Enamel rods were morphologically classified by using human deciduous molar teeth. The samples were decalcified with lactic acid, doubly embedded in celloidin solution, sliced into cross sections, and stained with hematoxylin-eosin. They were observed under a light microscope. The sections were classified into four regions : surface, intermediate layer, deep layer and under pit and fissure. Arrangements of the enamel rods were classified into four patterns : stone-wall pattern, fish-scale pattern, pillar pattern and polygonal mixed pattern. The fish-scale pattern was observed most frequently, and the polygonal mixed pattern, least frequently. The structures of the enamel rod were classified into 20 shapes as follows : keyhole (types A, B and C), arcade, fan, diamond, horseshoe, tadpole, pentagon, hexagon, circle, oval, gothic arch, groove (types A, B, and C), trapezoid, squared, stick, and spade-shaped.
The surface of the enamel was darkly stained with hematoxylin ; the degree of staining gradually decreased deeper into the layer. In particular, the neonatal line was darkly stained by hematoxylin. In the head of the enamel rod, the enamel rod sheath was darkly stained and the central region of the enamel rod was lightly stained with hematoxylin. The tail of the enamel rod was darkly stained with hematoxylin. However, the results of staining on other enamel rods showed an opposite tendency, that is a light enamel sheath and tail and a dark central region.

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Quick heating casting investments (QHIs) which require a storage time of only 30 minutes in a 700°C oven (30 minutes after completion of the investment mixture) are available. In this study, the adaptation of full cast crowns fabricated using QHIs was investigated by the master die method. Two technicians, a dentist with 6 years of experience and dental technician with 23 years of experience, fabricated 25 copper alloy (K-metal, GC Co.) full cast crowns using five stainless steel master dies (10 mm cervical diameter with 1/20 taper) and five different casting investments, respectively. The crowns were fit onto the respective dies and then shrinkage (-) or expansion (+) was measured with a profile projector. ANOVA showed significant differences between the casting investments and technicians. The crowns fabricated using FF exhibited the largest expansion and those fabricated using Fl and SC exhibited the same degree of shrinkage. A 0.2% mean difference was statistically significant between the two technicians. Even though a mean difference of 0.2% was observed between the technicians, the relative relationships of the values among the crowns fabricated using the different casting investments were identical for both technicians.

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The cement thickness of the full cast crowns fabricated using quick heating casting investments (QHIs) was investigated in this study. FF and Fl which exhibited typically different compensation ability among the QHIs in a previous study and the traditional investment (SC) were used. A dentoform replica of a lower right first molar was prepared for a full cast crown and 15 epoxy replicas of the prepared tooth were fabricated for use as master dies. The completed crowns were cemented to their respective master dies and cut mesio-distally and bucco-lingually. Cement thickness was measured with a profile projector. The crowns fabricated using Fl exhibited the same degree of cement thickness as the traditional type cristobalite investment (SC). However, the crowns fabricated using FF showed greater cement thickness than those using Fl or SC.

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This study was done to assess what auditory psychological factor and acoustic characteristics influence auditory discrimination of TMJ sounds. Auditory psychological experiments using semantic differential technique were done by four dentists to evaluate 73 TMJ sounds obtained from 45 patients with TMJ disorders. Acoustic analyses were also done to evaluate acoustic characteristics of the TMJ sounds. The results are as follows. 1. The 73 TMJ sounds were classified into clicking (28 sounds), crepitus (12), mixed (1), pseudoclicking (10), pseudocrepitus (4), pseudomixed (4), and others (14) by subjective evaluation. Evaluations across the 4 examiners were coincident for 56% of all TMJ sounds. 2. Two factors were extracted by factor analysis of auditory psychological measurements. Clicking sounds were clearly discriminated from crepitus sounds by factor 2 mainly composed of the two auditory psychological scales. 3. The durations of the clicking and pseudoclicking sounds were shorter than those of the crepitus sounds. Significant differences were found between them. 4. The maximum amplitudes of the clicking and pseudoclicking sounds were greater than those of the crepitus sounds ; however, no significant differences were found between them. 5. In the frequency domain analyses using the one-octave band analysis, the average amplitudes of both 31 Hz and 62 Hz bands of the crepitus sounds were greater than those of the clicking and pseudoclicking sounds.
No significant difierences were found between the pseudoclicking sounds and the crepitus sounds. 6. In the frequency domain analyses using 500 Hz band analysis, no significant differences were found between any two of classified TMJ sounds. These results suggest that the reliability of auditory evaluation of TMJ sounds is not so high and that the two auditory psychological scales and duration of TMJ sound concern the auditory discrimination of clicking from crepitus.

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It is well known that the application of physiological or orthodontic mechanical force to bone tissues is important in regulating bone remodeling. We have developed a new mechanical cell-stimulator which uses collagen gel strips supported by a nylon mesh, with which three-dimensional strain can be applied to bone cells derived from a calvariae. After 24 h of preincubation, cells were incubated for up to 6 days with or without intermittent mechanical stimulation (1 Hz, 10% stretch, 15, 30 min and 1 hr, 3 times a day) in αMEM supplemented with 10% FBS in a humidified CO₂ incubator. Microscopic observations suggested that mechanical strain applied to the nylon mesh was transferred to the cells, causing them to change shape. The DNA content in a stretched group was significantly increased compared to a shaken group after 4 and 6 days of mechanical stimulation (at 1 Hz for 15 and 30 min, 3 times a day). ALPase activity in a stretched group was significantly decreased to the level of a shaken group after 6 days of mechanical stimulation. PGE₂ production in a stretched group was significantly increased compared to that in both the shaken and stationary groups within 3 days of mechanical stimulation. The DNA contents in both the stretched and stationary groups were significantly decreased by the addition of indomethacin (10^-6 M). However, the DNA content in the stretched group with indomethacin (10^-6 M) was still higher than that in the stationary group. Under microscopic examination, cells in the stretched group were long and slender, and were oriented perpendicular to the applied stretch after 6 days of mechanical stimulation. In summary, bone cells embedded in a collagen gel matrix responded to mechanical stimulation by increasing DNA synthesis and decreasing ALPase activity.

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The tangentially polished surfaces of the outer enamel under the projections of the marginal ridges and the basal tubercle in the lingual side of maxillary incisor teeth, extracted from elderly periodontic patients, were observed by scanning electron microscopy after EDTA etching. In general, EDTA selectively erodes the prism sheath regions; however, our observations reversed this. It indicates that the prism sheath regions may have been penetrated by organic materials with minerals derived from saliva due to an exposure of the old teeth to the oral cavities for a longer duration since eruption and also the attrition for a longer period. The etched surfaces more or less showed a disordered orientation of enamel prisms. At the junctions of such disorders, there were scattered abnormal-shaped prisms including a spiral, a circle, and double borders. Moreover, the 'inner' prism-like sheaths of the double bordered prisms occasionally showed a circle or a dotted remnant other than an arcade, whereas the circular prisms frequently contained an arcade, a spiral, or a smaller circle in the 'outer' sheaths. These abnormal-shaped prisms are probably formed by the prism orientation disorders following the variable morphological changes of Tomes' processes during the formation of their enamel projections.

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In order to determine the functionally appropriate occlusal morphology of crowns, it is essential to record a large number of states of the occlusal facets and the occlusal contact areas obtained from the clinical case of the crowns and then to analyze these states with the clinical progress. In this paper, we report a convenient registration method for occlusal facets and occlusal contact areas. First, occlusal contact registration is obtained using a bite tray and a vinyl polysiloxane impression material and then poured into an improved dental stone. The cast and the occlusal contact registration are photographed and input through an image scanner into a personal computer. These two images are modified and processed by the computer and finally are precisely superimposed into one image. This convenient method requires few materials and equipment and can precisely superimpose occlusal facets and occlusal contact areas into one image. Therefore, this method will contribute greatly to clinical use.

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The speech patterns of denture wearers have been studied to evaluate speech disorders from the standpoint of orofacial articulatory movements during the pronunciation of the Japanese test sentence : /sakura-no-hana-ga-sakimasita/. The subjects were three edentulous patients who pronouced this sentence without their complete dentures (stage A), without their maxillary dentures (stage B), with both their maxillary and mandibular dentures (stage C). To assess the speech pattern of each subject, the following markers on each face were monitored : the subnasale (Sn), the vermilion border of the upper and lower lip (UL, LL), the modiolus (Mo), the menton (Me), and the incisal point (IP). The IP was represented by a point on a stainless wire extending from the lower incisal tooth of the mandibular denture to the outside of the mouth. We developed a cordless light-emitting target that was recorded as a shining point with clear outline when illuminated by a cold spot light. This enabled recording and autotracking of multiple reference points on an image processor. The face markers and voice of each subject were simultaneously recorded on a video tape by two high-speed TV cameras from two different directions, i.e., frontally and laterally. Then, the recorded video tape was reproduced on a high-speed video and both the image and the voice data were respectively fed into an image processor (Image Data : ID-8000) and a sound spectrograph (DSP Sona-Graph : KAY 5500). The frame number of each pronounced consonant was identified by its waveform and sound spectrogram (3-D sonagram) on the DSP Sona-Graph. Movements of each marker were automatically tracked by the Image Data and the resulting data of the 3-dimensional coordinates were fed into a computer. The trajectory of each monitored point during pronunciation of the test sentence was computed by a 3D analyzer (Movias 3D) with reference to the following parameters : the total length from start to finish of the trajectory (TL); the distance between the start and finish of the trajectory (SL); the ratio of the TL to the SL (T/S); the volume of the rectangular solid encompassing the entire trajectory (the cubical range : CR); and the average of the 3-dimensional angles made by differences in the direction of the preceding and following trajectories at each measured time point (TH). Our results have revealed that the TL, CR, and T/S of the entire trajectories at the mandible and at each reference point during the denture-wearing stage (C) were smaller than during the edentulous stage (A). Our results also revealed that specific trajectories were seen during the pronunciation of /s, f, and m/ from among the other constants and vowels included in the test sentence.

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Face shapes and maxillary central incisor shapes have been studied for the choice of artificial teeth, and the number of reports have been increasing. It has been reported that similarities exist between the face shapes and the maxillary central incisor shapes. The present study was undertaken to research the similarities between the contours of artificial teeth and those of maxillary central incisor. The materials used were plaster casts of maxillary dentitions of adult Filipinos (male : 63, female : 106) and three types of artificial teeth. Three types of artificial teeth were used : Livdent (Tapering, Square, Ovoid, Tapering Square, Square Ovoid, Tapering Ovoid, Short Square, V-shaped Tapering, V-shaped Tapering Square), Trubyte Bioblend (Square, Square Tapering, Square Ovoid, Tapering, Tapering Ovoid, Ovoid Square, Tapering Ovoid) and Real Crown [Combination (C), Ovoid (O), Square (S), Short Square (SS), Tapering (T)]. The criteria of the similarities were determined to be 0.3 or below of error of difference calculated by Fourier series.
The highest incidence between each artifical teeth type and maxillary central incisors were : with Livdent, Square Tapering in the right and Tapering in the left for both sexes; with Trubyte Bioblend, Square in the right and Tapering Square in the left for males and Square Ovoid in both sides for females; with Real Crown C in both sides for both sexes, respectively.
The high similarities between each type of artificial teeth and maxillary central incisors were : with Livdent, Square in the right for both sexes and Tapering in the left for both sexes; with Trubite Bioblend, Square in the right and Tapering Square in the left for males and Square Ovoid in both sides for females ; with Real Crown, T in the right and C in the left for males and C in both sides for females. Also, the similarities between each type of artificial teeth were : against seven classes of Trubyte Bioblend, three classes in the right and two classes in the left of Real Crown were matched ; against nine classes of Livdent, three classes in both sides of Real Crown were matched. From these observations, it can be said that there are differences between each type of artificial teeth even though they have the same or similar names. Also, it can be considered that there are similar shapes with different names.

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The purpose of this study was to observe and compare the morphological changes of human enamel and dentin irradiated by Er : YAG, Nd : YAG and CO₂ laser. Three enamel sections, two dentin sections of coronal portion and three dentin sections of root portion were prepared and each section was irradiated by three types of laser at the energy level of 300 mJ/pulse, 8 Hz; 2 W, 20 pps; and 1 W, CW respectively. The lased areas were observed by a telescopic light microscope and a scanning electron microscope. Er : YAG laser irradiation produced a white color zone and Nd : YAG laser irradiation produced a slight melt zone on each enamel surface. The dentinal tubules of coronal and root portion dentin sections were completely sealed by Er : YAG or Nd : YAG laser energy. The irradiated area of each enamel surface was changed into a white spot and severe carbonization was observed around the white spot in case of CO₂ laser irradiation. Each dentin surface was melted and recrystalized with CO₂ laser irradiation. Although some minor morphological heat damage changes were observed on the lased enamel and dentin surfaces irradiated by Er : YAG laser, these results suggested that the Er : YAG laser had the ability to remove enamel and dentin depending on laser conditions.

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