Oxygen distribution and consumption in rat lower incisor pulp

The aim was to determine the oxygen tension (P(O(2))) and rate of oxygen consumption in the pulp. Twelve rats were anaesthetised and artificially ventilated. Under an operating microscope, a recessed oxygen-sensitive microelectrode was inserted into the pulp through a small saline-covered cavity on the labial surface of the lower incisor. P(O(2)) was measured as a function of the transverse distance from the saline medium through to the middle of the pulp. Oxygen profiles were characterised by a decline of oxygen tension outside the pulp in the saline medium and a steeper gradient across the interface, before a localised oxygen consuming region corresponding to the odontoblasts. A plateau with some localised fluctuations was then followed by an increase in oxygen tension in the middle of the pulp. The average oxygen tension in the plateau region was 23.2 mmHg+/-2.1 mmHg (n=12). A mathematical model was used to extract oxygen consumption data from P(O(2)) profiles recorded from non-perfused pulp (created by reducing systemic blood pressure). The analysis revealed that there was a distinct oxygen consumption zone in the outer pulp, which anatomically corresponded to the odontoblast layer. The average oxygen consumption rate of the odontoblasts was 3.2+/-0.2 ml O(2)/min per 100g pulp tissue. The zone of high oxygen consumption was 68.7 micro m+/-6.9 micro m (n=24) thick. It is concluded that pulpal oxygen distribution is heterogeneous and that the odontoblast could be a major oxygen consumer within the rat incisor pulp.     

人牙周膜细胞体外三维立体培养模型的建立

目的：建立人牙周膜细胞（PDLC）体外三维立体培养模型，初步探讨两种支架材料应用于牙周组织工程的可行性，为进一步研究牙周组织生理病理及牙周组织工程奠定实验基础。方法：组织块法培养人PDLC，传代扩增后，接种于珊瑚和珊瑚转化羟基磷灰石（CHA）两种三维支架上，体外继续培养3d，进行细胞计数和扫描电镜观察。结果：细胞在两种支架材料上均能形成良好贴附并增殖，扫描电镜可见两种支架材料均具有良好的多孔网状结构，细胞在支架材料上生长旺盛，伸展充分。结论：可通过将人PDLC接种到珊瑚或CHA上建立体外三维立体培养模型，珊瑚和CHA均有望成为牙周组织工程的支架材料。     

Effects of erbium,chromium:YSGG laser irradiation on canine mandibular bone

BACKGROUND: Only relatively few reports have described the morphological effects on bone produced by erbium,chromium: yttrium,scandium,gallium,garnet (Er,Cr:YSGG) laser irradiation, and none has investigated the atomic changes or estimated the temperature increases involved. The objectives of this study were to investigate the morphological, atomic, and temperature changes in irradiated areas during and after laser irradiation, and to evaluate the cutting effect on canine mandibular bone in vitro. METHODS: Two canine mandibular bones were cut into 3 to 5 cm pieces and irradiated by an Er,Cr:YSGG laser utilizing a water-air spray at 5 W and 8 Hz for 10 or 30 seconds. During and after laser irradiation, temperature increases in the irradiated areas were measured by thermography. The samples were then observed by stereoscopy and scanning electron microscopy to determine morphological changes and by energy dispersive x-ray spectroscopy to evaluate atomic alterations. RESULTS: Regular holes or grooves having sharp edges and smooth walls were produced, but no melting or carbonization was observed. The maximum temperature increase was an average 12.6 degrees C for 30-second irradiation. The continuous time of a temperature increase of more than 10 degrees C was consistently less than 10 seconds. An atomic analytical examination revealed that the calcium:phosphorus ratio was not significantly changed between the lased and unlased areas (P>0.0 1). CONCLUSION: These results showed that the Er,Cr:YSGG laser cuts canine mandibular bone effectively without burning, melting, or altering the calcium:phosphorus ratio of the irradiated bone.     

23例恒牙根管机械预备断针的原因分析和处理

目的：近年来，临床上通过镍钛机用根管器械，采用逐步深入法进行患牙根管预备的病例越来越多，导致根管内断针的病例也在逐渐增多，对这类断针原因进行分析以减少并发症的发生。方法：针对23例近两年来采用Step-down或Crown-down技术进行机械根管预备后所出现的根管内断针进行分析和根管再处理。结果：断针位于根管上、中、下的比率为4：12：7，原因包括：①未按操作规程。②操作的方法不当。③忽视手动器械的作用。④根管冲洗不到位。⑤使用的器械不当。经过处理后，大部分病例通过取出断针或建立旁路的方法完成治疗。结论：不当操作还可导致根管内产生台阶、穿孔或折裂，同时，金属疲劳和扭矩是影响器械寿命的重要因素。通过合理操作，综合运用机械法、手动法甚至超声法的根管预备技术，大多数并发症均可避免。     

Microleakage Evaluation in Amalgam Restorations Used with Bases

Marginal leakage in amalgam restorations often precedes the development of secondary caries. One potential way to improve the marginal seal of such restorations, and thus minimize the risk of carles development, is to apply a glassionomer base prior to amalgam placement.
This study compared microleakage resistance among amalgam restorations placed with and without light-cured glass-ionomer base materials. Preparations were made in extracted human molar teeth. Four groups were studied, including copal varnish, which was used as a control. All specimens were restored with amalgam. Results indicated significantly greater leakage at the cavity wall/base interface for restorations with a copal varnish cavity liner than for those with a glass-ionomer base. Leakage differences among bases were also found at the amalgam/base interface. Best results were obtained with a dual-cure resin-based system. These samples showed minimal leakage at both the cavity wall/base and the base/amalgam interfaces. These findings suggest that light-cured glass-ionomer bases can be effective in the prevention of microleakage in amalgam restorations.     

牙源性角化囊肿上皮细胞增殖动力学初步研究

目的探讨角化囊肿上皮细胞增殖特性,进一步了解角化囊肿的生物学行为,为临床治疗和预防复发提供一定的依据。方法采用增殖细胞核抗原（ｐｒｏｌｉｆｅｒａｔｉｎｇｃｅｌｎｕｃｌｅａｒａｎｔｉｇｅｎ,ＰＣＮＡ）免疫组化法和细胞核ＤＮＡ含量分析,对牙源性角化囊肿、根尖囊肿、含牙囊肿和造釉细胞瘤上皮细胞进行对比研究。结果角化囊肿上皮细胞增殖活跃,与造釉细胞瘤相似。提示角化囊肿生物学特性为上皮细胞主动生长,而非被动性膨胀生长。结论角化囊肿可视为具有侵袭性生长的良性肿瘤,提出命名为“牙源性角化囊性瘤”更能反应其生物学特性     

Inhibitory effects on jaw muscle activity of innocuous and noxious stimulation of facial and intraoral sites in man

Controlled mechanical stimulation of the upper lip in seven subjects resulted in a period of complete or partial inhibition of the electromyographic activity of the masseter muscle. When a painful stimulus was delivered to the lip, a later inhibitory period with a more variable duration was produced. Innocuous stimulation at various intraoral sites led to an early inhibitory period with characteristics similar to those of inhibition produced by innocuous lip stimulation. An increase in stimulus intensity to a noxious level resulted in a second period of inhibition comparable to that produced by noxious lip stimuli. The intensity of the stimulus and the level of muscle activity maintained by the subject were found to influence the incidence and duration of the inhibitory periods. Thus, innocuous and noxious stimulation, whether applied intraorally or extraorally, may result in two distinct periods of inhibition in the jaw-closing muscles. The role in orofacial function of the first inhibitory period has yet to be demonstrated, but the second period is probably involved as a protective reflex.     

Evaluation of X-Ray Projection Angulation for Successful Radix Entomolaris Diagnosis in Mandibular First Molars In Vitro

Introduction

The aim of this study was to evaluate the radiographic features of permanent three-rooted mandibular first molars with radix entomolaris (RE), investigate the correlation between anatomical classification and radiographic type of RE, and to determine the most effective horizontal beam angulation for the diagnosis of RE.

Methods

Twenty-five extracted mandibular first permanent molars with RE were selected for taking radiographs in 7 horizontal angulations. By using set criteria, 3 evaluators assessed morphologic and radiographic features of the RE and optimum beam angulation for RE diagnosis. Intraexaminer variability was analyzed with Cohen kappa test.

Results

Three types of curvature of RE presented with 3 distinct types of typical radiographic appearance on orthoradial radiographs. We classified the radiographic features of RE into 3 types, as follows: type i, type ii, and type iii. Seven teeth showed type i radiographic features. Zero-degree, 5-degree, 15-degree, and 25-degree radiographs were significantly better than the mesially angulated -15-degree and -25-degree images for detecting the type i RE images (P < .05). Fifteen-degree, 25-degree, and -25-degree horizontal beam angulations showed significantly more accurate diagnoses of RE in 8 type ii images (P < .05). Only 25-degree-angled radiographs were found to have a high diagnostic yield of type iii RE images (P < .05). A significant correlation was found between morphologic and radiographic types of RE (P < .05, contingency coefficient = 0.473). Intraexaminer variability was low, with kappa = 0.68 (P < .05).

Conclusions

RE presents 3 types of typical radiographic features on orthoradial radiographs. Additional 25-degree mesial horizontal-angled radiographs are essential for preoperative identification and evaluation of RE, especially types ii and iii.     

Physostigmine-induced salivary secretion in the rat

The purpose of this study was to see if physostigmine, a reversible cholinesterase inhibitor, affects the secretion and composition of saliva of the major salivary glands of the rat. Low doses of physostigmine did not elicit secretion. At higher doses there was significant flow from the parotid and submandibular glands within 5 min; however, no sublingual secretion was observed. The submandibular flow rate was highest for the first 5 min, then declined rapidly. The parotid flow rate initially was one-fifth of the maximum submandibular rate and then gradually decreased. The concentrations of Ca, Na and K of physostigmine-induced parotid saliva, and the Na of submandibular saliva, were similar to those with carbachol stimulation. The Ca and K concentrations of submandibular saliva were significantly higher than with carbachol or parasympathetic stimulation, and resembled those of alpha-adrenergic stimulation. The protein concentrations of physostigmine-evoked saliva from both glands were similar. The amylase activity of physostigmine-evoked parotid saliva was much higher than that of carbachol or parasympathetic stimulation. Physostigmine-evoked secretion was completely blocked by atropine, a cholinergic antagonist, and by reserpine, partially blocked by phentolamine, an alpha-adrenergic antagonist and not affected by surgical sympathectomy. Morphologically, physostigmine resulted in a moderate decrease in the number of acinar, but not ductal, secretory granules of both the parotid and submandibular glands, while the sublingual gland was unaffected. Numerous patches of parotid acini also developed vacuoles or vesicles. These results suggest that physostigmine-induced salivary secretion is mediated primarily by direct effects on cholinergic and alpha-adrenergic receptors.