Modern Conservative Approach to Treat Deep Caries Lesions

With the modern philosophy of caries management, the use of preventive therapies and remineralization as well as the scientific progress in dental adhesives and restorative materials, dental professionals have options to deliver conservative minimally invasive, functional esthetic treatments to patients.

In order to provide patients with state-of-the-art caries management, the dentist needs to gain deeper understanding of the topics of caries management by risk assessment, early caries detection methods and techniques, management of non-cavitated lesions, defect specific preparations, conservative caries removal and appropriate material selection. The clinical application of conservative treatment requires in many instances a paradigm shift from the conventional caries removal concepts and practices of removing all soft and leathery dentin until a hard dentin surface is achieved. It is challenging for the dentist trained to use this traditional surgical approach.

Another challenge to integrate this current philosophy into practice is the disconnection between research, academics and clinical practice. Although caries research is expanding every day towards more remineralization and less invasive treatment, it is very hard for dental practitioners to manage this extensive amount of new information and receive proper training to incorporate this evidence into their daily practices. Additionally, many third party payers do not provide appropriate coverage to support the implementation of these best conservative management practices, limiting treatment options for patients.

Understanding the changes that occur in tooth structure with the progression of the caries process is the foundation for the current biological approach for caries removal. This article provides clinicians with current information, based on evidence, of the importance of minimal conservative removal of tooth structure during caries excavation to preserve tooth vitality, the structural changes associated with enamel and dentin during caries progression, the pulp-dentin complex reactions to the caries process as well as the alternative treatments involving incomplete caries removal, their advantages and limitations.

The concepts, treatments and techniques proposed in this article are based on current scientific evidence and have been adapted in accordance to our clinical practices and the philosophy followed in our academic institution.1,7

TREATMENT OF DEEP CARIES LESIONS: Traditional Complete Caries Removal (Removal Of All Soft And Leathery Dentin) vs. The Conservative Approach To Partial Caries Removal

The traditional caries removal technique (Fig. 1) involves the removal of all soft and leathery dentin until hard dentin is reached before placing a final restoration. In shallow to moderate dentinal cavitated caries lesions (that radiographically appear to extend less than 75 percent into the dentin) this technique is often used without the risk of exposing the pulp (Table 1).1,7

Traditional complete caries removal

FIGURE 1A. Initial composite resin with recurrent caries.

FIGURE 1B. Rubber dam isolation, composite removed and complete caries removed.

FIGURE 1C. Final composite resin restoration.

Deep caries lesions are cavitated caries lesions that radiographically extend more than 70 to 75 percent into dentin. When the traditional caries removal technique is used to treat the deep caries lesions of vital asymptomatic teeth, the risk of pulp exposure is high. Complete removal of the soft and leathery dentin may cause a pulpal exposure, introducing bacteria into the pulp. Such outcomes require either root canal therapy or extraction (Fig. 2). Evidence indicates that the traditional complete caries removal procedure may be detrimental to the pulpo-dentinal complex and does not take into consideration the biological natural response of the tooth to the caries stimulus.2,13,14,16

FIGURE 2. Clinical case of pulpal exposure during complete caries removal.

TABLE 1.

Pulp exposures can be due to mechanical reasons, caries or trauma. When the pulp exposure of a vital asymptomatic tooth is mechanical or due to trauma, the Direct Pulp Capping procedure has been used in an attempt to preserve tooth vitality. After rinsing and disinfecting the exposure site, a liner usually from calcium hydroxide or MTA material is placed directly over the exposed pulp followed by a sealing liner of resin modified glass ionomer and the final restoration. It is thought that pulp exposures due to trauma or mechanical reasons (iatrogenic) have a better success rate than a caries exposure since there is no bacterial contamination. When the pulp is exposed due to caries, the bacterial contamination will cause inflammation, decreasing the healing ability of the pulp and resulting in irreversible damage or necrosis. In deep caries lesions of asymptomatic, vital restorable teeth the pulp exposure should be avoided; it is preferable to use an incomplete caries removal approach rather than the direct pulp treatment.9

In these specific cases the option of treatment using a more conservative approach to caries removal is indicated, in an attempt to avoid pulp exposure and maintain pulp vitality. The use of incomplete caries removal techniques have been proposed based on the deeper understanding of the biological response of the tooth to caries stimulus and the structural changes that occur as a protective response of the tooth to bacterial invasion.2,3,7

The incomplete caries removal technique involves the partial removal of soft caries infected dentin starting peripherally (at the DEJ) and the sealing of the remaining caries lesion with an interim or final restoration (in one or two visits) with the goal to seal the partially demineralized affected dentin and arrest or reverse caries lesion progression.2,7,13,16

There are different techniques of incomplete caries removal described in the literature. The most widely known and used techniques are the Indirect Pul
p Treatment (formerly termed as “capping”)9 and Stepwise Caries removal. They differ in the amount of soft dentinal tissue removed, number of appointments involved (one or two), and restorative materials. Each technique has indications, advantages and limitations. To properly utilize these techniques for different clinical situations, tooth and pulpal diagnosis is crucial, as well as the understanding of the caries lesion activity, and related changes in the dental structures.2,7,9

CARIES PROCESS AND STRUCTURAL CHANGES IN ENAMEL AND DENTIN
The Caries Process is a dynamic sequence of biofilm-tooth interactions that can occur over time on and within a tooth surface. This process involves a shift in the balance between protective factors (that aid in remineralization) and destructive factors (that aid in demineralization) in favor of demineralization of the tooth structure over time. The process can be arrested and/or reversed at any time. If the caries process is not arrested, a caries lesion is formed.

A caries/carious lesion is a visually detectable change in the tooth structure that results from the biofilm-tooth interactions occurring due to the caries disease. It is the clinical visual manifestation (sign) of the caries process. When the enamel structure is seen only as demineralized and the surface of the enamel is intact, the caries lesion is considered to be non cavitated or incipient.4,1

A caries lesion with a distinct breakdown of the surface integrity that can be detected using visual and gentle tactile methods is a cavitated lesion. Cavitated lesions can be confined in enamel only or extended through dentin. Once the enamel is cavitated, the bacteria start penetrating dentin causing superficial tubular invasion. In a slowly progressing cavitated caries lesion, different layers (infected and affected) of carious dentin have been reported.6 The outer carious dentin is infected, insensitive, unremineralizable, and necrotic, while the inner carious dentin is uninfected, sensitive, remineralizable, and vital. In the deeper layer (closer to the pulp) of the inner carious dentin the subtransparent and transparent layers are found. These layers are formed by crystal deposition in the dentinal tubule lumen, and physiological remineralization can occur. Odontoblast processes are present in normal dentin as well as the inner portion of carious dentin. However, the odontoblast processes disappear from the outer carious dentin (Fig. 3).6,3

FIGURE 3. Layers of carious dentin. Courtesy of Dr. M. Vargas

 

PULPAL CHANGES DUE TO CARIES
Histological studies have suggested that the early visual changes in non-cavitated enamel caries lesions lead to morphological changes in odontoblasts and the dental pulp.3,15 These cellular reactions are associated with lesion activity determined by the external environment. When the non-cavitated lesion is arrested and is inactive, pulpal changes can be resolved. When the lesion progresses causing cavitation, more extensive dentin and pulp reactions occur including: the saturation of the dentinal fluid by minerals, presence of enzyme activity on carious dentin (alkaline-phosphatase), presence of fewer and cuboidal odontoblasts (instead of tall columnar shape), damaged odontoblasts which are replaced by odontoblast-like cells, increased synthesis of collagen type I and non-collagen proteins, and the formation of reparative (from odontoblast-like cells) and reactionary dentin (from the initial odontoblasts). These pulp responses will vary depending on caries activity. In an arrested, slow progressing lesion, the caries stimulus is usually mild and produces low grade inflammation. In an active, rapidly progressing lesion, there is fast and intensive inflammation, which the pulp may not be able to defend against. This leads to the production of atubular dentin or the complete absence of tertiary dentin formation resulting in pulp necrosis.3,15

Another important factor affecting pulp response is the remaining dentinal thickness (RDT). If the RDT is greater than 2.0mm there is a reduced concentration of bacterial toxins in the pulp and the recovery of the dental pulp increases. If the RDT is less than 1.5mm there is an increase of inflammatory cells in pulp that could lead to pulpal necrosis. Murray (2003) and Smith (2002)12,15 suggested that the RDT is the most critical variable in cavity preparation, which has an impact on pulpal health. Therefore the use of incomplete caries removal technique and preserving as much RDT as possible will promote arresting the lesion and may protect pulpal health.

INCOMPLETE CARIES REMOVAL TECHNIQUES (Fig. 4)

FIGURE 4. Decision tree for conventional caries removal vs incomplete caries removal.

The extent to which the carious dentin should be removed is an important decision for the clinician before placing a restoration, especially in deep caries lesions where the vitality of the pulp can be compromised. Although some morphological studies have shown a defined boundary between the highly caries infected and the caries affected dentin, clinically this presents a subjective and difficult decision regarding the amount of dentin that should be excavated.1,2,10 Some studies have shown that is not possible to eliminate all the micro-organisms even during a conventional caries removal, as a few bacteria will remain even after all soft dentin is removed. However, studies13,14,16 that have evaluated activity and progression of lesions restored with remaining infected dentin, have shown that the majority of the lesions appeared to be arrested both clinically and radiographically and showed a decrease or absence in micro-organisms with time. Therefore, a conservative approach to caries removal is suggested when removing caries over the pulpal surface in asymptomatic deep caries lesions. Discolored, leathery dentin (identified with scrapping spoon, not poking with the explorer) can be left once the cavity floor is reasonably firm to avoid the risk of pulp exposure. Good sealing with restorative materials that enhance the dentin’s potential to remineralize are recommended. Providing a good restoration seal has been suggested to be key in arresting and preventing caries progression.1,2,10

Case selection and preliminary planning of the procedure are critical steps in achieving success using any techniques of Incomplete Caries Removal for the treatment of deep caries lesions. The diagnosis is very challenging because it is based on clinical symptoms and it is very difficult to know the real status of the pulp. For example, a tooth with pulp severally damaged may respond to pulp testing in a similar way to normal or reversible pulpitis, and may progress to necrosis without significant signs or symptoms. A detailed preliminary assessment as well as long-term pulpal/periapical evaluation (pulp test, radiographs, signs and symptoms) is necessary when doing Incomplete Caries Removal.1,7,9,10

INDIRECT PULP TREATMENT (IPT)
ITP consists in the removal of all peripheral soft dentin of the deep caries lesion, leaving a thin residual layer (0.5mm–1.0mm) of leathery affected dentin over the pulpal floor or axial wall followed by a liner and placement of the f
inal restoration with the goal of preventing pulp exposure.1,7,9 This is a paradigm shift for many practitioners and a topic that can create controversy.

Several studies compiled in current systematic reviews have demonstrated that the use of incomplete caries removal techniques significantly decreases the risk of pulp exposure in deep caries lesions compared with the traditional complete caries removal procedure, and these restorations have shown similar success.13, 14,16

It has been also shown that if there is any remaining bacteria after the caries is partially removed, the placement of a restoration providing a good seal will arrest the lesion progression by isolating the bacteria from the substrate and decreasing acid production.2,13,14,16 These findings have been observed in microbiological studies and also by using clinical assessment of the color changes of the lesions from light yellow brown to dark brown and the tissue consistency from soft wet to hard and dry assuring the arresting of the caries lesion (Table 2).2,9

TABLE 2.

TECHNIQUE STEPS FOR INDIRECT PULP TREATMENT
 
   1. No history of spontaneous pain.

2. Proper Diagnosis: EPT (Electric Pulp Test), CO2 with (+) normal results.

3. Periapical radiograph with normal periapical structures, no peri-radicular pathosis

4. Good Isolation (Preferable Rubber Dam).

5. Peripheral caries at the DEJ removed while maintaining thin residual caries dentin over pulpal and axial walls.

6. Clean DEJ at cavosurface margin to achieve a good restoration seal.

7. Finish cavity preparation (clean and smooth walls) with design depending on material selection.

8. Liner placement (either calcium hydroxide, resin modified glass ionomer (ex:Vitrebond™ 3M) or a resin-modified calcium silicate filled liner® Theracal (Bisco).

9. Final restoration providing good seal.

10. Follow-upRecall within three to six months.

Figure 5 shows a clinical sequence of Indirect Pulp Treatment.

FIGURE 5A. After proper clinical and radiographic diagnosis to confirm (+) vitality, RD isolation and proper access to the dentinal lesion.

FIGURE 5B. Peripheral caries removal maintaining thin residual affected dentin. Clean DEJ.

FIGURE 5C. Finish cavity preparation and liner application to seal the remaining residual caries affected dentin.

FIGURE 5D. Composite resin final restoration and establish follow-up.

SETEPWISE CARIES REMOVAL
Stepwise excavation is an alternative technique for removal of deep caries lesions that radiographically involve 75 percent or more of the total dentin thickness and do not already penetrate to the pulp. The purpose of the stepwise excavation approach is to change the cariogenic environment of deep caries lesions by removing only the soft wet infected dentin and then sealing the remaining demineralized dentin with an interim restoration. The goal is to arrest the active caries lesion and stimulate dentinal tubule sclerosis and the formation of reparative dentin while maintaining pulp vitality.1,2,7,9,10

FIGURE 6 Clinical sequence of Stepwise Caries Excavation (first visit)

FIGURE 6A. Diagnosis, vitality test (+), periapical radiograph showing deep recurrent caries lesions but normal periapical structures.

FIGURE 6B. RD Isolation, access, peripheral caries removal maintaining leathery affected dentin.

FIGURE 6C. Restore with interim GI restoration. (Ex: Fuji IX, Fuji Triage, Fuji II LC or a combination of Fuji Triage Liner restored with Fuji IX Extra from GC®.)

FIGURE 6D. Diagnosis, vitality test (+), periapical radiograph showing normalk periapical structures after one year.

The difference between Stepwise Caries Removal and Indirect Pulp Treatment is that the stepwise procedure is performed in two visits (usually months apart). In the first visit, the soft necrotic carious dentin is removed partially and peripherally and the tooth is sealed with an interim restoration. The time interval between the two visits allows remineralzation to occur and tertiary dentin to develop. At the second visit, the tooth is re-entered, the residual affected soft dentin is removed and
the final restoration is placed.2,7,10 Two recent systematic reviews, Rickets et al14 and Schewendicke et al,16 have compiled and analyzed the evidence suggesting that there are potential benefits to reducing the risk of pulp exposure in using either one or two steps techniques compared with complete caries removal. There is still a need of more evidence and good standardize clinical research to determine whether is necessary to re-enter.

Clinical sequence of Stepwise Caries Excavation, second visit (after one year).

FIGURE 6E. RD isolation, GI removal, dentin evaluation.

FIGURE 6F. GI Liner, Vitrebond (3M®) and finish cavity preparation.

FIGURE 6G. Placement of final restorations.

To be able to do a good case selection, it is important to consider the lesion activity and its relationship with the status of the cavitated lesion. In a closed environment lesion, the bacterial ecosystem is very active, causing extensive demineralization and the lesion is rapidly progressing. Clinically this dentin usually has a yellow light color and is very soft and wet. Trying to remove most of the soft dentin to produce a good preparation in this situation will need extensive removal of the tooth structure. During the attempt to leave only a residual thin affected dentin over the pulpal floor or axial wall, the pulp may be exposed. In these rapidly progressing lesions no protective changes in dentin occur and the odontoblast may be irreversibley affected. On the other hand, the fast removal of this very soft dentin may cause more inflammation to the pulp and it can itself induce bacterial contamination. In these clinical situations the consideration of doing the caries removal in two steps is indicated, allowing time for the lesion to arrest as well as facilitating the process of dentin sclerosis and pulp repair.3,10

Figure 7- Clinical case using Stepwise Modified Technique, first visit.

FIGURE 7A. Diagnosis, vitality test (+), periapical radiograph showing deep dentinal caries lesion on tooth #2.5 but normal periapical structures.

FIGURE 7B. RD isolation, access to caries lesion.

FIGURE 7C. Peripheral caries removal maintaining thick layer of affected dentin over pulpal and axial wall.

FIGURE 7D.  Application of Fuji Triage (GC®) liner on pulpal and axial wall (colour code for re-entry).

FIGURE 7E. Interim DO restoration sing Fuji IX Extra (GC®).

Clinical case using Stepwise Modified Technique, second visit (after six months).

FIGURE 7F. Diagnosis, vitality test (+), periapical radiograph showing normal structures.

FIGURE 7G. RD isolation, GI restoration providing a good sal (six months).

FIGURE 7H. Partial removal of GI leaving the G margin sealed with GI for open sandwich technique.

FIGURE 7I. Final DO amalgam restoration.

During the second visit a much better en
vironment and solid structure is found allowing less removal of tooth structure during final preparation and providing an optimal environment for the placement of a final restoration. If during the re-entry appointment it is found that the interim restorations are well attached and provide a good seal as in the case of using glass ionomer cements, the arresting of the lesion is expected and there is no need for their complete removal. Therefore, it is suggested to partially remove the interim restoration maintaining the internal liner material with the purpose to prevent a pulp exposure during this second step. The walls can be refined and the preparation modified depending on the material selection for the final restoration. This is a suggested modification on the stepwise technique (Fig. 7). One of the major drawbacks for the stepwise excavation technique is the lack of patient compliance. If the patient does not come back for the second appointment where final restoration is placed, the interim restoration may start leaking or breaking down, thereby compromising the treatment success.

In contrast, in an open environment lesion, the dentin has been exposed to a remineralization process in the presence of minerals from saliva and fluoride and its progression is slow. This slow process may allow protective changes in dentin and pulp to occur such as: tubule sclerosis, reduced dentinal permeability and formation of protective tertiary dentin. Clinically a dark brown dentinal color is observed and the consistency of this dentin is more leathery and dry.3,10 In these clinical scenarios, there is a more solid substrate where the arresting of the lesion has happened naturally. This allows for conservative caries removal while achieving a good solid structure for the placement of a final restoration. In these situations the caries removal in one visit is more appropriate as in the case of Indirect Pulp Treatment.

TABLE 3.

TECTHNIQUE FOR STEPWISE EXCAVATION
After a detailed evaluation and correct case selection using the previous criteria, the stepwise approach is performed in two separate appointments with an interval of six to eight months.

Figure 6 shows a clinical sequence of Stepwise Treatment.

First Appointment

1. Inform the patient about the treatment options including benefits and possible drawbacks. Allow the patient to be part of the decision.

2. Rubber dam isolation is highly recommended.

3. Access to the caries lesion, peripherical excavation should be completed by cleaning the DEJ, removing the very soft, necrotic and infected dentin and leaving the soft, discolored yellow or dark leathery dentin over the pulpal floor and axial walls. Avoid excavating close to the pulp during this first step to reduce the risk of pulp exposure.

4. Restore with a temporary glass ionomer material. For example, first use Fuji Triage GC® as a liner (color coded for re-entry) and then place Fuji IX or Fuji II LC GC® as a restorative material.

5. Schedule appointment (six to eight months) for re-entry.

Second Appointment (Re- Entry)

1. Re-evaluate history of symptoms.

2. Clinical exam to evaluate for swelling or tenderness.

3. New periapical radiograph to verify lack of pathosis.

4. Pulp vitality tests (CO2 and EPT).

5. If all of the above are normal isolate teeth, preferable with Rubber Dam.

6. Remove the sedative filling peripherally first and then be especially careful when approaching the Fuji Triage liner. The Fuji Triage does not need to be completely removed if arrested and well-sealed dentin is observed, it may be maintained over pulpal and axial wall to prevent pulp exposure.

7. Dentin assessment (peripheral) and careful removal of any remaining soft dentin.

8. Placement of glass ionomer liner over the exposed dentin (Vitrebond 3M®)

9. Restore with the material of choice for final restoration.

10. Six month recall for evaluation of vitality tests and periapical radiograph.

11. Continue with similar annual recalls.

CONCLUSION
Current scientific evidence regarding the caries disease process and the remineralization ability of affected dentin in concurrence with advances in adhesive and restorative dentistry, support Incomplete Caries Removal techniques when treating deep caries lesions. The conservative Incomplete Caries Removal techniques includes Indirect Pulp Treatment and Stepwise Caries Removal. The evidence regarding the need to re-enter is not clear yet. Proper pulpal diagnosis, caries activity status, patient preferences and compliance must be considered when choosing the best Incomplete Caries Removal technique for your patient. OH

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Acknowledgments:
Department of Operative Dentistry, The university of Iowa, Iowa City Iowa and Dr. Marcos Vargas, Department of Family Dentistry, the University of Iowa, Iowa, City Iowa for their significant contributions on the development of the protocols, research and teaching materials that are part of this article.

Dr. Hernández received her DDs from Pontificia Universidad Javeriana in Bogota, Colombia in 1988. She then obtained a certificate in Operative Dentistry and Master of Science Degree from the University of Iowa in 2001. She is currently Clinical Associate Professor in the Department of Family Dentistry at the University of Iowa where she is involved in undergraduate and graduate teaching. She maintains an intramural practice limited to Operative Dentistry, with an emphasis on conservative and aesthetic dentistry and is a Diplomate of the American Board of Operative Dentistry.

Dr. Kolker received her DDS from the University of Iowa in 1996, a certificate in Operative Dentistry and PhD in Oral Science with emphasis in Oral Epidemiology and Health Sciences Research from the University of Iowa in 2003. She is currently Associate Professor in the Department of Operative Dentistry, and has certification from the America Board of Operative Dentistry. In addition to her undergraduate and graduate teaching commitments, she maintains an intramural practice limited to Operative Dentistry at the same institution.

Oral Health welcomes this original article.

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