All Ceramic Crowns & Shade Shade Selection
Definition of dental ceramic: An inorganic compound with non-metallic properties typically composed of oxygen and 1 or more metallic or semi-metallic elements that is formulated to produce the whole part of a ceramic based dental prosthesis Introduction: - Statistics published: 90% cemented restorations are metal ceramic crowns - All ceramic products are catching up, with improved strength and aesthetics - All ceramic crowns have better aesthetics for anterior teeth compared to metal-ceramic metal-ceramic crowns
Indications: 1. Anterior teeth – teeth – Destroyed, Destroyed, fractured, discoloured, abraded or malaligned (For posterior teeth, first choice should be metal-ceramic crown due to its better fracture resistant property) 2. Under favourable occlusal condition – condition – No No heavy bite, no parafunction Contraindications: 1. Too conical preparation of tooth crown cr own – – May May have pulp exposure and tooth is at a high risk of fracture 2. Insufficient lingual thickness of ceramic (< 0.8mm) 3. Deep bite – bite – This This leads to more forces transmitted anteriorly 4. Short clinical crown – crown – Offers Offers minimal retention after preparation 5. Presence of parafunctions such as heavy bruxism (Ceramic teeth when in occlusion with natural teeth will cause attrition very fast)
3 basic requirements of dental ceramics: 1. Function – Durability, strength and biocompatibility 2. Form – Ability to form complex shapes 3. Aesthetics – Colour, translucency and transmission of light
*The more translucent a ceramic is, the more aesthetic it is but the lesser the fracture resistance Properties of dental ceramics: 1. Firing shrinkage 30-40% - Crown must be overbuilt 2. Chemically inert provided the surface layer is intact 3. Low thermal conductivity 4. Good aesthetics 5. Brittle. The main cause of failure is crack propagation which almost invariable emanates from unglazed inner surface. This can be reduced by: - fusion of the inner surface to metal, as in the platinum foil and metal-bonded techniques - the use of a strengthened porcelain core 6. High resistance to wear 7. Glazed surface resists plaque accumulation Tooth preparation: 1. Depth cut - Place orientation grooves for : (a) 2.0mm incisal reduction (b) 1.0mm facial/labial reduction (in 2 planes. If cut in 1 plane will overcut)
2. Incisal and facial reduction - Using parallel rounded end diamond bur : Shoulder margin (margins can be shoulder or heavy chamfer using 010 bur all around the tooth) - Incisal reduction is done parallel to the incisal edge of the crown - Facial reduction reduced evenly in 2 planes and extended into the proximal areas
3. Proximal reduction - Initially using the long thin tapered diamond bur to relieve proximal contact area until the space is wide enough for the long parallel rounded end
4. Lingual reduction - Lingual-axial wall should be parallel to the gingival 1/3 rd facial wall
5. Finishing/refinement - Width of shoulder margin 1.0mm, all rounded surfaces, uniform and smooth (use TC burs. No sharp angles, will create stress points. Use green stone to refine the cavity) - Transitions between surfaces must be smooth - Right-angled rounded shoulder is preferred - All corners must be rounded off
* Before tooth preparation, impression has to be taken using silicone. After tooth preparation is done, place the silicone impression onto the prepared tooth. The space between prepared tooth and silicone impression should be around 1.0mm
Different types of ceramic systems (Different system uses different technique and has different contents)
System Alumina ceramic (Vita Hi-Ceram, Vitadur Alpha)
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Details Alumina ceramic has low flexural strength and high shrinkage during sintering (upon firing < melting point – self-diffusion of the particles in contact ‘grow’) Ceramic mass is condensed on platinum foil or on refractory die and fired to produce the core This core is covered with
Photos
Vitadur Alpha Ceramic
Vitadur Alpha Ceramic Dicor Ceramic
Glass
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The Cerapress Technique (Leucite Reinforced Ceramics Cerapress Technique)
Use glass ingots (not very abrasive therefore, does not attrite natural teeth very much) Glass ceramic is rounded as a glass Heat-treated to produce a crystal structure inside the glass (ceramming) – process that converts it into a stronger crystalline ceramic The structure is then stained, Dicor glass ceramic coloured and glazed Dicor glass ceramic can also be covered with Vitadur Alpha Ceramics Advantages: 1. Little abrasive ability 2. Very small crystal size (14 um)
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Indications: 1. Inlays 2. Veneers 3. Single crown of anterior teeth
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Patented ceramic pressing method > 10 years Used for crowns, inlays, onlays and veneers High aesthetic and fit Used with zirconium post and composite core It is the only technique with which it is possible to produce a zirconium oxide post on which ceramic mass can be pressed to produce all ceramic post and core
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Procera Ceram
All
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Glass Infiltrated Alumina Ceramic: In-Ceram
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Based on a lumina ceramic core mass – Processed by pressure injection Used as anterior crowns, inlays, onlays and veneers Base material consists of 1 Al2O3, no significant etching of the ceramics when cemented with resin cement Leucite enriched ceramics contain > two phases – after etching will provide better retention
Has outstanding fracture strength values Used for single crowns on anterior and posterior regions 3-unit anterior bridge possible at areas with less occlusal forces Marginal adaptation of crowns are good Slip mass consists of alumina applied on the refractory die and fired – Sintered Sintered ceramic is then infiltrated with glass and fired – To reinforce the core
Advantages: - Metal base is not necessary - Has very high flexural strength and excellent fit Disadvantages: - Opacity of core affects aesthetic appearance - Acid resistance of core causes the conventional etching of the core to be inefficient
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CAD/CAM System: CEREC
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Special laboratory equipment is required Etching of the ceramic surface is insignificant due to alumina content. Therefore, to enhance mechanical bonding, sandblasting the fitting surface of the crown is required Computer-aided direct/manufacturing Cerec 1 developed in 1989 based on an optical impression Consists of milling unit, a camera and computer systems 1995 Cerec 2 developed better fit of margin – Inlays, onlays produced Now Cerec 4
- Very good aesthetic
Turkom-Cera
In-Ceram Spinell Summary
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All ceramic restorations must be treated carefully. Processing technique may influence the fracture resistence / aesthetic of the final restoration Anterior crowns have shown very good aesthetic results
Dye spacer: Thickness is roughly 2mm. It should be applied 1mm away from gingival margin of the tooth preparation. This is to give space for tooth cement to flow and to prevent microleakage After sintering, the crown will be very glossy Pink ceramic : Can blend in with gingiva very well. Used when bone resorption is very severe. May also be used in cases with high upper smile line
Cementation 1. Resin luting cements - Ceramic needs to have a resin-based cement Eg: Calibra - It has different shades - Has a try-in paste. Apply the try-in paste onto the fitting surface of the crown and try it onto the prepared cavity. If everything fits well with good aesthetic, then only place the permanent paste
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Requires silane coupling agent to bond the cement to ceramic since it is resin based
Steps: 1. Try-in paste - Apply try-in paste to the crown. Seat the restoration and check the colour, then remove the restoration 2. Clean and dry - Thoroughly clean all internal surfaces of the crown with water spray and air dry 3. Tooth conditioner - Apply Caulk 34% tooth conditioner gel to available enamel (and dentine if desired) for 15 seconds. Rinse for 10 seconds. Blot dry to keep moist, do not rub
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In Europe : De Trey Conditioner 36% For full coverage crowns, etching dentine is not recommended as to minimize the possibility of post-operative sensitivity
4. Apply Silane - Apply Caulk Silane Coupling Agent to the crown according to instructions 5. Mix Prime and Bond (NT DUAL CORE) - Place 1-2 drops of adhesive and an equal number of drops of self-cure activator into a mixing well and mix with a new brush tip 6. Apply P&B to tooth surface - Apply prime & bond NT Dual Core mixture to thoroughly wet the tooth surfaces. These surfaces should remain wet for 20 seconds which may necessitate additional adhesive - Gently air dry for 5 seconds. Surface should have a uniform, glossy appearance. If it does not have a uniform, gloss y appearance, reapply the P&B - Light cure P&B NT Dual Core for 10 seconds 7. Apply Calibra - Apply a thin layer of cement to the internal surface of the restoration 8. Seat - Seat the restoration slowly. Maintain downward pressure and remove excess cement from marginal areas with a dry brush 9. Pre-cure (Soft cure) - A 10-second light ‘pre-cure’ at the margins will ‘gel’ the excess cement for easy clean up 10. Light cure - Once stabilized, light cure all the margins for 40 seconds 11. Finishing - Use white rubber stone
Tooth Shades COLOUR
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Light is radiant energy travelling in waves of varying lengths Visible light of electromagnetic spectrum is between 380-760 nm Different wavelengths either directly or as reflections from an object, will excite different sensations within the eye Sensations are interpreted by the central nervous system mental impressions
Interprets colour Colour Quality - Clinical light. No white light, no fluorescent light (more blue in colour) and no incandescent light (more white in colour) - For better colour quality, check tooth shade in the morning or afternoon . More blue, green and red lights penetrating the atmosphere - Afternoon with bright weather – ideal time due to balance of all lights
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In dentistry, tooth shade is of prime concern
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We use the Munsell Colour Order System : This system is based on colour determinations made by human eye through direct comparison with a standard, which in clinical setting, is the shade guide
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Munsell Colour Order System :
Created by Albert H. Munsell. It defines colour by 3 attributes: (a) Hue (Colour) (b) Value (Brilliance) (c) Chroma (Saturation) Natural tooth - Incisal edge and proximal areas : Greyish as light is absorbed in the mouth after passing through enamel. Has very thin dentine - Body : Yellowish, reflection from dentine - Gingival area : Orange, reflection of red gingival tissues through very thin enamel - Patients with gingivitis, the red gingiva will be reflected onto teeth. Therefore, tooth shade will not be accurate - Lipstick colour will also affect tooth shade. Very red lipstick will show very white teeth - Moustache can also affect tooth shade
*Before taking tooth shade, tooth surfaces have to be cleaned f rom plaque and stainings Perception of colour is affected by: - Lighting (Eg: Tungsten, fluorescence) - Surrounding colours (Eg: Lipstick, gingivitis) - Texture of surface (will change the reflection of light) - Materials (will change the reflection of light) - Form of object (will change the reflection of light) Colour blindness: 1. Blue – Green 2. Blue – Violet 3. Red – Yellow Hue -
Name of colour
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Primary determinant of hue is DENTINE that is covered by enamel Tooth shade has to be determined before tooth preparation, before rubber dam placement - Surrounding gingiva becomes whitish after giving LA. That is why must determine tooth shade first VALUE
- It is the brightness of colour - In scale of 0-10 - White : High value / brightness (10) - Black : Low value / brightness (0) - 0 (black) 10 (white) - Natural teeth is within 4-8 - Transluscency : varies with age (wear), disease and restorative treatments. Should be assessed with lips slightly parted - It is influenced by the translucency of enamel - Brightness of an object shows the amount of light energy it produces
CHROMA
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It is the saturation of the colour/hue Intensity/concentration of the colour’s hue Pale colours/pastel – Low chroma Bold – High chroma It is determined by dentine It is influenced by the thickness and translucency of enamel In choosing tooth shade, if no tooth shade is suitable, choose the tooth shade with lower chroma
How to select restoration shades? 1. 2. 3. 4. 5. 6. 7. 8.
Clean the teeth to be matched Assess apparent value and dominant hue and select a shade guide tab Moisten both teeth and guide tab Hold guide tab in close apposition to the tooth being matched, cervical to cervical and incisal to incisal Squint eyes to appraise value difference Note hue difference (Redder (orange) / yellower / browner) View with lips relaxed and retracted Limit viewing periods to 5 seconds or less. Will lose the sensitivity to yellow colour
If eyes are tired, look at distant objects (preferably blue in colour) 9. Use different light sources – First under clinical light, followed by cool white fluorescent and incandescent 10. If no shade guide is suitable, select the nearest shade tab which is higher in value and lower in chroma (A2 instead of A3)
11. Send shade guide tooth to technicians with adequate intsructions for modifications and characteristics
Shade, translucency and location -
Enamel colour : Opaque white – Translucent Young patient : Whiter colour with high value due to thick enamel – Higher light reflection Older patient : More orange colour due to less translucency of enamel
Tooth shade guide tab
