Pulp-dentin biology in restorative dentistry. Part 1: normal structure and physiology

Considerable knowledge has accumulated over the years on the structure and function of the dental pulp and dentin. Some of this knowledge has important clinical implications. This review, which is the first of seven articles, will be limited to those parts of the normal structure and physiology of the pulp and dentin that have been shown to result in, or are likely lead to, tissue reactions associated with the clinical treatment of these tissues. Although certain normal structures will be highlighted in some detail, a basic knowledge of pulpal and dentinal development and structure is a prerequisite for an understanding of this text.

Restorative considerations in the dental treatment of the older patient

The older person and his or her dentition will have a clinical presentation and a reaction to treatment that is influenced by his or her unique blend of aging and disease processes. Changes seen in enamel, dentin, pulp, and cementum of the older patient are described in terms of their causes and the impacts of the changes on clinical presentation and treatment choices.

In vitro temperature change at the dentin/pulpal interface by using conventional visible light versus argon laser

BACKGROUND AND OBJECTIVE

The argon laser has been promoted as a competing technology to multi-wavelength visible light as a curing source for dental restorative resins. However, the comparative thermal risk to the pulp between these two sources of light energy requires determination. The objective of this study is to compare the temperature induced at the dentin-pulpal interface between the argon laser and visible light curing unit at a variety of exposure regimens and conditions.

STUDY DESIGN/MATERIALS AND METHODS

In vitro temperatures were measured and recorded at the dentin-pulpal interface upon external light exposure. Independent variables included the dentin thickness, duration and waveform of exposure, and presence of composite resin.

RESULTS

In most instances, the argon laser resulted in less temperature rise on the pulpal-dentin interface.

CONCLUSION

The argon laser should not pose a serious thermal risk to the pulp if used at recommended energies.

The effect of physiological root resorption on the histological structure of primary tooth pulp

The aim of this study was to determine, the effect of physiological root resorption on the histological structure of healthy primary tooth pulp. Fourteen canine teeth, which needed to be extracted for orthodontic purposes and in which resorption had just begun (1st group, resorption did not exceed 1/3 of root length) or was in advanced resorption stage (2nd group, resorption was between 1/2 and 2/3 of root length), were used for this study. After the extraction of the teeth, they were prepared for histological examination. Then the samples were examined using light microscopy. The result no difference was found which could be detected by polarized light microscope that was related to physiological resorption and histological structure of primary teeth pulp.

CGRP immunohistochemistry in wound healing and dentin bridge formation following rat molar pulpotomy

The aim of the present study was to investigate the neuropeptide CGRP in order to determine the effect on dentin bridge formation during the healing process after pulpotomy. First maxillary molars in 56-day-old Wistar rats (n=60) were used. The rats were killed for a neurohistopathological examination at 1, 3, 7, 14, and 28 days postoperatively. Neuronal changes in the residual pulp were studied using CGRP immunohistochemistry. By 1-3 days postoperatively, the CGRP-IR nerve fibers with abnormal beaded or knob-like structures were found to be more swollen than in the control and the leakage of a CGRP-IR-positive substance from the involved end of the nerve fibers was seen. At 7 days postoperatively, a vast number of newly sprouted CGRP-IR nerve fibers appeared in the residual pulp and some of them terminated in the differentiating odontoblast layer and the initial matrix layer of the dentin bridge. By 14-28 days, the nerve density had become progressively lower in the residual pulp. Regenerated axons also terminated in the odontoblast layer and the fibrous matrix layer of the calcified dentin bridge. These findings suggest that such sensory neuropeptides as CGRP may, therefore, play a role in dentin bridge formation in the rat molar.

Development of transplanted pulp tissue containing epithelial sheath into a tooth-like structure

The aim of these studies was to find out whether intact neonatal pulp tissue containing residual epithelial cells can induce the development of a tooth-like structure in situ. First maxillary neonatal hamster molar pulps containing adhering undifferentiated epithelial cells were transplanted submucosally in the oral cavity of recipient mothers for periods ranging from 2-8 weeks and the tissues were then processed for light microscopy. Developing tooth-like structures containing mineralised tubular dentine, predentine and a vascularised pulp-like chamber lined with functional odontoblast-like cells were observed in the specimens within 2 weeks of transplantation. Enamel and root formation were not observed. These data indicate that neonatal dental pulp tissues containing epithelial cell remnants have the capacity to develop into tooth-like structures and that this could be the explanation for the development of tooth-like structures sometimes observed in infants after extraction of a natal tooth.

Endodontic therapy in the veterinary patient

Standard root canal therapy is more clearly described as conventional endodontics. Most modern endodontic treatment involves removal of the irreversibly damaged pulp followed by cleaning and shaping of the root canal space and subsequent filling, or obturation, with a semisolid material and a sealer. A general increase in awareness of the benefits of veterinary endodontics has created a rise in the demand for endodontic procedures that help to retain the teeth longer. This article on endodontic therapy includes endodontic anatomy, diagnosis of endodontic disease, pulpectomy techniques of access preparation, canal preparation and filling the canal, partial coronal pulpectomy, and treatment of the open apex. Familiarity of the techniques covered in this article and with advances in veterinary endodontics have become necessary for the veterinary dental practitioner.

Endodontic diagnosis in dogs

Complete endodontic evaluation should diagnose endodontic involvement, provide a treatment plan, and evaluate the true success or failure probabilities. Evaluation of the age, physical and oral health of the patient, the endodontic anatomy, clinical and radiographic findings can provide a treatment plan and a predictable prognosis.

Innervation of blood vessels in the rat incisor pulp: a scanning electron microscopic and immunoelectron microscopic study

Although two types of nerve endings have been proposed to innervate blood vessels in the dental pulp, the precise innervation pattern is not well understood. This is mainly due to the lack of information regarding the positional relationships of nerve fibers with blood vessels at the electron microscopic level. The rat incisor pulp was investigated by scanning electron microscopy (SEM) after connective tissue digestion and by transmission electron microscopy after immunohistochemical localization with polyclonal anti-PGP 9.5 antibody. SEM specimens revealed that unmyelinated nerve fibers passed through the tunica adventitia of the blood vessel in the center of the pulp and that these fibers then entered the tunica media of the smaller arterioles. The nerve fibers divided into many collaterals, and these terminated on the surface of smooth muscle cells and endothelial cells. The fibers extended toward smaller vessels. The terminal fibers then reached the subodontoblastic capillary plexus and terminated on pericytes, while the odontoblastic capillary plexus had no direct innervation. In the pulpal venules, nerve fibers were located adjacent to the pericytes and endothelial cells, and they extended toward postcapillary venules. The same results were confirmed by immunoelectron microscopy. The present study demonstrated that in the rat incisor pulp the microvasculature as well as larger vessels were directly innervated by free nerve endings, suggesting that the local regulation of blood flow could take place not only at larger vessels but also at the level of the microvasculature in this tissue.

Histologic study of pulp capping using chlorhexidine in dogs

This histological study was conducted to compare the pulp reactions to chlorhexidine and calcium hydroxide. Twenty permanent premolar teeth of beagle dogs were mechanically exposed under aseptic conditions. The pulp was then capped with one of the following: chlorhexidine 0.2% on the left side and calcium hydroxide (dycal) on the right side of the same dog. Maxillary second premolars were extracted from each dog three weeks after the pulp capping procedure. Maxillary third premolars and mandibular first premolars were extracted at 6 weeks and 9 weeks respectively. The mandibular second premolars were extracted three months after the pulp capping procedure. The specimens were fixed in 10% formalin and decalcified in 5% formic acid. Serial sections, 7 microns thick, were prepared and stained with hematoxylin and eosin. Teeth treated with chlorhexidine or with calcium hydroxide were well tolerated by the dental pulp at 3 and 6-week intervals. Pulps treated showed satisfactory pulp reaction and the odontoblastic layer appeared to be normal and in its configuration. Inflammatory response was not present at the 6-week time interval. At nine weeks, the inflammatory response was severe in those teeth treated with calcium hydroxide. There were no remarkable histological differences among the treatment groups at 12 and 15 weeks. These specimens showed complete loss of pulpal architecture. Regressive changes were seen and microscopic specimens revealed presence of spaces and intertwining bundles of films in the pulp.

In vitro magnetic resonance imaging of rodent teeth

OBJECTIVE

The anatomic structure of rat teeth was studied and observed using magnetic resonance imaging with high spatial resolution.

STUDY DESIGN

The right part of the low mandible of two rats of 3 and 12 weeks old were analyzed. Images with different orientations were performed in a 2 Tesla magnetic field using the spin-echo imaging technique.

RESULTS

Highly spatially resolved images revealed details of teeth, and anatomic differences between a young and an adult rat were demonstrated.

CONCLUSION

Magnetic resonance imaging is well suited to image the buccal area and may be a useful tool for the diagnosis of dental diseases.

Endodontic considerations in the geriatric patient

Endodontic needs of today's and tomorrow's growing older adult population present increasing challenges for dental care providers. Biologic and anatomic differences in the dental tissues between older and younger patients must be understood and considered in treatment planning and performance for appropriate endodontic procedures. These differences generally do not contraindicate treatment, which, when performed correctly, will be successful in the elderly patient.

Expression of TGF-beta superfamily receptors in dental pulp

Transforming growth factor-beta (TGF-beta) superfamily members and their cell-surface receptors may play inductive and/or regulatory roles in tooth development and repair. It will be important to identify the complete set of TGF-beta superfamily receptors, to examine their temporal and spatial localization during tooth development, and to elucidate the cascade of molecular events of tooth formation induced by the TGF-beta superfamily. In this report, we have cloned the cDNAs encoding potential receptors for TGF-beta superfamily members in rat incisor pulp and bovine adult pulp which are regarded as embryonic and adult pulp, respectively. We analyzed poly (A)+ RNA from rat incisor pulp and bovine adult pulp by reverse-transcriptase/polymerase chain-reaction (RT-PCR), using a degenerate primers corresponding to the most conserved amino acid sequences in the intracellular serine/threonine kinase of type I or type II like kinase-1 (ALK-1), ALK-2, ALK-3 (bone morphogenetic protein receptor type IA, BMPR-IA), ALK-4 (B1), ALK-5, ALK-6 (BMPR-IB), and BMPR-II (BMP type II receptor) was found to be in dental pulp. Northern blot analysis further detected TGF-beta type II receptor (T beta R-II) mRNA transcript in addition to the above-identified receptors. These results provide the first evidence of multiple type I and type II receptors for TGF-beta s, activins, and BMPs expressed in embryonic and adult pulp, implicating diverse function in tooth development and pulp tissue repair.

Pulpal response to cavity preparation by an erbium, chromium:YSGG laser-powered hydrokinetic system

The near red-pulsed erbium, chromium:yttrium-scandium-gallium-garnet laser hydrokinetic system, or Er,Cr:YSGG laser HKS, is effective in cutting dental hard tissues. In this longitudinal study, the authors studied the continuously erupting open-apex incisors of New Zealand albino rabbits and the constricted apex teeth of beagles to determine the effects of HKS-produced lesions at various energy levels and of preparations produced by a tapered fissure bur on dental pulp. No pulpal inflammatory responses could be identified either immediately or 30 days after surgery in HKS preparations that removed enamel and dentin without pulp exposure.

Distribution and possible origin of galanin-like immunoreactive nerve fibers in the mammalian dental pulp

Human, dog, cat and rat dental pulps were investigated for the presence and distribution of galanin-like immunoreactive (-IR) nerve fibers, and the possible origin of pulpal galanin-IR nerve fibers in the rat was examined. Galanin-IR nerve fibers were present in the dental pulps of all species examined. Two types of galanin-IR nerve fibers were distinguished with regard to morphology; thin varicose nerve fibers and thick smooth-surfaced nerve fibers. Thin varicose galanin-IR nerve fibers were seen to run along the blood vessel in the human, dog and cat root pulp. In the coronal pulp, galanin-IR nerve fibers ran toward the odontoblastic layer but they did not form the subodontoblastic nerve plexus. In rat molar pulp, few galanin-IR nerve fibers were observed; the distribution of these nerve fibers was similar to those in human, dog and cat pulp. In contrast, many thick smooth-surfaced galanin-IR nerve fibers were observed near the blood vessels in incisor pulp of the rat; occasionally a few varicose galanin-IR nerve fibers were also observed. Transection of the inferior alveolar nerve or mandibular nerve caused complete disappearance of galanin-IR nerve fibers in rat dental pulp, while surgical sympathectomy of the superior cervical ganglion did not affect their distribution. The present results indicate that galanin-IR nerve fibers are present in the mammalian dental pulp, and that the intrapulpal galanin-IR nerve fibers in the rat originate from the trigeminal ganglion and are primary afferents.

Cytodifferentiation of the odontoclast prior to the shedding of human deciduous teeth: an ultrastructural and cytochemical study

BACKGROUND

In human deciduous teeth, odontoclastic resorption takes place at the pulpal surface of the coronal dentine prior to shedding, and this resorption shows clear time-related histological changes (Sahara et al., 1992).

METHODS

Using this phenomenon as an observation system, we examined the cytodifferentiation of human odontoclasts by light and electron microscopy. For a histochemical marker of odontoclast differentiation and function, tartrate-resistant acid phosphatase (TRAP) activity was determined by light and electron microscopic enzyme histochemistry.

RESULTS

As root resorption neared completion, TRAP-positive mononuclear cells were initially detected in the pulp chamber. They had abundant mitochondria, small lysosomes, and moderately developed rough endoplasmic reticulum throughout their cytoplasm. In these mononuclear cells, TRAP activity was localized in compartments of the biosynthetic pathway, i.e., in cisternae of the endoplasmic reticulum and Golgi lamellae, as well as small lysosomes. The TRAP-positive mononuclear cells first made contact with the predentine surface by their elongated cellular processes. After attachment, they spread out along the predentine surface and developed specialized membrane structures, clear zones, and ruffled borders. Next, they fused with each other on the predentine surface and formed typical multinucleate odontoclasts. After termination of their resorption function, the odontoclasts lost their ruffled borders and became detached from the resorbed surface. Most of the detached odontoclasts had numerous large pale vacuoles and secondary lysosomes and appeared to be in the process of degeneration.

CONCLUSIONS

The present study demonstrates that: (1) odontoclasts differentiated from TRAP-positive mononuclear cells, which presumably originate from circulating progenitor cells, (2) membrane specialization of odontoclasts, i.e., development of a clear zone and ruffled border, is induced following their contact with the resorption surface, (3) multinucleation of odontoclasts takes place only after their attachment to the resorption surface, (4) mature multinucleate odontoclasts can resorb predentine as well as dentine in the same way as osteoclasts resorb bone, and (5) at the end of the resorption, odontoclasts gradually lose their ruffled borders and become detached from the resorbed surface.

Progressive changes in the pulpo-dentinal complex and their clinical consequences

With changes in the age structure and oral health in the population, changes in the pulpo-dentinal complex are becoming more relevant clinically. Age-related changes in the structure of dentine and pulp are reviewed. The influence of these changes on restorative dentistry are considered with particular emphasis on endodontics and the use of adhesive restorative materials.

Age estimation of adults from dental radiographs

Previous studies have shown that with advancing age the size of the dental pulp cavity is reduced as a result of secondary dentine deposit, so that measurements of this reduction can be used as an indicator of age. The aim of the present study was to find a method which could be used to estimate the chronological age of an adult from measurements of the size of the pulp on full mouth dental radiographs. The material consisted of periapical radiographs from 100 dental patients who had attended the clinics of the Dental Faculty in Oslo. The radiographs of six types of teeth from each jaw were measured: maxillary central and lateral incisors and second premolars, and mandibular lateral incisors, canines and first premolars. To compensate for differences in magnification and angulation on the radiographs, the following ratios were calculated: pulp/root length, pulp/tooth length, tooth/root length and pulp/root width at three different levels. Statistical analyses showed that Pearson's correlation coefficient between age and the different ratios for each type of tooth was significant, except for the ratio between tooth and root length, which was, therefore, excluded from further analysis. Principal component analyses were performed on all ratios, followed by regression analyses with age as dependent variable and the principal components as independent variables. The principal component analyses showed that only the two first of them had significant influence on age, and a good and easily calculated approximation to the first component was found to be the mean of all the ratios. A good approximation to the second principal component was found to be the difference between the mean of two width ratios and the mean of two length ratios, and these approximations of the first and second principal components were chosen as predictors in regression analyses with age as the dependent variable. The coefficient of determination (r2) for the estimation was strongest when the ratios of the six teeth were included (r2 = 0.76) and weakest when measurements from the mandibular canines alone were included (r2 = 0.56). Measurement on dental radiographs may be a non-invasive technique for estimating the age of adults, both living and dead, in forensic work and in archaeological studies, but the method ought to be tested on an independent sample.

A new biological approach to vital pulp therapy

Molecular biology is providing opportunities to develop new strategies or agents for the treatment of a wide variety of diseases. The availability of large amounts of highly purified proteins produced by recombinant DNA techniques is an obvious example. Recent evidence has implicated proteins belonging to the bone morphogenetic protein (BMP) subgroup of the transforming growth factor beta supergene family in tooth formation and dentinogenesis. It has long been known that bone and dentin contain bone morphogenetic protein activity. Recently, recombinant human BMP-2, -4, and -7 (also known as OP-1), have been shown to induce reparative dentin formation in experimental models of large direct pulp exposures in permanent teeth. The manner in which these agents act appears unique. New reparative dentin replaces the stimulating agents applied directly to the partially amputated pulp. Hence, the new tissue forms contiguous with, largely superficial to, and not at the expense of the remaining vital pulp tissue. This suggests a therapeutic approach permitting the induction of a predetermined and controlled amount of reparative dentin. Additionally, OP-1 has been associated with the formation of reparative dentin after application to a freshly cut but intact layer of dentin. These findings may provide future clinicians with additional options for the treatment of substantially damaged or diseased vital teeth.

Morphology of the deciduous tusk (tush) of the African elephant (Loxodonta africana)

The tusk of the African elephant is preceded by a deciduous tooth generally known as the tush. Tushes from nine elephant fetuses and six calves younger than 1 year were exposed by dissection and described morphologically. All tushes consisted of a crown, root and pulpal cavity, the formation of which is completed soon after birth. They reached a maximum length of 5 cm, appeared not to erupt through the skin and were pushed aside and resorbed during enlargement of the distally located primordium of the tusk. Dental enamel, which covered the crown, could easily be removed and consisted of rods with an interwoven arrangement; the dentine-enamel junction was flat. Cellular cementum extended for variable distances over the crown and the dentine was tubular in nature. Although the tush apparently has no function, it provides the anlage and orientation for the development of its permanent successor.

Pulpo-dentinal complex revisited

OBJECTIVES AND METHODS

The value of the concept of a pulpo-dentinal complex was assessed on human teeth treated according to the ISO test on biological evaluation. The teeth were extracted after 1 or 3 months and examined histologically. Biochemical and biological data available from the dental literature were also re-examined.

RESULTS

During the early development of the tooth, pulp and dentine establish close links and form an undivided organ. However, examination of the tissues at later stages of development casts doubt on the validity of such a concept. Major differences are reviewed in this report between the cells (odontoblasts and heterogeneous pulpal cells) and extracellular matrix (collagens, non-collagenic proteins and phospholipids) located either in the odontoblast-dentine area or in the pulp. It seems also that clear-cut differences are detected during inflammatory and repair processes.

CONCLUSION

It is concluded that, although the existence of a dentino-pulpal reaction cannot be denied, the concept of a pulpo-dentinal complex is an oversimplification and should be revisited. This may have implications in the evaluation of restorative treatments and in the design of a tissue repair strategy.

Optical characteristics of human extracted teeth and the possible application of photoplethysmography to the human pulp

In order to record pulp blood flow by photoplethysmography, the light transmission properties of extracted human teeth and human peripheral blood at wavelengths between 400 and 800 nm were first investigated. Transmission through peripheral blood and extracted teeth was lower at wavelengths shorter than 600 nm. Transmitted-light photoplethysmography (TLP) was applied to teeth in situ using a tungsten light, or one of two light-emitting diodes (LED) with peak wavelengths of 565 and 695 nm. A CdS-CdSe photoconductive cell was used as a detector. The LED with a peak intensity at 565 nm was the most efficient of the three light sources for recording the TLP. The results indicate that the TLP could be used to assess pulp vitality.