The present study examined the age-related changes of the physiological root resorption and the maturation process of odontoclasts during the physiological distal movement of rat molars. During physiological tooth movement, odontoclasts appeared to resorb the distobuccal root of the maxillary second molars. The number of odontoclasts increased in rats from 4 to 7 weeks of age, and gradually decreased from 10 to 13 weeks of age.
On the basis of light microscopic findings, it was found that root resorption was divided into the three stages of early, resorption, and final stage. During the early stage, odontoclasts, spindle-shaped mononuclear cells, and fibroblasts, were observed in the large and small resorption lacunae, and many blood vessels and fibroblasts were found in the periodontal space. During the resorption stage, resorption lacunae became larger, and the large odontoclasts were found within them. At the final stage, odontoclasts were rare, and the resorption lacunae were repaired by deposition of the cementum. The periodontal space became wider, and the arrangement of the periodontal fibers became regular.
Root resorption during the early stage was also examined by electron microscopy. The odontoclasts with the resorption zone, which was not clearly differentiated into clear zone and ruffled borders, began to resorb the root, resorbed the cementum, and extended to the dentin. At the surface of the resorption lacunae, lateral stripes of collagenous fibrils were found. As the resorption proceeded, the odontoclasts developed a well-formed ruffled border, and the deposition of new cementum produced by cementoblast-like cells was observed along the resorption lacunae.

View full abstract

The purpose of this study was to investigate the influence of the thermal cycling test on the adhesion of the resin on young permanent enamel which was etched with different etching times.
Labial surfaces of 50 extracted and frozen bovine mandibular young permanent incisors were used. The etchant used in this study was 37% phospholic acid gel and the etching times were 0,10,20,30 and 60 seconds. All of the specimens were washed with an air water spray after etching. The bonding agent and composite resin used in this study were Scotch Bond and Silux (3M Co.). After thermal cycling tests consisting of water baths with 10,000 temparature cycles between 60°C and 4°C, shear bond strengths on the ground enamel were measured. After the shear bond strength tests, all the test surfaces of the enamel and resin specimens were observed using the SEM.
The results of this study were compared with the previous results which were not thermal-cycled. The following conclusions were obtained.
1) The etching time which showed the highest bond strength was 60 seconds (33.40±5.75MPa).
2) The longer the etching times, the higher the bond strengths were.
3) In the etched groups, the bond strength with 10 seconds of etching time was significantly lower than those with 20,30 and 60 seconds of etching times and the bond strength with 60 seconds of etching time was significantly higher than that with 20 seconds of etching time.
4) In all the etching time groups, the bond strengths of the thermal-cycled groups were significantly lower than those of the non thermal-cycled groups.
5) The optimum etching time for Scotch Bond and Silux on the ground young permanent enamel was 60 seconds.

View full abstract

Laser Doppler flowmetry (LDF) was applied to measure pulpal blood flow in immatured human permanent incisors.
Eighteen young patients aged 6-12 and 7 adult volunteers participated in this study.
Heart beat synchronous oscillations were present in the recording singal from all of the matured vital teeth, which suggested that the pulpal blood flow was identified when the pulsatile oscillations were recognized in the LDF signal.
While the pulsatile oscillations were not so clear as were observed in matured teeth, LDF values of 26 imrnatured teeth (9.3±2.4) were slightly higher than those of 11 matured teeth (8.3±2.1). LDF values of 8 nonvital teeth (2.1±1.6)were distinctly lower than those of the vital teeth.
These observations suggested that the difference of LDF values between vital and nonvital teeth might be effective for identifying the pulpal vitality.
Five of the 26 immatured teeth, classified as a least formed apex group, were irresponsive to electrometric pulp testing. Although the LDF values of these teeth were apparently higher than the mean value of nonvital teeth, the vitality of these immatured teeth was not easily identified because the LDF values of the nonvital teeth occasionally exceeded the background level and showed irregular oscillations by artifacts such as blood flow in the adjacent gingiva and scattered laser beams in hard tissue.
Based on these facts, we monitored the pulpal blood flow and ECG simultaniously and analyzed the power spectra of both recording signals through a Fast Fourier Transform (FFT).
Prominent heart beat power was present in both ECG and LDF signals even from the least formed apex group but was not present in LDF signals from the nonvital teeth.
It would be useful for diagnosis of pulpal vitality of immatured teeth to compare the power spectrum of LDF signals with that of ECG.

View full abstract

Sucrose clearance was measured after sucrose loading to compare the results of three different loading concentrations and two sampling methods. In seven adults,5%,10% and 20% sucrose solutions were given and changes in the sucrose, lactate, and glucose were measured over time using two sampling techniques, the spitting method and the spot method. An enzyme electrode method capable of measuring samples on the microquantity level was utilized. The following conclusions were drawn:
1. The sucrose concentration changed in a biphasic way using both the spot and spitting methods. The spot method tended to yield higher sucrose readings. Increasing the load concentration resulted in delayed sucrose clearance.
2. The lactate concentration showed in initial increase followed by a decrease. The peak persisted for 5-7 minutes. The spot method appeared more reliable as it showed more pronounced changes as the load concentration was increased.
3. The glucose concentration changed in a similar fashion using the spot or spitting methods.
4. Using the spot method, the relationships among the sucrose, lactate and glucose after loading were more clearly shown than by using the conventional spitting method.
5. For sucrose clearance measurements utilizing techniques capable of measuring samples on the microquantity level, sampling using a spot technique appears easier and more accurate than using the conventional spitting method.

View full abstract

On the basis of the dental health examination of 361 infants at the age of 18months and the questionnaires to their mothers, we sought out the factors associated with dental caries at the age of 3. The caries activity tests were conducted on the infants and their mothers, using the pH value of Cariostat, estimated colonies of S. mutans in saliva grown in MSB broth and the charactersistic color reaction of RD test correlated with the number of S. mutans and Lactobacilli in saliva at the same time.
Statistical analysis was carried out by subjecting those items with the use of the second class of Hayashi's quantifying theory, in which the existence of decayed or filled teeth for each infant was chosen as external criteria. Furthermore, in order to predict the cariogenecity at 3 years of age from 18 months, the df-s index at the age of 3 was used by applying the first class of Hayashi's theory.
As a result, the main factors contributing to the existence of dental caries at 18 months were found to be the pH value of the Cariostat and MSBB in infants, the condition of the oral hygiene and the tooth brushing habit. On the other hand the factor contributing the most to dental caries at the age of 3 was found to be the result of MSBB in the infants, followed by pH value of Cariostat in mothers and habit concerning meal snacks. It was suggested that these factors might be the most important items when we try to pick out the high risk patient for dental caries at the early stages.

View full abstract

In exploring the diagnostic criteria for deep overbite in the deciduous dentition, the present study was conducted to investigate the relationship between the amount of vertical overbite of the anterior teeth in deciduous dentition and the size of the teeth, and the dental and apical base arches.
From the serial dental materials kept by the Department of Pediatric densitry, Nippon Dental University, the study used casts of deciduous dentition were obtained from a total of 85 children,42 boys and 43 girls (mean age,3 years and 8months), who had no dental caries and minimal attriction. The size of the teeth and the dental and apical base arches, the morphology of the teeth, and the interdental spaces were investigated in relation to the amount of vertical overbite of the left central deciduous incisor in these casts. The following results were obtained:
1) With respect to the size of the teeth, those subjects with a deeper overbite tended to have a greater coronal length of the maxillary anterior teeth and the maxillary and mandibular second deciduous molars. No significant relationship was found, however, between the depth of the overbite and individual values for or the sum total of the coronal mesicdistal width. The depth of the overbite was related to the longitudinal coronal length of the deciduous canine and second molar teeth.
2) Measurement of the dental and apical base arches showed that those with a deeper overbite had a narrower intercanine dental arch particularly in the mandible. No significant relationship was found, however, between the depth of the overbite and the size of the apical base arch or the dental arch. There was also no relationship between the depth of the overbite and differerences in size between the maxillary and mandibular apical base arches.
3) No significant relationship was found between the occlusal surface area of the deciduous molar and the depth of the overbite.4
) There was an apparent continuous incisal edge-cusp curve even in the deciduous dentition. The curvature became more pronounced as the depth of the overbite increased, indicating a close relationship with the occlusion.
5) In assessing the interdental space, closed denal arshes were frequently found in both the maxilla and mandible of subjects with deep overbite. A closed dental arch of the mandible contributed particularly to a deep overbite.
6) The incidence of morphological variations in the mandibular first deciduous molar was high,63.4%, in those with deep overbite, and their mandibular first deciduous molars, and dental and apical base arches differed in size from normal cases. Morphological variations in the mandibular first deciduous molar appeared to be a factor responsible for deep overbite in deciduous dentition.

View full abstract

Twenty five children participated in a dental survey to research the effective flossing interval for prevention of dental caries on proximal surfaces. Their ages ranged from 4.6 to 14.8 years. The samples were composed of the 77 interproximal sites where no caries lesion were detected by bite-wing radiography.
At first, dental plaque was collected as the baseline sample with use of a dental floss from each interproximal site, and then each interproximal site was cleaned with flossing. At intervals of 1 day,3 days,1 week or 2 weeks, each child visited our clinic again for collection of plaque samples from the same interproximal site, and then each proximal surface was cleaned with flossing. Each child visited repeatedly at each different intervals for the same purpose. The plaque sample was immediately put into a Cariostat tube (Sankin Industry Co. Ltd. ), and a Cariostat-value after a 24 hour incubation was scored. The mean Cariostat-values of the same interproximal site were compared among each group of each interval and interproximal site for flossing.
The results were as follows;
1) The differences among the groups of 1 day-interval,3 day-interval and 1 weekinterval visits were not significant. In comparing the Cariostat-values between the 1 week-interval group and 2 week-interval group, the former was smaller than the latter. The difference between the baseline and the 2 week-interval group was statistically significant (P<.05), and between the 2 week-interval and 1 week-interval group it was also statistically significant (P<.05).
2) For carious activity of the dental plaque on the proximal surface, the mean Cariostat-value of the 1 week-interval group was smaller than that of the baseline, resulting in less than 1.0. The order of the mean Carioatat-value of each interproximal site was D-E<E-6<1-2<5-6.
3) Less than 1.5 of the Carisotat-value of the baseline could decrease under 1.0 one week after flossing, suggesting that the flossing interval within 1 week might be adequate for such cases. On the other hand, more than 2.0 of the Cariostatvalue of the baseline could not decrease below 1.0, suggesting that the flossing interval within 1 week might not be enough for such cases.

View full abstract

Male rats of the Wistar strain, three weeks old, corresponding to the weaning period, were given calcium-dificient food and bone debility was induced in them. The effect of treatment by food on the alveolar bone was then studied with a scanning electron microscope.
The results were as follows:
1. In the control group (standard food), bone construction was accelerated, and in the osseous layer, the surrounding matrix in the bone lacuna consisted of bundles of collagen fibrills, collagen fibrills, calcospherites, and uncalcified collagen fibrills.
2. The calcium-deficient food group as compared with the control group showed bone resorption images and enlarged bone emarrow extensively and was weakened. In the osseous layer, there were many portions showing bone resorption. Resorption cavities were shallow and the boundaries were indistinct.
3. The calcium-deficient food+standard food group, as compared with the calcium-deficient food group, showed active bone remodeling and bundles of collagen fibrills running in about one direction at the bone formation site in the osseous layer.
4. In the calcium-deficient food+chigh calcium food group, bone marrow diminished extensively and bone remodeling progressed in the osseous layer, and bundles of collagen fibrills were distributed abundantly although the formation site of the bone matrix was incomplete as compared with the control group.
On the basis of the foregoing findings, with treatment by food for bone debility, bone construction by bone remodeling was most accelerated in the calcium-deficient food+high calcium food group.

View full abstract

The purpose of this study was to investigate the alternation of the activity of the masticatory muscles on the working and balancing sides during dentitional development.
A total of thirty persons were used in the study; 10 with deciduous dentition,10 with mixed dentition,10 with permanent dentition. EMGs were recorded from the anterior temporalis muscles and masseter muscles on both the working and balancing sides during chewing of boiled fish cake paste, chewing-gum and chewing of dried cuttlefish on both the habitual and non-habitual sides. Each muscle activity, while chewing, of 4 muscles (TW: the anterior temporalis muscle on working side, MW: the masseter muscle on the working side, TB: the anterior temporalis muscle on balancing side, MB: the masseter muscle on balancing side) and the ratio of each muscle activity to TAM (total muscle activity = TW+MW+TB+MB) were evaluated.
The results obtained in the present study were as follows:
1) There were significant differences (p<0.01) in EMG activities among muscles in all groups.
2) Muscle activity of MW showed a significant increase in accordance with denditional development from deciduous to permanent dentition (p<0.01).
3) Comparing the ratio of each muscle activity to TAM, no significant differences among foods were found.
4) Compared to children, the ratio of MW activity to TAM in adults showed a significant increase, whereas decrease in TB (p<0.01).
The results suggests that the alternation of masticatory muscles during dentitional development could be associated with the anatomical growth of muscles and the functional maturation of mastication.

View full abstract

The purpose of this study was to clarify the development of the eruption and root formation of the permanent successors in deciduous dentition. The materials used were serial standardized X-ray films taken every two weeks from thirty-two healthy infant dogs, and were classified into the following three groups for this experiment.
1. Healthy group (Control): Untreated teeth were observed which represented the opposites of all the teeth examined in the previous two groups of thirty-two dogs.
2. Extraction group with infected deciduous teeth: The infected deciduous teeth of twenty-one dogs were extracted after being left for four weeks following pulpectomy.
3. Extraction group with healthy deciduous teeth: Healthy deciduous teeth of eleven dogs were extracted from fourteen weeks old. A total of 1,280 mandibular observed teeth (P2, and P3) were used. The results from this study were made of the rate of crown movement, and the rate of root formation of the permanent successors in three groups. The results were as follows.
1. Rate of crown movement of permanent successors.
1) Healthy group (Control): For the eruption it showed a tendary towards resembling “S” curve and to be related to the period of weeks and rate of crown movement.
2) Extraction group with healthy deciduous teeth: Rate of crown movement of permanent successors was more accelated than the other experimental groups.
3) Extraction group with healthy deciduous teeth: Rate of crown movement of permanent successors appeared little different from that of the control group.
2. Rate of root formation of the permanent successors.
1) Healthy group (Control): For root formation it seemed that the even development tendency related to the period of weeks and rate of root formation.
2) Extraction group with infected deciduous teeth: Rate of root formation of the permanent successors was more accelated than the other experimental groups. But this accelated tendency did not seem stronger than rate of crown movement.
3) Extraction group with healthy deciduous teeth: Rate of root formation of the permanent successors appeared little different from that of the control group.

View full abstract

Adeno-tonsillar hypertrophy, which occurs in the pharynx, is said to cause malocclusion by affecting the tongue and perioral musculature. An examination was made of the degrees of such adeno-tonsillar hypertrophy and the growth changes taking place in the pharyngeal airway. The data used in this study came from lateral radiographic cephalograms taken of 109 young children (3 to 9 years of age)who had never undergone an adeno-tonsillectomy and had no marked abnormality in the dental occlusion. The following conclusions were obtained.
1) Since personal differences are considered to be substantial in the size of the pharyngeal tonsils, the changes resulting from the aging of a child have not yet been clarified. However, it was observed in this study that the size of the pharyngeal tonsil continued to increase during the period from the ages of 3 to 6 and peaked at the age of 6. After that, it kept on decreasing until the child reached 8 and, from the age of 9, it again began to show a tendency to increase.
2) The airway at the nasopharynx continued to narrow during the period of 3-4years of age, showed a maximum narrowing during the age of 4-6 and then again began to show a tendency to widen.
3) The pharyngeal airway is also influenced by the size of the skeletal nasopharynx. However, during the period from the ages of 3 to 9, it appeared that the pharyngeal airway was influenced more strongly by the size of the pharyngeal tonsil.
4) It was found that the lower pharynx, as measured at the oropharynx, showed almost no growth change resulting from the aging of the child.
5) The lower pharynx was observed as having a positive interrelationship with the adenoid area and also with the airway percentage.

View full abstract

The cariogenicity of palatinose oligomer was examined with in vitro and in vivo experiments. Mutans streptococci did not ferment palatinose oligomer. Palatinose oligomer inhibited both glucan synthesis by glucosyltransferases prepared from mutans streptoccoci and sucrose-dependent adherence of these organisms to glass surfaces. In the rat infected with mutans streptococci, palatinose oligomer showed significantly lower caries-inducing and plaque forming activity, when compared to sucrose. Moreover, palatinose oligomer inhibited sucrose-induced dental caries in rats infected with S. sobrinus. These results indicate that palatinose oligomer could serve as an excellent anti-cariogenic sweetener.

View full abstract

We made an analysis of 9-year secular caries prevalence of a set children of a region lacking in a dental treatment system. Also with the view of examining the effectiveness of the caries activity test (Cariostat) as a predictable index of the caries prevalence, we examined the relationship of the caries activity of same group with its subsequent caries prevalence. The following conclusions were obtained;
1) For caries prevalence, both primary and permanent teeth showed higher values than the prefectural mean value. Secular change of the number of caries teeth was most frequent for children age ca.6 and showed a decreasing (up to age ca.11) and subsequently a reincreasing tendency.
2) The results of the judgment by the Cariostat indicated the most highly cariesactive age-group to be 6∼7 year old children, best expressing the caries prevalence at the actual point of Cariostat, with CSI as an index.
3) The results of the judgment of primary dentition period by Cariostat and CSI, df+DMF teeth number showed a positive correlation from the beginning of the mixed dentition to the following fourth year, which correlation disappeared thereafter and came to reappear at the completement of the permanent dentition. The above results and DMF teeth number showed a correlation up to 3∼4 years following the beginning of eruption of permanent teeth and 1∼2years before the accomplishment of permanent dentition.
4) The results of the judgment of mixed dentition period by Cariostat showed a correlation with the caries prevalence at the permanent dentition period, and especially the most significant positive correlation with the results of the judgment at the beginning of permanent teeth.
The above indicated that the results of the judgment by Cariostat at primary dentition and mixed dentition periods, and especially at the beginning of eruption of permanent teeth were effective as index for predicting the caries prevalence at permanent dentition period.

View full abstract

The purpose of this study was to assest periodontitis at an early stage in children who are growing and developing, by understanding well the change of normal alveolar bone.
We used radiographs of 40 patients who had normal periodontal tissue shown by clinical examination and taking caries treatment and prevention every year. We observed the height of the interproximal alveolar bone crest, the form of the interalveolar septum and the prosperity and decline of lamina dura of molars in the mandibulla. The height of the interproximal alveolar bone crest of the deciduous molars changed little except for the medial of the first parmanent molar. We obtained the change of the height according to the replacement of the teeth. In the distal of the deciduous first molar (the first premolar), and the mesial and distal of the deciduous second molar (the second premolar), the height of alveolar crest decreased according to the replacement of the tooth. Until 1-2 years after the complete eruption of the second premolar, the height increased, and after that, it became stable.
In the mesial of the first molar, the height of the alveolar crest became higher year after year, but it is not little effected by the replacement of a tooth. The change of height continues for 5 years after complete eruption of the second premolar. We classified the following 5 types according to the pattern of the form of the interalveolar septum, the Flat type, the Gentle slope type, the Steep slope type, the Cup shape type, and the Roof type.
The deciduous dentition had almost all Flat type and Gentle slope types. Corresponding to the replacement of a tooth, the pattern of form became various. Finally, in all cases, the form of the interalveolar septum became the flat type.
Lamina dura was not clear until 5 years of age. After 5 years of age, it became clear gradually. Corresponding to the replacement of a tooth, the lamina dura became indistinct again, but after 3-5 years, after the complete eruption of second premolar, it became clear again.

View full abstract

A foreign body was accidentally inhaled by a tracheotomized 3-year-10-monthold girl with cerebral palsy. She did not shown any symptoms. The foreign body was incidentally discovered in her right bronchus when a radiograph of her chest was taken. The foreign body was removed from the bronchus by means of aspiration. A lower primary central incisor was identified by the morphological features. The surface and the ground sections of this tooth were examined by a binocular microscope and an optical microscope.
The results obtained were as follows:
1. The resorption was taking place on the root surface up to two-thirds of the root length, showing a different pattern from that of the physiological resorption which usually proceeded from the lingual root surface of the lower primary incisor. In this case, the external resorption proceeded evenly in every aspect, leaving a small jut of the inner layer of the dentin.
2. This tooth did not show any caries nor attrition from which the resorption might be derived.
3. A dentinal defect on the inner surface of the root canal was likely, indicating internal resorption.
For the prevention of a mis-deglutition accident, it is recommended that loose teeth be extracted in such patients to reduce the likelihood of aspiration into the lung.

View full abstract

We studied histopathologically five cases of prolonged retained primary teeth which were collected at the Department of Pedodontics, School of Dentistry, Hiroshima University. The teeth of the five cases were decalcified and made into specimens which were stained with hematoxylin-eosin, azan and thionin-picric acid.
The results obtained were as follows:
1) All of the cases had one prolonged retained primary tooth, but only one case had a missing successive permanent tooth and in the other cases for successive permanent teeth malposition was observed.
2) Considerable secondary dentin was formed in the wall of the pulp but the odontoblastic layer was not found in most cases.
3) For the pulp in all cases we did not observe the normal state and in most cases we observed periodontal membrane which had entered into the area of the root resorption. In the only case which had a missing successive permanent tooth, we found the component cells fo the pulp but that pulp showed regressive change, for example vacuolar degeneration, atrophy and fiberalized.
4) In one case the root was a little resorbed at the apex and in one case the root was almost totally resorbed, but we did observe root resorption in all cases.
5) We observed proliferation of cementum or cementoid for the resorbed lacunae in almost cases but only one case had the typical resorbed lacunae like Howship's lacunae. In particular we observed proliferate cementum in the wall of the coronal pulp.

View full abstract

A nine year old boy with meylodysplastic syndrome was treated with bone marrow transplantation (BMT) in the Division of Hematology of Chiba Children's Hospital. In the course of the treatment his oral hygiene was observed for 21 months by the dental staff.
The oral management for the BMT patient was divisible into 3 phases. Phase I was prior to BMT, Phase II was a period from the marrow infusion to the recovery of granulocytopenia, and Phase III was long-term follow up after Phase II.
Oral complications in Phase II mainly were gingival bleeding and hyperplasia. A gingival bleeding was observed on the third day after BMT with decreased number of blood platelet. The marked gingival hyperplasia induced by cyclosporine A developed around the region of upper and lower deciduous molars four weeks after BMT.
Over a 21-month period neither tooth infection nor periodontal diseases had occurred. Moreover, herpes virus and Canadida infections were not observed.

View full abstract

Cases of simple bone cysts (SBC) are comparatively rare in the oral region. Recently, we experienced a case of 12-year old female with SBC.
This patient has not particular general failures. Radiographical examinations showed some abnormal aspects as follows, we found a circumferentially obscure single cyst-like radio lucency in a panorama X-ray, a root apical projection of 7 into the radiolucent region in a mandibular lateral body view X-ray, and no absorptive findings of alveolar lamina dura in the dental X-ray film. We performed a curretage under local anesthesia with a clinical diagnosis as a left mandibular cyst. The bone cavity was filled with blood-like substances. Bundles of inferior alveolar nerve and vessels were observed on the floor part of the cavity. The granulative tissues and the epitherial cyst wall were not observed. The sarrounding of the bone of this cavity is flat and smooth. Based on the above mentioned findings, we diagnosed this lesion as SBC. After the operation no recurrence has been observed for 2 years 7 months.

View full abstract

A case of congenital epulis on the maxillary gingiva was found in a 2 year,3month-old Japanese female. Its histopathologic features corresponded to that of the so-called leiomyomatous hamartomas, which occur very rarely in the gingiva.
The findings were as follows:
Intraoral examination revealed a smooth, reddish gingiva-colored mass, attached to the palatal gingiva of the A⊥A region, measuring 8×5×4mm, with a pedicle.
Histopathologically, the lesion manifested the structure of the so-called leiomyomatous hamartoma, consisting of smooth muscle tissue, nerve fiber and muscular vessels. In addition, at the pedicle, there were myxomatous tissue and cartilage-like tissue.
No granular cells were detected.
The mass was excised with periosteal tissue under local anesthesia. The postoperative course was uneventful, and there was no evidence of recurrence after 9months of follow-up.

View full abstract