Defect-orientated onlay with cavity design optimization and cervical margin relocation: case report

Introduction

The decision to restore a vital tooth with severe carious lesions and the workflow involved depend on several factors, including the treatment options (direct or indirect restorations), the material choice for indirect restorations (composite resin or ceramic-based materials), the preparation (defect-oriented, tissue-conservative), and the detailed clinical protocol (cavity design, luting, etc) 1,2.

There has been a growing tendency over the last few decades toward minimally invasive restorations and the preservation of valuable tooth structure, which is supported today by the rapid development of high-strength restorative materials as well as advanced, durable luting agents. Several techniques and a variety of materials are available for the fabrication of inlays and onlays; however, the decision about which technique and materials to use should be based on the individual clinical situation in respect to evidence- based concepts. In extensive carious lesions, as in the case of severely damaged or decayed teeth, especially those with thin walls, indirect restorations are recommended rather than direct fillings because the latter can induce unfavorable stresses on the remaining tooth structure due to polymerization shrinkage 1-7.

Regarding indirect restorations for inlays and onlays, composite resin-based CAD/CAM materials are considered to have several advantages over ceramics such as easy manufacturing, lower cost, and simpler repairability 3. One clinical issue for such indirect restorations is finding the balance between tissue conservation and a stable, appropriate preparation design. Therefore, certain treatment concepts such as immediate dentin sealing (IDS), cavity design optimization (CDO), and cervical margin relocation (CMR) can be very helpful to the practitioner in order to avoid the unnecessary sacrifice of tooth structure. For instance, a slight cavity convergence is required for the insertion of a restoration; therefore, in case of undercuts, tooth structure needs to be removed to achieve this convergence.

Such undercuts can be filled using the CDO technique, which means that no removal of healthy tooth structure is required. These comprehensive clinical techniques were introduced originally by Dietschi and Spreafico 8,9 and are described in detail in several publications 1-4. The clinical case presented in this article employs some of these concepts and demonstrates how to utilize them in challenging clinical situations. To date, IDS has been extensively studied, with several clinical advantages reported in the literature 8-12. Immediate application of an adhesive dentin bonding agent to the freshly cut dentin prior to impression taking has several advantages such as reduced dentin sensitivity, improved bond strength, fewer gap formations, and less consequential bacterial leakage 10,11. Additionally, IDS was shown to stabilize the restoration, especially in the case of thin occlusal veneers 13.

The technique of CDO is implemented by applying a composite liner (mainly flowable composite resin) directly after IDS to fill any undercuts in the cavity and optimize the cavity geometry 1-3,8. Generally, highly filled flowable composites are recommended instead of conventional restorative composites due to their ease of use 2,3. Nowadays, these composites are available with different viscosities, so practitioners can choose according to their personal handling preferences. In the clinical case presented here, two viscosities of flowable composites were used.

In severely damaged teeth, the margins of the cavity can extend subgingivally, which complicates the impression-taking procedure. It also complicates proper adhesive luting, which is necessary for minimally invasive partial-coverage restorations. In such cases, therefore, CMR can be very useful. After proper positioning and adaptation of the matrix, CMR is implemented through the elevation of deep proximal cavity margins with composite resin 2,3,8,9. In the present case, the treatment plan and protocol combine multiple evidence-based clinical concepts and techniques 2-5,14-16 for restoring a maxillary right first molar with an indirect CAD/CAM onlay.

Case presentation

A 32-year-old male patient presented with an endodontically treated maxillary right first molar that was restored with a temporary restoration. The overall periodontal status was stable, and the patient had good oral hygiene with no other carious lesions. Therefore, according to a synoptic treatment concept, no pretreatment was deemed necessary. The patient was presented with all possible treatment options, starting with a conventional full-coverage crown. However, he was advised to choose, and decided upon, a minimally invasive defect-oriented overlay. After removal of the temporary filling, it was established that the palatodistal cusp and both buccal cusps were severely undermined, with a wall thickness of < 1 mm. After excavation of some remaining caries, the mesial cavity margins were located subgingivally (Fig 1).

Fig 1 Situation after removal of the temporary filling and remaining caries lesions showing a deep subgingival mesial cavity margin.

Clinical procedure

During the first session, the remaining caries were removed. Then, rubber dam was placed and positioned with the help of ligatures, a metal matrix band, and a wedge, to include the deep subgingival mesial margin (Fig 2). All exposed dentin was sealed through IDS using a universal one-bottle adhesive system (Clearfil Universal Bond Quick; Kuraray Noritake Dental, Japan) after an etch-and-rinse technique using phosphoric acid (K-Etchant Syringe; Kuraray Noritake Dental) on the enamel for 30 s and on the dentin for 10 s (Fig 3). The universal adhesive was applied and rubbed into the tooth structure for 3 s, according to the manufacturer’s instructions, followed by gentle air drying and light curing (Elipar 2500; 3M ESPE, Neuss, Germany) for 10 s. Directly after the IDS procedure, a flowable composite resin (Clearfil Majesty ES Flow Low A3; Kuraray Noritake Dental) was used to elevate the deep mesial margin to a supragingival level, and was carefully adapted and subsequently light cured (Elipar 2500) for 20 s. Then, CDO was performed to seal all sharp margins and fill the undercuts. This procedure was carried out using a more viscous, highly filled, flowable composite resin (Clearfil Majesty ES Flow Super Low A3; Kuraray Noritake Dental) that has less flowability and can therefore be easily adapted in one increment, followed by light curing (Fig 4).

Successively, the preparation was optimized under the continuous use of rubber dam by removing all walls of a thickness of < 1 mm and creating a proper path of insertion for the proximal boxes (Fig 5) 2. At the end of the first treatment session, an impression was taken and the tooth was isolated with Vaseline, except for a small central spot to create a semi-adhesion 2. The tooth was then temporarily restored using composite restorative material without adhesive (Clearfil Majesty ES-2; Kuraray Noritake Dental).

Fig 2 Adaptation of rubber dam and the matrix, allowing good accessibility for the CMR procedure.