The Study Of Root And Canal Morphology Of Primary Mandibular Molars By Using Cone-Beam Computed Tomography

Objective:This study were to acquire the number of roots, the canals per root, the shapes of root canal orifices and the length of roots of the primary mandibular first molars (PMFMs) and the primary mandibular second molars (PMSMs) by using cone-beam computed tomography (CBCT). Summarized the primary mandibular molars anatomy regulation and characteristic of the number of roots, the canals per root, the shapes of root canal orifices and the length of roots, which would provide the theory evidences of primary mandibular molars for dental education and clinic treatments.Methods:97 children including 65 male and 32 female of age 3 to 10 years old were elected from whose suffered CBCT examination in the Affiliated Stomatology Hospital of Kunming Medical University from March 2014 to March 2015. A total of 322 healthy, suitable primary mandibular molars including 147 PMFMs and 175 PMSMs were chosen. Each child’s name, gender, age and dental position were enrolled before experiment started. CBCT images were opened by NNT software. Then experimenters evaluated and recorded the tooth images including the number of roots, the canals per root, the shapes of root canal orifices and the length of roots in the morphology of the root canal system. A professional oral radiologist and two pediatric postgraduate students concurrently evaluate all of the images to each a consensus in the interpretation of the radio-graphic findings. Datas were analyzed using the SPSS 17.0.Results:1 The number of rootsThere were mesial and distal roots in all PMFMs and PMSMs. Most of the mesial and distal roots were single root, but there were 2 separate roots in some distal roots. The prevalence of three roots in PMFMs is 6.8% and three roots in PMSMs is 16.57%.2 The canals of per rootThe canals of PMFMs were mainly double canals in mesial roots (74.15%) and double canals in distal roots(59.86%), the prevalence of single canal in distal roots was 39.46%. The majority of root canal morphology of PMFMs were type 1212 (39.46%), type 1211 (31.97%) and type 1112(13.6%).The canals of PMSMs were most double canals in mesial roots(96.0%) and double canals in distal roots(70.28%), the single canal in distal roots was 28.57%. The majority of root canal morphology of PMSMs were type 1212 (51.43%), type 1211 (28.57%), type 1222 (16.0%).3 The shapes of root canal orificesThe majority shapes of root canal orifices in PMFMs were regular triangle (19.73%), inverse triangle (33.33%) and rectangle (32.65%). The majority shapes of root canal orifices in PMSMs were rectangle (44.57%), inverse triangle (29.71%) and regular echelon (16.0%). The distribution of distal double root canal orifices in PMFMs and PMSMs were more scatter than that of the mesial’s.4 The genders and bilateral relations of the number of roots, the canals per root and the shapes of root canal orifices.The data of 322 teeth which included the number of roots, the canals per root and the shapes of root canal orifices were tested using Chi-square test (P> 0.05). The results illustrated that there was no significant difference between the ratio in males and females of PMFMs and PMSMs. And there was also no significant difference between the ratio in left and right side of PMFMs and PMSMs.5 The length of teethThe percentage of mesial roots length were longer than that of distal roots length in PMFMs (93.88%) and PMSMs (78.29%). It showed that the PMFMs and PMSMs’s mesial roots length were universally longer than that of distal roots length.6 Physiological root absorptionCorrelation analysis in different age paragraphs had been made in mesial and distal roots length of PMFMs and PMSMs. The root length of mandibular primary mesial molars had positively correlated with the ages growth in 3-8 years’group, and the root length of mandibular primary distal root length had not correlation. Both mesial and distal roots length of mandibular primary molars were negatively correlated with the ages growth in 8-10 years’group. It pointed out that the roots length of mandibular primary molars stayed at the stability before the age of 8. However, the roots were being absorbed slowly after 8 years.7 The comparison of canal variants between PMFMs and PMSMs.There canal variants of the PMFMs are more complicated than that of the PMSMs. The reason might be related to its own anatomy and position.Conclusions:It is an objective, reliable, painless and scientific method for using CBCT to study the mandibular primary molars’roots and root canal morphology. The root canal morphology of PMFMs and PMSMs were complex and variable, which might be related to its own anatomy and position. There was no significant difference between the ratio in males and females of PMFMs and PMSMs. There was also no significant difference between the ratio in left and right sides of PMFMs and PMSMs. The distribution of distal double root canal orifices in PMFMs and PMSMs were more scatter than that of the mesial’s. This study had provided the detailed information for the roots and root canal morphology of PMFMs and PMSMs, which could help to root canal therapies for dentists.