Cleft Lip ; complications ; Cleft Palate ; complications ; Humans ; Maxillofacial Abnormalities ; pathology ; Orthodontics, Corrective

OBJECTIVETo develope a three-dimensional finite element model based on the individual occlusal contact data to analyze the influence of occlusal contact on the stress distribution in the temporomandibular joint (TMJ).

METHODSCT, cone-beam CT (CBCT), MRI and 3D scanner were used to create a three-dimensional finite element model of the stomatognathic system, which reflected the accurate morphological characteristics of the occlusal surface. The contact area was marked on the occlusal surface of the teeth based on the individual occlusal contact data obtained during the maximal volunteer clenching (MVC). Two occlusal contact conditions including normal occlusion and unilateral posterior crossbite (UPC) were constructed. The models were fixed on the contact areas to simulate the MVC condition in order to analyze the stress distribution in the TMJ.

RESULTSThe stress distribution of the TMJ was approximately symmetrical in normal occlusion, but the stress values were somewhat different. No significant difference was found in stress distribution between UPC and normal occlusion, but the values were significantly higher on the crossbite side. The maximum values of von Mises stress were 10.35, 3.82, 3.59 MPa, on condylar process, articular disk, articular fossa of the crossbite side, respectively while on the corresponding side of the normal occlusion maximum values were 7.32, 3.18, 2.84 MPa, respectively.

CONCLUSIONSThe stress distribution of the TMJ in three-dimensional finite element model which indicated the personal occlusal contact was highly sensitive to the change of the occlusal contact. The abnormal occlusal contact caused by the UPC could lead to the stress concentration of the TMJ on the crossbite side.

Cone-Beam Computed Tomography ; Dental Occlusion ; Dental Stress Analysis ; Finite Element Analysis ; Humans ; Malocclusion ; diagnostic imaging ; physiopathology ; Temporomandibular Joint ; diagnostic imaging ; physiology ; Temporomandibular Joint Disorders

Objective: Exploring the position and bone wall thickness characteristics of the maxillary central incisors in Southern Chinese adults to provide a clinical reference for the design of immediate maxillary central incisor implantation surgery. Methods: The hospital ethics committee approved the study, and the patients provided informed consent. CBCT images of 990 adult patients (aged 20-79 years) from the Stomatology Hospital (January 2018 to December 2021) were categorized based on the dental arch form and age-sex groups. Sagittal CBCT images of the maxillary central incisors were used to measure the labial and palatal bone thickness wall at 4 mm the CEJ to apical, the middle of the root, and the angle between the tooth long axis and the long axis of the alveolar process, to compare the thickness of the labial and palatal bone walls in samples of male and female patients, and to explore the relationship between the angle between the tooth long axis and the alveolar process long axis in samples of male and female patients in different age groups (20-39 years; 40-59 years; 60-79 years). Results: Significant differences were found in the labiopalatine side of the alveolar bone of the maxillary incisor root position. A total of 95.8% (948/990) of the maxillary incisors were positioned more buccally, 4.1% (41/990) were positioned more midway, and 0.1% (1/990) were positioned more palatally. The thicknesses of the bone wall at the CEJ of 4 mm below the palatal side, the middle of the root, and at the apex were greater (1.82 ± 0.56 mm, 3.20 ± 1.10 mm, and 7.70 ± 2.00 mm, respectively) than those at the labial side (1.21 ± 0.32 mm, 0.89 ± 0.35 mm, and 1.86 ± 0.82 mm, respectively), with statistical significance (P<0.05). Male bone wall thickness was generally greater than female bone wall thickness (P<0.05). The angle between the long axis of male teeth and the alveolar bone was 14.77° ± 5.66°, while that of female teeth was 12.80° ± 5.70°, with a statistically significant difference (P<0.05). The angle between the long axis of teeth and the alveolar bone in the 40-59-year-old group and the 60-79-year-old group was greater than that in the 20-39-year-old group, and the difference was statistically significant (P<0.05). Conclusion A total of 95.8% of adults in South China have maxillary central incisors with root deviation toward the labial bone cortex. The thickness of the labial bone wall is much thinner than that of the labial bone wall, which is the middle of the thickness of the root. In Southern Chinese adults, the angle between the upper central incisor and the long axis of the alveolar bone in males is greater than that in females, and the degree of the angle increases with age. It is recommended to pay attention to the thickness of the bone wall around the root and the angle between the teeth before immediate implantation surgery to choose a reasonable implantation plan.

Objective: To analyze the spatial relationship between the roots of maxillary anterior premolars and the maxillary sinus, thus providing an anatomical basis for timing, planning, surgical approaches, and implant selection at this site. Methods: Cone beam CT (CBCT) images were collected from 264 patients (aged 20-65 years) who visited the Ruihua Dental Clinic between January 2017 and March 2023. The minimum distance from the apex of the maxillary anterior premolar roots to the lower wall of the maxillary sinus was measured on the coronal plane. The classification of the vertical relationship between the tooth root and the lower wall of the maxillary sinus was performed, and comparisons were made bilaterally, between genders, and among different age groups. Results: The minimum distance (Q50) from the apex of the first maxillary premolar root to the lower wall of the maxillary sinus was 7.34 mm for the single-root type, 7.80 mm for the buccal root of the double-root type, and 7.36 mm for the palatal root. For the second maxillary premolar, the median distance was 2.56 mm for the single root type, 1.73 mm for the buccal root type, and 1.23 mm for the palatal root type. There was a significant difference in the shortest distance from the apex of the right second maxillary premolar single root to the lower wall of the maxillary sinus among the different age groups (P<0.05), with the 20-29-year-old group having the smallest median distance (1.52 mm) and the ≥ 40-year-old group having the largest (4.44 mm). There was no significant difference in the effect of sex or laterality on distance (P>0.05). The most common vertical relationship between the apex of the maxillary anterior premolar roots and the lower wall of the maxillary sinus was noncontact. There was no significant difference in the vertical relationship classification between the single-root and double-root types (P>0.05). Conclusion Most maxillary first premolar roots can provide sufficient bone height, which makes it easy to achieve immediate implantation. The maxillary second premolar root frequently involves insufficient bone, which is necessary to make full use of the bone wall of the extraction socket or the sinus floor cortical bone to achieve initial stability. The vertical relationship between the premolar root and maxillary sinus was influenced by age and dental position. Younger age groups often exhibit inadequate bone height, and the indication for immediate implantation should be carefully considered. The number of roots does not significantly affect the relationship between the sinus and root; however, double-rooted premolars offer more support for immediate implantation and socket healing due to the small root diameter and bony separation between the roots.