by Dr M K Vasant MBE MGDS RCS (Eng), MGDS RCS (Edin), FFGDP (UK), FDS RCS (Edin) Posterior composties often suffer from shrinkage, postoperative sensitivity and wear and other problems. Manny Vasant outlines faults that can develop and a possible solution to them.

Materials and methods for composites have evolved over the years (Figure 1 and 2).

Figure 1 and 2: The evolution of composite restorations

Although the BIS-GMA used in tin cans has in experiments been implicated for sterility in male rats (Sharpe, 1995), it is unlikely that dentists will be faced with a situation from our male patients 'Doc, could you please remove my composites, we are trying to have a baby!'

Many practitioners would accept that small class 1 and 2 cavities can be successfully restored with composites and this would indeed be the most conservative option. However, larger restorations are a taboo and may result in post-operative sensitivity, recurrent fractures, wear, poor contacts or secondary caries. This can be avoided with due attention to case selection and correct technique to make the most of the properties of the material used.

PROBLEMS WITH POSTERIOR COMPOSITES

Shrinkage and post operative sensitivity
The use of newer bonding agents prevents gaps between the tooth composite interface. However, the setting shrinkage of composites when bonded to tooth structure can cause cusp deformation in molars and premolars in MOD cavities (Causton and Miller, 1985). The sequel of this could be micro cracks within the dentine and subsequent sensitivity. One solution suggested for immediate post-operative sensitivity related to the above phenomenon is to cut a mesio-distal groove to relieve the stresses. Needless to say, in order to be effective, the depth of this groove should extend to the bottom of this cavity. The defect is then filled with composite again and as the shrinkage is volume related, this would be minimal.

There is also potential for shrinkage (towards the light) in the gingival seat area resulting in a marginal defect and secondary caries.

To prevent or minimise these shrinkage, many techniques have been suggested. These include incremental curing, indirect composite inlays, light transmitting wedges, conical light guides. These have met with limited success.

Over-desiccation of the preparation can also result in post-operative sensitivity. Wet or moist bonding technique has gained wider application in recent years whereby the preparation is dried with cotton pellets or suction only or with one second syringe blasts. Not surprisingly tooth dryers have lost their popularity in dentine bonding. The rationale behind wet bonding is that some moisture is essential if the hydrophillic HEMA found in many primers were to work effectively.

Composite fracture
This commonly results from undercuring of the inner core of the restoration. This can happen due to bulk filling, inadequate light intensity (less than 200 m watts) or holding the light too far away or not perpendicular to the surface. Tip distance greater than 4mm from the surface of resin being cured significantly decreases polymerisation 2mm below resin surface (Rueggeberg et al, 1993) (Figure 3). The crust will therefore crack soon after the placement of the restoration- a phenomenon commonly referred to as “soggy bottom”.

Figure 3: A tip distance greater than 4mm from the surface of the resin decreases resin polymerisation 2mm below the resin surface

Figure 4: Products such as Optiguard have been shown to reduce wear, enhance marginal integrity and reduce postoperative sensitivity

Wear
The wear is exaggerated in occlusal contact area and hence pre-operative assessment of centric spots is essential so that occlusal contact can be retained on natural tooth where possible (Lutz et al, 1984). Cavity preparation should not have any occlusal bevel, should have rounded internal line angles and a cervical bevel (Isenberg and Leinfelder, 1993).

Composite resins which have a proven track record of wear rate comparable to amalgam include, amongst others, Heliomolar, Herculite XR, Brilliant and Charisma.

Use of surface penetrating agent eg Fortify(Bisco) or Optiguard(Kerr) have been shown to reduce mean wear by 50 %. It also enhances marginal integrity (Dickinson and Leinfielder, 1993) and has a role in reducing post operative sensitivity due to surface marginal defects (Figure 4).

Poor contact points
Pre-operative wedging, band contouring or use of pre-contoured bands, inclusions and use of light cones (used to ensure polymerisation of the cervical area), condensable composites (eg Glacier SDI, Solitaire Kulzer) are some of the ways of counteracting this problem (Figure 5).

Figure 5: A transparent cone pressed into material before curing

Figure 6: Tofflemire Matrix Bands from Henry Schein

The author has found ultra thin .001 or .015 inches matrix used in a Tofflemire Band Holder with pre-wedging and contouring in the mouth particularly useful in this regard (Ultra thin 001 Matrix from Henry Schein, 135 Duryea Road, Melville, NY 11747) (Figure 6).

Secondary caries Despite the advent of modern dentine bonding agents, it is still extremely difficult to produce a well adapted, gap free class 2 composite restoration using light cured materials, particularly where the margin is subgingival in dentine or cementum. The “Sandwich Technique” was advocated whereby for deep subgingival restoration could be filled with glass ionomer cement prior to filling the rest with composite resin. In a 2 year study glass ionomer was lost in most restorations hence potentially prone to secondary caries (Welbury, 1990) (Figure 7).

Figure 7: In a two-year study, glass ionomer was lost in most restorations hence making the restorations potentially prone to secondary caries

A SOLUTION TO PROBLEMS OF COMPOSITES

Bertolotti Technique: (directed shrinkage technique)
Essentially this technique exploits the advantages and disadvantages of the chemically and light cured composite to overcome in minimise the above problems. The essential difference between the two groups of materials is that the light cured material has better aesthetics and wear resistance. The command cure of the light cured composite is an advantage in many situations. However, the shrinkage towards the light also poses its own problems. For example, the gingival seat area can lift up from the base opening up a gap especially in deep restorations situated in the cementum where the light may not reach easily or where the bond strengths are not optimal. The light transmitting wedges directing the intensity of light in this area to get a better margin have already been discredited.

The fundamental issue appears to be directing the shrinkage to minimise both the cuspal deformation and the gingival seat defect. Ironically, the improved bonding strengths, the peculiar shrinkage characteristics of the light cured composites and the more intense light sources are our worst enemies in this regard!

In contrast to light cured composites, the chemically cured composite shrink towards the cavity. This is so because, due to the oxygen inhibition, the first part to cure is the deepest part of the restoration. Due to the improved bonding strengths, this would result in a different pattern of shrinkage compared to their light cured cousins. The pattern of curing, related to the oxygen inhibition, results in an initial setting reaction at the composite tooth interface and the last setting reaction at the sub-surface of the restoration. At the surface of the restoration there remains an oxygen inhibited layer. The different sequence of setting and the volumetric shrinkage, results a concavity on occlusal part of the restoration rather than the cuspal deformation discussed above. Furthermore the oxygen inhibited layer at the surface provides a ready bondable surface for veneering with light cured composite.

Figure 8: Different tubes with or without neele tips and differing diameter are available

Figure 9: Instruments used for occlusal contours .

Hence if the inner core of a large restoration could be filled with chemically cured composite and the occlusal area with light cured composite, this would exploit the advantages of the two materials to the fullest potential. Bisfil (Bisco), a low viscosity chemically cured injectable composite was the material devised for the purpose. However any other flowable radiopaque self curing material would achieve the same result. The flowable composites provide void free delivery and could be done in one bulk without any deleterious effect on the final restoration. Different tubes with or without needle tips and differing diameter are available to enable one to use materials of various viscosities to be used in differing clinical situations and/or operator preferences (Figure 8). The operator has also got the ability to hold the matrix band tight against the adjacent tooth whilst the selg curing material is setting in order to retain a good contact. The deliberate occlusal underfilling (by about 1mm or so) is then made up with light cured composite. The materials suitable for latter use are the ones with established track record for wear and good aesthetics. Kerr's Herculite and Ivoclar Vivadent's Heliomolar have long track record for good wear characteristics and overall performance. The sculpability of these materials, using the cone shaped instruments (Figure 9) makes the reproduction of occlusal morphology far simpler.

SUMMARY OF TECHNIQUE AND MATERIALS

• Improving bond strength through acid etching of the dentin and bonding to wet dentine surface is preferred (Kanca, 1992)
  
  
• Liners containing fluoride, e.g. Vitrebond are desirable if margins are on dentine or caries is deep
  
  
• Use flowable chemically cured composite such as Bisfil in a Centrix syringe and tubes with needle tips. This will ensure void free delivery of the material in the base of the cavity.
  
  
• Thin matrixes .001 or .015 inches should be used and contoured in the mouth
  
  
• Pre-wedging is recommended
  
  
• Contour with teflon or titanium nitride (gold instruments) and establish occlusal contours with a cone shaped instrument
  
  
• Overfilling more than 0.5 mm is unnecessary as it makes finishing difficult
  
  
• Finish dry with airrotor 12 and 30 bladed tungsten carbide burs (Figure 10)
  
  
• Final finish with soflex discs and/or diamond polishing paste.
  
  
• Apply surface sealant and cure for 60 seconds each side as a final finish.

Figure 10: Jet 12 or 30-bladed finishing burs

The technique is simpler and far quicker than the incremental technique or indirect inlay fabrication. The author has found that it results in restorations that are sound and durable.

REFERENCES

Bertolotti RL. Int Aesth Chron 3: 53-58

Causton B, Miller B (1985). Br Dent J 159: 397-400

Dickinson G, Leinfielder K (1993). JADA Vol. 124

Isenberg BP, Leinfielder K (1990). J of Esth Dent 2:142-62

Kanca J (1992). JADA Vol. 123: 35-41

Lutz et al (1984). J Rest Dentistry 63: 914-920

Rueggeberg F et al (1993). Int J of Pros 6: 364-70

Sharpe R (1995). Medical Research Council

Welbury R (1990). Quint Int Journal Vol 21 No 6