Onlays Flashcards
what is an onlay
a restoration covering at least one cusp on the occlusal surface where the morphology is replaced by another material including ceramic, gold, amalgam, zirconia
what are the indications for an onlay
- when cusps have been undermined by caries
- when enamel is available for etch and bonding
- where there is presence of horizontal cracks which are too far apart to repair with composite or amalgam
- lack of supporting dentin under a cusp
- heavy occlusion
- discolored cusps in an esthetically oriented patient
- when remaining tooth structure is less than 1/3 to 1/2 the intercuspal distance
when done well an onlay with appropriate cusp coverage greatly increases the ____ of the natural tooth prior to decay
strength
what are the contraindications for an onlay
- poor OH
- severe bruxer
- more than 2/3 of the occlusal table requires restoration to support the onlay, a complete crown is generally recommended
- inability to create sufficient bulk for ceramic material in the preparation and with opposing occlusion. need 2mm of reduction for ceramics
- inability to maintain a dry field
- adhesive resin cements used for onlays are technique sensitive and may not be appropriate for every scenario
what is the primary reason for choosing an onaly
conservation of tooth structure
why are onlays used as conservative alternative to crowns
- leaving the tooth walls and additional tooth structure allows for further restoration preps in the future
- once you cut a crown prep you cant do anything else but another crown
why were onlays not used as often as indicated in the past
- more technical preparation
- difficult to temporize
- more precise fit and therefore more room for error to occur
- crowns are quicker to prepare and temporize
- sometimes insurance companies wouldnt pay for onlays but would pay for crowns
why are onlays used more with digital scanning
the digital scanning and milling without the temporization issues have brought back this more conservative restoration by eliminating the more challenging previous concern
many onlay margins require the ____ to do the final sealing of the margins
resin cement
what are the preparation guidelines for an onlay
- no sharp angles
- no undercuts
- cusp coverage away from occlusal contacts
what is the prep criteria for our posterior onlay project
- 2mm minimal thickness of all ceramic onlay restorations
- reduction should follow the occlusal anatomy
- finish line should allow for a 90 degree exit angle
- no sharp angles. all internal angles must be rounded
- there should be no bevel, unsupported, j-shaped or lipped margin
the contact area should be:
porcelain
the finish line is a:
shoulder and mimics the crown finish line but much more cervical
the margin of the onlay prep should not be:
in occlusion
what is the depth of the modified shoulder
1-1.2mm
