The role of biology in the orthodontic practice (Page 4)

It is estimated that 10-15 per cent of all children under the age of 16 are affected by chronic, long-term medical problems. These problems may affect the outcome of orthodontic treatment (Burden et al, 2001). Common medical problems in this age group include risk of infective endocarditis, bleeding disorders, leukemia, diabetes, cystic fibrosis, juvenile rheumatoid arthritis, and renal failure. An even higher percentage of adult patients may be afflicted by a variety of medical problems that involve one or more of the tissue systems. These conditions, and the medications used to treat them, may have profound effects on the response of dental and paradental cells to mechanical loading.

Endocarditis is a life-threatening disease, requiring primary prevention in the form of administration of antimicrobial agents prior to certain orthodontic procedures. The orthodontist must weigh the risk of endocarditis against the risk of an adverse reaction to the prescribed antibiotic therapy. Fortunately, most orthodontic procedures do not cause bacteremia. Lucas et al (2002) obtained blood samples from children 30 seconds after taking dental impressions, separator placement, band placement, and insertion of an adjusted arch wire. Significant bacteremia was found only after separator placement.

Orthodontic braces, fixed and removable, can accumulate bacterial plaque that may be harmful to oral soft and hard tissues. This problem has been addressed by adding antimicrobial agents to bracket bonding materials, elastic bands, and crown coating varnishes. The addition of benzalkonium chloride to a composite resin added antimicrobial properties to the compound without altering its mechanical properties (Othman et al, 2002). Likewise, coating teeth in orthodontic patients with a sustained-release chlorhexidine varnish decreases Streptococcus mutans levels in the patients’ saliva (Beyth et al, 2003).

Children treated for childhood cancers with both radiation and chemotherapy often exhibit disturbances in dental development, such as tooth agenesis, teeth with short roots, or with no roots altogether. A retrospective analysis of treatment outcome in 10 orthodontic patients with such a background revealed that five had been treated with lighter forces than usual, one displayed root resorption, and four achieved unsatisfactory results (Dahllof et al, 2001).

The development of inflammation in dental and paradental tissues during the course of orthodontic treatment implies that circulating plasma and leukocytes migrate out of capillaries, and interact with native cells. The blood plasma may contain endogenous hormones produced by endocrine glands, as well as a variety of molecules derived from consumed drugs and nutrients. Some of these molecules may interact with paradental target cells, augmenting or inhibiting the effects of mechanical forces on these cells. One of the main complications of such interactions is the development of root resorption.

Diabetes mellitus afflicts 3-4 per cent of the population, and is characterized by hyperglycemia caused by the body’s deficient management of insulin. There are two main types of diabetes, type 1 and type 2. In type 1 there is a total deficiency in insulin secretion, while in type 2 there is a combination of resistance to insulin action and insufficient compensatory insulin secretion. Diagnosis and monitoring of diabetes is based on blood glucose concentration or glycosylated haemoglobin concentration. Oral manifestations of the disease include xerostomia, chronic gingivitis and periodontitis, excessive loss of alveolar bone and PDL, poor healing of wounds, and soft tissue lesions, candidal and noncandidal (Bensch et al, 2003). Orthodontic treatment should be combined with frequent dental care sessions and maintenance of excellent oral hygiene. The magnitude of applied forces should be smaller than usual, reflecting the loss of dental support tissues.

Periodontitis, acute or chronic, may be present before the onset of orthodontic treatment, or occur during the course of treatment due to the accumulation of a bacterial plaque around the braces. Peripheral blood monocytes obtained from individuals with chronic periodontitis, synthesized large amounts of pro-inflammatory cytokines when incubated in vitro with bacterial lipopolysaccharides. If such primed monocytes find their way into strained paradental tissues, their increased production levels of cytokines may increase the risk of root resorption. An indicator of such an increased risk may be the concentration of cytokines in the gingival crevicular fluid. Previous studies reported on finding increased levels of cytokines, such as tumour necrosis factor  and interleukin 6 in the gingival crevicular fluid of orthodontically treated teeth in humans (Kim and Park 2000). The origin of these cytokines is most likely PDL cells.

Allergies and asthma are conditions involving periodic productions of large amounts of pro-inflammatory cytokines in the airway mucosa and the skin. Primed leukocytes derived from these tissues may travel through the circulation into the extravascular space of the tissues surrounding orthodontically treated teeth. Consequently, patients with a history of allergies and/or asthma seem to be at a high risk for developing excessive root resorption during the course of orthodontic treatment (Davidovitch et al, 1999). Hence, it is postulated that any inflammatory condition, such as gastroenteritis, arthritis, and thyroiditis, may increase the risk of orthodontic root resorption.

Allergy manifestations in orthodontics are infrequent, although the frequency of allergic diseases in the industrialized world is rising. The World Health Organization reports that 15% of the population has had or will have an allergic disease. Allergic reactions to orthodontic materials can develop during treatment, manifested as urticaria, angioedema, stomatitides, and cheilitis (Beaudovin et al, 2003). Metals in orthodontic appliances that can induce an allergic reaction are nickel, chromium, cobalt, and titanium. Other allergy-inducing materials include latex, resins, adhesives, and methyl methacrylates. When a reaction that seems to be allergy-related is detected in an orthodontic patient, a referral to an allergist for advice should occur. Close collaboration between the orthodontist and the allergist is essential for each future stage of the orthodontic treatment, in order to avoid further complications.

A method to detect patients sensitive to orthodontic alloys was developed, in the form of an in vitro cell proliferation assay (Marigo et al, 2003). The best parameters for inducing the strongest cell proliferation response were nickel sulfate at 10 μg/mL, 10% autologous serum, and 200,000 cells. With this method it was possible to distinguish between nickel-sensitive and non-nickel-sensitive patients. Moreover, it was found that exposure to nickel alloys for periods longer than 2 years, may lead to the development of oral tolerance mechanisms that modulate nickel sensitivity.

Consumption of low or moderate amounts of alcohol may have beneficial effects on the cardiovascular system, but chronic ingestion of large amounts of alcohol on a daily basis may have devastating effects on a number of tissue systems, including the skeletal system. Alcoholism may lead to severe complications, such as liver cirrhosis, neuropathies, osteoporosis, and spontaneous bone fractures. Circulating ethanol inhibits the hydroxylation of vitamin D3 in the liver, thus impeding calcium homeostasis. In such situations the synthesis of parathyroid hormone is increased, tipping the balance of cellular functions toward enhanced resorption of mineralized tissues, including dental roots, in order to maintain normal levels of calcium in the blood (10 mg). Therefore, chronic alcoholics receiving orthodontic treatment, are at a high risk of developing severe root resorption during the course of orthodontic treatment.

Demyelinating diseases such as multiple sclerosis are associated with an abnormally high incidence of trigeminal neuralgia. In MS, afferent nerve fibres loose their myelin sheaths, leading to “shorts” between axons. Such “shorts” in the trigeminal nerve, may precipitate trigeminal neuralgia. Orthodontic treatment evokes an inflammatory reaction in paradental tissues, including painful sensations that travel in an antidromic fashion from strained paradental sensory nerve endings. If areas of demyelination are present along the way to the Gasserian ganglion, trigeminal neuralgia may ensue.

Psychological stress is a common component of every day’s life. It may be found to exist in patients prior to the onset of orthodontic treatment, or it may develop during the course of treatment due to discomfort, resentment, or other reasons unrelated to orthodontics. Psychological stress affects the hypothalamic-pituitary-adrenal (HPA) axis, and the immune system. Since osteoclasts and odontoclasts are derived from the immune system, modification of their function by psychological stress may impact the process of root resorption. A recent survey revealed that orthodontic patients with psychological stress were at a high risk for developing excessive root resorption during the course of orthodontic treatment (Davidovitch et al, 1999). Furthermore, patients who are non-compliant, poor co-operators, and those who frequently break appointments and/or appliances, do it, most likely, because of psychological stress. Often, these noncompliant individuals express with their behaviour and deeds their objection to orthodontic care that had been imposed on them by their parents. In these individuals, the rate of orthodontic root resorption was found to be significantly higher than in compliant patients.

Among the reasons for partial and total loss of scalp hair is psychological stress, probably through effects on the HPA axis. A case of an adolescent orthodontic patient who developed alopecia totalis during orthodontic treatment was reported (Davidovitch et al, 1999). A review of the case revealed a normal medical background, with a presence of a persistent psychological stress due to the exposure to orthodontic mechanotherapy. Consequently, the patient’s paediatrician and the endocrinologist concluded that his alopecia had been most likely caused by psychological stress evoked by the orthodontic treatment.

Page 1     Introduction

Page 2     Tissue remodelling and orthodontic tooth movement

Page 3     The age factor

Page 4     The effects of pre-existing medical conditions and the development of complications

Page 5     The etiology of tooth resorption

Page 6     The biological nature of an optimal orthodontic force

Page 7     How to move teeth without resorbing their roots

Page 8     Summary