Ensuring a caries free cavity
When preparing a cavity for restoration, a vital process is to clear the cavity of carious tooth structure. This will ensure there is structurally solid tooth structure available for bonding to prevent loss of vitality, integrity of the restoration, reduced post operative sensitivity and reduce risk of decay progression. I thought I had written a post previously on how to ensure a caries free cavity but I couldn't find it in the search function. There are many methods to identify missed caries which I can write about in the future but I thought it would be more useful to write about areas where I often miss caries. This was extremely frequent straight after graduation and still catches me out. Be extra careful to check these areas before you restore.
1. Class V lesions:
For some reason I've had a large amount of these cavities to restore lately. Abrasion lesions tend to be equigingival as the gum receeds to the level of the toothbrush abrasion but sometimes they're supragingival in perio patients where the perio causes further recession or subgingival where the gingiva overgrows into the non carious cavity.
I see 2 main types of carious class V lesions: Plaque heavy lesions and plaque free lesions. The lesions that are covered in plaque tend to be in patients who don't brush and plaque collects at the cervical because it is below the height of the buccal contour and food movement doesn't clean the tooth there. They tend to have a high sugar intake with low clearance which encourages thick plaque growth and food accumulation in the buccal sulcus up around the upper 8s and lower 7s. The Class V lesions with minimal plaque tend to be high acid intake patients which inhibits thick plaque growth but causes erosion resulting in early dentine exposure at the thinnest part of the enamel (cervical). Those who also have high sugar intake will develop caries in this area.
In these class V lesions, the 2 areas I miss caries is:
a) The cervical margin. When the carious margin is equigingival/subgingival (most cases), retraction is needed to expose the margin, stem gingival crevicular fluid flow and avoid blood contamination. In most non carious and shallow caries cases, retraction cord will be sufficient but in the severe class V caries cases I have been seeing lately require teflon cord retraction. Roll some white teflon tape into a sausage shape and pack it into the sulcus with more force than you expect. A dry sulcus and a wet instrument help to manipulate the teflon as it will want to stick to dry surfaces. You will get a massive amount of retraction with the teflon tape that will allow you to caries free the cavity and restore it. Leave the teflon tape in place while you finish the restoration with a fine diamond or tungsten carbide finisher. Be sure to remove it afterwards. There will be a lot of bleeding. In my mind, the trauma from gingival retraction will be less than having a constant overhang or leaky margin after restoration but care must be taken in thin biotype cases as recession is likely.
b) At the interproximal extensions. Often i will take extreme care in the cervical and occlusal aspects of the cavity but will miss the interproximal extensions. ensure you clear the DEJ with a high speed diamond and take a round slow speed bur around the circumference of the cavity focusing on the cervical and interproximal extensions.
2. Class II cavities: Base of box.
Often I will take bite wings and notice "recurrent caries" at the cervical margin of the restoration. Partly this is biased due to the fact that caries anywhere else on the cavosurface margin will not be visible on the bitewing but it does make me wonder if what I am seeing is really recurrent decay or just failure to clear caries the first time around. This is a debate that could go on for days but what is most useful is to be more critical of your own cavity preparations before you restore them. The next time you think you've finished a class 2 cavity, check the base of your box. Take a sickle probe and scratch the dentine at the DEJ, take a spoon excavator and scrape at this dentine or better yet dye the cavity the caries detector dye. Alternatively, take a bitewing after you've restored a class II cavity. If you aren't aware of the risk of missing caries here almost inevitably you'll find that there is demineralised enamel or carious dentine at this point.
For a while now I have ensured that I have taken a slow speed round bur over this area very thoroughly when starting the preparation. It is important to me that I know how far cervically the decay will go because it allows me to plan how it will restore the cavity. I can see that the preparation this creates is much further cervically than my initial access form opening because of the rim of enamel that is left behind after the slow speed bur. Colour is not a reliable indicator of carious dentine at the DEJ as it is only recently started to decay and carious dentine margins will spread further than demineralised enamel margins.
3. Cusp tips and DEJ
Often I am so focused on the base of the prep and working out the extension of the prep towards the pulp that I miss what is happening at the DEJ which is the most important part of the preparation to clean. Caries at the cusp tips or generally on the occlusal aspect of the DEJ are often difficult to detect due to the angulation of vision into the preparation. You need to change the angle of your mirror to scan the entirety of the DEJ. It also highlights the importance of clearing the DEJ of caries before progressing deeper into the cavity. Before I finish my cavity preparation, I find it useful to take a slow speed round bur over the DEJ to ensure that I haven't missed any caries here. Oten at the cusp tips I will undermine the enamel which I then remove with a high speed diamond bur.
1. Class V lesions:
For some reason I've had a large amount of these cavities to restore lately. Abrasion lesions tend to be equigingival as the gum receeds to the level of the toothbrush abrasion but sometimes they're supragingival in perio patients where the perio causes further recession or subgingival where the gingiva overgrows into the non carious cavity.
I see 2 main types of carious class V lesions: Plaque heavy lesions and plaque free lesions. The lesions that are covered in plaque tend to be in patients who don't brush and plaque collects at the cervical because it is below the height of the buccal contour and food movement doesn't clean the tooth there. They tend to have a high sugar intake with low clearance which encourages thick plaque growth and food accumulation in the buccal sulcus up around the upper 8s and lower 7s. The Class V lesions with minimal plaque tend to be high acid intake patients which inhibits thick plaque growth but causes erosion resulting in early dentine exposure at the thinnest part of the enamel (cervical). Those who also have high sugar intake will develop caries in this area.
In these class V lesions, the 2 areas I miss caries is:
a) The cervical margin. When the carious margin is equigingival/subgingival (most cases), retraction is needed to expose the margin, stem gingival crevicular fluid flow and avoid blood contamination. In most non carious and shallow caries cases, retraction cord will be sufficient but in the severe class V caries cases I have been seeing lately require teflon cord retraction. Roll some white teflon tape into a sausage shape and pack it into the sulcus with more force than you expect. A dry sulcus and a wet instrument help to manipulate the teflon as it will want to stick to dry surfaces. You will get a massive amount of retraction with the teflon tape that will allow you to caries free the cavity and restore it. Leave the teflon tape in place while you finish the restoration with a fine diamond or tungsten carbide finisher. Be sure to remove it afterwards. There will be a lot of bleeding. In my mind, the trauma from gingival retraction will be less than having a constant overhang or leaky margin after restoration but care must be taken in thin biotype cases as recession is likely.
b) At the interproximal extensions. Often i will take extreme care in the cervical and occlusal aspects of the cavity but will miss the interproximal extensions. ensure you clear the DEJ with a high speed diamond and take a round slow speed bur around the circumference of the cavity focusing on the cervical and interproximal extensions.
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| Areas highlighted in red are areas I often miss caries in Class V lesions |
2. Class II cavities: Base of box.
Often I will take bite wings and notice "recurrent caries" at the cervical margin of the restoration. Partly this is biased due to the fact that caries anywhere else on the cavosurface margin will not be visible on the bitewing but it does make me wonder if what I am seeing is really recurrent decay or just failure to clear caries the first time around. This is a debate that could go on for days but what is most useful is to be more critical of your own cavity preparations before you restore them. The next time you think you've finished a class 2 cavity, check the base of your box. Take a sickle probe and scratch the dentine at the DEJ, take a spoon excavator and scrape at this dentine or better yet dye the cavity the caries detector dye. Alternatively, take a bitewing after you've restored a class II cavity. If you aren't aware of the risk of missing caries here almost inevitably you'll find that there is demineralised enamel or carious dentine at this point.
For a while now I have ensured that I have taken a slow speed round bur over this area very thoroughly when starting the preparation. It is important to me that I know how far cervically the decay will go because it allows me to plan how it will restore the cavity. I can see that the preparation this creates is much further cervically than my initial access form opening because of the rim of enamel that is left behind after the slow speed bur. Colour is not a reliable indicator of carious dentine at the DEJ as it is only recently started to decay and carious dentine margins will spread further than demineralised enamel margins.
3. Cusp tips and DEJ
Often I am so focused on the base of the prep and working out the extension of the prep towards the pulp that I miss what is happening at the DEJ which is the most important part of the preparation to clean. Caries at the cusp tips or generally on the occlusal aspect of the DEJ are often difficult to detect due to the angulation of vision into the preparation. You need to change the angle of your mirror to scan the entirety of the DEJ. It also highlights the importance of clearing the DEJ of caries before progressing deeper into the cavity. Before I finish my cavity preparation, I find it useful to take a slow speed round bur over the DEJ to ensure that I haven't missed any caries here. Oten at the cusp tips I will undermine the enamel which I then remove with a high speed diamond bur.
I agree. It's very important to be extra careful to check all these because if extensive-stage caries is not properly treated, the decay in the dentin will continue to worsen. Very informative!
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