Changes in the fine structure of the dental pulp in human caries pulpitis. 1. Nerves and blood vessels

The paradox of painless periodontal disease

Periodontal diseases, primarily gingivitis and periodontitis, are characterised by progressive inflammation and tissue destruction. However, they are unusual in that they are not also accompanied by the pain commonly seen in other inflammatory conditions. This suggests that interactions between periodontal bacteria and host cells create a unique environment in which the pro-algesic effects of inflammatory mediators and factors released during tissue damage are directly or indirectly inhibited. In this review, we summarise the evidence that periodontal disease is characterised by an accumulation of classically pro-algesic factors from bacteria and host cells. We then discuss several mechanisms by which inflammatory sensitisation of nociceptive fibres could be prevented through inactivation or inhibition of these factors. Further studies are necessary to fully understand the molecular processes underlying the endogenous localised hypoalgesia in human periodontal disease. This knowledge might provide a rational basis to develop future therapeutic interventions, such as host modulation therapies, against a wide variety of other human pain conditions.

Immune defense mechanisms of the dental pulp

Defense reactions of the dentin/pulp complex involve a variety of biological systems, in which the immune system plays a pivotal role. The knowledge of the organization and function of pulpal immunocompetent cells has been sparse, but in recent years a significant body of information of immune mechanisms in general has provided a footing for substantial new knowledge of the immune mechanisms of the dental pulp. The identification of pulpal dendritic cells (DCs) has generated research activities which have led to a concept of how an antigenic challenge may evoke a pulpal inflammatory response. Although DCs are not able to identify foreign antigens specifically, they provide necessary signals to activate T-lymphocytes which in turn will orchestrate other immunocompetent cells to mount the local immune defense of the dental pulp. The purpose of this review is to accent the organization and function of pulpal DCs and other tissue and cellular components and to provide a basis for how they may interact to instigate pulpal defense mechanisms.

Periapical innervation of the ferret canine and the local retrograde neural changes after pulpectomy

The amputation of the dental pulp severs a population of axons that are predominantly in the A delta and C fiber size range and are principally involved in nociception. Local periapical neuromas, if they are formed after pulpectomy, may be the sites of spontaneous nervous activity that may, in some circumstances, be involved in the genesis of chronic pain. The periapical tissues from the mandibular canines of four ferrets were examined 3 months after pulpectomies. Silver-stained paraffin sections were examined in three dimensions at the light microscope level. Ultrathin sections were examined at the electron microscope level. Compared with contralateral and independent controls, the principal changes were the loss of the periodontal plexus around the root apex, the extension of damage well below the apical foramen, and the persistence of inflammation 12 weeks postoperatively. While a somewhat disorderly mass of nerve fibers develops subapically, the arrangement has only some of the features usually associated with neuromas.

Developmental growth and degeneration of pulpal axons in feline primary incisors

The life history of pulpal axons in primary mandibular incisors was examined by light and electron microscopy in 56 kittens aged from 25 days postconception to 120 days after birth. Cells resembling Schwann cells preceded the first arrival of pulpal axons, 1 week postnatally. myelination was initiated during the second week. Two months after birth the incisors were fully grown and each pulp contained about 100 axons. Between 10 and 20% of these were myelinated and ranged in size from 1 to 5 micrometer. The relation between number of myelin lamellae and axon size appeared nonlinear and differed markedly from that in similarly sized inferior alveolar nerve axons. During the third month many unmyelinated axons showed signs of degeneration. With progress of root resorption an increasing proportion of both unmyelinated and myelinated axons degenerated. In highly resorbed incisors necrotic Schwann cells were associated with degenerating axons and there was a generalized pulpal tissue reaction. In some teeth with advanced root resorption pulpal axons were lacking. A progressive derangement of all pulpal tissue elements continued until shedding during the second half of the fourth month. In incisor nerve branches below the incisor teeth axon degeneration was very limited.

Pulpal response to bacteria in the dog

Twenty-six teeth from 8-month-old beagle dogs were used to evaluate the pulpal response to bacteria in bacterially contaminated minimally exposed and unexposed pulp in the dog. The effects were evaluated by means of serial radiographs, consecutive vital dye injections, and histologic sections. Periapical lesions developed in all of the eight teeth which were bacterially infected and exposed. Out of ten teeth which were bacterially infected and had cavities without pulp exposure, only two teeth in the acute group demonstrated inflammatory changes and loss of odontoblastic function directly beneath the infected dentinal tubules. Within the limits of the experimental design, this study demonstrated the pulpal responses of the dog with respect to bacteria.

Arteriovenous shunts demonstrated in the apical circulation of rat incisor teeth by the use of radio-labeled microspheres

The distribution of systemically introduced 85Sr-labeled tracer microspheres to unexposed and previously exposed rat lower incisor tooth pulps was investigated. Fewer tracer microspheres entered the microcirculation of pulps that had been previously exposed as compared to control unexposed pulps. The presence of large numbers of dilated blood vessels in the apical tissues of teeth with exposed pulps was observed, and it is postulated that these vessels may be operating as arteriovenous anastomoses so that the pulpal microcirculation of teeth with inflamed pulps is bypassed by the tracer microspheres. The possible clinical significance of these findings is discussed.

Changes in the fine structure of the human dental pulp subsequent to carious exposure

Sections of human pulp tissue taken from the region of a carious exposure in four young patients each having a clinical history of spontaneous dental pain were examined with the electron microscope. All the tissues examined exhibited a generalized edema, and an infiltration with lymphocytes, plasma cells, polymorphonuclear leukocytes and macrophages. Varying degree of lysis of pulp and inflammatory cells were evident. The unmyelinated nerve axons of the pulp appeared to be least affected. Extracellular lysosomes were present in many of the necrotic areas. Edematous vacuoles were noted in two of the pulp specimens. In some of the sections these vacuoles appeared to be responsible for a physical distortion of adjacent unmyelinated nerve axons. It was postulated that such distortion may be a contributing factor to the pain of pulpitis. In another of the pulp specimens, micro-organisms were found intracellularly and extracellularly. Intracellularly they were present within the cytoplasm of polymorphonuclear leukocytes and macrophages and exhibited evidence of lysis. Only two morphological forms, a gram positive rod, and a gram positive coccus were identified.