Three-dimensional finite element study of mandibular first molar distalization with clear aligner / 华西口腔医学杂志

OBJECTIVES@#This study aimed to construct the finite element model of the mandibular first molar with the invisible appliance and explore the dentition movement characteristics of the mandibular first molar when using micro-implant anchorage and different initial positions of the first molar.@*METHODS@#Models of the mandible, tooth, periodontal membrane, and invisible appliance were constructed using cone beam computed tomography (CBCT) data. The two groups were divided into the non-anchorage group and the micro-implant group (between the roots of the first molar and the second molar) based on whether the elastic traction of the micro-implant was assisted or not. The two groups were divided into the following conditions based on the starting position of the first molar: Working condition 1: the distance between the first molar and the second premolar was 0 mm; working condition 2: the distance between the first molar and the second premolar was 1 mm; working condition 3: the distance between the first molar and the second premolar was 2 mm; working condition 4: the distance between the first molar and the second premolar was 3 mm. The data characte-ristics of total displacement and displacement in each direction of dentition were analyzed.@*RESULTS@#In the non-ancho-rage group, all the other teeth showed reverse movement except for the first molar which was moved distally. Meanwhile, in the micro-implant group, except for a small amount of mesial movement of the second molar in wor-king condition 1, the whole dentition in other working conditions presented distal movement and anterior teeth showed lingual movement, among which the distal displacement of the first molar in working condition 4 was the largest. With the change of the initial position of the first molar to the distal, the movement of the first molar to the distal, the premolar to the mesial, and the anterior to the lip increased, while the movement of the second molar to the mesial decreased.@*CONCLUSIONS@#The micro-implant can effectively protect the anterior anchorage, increase the expression rate of molar distancing, and avoid the round-trip movement of the second molar. The initial position of the first molar movement is related to the amount of distancing and the remaining tooth movement.

Mandibular advancement with clear aligners and functional appliances in the treatment of skeletal ClassⅡmalocclusion: a systematic review and meta-analysis / 华西口腔医学杂志

OBJECTIVES@#This study aimed to conduct a meta-analysis of the efficacy of mandibular advance clear alig-ners with traditional functional appliances as the control group.@*METHODS@#PubMed, Web of Science, Embase, Cochrane Library, China Biomedical Abstracts Database, China Knowledge Network Database, Wanfang Database, and Weipu Database were used in this study. The two groups of researchers screened the literature and extracted data based on the inclusion and exclusion criteria established by PICOS entries, and used the ROBINS-I scale for quality evaluation. Revman 5.4 and Stata 17.0 software were used for meta-analysis.@*RESULTS@#Nine clinical controlled trials were included in this study with a total sample size of 283 cases. No significant difference was found in SNA, SNB, ANB, Go-Pog, U1-SN, Overjet, and other aspects between the invisible group and the traditional group in the treatment of skeletal class Ⅱ ma-locclusion patients; there was a 0.90° difference in mandibular plane angle between the two groups; the growth of the mandibular ramus (Co-Go) in the traditional group was 1.10 mm more than that in the invisible group; the lip inclination of the lower teeth in the invisible group was better controlled, 1.94° less than that in the control group.@*CONCLUSIONS@#The invisible group can better control the lip inclination of the mandibular anterior teeth when guiding the mandible. Furthermore, the mandibular plane angle (MP-SN) can remain unchanged, but the growth of the mandibular ramus is not as good as the traditional group, and auxiliary measures should be taken to improve it in clinical practice.

Influence of different surface treatments in bond strength of brackets to porcelain / 吉林大学学报(医学版)

Objective To observe the porcelain treated with Nd∶YAG laser irradiation and hydrofluoric acid (HF), and to explore the influence of integrated treatment of Nd ∶ YAG laser irradiation and HF etching in the bond strength of brackets to porcelain.Methods 48 metal ceramic prostheses were randomly divided into untreated control group,HF group,grooved treatment group,0.75W laser group,1.05W laser group,1.45W laser group. All samples were bonded to the brackets.After temperature cycling test,the shear bond strength (SBS)and tensile bond strength (TBS)were measured.Results There were significant differences in SBS and TBS between various surface treatment groups and untreated control group (P < 0.01).The SBS and TBS of brackets bonded in HF group was significantly higher than those in 1.05W laser and 1.45W laser groups (P <0.05).The SBS and TBS in 1.05W laser and 1.45W laser groups were higher than those in HF group (P <0.05).The SBS and TBS in 1.05W laser group were higher than those in other groups (P < 0.05).SBS showed positive correlation with TBS (r =0.426,P =0.000).Conclusion The use of Nd∶YAG laser irradiation with the energy parameter of 1.05W and HF could increase the bonding with formation of composite resin,and the more SBS,the more TBS.

Three-dimensional finite-element analysis of maxillary protraction based on labiolingual appliance / 华西口腔医学杂志

<p><b>OBJECTIVE</b>This study aims to analyze the biomechanical effects of four sutures that are related to maxillary growth during a maxillary protraction treatment cycle based on labiolingual appliance.</p><p><b>METHODS</b>A three-dimensional simulation of labiolingual appliance was performed based on a three-dimensional finite-element maxillofacial model combined with solid-modeled sutures.</p><p><b>RESULTS</b>The displacement and stress distributions were calculated. The labiolingual appliance was suitable for patients with underbites or deep overbites. Sutura frontomaxillaris and sutura zygomaticomaxillaris were vital to the forward displacement and counterclockwise rotation of the maxillary. The changes in sutura zygomaticotemporalis and sutura palatine were not significant.</p><p><b>CONCLUSION</b>The influences of the labiolingual appliance on the sutures during the treatment cycle of maxillary protraction can be effectively simulated by the three-dimensional finite-element maxillofacial model.</p>

Influence of different surface treatments on porcelain surface topography / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To evaluate the influence of different surface treatments on porcelain surface topography.</p><p><b>METHODS</b>Metal ceramic prostheses in 6 groups were treated according to the different surface treatment methods, and the surface topography was observed through scanning electron microscope (SEM). Group A was the control one (untreated), group B was etched by 9.6% hydrofluoric acid(HF), group C was deglazed by grinding and then etched by 9.6% HF, group D was treated with Nd: YAG laser irradiation(0.75 W) and HF etching, group E was treated with Nd: YAG laser irradiation (1.05 W) and HF etching, and group F was treated with laser irradiation (1.45 W) and HF etching.</p><p><b>RESULTS</b>Surface topography was different in different groups. A lot of inerratic cracks with the shapes of rhombuses and grid, and crater with a shape of circle were observed on the ceramic surface after treatment with energy parameters of 1.05 W Nd: YAG laser irradiation and 9.6% HF etching (group E). Surface topography showed a lot of concaves on the inner wall of the cracks, and the concaves with diameter of 1-5 microm could be observed on the inner wall of the holes, which had a diameter of 20 microm under SEM.</p><p><b>CONCLUSION</b>The use of Nd: YAG laser irradiation with the energy parameters of 1.05 W and the HF with a concentration of 9.6% can evenly coarsen the porcelain surface, that is an effective surface treatment method.</p>

Three dimensional finite element analysis of tooth movement tendency in maxilla using mini-screw cooperated with upper accentuated-curve to close tooth space / 华西口腔医学杂志

<p><b>OBJECTIVE</b>In order to find out the cause of molar intrusion and how to avoid molar intrusion, we analyze the movement tendency of tooth by changing the angles of upper accentuated-curve and the height of free traction hook.</p><p><b>METHODS</b>Spiral CT scanning and Mimics 10.0 software were employed in this study to construct the three dimensional finite element model of maxillary teeth, periodontal ligaments and alveolar bone as well as the inch stainless steel upper accentuated-curve archwires with different angles (5 degrees, 10 degrees, 15 degrees, 20 degrees, 25 degrees) and the free traction hook with different height (2.1, 4.0, 5.5 mm). By exerting 1.5 N backward force to analysis the displacement trend of maxillary tooth.</p><p><b>RESULTS</b>Upper accentuated-curve archwires made the incisors labially tip, intruse, distally upright and mesilabially torsion; made the canines labially tip, prolong, mesial-tipped and mesi-labially torsion; made the second premolars and the first molars buccal tip, intruse, distal upright and mesi-labially torsion. With the angle of upper accentuated-curve archwires increased, all tooth movement tendency increased; while with the height of free traction hook increased, all tooth movement tendency decreased.</p><p><b>CONCLUSION</b>When the angle of upper accentuated-curve archwires increased, the extent of molar intrusion increased, but when the height of free traction hook increased, the degree of molar intrusion decreased. The degree of molar intrusion was minimum using 5 degrees upper accentuated-curve archwires cooperated with 5.5 mm free traction hook.</p>

A study on expression of basic fibroblast growth factors in periodontal tissue following orthodontic tooth movement associated with low power laser irradiation / 华西口腔医学杂志

<p><b>OBJECTIVE</b>The purpose of this study was to investigate the effects of low power laser on basic fibroblast growth factors (bFGF) expression in periodontal tissue during tooth movement.</p><p><b>METHODS</b>18 white rabbits were randomly divided into 6 groups with 3 rabbits in each group, including groups of 1, 3, 5, 7, 14 and 21 days. Under an anesthesia condition by 2% pentobarbital sodium, the stainless coil springs were fixed between the first maxillary molar and the incisor producing the force of 80 g. The right side of maxilla was considered as the experimental group under the irradiation of low power laser with the left side as the control groups. The expression of bFGF was investigated half-quantitatively through immunohistochemical analysis.</p><p><b>RESULTS</b>The expression of bFGF in periodontal tissue with irradiation of low power laser was higher than the control side. There were significant differences among the 5, 7, and 14 day groups. In the tension area of the experimental side, the expression of bFGF in the osteoblastic surface of alveolar bone was characteristically greater than that of the control side.</p><p><b>CONCLUSION</b>The laser of low power promotes the expression of bFGF in the periodontal tissue and alveolar bone remodeling.</p>