Henry O. Trowbridge

Assessment of reliability of electrical and thermal pulp testing agents

The reliability of several pulp testing agents was compared in intact human premolar teeth. The electric pulp tester, CO 2 snow and dichlorodifluoromethane were found to be more dependable than ethyl chloride and ice in producing a positive response. However, in young patients the electric pulp test was less reliable than CO 2 snow and dichlorodifluoromethane but more reliable than ethyl chloride and ice. The thermal agents were also compared for their ability to decrease intrapulpal temperature in vitro. The rate of temperature decrease was greater when CO 2 snow or dichlorodifluoromethane were applied to the tooth than in the case of either ethyl chloride or ice.

Sensory response to thermal stimulation in human teeth

This study investigated the response of teeth to thermal stimulation. The sensory response occurred before the temperature was changed in the region of the pulpodentinal junction where sensory structures are located. A theoretical model was developed to examine the hydrodynamic forces produced by temperature change in the dentin. It is theorized that these forces may be capable of exciting sensory structures in the tooth.

2. Pathogenesis of pulpitis resulting from dental caries

Summary Demonstrable evidence suggests that the pattern of inflammation in the tooth affected by carious attack is determined by the permeability of dentin and the proximity of the carious lesion to the pulp. Accumulation of immunologically competent chronic inflammatory cells either accompanies or follows retrogressive changes in the odontoblast layer beneath the lesion. Deposition of collagen and proliferation of small vessels are also features of early inflam matory changes in the pulp. A transition from a chronic to an acute inflammatory reaction occurs as the lesion approximates the pulp or invades reparative dentin. Progressive accumulation of large numbers of neutrophils, presumably drawn by chemotactic influences, results in suppuration that may be diffuse or may become localized to form an abscess. Surface ulceration may develop as a result of chronic suppuration, which remains confined to the areas of the pulp beneath the carious lesion, and results in the creation of a space. In slow progressing lesions, continued formation of reparative dentin may be capable of preventing pulp exposure. Degeneration of the pulp occurs when the number of bacteria entering the pulp exceeds the ability of the blood vessels of the pulp to furnish a sufficient number of blood leukocytes to repel the bacteria. Hyperplastic pulpitis represents a proliferation of chronic inflammatory tissue in response to carious exposure to the young pulp.

Review of dental pain—histology and physiology

The sensory system of the pulp appears to be well suited for signaling potential damage to the tooth. The tooth is innervated by a large number of A (myelinated) and C (unmyelinated) nerve fibers. These include both sensory afferent fibers and sympathetic fibers that modulate pulpal blood flow. In the peripheral pulp, branches of the sensory nerves give rise to an interlacing network of fibers known as the subodontoblastic plexus. From this plexus nerve fibers extend to the odontoblastic layer, predentin, and dentin and terminate as free nerve endings. All forms of pulpal stimulation are perceived as noxious and stimulation gives rise only to pain. Available evidence suggests that the sensitivity of dentin involves displacement of fluid in dentinal tubules that in some way activates A fibers. It appears that C fibers only respond to noxious stimuli that directly affect the pulp. The role of odontoblasts in the registration of pain is still unclear, but dentin sensitivity does not seem to be altered by their demise. Evidence indicates that certain inflammatory mediators and intrapulpal pressure changes lower the pain threshold of nerve endings in the pulp.

Effects of thermal vitality tests on human dental pulp

Experiments were conducted to determine the effects of thermal pulp testing agents on the human dental pulp. Histological evaluation of the pulps of premolar teeth to which heated gutta-percha had been applied for up to 10 s revealed no evidence of injury. Teeth to which carbon dioxide (CO 2 ) snow was applied for as long as 5 min were found to have structurally intact pulps. When the thermal testing agents were applied to teeth in vitro, temperature in the region of the pulpodentinal junction did not reach noxious levels. This study indicates that assessment of tooth vitality with either heated gutta-percha or CO 2 snow does not jeopardize the health of the pulp.

Ability of bacterial endotoxin to diffuse through human dentin

An in vitro system was developed to determine whether bacterial endotoxin is capable of diffusing through dentin without the use of filtration pressure. Cavities were prepared in five third molar teeth in order to produce a split chamber device consisting of occlusal and pulpal chambers with 0.5 mm of intervening dentin. Endotoxin was introduced into the occlusal chamber and the effluent in the pulpal chamber was sampled every 30 min for 5 h and at 24 h using the limulus lysate assay. In four specimens the initial appearance of endotoxin in the effluent ranged from 15 min to 4 1/2 h. In two specimens the concentration of endotoxin in the effluent leveled off in 4 1/2 and 5 h, respectively, whereas in another two the concentration continued to increase throughout the experiment. In one specimen no endotoxin was detected. The results indicate that endotoxin is capable of passing through 0.5 mm of dentin.

Intradental sensory units: Physiological and clinical aspects

Knowledge of the anatomical and physiological characteristics of intradental neurons provides insight into the origin and nature of sensory signals in the tooth. The emphasis of this review is on patterns of innervation and mechanisms of dentin sensitivity and hyperalgesia as they relate to dental pain. Special consideration is given to the role of zinc oxide and eugenol mixtures in dental analgesia.

Apical closure of nonvital permanent incisor teeth where no treatment was performed: Case report

Summary Although apical closure in nonvital teeth has occurred following treatment with various root canal medicaments, our case suggests that root end closure may take place in the absence of endodontic therapy. Thus, debridement of the pulp chamber may not be a prerequisite for apical closure. Furthermore, the results in this case indicate that the use of root canal medicaments is not always essential to induce root end closure.

Dentin ablation by Ho:YAG Laser: Correlation of energy versus volume using stereophotogrammetry

The future use of lasers in endodontics is dependent upon predictable and consistent ablation of dentin. In this pilot study we used an Ho:YAG laser fiberoptic delivery system to apply laser energy to prepared tooth sections in vitro. Longitudinally sectioned single-rooted human teeth were subjected to single-energy pulses varying from 25 to 1750 mJ at a focal length of 1 mm. At different energy levels we observed changes in the dentin surface ranging from minute surface pitting to the formation of large craters. Scanning electron microscopy and stereophotogrammetry were used to determine the relationship between the amount of energy applied to dentin and the extent of dentin ablation. Dentin crater formation was quantified by determining surface area, depth, and volume of craters produced. Increases in laser energy were compared with increases in surface area, depth, and volume of craters produced within the range of 150 to 1200 mJ. The Ho:YAG laser fiberoptic delivery system used in this study provides an effective means of ablating dentin. Three-dimensional stereophotogrammetry may prove to be a useful method for further studies on the effects of laser energy on mineralized tissues.