INJECTION MOLDED COMPOSITE DENTISTRY

By David Clark, DDS

Traditional composites have historically been hand-packed and layered into retentive cavity preparations for Class II restorations. They are hand-spackled around the tooth for anterior restorations, such as attempting to close a black triangle. Until recently, layered composites were considered the gold standard. Dr. Richard Price of Dalhousie University demonstrates that layering creates knit lines that compromise a Class II restoration’s structural and optical integrity and that a monolithic injection molding approach can create a superior structural outcome. (Fig. 1)

This article will present posterior and anterior cases demonstrating injection over-molding of heated composite into transparent anatomic matrices. This allows us to go “around” the tooth rather than “in” the tooth. This solves many problems, such as C-factor issues, pulpal death and tooth fracturing.

Case 1: Treating Severe Black Triangles

This 31-year-old female presented with the chief complaint of post-orthodontic black triangles. (Fig. 2) She lacked confidence in using the teeth for mastication because of the mobility of the teeth and chronic embarrassing food impaction. Black triangles are a very common problem in adults, especially after adult orthodontics.1-4 This case was treated with the Bioclear BT matrix kit. The color-coded sizing gauge is inserted buccal-lingually under the contact to aid in matrix selection. (Fig. 3) Corresponding Black Triangle matrices with a range of four different emergence profiles are tried in to verify fit (Fig. 4).

The rubber dam was then placed over the anterior segment, and after properly tucking the dam into the sulci, the teeth were dried, disclosed with disclosing solution and rinsed. Teeth were then cleared of all biofilm and protein pellicles with a blasting using aluminum tri-hydroxide powder under a high-pressure water spray.

Before placing the matrices, interproximal contacts were entered with the Tru-Contact® serrated handheld strip and then lightly sanded with Tru-Contact® diamond sanders. This allows further biofilm removal in these tight areas and complete seating of the matrices as contact tightness is reduced. The final amount of black triangle closure can be visualized by placing the matrices before the rubber dam is applied. The dentist can assess whether the matrices are correct to close the space. If not, the matrix can be customized or replaced with another that might improve the outcome.

Then, 37% Phosphoric acid was used to etch the entire tooth, rinsed after 15 seconds and excess water was removed. 3M® Scotchbond Universal Adhesive was scrubbed into exposed dentin areas for 20 seconds and air thinned. Then the entire tooth was copiously wetted with more adhesive to act as a surfactant for the composite as it is injection molded. No pre-curing was done to the adhesive.

Warmed 3M® Filtek Supreme Flowable Restorative was slowly injected into the matrices around the teeth by placing the tip of the syringe into one interproximal area on the facial side, allowing the composite to flow slowly to the lingual half of the tooth. The same process was repeated to the other interproximal area. The lingual half of the tooth was then filled to completion. Great care was taken to ensure that void-free flowable composite had filled much of the matrix system before adding the paste composite. Heated 3M® Filtek Supreme Ultra Universal paste composite was then injection-molded into the matrix system. The heated paste composite displaces excess adhesive and much of the flowable composite leaving a dense monolithic mass composed chiefly of the paste composite. The two-year postoperative result demonstrates healthy tissue and restoratively-driven papilla regeneration. (Fig. 5)

Case 2: Deep Posterior Caries Management.

As the Bioclear Learning Center works with multiple dental schools, it is challenging to standardize restorative protocols, especially standardized cavity preparations and caries removal methods. For example, Selective Caries Removal (SCR) is now taught at some level in nearly each of the 76 dental schools in North America. However, implementation in the actual clinics is another story, as there is a general lack of consensus among instructors.

This case demonstrates a recipe for success in a very challenging tooth, Fig. 6. SCR with the benefit of pre-wedging is shown in Fig. 7. Pre-wedging is a splendid trick. Place the appropriate wedges before the cavity prep is begun. This will protect the rubber dam and soft tissue. Greater visual access is afforded because the prewedges retract the soft tissue.

Finally, pre-wedging can create tighter contacts as the periodontal ligament is being stretched while the cavity prep is being performed. When treating multiple teeth, it can be advantageous to a matrix and wedge them at once. (Fig. 8) Then, each tooth can be individually injection molded, and the matrices and wedges removed before moving o to the next tooth (not shown).

Powerful separators (Fig. 9) can create more tooth separation than even the largest wooden wedge in your wedge kit. Use them in addition to your wedges. The postoperative view of the restorations demonstrates the durable look of a monolithic restoration. (Fig. 10) There was a small initial layer of Filtek Bulk fill flowable composite placed and cured in the interproximal areas before injection molding, because the interproximal areas were deeper than 5mm. 5mm is the max depth of cure for 3M Filtek One Bulk Fill Restorative composite. Pre and Postoperative radiographs (Fig. 11) demonstrate excellent marginal integrity and a seamless restoration.

Dr. Clark earned his dental degree from the University of Washington School of Dentistry. He is the director of Bioclear Learning Centers International, founder of the Academy of Microscope Enhanced Dentistry and developer of Bioclear Matrix System. Dr. Clark has a private practice in Tacoma, Wash. Dr. Clark will offer “The Epidemic of Cracked Teeth: New Science of Strong Teeth” (C31), Friday, June 30, 9 a.m.-12 p.m., “21st Century Composites: Stop Layering and Start Injecting” (C46), Friday, June 30, 2-5 p.m. and “Modern Monolithic Injection-Molded Composite Dentistry Workshop: Concepts, Materials, Instruments and Techniques” (W25 & W29), Saturday, July 1, 9 a.m.-12 p.m. & 2-5 p.m. Learn more about Dr. Clark’s courses being offered at the 2023 Florida Dental Convention at floridadentalconvention.com.

References

1) Kurth J, Kokich V. Open gingival embrasures after orthodontic treatment in adults: prevalence and etiology. Am J Orthod Dentofacial Orthop 2001; 120:116-123.

2) Ko-Komura N, Kimura-Hayasi M et al. Some factors associated with open embrasures following orthodontic treatment. Aust Orthod J 2003; 19:19-24.

3) Joshi K, Baiju CS, Khashu H, Bansal S, Maheswari IB. Clinical assessment of interdental papilla competency parameters in the esthetic zone. J Esthet Restor Dent. 2017 Jul 8;29(4):270-275. doi: 10.1111/jerd.12307. Epub 2017 May 25. PMID: 28544578.

4) An SS, Choi YJ, Kim JY, Chung CJ, Kim KH. Risk factors associated with open gingival embrasures after orthodontic treatment. Angle Orthod. 2018 May;88(3):267-274. doi: 10.2319/061917399.12. Epub 2018 Jan 16. PMID: 29337634; PMCID: PMC8288320.