OBJECTIVES: This study aimed to investigate the incidence, imaging characteristics, and clinical manifestations of the eruption failure of deciduous molars using panoramic radiographs to provide a foundation for diagnosis and treatment in this population. METHODS: This study retrospectively reviewed panoramic radiographs of children aged 4-8 years obtained from Stomatology Hospital, Zhejiang University School of Medicine between January 2021 and December 2023. A total of 31 331 subjects were included for the radiographic assessment of the tooth eruption failure of deciduous molars. Incidence, radiographic characteristics, and associated complications were documented. Statistical analysis was performed using SPSS 26.0. RESULTS: The incidence of the eruption failure of deciduous molars among children aged 4-8 years was 0.94% (296/31 331). The rate was 1.55 times higher in females than in males, demonstrating a significant gender difference (P<0.001). Among the affected deciduous molars, mandibular first deciduous molars accounted for 76.4%, followed by the mandibular second deciduous molars (13.8%), and the maxillary deciduous molars collectively comprised 9.8%. The severity of eruption disorders was significantly associated with the mesial and distal tilting of adjacent teeth and elongation of the antagonist (P<0.001). CONCLUSIONS The incidence of the eruption failure of deciduous molars in children aged 4-8 years was 0.94%, with a high prevalence in females and a predilection for the mandible, particularly the mandibular first deciduous molar. For deciduous molars with severe eruption failure, early intervention is crucial to mitigate complications such as malocclusion and space loss.
Humans ; Child ; Child, Preschool ; Tooth, Deciduous/diagnostic imaging* ; Female ; Molar/physiopathology* ; Male ; Retrospective Studies ; Tooth Eruption ; Radiography, Panoramic ; Incidence

OBJECTIVE: To investigate the stress distribution to the mandible, with and without impacted third molars (IM3s) at various orientations, resulting from a 2000-Newton impact force either from the anterior midline or from the body of the mandible. MATERIALS AND METHODS: A 3D mandibular virtual model from a healthy dentate patient was created and the mechanical properties of the mandible were categorized to 9 levels based on the Hounsfield unit measured from computed tomography (CT) images. Von Mises stress distributions to the mandibular angle and condylar areas from static impact forces (Load I-front blow and Load II left blow) were evaluated using finite element analysis (FEA). Six groups with IM3 were included: full horizontal bony, full vertical bony, full 450 mesioangular bony, partial horizontal bony, partial vertical, and partial 450 mesioangular bony impaction, and a baseline group with no third molars. RESULTS: Von Mises stresses in the condyle and angle areas were higher for partially than for fully impacted third molars under both loading conditions, with partial horizontal IM3 showing the highest fracture risk. Stresses were higher on the contralateral than on the ipsilateral side. Under Load II, the angle area had the highest stress for various orientations of IM3s. The condylar region had the highest stress when IM3s were absent. CONCLUSIONS High-impact forces are more likely to cause condylar rather than angular fracture when IM3s are missing. The risk of mandibular fracture is higher for partially than fully impacted third molars, with the angulation of impaction having little effect on facture risk.
Adult ; Algorithms ; Biomechanical Phenomena ; Computer Simulation ; Dental Stress Analysis ; Elastic Modulus ; Female ; Finite Element Analysis ; Humans ; Imaging, Three-Dimensional ; Mandible/physiopathology* ; Mandibular Fractures/physiopathology* ; Models, Biological ; Molar, Third/physiopathology* ; Stress, Mechanical ; Tomography, X-Ray Computed

OBJECTIVETo investigate the effect of the restoration for pathological tooth wear.

METHODSA total of 48 pathological weared premolars and molars with restorable space in occlusal surface in 10 patients were restored by composite resins. The patients' masticatory function (biting force, masticatory efficiency, the surface electromyographic (EMG) activity of masseter muscles and anterior temporalis) were compared before and after the treatment. At the same time, the restorations were evaluated according to the modified the United States Public Health Service (USPHS) criterion.

RESULTSAfter the treatment, patients' clinical syndrome disappeared, the biting force was improved (P < 0.05) and the masticatory efficiency was increased significantly (P < 0.01). EMG activity, the asymmetry index and the action index of the tested muscles during different status had no significant change (P > 0.05). The composite resin restorations of the 48 teeth were all evaluated as A after three month and one year.

CONCLUSIONSRestoring the pathological weared posterior teeth with composite resins is an effective treatment to relieve the patients' syndrome, improve their masticatory efficiency and biting force.

Aged ; Bite Force ; Composite Resins ; therapeutic use ; Female ; Humans ; Male ; Mastication ; Middle Aged ; Molar ; pathology ; physiopathology ; Tooth Attrition ; physiopathology ; therapy ; Treatment Outcome

OBJECTIVETo investigate the correlation between the extent of cutting of the root canal wall and the root fracture strength and the stress distribution.

METHODSFifteen pairs of root sections were into 3 groups with canal wall thickness of 1.00 mm, 0.75 mm and 0.50 mm respectively. The maximum load was tested required for fracture for each group through fracture test in a universal testing machine, and compared with that for the original canal. The stress and its distribution of the root with normal wall thickness (1.2 mm) and roots with 75%, 50% and 25% respectively of the normal wall thickness were examined by three-dimensional finite analysis. The maximum Von Mises stress of the root of each model was calculated.

RESULTSThe mean fracture strengths of the groups with canal wall thickness of 1.00 mm, 0.75 mm and 0.50 mm were (4 432.41 +/- 563.59) N, (4 137.43 +/- 680.29) N and (3 749.87 +/- 554.17) N respectively. The maximum load of fracture resistance is a linear function of the root canal wall thickness (r = 0.972, P < 0.001). The three-dimensional finite analysis revealed that the enlargement of root canal diameter brought on increase of stress of root canal wall, and the stress and its distribution altered with further decrease of the wall thickness. The stress of lateral loading was greater than that of vertical loading.

CONCLUSIONSThe results suggests that clinical root canal treatment should be designated to remove just the infected tissue and avoid over-cutting of the hard tissue.

Dental Pulp Cavity ; pathology ; physiopathology ; Dental Stress Analysis ; Finite Element Analysis ; Humans ; In Vitro Techniques ; Molar ; Root Canal Preparation ; methods ; Tooth Root ; pathology ; physiopathology

OBJECTIVETo investigate the effects of tooth apical stress changes caused by different types of occlusion on the TMJ stresses.

METHODSThe apical stresses measured from photo-elastic experiments (2 Kg centric vertical loading to seven types of occlusions separately) were applied to the established 3D finite elemental model. The stress distributions on condyle, superfacial cartilage of condyle and TMJ disc were compared.

RESULTS(1) The stress on both anterior surface of condyle and its superfacial cartilage and on the intermediate band of disc were mainly compressive, while the stress on both posterior surface of condyle and its superficial cartilage and on the posterior band of disc were mainly tensile (P < 0.01). (2) The values of TMJ stresses of models with flat surface occlusion, distal occlusion, unilateral partial molar teeth cross bite, and occlusion with right second and third molar tooth missing were different to some extent from that with normal occlusion, among which the TMJ stress from the flat surface occlusion differed most significantly (P < 0.01). The TMJ stresses of models with unilateral upper third molar hyper-eruption occlusion and unilateral lower third molar hyper-eruption occlusion did not significantly differ from that with normal occlusion.

CONCLUSIONSChanges of apical principle stress resulted from different types of occlusions during centric biting have effects to some extent on TMJ stress quantitatively but not qualitatively.

Bite Force ; Dental Stress Analysis ; methods ; Finite Element Analysis ; Humans ; Malocclusion ; classification ; physiopathology ; Molar ; Stress, Mechanical ; Temporomandibular Joint ; physiopathology ; Temporomandibular Joint Disc ; physiopathology ; Tensile Strength

OBJECTIVETo verify whether it is effective to treat open bite cases with tip-forward bend.

METHODSThree-dimensional finite element (TDFE) models of the lower left central incisor and first molar were set up by means of CT. Stress distribution in root, PDL and alveolar bone, and the tendency of the tooth movement were obtained by calculation under different orthodontic forces.

RESULTS(1) The molar model revealed that the tensile stress concentration was at the distal cervix and the compressive stress concentration at mesial cervix. (2) The incisor model showed that the tensile stress was concentrated at apical tip and the compressive stress concentration was at the lingual side of the cervix. (3) The incisor had the tendency to elongate and move lingually. The molar tended to tip mesially and buccally.

CONCLUSIONSArch wire with tip forward bend depends on the elongation and lingual movement of anterior teeth to treat open bite, but the anchorage molar will incline mesially further, which is not consistent with the mechanism to treat open bite.

Biomechanical Phenomena ; Dental Stress Analysis ; Diastema ; therapy ; Finite Element Analysis ; Humans ; Incisor ; physiopathology ; Molar ; physiopathology ; Orthodontic Appliance Design ; Orthodontics, Corrective ; methods ; Periodontal Ligament ; physiology