A mechanical and three-dimensional finite element study of the optimum tooth sectioning depth during the extraction of low-level horizontally impacted mandibular third molar.

The present study aims to determine the optimum sectioning depth for the extraction of low-level horizontally impacted mandibular third molar (LHIM3M) using mechanical and finite element analysis. One hundred and fifty extracted mandibular third molars were randomly divided into three groups: 1, 2 or 3 mm of tooth tissue was retained at the bottom of the crown. The breaking force of teeth was tested in a universal strength testing machine. The fracture surface was observed and the type of tooth breakage was recorded. According to the three groups, corresponding 3D finite element models were created. The breaking force obtained in the mechanical study was, respectively, applied and the stress and strain of the teeth and surrounding tissues were analysed. Breaking force decreased as sectioning depth increased. The 2 mm group produced the lowest rate of incomplete breakage (10%). In the 2 mm model, the stresses were evenly distributed in the tooth tissue at the bottom of the fissure, and the maximal stress was located in the tissue close to the root segment. The maximum values of stresses in the bone and of strains in the periodontal ligament of the second molar and bone were lower in the 1 mm model than in other models. Their distribution was similar in the three models. A sectioning depth of 1 mm group saves labour during the extraction of LHIM3M, compared to 2 and 3 mm; 2 mm might be the appropriate sectioning depth in terms of breakage shapes.

Breakage and displacement of the high-speed hand-piece bur during impacted mandibular third molar extraction: three cases.

BACKGROUND: The high-speed hand-piece bur is one of the methods to perform tooth sectioning during the minimally traumatic extraction of impacted mandibular third molars. During tooth sectioning, the breakage of the bur might take place when it is improperly used. Three cases of the breakage and displacement of a high-speed hand-piece bur during extraction are reported, aiming to remind dental surgeons of this complication. CASE PRESENTATION: The bur fragment in case 1 was embedded in the mandibular bone under the previously removed crown of tooth 48 and distal to tooth 47. The bur fragment in case 2 was embedded in the lingual edge of the socket and partly beneath the mucosa on the lingual side. The position of the bur fragment in case 3 was similar to that of case 1 but was completely embedded in the spongious bone. The three cases were performed by first-year residents, and all of the bur fragments were successfully removed by attending doctors after accurately locating them by radiological examination. CONCLUSIONS: In order to avoid breakage of the high-speed hand-piece bur, the number of uses of the bur should be monitored and the integrity and state of the bur should be carefully checked. Moreover, light pressure with little lateral force should be used during tooth sectioning. If bur breakage and displacement occur, the retrieval protocol should be determined based on the imaging findings and conducted as soon as possible to avoid serious consequences.

The radiological and histological investigation of the dental follicle of asymptomatic impacted mandibular third molars.

OBJECTIVES: The indication for removal of asymptomatic fully impacted third molars is still controversial. In this study, radiological and histological investigation of the dental follicle of asymptomatic impacted mandibular third molars was performed, aiming to provide a reference for clinical prophylactic extraction of these teeth. METHODS: Patients with impacted mandibular third molars were included and the maximum width of the dental follicle around the crown was measured in horizontal, sagittal and coronal sections by cone beam computed tomography. The dental follicles were stained with haematoxylin-eosin, analysed by a pathologist and classified as normal, inflammatory or cystic. A Chi-squared test was used to analyse the association of the incidence of inflammation and cysts with the clinical variables of the impacted mandibular third molars. RESULTS: Thirty-seven samples were normal dental follicles; 52 samples showed inflammatory infiltration with an incidence of 57.14%; 2 samples with a maximum dental follicle width of 2-3 mm were diagnosed as odontogenic cysts, and the incidence was 2.20%. There was no significant difference in the incidence of inflammatory and cystic dental follicles between males and females, or between different age groups (P > 0.05). With an increase of the maximum width of the dental follicle, there was a rise in the incidence and degree of infiltration of chronic nonspecific inflammation. CONCLUSION: Asymptomatic impacted mandibular third molars tend to be extracted, especially for teeth with a 2-3 mm maximum width of the dental follicle on radiological examination.