Dental caries

Etiology: The Causes of Dental Caries

Dental caries is primarily caused by the demineralizing action of organic acids on tooth enamel. These acids are produced by specific cariogenic (caries-causing) bacteria within dental plaque when they metabolize fermentable carbohydrates (sugars and starches) from the diet. For dental caries to occur and progress, three primary conditions must be met over a period of time:

• Presence of Cariogenic Microflora: Specific bacteria, notably *Streptococcus mutans* and *Lactobacillus* species, are key players in initiating and progressing carious lesions. These bacteria adhere to tooth surfaces forming dental plaque (a biofilm).
• Dietary Substrate (Easily Digestible Carbohydrates): Frequent intake and retention of fermentable carbohydrates (sugars like sucrose, glucose, fructose, and cooked starches) on the tooth enamel surface provide the fuel for cariogenic bacteria to produce acids.
• Susceptible Host and Tooth Surface (Reduced Caries Resistance): Factors that reduce the tooth's resistance to cariogenic challenges (caries resistance) contribute to decay. These include:
  • Poor enamel quality or developmental defects.
  • Reduced salivary flow (xerostomia) or altered saliva composition (e.g., lower buffering capacity).
  • Inadequate fluoride exposure.
  • Poor oral hygiene leading to plaque accumulation.
  • Tooth morphology (e.g., deep pits and fissures that trap plaque).
  • Host immune factors and general health status.
• Time: Caries is a chronic process; demineralization occurs over time with repeated acid attacks.

Classification of Dental Caries

Dental caries can be classified in several ways, including by anatomical location (Black's classification) and by the depth or stage of the lesion (topographic classification).

Black's Classification of Carious Cavities

Developed by G.V. Black, this system classifies carious lesions based on their location on the tooth surface, which often dictates the design of cavity preparations for restorations:

1. Class I: Cavities located in pits and fissures. These occur on:
   • The occlusal (chewing) surfaces of molars and premolars.
   • The occlusal two-thirds of the buccal (cheek-side) and lingual (tongue-side) surfaces of molars.
   • The lingual or palatal surfaces of maxillary (upper) incisors (often in the cingulum pit).
2. Class II: Cavities on the proximal (contact) surfaces of molars and premolars (i.e., the surfaces between adjacent posterior teeth).
3. Class III: Cavities on the proximal (contact) surfaces of incisors and canines that do *not* involve the incisal angle (biting edge).
4. Class IV: Cavities on the proximal (contact) surfaces of incisors and canines that *do* involve and require restoration of the incisal angle or edge.
5. Class V: Cavities in the gingival (cervical) third of the facial (buccal/labial) or lingual/palatal surfaces of any tooth (i.e., near the gumline).
6. Class VI (added later, not by Black): Cavities on the incisal edges of anterior teeth or on the cusp tips of posterior teeth (often due to attrition or erosion combined with caries).

Topographic Classification (Stages of Caries)

This classification describes the depth of the carious lesion:

• Initial Caries (Caries in the Spot Stage / White Spot Lesion): Characterized by focal demineralization of the enamel without the formation of a macroscopic cavity. The enamel surface may appear chalky white or opaque when dried. This stage is potentially reversible with remineralization therapies.
• Superficial Caries (Enamel Caries): The carious lesion has progressed to form a cavity, but it is confined within the enamel layer.
• Medium Caries (Moderate Caries / Dentin Caries): The carious cavity extends through the enamel and involves the superficial or middle layers of the underlying dentin.
• Deep Caries: The carious cavity has progressed significantly into the dentin and is close to the dental pulp (peri-pulpal dentin). There is a risk of pulpal involvement (pulpitis).

Diagnosis of Dental Caries

Diagnosing dental caries involves a combination of methods:

1. Visual Examination: Direct observation of tooth surfaces under good illumination and magnification. Dentists look for changes in color (white spots, brown/black discoloration), translucency, and surface texture (roughness, cavitation).
2. Tactile Examination: Using a dental explorer (probe) to gently feel for softness, cavitation, or "stickiness" in pits, fissures, and on smooth surfaces. (Note: overly aggressive probing of incipient lesions is now discouraged as it can damage the enamel).
3. Radiographic Examination (X-rays): Bitewing radiographs are essential for detecting interproximal (between teeth) caries that are not visible clinically. Periapical radiographs can show caries extending into dentin and assess periapical status.
4. Transillumination: Shining a bright light through anterior teeth can help visualize interproximal caries as dark shadows.
5. Laser Fluorescence Devices (e.g., DIAGNOdent): These devices measure laser fluorescence within tooth structure to aid in detecting early carious lesions, particularly in pits and fissures.
6. Patient Symptoms: Sensitivity to sweets, cold, or hot stimuli can indicate caries, especially if it has reached the dentin. Pain may indicate pulp involvement.

Early detection is key for minimally invasive treatment and better prognosis.

Treatment of Dental Caries: Principles and Stages

The treatment of dental caries depends on the stage and extent of the lesion. The primary goal is to arrest the carious process, remove infected and demineralized tooth structure, and restore the tooth's form, function, and aesthetics.

Treatment generally consists of the following stages for cavitated lesions:

• Anesthesia (if necessary).
• Isolation of the tooth (e.g., with a rubber dam).
• Preparation (dissection) of the carious tooth cavity.
• Placement of liners or bases (if indicated).
• Tooth filling (restoration).
• Finishing and polishing the restoration.

For initial caries (white spot lesions), non-invasive remineralization therapies (e.g., fluoride application, CPP-ACP pastes, resin infiltration) may be employed instead of cavity preparation and filling.

Cavity Preparation (Dissection) of a Carious Tooth Cavity

Cavity preparation involves several steps based on G.V. Black's principles, adapted by modern concepts of minimally invasive dentistry:

1. Opening the Carious Cavity (Gaining Access): This stage involves removing any overhanging and undermined enamel edges to gain adequate access and visibility to the carious lesion. The purpose is to provide clear access for further manipulations and a good view of the extent of the decay.
2. Outline Form (Expansion of the Carious Cavity / Prophylactic Expansion): This step defines the external outline of the cavity preparation. Historically, "extension for prevention" involved extending the cavity margins into self-cleansing areas to prevent recurrence. Modern approaches are more conservative, aiming to remove only carious tissue and place margins on sound tooth structure, relying more on adhesive restorative materials and preventive measures.
3. Removal of Carious Dentin (Necrectomy / Necrotomy / "Caries Removal"): This crucial stage involves the complete excavation of all softened, infected, and demineralized dentin from the carious cavity. This is typically done with burs at low speed or with hand instruments (excavators). If this operation is performed poorly and infected dentin is left behind, recurrent caries ("continuing" or "secondary" caries) will likely develop under or next to the filling. If infected dentin is not completely removed from the bottom of a deep carious cavity, pulpitis may develop.
4. Resistance and Retention Form (Formation of the Cavity): The goal of this stage is to shape the carious cavity to provide the restored tooth with sufficient stability and resistance to functional stresses (chewing forces) and to ensure strong retention of the filling material. This involves creating appropriate wall angulations, flat floors, and sometimes retentive features like grooves or undercuts (less critical with modern adhesive materials). At this stage, the final internal shape of the cavity is created.
5. Finishing Enamel Walls and Margins: Smoothing the cavity walls and cavosurface margins to ensure a good seal with the restorative material.
6. Cleaning the Cavity (Toilet of the Cavity): Thoroughly rinsing and drying the prepared cavity to remove debris before placing the restoration.

Tooth Filling (Restoration)

The purpose of filling a tooth affected by dental caries is to restore its anatomical shape, aesthetic appearance, and normal function (chewing, speech), and to prevent the further development or recurrence of caries.

The requirements for an "ideal" filling material for dental caries were formulated by W.D. Miller at the end of the 19th century and, with some modifications, remain relevant today. An ideal filling (restorative) material for dental caries should:

• Be chemically stable and resistant (does not dissolve or degrade under the influence of saliva, liquid food, oral fluids, or dentinal fluid).
• Be mechanically strong and durable, as it must withstand significant chewing loads (which can be 30-70 kg or more on posterior teeth).
• Be resistant to abrasion and wear.
• Fit snugly against the cavity walls, ensuring good marginal adaptation (minimizing microleakage). This may involve micromechanical retention or chemical bonding (adhesion) of the material to tooth tissues and other intermediate materials (liners, bases).
• Maintain its shape and volume over a long period, exhibiting minimal shrinkage during and after setting to ensure long-term spatial stability of the filling.
• Be minimally sensitive to moisture during the filling and curing (setting) process.
• Be biocompatible: harmless to the dental pulp, surrounding tooth tissues, oral mucous membranes, and the body as a whole.
• Match the natural appearance (color, translucency) of teeth for aesthetic restorations.
• Have low thermal conductivity to prevent thermal irritation of the pulp from hot or cold stimuli.
• Have a coefficient of thermal expansion similar to that of natural tooth tissues to minimize stress at the tooth-restoration interface during temperature changes.
• Possess good handling properties: sufficient plasticity for easy insertion into the cavity, ability to be shaped and contoured, not sticking excessively to dental instruments, etc.
• Be radiopaque (visible on X-rays) to allow for detection of recurrent caries underneath or around the restoration and to assess marginal integrity.
• Ideally, have an anti-caries action (e.g., by releasing fluoride).
• Have a long shelf life and not require overly specialized or complex storage and transportation conditions.

Although modern dental materials have allowed dentists to come very close to solving many of these challenges, an ideal material that perfectly meets all these requirements for all situations has not yet been created. Therefore, dentists are often forced to combine various materials or use a layering technique, applying 2-3, or sometimes even 4, different materials into the prepared cavity. The choice of materials depends on the nature of the cavity (depth, location, size), the specific properties (both negative and positive) of the materials being used, and the individual characteristics of the caries process and oral environment in that particular patient.

Dental Materials Used in Caries Management

Modern filling materials for dental caries are broadly divided into several groups based on their application:

• Materials for dressings and temporary tooth fillings.
• Materials for therapeutic (medicated) liners (pads).
• Materials for insulating liners or bases (pads).
• Materials for permanent tooth fillings (restorations).
• Materials for filling (obturating) root canals of the tooth (endodontic materials).

Dressings and Temporary Tooth Fillings

These materials are used for short-term applications. Dressings are typically placed for a few days (1-14 days), often to carry medication or pending further treatment. Temporary fillings are designed to last for several months (usually up to six months), for example, during multi-visit endodontic treatment or as an interim restoration.

The main requirements for materials in this group are:

• Ensure a tight marginal seal of the tooth cavity to prevent leakage.
• Have sufficient compressive strength for the intended duration.
• Be chemically indifferent to the pulp, surrounding tooth tissues, and any medicinal substances placed underneath.
• Be easy to insert into and remove from the cavity without damaging tooth structure.
• Not dissolve in oral fluid and saliva.
• Not contain components that interfere with the adhesion or setting processes of subsequent permanent filling materials.

Common materials used for dressings include: artificial dentin (zinc oxide-phosphate cement mixed to a putty consistency), dentin paste (zinc oxide-eugenol based), zinc oxide-eugenol (ZOE) cements, Cavit™, and historically, gutta-percha.

For temporary fillings, materials like reinforced ZOE cements, zinc-phosphate cements, sometimes polycarboxylate cements, or glass ionomer cements (GICs) are most often used.

Insulating Liners (Pads) or Bases

Most modern permanent filling materials, particularly metallic ones like amalgam (though less used now) or even some composites, can have an adverse effect on the dental pulp, either through chemical irritation, thermal conductivity, or galvanic effects. Therefore, when a cavity is moderately deep or deep (extending significantly into dentin), a liner or base is often placed between the permanent filling and the floor of the carious cavity. This insulating layer (gasket or lining) performs several functions:

• Provides long-term protection of the dentin and pulp from chemical, thermal, and electrical (galvanic) irritation.
• Helps prevent postoperative hypersensitivity after cavity preparation and filling.
• Can withstand mechanical stresses associated with the condensation of some filling materials and help redistribute chewing pressure.
• May improve the retention of some permanent fillings by creating a smoother, more ideal cavity floor.
• Should be easy to insert into the cavity, harden quickly, and ideally form a stronger bond with the tooth tissues than with the permanent filling material, so that if the permanent filling shrinks, the liner does not detach from the cavity floor.
• Ideally, should have an anti-caries effect or a remineralizing effect on the underlying dentin (some GICs and calcium hydroxide liners).
• Must not have a toxic effect on the pulp.
• Should not adversely affect the properties (e.g., setting, color) of the permanent restorative material placed over it.
• The liner or base should not be destroyed or dissolved by gingival fluid or dentinal fluid that might seep in.

Common materials for insulating liners/bases include: calcium hydroxide cements, glass ionomer cements (GIC), resin-modified glass ionomer cements (RMGIC), zinc phosphate cement, and polycarboxylate cement.

Therapeutic (Medicated) Liners (Pads) and Pulp Capping

A fundamental principle of modern dentistry is a minimally invasive and gentle approach to tooth tissues, with a strong emphasis on preserving pulp vitality whenever possible. Removal of the pulp (pulpectomy) should be avoided in cases where pathological changes within it are reversible and its preservation is feasible. In such situations, a therapeutic pharmacological effect on the pulp is necessary. This aims to stop the inflammatory process, prevent its further spread, and stimulate healing and reparative processes, such as the formation of tertiary (reparative) dentin.

To achieve these goals, therapeutic or medicated liners (pads) are used. These materials contain active substances with various intended purposes. Materials for treatment pads should ideally:

• Possess anti-inflammatory, antimicrobial, and odontotropic (stimulating dentin formation) actions.
• Not irritate the dental pulp; be biocompatible.
• Provide a strong seal over the underlying dentin.
• Bond well with tooth tissues, any intermediate lining materials, and the final permanent filling material.
• Have physical and mechanical properties compatible with the overlying permanent filling materials.

Therapeutic liners are indicated in the following clinical situations involving dental caries:

• Treatment of deep caries (when the cavity floor is very close to the pulp, but no actual exposure).
• Biological treatment of acute focal reversible pulpitis (direct or indirect pulp capping).
• Conservative treatment for accidental mechanical exposure of a healthy pulp during cavity preparation (traumatic pulpitis).

Methods for treating dental caries aimed at preserving the viability of an inflamed but recoverable pulp and restoring its function involve various pharmacological approaches. Treatment in such cases is often carried out in two stages (especially for indirect pulp capping or reversible pulpitis management):

• Stage 1 of Dental Caries Treatment (Initial Medication): Focuses on relieving the inflammatory process in the pulp, controlling microbial contamination, and reducing pain. For this purpose, drugs with a strong but relatively short-term effect are used. They are usually applied for several days as a medicated dressing under a temporary seal. Examples include corticosteroids combined with antibiotics or calcium hydroxide preparations.
• Stage 2 of Dental Caries Treatment (Reparative Phase): Aims to stimulate the formation of reparative (replacement) dentin and normalize metabolic processes within the dental pulp. At this stage, drugs with a prolonged, "mild" effect, which do not decompose during an extended period in the carious cavity, are used. They are applied in the form of a therapeutic liner under a temporary or, more commonly, a permanent filling. Calcium hydroxide-based materials and Mineral Trioxide Aggregate (MTA) are frequently used for their ability to stimulate dentin bridge formation.

In the routine treatment of deep dental caries (without pulp exposure or signs of irreversible pulpitis), the procedure is typically limited to the application of a therapeutic liner with long-term odontotropic and antiseptic effects directly under the permanent restoration, often in a single visit.

Permanent Filling Materials (Brief Overview)

Once the carious lesion has been removed and the cavity is prepared, a permanent filling material is placed to restore the tooth's structure, function, and often, its appearance. The choice of material depends on the size and location of the cavity, aesthetic requirements, chewing forces, and patient preference.

• Dental Amalgam ("Silver Fillings"): A durable, long-lasting, and cost-effective alloy of mercury mixed with silver, tin, and copper. It is very strong and well-suited for large restorations in posterior teeth. Its main disadvantages are its metallic appearance and the need for a more extensive cavity preparation for mechanical retention.
• Composite Resin ("Tooth-Colored" or "White" Fillings): A mixture of a resin matrix and inorganic filler particles. Composite resins are popular for their excellent aesthetics, as they can be matched to the natural shade of the tooth. They bond directly to the tooth structure, allowing for more conservative cavity preparations. They are the standard for anterior teeth and widely used in posterior teeth.
• Glass Ionomer Cement (GIC): This material chemically bonds to the tooth and is known for releasing fluoride, which can help prevent recurrent caries. Traditional GICs are not as strong or wear-resistant as amalgam or composite, so they are often used in non-stress-bearing areas (like root surfaces), as liners, or for temporary restorations. Resin-modified glass ionomers (RMGICs) offer improved strength and aesthetics.
• Ceramics (Porcelain): Used for indirect restorations like inlays, onlays, and crowns. They are fabricated in a dental laboratory and then cemented onto the tooth. Ceramics offer excellent aesthetics and stain resistance but can be more abrasive to opposing teeth and are more expensive.
• Gold and other Cast Metal Alloys: Also used for indirect restorations (inlays, onlays, crowns). Gold is extremely durable, biocompatible, and long-lasting, but it is not tooth-colored and is the most expensive restorative option.

Differential Aspects of Caries Stages and Related Conditions

Accurate diagnosis of the stage of caries and differentiating it from non-carious lesions is crucial for appropriate treatment planning.

Prevention of Dental Caries

Preventing dental caries involves a multi-pronged approach targeting the etiological factors:

• Effective Oral Hygiene:
  • Brushing teeth at least twice a day with fluoride toothpaste.
  • Daily interdental cleaning (flossing or interdental brushes) to remove plaque from between teeth.
• Dietary Modification:
  • Reducing the frequency and amount of sugary and starchy food and beverage consumption, especially between meals.
  • Choosing healthier snack options.
• Fluoride Use:
  • Using fluoridated toothpaste.
  • Drinking fluoridated water (if available and appropriate).
  • Professional fluoride applications (gels, varnishes) by a dentist.
  • Prescription fluoride supplements if indicated (especially for children in non-fluoridated areas).
• Dental Sealants: Application of thin plastic coatings to the pits and fissures of posterior teeth (molars and premolars) to prevent plaque accumulation and caries in these susceptible areas.
• Regular Dental Check-ups and Professional Cleanings: Allow for early detection of caries and removal of plaque and calculus. Frequency depends on individual risk.
• Saliva Stimulation: Chewing sugar-free gum (especially with xylitol) can stimulate saliva flow, which helps buffer acids and remineralize enamel.
• Antimicrobial Rinses (in specific high-risk cases): Prescription rinses like chlorhexidine may be used short-term to reduce cariogenic bacteria under dental supervision.

When to See a Dentist

It is important to see a dentist regularly for check-ups and cleanings, typically every 6 months, or as recommended. Additionally, a dental visit is warranted if you experience:

• Tooth sensitivity to hot, cold, or sweet foods/drinks.
• Pain or ache in a tooth, especially if spontaneous or lingering.
• Visible holes, pits, or dark spots on your teeth.
• Pain when biting or chewing.
• Food getting frequently trapped between certain teeth.
• A lost or broken filling.

Early detection and treatment of dental caries can prevent more extensive damage and the need for more complex and costly dental procedures.