Cementoenamel junction: An insight.

The location and nature of cemento-enamel junction (CEJ) are more than descriptive terms used simply to describe some aspects of tooth morphology; however, CEJ gains a lot of clinical significance due to various measurements dependent on it. It may be necessary to determine the location and pathological changes occurring at CEJ to make a diagnosis and treat diseases pertaining to epithelial attachment and gingival margin. However, the information related to CEJ is not discussed commonly. Hence, the present review paper provides an insight on CEJ in both primary and permanent dentition.

INTRODUCTION

One of the most important parameters for assessing periodontal destruction is loss of connective tissue attachment to the tooth root surface.[1] The cemento-enamel junction (CEJ) represents the anatomic limit between the crown and root surface[2] and is defined as the area of union of the cementum and enamel at the cervical region of the tooth.[3] In periodontal research, attachment loss is considered to be a more informative method of assessment of periodontal disease for both cross-sectional and longitudinal studies. The clinical location of CEJ which is a static landmark, serves as an important anatomical site for measurement of probing pocket depth (PPD) and clinical attachment level (CAL) for both, a clinician and an academician. However, the depth of scientific information pertinent to CEJ is lacking compared with its clinical significance. Hence, the present review paper provides an insight on CEJ in both primary and permanent dentition.

FORMATION OF CEJ

In the tooth bud, regions where enamel formation is completed, the enamel organ gives rise to Hertwig's epithelial root sheath, composed of two epithelial layers derived from the external and internal epithelia. The sheath is irregularly fragmented in time and space as it promotes cementum deposition on the newly formed dentin. After this fragmentation, Hertwig's epithelial root sheath also participates in cementogenesis and formation of the periodontal ligament, giving rise to the epithelial rests of Malassez. This irregular fragmentation of Hertwig's epithelial root sheath yields an equally irregular limit of cervical enamel and an irregular onset of formation and deposition of cementum. Consequently, the relationship between cementum and enamel at the CEJ presents an irregular contour, as observed during scanning electron microscope (SEM) analysis of the primary teeth.

Fragmentation of Hertwig's epithelial root sheath and exposure of dentin covered by a thin layer of intermediate cementum are fundamental for the onset of cementogenesis. If Hertwig's epithelial root sheath is not fragmented, there will be enamel deposition and it will be transformed into reduced epithelium, thus preventing cementum deposition on its surface.[4]

TYPES AND DISTRIBUTION OF CEJ

In CEJ area, three types of mineralized tissues are present: Enamel, dentin and cementum.[2] The CEJ is not a uniform line with a mild and regular contour, but a complex line with a linear and regular trajectory.[5] In the odontogenesis of primary and permanent teeth all three types of relationships between enamel and cementum at the cervical region may occur which are described as follows:

Pattern I

The cementum overlaps the enamel for a short distance. This is seen in 60% of all teeth. This type of overlapping occurs when the enamel epithelium degenerates at the cervical region thereby allowing the connective tissue consisting of cementoblasts to contact the enamel directly. The cementoblasts produce a type of cementum called afibrillar cementum which appears dense and laminated and does not contain collagen fibers with 64 nm periodicity [Figure 1a].

Figure 1

(a) Pattern I - the cementum overlapping the enamel for a short distance, (b) Pattern II - an end-to-end approximating cemento-enamel junction, (c) Pattern III - there is absence of connecting enamel and cementum so that the dentin is an external part of the surface of the root, (d) Pattern IV - enamel overlapping cementum

Pattern II

An end-to-end approximating CEJ. In this case, cementum and enamel meet at a butt joint. It is seen in about 30% of teeth [Figure 1b].

Pattern III

There is the absence of contact between enamel and cementum and hence that the dentin is an external part of the surface of the root.[6] It is seen in 10% of teeth. This occurs when enamel epithelium in the cervical portion of the root is delayed in its separation from dentine. In this situation, the CEJ is absent[7] [Figure 1c].

Pattern IV

A yet another pattern seen is the overlapping of the enamel on cementum.[4] This was observed under an optical microscope.[8] It is seen in about 1.6% of teeth[9] [Figure 1d].

Although, one of these patterns may predominate in an individual tooth, all forms can be present when traced circumferentially.[10]

From an embryological standpoint, odontogenesis does not explain the fourth possible type of CEJ, namely enamel over cementum; since cementogenesis is initiated only after completion of enamel formation. Presence of enamel over cementum may be observed in ground sections, according to the thickness and plane of sectioning. Muller and van Wyk,[11] demonstrated that, this in fact is caused by an optical illusion. Conversely, Ceppi et al.,[2] observed rare micro regions of enamel over cementum during SEM analysis of primary teeth. Hence, the existence of this pattern (i.e., enamel overlapping cementum) is controversial.

CURVATURE OF CEJ

The curvature of CEJ follows a variable pattern and is dependent upon the height of the contact area above the crown cervix and also upon the diameter of the crown labiolingually or buccolingually.[12] In general, teeth have a greater proximal cervical line curvature on the mesial, which is about 1 mm more than the distal [Figure 2a and b]. Proximal cervical line curvatures are greatest on the mesial surfaces of central incisors and tend to get smaller when moving toward the last molar [Figure 2a, c and d], where there may be no curvature at all. On many posterior teeth, the cervical line is in a more occlusal position on the lingual than on the facial surface [Figure 2e and f].[13] The curvature of CEJ is more pronounced on the interproximal aspect than the buccal aspect; hence, the measurement of CAL becomes compromised on the interproximal aspect.

Figure 2

(a) Curvature of cemento-enamel junction on the mesial aspect of maxillary central incisor, (b) Curvature of cemento-enamel junction on the distal aspect of maxillary central incisor, (c) Curvature of cemento-enamel junction on the mesial aspect of maxillary first premolar, (d) Curvature of cemento-enamel junction on the mesial aspect of maxillary first molar, (e) Curvature of cemento-enamel junction on the buccal aspect of mandibular first molar, (f) Curvature of cemento-enamel junction on the lingual aspect of mandibular first molar

RELATIONSHIP OF GINGIVAL MARGIN TO THE CERVICAL LINE

Clinically, in a 25-year-old patient with healthy gingiva, the gingival margin approximately follows the curvature of the cervical line. However, it is not always at the level of the cervical line because of the eruption process or recession of the gingiva. In a 10-year-old with a healthy gingival status, the gingival margin may cover some of the anatomic crown of the tooth enamel; in older subjects who have had periodontal disease or periodontal therapy resulting in gingival recession, the gingiva may not cover the entire anatomic root (cementum).[13] These observations suggest that the level of the gingival margin relative to CEJ is age related.

CEJ IN THE PRIMARY DENTITION

Detailed information on the morphology of the CEJ in all groups of primary teeth is not available so far; the reports available are limited to analysis of some specimens.[2]

Morphological/anatomical features of CEJ

Information on CEJ of primary teeth is limited. A study done by Leonardi et al.,[14] investigated this area by means of SEM and highlighted prevalence of overlapping cementum on the enamel and an edge-to-edge relationship. No gaps between enamel and cementum were observed. The CEJ appeared as a 40-60 μm broad sinuous band and the cementum was reported to be acellular, as in permanent teeth, but thinner and rougher. Near the CEJ, calcium spherites (calcified sharpey's fibers) were observed with a diameter from 2 to 10 μm, which attributed to the rough appearance.[2]

In the odontogenesis of primary and permanent teeth, all three types of relationships between the enamel and cementum at the cervical region may occur.[2] The CEJ was considered regular when a linear contour was observed without a zigzag or zipper-like aspect. The CEJs of all primary teeth groups were morphologically similar, without specific characteristics. The CEJ was linear and uniform in some areas, yet presented repeated mild undulations in others. In many specimens, the undulations were anfractuous and presented marked twisting, leading to the formation of cementum and enamel islets. In some teeth, the CEJ undulations were small and repeated, simulating a zipper-like appearance. A total of 39 specimens presented cervical foramina, regardless of the tooth group and CEJ type.[15]

The CEJ of primary teeth should be protected by the gingival connective tissue.[16] The continuous passive eruption and growth vectors of the jaws displace the primary teeth from their original position and expose the CEJ to the oral cavity of 6-to 10-year-old children.[17] Bimstein et al.,[18] in their study reported that on the root surfaces of two primary teeth without evidence of periodontitis which were extracted for orthodontic reasons, no resorption lacunae nor cuticle or bacteria were found. At the CEJ area of teeth from children with prepubertal periodontitis they highlighted dense colonies of short and long filaments, resorption lacunae and crystals of calcium oxalate dihydrate (4-5 μm).

Prevalence of types of CEJ

Investigating the CEJ of primary teeth, Carvalho et al.,[8] described that 42% of teeth presented cementum over enamel, 41% exhibited the edge-to-edge relationship and 12% presented gaps between enamel and cementum. According to the results in percentages reported by these authors, no primary tooth presented more than one type of relationship between enamel and cementum. In the study by Ceppi et al.,[2] root cementum and enamel edge to-edge interrelation was the most frequent type observed in overall samples [Figure 1b], root cementum overlapping enamel tissues was observed in more than one-third of the CEJ area [Figure 1a], whereas exposed dentin was a rare observation [Figure 1c]. In few, small and rare areas, enamel overlapped cementum [Figure 1d].[2] The CEJ appeared as a sinuous line. Cervical cementum appeared rough owing to the presence of calcified Sharpey's fibers that was referred as calcium spherites.[14] At the bottom of the gaps, the dentinal tubuli were clearly opened on the surface [Figure 1a]. Often, however, they were partially covered by delicate material, probably representing thin layers of intermediate cementum.[5]

CEJ IN PERMANENT TEETH

The CEJ was initially studied by Choquet in 1899 who analyzed ground sections of permanent teeth under light microscopy.[19] The first comprehensive report on the morphology of the CEJ in all groups of permanent teeth by SEM was published by Neuvald and Consolaro.[19] Several relationships between cementum and enamel as mentioned in previous sections may be observed along the CEJ of a single tooth.[6] It is expected that cervical and root surface lesions involving the CEJ will become more prevalent along with the predicted increase in the numbers of potentially dentate elderly.[20] Researchers have encountered this problem in the past and have mentioned the difficulty of obtaining teeth with cementum present on the roots and with no forceps injury at the CEJ. There is little information on the SEM appearance of CEJ.[20]

Schroeder and Scherle,[21] while observing enamel extensions and scalloping of CEJ, stated that the distribution of the three hard tissues found at the CEJ region is unpredictable and irregular on a single tooth and between contralateral teeth.

Grossman and Hargreaves,[20] in their study on 18 permanent teeth showed cementum overlap relationship at CEJ, with the cementum directly or indirectly attached to the underlying enamel. They also demonstrated edge to edge contact of cementum to enamel.

In young adults, the CEJ of permanent teeth is covered by the gingival tissue and is in contact with the connective tissue's extracellular matrix.[421] After the third decade of life, continuous passive tooth eruption compensates for wear at the incisal and occlusal aspects. The CEJ is then located in the gingival sulcus. The exposure to the oral environment may lead to dentin hypersensitivity upon ingestion of hot, cold, sweet or salty foods. Tooth abrasion and erosion in adults are initiated after the CEJ is exposed to the oral cavity.[21]

DIFFERENCES IN CEJ OF PRIMARY AND PERMANENT DENTITION

The cementum is reported to be acellular in primary teeth as in permanent teeth, but thinner and rougher

In permanent teeth the CEJ is placed at the bottom of the gingival sulcus, whereas in primary teeth, the CEJ is placed more apical as the epithelial junction is at the equator of the crown.[2] The clinical implication of this anatomic feature could be protection toward decay of the cervical region and in fact, dentinal sensitivity is rarely observed in the primary dentition[14]

Scarcity of gaps between cementum and enamel, globosity of crown, apical placement of CEJ are the possible protective factors towards decay in the primary dentition[2]

Primary teeth present a smaller number of incremental lines and have a thinner calcification, clinically implying that the smaller thickness of cementum and possibly of enamel, may allow the passage of greater amount of chemicals, including bleaching agents, when applied both externally and internally in primary teeth[5]

The pattern enamel overlapping cementum is not discussed in relation to permanent dentition.

VARIOUS METHODS OF CEJ LOCATION

Methods for location of CEJ include following two kinds:

Conventional

Modified

In conventional methods we have:[2223]

Visual

Tactile

By straight explorer

By periodontal probe; examiner feels for the cervical line with the tip of the probe[24]

Radiographic

Intraoral periapical (IOPA) radiograph

Bite wings

RVG.[25]

In modified methods we have:[72627]

Computer linked electronic constant pressure probes

Florida probe

Inter probe/Perio probe

Birek probe/Toronto automated probe

Jeff coat probe/Foster miller probe.

The comparison between various methods of detection of CEJ is presented in Table 1.

Table 1

Comparison of conventional and modern methods of CEJ detection

ALTERNATES TO CEJ

With the difficulties in identifying CEJ in studies on disease progression or the effect of periodontal treatment on the attachment level, other landmarks were explored for a valid clinical attachment measurement

Osborn et al. introduced the occlusal surfaces or the incisal edge of the tooth as a reference for the CAL[32]

Pihlstrom[33] studied the reproducibility of relative probing attachment level measurements using a stent as a reference point and concluded that stents increase the intra- and inter-examiner reproducibility and are therefore useful in studies evaluating treatment modalities. The second measurement per site is probably not independent of primary measurement, if the time difference is not wide.

CLINICAL IMPLICATIONS

CEJ a significant landmark for probing the level of the attachment of fibers to the tooth root in the presence of periodontal disease

The different patterns of CEJ have clinical significance in the presence of disease, e.g., gingivitis, recession of the gingiva with exposure of the CEJ, loss of attachment of the supporting periodontal fibers in periodontitis, cervical sensitivity, caries and erosion; and also placement of margins of dental restorations.

SEM examination of the surface textures of enamel (e.g., hypoplastic enamel, perikymata), exposed dentin and cementum at the CEJ and topographic contours of the various CEJ hard-tissue relationships reveals structural features that would appear to facilitate attachment of bacterial biofilms and if left undisturbed, the transition to dental calculus.[34]

The location of CEJ to measure CAL is a critical situation clinically as discussed by Vandana and Gupta,[35] in their study, where the distance between stent and CEJ was measured before and after reflection of flap. The percentage increase in over and under estimation of CEJ to stent measurement during flap reflection was clinically evident than equivalent measurement.

CEJ a landmark to diagnose cervical enamel projections (CEPs)

The CEJ serves as an important reference for diagnosis of CEPs. These are the extensions of enamel from the CEJ onto the root surface. Masters and Hoskins,[36] classified these unusual anatomical structures based on the degree of extension of enamel beyond the CEJ and depending on their location in relation to furcation topography.

Enamel extension apical to the normal CEJ level is a risk factor for periodontal disease because the periodontal fibers embedded in the cementum to support the tooth, are not in their usual position and thus, do not act as barrier to the advancement of periodontal disease. In effect, the epithelial attachment over the surface of the enamel, which does not have this kind of attachment, may become detached in the narrow and difficult-to-clean bifurcation area because of plaque and calculus, increasing the vulnerability to periodontal disease.

CEJ and dental surface defects

CEJ serves as an important reference landmark in diagnosis and treatment of dental surface defects. In situations where CEJ is not identifiable clinicians encounter difficulty in accurately measuring the depth and width of recessions during diagnostic phase and during surgical phase in precisely locating the gingival margin when suturing. Moreover, the accurate evaluation of clinical outcome of root coverage procedure is if difficult at the end of therapy or if CEJ is lacking. Based on these observations, Pini-Prato et al., classified dental surface defects based on the criteria of presence or absence of CEJ.[37]

Role of CEJ in gingival recession management

During routine clinical practice, recording an identifiable CEJ is of paramount importance for measuring recession depth and evaluating treatment outcome after treatment. In teeth with gingival recession, affected by cervical abrasive trauma involving both enamel and root cementum, identifying CEJ is a difficult task. In such situations, a line separating enamel from coronal dentin is confused for anatomic CEJ. This error in localization of CEJ makes desired root coverage unobtainable because the most coronal portion of the exposed dentin belongs to anatomic tooth crown. Zucchelli et al., considered clinical CEJ to substitute anatomic CEJ when it is no longer identifiable on teeth with recession, to predetermine the line of root coverage, which may improve the final outcome of mucogingival surgery, allow for a more esthetic treatment of cervical abrasion associated with gingival recession and meet patient demands even when local conditions are not favorable to accomplish a good esthetic result. By the same authors, it was proposed that the clinical CEJ can be used as a guideline for the apical preparation of the composite restoration in cases of deep abrasion defects associated with gingival recession.[38]

Implications in restorative dentistry

The presence of gaps with dentin exposure in all junctions of primary teeth indicates the need for special care upon placement of clamps, wedges and stainless steel crowns, application of restorative materials, utilization of extractors and gingival retractors, surgical curettage at the cervical region of unerupted teeth and specifically during internal and external tooth bleaching. Even though these procedures are routinely performed in dental clinic, special care should be taken with the CEJ area to avoid dentin hypersensitivity and external cervical resorption.[5]

In the oral environment, the CEJ may be subjected to the action of chemicals from foods, oral hygiene products and dental materials especially tooth bleaching agents, widely used on permanent teeth than on primary teeth. Physical agents such as tooth-brushing, dental instruments and clamps also may change the relationship between mineralized dental tissues at the CEJ, with important clinical consequences. Similarly, morphology of the CEJ also should be considered in cavity preparations and restorations.[5] The greater exposure of the CEJ of primary teeth to the oral environment is related to more than tooth attrition. Bimstein et al.[23] in their study reported that facial growth increases the distance between the CEJ and the alveolar bone crest in a specific manner. Even if the primary teeth do not present incisal wear, the CEJ is exposed to the oral environment with the increase of age.

Thus, all in all, identification and location of CEJ serves various purposes which can be summarized as follows:

CEJ is used as a fixed/static landmark to measure CAL/PPD or periodontal destruction[21]

To assess alveolar bone destruction by measuring CEJ-bone crest distance[39]

To study furcation by finding out furcation CEJ distance,[40] thus helping in treatment planning for furcation involvements[41]

To measure gingival recession,[16] which is helpful to determine the dimensions of graft needed to cover it

For bi-laminar grafting procedures for coverage of multiple shallow gingival recession[42]

For development of a system to assess visible and hidden gingival recession[43]

CEJ is important for placement of various membranes during surgical procedures

In case of wasting diseases, tooth resorption often starts at CEJ

Caries in primary teeth is limited more often at CEJ than the contact point[44]

Enamel spurs projecting from CEJ into the furcation act as etiological factors for periodontal disease[45]

The furcal surface closest to the CEJ of the tooth is the most susceptible area to bone denudation as a result of periodontal disease.[45]

Thus, the location and nature of the CEJ are more than descriptive terms used simple to describe some aspects of tooth morphology; they have definite clinical significance. It may be necessary to determine the nature, location and pathological changes occurring at the CEJ to make a diagnosis of and to treat, for example, cervical caries, keeping in mind that the CEJ generally lies apical to the epithelial attachment and gingival margins in young adults.[7]

CONCLUSION

Due to the variable nature of the anatomy of CEJ differing with different tooth types and surfaces of teeth; and due to the subgingival location of CEJ, a clinician confronts great difficulty in exact identification and location of this important landmark, due to which the clinical measurements are jeopardized; leading to lack of intra and inter-examiner reproducibility while measuring clinical parameters in periodontal studies like CAL which are of utmost significance in periodontal studies.

Thus, the clinical applicability of CEJ as a standard reference point either in establishing a diagnosis or evaluation of prognosis should be comprehended critically and remains to be questionable over the centuries. The information related to CEJ in both permanent and primary dentition are significantly neglected as against to its clinical utility for diagnosis and clinical implication. Therefore, the present review throws light on various aspect of CEJ. However, further elaborate research should be devoted to study CEJ using SEM analysis of all teeth types, with evaluation of the prevalence of types of CEJ.