Step by Step: minimal invasive posteriors
What do we mean by minimal invasion? First, when starting preparations, we must preserve as much healthy tooth structure as possible. In this article we analyse one of the most popular methods today – preparation using air abrasion. Using a stream of aluminium oxide particles we can easily remove tooth structure and prepare cavities for restoration. The strike of abrasive particles at high speed remove small amounts of tooth structure especially the softer one as the carious tissue.
Air abrasion is a good choice in the following situations:
1) Removal of superficial enamel defects
2) Excellent tool for detection of pit and fissure caries
3) Abfractions and abrasions conditioning
4) Removal of old restorations (composites, amalgams, glass ionomers, porcelains)
5) Cleaning the surface of the enamel and dentin for better bonding when done at proper pressure
Img. 1 – First of all, we take a picture of the quadrant to see the details of the all defects. Here we can see active caries in all 3 molars. Pits were cavitated and the clinical finding was corroborated with a caries detection device DiagnoCam (Kavo).
Img. 2 – The scattering of the powder particles within the oral cavity and/or their accidental ingestion is another area of concern for which rubber dam isolation is a must. We usually isolate a quadrant using heavy (Nictone) rubberdam. After isolation we can start preparation using 27 microns Al2O3 with regulated pressure and with water spray (Rondoflex) or AquaCare (Velopex).
Img. 3 – Most common particle sizes are 20, 27, 50 and 53 micron ø. Larger particles allow the clinician to work faster, but will result in comparatively larger-sized cavity preparations than those with the 20 or 27 micron particles.
Higher particle flow rate will provide more consistent, faster abrasion of the surface.
The speed depends upon gas pressure, nozzle diameter, particle size, and distance from the surface.
Average operating distance usually stands between 0.5 and 2 mm. The bigger the distance, the more diffuse the stream and the less the cutting ability.
Fig 4.- The ability to regulate:
a) air pressure
b) water flow
c) media delivery
Makes the air abrasion an extremely reliable and powerful tool. In the image one popular device Aquacare (Velopex)
Img. 4 – The whole preparation is finished. For the 3rd molar we used a carbide bur to selectively remove soft carious tissue, as air abrasion is not effective for cutting of soft caries. Usage of carbide burs decreases the formation of the smear layer that is of outmost importance for self etching adhesion.
Img. 5 – In this case we used selective etching technique of the enamel. 37% phosphoric acid was applied and brushed actively for 20 seconds.
Img. 6 – We start to apply the adhesive (multilayer) – brushing actively, much on the the dentin and less on the enamel.
Img. 7 – We must wait minimum 20 seconds for the exposition of the adhesive followed by 5-10 second air drying. Light curing will be done for 60 seconds.
Img. 8 – After polymerization of the bonding agent we must apply adhesive protection layer. Bulkfill flowable is one of the best choices, otherwise highly filled flowable composites are another excellent alternative.
Img. 9 – Dentin layer is finished with Bulkfill composite and the thickness left for the enamel layer is 1-1.5 mm.
Img. 10 – The enamel layer was done with 1 body shade composite using the new (Fast Modeling Technique) which will be described in further publications. The use of stains is not mandatory but can help in increasing the depth of those restorations. This is optional and up to the clinician.
Img. 11 – Air blocking with glycerine and light curing for 1 minute.
Img. 12 – Finishing was done with carbide bur from (Styleitaliano Finishing kit)
Img. 13 – With a rubber abrasive point we start polishing.
Img. 14 – Polishing is finished with a silicone abrasive wheel which is enough for a good polishing.
Img. 15 – Restorations after polishing.
Img. 16 – Restorations right after rubber dam removal.
Img. 17 – Restoration after 2 days recall. We can notice a perfect color integration.
Be Conservative! This is a main approach if we want to preserve more sound tissuses of tooth and air abrasion will help us in this way