Direct composite injection molding with bilayered three-dimensional-printed clear index: a fully digital workflow case report of post-orthodontic anterior tooth wear

Article information

Restor Dent Endod. 2026;.e36

Publication date (electronic) : 2026 July 16

doi : https://doi.org/10.5395/rde.2026.51.e36

Yuta Utsumi¹, Junji Tagami^2,3, Bas Loomans⁴, Nicola Scotti⁵, Keiichiro Watanabe⁶, Sooha Matsuki⁶, Eiji Tanaka⁶, Keiichi Hosaka^1,2,

¹Department of Conservative Dentistry, Tokushima University Graduate School of Biomedical Sciences, Tokushima, Japan

²Smart Innovations for Preventive and Restorative Dentistry Research Group, Department of Operative Dentistry, Faculty of Dentistry, Chulalongkorn University, Bangkok, Thailand

³Cariology and Operative Dentistry, Institute of Science Tokyo, Tokyo, Japan

⁴Department of Dentistry, Research Institute for Innovation, Radboud University Medical Center, Nijmegen, The Netherlands

⁵Department of Surgical Sciences, University of Turin, Dental School Lingotto, Turin, Italy

⁶Department of Orthodontics and Dentofacial Orthopedics, Tokushima University Graduate School of Biomedical Sciences, Tokushima, Japan

^*Correspondence to Keiichi Hosaka, DDS, PhD Conservative Dentistry, Tokushima University Graduate School of Biomedical Sciences, 3-18-15 Kuramoto-cho, Tokushima 770-0042, Japan Email: hosaka@tokushima-u.ac.jp

Citation: Utsumi Y, Tagami J, Loomans B, Scotti N, Watanabe K, Matsuki S, Tanaka E, Hosaka K. Direct composite injection molding with bilayered three-dimensional-printed clear index: a fully digital workflow case report of post-orthodontic anterior tooth wear. 2026;51(3):e36.

Received 2025 November 15; Revised 2026 March 29; Accepted 2026 March 30.

Abstract

INTRODUCTION

Direct composite restoration of worn dentition is supported by a variety of clinical techniques. Several studies have shown that the choice of restorative approach does not significantly influence survival outcomes and that direct restorative approaches demonstrate favorable outcomes in the mid- to long-term [1,2]. A recent systematic review further confirmed that direct composite restorations are reliable treatment options, although their clinical execution may be technically demanding [3]. Consequently, new techniques and modifications to established protocols continue to emerge to improve predictability and efficiency.

Among these approaches, direct composite injection techniques have gained increasing attention for their minimally invasive nature [4–7]. This technique enables accurate reproduction of planned tooth morphology, reduces the need for extensive freehand sculpting, and facilitates the simultaneous treatment of multiple teeth. The growing adoption of this technique has been supported by advances in resin composite materials, particularly the development of injectable composites that combine improved flowability with adequate mechanical strength for clinical use. These material developments have expanded the clinical applicability of injection-based restorative procedures [8]. However, in multiunit anterior cases, precise placement and stabilization of the index can still be challenging.

Conventionally, clear silicone indices fabricated from wax-ups on stone models have been used to guide composite placement [9,10]. Although clinically useful, achieving the high level of precision required in contemporary restorative dentistry under high magnification remains a clinical challenge with these indices [11–14]. Digital technologies have therefore been introduced to enhance accuracy, reproducibility, and clinical efficiency. Computer-aided design (CAD) enables virtual wax-ups and the fabrication of silicone matrices [11,12], or fully three-dimensional (3D)-printed indices [15–19], thereby reducing manual steps and improving clinical control.

Despite these innovations, monolithic 3D-printed indices created from a single resin material may present several limitations, including limited translucency, insufficient adaptability, and potential deformation caused by polymerization shrinkage. Similarly, conventional silicone indices may deform when used for multi-tooth restorations and often require additional stabilization [20]. Although newer approaches, including flexible 3D-printed indices and hybrid stabilization systems [16,17], have provided incremental improvements, an efficient workflow for multiunit anterior restorations is still sought.

As a potential approach to these challenges, the present case report describes a fully digital workflow utilizing a bilayered 3D-printed clear index system. This index design incorporates a rigid transparent outer shell that provides structural stability and a flexible inner liner that passively adapts to the tooth surface. This bilayered configuration is intended to facilitate injection control, reduce excess composite resin, and minimize the risk of unintended interproximal bonding. In addition, the reduced internal volume may help limit 3D deformation associated with polymerization shrinkage. By eliminating the need for stone models and conventional silicone impressions, this workflow aims to simplify the clinical procedure. Therefore, the purpose of this case report was to present a fully digital workflow for direct composite injection molding using bilayered 3D-printed clear indices and to describe their clinical application in the minimally invasive management of post-orthodontic anterior tooth wear.

CASE REPORT

This case report complies with established ethical standards. Written informed consent was obtained from the patient for the publication of her clinical information and images. This report was prepared in accordance with the CARE (CAse REport) guidelines.

A 31-year-old female patient presented with complaints of masticatory disturbance and esthetic concerns. Clinical examination revealed significant wear of the maxillary and mandibular anterior teeth, which was attributed primarily to long-standing parafunctional activity. Posterior cusp wear was also observed, suggesting occlusal loading concentrated on the molars due to the anterior open bite. The anterior teeth exhibited moderate incisal enamel loss without obvious dentin exposure, corresponding approximately to a Basic Erosive Wear Examination (BEWE) score of 2 [21]. As posterior support and the vertical dimension of occlusion (VDO) were preserved, the overall wear risk was considered low to moderate.

At the initial examination, the patient also presented with anterior crowding (Figure 1). Orthodontic treatment was therefore planned in conjunction with restorative considerations. Because the maxillary anterior teeth were relatively small and space was available for morphological correction, it was anticipated that discrepancies in clinical crown lengths would become apparent once proper alignment was achieved. This possibility was discussed with the patient, and restorative procedures were planned to harmonize crown lengths following orthodontic treatment.

Figure 1.

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Accordingly, orthodontic tooth movement was directed toward aligning the gingival margins rather than the incisal edges, anticipating subsequent restorative correction of crown height discrepancies (Figure 2A). The patient was diagnosed with a severe anterior open bite, primarily associated with parafunctional habits. To address the skeletal discrepancy, corticotomy was performed on both buccal and palatal aspects of the maxillary molar regions (Figures 2B and C). Orthodontic anchorage was achieved using bilateral anchor plates placed on the zygomatic buttress and a mini screw inserted at the center of the hard palate. Following corticotomy, the bilateral molar segments were intruded by approximately 4.0 mm to correct the open bite.

Figure 2.

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The total active orthodontic treatment duration was 43 months, resulting in a functionally stable occlusion and improved facial profile. This outcome provided favorable conditions for anterior direct composite restorations. Near the completion of orthodontic treatment, the patient requested restorative enhancement. Therefore, fully digital preoperative records were obtained immediately prior to debonding, and minimally invasive definitive procedures were planned on the day of multibracket appliance removal.

Post-orthodontically, the patient presented with moderate incisal wear affecting the six maxillary anterior teeth. Although dentin exposure was not evident, she expressed esthetic dissatisfaction due to slight contour irregularities and incisal shortening. The occlusion remained stable, with maintained posterior occlusal stops and no clinical signs of VDO collapse. Despite the presence of posterior cusp wear, posterior support was preserved, and no reduction in lower facial height was observed. No signs or symptoms of occlusal instability or temporomandibular dysfunction were reported. Given this stable occlusal condition, the patient requested minimally invasive esthetic enhancement limited to the anterior region (Figure 3).

Figure 3.

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During restorative planning, a slight asymmetry in gingival levels between teeth #12–11 and #21–22 was evaluated. Because the periodontal tissues were healthy and the discrepancy was clinically subtle, periodontal recontouring was not indicated. In keeping with the minimally invasive treatment concept, surgical intervention solely to improve gingival symmetry was avoided. The restorative plan, therefore, aimed to refine anterior guidance and restore natural contours, with an incisal length increase of no more than 1 mm.

A fully digital workflow was employed. Intraoral scans were obtained using an intraoral scanner (Medit i700; Medit Corp., Seoul, Korea) (Figure 4A), and facial scans were captured using the RAYFace system (Ray Co., Ltd., Seoul, Korea) (Figure 4B). The datasets were imported into dental CAD software (3Shape A/S, Copenhagen, Denmark), and a complete digital wax-up was created for all six maxillary anterior teeth (#13–23) (Figure 4C).

Figure 4.

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To minimize interproximal bonding and improve finishing control, a skip-tooth version of the wax-up was subsequently generated according to the technique reported by Coachman et al. [22]. This approach allowed alternate-tooth restoration in two phases: first, teeth #13, #11, and #22, followed by #12, #21, and #23, using separate bilayered indices (Figure 4D–F).

Although no intraoral mock-up was performed prior to index fabrication, the digital design was evaluated with integrated facial scan data, and the patient approved the proposed outcome based on simulated smile previews (Figure 4G and H). Given the additive nature of the restorations and the minimal incisal adjustment required, direct application was considered clinically appropriate.

The bilayered clear index system consisted of a rigid transparent outer shell designed for structural accuracy and a flexible semitransparent inner liner for passive adaptation (Figure 4I–K). Each layer was independently fabricated using 3D printing: the outer shell using Dima Print Splint Clear (Kulzer GmbH, Hanau, Germany) and the inner liner using IBT-Flex resin (Formlabs, Somerville, MA, USA), both printed at a 50-μm layer thickness with a minimum material thickness of 1.5 mm. The indices were digitally designed with conical access and vent holes to enable controlled composite injection and material escape (Figure 4L).

Isolation was achieved using a cheek-lip-tongue retractor (Umbrella; Ultradent Products Inc., South Jordan, UT, USA) in combination with a split rubber dam (Optradam; Ivoclar, Schaan, Liechtenstein), allowing stable and passive seating of the flexible inner liner. The enamel surfaces of teeth #13, #11, and #22 were selectively etched with 37% phosphoric acid (K-etchant syringe; Kuraray Noritake Dental Inc., Tokyo, Japan) for 15 seconds, rinsed thoroughly with water, and air-dried (Figure 5A and B). A universal adhesive (Clearfil Universal Bond Quick 2; Kuraray Noritake Dental Inc.) was then applied following the manufacturer’s instructions and light-cured for 10 seconds using an LED curing unit (Pencure 2000; MORITA, Tokyo, Japan) with an output of ≥1,200 mW/cm².

Figure 5.

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Using the first index, a highly filled universal-shade injectable composite resin (Clearfil Majesty ES Flow Universal Low; Kuraray Noritake Dental Inc.) was injected through the access holes (Figure 5C). The index was fully seated with gentle pressure, allowing excess material to escape through the vent holes. Each restoration was light-cured for 20 seconds (Figure 5D). After polymerization, the index was removed (Figure 5E), and interproximal excess was refined with abrasive strips (New Metal Strips; GC Corp., Tokyo, Japan) (Figure 5F). Following index removal, an additional 20 seconds of light curing was performed for each restoration. The surfaces were then cleaned using a 10-methacryloyloxydecyl dihydrogen phosphate salt-based surface cleaner (Katana Cleaner, Kuraray Noritake Dental Inc.) (Figure 5G).

The second index was subsequently used to restore the remaining teeth (#12, #21, and #23) using the same protocol. Occlusion was verified with 40 μm articulating paper, and minor occlusal adjustments were intentionally performed to refine functional contacts and harmonize lateral movements. This clinical decision prioritized dynamic functional occlusion over the static digital design, resulting in a slight modification of the planned canine morphology for tooth #23. All restorations were finished and polished using silicone points (Jiffy Natural; Ultradent Products Inc.) (Figures 5H and I).

At the 6-month follow-up, all restorations remained intact with excellent marginal adaptation. Anterior guidance was maintained during protrusive movement, while lateral excursions were characterized by stable canine guidance. Functional disocclusion was clinically verified, confirming canine-dominant contact without premolar-only guidance. No fractures or material failures were observed. The slight difference in the incisal morphology of tooth #23 compared with the initial digital plan reflected minor occlusal adjustments aimed at optimizing functional guidance, as well as small discrepancies inherent to the clinical injection procedure (Figure 6A–C).

Figure 6.

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The patient reported high satisfaction with both esthetic and functional outcomes. Because the tooth wear was associated with parafunctional activity, a maxillary night guard was delivered. Regular recall visits were scheduled at 3-month intervals for occlusal and restorative reevaluation. Clinical findings remained stable during subsequent follow-up visits. The observation period currently extends to 15 months (Figure 6D and E); however, continued long-term monitoring is necessary to evaluate the durability and functional stability of this minimally invasive restorative approach.

DISCUSSION

The minimally invasive restoration of anterior tooth wear, particularly in young adults, requires treatment strategies that preserve enamel while providing predictable esthetic and functional outcomes. In the present case, the discrepancy in clinical crown lengths was not primarily caused by orthodontic treatment but was already present at the initial examination. It was anticipated that once proper alignment was achieved, the disharmony of crown lengths would become more evident. Although minor additional incisal wear may have occurred during orthodontic treatment, the main discrepancy reflected the pre-existing condition. This factor was incorporated into the interdisciplinary treatment plan. Orthodontic tooth movement was intentionally directed toward aligning the gingival margins rather than the incisal edges, allowing the correction of crown height discrepancies to be achieved by subsequent restorative procedures.

In the present case, the residual gingival asymmetry was clinically minor and considered acceptable. Complete correction would have required additional orthodontic or periodontal intervention, which would have increased treatment invasiveness without providing meaningful esthetic or functional benefit. Therefore, further correction was not pursued in view of overall facial harmony and the patient’s satisfaction with the outcome. This treatment strategy highlights the importance of early interdisciplinary collaboration between orthodontics and restorative treatment planning, ensuring that tooth movement is guided by the anticipated restorative outcome and leading to a more predictable and esthetic result.

Direct composite injection molding using an index-guided approach has emerged as a conservative alternative to indirect restorations [7]. However, conventional workflows often involve multiple manual steps and may provide limited precision when applied to multi-tooth restorations. The bilayered index configuration used in this report was designed to address several of these limitations.

The system incorporates a rigid transparent outer shell that provides structural stability during flowable composite injection and a flexible inner liner that passively adapts to the tooth surface. This dual-layered design may facilitate accurate seating of the index, controlled composite injection, and simplified removal after polymerization. In addition, the reduced internal injection volume may help limit excess composite flow and potentially reduce the risk of unintended interproximal bonding.

Previous designs involving flexible indices typically required auxiliary stabilization devices to maintain positioning [16,17], and earlier bilayered concepts have mainly been reported in limited clinical situations, such as pediatric cases [20]. In contrast, the present configuration was applied to adult anterior restorations within a fully digital workflow. The use of a skip-tooth wax-up design, based on the concept described by Coachman et al. [22], further improved control of interproximal contours and facilitated finishing procedures. By restoring alternate teeth in the first phase, sufficient interproximal space was maintained during composite injection, which helped limit unintended interproximal bonding and improved access for finishing and polishing.

From a structural perspective, the current design differs from previously reported indices in several aspects. Technically, structural stabilization and surface adaptation are separated into two independent components. Geometrically, the internal injection volume is intentionally reduced, providing a more controlled pathway for composite flow and potentially limiting deformation associated with polymerization shrinkage. From a material standpoint, the combination of resins with different elastic moduli allows controlled seating while maintaining passive adaptation. Together, these characteristics may distinguish the present configuration from previously reported flexible matrices or monolithic printed indices.

The structural rationale of this concept is supported by a recent in vitro study evaluating different index designs using root-mean-square (RMS) analysis, which demonstrated improved trueness and precision of the bilayered configuration compared with conventional monolayer indices [23]. However, these laboratory findings should be interpreted with caution when extrapolated to clinical situations, and further clinical studies are necessary to confirm these observations. In addition, pre-clinical verification can be performed through a trial composite injection on a 3D-printed model, allowing the injected composite to be compared with the original CAD design. In the present workflow, such verification suggested that dimensional discrepancies appeared to remain within a clinically acceptable range.

Despite these advantages, several limitations should be considered. First, the 3D printed flexible inner layer may exhibit limited elastic recovery after repeated use, which could potentially affect adaptation. Second, fabrication of the index requires access to CAD software and high-resolution 3D-printing equipment, which may not be available in all clinical or laboratory settings. Third, proper post-processing of the printed index is critical. Incomplete washing or insufficient post-curing of the printed index may leave residual uncured monomer on the internal surface, potentially causing adhesion between the index and the composite resin. Thorough cleaning, typically using isopropyl alcohol, followed by appropriate post-curing under standardized conditions, is therefore essential. Fourth, cost considerations should be acknowledged. The technique requires fabrication of two separate indices, which may increase material consumption and production time compared with single-index approaches. Nevertheless, when compared with indirect ceramic restorations, the technique may represent a conservative and cost-effective alternative, particularly in multiunit anterior cases where preservation of tooth structure is a primary objective.

Although full-arch rubber dam isolation is generally recommended for adhesive procedures, it was not employed in this case because the tension generated during placement could potentially distort the flexible inner liner of the bilayered index. Instead, effective isolation was achieved using a cheek-lip-tongue retractor in combination with a split-dam technique, which provided sufficient control of moisture and visibility. In addition, the use of Katana Cleaner has been reported to efficiently remove contamination from saliva, blood, and temporary materials [24], thereby supporting reliable bonding performance.

While the relatively rigid outer layer of the index may help counteract dam tension and allow seating under compression, future CAD developments may further improve dam adaptation through margin-scalloped designs. Nevertheless, isolation strategies should remain flexible and goal-oriented, prioritizing optimal clinical control rather than strict adherence to a single standardized approach.

As this report describes a single clinical case without quantitative validation, the findings should be interpreted with caution as clinical observations rather than outcomes. Minor deviations from the digital plan may occur due to the inherent variability of the injection procedure or intentional occlusal adjustments to harmonize the restoration with functional guidance. While the short-term outcome was favorable, future prospective studies with larger cohorts and quantitative measurements are required to objectively evaluate the durability, seating accuracy, dimensional stability, and clinical reproducibility of this digital workflow. Nevertheless, this case illustrates the clinical feasibility of the proposed technique and provides a foundation for further systematic investigation.

CONCLUSIONS

The bilayered 3D-printed clear index system used within a fully digital workflow facilitated precise, minimally invasive restoration of post-orthodontic anterior tooth wear in a single clinical session. This approach enabled controlled composite injection and efficient finishing while maintaining the planned tooth morphology. Within the inherent limitations of this single case study, this technique suggests a potential conservative alternative for the management of anterior tooth wear. Further clinical studies with larger sample sizes and longer follow-up periods are required to confirm its long-term performance and broader applicability.

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