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Biomedical subjects

G R Holland

Publications and source records attributed to G R Holland.

At least 19 recordsLinked to original sources
PubMed1998

Phosphoprotein analysis of sequential extracts of human dentin and the determination of the subsequent remineralization potential of these dentin matrices.

Phosphoprotein appears to play an important role in the mineralization of dentin during tooth development and remineralization after demineralization by dental caries. To better understand this role, we describe the extraction and characterization of phosphoprotein from immature, human root apex dentin during and after EDTA demineralization. The extraction procedure included dissociation of the demineralized dentin matrix by guanidine hydrochloride (Gdn.HCl) followed by subsequent digestion with cyanogen bromide (CNBr) and collagenase. Characterization of these extracts included 'Stains-All' staining of SDS polyacrylamide gels (SDS-PAGE) and amino acid, protein and phosphorus analyses. The ability of these matrices to remineralize was determined by TEM and measuring calcium levels in the remineralized tissue by atomic absorption spectroscopy. The staining of SDS-PAGE gels and amino acid analysis showed that an intact phosphophoryn was extracted from the dentin of the immature apices during EDTA demineralization and that it had an apparent Mr approximately 140,000. In the subsequent extracts and digests, the phosphoprotein has a range of molecular weights, some of which may have been degraded products of the intact phosphoprotein. A greater quantity of phosphoprotein was found in the EDTA-demineralized dentin matrices than in dentin after Gdn.HCl, CNBr and collagenase digests. These EDTA-demineralized matrices also remineralized to a greater extent than those dissociated with Gdn.HCl. The differences in both the quantity and the quality, as defined by the amino acid residue profile, of the phosphoprotein in the sequential extracts of the root apex dentin may be important in affecting the ability of this tissue to remineralize.

Adolescent↗
PubMed1997

Guidelines for the design and conduct of clinical trials on dentine hypersensitivity.

Clinical trials on dentine hypersensitivity have been numerous and protocols varied. To date there is little consensus as to the conduct of studies on this poorly-understood yet common and painful dental condition. A committee of interested persons from academia and industry was convened to discuss the subject of clinical trials on dentine hypersensitivity and a consensus report is presented. A double-blind randomized parallel groups design is recommended, although cross-over designs may be used for the preliminary screening of agents. Subjects may have multiple sites scored. Sample size will be determined by estimating the variability in the study population, the effect to be detected and the power of the statistical test to be used. Subject selection is based on a clinical diagnosis of dentine hypersensitivity, excluding those with conflicting characteristics such as currently-active medical or dental therapy. The vestibular surfaces of incisors, cuspids and bicuspids are preferred as sites to be tested. A range of sensitivity levels should be included. Tactile, cold and evaporative air stimuli should be applied. Negative and benchmark controls should be incorporated. Most trials should last 8 weeks. Sensitivity may be assessed either in terms of the stimulus intensity required to evoke pain or the subjective evaluation of pain produced by a stimulus using a visual analog or other appropriate scale. The subject's overall assessment may be determined by questionnaire. Outcomes should be expressed in terms of clinically significant changes in symptoms. Follow-up evaluation is required to determine the persistence of changes. At least 2 independent trials should be conducted before a product receives approval.

Air↗
PubMed1996

Steroids reduce the periapical inflammatory and neural changes after pulpectomy.

Root canal treatment, including obturation with gutta-percha and a zinc oxide and eugenol sealer, was conducted, under general anesthesia, on the canine teeth of 12 young ferrets. Six of the ferrets were given 0.5 mg/kg dexamethasone daily. Three months after the root canal treatment, under general anesthesia, the animals were perfused with fixative and the canine periapical tissues prepared for histological examination. The extent of periapical inflammation was measured and the degree of neural sprouting in the periodontal and subapical regions estimated. Periapical lesions in steroid-treated animals were 30% of the size of those in untreated animals. Innervation density in the subapical region of the steroid-treated animals was lower than that in the animals who did not receive steroids and not significantly different from controls. Reduction in periapical inflammation induced by systemic steroids is accompanied by a reduction in neural sprouting.

Animals↗
PubMed1996

Periapical changes after orthodontic movement of root-filled ferret canines.

The effectiveness of orthodontic forces in moving root-filled teeth and the degree of apical resorption it causes have been observed in an animal model. Under general anesthesia, root canal therapy was performed on the mandibular canines on one side of 12 young male ferrets. Bilateral movement of the canines was induced with an orthodontic spring (150 to 175 g). Procion red dye was injected 1 wk presurgically to mark bone and cementum deposition. Three months later, tooth movement was assessed from pre- and posttreatment mandibular casts and by fluorescence microscopy from labeled bone deposition. Vital and nonvital teeth moved similar distances when subjected to the same forces. Root-filled teeth showed greater loss of cementum after tooth movement than vital teeth (p < 0.05), but without significant differences in radiographic root length.

Animals↗
PubMed1996

A quantitative morphological comparison of cat lingual nerve repair using epineurial sutures or entubulation.

Since lingual nerves may be transected during a variety of oral surgical procedures, including third molar removal, we have investigated two possible methods of repair. Quantitative morphological observations were made on feline chorda tympani and lingual nerves proximal and distal to transection injuries repaired either by epineurial suturing or by insertion of the cut ends into a perforated silicon tube. Proximal to the repair, the most prominent difference was an increase in the number of myelinated axons in the lingual nerve following epineurial suturing but not entubulation. Proximal to the repair site, the number of nonmyelinated axons increased in comparison with controls in both chorda tympani and lingual nerves after both procedures, though the difference was statistically significant only in the lingual nerve proximal to entubulation. Distal to the injury, both types of repair showed a reduction in the number, size, and sheath thickness of myelinated axons in comparison with unoperated controls, but the difference in numbers was statistically signIficant only distal to repair by entubulation. The number of non-myelinated axons distal to the repair sites was much higher than that in controls, the difference being greater distal to entubulation repair. There were more axons per Remak bundle distal to entubulation repair than to epineurial suturing, suggesting, perhaps, that fewer axons would ultimately become myelinated. Though the morphological differences between the two repair techniques are not as striking as the parallel electrophysiological differences reported previously (Smith and Robinson, 1995a,b), they are consistent with them and support the conclusion that, for transected lingual and chorda tympani nerves, epineurial suturing is the preferred approach.

Animals↗
PubMed1996

Experimental trigeminal nerve injury.

The successful reinnervation of peripheral targets after injury varies with the axonal population of the nerve that is injured and the extent of the dislocation of its central component from the peripheral endoneurial tube. Larger-diameter axons such as those supplying mechanoreceptors recover more readily than narrower axons such as those supplying taste. A complex, bi-directional interaction between lingual epithelium and sprouting nerve results in the redifferentiation of taste buds after denervation. Dentin and the dental pulp provide a strong attraction to sprouting nerves and will become reinnervated from collateral sources if recovery of the original innervation is blocked. The most effective repair technique for transected lingual nerves is one which brings the cut ends together rather than one that provides a temporary bridge. Injuries can result in cell death in the trigeminal ganglion but only if the injury is severe and recovery is prevented. Lesser damage results in chromatolysis and the increased expression of neuropeptides. All nerve injuries bring about changes in the trigeminal nucleus. These occur as changes in receptive field and the incidence of spontaneously active neurons, effects which are consistent with the unmasking of existing afferents. These functional changes are short-lived and reversible. Morphologically, nerve injury results in terminal degeneration in the nuclei and an increased expression of the c-Fos gene and some neuropeptides. Only a chronic constriction injury induces behavioral changes. The adult trigeminal system retains considerable plasticity that permits it to respond successfully to nerve injury. Much remains to be learned about this response, particularly of the trophic factors that control peripheral recovery and the central response to more severe injuries.

Adult↗
PubMed1996

A quantitative morphological study of the recovery of cat lingual nerves after transection or crushing.

The morphological changes were examined proximal and distal to crush and transection injuries of the lingual/chorda tympani nerve. Under general anaesthesia the nerve was transected unilaterally in 6 adult cats and crushed with watchmakers forceps in 6 others. After 12 wk, again under general anaesthesia, the injured and contralateral (control) nerves were removed, fixed and embedded for histological examination. Sections were cut from sites proximal and distal to the injury and from a site equivalent to that of the injury on the control side. Using systematic randomised sampling techniques the number of nonmyelinated axons and the number and size of myelinated axons in each nerve at each location was estimated. In addition, the mean number of nonmyelinated axons in each Schwann cell unit was determined. The only significant difference between control and injured nerves proximal to either injury was a reduction in the number of myelinated axons in the chorda tympani after transection, and an increase in their mean size. This indicates a selective loss of smaller fibres and is consistent with the poor recovery of gustatory and thermosensitive fibres previously reported (Robinson, 1989). Distal to both types of injury there was an increase in the number of fascicles. The mean number of myelinated axons was reduced distal to a crush injury but unchanged distal to transection. The number of nonmyelinated axons distal to a transection injury was 5 times control counts and after a crush injury double. These findings suggest that sprouting persists 12 wk after both injuries but is much greater after transection.

Animals↗
PubMed1995

Periapical neural changes after pulpectomy.

Pulpectomy and pulpal necrosis result in severance of the nerves that supply the pulp as well as loss of their target organ. Inflammatory changes commonly extend into the periapical region to involve those nerves. The neural response to pulpal loss combined with periapical inflammation is a derangement of the periodontal plexus normally located in the center of the periodontal space around the apical third of the root; the result is the formation of a disorganized group of sprouting and branching axons that have some features in common with neuromas. The inflammatory and neural responses continue for at least a year even when pulpectomy is followed by canal debridement and obturation. Then the responses are reduced but not eliminated by steroids. Root canal therapy with techniques that do not leave residual inflammation still results in increased periapical innervation; the increase seems to be an organized addition to the normal periradicular plexus.

Animals↗
PubMed1994

A histological comparison of periapical inflammatory and neural responses to two endodontic sealers in the ferret.

Previous studies have shown that there is a proliferation of nerves beneath the apices of pulpectomized teeth. This may be due to the inflammation induced after the procedure, resulting, perhaps, from the irritant nature of the materials used to fill the root canal. The experiment reported here was conducted to determine whether this inflammation was induced by the sealer rather than arising as a result of tissue damage and whether, if inflammation is eliminated or reduced, the neural changes are also reduced. In 12 young adult ferrets under general anaesthesia the pulps of the lower canine teeth were removed and replaced with gutta percha and sealer. A sealer of Grossman's formulation with eugenol as the liquid phase was used on one side and a calcium hydroxide sealer that contained no eugenol on the other. Three months later the animals were, again under general anaesthesia, perfused with a fixative mixture. The mandibles were removed and the presence and size of any periapical inflammatory lesions and the density of periapical innervation determined histologically. All 12 teeth sealed with the Grossman's sealer had inflammatory lesions at their apices. Three of the 12 teeth treated with the calcium hydroxide sealer showed similar lesions. In all the teeth with inflammatory lesions the normal arrangement of nerves in a periodontal 'plexus' was disrupted but there was no statistically significant difference between the overall innervation density in inflamed and non-inflamed periapical areas nor between areas beneath teeth sealed with Grossman's sealer and with calcium hydroxide. The incidence of periapical inflammation is related to the nature of endodontic sealer used.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Morphological features of dentine and pulp related to dentine sensitivity.

This review considers those structural features of the pulp and dentine relevant to an understanding of dentine sensitivity. It does not discuss innervation, or microvasculature, which are covered in other contributions. The sensitivity of dentine is directly related to the size and patency of the dentinal tubules. Tubular occlusion by peritubular dentine deposition or the formation of other intratubular material would reduce the flow of fluid and diffusion of molecules through dentine. Irregular (reparative) secondary dentine would, because its tubules are not continuous with those of primary dentine, be expected to reduce permeability and fluid flow and decrease sensitivity. Regular secondary dentine would have little or no effect other than by increasing diffusion distances. The odontoblast layer is of limited permeability and could restrict the access of materials diffusing through the dentinal tubules to pulpal axons. Odontoblasts are not involved in the sensory process as special sensory receptors but may, by modifying the local ionic environment, alter the threshold of intradentinal nerves.

Animals↗
PubMed1993

The distribution and morphological characteristics of axons innervating the periodontal ligament of reimplanted teeth in cats.

Twelve weeks after reimplanting lower canines the distribution and characteristics of myelinated and non-myelinated axons within the periodontal ligament were investigated by light and electron microscopy. The ligament was examined at 2-mm intervals along the length of the root of four reimplanted teeth and of the contralateral canines, which served as controls. In each case the periodontal ligament was reinnervated. In two of the teeth, which showed extensive apical resorption, the innervation was much less than in control teeth. In two teeth showing minimal or no apical resorption the degree of innervation at the most apical level did not differ significantly from controls.

Animals↗
PubMed1993

Neural changes in periapical lesions after systemic steroids in the ferret.

This study was intended to clarify the relationship between the neural changes which occur around the apex of the ferret canine after pulpectomy and the inflammatory process induced by the procedure. In 12 young adult ferrets, under general anesthesia, the pulps in the mandibular canine teeth were removed and replaced with gutta percha and Grossman's sealer. Six of the animals were treated with dexamethasone to reduce the inflammatory response. Three months later, the animals, again under general anesthesia, were perfused with a fixative mixture. Three unoperated animals that had not been treated with dexamethasone were also perfused. The mandibular canine teeth and their supporting tissues were removed, processed, and serially sectioned. Three-dimensional reconstructions of the periapical lesions in each animal were assembled and their volumes measured. The density of innervation in the periapical region was estimated. The mean lesion volume in the pulpectomized animals not treated with dexamethasone was 3.54 (+/- 2.27) mm3 and in the dexamethasone-treated animals 1.33 (+/- 1.31) mm3. The differences were statistically significant when tested by the Mann-Whitney U test (p < 0.01). Bacteria were not seen within any of the lesions. The innervation density beneath the canines in the pulpectomized animals not treated with dexamethasone was 164 units per mm2 (+/- 80) and in the steroid-treated animals 151 +/- 68 units per mm2. In the control, untreated animals, the innervation density was 22 +/- 10 units per mm2. The difference between the steroid-treated pulpectomized animals and the untreated pulpectomized animals was not statistically significant (p > 0.5).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

The reinnervation of healing extraction sockets in the ferret.

The objective of this study was to describe the pattern of healing of pulpal and periodontal nerve fibers following tooth extraction. The mandibular canine teeth were, under general anesthesia, removed from one side of nine young ferrets. One week (two animals), one month (four animals), and three months (three animals) later, again under general anesthesia, the animals were perfused with fixative. The mandibles were decalcified, paraffin-embedded, and serially sectioned. Sample sections were stained with hematoxylin and eosin, the remainder with a silver stain for nerves. Serial reconstructions were made of the innervation in control teeth and in the extraction sockets. A grid sampling technique was used for the estimation of the innervation density in different regions at various levels in the healing socket. One week after extraction, although osteoid material was beginning to fill the socket, the pattern of innervation remained similar to that of controls in being restricted to the former location of the periodontal ligament and being densest in the apical third of the socket. One month after extraction, the innervation consisted of many fine axons or small bundles distributed throughout the healing osteoid tissue though still most dense in the periphery of the socket. The overall innervation density increased between one week and one month post-extraction. At three months, as the margins of the socket were becoming obscured, the innervation consisted largely of one or two organized nerve trunks running from the apical to the coronal aspect in either the central or lateral aspects of the socket. At no time was there evidence of neuroma formation.

Alveolar Process↗
PubMed1992

Periapical innervation of the ferret canine one year after pulpectomy.

Previous studies have shown that, following removal of the dental pulp and its replacement with a filling material, the nerves in the periapical region proliferate within an area of chronic inflammation. This study examined these responses in the ferret in more detail, both quantitatively and in three dimensions, 12 months after pulpectomy which was followed by obturation with gutta percha and zinc oxide and eugenol sealer. The results were compared with the responses after three months. The basic patterns, in terms of both inflammation and neural proliferation, were similar at the two time periods. Both the sizes of the inflammatory lesions and the degree of neural proliferation were lower at 12 months than at three, although the differences were not significantly different in the small number of specimens examined. Bacterial stains failed to show bacteria either in the apical root canal delta or in the periapical area. It is possible that the persistent inflammation was due to the irritant nature of the obturating materials used but not due to the original tissue damage, since extraction sites, by comparison, healed very quickly. Apparently, following endodontic treatment, chronic periapical inflammation and concomitant neural proliferation can continue for long periods.

Animals↗
PubMed1992

Axon populations in cat lingual and chorda tympani nerves.

The lingual and chorda tympani nerves from five cats were examined so that normal axonal populations could be determined. After perfusion fixation, the chorda tympani and lingual nerves were removed and processed, and sections were taken from individual and combined nerves for both light and electron microscopy. The chorda tympani remained as a distinct group of smaller axons for at least 4 mm distal to its junction with the lingual nerve. The mean number +/- S.D. of myelinated axons in the chorda tympani central to the junction was 1322 (+/- 268) and in the lingual nerve central to the junction, 3227 (+/- 510). The counts were not significantly different distal to the junction, and there were no side-to-side differences. Mean myelinated axon circumferences were significantly smaller in the chorda tympani (12.86 +/- 0.87) than in the lingual nerve (22.79 +/- 1.99; p less than 0.01). The mean size of axons in the chorda tympani was slightly but consistently larger on the left (13.1 +/- 0.73) than on the right side (12.61 +/- 1.01; p less than 0.05). Distal to the junction, the average proportion of non-myelinated axons was 44% in both chorda tympani and lingual nerves.

Animals↗