|Year : 2021 | Volume
| Issue : 1 | Page : 100-104
|Morphology-driven preparation technique for posterior indirect bonded restorations
Vibha Rahul Hegde1, Sharmika Rajan Joshi2, Sanjeevani A Hattarki3, Ashwin Jain4
1 Department of Conservative Dentistry and Endodontics, Dr GD Pol Foundations YMT Dental College and Hospital, Navi Mumbai, India
2 Department of Conservative Dentistry and Endodontics, Dr GD Pol Foundations YMT Dental College and Hospital, Thane, Maharashtra, India
3 Department of Conservative Dentistry and Endodontics, Maratha Mandal Dental College and Research, Belgavi, Karnataka, India
4 Department of Conservative Dentistry and Endodontics, YMT Dental College and Hospital, Navi Mumbai, India
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|Date of Submission||22-Sep-2020|
|Date of Decision||10-Oct-2020|
|Date of Acceptance||10-Oct-2020|
|Date of Web Publication||05-Jul-2021|
| Abstract|| |
Restorative treatment in recent times has seen a paradigm shift due to minimally invasive adhesive dentistry. With advent of material science, bonding mechanisms, and superior isolation techniques, treatments based entirely on adhesion are effectively attainable. The choice between direct and indirect restorative technique, mainly in posterior areas, is still a challenge and involves biomechanical, anatomical, functional, esthetic, and economic considerations. The rationale of this case report is to demonstrate a revised cavity design based on morphological principles in terms of geometry (height of contour and cuspal inclines) and structure (dentinoenamel junction morphology) inspired from conventional preparation techniques.
Keywords: Bioemulation; bonded; height of contour; immediate dentin sealing; lithium disilicate
|How to cite this article:|
Hegde VR, Joshi SR, Hattarki SA, Jain A. Morphology-driven preparation technique for posterior indirect bonded restorations. J Conserv Dent 2021;24:100-4
|How to cite this URL:|
Hegde VR, Joshi SR, Hattarki SA, Jain A. Morphology-driven preparation technique for posterior indirect bonded restorations. J Conserv Dent [serial online] 2021 [cited 2021 Aug 4];24:100-4. Available from: https://www.jcd.org.in/text.asp?2021/24/1/100/320672
| Introduction|| |
In modern restorative dentistry, the development of adhesive procedures has driven the occurrence of a significant cultural and methodological revolution. Adhesive dentistry in the posterior quadrant is not only linked to esthetic purposes but also to bioeconomic principles and biomechanical strengthening of the existing tooth structure. Microhybrid and nanoparticle composites are the materials of choice for posterior restorations. However, there a few technical and clinical challenges inherent in the performance of direct composite restorative techniques. The technical challenges include polymerization shrinkage and adhesion to dentin, while the clinical challenges include the ability of the clinician to achieve adequate isolation as well as reestablish the original tooth morphology. Thus, to address these concerns, there has been an increase in the use of posterior indirect bonded restorations, creating a new paradigm balance between operative “restorative” dentistry and prosthodontics.
An “adhesive indirect restoration” has been defined as a partial crown restoration made of composite or full ceramic that must be seated passively and adhesively cemented in a cavity characterized by specific attributes. Current indications for indirect adhesive restorations are summarized as wide Class II cavity with cusp coverage (one or more); restoration of a large occlusal surface compromised by wear and/or biocorrosion; the necessity of performing multiple restorations in several quadrants with modification of the entire occlusion; the need to reestablish or increase the vertical dimension; cuspal coverage of endodontically treated teeth; and to manage teeth prone to fracture due to loss of tooth structure. Hitherto, clinicians have been following conventional preparation techniques for posterior adhesive indirect restorations for cuspal coverage; however, such could expose sound dentin with a significant loss of tooth structure. Hence, the bioemulation models put forth by Bazos and Magne suggest certain structural and geometrical criteria that should be considered before planning an indirect adhesive restoration requiring cuspal coverage. These criteria include the height of contour, the sigmoid nature of the enamel dentin interface, and the direction of enamel rods with respect to the axial and proximal surfaces. These concepts of bioemulation were incorporated by Veneziani to devise this novel cavity design. The objectives of the novel morphological driven cavity designs are to improve the quality of adhesion by optimizing the cutting of enamel prisms and increasing the available enamel surface, to minimize dentin exposure, to maximize hard tissue conservation, and to optimize esthetic integration. The rationale of the present two patient case series is to demonstrate the use of a revised cavity design based on morphological principles in terms of geometry (height of contour and cuspal inclines) and structure (dentinoenamel junction morphology) inspired by conventional preparation techniques.
| Case Reports|| |
A 23-year-old male was referred to the Department of Conservative Dentistry and Endodontics with a chief complaint of food lodgment in the left maxillary second molar. His medical history was noncontributory. Clinical examination revealed a carious lesion involving the distobuccal cusp of the left maxillary second molar. Pulp vitality was performed using cold test which inferred as normal pulp as per the AAE classification. Radiographic evaluation revealed a radiolucency with the distobuccal cusp, involving the enamel and dentin [Figure 1]a and [Figure 1]b. The treatment plan was to restore the distobuccal cusp with an indirect ceramic restoration. An excavation of caries was performed using a number 2 carbide bur [Figure 1]c. Immediate dentin sealing (IDS) was subsequently executed using a flowable microhybrid composite (Tetric N-Flow Ivoclar Vivadent, Schaan, Liechtenstein) [Figure 1]e. Preparation and finishing of the cavity was completed according to the new modified principles of a morphology-driven preparation technique [Figure 1]d: red: divergent walls 6° to 10°, yellow: shoulder margin (one - one point two mm), and white: anatomical reduction. This technique involved preparing the buccal margin of the restoration into a shoulder influenced by the enamel dentin morphology and arranging the inner walls into a divergence of 6°–10°, as discussed further in this article [Figure 1]d. A definitive impression was made using an addition silicone elastomeric impression material (Aquasil Soft Putty; Aquasil Soft Putty, York, PA, USA). The preparation was provisionalized using provisional composite resin (Systemp.onlay; Ivoclar Vivadent, Schaan, Liechtenstein) [Figure 1]f. Final restoration was fabricated with a pressed lithium disilicate glass ceramic material (IPS e.max; Ivoclar Vivadent, Schaan, Liechtenstein). Adhesive cementation was performed using an adhesive dual-cure luting resin (Variolink Esthetic DC; Ivoclar Vivadent, Schaan, Liechtenstein) [Figure 1]g. Follow-up after 2 years showed slight discoloration at the margins. Otherwise, the restoration was in perfect health [Figure 1]h.
|Figure 1: (a and b) Preoperative images. (c) Caries excavation. (d and l) Illustration. (e) Immediate dentin sealing. (f) Temporisation. (g) Bonding. (h) Two-year follow-up. (i and j) Preoperative images. (k) Preparation. (m and n) Bonding. (o) Final restoration. (p) Two-year follow-up|
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A 35-year-old female reported to the Department of Conservative Dentistry and Endodontics with pain in the right maxillary first molar. Her medical history was deemed to be noncontributory. Clinical examination revealed a deep carious lesion on the mesioproximal surface. Radiographic evaluation revealed a radiolucency that involved enamel dentin and pulp. A subsequent evaluation after vitality tests confirmed a diagnosis of symptomatic irreversible pulpitis. Following the completion of endodontic therapy, the patient was rendered symptomless and considered for an indirect bonded restoration with cuspal protection [Figure 1]i and [Figure 1]j. First, the interproximal box on the mesial and distal aspects was prepared into a butt joint or a rounded shoulder with a 1 mm to 1.2 mm thickness using a rounded taper fissure bur. Second, the interior walls were prepared using a divergence of 6°–10° with rounded inside angles to prevent stress concentration. Third, occlusal reduction up to a clearance level of 1.5 mm following the cuspal morphology was ensured. Finally, axial wall preparation on the buccal and lingual surfaces was completed, involving the placement of a chamfer margin. The preparation design along with an illustration is presented in [Figure 1]k and [Figure 1]l yellow: shoulder margin (1–1.2), green: hollow chamfer on the axial walls, white: anatomical reduction. The final optimization of the restoration was carried out as per the first case [Figure 1]m,[Figure 1]n,[Figure 1]o. Two-year follow-up was done [Figure 1]p; no significant changes were observed in the restoration.
| Discussion|| |
It has been affirmed that conserving the original healthy tooth structure retains the resistance form of the tooth by improving the tooth biomechanics and stress distribution., Furthermore, while restoring endodontically treated teeth, lithium disilicate bonded overlays instead of full-coverage crowns have been proven to conserve tooth structure at the critical pericervical area. The morphology-driven technique is governed by certain structural and geometric characteristics for optimizing tooth preparation for indirect adhesive restorations. As put forth by Bazos and Magne, the preparation design should consider the bioemulation criteria such as the height of contour, the sigmoid nature of the enamel dentin interface, and the direction of enamel rods with respect to the axial and proximal surfaces.
A three-dimensional structural analysis has indicated that dentin and enamel have a sigmoid interface at the height of contour, with dentin being concave and enamel being convex, respectively. In the case of maxillary teeth, the buccal and palatal axial walls are inclined and converge in the coronal direction, with the height of their contour occurring in the cervical third [Figure 2]a. Hence, employing sharp-cut margins would produce oblique sectioning of the enamel prisms along their long axis, making them less favorable for bonding [Figure 2]d and [Figure 2]e. Dietschi et al. and Veneziani, have proposed that, whenever the axial margin is above the height of contour, a hollow ground or concave bevel can be used to prepare the enamel rods transversely to their long axis, making it a more desirable substrate for bonding [Figure 2]c. Furthermore, topographically, the concavity of the dentin is located in the middle third and coronal to the height of contour. A shoulder margin in this scenario would lead to unnecessary exposure of dentin and prepare the enamel rods longitudinally, resulting in the substrate being less favorable for bonding. A hollow ground or a concave bevel margin, however, would precisely cut the enamel convexity only, refraining from exposing the dentin concavity.
|Figure 2: (a and b) Bioemulation model maxillary premolar and mandibular premolar, Credit note: (a and b) Bazos and Magne. (c and d) Transverse, longitudinal sectioning of enamel rods. (e) Hollow chamfer preparation, Credit note: (c-e) Veneziani|
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On the contrary, in mandibular teeth, structural considerations suggest that the enamel is convex, but the dentin is more rectilinear on the lingual aspect with the height of contour occurring more occlusally [Figure 2]b. Hence, a shoulder on the lingual surface and a chamfer on the buccal aspect are justified. Interproximally for both maxillary and mandibular teeth, the walls converge apically, and the maximum contour line is positioned occlusally. Hence, the margin design here is a rounded shoulder. Any inclined or beveled plane is contraindicated, because such would shift the margin apically, thereby reducing the cervical enamel thickness that is critical to exist for bonding. This shoulder preparation also yields adequate thickness and enhanced fracture resistance for the restoration.
The occlusal reduction is driven by cuspal morphology, desired thickness of the material of choice (1–2 mm for lithium disilicate or composite) and quantity of unsupported enamel. The reduction of the wall was performed until sound dentin buttressed the enamel. In order to impart a resistance form to the tooth, both the thicknesses of the enamel and dentin must be considered. The occlusion and the masticatory load under function should be evaluated. The extent of the occlusal reduction is a function of the strength parameters of the restorative material; thus, 12 mm is recommended for lithium disilicate (pressed or computer-aided design/computer-aided manufacturing)., It is desirable to perform the occlusal reduction guided by the depth cuts or, when possible, by properly cut silicone indices placed on the tooth before preparation. The interior walls should have a divergence of 6° to 10° with rounded inside angles to prevent stress concentration.
With regard to material selection, Kois et al. demonstrated that lithium disilicate-reinforced ceramic showed a higher degree of fracture resistance and a lower risk of catastrophic failures as compared with composite restorations. The modulus of elasticity of lithium disilicate (95 GPa), which is almost as close as that of enamel (84.6 GPa), mimics the biomechanical behavior of the tooth. In addition, in a finite element analysis performed by Ma et al., it was concluded that, when supported by enamel, the load-bearing property of minimally invasive lithium disilicate occlusal onlays (0.6–1.4 mm thick) can exceed 70% of that of zirconia. Furthermore, the hollow ground or concave bevel preparation on the axial wall helps to maintain the bulk of the ceramic material. The first case in the present case series is a vital tooth requiring a cuspal restoration. IDS was incorporated in this case before making impressions for indirect restoration. This technique has been shown to improve bond strength, as freshly cut dentin is an ideal substrate for bonding and helps to protect dentin against bacterial leakage and sensitivity during provisionalization.,
The morphologically driven preparation technique improves resistance by preserving dentin and enamel, bond strength by improving the quality of bonding substrate, and the marginal integrity and esthetics of the restoration, respectively. However, the primary limitation faced in both of the present cases was in maintaining the thickness of the restorations, which becomes crucial during fabrication. Gupta et al., when comparing the fracture resistance of endodontically treated teeth restored with bonded partial coverage restorations and full-coverage crowns, concluded that teeth with a loss of functional cusp can be better treated with full-coverage restorations than with partial coverage ones.
| Conclusion|| |
According to the morphologically driven preparation technique, when the axial margin is below the height of contour, a shoulder is recommended, and when it is above the height of contour, a concave hollow ground bevel is recommended, respectively, to achieve a better bonding substrate influenced by the morphological and structural criteria. The use of this cuspal restorative approach for posterior teeth instead of full-coverage crowns will create a balance between prosthetic and restorative treatment planning.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initial s will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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Dr. Sharmika Rajan Joshi
Department of Conservative Dentistry and Endodontics, Dr GD Pol Foundations YMT Dental College and Hospital, Thane - 400 601, Maharashtra
Source of Support: None, Conflict of Interest: None
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