The restoration of teeth with extensive structural damage is an important clinical procedure in dental practice. However, despite the availability of a variety of materials, techniques and studies in the scientific literature, the criteria for selection of such teeth for restoration need clarification. The approach to severely compromised teeth should be based on consistent scientific evidence to reduce dental error and improve the prognosis. If restoration is indicated, it must conserve and protect the remaining tooth structure. In this article, we develop and suggest clinical criteria and guidelines that clinicians may use to identify and classify extensively damaged teeth to help in the diagnosis, treatment plan and prognosis.
A tooth with extensive damage is one that has lost substantial structure as a result of caries, previous restoration failures, fractures or even procedures related to endodontic treatment. The restoration of such teeth with endodontic treatment is an important clinical procedure in dental practice; however, various studies have taken different perspectives on this issue.1,2 The loss of dental tissue and the weakening of the remaining structure present a challenge in terms of prosthetic rehabilitation. Although the current success rate of dental implants is high,3 the clinician must be able to assess the probability of restoring severely damaged teeth successfully.4-10 The dimensions of the remaining tooth tissues as well as several biological and occlusal factors must be properly assessed to establish the correct treatment plan.
The aim of this article is to present clinical guidelines to help the clinician easily diagnose and establish a treatment plan for the rehabilitation of severely damaged teeth.
Assessing the Probability of Successful Restoration
Remaining Tooth Tissues
The extent of the remaining tooth structure is among the most important and critical factors in determining the prognosis for restoration of a damaged tooth. Evidence indicates that the dimensions of the crown dentin are important.4 Some studies11,12 agree that a dentin thickness < 1 mm increases the risk of failure. This minimum thickness is more often achieved in buccal or palatal/lingual than interproximal areas after endodontic treatment and tooth preparation.4,13-15 The ferrule effect—the need for a 360º collar 2 mm in height (1.5 mm minimum)—was described by Sorensen and Engelman11 in 1990. Smaller dimensions are associated with a greater risk of failure.4,6,9,16-22
A post should be used only when there is insufficient tooth substance remaining to support core material or the final restoration. The height of the post should always be the same or greater than that of the future crown, and its width should be established by the width of the canal after root canal treatment. Increasing post diameter in an effort to increase retention is not recommended, as this creates unnecessary weakening of the remaining tooth structure.1,9,23-25
Caries, previous restorations and fractures can affect the biologic width of the remaining structure and lead to accumulation of bacteria, inflammation, increased probing depth, gingival recession or a combination of these problems. When sulci are normal (2–3 mm) and healthy and bands of attached gingiva are adequate, margins can be placed up to 0.5 mm inside the sulcus. When tooth structure is insufficient to allow adequate soft tissue attachment, other procedures (such as surgical crown lengthening or orthodontic extrusion) may be necessary to achieve optimal results.26-34
In preparing a root canal for a post, the main barrier against reinfection of the periapical region is the endodontic obturation material. The length of the remaining apical seal after post preparation can influence the long-term success of the restoration.4,5,10,35-38 There is some evidence for leaving 3–5 mm of undisturbed apical endodontic obturation material after post preparation. Only some teeth have a 1-mm thick layer of dentin 5 mm from the apex. At distances less than 3 mm from the apex, there is unlikely to be 1 mm of sound dentin surrounding the apical end of the post.4,10,39
Occlusal load is also an important consideration in estimating the chances of successful restoration of a damaged tooth. In a retrospective study, Sorensen and Martinoff40 found that, although the success rate for single-unit crowns was 94.8%, it was 89.2% for fixed partial denture abutments and only 77.4% for removable partial denture abutments. Nyman and Lindhe41 found that fractures in abutment teeth occurred more frequently in root-treated teeth. Hatzikyriakos and colleagues42 reported a failure rate for endodontically treated teeth used as abutments for fixed and removable partial dentures that was more than twice that for such teeth not used as abutments.
Some conclusions can be drawn from these studies. Extensively damaged teeth cannot be considered reliable as abutments for fixed or removable dentures (especially long-span fixed bridges and distal extensions of removable dentures) or cantilevers or for patients with severe bruxism and clenching habits.4,8,9,11,41,42
Clinical Protocol for Diagnosing Extensively Damaged Teeth
For a severely damaged tooth, some elements of a treatment plan are mandatory:
- Removal of all caries and old restorations to achieve access to the remaining tooth structure.
- Elimination of all periodontal infection and control of plaque.
- Predetermination of the value of the tooth, e.g., is it important for occlusion or esthetics?
The following criteria should then be assessed in this sequence: ferrule effect, relation between root and crown length, endodontic condition.
Criterion 1 – Ferrule Effect
The ferrule effect is determined from vertical and horizontal intraoral measurements. The vertical measurement is from the top of the gingival margin to the top of the remaining tooth wall at 4 points: mesial, distal, buccal and lingual or palatine. This can be easily assessed using a periodontal probe with a stop and an endodontic ruler. Values are positive if the top of the remaining tooth is above the gingival margin (Fig. 1) or negative if it is below (Fig 2).
The horizontal measurement is the thickness of the remaining tooth walls at the level of the future crown margin at 4 points: mesial, distal, buccal and lingual or palatine (Fig. 3). This can be easily measured with calipers, which are commonly used to measure framework thickness of fixed prosthodontics (Fig. 4). If space does not permit the use of calipers, a periodontal probe (with a stop) can be used instead (Fig. 5).
Criterion 2 – Relation of Crown to Root Length
This factor is important in predicting the retention of the future restoration. As noted above, to promote retention of the crown, a post should be at least the same length as the future crown. Future crown length may be measured from the top of the supposed tooth to the hypothetical margin, intraorally or using a model (Fig. 6).
Root length may be measured radiographically (Fig. 7).
If needed, on a buccal (Fig. 8), palatine or lingual face, it is possible to measure the distance of the reference level to the top of the remaining tooth and transfer this measure to the radiograph (see d′ on Fig. 8). Then measure the root length from this level to the apex on the radiograph (see r′ on Fig. 8). Using the ratio of d to d′, calculate the real dimension of the root, r, from r′.
Criterion 3 – Endodontic Condition
The remaining tooth should be evaluated related to the extent of endodontic treatment required: can treatment be performed without predictable complications, are complications likely and, thus, treatment outcome is uncertain or are complications irreversible and cannot be resolved with endodontic treatment.
Classification of Teeth with Extensive Endodontic Damage
- Ferrule effect: Height of remaining tooth ≥ 2 mm at 4 locations (mesial, distal, buccal, palatine or lingual) and thickness of remaining tooth walls ≥ 2.2 mm for an esthetic restoration or ≥ 1.6 mm for non-esthetic restorations
- Remaining root length: At least as long as the future crown height plus 5 mm for the apical seal
- Endodontic condition: Endodontic treatment may be performed without predictable complications
- Prognosis: Good
- Ferrule effect: Height of remaining tooth 0.5–2 mm or width of remaining tooth walls 1.6–2.2 mm with visible margins or 1.2–1.6 mm with non-visible margins
- Remaining root length: Less than crown height plus 5 mm but equal or greater than crown height plus 3 mm
- Endodontic condition: Without predictable complications or with uncertain results
- Prognosis: Moderate
Note: A tooth in this class should not be used as an abutment. A new evaluation should be performed after endodontic treatment in cases where pretreatment prognosis is uncertain.
- Ferrule effect: Height of remaining tooth < 0.5 mm or width of remaining tooth wall < 1.2 mm at future margin level
- Remaining root length: Less than crown height plus 3 mm
- Endodontic condition: With irreversible complications
- Prognosis: Poor
Note: A tooth in this class is not a candidate for treatment; it should be extracted and replaced by a prosthesis.
The clinical record form below may be used to evaluate severely damaged teeth using these criteria. Each parameter is evaluated and individually classified as I, II or III. Final classification is the highest class for any parameter, i.e., a tooth rated I, II, I for the 3 parameters, is Class II.
Clinical record form for scoring teeth with extensive damage
|Ferrule effect||Height ≥ 2mm
Width ≥ 2.2 mm (esthetic)
|Height ≥ 0,5–2 mm
Width 1.6–2.2 mm (visible margins)
1.2–1.6mm (non-visible margins)
|Height < 0.5mm
Width < 1.2 mm
|Root length||≥ crown height + 5 mm||< crown height + 5 mm
≥ crown height + 3 mm
|< crown length + 3 mm|
|Endodontic condition||Without predictable complications||Without predictable complications or uncertain treatment results||With irreversible complications|
Final classification _________________________
Additional Clinical Considerations
- Pre-prosthetic treatment may affect the initial classification.
- Concern about special stress patterns (bruxism, abutments for a removable partial denture, cantilevers, extensive bridges or secondary abutments) raises the class level from I to II or from II to III.
- Class level also increases by 1 if there are esthetic concerns.
- In cases where there is no antagonist, no occlusal issues, the antagonist is a removable denture or there is clinical evidence of small to no loads over the remaining tooth, the class level decreases by 1.
- For patients with poor oral hygiene, uncontrolled periodontal disease or caries, an extensively damaged tooth should be considered Class III.
Clinical guidelines help the dentist arrive at the correct diagnosis and treatment plan, avoid errors, increase the predictability of dental treatment and increase the quality of service. Although the literature describes the rehabilitation of teeth with extensive endodontic damage, no clinical guidelines have been published. Our goal in this article is to provide the clinician with such guidelines for selection of extensively damaged teeth for rehabilitation.
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