Analysis of congenital deciduous teeth absence and its permanent teeth phenotype.

OBJECTIVES: This study aimed to investigate the clinical characteristics of congenital deciduous teeth absence and its permanent teeth performance type by using panoramic radiographs. METHODS: A total of 15 749 panora-mic radiographs of 3-6-year-old children with deciduous dentition were collected from January 2020 to December 2021. The incidence of congenital deciduous teeth absence was observed, and the abnormality of permanent teeth was recor-ded. SPSS 24.0 software was used for statistical analysis. RESULTS: The incidence of congenital deciduous teeth absence was 2.54% (400/15 749), which was found in 217 girls and 183 boys, and the difference between the genders was statistically significant (P=0.003). The absence of one and two deciduous teeth accounted for 99.75% (399/400) of the subjects. In addition, 92.63% (490/529) of mandibular deciduous lateral incisor was congenitally absent, 44.80% (237/529) of deciduous teeth was absent in the left jaw, and less than 55.20% (292/529) was absent in the right; the difference between them was statistically significant (P=0.017). The absence of 96.41% (510/529) deciduous teeth in the mandibular was significantly more than that of 3.59% (19/529) in the maxillary, and the difference between was statistically significant (P=0.000). Furthermore, 68.00% (272/400) and 32.00% (128/400) of deciduous teeth were absent in unilateral and bilateral, respectively, and the difference was statistically significant (P=0.000). Four types of congenital deciduous teeth absence with permanent teeth were observed as follows: 1) 73.91% (391/529) of permanent teeth was absent; 2) 20.60% (109/529) of permanent teeth was not absent; 3) the number of fused permanent teeth accounted for 4.91% (26/529); 4) the number of supernumerary teeth was 0.57% (3/529). CONCLUSIONS: Although the absence of congenital deciduous teeth is less common than that of permanent teeth, it affects deciduous and permanent teeth to some extent. Dentists should pay attention to trace and observe whether abnormalities are present in the permanent teeth and take timely measures to maintain children's oral health.

Retrospective study of concomitant hypodontia and hyperdontia in 145 subjects.

OBJECTIVES: This study aims to investigate the incidence and clinical characteristics of concomitant hypodontia and hyperdontia (CHH) by performing panoramic radiographs. METHODS: A total of 41 648 panoramic radiographs of pediatric patients who were admitted to the hospitals from January 2019 to May 2021 were reviewed, and 145 CHH patients were included in the study. The presence of CHH was recorded. SPSS 24.0 software was used for statistical analysis. RESULTS: The prevalence of CHH was 0.35% (145/41 648). Males (102 cases) were obviously more than females (43 cases), and the difference between genders was statistically significant (P<0.001). The features of congenital permanent tooth loss in this group were predominantly 1 and 2 teeth missing and preferably mandibular lateral incisors and mandibular second premolars missing. The incidence of congenital permanent teeth loss was higher in the mandible than in the maxilla (P<0.001), but no difference was found in the distribution between left and right (P=0.84). The features of supernumerary teeth in this group were 1 and 2 teeth, mostly in the maxillary anterior area, mostly conical, mostly vertical inversion and orthotopic growth. CONCLUSIONS: CHH is a rare mixed numeric dental anomaly characterized by congenital missing teeth and supernumerary teeth occurring in the same individual. CHH cases are higher in men than in women. The characteristics of their hypodontia and hyperdontia are similar to those of patients with congenital permanent tooth absence or supernumerary teeth. Early diagnosis of the condition and a multidisciplinary approach for management of such case is recommended.

[Effects of recasting in vacuum with argon on the chemical composition of ceramic alloys].

OBJECTIVE: This study aimed to determine the effect of recasting in vacuum with argon on the chemical composition of cobalt-chromium (Co-Cr), commercially pure titanium (cpTi), palladium-based (Pd-based), and aurum-platinum (Au-
Pt) ceramic alloys. METHODS: Without adding new alloys, Co-Cr, cpTi, Pd-based, and Au-Pt ceramic alloys were recast one to three times under the condition of vacuum compressive casting with argon. Before recasting, four previously cast ceramic alloys were treated with the corresponding method. After polishing, the chemical composition of the four ceramic alloys recasted one to three times were determined by energy-dispersive spectrometry. RESULTS: No significant difference was observed in the chemical composition of the four ceramic alloys recast 1-3 times (P>0.05). CONCLUSIONS: Under the condition of vacuum with argon, the recasting had no obvious influence on the chemical composition of Co-Cr, cpTi, Pd-based, and Au-Pt ceramic alloys.

[The effect of recasting on microstructure of dental ceramic alloys].

PURPOSE: To investigate the effects of recasting on metallographic microstructure of cobalt-chromium(Co-Cr), commercially pure titanium(cpTi), palladium-copper-gallium(Pd-Cu-Ga), aurum-platinum(Au-Pt) ceramic alloys. METHODS: Without adding new alloys, Co-Cr, cpTi, Pd-Cu-Ga and Au-Pt ceramic alloys were recasted for 1-3 times under the circumstance of vacuum compressive casting with argon. Before each recasting, these 4 ceramic alloys casted previously were treated by the most appropriate way which has been reported by our previous study. According to GB/T13298-2015 standards, the specimens of 4 ceramic alloys after recasting 1-3 times were grinded, polished, and etched and then the metallographic microstructure of them were determined by a metallographic microscope or scanning electron microscopy(SEM). RESULTS: With the increase of recasting times, the microstructure of Co-Cr ceramic alloy showed grain growth, grain matrix increase, and the intermetallic compound in the grain boundary increase, the microstructure of the cpTi ceramic alloy showed grain growth. The samples of cpTi ceramic alloy recasting twice appeared shaft tendency, and the ones which were recasted 3 times were compound of α-phase and ß-phase. The microstructure of the Pd-Cu-Ga ceramic alloy showed grain growth slightly after casting 2-3 times, while no significant change was found on the microstructure of the Au-Pt ceramic alloy. CONCLUSIONS: Recasting changes the microstructure of Co-Cr, cpTi, and Pd-Cu-Ga ceramic alloys, and the ceramic alloys may recycled by the manufacturers.