Notes on Porcelain Buildup and Baking

Course Objectives

The course aims to meet the aesthetic demands of ceramic dental restorations by replicating the natural appearance of teeth through the process of dental ceramic fabrication, which will achieve aesthetic excellence in prosthodontics.

Course Outline

• Introduction to ceramic concepts and color layers.
• Fundamental concepts of ceramic buildup.
• Manufacturing process and methods of ceramic buildup.
• Practical examples of ceramic buildup.

Components and Functions of Dental Porcelain

Types of Dental Porcelain

Dental porcelain is classified based on its firing temperature:

• High-fusing: 1200-1400°C
• Medium-fusing: 1050-1200°C
• Low-fusing: 800-1050°C
• Ultra-low-fusing: < 800°C

Dental Porcelain Layers and Main Components

The different layers of dental porcelain are:

• Opaque
• Cervical
• Dentin/Body
• Enamel/Incisal
• Translucent
• Stain
• Glaze
• Other (Margin, Modifier, Opaque modifier, Add on repair, Glazing power)

Objectives of Ceramic Restoration

• Contour of the restoration.
• Surface characterization & glazing
• Color match
• Esthetic
• Biologic
• Mechanical

Classification of Dental Porcelain Layers in Crowns

• Opaque Porcelain: Blocks metal color and serves as a base color layer.
• Cervical Porcelain: Provides saturated color tones and masks opaque at the thin cervical areas or pontic base.
• Dentin/Body Porcelain: Provides the main body color shade.
• Enamel/Incisal Porcelain: Represents the enamel and incisal edge color.
• Translucent Porcelain: Exhibits high translucency at the incisal edge.

Additional Types of Porcelain

• Stain Porcelain: Used for staining.
• Glaze Porcelain: Used for glazing.
• Margin Porcelain: For margin.
• Modifier Porcelain
• Opaque Modifier Porcelain
• Add on Repair Porcelain
• Glazing Power

Components of Ceramic Color

• Organic Pigments (External Layers):
  • Dentin/Body Porcelain
  • Enamel Porcelain
  • Translucent Porcelain
• Metal Oxides (Internal Color Representation):
  • Titanium Oxide: White-Yellow
  • Titanium-Iron: Yellow-Red
  • Cobalt-Aluminum: Cyan
  • Nickel-Tin: Gray
  • Iron-Chromium: Gray, Yellow, Brown
  • Manganese Phosphate-Aluminum: Red
  • Vanadium-Tin: Yellow

Types of Dental Porcelain and Manufacturing Processes

• Feldspathic
• Aluminous
• Leucite-based
• Fluorapatite
• Lithium Disilicate
• Sintering
• Glass-infiltration
• Heat-pressing

Characteristics of Dental Porcelain

• High compressive strength but fragile under tensile and shear forces.
• Significant volume shrinkage during baking.
• Smooth surface that inhibits plaque accumulation.
• Good tissue compatibility.
• Good wear resistance.
• Aesthetic appeal.

Physical Properties of Dental Porcelain

• Coefficient of Thermal Expansion (CTE): Measured in ppm/°K or μm/m°K.
  • PFM alloy ≈ 13.8 ilda 14.9 \times 10^{-6}

Bonding Porcelain to Metal

• Mechanical bonding
• Chemical bonding
• Secondary bonding (Van der Waals Force)

Dental Porcelain Firing Schedule

Temperature control during firing to manage shrinkage, porosity, and stress.

Porcelain Fused to Metal Crown (PFM) Procedure

1. Working cast & Die
2. Wax-up
3. Cut-back
4. Investment & casting
5. Metal finishing
6. Building & baking of ceramics
7. Morphology adjustment
8. Staining & glazing
9. Metal polishing

Cut-back Technique

• To achieve tonal and layer composition.
• To achieve a good wrap-around effect.

Color and Cutting Volume

The shade of a porcelain-sintered cast crown is related to the cutting volume of the teeth:

• Metal coping: 1.3-1.5mm
• Opaque: 1.5-2.5mm
• Dentin: 1.5-1.7mm
• Enamel
• Translucent

Absorbent Technique

• Porcelain powder particles infiltrate the ceramic interface, affecting shade.
• Increases translucency but darkens the color.
• Easy to cause deformation, do not apply pressure during operation.
• Maintain moisture.

Condensation Technique

• Keep the porcelain moist and properly condense the porcelain particles close to reduce baking/firing shrinkage.
• Increases the strength after baking/firing.
• Prevent porosity/bubbles

Factors Affecting Condensation

• Surface tension of water
• Ceramic powder size and distribution
• Condensation method
• Buildup shape

Condensation Methods

• Brush method
• Spatula method
• Vibration method
• Precipitation

Porcelain Build-up Techniques

• Brush Method:
  • Incremental buildup with good moisture control.
  • Risk of porosity and time-consuming.
• Spatula Method:
  • Adding large amounts of porcelain at once to reduce porosity.
  • Achieve uniform density for better color
  • Reduce excess water.
• Vibration Method:
  • Le cron method
  • Tapping method
  • Ultrasonic vibration method
    • 20,000~28,000Hz/sec
    • Buildup-Compaction-Water absorption
• Precipitation

Instruments for Ceramic Buildup

• Porcelain mixing instruments
• Glass slab
• Towel
• Water gun (syringe)
• Brushes (preferably sable hair, sizes No.000-10)
  • Large: porcelain buildup
  • Small: staining & glazing
• Carving instrument
  • Bella de St Claire carving instrument
  • Razor knives~ thin & flexible
  • Spatulas
  • Glass rod
  • Metal instrument
• Hemostats Small, straight & curve
• Condensing mallets
• Porcelain furnace: controlled temperature, heating rate, and vacuum.
  • Manual porcelain furnaces (Ney Mark III)
  • Horizontal muffle
  • Vertical muffle (clam shell: Programat P500/510/300)
• Glass or ceramic mixing slabs

Porcelain Buildup Techniques

• Brush-on/brush additive technique
  • Incremental buildup
  • Easier to manipulate and control.
  • Maintains moisture.
  • Suitable for mixing ceramic materials and enamel porcelain layers
  • Need to compact
  • Instruments: Le Cron knife, mallets and Ultrasonic vibrator
• Spatula technique
  • Apply large amounts of ceramic material at once
  • Fast operation and less bubbles
  • No excessive water
  • Suitable for dentin color buildup
  • No equipment change required for compaction.

Comparison of Porcelain Buildup Techniques

Humidifier Use

• Porcelain is prone to uneven dryness.
• Impurities are easily mixed in.
• Density uneven under pressure.
• Surface metal oxides are adsorbed (affecting color).
• Ultrasonic humidifier:
  • Surface is evenly supplied with water mist.
  • Saves buildup time
• Good texture after sintering

PFM Fabrication Process

• Make a working model.
• Make a wax thin veneer crown.
• Wax type design.
• Investment and casting.
• Metal frame modification and surface treatment.
• Degassing. Opaque porcelain buildup and baking.
• Crown color buildup and baking.
• Morphological correction.
• Staining.
• Glazing.
• Finishing of metal parts, polishing, and completion.

Opaque Porcelain Buildup

• Blocks metal color and provides bonding between metal and ceramic.
• High refractive index & high-density opaque oxides.
• Contains metal oxides (Sn, Ti, Zr) causing refraction and reflection making it opaque.

Types of Opaque Porcelain

• Oily opaque porcelain/paste: Easier to apply and manipulate and Uniform thickness
• Aqueous opaque porcelain/powder Use before metal surface moistening.

Opaque Porcelain Technique

• Apply a very thin layer of wash opaque.
• Slightly concentrated color at the cervical area.Bake slightly lower temperature for a rough surface.
• Compensate for porcelain shrinkage by building up from the cervical to the incisal edge.
• Slightly overbuild the cervical edge (teardrop shape).

Cervical Porcelain

• Prevents direct light reflection from the opaque layer, presenting the cervical color.

Dentin/Body Porcelain

• Cut back technique needed.
• Minimum thickness: Cervical > 1mm, Incisal > 0.7mm

Enamel Porcelain

• Use different amounts of enamel porcelain according to different situations and match special colors.
• Cervical ≈ 0.2mm, Incisal ≈ 0.5mm
• First bake: Make a dentin of the same size and occlusal height as the tooth shape. After proper filling, put it in the porcelain furnace.
• Second bake:
  • Color error: stain the outside of the dentin layer and put it into the furnace again (the temperature is slightly lower).
  • Foreign matter is mixed in: After grinding with bur, cover dentin again

Translucent Porcelain

• The buildup extends to the cervical 15-25% area

Avoiding Interface Movement During Porcelain Build-up

• Quick procedure
• Vibrate + condense + absorbent

Dental Porcelain Crown Layer Thickness

• Cervical: 0.1mm
• Opaque: ≥ 0.7mm
• Dentin: 0.2~3mm

Porcelain Baking/Firing Process

• Porcelain furnace baking ceramic (first baking/firing, second baking/firing)
• Drying preheating, starting temperature, heating temperature, vacuum, cooling
• 5-7min, 40-45°C/min

Porcelain Morphology Correction Steps

1. Adjacent surface
2. Pontic base
3. Adjust the occlusal relationship and crown height
4. Set the crown mesiodistal diameter
5. Modify the labial (buccal) and lingual plumping and shape
6. Modify the mesiodistal corner and line angle
7. Incisal edge thickness and occlusal relationship guidance for anterior teeth
8. Pontic and interdental space, base surface adjustment
9. Overall fine-tuning

Shade Characterization

• Color characteristics
• Shape characteristics
• Surface texture

Metal Subframe Correction and Surface Treatment

• Diamond abrasive instruments are available in a variety of shapes, sizes, and grits, making them useful for all phases of adjusting and finishing
• Ceramic stones also come in different shapes, sizes, and grits for use on metal or porcelain.
• Polishing wheels (Cerami-Pro Universal Polishers, Brasseler). The porcelain prepolisher wheel (left) is gray and may look similar to a coarse stone wheel.
  *It is designed for adjusting ceramic surfaces without leaving a rough surface. The final polisher wheel (right) is diamond impregnated and has a distinctive pink color. It is excellent for creating a smooth porcelain surface. Both wheels are available in round and knife-edge designs
• Fig 9-5 Glazed porcelain surface contaminated with metal debris (arrow) appearing as a dark speck.
• Fig 9-6 A diamond disk (Horico, Pfingst) is recommended for adjusting and contouring interproximal areas.

Staining

• Presents subtle shade changes and pigmentation on the natural tooth surface
• Internal Staining & External staining
• Main components: Fe, Co, Cu, Au
• Lower baking temperature than normal

Glazing

• The final baking process makes the ceramic surface smooth/glossy (plaque is not easy to adhere to).
• The surface properties are coordinated with natural teeth to enhance aesthetics.
• The hardness of the ceramic surface is improved, which helps to improve wear resistance.

Component of Porcelain

Glazing Techniques

• Self-glaze/autoglaze:
  • Without glazing powder after correcting the form.
  • Porcelain surface is slightly dissolved and glassy (shape/color change).
• Artificial/natural glaze:
  • Bake with glaze powder and low temperature.
  • Stable luster and prevent deformation.
  • Carry out in the atmosphere instead of vacuum.
  • Higher temperature for a short time to prevent deformation.
  • Too rough surface, gloss is not easy to present

Staining & Glazing

• Porcelain-specific liquid gives proper viscosity to the porcelain mud and makes the porcelain powder dry more slowly. Prevents movement of fine particles in porcelain during compaction

Polishing

• Grinding
• Sandblasting
• Polishing

Polishing vs. Glazing

• Polishing can better control the surface glossiness and distribution than glazing.
• Glazing can improve surface strength and reduce defects that cause fracture, but good polishing can have the same effect.
• Abrasion of teeth: The effects of polishing and glazing are comparable
• If the polish is done well, it will not only achieve aesthetics, but also abrasion of the teeth and plaque accumulation due to the rough surface

Polishing Procedure

• Rough grinding
• Medium grinding
• Fine grinding
• Paper cone
• Rubber wheel
• Silicone point
• 1um diamond paste
• 0.3um Al2O3
• Diamond bur
• Carborundum point

Porcelain Baking Procedure Sheet