| Background and objectiveSince the indirect bonding technology(IDB)was first proposed by Silverman and Cohen in the 1970s,through decades of continuous development and improvement,the technology has become increasingly mature and widely used in clinical practice.Indirect bonding refers to making the model of patients’tooth and jaws,positioning the brackets on the model accurately under the condition that all angles can be viewed directly,making the indirect bonding transfer tray,and transferring the brackets to the oral tooth surfaces through the transfer tray,With the development of bonding materials and the continuous innovation of transfer tray manufacturing technology,indirect bonding technology is constantly improved and optimized,which simplifies the operation steps of technicians,reduces the operation difficulty and cost,and makes this technology more and more popular with clinical orthodontists.However,the traditional direct bonding technology consumes a lot of chairside time,because the bonding of the posterior segment cannot be performed under direct vision,the brackets positioning may often be offset,which will directly affect the final alignment of the tooth.The effect makes the orthodontists must bend various types of compensation curves on the archwire to eliminate the positional deviation of the tooth in the dentition.This not only further consumes the time by the chair,but also causes the back and forth movement of the tooth,prolonging the correction time and affecting the effect.In recent years,with the prevalence of Straight Wire Appliance,the requirements for the accuracy of brackets positioning have gradually increased,and the advantages of indirect bonding technology have become more prominent.Compared with the traditional direct bonding technology,whether the indirect bonding technology has comparable or higher accuracy of brackets positioning has always been a topic of concern to scholars at home and abroad.At present,domestic and foreign researches on the accuracy of brackets transfer in indirect bonding technology are mostly concentrated on transfer trays made by various materials and different manufacturing methods,and little research has been done on the impact of working models with different replication accuracy obtained by different impression materials or different ways of making models.Clinically,alginate is often used as the impression material to obtain dental molds,and anhydrite is used to obtain dental working models,which is easy to operate and inexpensive.Whether other impression materials or other methods of making models can bring more accurate brackets positioning is also worthy of attention.In this study,the working models obtained by alginate as impression material and super hard gypsum as model material,and the working models produced through 3D intra-oral scanning and 3D printing were selected as the research objects.Compare and analyze whether there is a significant difference in the brackets transfer accuracy of transfer trays made on working models made by different methods,to provide a reference for clinical orthodontists to choose impression materials and methods in the process of obtaining working models in indirect bonding.Materials and MethodsUsing a silicone rubber mold of standard maxillary as a female mold,50 standard maxillary plaster models were fabricated and divided into four groups:alginate impression material group,silicone rubber impression material group and 3D printing group,10respectively,and standard control group,20.The alginate impression material group used the alginate impression material to take out the female molds of these 10 standard models,and used super hard gypsum to make theirs male molds as the working models and the standard models as the patient models;the silicone rubber impression material group used the silicone rubber impression material to make the female molds by secondary impression method,Similarly,the male molds made of super hard gypsum were used as the working models,and the standard models were used as the patient models;the 3D printing group used a 3-Shape TRIOS Pod~?intra-oral scanner to obtain 3D digital models of these standard plaster models.A Envision Vida 3D printer printed out theirs photosensitive resin male molds as working models;In the control group,10 standard models were used as working models,and the remaining 10 standard models were used as patient models.Four groups with 40 working models and 40 patient models.According to the method of drawing vertical reference lines and horizontal reference lines on the working model proposed by Kalange,a visual system of bracket positioning was established,and as a standard,the brackets were positioned and bonded on the working models.10 brackets and 2 buccal tubes were bonded to each working model.A total of 400 brackets and 80 buccal tubes were bonded to 40 working models.Double transfer trays(Double-PVS)with inner material of silicone rubber light body and outer material of silicone rubber heavy body were used to transfer brackets and buccal tubes on the working models to their corresponding patient models.The 40 working models with brackets and the 40 patient models after brackets transferring were scanned by the same technician using a 3-Shape TRIOS Pod~?3D intra-oral scanner to obtain three-dimensional digital models,the professional software of Materialise Magics 21.0 was used to measure and compare the difference between data of brackets on the working models and the patient models.ResultsBefore and after bracket transfering,there was a difference in the position of the 13bracket with respect to the tooth neck,and a difference in the position of the 24 bracket with respect to the tip of buccal cusp in the control group;there was a difference in the position of the 11 bracket with respect to the mesial and distal incisal angle,a difference in the position of the 22 bracket with respect to the mesial incisal angle,differences in the position of the 14bracket and 25 bracket with respect to the palatal surface,and differences in the position of the 12 bracket 24 bracket and 26 bracket with respect to the tooth neck in the alginate impression material group;there was a difference in the position of the 25 bracket with respect to the distal marginal ridge,and a difference in the position of the 26 bracket with respect to the buccal groove in the silicone rubber impression material group;there was a difference in the position of the 26 bracket with respect to the mesial and distal marginal ridge in the 3D printing group(P<0.05).Compared with the silicone rubber impression material group and the 3D printing group,the number of tooth with position differences before and after bracket transfer significantly increased in the alginate impression material group.However,the measurement differences of all the brackets before and after transfer were less than 0.50 mm,which would not significantly affect the final clinical treatment effect.Conclusion1.The double-layer transfer tray with the inner layer made of silicone rubber light body and the outer layer made of silicone rubber heavy body has reliable and stable accuracy.Clinical orthodontists can safely use this simple and inexpensive transfer tray to achieve indirect bonding.2.Working model with high replication accuracy made with silicone rubber as impression material or produced by 3D digital technology can bring accurate brackets positioning,and the indirect bonding technology with the participation of 3D digital technology avoids the errors brought by the intermediate steps,showing accuracy and efficiency.3.Although indirect bonding involving alginate impression material compared to indirect bonding involving silicone rubber impression material or 3D scanning and 3D printing,the brackets transfer accuracy is decreased,working model with poorer replication accuracy will lead to less accurate brackets positioning,it will not significantly affect the clinical treatment results,the mistakes are all within the clinically acceptable range.Alginate impression material and silicone rubber impression material or 3D digital technology can all meet the requirements of clinical indirect bonding technology for the accuracy of working model.Clinicians can choose freely according to the medical facilities and patient’s economic conditions. |
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