Dental Post - 3
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This blog is to simplify our concepts of caries removal strategies.
Previously the aims of carious tissue removal were to remove all bacterially contaminated and demineralized tissue, without any discrimination about different qualities of carious tissue like hardness, moisture and colour, even at the expense of the dental pulp, with high risks of pulp exposure, especially if performed in deeper lesions.
So, by avoiding this,
Q. : “How can we achieve the best longevity for the tooth?”
A. : By preserving remineralizable tissue and Achieving an adequate seal by placing the peripheral restoration onto sound dentin and/or enamel, thus controlling the lesion and inactivating remaining bacteria by ‘Selective Caries removal protocol'.
What is Selective Caries removal protocol? (SCR Protocol)
• Selective removal protocol aims at preventing pulp exposure while successfully restoring a tooth that has a moderate to very deep carious lesion, where the tooth has no signs or symptoms of irreversible pulp pathology.
Selective caries removal protocol can be done in two ways :
1. Selective Carious Tissue Removal To 'Firm Dentin'
• In moderate lesions that is lesions not reaching the inner one third of dentin and with no anticipated risk of pulp exposure should be excavated to a caries-free DEJ and firm dentin.
2. Selective Carious Tissue Removal To 'Soft Dentin'
• In advanced (deep) lesions that is lesions reaching the inner one third of dentin and with anticipated risk of pulp exposure should be excavated to a caries-free DEJ and soft dentin.
• In the periphery, achieving a good seal and maximizing restoration survival are prioritized, with peripheral enamel and dentin being hard at the end of the removal process.
• Generally while excavating caries, terms like ' complete' or ‘Incomplete’ are used. It remains completely unclear what is completely or incompletely removed. Is it…bacteria? soft dentin? discolored dentin? degraded collagen?
• Caries removal strategies should be termed according to what is done, i.e., descriptively, instead of what one aims to remove or retain. So following terms have been agreed on to describe the dentin which is left or removed.
Basically there are 3 types of dentin :
1. Soft dentin
2. Firm dentin
3. Hard dentin
• Soft Dentin/ Infected Dentin :
- Soft dentin is also called as outer carious dentin/infected dentin.
- It is characterized by the presence of bacteria, low mineral content and irreversibly denatured collagen.
- It is necrotic, contaminated and dose not self repair.
- Clinically it lacks structure and can be easily excavated with hand instruments.
• Firm Dentin / Affected Dentine :
- Firm dentin is also called as inner carious dentin/affected dentin.
- It is characterized by demineralization of intertubular dentin and initiation of intratubular fine crystals at the advancing front of carious lesion.
- Because of the caries demineralization process, firm dentin is softer than hard Dentin.
- Although organic acids attack the mineral and organic contents of dentin the collagen cross-linkings remains intact in this zone and conserve as a template for remineralization of intertubular dentin.
- Therefore, provided that the pulp remains vital, firm / affected dentin is remineralizable.
- The trasition between soft and firm dentin can have a leathery texture, particularly in slowly advancing lesions and has been called ‘Leathery Dentin'.
- Clinically firm dentin does not deform when an instrument is placed into it, but it can be scrapped off with medium pressure.
• Hard Dentin :
- It represents the deepest zone of caries lesion assuming the lesion has not yet reached the pulp.
- It may include tertiary dentin, sclerotic dentin and sound dentin.
- Clinically hard Dentin requires a strong force to engage the dentin and it cannot be removed without a sharp cutting edge or bur. A scratchy sound can be heard when dragging an explorer across hard dentin.
What is the rationale of this technique?
- The rationale behind this technique is that the microorganisms, in the carious tissue left behind during selective removal, are deprived of micronutrients from the oral cavity when the carious lesion is hermetically sealed.
- The microorganisms then become less potent thereby slowing down or arresting the carious process.
- This leaves the pulp-dentinal complex with conditions that are favorable for depositing reactionary dentin over the pulp.
Some Important Consideration :
- In recent years, Polymer burs are used for Selective removal of caries and it is described as “dentin safe,” it means that it removes only carious dentine; the bur will be self-limiting when it reaches sound, healthy dentin.
- A sealed tooth-restoration interface is critical for the success of the restorative procedure. When a proper seal is NOT obtained, or when/if the seal is compromised, marginal leakage and ingress of bacteria/luids/nutrients will allow lesion progression.
- Removal of the bacterial infection has been seen as an essential part of all operative procedures; however, even removal of dentin up to hard dentin in deep, advanced caries lesions does not ensure a “sterile” dentin as bacteria have been found to be present in all dentinal layers in deep caries lesions.
- So, Evidence indicates that when a good seal is present the lesion will arrest, therefore it is not necessary to remove all of the dentin that has been compromised by the caries process.
- Caries detection solutions such as 1% acid red in propylene glycol have been developed to help stain the infected layer, these dyes bind and stain the demineralized dentin matrix and do not stain bacteria exclusively.
- Complete removal of all stained tooth structure in the preparation therefore ultimately leads to significantly larger preparations than the traditional visual-tactile method of evaluating for caries removal, so their use is no longer recommended.
- Patient should be clearly informed that in the treatment of advanced (deep) dentin caries some leathery and soft dentin may remain under the restoration.
- Remaining caries affected dentin has many implications, including higher risk for endodontic complications not because “caries was left under the restoration” but because deep caries was present to begin with.
- If the patient is not willing to accept the risks, then the alternative, either complete caries removal with a higher risk of complications like endodontic therapy, postoperative sensitivity or tooth extraction, should be presented.
- Teeth that are restorable only by use of full cuspal coverage restoration generally are not appropriate for the SCR technique because of the difficulty of evaluating the tooth for possible failures such as continuing caries activity under the full coverage restoration.
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