Current Concepts on Caries Removal

Abstract

This chapter offers a comprehensive introduction of dental caries management, with a central emphasis on selective caries removal as a cornerstone of minimally invasive dentistry. Rooted in evidence-based dentistry and a grasp of carious dentin progression, the shift from conventional dental paradigms is explored. Various challenges and debates surrounding selective caries removal techniques are discussed, encompassing non-selective, selective, and stepwise methods. Histological and clinical identification methods for carious dentin are explored till the date, including color, hardness, and texture variations. It is important to pay attention to the connection between tactile examinations and the International Caries Detection and Assessment System (ICDAS) index. The relationship between clinical staging and histological aspects of carious dentin is established. Diverse techniques like hand excavation, polymer-based burs, chemomechanical agents, air abrasion, lasers, and tungsten carbide burs are evaluated, highlighting benefits, limitations, and comparisons. The chapter underscores selective caries removal’s role in minimally invasive dentistry, focusing on tissue preservation and its impact on pulp vitality, restoration durability, and patient well-being. This comprehensive presentation covers clinical, histological, and technological facets of caries management in a minimally invasive context.

1. Introduction

Dental caries is the most common dental disease caused by an imbalance between healthy microorganisms and cariogenic species. This ecological shift is developed and maintained by frequent consumption of fermentable dietary carbohydrates. This imbalance might disrupt the demineralization and compensation cycles, resulting in net mineral loss of the tooth structure, which leads to dental cavities [1].

Dental caries cannot be completely cured by only eliminating the causative microorganisms. Instead, it can also be treated by behavioral management. It includes reduction in consumption of fermentable dietary carbohydrates and frequent disruption of bacterial biofilm from the tooth surface. Bacterial penetration cannot be prevented if such management is not being practiced by the patients which can result in irreversible inflammatory damage to the pulp [2].

Contemporary dental practice is based on evidence-based dentistry, a clear understanding of carious dentin progress, and an awareness of potential of remineralizable dentin. Therefore, a shift from G. V. Black’s concept of ‘extension for prevention’ to minimally invasive dentistry is being employed in the clinical practice [3]. Despite the development of adhesive dentistry and spreading awareness of environmental alarms over mercury levels, the acceptance towards minimally invasive techniques for caries removal is debatable. Therefore, Selective Caries Removal in Permanent Teeth (SCRiPT) Trial is being conducted to remove the barrier of confusion on this subject [4].

This chapter emphasizes the importance of selective caries removal approach, highlighting its advantages in preserving tooth structure, pulp vitality, and longevity. Different methods of caries removal, including non-selective, selective, and stepwise techniques, are discussed, with selective removal offering favorable outcomes. Histological analysis assists in distinguishing remineralizable and healthy dentin layers that provide guidance for an accurate excavation. The use of various caries removal techniques like polymer-based burs, chemomechanical agents, air abrasion, lasers, and tungsten carbide burs are explored.

2. Concepts of caries removal

According to a consensus assessment published by Schwendicke et al. numerous approaches of caries eradication have been explained in the literature and can be classified into three types [5]:

• Non-selective caries removal: The softened dentine in the cavity is removed until hard dentin is reached throughout the cavity, and the tooth is permanently restored.

• Selective caries removal: Caries removal differs depending on the location of the cavity. When all caries has been eliminated, the cavity will have hard dentin around its outer perimeter and soft dentin in the middle of the cavity, which can be readily excavated with a spoon excavator without exposing the pulp. Following that, a permanent restoration is placed at the same appointment.

• Stepwise caries removal: This procedure consists of two different sessions scheduled 6–12 months apart. The initial session involves selective caries removal and the temporary restoration of the cavity. In the subsequent visit, the caries is completely removed, and the tooth is restored with a permanent restoration.

Although selective caries removal in a single visit presents more favorable outcome than step-wise selective caries removal approach, this has been remained as a controversy among the dental practitioners [6]. This can be due to inability to compare the long-term outcome between two techniques. One explanation for the preference for one-step selective caries removal is the avoidance of iatrogenic damage to the tooth structure while re-entering the cavity in order to replace the tooth with a permanent restoration, which would have been unavoidable with stepwise caries removal [7].

The primary goal of removing carious lesion is to preserve the pulp vitality in order to increase the tooth longevity in the mouth [8].

Recent recommendation on caries removal by consensus statement by Schwendicke et al. [9]:

• Selective caries removal to firm dentin is advisable for the teeth with shallow or moderate cavity lesion.

• Selective removal to soft dentin is strongly advised for the primary teeth with radiographic evidence of deeper lesion (into pulpal third of the dentin); whereas for permanent teeth with the same criteria, either selective (to soft dentin) or stepwise removal should be performed.

3. What makes selective caries removal the cornerstone of minimally invasive dentistry?

Minimally invasive dentistry focuses on preservation of soft and hard dental tissue when managing carious lesions. This technique not only encompasses removal of carious lesion to firm dentin, but it also includes conservative approach including behavioral modification. This approach comprises of diet modification, disruption of biofilm by chemical or mechanical ways, and cutting of the nutrient supply of cariogenic biofilm by sealing it hermitically [10]. When this principle is applied to the operative dentistry, it can be inferred that selective caries excavation followed by placement of a restoration with hermetic peripheral seal will preserve the dental tissue even without having complete eradication of bacteria from carious dentin.

Traditional non-selective caries removal technique can result in dentin-pulp complex damage, compromised mechanical integrity of tooth structure, and in some cases, it can also lead to irreversible damage primary odontoblasts. Conversely, contemporary selective caries removal can preserve the remineralizable dentinal structure and primary odontoblast that will help in forming tertiary or reactionary dentin [10]. By dropping the burden of cariogenic bacteria, it reduces the number of bacteria approaching pulpal tissue via dentinal tubules. By and large, it boosts the tooth life and decreases management cost and burden associated with teeth overtime [9].

It should be noted that even though the adhesion of composite resin to remineralizable dentin is weaker, it is clinically nonsignificant and cannot hamper the overall outcome of tooth restoration. This can be explained by formation of hermetic seal of resin-based adhesive to peripheral sound enamel or dentin in aptly prepared cavity [11].

The primary challenge with the selective caries removal procedure is the ability to distinguish carious dentin clinically. Sometimes, it becomes difficult to decide the extent of removal, which may impact overall long-term outcome of the restoration.

4. How can we clinically distinguish between different stages of dental caries?

Carious dentin can be identified clinically based on the color, hardness, texture and results of caries detecting dyes. Following part describes the different techniques of caries identification, and their clinical comparison based on the literature.

Among all the techniques, visual and tactile examination are the most commonly employed techniques. The primary dentinal carious lesion can be categorized into four different types when it is examined under natural daylight or standard dental light. These four colors are yellow, light brown, dark brown, and black. Whereas, Hellyer et al. categorized hardness of dentinal carious lesion as hard, medium (leathery), and soft [12].

The hardness of non-carious dentin ranges between 51 and 65 KHN. It drops down to 6.7 KHN in presence of active lesion, whereas hardness of arrested lesion reduces to 39.2 KHN. In other words, hardness of remineralizable and healthy dentin is 30.7 and 60 KHN, respectively [13].

Clinically, the texture or hardness can be evaluated using a new Ash No. 6 prob. The hard lesions are similar to the intact dentin. When moderate pressure is employed, a fresh Ash No. 6 probe can easily penetrate medium or leathery lesions and encounters resistance during withdrawal. Although soft lesions demonstrate smooth penetration of a fresh Ash No. 6 prob. with no resistance upon its withdrawal [14, 15].

The active and inactive carious lesions show different characteristics in terms of color and texture. Table 1 and Figure 1 show the difference in signs of staging of carious lesions [16]. The visual and tactile examinations show high specificity but due to subjective nature of tests, they show less reproducibility, and low sensitivity [17].

		Initial and moderate stage	Extensive Stage
Active lesion	color	Whitish/yellowish opaque area
	Gloss	Loss of luster
	Hardness and texture	Rough upon probing	Soft and leathery upon probing
	Plaque	Presence of thick plaque
Arrested lesion	color	Whitish, brownish or black area
	Gloss	Shiny
	Hardness and texture	Hard and smooth upon probing
	Plaque	Absence of plaque

Table 1.

Outlines clinically identifiable aspects of active and inactive lesions at various stages of cavity lesion progression.

Figure 1.

Three distinct case situations that demonstrate active and inactive lesions depending on certain characteristics. The images on the left and center show active lesions, whereas the image on the right shows a tooth with both types of lesions.

According to the recent systemically reviewed evidences, when we compare the visual and tactile examination, the later produces results with more reliability and specificity. Therefore, it is desirable to opt for the tactile examination over the visual inspection when performing routine inspections to identify caries. It could be stated that texture variations warrant a higher index score. This evidence is in accordance to the current recommended dental caries scoring index, the International and Caries Detection Assessment System (ICDAS) [18].

5. How is the clinical categorization of stages connected to the histological characteristics of dentinal caries?

In the literature, correlation between different color, hardness, and texture of the carious dentin to histological staging of the carious process has been described. The clinical changes of the carious lesion can be resulted from the acidic attack of the cariogenic microorganisms. This acidic dissolution can change the color, texture, and the moisture element of dentinal tissue. Based on the color and texture of the dentinal tissue, the histological staging can be discriminated [19].

To identify the clinical carious examination technique with high sensitivity and specificity, it is advisable to compare the available methods in relation to the microbial activities in form of CFU. This will enable us to identify an accurate consistent method to evaluate caries quantitatively and qualitatively [18].

There are a few research that investigated the relationship between bacterial CFU and the color or hardness of carious dentin in the literature. Orhan et al. found no significant difference in bacteria CFU and color of carious dentin, although harder lesions had considerably fewer bacteria CFU than softer dentin [20]. Comparable outcomes were noted in the Lynch et al. investigation. They discovered that soft and leathery lesions, regardless of color, had greater CFU. There was no association between the color of the lesion and the overall number of bacterial species [21].

6. Which portion of the dentinal caries needs to be eliminated during the selective caries removal?

The precise point at which caries excavation ends clinically is ambiguous and remains subjective. As a particular dentist may be influenced by their own personal experiences, diagnostic tests such as surface hardness, dentin color, or caries detector dyes, are not completely reliable. As a result, a histological analysis is the optimal tool for evaluating carious changes in the dentin and obtaining consistent results to evaluate excavation procedures.

It has been observed that the carious dentin can be divided into distinctive layers using histological staining such as outer dentin containing non-remineralizable necrotic collagen matrix and cariogenic bacteria, and inner layer composed of non-altered collagen fibers. The bacterial count is negligible in the inner layer, and the possibility of remineralization is higher [22].

Mallory-Azan staining allow to differentiate histological staging of carious dentin. Blue staining is identified as un-denatured collagen containing dentin; while altered collagen matrix will catch red staining. Thus, clinically it enables accurate identification of remineralizable or healthy dentin and demineralized dentin, respectively [23].

As previously mentioned in the chapter, hardness is a better ____ to evaluate the severity of carious lesion and plays an important role in determining treatment modalities as well. For instance, softer lesion needs the immediate intrusive clinical modality (e.g., debridement and restoration) as it harbors more cariogenic microorganisms as compare to the harder lesions which does not contain any cariogenic microorganisms. Therefore, harder shallow lesion does not demand any clinical interventions [14].

Selective carious removal to firm dentin is advisable for moderately deep active areas. This procedure allows leathery dentin to left behind at the center of cavity towards pulpal area, whereas caries should be removed until firm hard dentin is reached towards the peripheral dentin and marginal walls of the cavity. Clinical terminology refers to leathery dentine as having a small “tackiness” and not deforming when an object is placed against it. Hard dentine requires pushing pressure to engage, and a scratchy sound known as “cri dentinaire” can be heard [3].

7. What is the recommended method for removing dental caries?

The traditional approach of treating dental caries entails removing the remineralizable tooth tissue and replacing it with a restorative substance. Using a dental air rotor drill is currently the most popular way to remove cavities. Despite its extensive use, potential side effects include dentinal sensitivity, intense noises while using, thermal stimulation of the pulpal tissue, bone-conducted vibration, and pressure inside the tooth itself. Whereas hand excavation allows the operator to have tactile sensation while removing carious tissue. Rotary instruments greatly limit tactile feedback during selective excavation and increase the possibility of iatrogenic removal of extra tooth structure at this critical region [24]. Other techniques investigated include air abrasion, chemical agents, polymer burs, and lasers for the eradication of caries.

7.1 Tungsten carbide bur

Utilizing burs on a high-speed handpiece to reach the carious area and a low-speed handpiece to eliminate carious dentine are the most common approaches for removing caries and preparing cavities. Steel bur excavation and traditional rotary practices result in over-preparation by removing greatest amount of sound tissue possible while potentially overextending the cavity and destroying healthy tissue. Additionally, it generates pressure and heat on the pulp, vibration, noise, causes pain stimulus, and requires the need for local anesthetic. This approach leaves aversion and pain anxiety in many individuals, particularly children [25].

Studies have been conducted to compare the traditional approach with other techniques. Divya et al. investigated the time required to remove the caries and found that the traditional burs (151 sec) remove caries faster as compared to Polymer bur (344.80 sec), Papacarie (359.60 sec), and Carisolv (461.60 sec). The number of bacterial colonies after caries excavation differed considerably among the four agents utilized, with Polymer bur samples containing the highest and Stainless Steel Bur representing only 10% of the specimens [26]. Whereas Somani et al. found no significant difference in the presence of microorganisms following caries eradication between traditional burs and smart burs [27].

7.2 Polymer based bur

The fundamental objective behind developing a polymer-based bur was to create a device with a hardness of 40–50 KHN, which falls between the hardness of healthy and cariously infected dentin. As a result, they selectively remove demineralized dentin and whenever the cutting edges come into touch with either healthy or remineralizable dentin, they become blunted. Table 2 described characteristics and specifications of available the polymer based burs and traditional carbide bur.

Bur type	Specifications	Hardness	Recommended speed	Specifications
Conventional carbide bur	Tungsten carbide	1600 KHN	1250 rpm–5000 rpm	—
SmartP (2003)	Polyether-ketonne-ketone (PEKK)	50 KHN	500 rpm–800 rpm	First polymer bur
SmartBur II	Glass-bead reinforced blades	50 KHN	5000 rpm–10,000 rpm	Available in three different sizes (#4, #6, and #8); Remove decay in a circular motion, starts from the center and proceed to the periphery.; Reduce the contact with axial walls
PolyBur P1	Reinforced polymer	40–50 KHN	2000 rpm - 8000 rpm	Recommended for small cavities, and area close to the pulp; Delicate shaft design, more contact pressure tends to bend the shaft; No rounding of cutting edges; Contraindicated for dark demineralized dentin, hard mineralizable dentin, and caries along the enamel-dentin junction

Table 2.

Describes the available polymer-based burs and conventional carbide burs along with their properties and specifications.

There was no significant difference in the outcome was observed by Usha and Ranjani when different types of polymer bur were compared [28]. Furthermore, Lohmann in et al. concluded that PolyBur P1 was only able to remove carious dentin from 33.9% of the carious teeth specimen. Additionally, the remaining denatured collagen layer was significantly thicker (more than 1 mm) than in the conventional carbide bur group [13].

7.3 Chemomechanical caries removal agents (CMCR)

Since 1975, this modality has been utilized to soften diseased dentin before carefully removing it with hand devices. Because it only affects demineralized dentin, the goal of conserving damaged dentin can be achieved [29]. They are classified into two types: sodium hypochlorite (NaOCl)-based agents (e.g. GK-101, GK-101e, Carisolv) and enzyme-based agents (Papacarie, Biosolv, Carie-Care, Brix3000).

By subsequently destroying the irreparably weakened collagen fibers in demineralized dentin, CMCR chemicals enable removal while preserving the remaining intact impacted dentin [30]. Chlorination, which entails hydrolysis of linkages between tropocollagen components and/or breaking of polypeptide chains in the triple helix, is the key technique used to do this [31]. However, little is yet known about the chemistry of amino acid chlorination and its effects. In contrast to enzyme-based CMCR agents, which rely on an additional mechanism, NaOCl-based CMCR products use the chlorination process as their main mode of action [32].

The fundamental mode of action in enzyme-based CMCR agents is papain, which is considered an effective chemical debriding agent with antibacterial and anti-inflammatory properties. It is a cysteine protease developed from the fruits and latex of green papaya (Carica papaya. The papain is believed to work by promoting the decomposition of partially deteriorated collagen strands and assisting in the deconstruction and removal of fibrin mantle created by carious process and causing no harm to unaffected collagen filaments. As a result, the demineralized dentin softens, making it possible to remove it with no anesthesia and using non-cutting instruments. An absence of −1-antitrypsin in demineralized dentin rationalizes such unique relationship [33].

A risk to dental practitioners’ wellbeing exists during the COVID-19 pandemic because many dental treatments generate aerosols that could be associated with the transmission of serious respiratory illnesses. Consequently, dental and health professionals cautioned against overusing aerosol-generating therapies during the outbreak. Given the aforementioned suggestions, utilizing CMCR products that need little to no aerosol-generating techniques instead of surgery in caries prevention may be more proficient for people of all ages, especially those who suffer from anxiety or have special needs [34].

The CMCR approach is becoming more commonly recognized and comfortable for patients, as it reduces pain, anxiety, and the need for a local anesthetic. Hosein and Hasan reported the procedural time for CMCR as 12.97 min in 27 cases, whereas convention steel bur took 7.4 min for caries removal [35]. The CMCR approach could be taken into account as a possible replacement therapy modality in the field of dental care in the future, despite its extended length and greater expense.

7.4 Air abrasion

Air abrasion, utilized as a method for removing caries, involves the non-rotary abrading of a surface by directing a stream of high-speed abrasive particles produced from compressed air. Its mechanism involves cutting at the tip and shapes shallow, saucer-like cavities with vague boundaries. In contrast to rotary drilling, air abrasion’s use of extremely small particles in contact with the tooth prevents the generation of vibrational forces, resulting in enhanced comfort and reduced stress on the tooth structure. This is especially beneficial in the dentine area near the pulp, where delicate caries elimination using the slow-speed handpiece is often uncomfortable due to the resulting vibrations. In this context, employing air abrasion with a slow cutting action becomes a practical choice. The forceful expulsion of particles through the air stream also reduces the effort required by the operator [36].

Aluminum oxide abrasives are commonly used for air abrasion in dentistry, but concerns exist regarding their potential to damage healthy tooth structure and controversial safety issues [37]. An alternative option is bioactive glass (Sylc), initially designed for bone replacement. Sylc, a bioactive glass abrasive, is available for tooth polishing and has shown potential for selective cutting. However, its cutting time is significantly longer than alumina, making it less practical [38]. Neither alumina nor Sylc contains fluoride, despite evidence of fluoride-assisted remineralization in dentine.

Farooq et al. have explored fluoride-incorporated bioactive glass, discovering that reducing sodium content increases its hardness, which could be advantageous for creating bioactive glass air abrasives. Additionally, they demonstrated apatite formation in bioactive glass in Tris buffer solution, with potential implications for its abrasiveness compared to alumina in dentine air abrasion [39]. Tan et al. invented a new customized fluoridated bioactive glass particles (Na0SR) and compared its efficacy against standard aluminum oxide particles. It was concluded that Na0SR can be considered a viable abrasive alternative for alumina in air abrasion cutting because it performs similarly and has the added benefit of potentially facilitating remineralization and hydroxyfluorapatite production [40].

7.5 Lasers

The initial dental lasers (ruby, Nd:YAG, holmium-doped Ho:YAG, CO₂ lasers) led to elevated pulp temperature, microcracks, and carbonization. In the mid-1990s, the safety and effectiveness of erbium-doped Er:YAG laser were explored. Proper settings and water cooling minimized thermal damage [41]. Effective caries removal requires a laser wavelength that interacts significantly with mineral, water, or both, unless ultrashort pulses cause plasma-mediated ablation.

Er:YAG and erbium: yttrium-scandium-gallium-garnet Er:YSGG lasers (λ = 2.940 μm and λ = 2.790 μm) are highly absorbed by water and Er:YSGG is also absorbed by hydroxyl ions in tooth mineral, heating and exploding tissue from the surface. For effective caries removal, the laser pulse duration should approximately match the tissue’s “thermal relaxation time,” avoiding excessively short or long pulse durations that result in excessive or unnecessary energy distribution within the tissue [42]. The Food and Drug Administration (FDA) granted approval for its use in these applications in May 1997. This laser functions in a pulsed manner and incorporates a water spray in its handpiece to prevent tissue dryness and the accumulation of heat. This ensures efficient absorption of energy without causing tissue carbonization or significant heat production [43].

Montedori et al. conducted a systematic review and found no studies reported presence of residual caries after using laser to remove primary caries [44]. In a study conducted by Lui et al.; patients reported limited incidence of pain in Er:YAG laser group than drill group [45].

The carbon dioxide laser lasers can function within the wavelength range of 9000 to 11,000 nm. The most prevalent variant, working at 10,600 nm, is commonly utilized for dental procedures. This laser enables surgical operations without bleeding and minimizes discomfort following soft tissue dental surgeries. Investigations demonstrated that a 9300 nm carbon dioxide laser can prompt both chemical and structural alterations in hard dental tissues [46]. Moreover, it was observed that this laser efficiently eradicates enamel and dentine. Due to its capacity to prevent enamel cavities and eliminate caries lesions, the 9300 nm carbon dioxide laser is gaining increased attention in the field of dentistry for managing dental caries [47].

For laser treatment, the increase in pulp chamber temperature should not be greater than 5.5°C. Otherwise, severe heat buildup could harm the dentine-pulp complex by disrupting odontoblasts, destroying them, or possibly causing pulp necrosis. According to a series of studies, the thermal effect of 9300 nm carbon dioxide laser irradiation on pulp is minimal because the laser is absorbed extremely close to the surface of the hard tissues and shortly converted into heat [48]. Assa et al. also reported that the usage of water aerosol spray with laser would significantly decreases the heat accumulation.

Exposure of enamel to a 9300 nm carbon dioxide laser leads to decomposition of its constituents. This process can cause enamel to melt and fuse due to the temporary elevation in temperature, which exceeds a certain threshold. The laser modifies the enamel’s microstructure and surface appearance after it cools down. Additionally, the laser induces chemical transformations in dental hard tissues, including a reduction in carbonate levels. This change transforms carbonated apatite crystals into purer forms, rendering enamel less susceptible to acid erosion. Moreover, the calcium and phosphorus content in both enamel and dentine increases following laser treatment. The dentine subjected to irradiation displays three distinct intrinsic phosphate bands under Fourier transform infrared microscopy, indicating heightened crystallinity. A study highlights that the 9300 nm carbon dioxide laser raises the calcium-phosphorus ratio in healthy enamel and dentine, thus reducing their solubility. Furthermore, the results imply that the laser treatment eliminates organic components from decayed enamel and dentine [49].

8. What factors contribute to a favorable prognosis for the selective caries removal method?

A growing database of studies has also demonstrated that the selective caries excavation technique is prognostically effective. This procedure avoids injuring the dentine-pulp complex and removing a significant quantity of tooth tissue, preserving the pulp’s vitality and improving the tooth’s long-term prognosis.

In the management of deep carious lesions, it’s essential to thoroughly assess the final restoration to prevent potential failures in the tooth-restorative complex. Dentists should carefully inspect the restoration for surface irregularities and proper marginal integrity to avoid creating areas where plaque can accumulate. Leaving some carious tissue under a restoration after selective excavation could lead to legal issues. Patients need to be informed about the rationale behind this approach and the need for regular check-ups to ensure the tooth’s pulp health over time Nevertheless, for long-term stability, cuspal coverage would be necessary to counteract the impact of repeated stress on the restoration for some cases.

9. Conclusion

In conclusion, dental caries, a prevalent condition resulting from an imbalance in oral microorganisms triggered by fermentable carbohydrates, causes mineral loss in tooth structures. Traditional treatment approaches, involving complete bacterial eradication, have shifted towards minimally invasive strategies. Selective caries removal, a pivotal aspect of minimally invasive dentistry, preserves remineralizable dentin, vital odontoblasts, and supports the formation of reactionary dentin. Techniques like polymer-based burs, chemomechanical agents, air abrasion, and lasers offer less discomfort, reduced bacterial count, and more conservative excavation. Clinical staging, utilizing color, hardness, and texture evaluations, assists in precise diagnosis and treatment planning. While challenges persist, evidence supports the effectiveness of selective caries removal, enhancing tooth longevity and patient comfort.

Conflict of interest

The authors declare no conflict of interest.