1980: Mormann and Brandestini developed chairside CAD/CAM system
1985: Alumina infiltrated glass ceramics developed by Sadoun
1990: Technique of pressed glass reported on by Wohlvend and Scharer
Early ceramic inlays weren’t very successful due to problems relating to marginal integrity, lack of bond between restoration and tooth tissue, ‘wash-out’ of luting cements and; discolouration, marginal openings and secondary caries.
The teaching of inlays & onlays has also been seen as a side thought with the emphasis put on direct restorations or indirect full coverage.
Table 1 - A Comparison of some materials used for posterior restorations (M Abdul Razak. The Tooth-Coloured Inlay/Onlay Restorations Annals Dent Univ Malaya 1998 5: 7-23)
Once considered ‘The Gold Standard’.
Advantages: Excellent physical and mechanical properties, corrosion resistant and excellent survival rates.
Disadvantages: Not very aesthetic (personal opinion) and wedge effect on inlays (increased stress in wide/deep inlay preparations).
The advent of acid etch (Buonocore 1955) allowed adhesive restorations to become a viable alternate.
As mentioned earlier, conventional ceramics were problematic due to: Material weakness, Poor marginal integrity and Lack of adequate cement.
Advantages: Aesthetic, Decreased marginal leakage associated with polymerisation shrinkage and Less wear and discoloration
Disadvantage: Technique sensitive, Moisture sensitive, Weak until bonded and can fracture during try-in, Expensive, Unable to adjust.
Uses process similar to lost wax technique for processing
Suitable for single units
Advantages: Far superior fit (allowing for less resin luting cement, decreasing the possibility for ditching), Less wear to opposing dentition, Similar thermal cycling properties to enamel, Greater mechanical properties.
Disadvantages: Adjustment or wear results in loss of surface stain.
All-ceramic restoration using pressing of pre-cerammed ceramics under high temperature (using hydrostatic pressure) within a vacuum. Layered with leucite for aesthetics.
Advantages: Dimensionally accurate (lost wax procedure), Even greater mechanical properties (dense micro-crystals of leucites), Very esthetic
IPS Empress II
Uses lithium disilicate glass ceramic rather than leucite (greater mechanical properties compared with leucite) & layered with a flouroapatite glass ceramic (apatite relates to natural tooth structure allowing for a more natural appearance)
CAD-CAM uses a pre-manufactured single unit of ceramic that is milled by a machine.
‘In-house’ units. Information from intra-oral camera is sent directly to milling machine within practice.
Lab made units. Information sent to lab to fabricate coping +/- separate porcelain veneer.
Advantages: No need for lab (if milled in-house), greater dimensional accuracy (no impressions), Materials less porous and even greater mechanical properties, Increased fracture resistance (single homogeneous block material), Improved aesthetics.
Indirect Resin Composites
There are three main choices of Indirect resin composites: Hybrid composites, Microfilled resins, Ceramic optimised resins (Ceromer).
Advantages: High esthetics, Easier to adjust or repair, Less abrasive to opposing dentition, Good marginal integrity (polymerisation shrinkage occurs prior to cementation), Can be completed chairside (Indirect immediate) and most importantly they are Cheaper!!!
Disadvantages: Increased wear (restoration worn rather than opposing dentition), Less dimensionally stable, Poorer mechanical properties, Uncured cement if >2mm thickness.
Which should I use?
Rule of thumb: Unfortunately there isn’t one!
Each case has to be decided on its merits. But I have listed a few of the key factors to consider.
Inlay or Onlay?
Size of Cavity (If the isthmus is <1/4 width tooth do a direct restoration, if it is between 1/4 -1/3 choose a direct or inlay, if it is >1/3 do an onlay- as cuspal coverage should be required)
Weakened cusp (By checking occlusal contacts you can identify if excessive force is being transferred through a cusp – if so an onlay is indicated. See Fig 1)
Figure 1. Wedging stresses due to inadequate design considerations (Fisher et al. Photoelastic analysis of inlay and onlay preperations J Proshetic Dentistry,1975 33:47)
How do I do it?
There are specific guidelines depending on the material being used.
Box shaped cavities
Slightly divergent walls to allow for path of insertion (undercuts may require blocking out with adhesive restorative material)
Avoid occlusal contacts on margins (lead to deterioration and leakage)
Floor cavity should be flat or concave, following occlusal form
Rounded line angles (Ceramic & Composite)
Rounded shoulder or Butt join margin (Ceramic & Composite)