Natural canal deviation and dentin thickness of mesial root canals of mandibular first molars assessed by microcomputed tomography

Abstract The aim of this study was to assess the centralization and dentin thickness of mesial root canals of the first mandibular molars by microcomputed tomography (micro-CT). Material and methods: Ninety-nine mandibular molars of Vertucci's type IV canals were scanned by micro-CT. The mesiodistal deviation and centroid were assessed, in both mesiobuccal (MB) and mesiolingual (ML) canals, for the apical 4mm and the full canal length. Results: The dentin thickness was similar for both MB and ML canals. The narrowest thickness was in the distal wall of an MB canal (0.07mm), while the widest was found in the mesial wall of an MB canal (2.46mm). In centroid analysis, both the MB and ML canals exhibited deviations when compared to the root centroid, along the full canal length and the apical 4mm. For the MB canal, the mean deviation was 0.83mm (0.02 mm-2.30 mm) for the full canal and 0.18mm (0.01 mm-1.01 mm) for apical 4mm. Similarly, for the ML canal, the mean deviation measured 0.83 mm (0.05mm-3.99mm) for the full canal and 0.21 mm (0.01mm-1.01mm) for the apical 4 mm. Overall, deviations were observed towards the mesial of the roots, with 69% for MB and 57% for ML canals for the full canal, and 51% for MB canals within the 4 mm. The exception was the ML canal, which exhibited a higher deviation towards distal in the apical 4mm, accounting for 52% of cases. The dentin thickness was consistent between the mesial canals of mandibular molars. However, there is no centrality of mesial canals in their roots, with frequent deviation to mesial.

Resumo O objetivo deste trabalho foi avaliar a centralização e a espessura da dentina dos canais radiculares mesiais de primeiros molares inferiores por meio de microtomografia computadorizada (micro-CT). Material e métodos: Noventa e nove molares inferiores com canais tipo IV de Vertucci foram escaneados por micro-TC. O desvio mesiodistal e o centroide foram avaliados para os canais mesiovestibular (MB) e mesiolingual (ML), nos 4mm apicais e em todo o comprimento do canal. Resultados: A espessura da dentina foi semelhante para os canais MB e ML. A espessura mais estreita foi encontrada na parede distal de um canal MB (0,07mm), enquanto a mais larga foi encontrada na parede mesial de um canal MB (2,46mm). Na análise centroide, tanto o canal MB quanto o ML exibiram desvios quando comparados ao centroide da raiz, ao longo de todo o comprimento do canal e nos 4 mm apicais. Para o canal MB, o desvio médio foi de 0,83mm (0,02mm-2,30mm) para canal inteiro e 0,18mm (0,01mm-1,01mm) para o apical de 4mm. Da mesma forma, para o canal ML, o desvio médio mediu 0,83 mm (0,05 mm-3,99 mm) para o canal inteiro e 0,21 mm (0,01 mm-1,01 mm) para os 4 mm apicais. No geral, foram observados desvios em direção mesial das raízes, sendo 69% para canais MB e 57% para canais ML para canal inteiro, e 51% para canais MB dentro dos 4 mm. A exceção foi o canal ML, que apresentou maior desvio para distal nos 4mm apicais, representando 52% dos casos. A espessura da dentina foi consistente entre os canais mesiais dos molares inferiores. Entretanto, não há centralidade dos canais mesiais em suas raízes, com frequente desvio para mesial.

Analysis of the Internal and External Morphology of the Mandibular First Molar in a Chilean Sub-Population Using Cone-Beam Computed Tomography / Análisis de la Morfología Interna y Externa del Primer Molar Mandibular en una Subpoblación Chilena Mediante Tomografía Computarizada de Haz Cónico

SUMMARY: The mandibular first molar (MFM) commonly presents two roots with two canals in the mesial root and one or two canals in the distal root. However, morphological variations have been described in different populations, which must be considered when planning endodontic treatment. The aim of this study was to analyze the internal and external morphology of the MFM in a Chilean sub-population using cone-beam computed tomography (CBCT) images. An in vivo cross-sectional, descriptive, and observational study was conducted using CBCT exams from 351 right and left MFM. The data were analyzed by descriptive statistics using the Chi- Square test for categorical variables, Fisher's exact test, the Mann-Whitney U non-parametric test for two independent samples, and the Wilcoxon non-parametric test for related samples. Of the total sample, 1 root was observed in 2.27 % of the cases, 2 roots in 93.73 %, and 3 roots in 4 %. In relation to the number of canals, 71.23 % of the MFM showed 3 root canals, 16.81 % 4 canals, 9.69 % 2 canals, and 2.28 % 1 canal. Of all the studied cases, 2.3 % had a C-shaped anatomy. In terms of morphology, using Zhang's classification, variant 3 was observed in 71.23 %, variant 4 in 12.82 %, variant 1 in 9.67 %, variant 6 in 4 %, and variant 8 in 2.28 %. In conclusion, the morphology of the MFM is variable in a Chilean sub-population, and these variations must be considered before and during endodontic therapy. CBCT proved to be an effective tool for the in vivo study of tooth morphology.

El primer molar mandibular (MFM) comúnmente presenta dos raíces con dos canales en la raíz mesial y uno o dos canales en la raíz distal. Sin embargo, se han descrito variaciones morfológicas en distintas poblaciones, las que se deben tener en consideración al momento de planificar el tratamiento endodóntico. El objetivo de este estudio fue analizar la morfología interna y externa del MFM en una sub población chilena mediante el uso de imágenes de tomografía computarizada Cone Beam (CBCT). Se realizó un estudio transversal, descriptivo y observacional in vivo empleando exámenes CBCT de 351 MFM tanto derechos como izquierdos. Los datos se analizaron mediante estadística descriptiva empleando la prueba Chi-Cuadrado para variables categóricas, el test exacto de Fisher, la prueba no paramétrica de U-Mann-Whitney para dos muestras independientes y la prueba no paramétrica de Wilcoxon para muestras relacionadas. Del total de la muestra se observó 1 raíz en un 2.27 % de los casos, 2 raíces en 93.73 % y 3 raíces en un 4 %. En relación al número de canales un 71.23 % de los MFM mostraron 3 canales radiculares, un 16.81 % 4 canales, un 9.69 % 2 canales y un 2.28 % 1 canal. Del total de los casos estudiados un 2.3 % se presentó anatomía en forma de C. En relación a la morfología, empleando la clasificación de Zhang, se observó en un 71.23 % la variante tipo 3, en un 12.82 % la variante tipo 4, en un 9.67 % la variante tipo 1, en un 4 % variante tipo 6 y en un 2,28 % variante tipo 8. En conclusión, la morfología del MFM es variable en una subpoblación chilena y estas variaciones deben ser consideradas antes y durante la terapia endodóntica. El CBCT demostró ser una herramienta eficaz para el estudio in vivo de la morfología dentaria.

Design and fabrication of anatomic healing abutment for mandibular first molar implant / 口腔疾病防治

Objective@# To explore the design and manufacture of anatomical healing abutment for mandibular first molar implant in order to provide more choices for clinical healing abutment@*Methods@# The buccal lingual diameter and mesial distal diameter of the tooth neck, as well as the slope data of the four axial surfaces of the natural isolated teeth, were obtained by scanning the isolated mandibular first molar with a shining scanner. After statistical analysis of the data, the anatomical healing abutment of the mandibular first molar was designed and constructed using computer aided design/computer aided manufacturing (CAD/CAM).@*Results@#The mean buccal and lingual diameters of the mesial and distal diameters of the isolated mandibular first molars were (8.54 ± 0.78) mm and (7.87 ± 0.86) mm, and the tooth neck slopes of each axial surface of the isolated mandibular first molars were 17.53 °(buccal), 14.41 °(lingal), 13.40 °(mesial) and 13.43 °(distal), respectively. Three anatomical healing abutments with different peripheral diameters and heights of 5 mm were obtained according to a certain proportion of reduction of the natural teeth of the mandibular first molars@*Conclusion@#The anatomical healing abutment of the mandibular first molar can be quickly obtained by Shining scanning and CAD/CAM technology.

Prevalence of radix entomolaris in mandibular first molars by cone-beam computed tomography in a southern Chilean sub-population / Prevalencia de radix entomolaris en primeros molares mandibulares usando tomografía computarizada cone-beam en una subpoblación del sur de Chile

SUMMARY: The aim of this of this study was to evaluate the prevalence and morphology of radix entomolaris (RE) in the mandibular first molar (MFM) in a southern Chilean sub-population by cone-beam computed tomography (CBCT). Two hundred ten CBCT images of MFM were analysed. To detect the presence of RE, the observation and measurements were standardised, advancing 1 mm to apical from the floor of the pulp chamber to the most apical zone of the tooth. The data were analyzed using descriptive statistics, with a value of P < 0.05 being statistically significant. The prevalence of a third root in the permanent MFM was 5.7 % (12/210). The incidence of RE was the same in male patients (2.9 %) as in female patients (2.9 %) (p=0.324). The occurrence of an RE in the left MFM was 7.3 % (3/41 patients) for male patients and 4.5 % (3/66) for female patients (p=0.398). The right MFM in male patients had an incidence of 8.1 % (3/37) and 4.5 % (3/66) for female patients (p=0.340). When the presence of an RE was compared between the left (5.6 %) and right side (5.8 %), no statistically significant differences were found (p=0.998). The frequency of bilateral three-rooted MFM was 71.43 % (5/7) and 28.57 % (2/7) were unilateral. The prevalence of RE in MFM in a southern Chilean sub-population was 5.7 %. The occurrence was bilateral in the majority of cases and no significant differences were observed by sex or side. The commonest type of RE was Type 1 (83.3 %). The use of CBCT can improve the endodontic treatment outcome.

RESUMEN: El objetivo de este estudio fue evaluar la prevalencia y morfología de radix entomolaris (RE) en el primer mo- lar mandibular (MFM) en una subpoblación del sur de Chile mediante tomografía computarizada de haz cónico (CBCT). Se analizaron doscientas diez imágenes CBCT de MFM. Para detectar la presencia de OD se estandarizó la observación y las medidas, avanzando 1 mm apical desde el suelo de la cámara pulpar hasta la zona más apical del diente. Los datos fueron analizados mediante estadística descriptiva, siendo estadísticamente significativo un valor de P < 0,05. La prevalencia de una tercera raíz en el MFM permanente fue de 5,7 % (12/210). La incidencia de ER fue la misma en pacientes masculinos (2,9 %) que en pacientes femeninas (2,9 %) (p=0,324). La aparición de un ER en el MFM izquier- do fue del 7,3 % (3/41 pacientes) para los pacientes masculinos y del 4,5 % (3/66) para las pacientes femeninas (p=0,398). El MFM derecho en pacientes masculinos tuvo una incidencia de 8,1 % (3/ 37) y 4,5 % (3/66) para pacientes femeninos (p=0,340). Cuando se comparó la presencia de un OD entre el lado izquierdo (5,6 %) y derecho (5,8 %), no se encontraron diferencias estadísticamente significativas (p=0,998). La frecuencia de MFM de tres raíces bilaterales fue 71,43 % (5/7) y 28,57 % (2/7) fueron unilaterales. La prevalencia de RE en MFM en una subpoblación del sur de Chile fue de 5,7 %. La presentación fue bilateral en la mayoría de los casos y no se observaron diferencias significativas por sexo o lado. El tipo de ER más frecuente fue el tipo 1 (83,3 %). El uso de CBCT puede mejorar el resultado del tratamiento endodóntico.

Relationship of Nutritional Status With Incidence of Permanent Mandibular First Molar Caries

@#Introduction: Nutritional status is a condition of the body which is the result of a balance between food intake and nutritional needs. Good nutritional status is very important for children, but in reality there are still many malnourished children. Lack of nutrition and the habit of consuming excess food can make teeth susceptible to caries. The tooth with the highest caries incidence is mandibular first molar which is the most important tooth in mastication process. The purpose of this research is to determine the relationship between nutritional status and the incidence of caries in permanent mandibular first molar children aged 7 years in Plalangan Village, Jember, East Java, Indonesia. Methods: This is an analytic observational research with a cross-sectional approach. The sampling technique of this research is Total Sampling, which uses the entire population as the sample of this study. This research was conducted by measuring the nutritional status of BMI-for-age based on anthropometric standards from the Minister of Health of the Republic Indonesia No. 2 of 2020 and examining the oral cavity to see whether there is caries or not in the permanent mandibular first molar. Results: The results of the Chi-Square Test showed a value of 0.036. Conclusion: The result shown that thinness and overweight children have a higher caries incidence than normal weight children. There is a significant relationship between nutritional status and incidence of permanent mandibular first molar caries.

Periodontal treatment of furcation involvement at the mandibular first molar with a follow-up of 27 years / 华西口腔医学杂志

Due to the complicated anatomical structures in the furcation area of multirooted mandibular first molars, dental hygiene is greatly compromised once the furcation is involved in the periodontitis, leading to the unfavorable prognosis of teeth with furcation involvement. A patient came to a dental office with the chief complaint of "mobile mandibular posterior tooth" 27 years ago. The periapical film showed alveolar bone resorption at the root furcation of the right mandibular first molar. Flap surgery and fine supportive therapy were conducted. The patient was diagnosed with "furcation involvement Class Ⅲ" during a revisit three years ago. Satisfactory and healthy periodontal statuses were observed 2, 9, 24, and 33 months after the periodontal flap surgery plus tunneling procedures. A follow-up of 27 years in the present case demonstrated that a favorable prognosis of furcation involvement can be achieved after adequate periodontal treatment.

Stress distribution of composite resin filling in Class I cavity of molars with different cavosurface angle / 口腔疾病防治

Objective @#To analyze the effect of different cavosurface angles on the stress distribution of ClassⅠ cavity composite resin filling of molars through the three-dimensional finite element method and to provide references for the preparation of ClassⅠ cavities.@*Methods@#Three-dimensional finite element models of ClassⅠ composite resin filling of mandibular first molars with three different cavosurface angles (group A: 90°, group B: 120°, group C: 135°) were established. Polymerization shrinkage of composites was simulated with a thermal expansion approach. The mechanical behavior of the restored models in terms of stress and displacement distributions under the combined effects of polymerization shrinkage and occlusal load (600 N) was analyzed.@*Results@# For ClassⅠ cavities with the same cavity size, the total stress of the restoration model and the maximum stress of the enamel in group A were less than those in groups B and C after cavity composite resin restoration with three cavity cavosurface angles (in which the width of the enamel bevel was 1 mm in groups B and C). The maximum stress of the dentin and adhesive was similar in the three groups, the maximum stress of the composite in group C was the largest, and the maximum stress of the composite in group B was the smallest. In terms of stress distribution, the maximum stress in each restoration model was mainly concentrated in the enamel at the cavosurface, near the enamel-dentin interface and at the edge of the restoration material.@*Conclusion@#From the point of reducing the stress of residual tooth tissue, the preparation of 90° angle without enamel bevel is an ideal method for cavity preparation when composite resin is used to fill ClassⅠ cavities of molars.

The Radix Entomolaris and Paramolaris: A Review and Case Reports with Clinical Implications

Normally, the permanent mandibular first molar has two roots, mesial and distal. However, mandibular molars may have anadditional root located either buccally (radix paramolaris) or lingually (radix entomolaris [RE]). Understanding of the presence ofan additional root and its root canal, anatomy is essential for successful treatment outcome. The aim of this paper is to reviewthe prevalence and morphology of RE and to present two cases of permanent mandibular first molars with an additional thirdroot (RE) in the Indian population. In this study, we did a clinical investigation of two cases; one case of successful endodonticmanagement of permanent mandibular first molar characterized as RE, whereas the second one is a presentation of a case ofsevere bone loss around permanent first molar with an additional third root. The presence of an additional third root in permanentmandibular first molars may affect the prognosis of the tooth if it is misdiagnosed. Thus, an accurate diagnosis and thoroughunderstanding of variation in root canal anatomy are essential for treatment success.

The prevalence of radix molaris in the mandibular first molars of a Saudi subpopulation based on cone-beam computed tomography

OBJECTIVES: The purpose of this study was to determine the incidence of radix molaris (RM) (entomolaris and paramolaris) in the mandibular first permanent molars of a sample Saudi Arabian subpopulation using cone-beam computed tomography (CBCT).MATERIALS AND METHODS: A total of 884 CBCT images of 427 male and 457 female Saudi citizens (age 16 to 70 years) were collected from the radiology department archives of 4 dental centers. A total of 450 CBCT images of 741 mature mandibular first molars that met the inclusion criteria were reviewed. The images were viewed at high resolution by 3 examiners and were analyzed with Planmeca Romexis software (version 5.2).RESULTS: Thirty-three (4.5%) mandibular first permanent molars had RM, mostly on the distal side. The incidence of radix entomolaris (EM) was 4.3%, while that of radix paramolaris was 0.3%. The RM roots had one canal and occurred more unilaterally. No significant difference in root configuration was found between males and females (p > 0.05). Types I and III EM root canal configurations were most common, while type B was the only RP configuration observed.CONCLUSIONS: The incidence of RM in the mandibular first molars of this Saudi subpopulation was 4.5%. Identification of the supernumerary root can avoid missing the canal associated with the root during root canal treatment.

Finite-element analysis of mandibular first molar with two marginal designs of endocrown for the repair of different defects / 华西口腔医学杂志

OBJECTIVE@#This study aimed to evaluate the stress distribution of the mandibular first molar with different thicknesses and heights of the axial wall restored by the endocrown with two marginal designs and thus provide a theoretical basis for selecting clinical preparation through the finite-element method.@*METHODS@#Two marginal endocrowns of the mandibular first molar with different axial-wall thicknesses (t=1, 2, 3 mm) and heights (h=2, 3, 4 mm) were established. Group A was the butt-joint design, whereas group B was the shoulder-surrounded design. After applying vertical and oblique loads , the size and distribution of the maximum principal stress and equivalent stress of residual tooth tissue were recorded.@*RESULTS@#The maximum principal stress and equivalent stress distribution of residual tooth tissue were similar among different models. Group A showed a lower maximum principal stress and equivalent stress than group B at the same thickness and height under vertical load. Meanwhile, under oblique load, the maximum principal stress values of groups A and B decreased with increased thickness at constant height. Group A showed lower equivalent stress than group B at the same thickness and height of 2 and 
3 mm. However, when the height was 4 mm, the trend was reversed.@*CONCLUSIONS@#In mastication, when bearing the vertical force, the retention of the butt-joint marginal endocrown preferred to the shoulder-surrounded one. Given the higher axial wall of the shoulder-surrounded marginal endocrown, it showed better ability to bear the oblique force than the butt-joint one.

Vital pulp preservation treatment in mandibular right first molar with vertical root fractures: a case report / 华西口腔医学杂志

This case presents vertical root fracture with vital pulp in mandibular right first molar. Examinations of the history, clinical tests, laser Doppler flowmetry, and radiographs revealed that the tooth showed positive response to electric pulp testing and was normal compared with the healthy control tooth. This study aimed to use a novel vital preserving surgical technique (microapical surgery and nanometer bioactive materials) to make an effective therapeutic decision for the vital tooth with vertical root fracture.

Establishment and stress analysis of buccal-occlusal-lingual inlay finite element model of mandibular first molar / 口腔疾病防治

Objective@#To observe the stress distribution according to a model of the bucco-occluso-lingual (BOL) inlay of mandibular first molar after restoration to provide a basis for the clinical treatment of cracked tooth with BOL inlay.@*Methods@#A three-dimensional finite element model of mandibular first molar was established by combining micro-CT scanning technology with Mimics, UG, Ansys and Midas-FEA software. Based on this model, a BOL inlay restoration model was established. The material parameter of inlay IPS e.max CAD was given, and a Von-mises stress distribution nephogram under the same loading condition was obtained. The results of the stress distribution in each model were compared.@*Results @#The stress of intact teeth is mainly concentrated in the central fissure of the occlusal surface at the crown. The stress of the cavity after BOL inlay restoration is mainly concentrated in the mesial and distal walls of the cavity, the axial-pulpal line angle and the gingival wall. The stress of the inlay is mainly distributed at the bottom of the inlay, axial wall and the gingival wall.@*Conclusion@#BOL inlay restoration change the stress distribution in the complete dental model, which relieves the stress concentration in the fossa and groove of the occlusal surface and can play an active role in the treatment of cracked tooth.

Five canals on mandibular first molar successfully managed by undergraduate dental student: an educational case report

Undergraduate dental student's eligibility and ability to treat difficult endodontic cases is a new area open for debate. a fifth year undergraduate dental student managed to perform a successful root canal treatment (RCT) on a 42 year old male patient diagnosed as a rare case of mandibular first molar with five root canals. as an educational case report, in a country like Sudan, close supervision and clinical training of undergraduate students in treating difficult endodontic cases is recommended.

Cone-beam computed tomography evaluation of the distance between the root apex of mandibular molars and the inferior alveolar nerve canal in adults / 口腔疾病防治

Objective@# To evaluate the spatiotemporal relationship between the root apex of mandibular molars and the inferior alveolar nerve canal (IANC) in adults. @*Methods@#Cone-beam computed tomography (CBCT) images were collected in 236 patients, and the distances from the root apexes of mandibular molars to the IANC were measured in NNT 4.6 software. The relationship between distance and gender was evaluated. @*Results@#In two-rooted mandibular first molars, the distances from the mesial root and distal root to the IANC were 7.34 ± 2.07 mm and 6.69 ± 2.08 mm, respectively, in males and 6.47 ± 2.22 mm and 5.94 ± 2.11 mm in females. In three-rooted mandibular first molars, the distances from the mesial root, distobuccal root, and distolingual to the IANC were 7.29 ± 1.30 mm, 7.40 ± 2.33 mm, and 9.97 ± 2.19 mm, respectively, in males and 6.08 ± 2.57 mm, 6.35 ± 2.40 mm, and 9.01 ± 2.90 mm, respectively, in females. In one-rooted mandibular second molars, the distance from the root to the IANC was 4.09 ± 1.64 mm in males and 3.89 ± 1.76 mm in females. In two-rooted mandibular second molars, the distances from the mesial root and distal root to the IANC were 5.14 ± 2.08 mm and 4.39 ± 1.85 mm, respectively, in males and 3.78 ± 1.69 mm and 3.24 ± 1.72 mm, respectively, in females. There were no significant with in-gender differences between the left and right side in the distances from the root apexes to the IANC (P>0.05). The distances from the mandibular first molar were greater in males than in females. The longest average distance was from the distolingual root apexes of three-rooted mandibular first molars to the IANC, and the distances were longer from the distobuccal root apexes of three-rooted mandibular first molars to the IANC than from the distal root apexes of two-rooted mandibular first molars to the IANC (P<0.05). There was no within-gender difference in the distances from the root apexes of single-rooted mandibular second molars to the IANC (P>0.05), but the distances in two-rooted mandibular second molars were larger in males than in females (P<0.05). The distances from the root apexes to the IANC were smaller in mandibular second molars than in mandibular first molars (P<0.05). @*Conclusion @#There are significant differences between adult males and females in the distance from the root apex to the IANC for mandibular first molars and two-rooted mandibular second molars. The distances from the root apexes to the IANC were smaller in mandibular second molars than in mandibular first molars.

Mandibular first molar with C-shaped root canal system: a two-case report / 华西口腔医学杂志

The root and canal anatomy of the mandibular first molar is highly complicated. A mandibular first molar with a C-shaped root canal system is rare. This article describes two different cases of this system. Case 1 has a complete C-shaped fused root. The root canal is characterized by a mesial lingual root canal and a C-shaped fused root canal. Case 2 has a C-shaped fused root in the buccal region and a distal lingual root. The root canal is characterized by a type Ⅱ-Ⅰroot canal in the buccal region and a distal lingual root canal.

Relationship between Pre-Eruptive Buccal Pit Radiolucency and Restoration in Mandibular First Molar / 대한소아치과학회지

Pre-eruptive intracoronal resorption (PEIR) is a developmental defect in the crown of a pre-eruptive tooth. The purpose of this study was to investigate the relationship between the size of the pre-eruptive buccal pit radiolucency, which is suspected as PEIR on a panoramic radiography, and the need for restoration after the eruption of a mandibular first molar.The experimental group included 35 mandibular first molars, in which lesions requiring definite restoration were observed during eruption. The control group consisted of 64 sound mandibular first molars after eruption. The sex, age, tooth position, tooth formation stage, size of the pre-eruptive buccal pit radiolucency, and restoration methods in the experimental group and control group were examined.Compared with the control group, the experimental group showed a statistically significant difference in the size of the buccal pit before eruption. The buccal pit size for predicting the need for restoration was further examined by receiver operating characteristic curve analyses, and the area under the curve was 0.813 ± 0.047.If radiolucency is observed at the buccal pit of the mandibular first molar before eruption, periodic observations and post-eruption examinations are required.

Clinical application of cone beam computed tomography combined with micro-ultrasound technique in treating three mesial canals in mandibular first molars / 华西口腔医学杂志

Objective The aim of this study is to investigate the influence of cone beam computed tomography (CBCT) and micro-ultrasound technique for the treatment of three mesial canals in mandibular first molars. The three mesial canals according to Pomeranz's classification were characterized. Methods A total of 75 permanent mandibular first molars for root canal treatment were randomly selected from patients belonging to the age group of 14-60 years. After preparing the access cavity and locating the main canals, the middle mesial canal orifices in all teeth were determined with an endodontic explorer under direct vision (StageⅠ), under magnification with the aid of micro-ultrasound (Stage Ⅱ), and with the combined use of CBCT and micro-ultrasound to remove the dentin wall and calcifications (Stage Ⅲ). Results Middle mesial canals were detected in 4.0%, 18.7%, and 22.7% of the teeth in StagesⅠ-Ⅲ, respectively. Statistical analysis showed significant differences (P<0.05) between StagesⅠand Ⅱ with regard to middle mesial canal detection. The number of Stage Ⅲ was more than that of Stage Ⅱ. The difference between the two stages was no significant. Among the 17 middle mesial canals, "confluent", "fin" and "independent" anatomies were 52.9%, 35.3%, and 11.8%. Conclusion When used with adjunctive aids, including CBCT, micro-ultrasound facilitates dental clinicians in the location and treatment of middle mesial canals.

A study on effects of immediate bone grafting at mandibular first molar fresh extraction socket on maintaining alveolar bone height after space closure / 中华口腔医学杂志

Objective@#To investigate the effect of immediate bone grafting at mandibular first molar extraction socket on maintaining alveolar bone height after space closure.@*Methods@#Thirty adult orthodontic patients who need to extract mandibular first molar, totally 38 target teeth, were included. The samples were divided into two groups randomly: graft group and non-graft group. All extraction space was closed orthodontically. Dental models of all patients were taken before extraction (T0), before space closure(T1) and after space closure (T2). The distance, time of the space closure and the velocity of tooth movement were recorded. Probing depth (PD) and clinical attachment level (CAL) at six sites (mesial buccal, buccal, mesial lingual, lingual, distal buccal and distal lingual) on adjacent teeth were measured before extraction (T0) and after space closure (T2). Cone-beam CT (CBCT) was taken at T0 and T2 to compare the changes of alveolar bone height at six sites on adjacent teeth using Invivo Dental 5.0 software.@*Results@#The extraction space in both graft group and non-graft group was closed successfully. However, the space in graft group was closed more slowly than in non-graft group. In graft group, PD and CAL at the six sites on both the second molar and the second premolar did not change significantly after space closure, and CBCT showed that the alveolar bone height of the second premolar had no significant difference after treatment. In non-graft group, alveolar bone height decreased in both adjacent teeth and periodontal attachment loss was found after space closure. On average, alveolar bone height and periodontal attachment of the second premolar decreased (0.75±0.16) mm and (0.64±0.15) mm, respectively. Meanwhile, alveolar bone height and periodontal attachment of the second molar decreased (0.79±0.23) mm and (0.80±0.24) mm, respectively.@*Conclusions@#Bone graft immediately after mandibular first molar extraction could delay alveolar bone resorption and preserve the periodontal attachment of the adjacent teeth during space closure. However, the procedure could slow down tooth movement.

Correlations of pulp chamber height and dentine thickness of mandibular first molar with age in Chinese Han population based on cone beam computed tomography / 实用口腔医学杂志

Objective:To investigate the relationship between pulp chamber height and dentine thickness of mandibular first molar on long axis with age in a Chinese Han population by cone-beam computed tomography(CBCT).Methods:CBCT images of 420 Chinese Han subjects(210 males and 210 females) were divided into 6 age groups as follows:15-24,25-34,35-44,45-54,55-64 and 65-74 years(n=70,35 males and 35 females).The height of pulp chamber and dentine thickness of the chamber root and floor of mandibular first permanent molar on long axis was measured by Galileo software of CBCT in vertical direction and then statistical analysis was carried out.Results:On long axis,the height of pulp chamber was (0.85±0.54) mm in males and (0.79±0.51) mm in females(P>0.05);dentine thickness of the pulp chamber roof was (3.60±0.49) mm in males and (3.50±0.49) mm in females(P>0.05);and dentine thickness of the pulp chamber floor was (2.57±0.52) mm in males and (2.49±0.5) mm in females(P>0.05).With aging,the height of pulp chamber was decreased(P<0.05) and dentine thickness of mandibular first permanent molar on long axis was increased(P<0.05).Conclusion:In Chinese Han population,the of pulp chamber height of mandibular first permanent molar on long axis is related to age,The dentine thickness increased with ages,the increase of dentine thickness of pulp chamber floor is more significant than that of the roof.

Assessing the effect of pit and fissure sealing on 733 six-year-teeth four years later / 口腔疾病防治

Objective@# Assessing the effect of pit and fissure sealing on children’mandibular first molar in four years follow-up.@*Methods@#The second grade pupils of five primary schools in Guangzhou were given pit and fissure sealing, 733 teeth were performed pit and fissure sealant. The retention rate of the sealant and caries incidence of the mandibular first molar were analysed in four years follow-up. @*Results @# In four years follow-up, the retention rate of mandibular first molar was 57.16%. In terms of the caries incidence, the sealing group was 9.82%, while the unsealing group was 15.77%(χ2 = 7.045, P < 0.05). The decrease rate of caries in the sealing group was 37.73%, the caries incidence for the shallow pit and fissure group was 7.76%, no statistical differentce could be found two groups (χ2 = 0.844,P = 0.358).@*Conclusion@#Caries incidence of mandibular first molar obviously decreased 4 years later after the pit and fissure sealing.