1. Dental resin/synthetic resin

2. Synthetic resins
Are non-metallic compounds which are molded into various forms and then hardened for commercial use (e.g., clothing, electronic equipment, building materials and household appliances).
These are materials are composed of polymers or complex molecules of high molecular weight.
A variety of resins are used in dentistry which includes:
Acrylics
Polycarbonates
Vinyl resins
Polyurethanes
Styrene
Cyanoacrylates
Epoxy resins

3. Classification of resins
Based on the THERMAL BEHAVIOR
THERMOPLASTIC –
resin that can be repeatedly softened and molded under heat and pressure without any chemical change occuring
They are fusible and are usually soluble in organic solvents
THERMOSETTING –
Resin that can be molded only once.
They set when heated
They are generally infusible and insoluble

4. Uses of resins in dentistry
Fabrication of dentures (denture base resins)
Artificial teeth (cross- linked acrylic resins)

5. Uses of resins in dentistry
Orthodontic and pedodontic appliances
Provisional restorations in FPD

6. Tooth restorations (fillings)
Inlay and post-core patterns (pattern resins)

7. Crown and FPD facings (tooth colored acrylic or composite resins)
Cementation of orthodontic brackets, crowns and FPDs (resin cements)

8. Custom impression trays
Dies (epoxy resins)

9. Maxillofacial prostheses (obturators for cleft palates)
Endodontic and core filling material
Athletic mouth protectors
Splints and stents
Models

10. Ideal requirements of dental resins
Be tasteless, odorless, non-toxic and non-irritant to the oral tissues
Be esthetically satisfactory (color should be permanent)
Be dimensionally stable (not expand, contract or warp during processing and subsequent used by the patient)
Have enough strength, resilience and abrasion resistance
Be insoluble and impermeable to oral fluids
Have a low specific gravity (light in weight)

11. Be easy to fabricate and repair Have good thermal conductivity
Tolerate temperatures well above the temperature of any hot foods or liquids taken in the mouth without undue softening or distortion
Be easy to fabricate and repair
Have good thermal conductivity
Be radiopaque
When used as filling material it should:
Bond chemically with the tooth
Have coeeficient of thermal expansion which match that of tooth structure
Be economical

12. Acrylic resins
Are derivatives of ethylene and contain a vinyl group in their structure formula.
The acrylic resins used in dentistry are the esters of:
Acrylic acid, CH2=CHOOH
Methacrylic acid, CH2=C(CH3)COOH

13. Poly (methyl methacrylate ) resins
Widely used in dentistry to fabricate various appliances
Although, it is a thermoplastic resin, in dentistry it is not usually molded by thermoplastic means
The liquid (monomer) methylmethacrylate is mixed with the polymer (powder)
Types (based on the method used for its activation)
Heat activated resins
Chemically activated resins
Light activated resins

14. Heat activated denture base acrylic resins
Heat activated polymethyl methacrylate resins are the most widely used resins for the fabrication of complete dentures
Available as:
Powder and Liquid
Powder may be transparent or tooth colored or pink colored
The liquid (monomer) is supplied in tightly sealed amber colored bottles
Gels – sheets and cakes

15. Components of Acrylic Resin
Dispensing Form: Powder (polymer) Liquid (monomer)
Powder
Polymethyl Methacrylate – main component, in beads or pear form
Benzoyd/Benzoyl Peroxide – an initiator, starts the polymerization process
Dibuthyl Pthalate – plasticizer, improves the workability
Talc or Gelatin – prevents cohesion of the beads during storage/ prolong storage life
Dyed Synthetic Fibers – improves aesthetics appearance as it produce reddish and bluish small blood vessel appearance
Titanium Dioxide – fibers, hardening agents
Coloring Material/Pigments

16. Liquid (Monomer)
Methyl Methacrylate – main component, transparent, colorless liquid with sweetish odor, toxic when inhaled in prolong periods of time
Hydroquinone – prevents premature polymerization during storage
Glycol Dimethacrylate – cross linking agent makes resin hard, stronger, serves as bridge that unites two polymerized chains, improves physical property

17. Custom Tray Construction
With a red pencil, outlined the planned area of the denture base in the diagnostic cast. Use the the following landmarks as basis for the design of the denture base:
Mucobuccal fold
External oblique ridge
Masseteric notches
Retromolar pads
Mylohyoid ridges
frenae
With a blue pencil, outline the tray design. The tray design should be about 2 mm shorter the planned denture base.
Mix the resin , form it into a ball during the dough stage and flatten it to an even thickness using a roller or two wet glass slabs. (omit this step if using VLC resin).
Apply petroleum jelly on the diagnostic cast to prevent acrylic from sticking.
Adapt the resin to the cast and trim the excess with a sharp knife. Allow the material to set. (place in a curing unit for VLC).
Finish the tray by trimming the border. Border thickness should be about 2 to 3mm.
Attach a handle made of the same tray material. Position the handle at the anterior ridge crest area.

18. Custom tray Construction
With a red pencil, outlined the planned extent of the denture base. Use the following landmarks as basis for the design:
Mucobuccal fold
Coronomaxillary space
Hamular notches
Vibrating line
Frenae
With a blue pencil, outline the tray design. The tray must be designed about 2 mm shorter along the muccobuccal fold, except along the posterior palatal seal area.
An apron about 3-4mm wider than the planned postdam area, should be made instead.
Apply petroleum jelly on the diagnostic cast to prevent acrylic from sticking.
Adapt the acrylic tray material to the cast following the same procedure for mandible and attach a handle.

19. Visible light cured resin(polymerizing Resin)

20. Steps in Making Denture Base
Impression Taking
Cast Construction
Wax Pattern Construction
Investing of Wax Pattern
Wax Elimination/Burnout Procedure
Preparation of Mold Space
Packing of Resin Dough
Curing
Deflasking
Trimming and Poishing

21. Impression Taking Outlining of the study cast
Preliminary impression-modeling compound, plaster of paris
Outlining of the study cast

22. Working cast with outline
Secondary impression – to construct individual tray for working cast
Working cast with outline

23. Cast construction
Working cast

24. Shellac Base Plate

25. Wax Pattern Construction
Use pink wax and pass over flame to soften
Place the softened wax over the cast and press it hard to get the exact shape of the cast
Then place another wax over the 1st wax
Pour melted wax (using the carver) into the periphery of wax pattern and allow it to flow to prevent Plaster of Paris from going inside wax pattern during investing
Wax pattern should be stable to the working cast

26. Wax pattern construction

28. Investing the wax pattern
Prepare the flasks for investing the wax pattern by applying petroleum jelly on the inside part of the upper and lower halves, knock out plate and cover of the flask.
Soak the cast in water until it is entirely wet. Do not over soak, as this will cause the cast to etch. Apply separating medium to the base
Mix plaster of paris and then fill the sides of the lower half of the flasks, leaving the center portion with an amount of plaster mix just enough to accommodate the cast.
Press the cast at the center of the lower half of the flask. The bottom of the cast must touch the base of the flask. See to it that the land area is slightly above or at level with the rim of the flask

32. 5. Using the plaster spatula, work around the cast so the plaster is smoothed even with the base of the cast. Contour the plaster so that no undercut around the cast is present.
6. Allow to partially set. Moisten a finger and complete the smoothening of the lower half. Let the plaster set completely.
7. Apply separating medium all around the plaster investment and allow it to dry.
8. Secure the upper half of the flask to the lower part. Be sure that there is metal-to- metal contact between them. Clean the rim with a sharp knife if the plaster investment interferes with this or re- contour the investment to accommodate the upper half.
9. Mix plaster of paris and pour it onto the upper half. Place the flask on a vibrator to ensure that plaster flows to the crevices, thus reducing the chances of air bubble formation. Add plaster until the flask is full, to complete the investment. Put the flask cover and firmly tap it to allow the excess plaster to escape. Allow the plaster to completely set

33. Two Methods of Pouring the Plaster of Paris to the Upper Half of Metal Flask
Single Pour Technique
Mix the plaster then pouring it to the upper half then place the cover
Double Pour Technique/Two Capping Technique
Pouring is done twice, 1st pour of the investing medium is only to the level of the wax pattern. This is good in the presence of artificial teeth

34. Wax Elimination/Burnout Procedure and Mold Space Preparation
Prepare two metal water containers. One of these should be big enough to be filled with water and hold two flasks.
Fill the containers with water and bring it to a running boil. One container will be used to heat-soak the flasks and the other to hold clean, hot water.
Soak the flasks in boiling water for about 4-5 minutes. The wax should have softened by this time.

35. 4. Separate the upper and lower halves of the flasks by inserting a blunt knife at the slot at the back of the flask. Peel off the softened wax and discard.
5. Flush the mold space with hot water coming from the boil-out container. Use a dipper with a hole at the bottom. Do not use all the water in the dipper. Discard it because the top portion contains wax that can contaminate the old
6. Apply detergent and brush all the areas to remove any trace of wax.

36. Packing the Resin (Stages Occur Once the Resins are mixed)
Damp/Sandy Stage
Sticky/Stringy Sage
Gel/Dough Stage
Rubbery Stage
Stiff Stage

37. Damp/sandy stage Mixture is cloudy and sandy
No reaction yet between monomer and polymer

38. Sticky/stringy stage Monomer attacks the surface of polymer
The mixture becomes viscous and sticks to the stirring rod

39. Gel/dough stage
Mixture is easily molded into different forms and shapes
Ideal for compression molding, no longer sticky

40. Rubbery stage stiff stage
Mixture is rubber-like in character and no longer flows freely
Cannot be molded anymore
Mixture is dry and resistant to mechanical deformation

41. Packing the resin
Prepare the acrylic mixing jar and soak a piece of polyethylene sheet in water.
Measure enough amounts of polymer and monomer, following manufacture’s instruction.

42. Empty the measured monomer into the mixing jar
Empty the measured monomer into the mixing jar. Add polymer in a sprinkling fashion. Make sure that the powder is completely wet with the monomer. A stirring rod may be used for this purpose, taking care not to stir, as this may introduce air into the mixture

43. Cover the mixing jar to prevent evaporation of the monomer.

44. Constantly monitor the polymerization process
Constantly monitor the polymerization process. The resin is ready for packing during the “dough” stage.

45. During the “dough” stage, wet your hand with water and knead the acrylic material. Form it into a ball and then roll it. Pack it in the mold space using your fingers.

46. Get the polyethylene sheet and line it over the acrylic
Get the polyethylene sheet and line it over the acrylic. This will enable you to do a trial closure. Close the flask with the lower half and apply a palm pressure.

47. Put the assembled flask into a press
Put the assembled flask into a press. This could be accomplished by either of the following:
Bench press
Pneumatic press

48. Pneumatic Press
Bench Press

49. Release the pressure and gradually separate the lower and upper halves using a dull knife. Lift away the polyethylene sheet and see to it that the mold is totally filled with resin.

50. The flash on the investment is cut away using a sharp knife.

51. Trial-closure technique

52. Reassemble the flask. Clamp this using a spring clamp and bench cure for about 30 minutes to allow excess monomer to evaporate.
Repeat the procedure for other investment.

53. Curing Heating process of resin to allow complete polymerization.
Rapid curing: 74°C/165°F water bath for 2 hours then increase to 100°C for 1 hour.
Slow curing: °C water bath for 8-9 hours
Turn the curing unit on. Set the temperature at 65-70°C and the timer to about 8-9 hours.
Place the flask in the water bath and leave it to cure for the time duration.

54. Bench cooling
After curing cycle, retrieve the flasks from the water bath. Allow them to bench- cool before divesting the denture base. Rapid temperature change alters the dimensions of the base.

55. Dimensional Changes during Curing
Thermal Expansion – change from room temperature to temperature of water bath
Contraction – polymerization shrinkage of resin
Thermal Contraction – change from room temperature of water bath to room temperature

56. Deflasking
Remove the lid of the flask and put the flask into a flask ejector. Carefully separate the halves of the flask from the investment by inserting levers at the sides of the ejector and engaging the flask at the recess provided for this purpose.
An alternative way would be to use a mallet. Remove the flask cap and invert the flask. Tap the knock-out plate until the lower half of the flask separates. Re-invert the flask and tap the stone cap until the investment is completely free from flask.

57. Saw through the investment, making several linear cuts
Saw through the investment, making several linear cuts. The cut must be deep enough, without damaging the denture base, so that the parts will be done easily if the cast has been prepared well with the separating medium.
Slowly lift the denture base from the cast. Do not force it out if there is difficulty or it may break. Saw the cast and pry the pieces out until the base is free from the investment.

59. Trimming and Polishing
Trim the “flash” (excess resins at the sides of denture base) from the processed denture and clean off the investing plaster.
Polish it using a wheel rag and acryluster.
It is important to remove the residual monomer from the finished denture base because it can cause irritation to the oral tissues.

60. Defects of Denture Base
Presence of porosities
External Porosities – caused by improper manipulation of investing medium
Internal porosities – caused by too rapid curing process and improper manipulation of resin and packing too soon
Crazing – linear small cracks caused by too much pressure exerted during deflasking
Fracture – caused by too much pressure during packing and by accidental dropping of denture base during deflasking.

61. Injection molding technique
Used a special thermoplastic resin (Ivoclar)
This technique uses special equipment including a special bath for curing
A sprue hole and a vent hole are formed in the gypsum mold
The soft resin is contained in the injector and is forced into the mold space as needed
It is kept under pressure until it has hardened

62. Advantages:
Dimensional accuracy (low shrinkage)
No increase in vertical dimension
Homogenous denture base
Low free monomer content
Good impact strength
Disadvantages:
High cost of equipment
Difficult mold design problems
Less craze resistance
Special flask is required

63. Chemically activated denture base acrylic resins
Also known as “self- curing” “cold cure” or “auto-polymerizing resin”
Supplied as powder (clear, pink, tooth colored) and liquid
Polymerize at room temperature

64. Uses For making temporary crowns and FPDs
Construction of special trays
For denture repair, relining and rebasing
For making removable othodontic appliances
For adding a post-dam to an adjusted upper denture
For making temporary and permanent denture bases
For making inlay and post core patterns

65. Light activated denture base resins
Consists of a urethane dimethacrylate matrix with an acrylic coplymer, microfine silica fillers, and a camphoroquinone- amine photoinitiator system
Supplied in premixed sheets having a clay like consistency