应用口腔手术显微镜探查和疏通下颌磨牙近中中央根管的临床研究

目的:评价口腔手术显微镜用于下颌磨牙探查和疏通近中中央根管的临床效果。方法:采集门诊患者126人,下颌磨牙139颗。由3位高年资医生分别在常规肉眼下和口腔手术显微镜下进行下颌磨牙近中中央根管的探查和疏通,比较两者成功率。对下颌磨牙近中中央根管口进行定位测量,并采用偏移投照方法描记该根管走行特点。结果:在显微镜帮助下,所有下颌磨牙近中中央根管的探查和疏通成功率分别提高了11.5%和10.1%。下颌第一磨牙和第二磨牙近中中央根管的疏通率,分别由5.0%增加到15.0%,3.4%增加到了13.6%;而它们的探查成功率分别提高了12.5%和10.2%。所有近中中央根管口均位于髓底发育沟,46.2%靠近近中舌根管口,30.8%在两根管口中间,23.1%靠近近中颊根管口。所有疏通的近中中央根管有45%与近中舌侧根管融合,未发现独立根尖孔类型。结论:在口腔手术显微镜的帮助下,探查和疏通下颌磨牙近中中央根管的数量均有显著提高。     

Middle Mesial Canal Preparation Enhances the Risk of Fracture in Mesial Root of Mandibular Molars

IntroductionThe aim of this investigation was to evaluate the effect of the presence and preparation of middle mesial (MM) canals on the fracture resistance of the mesial root of mandibular molars.MethodsForty intact mesial roots of mandibular first molars having 2 (n = 20) or 3 (n = 20) independent canals from the furcation level for up to at least 5 mm apically were selected based on preoperative micro–computed tomographic scanning. The selected roots were then distributed into 2 experimental (n = 10) and 2 control groups (n = 10) according to the root length, canal configuration (2 or 3 independent canals), and root thickness at the furcation level. In the experimental groups 1 (2 independent canals) and 3 (3 independent canals), root canals were enlarged up to the ProTaper Next X3 rotary instrument (Dentsply Sirona, Ballaigues, Switzerland), whereas in groups 2 (2 independent canals) and 4 (3 independent canals) root canals were not prepared. The specimens were embedded in acrylic resin after their surfaces were coated with a thin layer of silicone and subjected to a fracture strength using a universal testing machine. The types of fracture extension and course were recorded and statistically compared with the chi-square test, whereas fracture strength was analyzed using 1-way analysis of variance and post hoc Tukey tests (α = 5%).ResultsNo statistical difference in fracture strength was observed between nonprepared roots with 2 (group 2, 696.1 ± 186.3 N) or 3 (group 4, 558.4 ± 154.6 N) independent canals (P > .05), whereas the lowest values were obtained in the prepared roots with an MM canal (groups 3, 377.1 ± 77.2 N) (P < .05). The mean fracture strength observed in the prepared roots with 2 canals (group 1, 528.4 ± 134.3 N) showed no statistically significant difference compared with nonprepared roots with 3 canals (group 4, 558.4 ± 154.6 N) (P > .05). The chi-square test revealed no significant differences in fracture extent, types, and courses among groups (P > .05). Fracture extensions in all groups were mostly central and buccal-central types, whereas the highest frequency of fracture course was the curved and zigzag types.ConclusionsThe fracture resistance of the mesial roots of the mandibular molars decreased after the preparation of mesial canals with large-tapered instruments. Preparation of the MM canal further diminished the fracture resistance of the mesial roots. The resultant fracture displayed a distinct pattern in the buccolingual plane.     

青海地区人群下颌第三磨牙的形态研究

目的:研究青海地区人群下颌第三磨牙形态特征,为临床诊疗提供科学依据.方法:收集122个青海地区人群下颌第三磨牙,测量牙齿的全长、冠长、根长、近中远中径、颊舌径、牙尖数目和牙根数目等并进行统计学分析.结果:青海地区人群中下颌第三磨牙全长、冠长及颊舌径男女之间有统计学差异(P＜0.05),牙尖型和牙根型存在正相关关系.结论...     

The Global Prevalence of Middle Mesial Canal in Mandibular First and Second Molars Assessed by Cone Beam Computed Tomography: A Systematic Review and Meta-Analysis

IntroductionThis meta-analysis sought to identify the in vivo prevalence and influencing factors of middle mesial canal (MMC) in mandibular first and second molars based on cone-beam computed tomography (CBCT) scans.MethodsMEDLINE/PubMed, Web of Science, Scopus, SciELO, Google Scholar databases/search engines were searched in period between 15^th and 21^st November 2022, to retrieve the in vivo CBCT-based studies that assessed the prevalence of MMC in mandibular first and/or second molars. The studies were strictly assessed using predefined inclusion and exclusion criteria for relevancy and eligibility through screening the title and abstract, and then assessed through reading the full texts using the same criteria. Subsequently, the fulfilled studies were assessed qualitatively using the Newcastle-Ottawa Quality Assessment Scale, and quantitatively using meta-analysis to calculate the pooled prevalence rates of MMC. The publication bias was assessed using funnel plot and Egger's test.ResultsOut of 1122 studies, 33 studies comprised of 13,349 and 7624 mandibular first and second molars, respectively, were eligible for inclusion. Twenty studies scored high quality, while 13 scored moderate quality. The global prevalence of MMC in the first molar was 4.4% (95% CI = 0.035–0.053, P < .001), significantly higher than that of the second molar which was 1.3% (95%, CI = 0.008–0.018, P < .001). Gender, molar side, and age were not influencing factors of MMC prevalence.ConclusionsThe prevalence of MMC is not uncommon, being higher in the mandibular first molar compared to the mandibular second molar. The prevalence of MMC is not influenced by age, molar's side, and gender.     

层递法探查疏通中青年患者下颌磨牙近中中央根管的初步研究

目的:评估层递法探查中青年患者下颌磨牙近中中央根管的应用价值。方法:采集20~45岁患者60人,下颌第一磨牙45颗,下颌第二磨牙25颗。应用层递法对根管系统进行探查,记录探查结果,应用卡方检验统计分析。采用分角度X线投照描计下颌磨牙MM根管的走行特点。结果:肉眼探查确定MM根管 3个(4.3%),显微镜下确定7个(10.0%),显微超声技术辅助下确定15个(21.4%),CBCT结合显微超声技术辅助下确定17个(24.3%),第四阶段与前两个阶段间存在显著统计学差异(P<0.05),但与第三阶段探查分析无统计学差异。在确定的17个MM根管中,显示“独立”根尖孔的2个; “歧状”解剖8个;“融合”解剖7个。结论:层递法应用于中青年下颌磨牙MM根管的探查,可以有效提高下颌磨牙MM根管的探查成功率。     

Incidence of Middle Mesial Canals Based on Distance between Mesial Canal Orifices in Mandibular Molars: A Clinical and Cone-beam Computed Tomographic Analysis

IntroductionThis study evaluated the presence of midmesial canals (MMCs) in a random sample of mandibular molars and the relationship of the intracanal distance between mesiobuccal (MB) and mesiolingual (ML) canal orifices.MethodsFifty-one extracted mandibular molars were divided into samples of 3 to 4 teeth, mounted in plaster and boxing wax, and immersed in water before cone-beam computed tomographic (CBCT) imaging. Two endodontic residents completed the access openings. The teeth and the CBCT images were interpreted for the presence of MMCs and the mesial intracanal distance. CBCT software measured the distance between the buccal of the MB canal to the lingual of the ML canal at the pulpal floor to determine the average length between the canals.ResultsSeven distinct MMCs were seen both clinically (incidence of 13.725%) and on the CBCT images. Twenty-seven teeth (52.94%) had ambiguous broad isthmi between the MB and the ML orifices. MMCs were present at the furcation level but merged with the MB or ML canal toward the apex in 6 of 7 teeth (85.71%). The mean distance between the mesial canals in teeth with MMCs was 3.643 mm, and it was 3.818 mm for teeth without MMCs. According to independent sample t testing, the P value was >.05.ConclusionsThe incidence of MMCs in mandibular molars appears consistent with the literature. However, there does not appear to be a statistically significant difference in the mesial intracanal distance in teeth with and without MMCs. Visualization of MMCs on CBCTs may be subjective. There does not appear to be a correlation between the presence of MMCs and an increased or decreased mesial intracanal distance.     

下颌第二磨牙"C"形融合根及其根管形态的观察

目的　观察具有“C”形融合根的离体下颌第二磨牙牙根外形及根管形态。方法　通过牙根水平片切及透明标本的制作 ,观察 4 0颗下颌第二磨牙牙根的形态特点 ,并测量其长度。结果　牙根均在颊侧融合 ,牙根长度较正常牙长且有显著性差异 (P <0 .0 5 )。根管形态变异较多 ,仅 4 0 %呈现根颈到根尖的“C”形 ,3 0 %为“分号”形 ,10 %为“分离”形 ,2 0 %的牙根内各横断面形态可有不同。结论　下颌第二磨牙“C”形融合根的变异较多 ,不利于根管的彻底清理和充填     

Symmetry of Root and Root Canal Morphology of Maxillary and Mandibular Molars in a White Population: A Cone-beam Computed Tomography Study In Vivo

Introduction

The aim of the present study was to use cone-beam computed tomography (CBCT) to analyze root canal anatomy and symmetry of maxillary and mandibular first and second molar teeth of a white population.

Methods

A total of 201 patients who required CBCT examinations as part of their dental diagnosis and treatment were enrolled in the present study. Overall, 596 healthy, untreated, well-developed maxillary and mandibular molar teeth (161 maxillary first molars, 157 maxillary second molars, 117 mandibular first molars, and 161 mandibular second molars) were examined by CBCT to establish the symmetry in root and canal anatomy between right and left sides in the same patient by evaluating the number of roots and root canals and the root canal configuration.

Results

Three separate roots with 3 separate canals was the normal anatomy of maxillary first and second molars. Most mandibular first and second molars had 2 separate roots, and the majority had 3 canals. In the present study, first molars, both maxillary and mandibular, exhibited greater asymmetry than the second molars. Maxillary first molars were found to be symmetrical in 71.1% of patients, whereas maxillary second molars were symmetrical in 79.6%. The remaining 28.9% and 20.4% of patients, respectively, showed asymmetry. Around 30% of the mandibular first molars and 20% of the mandibular second molars showed asymmetry.

Conclusions

The results of the present study reported a percentage of symmetry that varied from 70%–81%. These variations in symmetry should be taken in high consideration when treating 2 opposite molars in the same patient, because their anatomy may be different in up to 30% of the cases.     

应用PAR指数评估拔除下颌第一磨牙患者的矫治效果

目的探讨影响拔除下颌第一磨牙患者正畸治疗疗效的相关因素。方法采用PAR指数对28例拔除下颌第一磨牙错验畸形患者的治疗前后模型进行评估分析。结果①治疗后PAR总分值较治疗前减少26.11±8.09,总分值减少百分率为（92.49±4.00）％,权重PAR总分值减少29.61±2.33,权重减少百分率为（96.43±5.20）％。②变差或无改变0例,改善6例（21.43％）,明显改善22例（78.57％）。③后牙猞关系PAR分值减少4.29±3.10,减少百分率为79.64％。结论选用直丝弓矫治系统,尽早使用不锈钢方丝,合理施力和必要矫治技巧是对磨牙进行有效三维控制,取得良好矫治效果的关键。     

Debris Removal from the Mesial Root Canal System of Mandibular Molars with Laser-activated Irrigation

Introduction

The purpose of this study was to compare in vitro the canal and isthmus debridement of manual-dynamic, passive ultrasonic, and laser-activated irrigation with an Er:YAG laser in mesial roots of human mandibular molars.

Interradicular Root Canals in Mandibular First Molars: A Literature Review and Ex Vivo Study

Introduction

Successful endodontic treatment vastly depends to a high degree on an accurate knowledge of root canal system morphology. It is a prerequisite to be aware of all possible reservoirs where bacteria and/or toxins can persist, compromising the surrounding tissues; such knowledge results in endodontic success.

Optimum Shaping Parameters of the Middle Mesial Canal in Mandibular First Molars: A Finite Element Analysis Study

IntroductionThis study investigated the effect of shaping parameters of 2 different configurations of middle mesial canals (MMCs) on the biomechanical behavior and life span of a mandibular first molar using finite element analysis (FEA).MethodsA mandibular molar with an independent MMC and another with a confluent MMC were scanned via micro-computed tomography, and FEA models were produced. For each tooth, an intact model and 5 experimental models were produced that differed by parameters of how the MMC was shaped: unshaped MMC, 25/.04, 25/.06, 30/.04, and 30/.06. Cyclic loading of 50 N was applied on the occlusal surface in vertical and oblique scenarios, and the number of cycles until failure (NCF) was compared with the intact models. In addition, mathematical analyses evaluated the stress distribution patterns and calculated maximum von Mises and maximum principal stresses.ResultsFor both the independent and confluent MMC models, shaping the MMC reduced the NCF. The lifelog percentage of models was inversely proportional with radicular shaping parameters during the vertical and oblique loading scenarios. The shaping size of 30/.06 resulted in lower lifelog percentage than the cases with shaping size of 25/.04 in both of the independent and confluent MMC models. For all models, oblique loading reduced NCF more than vertical loading.ConclusionShaping the MMC should be kept as conservative as 25/.04. Also, whether the MMC is independent or confluent is a deciding factor in whether to increase the apical diameter or the root canal taper when larger shaping parameters are needed.     

下颌第二磨牙C形根管预备方法的临床探讨

目的 探索预备下颌第二磨牙C形根管的有效方法.方法 对下颌第二磨牙C形根管初诊或根管再治疗的患牙,采用"拉网法"进行根管预备,完成根管充填后拍X线片检查充填效果.结果 C形根管的峡区被充分预备和成形,根充后峡区有均匀稀薄的X线阻射影像.结论 该根管预备方法能有效地预备C形根管的峡区,且不易发生根管侧穿.     

The Effect of Root Canal Preparation Size and Taper of Middle Mesial Canals on Fracture Resistance of the Mandibular Molar Teeth: An In Vitro Study

IntroductionThe aim of the present study was to investigate the influence of root canal preparation size and taper of middle mesial (MM) canals on fracture resistance of mandibular molars.MethodsFifty-five mandibular molar teeth having an MM canal were selected based on the cone-beam computed tomographic analysis. After the decoronation and distal root separation procedure, the lengths of the mesial roots were standardized to 13 mm. The specimens were randomly distributed into 5 groups (n = 11). Mesiobuccal and mesiolingual canals were prepared up to size 30.06 using VDW.ROTATE rotary files (VDW, Munich, Germany). The MM canal was prepared up to size 25.04, 25.06, 30.04, and 30.06, respectively. No preparation was done in the MM canal in the control group. After the irrigation protocol, the canals were obturated with the single-cone technique. A thin layer of silicone-coated specimens was embedded in acrylic resin and subjected to a fracture strength test by a universal testing machine. A vertical force was applied to the roots until they fracture. Statistical analysis was performed with 1-way analysis of variance and post hoc Duncan tests (P = .05).ResultsThere was no significant difference between group 25.04 and the control group, but the fracture strengths of these groups were found to be significantly higher than that of groups 25.06, 30.04, and 30.06 (P < .05).ConclusionsWithin the limitations of this study, we concluded that increasing the apical diameter and taper in the MM canal reduces the fracture strength of mandibular molar teeth. Among the tested instrumentation sizes, fracture strength decreased significantly when greater than 25.04 instrumentation sizes were chosen.     

儿童下颌第二磨牙冠周炎致下颌骨骨髓炎的临床诊治

目的:探讨儿童下颌第二磨牙冠周炎导致下颌骨骨髓炎的临床特点及治疗方法.方法:选取2016年1月～2019年3月共收治10例儿童下颌第二磨牙冠周炎致下颌骨骨髓炎患者,平均年龄12.1岁,临床表现为面部肿胀、发硬、张口受限.10例患者均在全麻下行"下颌骨骨髓炎探查刮治活检术+冠周龈瓣切除术",预防性"拔除下颌第三磨牙胚"....     

锥体束CT对维吾尔族成人下颌第二磨牙C形根管的研究

目的: 通过锥体束CT(cone-beam computed tomogphy,CBCT)成像系统对新疆维吾尔族成人下颌第二磨牙C形根管的发生率及其形态特征进行研究。方法: 选择来我院体检且下颌牙列完整的100名维吾尔族成人,进行CBCT扫描,观察下颌第二磨牙的根管形态。结果: C形根管的发生率为15.0%,C 形根管类型变化多样。结论: C形根管在下颌第二磨牙有较高的发生率,且解剖形态存在较大差异。CBCT在C形根管的诊断方面具有重要作用,可以为维吾尔族成人下颌第二磨牙C形根管的临床诊疗提供依据。     

A Microcomputed Tomographic Study of Canal Isthmuses in the Mesial Root of Mandibular First Molars in a Chinese Population

Untreated isthmuses can be a cause of endodontic treatment failure. We investigated the anatomic features of the isthmus in the mesial root of mandibular first molars using microcomputed tomography scans. Thirty-six extracted mandibular first molars were collected from the Chinese population and divided into three age groups as follows: 20 to 39 years (group A), 40 to 59 years (group B),and ≥60 years (group C). Each tooth was scanned and reconstructed, and then the prevalence and type of isthmus were recorded. The percentage of sections showing isthmuses for groups A, B, and C were 50%, 41%, and 24%, respectively. The chi-square test indicated a significant correlation of the distribution of isthmuses with age (p < 0.001). The ratio of partial isthmus to complete isthmus for group C (17.1:1) was significantly higher than group A (5.9:1) and group B (7.0:1) (p < 0.001). By understanding the configuration and location of isthmus, a more efficient endodontic microsurgery can be guaranteed.     

Morphology and Microhardness of Dentin at the Furcation Area of Mandibular Molars

Introduction

This study evaluated dentin morphology and microhardness at the furcation area of mandibular molars.

Methods

Tooth segments of mandibular molars were embedded in resin blocks and bisected longitudinally (n = 20), and the furcation area was delimited by tracing 2 orthogonal lines from the most concave point of the outer surface of the furcation toward the mesial and distal canal entrances. In half of the specimens, Knoop microhardness was measured in 2 directions in the furcation area: vertically, parallel to the orthogonal lines and the bisector of the angle formed by them; and horizontally, in the outer (close to the pulp chamber floor), inner (close to the cementum), and middle dentin layers. Data were analyzed statistically by one-way analysis of variance and Tukey-Kramer test (α = 0.05). The other half of the specimens were examined by scanning electron microscopy to evaluate dentin morphology and trajectory of the tubules.

Results

No statistically significant difference (P > .05) was found among the mesial (46.5 ± 6.4), central (47.3 ± 8.1), and distal (49.7 ± 6.5) orthogonal lines. The inner dentin layer (51.7 ± 2.5) was statistically similar to the middle (46.3 ± 2.9) (P > .05), which was similar to the outer layer (41.4 ± 2.4) (P > .05). The inner layer was significantly harder than the outer layer (P < .05). The morphologic analysis revealed a tendency of calcification of the tubules from the outer toward the inner layer.

Conclusions

Dentin microhardness at the furcation area is uniform in its 3 vertical axes, but the inner dentin layer is harder than the outer layer. The dentinal tubules follow a centripetal direction toward the inner layer, in which dentin is much more mineralized.     

Dentin Thickness at Danger Zone and Canal Morphology of Maxillary Molars

ObjectivesDentin thickness in concave areas of the root creates risk for complications such as strip perforation during endodontic treatment. The study aims to examine dentin thickness of the danger (DZ) and safety zone (SZ), canal configuration, and the presence of isthmus in the mesiobuccal root of maxillary molars.Material and MethodsCone-beam Computed Tomography (CBCT) images of 1251 teeth belonging to 642 patients were retrospectively reviewed. The dentin thicknesses at DZ and SZ in maxillary molars with one (MB) or two mesiobuccal canals (MB1, MB2) were measured at the 3 mm apical to the furcation level. Vertucci''s canal configurations and the isthmus rate were recorded. The Chi-square test andThe Student’s t-test were performed.ResultsMB2 rate was higher in maxillary first molars (61.68%) than second molars (39.36%). Isthmus rates were 27.3% and 44.11% in first and second molars. DZ thickness was thinner than the dentin thickness in the SZ in both first and second molars with one or two mesial canals (p< 0.05). In teeth with single canal, the mean DZ thickness was 0.88mm. In teeth with two canals, the mean DZ thicknesses were 0.83mm and 0.80mm for MB1 and MB2 canals, respectively.ConclusionMB2 rate was higher in the first molar (61.68%), and the isthmus rate was higher in the second molar (44.11%). DZ and SZ were thinner in MB2 than in MB1 at the maxillary molars with two mesial canals. The results indicated that more conservative preparation must be applied to the MB2 canal in the maxillary molars.