropriate filtration to eliminate harmful elements of the light spectrum, thereby generating the required power of light output.  These bulbs also generate a considerable amount of heat, thus the fan is necessary to cool the bulb and assembly.  The power output from the bulb deteriorates as the bulb ages reducing the effectiveness of the curing process. Therefore, maintenance of QTH lights must be provided on a regular basis. The bulb life ranges from 50 to 75 hours. Plasma arc lamps:  The plasma arc lamps use a Xenon bulb where a spark is produced by generating a large potential difference across the gas which becomes ionized to form ‘plasma’. This will be accompanied by the production of light.  The power output from these light units is about 10 times that of a halogen bulb resulting in considerably shorter curing times.  Plasma arc lamps also generate a great deal of heat and require very efficient cooling systems. Laser curing units:  Argon lasers emit a blue light which can be used to activate polymerization. Laser curing units can polymerize composite in a time shorter than that required for QTH units, but longer than that required for plasma arc units.  Minimal heat is produced by laser curing units, however, they remain a quite expensive alternative. Also, laser curing units are not suitable for use with all types of photo-initiators and are relatively expensive. Blue Light-Emitting Diodes (LED):  Light-Emitting Diodes (LED) units are effective for curing materials with camphorquinone photo-initiators. LEDs have a number of advantages: 1. Low power consumption: They can be designed and manufactured as portable rechargeable light curing units. 2. They do not require a filter. 3. They have a long life span. 4. They do not produce as much heat as QTH devices, thus they do not require a fan. 79  Plasma arc lamps QTH light curing unit LED curing unit Depth of cure of resin composites is dependent on: a. The characteristics of the light source, e.g. a new bulb would give the highest intensity. b. The distance between the source and the composite resin surface. Light intensity varies as the inverse square of the distance. c. The time of exposure to light. d. The initiator system absorption characteristics. With the development of light sources of improved intensity, at least a 2 mm depth of the material can be polymerized in 10 to 20 seconds. Light curing variables that may affect the degree of polymerization Recently, composites that polymerize to a depth of 4-5 mm, Bulk Fill Composites, have been introduced. 80  Observation sheet for curing a composite sample Procedure Observation Comment 1. Cure two composite samples: 2 and 4 mm-thick while placing a Mylar strip on both the top and bottom surfaces:  Inspect the top and bottom surfaces with an explorer.  Check both surfaces for improperly polymerized material. 2. Cure a 1 mm-thick sample of composite: bottom side against a Mylar strip and top side exposed to air.  Compare both top and bottom surfaces. 3. Place additional composite material on the top surface of the above sample. Cure and attempt to push the second increment off the first.  Describe the force required to debond the two composite layers. 81 V. Adhesive Systems: 1. Total etch approach: Depends on simultaneous etching of both enamel and dentin (phosphoric acid-etching) and includes: a. Three step approach: Etching, application of primer and application of bonding agent, in three successive steps separately b. Two-step approach: Etchant applied in one step then Primer and adhesive applied in another step. 2. Self etch approach: These systems use an acidic primer (mild acids) that is applied to dentin and not rinsed off. a. Two step approach “self-etch primer”: The acidic conditioner with the primer in one bottle and applied as initial step, then the bonding resin is applied in the second step. b. Single step approach “All in one”: The single liquid contains self- etch primer and adhesive. 82 Study Questions I. Give reason(s) for: 1. Incremental addition of light cured composites. 2. Direct aesthetic restorative materials should have their coefficient of thermal expansion closely matching that of enamel and dentin. 3. BIS-GMA and UDMA are used in composites instead of MMA. 4. Diluents should be included in Bis-GMA composite formulations. 5. Care should be taken to avoid unpolymerized composite at the base of a restoration. 6. Ultraviolet stabilizers should be added to composites. 7. Microfine composites are not ideal for posterior restorations. 8. The coefficient of thermal expansion and contraction of microfilled composites is higher than that of conventional composites. 9. Water sorption of fine and hybrid composites is less than that of microfine. 10. Composite inlay is one of the methods that overcomes polymerization shrinkage of resin composite. II. Choose the single best answer: 1.Which of the following statements is related to light-activated resin composites? a. Air bubbles incorporation increase the opacity of the restoration. b. No mixing is required for these composites. c. The working time is about 2 to 3 minutes after mixing. d. UV light is essential to initiate polymerization. 2. High and low molecular weight monomers/oligomers; with different viscosities, may constitute the organic matrix of resin composite restorative materials. Which of these compounds has the highest viscosity? a. Bisphenol A-glycidyl methacrylate b. Methyl methacrylate c. Tri ethylene glycol dimethacrylate d. Urethane dimethacrylate 3. Which of the following is higher for fine particle-composites compared to micro- filled composites? a. Polymerization shrinkage b. Strength properties c. Thermal expansion d. Water sorption 4. Radio-opacity is among the requirements of restorative materials. Which of the following elements/compounds render composites radio-opaque? a. Barium b. Glass c. Silica d. Silver 5. What is the similarity between resin composite restorative materials and giomers? a. Chemical bonding to tooth. b. Fluoride recharge. c. Fluoride release. d. Light curing. 83  Quiz Answer Sheet Name: ID: 84  Chapter 12 Dental Cements  Dental Cements 1. Zinc Oxide and Eugenol: Presentation: The cement is available in two forms: a. Powder and liquid form b. Ready-made paste of zinc oxide and eugenol Mixing:  Powder and liquid are mixed using stainless steel spatula on oil resistant pad/glass slab.  Powder is incorporated into a dispensed amount of liquid until a suitable consistency is achieved. 86 2. Zinc Phosphate Cement: Presentation: The cement is available in the form of powder and liquid Mixing:  Shake both bottles prior to dispersion to ensure that all the constituents are mixed together.  Powder and liquid are mixed on a cool, glass slab to increase the working time  Powder is divided into six increments to delay the onset of setting and to dissipate heat.  Incorporate the proper amount of powder incrementally into the liquid using stainless steel spatula to attain the required consistency.  Mixing is done over wide area to allow the dissipation of heat and increase the working time. Dental cement (luting) consistency Dental cement consistency for temporary for cementation filling 87 3. Zinc Polycarboxylate Cement: Presentation: Zinc polycarboxylate cements are available in three forms: a. Powder and liquid form b. Water settable cement c. Pre-proportioned capsules: For mechanical mixing Mixing:  Powder and liquid are mixed on a glass slab or a special paper pad.  Powder and liquid are mixed in a ratio of 1:1 or 2:1 according to the purpose of use.  Dispense liquid immediately before mixing to prevent evaporation of water and subsequent thickening.  Powder is divided into half where each half is incorporated at a time.  The mix is used when it is still glossy. 88 4. Glass ionomer Cement: Presentation: Glass ionomer cements are available in three forms: a. Powder and liquid form b. Water settable cement c. Pre-proportioned capsules Mixing:  Manipulation as zinc polycarboxylate cement  Coat the cement margins with the coating agent (varnish) supplied with the cement. 5. Resin Cement: Presentation: a. Self-cured resin composite cements b. Light-cured resin composite cements supplied as two paste system supplied as a single paste that does not require mixing. 89 Cavity Varnish:  Apply by a small cotton pledged or micro-brush.  Use gentle stream of air for drying.  Apply new layer to a previously dried one. Calcium hydroxide cavity liner Presentation: Supplied as 2 forms: a. Two paste system b. Light-cured (two collapsible tubes) (one paste system i.e. needs no mixing) Mixing of the two paste system:  Equal length of the two pastes are dispensed and mixed to uniform color 90 Observation sheet Procedure Observation Explanation 1. A drop of water is added during mixing of zinc oxide/Eugenol cement. 2. Zinc oxide/Eugenol cement is used as a base under composite restoration. 3. Zinc oxide/Eugenol cement is used as a base under amalgam restoration. 4. During storage of zinc phosphate cement, the liquid bottle was left open for a while. 5. During mixing of zinc phosphate cement, the powder was incorporated in one increment 6. During mixing of zinc phosphate cement, the operator used a cooled slab below dew point. 7. Dull Zinc polycarboxylate cement mix was loaded in the fitting surface of the crown. 8. Zinc polycarboxylate powder and liquid were mixed using stainless steel spatula. 9. Glass ionomer restoration was not covered with varnish after placement. 10. Glass ionomer powder and liquid were mixed using stainless steel spatula. 91 Use the following table to summarize the differences between the different dental cements Point of Zinc oxide- Zinc Zinc poly- Glass Resin Comparison eugenol phosphate carboxylate ionomer cement Presentation Composition Setting Reaction Manipulation Biological Properties Film Thickness Solubility Strength Bonding Optical Properties Main Advantage Main Disadvantage 92 Study Questions I. Choose the single best answer: 1. What is the effect of increased amount of powder in a cementing consistency mix of zinc phosphate? a. Decreasing the film thickness. b. Decreasing the solubility. c. Increasing the setting time. d. Increasing the strength. 2. Which of the following cement bases has the highest elastic modulus to best support an extensive amalgam restoration? a. Glass ionomer. b. Hybrid ionomer. c. Zinc oxide and eugenol. d. Zinc phosphate. 3. Which of the following materials are used as a pulp capping material? a. Calcium hydroxide. b. Glass ionomer. c. Zinc phosphate. d. Zinc polycarboxylate. 4. Which of the following cements is the most soluble? a. Glass ionomer. b. Zinc oxide and eugenol c. Zinc phosphate. d. Zinc polycarboxylate. 5. Which of the following cements should as much as possible be mixed over a large area on the glass slab to reduce the exothermic heat of reaction? a. Glass ionomer. b. Zinc oxide and eugenol. c. Zinc phosphate. d. Zinc polycarboxylate 6. Which of the following is a common additive to glass powder, to reduce melting temperature and improve the flow of the molten glass? a. Fluoride b. Oxides c. Quartz d. Silicate 7. Which cement is considered the best choice for luting ceramic restorations to tooth structure? a. Resin composite cement. b. Zinc oxide and eugenol. c. Zinc phosphate. d. Zinc polycarboxylate. 93  8. What is the reason for coating the glass ionomer cement margins with a coating agent? a. Enhance bonding. b. Lubricate the tooth. c. Protect against light. d. Protect against moisture. II. Give reason(s) for: 1. Zinc oxide and eugenol is contraindicated as sub-base under resin composite fillings. 2. Dental cements based on zinc oxide powder are contraindicated as sub-base under esthetic restorations. 3. Glass ionomer cements bond chemically to tooth structure. 4. Glass ionomer cements are technique (moisture) sensitive. 5. The margins of the restoration should be coated with oxygaurd during cementation with adhesive resin cement. 6. Minimal irritant effect of polycarboxylate cements on the pulp. 94  Quiz Answer Sheet Name: ID: 95  Chapter 13 Dental Ceramics  Dental Ceramics 1. Shade selection 2. Preparation of teeth for porcelain restorations The prepared tooth 3. Armamentarium Porcelain kit Porcelain powder 97 4. Cleaning of the metal frame work The metal frame work on the stone die 5. The opaque layer is 1st added to mask the color of the underlying metal Fired opaque layer 6. Build up with the desired Body color. Match the dimension and form to the symmetric tooth in order to recreate the shade precisely. 7. Build up translucent porcelain to cover the whole crown surface. To minimize shrinkage, hold the crown with tweezers and repeat the condensation with an instrument for 2 or 3 times. 98 8. Add-on glaze Steps of Porcelain Layering Technique Porcelain restorations before and after firing 99  CEREC SYSTEM 1. Create 3D image of the tooth with the aid of CEREC camera The CEREC camera acquisition unit and 3D imaging of the tooth with the aid of milling unit CEREC camera A virtual cast for the entire quadrant on the monitor 2. The restoration is designed on the monitor of CEREC acquisition unit Milling unit CEREC acquisition unit Designed restoration is transmitted The CEREC milling unit machines the to a remote milling unit for fabrication restoration out of ceramic block 100  Hard machining technique Leucite-reinforced glass-ceramic blocks for CAD/CAM Blocks for Soft machining technique 101  Celay CERCON BRAIN (Resin pattern for copy milling) Copy Milling of Bridges Presintered zirconia blocks The milling machine Cercon heat furnace 102 Clinical cases 1. During shade selection for an All-ceramic restoration, you noticed that the patient’s teeth are extremely lustrous and shiny. Which type of glaze will you recommend to the lab technician? What are its disadvantages from the clinical point of view? 2. During delivery of an All-ceramic restoration done by CAD/CAM (Cerec), the fit of the restoration was too tight that you cannot completely seat it on the prepared tooth. What are the possible cause(s) of this problem during manufacturing of the crown? How can this problem be avoided? 3. A patient came to your clinic after several days of cementing a creamo-metallic crown on his lower first molar tooth. He said that after eating a hard snack he heard a cracking sound and felt that a piece of his crown was broken. Upon examination, you found a part of the porcelain veneer was broken and the underlying color of metal revealed. What is/are the possible error(s) done by the laboratory technician during fabrication of the PFM crown causing such a problem? 103 4. What would be the cause(s) of the same previous problem if the crown was manufactured using heat pressing technique? 5. A young patient came to the dental clinic with a badly broken premolar tooth. You decided to make a full coverage ceramo-metallic restoration to protect the remaining tooth structure. From the pre-operative radiograph, you found that there is a high probability of pulp exposure during tooth preparation in order to give enough space for a conventional PFM crown. What are the possible alternatives to conventional PFM crown to minimize the amount of tooth structure removed during preparation? Study Questions: I. Give reason(s) for: 1. High concentration of glass modifiers in dental porcelain is contraindicated. 2. Ceramics are inert materials. 3. Porosity of dental porcelain. 4. During construction, porcelain restorations should be thoroughly compacted before firing. 5. Alloys used for ceramo-metallic restorations should have high modulus of elasticity. 6. For ceramo-metallic restorations, the alloy should have a melting temperature higher than the firing temperature of porcelain by 100-150оC. 7. Degassing is necessary in all gold-porcelain systems. 8. Leucite increases the strength of dental ceramics. 9. Copper and silver should be avoided in alloys used in ceramo-metallic restorations. 10. Heat-pressed all ceramics result in excellent fitting of restorations. 104 II. State true or false and correct the false: 1. The devitrification process increases the strength and translucency of the glass. 2. Porcelain teeth are more brittle and more resistant to wear than acrylic teeth. 3. The coefficient of thermal expansion of the alloy used in ceramo-metallic restorations should be slightly higher than that of the porcelain. 4. Developing residual tensile stresses in the surface of the ceramic material is a method of strengthening of ceramics. III. Choose the single best answer: 1. Quartz is one of the major constituents in dental porcelain. What is the role of quartz in porcelain? a. Binder b. Frit c. Opacifier d. Strengthener 2. Dental porcelains are formed of metallic and non-metallic elements. What is the manufacturing process by which it is formed? a. Firing b. Fritting c. Sintering d. Vulcanizing 3. Porosity is an inherent property of ceramic restorations. However, many fabrication techniques have been employed to minimize porosity. Which of the following techniques is best in decreasing porosity in dental ceramic restorations? a. Alumina-based sintered ceramic. b. Ceramo-metallic restorations. c. Leucite reinforced sintered ceramic. d. Lithium disilicate heat-pressed ceramic. 4. Porcelain ceramics are very brittle materials, and their strength values are much lower than the predicted values. Strengthening of ceramics can be done in several ways like adding Alumina crystals. What is the strengthening mechanism of Alumina? a. Absorb energy at the crack tip. b. Develop residual compressive stresses. c. Reduce size and number of surface flaws. d. Use crack energy to change its crystal structure. 5. Metal ions like Na+, K+ or Ca2+ can be added to dental porcelain powder to act as glass modifiers. What is the major role of glass modifiers? a. Enhance crystallization during firing. b. Increase fluidity during self-glazing. c. Increase fusion temperature of glass. d. Interrupt the integrity of the Si04 network. 105  Quiz Answer Sheet Name: ID: 106