Additive Manufacturing Strategies

3Doodler Used to Improve Indirect Orthodontic Bracket Transfer Trays

ST Medical Devices

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3D printing pens are often used when making fun and beautiful works of art, as well as for educational purposes, but they have also proved useful for medical applications as well. A trio of researchers from the KM Shah Dental College and Hospital published a paper, “3D Printing Pen: A Novel Adjunct for Indirect Bonding,” about their work using a 3D printing pen to create partial and complete transfer trays for indirect orthodontic bracket bonding, which takes far less chairside time than direct bonding.

“The primary drawback of indirect bonding is incomplete penetration of the curing light through transfer trays, leading to bracket bond failure,” the researchers explained. “The primary objective in a clinical setting is to minimize the chairside time. This technique of indirect bonding reduces chairside time, is economical, utilizes minimum armamentarium, and provides adequate light penetration and accuracy.”

Indirect orthodontic bonding first came about in the 1970s, and funnily enough, caramel candy, which is water-soluble, was used as the adhesive for brackets back then. We’ve obviously come a long way, moving to thermally cured composites, sticky wax, and soluble wallpaper paste, until the tray transfer system was developed in the 1990s.

“Read and O’Brien (15) and Read and Pearson (16) suggested the use of a transparent thermoplastic sheet for tray transfer for making the indirect bonding technique compatible for light cure composite,” the researchers wrote.

While it’s faster for the patient and more accurate, indirect bonding has its own problems, including increased laboratory time, the need for an extra set of impressions, and weaker bracket bonds, due to incomplete curing of the composite because of partial light penetration. That’s why the researchers wanted to see if they could use a 3D printing pen to improve the process, along with popular biodegradable polymer PLA, which is good for making the transfer tray because of its transparency and rigidity.

Laboratory procedures. (A) Markings for bracket positioning and layer of bonding agent applied on maxillary study model; (B) Markings for bracket positioning and layer of bonding agent applied on mandibular study model; (C) Brackets fixed on maxillary study model; (D) Brackets fixed on maxillary study model; (E) Fabrication of transfer tray; (F) Fabricated transfer tray; (G) Complete transfer tray; (H) Partial transfer tray

The team selected five consenting orthodontic patients and made alginate impressions of their upper and lower arches and poured casts of them, which were then marked for ideal bracket positioning per MBT prescription before having a layer of bonding agent applied and being light-cured. The brackets were added and light-cured again, after another layer of bonding agent was added for stability. A 3Doodler PRO, set at 210°C and maximum flow, was used to help make the transfer trays out of MatterHackers PRO PLA.

“The tip of the 3D printing pen was held in proximity to the brackets; molten PLA was flown in such a way that three margins of the bracket, i.e., mesial, distal, and gingival, remained free of PLA; however, it engaged the slot of the bracket and extended on the occlusal and palatal surfaces of the tooth. Once the transfer tray was fabricated, the brackets were dislodged from the study model with the help of deboning pliers, maintaining the PLA tray intact,” the team explained.

The researchers then transferred the 3D printed tray, with the brackets inside, to the mouth, and light-cured it after they determined the fit was good. A straight probe was used to remove the tray from the brackets, any PLA that broke in the bracket slot was removed with a heated probe, and a tungsten carbide bur completed the process, used to remove any residual resin on “the incisal margin of the bracket.” Out of the five study participants, only three total bracket failures were observed.

Clinical procedures for indirect bonding. (A) Tray placement on maxillary dentition; (B) Tray placement on mandibular dentition; (C and D) Curing of composite; (E) Removal of the maxillary tray from the mouth; (F) Removal of the mandibular tray from the mouth

The team didn’t find any other studies in which the brackets were attached on the study models using a bonding agent as adhesive. It’s a highly biocompatible material, and also wasn’t affected by the heat from the molten PLA.

“We used a bonding agent as an adhesive to attach brackets to the study models in this case because it can be applied on the bracket base and a layer on the cast effortlessly. It also forms a very thin interface between the bracket base and the study model, thus increasing the accuracy in the expression of bracket prescription,” they explained.

While the 3D printed PLA tray took longer to make than a vacuum-formed thermoplastic one, it fit better and offered good rigidity, in addition to being easier to make and manipulate, more clinician-friendly, resulted in less chairside corrections, was easier to remove from the mouth, and offered three surfaces for curing and “optimal bond strength.” Plus, when the researchers compared their 3D printed tray to other indirect bonding methods, they found that theirs allowed for the removal of flash—a major element of plaque accumulation—from bracket bases.

A previous study found that the average time required for both the laboratory and clinical steps for indirect bracket bonding was almost 39 minutes, while it took a little less than 30 minutes for direct bracket bonding. In this study, it took 18.44 minutes for the bonding agent and 3D printing pen lab procedures, and 11.86 minutes for clinical procedures, for a total of 30.3 minutes—right in between the average times for direct and indirect bracket bonding using conventional methods.

Completed bonding procedure

The researchers assessed bracket failure for the five patients every four weeks for a year, and have concluded that using a 3D printing pen, PLA, and a bonding agent to fabricate complete or partial indirect bonding trays is “a precise, easy-to-use, economical, and reliable method that reduces chairside time.”

“A 3D printing pen and PLA were used to fabricate transfer trays for indirect bonding which provided us with advantages like ease of manipulation, immense control over the flow of materials and the parts of bracket and cast to be covered in PLA, cost effectiveness, and transparency. This method does not require any expensive equipment and the materials being used are easily portable,” the team concluded.

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