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 Air Abrasive Technique

In the air abrasive technique, aluminum oxide sprayed under pressure is used as an abrasive for the cavity preparation and surface treatment. The main drawback of this procedure is, it does not allow the operators’ stereognostic ability to control the depth of cutting. However Ferrazzano et al, based on their study in 60 mandibular third molar concluded that the macroscopic size and shape of cavities is connected to working distance, while working time is important to determine the depth of preparation. Also the abrasive dust is a potential health hazard to the operator and the patient. Nowadays it is used only to clean the pit and fissures prior to the application of sealants.

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.

Effects on Pulp

The pulps of teeth in animals subjected to laser radiation have been described by Taylor and his associates as showing severe pathologic changes, including hemorrhagic necrosis with acute and chronic inflammatory cell infiltration. The odontoblastic layer also underwent coagulation necrosis, although the severity of the response varied with the amount of radiation.

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.

Self-polymerizing Acrylic Resin

Self-curing resins were extensively used as restorative materials, particularly in anterior teeth. There is evidence to indicate, however, that these resins may cause serious damage to the dental pulp. Still, not all investigations are in complete agreement.

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.

Cement Bases

A cement base is a layer of cement commonly used beneath the dental restoration either to encourage recovery of the injured pulp or to protect the pulp against the injuries. Intermediary base materials that are commonly used under permanent restorations include zinc phosphate cement, zinc oxide-eugenol cement, and calcium hydroxide cement. Ideally, a cement base should be biologically compatible with the dental pulp and such is the case with zinc oxide-eugenol and calcium hydroxide. However, zinc phosphate cement, when placed against dentin, acts as an irritant to the dental pulp because of the acid content which varies between pH 3.5 and 6.6, as discussed previously.

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.

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.

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.

Histologic Features

Healing in such cases may be of several types. The most satisfactory form of healing is the union of the two fragments by calcified tissue, and this is analogous to the healing of a bony fracture. The clot between the root fragments is organized, and this connective tissue is subsequently the site of new cementum or bone formation. There is nearly always some resorption of the ends of the fragments, but these resorption lacunae ultimately are repaired. If the apposition between the two fragments is not close, the union is by connective tissue alone. It appears likely that the repair process can be organized from connective tissue cells in both the pulp and the periodontal ligament.

Treatment and Prognosis

The site, direction, and size of the crack or fracture dictates the choice of the treatment. It ranges from stabilization with a stainless steel band or crown to endodontic treatment and restoration. If untreated, CTS can lead to severe pain, possible pulpal necrosis and periapical abscess. Unfortunately, management of CTS is not always successful. In some cases, such as in vertical root fractures (split root) in single rooted teeth, the only treatment option is tooth extraction.

Clinical Features

Ankylosis of the permanent tooth seldom manifests clinical symptoms unless there is a concomitant pulp infection which may be the underlying cause. If there is an extensive area of the root surface involved, the tooth may give a dull, muffled sound on percussion rather than the normal sharp sound. The fact that this condition exists may become apparent only at the time of extraction of the tooth, when considerable difficulty will be encountered, sometimes necessitating surgical removal.

Radiographic Features

If the area of ankylosis is of sufficient size, it may be visible on the radiograph. There is loss of the normal thin radiolucent line surrounding the root that represents the periodontal ligament, with a mild sclerosis of the bone and apparent blending of the bone with the tooth root.

Histologic Features

Microscopic examination reveals an area of root resorption which has been repaired by a calcified material, bone or cementum, which is continuous with the alveolar bone. The periodontal ligament is completely obliterated in the area of the ankylosis (Fig. 12-4).

Treatment and Prognosis

There is no treatment for ankylosis. Ankylosed teeth have a good prognosis and, unless removed for some other reason, should serve well indefinitely.

Clinical Features

Pain during movement, occlusal derangement, abnormal mobility, gingival lacerations, crepitus on movement, trismus, loss of sensation of the involved side, and ecchymosis are common features of mandibular fracture.

Treatment

Like other fracture management jaw fractures are also treated by reduction and immobilization. Complications include nonunion, malunion, and fibrous union.

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.

Treatment and Prognosis

Since the definitive diagnosis of the solitary bone cyst cannot be established without surgical exploration, the dentist usually opens into the cavity, attempts to enucleate a lining and, in the course of manipulation, reestablishes bleeding into the lesion. If the cavity is then closed, it has been found that healing and filling of the space by bone occur in most cases in 6–12 months. Seldom is a second surgical procedure necessary. If the space is a large one, bone chips have been used to aid in filling the defect with good results.

The extreme rarity of these lesions in older patients would suggest that not only may they be self-limiting, but at least some are capable of complete and spontaneous remission.

Clinical Features

In the three reported series of cases, approximately 75% of the focal osteoporotic bone-marrow defects of the jaws occurred in women, and they involved the mandible in approximately 85% of the cases. In nearly every instance the lesions were asymptomatic and discovered only during routine radiographic examination.

Radiographic Features

This lesion, which has a predilection for the mandibular molar area, generally appears as a radiolucency of variable size, a few millimeters to a centimeter or more, with a poorly defined periphery indicative of lack of reactivity of adjacent hone (Fig. 12-8A).

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.

Treatment

The radiographic appearance of these lesions is not sufficiently characteristic to permit diagnosis with certainty, and for this reason they must be investigated surgically to rule out osteomyelitis, traumatic bone cyst, and other odontogenic tumors. Once the diagnosis has been established, no additional treatment is necessary.

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.

Treatment

The treatment of this lesion consists in enucleation of the cyst. It does not tend to recur.

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.

Extrusive Movement

Extrusion of a tooth by an orthodontic appliance is similar to normal tooth eruption. The tissue changes induced by this form of movement consist apposition of new bone spicules at the alveolar crest and at the fundus of the alveolus arranged in a direction parallel to the direction of force. The direction of the spicules then is parallel to the long axis of the tooth and tends to increase the height of the alveolar crest. The normal width of the apical periodontal ligament is maintained by the new bony spicules here formed in the same direction. The relation between the tooth and the alveolus tends to remain constant.

Intrusive or Depressive Movement

The application of orthodontic force in such a manner as to cause depression of a tooth results in tissue changes that are the opposite of those found during extrusion, or elongation. In tooth depression, resorption of bone occurs at the apical area and around the alveolar margin. New bone formation is actually minimal.

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.

Effect of Deciduous Tooth Movement upon Permanent Tooth Germs

Breitner and Tischler based on their study in young monkeys found that when a deciduous tooth was moved, the associated permanent tooth germ followed this movement.

Whenever a deciduous tooth was moved away from a tooth germ, the permanent tooth germ quickly followed. If a deciduous tooth was moved toward a permanent tooth germ, this germ moved in the same direction as the deciduous tooth.

These studies offered suggestive evidence that the form of the permanent dental arch may be modified by altering the deciduous arch through orthodontic treatment of the deciduous dentition.