Current concepts in restoring endodontically treated teeth

Case selection and treatment planning

Prior to the restoration of ETT, conducting a thorough restorability assessment is essential. Multiple systems have been developed to evaluate the complexity involved in restoring ETTs. Among these, the Restorative Difficulty Evaluation System (RDES) offers a structured approach to categorizing the challenges.⁸ The RDES classifies restoration parameters into three risk levels: low-risk, moderate-risk, and high-risk.

According to the RDES criteria, a tooth is considered low-risk if all parameters are within the low-risk category or, at most, one falls into the moderate category. A moderate-risk classification is given when at least two parameters are moderate, with none in the high-risk category. A tooth falls into the high-risk category if there is at least one parameter assessed as high-risk. This system provides a framework to assist in the decision-making process for the restoration of an ETT.

The RDES criteria are presented in Table 1, which summarizes the categories into low (green), moderate (orange) and high (red) risk.

Number of residual walls or ferrule effect and residual tooth volume

The ability of a tooth to endure and withstand chewing forces is directly linked to the amount of remaining tooth structure.⁹ Hence, assessing the remaining tooth structure before restoring an ETT is considered crucial.

A coronal residual tooth height of 1.5–2 mm contributes to the ferrule effect, positively influencing the prognosis for restoring ETT.¹⁰ The presence of sufficient peri-cervical dentine further augments tooth survival.¹¹ Recent evidence challenges the traditionally held belief that a complete circumferential band of ferrule (Figure 1), is imperative for a favourable prognosis. Instead, emerging perspectives suggest that the presence of a partial ferrule (involving one to three walls) may suffice.^12,13 However, this still needs to be validated through long-term prospective clinical studies.

Preserving the peri-cervical dentine and access cavity preparation

Peri-cervical dentine (PCD) is an area approximately 4 mm coronal and 4 mm apical to the crestal bone.¹¹ This region serves as the neck of the tooth, facilitating the transmission and dissipation of masticatory forces to the root and surrounding bone. Gaining access for root canal therapy often results in cavity preparations that are large, gouged, and undermined, leading to the loss of PCD. Consequently, there has been a shift from traditional access cavity shapes to more conservative forms to preserve PCD.

In contrast to the traditional access cavities (TAC) that are associated with greater removal of tooth structure, conservative access cavities (CAC) are designed to retain more tooth structure, thus providing enhanced structural support.¹⁴ This may prompt considerations for materials that can effectively function with the remaining walls while ensuring structural integrity.⁹

In ultra-conservative access cavity design (UCAC), also recognized as orifice-directed design or ‘truss’ access cavity or ninja access cavity, distinct preparations involve separate cavities to access the mesial and distal canal systems in a mandibular molar. In the case of maxillary molars, a single cavity is employed to access both the mesio- and distobuccal canals, while another cavity is used for the palatal canal (Figure 2).¹⁵

UCAC aims to preserve even more tooth structure, potentially impacting disinfection and obturation owing to its limited access. While it may hinder complete debridement and canal visualization, advances in endodontic technology may mitigate these issues. This approach is recommended for teeth with sufficient structural integrity where conservation is a priority, but may not be suitable for cases requiring extensive canal treatment, or in the presence of complex root canal anatomy. Clinical judgement should guide the decision to employ UCAC, balancing the need for structural preservation against the requirement for effective canal disinfection and filling. This response succinctly addresses the disinfection and obturation concerns associated with UCAC and outlines the considerations for its recommended use.

Relationship of ETT cavity margins with gingiva and periodontium (Figure 3)

Tooth-restoration margins are a critical link between the tooth structure and the restoration. The relationship of cavity margins with supporting soft tissues directly affects the survival of ETT. The presence of a gap, or interference in this area of the tooth, can lead to detrimental consequences, including microleakage-induced secondary caries, increased vulnerability to fractures, displacement of the restorative material, reduced strength, compromised aesthetics and localized periodontitis through plaque stagnation.¹⁶

Restoring large carious defects resulting from proximal caries that extend below the cemento-enamel junction (CEJ), with subgingival cavity margin location in an ETT is a prevalent clinical scenario.

A deep proximal cavity margin presents unique challenges, notably in ensuring effective moisture control, achieving reliable dentine bonding, and delivering adequate light curing in a deep box preparation. Such procedures are inherently technique sensitive owing to the intricate nature of operating in a confined space close to the gingival tissue. Additionally, there is a heightened risk of violating the supracrestal attachment, also known as the biological width, which can lead to periodontal inflammation and recession if not carefully managed. To prevent any detrimental effect of cavity margins on adjacent gingival and periodontal tissues, a recommended distance of 3 mm or more between the restorative margins and the alveolar crest is considered necessary.¹⁷

In many clinical scenarios, when the biological width is compromised, procedures, such as surgical crown lengthening or ortho-extrusion, can be performed to obtain adequate coronal tooth structure.¹⁶ However, these procedures are invasive and may not necessarily facilitate improved access to the deeper portions of cavities in posterior teeth. Furthermore, these procedures present difficulties in efficiently isolating the operative field using a rubber dam. Insufficient moisture control and the potential for blood and saliva contamination during clinical procedures pose a threat to the survival of restored ETT in posterior regions.¹⁷

The cervical margin relocation (CMR) technique could be regarded, to a certain extent, as a non-invasive alternative to surgical crown lengthening. This procedure which is also known as deep margin elevation (DME), or proximal box elevation (PBE) aims to overcome the challenges mentioned above, making clinical procedures simpler and less prone to errors.¹⁸ This technique proposes careful application of composite resin in the deepest parts of the proximal areas to reposition the cervical margin supragingivally. This facilitates improved isolation, impression-making, and the adhesive protocol for both direct and indirect restorations.¹⁷

In case of a localized deep margin where the remaining walls provide sufficient enamel for bonding, and when final adhesive restoration is planned, CMR needs to be carried out. Prior to initiating root canal therapy, this technique facilitates rubber dam isolation. The success and precision of this technique significantly influences the longevity of subsequent restoration after root canal treatment.

Current evidence suggests that various types of composite resins, including flowable, packable (viscous), or bulk-fill, can be effectively employed for DME procedures.¹⁹

Ensuring long-term functionality and aesthetics with appropriate post-treatment restoration

During endodontic treatment, sodium hypochlorite (NaOCl) irrigation influences bonding between pulp chamber dentine walls and adhesives. NaOCl concentration ranges from 0.5% to 5.25%, effectively removing infected pulp tissue and killing micro-organisms. However, higher concentrations lead to increased collagen degradation, dentine deproteinization, and reduced microhardness, elastic modulus and flexure.²⁰

The pre-endodontic build-up, or doughnut technique, involves creating an access cavity where the proximal, buccal, and lingual walls are built with direct restoration using flowable composite. The use of a suitable barrier such as a cotton pellet, thermoplastic gutta-percha, polytetrafluoroethylene (PTFE), or liquid dam is employed to prevent the blockage of root canal orifices, facilitating isolation. Once the circumferential build-up is complete, it aids in containing irrigating solutions and medicaments within the access cavity.^21,22

Following access cavity restoration, endodontically treated teeth are commonly restored with full-coverage crowns to provide optimal structural support and protection.

Crowns are typically made from materials such as porcelain fused to metal or all ceramics.⁵ However, full coverage crowns may pose issues such as poor fit, excessive tooth reduction, and periodontal concerns impacting ETT. Advances in adhesive dentistry and biomimetic principles challenge routine use of full coverage crowns for ETT. Biomimetic dentistry prioritizes preserving tooth structure, mimicking natural biomechanics through minimally invasive preparations and selective caries removal.

The biomimetic restoration protocol employs modern adhesion techniques and advocates for stress-reduced cavity preparation to minimize the configuration factor (C-factor) and stress in dental composite restorations.²³ This approach involves the use of flowable resin liners, allowing time for the maturation of the adhesive/dentine hybrid layer, incorporating ultra-high molecular weight polyethylene fibre (UHMWPEF), and using 1 mm horizontal increments of composites in direct restorations. However, the biomimetic restoration of endodontically treated teeth varies depending on the residual wall volume and the type of access cavity preparation.²⁴

Steps in restorative management of ETT with one or more than one wall missing (minimal to moderate destruction):

In Step 1, remove caries, prepare the access cavity, locate orifices, and place sterile Teflon tape on the deroofed pulp chamber (Figure 4). This action prevents interference of adhesive restoration with subsequent root canal procedures.

In Step 2, perform air abrasion to prepare enamel and dentine, ensuring the removal of decayed areas and preventing over-removal of enamel and dentine. This step creates more surface area for the adhesive agent to form resin tags.²⁵

For Step 3, immediately seal the freshly prepared dentine (immediate dentine seal/IDS) using flowable resin, ensuring a thickness not exceeding 0.5–1 mm.²⁶

In Step 4, layer the composites, starting by replacing the proximal/facial/lingual enamel shell. Following this, replace dentine by placing a 0.5–1.0-mm layer of flowable composite on the floor of the preparation over the filled adhesive of the bonding system used to hybridize the dentine. Alternatively, use ultra-high molecular weight polyethylene fibre (UHMWPEF) or short fibre-reinforced flowable composite along with horizontal increments of composites in direct restorations.²⁷

For Step 5, in cases where the functional cusp width is less than 1 mm and the non-functional cusp is 1.2–2 mm, opt for semi-direct or indirect restorations. This involves using inlays, onlays, or overlays that are bonded to the tooth while preserving healthy cusps and the peripheral enamel bio-rim (Figure 5).²⁸

Restorative management of ETT with more than two or three missing walls

The approach to managing extensively destructed ETT remains consistent with the aforementioned, with additional techniques employed to augment the resistance form of the tooth, particularly in posterior teeth. Using UHMWPEF in a wall-papering technique or as a post, serves to reinforce both the tooth and the core of ETT.²⁹ In the wall-papering technique, these fibres are positioned on the pulpal floor, serving as reinforcement for cavity walls and axial walls.³⁰ Furthermore, these fibres can substitute rigid posts to secure the composite core (Figure 6).

To facilitate reader comprehension, a Table 2 outlines the recommended restorations based on the access cavity type, remaining residual walls, height of the coronal tooth structure, type of core build-up and gingival preparation. This Table serves as a quick reference to make informed decisions at a glance (Table 2).

Table 2. Recommended restorations based on type of access cavity and remaining cavity walls.

Type of access cavity	No. of remaining residual walls	Height of affected coronal tooth structure	Post placement required	Type of core build-up and gingival preparation	Recommended restoration
TAC/CAC	4	Supragingival tooth structure with core ferrule of more than 2 mm and thickness is more than 1 mm	–		Direct adhesive composite restoration
		Supragingival tooth structure with core ferrule within 1–2 mm and thickness is at least 1 mm			Indirect restoration
		1–2 mm core ferrule height, but width is compromised			Endo crown with or without gingivectomy
	3	Supragingival core ferrule more than 2 mm above gingiva and thickness is more than 1 mm			Direct adhesive composite restoration/indirect restoration
		1–2 mm core ferrule more than 2 mm above gingiva and thickness is more than 1 mm)
		Subgingival		DME +IDS or gingivectomy +DME +IDS	Direct adhesive composite restoration/indirect restoration
	2	Supragingival (more than 2 mm above gingiva)		Fibre-reinforced bio-based preparation	Direct adhesive composite restoration/indirect restoration
		1–2 mm subgingival		DME +IDS or gingivectomy +DME +IDS	Direct adhesive composite restoration/indirect restoration/inlay/onlay/partial crown
				Fibre-reinforced bio-based preparation	Indirect restoration/partial crown
	1	Supragingival (more than 2 mm above gingiva)	Yes	DME +IDS/composite resin	Indirect restoration/single full coverage crown/partial crown
		1–2 mm subgingival		Gingivectomy with DME +IDS/composite resin
	0	Supragingival tooth structure with core ferrule of more than 2 mm and thickness is more than 1 mm		Ortho extrusion/gingivectomy/both with composite	Single full coverage crown

Tooth type and its position in arch:

The position of ETT in an arch also influences the prognosis. Anterior regions endure lower forces, whereas posterior regions must withstand greater forces, requiring careful selection of restoration. Table 3 depicts the choice of restorations for anterior and posterior teeth.

Occlusal considerations

The choice of restoration is significantly affected by the type of occlusion.³⁰ Occlusal guidance is an important consideration, with canine guidance being favourable in situations where lateral forces need to be directed away from posterior teeth, and group function being suitable when distribution of these forces across multiple teeth is desired. Additionally, identifying and addressing occlusal interferences is crucial to prevent undue stresses on the restoration. Parafunctional activities, such as bruxism, also play a role in the selection process as they can influence the durability and design of the restoration. The accompanying diagram provides an overview of these occlusal considerations, outlining which factors are typically seen as favourable or unfavourable in the context of restorative dentistry.

Figure 7 summarizes favourable and unfavourable occlusal factors.