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PubMed1998

Scanning electron microscopy and immunohistochemical observations of the vascular nerve plexuses in the dental pulp of rat incisor.

BACKGROUND: The innervation of rat incisors, which are continuously erupting teeth, is quite unique. Although many reports have documented the neural control of the pulpal blood flow, only a few studies have examined the structure and distribution of vascular nerves in the rat incisors. This study examined the nerve plexuses and the spatial relationship of nerve terminals to smooth muscle cells of the pulp vessels of rat incisors. METHODS: The innervation of the pulp vessels of rat incisors was studied using immunohistochemical evaluations of calcitonin gene-related peptide (CGRP) and neuropeptide-Y (NPY). The three-dimensional ultrastructure of nerve meshworks and terminals on smooth muscle cells of pulp arterioles were examined by scanning electron microscopy (SEM) with a KOH digestion method. RESULTS: The blood vessels were associated with many nerve fibers immunoreactive for CGRP and NPY. Some NPY and frequent CGRP-immunoreactive nerve fibers were observed in the labial odontoblast layer. Three different morphologies of nerve fibers could be distinguished: fine nerve fibers with numerous terminal varicosities, medium-sized fibers associated with occasional or much scarcer varicosities, and thick fibers that had no varicosity and sometimes ran apart from blood vessels. The SEM observations identified five vascular segment types: terminal arterioles, precapillary arterioles, capillaries, postcapillary venules, and muscular venules. Nerve meshworks were observed around the large terminal arterioles; these meshworks were very comparable to those revealed by immunohistochemistry. The vascular smooth muscle cells were closely attached by one or more terminal varicosities. CONCLUSIONS: It has become evident that the large terminal arterioles in the rat incisors receive a dense nerve supply and provide well-developed wall architecture, suggesting an important role of neuronal regulation on the vessels.

Animals↗

PubMed1981

Pulpal axons in developing, mature, and aging feline permanent incisors. A study by electron microscopy.

The ingrowth, maturation, and aging of pulpal axons was followed by electron microscopy in permanent mandibular incisors of 44 cats aged 35 days-11 years. The first axons entered the incisor pulps about 2 months after birth. Cells resembling Schwann cells, but lacking an axonal relation, were also observed at this time. Axonal ingrowth and maturation continued until 7 months, when the pulps contained 92-394 axons, 81-88% of which were unmyelinated. Between month 7 and 20 months the character of the incisor pulpal axons remained largely unchanged. In adult cats the myelinated pulpal axons had diameters of 1-6 micrometer. The relation between the number of myelin lamellae and the axon size correlated better with linear + logarithmic than linear functions. The g-ratios were higher than in most peripheral nerves, and tended to increase with axon diameter. In the old adult this tendency was more evident and the g-ratios were generally lower. From 3 years on the incisors displayed various age-related or pathological alterations. These were accompanied by axonal changes and axon loss. In contrast to earlier stages perineuriumlike sheaths were frequent in old teeth. The findings are discussed in relation to axon development in the inferior alveolar nerve and in primary incisor pulps.

Aging↗

PubMed1981

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.

Aging↗

PubMed2006

Study of Pax6 mutant rat revealed the association between upper incisor formation and midface formation.

In this study, we investigated the process of supernumerary upper incisor formation in the Pax6 mutant rat, rSey(2)/rSey(2), which exhibits a facial cleft between the medial nasal and maxillary processes. Histological investigation and epithelial labeling studies of wild type rat embryos indicated that the upper incisor develops by fusion of two primary dental placodes (PDPs) in the medial nasal process with a contribution from the epithelium of the maxillary process. In the rSey(2)/rSey(2) embryo, both PDPs are formed but they stay apart, then subsequently these PDPs independently develop into upper incisor tooth buds. In order to examine if the failure of the two placodes to fuse is due to the cleft between the maxillary and medial nasal processes, maxillary and medial nasal process fusion was inhibited with a barrier in wild type embryos. This resulted in the maintenance of the two distinct PDPs. These results demonstrate that fusion of the facial processes reduces the number of odontogenic placodes and is required to assemble all components at one site for rat upper incisor formation. The results also provide further insight into the mechanism of supernumerary incisor formation in human cleft lip conditions.

Animals↗

PubMed1999

Evaluation of labio-lingual bony support of lower incisors in orthodontically untreated adults with the help of computed tomography.

The aim of the present study was to assess bone volume and bone density in orthodontically untreated adults using a CT analyzing method, with reference data in the clinically essential area of the lower incisors being obtained. For quantitative and qualitative assessment of the labial and lingual bony support of the lower incisors, existing CT-images of 20 adult men with a near-to-normal occlusion and a clinically healthy periodontal situation were evaluated. With the help of a special program (SIM/Plant) and on the basis of axial scans, sagittal scans were constructed, permitting the individual imaging of the lower incisors and their alveolar process. The bony support of each tooth was registered labially and lingually perpendicular to the tooth axis at intervals corresponding to 10% of the root length. At the various root levels, especially at the upper parts of the roots, only small amounts of bony support, if any, were frequently observed. Labially, bony fenestrations and dehiscences were frequently seen, but lingually mostly dehiscences. No clinically relevant association was found between labial bony support and cephalometrically registered inclination of the lower incisors. Bone density, which was registered in Hounsfield units at the gingival, middle and apical thirds of the root levels, increased from the gingival to the apical thirds of the roots, generally with lower lingual than labial values. Before initiating orthodontic treatment a thorough clinical assessment of the anatomical situation in the lower incisor segment should be carried out. At present bone volume in this area can be reliably assessed only with computed tomography; however, this has to be weighed up against increased radiation risks. Therefore, the form of the symphysis should initially be roughly assessed by means of conventional cephalometry, with additional CT-based analysis of individual teeth being confined to special indications.

Adult↗

PubMed2006

Comparison of dynamic shear properties of the porcine molar and incisor periodontal ligament.

The role of the periodontal ligament (PDL) is to support the tooth during function and resist external forces applied to it. The dominant vertical component of these forces is associated with shear in the PDL. The mechanical response to vertical force may, however, be different between the molar and incisor as their loading regimen is different. The present study was designed to determine the viscoelastic behavior in shear of the PDL of the porcine molar and incisor (n = 10 for each). From dissected mandibles transverse sections including the mesial root of first molar and the incisal root were obtained and used for dynamic shear tests. Shear strain of 1.0% was applied in superoinferior direction parallel to the root axis with a wide range of frequencies (0.01-100 Hz). The viscoelastic behavior was characterized by the storage and loss modulus and loss tangent as a function of the frequency. For the incisor and molar, the complex and storage moduli increased significantly with the frequency. For the incisor, the loss modulus also increased with the frequency. The loss modulus and loss tangent were significantly (p < 0.05) larger in the incisor than in the molar. The present results suggest that the incisal PDL revealed more viscous behavior during dynamic shear than the molar one, which might have important implications for the principal role of the anterior teeth such as PDL sensation.

Animals↗

PubMed1979

The orthodontic center of rotation of the maxillary central incisor.

The cephalometric records of sixty-four Class II, Division 1 cases treated exclusively with removable orthodontic appliances have been used in a study of the manner in which maxillary central incisors tilt. The center of rotation was most frequently located in the middle third of the incisor root. The longer the time interval between the pre- and posttreatment cephalograms, the more apical was the rotation axis likely to be, an effect ascribed to growth changes in the maxilla. If the effects of growth are taken into account, it seems that the maxillary central incisor seldom, if ever, tilts about the apical third of its root when force levels customarily recommended for tipping movements are employed. The results suggest that the instantaneous and orthodontic centers of rotation are one and the same and support the view that the manner in which incisor teeth move in response to a single applied force depends principally on the physical properties of the tooth root, supporting bone, and periodontal membrane. An unexplained correlation was found between the rate of incisor movement measured at the cervical margin of the tooth and the level of the rotation center.

Adolescent↗

PubMed1984

Tooth morphology and lower incisor alignment many years after orthodontic therapy.

The dental models of seventy-seven orthodontically treated patients were evaluated to determine the contribution of lower incisor tooth dimensions to their alignment many years after treatment. Tooth dimensions included the maximum mesiodistal (MD) and faciolingual (FL) dimensions and the shape ratio represented by MD/FL. Incisor alignment was assessed by means of Little's irregularity index, and all measurements were recorded to the nearest 0.1 mm with modified dial calipers. Multiple regression analysis revealed that the total contribution of all these lower incisor dimensions accounted for only 7.4% of the variability in their alignment, which was not statistically significant. A similar lack of association between lower incisor tooth dimensions and their alignment was found in a sample of eighty-six adults with untreated malocclusions. It therefore appears that the size and shape of the lower incisors do not significantly contribute to their alignment many years after orthodontic treatment.

Adult↗

PubMed1983

Partial pulp resection increases unimpeded eruption rates of the rat incisor.

Thirty rats were divided into 3 equal groups. Following 9 days of induced unimpeded eruption, a single partial pulp resection was performed on the repeatedly-shortened lower left incisor of one group. A total of 3 resections, each repeated after 48 h, was performed on the animals in a second group. The lower left incisor was shortened but the pulp was not resected in the 3rd sham-operated control group. Eruption rates of all of the incisors were recorded daily. Partial resection of the pulp increased the unimpeded rate of the experimental incisors in the first group by 50 per cent at 24 h after operation and an increase occurred 3 times in the second group of rats (by 45, 36 and 25 per cent respectively). The rate returned to control levels 24 h later. No significant differences were observed between the eruption rates of the right maxillary and mandibular incisors of the animals in the 3 groups. The increased rate of eruption may be induced by local regulators from the traumatized pulp that are transmitted to components of the periodontal ligament which provide the force for eruption.

Animals↗

PubMed1986

Scanning electron microscopy of developing human deciduous incisor teeth.

The mineralized parts of the teeth of 17 human fetal dentitions, aged 15-38 weeks, were measured mesio-distally and occluso-cervically. The growth pattern of the incisors, with particular emphasis on the changes at the developing incisal edge was studied. Contralateral teeth in the same arch developed at approximately the same rate and with mirror-image morphology. Mineralization started in the upper and lower central incisors, followed by the corresponding lateral incisors. It then progressed at approximately the same rate for both incisors. At first, mesio-distal enamel growth was more significant, but was surpassed by occluso-cervical development later. Five development stages were identified as the incisors developed from a central lobe to the mature form. The main component of growth for the mesial lobe was in the incisal direction, and for the distal lobe in a distal direction, resulting in the characteristic approximal asymmetry of these teeth.

Humans↗

PubMed1989

A longitudinal cephalometric study of incisor supra-eruption in young and adult rhesus monkeys (Macaca mulatta).

Supra-eruption was examined in 28 adult (N = 19 experimental and 9 control) and 12 juvenile monkeys (N = 7 experimental and 5 control). The experimental animals had a bite splint cemented to the posterior maxillary teeth which opened the bite inter-incisally by 15 mm and was worn continuously for 48 weeks. Lateral cephalograms were taken prior to the cementation and at 12-week intervals thereafter. Radio-opaque bone implants placed in the basal bone of the jaws served as fixed reference points from which to assess the vertical and horizontal components of central incisor movement. Significantly greater movement of both upper and lower incisors towards the occlusal plane occurred in the experimental animals of both age groups over the 48 weeks when compared to the same aged controls (p less than 0.01). Mean vertical movement ranged from 4 mm (about 40% of crown length) in the juvenile upper incisors to 1.5 mm (15%) in the adult lower incisors. The overall pattern of movement of upper and lower incisors in the experimental juveniles differed from that in the controls only in the vertical component (p less than 0.01), indicating that the supra-eruptive response was superimposed on the antero-occlusally directed tooth movement and alveolar growth that normally occurs in rhesus monkeys of this age. In contrast to the more evenly distributed response found in the juveniles, the majority of the supra-eruptive response occurred during the first 12 weeks in the experimental adults.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗

PubMed1990

Histochemical demonstration of neural carbonic anhydrase activity within the mandibular molar and incisor tooth pulps of the rat.

Carbonic anhydrase (CA) activity was enzyme histochemically assessed in: (1) neuronal cell bodies in the rat trigeminal ganglion that were retrogradely labeled with FITC-WGA from the mandibular molar and incisor tooth pulps; (2) cell bodies retrogradely labeled with HRP-WGA from the mandibular molar tooth pulp; and (3) nerve fibers within the decalcified mandibular molar and incisor tooth pulps. The cell size spectrum of the FITC-WGA-labeled neurons was similar for both molar and incisor tooth pulps with about 90% being medium or large (greater than or equal to 300 microns2 in cross-sectional area). About 30% of the FITC-WGA-labeled cell bodies exhibited CA activity for both tooth pulps. The HRP-WGA-labeled cells also showed CA activity. In the molar root pulp, finely myelinated nerve fibers exhibited CA activity. Histochemical reaction products were distributed in the axoplasm and the cytoplasmic pocket of Schwann cell inside the compact myelin. In the incisor pulp, CA-reactive unmyelinated axons coexisted with non-reactive axons within the same Schwann units. The Schwann cell cytoplasm directly surrounding reactive axons also exhibited histochemical stainability. In the light of known distribution of CA in the peripheral nervous system, the present data suggest that the rat molar and incisor tooth pulps receive substantial innervation of large myelinated primary afferent fibers. The finely myelinated and unmyelinated axons, that have been repeatedly shown to predominate the intrapulpal nerve fibers, are considered to represent intrapulpal, terminal and preterminal specialization of otherwise large myelinated nerve fibers.

Animals↗

PubMed1987

Epidermal growth factor-induced precocious incisor eruption is associated with decreased tooth size.

Epidermal growth factor (EGF) causes precocious eruption of incisors in vivo and is mitogenic for tooth-derived cells in vitro. These two observations lead to the hypothesis that the EGF-induced precocious eruption is the result of an increase in the size of the incisor. To test this hypothesis, neonatal mice were injected daily with various doses of EGF and, seven days after birth, were perfused with fixative. EGF causes a retardation of overall growth (as measured by body weight) and a dose-dependent thickening of the epidermis. The incisors were examined in midsagittal histological sections and in X-ray microradiographs. Contrary to our expectations, EGF causes a dose-dependent decrease in the size of the incisors. This result suggests that the stimulation of the growth of odontogenic cells seen in tissue culture is not part of the physiological response to EGF in vivo and that EGF-induced precocious eruption of incisors is not due to an increase in the growth rate of the tooth.

Animals↗

PubMed1986

Is electrical stimulation of the rat incisor an appropriate experimental nociceptive stimulus?

The purpose of this study was to determine whether or not tooth pulp stimulation in the rat can selectively activate the pulp nerve fibers without excitation of the periodontium and to decide if the nerve fibers situated in the pulp of the rat's incisor are involved in the nociceptive reactions caused by an intrapulpal stimulation. The experiments were carried out on 20 awake and freely moving Sprague-Dawley rats. Bipolar stimulating electrodes were inserted into the pulp of the left lower incisor and in the right incisor after removal of the pulp. Special cares were taken to avoid, on the right side, direct stimulation of the stump of the apical nerve. The jaw opening reflexes were recorded from the digastric muscles ipsilaterally to the stimulated teeth and the thresholds were compared. Using the same animals, four typical and reproducible nociceptive behavioral reactions caused by a long tooth pulp stimulation were also observed (shock of 0.5 ms at 50 Hz during 1 s). The stimulus intensity was progressively increased, and the threshold of each reaction was recorded. For each of the 20 rats tested, the jaw opening reflex and the nociceptive reactions did not disappear after removal of the pulp, but the threshold of the responses to the stimulation of the nonvital tooth were significantly above the threshold of the responses to the stimulation of the vital incisor. The conclusion was tooth pulp stimulation activates the periodontal nerve fibers in the rat, and stimulation of the incisor pulp is significant in pain study in the rat because the thresholds of the jaw opening reflex and the nociceptive reactions were increased after the tooth pulp tissue was removed.

Animals↗

PubMed2005

Factors of importance for the development of dehiscences during labial movement of mandibular incisors: a retrospective study of adult orthodontic patients.

PURPOSE: Labial movement of mandibular incisors has traditionally been considered a risk factor for gingival recession. The aims of this study were to assess changes in prevalence and severity of gingival recession of mandibular incisors during orthodontic treatment of adults in whom the incisors had been moved labially and to identify parameters that could predict recession. MATERIAL: The sample consisted of 150 adult patients (aged 33.7 +/- 9.5 years, mean +/- SD) treated nonextraction with fixed appliances. Pretreatment overjet, overbite, degree of crowding, presence of tooth rotation, canine relationship, vertical face height, and position of the mandibular incisor to A-pogonion and mandibular lines were registered on study casts and lateral headfilms. Pretreatment gingival recession, width of keratinized gingiva, gingival biotype, gingival inflammation, and visible plaque accumulation were recorded, as was posttreatment gingival recession. Labial movement was determined by measuring pretreatment and posttreatment casts. Descriptive statistics were used to describe gingival recession at baseline and follow-up. Variables to be included in a logistic regression analysis as possible predictors of recession were identified with a bivariate correlation analysis. RESULTS: No significant increase in the mean gingival recession was observed during treatment. The prevalence of gingival recession greater than 0.1 mm increased from 21% before treatment to 35% after (P < .05). Only 2.8% of the subjects developed recession greater than 2 mm, and 5% of the pre-existing gingival recessions improved. The presence of baseline recession (P < .001), gingival biotype (P < .0179), and gingival inflammation (P < .003) were identified as possible predictors of recession. None of the orthodontic variables was significantly associated with recession. CONCLUSIONS: Gingival recession of mandibular incisors did not significantly increase during orthodontic treatment. After treatment, fewer than 10% of subjects had gingival recession greater than 2 mm, and, at follow-up, 5% of the pre-existing gingival recession had improved. Thin gingival biotype, visual plaque, and inflammation are useful predictors of gingival recession.

Adult↗

PubMed2006

Correlation between mandibular incisor crown morphologic index and postretention stability.

INTRODUCTION: Considering postretention stability as a result of successful orthodontic treatment, we aimed to verify the influence of mandibular-incisor-crown morphology in the relapse of mandibular anterior crowding. METHODS: The sample comprised 56 white subjects of both sexes with Class I and Class II malocclusions at pretreatment, treated with extraction of 4 first premolars and edgewise mechanics. No patient underwent interproximal stripping during or after treatment. Mean pretreatment age was 13.23 years. Mean treatment time was 2.11 years, and mean posttreatment evaluation time was 5.12 years. Mandibular anterior crowding was measured with the Little irregularity index, and the mesiodistal and buccolingual proportion of the mandibular incisor crowns was measured with the Peck and Peck index. The measurements were obtained from dental casts at the pretreatment, posttreatment, and postretention stages. The Pearson correlation coefficient was calculated to determine the correlation between mandibular-incisor-crown morphology and the amount of postretention-crowding relapse. RESULTS: The mandibular-incisor-crown morphologic index was not significantly correlated with the amount of mandibular-anterior-crowding relapse. CONCLUSIONS: Mandibular-incisor-crown morphology is not correlated with the amount of mandibular-anterior-crowding relapse.

Adolescent↗

PubMed2004

Is the lingual forming part of the incisor a structural entity? Evidences from the fragilitas ossium (fro/fro) mouse mutation and the TGFbeta1 overexpressing transgenic strain.

Our objective was to study the teeth of a mutant mice fro/fro that display severe forms of osteogenesis imperfecta. One day and 8 week-old fro/fro and +/fro heterozygote mice (wild type, WT) were processed for light and scanning electron microscopy. The genetic defect, shown to be located on chromosome 8, induced alveolar bone and teeth hypomineralisation. Due to defective cell proliferation in the fro/fro, the distal growth of the mandibular incisors was impaired. Immunolabelling revealed an increase of chondroitin/dermatan sulphate, whereas no difference was detected in dental tissues for decorin and biglycan. Amelogenin expression was decreased in the incisor and enhanced in the molar. Dentin sialoprotein was below the level of detection in the fro/fro, whereas osteonectin and osteopontin were unchanged. The main target of the mutation was seen in the lingual part of the incisor near the apex where dentine formation was delayed. In the molars, bulbous roots with obliteration of the pulp chamber were seen. In the TGFbeta1 overexpressing mice, the lingual root-analogue part of the incisor was missing. In the molar, short roots, circumpulpal dentine of the osteodentine type and pulp obliteration were seen. It may be noted that, although the mutant and transgenic strains mutations are two different genetic alterations not related to the same defective gene, in both cases the expression of the dentin sialoprotein is altered. Altogether, the present data suggest that the lingual forming part of the incisor seems to be an anatomical entity bearing its own biological specificities.

Amelogenin↗

PubMed2006

Fracture resistance of upper and lower incisors restored with glass fiber reinforced posts.

The aim of this in vitro study was to evaluate the fracture resistance of upper and lower incisors restored with glass fiber reinforced posts (FRP). There were 32 upper and 32 lower incisors endodontically treated and FRPs were cemented, using pretreated (Rocatec) and non-pretreated posts. Crowns were fabricated and cemented with Ketac-cem or Panavia. Additionally, eight upper and lower incisors with intact natural crowns were used as control groups. Mandibular incisors restored with FRPs attain fracture strengths comparable to those of natural teeth. The fracture strength of all teeth was increased by using Rocatec. Cementation of the crowns using Panavia only increased the fracture strength in upper incisors. Rocatec used to pretreat the posts and crowns cemented using an adhesive cement appear to reduce the risk of clinical failure.

Bite Force↗