Dental Plaque. Composition, Structure, Development, Classification. Black Stain Plaque. Mechanical Polishing in Professional Dental Hygiene

Dental plaque is a natural biofilm with essential physiological functions. However, under stress – such as frequent sugar intake – it can develop pathogenic properties, becoming a significant risk factor for tooth decay. Effective removal of plaque through mechanical cleaning and other preventive measures should be guided by evidence-based dentistry.

The formation of dental plaque is a normal physiological process. While it serves certain protective roles, overwhelming scientific evidence links plaque to dental caries and chronic periodontal diseases. Research on its role in disease progression is ongoing. When plaque is left undisturbed for just 1–2 days, a yellowish layer becomes visible on the tooth surface in areas not naturally cleaned. Even at this early stage, biochemical processes within the plaque can trigger enamel demineralization, increasing the risk of cavities. Over the course of a few weeks, plaque near the gumline hardens into tartar, a major contributor to chronic gingivitis and periodontitis.

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The rate and location of plaque buildup vary among individuals due to factors such as diet, saliva secretion, and its mineral composition. While plaque itself is a natural formation, it plays a critical role in the development of common dental diseases, making its removal an essential part of oral hygiene.

Composition of Dental Plaque

The fundamental composition of plaque has remained largely unchanged over the years. It consists of approximately 80% water, along with microorganisms and a small amount of inorganic substances such as calcium, phosphorus, and fluoride. Notably, plaque has a much higher fluoride concentration than saliva, which may influence tooth resistance to decay. Fluctuations in calcium levels within plaque also correlate with an individual’s susceptibility to cavities. Clinical studies have explored the use of calcium-based treatments to enhance the mineral content of saliva and support enamel remineralization.

Microbial Homeostasis and Oral Health

Oral health depends on maintaining microbial homeostasis within plaque. This delicate balance is achieved through interactions between different bacterial species, the host’s immune system, and external factors like hygiene and diet. The formation of plaque depends on the presence of microorganisms in the mouth and the role of saliva. When the body’s defenses weaken, or when dietary habits favor harmful bacteria (such as excessive sugar consumption), the microbial balance shifts, allowing pathogenic bacteria to colonize and increasing the risk of oral diseases.

Age-related changes also impact plaque composition. Factors like declining immune function, hormonal shifts, gum recession, and alterations in saliva affect microbial stability. Additionally, dietary modifications, dental prosthetics, medications, and treatments like radiation therapy can indirectly disrupt the balance of oral microflora.

The microorganisms in dental plaque can be divided into two main groups: acidophilic bacteria (which thrive in acidic environments, such as Streptococcus, Lactobacillus, Actinomyces, Leptotrichia, and Corynebacterium) and proteolytic bacteria that produce proteinases (Veillonella and Neisseria).

Among the many bacterial species found in plaque, the most significant in cavity formation are Streptococcus mutans and Lactobacilli. These acid-producing bacteria play a central role in the demineralization of enamel.

Interestingly, even individuals resistant to cavities still harbor Streptococcus mutans, albeit in lower quantities. This suggests that the mere presence of these bacteria is not enough to cause decay – they require specific conditions to express their harmful potential. Rapid and aggressive cavity formation has been linked to increased levels of these bacteria in plaque, but their growth alone is not the primary trigger. Instead, a combination of risk factors – such as diet, poor hygiene, and genetic predisposition – sets the stage for disease development. While research into the precise mechanisms of cavity formation continues, one thing remains clear: controlling dental plaque through regular hygiene and preventive care is essential for maintaining oral health.

The Structure and Development of Dental Plaque

Modern research focuses heavily on the microorganisms within plaque, particularly in the search for specific bacterial culprits behind cavities and periodontal diseases. 

Within minutes of brushing, the first bacterial cells begin to colonize the tooth surface, forming visible colonies within 12–24 hours. Over time, plaque thickens and spreads, becoming a densely packed microbial layer dominated by streptococci. Within 48 hours, it returns to its original volume prior to brushing and can contribute to disease if left undisturbed. Individual differences in plaque structure may help explain why some people are more susceptible to cavities than others.

Stages of Plaque Formation

1. Stage One: Pellicle Formation
   The first stage involves the creation of an acellular organic film on the tooth surface known as the pellicle. This layer serves a protective function, reducing the solubility of hydroxyapatite in tooth enamel by 4–6 times. The pellicle, which forms spontaneously from proteins in saliva, is not influenced by bacterial activity but is enhanced by the presence of calcium and phosphate ions. It takes minutes to hours to form and has a thickness of 2–4 microns.
2. Stage Two: Initial Plaque Formation
   The second stage begins shortly after the pellicle forms, typically within minutes, and continues to develop over the next two hours. During this phase, proteins are deposited on the pellicle, becoming an essential part of the plaque matrix. Additionally, sticky polysaccharides, such as dextrans, produced by Streptococcus bacteria using sucrose as a substrate, contribute to the matrix. This stage sets the foundation for microbial colonization, as microorganisms from the oral cavity begin to settle.
3. Stage Three: Mature Plaque Formation
   Over the course of several days to two to three weeks, plaque reaches maturity. At this stage, it becomes a structurally complex, multi-microbial formation that is up to 200 microns thick. Mature plaque poses a significant threat to both tooth enamel and gums.
4. Stage Four: Mineralization and Tartar Formation
   In some cases, mature plaque becomes anaerobic, causing a shift from aerobic to anaerobic microorganisms. This change reduces acid production and raises the pH of the plaque. Over 12 days, the plaque begins to mineralize due to calcium accumulation and deposition as phosphates. After 3–4 weeks, this mineralization results in the formation of dental calculus, or tartar. The rough surface of tartar promotes the retention of microorganisms, and its growth is a result of plaque accumulation.

Classification of Dental Plaque

The International Classification of Diseases (ICD) provides standardized codes for dental plaque and other deposits on teeth.

ICD-10 Classification

• K03.6 – Deposits [accretions] on teeth
  • This includes dental plaque and pigmented deposits on teeth.
  • It covers various forms of plaque and stains that adhere to the tooth surface.
• K03.61 – Stains on teeth due to tobacco use
  • Specifically for discoloration caused by smoking or tobacco chewing.
• K03.66 – Dental plaque
  • This code is used for bacterial plaque accumulation on teeth.

ICD-11 Classification

• DA08.0 – Dental plaque and other deposits on teeth
  • This is the primary classification for dental plaque and other accumulations on teeth.
  • It includes both bacterial plaque and external stains from food, tobacco, or chromogenic bacteria.
• DA08.01 – Dental plaque
  • A more specific code for soft bacterial deposits forming a biofilm on the tooth surface.
• DA08.02 – Exogenous stains on teeth
  • Used for extrinsic stains caused by substances like coffee, tea, tobacco, or chromogenic bacteria (e.g., Black Stain).

The formation of dental plaque is a natural physiological process that is influenced by the characteristics of the tooth and gum surfaces. Plaque appears as a white or yellowish substance that is not physiologically removed unless regular brushing is practiced. It tends to form more quickly on molars than on incisors due to their size and anatomical features. The presence of plaque on the tooth surface at any given moment reflects the balance between plaque formation and removal.

Extrinsic tooth discoloration can be caused by two main factors: compounds that integrate into the pellicle and produce staining based on their inherent color, and those that cause staining through chemical reactions on the tooth surface.

Direct staining typically results from various sources such as foods, drinks, or habits. Organic chromogens, which are absorbed by the pellicle, contribute to the staining. Substances like tobacco, tea, and coffee are known culprits, with polyphenolic compounds being the primary contributors to color changes in the teeth.

Extrinsic stains are typically categorized as either metallic or non-metallic. 

Non-metallic stains, such as those from diet, tobacco, and certain mouthwashes, tend to adhere to the tooth surface, often in the form of plaque or pellicle deposits. Certain bacteria, particularly in children, have also been linked to specific colors of staining, but evidence for this is inconclusive.

Metallic stains often result from exposure to metallic salts in certain jobs or medications. For example, iron supplements and exposure to iron in foundries can cause a black stain, while copper can lead to a green stain. Other metals, like silver and tin, contribute to various color changes. It was once believed that these stains were caused by metal sulfides, but this theory has been questioned as further research revealed the complexity of the chemical processes involved.

Black Stain Plaque: A Form of Dental Deposits

Dental discoloration, especially on front teeth, can present a significant aesthetic challenge, particularly in children and adolescents. The impact of compromised dental appearance during these formative years can negatively affect psychosocial development and peer interactions. One common type of extrinsic discoloration in pediatric patients is black stain. 

Black stain appears as dark brown or black discolorations, often forming as lines or clusters of dots along the cervical third of the tooth, running parallel to the gumline. Unlike typical dental plaque, black stain is a more stubborn deposit, which tends to calcify. It is primarily composed of microorganisms embedded within a dense matrix, with bacterial species like Prevotella nigrescens, Prevotella melaninogenica, Porphyromonas gingivalis, and Actinomyces spp. as frequent contributors. However, it is believed to be formed by an iron compound, possibly ferric sulfide, resulting from bacterial interactions with iron present in saliva or crevicular fluid. Several factors, such as an iron-rich diet, iron supplements, and consumption of chromogenic foods, have been associated with the development of black stain.

Although more commonly seen in children, black stain can also occur in adults, with prevalence rates ranging from 2.4% to 18%. Both genders are affected equally. Several studies suggest that black stain may be linked to a reduced risk of dental caries. However, the exact mechanism by which black stain might prevent cavity formation is not well understood. Since these deposits primarily form on smooth tooth surfaces – areas that are not naturally more resistant to decay – it is hypothesized that children with black stain tend to have a lower overall risk of caries, rather than experiencing localized protection against it. Individuals with black stain tend to have lower levels of Streptococcus mutans and Lactobacilli, bacteria commonly associated with dental caries. This suggests that the microbial environment in black stains might inhibit caries development.

Black stains are more common in children, particularly those in the early stages of their primary and mixed dentition. If you're seeing this in a young patient, it's always a good idea to rule out other potential causes and provide guidance on preventive care. Children’s early experiences with dental visits can shape their attitudes toward oral health for life. A dentist who is skilled in managing pediatric patients can create a positive, less stressful experience, helping to build trust and fostering good long-term oral hygiene habits. That is why we invite you to join our course “Daily Manipulations of a Pediatric Dentist: From Communication to Restoration” – your perfect opportunity to learn from world-renowned experts in the field. Whether you're refining your behavior management techniques, exploring minimally invasive treatments, or diving into advanced endodontics for primary teeth, this course covers it all!

Research indicates that individuals with black stain have higher calcium concentrations and enhanced salivary buffering capacity compared to those without. Moreover, caries-associated bacteria exhibit increased metabolic activity related to carbohydrate metabolism, while black stain-related bacteria show higher amino acid metabolism, which may contribute to caries resistance. In general, the bacterial composition of black stain deposits contains fewer cariogenic bacteria, further supporting the idea that specific physiological and microbial factors contribute to the reduced caries risk seen in affected individuals.

Black Stain Removal Techniques

While black stain is not harmful to the teeth, it is often removed for cosmetic purposes. However, patients should be informed that the stain may reappear over time and recommended appropriate oral hygiene practices to manage the condition. Regular professional cleanings are typically sufficient to address black stains and prevent complications.

Effective removal of black stain involves:

• Mechanical Polishing: Utilizing rubber cups and non-abrasive pastes can effectively remove stains without damaging tooth surfaces.
• Air Polishing: Devices that use a stream of air and powder can efficiently eliminate black stains, especially in interproximal areas.
• Ultrasonic Scaling: High-frequency sound waves can disrupt and remove black stain deposits.

Intricacies into Mechanical Polishing in Professional Dental Hygiene

The concept of "selective polishing" focuses on removing external stains after scaling, emphasizing that polishing serves aesthetic rather than therapeutic purposes. At the same time the term "necessary selective polishing" highlights the importance of choosing polishing methods based on individual patient factors, such as enamel condition, staining nature, gum recession, and hypersensitivity.

The advent of modern air-polishing devices and minimally abrasive powders has revolutionized the way dental hygienists approach polishing. These technologies effectively remove stains and biofilm while being more patient-friendly. However, many practitioners still revert to traditional polishing methods using rotary instruments and pastes. This shift necessitates careful consideration of polishing techniques to ensure both efficacy and safety.

Safe Polishing: Minimizing Risks and Complications

Proper technique is crucial to minimize the risks associated with polishing. A variety of factors contribute to safe polishing:

1. The Tooth Surface
   Certain areas should never be polished with traditional rotary instruments, including:
   • Exposed dentin and cementum
   • Enamel demineralization
   • Composite restorations
   • Recently erupted teeth
   • Areas without visible stains
2. The Polishing Instrument
   The choice of instrument significantly affects the outcome of the polishing procedure:

• Rubber cups: Ideal for removing stains from the vestibular and lingual surfaces, especially near the gum line.
• Rubber cones: Best for cleaning interdental areas, embrasures, and around orthodontic appliances.
• Brushes: Used for cleaning fissures.

1. The Abrasive Agent
   Using a universal, often abrasive, paste can lead to complications such as:
   • Increased post-treatment sensitivity
   • Damage to restorations
   • Progression of enamel demineralization

Abrasive polishing agents create microscopic scratches on the tooth surface. Larger and harder particles cause deeper scratches, while finer particles create a smoother, shinier surface. For stubborn stains, it's best to use a series of pastes with progressively smaller particles. Always change polishing cups when switching pastes.

To prevent complications during polishing:

• Use the lowest possible speed—just enough to prevent the instrument from stalling.
• Refill the polishing cup every 1-2 teeth to avoid overheating.
• Stabilize your handpiece by resting it on adjacent teeth or the patient's cheek/chin.
• Control pressure – greater pressure increases abrasiveness.
• Limit time per tooth – use short, sweeping strokes for no more than 1-2 seconds per spot.
• Keep the polishing cup perpendicular to the tooth – tilting increases abrasiveness.
• Thoroughly rinse off paste residues, as abrasive particles are insoluble in water. Use floss to clean interproximal areas.

With careful attention to patient needs, materials, and best practices, polishing can be a safe, effective, and patient-friendly procedure, enhancing both dental health and aesthetics.

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