To explore the effect on children's occlusion and temporomandibular joint (TMJ) after placement of preformed metal crowns and provide a reference for the restoration of defective primary molars.

A total of 39 children who underwent all primary molar metal crown restorations under general anesthesia were enrolled. The participants underwent occlusal contact area, percentage of total occlusal force, asymmetric ratio of occlusal force and occlusal contact time examinations with the T-scan computerized occlusal analysis system. Vertical dimension of occlusion (VDO) was measured using a dental vertical dimension gauge. TMJ dysfunction signs were recorded using the modified clinical dysfunction index (Di), and TMJ dysfunction symptoms were recorded using questionnaires. All data were collected at pretreatment, 1-week, 1-month, 3-month, and 6-month follow-up visits.

The occlusal contact area at the 3-month and 6-month follow-up visits returned to the occlusal contact area of pretreatment, and the difference was statistically significant (P>0.05). Compared with pretreatment, the percentage of total occlusal force at the 3-month and 6-month follow-up visits increased significantly, and the difference was statistically significant (P<0.05). The asymmetric ratio of occlusal force and the occlusal contact time were significantly decreased at the 6-month follow-up visit (P<0.05). The vertical dimension of occlusion recovered after one month of treatment (P>0.05). The final statistical analysis of the TMJ assessment showed that there was no significant difference in the clinical disorder index and TMJ dysfunction symptoms before and after treatment (P>0.05).

After undergoing all primary molar metal crown restorations, occlusal re-equilibrations were attained after approximately one month. The percentage of total occlusal force and occlusal stability were significantly increased after six months of treatment, without significant temporomandibular joint dysfunction.

To investigate the clinical characteristics and prognosis of crown fractures in immature permanent incisors due to trauma, and identify factors affecting their prognosisto provide a reference for clinical treatment.

This study was approved by the Medical Ethics Committee of West China Stomatology Hospital, Sichuan University. The study subjects were patients admitted to the pediatric stomatology department from December 2011 to December 2021, and a retrospective analysis was conducted on young permanent teeth with anterior crown fracture caused by injury and followed up for at least 1 year, which were diagnosed as enamel fractures, enamel-dentin fractures, and complicated crown fracture and treated by observation, pulpotomy etc. in the first appointment. The age, sex and time elapsed from trauma to baseline visit of the patients and the location, mobility, stage of root development, diagnosis and treatments were collected. The occurrence of pulp infection, pulp necrosis, and other events in the affected tooth is defined as clinical failure. Record whether clinical failure occurred and the timing of their occurrence of the traumatized tooth. Analyze factors related to the prognosis of various types of crown fractures in young permanent incisors and performsurvival analysis on the affected teeth.

Among 358 cases of young permanent incisors, 50 cases were diagnosed with enamel fracture, 176 cases with enamel-dentin fracture, and 132 cases with complicated crown fracture. The clinical success rate of crown fractures was 73.7% (264/358) in young permanent incisors. The incidence rates of clinical failure cases, including pulp infection and necrosis, were 4% (2/50) for enamel fractures, 33.3% (58/176) for enameldentin fractures, and 25.8% (34/132) for complicated crown fractures respectively. The clinical failure rate of enameldentin fracture treated with indirect pulp capping and restoration was higher than restoration only and pulpotomy (χ² =10.077, P = 0.004). The clinical failure rate of complicated crown fractures treated with direct pulp capping was higher than pulpotomy (χ² = 5.501, P = 0.038). The clinical failure rates between observation, smoothing edges and restoration of enamel fractures exhibit no significant differences (χ² = 0.588, P = 0.999). Risk factors for clinical failure in this study population included patient age over 9 years old (HR = 2.11, 95%CI: 1.1-3.9, P = 0.017)、time elapsed from trauma to baseline visit greater than 3 days (HR = 2.3, 95%CI: 1-4.8, P = 0.028), traumatized teeth with mobility (HR =1.95, 95%CI: 1.2-3, P = 0.004), enamel-dentin fractures treated with restoration (HR = 6.89, 95%CI: 1.6-29.6, P =0.010), enamel-dentin fractures treated with indirect pulp capping and restoration (HR = 13.8, 95%CI: 3.2-58.3, P < 0.001) and complicated crown fractures treated with direct pulp capping (HR = 46.07, 95%CI: 8-263.8, P < 0.001).

Enamel fractures treated by observation, smoothing edges and restoration, and complicated crown fractures treated with pulpotomy generally had a good prognosis in young permanent incisors. Close follow-up was recommended for crown fractures in young permanent incisors with identified risk factors for poor prognosis.