Dentinal Hypersensitivity

Tooth sensitivity is a significant clinical problem which is frequently encountered in clinical practice. It is most commonly reported from the buccal cervical zones of permanent teeth, sites that most frequently exhibit dentin exposure. It is a domain where man has continued his pursuit towards approximation of that gold standard for its management. The management of this condition requires a good understanding of the complexity of the problem, as well as a variety of treatments available. Thus it is imperative that every dentist should have a basic understanding of this chronic condition. This review considers the etiology, methods of measurement, differential diagnosis and management of dentinal hypersensitivity.

Dentinal Hypersensitivity

Introduction –
Dentinal hypersensitivity is a very common clinical presentation which can cause considerable concern for patients. It can be particularly uncomfortable and unpleasant for patients and can dictate types of foods and drinks ingested. Patients may describe the condition as dull or sharp, vague or specific and intermittent or constant. Dentinal hypersensitivity can be described clinically as an exaggerated response to non-noxious stimuli1 and is characterized by pain of short duration arising from exposed dentin in response to stimuli, typical thermal, evaporative, tactile, osmotic, or chemical & which cannot be ascribed to any other dental defect or pathology1. Dentinal hypersensitivity is a response from a non-noxious stimuli & a chronic condition with acute episodes whereas dentinal pain is a response from a noxious stimulus & usually an acute condition1.

Etiology –
Hypersensitivity is usually caused by loss of enamel covering due to attrition (para functional habits), abrasion (improper brushing technique), erosion (dietary components, gastric disorders). Dentin exposure due to gingival recession, chronic trauma from faulty restoration, following iatrogenic removal of cementum during root planing and curettage can lead to sensitivity. Following application of citric acid to remove smear layer and after surgical periodontal treatment have also been found to be contribute to hypersensitivity2.

Hypersensitivity can be elicited by various stimuli such as tactile- touching the surface with fingernail, toothbrush, thermal- application of cold food, hot stuffs, blowing air over the affected surface. Sweet substances (osmotic), dissimilar metals and electrical stimuli have also shown to effectively elicit sensitivity2.

Methods used to measure tooth hypersensitivity

Tactile –
The simplest tactile method used is to lightly pass a sharp dental explorer over the sensitive area of the tooth (usually the cemento – enamel junction) and to grade the response of the patient on a severity scale from 0 to 3. If no pain is felt – 0, slight pain or discomfort – 1, severe pain – 2, severe pain that lasts – 33. Other sophisticated tactile methods used were a device by Smith and Ash4, force sensitive electronic probe devised by Yeaple5, pressure probe device used by McFall and Hamrick6 and a hand held scratch device3.

Thermal –
A simple thermal method for testing for tooth sensitivity is directing a burst of room temperature air from a dental syringe onto the test tooth. Blowing air on a tooth involves drying and pain can be easily detected by this method if the teeth are sensitive. Air stimulation has been standardized as a one – second blast from the air syringe of a dental unit, where its temperature is set generally between 65 – 70 degrees fahrenheit and at a pressure of 60 psi6,7. An air thermal device has been devised8. Instruments that involve electric cooling or heating of direct contact metal probes have also been used in some studies9,10.

Osmotic –
An osmotic method consisting of the subjective pain response to a sweet stimulus was used to measure the effect of several test dentifrices on dentinal sensitivity6.

Electrical –
Electrical measurements differ from others in that a pain response can be obtained from non–sensitive as well as from sensitive teeth and with either an enamel–covered crown or a cementum–covered root site of stimulation. Improvements in pulp testers led to better quantification of the electric stimulus and discovery that a condition of “pre-pain” consisting of a tingling or warm sensation is observed before real pain and discomfort are felt by the subject as the magnitude of a stimulus is increased3. A stark device and a commercial digital pulp tester have also been tried3.

Management of hypersensitivity

Over the years, there is surprisingly a very large number of agents that have been used to manage this condition. Current therapeutic agents used to manage hypersensitivity are described below. Chemical or physical agents are used to either desensitize the nerve or cover the exposed dentinal tubules.

Potassium nitrate-
Potassium nitrate in bioadhesive gels at 5% and 10% have been shown to be highly effective in reducing hypersensitivity12. Potassium ions are the active component, and potassium nitrate can reduce dentinal sensory nerve activity due to the depolarizing activity of the K+ ion13.

Strontium chloride –
It has been effectively and widely used to combat hypersensitivity. It has been suggested that strontium deposits are produced by an exchange with calcium in the dentin resulting in recrystallisation in the form of a strontium apatite complex15.

Sodium fluoride –
Treatment of exposed root surfaces with fluoride toothpaste and concentrated fluoride solutions has been found to be very efficient in managing dentinal hypersensitivity16. The improvement appears to be due to an increase in the resistance of dentine to acid decalcification as well as precipitated fluoride compounds mechanically blocking exposed dentinal tubules or fluoride within the tubules blocking transmission of stimuli16.

Sodium monofluorophosphate –
Toothpastes containing this agent have been shown to be effective in reducing hypersensitivity17.

Stannous fluoride –
This agent either in aqueous solution or in glycerine has been found effective18. The mode of action appears to be through the induction of a high mineral content which creates a calcific barrier blocking the tubular openings on the dentine surface18. Alternatively, it may precipitate on the dentine surface leading to occlusion of the exposed dentinal tubules18.

Fluoride Iontophoresis-
Iontophoresis is the process of influencing ionic motion by an electric current and has been used as a desensitizing procedure in conjunction with sodium fluoride. There is immediate reduction in sensitivity after treatment with iontophoresis, but the symptoms gradually return in the next six months19.

Oxalates–
Since their initial development as a desensitizing agent, the oxalates have gained rapid popularity. Potassium oxalate and ferric oxalate solutions make available oxalate ions that can react with calcium ions in the dentinal fluid to form insoluble calcium oxalate crystals that are deposited in the apertures of the dentinal tubules25.

Resins and adhesives–
Sealing of dentinal tubules with resins and adhesives have been advocated for managing this condition with encouraging results however problems arise when they break away resulting in exposure of the tubules20. It is usually reserved for cases of specific and localized areas of hypersensitivity rather than generalized dentinal pain.

Lasers–
The Nd:YAG laser has been used in conjunction with sodium fluoride varnish with encouraging results showing up to 90 percent of the dentinal tubules being occluded through the use of this combined therapy21. CO2 laser irradiation and stannous fluoride gel has also been shown to be effective for inducing tubule occlusion for upto 6 months after treatment22.

Combination agents–
A combination 5% potassium nitrate:fluoride dentifrice has been found to be safe and effective in providing patients relief from sensitivity and protection against dental caries23.

Restorative materials–
The use of materials like composite resins and glass ionomer restorations can be used in situations where there has been significant prior loss of cervical tooth structure or as a last resort for a tooth which does not respond to other less invasive desensitizing protocols24.

Differential Diagnosis25

• Cracked tooth syndrome.
• Fractured restorations.
• Chipped teeth.
• Dental caries.
• Post-restorative sensitivity.
• Teeth in acute hyperfunction.

Conclusion –
Dentinal hypersensitivity is a very common condition which has been managed by agents and formulations applied locally, either “in office (iontophoresis, resins, restorations, burnishing of dentin)” or “at home (available in the form of gels, cream or oral rinse)”. For products developed for personal application at home, potassium nitrate, stannous fluoride, sodium fluoride, sodium monofluorophosphate and strontium chloride have been found to be safe to use and beneficial to patients in combating this condition.