Three-dimensional reconstruction of the rat incisor by means of computerized histomorphometry

Effects of Mandibular Advancement plus Prohibition of Lower Incisor Movement on Mandibular Growth in Rats

Introduction: To test the hypothesis that mandibular advancement with the use of a fixed functional appliance combined with prohibition of labial movement of the lower incisors will have no effect on mandibular growth in growing rats.

Materials and Methods: Fifteen 4-week-old male rats were divided into fixed, unfixed, and control groups (n = 5, each). Bite-jumping appliances were used in the fixed and unfixed groups. Sites of bone perforation and the lower incisors were connected with ligature wires in the fixed group. The ramus height, mandibular length, and inclination of lower incisors were examined for 4 weeks, and those values were compared among five intervals and three groups by through one-way analysis of variance models and the Bonferroni multiple comparison test for post hoc comparison.

Results: Increases in ramus height and mandibular length during the experimental period were 1.5 mm and 2.5 mm in the fixed group, 1 mm and 1.5 mm in the unfixed group, and 1.2 mm and 1.9 mm in the control group, respectively. Growth of ramus height and growth of mandibular length in the fixed group were greater than in the unfixed and control groups during the experimental period. The inclination of lower incisors in the unfixed group was increased 8.0 degrees throughout the experimental period, which differed from results obtained in the other groups.

Conclusions: Mandibular growth was accelerated effectively before and during the pubertal period in rats by mandibular advancement with a fixed functional appliance combined with prohibition of labial movement of the lower incisor.

The effect of age on morphology and eruption of the lower incisors in mature rats

OBJECTIVE

This study investigated the effect of age on tooth and periodontium morphology and on tooth eruption in the lower incisors of 28 female rats, initial age 10 weeks.

DESIGN

Morphometric data of the incisors in three young mature rats (weight 199+/-2.4 g) were compared to that of three 18-week-old (weight 260+/-5 g) animals. The rate of eruption was monitored during 12 months in 11 rats with all teeth in occlusion and in 11 rats with one lower incisor kept constantly out of occlusion.

RESULTS

: The incisors continued to enlarge after the animals reached maturity with the size of the teeth increasing both longitudinally and circumferentially. Tooth volume increased by 21%, while that of the periodontal ligament was enlarged by only 12%. The rate of impeded eruption declined steadily from a mean value of 542+/-49 microm/day during the first experimental month to a mean value of 443+/-25 microm/day during the concluding month (p<0.05). The eruption rate of the teeth exceeded that of attrition rate by 2.4%. The unimpeded eruption proceeded steadily throughout the experimental year, at a mean rate of 811+/-12.

CONCLUSIONS

Apparently in mature rats age has no effect on the genetic potential as expressed by the unimpeded eruption. In the impeded teeth age does affect the phenotypic expression of the eruptive function governed by occlusal forces as well as by the form and size ratio of the tooth and its PDL.

The effect of functional occlusal forces on orthodontic tooth movement and tissue recovery in rats

The influence of physiologic occlusal forces on tissue response to orthodontic tooth movement and its subsequent recovery was investigated in rats. The mandibular incisors were subjected to tipping and intrusive loads for 2 weeks. In 27 animals, the teeth remained in occlusion, while the incisors were shortened out of occlusion in 29. In each group, some rats were killed at the end of the tooth movement process, and the rest were kept alive for a 13-week recovery period. The subgroups were matched with corresponding controls. Tooth intrusion and eruption were monitored throughout the experiment; then histomorphometric and histopathologic evaluations were performed on the incisors and their periodontal tissues. Tooth movement was barely affected by the functional forces. However, immediately upon 2-week load application, damage to the pulp was more extensive in the occluding teeth; this might be due to the combined intrusive vectors of functional and mechanical loads. The effect of the physiologic function was expressed primarily during the recovery period, in which the eruptive function and distorted periodontal ligament space returned to normal significantly faster in the occluding teeth. This was also true for the healing of dental and periodontal lesions. The incidence of tooth resorption was also reduced. Normal occlusal function is imperative for rapid reconstitution of the damage caused by orthodontic forces.

Histomorphometric study of the periodontal vasculature during and after experimental tipping of the rat incisor

The periodontal vasculature encircling the entire length of the rat lower incisor was studied at the time of tipping movement and 3 months later. In 12 rats (212+/-4 g b.w.), loads (0.19+/-0.016 N) were applied to the lower left incisor in a linguointrusive direction. After 2 weeks of loading, six experimental animals were killed with the loading springs in place. The springs were removed in the six remaining rats, which were killed 12 weeks later. Six additional rats with intact teeth served as control. All incisors were fixed, demineralized, embedded in glycol methacrylate and cross-sectioned perpendicular to the long axis of the tooth. The distance of each section (2 microm) from the apex was calculated. A computerized image-analysis program was used to measure the width and area of the labial and lingual periodontal ligament to establish whether the measured segments corresponded to the compressed or expanded zones. In each cross-section, the various types of blood vessels were counted and the cross-sectional area of all venous vessels was measured. The results showed that after 2 weeks of loading (1) the general trend of vascular changes was similar under pressure and tension; (2) the large-diameter vessels were unaffected by loading; (3) the mean number of terminal arterioles had decreased significantly, while the number of capillaries and postcapillary venules had increased significantly in the apical tooth part; (4) the venous blood vessel area had decreased significantly in the apical tooth part; (5) the intensity of the vascular reaction was dependent on the degree of tissue distortion; and (6) after 12 weeks' recovery the vascular changes were still present, demonstrating a rebound effect. The findings suggest that microvascular alterations following tooth loading are not directly related to the spatial effect of loading itself and are of a much longer duration than expected.

Stereological determination of the volume of the rat hemimandible tissues

Rodent incisors are useful models to study the development and behavior of dental and periodontal tissues. Some studies require three-dimensional reconstructions of the tooth but none of the described methods yield actual volumetric data. Unlike the rat lower incisors the hemimandible can be easily isolated and its volume was determined by Cavalieri's geometrical principle. This method associated with point-counting volumetry was used to calculate the volume of the structures found in that bone mainly those related to the lower incisor. For 172 g male rats the mean volume of the hemimandible was 182.7 mm(3), statistically not different from 184.9 mm(3) the mean volume of the same hemimandibles determined by Archimedes' principle. The coefficients of error (CE) of Cavalieri's estimates for the hemimandible, incisor as a whole (the tooth itself, odontogenic region and periodontium) and bone tissue were less than 0.04. For the incisor individual tissues the CEs were usually above 0.05, however their calculated volumes are probably not different from the actual ones. The data for incisors and their periodontal tissues and for bone, because of continuous growth of these structures, are meaningful only for rats of the same gender, strain and weight range.

3D reconstruction based on hard tissue microtome cross-section pictures in dentistry

The aim of this study was to examine the accuracy of the computerized 3D surface analyzing and volume measuring method in dentistry. Two different types of test objects were used in the first part of the measurements. Each sample of the two groups was cross-sectioned using a hard tissue microtome. The sections were photographed on both sides and were projected on a graphical tablet and analyzed using a computer program. The measured and calculated parameters were compared. In the second part, 200 microm thick horizontal sections were prepared from 11 human incisor roots using the hard tissue microtome. This way, five sections were prepared from the apical 2 mm of each root. The effects of section thickness and number were modeled by decreasing the inclusion rate of the obtained number of sections from 10 to 2 and its influence on the calculated results was determined. This method was suitable for the approximation and analysis of 3D parameters. The results indicated that using 200-300 microm section thickness, the measured values were approximately 8-21% lower than the real parameters.

Effect of repeated orthodontic treatment on the dental and periodontal tissues of the rat incisor

This study evaluated the response of treated teeth to renewed orthodontic force. Thirty female rats (201 +/- 2.7 g) were divided into groups A and B. Linguointrusive loads (20.58 +/- 1.88 g) generated by springs were applied to the lower left incisor for 2 weeks and then removed to allow recovery during 27 weeks (group A). Identical loading was then repeated in group A and applied as primary treatment in group B. Five animals from each group were killed with the springs in situ (A-1 and B-1), while the remaining 20 animals were killed after a 3-month recovery (A-2, B-2). The decalcified incisors were cross-sectioned serially (2 microm), and the distance of each section from the apex was computed. Dental and periodontal injuries were evaluated by light microscopy and plotted according to their location on the tooth axis. The intrusion of the teeth in group A-1 was significantly greater, whereas recovery of the normal eruption rate in group A-2 was significantly slower compared with groups B-1 and B-2. The histopathologic lesions in groups A-1 and B-1 did not differ. However, group A-2 showed a higher frequency of injured enamel organ, tissue infiltration by inflammatory cells, necrotic areas, and dentin resorption than group B-2. Initial orthodontic loading had a detrimental effect on the ability of the periodontal and dental tissues to cope with, and to recover from, repeated stress, probably because of a decrease in the number of periodontal fibroblasts and damage to the dentin-protecting cementoblastic layer.

Effect of loading on the migration of periodontal fibroblasts in the rat incisor

The influence of occlusal loading on periodontal fibroblasts was investigated in hypoloaded (shortened out of occlusion), functionally loaded and hyperloaded (constant linguointrusive mechanical loads of 9.4 +/- 0.06 g) lower left rat incisors. One hour following injection of 3H-thymidine, half of the animals in each group were killed, while the remaining rats were killed 2 weeks later. The decalcified incisors were embedded in glycolmethacrylate and sectioned (2 microns) serially, perpendicularly to the long tooth axis. Labeled and unlabeled fibroblasts in the tooth-related periodontal ligament were counted in 8 x 80 microns consecutive layers. Cell density (CD) and labeling index (LI) were plotted according to their location on the apico-incisal and cementum-bone axes. Loading caused a decrease in CD and a shift of cells from the cementum towards the middle of the ligament, proportionally to load intensity and duration. The average tooth-to-bone movement of the cells was 2 microns/day in the hypoloaded and 4 microns/day in the two loaded groups. The mean daily tooth eruption rate was 975 +/- 60 microns, 499 +/- 18 microns and 103 +/- 27 microns in the hypo-, functionally- and hyperloaded teeth, respectively. The respective concomitant average daily cell migration rates in the incisal direction were 786 microns, 500 microns, and 500 microns, i.e. 80%, 100% and 485% of the tooth eruption rates. The gross disparity between cell velocity and tooth movement under conditions of restrained eruption indicates active motility of the fibroblasts, rather than their passive tooth-eruption dependent translation.

Histomorphometric study of the periodontal vasculature of the rat incisor

This study assessed quantitatively the vascular system in the cementum-related periodontal ligament (PDL) along the rat incisor. The lower left incisors of six rats (+/- 200 g) were subjected to routine histological procedures and cross-sectioned serially (2 microns), and the distance between each section and the apex was computed. The PDL of five sections at different levels along the tooth was divided into mesial, lingual, and lateral parts. The number and area of small and terminal arterioles, capillaries (C), sinusoids (S), post-capillary venules (PCV), and connecting venules, as well as the area of the PDL, were established. Blood vessels (BV) occupied 47 +/- 2% of the PDL area in the apical half and 4 +/- 2% at the incisal end. Of the total BV area, 41%, 32%, and 27% were located on the lingual, mesial, and lateral tooth sides, respectively. The majority of BV belonged to the venous system (98.5 +/- 0.6% and 82.5 +/- 3.0% in the apical and incisal parts, respectively). The apical venous system comprised 95.4 +/- 1.6% S and 3.2 +/- 1.0% PCV, reversing to 27.2 +/- 14.2% S and 55.2 +/- 11.3% PCV in the incisal half. The number of arterial profiles increased gradually from 6.8 +/- 1.5 at the apex to 25.3 +/- 2.4 in the incisal part and that of C from 9.0 +/- 1.18 to 25.0 +/- 4.3. The extensive vascularization in the apical half of the PDL is consistent with the high metabolic demands and with the need for protective cushioning of the constantly growing dental and periodontal tissues.2+_

Dynamics of tissue changes found after mechanical loading of the rat incisor. I. A three-dimensional longitudinal study of the morphologic aspects

A three-dimensional morphometric method was used to evaluate progressive changes in shape and size of recovering dental and periodontal tissues after orthodontic loading. In 35 female rats weighing 212 +/- 4 gm, loads of 19.7 +/- 1.6 gm generated by closed-coil springs were applied for 2 weeks to the shortened lower left incisor. The rats were killed in groups of five at 0, 1, 3, 5, 7, 9, and 10 weeks (groups 0-w to 10-w) after the springs were removed. A group of rats with normal incisors (group C-1) and one with five incisors that had been continually shortened for 10 weeks (group C-2) served as controls for groups 0-w and 10-w, respectively. Width, area, and volume of the tooth and enamel-bordering periodontal ligament (e-PDL) and cementum-bordering PDL (c-PDL) were measured. After 2 weeks of loading (group 0-w), the volume of the compressed e-PDL had decreased by 22%, and the volume of the stretched c-PDL had increased by 72%, suggesting that bone apposition lags behind the rate of tooth movement. During the recovery period, the dental and periodontal parameters tended toward a gradual return to control (C-2) values, although at the end of 10 weeks many still lagged significantly behind the controls. Recovery was slowed by repeated reversals at different sites in the various groups. The ability of the preloaded incisor to adjust to changes in occlusal function was lastingly impaired.

A three-dimensional evaluation of the effects of functional occlusal forces on the morphology of dental and periodontal tissues of the rat incisor

We examined the effect of function on tooth and periodontal ligament (PDL) morphology in 40 lower incisors of adult female rats. Ten teeth were exposed to occlusal hyperfunction for three months, ten to hypofunction for three weeks, ten to hypofunction for three months, while ten teeth in normal occlusion served as control. Transverse ground sections were cut at various levels perpendicular to the tooth long axis, and their distances from the apex were calculated. The outlines of the tissues were traced and fed into a computer. We plotted the measurements according to their location and fitted them by second-order polynomials. We calculated tissue volume for the proximal 18 mm of bone-embedded tooth. Hyperfunction affected tooth shape, in that it became more rounded. The volumes of the dental tissues remained unchanged, while width and volume of the cementum-bordering PDL increased. Hypofunction did not alter tooth shape, but influenced its size: After three weeks, tooth circumference decreased, and after three months, it expanded. Dentin width was reduced, with concomitant increase of pulp size. The amount of enamel diminished initially, but after three months returned to normal values. The PDL bordering enamel expanded proportionally to the duration of hypofunction. The changes in socket size reflected the total dimensional variations in the tooth and its PDL. The results demonstrate that the shape and size of growing teeth and their periodontium are influenced by functional occlusal forces.

Three-dimensional presentation of cell migration in the periodontal ligament of the rat incisor

The progenitor compartments and cell migration were examined in the tooth-related periodontal ligament (t-PDL) of rat incisors. A pulse injection of 3H-Tdr was administered to 15 rats (200 gm each) and the animals were killed in groups of five, at 1 hr and at 1 and 2 weeks after injection. Three-dimensional analysis of cell counts and labeling index demonstrated the existence of two progenitor compartments (PC). The apical PC (responsible for 70% of synthesizing cells) was concentrated in the apical 5 mm of the t-PDL. The paracemental PC (30% of synthesizing cells) was located along and around the cementum, occupying 24 micron of the t-PDL. The cells from the apical PC migrated incisally at a rate of 6 mm/week, which is a rate similar to that of tooth eruption. The cells from the paracemental PC moved in a transverse direction toward either bone or cementum at the much slower rate of 16 micron/week.

Three-dimensional presentation of the fibroblast progenitor compartment in the periodontal ligament of the rat incisor

The purpose of this study was to determine the shape, size, and spatial configuration of the fibroblast progenitor compartment (PC) of the tooth-related periodontal ligament (PDL). Five albino rats (weight 200 gm) were killed 1 hr following intraperitoneal injection of 3H-thymidine. The incisors were decalcified, embedded in glycol-methacrylate, and sectioned serially, perpendicularly to the long axis of the tooth. Ten 2-microns-thick sections along each tooth were selected, processed autoradiographically, and the distance from the apex measured. Labeled and unlabeled fibroblasts were counted in 8 x 80-microns consecutive layers. Cell density (CD) and labeling index (LI) were plotted on a three-dimensional system of coordinates depicting the directions: apex to incisal edge, cementum to bone, and cemento-enamel junction (CEJ) to lingual tooth surface. The CD along the tooth was constant, except at 2-6 mm distant from the apex, where it was significantly higher. The highest concentration of cells around the tooth was in the 20-microns region adjacent to the cementum. The PC on the mesial and lateral tooth sides extended 1-4 mm from the apex, with the LI peak (6.5%) occurring at 2 mm. The PC on the lingual tooth side was located at 2-6 mm from apex, peaking (14%) at 4 mm. On the cementum-bone coordinate, the PC extended to about 50 microns from the cementum on all sides, the LI peak appearing at a distance of 20-40 microns from the tooth. The LI was consistently higher on the lingual side than on the mesial and lateral aspects.

Long-term effect of loading on the fibroblast population of the periodontal ligament in the rat lower incisor

The number and density of the cells in the tooth-related periodontal ligament (t-PDL) were related to the recovery of eruptive potential 2.5 months after load removal. Four left incisors in which eruption returned to normal (group A) and six in which eruption remained grossly impaired after a two-week application of latero-intrusive loads of 18.5 +/- 0.69 (group B) were compared to four control rats with unimpeded eruption. The incisors were demineralized, embedded in paraplast and cut into 6 micron transverse serial sections from which a three-dimensional reconstruction of the PDL was made by computerized histomorphometry, and the fibroblast population counted. The t-PDL volumes in controls and in groups A and B reached 1.15, 1.05 and 1.53 mm3, respectively; the estimated number of cells in the same PDL volumes were 2244 X 10(3), 1.659 X 10(3) and 2094 X 10(3) cells, respectively. The mean cell count/segment of PDL and the calculated number of cells/unit of periodontal tissue were significantly lower (p less than 0.001) in the formerly stressed, lateral periodontium of both experimental groups. In group B, these values were also decreased in the mesial periodontium.

Structural changes in the dental and periodontal tissues of the rat incisor following application of orthodontic loads

The present study deals with the morphometric changes in the loaded rat incisor and its supporting structures 3 months after load removal. The material examined was limited to that part of the tooth that is located between 8 and 20 mm from the tooth apex. Of the ten albino rats in whom laterointrusive loads (19 +/- 0.6 g) were applied to the lower left incisor for a period of 2 weeks, the rate of tooth eruption returned to normal in four animals (group A); in six rats, eruption remained grossly impaired (group B). These two groups were compared with a control group of four rats in whom the incisors were allowed to erupt normally during the 3 months of the experiment. The left mandibles were dissected and fixed; the incisors were demineralized, embedded in paraplast, and cut into transverse serial sections of 6 micron, which were used to produce a three-dimensional reconstruction of all tissue components by means of computerized histomorphometry. The parameters of pulp and dentin, and the total tooth size and shape in group A were similar to those of the control group. In group B, pulp and dentin were changed significantly, tooth size increased, and the oval shape was altered into a more rounded contour, together with a significant enlargement of the socket. Although the total PDL volumes remained similar in all three groups, the tooth/socket relation, as expressed by PDL width and PDL area at the different tooth sides and at varying distances from tooth apex, diverged from normal significantly in all teeth that had been subjected to loading.

A computerized histomorphometric study of the effects of intoxication with vitamin D3 or 1,25 (OH)2D3 on growth and dentin production of impeded and unimpeded rat incisors

The effects of Vitamin D3 and 1,25(OH)2D3 intoxication on growth and dentinogenesis were studied in impeded and unimpeded rat incisors. Animals were intoxicated either with Vitamin D3 (2 mg/kg/day) or 1,25(OH)2D3 (400 ng/kg/day) for 19 days. Undecalcified transverse sections were obtained from all lower incisors. The outlines of all dental tissues were traced and fed into a computer which depicted the changes in all variables measured (circumference and cross-sectional area of tooth, pulp and dentin, width of dentin, CEJ [cemento-enamel junction] diameter and maximal labio-lingual diameter). Eruption rates, which had been recorded previously every 48 h, were used to compute the physiological age of each tooth site, so that only areas of similar age be compared. Growth. External dimensions of all intoxicated teeth decreased as the experiment progressed in contrast with control incisors which continued to increase in size. This effect was more pronounced in unimpeded incisors and may be due to the inhibitory influence of 1,25(OH)2D3 on cellular proliferation at the apical progenitor end. Dentinogenesis. 1,25(OH)2D3 intoxication had no significant effect on the rate of eruption and dentin formation in both impeded and unimpeded incisors. The same was true for impeded incisors intoxicated with Vitamin D3 but, both eruption and dentin production rates were impaired in Vitamin D3 unimpeded incisors.

A microcomputer-based graphical reconstruction technique for serial sectioned objects, with hidden line removal

The presented software package fulfills the need for processing serial sections with a microcomputer configuration, enabling three-dimensional reconstruction with hidden line removal. The language used is an interpreted BASIC-dialect (HPL). The input is performed via an interactive program. The object can be rotated in space. The Hidden Line algorithm does not depend upon a raster technique. Points of intersection of successive contours are calculated and inserted, thus providing drawings of high resolution and quality. The handling time can be said to be short, especially when considering the capacities of the microcomputer configuration used.

Recovery of the dental and periodontal tissues of the rat incisor following application of continuous intrusive loads: a long-term study

The present investigation deals with the functional recovery of the rat incisor periodontium following application of optimal intrusive loads for a period of 2 weeks and addresses the relationship between function and integrity of dental and periodontal tissues. The daily rate of eruption served as an indicator of the functional capacity of the rat periodontal ligament (PDL), while the condition of the PDL was evaluated by means of serial histologic sections. The left mandibular incisors of thirteen experimental and seven control rats were shortened to prevent occlusion, and calibrated loads of 19 +/- 1.6 grams were applied to the teeth of the experimental animals. Following removal of the springs, the daily rate of eruption of all teeth was measured during a recovery period of 80 days. In all experimental animals, prolonged impairment of the eruptive potential had occurred: In 50% the rate of eruption was fully restored 8 weeks after removal of the loads, and in these animals the histologic evaluation showed an almost normal PDL. In the remaining 50% gross impediment in the eruption rate persisted throughout the entire experimental period. The intratissue forces operating during the recovery period had sufficient strength to cause a degree of periodontal injury equivalent to that ensuant on direct loading. Extensive newly developed necrotic lesions were evident in the initially stretched mesial PDL. Areas of dentin resorption, denuded cementum, and injured enamel appeared a considerable time after load removal. Periodontal injury included disorientation and loss of attachment of collagen fibers, presence of scarlike tissue, and infiltration of inflammatory cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Odontoblast turnover in the impeded and unimpeded rat incisor derived from computerized histomorphometry

A computerized histomorphometric method was devised to estimate the kinetics of odontoblast turnover and dentinogenesis in rat incisors. The method was applied to two groups of rats: one group with lower incisors in impeded eruption and another group with the left lower incisor in the unimpeded state. The teeth were divided into six equal segments, from which consecutive ground sections were obtained. The distance of each ground section from the posterior border of the alveolar bone was calculated. Each section was magnified, traced, and the tracings fed into a computer by a sonic digitizer. The perimeters and areas of dentine and pulp in each ground section were calculated by the computer. The mean odontoblast density along the predentine was evaluated from histological sections taken both from the same tooth segments and from teeth sectioned midsagittally. These served for the estimation of the predentine area occupied by the average odontoblast. In the impeded group, this area was 11% larger than in the unimpeded one. Outer dimensions of teeth, namely the circumference of the dentine, the labiolingual width, and the mesiolateral width remained constant and equal for both groups. Daily rates of dentine apposition were computed and were found to vary according to the age of the odontoblasts. Odontoblasts of impeded teeth started to secrete matrix at a rate of 17 microns/day, which increased slightly to 19 microns/day and later declined to 7 microns/day on the 38th day. Dentine production of unimpeded odontoblasts, on the other hand, started at a rate of 16 microns/day and gradually increased to 34 microns/day on the 17th day.(ABSTRACT TRUNCATED AT 250 WORDS)

Histomorphometric evaluation of the dimensional changes in rat-incisor tissues following histological processing and embedding in paraffin wax and glycol methacrylate

A three-dimensional reconstruction of undemineralized and paraffin wax- or or glycol methacrylate-embedded demineralized rat incisors was made using a computerized histomorphometry. Compared to the undemineralized ground sections, the two demineralizing and embedding procedures grossly distorted the tooth sections. In general, embedding in wax caused shrinkage and in methacrylate caused swelling. Direction and magnitude of the deformation varied in the different tissues of the tooth and its surrounding structures. The distortion was influenced by the ratio between the soft and hard tissues at different cross-sectional levels of the tooth.