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The International Journal of Periodontics & Restorative Dentistry

© 2012 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.

Volume 32, Number 6, 2012

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A Novel Diagnostic and Prognostic Classification for the Clinical Management of Endodontically Treated Single Anterior Teeth

Rafael Murgueitio, DDS* Gustavo Avila-Ortiz, DDS, MS, PhD**

Restorative criteria for endodon-tically treated teeth should dis-tinguish between anterior and posterior teeth.1 Morphologic char-acteristics of anterior teeth make them more delicate than posterior teeth since they usually present with less remaining dental struc-ture.2 Additionally, the anatomical position and natural angulation of anterior teeth contribute to a less favorable biomechanical response under masticatory forces compared to posterior teeth.3 Restorative treatment of anterior teeth greatly varies depending on the amount of residual tissue. For endodontically treated anterior teeth (ETAT) with minimal structure loss, the use of direct restorative materials such as composite resin without the need for a post and full crown is gener-ally recommended.4 On the other hand, ETAT presenting with exten-sive tissue loss may require the use of a post and abutment to allow retention of a full crown.5,6 Proper case analysis to assign prognosis, determination of the restorability of ETAT, and selection of an ad-equate restorative therapy should

The restoration of endodontically treated anterior teeth (ETAT) may pose a significant clinical challenge given the wide variety of therapeutic options available. Accurate analysis of the remaining tooth structure is critical in the diagnostic process, leading to selection of the proper treatment option. A novel, simple, and precise classification that allows the evaluation of ETAT is presented. Important factors related to the crown or abutment such as height, wall thickness, and circumferential integrity and root-related factors such as diameter of the canal, depth of the preparation, and canal shape are discussed. This classification may serve to establish a comprehensive diagnosis and assign prognosis to ETAT, which may be helpful for interclinician communication and standardized comparisons in clinical research. (Int J Periodontics Restorative Dent 2012;32:713–720.)

* Assistant Professor, Advanced Prosthodontic Graduate Program, School of Dentistry, Universidad del Valle, Cali, Colombia; Assistant Professor, Unicoc, Cali, Colombia.

** Assistant Professor, Department of Periodontics, University of Iowa College of Dentistry, Iowa City, Iowa, USA. Correspondence to: Rafael Murgueitio, Cra. 35 A #3bis-65, Cali, Colombia; fax: 572 5579880; email: [email protected].



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be based on a precise classification that considers specific structural characteristics of ETAT. To the au-thors’ knowledge, there are three classification systems available to date to diagnose and treat end-odontically treated teeth. In 1991, Kurer7 proposed a classification for nonvital single-rooted teeth that took into account variables such as abutment height, post length and shape, and presence of infraosse-ous root fractures. Yet, it did not consider other variables such as the diameter of the canal or thickness of the abutment walls. In 2005, Peroz et al8 proposed a system to classify endodontically treated teeth taking into account the fea-tures of the residual tooth struc-ture. This classification was based on a numeric scale (from I to V) depending on the number of re-maining walls (considering a mini-mum of 2 mm for ferrule effect and 1 mm for wall thickness) and was equally applied for anterior and

posterior teeth. In 2006, Naumann and coworkers1 proposed a classi-fication to define structural defects of endodontically treated teeth as a function of wall height, thickness, and depth in both anterior and posterior teeth. Interestingly, it was recognized that confusion may be generated when therapeutic alter-natives are proposed that apply the same system for both anterior and posterior teeth. The purpose of this paper is to present a classification system that considers multiple fac-tors related to the residual tooth structure to facilitate a restorative treatment plan for ETAT.

Classification

Crown or abutment factors

Wall thickness and height of the crown or abutmentAbutment wall thickness is mea-sured from the inner surface (root

canal) to the external surface of the residual tooth structure. In this classification, abutment walls pre-senting a thickness less than 1 mm are considered nonexistent.9 Wall thickness should be measured us-ing a caliper, but a periodontal probe can also be used.

Likewise, height of the residual dental structure should be consid-ered since it is a critical factor in the process of determining the viability of residual structure. Height may be defined as the distance from the gingival margin to the highest point of the abutment or crown in a vertical direction, parallel to the major axis of the tooth, and can be assessed using a periodontal probe. A wall must present a mini-mum height of 1.5 mm (ferrule ef-fect) to be considered existent. Based on this description, the au-thors propose four categories ac-cording to abutment height (Fig 1). Teeth presenting with intact crowns (excluding minor defects related

Fig 1 Supragingival dental remanent or abutment height. Type I = intact crown except for the endodontic access opening and minor restorations (preparation for a full crown is not needed); type II = abutment height > 3 mm; type III = abutment height between 1.5 and 3 mm; and type IV = abutment height < 1.5 mm.

Type I Type II Type III Type IV



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to endodontic access opening and small restorations that do not compromise its structural integrity) are classified as type I. Preparation for a full crown is not necessary in these teeth. However, clinicians of-ten have to treat teeth presenting compromised clinical crowns that need to be prepared to receive full crowns. These are classified accord-ing to their height into type II (abut-ment height greater than 3.0 mm),

type III (abutment height between 1.5 and 3.0 mm), or type IV (abut-ment height less than 1.5 mm).

Circumferential integrity and irregular abutmentsAnterior teeth prepared for a full crown in which the abutment main-tains all of its walls have a circum-ferential integrity of 100% (Figs 2a and 2b). Nonetheless, tooth prepa-ration may result in partial loss of

the circumferential integrity. In these instances, the fraction of the abut-ment that presents a circumferential integrity greater than 50% dictates the classification for wall thickness and height (Figs 3a and 3b). In cases in which abutments with two differ-ent walls present similar circumfer-ential proportions (50%:50%), the classification is dictated by the fraction that presents the shortest abutment height (Figs 4a and 4b).

Figs 2a and 2b Type II classification: wall thick-ness ≥1 mm, wall height > 3 mm, and abutment circumferential integrity = 100%.

Figs 3a and 3b Type II classification: wall thick-ness ≥ 1 mm, wall height > 3 mm, and abutment circumferential integrity ≥ 50%.

Figs 4a and 4b Type IV classification. Vestibular portion: wall thickness ≥ 1 mm, wall height > 3 mm, and abutment circumferential integrity = 50%. Lingual portion: wall thickness = 0 mm, wall height < 1.5 mm, and abutment circumferential integrity loss = 50%. A missing wall that affects at least 50% of the circumferential integrity dictates the classification.

1 mm 1 mm

1 mm

100% 60%

50%

3.5 mm3.5 mm

a a

a

b b

b



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Root factors

Root factors should also be taken into consideration when insertion of a post has been indicated for the retention of a crown. Such factors include the canal diameter, depth, and shape.

Canal diameterThe canal diameter is the ampli-tude of the root canal in relation to the root diameter in both a bucco-lingual and mesiodistal dimension. A periapical radiograph usually provides valuable information to assess the dimension of the canal in a mesiodistal direction. However,

this analysis should be accom-panied by a clinical examination since some teeth, particularly the canines, present a greater canal diameter in the buccolingual direc-tion, and this must be considered for the fabrication of posts.

This classification considers the largest diameter of the canal, regard-less of the direction and apico- coronal location. Three categories are proposed: narrow (canal ampli-tude is less than one-third of the total root diameter), medium (canal ampli-tude is equal to one-third of the total root diameter), and large (canal amplitude is greater than one-third of the total root diameter) (Fig 5).

Canal depthCanal depth is the remaining length of the root canal after the tooth has been prepared to receive a post. This measurement should be ob-tained from the most apical level of the preparation margin to the api-cal end of the canal, as assessed by a periapical radiograph obtained using a parallel technique (Fig 6). Three categories are proposed: short (intraradicular post length is less than one-half of the radicular length), medium (intraradicular post length is equal to one-half of the radicular length), and long (intra-radicular post length is longer than one-half of the radicular length).

Fig 5 Canal diameter: narrow = canal diameter less than one-third of the total root diameter; medium = canal diameter equal to one-third of the total root diameter; and large = canal diameter less than one-third of the total root diameter. MD = mesiodistal; BL = buccolingual.

Short Medium Long

Fig 6 Canal depth: short = canal depth less than one-half of the root length; medium = canal depth equal to one-half of the root length; and long = canal depth longer than one-half of the root length.

Narrow Medium Large MD Large BL



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Canal shapeRoot canal shape is highly deter-mined by the technique and in-struments used to perform the preparation for a post. There are basically two types of canal shape preparations: tapered and parallel (Fig 7).

Practical application and discussion

Prior to the initiation of ETAT re-construction, tooth restorability must be carefully evaluated. From a restorative standpoint, the most important factor that determines

ETAT restorability is the crown-to-root ratio, which in most cases is directly related to the extent of periodontal support loss. Ideal-ly, it should be at least 1:1. A 2:1 relationship contraindicates the restoration of ETAT because of unfavorable biomechanics.10,11 An-other critical question concerning the restorability of ETAT is whether a post must be inserted and how much structure would remain after post placement. This decision is di-rectly related to crown factors, such as the number, distribution, thick-ness, and height of the residual abutment wall.7,8 Regarding wall thickness, there is limited evidence

to define the minimum thickness for abutment wall integrity. None-theless, most studies consider a wall with a thickness ≥ 1 mm to be acceptable therapeutically.1,8,9 Yet, whether to measure before or after tooth preparation procedures have been completed may be controver-sial. While Creugers et al12 recom-mended that the measurement be taken before tooth preparation, the authors’ opinion is that this could be problematic from a clinical standpoint because after preparing a tooth to receive a new restora-tion, the actual amount and shape of the change in residual dental structure and the application of

Tapered Parallel

Fig 7 Canal preparation shape: tapered and parallel.



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the classification may be unreliable. For this reason, the authors propose that measurements of the remain-ing dental structure be taken and recorded when all restorative proce-dures and other tooth preparation procedures, such as crown length-ening, have been completed.

In a conventional treatment plan, determination of tooth re-storability is typically followed by the selection of the restorative treatment. Endodontically treated teeth exhibit different wall heights and canal diameters and shapes.

Hence, they should receive differ-ent treatment regimens depending on these factors. This classification proposes four alternatives regard-ing the height and remaining den-tal structure of ETAT. These four groups are correlated with different recommended restorative options depending on the canal diameter, which are summarized in Table 1.

ETAT with almost intact crowns (eg, endodontic access opening or minor restorations) do not require a post. In fact, an adhesive resto-ration is usually enough to achieve

Table 1 Recommended therapeutic options for single ETAT considering the residual crown and root canal diameter*

Canal diameter Recommended post Recommended type of restoration Studies

Type I Narrow and medium No post: glass ionomer† and/or composite resin

Composite resin or ceramic veneer§ 4, 5,11

Type I Large Metal or fiber prefabricated post Composite resin or ceramic veneer§ 12,13,14

Type II Narrow and medium Metal or fiber prefabricated post Ceramic or metal-ceramic crown 12,13,14

Type II Large Metal or zirconia custom-made post and abutment

Ceramic or metal-ceramic crown 5, 6, 15, 16

Type III Narrow, medium, and large Prefabricated metal or fiber post‡

Metal or zirconia custom-made post and abutment


Type IV Narrow, medium, and large Metal or zirconia custom-made post and abutment


ETAT = endodontically treated anterior teeth.*Not applicable for fixed partial denture abutments.†To be used like a liner over the gutta-percha followed by acid etching and final obturation with composite resin. ‡Selection should be made by the clinician since there is no clear clinical evidence supporting its use for these indications.§Indicated when vestibular enamel is compromised by more than 30% or if fracture lines are noticed.



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an acceptable clinical outcome.13 A similar criterion is applied when porcelain veneers are planned.14 On the other hand, ETAT present-ing extensive crown defects can-not be restored using conservative techniques. They must be prepared to receive crowns and often posts. Placement of prefabricated glass-fiber or metal posts followed by a composite resin abutment buildup is a commonly used approach to increase the ferrule effect, which may be useful in cases of abut-ments classified as type II or III.17,18 For abutments shorter than 3 mm, placement of a cast post and core is recommended.15,16 Abutments are classified as type IV when there is nonexistent supragingival residual structure (height less than 1.5 mm) to meet the ferrule effect criterion, which may be detrimental from a biomechanical standpoint. None-theless, studies that longitudinally evaluated the integrity of teeth restored in absence of the ferrule effect have shown long-term sur-vival rates comparable to those reported for teeth restored with a minimum 1.5-mm ferrule.15 Based on this information, the restoration of ETAT that present an insufficient ferrule effect can be performed as long as patients are informed of the potential risks and other pos-sible therapeutic alternatives to ETAT preservation.

Controversy exists with regard to whether implant therapy should be performed or an attempt should be made to preserve highly com-promised single teeth.19–21 When natural tooth preservation is indi-

cated, there are therapeutic alter-natives that can be used to achieve the ferrule effect, such as crown lengthening or orthodontic extru-sion.22–24 However, these alterna-tives cannot always be applied, especially in teeth with short roots or in situations where esthetics are highly involved. When post place-ment is indicated to provide sup-port for a restoration because of insufficient residual structure, root factors such as diameter, depth, and shape of the canal should be taken into account. When possible, the diameter of the canal must not exceed one-third of the mesiodis-tal or buccolingual thickness of the root to preserve healthy dentin and avoid significant weakening of the tooth.25,26 Some research-ers suggest that the depth of the canal must be equal to two-thirds of the radicular length or at least equal to the clinical crown length (1:1 ratio) to achieve sufficient sta-bility of the intraradicular element.5 However, in some clinical scenari-os, this concept may contradict an-other variable rule suggesting that a minimum 4-mm gutta-percha apical seal be preserved to dimin-ish microleakage.27,28 Therefore, the length of a post must follow two requirements: be long enough to achieve stability and have a 4- to 5-mm apical seal. With regard to the shape of the intraradicular canal preparation, there are ba-sically two alternatives: tapered and parallel. Some researchers suggest that a parallel prepara-tion improves the retention of the intraradicular element and gener-

ates less biomechanical stress.29,30 However, this type of preparation needs more dentin removal to shape the canal walls to the parallel intraradicular segment of the post. This may increase the weakness of the root in the finish area of the post.31 On the other hand, the ta-pered preparation is more natural because it respects the canal anat-omy. Another variable that was not considered in this classification but has been investigated previ-ously is the post depth in relation to the osseous level. Some inves-tigations suggest that post depth must exceed the osseous level by at least 4 mm.32,33 This is poten-tially problematic in cases of ETAT with reduced periodontal support, making it impossible to follow this recommendation with a tooth that presents ≥ 50% circumferential al-veolar bone loss.

Conclusions

This classification may serve to es-tablish a comprehensive diagno-sis and assign prognosis to ETAT, which may be helpful for intercli-nician communication and stan-dardized comparisons in clinical research. The classification is cor-related with a therapeutic guide that may assist clinicians in mak-ing therapeutic decisions depend-ing on the clinical scenario. These recommendations may also serve as a complement to previous clas-sifications aimed at assigning tooth prognosis based on restorative and periodontal parameters.



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