pyri ORIGINALBamiseC o andARTICLE Esangh Not for Publicationt b y Q u Mechanisms and Treatment Approaches of Dentine N i n o t t r f e o Hypersensitivity: A Literature Review ssence Cornelius Tokunbo Bamisea/Temitope Ayodeji Esana Purpose: To review major mechanisms of dentine hypersensitivity and the treatment approaches offered. Materials and Methods: Medline was used to find relevant literature published up to December 2006. Based on ab- stracts and full articles, studies (in human and in animals) were identified describing mechanisms and management of dentine hypersensitivity. Additional information was also obtained by using manual library search for relevant topics in standard texts and journals of dentistry. Results: Discussion about the sensitivity of dentine started over a century ago, but it was not until sixty years later that a possible theory was posited. The so-called hydrodynamic theory became popular and was applied to understand the mechanism responsible for hypersensitive dentine. Nevertheless, because of the discrepancies in the pattern by which the dentine responds to various stimuli, several theories of dentine hypersensitivity were proposed which include the hydrodynamic theory, odontoblast transducer mechanism and direct innervation theory. None of these mechanisms was said to fully explain dentine hypersensitivity, thus indicating that as-yet unexplained mechanisms were possibly respon- sible. A multitude of products were tried and reported to be effective. The efficacy of many was not clearly established and their mechanisms of action were inadequately elucidated. The potential of gene therapy to reduce the burden of dentine hypersensitivity in the future is being examined. Conclusions: Considerable effort has been made to precisely explain dentine hypersensitivity, but doubt still exists whether any one theory can be applied to understanding this condition. This has led to a constant increase in therapeu- tic approaches worldwide, but with no conclusive evidence of reliable, successful treatment regimens. Key words: dentine hypersensitivity, mechanisms, review, treatments Oral Health Prev Dent 2011; 9: 353-367. Submitted for publication: 17.04.07; accepted for publication: 15.08.07 entine hypersensitivity is characterised by Dentine desensitisation may occur spontaneous- Dshort, sharp pain arising from the exposed den- ly in some patients, but in most cases treatment is tine in response to thermal, evaporative, tactile, necessary. An array of tried and suggested treat- osmotic or chemical stimuli, which cannot be ment regimens has been offered to relieve the pain ascrib ed to any other form of dental defect or path- of dentine hypersensitivity. Some workers (Morris ology (Holland et al, 1997). There is a wide vari- et al, 1999) expressed concern about the efficacy ation in prevalence values reported for this condi- of most of these treatments, which seem unrelia- tion, as illustrated in Table 1. ble and not well established, while others (Schuurs Dentine exposure may result from enamel loss et al, 1995) call into question the longevity of their by attrition, abrasion, erosion, abfraction and root desensitising effect. The conventional conservative surface stripping from gingival recession or perio- approach is based on using topically applied de- dontal treatment. Most hard tissue loss probably sensitising agents which can be applied either pro- occurs from a combination of these factors. fessionally or prescribed for home use. a Senior Lecturer, Department of Restorative Dentistry, Obafemi Awolowo University, University Campus, Ile-Ife, Nigeria. PULP–DENTINE COMPLEX Correspondence: Cornelius Tokunbo Bamise, Department of Restorative Dentistry, Obafemi Awolowo University, University The dentine is permeated throughout by minute Campus, Ile-Ife, 22005 Nigeria. Tel: +234-803-711-5388. tubes, the dentinal tubules, which contain the pro- Email: [email protected] Vol 9, No 4, 2011 353 pyri Bamise and Esan Co gh Not for Publicationt b y The pulp tissue is innervated by theQ fibres of the Table 1 Prevalence of dentine hypersensitivity as re- u sensory divisions of the trigeminal ganglion andN ported by various authors i those of autonomic (principally nsympathetic)o t t r f e o Prevalence (%) References branches of the superior cervical ganglion.ss Theen cprin-e 25 Abel (1958) cipal function of the sensory nerves is to detect stimuli and to conduct that to the central nervous 30 Jensen (1964) system, while the function of the autonomic system 14.5 Graf and Galasse (1977) is to keep the internal state of the organism con- 8.7 (probing), 18.0 (cold water) Flynn et al (1985) stant and maintain homoeostasis. These basic functions operate in the pulp (Torabinejad and Wal- 17 Fischer et al (1992) ton, 1989). 57.2 Irwin and McCusker (1997) 25 Liu et al (1998) TRANSMISSION OF DENTINE 8.0–57.0 Dababneh et al (1999) HYPERSENSITIVITY PAIN 4.1 Rees and Addy (2002) Odontogenic pain transmission is mediated primar- 67.7 Rees et al (2003) ily by peripheral sensory neurons of the trigeminal 1.34 Bamise et al (2007) nerve. The peripheral terminals of these nerves in- nervate the dental pulp and other oral tissues, whereas the central terminals release neurotrans- mitters that are involved in the initiation of pain. There are myelinated and unmyelinated nerve fibres toplasmic processes of the odontoblasts. The den- within the nerve bundles. The myelinated fibres, tinal tubules run parallel to each other and in one called the A-fibres, are grouped according to their direction, from the outer surface of the dentine to diameter and conduction velocities. Predominantly, the pulp cavity. The dentinal tubules are more A-fibres innervate the dentine (Ahlquist and Franzen, closely packed towards the pulp than in the outer 1999). The unmyelinated fibres, known as C-fibres, part of the dentine; the amount of intertubular ma- innervate the body of the pulp and its blood ves- trix, therefore, varies considerably at different lev- sels. Differences between the two sensory fibres els in the dentine. This is a result of the greater enable the patient to discriminate and characterise area of the external surface of the dentine com- the quality, intensity and duration of the pain re- pared with its inner or pulpal surface. At the pulpal sponse. Although due to the short distance be- surface of the dentine, there are 30,000–70,000 tween the site of stimulation and the brain, the two tubules per mm2 and it has been calculated that sensations might not be as clearly separated as in halfway between the pulpal surface and the amelo- stimulation of, for example, the extremities. dentinal junction, the total cross-sectional area of the tubules is equal to a 0.3-mm-diameter tube for each square millimetre of dentine. Such a degree of PROCESSING OF IMPULSES porosity could permit a considerable amount of flu- id movement through the dentine (Scott and Sy- The cell bodies of the trigeminal nerve are located mons, 1977). in the Gasserian ganglion; the primary neuron syn- The pulp is composed of cells and intercellular apses with the second-order neuron in the subnu- substance. The intercellular tissue consists of fi- cleus caudalis region of the trigeminal spinal tract bres and an amorphous ground substance of a ge- nucleus. Once the second order receives the input, latinous consistency. The principal cells present in it is carried to the thalamus. The second order the dental pulp are odontoblasts, fibroblasts, undif- crosses the brain stem to the opposite side of the ferentiated cells and defence cells. In addition, brain and ascends to the higher centres. A-delta-fi- there are blood vessels, lymphatics and nerves. bres from the pulp synapse in the lamina I area of Odontoblasts are highly differentiated mesenchy- the subnucleus caudalis, and C-fibres synapse in mal cells of the pulp with cell processes that ex- the lamina II and III areas. The A-delta neurons tend into the dentinal tubules. pass to the thalamus directly, by way of the neo- 354 Oral Health & Preventive Dentistry pyri BamiseC oand Esangh Not for Publicationt b y Q u i N n o t t r f e o ssence Fig 1 Schematic representation of fluid moving away from Fig 2 Schematic representation of fluid moving away from the odontoblast in response to cold stimulus (Drisko, 2002). the odontoblast in response to hot stimulus (Drisko, 2002). spinothalamic tract and are said to carry fast pain. would prove the presence of nerves deep in dentine The second-order C-fibre neuron carries impulses have indicated otherwise because application of via the palaeospinothalamic tract, which pass pain-inducing substances, such as histamine, ace- through the reticular formation where they are influ- tylcholine and potassium chloride, to the dentine enced by modulating interneurons before they reach fails to produce pain. Furthermore, the application the thalamus. Because these impulses take longer of local anaesthetics to exposed dentine does not to reach the thalamus, it is said to carry slow pain. prevent dentine hypersensitivity. Finally, application Fast pain tends to be sharp and easy to localise; of hypertonic fluids to dentine does produce pain. whereas slow pain tends to be dull and aching. Because of these discrepancies in the pattern by A comparison of the response characteristics of which the dentine responds to various stimuli, sev- the pulp nerve fibres and the sensations induced eral hypotheses for dentine hypersensitivity have from human teeth indicates that: been proposed (Torabinejad and Walton, 1989). r A-fibres are responsible for the sensitivity of den- tine and thus for the mediation of the sharp pain induced by dentinal stimulation. Hydrodynamic theory r Pre-pain sensations induced by electrical stimu- lation result from the activation of the lowest Of the several theories proposed, the most widely threshold A-fibres, some of which can be classi- accepted is the hydrodynamic theory of sensitivity. fied as A-beta-fibres according to their conduction This theory postulates that rapid shifts, in either velocities.