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The major reasons for op sensitivity is because of Micro- Leakage: Especially due to  improper bonding and condensation. Most of the clinicians in fact avoid composite fillings due to post op sensitivity phobia. There are lot many advancements evolved  in adhesion mechanism to counteract bonding failure, we need to understand many aspect of composite restorations to avoid these complications. This article will help you construct clarity on the right methods of composite filling:
Proper Marginal Seal:
  • Proper Marginal Seal can be achieved by clear understanding of the complex interplay between polymerization shrinkage and adhesion.
  • The cross-linking of resin monomers into polymers is responsible for an unconstrained shrinkage of 2% to 5%.
  • The uncompensated forces may exceed the bond strength of the tooth-restoration interface, resulting in a gap formation from a loss of adhesion.
  • The shrinkage forces generated by a high modulus material or a high volumetric shrinkage can result in stresses, being transferred in a pulpal direction, resulting in dentinal tubular fluid movement that stimulates the odontoblastic process.
  • This pressure change may be responsible for postoperative sensitivity upon mastication.
  • There are lot factors which can decrease this gap formation and thus Post op sensitivity.
How to get proper adhesion:
  • Understanding Basics of adhesion principles or Dentin bonding is must to get proper adhesion
  • There are Two concepts of Bonding
  • Total etch (etchant + prime and bond) and self etch (single Bottle, all in one)
  • Total etch should be prefered for cavities or preparations involving only enamel surfaces and Self etch should be used for Dentin preparations, and for deeper restorations Resin modified glass inomers liners should be used.
Note: The most  important thing is to prepare the tooth surface for Bonding,  creating the moist tooth surface will facilitate good bonding and remember  at any circumstances Dentin should not be dried thoroughly but moderately moist.  
Now Steps for bonding:
  1. The cavosurface enamel margins of the preparation should be etched for 30 seconds with 37.5% phosphoric.
  2. A self-etch primer should be applied to the dentin for 20 seconds and air-dried for 2 seconds.
  3. A bonding agent was applied to the enamel and dentin surfaces for 20 seconds, lightly air-dried and light-cured.
  4. If it is self etch one, apply the bonding agent for 40 seconds, air dry it by chip blower for 2 seconds
  5. Curing should be done for each surface in the perpendicular direction.
Now how to reduce shrinkage??
Before we get on to the procedure, lets know the  major factors that influence polymerization shrinkage: 1.Type of resin, 2.filler content of the composite, 3.Elastic modulus of the material, 4.Curing characteristics, 5.Water sorption, 6.Cavity configuration, and the intensity of the light used to polymerize the composite
To Elaborate:
1.First three factors are related to the Material which can not be controlled by dentist 2.Rest all are operator dependent.  
How does Light affects polymerization??
1.Intensity of light, the illumination must be in the range of 460-480 nms. I recommned all to please check the curing unit light intensity at least once a year. 2.Time: strictly follow manufacturers instructions, 3. Distance from the curing material,  It should be as near as possible.   For each mm light intensity is reducing drastically. This diagram explains the intensity of light at 0-1mm, 1-2mm, 2-3mm. For the first 1 mm it is 65% and for 3mm it is negligible.
  • The light coming out of the tip is like a stream of water from a hose. The flow is highly acclimated. There fore, light only goes where you point the tip.
  • Unusual features of the cavity preparation design require that you angulate the light from a variety of directions (usually requiring more curing cycles).
Proper Condensation:
  • Avoid bulk filling and bulk curing, follow layering technique to avoid Marginal leakage
  • Use clean instruments
  • Don’t keep any voids in between the layers
  • Give sufficient time after each layer of condensation and each cycle of curing to compensate material to shrink
  • Understand the basic principles of C- Factor
C-Facto or configuration factor is the ratio of the bonded surface to the unbonded or free- surfaces in a tooth preparation. The higher the c factor greater is the potential for bond disruption from polymerization effects.
  • Don’t keep premature occlusal contacts
  • Fully excavate residual tooth decay
  • Polishing should be done after complete adjustments of occlusal contacts
  • Liquid polishers will be more useful to fill the Voids on the surfaces
  • Don’t use bonding agent as polisher
  • These are the few basic things which needs to be understood.
  • Composite restoration is purely artistic job we need to invest lot of time to master this art
  • For any query please write us in comment box
  • If you liked please do forward to your fellow colleagues.

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