Abrasion of human enamel by brushing with a commercial dentifrice containing hydroxyapatite crystals in vitro.

Automatic toothbrushing with a commercial dentifrice containing hydroxyapatite (HAP) crystals was performed on the tangential polished surfaces of sound human enamel, mainly consisting of biological apatite similar to HAP, for 10 min in vitro. The X-ray diffraction peaks of HAP, brushite (DCPD), and monetite (DCP) crystals were detected from the dentifrice. After brushing, the enamel surfaces were observed with a scanning electron and a confocal scanning laser microscope. The brushing caused larger abrasive loss and more remarkable roughness of the enamel surfaces following the broad traces of brush bristles and the exposure of prism structures than brushing with a dentifrice containing only DCPD, which we previously reported. We claim that the fine granular-shaped HAP crystals of the dentifrice indicated as an active ingredient for preventing enamel caries possess stronger abrasivity of sound enamel than the DCPD and DCP as abrasives on account of their Mohs hardness values rather than sizes and shapes. The HAP crystals of dentifrices may not occlude the small defects of early caries enamel, but erode them more strongly as an abrasive than the other abrasives.     

Er:YAG激光对牙本质超微结构作用的电镜观察

激光照射牙本质被认为是一种改善粘接效果的新方法。此研究的目的是采用电镜观察Er:YAG激光照射后牙本质的超微结构,评价激光处理牙本质以改善牙体组织和修复体之间粘接性能的可行性。共8颗新鲜拔除的人上颌第三磨牙按照牙合贴面的要求进行牙体预备,拔除牙齿进行牙体预备后接受激光照射,采用电镜观察牙本质的超微结构。分为两组,4颗牙齿为对照组,4颗牙齿为实验组。牙体预备后,对实验组牙齿的牙本质进行Er:YAG激光照射。采用电镜观察牙本质小管,熔融和裂隙等情况。对于实验组,观察结果未见玷污层,牙本质小管清晰。同时,对照组可以见到牙本质小管内有明显的玷污层,因此牙本质小管不清晰。该研究提示Er:YAG激光照射牙本质可以清除牙本质小管内的玷污层,这可能会提高牙体组织和修复体之间的粘接性能。     

Ultrastructural and cytochemical study of the odontoclasts in physiologic root resorption of human deciduous teeth.

Using extracted human deciduous teeth undergoing physiologic root resorption, this author studied the ultrastructural and cytochemical features of odontoclasts. The scanning electron microscopic observation of trypsin-treated dentin and cementum surfaces of resorption lacunae showed the exposure of collagen fibrils and prominent loss of the peritubular matrices around the dentinal tubules. In the resorption lacunae formed in enamel, there was dissolution of either the rod or the interrod regions. The odontoclasts developed extensive ruffled borders apposed to these resorbing matrices and had round phagosomes containing tannic acid-stainable fine amorphous inclusions, which were identical to those in the extracellular canals of the ruffled borders. The odontoclasts did not phagocytose the collagen fibrils. The odontoclasts showed the enzymatic activities of the acid trimetaphosphatase and acid p-nitrophenyl phosphatase (p-NPPase) in the Golgi-lysosome system, the ruffled border region, and along the resorbing dentin surfaces. The p-NPPase activity was inhibited by sodium tartrate. Also, the odontoclasts showed H(+)-K(+)-ATPase activity in the cytoplasm along the plasma membranes including those of ruffled border and the limiting membranes of the lysosomes. These results suggest that: 1) the odontoclasts are associated with resorption of non-collagenous organic matrices and/or extracellularly-degraded collagenous fragments rather than the incorporation of intact collagen fibrils; 2) the odontoclasts release the hydrolytic enzymes onto the lacunal surfaces and/or the lysosomes for the extra/intracellular degradation of the organic matrices; and 3) they also have H(+)-K(+)-ATPase for extracellular demineralization of the inorganic crystals.     

A scanning electron microscopy study of diseased root surfaces conditioned with EDTA gel plus Cetavlon after scaling and root planing

In the present investigation, a scanning electron microscopy analysis was performed to evaluate the effects of the topical application of ethylenediaminetetraacetic acid (EDTA) gel associated with Cetavlon (EDTAC) in removing the smear layer and exposing collagen fibers following root surface instrumentation. Twenty-eight teeth from adult humans, single rooted and scheduled for extraction due to periodontal reasons, were selected. Each tooth was submitted to manual (scaling and root planing) instrumentation alone or combined with ultrasonic instruments, with or without etching using a 24% EDTAC gel. Following extraction, specimens were processed and examined under a scanning electron microscope. A comparative morphological semi-quantitative analysis was performed; the intensity of the smear layer and the decalcification of cementum and dentinal surfaces were graded in 12 sets using an arbitrary scale ranging from 1 (area covered by a smear layer) to 4 (no smear layer). Root debridement with hand instruments alone or combined with ultrasonic instruments resulted in a similar smear layer covering the root surfaces. The smear layer was successfully removed from the surfaces treated with EDTAC, which exhibited numerous exposed dentinal tubules and collagen fibers. This study supports the hypothesis that manual instrumentation alone or instrumentation combined with ultrasonic instrumentation is unable to remove the smear layer, whereas the subsequent topical application of EDTAC gel effectively removes the smear layer, uncovers dentinal openings and exposes collagen fibers.     

In situ quantitative analysis of etching process of human teeth by atomic force microscopy

Etching is one of the most fundamental steps in the restoration of teeth by adhesion of composite resin in dental clinics. Atomic force microscope (AFM) was used for the in situ observation of the etching process of human enamel, dentin and synthetic hydroxyapatite in the three different acid agents, 2% phosphoric acid, 10% citric acid and 10% polyacrylic acid. To measure the absolute depth from the initial level before etching and to correlate the surface height between the changing AFM images obtained, the depth profiles were recorded with etching time by carrying out the line scan consecutively at the representative place of the observed area. These chronological series of depth profiles enabled us to perform quantitative analysis of etched amount in addition to the surface roughness obtained from relative depth profile within one image. The course of etching process from the dissolution of smear layer, appearance of enamel prizms or dentinal tubules to progress of demineralization could clearly be observed. The depth profile, surface roughness, etching amount, etching rate and smear layer thickness could then be evaluated. The different etching characteristics of three acid agents and the effect of surface roughness produced by different mechanical prepolish were compared and discussed.     

Application of the environmental SEM in human dentin bleached with hydrogen peroxide in vitro.

The environmental SEM (E-SEM) can be used unfixed biological samples under a low vacuum and wet condition. In this study, the fractured dentin of unfixed human teeth was treated with a 30% hydrogen peroxide solution (H2O2) for the examination of tooth-bleaching prior to the E-SEM and a conventional SEM. The peritubular matrix (PM) always showed a few cracks along the long axis of a dentinal tubule, and the ends of fine fibrils rose to the smoothly changed surface of the intertubular matrix (IM). The E-SEM with non-fixation and the conventional SEM following fixation indicated that the hydrogen peroxide solution easily permeated the PM and dissolved the non-fibrillar substance including the cracks of the PM by the constriction. In the IM, the solution may partially dissolve the organic parts within mineralized fibrils as well as non-fibrillar substance between the fibrils, although these remnants might precipitate again there.     

Possible role of dentin matrix in region-specific deposition of cellular and acellular extrinsic fibre cementum

The mechanism whereby a region-specific deposition of the two types of cementum (cellular cementum and acellular extrinsic fibre cementum) is regulated on the growing root surface was tested using bisphosphonate-affected teeth of young rats and guinea pigs. The animals were injected subcutaneously with 8 or 10 mg P x kg body weight(-1) x day(-1) of 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) for 1 or 2 weeks. In rat molars, HEBP prevented mineralization of newly formed root dentin matrix and totally inhibited de novo deposition of acellular extrinsic fibre cementum. Instead, thick cellular cementum was induced on the non-mineralized root dentin surface, irrespective of the position of the root. In both animals, cellular cementum was also induced on the non-mineralized surface of root analogue dentin in HEBP-affected incisors, where only acellular extrinsic fibre cementum is deposited under normal conditions. In normal rat molars, dentin sialoprotein (DSP) was concentrated along the dentin-cellular cementum border, but not that of dentin and acellular extrinsic fibre cementum. In HEBP-affected rat incisors, DSP was shown to penetrate through the non-mineralized dentin into the surrounding tissues, but not through the mineralized portions. These data suggest that, at the site of cellular cementum formation, putative inducing factors for cellular cementum might diffuse into the periodontal space through the newly deposited mantle dentin matrix before it is mineralized. At earlier stages of root formation, mantle dentin might mineralize more promptly not to allow such diffusion. The timing of mineralization of mantle dentin matrix might be the key determinant of the types of the cementum deposited on the growing root surface.     

子脉冲序列模式Er∶YAG激光消融牙本质的实验观察

研制了一台子脉冲序列模式Er∶YAG激光器,获得了每秒80个和100个子脉冲高能量激光输出,开展了不同脉冲宽度的子脉冲对离体牙本质的激光消融实验。实验中使用的是子脉冲序列模式激光器,其重复频率为20 Hz,脉冲包络能量为45 mJ,子脉冲宽度分别为20,30,40,50μs,在无冷却水雾条件下分别对比了子脉冲宽度对牙本质消融量、牙髓腔温升和坑洞组织形貌的影响。结果表明:在相同的激光脉冲能量下,较窄的子脉冲宽度不仅能够增加消融量,降低牙髓腔温升,从而延长操作时间,而且可以获得更好的消融坑洞组织形貌,牙小管的开放程度较高,有利于黏接修复治疗。     

1.06μm激光辐照牙本质光热作用的数值模拟

激光技术已经成为牙科应用领域中重要的治疗手段.但是激光辐照牙齿时所产生的温升容易引起牙髓腔中细胞不可逆的损伤,导致牙髓细胞坏死,因此必须对相关的激光参数加以控制.本文建立了激光对牙齿光热作用的理论模型,对不同Nd:YAG激光参数照射下牙齿表面及内部的温度场进行了数值模拟.对相关的光热机理进行了探讨,提出了光热蚀除牙齿应采用的最佳措施.     

红外激光辐照下牙齿温度场的仿真研究

激光技术已经成为硬组织蚀除、口腔手术、激光理疗、牙齿脱敏治疗等牙科应用领域中重要的治疗手段。但是激光辐照牙齿时所产生的温升容易引起牙髓腔中细胞不可逆的损伤,导致牙髓细胞坏死,因此必须对相关的激光参数加以控制。本文建立了激光对牙齿光热作用的理论模型,对不同Nd:YAG激光参数照射下牙齿表面及内部的温度场进行了仿真研究。对相关的光热机理进行了探讨,提出了光热蚀除牙齿应采用的最佳措施。     

Toothbrushing region detection using three-axis accelerometer and magnetic sensor

Due to the possible occurrence of periodontal disease at an early age, it is important to have proper toothbrushing habits as early as possible. With this aim, the feasibility and concept of a smart toothbrush (ST) capable of tracing toothbrushing motion and orientation information was suggested. In this study, we proposed the advanced ST system and brushing region classification algorithm. In order to trace the brushing region and the orientation of a toothbrush in the mouth, we required the absolute coordinate information of ST. By using tilt-compensated azimuth (heading) algorithm, we found the inclination and orientation information of the toothbrush, and the orientation information while brushing inner tooth surfaces showed specific heading features that could be reliably discriminated from other brushing patterns. In order to evaluate the feasibility of clinical usage of the proposed ST, 16 brushing regions were investigated by 15 individual healthy subjects. The proposed ST system demonstrated 97.1%(±0.91) of the region detection accuracy and 15 brushing regions could be classified. This study also showed that the proposed ST system may be helpful for dental care personnel in patient education and instruction for oral hygiene regarding brushing habits.     

Analysis of tooth formation by reaggregated dental mesenchyme from mouse embryo

Tooth morphogenesis is a well-known developmental system related to epithelial-mesenchymal interactions. In mice, the dental epithelium has the potential to induce tooth formation prior to the bud stage, whereas this potential shifts to the dental mesenchyme from the dental epithelium. The reaggregation of mesenchymal tissue leads to previous memories of individual cells being reset, which is useful for studying the predetermination of mesenchyme. Here, the mesenchyme was triturated into single cells after separation of the epithelium and the mesenchyme. These single cells were repelleted and combined with the epithelium. The reaggregated tooth was transplanted into a mice kidney capsule. In order to investigate the essential functions of both the dental epithelium and the dental mesenchyme regarding their mutual interaction, a reaggregation system was introduced using the late bud stage of the mouse first molar. Amelogenin expression was examined to confirm the cytodifferentiation in the reaggregated tooth. The results showed that a new tooth formed after reaggregating the dental mesenchyme. This tooth contained enamel, dentin, dentinal tubules and dental pulp. The inner enamel epithelium of the reaggregated tooth differentiated into ameloblasts. Immunohistochemistry for amelogenin was observed both in the ameloblasts and the enamel. However, the structure of the enamel was different from that of the normal tooth, with the thickness of the predentin becoming wider. These findings suggest that reaggregated dental mesenchyme cells can produce a tooth. The fate of dental epithelium was not affected by reaggregated dental mesenchyme, although the dental mesenchyme appears to lose the information from the dental epithelium.     

Development of a magnetic sensing device for tooth displacement under orthodontic forces

We have developed a system for measuring tooth displacement from orthodontic force. Eight small magnetic sensors and a magnet are combined to measure three-dimensional displacement. Sensors, arranged cubically in the three planes of space, are placed in the mouth and fixed to the posterior teeth by a splint. A magnet is placed in the center of the eight sensors and attached to a front tooth that is subjected to orthodontic force. Sensors detect the magnet's movement as target tooth displacement. The system was designed to achieve displacement resolution of 1 microm. The mean percentage of measurement errors was determined to be less than 1% in a 600-cubic-microm volume from calibration. The system was tested clinically on human teeth. Although the oral environment, with high temperature and humidity, was not agreeable with the sensors, this system was stable and accurate enough for quantitative measurement of tooth displacement. The advantage of this system is the ability to detect tooth trajectories by decomposing displacement into translation and rotation and to determine the position of the center of rotation from these parameters.     

Nd:YAG激光辐照牙齿的光热作用理论研究

激光辐照牙齿时所产生的温升容易引起牙髓细胞不可逆的损伤,导致牙髓细胞坏死,因此必须对相关的激光参数加以控制.建立了激光与牙齿相互作用的热传输模型,利用Crank-Nicolson有限差分法数值模拟了不同Nd:YAG激光参数照射下牙齿表面及内部的温度场的分布.计算结果表明,激光脉冲的宽度、间隔、个数决定了牙齿表面和牙髓腔壁的最终温度,将激光的总能量分配到几个脉冲之中,导致了牙齿表面温度的降低;而在牙髓腔壁出现了相反的情况,即脉冲数越多,牙齿内壁的温度也就越高.对相关的光热机理进行了探讨,提出控制单脉冲能量是光热蚀除牙齿应采用的最佳措施.     

In vitro interaction between gingival fibroblasts and various root surfaces

The objective of the present in vitro study was to examine the effect of various root surface treatments on the initial attachment of gingival fibroblasts. Cultured fibroblasts were well spread and attached to demineralized dentin with citric acid, superficially curetted cementum, and root surface with periodontal ligament, while those on the planed dentin showed a poorly spread appearance. The first three root surfaces exhibited rough and irregular surface appearances with a well-developed filopodia and the latter root surface exhibited a smooth appearance, suggesting the texture of the root surface is closely associated with cell attachment. Interiorized collagen fibrils and numerous cytoplasmic vesicles were seen along the cell membrane of fibroblasts facing the root surfaces of the planed dentin, demineralized dentin, and superficially curetted cementum. Thus even the artificially exposed tooth surface with citric acid may be subjected to further alteration by fibroblasts.     

Effect of abrasive particle concentration on preliminary chemical mechanical polishing of glass substrate

Effect of abrasive particle concentration on material removal rate (MRR), MRR per particle and the surface quality in the preliminary chemical mechanical polishing (CMP) of rough glass substrate was investigated. Experimental results showed that the MRR increases linearly with the increase of abrasive concentration and reaches to the maximum when the abrasive concentration is 20 wt.%, and then tends to be stable. When the abrasive concentration increases from 2 to 5 wt.%, the MRR per particle increases greatly and reaches a peak. Then the MRR per particle decreases almost linearly with the increase of the abrasive concentration. The root mean squares (RMS) roughness almost decreases with increasing particle concentration. In addition, in situ coefficient of friction (COF) was also conducted during the polishing process and the zeta potentials of abrasive particles in slurry with different solid concentration were also characterized. Results show that COF value is not related to zeta potential but be sensitive to glass surface conditions in terms of rough peaks in preliminary polishing of glass substrate.     

Effects of radiofrequency energy on human chondromalacic cartilage: an assessment of insulation material properties

The objective of this study was to establish guidelines for the selection of an insulation material used to surround the electrode of radiofrequency energy (RFE) probes used for thermal chondroplasty. These guidelines were established by identifying which insulation materials resulted in the least amount of chondrocyte death while smoothing the surface of chondromalacic cartilage. RFE causes electrolyte oscillation and molecular friction in the tissue to heat it and subsequently smooth the surface. Material properties investigated included the coefficient of thermal expansion (CTE), thermal conductivity (TC), and volume resistivity (VR). Fresh human chondromalacic cartilage samples of Outerbridge grades II and III were obtained from patients undergoing total knee arthroplasty. Stiffness measurements were taken pretreatment and posttreatment. RFE was applied to a 1-cm2 area for 15 s in a paintbrush treatment pattern. The insulation materials evaluated included Macor (decrease CTE, decrease TC, increase VR; in relation to CTE = 10 x 10(-6)/degrees C at 20 degrees C, TC = 3 W/mK, VR=1 x 10(14) ohm x cm), zirconia toughened alumina (ZTA) and 99.5% alumina (decrease CTE, increase TC, increase VR), aluminum nitride (decrease CTE, increase TC, decrease VR), Teflon (PTFE) (increase CTE, decrease TC, increase VR), partially stabilized zirconia (YTZP) (decrease CTE, decrease TC, decrease VR), and Ultem (increase CTE, decrease TC, decrease VR). There were no significant differences between pretreatment and posttreatment stiffness of the cartilage for any material investigated. Subjectively scored scanning electron microscopy (SEM) images revealed that the surfaces of all samples treated with RFE were relatively smooth with melted fronds. Prototype probes made with Macor, 99.5% alumina, and ZTA had TC < or = 30 W/mol x K and resulted in a mean of 35% less cell death (176+/-56 microm, 130+/-48 microm, and 114+/-33 microm, respectively) than aluminum nitride, PTFE, and YTZP (246+/-68 microm, 231+/-108 microm, and 195+/-89 microm, respectively). Macor, 99.5% alumina, and ZTA prototype probes all had VR > or = 1 x 10(14) ohm x cm and resulted in a mean 37% less cell death than aluminum nitride or YTZP. There was no apparent relationship between CTE and the depth of chondrocyte death.     

脉冲式Nd：YAG激光与氟治疗牙本质过敏症的临床研究

本文通过对６１例患者１６５颗牙本质过敏症患牙进行脉冲式Ｎｄ：ＹＡＧ激光＋氟治疗与单纯脉冲式Ｎｄ：ＹＡＧ激光治疗的对照研究，揭示了两者疗效的差异，并进行了有关分析和讨论。     

Possible role of immunocompetent cells and the expression of heat shock protein-25 in the process of pulpal regeneration after tooth injury in rat molars

Recent studies have established that heat shock proteins (HSPs) potentially play a role in immunosurveillance. The purpose of the present study was to clarify the relationship between the chronological changes of immunocompetent cells and the expression of HSP-25 in the process of pulpal regeneration after tooth injury in rat molars by immunocytochemistry for HSP-25 and class II major histocompatibility complex (MHC) antigen. In untreated control teeth, intense HSP-25 immunoreactivity was found in the cell bodies of odontoblasts. Both cavity preparation and tooth replantation caused the degeneration of the odontoblast layer to result in the loss of HSP-25 immunoreactions in the suffered dental pulp at the early stages after tooth injury. Numerous class II MHC-positive cells appeared along the pulp-dentin border and extended their cell processes into the dentinal tubules at 12-24 h after cavity preparation and 3 days after tooth replantation. Newly differentiated odontoblast-like cells with HSP-25 immunoreactivity were arranged at the pulp-dentin border and the class II MHC-positive cells retreated towards the subodontoblastic layer by post-operative days 3-5 after tooth injury. Thus, the common cellular events occur during pulpal regeneration following two different experimental injuries. These findings indicate that the time course of changes in the expression of HSP-25 immunoreactivity reflects the degeneration/regeneration process of odontoblasts and that the temporal appearance of the class II MHC-positive cells at the pulp-dentin border suggests their participation in odontoblast differentiation as well as in initial defence reactions during the pulpal regeneration process.     

Spectroscopic Study of Human Teeth and Blood from Visible to Terahertz Frequencies for Clinical Diagnosis of Dental Pulp Vitality

Transmission spectra of wet human teeth and dentin slices, together with blood of different flow rates were investigated. The measurements carried out over a wide spectral range, from visible light down to terahertz radiation. The results make it possible to find the optimum light frequency for an all-optical determination of pulpal blood flow and, consequently, for clinically diagnosis of tooth vitality.