Rhythmic dentinogenesis in the rabbit incisor: Circadian,ultradian, and infradian periods

Summary We have identified a variety of biological rhythms involved in the apposition and mineralization of dentin in the rabbit incisor. Animals were injected during the day or night with lead acetate at 2-week intervals—to provide biological time markers in forming dentin—and transverse undecalcified sections of the lower incisors were prepared for electron microprobe analysis. The positions of the lead markers were identified, and the continuous distribution of calcium and sulfur was measured at 1 μm intervals between the markers. In thin sections stained with hematoxylin after decalcification, the widths of a series of structural increments (bands) were measured with an ocular micrometer. Fourier analysis of the data revealed spectra of structural and compositional rhythms with a range of periodicities which extended from a matter of hours [ultradian (<24 h)] to days [infradian (>24 h) and circadian (approximately 24 h)]. The structural and compositional rhythms appeared to be independent to the extent that they did not necessarily have the same periods, or amplitudes. Nor were there simple phase relationships between all of the rhythms. At some times, Ca and S fluctuations are inversely proportional (180° out of phase), but in other cases they are directly proportional or out of phase by varying degrees other than 180°. The analyses thus suggest that calcium and sulfur deposition (representing mineral and glycosaminoglycan deposition, respectively) are not simply inversely proportional, and that the hematoxylin-stained structural increments did not solely reflect differences in the distribution of the mineral components in dentin.     

Unusual collagen aggregates induced in rat incisor dentin after vinblastine administration

Summary Young male Wistar rats weighing 100 g were injected intravenously with 0.2 mg of vinblastine sulfate (VBL). At 24, 27, and 36 hours and 2, 4, and 6 days after introduction of the drug, the rats were fixed by means of perfusion and the upper incisors were removed for electron microscopy. Many secretion granules had accumulated in the young odontoblasts 24 hours after VBL administration. Newly formed predentin located between odontoblasts contained small amounts of an unusual collagen aggregate characterized by a fine, symmetrically striated structure, and paired, dense bands, which were present at both ends. After 27 hours, following the disappearance of the secretion granules in the odontoblasts, unusual collagen aggregates had increased in amount. Two days after administration, the predentin layer, which was close to the odontoblasts, was composed largely of unusual collagen aggregates. During dentinogenesis, the layer of unusual collagen aggregates gradually shifted into the dentin, where, 4 days after VBL administration, it was, to a large degree, located. Mineralization of the unusual collagen aggregates began with the deposition of fine, filamentous crystals that later grew into needle-shaped crystals 40 ? thick. These findings suggest that unusual collagen aggregates are produced as a result of the secreting function of odontoblasts and are mineralized, as are normal collagen fibrils in dentin.     

Effects of fluoride,calcium, and phosphate administration on mineralization in rats

Summary Seven days before a fluoride injection of 20 mg sodium fluoride per kg body weight, 3-month-old rats grown on a standard pellet diet containing 0.8% calcium and 1.4% phosphate were given a diet of rice with only 0.025% calcium and 0.1% phosphate. Microradiographs of the continuously growing incisors showed a hypermineralized and a subsequent hypomineralized zone. Blood analysis demonstrated a decrease and a subsequent reestablishment of plasma calcium concentration. In some experiments calcium and phosphate were administered to compensate the hypocalcemia which prevented the hypomineralized zone from arising. A delay of calcium and phosphate administration led to formation of a mineralized band within the hypomineralized zone. The results are discussed with reference to calcium homeostasis.     

Cathepsin D: Ultra-immunohistochemical localization in dentinogenesis

Summary Cathepsin D was purified from rat liver using a new affinity chromatographic method, based on the coupling to the specific inhibitor pepstatin. This preparation was used for the production of specific antibodies from rabbit. The purified IgG fraction was conjugated to horseradish peroxidase in a two-step coupling procedure and used for electron microscopic immunohistochemistry of the odontoblast-predentine region of the rat incisor. Precipitates, indicating the presence of cathepsin D, were seen in the odontoblast, odontoblast process, and in the extracellular unmineralized matrix, the predentine. The observations are discussed in relation to proteoglycan degradation at the mineralization front simultaneous with crystal formation, and in relation to the function of lysosomal enzymes in the turnover of connective tissue.     

Technical aspects of perichondrial grafting in the rabbit

A screening process to determine the most appropriate model for the study of cartilage growth from perichondrium obtained from the rabbit's left tenth costal cartilage has resulted in the following observations: (1) best growth is achieved when fixation of the graft is secure and conformity to the recipient bed is complete; (2) immobilization enhances fixation, but permits fibrous tissue growth onto the graft, and (3) diminishing periods of immobilization enhance perichondrial growth, but have a deleterious effect on fixation.     

Studies on dentinogenesis in the rat

Three-day-old rats were fixed by perfusion with glutaraldehyde and thin slices were cut of the first molar germs. The slices were treated with EDTA and activated with buffered solutions containing Mg²⁺, Ca²⁺ or Zn²⁺. Incubation was carried out in buffered solutions (pH 8.5) containing inorganic pyrophosphate and Pb²⁺. In the Mg²⁺-activated specimens incubation products were localized to the plasma membranes in the stratum intermedium and the subodontoblastic area. Lead deposits were found on the periphery of the dentinal globules. Incubation products were more randomly distributed in Ca²⁺-activated specimens whereas those activated with Zn²⁺ displayed a deposition of lead precipitates mainly corresponding to that seen after activation with Mg²⁺. The findings are discussed in reference to the localization of alkaline phosphatase in the dentin-producing tissues and it is proposed that the results are indicative of the presence of an inorganic pyrophosphatase in these tissues.     

Ultracytochemical demonstration of ATP-dependent calcium pump in ameloblasts of rat incisor enamel organ

Summary The enamel organ of the growing rat incisor was fixed with a mixture of formaldehyde and glutaraldehyde and processed for ultracytochemical demonstration of Ca- and Mg-activated membrane ATPase by a one-step lead technique at alkaline pH. To inhibit nonspecific alkaline phosphatase, 5 mM levamisole was added to the incubation media. Intense Ca- and Mg-ATPase activity was demonstrated in the cell surfaces of the secretory ameloblasts, except at the proximal and distal junctional complexes and the gap junctions in the lateral and basal cell surfaces. Deep plasma membrane invaginations at the proximal and distal parts of Tomes processes facing interrod- and rod-enamel growth regions exhibited the strongest enzymatic reaction. Mg-ATPase activity was also shown to be present in the plasma membranes of secretory ameloblasts but it was less intense than Ca-ATPase. Except for a slight reaction in the Golgi membranes, all other cell organelles of the secretory ameloblasts and the adjacent enamel matrix were free of enzymatic reaction. However, when the tissues were incubated in media lacking levamisole, a prominent enzymatic reaction was observed in the newly secreted enamel matrix of the rod and interrod growth regions as well as on the plasma membranes of the cells. In maturation ameloblasts of both ruffleended and smooth-ended types, a weak reaction for Ca- and Mg-ATPase was restricted to basal cell surfaces facing the papillary cell layer. In tissues incubated in media lacking levamisole, a variable deposition of reaction products was observed in the Golgi membranes, mitochondrial membranes, tubular elements of smooth endoplasmic reticulum in the ruffled border zone, and along the plasma membranes of the ruffled border. Throughout the secretory and maturation stages, a moderate and/or weak enzymatic reaction for both Ca- and Mg-ATPase was seen in the plasma membranes of the cells of the stratum intermedium and the papillary layer when incubated in media with levamisole. Omission of substrate ATP and/or the enzyme activator CaCl₂ from the incubation media for Ca-ATPase produced a negative reaction in the tissues examined. When the calmodulin blocker trifluoperazine was administered to the rats intravenously, Ca-ATPase activity was almost completely abolished from the plasma membranes of secretory ameloblasts, but not of other cell types.     

The effects of diets high in zinc at different levels of calcium and vitamin D on the rat humerus and incisor

Two groups of weanling rats were maintained on diets containing an excess of zinc, with low calcium intake and with, or without, added vitamin D. Two thirds of the animals in the two groups were killed after five and ten weeks respectively while the remainder received these diets for five weeks and were then maintained for a further five weeks on the corresponding diets with a normal level of zinc. Histological and microradiographical observations of the humeri and incisors were then carried out. The known porotic effect of low calcium-normal vitamin D diets was markedly increased in zine excess. After adjusting the intake of zinc to normal, the degree of porosis was reduced to that typical of low calcium conditions, with little effect on the dentine. Absence of vitamin D from the zinc-low calcium diet resulted in both porotic and osteomalacic changes in the bones, while subsequent removal of the zinc excess resulted in a condition typical of osteomalacia. Dentine was drastically affected and, alternating bands of poorly and adequately-mineralized tissue were observed. Adjusting the zinc intake to normal resulted in wide seams of unmineralized dentine with a narrow band of mineralized tissue. In the absence of vitamin D, zinc excess appears to exert a porotic effect in bone and a mineralizing effect in dentine, while it also increases the degree of porosis found in bone when the vitamin is present.

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Zusammenfassung Zwei Gruppen entwöhnter Ratten wurden mit Calcium-armen Futter mit oder ohne Vitamin D-Zusatz und einem Zinküberschuß ernährt. Zwei Drittel der Tiere in beiden Gruppen wurden nach 5, beziehungsweise nach 10 Wochen getötet, während die übrigen Tiere dieses Futter während 5 Wochen erhielten und anschließend für weitere 5 Wochen die entsprechende Nahrung mit einem normalen Zinkgehalt bekamen. Die Humeri und die Schneidezähne wurden dann histologisch und mikroradiographisch untersucht. Der bekannte porotische Effekt der Calcium-armen, normal Vitamin D-haltigen Nahrung war bei Zinküberschuß deutlich erhöht. Wurde die Zinkaufnahme zur Norm gebracht, so reduzierte sich der Grad der Porose auf denjenigen, der typisch für niedrige Calcium-Einnahmen ist, mit wenig Wirkung auf das Dentin. Fehlte das Vitamin D in der Zink-reichen und Calcium-armen Nahrung, so entstanden in den Knochen sowohl porotische als auch osteomalazische Veränderungen; nach Absetzen des Zinküberschusses jedoch entstanden typische Anzeichen einer Osteomalacie. Das Dentin wurde stark angegriffen, und es wurden abwechslungsweise Banden von normal und schlecht mineralisiertem Gewebe beobachtet. Wenn die Zinkeinnahme zur Norm gebracht wurde, so entstanden breite Säume von unverkalktem Dentin mit einer schmalen Bande von mineralisiertem Gewebe. Bei Fehlen von Vitamin D scheint der Zinküberschuß eine porotische Wirkung auf den Knochen und eine verkalkende Wirkung auf das Dentin zu haben; dieser Überschuß erhöht den Grad der Knochenporose auch in Anwesenheit des Vitamins.

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Résumé Deux groupes de rats sevrés sont soumis à une alimentation contenant un excès de zinc, une faible quantité de calcium avec ou sans vitamine D. Deux tiers des animaux dans les deux groupes sont sacrifiés respectivement après cinq et dix semaines, alors que les animaux restants sont soumis à ce régime pendant cinq semaines, puis, pendant les cinq semaines suivantes, reçoivent les régimes correspondants, avex une concentration normale de zinc. Des études histologiques et microradiographiques sont réalisées sur l'humérus et les incisives. L'effet porotique connu des régimes pauvres en calcium et normaux en vitamine D est notablement augmenté avec un excès de zinc. Après avoir ramené le zinc à la normale, la gravité de l'ostéoporose est réduite à celle recontrée au cours de concentration faible en calcium, avec peu d'effet sur la dentine. L'absence de vitamine D, dans les régimes à contenu élevé en zinc et faible en calcium, provoque des changements porotiques et ostéomalaciques des os, alors que le ratrait consécutif de l'excès de zinc provoque une ostéomalacie typique. La dentine est nettement atteinte et des bandes alternantes de tissus bien mal minéralisés sont observées. En ajustant le zinc ingéré à une concentration normale, de larges couches de dentine non minéralisée sont observées avec une bande étroite de tissu minéralisée. En l'absence de vitamine D, l'excès de zinc semble exercer un effet porotique sur l'os et un effet de minéralisation sur la dentine, alors qu'il augmente l'effet porotique au niveau de l'os lorsque la vitamine est présente.

     

Expression of parathyroid hormone-related protein in the partially obstructed and reversed rabbit bladder

Objectives  Parathyroid hormone-related protein (PTHrP), the main factor responsible for malignant hypercalcemia, is produced by a wide range of normal and malignant tissues. Prior studies in the rabbit model demonstrated that partial bladder outlet obstruction results in calcium-dysregulation characterized by a marked increase in free calcium within the smooth muscle compartment and the stimulation of calcium-activated enzymes, such as calpain and phospholipase A₂. Methods  Twenty-four male New Zealand white rabbits were divided into four groups of six each. Following 4 weeks of obstruction, one group of animals was killed, while outlet obstruction was reversed in two additional groups of animals, which were killed 4 and 8 weeks after relieving the obstruction. A group with six sham-operated rabbits served as controls. The expression and localization of PTHrP were detected in muscle and mucosa by immunohistochemistry, using a PTHrP-specific antibody. Results  In the sham-operated group, rabbit bladders showed a low expression of PTHrP in both the mucosa and muscle layers. PTHrP in the 4-week obstructed bladder group, in muscle and mucosa, were 266% and 134% higher than the sham group, respectively. Strong PTHrP immunostaining persisted in the 4-week reversal groups, but it returned to the sham level after 8 weeks of reversal in the muscle layer. As mentioned about the mucosa layer, the PTHrP level returned to control levels more rapidly after 4 weeks of reversal and continued after 8 weeks of reversal. Conclusion  This study showed that PTHrP is increased after partial bladder outlet obstruction and decreased after relieving the obstruction.     

Various aspects of the microvascularization of the thyroid follicles in the rabbit

The authors, use histology and diaphanization after the injection of Micropaque 25% with gelatin 10% in 35 rabbits, 25 female and 10 male, with race, weight and age variable, to show some aspects of the thyroid follicles microvascularization. In this experimental animal we observe a follicle vascularization like the one described by other authors.     

Effects of the calcium channel blocker nifedipine on epiphyseal growth plate and bone turnover: A study in rabbit

Summary The potential effects of a calcium channel blocker (nifedipine) on epiphyseal growth plate and bone remodeling have been investigated in growing rabbits. The treated group received 6 mg/kg/day nifedipine twice daily by gavage for 10 weeks. An untreated group was used as control; with this dose, neither toxic effects nor decrease in the body weight have been observed. No modifications of blood phosphocalcic parameters have been found. In the treated group there is a significant lower cancellous bone volume, lower osteogenesis, shorter labeled perimeters, and lower mineral apposition rate than in the control group. Epiphyseal growth plate thickness is lower than in the untreated animals and considerable morphological changes are observed in the growth zone compared with the control group. A decrease in the growth of humerus length was found. In conclusion, nifedipine affects bone physiology, especially with consequences on bone growth. These effects appear to be quantitatively important, and there is the possibility of bone side effects on therapeutic use in humans, especially in young subjects.     

Does potassium induce the release of nitric oxide in the rabbit corpus cavernosum?

We investigated the effects of increases in the extracellular potassium concentration on the function of the rabbit corpus cavernosum. The resting tissue tension increased as the potassium concentration was increased from 4.7 mM to 20 mM or 30 mM. The maximum contraction induced by 200 μM phenylephrine was significantly decreased in the presence of 30 mM potassium compared with 4.7 mM potassium. After precontraction was induced with 200 μM phenylephrine, the magnitude of field-stimulated relaxation increased significantly as the potassium concentration was increased from 4.7 mM to 10 or 20 mM, but was almost completely abolished at 30 mM potassium. There was no difference in the suppressive effect of l-NAME on field-stimulated relaxation between specimens treated with 4.7 mM or 20 mM potassium. ATP- and bethanechol-induced relaxation was not affected by increases in the extracellular potassium concentration. A high-dose potassium solution (124 mM) induced contraction of the corpus cavernosum. In tissue precontracted with phenylephrine, a high-dose potassium solution that contained phenylephrine induced relaxation of corpus cavernosum; this relaxation was completely suppressed by l-NAME. These findings suggest that small increases in the extracellular potassium concentration increase field-stimulated relaxation of the corpus cavernosum and that this relaxation is not related to the effects of nitric oxide. Relaxation induced by high-dose potassium in tissue precontracted with phenylephrine is probably the result of release of nitric oxide. Received: 6 March 1997 / Accepted: 27 October 1997     

Effects of verapamil and sodium nitroprusside on acetylcholine-induced contraction of the rabbit detrusor muscle

Summary Effects of extracellular and intracellular Ca²⁺ on acetylcholine-induced contraction of the bladder detrusor muscle were studied in vitro, utilizing two types of Ca²⁺ antagonists of different mechanisms of action; verapamil and sodium nitroprusside (NP). Acetylcholine (10^-8 to 10^-2 M) caused dose-dependent contractions of the detrusor muscle strips. Pretreatment of the strips with verapamil (10^-7, 10^-6 M) significantly inhibited the acetylcholine-induced contraction in a dose-dependent manner, whereas NP (10^-7 to 10^-5 M) failed so suppress the contraction. The contraction of the strips once elicited by acetylcholine (10^-6 M) could be completely relaxed by verapamil (10^-5 M) addition, but only incompletely by NP (10^-5, 10^-4 M). In Ca²⁺-free solution containing 0.01 mM EGTA, replenishment of Ca²⁺ (2.5 mM) to the medium caused contractions of the strips. Addition of acetylcholine (10^-6 M) to the medium enhanced the Ca²⁺-induced contration, which was significantly inhibited by pretreatment with verapamil (10^-6 M), but not affected by NP (10^-6 M). In Ca²⁺-free medium containing 0.1 mM EGTA, acetylcholine caused a slight degree of tension increase of the strips in a dosedependent fashion, at higher concentrations exceeding 10^-6 M. These results suggest that the detrusor muscle contraction induced by acetylcholine is mostly dependent of extracellular Ca²⁺ influx both in its initiation and maintenance. It is also supposed, however, that in tracellular Ca²⁺ fractions will partly participate in the acetylcholine-induced contration and possibly in its maintenance.     

Effect of magnesium on the function of the rabbit corpus cavernosum

Contraction and relaxation of the smooth muscle, including the corpus cavernosum, are mediated by changes in the intracellular concentration of calcium. Since magnesium modulates the movement of calcium it can modify the function of the erectile tissue. We designed this study to investigate the effects of magnesium in doses ranging from 5 to 30 mM on the function of the rabbit corpus cavernosum in vitro. The resting tension of tissue strips was significantly reduced by exposure to a solution high in magnesium (5–30 mM). The contractile response to field stimulation under resting conditions, and the contraction to phenylephrine, were significantly decreased by magnesium (5–30 mM). There were no differences in the contractile strength of the corpus cavernosum to KCl. Although the relaxation induced by field stimulation under preincubation with 200 M phenylephrine was abolished in the presence of 30 mM magnesium, there were no differences at a concentration of 5 mM or of 10 mM magnesium. The relaxation induced by sodium nitroprusside under precontraction with 200 M phenylephrine was further increased by magnesium dose dependently. A high concentration of magnesium (30 mM) enhanced both bethanechol-induced and ATP-induced relaxations under precontraction with phenylephrine. Our study demonstrated that magnesium reduced the receptor-mediated contraction of the rabbit corpus cavernosum and enhanced the relaxation of this tissue induced by sodium nitroprusside, bethanechol, and ATP.     

川芎嗪对离体兔阴茎海绵体平滑肌条收缩的影响

目的 初步探讨川芎嗪(Ligustrazine)对离体兔阴茎海绵体平滑肌条的舒张作用及其机制。方法 离体家兔阴茎海绵体平滑肌实验方法,观察川芎嗪对阴茎海绵体平滑肌的舒张效应,测定去氧肾上腺素(PE)和氯化钾(Ka)的浓度-效应曲线。结果 川芎嗪浓度依赖性地舒张PE诱发的阴茎海绵体平滑肌收缩作用,最大舒张效应为(74.1±6.2)％[对照组为(21.9±5.6)％,P<0.01]。不同浓度的川芎嗪可使PE和KCL的浓度-效应曲线右移,最大收缩反应降低,高浓度(0.8g/L)时抑制收缩作用更显著。结论 川芎嗪有明显的舒张阴茎海绵体平滑肌作用,并呈剂量依赖性。川芎嗪舒张阴茎海绵体平滑肌机制可能与抑制细胞外钙内流有关。     

Rhythmic spontaneous activity in the piriform cortex

Slow spontaneous rhythmic activity is generated and propagates in neocortical slices when bathed in an artificial cerebrospinal fluid with ionic concentrations similar to the ones in vivo. This activity is extraordinarily similar to the activation of the cortex in physiological conditions (e.g., slow-wave sleep), thus representing a unique in vitro model to understand how cortical networks maintain and control ongoing activity. Here we have characterized the activity generated in the olfactory or piriform cortex and endopiriform nucleus (piriform network). Because these structures are prone to generate epileptic discharges, it seems critical to understand how they generate and regulate their physiological rhythmic activity. The piriform network gave rise to rhythmic spontaneous activity consisting of a succession of up and down states at an average frequency of 1.8 Hz, qualitatively similar to the corresponding neocortical activity. This activity originated in the deep layers of the piriform network, which displayed higher excitability and denser connectivity. A remarkable difference with neocortical activity was the speed of horizontal propagation (114 mm/s), one order of magnitude faster in the piriform network. Properties of the piriform cortex subserving fast horizontal propagation may underlie the higher vulnerability of this area to epileptic seizures.     

Case report: actinomycosis of the appendix--an unusual cause of acute appendicitis in children

Abdominal actinomycosis in children is a rare disease, which is occasionally found on histologic examination after an operation for acute appendicitis. Because of its nonspecific clinical and radiological signs and symptoms and low prevalence, the diagnosis is hardly ever made before the patient undergoes an operation and tissue is available for pathologic evaluation. When the diagnosis is made, the patient should be treated with the appropriate long-term antibiotics. With antibiotic therapy, the prognosis is favorable.We describe a 13-year-old girl who presented with acute appendicitis and was found to have abdominal actinomycosis after undergoing open appendectomy, which was treated successfully with penicillin and piperacillin-tazobactam.     

利福平硫酸钙植入剂修复动物骨缺损的体内实验研究

目的探讨利福平硫酸钙植入剂（RCPPs）在体内的生物相容性、降解情况及成骨特点。方法将利福平硫酸钙植入剂（RCPPs）随机植入成年新西兰白兔1．5cm的桡骨缺损内．并设立不植入任何材料的空白对照。观察利福平硫酸钙植入剂（RCPPs）植入后动物的局部反应；于术后6、12周取材．作X线、大体标本及组织形态学观察，分析不同时期组织反应、骨缺损修复及材料降解情况。结果利福平硫酸钙植入剂（RCPPs）植入后无明显的局部不良反应。X线检查、大体标本及组织形态学观察显示利福平硫酸钙植入剂（RCPPs）的成骨方式主要是骨传导成骨，至术后12周时骨缺损基本修复，RCPPs与宿主骨结合紧密。而空白对照骨缺损断端仅有少量骨修复，形成骨不连。利福平硫酸钙植入剂（RCPPs）植入后即开始其降解过程，12周以后材料周围出现较多吞噬有材料颗粒的巨噬细胞和多核口细胞，仍有部分材料未降解吸收。结论利福平硫酸钙植入剂（RCPPs）具有持续的成骨能力、良好的生物相容性。     

硫酸钙骨水泥修复骨质疏松兔胫骨平台骨折的研究

目的探讨硫酸钙对骨折修复活动的影响。方法建立兔骨质疏松胫骨平台塌陷骨折模型,用硫酸钙填充植骨,进行一般观察、大体X线及骨密度fBMD）分析。结果普通X线观察提示骨折区填充的硫酸钙逐渐降解吸收,被新生的骨组织替代。骨水泥治疗组兔硫酸钙骨水泥填充后1、2、3、4、6、8、12周骨折处样本BMD明显高于空白对照组,差异有统计学意义（P〈0．01）,8周时骨折区骨密度下降,低于正常胫骨平台：12周时较8周时增高接近正常胫骨平台。结论骨质疏松兔胫骨平台骨折填充硫酸钙骨水泥早期能增加骨密度,硫酸钙体内能够降解吸收,不干扰新骨的形成,能有效修复骨质疏松状态下的骨缺损。     

Comparative evaluation of the effects of Nd:YAG and Er:YAG laser in dentin hypersensitivity treatment

Dentin hypersensitivity (DH) is one of the most common complications that affect patients after periodontal therapy. So far, many investigators have successfully used different types of laser on DH treatment. The aim of this study was to evaluate the comparative effect of Nd:YAG laser and Er:YAG laser on human teeth desensitization. A group of nine patients with a total of 63 chronic hypersensitive teeth were selected. Each one of them should at least have three hypersensitive teeth. These teeth were randomly allocated into three groups. Group 1, Nd:YAG laser (1 W, 15 Hz, 60 s, two times); group 2, Er:YAG laser (100 mJ, 3 Hz, 60 s, two times); and group 3 serves as control group without any treatment. Assessment of pain was performed by a visual analysing scale (VAS) after stimulation of sensitive tooth by using the sharp tip of an explorer. This test was performed before treatment, immediately after that and at 1-, 3- and 6-month intervals after treatment by one blinded examiner. Analysis of VAS score between the three groups at the time of treatment did not show any significant difference (p = 0.506). However, by using repeated-measurement analysis of variance test, significant differences were seen in the three groups between before-treatment VAS score and after treatment (p < 0.0005). This statistically significant difference in the control group demonstrated a placebo effect. However, the effect of using Nd:YAG and Er:YAG lasers was stronger than this placebo effect, so that after removing the effect of the placebo, differences immediately after, 1, 3 and 6 months post treatment between all three groups still were statistically highly significant (p < 0.0005). Compared to the Er:YAG laser group, using Nd:YAG laser resulted in a significant reduction of VAS score at each follow-up examination (p < 0.0005). Although using Nd:YAG and Er:YAG laser in desensitization of hypersensitive teeth showed a placebo effect limited to a short time, results of this study demonstrated that both of these lasers have an acceptable therapeutic effect. The observed effects seemed to last for at least 6 months. It was concluded that Nd:YAG laser is more effective than Er:YAG laser in reduction of patients’ pain.