12: Physical and Chemical Injuries of the Oral Cavity

Physical and Chemical Injuries of the Oral Cavity

Injuries of the oral cavity may be caused by physical or chemical causes. Physical injuries may be iatrogenic, self-inflicted, traumatic, or occupational. The most important iatrogenic cause is the repair of tooth affected by dental caries or other developmental defects and restoration of missing tooth. Iatrogenic cause also includes X radiation and laser radiation. Self-induced or factitious injuries are due to overzealous oral hygiene practices, caused by psychotic or neurotic condition, or habitual. Traumatic causes include a fall, fight, road traffic accidents, and sports injuries.

Although chemical injuries are caused by environmental elements such as toxic levels of chemicals in the water, air, or consumables, the restorative and endodontic materials used in the routine dental practice play an important role.

Injuries of Teeth Associated with Tooth Preparation

The teeth, particularly the dentin and pulp, may be injured not only by dental caries, but also from those procedures necessary for the repair of lesions involving dental hard tissues. Preparation of the teeth for receiving the restorations include cutting, grinding, and etching with acids etc. These physical and chemical methods of tooth preparation as well as the various medicaments and filling materials which are inserted into the prepared tooth, have their own effects.

Effect of Tooth Preparation

The effect upon the dental pulp of restorative procedure alone is difficult to assess except in the sound tooth, since the carious lesion itself produces demonstrable changes in both the dentin and the pulp. Even when a sound tooth is prepared for experimental purpose, care must be taken in observing the effects to separate those which are due solely to the tooth preparation from those which are due to the restorative materials applied.

Tooth preparation is usually done by rotary instruments such as tungsten carbide burs and diamond burs of different sizes and shapes. Lasers and air abrasion are also used alternatively. Pulpal responses to these various procedures depend on the heat generated by friction, cutting of odontoblastic processes and drying of dentinal tubules, thickness of remaining dentin, vibration, removal of minerals and exposure of the organic matrix of dentin, and formation of smear layer.

Reaction to Rotary Instrumentation

Stainless steel burs revolving at low speed were used in the past for cavity and crown preparation. As the hardness of the enamel is high, these burs could not abrade instead they cut or chip away the tooth material. Also a considerable amount of pressure is applied during the procedure, which results in excessive heat production and evaporation of the contents of the dentinal tubules. High speed rotary instrumentation with tungsten carbide and diamond burs has replaced the steel burs in recent years. Nevertheless stainless steel burs are used in procedures involving bone.

The reaction of the dental pulp to cutting of dentin with a dental bur has been studied by Fish in both dogs and monkeys. When dentin is injured, there is stasis of the contents of the dentinal tubules, which lose their fluid communication with the pulp because of the formation of secondary dentin. Involved dentinal tubules are occluded by the deposition of calcium which separates these sclerosed dentinal tubules physiologically from the rest of the tooth.

The cavities prepared by Fish in the teeth of dogs or monkeys were cut with steel burs which were kept wet to prevent the complication of heat-induced damage to the pulp. In some cases the cavities were then filled with copper oxyphosphate cement and in other instances they were left open and exposed to the oral fluids. The animals were sacrificed after varying periods of time, and sections of the filled teeth were prepared for microscopic study. Three general reactions to cavity preparation were noted: (1) the production of secondary dentin, (2) changes in the odontoblasts associated with injured tubules, and (3) general changes in the pulp. Fish carefully pointed out that the reaction of the tooth with the formation of a calcified barrier and secondary dentin production is always strictly confined to the pulp surface of the injured dentinal tubules. There is never overlap of uninjured tubules, and for this reason the changes may be regarded as a specific reaction to injury of the dentinal tubules.

The pulp reaction to superficial injury of the dentin varies in degree of severity, depending partially upon the depth of the prepared cavity and partially upon the elapsed time between cutting the cavity and extraction of the tooth for study. In mild reactions the odontoblasts become distorted and reduced in number. Small vacuoles may appear between them, probably lymph exudate. Capillaries in the damaged area may be prominent. In more severe injuries, there may be complete disorganization of and hemorrhage in the odontoblastic layer (Fig. 12-1). The bulk of the pulp tissue away from the cut tubules may exhibit little or no reaction.

In more serious injuries there is a greater infiltration of the injured locus by polymorphonuclear leukocytes, which gradually become replaced by lymphocytes. The majority of the severe pulp injuries are probably associated with irritation brought about by the open cavities, with the sudden exposure of large numbers of open dentinal tubules to oral fluids and bacteria.

Even after such severe injuries the majority of damaged pulps undergo spontaneous healing or at least enter a quiescent phase and produce no signs or symptoms of persisting damage (Fig. 12-2). The factors responsible for this phenomenon, especially from the clinical aspect, are unknown.

It appears that dentin has a heat-dissipating action which reduces the temperature rise within the pulp to only a fraction of the actual temperature applied to the tooth. This is due to the low thermal conductivity of dentin, which acts as an effective insulating medium. Nevertheless the application of heat to a dental pulp already injured from a carious lesion of the dentin, but not an actual pulp exposure, may be sufficient to affect adversely the repair or healing of the pulp even though an apparently successful restoration is given to the tooth.

The preparation of tooth under the constant application of water to cool the cutting instrument and tooth will prevent many of the serious consequences due to heat, and this procedure is strongly recommended.

High-Speed Instrumentation

The development of high-speed dental engines and hand-pieces necessitated investigation of the possible effects which their use might have on pulp tissue, and numerous reports of such studies have been published.

Bernier and Knapp reported a study on high-speed instrumentation utilizing various speeds up to 100,000 rpm. They found evidence of mild pulpal damage, but, in addition, observed a new type of lesion which they termed the ‘rebound response’. This consisted variously in: (1) an alteration in ground substance, (2) edema, (3) fibrosis, (4) odontoblastic disruption, and (5) reduced predentin formation in a region directly across the pulp opposite the cavity site or at a distant pulpal site, and thought to be caused by waves of energy transmitted to the pulp focused into a certain region by the pulpal walls. The significance of this phenomenon is still not clear.

Swerdlow and Stanley in their study involving 450 human teeth found that speeds over 50,000 rpm with coolants were less injurious to the pulp than lower speeds. They concluded that the combination of high speed, controlled temperature, and light load produced minimal pathologic pulpal alteration. When heavy loads were used, even coolants did not minimize inflammatory responses. Extending this investigation to 13 operative techniques, Diamond and his coworkers found that the 300,000 rpm air-water spray—No. 35 carbide bur technique—provided all the cutting efficiency of a high-speed instrument without producing extended or burn lesions and caused the highest incidence of reparative dentin formation, a favorable protective reaction. A speed of 250,000 rpm with water coolant was reported by Nygaard-Ostby to produce even less pulpal reaction than the conventional (6,000 rpm) machine without water-spray. Caviedes-Bucheli and coworkers in their study found that substance P expression is increased in tooth where cavity preparation is done and concluded that it may have an important clinical significance in terms of inflammation and pain experience.

The practicability of use of accelerated hand-piece speeds has been accurately summarized by Stanley and Swerdlow, who stated: ‘In principle, high speed techniques approach the ideal but at the same time these methods can be easily abused… properly used, ultraspeed is an extremely safe and efficient method of reducing tooth structure’.

Effect of Ultrasonic Technique

The use of ultrasonic equipment for cutting cavities in teeth has been advocated because it involves less heat, noise, and vibration in contrast to rotary instruments. Essentially, the technique consists in the conversion of electrical energy into mechanical energy in the form of vibration of a tiny cutting tip, approximately 29,000 vibrations per second with an amplitude of about 0.0014 inch. Aluminum oxide abrasive in a liquid carrier is washed across this tip, and the vibration of the particles in turn results in a rapid reduction of tooth substance.

The effects of this technique, as used in cavity preparation, on the tooth and dental pulp have been evaluated by a number of investigators whose results are in essential agreement. Zach and Brown, Healey and his coworkers, and Lefkowitz among others have found that there are no remarkable differences in the reaction of the dental pulp to the preparation of cavities by the steel bur, the diamond stone or the ultrasonic instrument. This again emphasizes that only the dentinal injury itself is important, not how this injury is produced.

Mitchell and Jensen, studying the effect of steel bur and ultrasonic cavity preparation on the human tooth, also reported that no differences could be observed in the reaction of the pulp to these two techniques. Mild hyperemia, hemorrhage and a slight neutrophilic and lymphocytic infiltration of the pulp tissue immediately below the cut dentinal tubules were noted during the 6–12 day period following cavity preparation by either means. After several weeks the late reaction consisted in slight, irregular secondary dentin deposition and the formation of a ‘calciotraumatic’ line, a hematoxyphilic line between the regular dentin and the postoperative dentin apparently representing a disturbance in dentin formation at the time of the operative procedure.

Lasers

Laser is an acronym for Light Amplification by Stimulated Emission of Radiation. It is an electro-optical device which, upon stimulation, can convert jumbles of light waves into an intense, concentrated, uniform, narrow beam of monochromatic light with an energy source of great intensity and exceptional flexibility. The radiation may be continuous or modulated, or the emission may occur in short pulses. This high-intensity radiation can be focused on an extremely small area, approximately 1 micron in diameter, because of the small angle of divergence and coherency of the beam. Light photons of characteristic wavelengths are produced, amplified, and filtered to produce the laser beam. Carbon dioxide and neodymium:yttrium-aluminum-garnet (Nd:YAG) lasers are most commonly used. The main problem with laser cutting of hard dental tissues is the generation of heat and forbidden tactile control.

Lasers are used in dental practice to coalesce pits and fissures to eliminate retention sites for bacteria, to desensitize the exposed root surfaces, to make the hard tissue surfaces rough to promote bonding as an alternative to acid etching, to vaporize the carious tissue, to vaporize the organic tissues in the root canal in endodontic procedures, cavity preparation, restoration removal, treatment of dentinal sensitivity, caries prevention and bleaching.

Effects on Teeth

The effects of laser on teeth were first reported by Stern and Sognnaes, who found that exposure of intact enamel, caused a glass like fusion of the enamel, whereas dentin exposed to laser exhibited a definitive charred crater. Chalky spots, craters, or small holes in enamel may also be produced under other conditions. Scanning electron microscopic analysis showed the effects of laser on dentin vary from no effects to disruption of the smeared layer to actual melting and recrystallization of the dentin, depending on power level, duration of exposure, and color of the dentin. Although it has been shown that selective deep destruction of carious tooth substance can be accomplished, the practicality of its use in removing carious lesions is still questionable. Laser irradiation alters the dentin structure and produces surface layers that give the appearance of being more enamel-like. The laser-modified surface may be more resistant to demineralization; hence, many investigators are proposing continued development of the laser for caries prevention.

Open dentin surface exposed to laser results in melting and closure of the orifices of the dentin and this property is used to treat dentin hypersensitivity.

Bleaching of stained teeth has also been accomplished by lasing.

Effect of Heat

The reaction of the dental pulp to heat is an important clinical problem because of the extraordinary amount of heat that may be generated by the revolving cutting and grinding instruments used in tooth preparation. Actually, temperatures over 700° F have been recorded on the cutting surfaces of stones and burs under abusive conditions.

Thermal change may be influenced by: (1) the size, shape, and composition of the bur or stone, (2) the speed of the bur or stone, (3) the amount and direction of pressure applied, (4) the amount of moisture in the field of operation, (5) the length of time that the bur or stone is in contact with the tooth, and (6) the type of tissue being cut, enamel or dentin. Of further significance is the heat generated during the setting of various restorative materials, particularly the direct resins. In in vitro experiments, Wolcott and his associates showed that the temperature at the dentin-resin junction may reach 212° F, and they recorded a temperature of 133° F in the pulp chamber.

Smear layer

Smear layer is an amorphous micro layer deposited on the prepared tooth surfaces and consists of inorganic enamel and dentin debris, organic pulp materials, dentinal fluid, bacteria, and saliva. The thickness of smear layer may vary from 1μm to 5μm. Its morphology, composition, and biological behavior still remain controversial. Smear layer has the protective effect by forming a physical barrier, which reduces the permeability of dentin and prevents the exit of dentinal fluid. On the other hand it also acts as a barrier against the microoraganisms, which already penetrated before the treatment, may flow back and express their pathogenicity. Many investigators advocate the removal of smear layer as it interferes with the bonding between the restorative material and the tooth structure in restorative treatment and affects the action of irrigants and disinfectants and penetration and adhesion of sealers in endodontic treatment.

Effect of Restorative Materials

The dentist has at his/her disposal a great many materials prepared commercially to restore the original contour of the tooth attacked by dental caries and other lesions of the tooth including trauma. The dentist must be familiar with the advantages and disadvantages of each material from the point of view of its physical and chemical properties and its ability to fulfil the purpose for which it is intended. In addition, he must be acquainted with the biologic effects of the restorative materials on the tooth, especially on the dental pulp.

A great many experimental studies have been carried out to investigate the effects of the different restorative materials on the dental pulp, and today such testing is routine before new restorative materials are released by ethical manufacturers for use by dentists. It should be obvious that a restorative material applied to a prepared tooth is in contact with more than just a mass of inert calcified material. The dentinal tubules, containing odontoblastic processes which have been freshly cut, form a series of passage ways leading directly to the pulp through which a fluid or soluble material may reach the pulp tissue. If this material is irritating, it may lead to serious injury. For this reason a comparison of the effects of the various common restorative materials is important.

Remaining dentin thickness

It is generally agreed that if the cavity depth is shallow, with 2.0 mm or more of primary dentin remaining between the floor of the cavity preparation and the dental pulp, dentin probably provides its own insulation against traumatic, thermal or restorative material irritation. However, if the remaining thickness of primary dentin is less than 2.0 mm, it is necessary that a cement base of one type or another be utilized.

Zinc Oxide and Eugenol

It is used routinely as a temporary filling material or root canal sealer. Eugenol of this cement fixes cells, depresses the cell respiration, and reduces the neural transmission in vitro. There is almost universal agreement that zinc oxide and eugenol is the least injurious of all filling materials to the dental pulp. Not only is there no irritation produced by this substance, but actually it exerts a palliative and sedative effect on the mildly damaged pulp, since it inhibits synthesis of prostaglandins and leukotrienes. It seems to be such a bland substance that it may lack even the necessary irritating properties requisite to the stimulation of secondary dentin formation. In view of these findings, zinc oxide and eugenol is the material of choice for use over injured pulps or as a base in deep cavity preparations.

Zinc Phosphate (Oxyphosphate) Cement

This particular cement is widely used in dentistry both as a protective base in deep cavities before the insertion of the restoration and also in cementing cast inlays, crowns, and other similar restorations. The majority of investigators have reported significant deleterious effects on the pulp when the material is placed in cavities, the actual injurious agent supposedly being the phosphoric acid.

Gurley and Van Huysen prepared cavities in teeth of young dogs and filled them with zinc phosphate cement. After approximately 1½ months they found hyperemia and inflammatory cell infiltration of the pulp with disarrangement of the odontoblastic layer. Secondary dentin had formed under the shallower cavities. The more severe pulpal reactions occurred under the deeper cavities.

Studies on human teeth, such as those by Manley, by Shroff, and by Kramer and McLean, show that hyperemia or hemorrhage with inflammatory cell infiltration of the pulp accompanied by reduction in the size and number of the odontoblasts occurs after placement of this cement in prepared cavities.

The studies generally indicate that zinc oxyphosphate cement is an irritant when placed in the base of a deep cavity, particularly in bulk, although the human pulp may be able to localize this reaction in most instances. When this cement is used in shallow cavities, it is relatively innocuous and reportedly serves a useful function in the stimulation of secondary dentin formation.

Polycarboxylate or polyacrylate cements have properties comparable to those of the phosphate cements, but have a low degree of pulpal irritation similar to that of the zinc oxide-eugenol cements.

Silver Amalgam

Silver amalgam is used as a filling material in dentistry. It is an innocuous material, particularly in shallow cavities. Beneath deep cavities filled with amalgam, Manley found a decrease in the number of odontoblasts, as well as mild inflammatory cell infiltration of the pulp. The complication of thermal shock transmitted by deep amalgam restorations is difficult to evaluate, but is a source of potential damage.

In contrast, Swerdlow and Stanley studied the pulpal responses in 73 intact human teeth with cavities prepared at speed of 20,000–300,000 rpm and filled with either amalgam or zinc oxide and eugenol. They reported that the amalgam increased the intensity of mild pulpal response to cavity preparation and that this appeared to be due, in part at least, to the mechanical aspects of amalgam condensation. Brännström studied the effect of amalgam restorations on pulp tissue, and concluded that any damage to the pulp was due to leakage around the restoration, not to the filling material itself. Dark colored metallic components of the silver alloy turn the dentin dark gray and tooth may appear discolored.

Amalgam restorations when in contact with gingiva cause inflammation because of corrosion products and dental plaque.

Relationship between oral lichenoid reactions and silver amalgam fillings is a matter of controversy. A number of studies have been published with respect to amalgam filling and lichenoid reactions. A Dunsche and coworkers suggest the removal of amalgam fillings in all patients with symptomatic oral lichenoid reactions associated with amalgam fillings if no cutaneous lichen planus is present.

Glass-ionomer

Glass-ionomer cement is considered as biocompatible and is widely used as filling and lining material and as a luting agent. It consists of fluoroaluminosilicate glass powder and polycarboxylic acid. Glass-ionomers are water-based, and the set materials are composed of an inorganic-organic complex with high molecular weight. In contrast to other cements, glass-ionomer has the advantages of chemically bonding to mineralized tissues and release of fluorides.

Glass-ionomer cement bonds to the dentin by chemical and mechanical means. The chemical bonding is based on the exchange of ions between carboxylic groups of the substrate and calcium ions derived from partially dissolved apatite crystallites. The mechanical interlocking is based on the demineralization of exposed dentin by polycarboxylic acid treatment. Collagen fibers can be exposed and an intermediate layer can be formed between glass-ionomer material and undemineralized dentin.

Biocompatibility of glass-ionomer cement is due to the weak nature of polyacrylic acid. Histologically there is minimal or absence of inflammation in pulp after a month. Pulpal pain may be present for a short period after the filling of cervical cavities, and is due to the increased dentin permeability after acid etching.

Conventional Composite Resins

These are restorative materials developed chiefly because methyl methacrylate or unfilled acrylic resins have restrictive characteristics such as low hardness and strength, a high coefficient of thermal expansion and a lack of adhesion to tooth structure. The resin matrix is a compromise between epoxy and methacrylate resins. This resin is combined with a filler of dispersed particles of varying types in relatively high concentration. While most conventional composite resins are chemically activated, some are now marketed whose cure is based on light activation.

The biologic properties of the composite resins show the same irritational characteristics as the unfilled acrylic resins. For this reason, the same measures should be taken to protect the pulp from possible injury, especially when the cavity preparation is deep. A calcium hydroxide base is preferable to a zinc oxide and eugenol base because of the possible interaction of eugenol and resin.

Microfilled Composite Resins

These are a newer group of resins which contain the same resin matrix as the conventional composite resins but differ in that the size of the filler is much smaller than in the conventional resin. The biologic properties of the microfilled resins, including their irritational effects on the pulp, are comparable to those of the conventional composite resins. Thus, some pulpal protection is necessary under deep cavities.

The many experimental studies cited would indicate superficially that the majority of restorative materials used in dentistry today are dangerous because of the serious effects on the dental pulp which they often induce. It is true that many of these materials are potentially injurious. Nevertheless, literally millions of restorations with these substances are placed each year, and clinical experience has shown that, unless actual pulp exposure has occurred, the death rate of dental pulps directly attributable to the restorative material is extremely low. Even the occurrence of clinical symptoms of pulp injury is uncommon. Although this seems contradictory to experimental evidence, it should be appreciated that most cavities prepared by the dentist in which these materials are inserted are to repair a destructive carious lesion. The presence of this carious lesion, in contrast to the experimental cavities prepared in sound human and animal teeth, has usually induced the deposition of secondary dentin and has caused a certain amount of dentinal sclerosis, and these reactions offer considerable protection to the pulp. It is on this basis that the dentist is justified in continuing to use these filling materials. There is a need, however, for continued study of this general problem.

Effect of Cement Bases, Cavity Liners, Varnishes and Primers

A variety of materials commonly used in dental practice are inserted in a cavity preparation between the tooth and the restoration for the following purposes:

These materials are generally classified as cement bases, cavity liners, cavity varnishes and cavity primers, and they are important because of their possible effects on the dental pulp.

Cavity Liners

Cavity liners are aqueous or volatile organic liquid suspensions or dispersions of zinc oxide or calcium hydroxide that can be applied in a relatively thin film to the surface of a cavity. They may also be solutions of resins in an organic solvent to which has been added calcium hydroxide or zinc oxide, or aqueous suspensions of calcium hydroxide in methylcellulose. The cavity liner provides the beneficial effects of zinc oxide and calcium hydroxide as thin films in shallow cavities and, in addition, neutralizes the free acid of zinc phosphate and silicate cements. The cavity liners themselves have no effect on dental pulp and, in fact, actually form a chemical barrier to provide reliable protection for the pulp under certain deep restorations.

Stanley has compared the protective effect of reparative dentin with cavity liners and bases, and generally concluded that: (1) pulpal tissue beneath preoperatively formed reparative dentin is safe from most subsequent procedures; (2) cavity liners and/or bases, should be employed since the completeness of the reparative dentin barrier cannot be ascertained; (3) the unrestored tooth being utilized as an abutment lacks reparative dentin and is more subject to the damaging effects of chemical agents because of patent dentinal tubules; (4) although 2 mm of primary dentin between the floor of the cavity preparation and the dental pulp is usually a sufficient protective barrier, the condensation of amalgam or gold foil, as well as the chemical irritation of cements and self-curing resins, may render this thickness of protection insufficient; (5) age changes in the tooth, with the production of reparative dentin in the involved area, are of no recognizable benefit regarding pulp protection; (6) high-speed, water-cooled cutting techniques produce an average incidence of reparative dentin formation of under 20%; even less reparative dentin formation is produced if more than 1 mm of primary dentin remains beneath the cavity preparation; (7) if reparative dentin does not form within the first 50 days following a restorative procedure, then there will be none; (8) nearly 20 postoperative days are required for new odontoblasts to differentiate and produce reparative dentin, and it has been shown that an average of 100 productive days of matrix formation is required to produce a reparative dentin barrier of 0.15 mm; (9) final cementation of restorations need not be delayed in allowing time for reparative dentin to form, since the use of cavity-lining materials is a reasonable substitute; and (10) cavity varnish and calcium hydroxide lining materials appear capable of protecting pulp if used appropriately.

Cavity Varnishes

Cavity varnishes are solutions of one or more resins from natural gums, synthetic resins, and rosin in organic solvents. It is generally agreed that varnishes may be of aid in reducing postoperative sensitivity, but their film thickness is insufficient to provide thermal insulation. This film also acts as a semipermeable membrane so that certain types of ions penetrate it, while others do not. It has been found also that varnishes are effective in reducing the microleakage of fluids around the margins of restorations.

While cavity varnishes themselves appear to have no significant effect upon a dental pulp, neither do they have a sedative effect. Therefore, in deep restorations, it may be advisable to utilize calcium hydroxide or zinc oxide-eugenol cements first, and then apply the varnish over this base.

Effect of Cavity-sterilizing Agents

Cavity-sterilizing agents are frequently used as a final step in routine cavity preparation and also in an attempt to sterilize discolored, infected dentin in the base of deep carious lesions when this dentin cannot be completely removed without risk of pulp exposure. It has been suggested that cavity sterilization is unnecessary, since microorganisms persisting in the dentinal tubules after a restoration has been placed do not flourish but, rather die or exist in an inactive state. Furthermore, should the dentin be carious so near the pulp that exposure is feared were it all to be removed, the pulp tissue by this time would almost certainly have become infected, and attempts at sterilization would be worthless.

Mineral trioxide aggregate (MTA)

Mineral trioxide aggregate (MTA) is a moisture friendly biocompatible material composed of refined Portland cement and bismuth oxide. Portland cement is a mixture of dicalcium silicate, tricalcium silicate, tricalcium aluminate gypsum, and tetracalcium aluminoferrate. MTA has wide endodontic applications, which include pulp-capping, pulpotomy dressing, root-end filling, perforation repair, and apexification. The effect of white mineral trioxide aggregate on dental pulp was investigated by Moghaddame-Jafari and coworkers on mouse MDPC-23 odontoblast-like cells and OD-21 undifferentiated pulp cells. They found that there was no induction of apoptosis and increased DNA synthesis. In another in vitro study where exposed pulps were covered with MTA or calcium hydroxide, histological evaluation demonstrated less inflammation, hyperemia and necrosis, a thicker dentinal bridge, and more frequent odontoblast layer formation with MTA than with calcium hydroxide. There are many reports available comparing the effect of calcium hydroxide and MTA on pulp-capping procedures and pulpotomy dressing and most of them claim MTA is superior over calcium hydroxide. Although the overall results in human studies involving MTA is promising further extensive, long-term studies are needed to find out its adverse reactions if any.

Physical Injuries of the Teeth

Bruxism: (‘Night-grinding’, bruxomania)

Bruxism is the habitual grinding or clenching of the teeth, either during sleep or as an unconscious habit during waking hours. This term is generally applied both to the clenching habit, during which pressure is exerted on the teeth and periodontium by the actual grinding or clamping of the teeth, and also to the repeated tapping of the teeth. Bruxism is one of the most common sleep disorders. The incidence of bruxism has been variously reported as between 5 and 20%.

Etiology

In a review of the subject by Nadler and Meklas, the causes of bruxism have been described as: (1) local, (2) systemic, (3) psychologic, and (4) occupational.

Local factors are generally associated with some form of mild occlusal disturbance which produces mild discomfort, and chronic, even though unrecognized, tension. It has been suggested that in many cases bruxism becomes a firm habit as a result of an unconscious attempt by the patient to establish a greater number of teeth in contact or to counteract a local irritating situation. In children the habit is frequently associated with the transition from the deciduous to the permanent dentition and may result from an unconscious attempt to place the individual tooth planes so that the musculature will be at rest.

Systemic factors have been proposed as etiologically significant, but the role of most of these is difficult to assess. Gastrointestinal disturbances, subclinical nutritional deficiencies, and allergy or endocrine disturbances have all been reported as causative factors. A hereditary background has been described in some cases.

Psychologic factors are believed by some investigators to be the most common cause of bruxism. High levels of anxiety, stress, and emotional tension may be expressed through a number of nervous habits, one of which may be bruxism. Thus, when a person suffers from fear, rage, rejection, or a variety of other emotions which he/she is unable to express, these become hidden in the subconscious but are expressed periodically by numerous means. It has been observed that bruxism is common in mental institutions. Bruxism is a manifestation of nervous tension in children also and may be related to chronic biting or chewing of toys. Polysomnographic studies suggested that sleep bruxism episodes are part of sleep arousal response. The sleep arousal response is nothing but sudden change in the depth of sleep. Besides the sleep bruxism appears to be a disturbance in the dopaminergic system.

Occupations of certain types favor the development of this habit. Athletes engaged in physical activities often develop bruxism, although the exact reason for this is uncertain. Occupations, in which the work must be unusually precise, such as that of the watchmaker, are prone to cause bruxism. Voluntary bruxism is also recognized in those persons who habitually chew gum, tobacco, or objects such as toothpicks or pencils. Although voluntary, this too is a nervous reaction and may lead eventually to involuntary or subconscious bruxism.

Clinical Features

The person who engages in bruxism performs the typical grinding or clenching motions during sleep or subconsciously when awake. These may be associated with a grinding or grating noise. The symptomatic effects of this habit have been reviewed by Glaros and Rao, who have divided them into six major categories: (1) effects on the dentition, (2) effects on the periodontium, (3) effects on the masticatory muscles, (4) effects on the temporomandibular joint, (5) head pain, and (6) psychologic and behavioral effects.

When the habit is firmly established, severe wearing or attrition of the teeth may occur, not only occlusal wear, but also interproximal wear which produces sensitivity. On both surfaces actual facets may be worn in the teeth. As the bruxism continues, there may be loss of integrity of the periodontal structures, resulting in loosening or drifting of teeth or even gingival recession with alveolar bone loss. Temporomandibular joint disturbances are also reported to occur as a result of the traumatic injury of continuous tooth impact without normal periods of rest. Hypertrophy of the masticatory muscles, particularly the masseter muscle, may interfere with maintenance of the rest position, cause trismus, and alter occlusion and the opening and closing pattern of the jaws.

Finally, while it has been suggested that bruxism may give rise to facial pain and headache as well as psychologic and behavioral effects, these are very difficult manifestations to evaluate and correlate.

Treatment and Prognosis

If the underlying cause of the bruxism is an emotional one, the nervous factor must be corrected if the disease is to be cured. Removable splints to be worn at night may be constructed to immobilize the jaws or to guide the movement so that periodontal damage is minimal. Recently Botulinum toxin (Botox) has been very successful in treating the grinding and clenching of bruxism. Botox when injected into the masseter muscle, weakens the muscle enough to stop the grinding and clenching, but not so much as to interfere with chewing or facial expressions. RC DiFrancesco and coworkers suggest that there is a positive correlation between sleep-disordered breathing and bruxism and stated that there was an important improvement of bruxism after adenotonsillectomy based on their study of 69 children. If the disease is left untreated, severe periodontal and/or temporomandibular disturbances may result.

Fractures of Teeth

Tooth fracture is a common injury which may arise in a variety of situations, the most frequent of which is sudden severe trauma. This is usually a fall, a blow, an automobile accident or any of a large number of incidents in which children especially are frequently involved. Some cases of fracture occur when a tooth is weakened as by a large restoration, leaving thin walls or unsupported cusps which give way under the stress of mastication. A similar weakening and subsequent fracture occurs also in cases of internal resorption of teeth. Teeth which have had root canal therapy are often described as being somewhat brittle and susceptible to fracture.

Clinical Features

Although fracture of teeth may occur at any age, children are especially prone to sustain this type of injury. The prevalence of tooth fracture is difficult to assess or evaluate, particularly since minor chipping of teeth is common. As might be expected, boys are more frequently involved than girls. There is a definite predilection for involvement of maxillary teeth, with between 75 and 90% of fractures occurring there (Fig. 12-3).

There are several classifications of fractured teeth, the simplest being only whether or not the fracture line involves the pulp. A more detailed classification is that of Ellis, who divides all traumatized anterior teeth (for these constitute the vast majority of such injuries) into nine classes:

The clinical manifestation as well as the treatment and prognosis of the fractured tooth depend chiefly upon whether the dental pulp is pierced by the fracture and whether the crown or the root of the tooth is involved. If there is crown fracture without pulp involvement, vitality of the tooth is usually maintained, although there may be mild pulp hyperemia even when the overlying dentin is relatively thick. If the dentin over the pulp is exceedingly thin, bacteria may penetrate the dentinal tubules, infect the pulp and produce pulpitis, leading to death of the pulp. When vitality is maintained, usually a layer of secondary dentin is deposited over the involved dentinal tubules. The tooth may be sore and slightly loose because of the traumatic injury, but severe pain is usually absent.

A fractured tooth crown which exposes the pulp is a more serious problem, but pulp exposure does not necessarily imply that death of the pulp will occur. In some cases the exposure can be capped by calcium hydroxide, and a dentinal bridge will form as a part of the healing reaction. Pulpotomy or pulpectomy may often be necessary; however, since the pulp becomes infected almost immediately after the injury.

Root fractures are somewhat uncommon in young children, since their tooth roots are not completely formed and the teeth have some resilience in their sockets. It occurs in patients between the ages of 10 and 20 years and most are traumatic in origin. Root fractures involve mostly the middle third of the root and are horizontal. When fracture does occur, the tooth is loose and sore and there may be displacement of the coronal portion of the tooth. Most of the time tooth becomes nonvital after fracture. Some teeth may be repaired by forming a layer of reparative dentin along the pulp wall and cementum on the outer surface, or form granulation tissue between the fractured segments. Few may remain vital with resorption of the sharp edges of the fractured fragments.

In certain situations where the injury is sufficient to cause root fracture, fragments of cementum may be severed from dentin and is called cemental tear.

Cracked Tooth Syndrome

Cracked tooth syndrome (CTS) is characterized by sharp pain on chewing without any obvious reason, which is actually caused by a ‘hidden’ crack of the tooth. These are incomplete fractures that are too small to be seen on radiographs. The typical symptom is sharp fleeting pain when releasing biting pressure on an object. This is because when biting down, the segments are usually moving apart and thereby reduce the pressure in the nerves of the pulp. When the bite is released, the ‘segments’ snap back together sharply increasing the pressure causing pain. The pain is often inconsistent, and frequently hard to reproduce. Causes of CTS include attrition, bruxism, trauma, accidental bitting on a hard object, presence of large restoration, and improper endodontic treatment. The American Association of Endodontists have classified five specific variations of cracked teeth; craze line, fractured cusp, cracked tooth, split tooth, and vertical root fracture.

Injuries to the Supporting Structures of the Tooth

Concussion is produced by injury which is not strong enough to cause serious, visible damage to the tooth and the periodontal structures. On clinical examination tooth may not be mobile or displaced from its original position. Crown appears normal and patient may not feel any difference in occlusion. Pulp gives normal response to vitality test. But the characteristic feature is the increased sensitivity of the tooth to percussion from any direction.

Treatment consists of selective grinding of the tooth to eliminate occlusal forces.

Subluxation refers to abnormal loosening of tooth without displacement due to sudden trauma. Tooth is mobile on palpation and sensitive to percussion and occlusal forces. Rupture of the periodontal tissue is usually evident by bleeding at the gingival marginal crevice. In time tooth becomes nonvital due to severance of apical blood supply.

Avulsion is dislocation of the tooth from its socket due to traumatic injury. It can be partial or total. Partial avulsion includes intrusion, extrusion, or facial, lingual or palatal, or lateral displacement.

Avulsion is usually accompanied by fracture of the alveolar bone. Partial avulsion is managed by reposition of the tooth and stabilization with splints. Completely avulsed tooth can be replanted in its socket. The prognosis of the replantation will be good if the extraoral time is minimal and the avulsed tooth is kept in a suitable medium during transportation. Nevertheless many of the replanted teeth undergo ankylosis to the alveolar bone.

Tooth Ankylosis

Fusion between the tooth and bone, termed ankylosis is an uncommon phenomenon in the deciduous dentition and even more rare in permanent teeth. The condition of deciduous tooth ankylosis (submerged tooth) has been described in Chapter 1 on Developmental Disturbances of Oral and Paraoral Structures.

Ankylosis ensues when partial root resorption is followed by repair with either cementum or bone that unites the tooth root with the alveolar bone. It must not be inferred that root resorption invariably leads to ankylosis. Actually, it is an uncommon sequela, and the cause for this sporadic happening is unknown. Ankylosis does occur rather frequently after a traumatic injury to a tooth, particularly occlusal trauma, but it is also seen as a result of periapical inflammation subsequent to pulp infection. Periapical inflammation is a well-recognized cause of root resorption. Ankylosis sometimes also follows root canal therapy if the apical periodontal ligament is irritated or seriously damaged. Resorption and ankylosis is more common in replanted teeth.

Physical Injuries of the Bone

The most common physical injury involving the bone is fracture.

Fractures of Jaws

Fractures of the craniofacial complex occur commonly due to automobile, industrial, and sports accidents, and fights. Fracture can occur more easily in bones, which are already weakened by certain developmental and systemic disorders. Fracture may be simple, greenstick, compound, or comminuted. In simple fracture, the bone is broken completely; the overlying structures are intact and are not exposed to exterior. Greenstick fracture common in children is characterized by break of bone in one side and bend on the other side. In compound fractures external wound is associated with the break and is common in road traffic accidents. Bone is crushed or splintered in comminuted fractures and may or may not be exposed to the exterior.

Mandible is more prone for fractures, since chin is a prominent feature of the face. Fractures of the jaw are more common in males.

Classification

Le Fort I or horizontal fracture, also known as floating fracture is characterized by separation of body of the maxilla from the base of the skull, below the level of zygomatic process.

Le Fort II or pyramidal fracture is characterized by vertical fractures through the facial aspects of the maxilla and extend upward to the nasal and ethmoid bones and usually extends through the maxillary sinus.

Le Fort III or transverse fracture is a high level fracture that extends across the orbits through the base of the nose and ethmoid region to the zygomatic arch. Bony orbit is fractured and the lateral rim is separated at the zygomaticofrontal suture. Zygomatic arch is fractured.

Displacement, anterior open bite, swollen face, reddish eye due to subconjunctival hemorrhage, and nasal hemorrhage are the common features. If the skull is involved, history of unconsciousness, cerebrospinal fluid rhinorrhea, cranial nerve involvement are characteristic.

Traumatic Cyst: (Solitary bone cyst, hemorrhagic cyst, extravasation cyst, unicameral bone cyst, simple bone cyst, idiopathic bone cavity)

The traumatic cyst is a pseudo cyst (lacks an epithelial lining) and an uncommon lesion comprises about 1% of all jaw cysts. It occurs in other bones of the skeleton as well.

Etiology

The etiology of the solitary bone cyst is unknown, although a number of theories have been proposed and at least one, the trauma—hemorrhage theory has been rather widely accepted. Howe and also Sieverink have carried out extensive reviews of the literature and pointed out the wide acceptance of the theory of origin from intramedullary hemorrhage following traumatic injury. Hemorrhage occurring within the medullary spaces of bone after trauma heals in most cases by organization of the clot and eventual formation of connective tissue and new bone. According to the traumatic theory, the clot breaks down and leaves an empty cavity within the bone. Steady expansion of the lesion occurs secondary to altered or obstructed lymphatic or venous drainage. This expansion tends to cease when the cyst-like lesion reaches the cortical layer of bone, so that expansion of the involved bone is not a common finding in the solitary bone cyst.

It is not at all unusual; however, for the patient to be unable to recall any traumatic injury to the jaw. This may indicate that an injury so mild that the patient would not be aware of it or remember it, is sufficient to cause this lesion to develop. In the series reported by Howe, only slightly over 50% of the patients gave a history of trauma, the time lag between injury and discovery of the lesion varying from one month to 20 years.

Other theories of origin, reviewed by Whinery, have included:

Clinical Features

The traumatic cyst occurs most frequently in young persons, the median age being 18 years in a series of 45 cases reviewed and reported by Gardner and Stoller. According to Howe, over 75% of cases occur in the second decade of life. There is no definite sex predilection although many series have shown the males being affected more commonly than females. Although it has been stated that the posterior portion of the mandible is more commonly involved than the anterior, numerous cases have been reported in the incisor region, since in the young person this area contains hemopoietic marrow. The maxilla has been known to develop the solitary bone cyst, but only on extremely rare occasions. In some cases enlargement of the mandible has been observed, but often the lesion is discovered during routine radiographic examination of the patient. In the majority of cases the pulps of the teeth in the involved area are vital, and this is important to ascertain, because the vital teeth should not be sacrificed. The presenting complaint may be swelling or rarely pain.

When the cavity is opened surgically, it is found to contain either a small amount of sero-sanguinous fluid, shreds of necrotic blood clot, fragments of fibrous connective tissue, or nothing. The dentist is frequently astonished to open into an empty space in bone and find that it has no clinically demonstrable membrane. It was reported by Toller in one case that the hydrostatic intracystic pressure was exceptionally low and comparable with capillary pressure, quite unlike that in other cysts of the jaw.

Radiographic Features

Radiographic examination usually reveals a rather smoothly outlined radiolucent area of variable size, sometimes with a thin sclerotic border, depending upon the duration of the lesion. Some traumatic cysts may measure only a centimeter in diameter (Fig. 12-5), whereas others may be so large that they involve most of the molar area of the body of the mandible as well as part of the ramus. When the radiolucency appears to involve the roots of the teeth, the cavity may have a lobulated or scalloped appearance extending between the roots of these teeth (Fig. 12-6). Seldom is there any displacement of teeth and, in many cases, the lamina dura appears intact. Rodrigues and Estrela reported a case of traumatic bone cyst in upper premolar-molar region, mimicking a large periapical lesion.

Care must be taken to differentiate the small solitary traumatic cyst occurring in the molar area and appearing as a round or ovoid radiolucent area associated with vital teeth from the lingual salivary gland depression of the mandible (q.v.) which has a similar radiographic appearance. However, the latter lesion is usually located below the mandibular canal, whereas the traumatic cyst usually lies above it.

Histologic Features

Histologic examination of the solitary bone cyst may reveal a thin connective tissue membrane lining the cavity, but no other significant features. Sometimes no such membrane is demonstrable. Waldron had the opportunity to study a solitary bone cyst in toto in a resected mandible. His case exhibited a thin connective tissue membrane and, in addition, an extensive osteophytic reaction on the outer surface of the cortical plate (Fig. 12-7). There may be presence of few red blood cells, blood pigments, or giant cells adhering to the bone surface.

Focal Osteoporotic Bone-marrow Defect of the Jaw

The focal osteoporotic bone-marrow defect of the jaw is an uncommon lesion producing a focal radiolucency away from normal hematopoietic marrow. Hematopoietic marrow occurs normally in the jaws at the angle of the mandible, the maxillary tuberosity and occasionally other areas. It is well recognized that bone marrow may be stimulated in response to unusual demands for increased blood cell production and that this hyperplastic marrow may extend between adjacent trabeculae of bone, producing radiographically obvious osteoporosis and even thinning of the cortex. Other views regarding its pathogenesis include abnormal healing following tooth extraction since these lesions are most common in extracted sites, and persistence of remnants of fetal marrow.

Histologic Features

The tissue removed from these defects consists of either normal red marrow, fatty marrow or a combination of the two (Fig. 12-8B). Megakaryocytes and small lymphoid aggregates may be present. The trabeculae of bone usually present in the sections are long, thin, irregular, and devoid of an osteoblastic layer.

Surgical Ciliated Cyst of Maxilla: (Sinus mucocele)

The surgical ciliated cyst of the maxilla was originally reported by Gregory and Shafer. This cyst develops either after surgical entry into the maxillary sinus, usually a Caldwell-Luc operation or due to the obstruction of ostium. Basically, it is an implantation type of cyst in which epithelium of the maxillary sinus becomes entrapped along the line of surgical entry into the sinus and subsequently proliferates to form a true cystic cavity, anatomically separated from the sinus.

Clinical Features

The majority of patients with this type of lesion are middle-aged or older and present with a complaint of a nonspecific, poorly localized pain, tenderness, or discomfort in the maxilla. Extraoral or intraoral swelling is also frequently evident. Careful questioning of the patient usually reveals a history of some type of surgical procedure involving the maxilla and maxillary sinus, frequently 10–20 years previously. When content of the mucocele is infected, the lesion is called mucopyocele. Interestingly, it has been emphasized by Ohba and his associates among others that this lesion is more common in Japan than in America or Europe, possibly because of the higher incidence of maxillary sinusitis in Japan. Yamamoto and Takagi in their study involving 60 cases reported that postoperative maxillary cyst accounted for 19.5% of all oral cystic lesions.

Radiographic Features Radiographic examination shows a well-defined unilocular radiolucent area closely related to the maxillary sinus, often appearing to encroach upon the sinus but anatomically separate from it, as may be demonstrated by injection of the sinus with a radiopaque material. A filling defect of the cyst can then be seen (Fig. 12-9A).

Histologic Features

The surgical cyst is lined by pseudostratified ciliated columnar epithelium identical with that of the maxillary sinus (Fig. 12-9B). If infection or inflammation is present, squamous metaplasia may be found. The wall of the cyst is composed of fibrous connective tissue with or without inflammatory cell infiltration.

Effects of Orthodontic Tooth Movement

The science of orthodontics is based upon the ability of teeth to be moved through bone, without their subsequent extrusion or loss, by the application of pressure or tension under appropriate and controlled circumstances. Although the exact biologic mechanism responsible for this phenomenon is unknown, it is generally agreed that bone under pressure responds by resorbing, whereas the application of tension results in deposition of new bone. The periodontal ligament transfers the pressure or tension applied through orthodontic appliances.

Sandstedt applied force to the maxillary incisors of a dog, moving them lingually by means of a labial arch wire, and described the histologic findings of bone resorption, with numerous associated osteoclasts, on the pressure side of the teeth and formation of new bone on the tension side. He noted no tooth resorption, although necrosis or at least hyalinization of the periodontal ligament was found in the areas of pressure.

Tipping Movement

The exact movements which a tooth will undergo and the exact position it will assume after the application of orthodontic force will depend upon the degree and direction of the force and the position of the fulcrum around which the force acts. The general statement can be made, however, that pressure upon a tooth results in the resorption of bone in the direction of the application of force and compensatory new bone formation on the opposite side of the tooth, the tension side (Fig. 12-10).

The initial reaction on the pressure side is a compression of the periodontal ligament which, if excessive and prolonged, may result in ischemia with hyalinization and/or actual necrosis of tissue (Fig. 12-11B). On the opposite side under excessive force there may be actual tearing of the periodontal fibers and small capillaries with hemorrhage into the area. With reasonable forces, the periodontal ligament on the tension side of the tooth demonstrates stretching and widening of the periodontal space. Within a matter of hours or at the most a few days, large numbers of osteoclasts make their appearance along the surface of the bone under pressure, and resorption begins. This continues until the force of the pressure has been entirely dissipated.

New trabeculae of bone on the tension side become evident early and appear as thin, elongated spicules arranged parallel to the periodontal fibers and confluent with them at their bony attachment (Fig. 12-11A). These spicules show evident osteoblastic activity along the sides and the end adjacent to the tooth, but usually there is intense osteoclastic activity at the ends of the spicules away from the tooth. As stabilization occurs, the alveolar bone gradually assumes its compact pattern that existed before movement occurred.

A secondary but most important occurrence is the deposition of new spicules of bone on the outer surface of the labial plate in instances of pressure in the labial direction. This serves to maintain the thickness of the already thin labial plate and prevent its perforation by the tooth. It is not entirely certain why resorption of even compact bone occurs before resorption of cementum and the tooth root. It is known that resorption of calcified tissues is favored by increased local vascularity, and the hypothesis has been advanced in explanation that the bone of the alveolus is in a more vascular environment than the cementum when orthodontic pressure is applied, particularly since ischemia of the periodontal ligament adjacent to the cementum is the usual situation.

It is generally recognized that the teeth of young persons respond much more rapidly and with less applied force to orthodontic movements than do the teeth of older adults. Although differences do exist in the chemical constitution of bone at varying ages, the difference in orthodontic response is probably due to variation in general tissue reactivity and local vascularity. Although bone retains the ability to undergo resorption throughout life, the degree of the stimulus needed to evoke this response shows dramatic differences between the various age groups.

Tissue Reactions during Retention Period

Discontinuance of the active phase of orthodontic force signals the beginning of alterations in the bone characteristic of the retention period. During this period there is gradual reformation of the normal dense pattern of the alveolar bone by apposition of bone around the bony spicules until they meet, fuse, and gradually remodel. The studies of Oppenbeim indicated that this reformation is slower around teeth held in position during the retention period by a retaining appliance as compared to teeth which remained free during this time. In any event, the final remodeling and the attainment of absolute bone-tooth equilibrium following orthodontic movements involve an extremely slow process, and a breakdown in this process is probably one of the most important contributing factors in cases of orthodontic failure due to relapse during the retention period.

Physical Injuries of Soft Tissues

Linea Alba

Linea Alba is a white line seen on the buccal mucosa extending from the commissures posteriorly at the level of the occlusal plane (Fig. 12-12). It is caused by the physical irritation and pressure exerted by the posterior teeth. It is usually bilateral and is more pronounced in persons who have clenching habit or bruxism. Histologically hyperkeratosis and intracellular edema of the epithelium is seen.

Toothbrush Trauma

This injury occurs to the gingiva and is produced by the toothbrush. It appears as white, reddish, or ulcerative lesions or linear superficial erosions, involving marginal and attached gingiva of maxillary canine and premolar region. They may be mistaken for vesiculobullous or infectious lesions if the history is not elicited properly. Severe form of toothbrush injury is characterized by clefting of the gingival margin and gingival recession. In more severe form there will be notching of the tooth and loss of alveolar bone. Presenting complaints are pain and burning sensation.

The above mentioned injury is caused by faulty brushing technique or rabid practice of cleanliness. But B Saravanan reported a case of penetrated injury of the buccal mucosa caused by toothbrush in middle-aged man due to a freak accident and reviewed literature with respect to such simil/>

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Jan 12, 2015 | Posted by in Oral and Maxillofacial Pathology | Comments Off on 12: Physical and Chemical Injuries of the Oral Cavity
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