How to create a peripheral seal zone that prevents recurring failures and keeps the tooth alive can be a tricky thing.  Complete removal of caries by the traditional visual and tactile techniques has been fairly unsuccessful. The minimally invasive dental treatments for these smaller lesions using air abrasion, sonic diamond tips, glass-ionomer cement, and bonded composite resin have reduced the need for traditional preparations. 

Lesions of medium and large depths require more sophisticated techniques for determining ideal caries removal end points. Using traditional visual and tactile techniques for large lesions is often inconsistent for determining optimal caries removal end points and can often  progress to exposing the pulp. 

Ideal caries removal end points are needed to preserve vitality of the pulp without limiting the strength and durability of the adhesive reconstruction.

By using only visual and tactile methods for deep caries removal, the pulp is often exposed because the transparent zone, sub-transparent zone, normal deep dentin, and reparative dentin are all softer than superficial and intermediate dentin.

Histology of dental caries

Using histologic, biochemical, biomechanics, microscopic, and microbiologic techniques, researchers were able to distinguish there are two layer of caries and are very different in nature.

The first layer was named outer carious dentin.  It is highly infected, acidic and demineralized. This layer is not sensitive to contact and can be removed without anesthesia. This layer also failed to remineralize because collagen frame work could not return to normal.

The second layer was named inner carious dentin.  This layer is partially demineralized and slightly infected. The collagen fibrils remain intact causing this layer to remain sensitive to removal without anesthesia.  The inner carious dentin has three parts: the turbid layer, transparent zone, sub-transparent zone, and normal dentin.

Technology that guides us to determine caries removal end point and the peripheral seal zone 

1.  DIAGNOdent:  reads bacterial products called porphyrins and is used to assess the relative amount of bacteria present in a caries lesion.

2.  Caries detector dye(CDD): This type of staining method can help us differentiate the different layers based on its molecular weight and how it stains the infected and affected areas.  

3.  Combining DIAGNOdent and CDD can give a bacteria free lesion without removal of affected dentin at peripheral zone area.

4.  Anatomical measurement using perioprobe:  caries removal achieved predictably inside the peripheral seal zone by further excavation of outer carious red zone. However, when excavation is near to the pulp (> 5 mm from the occlusal surface or > 3 mm from the DEJ) and the caries-detecting dye still stains red, excavation should stop, this will eliminate most pulp exposures.

5.  Carisol chemo mechanical; can leave residual outer carious lesion so it's useful only for shallow and small cavities not for large one.

6.  Ceramic burs: help to create caries removal end point and leave carious soft dentin, it facilities controlling and intuitive excavation. The studies showed that the service life of cera bur k1SM is three times as long as that of a round tungsten carbide bur.

Treatment goals 

1. Create PSZ of enamel, DEJ and normal super facial dentin near DEJ 

2.  Leave inner carious dentin ICD inside peripheral seal zone (psz).  It can bond at 30 Mpa.

3.  Remove highly infected outer carious dentin inside psz without exposing the pulp and small area of outer carious dentin are left to prevent pulp exposure.

4.  Deactivate and seal any remaining bacteria left inside PSZ.

5.  Use adhesive tech that will maximize bond strength of the PSZ and ICD inside PSZ.

Step by step tech to achieve caries end point and peripheral seal zone.

1.  Test for pulp vitality with ice if positive go for caries removal, if negative inform patient for root canal treatment (RCT).

2.  Anesthesia and isolate the tooth with rubber dam. 

3.  Access the lesion after removal of any failed restoration.

4.  Stain the caries with red CDD wait 10 seconds and rinse.

5.  Starting near the DEJ, use 1mm round diamond bur to create peripheral seal zone (plz) area of red stained outer caries and pink stained inner caries. 

6.  Staining and removing outer and inner caries is repeated until the caries removal end point in PSZ is stain free. 

7.  After removing the red area and leaving the pink between pulp horns, these pinks can be evaluated by using DIAGNOdent to be sure bacteria free area in our peripheral seal zone.

8.  Move to deep pulp horns if tissues continue to give red stain and the periodontal probe indicate that you aren’t deeper than 5mm from occlusal surface and 3mm from DEJ.  If so, stop excavation to prevent pulp exposure.

9.  Optional step: treat PSZ, ICD and OCD with CHX 0.2 to 2.0% to inhibit MMPs and residual bacteria to prevent deterioration of hybrid layer, if using total etch bonding system this step should be performed after etch & rinsing. If using a self-etch bonding system,  apply CHX for 10 seconds then dry before self-etch primer application.

10.  Finally if using two step self-etch bonding system, it's preferred to use air abrasion before to maximize the micro tensile bond strength.

Conclusion

Combining anatomical and pathological knowledge with technology of caries detection dye (CDD) and laser fluoresce will achieve a caries removal end point.   These ideal end points will preserve more vital pulps, conserve dental hard tissue and create high bondable peripheral seal that mimic the natural tooth.

Summary

The peripheral seal zone (PSZ) is 2-3mm wide circumferential area, caries free zone, around pulp horns. The main benefits of this technique are: 

1. To preserve pulp in case of deep caries.
2. To create a bondable surface that we can use to build our restorations.
3. Allows biomimetic dentist to reduce root canal treatment in dental daily practice.

Source

1. A Systematic approach to deep caries removal endpoints:s the peripheral seal concept in adhesive dentistry

Fig 1: showed how to create PSZ of sound enamel, dentin and selectively removal of remaining caries according to measurements by  perioprobe to avoid pulp exposure. Photo by Dr Hashem Ahmed