Onlays

Question 1

What principles govern gold inlay preps?

Answer 1

• Tapered intracoronal walls about 6 degrees
• No undercuts or undercuts blocked out
• Flat floors with rounded internal line angles
• Bevel: gingival, proximal, occlusal

Question 2

What are some contraindications of inlays/onlays? What are some of their disadvantages?

Answer 2

Contraindications

• Lack of surface area to bond to or resistance/retention form
• Lack of dimensions
• Tooth periodontally unsound

Disadvantages:

• Unaesthetic (gold)
• Unconservative vs direct

Question 3

What are some methods of placing pins?

Answer 3

Vertical channel:

• Cut with 700 tapered fissure bur
• Take impression with rubber base material

Cast pin system

• Pin channel cut with special drills
• Use plastic impression pins

Question 4

How is an MOD ceramic onlay prepared? (sim clinic)

Answer 4

MOD cavity with 856

• Depth 2.5mm; width 2.0mm
• Taper occlusal and proximal walls 6-10 degrees
• Locate proximal gingival floor in enamel, 1mm above CEJ
• Flare proximal box walls mesio-distally (i.e. so that walls splay outwards in a mesio-distal direction)–>avoids sharp line angles in ceramic as if crack at stress area this tends to propogate)
• Clear contact (by extending 0.25mm into B/L embrasures)

Reduce Cusps (856)

• 2mm functional cusp + functional cusp bevel 1.0mm wide
• 1.5mm non-functional cusp

Final finishing and smoothing (8877 and L10)

• Smooth margins
• Round internal line angles (this is more so important in ceramic than gold, again due to crack propogation)
• No undercuts

Basically in clinic:

0. Remove caries, assess adequate occlusal depth (2mm, isthmus width 1.5mm)
1. Taper walls
2. Flare proximal box mesio-distally
3. Reduce cusps (Functional 2mm + 1mm bevel, non functional 1.5mm)
4. Finish and smooth + round angles, ensure no opposing tooth contact with margins and no unsupported enamel

• NO BEVELS, 90 degree butt joint required at cavosurface margins as:
  (1) thin sections of ceramic are difficult to fabricate and can crack easily
  (2) Margins can not be burnished into place to fix defects

Question 5

How is an MOD gold onlay prepared? (sim clinic)

Answer 5

Occlusal using 856

• Depth 2.5mm; width 2.0mm
• Taper occlusal and proximal walls 6-10 degrees
• Locate proximal gingival floor in enamel, 1mm above CEJ
• Clear contact (by extending 0.5mm into B/L embrasures)
• DO NOT FLARE PROXIMAL like in ceramic (i.e. don’t make the walls splay outward in mesio-distal direction, as you need it more square to create mechanical retention since gold can not bond to tooth structure via the cement)

Reduce cusps (856)

• 1.5mm functional cusp + functional cusp bevel (1.0mm)
• 1.0mm non functional cusp (in buccal cusp of upper premolar can reduce by 0.5mm to avoid excessive gold showing in aesthetic zone)

Finalise proximal boxes

• Place proximal box flares using L10 in path of draw (in this case refers to taper outwards towards occlusal to avoid undercuts)
• Place 0.25mm bevel at gingival margin (removes unsupported enamel and protects tip of non-functional cusp–>can place in gold as margins can be burnished and gold can survive in thin sections)
• ‘square up’ internal proximal box using Fiz10 and use 169L to place grooves in line angles (axio-buccal and axio lingual)–>creates more mechanical retention to avoid total dependance on resin cement

Place contra-bevel in non-functional cusp using 8877 to ensure the margin flows along all surfaces of tooth

Final finish
-check all margins are smooth

Basically in clinic:

0. Remove caries, assess adequate occlusal depth (2mm, isthmus width 1.5mm)
1. Taper walls, do not flare proximal walls mesio-distally (as need more retention with gold due to no bonding)
2. Reduce cusps (Functional 1.5mm + 1mm bevel, non-functional 1mm but 0.5mm in upper premolars for aesthetics)
3. Bevel all along the margins
4. Finishing and smoothing, ensure no opposing tooth contact with margins and no unsupported enamel

Question 6

What are the indications (uses) of inlays and onlays? What are the prerequisites to doing an inlay/onlay?

Answer 6

Indications:

• Aesthetic alternative to alloy based restorations
• Access for direct restoratives a problem
• Protection of teeth with cusps at risk of fracture or heavily worn teeth
• Conservative modification of tooth shape (occlusal reconstruction)
• Retainers for some types of bridges

Prerequisite:

• Large cavity: sufficient dimensions for thickness of material
• Sufficient area for bonding
• Periodontally sound

Question 7

What are some advantages of inlays/onlays?

Answer 7

• Aesthetics (ceramic)
• Better contact and higher strength vs direct fillings
• If all ceramic: good tolerance by gingiva, higher durability than resin, good clinical record
• More conservative than a crown
• Longevity
• Low creep and corrosion
• Not lead to tooth discoloration

Onlay only:
-Support cusps, reduce risk of tooth fracture

Question 8

What are the principles for a prep design for inlays/onlay?

List the steps you would take to create ceramic onlay prep and a gold onlay prep.

Answer 8

• Adequate occlusal depth (at least 2mm)
• Adequate isthmus width (1.5-2mm)
• Divergent walls
• Rounded line angles
• Shoulder finish on gingival margins
• Remove unsupported enamel
• Block out undercuts with GIC
• No bevels at margins (ceramic onlays, gold and ceramic inlays)
• No opposing cusp contact with margins
• Similar principles for onlays

Ceramic:

1. Remove all the caries
2. Assess for adequate occlusal depth and isthmus thickness, adjust if necessary
3. Create 6-10 degree divergence in the walls to avoid undercuts. Ensure there is no opposing cusp contact with the margins
4. If proximal box involved, flare proximal box walls mesio-distally (i.e. so that walls splay outwards in a mesio-distal direction)–>avoids sharp line angles in ceramic as if crack at stress area this tends to propogate)
5. Reduce Cusps with 856 bur:
   - 2mm functional cusp + functional cusp bevel 1.0mm wide
   - 1.5mm non-functional cusp
6. Final finishing and smoothing: smooth margins, round internal line angles (very important in ceramic due to crack propagation), no undercuts, no u/s enamel

Gold:

1. Remove all the caries
2. Assess for adequate occlusal depth and isthmus thickness, adjust if necessary
3. Create 6-10 degree divergence in the walls to avoid undercuts. Ensure there is no opposing cusp contact with the margins
4. Reduce cusps (856)
   - 1.5mm functional cusp + functional cusp bevel (1.0mm)
   - 1.0mm non functional cusp (in buccal cusp of upper premolar can reduce by 0.5mm to avoid excessive gold showing in aesthetic zone)
5. Square up’ internal proximal box using Fiz10 and use 169L to place grooves in line angles (axio-buccal and axio lingual)–>creates more mechanical retention to avoid total dependance on resin cement
6. Place 0.25mm bevel at gingival margin and continue all the way along the entire margin (removes unsupported enamel and protects tip of non-functional cusp–>can place in gold as margins can be burnished and gold can survive in thin sections)
7. Final finishing and smoothing: smooth margins, round internal line angles (less critical for gold than ceramic but nonetheless important), no undercuts, no u/s enamel

*Differences in steps highlighted in google docs

Question 9

What should be checked at the insertion appointment?

Answer 9

• Passive fit
• Good proximal contact
• Good margins
• Good aesthetics

Question 10

What cement is generally suggested with gold inlays/onlays?

Answer 10

-Rely X Unicem

Question 11

What is the procedure to cement CEREC?

Answer 11

• Same steps as porcelain
• Note that HF etch is done in laboratory, unnecessary to do in clinic.
• Clinic steps are:
• Apply silane to inside of CEREC
• Etch/wash/dry tooth
• Apply Optibond to tooth for 15 seconds, air dry for 3 seconds + light cure for 20 seconds
• Apply cement to CEREC, seat, light cure
• Finish and check occlusion