Bacterial Diseases of the Mouth

Tooth and Gum Infections

The mouth contains a wide variety of oral bacteria, but only a few specific species of bacteria are believed to cause tooth and gum infections.

Learning Objectives

List the types of bacteria and issues associated with oral bacteria: Streptococci spp and Lactobaccilus acidophilus

Key Takeaways

Key Points

  • Dental caries, also known as tooth decay or cavity, is a bacterial infection that causes demineralization and destruction of the hard tissues (enamel, dentin, and cementum).
  • Tooth decay results from the production of acid by bacterial fermentation of the food debris accumulated on the tooth surface.
  • Bacteria occupy the ecological niche provided by both the tooth surface and gingival epithelium. However, a highly efficient innate host defense system constantly monitors the bacterial colonization and prevents bacterial invasion of local tissues.
  • Porphyromonas gingivalis is a Gram-negative oral anaerobe strongly associated with chronic adult periodontitis.
  • Dental plaque is the material that adheres to the teeth and consists of bacterial cells (mainly S. mutans and S. sanguis), salivary polymers, and bacterial extracellular products.

Key Terms

  • cavity: A soft area in a decayed tooth.
  • plaque: a clearing in a bacterial lawn caused by a virus
  • dental plaque: Dental plaque is the material that adheres to the teeth and consists of bacterial cells (mainly S. mutans and S. sanguis), salivary polymers, and bacterial extracellular products.
  • biofilm: A thin film of mucus created by and containing a colony of bacteria and other microorganisms.

Tooth and Gum Infections

Dental caries, also known as tooth decay or cavity, is a bacterial infection that causes demineralization and destruction of the hard tissues (enamel, dentin, and cementum). This usually happens from the production of acid by bacterial fermentation of the food debris accumulated on the tooth surface. If demineralization exceeds saliva and other remineralization factors, such as from calcium and fluoridated toothpastes, these hard tissues progressively break down, producing dental caries (cavities, holes in the teeth). The bacteria most responsible for dental cavities are the mutans streptococci, most prominently Streptococcus mutans and Streptococcus sobrinus, and lactobacilli. If left untreated, the disease can lead to pain, tooth loss, and infection. Today, caries remain one of the most common diseases throughout the world.

The mouth contains a wide variety of oral bacteria, but only a few specific species of bacteria are believed to cause dental caries: Streptococcus mutans and Lactobacilli among them. Lactobacillus acidophilus, Actinomyces viscosus, Nocardia spp., and Streptococcus mutans are most closely associated with caries, in particular root caries. Bacteria collect around the teeth and gums in a sticky, creamy-colored mass called plaque, which serves as a biofilm. Some sites collect plaque more commonly than others. Grooves on the occlusal surfaces of molar and premolar teeth provide microscopic retention sites for plaque bacteria, as do the approximal sites. Plaque may also collect above or below the gingiva where it is referred to as supra- or sub-gingival plaque respectively.

image

Gram stain of Streptococcus mutans.: Morphology is rod-like with chains when cultured on broth. Can cause subacute bacterial endocarditis and dental caries.

Oral bacteria have evolved mechanisms to sense their environment and evade or modify the host. Bacteria occupy the ecological niche provided by both the tooth surface and gingival epithelium. However, a highly efficient innate host defense system constantly monitors the bacterial colonization and prevents bacterial invasion of local tissues. A dynamic equilibrium exists between dental plaque bacteria and the innate host defense system. The oral cavity of the newborn baby does not contain bacteria but rapidly becomes colonized with bacteria such as Streptococcus salivarius. With the appearance of the teeth during the first year, colonization by Streptococcus mutans and Streptococcus sanguinis occurs as these organisms colonize the dental surface and gingiva. Other strains of streptococci adhere strongly to the gums and cheeks but not to the teeth. The gingival crevice area (supporting structures of the teeth) provides a habitat for a variety of anaerobic species. Bacteroides and spirochetes colonize the mouth around puberty.

image

Dental caries: This image shows destruction of a tooth by cervical decay from dental caries. This type of decay is also known as root decay.

The levels of oral spirochetes are elevated in patients with periodontal diseases. Among this group, Treponema denticola is the most studied and is considered one of the main etiological bacteria of periodontitis. Treponema denticola is a motile and highly proteolytic bacterium.

Spirochetes and fusi-form bacilli live as normal flora in the mouth, but the bacteria can cause infection and diseases to the oral cavity.

Porphyromonas gingivalis is a Gram-negative oral anaerobe strongly associated with chronic adult periodontitis. The bacterium produces a number of well-characterized virulence factors and can be manipulated genetically. The availability of the genome sequence is aiding our understanding of the biology of P. gingivalis and how it interacts with the environment, other bacteria, and the human host.

Aggregatibacter actinomycetemcomitans is considered an oral pathogen due to its virulence factors, its association with localized aggressive periodontitis in young adolescents, and studies indicating that it can cause bone loss.

Dental plaque is the material that adheres to the teeth and consists of bacterial cells (mainly S. mutans and S. sanguis), salivary polymers, and bacterial extracellular products. Plaque is a biofilm on the surfaces of the teeth. This accumulation of microorganisms subject the teeth and gingival tissues to high concentrations of bacterial metabolites which results in dental disease. If not taken care of, via brushing or flossing, the plaque can turn into tartar (its hardened form) and lead to gingivitis or periodontal disease.

Dental Caries

Dental caries cause demineralization of the hard tissues and destruction of the organic matter of the tooth.

Learning Objectives

Explain how dental caries can be prevented

Key Takeaways

Key Points

  • Dentin is produced continuously throughout life by odontoblasts.
  • Caries can be classified by location, etiology, rate of progression, and affected hard tissues.
  • Enamel is a highly mineralized acellular tissue. Enamel rods, which are the basic unit of the enamel structure, run perpendicularly from the surface of the tooth to the dentin.
  • There are four main criteria required for caries formation: a tooth surface (enamel or dentin), caries-causing bacteria, fermentable carbohydrates (such as sucrose), and time.
  • Dental caries can occur on any surface of a tooth that is exposed to the oral cavity, but not the structures that are retained within the bone.
  • The two bacteria most commonly responsible for dental cavities are Streptococcus mutans and Lactobacillus.
  • The use of dental sealants is a means of prevention.
  • Professional hygiene care consists of regular dental examinations and cleanings.
  • An extraction can also serve as treatment for dental caries.
  • In general, early treatment is less painful and less expensive than treatment of extensive decay.
  • Recurrent caries, also described as secondary, are caries that appears at a location with a previous history of caries.
  • Dentin is produced continuously throughout life by odontoblasts.
  • Personal hygiene care consists of proper brushing and flossing daily. The purpose of oral hygiene is to minimize any etiologic agents of disease in the mouth.
  • Primary diagnosis involves inspection of all visible tooth surfaces using a good light source, dental mirror and explorer. Dental radiographs (X-rays) may show dental caries before it is otherwise visible, in particular caries between the teeth.
  • Caries can be classified by location, etiology, rate of progression, and affected hard tissues.
  • In dentin from the deepest layer to the enamel, the distinct areas affected by caries are the advancing front, the zone of bacterial penetration, and the zone of destruction.
  • Intrauterine and neonatal lead exposure promote tooth decay. Other divalent cations, such as cadmium, mimic the calcium ion and therefore exposure may promote tooth decay.
  • From the deepest layer of the enamel to the enamel surface, the identified areas are the: translucent zone, dark zones, body of the lesion, and surface zone.
  • Enamel is a highly mineralized acellular tissue. Enamel rods, which are the basic unit of the enamel structure, run perpendicularly from the surface of the tooth to the dentin.
  • Some brands of smokeless tobacco contain high sugar content, increasing susceptibility to caries. Tobacco use is a significant risk factor for periodontal disease, which can cause the gingiva to recede.
  • Reduced saliva is associated with increased caries.
  • There are four main criteria required for caries formation: a tooth surface (enamel or dentin); caries-causing bacteria; fermentable carbohydrates (such as sucrose); and time.
  • If demineralization exceeds saliva and other remineralization factors such as from calcium and fluoridated toothpastes, these tissues progressively break down, producing dental caries (cavities, holes in the teeth).
  • The presentation of caries is highly variable.
  • Bacteria collect around the teeth and gums in a sticky, creamy-coloured mass called plaque, which serves as a biofilm.
  • Dental caries can occur on any surface of a tooth that is exposed to the oral cavity, but not the structures that are retained within the bone.
  • The mineral content of teeth is sensitive to increases in acidity from the production of lactic acid.
  • Radiographs are used for less visible areas of teeth and to judge the extent of destruction.
  • Depending on the extent of tooth destruction, various treatments can be used to restore teeth to proper form, function, and aesthetics, but there is no known method to regenerate large amounts of tooth structure. Instead, dental health organizations advocate preventive and prophylactic measures, such as regular oral hygiene and dietary modifications, to avoid dental caries.
  • Tooth decay disease is caused by specific types of bacteria that produce acid in the presence of fermentable carbohydrates such as sucrose, fructose, and glucose.
  • Before the cavity forms, the process is reversible, but once a cavity forms, the lost tooth structure cannot be regenerated.
  • The two bacteria most commonly responsible for dental cavities are Streptococcus mutans and Lactobacillus.

Key Terms

  • cementum: A bony substance that covers the root of a tooth; cement.
  • enamel: The hard covering on the exposed part of a tooth.
  • dentin: The hard, dense calcareous material that makes up the bulk of a tooth

Dental caries, also known as tooth decay or a cavity, is an infection, usually bacterial in origin, that causes demineralization of the hard tissues (enamel, dentin, and cementum ) and destruction of the organic matter of the tooth, usually by production of acid by hydrolysis of the food debris accumulated on the tooth surface. If demineralization exceeds saliva and other remineralization factors such as from calcium and fluoridated toothpastes, these tissues progressively break down, producing dental caries (cavities, holes in the teeth). The two bacteria most commonly responsible for dental cavities are Streptococcus mutans and Lactobacillus. If left untreated, the disease can lead to pain, tooth loss, and infection. Today, caries remain one of the most common diseases throughout the world.

Caries can be classified by location, etiology, rate of progression, and affected hard tissues. These forms of classification can be used to characterize a particular case of tooth decay in order to more accurately represent the condition to others and also indicate the severity of tooth destruction.

Tooth decay disease is caused by specific types of bacteria that produce acid in the presence of fermentable carbohydrates such as sucrose, fructose, and glucose. The mineral content of teeth is sensitive to increases in acidity from the production of lactic acid. To be specific, a tooth (which is primarily mineral in content) is in a constant state of back-and-forth demineralization and remineralization between the tooth and surrounding saliva. For people with little saliva, especially due to radiation therapies that may destroy the salivary glands, there also exists remineralization gel. These patients are particularly susceptible to dental caries. When the pH at the surface of the tooth drops below 5.5, demineralization proceeds faster than remineralization (meaning that there is a net loss of mineral structure on the tooth’s surface). Most foods are in this acidic range and without remineralization result in the ensuing decay.

As the enamel and dentin are destroyed, the cavity becomes more noticeable. The affected areas of the tooth change color and become soft to the touch. Once the decay passes through enamel, the dentinal tubules, which have passages to the nerve of the tooth, become exposed, causing a toothache. The pain may worsen with exposure to heat, cold, or sweet foods and drinks. Dental caries can also cause bad breath and foul tastes. In highly progressed cases, infection can spread from the tooth to the surrounding soft tissues. Complications such as cavernous sinus thrombosis and Ludwig’s angina can be life-threatening.

image

Dental caries: (A) A small spot of decay visible on the surface of a tooth. (B) The radiograph reveals an extensive region of demineralization within the dentin (arrows). (C) A hole is discovered on the side of the tooth at the beginning of decay removal. (D) All decay removed.

There are four main criteria required for caries formation: a tooth surface (enamel or dentin) caries-causing bacteria, fermentable carbohydrates (such as sucrose), and time. The caries process does not have an inevitable outcome, and different individuals will be susceptible to different degrees depending on the shape of their teeth, oral hygiene habits, and the buffering capacity of their saliva. Dental caries can occur on any surface of a tooth that is exposed to the oral cavity, but not the structures that are retained within the bone. All caries occur from acid demineralization that exceeds saliva and fluoride remineralization, and almost all acid demineralization occurs where food (containing carbohydrate like sugar) is left on teeth. Though most trapped food is left between teeth, over 80% of cavities occur inside pits and fissures on chewing surfaces where brushing, fluoride, and saliva cannot reach to remineralize the tooth as they do on easy-to-reach surfaces that develop few cavities.

In most people, disorders or diseases affecting teeth are not the primary cause of dental caries. Ninety-six percent of tooth enamel is composed of minerals. These minerals, especially hydroxyapatite, will become soluble when exposed to acidic environments. Enamel begins to demineralize at a pH of 5.5. Dentin and cementum are more susceptible to caries than enamel because they have lower mineral content. Thus, when root surfaces of teeth are exposed from gingival recession or periodontal disease, caries can develop more readily. Even in a healthy oral environment, however, the tooth is susceptible to dental caries.

Bacteria in a person’s mouth convert glucose, fructose, and most commonly sucrose (table sugar) into acids such as lactic acid through a glycolytic process called fermentation. If left in contact with the tooth, these acids may cause demineralization, which is the dissolution of its mineral content. The process is dynamic, however, as remineralization can also occur if the acid is neutralized by saliva or mouthwash.

At times, pit and fissure caries may be difficult to detect. Bacteria can penetrate the enamel to reach dentin, but then the outer surface may remineralize, especially if fluoride is present. These caries, sometimes referred to as “hidden caries”, will still be visible on x-ray radiographs, but visual examination of the tooth would show the enamel intact or minimally perforated.

image

Pit and fissure caries.: The progression of pit and fissure caries resembles two triangles with their bases meeting along the junction of enamel and dentin.

Periodontal Disease

Plaque-induced inflammatory lesions make up the vast majority of periodontal diseases, which are divided into peridontitis or gingivitis.

Learning Objectives

Differentiate between peridontitis and gingivitis

Key Takeaways

Key Points

  • Peridontal tissues are the cementum, or the outer layer of the roots of teeth; the gingiva, or gums; the alveolar bone, or the bony sockets into which the teeth are anchored; and the periodontal ligament, which are the connective tissue fibers that run between the cementum and the alveolar bone.
  • Periodontitis is an inflammatory disease affecting the periodontium, or the tissues that surround and support the teeth. Periodontitis involves progressive loss of the alveolar bone around the teeth, and if left untreated, can lead to the loosening and subsequent loss of teeth.
  • Periodontitis is caused by microorganisms that adhere to and grow on the tooth ‘s surfaces, along with an overly aggressive immune response against these microorganisms.
  • In the early stages, periodontitis has very few symptoms and in many individuals the disease has progressed significantly before they seek treatment. The gingival inflammation and bone destruction of peridontitis are largely painless.
  • Gingivitis, or inflammation of the gums, is a non-destructive peridontal disease. The primary cause of gingivitis is poor oral hygiene which leads to the accumulation dental plaque at the gum line. Gingivitis can progress to periodontitis.
  • Daily oral hygiene measures to prevent periodontal disease include brushing and flossing daily and using an antiseptic mouthwash.
  • There are many surgical approaches used in treatment of advanced periodontitis, including open flap debridement, osseous surgery, as well as guided tissue regeneration and bone grafting.
  • Several conditions and diseases, including Down syndrome, diabetes, and other diseases that affect one’s resistance to infection also increase susceptibility to periodontitis.
  • The primary etiology (cause) of gingivitis is poor oral hygiene which leads to the accumulation of a mycotic and bacterial matrix at the gum line, called dental plaque. Other contributors are poor nutrition and underlying medical issues such as diabetes.
  • Once successful periodontal treatment has been completed, with or without surgery, an ongoing regimen of “periodontal maintenance” is required.
  • In the early stages, periodontitis has very few symptoms and in many individuals the disease has progressed significantly before they seek treatment. Symptoms may include the following: redness or bleeding of gums, gum swelling that recurs, spitting out blood after brushing teeth, halitosis, or bad breath, and a persistent metallic taste in the mouth, gingival recession, resulting in apparent lengthening of teeth, deep pockets between the teeth and the gums, and loose teeth
  • Periodontitis is caused by microorganisms that adhere to and grow on the tooth’s surfaces.
  • The extent of disease refers to the proportion of the dentition affected by the disease in terms of percentage of sites. Generally, six probing sites around each tooth are recorded, as follows: mesiobuccal, mid-buccal, distobuccal, mesiolingual, mid-lingual, and distolingual.
  • The severity of disease refers to the amount of periodontal ligament fibers that have been lost, termed clinical attachment loss.
  • Smoking is a factor that increases the occurrence of periodontitis
  • The 1999 classification system for periodontal diseases and conditions listed seven major categories of periodontal diseases, of which the last six are termed destructive periodontal disease because the damage is essentially irreversible. The seven categories are as follows:
  • Gingivitis
  • Chronic periodontitis
  • Aggressive periodontitis
  • Periodontitis as a manifestation of systemic disease
  • Necrotizing ulcerative gingivitis/periodontitis
  • Abscesses of the periodontium
  • Combined periodontic-endodontic lesions

Key Terms

  • periodontitis: An inflammatory disease that affects the periodontium—the tissues that surround and support the teeth–and can lead to tooth loss.
  • periodontium: The specialized tissues that both surround and support the teeth, maintaining them in the maxillary and mandibular bones; the tissues including alveolar bone, cementum, gums, and periodontal ligament.
  • gingivitis: Inflammation of the gums or gingivae.

Periodontal disease is a type of disease that affects one or more of the periodontal tissues, which include:

  • the cementum, or the outer layer of the roots of teeth
  • the gingiva, or gum tissue
  • the alveolar bone, or the bony sockets into which the teeth are anchored
  • the periodontal ligament, which are the connective tissue fibers that run between the cementum and the alveolar bone.

While many different diseases affect the tooth-supporting structures, plaque-induced inflammatory lesions make up the vast majority of periodontal diseases and have traditionally been divided into two categories: peridontitis or gingivitis.

Peridontitis

Periodontitis is an inflammatory disease affecting the periodontium, or the tissues that surround and support the teeth. Periodontitis involves progressive loss of the alveolar bone around the teeth, and if left untreated, can lead to the loosening and subsequent loss of teeth. Periodontitis is caused by microorganisms that adhere to and grow on the tooth’s surfaces, along with an overly aggressive immune response against these microorganisms.

image

Periodontal disease: This radiograph shows significant bone loss between the two roots of a tooth (black region). The spongy bone has receded due to infection under the tooth, reducing the bony support for the tooth.

In the early stages, periodontitis has very few symptoms and in many individuals the disease has progressed significantly before they seek treatment. Symptoms may include the following:

  • Redness or bleeding of gums while brushing teeth, using dental floss, or biting into hard food
  • Gum swelling that recurs
  • Spitting out blood after brushing teeth
  • Halitosis, or bad breath, and a persistent metallic taste in the mouth
  • Gingival recession, resulting in apparent lengthening of teeth
  • Deep pockets between the teeth and the gums, that are sites where the attachment has been gradually destroyed by collagen-destroying enzymes, known as collagenases
  • Loose teeth, in the later stages

The gingival inflammation and bone destruction of peridontitis are largely painless. Hence, people may wrongly assume that painless bleeding after teeth cleaning is insignificant, although this may be a symptom of progressing periodontitis in that patient.

A diagnosis of periodontitis is established by inspecting the soft gum tissues around the teeth with a probe and by evaluating the patient’s x-ray films to determine the amount of bone loss around the teeth.

image

Gingivitis: Severe gingivitis before (top) and after (bottom) treatment.

Gingivitis

Gingivitis, or inflammation of the gums, is a non-destructive peridontal disease. The primary cause of gingivitis is poor oral hygiene which leads to the accumulation of bacterial matrix at the gum line, called dental plaque. Other contributors are poor nutrition and underlying medical issues such as diabetes.

In some people, gingivitis progresses to periodontitis –- with the destruction of the gingival fibers, the gum tissues separate from the tooth, forming pockets between the tooth and gum. Subgingival microorganism (those that exist under the gum line) colonize the periodontal pockets and cause further inflammation in the gum tissues and progressive bone loss.

If left undisturbed, microbic plaque calcifies to form calculus, which is commonly called tartar. Calculus above and below the gum line must be removed completely by the dental hygienist or dentist to treat gingivitis and periodontitis. Although the primary cause of both gingivitis and periodontitis is the microbic plaque that adheres to the tooth surface, there are many other modifying factors. A very strong risk factor is one’s genetic susceptibility. Several conditions and diseases, including Down syndrome, diabetes, and other diseases that affect one’s resistance to infection also increase susceptibility to periodontitis.

Prevention

Daily oral hygiene measures to prevent periodontal disease include:

  • Brushing teeth properly at least twice daily, with the patient attempting to direct the toothbrush bristles underneath the gum-line, to help disrupt the bacterial-mycotic growth and formation of subgingival plaque.
  • Flossing daily and using interdental brushes as well as cleaning behind the last tooth, the third molar, in each quarter.
  • Using an antiseptic mouthwash. Chlorhexidine gluconate-based mouthwash in combination with careful oral hygiene may cure gingivitis, although they cannot reverse any attachment loss due to periodontitis.
  • Using periodontal trays to maintain dentist-prescribed medications at the source of the disease. The use of trays allows the medication to stay in place long enough to penetrate the biofilms where the microorganism are found.

Regular dental check-ups and professional teeth cleaning as required. Dental check-ups serve to monitor the person’s oral hygiene methods and levels of attachment around teeth, identify any early signs of periodontitis, and monitor response to treatment.

image

Extensive periodontal disease: This section from a panoramic x-ray film depicts the teeth of the lower left quadrant, exhibiting generalized severe bone loss of 30–80%. The red line depicts the existing bone level, and the yellow line depicts where the gingiva was originally (1–2 mm above the bone), prior to the patient developing periodontal disease. The pink arrow, on the right, points to a furcation involvement, or the loss of enough bone to reveal the location at which the individual roots of a molar begin to branch from the single root trunk; this is a sign of advanced periodontal disease.