Case Report on Tunnel Restoration: A Minimally Invasive Approach for Interproximal Caries

By Prof. Hien Ngo and Dr. Vivian Nguyen

Introduction  

The evolution of dental treatment modalities has increasingly shifted toward conservative and preventive strategies. Within this context, the techniques of tunnel preparation and tunnel restoration (TR) have garnered renewed interest (Mount et al. 2005). Developed over fifty years ago, tunnel preparation was specifically designed for the restoration of interproximal caries in molars, accessed through the occlusal surface beneath the marginal ridge (Knight, 1991). A key advantage of tunnel restoration, as compared to traditional box or slot preparations, is its conservative nature, significantly enhancing tooth integrity and strength by preserving the marginal ridge.

Historically, tunnel restoration faced challenges related to high failure rates; however, it has regained prominence due to advancements in adhesive formulations and restorative materials, notably Equia Forte HT (GC, Japan), an innovative glass ionomer cement that employs Glass Hybrid Technology. Additionally, enhancements in dental technologies — including compact electric handpieces equipped with LED lighting and magnifying loupes — have facilitated more effective implementation of this technique. The use of cone beam computed tomography (CBCT) has further contributed to the planning of this procedure when available.

Background  

Research studies conducted before 2000 indicated that the success rate of tunnel restorations utilizing glass ionomer ranged from 57% to 90% over periods of up to three years, with a median survival rate of approximately six years (Strand et al. 2000). Long-term follow-up studies have reported a success rate of about 50% over a seven-year period. In contrast, (Kinomoto et al. 2004) demonstrated that tunnel restorations achieved a notable 96% success rate within two years. Although technically demanding, tunnel restoration can proficiently address proximal carious lesions when undertaken with meticulous case selection and skilled technique.

Cavity Preparation for Tunnel Restoration  

The cavity preparation process associated with tunnel restoration is distinguished by the minimal removal of dental tissue compared to conventional Class II box and slot preparations (Nizami et al. 2022). A significant advantage of this technique is its ability to preserve demineralized enamel in the interproximal area, provided that the enamel remains uncavitated, thereby maintaining tooth structure integrity through the retention of the marginal ridge.

The remineralizing properties of glass ionomer cement are well-documented, attributed to the release of fluoride and strontium ions from the material. This characteristic renders glass ionomer particularly suitable for tunnel restorations.

Tunnel preparations may be classified (Nizami et al. 2022) based on the extent of enamel preservation as follows:

1. Total Tunnel: Complete removal of demineralized proximal enamel.

2. Partial Tunnel: Partial removal of the proximal surface, retaining some demineralized enamel.

3. Internal Tunnel: Complete retention of proximal enamel.

Case Example  

This case report details a patient presenting with a carious lesion on the distal aspect of the right maxillary first molar. Informed consent was obtained for both the dental intervention and the publication of clinical photographs. A cone beam computed tomography (CBCT) scan performed prior to planning an implant replacement for a significantly damaged first premolar allowed for the assessment of the carious lesion and confirmed that the distal proximal enamel was intact (Figures 1a and 1b), thereby providing valuable information for determining the access path to the lesion. An internal tunnel restoration was performed using glass ionomer cement reinforced with a nano-filled resin coat (Equia Forte HT, GC, Japan) as these have been indicated for Class II restorations in posterior teeth.

Following the placement of a rubber dam, an occlusal access cavity was prepared at the dentin-enamel junction (DEJ) to facilitate access to the carious area, with adjacent tooth surfaces protected by a Fender Wedge (Directa, Sweden) (Figure 2). A long-shank size 3 round bur was utilized to remove any residual carious tissue (Figure 3). The cavity was conditioned with 10% polyacrylic acid (Dentin Conditioner, GC, Japan) for 20 seconds, followed by thorough rinsing and drying (Figure 4). The completed cavity preparation was recorded (Figure 5).

Glass ionomer (Equia Forte HT, GC, Japan) was carefully injected into the cavity, minimizing the risk of air entrapment at the base (Figure 6). Excess material was diligently removed using a large microbrush to ensure optimal anatomical conformity (Figure 7). The glass ionomer restoration was then coated with a nano-filled resin (Equia Forte Coat, GC, Japan) (Figure 8). No occlusal adjustments were necessary, and postoperative radiographs confirmed satisfactory adaptation of the restoration.

Conclusion  

Tunnel restoration represents a viable and conservative permanent intervention for the management of proximal caries. Ongoing research is essential to refine diagnostic approaches, establish site-specific indicators for future caries risk, and develop comprehensive guidelines for caries management. Given the technical complexities associated with tunnel restoration, successful outcomes depend on meticulous case selection, precise preparation techniques, and judicious choices in restorative materials. The integration of advanced technologies, such as magnifying loupes, digital radiography, and LED-equipped handpieces, significantly enhances the likelihood of favorable outcomes. Further long-term clinical studies are imperative to elucidate the success and failure rates of tunnel restoration techniques in comparison to conventional restorative methods. 

Keywords: Tunnel Restoration, Interproximal Caries, Minimally Invasive Dentistry, Glass Ionomer, Conservative Restoration Techniques.

References

• Mount GJ, Hume WR. Classification and Cavity Preparation for Caries Lesions; Preservation and Restoration of Tooth Structure. Knowledge Books and Software; 2005.
• Knight GM. The tunnel restoration. Dent Outlook. 1984;10:53–57.
• Strand GV, Nordbø H, Leirskar J, von der Fehr FR, Eide GE. Tunnel restorations placed in routine practice and observed for 24 to 54 months. Quintessence Int. 2000;31(7):453–460.
• Nizami MZI, Yeung C, Yin IX, Wong AWY, Chu CH, Yu OY. Tunnel restoration: A Minimally Invasive Dentistru Practice. Clinical, Cosmetic and Investigational Dentistry 2022:14