In 1953, Zander explored the mechanisms of calculus attachment upon 50 freshly extracted teeth.31 Four main types of attachment were identified: (1) secondary cuticle, (2) direct attachment into irregularities of cementum, (3) penetration into cementum, and (4) mechanical retention in areas of resorption. In addition, various forms of combinations were also described (Box 5-1).31 Types II (20%) and III (10%) were noted as the most frequent modalities of calculus attachment, and the cementoenamel junction (CEJ) was the favored site for calculus formation.31
BOX 5-1 Mode of calculus attachment to cementum31
| Type IType IIType IIIType IVType VType VIType VIIType VIIIType IXType X | Secondary cuticleDirect attachment into irregularities of cementumPenetration into cementumMechanical retention in areas of resorptionCombination of Types III and IVCombination of Types II, III, and IVCombination of Types I, II, III, and IVCombination of Types I and IICombination of Types II and IIICombination of Types II and IV |
Following Zander’s findings, multiple authors questioned specific types of calculus attachment and attempted to employ more sophisticated technology to test his conclusions.19,32–40 Notably, Canis et al rejected the possibility that microorganisms can penetrate the cementum surface and considered this phenomenon as an artifact due to superimposition of a detached cementum onto the tooth structure during sample preparation.41 These findings were confirmed using light microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM).
Developmental Deformities
ENAMEL PROJECTIONS
Defined as an apical extension of enamel usually toward a furcation,1 enamel projections (also known as cervical enamel projections [CEPs]) are common anatomical variations where a definitive projection of enamel extends into the furcation area, preventing true attachment of periodontal ligament (PDL) fibers upon the root surface7 (Fig 5-1).
Fig 5-1 Classification of cervical enamel projections.
Early observations in dental anatomy described how the enamel dips into the furcation area of multirooted teeth in a tongue-like fashion.42–48 A landmark article by Masters and Hoskins examined extracted teeth with CEPs and suggested a grading system to determine the severity of these projections (Box 5-2).7 The authors reported the prevalence of CEPs in mandibular and maxillary molars as 28.6% and 17%, respectively. In addition, clinical observations revealed that 90% of isolated furcation involvements were associated with CEPs and mainly affected buccal furcation entrances.7
BOX 5-2 Grading system for cervical enamel projections by Masters and Hoskins7
| Grade IGrade IIGrade III | A distinct change in CEJ attitude with enamel projecting toward the bifurcation.Enamel projection approaching the furcation but not actually making contact with it.Enamel projection extending into the furcation proper. |
A myriad of studies continued exploring the prevalence, incidence, and association between CEPs and furcation involvement (Table 5-2).7,49–55 Variations within these investigations might arise from differences in tooth type, reason for tooth extraction (eg, caries, severe periodontitis, endodontic failure), and patient population. With the exception of Leib et al,50 most studies confirmed a positive correlation between CEPs and furcation defects. Notably, Hou and Tsai reported a high prevalence (63.2%) of furcation defects associated with CEPs and intermediate bifurcational ridges (IBRs) affecting primarily mandibular molars.55
TABLE 5-2 Prevalence of enamel projections
| Authors | Material and methods | Main findings |
| Masters and Hoskins7 | Extracted teethPopulation not specified | Prevalence:– Mandibular molars: 28.6%– Maxillary molars: 17%90% of isolated furcation involvements were associated with CEP |
| Grewe et al49 | Extracted teethPopulation not specified | Prevalence:– Mandibular: 25.2%– Maxillary: 15.8%Frequency (in order):– Mandibular second molars– Maxillary second molars– Mandibular first molars– Mandibular third molars– Maxillary third molars– Maxillary first molars |
| Leib et al50 | Extracted teethPopulation not specified | Prevalence:– Mandibular molars: 25.4%– Maxillary molars: 21.9%Not associated with furcation defects. |
| Bissada and Abdelmalek51 | Egyptian skulls | Incidence:– Overall: 8.6%Frequency (in order):– Mandibular second molars– Maxillary second molars– Mandibular first molars– Mandibular third molars– Maxillary third molars– Maxillary first molars |
| Tsatsas et al52 | Extracted teethPopulation not specified | Prevalence:– Overall: 29.9% |
| Swan and Hurt53 | East Indian skulls | Prevalence:– Overall: 32.6%– Mandibular molars: 33.7%– Maxillary molars: 31.4%Frequency (in order):– Mandibular second molars– Maxillary second molars– Maxillary third molars– Mandibular first molars– Mandibular third molars– Maxillary first molars |
| Hou and Tsai54 | Surgical accessPopulation: Taiwanese | Prevalence:– Overall: 45.2%Frequency (in order):– Mandibular first molars– Maxillary first molars– Mandibular second molars– Maxillary second molars |
| Hou and Tsai55 | Hopeless teeth with Class III FIPopulation: Taiwanese | Prevalence:– FI with CEPs and IBR: 63.2%– FI with CEPs alone: 21.8%– FI with IBR alone: 2.3% |
FI, furcation involvement; IBR, intermediate bifurcational ridge.
ENAMEL PEARLS
An enamel pearl is defined as a focal mass of enamel that has formed apical to the CEJ and is typically located in the area between the roots of molars.1 Historically, enamel pearls have also been referred to as droplets, nodules, globules, knots, and exostoses, based on their surface morphology.46,56 Interestingly, some authors referred to them as enamelomas as an early inaccurate delineation of an odontogenic tumor.57,58 These enamel anomalies are described as spheroid masses with a mean diameter of 0.96 mm and a prevalence of 4.6%. They are generally located at the coronal third of the root with a mean distance of 2.8 mm from the CEJ.59 Moskow and Canut performed a literature review and reported an incidence rate ranging from 1.1% to 9.7% (mean: 2.69%) and a predilection for maxillary third and second molars.60 Furthermore, Cavanha introduced a classification based on macroscopic and microscopic observations based on the number, location, and composition of the enamel pearls (Table 5-3).61
TABLE 5-3 Classification of enamel pearls61
| Enamel pearls | Extradental | Solitary | Enamel nodules in periodontiumEnamel-cementum nodules in periodontium |
| Adherent | True enamel pearlEnamel-dentine pearlEnamel-dentine-pulp pearl | ||
| Intradental | CoronalCervicalRadicular | ||
The formation of extradental enamel pearls is attributed to activity of the Hertwig epithelial root sheath (HERS) that failed to detach from the dental surface after root formation.62 Interestingly, Slavkin et al developed a model to explore the HERS differentiation as well as root, cementum, and bone formation.63 They noted deposits that resembled enamel pearls during the differentiation, disintegration, and detachment of the HERS. Conversely, others