Sign In Often a patient will require a dental crown and a dental clinician/student should be well prepared for such a situation. This page will discuss everything you need to know to be competent regarding crowns. From the problems of dental crown to the clinical procedure of delivering a crown, we will cover it all!
Theory
- Loss of vitality (10%) over 5 years, 20% over 20 years (Cheung et al)
- Don’t last a life time
- Have to have excellent OH as the margins are plaque risk factor
- Appearance may not be exact
- May need replacing in the future
- Tissue removal
– Can lead to sensitivity – more tubules will be exposed
– Susceptible to caries: Loss of surface enamel which is super saturated with fluoride
- Caries
- Leakage: poorly fitting restorations causes exposure of cement, this dissolves over time and caries result
- The tooth is entered into the restorative cycle
- Periodontal
– Margins act as a plaque retention factor
– Subgingival placement of margins can impinge on the attachment of the periodontal soft tissue and cause inflammation and bone loss or recession.
- Pulpal health
– 20% of crowned teeth undergo pulpal necrosis over twenty years. It is even more common in younger patients.
- Occlusal problems: Problems linked to grinding, TMJ problems, occlusal overload
- Irregular attendance – poor motivation
- Poor oral hygiene
- High caries risk
- Active caries
- Periodontal disease
- Insufficient tooth tissue available
- Bruxist, in certain situations
Intra-coronal restoration
- Fit within the internal contours of the tooth e.g. inlays, cast post
Extra-coronal restoration
- Cover the outside surface of the tooth and recreate the external contour e.g. full coverage dental crowns, veneers
| PRINCIPLE | EXPLANATION |
|---|---|
| Retention | Minimal taper, but no undercut |
| Resistance | Crown height |
| Occlusal stability | Maintain occlusal morphology |
| Marginal integrity | Well defined, supragingival, on natural tooth |
| Strength and durability | Good strong core |
| Preservation of tooth tissue | Reduce risk of necrosis |
- Luting/adhesive cement
- Retention form
- Resistance form
Retention form :
Features of the preparation which resist movement along its path of insertion.
For full coverage restorations, retention is gained from the extra-coronal walls which are two opposing vertical surfaces
The more parallel the walls the greater the retention (but the greater the risk of undercuts!)
Retention is dependent on:
- Taper:
– Ideal taper 5-7 degrees on each side, see pic on side.
– Increasing taper from 5 degrees to 10, halves the retention
of the dental crown
- Height of preparation :
– Anterior teeth height: 3mm
– Posterior ideal height: 4mm
- Diameter of preparation:
– More tooth tissue providing a greater surface area for resistance
- Surface roughness of preparation
Resistance form:
This is resistance against lateral or rotational forces
- To increase resistance add grooves e.g. mesial and distal slots
Location of margins:
- Supra gingival: This is the gold standard in most situations. It is the best for periodontal health and plaque control. May not be acceptable on anterior teeth due to aesthetics.
- Juxta-gingival: Same level as the gingival margin. Ideal for anterior teeth in aesthetic zones. Allows efficient plaque control without encroaching on the periodontal tissues.
- Sub gingival: Avoid where possible. Can result in periodontal inflammation. Some parts of the preparation can be subgingival, such as the proximal bits only. It is harder to take the impression. Absolutely contraindicated for some preps, such as resin bonded dental crowns. There are 3 indications for this type of crown margin:
– To gain retention
– Aesthetic reason
– When supra-gingival tissue is carious or deficient
Key points:
- If you can feel the gap between tooth and margin with your probe, it is unacceptable
- If there is blanching of the tissue on crown fitting, this can be an indicator of an edge or over built emergence profile.
- Gingival recession can occur post crown placement if the margins are subgingival or if the gingival biotype is thin.
- HUE: A,B,C,D [Refers to 4 different colours]
- VALUE: 1,2,3,4 [Light/dark]
- CHROMA: [Purity, difference between a strong colour
and a weak colour]
Clinical aspect of dental crowns
- PLANNING
– H+E
– Special tests – PA, vitality, percussion test etc
– Treatment plan
– Facebow (for diagnostic wax up and future crown) – note this is not always necessary for a successful crown
- BUILD UP TOOTH IF REQUIRED
– Remove caries
– Provide structural/space filling core
- TOOTH PREPARATION
– Silicone index of the tooth/diagnostic wax up for temp
– Tooth prep
- IMPRESSION
– May need to use a retraction cord to retract the gingiva especially if crown margins are subgingival (see gingival displacement)
– Tooth preparation impression (full arch) – using silicone index (see impressions)
– Opposing arch impression – using alginate
– Occlusal bite registration
– Shade
– Facebow (if not taken)
- TEMPORISE TOOTH
– Construct temporary and cement
– Check occlusion
- LABORATORY STAGE
– Pour models, and articulate using facebow and bite registration
– Section master die
– Construct crown (lost wax technique, porcelain bake, CADCAM)
- DELIVERY AND CEMENT
– Remove temporary
– Try in crown (protect airways with gauze) (Check contacts, shade, fit) (If bisque try in, send back to lab before cementing)
– Cement, check occlusal contacts
– Give cleaning instructions to the patient
- REVIEW
Types of dental crowns
Criterias for a temporary crown:
- Cover the entire prep to protect exposed dentine
- Maintain occlusal contacts to prevent over-eruption and mesial and distal contacts to prevent drifting
- Provide acceptable aesthetics
- Allow the pt to function
- Be comfortable for the patient
- Have correct contour to allow acceptable cleaning
- Prevent gingival overgrowth around the prep margins
- No overhangs to prevent it being a plaque trap or a cause for trauma/irritations
Temporary crowns come in the form of a preformed stainless steel crown or a constructed pro-temp crown:
1. Preformed SSC clinical stages:
- Select suitable size crown by measuring distance between the adjacent teeth and finding a complementary sized crown
- Try the crown an adjust the margins with crown shears
- Once the margins are satisfactory, smooth them with a diamond bur.
- Apply protemp the inside and seat, remove excess protemp
- Once it has set, remove the crown from the mouth
- Cement the crown with temp bond, check the margins and the occlusion
2. Constructed protemp crown clinical stages:
- Take an index
- Fill index with protemp and seat it onto the impression, place small amount on the back of your glove as well
- Remove when soft cheese consistency and take any bits out of the contact points
- Once full set, remove the excess martial of the crown with the polishing discs
- Re-seat to ensure it seats correctly and check occlusion.
- Lightly coat the fitting surface with temp bond and finally seat it back on the impression
- Remove excess temp bond
- Polish margins with ‘impregnated rubber burs’
Full gold crowns are the strongest crowns and so are a good option in bruxists and those with large masticatory forces. For this reason, for full gold crowns a chamfer finish line is produces as metal is strong in thin sections.
Dimensions:
- Anatomical occlusal reduction of functional cusp: 1.5 mm
- Anatomical occlusal reduction of functional cusp: 1.0 mm
- Functional cusp bevel: 1.5 mm (allows sufficient thickness of metal in a high stress beargin area)
- Non-functional cusp bevel: 1.0 mm
- Chamfer: 0.5 mm
- Smooth rounded angles
VIa @iwata_jun
Note: Functional cusp bevel allows correct contour of the functioning cusps to prevent working side interference on the crown.
Via @iwata_jun
Ceramic definition: a material fabricated from a flowable state and then converted to crystalline by heat treatment.
| DENTINE BONDED CERAMIC CROWNS (FORTRESS PORCELAIN) | LUCITE OR LITHIUM DISILICATE REINFORCED CERAMIC CROWNS (EMAX) | ZIRCONIA/ALUMINA STRENGTHENED CERAMIC CROWNS (LAVA/PROCERA) | ZIRCONIA LAYERED WITH (EMAX) | MONOLITHIC ZIRCONIA (WITHOUT PORCELAIN) |
|---|---|---|---|---|
| – Feldspathic porcelain etched fitted surface – Resin cement required – Avoid RMGIC cements as they can absorb water and expand leading to fracture of porcelain – Provides best aesthetics | – Feldspathic porcelain reinforced with lucite or lithium disilicate – Etched fitting surface suggest use of resin cement – More opaque in appearance – Relatively new to the market, manufacturer’s suggest conventional cement can be used | – Zirconia or alumina core constructed with CADCAM – Veneering porcelain added – Fitting surface is not etched, conventional cement can be used i.e. RMGIC cement – Requires retentive preperations | – Very opaque and usually used to block out discoloured teeth – Zirconia core with layering (EMAX) – Fitting surface is not etched, conventional cement can be used i.e. RMGIC | – very opaque with significant strength – Usually used for posterior teeth |
- Anatomical occlusal reduction of functional cusp: 2.0 mm
- Anatomical occlusal reduction of functional cusp: 1.5 mm
- Functional cusp bevel: 2.0 mm
- Non-functional cusp bevel: 1.0 mm
- Chamfer: 1.5 mm
- Smooth rounded angle
This is essentially a complete coverage metal crown veneered with a layer of porcelain fused to mimic natural tooth
To mask the colour of the metal, sufficient thickness of porcelain must be used resulting in a more destructive preparation. If there is insufficient tooth reduction the opaque layer will shine through resulting in poor aesthetics.
Although the aesthetics are generally inferior to all-ceramic crowns, metallo-ceramic crowns are much stronger.
Wherever possible a metal occlusal surface should be provided for the following reasons:
- Occlusal porcelain requires 2-2.5 mm occlusal reduction which is more destructive resulting in shorter clinical height. This in turn may compromise retention and resistance form of the prep. Bruxists also already have a short crown height.
- If the occlusal porcelain has been left unglazed then it can cause increased wear on the opposing dentition
Metallo-ceramic dental crowns are contra-indicated in young patients as they have large pulps so pulpal necrosis is more likely.
Dimensions:
- Anatomical occlusal reduction:
– 1.5 mm – 2.0 mm (occlusal metal)
– 2.0 mm – 2.5 mm (occlusal porcelain)
- Functional cusp bevel: 1 – 1.5 mm
- Buccal reduction: 1.5 mm
- Buccal shoulder: 1.5 mm
- Palatal/lingual reduction: 0.8 mm
- Palatal/lingual chamfer: 0.5 mm
- Smooth rounded angles (ensure a smooth transition from the buccal shoulder to the palatal/lingual chamfer
Strength of resin-bonded crowns are reliant on the bond to the tooth (like veneers) as there is no high strength core unlike conventional all-ceramic crowns.
They are less destructive than all other crowns preparations.
Good for young Pt with large pulps
Commonly used in anterior teeth
Preparation margin must be in enamel
Dimesions:
- Incisal reduction: 1.5 mm
- Labial reduction: 1.5 mm
- Interproximal reduction: 0.8 mm
- Cingulum reduction – using rugby shaped bur
- Rounded shoulder buccally : 1.5 mm
- Chamfer palatally: 0.5 mm
Note: the reason more reduction is done labially is because a thicker layer of porcelain is required due to aesthetics being vital in this area. Palatally aesthetics is less important and so less porcelain is required, thus more tooth can be preserved here.
Three-quarter crowns were originally devised to preserve the buccal enamel of a tooth that required a crown, for aesthetic purposes. The advent of ceramics in dentistry has largely solved the aesthetic crown problem, but they are still useful as a way to conserve tooth tissue.
- Posts are used to assist in the provision of indirect, fixed restoration involving root treated teeth
- Root treated teeth often have little amount of coronal tooth tissue to retain a restoration
- Hence posts can be used, commonly for anterior teeth
- Posts however lead to further tooth tissue loss and hence weakens the tooth structure
- Posts help retain a core upon which a crown can then be cemented, these are known as post crowns
- Posts are less commonly used in molars
Parapost system
Here the post cores are constructed directly using a preformed post (metal or fibre) alongside a composite core (direct).
Can be made from metallic material or non-metallic material
Examples of metallic material used are:
- Stainless steel
- Titanium
- Ni-Cr alloy – less common
Examples of non-metallic material used are:
- Fibre reinforced resin – most common
- Zirconia
- Ceramic
Fibre reinforced resin posts have a modulus of elasticity more closely matched to that of dentine and so put less stress on the tooth.
- The canal is prepared first using a set of proprietary drills (Para post system is most common)
- A matching size fibre post is selected to fit snuggly
- The post is cemented in using RMGIC
- Composite is used to build up the crown and then is prepped for the crown
- Provision of anti-rotation notch is essential
| PROS OF DIRECT POSTS | CONS OF DIRECT POSTS |
|---|---|
| Decreased stress on root | Cannot incorporate angle between core and root to compensate for incline roots |
| Good aesthetics for all-ceramic crown | Possibly poor adaptation of post to canal |
| No lab cost and can be performed in single visit | Increased possibility of post fracture |
| More surgery time (placing post and will also still need an impression for the crown) |
The post cores here are custom made in the laboratory from an impression taken of the prepared post space.
They are made from cast gold alloy which can be precious metal or more commonly non-precious metals.
Other harder alloys may increase chance of fracture.
Provision of anti-rotation notch is essential
| PROS OF INDIRECT POSTS | CONS OF INDIRECT POSTS |
|---|---|
| Can incorporate angle between post and core (for inclined roots) | Increased stress on root |
| Leads to excellent adaption of post to canal | Poor aesthetics under all ceramic crown (often the opaqueness will shine through so require an opaquer) |
| Its strong preventing separation of post form core | Requires lab work (time consuming and extra visit required) |
| Minimum surgery time |
Design considerations for posts:
- Longer posts are more retentive
- Longer canals may risk perforation
- Curved roots may prevent longer posts
- Short posts are more likely to cause root fracture
- Must leave 3-5 mm gutta percha (GP) at apex due to possible apical delta (Apical delta refers to the branching pattern of small accessory canals and minor foramina seen at the tip or apex of some tooth roots.)
- A ferrule is highly desirable
- Anti-rotation notch is essential – one of the most important factors in determining the success of a post crown alongside a ferrule
- Guideline about the post specifically
- Post should be as long as crown
- Post should be equal to ½ – 2/3 length of root
- Post should not terminate any higher than half way between the crest of the alveolar bone and root apex (i.e. the post should extend to one-half the length of the root that is embedded in bone)
The importance of shape:
- Parallel sided posts are the most retentive
- However tapered posts are better shaped as the root narrows apically
- Grooved or etched surface improve retention
- Threaded posts are more likely to cause fracture and prone to becoming loose (AVOID)
Threaded posts
The importance of diameter:
- Narrow posts can fracture, wide posts cause root fracture – find a post in the middle
- At its most narrow point there should be 1 mm of dentine surrounding the post
Ferrule:
This is a 360-degree metal collar of crown surrounding the parallels walls of healthy dentine that is 2 mm in height.
- A ferrule can decrease the risk of root fracture by 1/3rd and also enhances retention
- Provides a bracing action to protect root integrity
- Promotes a hugging action between the tooth and artificial crown
It is important that the dentine walls above the finish line are parallel
Amalgam Nayyar Core
This method takes advantage of the natural undercuts in the pulp chamber and canal entrances to retain the core instead of a post.
- Remove all the existing restoration including that in the pulp chamber
- Find the root canal entrances and remove 2mm of gutta percha (GP) from each canal using a GG No.4 (Gates Glidden)
- Refine the cavity and add extra retentive features if required
- Pack the amalgam, check the occlusion and burnish
- This is an intra-coronal restoration with no cuspal coverage
- They are made to fit a specific cavity shape
- Made from metal (mostly gold alloy) ceramic or composite
– Gold: less corrosive, less allergic reactions, stronger
– Composite: cheaper, improved aesthetic
- Since it’s made in the lab it is essential that there are no undercuts in the prep as it won’t seat.
Dimensions:
- Prep occlusal portion 2mm deep Prep mesial box which is deeper and broader
- Pulpal floor and floor of the box should be flat
- Can put a groove at the gingival axial line angle to help resist displacement from occlusal forces
- Place a bevel at all the external line angles of the mesial box, this gives an acute angle of gold
- This is essentially an inlay which provides cuspal coverage.
- This is indicated when there is a buccal and lingual wall, as it is less destructive than a dental crown.
Dimensions:
- Occlusal reduction
– Functional cusp 1.5-2 mm
– Non functional cusp 1-1.5 mm
- Functional cusp bevel 2mm which gradually fades interproximally
- Occlusal shoulder: 1-1.5mm along the functional cusp
- Prepare an occlusal cavity 2mm deep ensuring the floor is flat
- Prepare mesial and/or distal cavities slightly wider and deeper than the occlusal cavity
- Place a bevel on the external line angles of the boxes
| INDICATIONS | CONTRAINDICATIONS |
|---|---|
| Discoloured teeth – Fluorosis – Tetracycline staining – Non vital discoloration | No enamel |
| Malformed teeth – Hypoplasia – Hypocalcification | Severe discoloration |
| Small malpositions | Poor oral hygiene |
| Diastema | High caries rate |
| Small enamel fractures | Uncontrolled periodontal disease |
| Loss of enamel | Excessive wear/parafunction/bruxism |
| Unfavourable anterior segment occlusion |
Dimensions:
- Keep the prep in enamel
- Section the silicone index
- Use round ended diamond bur to create pits 0.5mm deep
- Reduce labial surface to form a long chamfer finish line at or just below the gingival margin
- Respect the labial contour of tooth by angling the bur appropriately
- Extend the prep interproximally to produce a finish line labial to the contact points
- Reduce the incisal edge by 0.75-1mm to produce an incisal butt finish (see table below)
| TYPE OF PREPARATION | FEATURES |
|---|---|
| Incisal feather | (+)Guidance on the natural tooth is maintained (-)Subject to fracture |
| Incisal butt | (+)Increase SA Better aesthetics Increase strength (-)More tooth removal Most common More enamel lost, so more dentine bond reliant Incisal wear prone |
| Incisal overlap | (+) Increased surface area (-) Tooth destructive |
| Window preperation | (+)Enamel is preserved on the edge (-)Incisal edge enamel is weakened |
Dental crown labwork
- Metal substrate
- Opaque layer
- Dentine porcelein
- Enamel procelein
- Glaze
- Base/core porcelain
- Dentine porcelain
- Enamel porcelain
Dental crown impressions
Types of gingival displacement:
- Surgical – electrosurgery
- Chemical – ferric sulphate, alum, racemic adrenaline
- Mechanical – paste systems used with directed pressure
- Retraction cord – most common (see below)
Why?
- Displace the gingival tissues around the preparation margin to achieve an accurate impression of the finish line of the prep and a small amount apical to this. It does this by pushing the gingival tissues away from the tooth.
- This allows the technician to create the correct emergence profile for the restoration. It also is used to stop bleeding
When?
- The soft tissues should be healthy before any indirect restoration placement, any bleeding or gingival inflammation will make it almost impossible to get a good impression
- If you cant see the full margins of the preparation, then retraction could should be done. But it shouldn’t be done routinely if its not required.
Retraction cord:
- Can be braided or non-braided (braided types are most commonly used as it prevents them from unravelling
- It pushes the gingival tissues away from the tooth for a short period to permit taking an impression
- The retraction cord can be soaked in an aqueous solution of ferric sulphate (astrindegent), this helps to coagulate the proteins.
- Do not use a cord which with to large requiring you to force it into the sulcus as this will damage the gingival tissues and cause bleeding potentially
Clinical stages:
- Cut cord
- Cord may be soaked in solution of ferric sulphate (astrindigent) This helps coagulate proteins.
- Pack the cord at the mesial/distal corner.
- Two flat plastics will be required to hold down the cord and prevent it lifting
- Leave to cord for 4-5 minutes.
- Remove it just before impression taking and take impression straight away
- Often a single cord is enough. Sometimes a double cord technique is required. A fine cord is placed at the base of the sulcus witch is left during impression taking, the winder cord is packed d over the top of this and only the top one is removed prior to impression taking.
Requirements for an impression material:
- Capable of recording fine detail
- Dimensionally stable
- Elastic
- Adequate tear strength
Addition cured silicone is most commonly used. This comes in a range of viscosities including low, medium, high and putty.
Two different viscosities of silicone are used:
- Low viscosity around the preparation and occlusal surfaces of the teeth
- High viscosity in the rest of the tray
The reason for this is:
- Low viscosity is good for recording fine detail but easily displaced
- High viscosity has more favourable handling properties but records fine detail poorly
The impression can be taken single stage or a two stage procedure.
This is where the high viscosity material and low viscosity material are made to polymerise simultaneously by taking an impression involving them both together. This way reduces chair-side time.
Procedure:
- Check the tray fits
- Apply adhesive on surface and sides of the trays and let it dry for 5-10 minutes
- Low viscosity:
– Squeeze a bit of the end out on a pad
– Attach the tip and the tip nozzle
- Get your nurse to fill the tray with the high viscosity material, and tell them to tell you once its half filled
- Dry the teeth, especially the impression with 3 in 1
- Remove and retraction cord
- Apply the light bodied material on the mesial of the preparation and then work your way around it, keep the nozzle in the material to prevent air bubbles forming. Place some material on the occlusal surfaces of all the teeth.
- Place some of the light viscosity material on the back of the glove, ensure your nurse has put some high viscosity material on the back of their glove.
- Take impression
– Seat the tray vertically
– In a single movement
– Don’t move the tray once its seated, otherwise you will get a drag
– Remove in a swift movement without rocking it
– Dry the impression, look under the light and check for flaws, drags, air bubbles, check the finish line.
- Opposite arch impression
– Alginate is used for this. Rub a small amount of alginate on the occlusal surfaces before taking the impression, this ensures there are no air bubbles.
Here, the initial impression is taken with the high viscosity material, with final impression being taken with the low viscosity material to record the finer details.
Procedure:
- Check the tray fits
- Apply adhesive on surface and sides of the trays and let it dry for 5-10 minutes
- Mix the putty, roll the mixture up into a “sausage” and fit it into the the tray
- Making sure the tongue and lips are out of the way, press the
tray firmly into the teeth. Wait for the putty to set, then take the tray
out and remove the plastic wrap. - Express the light body impression material into the high viscosity material where the teeth indentations are.
- Press the tray into the teeth, but not too hard—you don’t want
the teeth to push all the way through the impression material
and touch the tray - Remove the tray
- Futar d is used; a quick setting addition cured bite registration material
- Expel as small amount of material on a pad
- Dry upper and lower teeth
- Place material in the posterior occlusal surfaces and then work forewords
- Close the jaws into ICP.
- Add more material around the incisal edge of the maxillary teeth if required
- Check the jaws can be located with the registration
- Drags and voids
- Finish line not visible
- Air bubbles in critical places
- Unset impression material
Dental crown delivery
- Check fit on the master die (not for all indirects such as Maryland wings)
- Check occlusion on the articulator
- Remove the temporary, and also remove the cement on the temporty using a flat plastic for example:
- Try in the mouth (gauze to protect the pharynx)
- Check the contact points with floss
If all is satisfactory, proceed with the cementation:
- Apply the cement, seat it, and get the patient to bite on a cotton wool roll
- If it fails to seat, clear the contact points of the tooth and dental crown
- If it still doesn’t seat, adjust the contact points with a porcelain adjusting bur in the straight hand piece, be careful not to overheat the porcelain (same applies for any dental crown type)
- If it still doesn’t fit, check the die prep and see if there is any irregularities between this and the actual preparation
– See if any die spacer has rubbed off too, if so, carefully adjust the fitting surface
- If the restoration fails to seat, it could be because of a problem with the impression
- Check occlusal contacts with articulating paper and milers forceps
- Occlusal contacts of the teeth, with and without the dental crown should be the same.
- Check contacts in ICP and lateral excursions and check this is the same as what you prescribed
- Isolate tooth with rubber dam, invert the dam into the gingival sulcus with 3 in 1, use floss ligature to hold the rubber dam down
- Etch the ceramic fitting surface with hydrofluoric acid
- Apply silane agent (monobond plus) to the fitting surface of the dental crown followed by resin (heliobond)
- Apply etch to the enamel for 15 seconds followed by etch to the dentine for 15 seconds and then wash
- Apply primer to the tooth and air dry, apply the adhesive and leave to dry.
- Apply resin bond to the tooth
- Apply resin cement (vario link 2) to the fitting surface of the dental crown, seat and light cure
See also bridges
