Analysis of the surface characteristics and mineralization status of feline teeth using scanning electron microscopy

External resorption of teeth by odontoclasts is a common condition of unknown origin affecting domestic cats. Odontoclastic resorptive lesions involve the enamel cementum junction (ECJ, cervix) and root surface, leading to extensive loss of enamel, dentine and cementum. This study was undertaken in order to determine whether features of the surface anatomy and mineralization of feline teeth could explain why odontoclastic resorptive lesions are so prevalent in this species. Backscattered electron scanning electron microscopy was used to study enamel, cementum and dentine in non-resorbed, undemineralized teeth from adult cats. Analysis of the ECJ revealed thin enamel and cementum and exposed dentine at this site. Furthermore, enamel mineralization decreased from the crown tip to the ECJ, and dentine mineralization was lowest at the ECJ and cervical root. Analysis of cementum revealed variations in the organization and composition of fibres between the cervical, mid- and apical root although no significant differences in mineralization of cementum were detected between different regions of the root. Reparative patches associated with resorption of cementum by odontoclasts and repair by cementoblasts were present on the root surface. In conclusion, results suggest that the ECJ and cervical dentine could be at a greater risk of destruction by odontoclasts compared with other regions of the tooth. The relationship of these features to the development and progression of resorption now requires further examination.     

Scanning electron microscopy of the apical structure of human teeth

The objective of this research was to evaluate, by scanning electron microscopy, the apical structure of extracted human permanent teeth with different degrees of pulp and periapical pathology. A total of 25 teeth were extracted: 5 teeth with vital pulp (group I); 10 teeth with pulp necrosis without radiographically visible periapical lesion (group II); 10 teeth with pulp necrosis with radiographically visible periapical lesion (group III). The root apex was sectioned and processed for scanning electron microscopy. In groups I and II, fibers covered the root cementum and there was no cementum resorption or microorganisms. There were areas of cementum resorption in group III with microorganisms on the root apex surface (biofilm) and no fibers. The authors conclude that the presence of chronic periapical lesions causes severe changes in the apical structure with a destruction of fibers and different degrees of cementum resorption forming lacunae in which bacterial biofilm persisted.     

Histological study of deposited cementum in human deciduous teeth with pathological root resorption

Physiological root resorption is a characteristic feature of human deciduous teeth. Pathological root resorption due to apical periodontitis, dental trauma or excessive orthodontic force is also observed in deciduous roots. The root resorption is not continuous, and has resting periods. In the resting period, cementum deposits in resorbed root surface. The deposited cementum in permanent teeth has been reported in detail. However, the deposited cementum in deciduous teeth is unclear. The present study examined apices of roots of human deciduous incisors with apical periodontitis and roots of sound deciduous incisors by light and transmission electron microscopy. Root dentin and original cementum had a severe irregular caved surface. Cementum was partially deposited on the caved root surfaces. The deposited cementum had made the caved root surface relatively flat. The cementum was lax and had some defects. The deposited cementum was belt-like in shape and had a stratified structure. Each layer had various structures consisting of abundant microfibrils and fine granular materials, microfibrils, granular materials, and collagen fibrils, a few fibrils and granular materials and a relatively homogeneous structure. The original cementum had many collagen fibrils, such as intrinsic and extrinsic fibers, and no granular materials or homogeneous structure. Therefore, structure of the deposited cementum was very different from that of original cementum in deciduous teeth and from that of deposited cementum in permanent teeth.     

Ultrastructural features of odontoclasts that resorb enamel in human deciduous teeth prior to shedding

Three dental hard tissues, i.e., cementum, dentin, and enamel, are resorbed by multinucleated cells referred to as “odontoclasts.” These cells have morphological and functional characteristics similar to those of bone-resorbing osteoclasts. However, concerning enamel resorption, which is a process that may occur during tooth eruption, satisfactory ultrastructural data on odontoclastic resorption are still lacking. Ultrastructural and histochemical characteristics of odontoclasts resorbing enamel of human deciduous teeth prior to shedding were examined by means of light microscopy and transmission and scanning electron microscopy. Odontoclasts that that resorbed enamel were tartrate-resistant acid phosphatase (TRAP)-positive multinucleated giant cells that were essentially the same as those that resorbed dentin and cementum. Ultrastructurally, they had numerous mitochondria, lysosomes, and free polysomes in their cytoplasm. In addition, they were characteristically rich in large cytoplasmic vacuoles containing enamel crystals in the cytoplasm opposite the ruffled border. Although they extended a well-developed, ruffled border against enamel surface, a clear zone—an area typically devoid of organelles—was rarely seen in these cells. In many cases, the cells were in very close contact with the enamel surface by the peripheral part of their cytoplasm. The enamel prisms at the resorption surface contained more loosely packed and electron-lucent enamel crystals compared with those of unresorbed, intact enamel. Furthermore, numerous thin needle- or plate-like enamel crystals that were liberated from the enamel matrix were found in the extracellular channels of the ruffled border and in various-sized cytoplasmic vacuoles in their cytoplasm. The superficial layer of the enamel matrix undergoing odontoclastic resorption stained positively with toluidine blue and for TRAP activity. The results of the present study suggest that odontoclasts resorbing enamel secrete acids as well as organic components, including hydrolytic enzymes, into the resorption zone underlying their ruffled border and that they phagocytose crystals that have been liberated from the partially demineralized enamel matrix by acids, subsequently dissolving them intracellularly. Anat. Rec. 252:215–228, 1998. © 1998 Wiley-Liss, Inc.     

In vitro detection and quantification of enamel and root caries using infrared photothermal radiometry and modulated luminescence

Artificially created demineralized and remineralized carious lesions on the root and enamel of human teeth were examined by photothermal radiometry (PTR) and modulated luminescence (LUM). Fourteen extracted human teeth were used and a lesion was created on a 1 mmx4 mm rectangular window, spanning root to enamel, using a lactic acid-based acidified gel to demineralize the tooth surface. The lesion was then exposed to a remineralization solution. Each sample was examined with PTR/LUM on the root and enamel before and after treatment at times from 1 to 10 (5 on root) days of demineralization and 2 to 10 days of remineralization. Ten-day (5 on root) demineralized samples were remineralized. After completing all the experiments, transverse microradiography (TMR) analysis was performed to compare and correlate the PTR/LUM signals to the depth of lesions and mineral losses. The PTR and LUM amplitudes and phases showed gradual and consistent changes with treatment time. In this study, TMR showed good correlation coefficients with PTR and LUM. It was also found that the length of the treatment time did not correlate very well to any technique, PTR/LUM or TMR, which implies a significant degree of inhomogeneity of the demireralization and remineralization rates in each and every tooth.     

无托槽隐形矫治器内收上颌前牙的三维有限元分析

目的:通过有限元分析探讨无托槽隐形矫治器内收上颌前牙时的生物力学特性。方法:选取1名健康青年志愿者,获取其上颌骨及牙齿CBCT影像资料,构建上颌骨复合体及无托槽隐形矫治器的三维有限元模型,分析矫治器施力控根内收（工况一）以及矫治器施力控根内收辅以微种植钉与Power arm 150 g牵引力内收（工况二）下牙齿位移趋势及牙周膜应力分布情况。结果:工况一,前牙的冠根位移差分别为113.3、92.2、128.6 μm,最大牙周膜等效应力为79.6 kPa;工况二,前牙冠根位移差分别为89.3、74.3、184.2 μm,最大牙周膜等效应力为37.5 kPa。结论:无托槽隐形矫治器联合微种植钉和Power arm可改善上颌切牙倾斜移动的趋势并减少牙根吸收的风险,但对于尖牙的控制尚不足。     

Cementum-like tissue deposition on the resorbed enamel surface of human deciduous teeth prior to shedding

Prior to the shedding of human deciduous teeth, odontoclastic resorption takes place at the pulpal surface of the coronal dentin, and this resorption occasionally extends coronally from the dentinoenamel junction into the enamel. After the end of resorption, however, the resorbed enamel surface is repaired by the deposition of a cementum-like tissue. Using this phenomenon as an observation model, in this study we examined the sequence of cellular and extracellular/matrix events involved in the enamel resorption repair by light and electron microscopy. As the odontoclast terminated its resorption activity, it detached from the resorbed enamel surface; thereafter, numerous mononuclear cells were observed along the resorbed enamel surface. Most of these mononuclear cells made close contact with the resorbed enamel surface, and coated pits or patches were observed on their plasma membrane facing this surface. Furthermore, they frequently contained thin needle- or plate-like enamel crystals in their cytoplasmic vacuoles as well as secondary lysozomes. Following the disappearance of these monononuclear cells, the resorbed enamel surface now displayed a thin coat of organic matrix. Ultrastructurally, this organic layer was composed of a reticular and/or granular organic matrix, but contained no collagen fibrils. Energy-dispersive X-ray microanalysis of this thin organic layer in undecalcified sections revealed small spectral peaks of Ca and P. Cementum-like tissue initially formed along this thin organic layer, increased in width, and appeared to undergo mineralization as time progressed. The results of our observations demonstrate that regardless of type of matrix of dental hard tissues, tooth repair may be coupled to tooth resorption, and suggest that mononuclear cells and an organic thin layer found on the previously resorbed enamel surface may play an important role in the repair process initiated after resorption of the enamel.     

尼古丁对大鼠实验性牙移动牙根吸收的影响

背景：吸烟严重影响牙周组织及牙根的健康,烟草中的尼古丁会加速牙周病患者牙周组织的破坏,影响骨改建,引起骨吸收。而整合素αvβ3参与正畸牙移动过程中的牙根吸收。 目的：以整合素αvβ3在破牙骨质细胞的表达量为主要观察指标,初步探讨尼古丁对正畸牙移动牙根吸收的影响。 方法：将110只实验SD大鼠随机分为空白对照组、生理盐水组以及0.5 mg/kg尼古丁组、0.75 mg/kg尼古丁组、1 mg/kg尼古丁组。后4组上颌第一磨牙施加50 g近中向拉力,同时每日向各组的大鼠腹腔注射一定剂量的尼古丁酒石酸溶液或生理盐水,运用苏木精-伊红染色和免疫组织化学染色,观察各组大鼠上颌第一磨牙加力1,3,5,7,14 d的组织变化情况和整合素αvβ3的表达量。 结果与结论：随着加力时间的延长的,牙根周围的牙周膜纤维变形,排列紊乱,炎性细胞浸润,压力侧、张力侧以及根分叉处牙根表面开始出现吸收陷窝、破牙骨质细胞。尼古丁注射的剂量越大,牙根表面的吸收陷窝越多越深,破牙骨质细胞显著增加。免疫组化染色结果显示,除空白对照组外,整合素αvβ3在各个实验组的破牙骨质细胞中表达,并且随着加力时间的延长,其表达强度增强,加力7 d时呈现强阳性表达,加力达到14 d时,表达随之减弱。随着尼古丁注射剂量的增加,整合素αvβ3阳性表达的破牙骨质细胞逐渐增加。结果说明,尼古丁会加重正畸牙移动过程中的牙根吸收,并且可能具有时间依赖性以及剂量依赖性。     

非阻生第三磨牙对邻牙健康的影响

目的 研究非阻生第三磨牙对其邻牙健康状况的影响,对是否预防性拔除非阻生第三磨牙提供理论依据。方法 选择2017年1月~12月在十堰市太和医院医院口腔外科就诊并拍摄全景曲面断层片的858例患者为研究对象,分析其第三磨牙阻生与非阻生情况,及其对第二磨牙远中邻面龋、远中根吸收和牙槽骨吸收的影响。结果 第三磨牙缺失时,其相邻第二磨牙远中发生邻面龋、根吸收、牙槽骨吸收的患病率分别为4.55%、0.32%、10.31%;第三磨牙存在时,患病率分别为15.91%、2.39%、24.94%,其中第三磨牙非阻生状态时,患病率分别为5.22%、0.38%、13.84%。结论 第三磨牙的存在较第三磨牙缺失更易增加其邻牙发生病变风险。非阻生第三磨牙对相邻第二磨牙发生龋病和根吸收并无明显影响,但可显著增加相邻第二磨牙发生牙槽骨吸收风险,采取预防性拔除第三磨牙,可能会避免其对邻牙造成进一步损害。     

A study of mineral density surrounding resorption sites in teeth

An investigation of mineral density surrounding lacunar resorption sites in cases of both internal and external root resorption, was carried out on 37 human primary and permanent teeth. In addition, equivalent areas of the roots of 14 normal appearing teeth were studied for comparison. Thirty-two of the teeth were analyzed using microradiographic and microhardness techniques and the remainder were studied microscopically after histologic preparation. The teeth used for microradiographic analysis were embedded in plastic, bisected and half of each tooth was sectioned at 70–100 μ. Microadiographs were taken at 9.5 kv and exposed to 30 milliamperes for 25 to 40 minutes. The other halves of the teeth were used for microhardness tests using a Tukon Microhardness Tester. One series of microhardness measurements was made 10 to 40 μ from sites of active resorption in root dentin and a second series was made 250 to 500 μ from these sites. The hardness measurements of the first series were found to be significantly lower than those of the second in cases of both external and internal resorption. Hardness values of the surface of normal appearing roots were also less than areas 250 to 500 μ deeper in the dentin. Microradiographs did not reveal any definite zone of subsurface demineralization although some resorption sites were bordered by irregular areas of decreased radiodensity which may be due to superimposition of several resorption sites within the thickness of the tooth section. Histologic observations did not reveal a definite subsurface demineralization gradient. The lacunar resorption front was found to be a multilocular and completely interconnected system.     

Anatomic characteristics of the furcation and root surfaces of molar teeth and their significance in the clinical management of marginal periodontitis

Treatment of periodontitis which involves the furcation area of molar teeth has always been a challenge. Sixty extracted human molar teeth were used for an anatomic study to clarify the possible morphologic factors which may affect the diagnosis, prognosis, and clinical management of periodontally involved teeth. Teeth were embedded in methylmethacrylate and cut in 70 μm cross sections from the cementoenamel junction to the apex. Cervical enamel projection, root and root trunk lengths, root proximities as well as depths of root concavities coronally, apically, and at the furcation roof were measured. Cervical enamel projections were observed in 30% of the teeth examined. The shortest root trunk was found at the buccal aspect of mandibular first molars, permitting furcation involvement at early stages of periodontal disease. The most apically located furcation was found at the distal site of maxillary first molars. Furcation roofs showed severe concavities and complex cementum morphology. Teeth exhibiting cervical enamel projection were found to have deeper root concavities compared to teeth without cervical enamel projection and mesial roots of mandibular molars possessed greater furcal concavities than distal roots. The presence of root concavities complicates the diagnosis of furcation involvement and restricts access of periodontal instruments, resulting in incomplete treatment. Furcation anatomy may also influence the long-term prognosis of the teeth by favoring the retention of bacterial deposits and making oral hygiene procedures almost impossible. The present study shows that knowledge of a tooth's unique anatomic characteristics is a prerequisite for effective periodontal therapy. Clin. Anat. 11:177–186, 1998. © 1998 Wiley-Liss, Inc.     

下颌全牙列-直丝弓矫治器的生物力学建模

目的建立下颌全牙列-直丝弓矫治器的生物力学模型,分析其在滑动法关闭间隙的载荷作用下牙根及牙周组织的应力和位移分布。方法根据志愿者颌面部CT扫描图像建立下颌骨(皮质骨和松质骨)和全牙列(牙釉质、牙本质、牙髓、牙周膜)的模型,并以Roth托槽的实际数据建立一套托槽模型,与牙齿间的空隙用粘结剂来填充;弓丝和每个托槽都考虑接触,并使用弹簧元连接托槽和弓丝,模拟扎丝的作用,施加滑动法关闭间隙的载荷。结果切牙出现牙冠向舌侧、牙根向唇侧的转矩移动,其牙周组织和牙根的应力较高,特别是中切牙,其牙周膜的最大应力为3.97 kPa;第1磨牙远中根也出现应力集中,牙周膜的最大应力达到5.75 kPa。结论为了避免切牙的牙根吸收,可考虑增加前牙托槽的转矩;第1磨牙远中根也容易发生牙根吸收,建议适当降低正畸力值或采用微植体作为支抗。     

锥形束计算机体层摄影术检测口腔正畸中牙槽骨、牙根吸收状况的效果

目的 观察锥形束计算机体层摄影术（CBCT）检测口腔正畸中牙槽骨、牙根吸收状况的效果。方法 选择2016年1月~2017年7月我院进行口腔正畸治疗患者92例,均接受CBCT检测,比较治疗前、后中切牙牙槽骨厚度、牙根吸收情况。结果 治疗前后下颌、上颌根尖部、根中部、牙颈部牙槽骨厚度比较,差异无统计学意义（P＞0.05）;治疗后,下颌、上颌侧切牙牙根长度[（20.63±1.20）mm、（19.41±0.85）mm]、中切牙牙根长度[（21.12±1.19）mm、（21.74±1.02）mm]小于治疗前[（21.84±1.52）mm、（20.39±1.27）mm]、[（22.84±1.37）mm、（22.31±1.19）mm],差异有统计学意义（P＜0.05）。结论 口腔正畸患者存在一定牙根吸收现象,但未见明显牙槽骨改建,CBCT检测可对口腔正畸患者牙根吸收进行评估,以期为临床预防牙根吸收提供确切信息。     

Root resorption in relation to orthodontic tooth movement

Root resorption is an undesirable sequela of orthodontic tooth movement. The odontoclasts are responsible for root resorption and the process of hyalinization is known to preceed the orthodontic root resorption. It is found that there are several predisposing factors, therefore an evaluation of these factors should be done by careful examination of personal medical history, severity of malocclusion and dental treatment (if any due to previous history of trauma), anterior crossbite etc. The evaluation becomes an essential factor as it helps the orthodontists in detecting the occurance and severity of the root resorption and thereby plan out the treatment more effectively. Orthodontic tooth movements especially intrusion and other movements like tipping, torque are all known to influence the root resorption, therefore the detection using radiographs and repair of root resorption is of utmost significance as root resorption is a more serious problem from a medicolegal stand point of view. However some studies have shown that the repair process is known to occur after the cessation of orthodontic treatment by the deposition of cementum of cellular type. In the light of orthodontist's liability of what is basically an unpredictable phenomenon, it is necessary that the speciality define this uncertainity and protect its members against unnecessary and unjustified litigation.     

Odontoclastic resorption at the pulpal surface of coronal dentin prior to the shedding of human deciduous teeth.

Histological and histochemical observations of more than 150 extracted human deciduous teeth revealed that, prior to shedding, odontoclastic resorption as a rule takes place at the pulpal surface of coronal dentin. We also found that this phenomenon occurs in all kinds of deciduous teeth. The process of this internal resorption of coronal dentin of deciduous teeth clearly showed time-related histological changes. During the time the roots were actively being resorbed, the pulpal tissue retained its normal structure. However, when root resorption neared completion, inflammatory cells started to gradually infiltrate into the pulp, and odontoblasts began to degenerate. After that, multinucleate odontoclasts appeared, and resorption proceeded from the predentin to the dentin. The odontoclastic activity was initially detected only on the pulpal surface at the bottom areas of the crown. It gradually spread towards the pulpal horn regions along the wall of the pulp chamber. However, this internal resorption of coronal dentin did not continue until the teeth were finally shed. After the elimination of resorption, the resorbed dentin surface was repaired by a cementum-like deposition or covered with fibrous connective tissue.     

Ultrastructural study of the root dentine surface resuming resorption on human deciduous teeth

Resorption of deciduous teeth is not continuous, but alternates with periods of repair or rest. Dentine surfaces in periods of rest or repair resume resorption by odontoclasts during physiological root resorption of the deciduous teeth. However, no observations of such dentine surfaces have been shown. The characteristic feature of the dentine surfaces resuming resorption remains unknown. Tartrate-resistant acid phosphatase activity (TRAP) was detected on human deciduous teeth. The root resorbing surfaces on these teeth were photographed with a whole-mount light microscope, and the photographed areas were serially sectioned into 0.5 micron semithin sections. Preodontoclasts and odontoclasts were three-dimensionally reconstructed. On root resorbing surfaces, areas with small scattered TRAP-positive cells were observed among areas with many TRAP-positive resorbing odontoclasts and TRAP-negative areas. The sections showed that areas with small scattered TRAP-positive cells have features similar to those of TRAP-negative areas, but there were three kinds of characteristic TRAP-positive cells: preodontoclasts, odontoclasts forming small lacunae, and preodontoclasts, and odontoclasts with cytoplasmic processes extending to the dentine surface, which is covered with cells. These results suggest that the areas with small scattered TRAP-positive cells could be at the stage of resuming resorption, and show that the presence of preodontoclasts and odontoclasts with cytoplasmic processes extending to the covered dentine surface is a characteristic feature of the dentine surface at this stage.     

Development of coronal cementum in hypsodont horse cheek teeth

The horse is a grazing herbivore whose cheek teeth are hypsodon; that is, they possess long crowns that are completely covered by coronal cement at eruption. For elucidation of the sequential events in the formation of this coronal cementum in the mandibular horse cheek teeth, in the present study the lower 3rd permanent premolar teeth (PM₄) from 3.5‐, 4‐, and 5‐year‐old horses were compared by using radiography, microcomputed tomography (Miro‐CT), light microscopy (LM), and scanning electron microscopy (SEM). The present study clearly showed that prior to coronal cementogenesis tartrate‐resistant acid phosphatase (TRAP)‐positive odontoclasts resorbed on the enamel surface of the reserve crown in horse cheek tooth. Enamel resorption areas were relatively narrow, and started from the cuspal tips, and moved in the apical direction during tooth development. A primary cementum was initially deposited on the irregularly pitted enamel–cementum junction (ECJ) of the infolding and peripheral enamel. The infolding cementum filled grooves completely by the time of tooth eruption. On the other hand, in the peripheral cementum, the secondary and tertiary cementum layers were sequentially deposited on the primary cementum. These two cementum layers were sites for the insertion of the periodontal ligaments, and were continually laid down on the primary cementum coronally rather than apically throughout the life. The results of the present study suggest that the coronal cementum of horse cheek teeth is a multistructural and multifunctional tissue, meeting the requirements of its many different functions. Anat Rec, 297:716–730, 2014. © 2014 Wiley Periodicals, Inc.     

In vivo confocal microscopy analysis of enamel defects after orthodontic treatment: A preliminary study

After orthodontic treatment with fixed appliances, bonded brackets and residual adhesive must be removed. This procedure should lead to restitutio ad integrum of the enamel or, at least, restore the enamel surface as closely as possible to its pre-treatment conditions. The purpose of this study is the in vivo assessment at a microscopic resolution of enamel surfaces after bracket debonding while avoiding the tooth extraction. Nine orthodontic patients who had brackets removed at the conclusion of orthodontic treatment were enrolled. In vivo reflectance confocal microscopy imaging of dental enamel surface after debonding was performed for each patient. Eighteen upper incisors were analyzed, 10 in which the enamel demineralization appeared after the treatment and 8 in which the demineralization was present before the treatment. RCM analyses showed some speckled or roundish dark areas within the enamel. Moreover enamel alterations were detected at different levels of depth. The present in vivo microscopic study allowed for highlighting structural features in dental enamel, after debonding, at a microscopic resolution in real-time and in a non-invasive way, without the need for extraction or processing of the samples.     

酪蛋白磷酸多肽/无定形磷酸钙复合物与氟化钠预防正畸托槽周围的牙釉质脱矿

BACKGROUND: In clinical practice, both casein phosphopeptides/amorphous calcium phosphate compound and fluoride can effectively prevent the occurrence of enamel demineralization and caries. OBJECTIVE: To investigate the preventive effects of casein phosphopeptides/amorphous calcium phosphate compound and fluoride on enamel demineralization in the orthodontic treatment, so as to seek a remineralization agent with good effect. METHODS: Totally 40 human in vitro teeth which had been well bonded to brackets were randomly divided into four groups: control group (the surface was not coated with any substance), GC tooth mousse group (the surface was coated with casein phosphopeptides/amorphous calcium phosphate compound), duraphat group (the surface was coated with fluoride) and combined group (the surface was coated with casein phosphopeptides /amorphous calcium phosphate compound and fluoride). The enamel surface porosity was observed by scanning electron microscopy after the successive 14-day demineralization-remineralization experiments in these four groups. The change value of microhardness was measured before and after the experiment in each group. RESULTS AND CONCLUSION: There was obvious enamel demineralization in the control group, but not in the other three groups. The change value of microhardness in GC tooth mousse, duraphat and combined groups was lower than that in the control group (P < 0.05), and there was no significant difference between GC tooth mousse, duraphat and combined groups. These results demonstrate that fluoride, casein phosphopeptides/amorphous calcium phosphate compound and their combination can prevent enamel demineralization, promote remineralization; however, their combination does not improve the effect of preventing enamel demineralization.         

Electronic root canal length measurement before and after experimentally induced pulpitis and apical periodontitis in dogs

The aim of the study was to examine the influence of the state of the pulp and apical periodontium on the results of electronic root canal length measurement (ERCLM) with a resistance measuring device in dogs. Pulpitis and apical periodontitis were induced by pulp exposure and contamination by the oral flora in the premolar teeth of six mongrel dogs, comprising four experimental groups (36 root canals). In a control group, measured lengths of teeth with uninfected pulps were performed on the first experimental day (44 root canals). In all animals the ERCLMs were performed on teeth with healthy pulps, and at the end of the experimental period (20, 35, 50 and 65 days) following pulp exposure. The point of measuring canal lengths was the anatomical obstacle above the apical delta. Electronically measured lengths (EML) were compared between each other and with the root canal length established by tactile-sense measurement verified radiographically. The EMLs were less accurate in teeth with healthy pulps and teeth with pulpitis in the third experimental group (dif = 2.27 × 2.65 mm²; t test, p < 0.05), while they were most precise after 65 days in teeth with completely necrotic pulp and established chronic apical periodontitis (dif = 0.54 × 1.36 mm²; t test, p > 0.05). These results suggest that the state of the pulp and periapical tissue may have an influence on the ERCLM.