Effects of different tooth movement patterns and aligner thicknesses on maxillary arch expansion with clear aligners: a three-dimensional finite element study.

Objectives: The objective of this study was to investigate the biomechanical effects of different tooth movement patterns and aligner thicknesses on teeth and periodontal tissues during maxillary arch expansion with clear aligners, to facilitate more precise and efficient clinical orthodontic treatments. Methods: Three-dimensional models including teeth, maxilla, periodontal ligament, and aligner were constructed and subjected to finite element analysis. Tooth displacement trends and periodontal ligament stresses were measured for seven tooth displacement patterns (divided into three categories including overall movement of premolars and molars with gradually increasing molar expansion in each step; distributed movement of premolars and molars; and alternating movement between premolars and molars at intervals) and two aligner thicknesses (0.5 mm and 0.75 mm) during maxillary arch expansion with clear aligners. Results: When expanding the maxillary arch with clear aligners, the effective expansion of the target teeth mainly showed a tilting movement trend. Increasing the amount of molar expansion increased the buccal displacement of the first molar but decreased the buccal displacement of the premolars. The mean buccal displacement of the target teeth was greater in the posterior teeth interval alternating movement group (0.026 mm) than in the premolar/molar distributed movement group (0.016 mm) and the overall movement group (0.015 mm). Increasing aligner thickness resulted in greater buccal displacement of the crowns and increased stress on the periodontal ligaments. Conclusion: Increasing the amount of molar expansion reduces the efficiency of premolar expansion. Alternating movement of premolars and molars at intervals achieves a higher arch expansion efficiency, but attention should be paid to the anchorage of adjacent teeth. Increasing the thickness of the aligner increases the expansion efficiency but may also increase the burden on the periodontal tissues.

Three-dimensional finite element analysis of retracting pathological migration of the right upper central incisor with a clear aligner.

We aimed to explore the best orthodontic step distance of the right upper central incisor with mild, moderate, and severe pathological displacement achieved via a clear aligner. Three-dimensional models of maxilla-tooth-periodontal ligament clear aligner of the right upper central incisors with five different steps of 0.1, 0.125, 0.15, 0.165, 0.25 mm and three different alveolar bone heights were established via finite element analysis. We analysed the changing trends in initial displacement, the periodontal ligament, the alveolar bone, and apical stress of right upper central incisor. In the process of retraction, the right upper central incisor a movement trend of the crown deviating from the distal root to the mesial, and with the decrease of the height of the alveolar bone and the increase of the displacement, the crown would appear distal labial torsion with a deepening trend of vertical overlay.The maximum stress distribution of the periodontal ligament and alveolar bone showed a positive correlation. The overall stress distribution of the periodontal ligament and apical stress increased with decrease of alveolar bone height and the increase of alveolar bone displacement. In patients with mild, moderate, and severe pathological displacement of the right upper central incisor, the best step distance of anterior tooth retraction is 0.165, 0.15, and 0.125 mm, respectively.

[Comparison study between main influencing factors and diurnal variation of net photosynthetic rate in different types of Pueraria thomsonii].

OBJECTIVE: To study the diurnal variation of net photosynthetic rate (P(n)) and main influencing factors in different types of Pueraria thomsonii, aimed at providing the theoretical basis for breeding the fine varieties of P. thomsonii suitable for the local light condition. METHOD: Diurnal variations of photosynthesis in leaves of different types of P. thomsonii were determined with the Li-6400 Portable Photosynthesis System. RESULT: (1) Diurnal variation of P(n), transpiration Rate (T(r)), stomatal conductance (G(s)) in leaves of six varieties of P. thomsonii showed unimodal curve and asymmetric bimodal curve. Diurnal variation of water use efficiency (WUE), intercellular CO2 concentration (C(i)) showed single valley curve. Diurnal variation curve of stomatal limitation value (L(s)) was single peak and S-type. (2) P(n) in leaves of six varieties of P. thomsonii was positively correlated with photosynthetic active radiation (PAR), air temperature (T(a)), G(s), and negatively correlated with air relative humidity (RH), C(i), P(n) of all varieties were very significantly correlated with PAR, G(s). CONCLUSION: Diurnal variations of photosynthesis in leaves of different types of P. thomsonii show significant difference. Jiuding, Chuanyu, Gange, Dijin No. 1 planted in Ya'an overcome "midday depression" phenomenon. Hechuan has the greatest photosynthetic potential, suitable for planting in forest understory and intercropping with high stalk to avoid the strong flashes. Planted in long-day region was beneficial to its growth. CO2 use efficiency of Geboshi No. 11 and Dijin No. 1 were significantly higher than that of the others. The accumulation efficiency of organics can be increased in cultivation management by fertilizing CO2.