pearl formation occurs at the early stages of tooth development because they have been associated with dentin and pulp.64 In fact, this theory could explain the formation of intradental enamel pearls resulting from focal ameloblastic activity of invaginated cells or entrapped enamel epithelium from the cervical loop during root formation within newly forming dentin.65 Nevertheless, the process of formation of enamel pearls at some locations remains to be further elucidated.60
Furcations
FURCATION MORPHOLOGY
The furcation morphology has been a subject of interest for multitude of investigations, including research evaluating the effectiveness of mechanical instrumentation.66,67 Bower noted that 81% of the furcations had a diameter less than 1 mm, while 58% were less than 0.75 mm in diameter.66 At the time, such findings were clinically relevant because the diameter of tested curettes (ie, Gracey, Columbia, and McCall) had a blade face width ranging between 0.75 and 1.1 mm, resulting in limitations for mechanical instrumentation. Similarly, Chiu et al reported that 49% of furcation entrance dimensions were equal to or less than 0.75 mm, which reinforced the need to use narrow instruments and ultrasonic devices with narrow tips for the management of furcation defects.67
LOCATION OF FURCATION ENTRANCE
Gher and Dunlap performed a series of studies to determine variations in the root anatomy.13,68,69 One study reported that the mean distance from the CEJ to the furcation entrance for maxillary first molars was 3.6 mm, 4.2 mm, and 4.8 mm for mesial, buccal, and distal furcations, respectively68 (Fig 5-2). In a similar study using mandibular first molars, the mean distance was 4 mm for both buccal and lingual furcation entrances.69 Ultimately, the furcation anatomy of maxillary first premolars was explored, and authors reported a mean distance of 6 mm from the CEJ70 (Table 5-4).68–75
Fig 5-2 Location of furcation entrance of maxillary (a) and mandibular (b) first molars.
TABLE 5-4 Location of furcation entrance with respect to the CEJ
| Tooth type | Authors | Distance from CEJ to furcation entrance (mm) |
| Maxillary first molars | Gher and Dunlap68 | Mesial: 3.6Buccal: 4.2Distal: 4.8 |
| Kerns et al71 | Mesial: 4.73Buccal: 4.11Distal: 4.66 | |
| Maxillary second molars | Kerns et al71 | Mesial: 6.40Buccal: 4.29Distal: 4.83 |
| Mandibular first molars | Dunlap and Gher69 | Buccal/lingual: 4 |
| Mandelaris et al72 | Buccal: 3.19Lingual: 4.08 | |
| Kerns et al71 | Buccal: 3.27Lingual: 4.28 | |
| Wheeler73 | Buccal: 3Lingual: 4 | |
| Mandibular second molars | Mandelaris et al72 | Buccal: 3.09Lingual: 4.27 |
| Kerns71 | Buccal: 3.28Lingual: 3.83 | |
| Maxillary first premolars | Gher and Vernino70 | 6 |
| Booker and Loughlin74 | 7.9 | |
| Joseph et al75 | Range of 7.6–7.9 |
CLASSIFICATION OF FURCATION DEFECTS
Classification systems for furcations were developed to help determine the extension of the defect, tooth prognosis, and treatment approaches. These classifications were mostly developed with the use of a Nabers probe. Both horizontal and vertical components represent the primary endpoints of these classification systems.1,76–94 Table 5-5 summarizes some of the most commonly employed classifications.1,76,83,84,87,90
TABLE 5-5 Classification systems for furcation defects
| Authors | Criteria |
| Glickman76 | Pattern of destruction: Horizontal and vertical component.Grade I: Furcation area without gross or radiographic evidence of loss of alveolar bone loss (incipient defect).Grade II: Bone loss in one or more aspects of the furcation area, but a portion of the alveolar bone and periodontal membrane remains intact (also known as cul-de-sac lesion).Grade III: Alveolar bone destruction permits the complete passage of a probe through the furcation. Entrance might be occluded by gingival tissues (through-and-through defect).Grade IV: Alveolar bone destruction creates an open area through which a probe can be passed without difficulty. The entrance is exposed and clearly visible to clinical examination. |
| Hamp et al,83 Lindhe and Nyman87 | Pattern of destruction: Horizontal component.Degree I: Horizontal loss of periodontal support less than 3 mm.Degree II: Horizontal loss of periodontal support exceeding 3 mm, but not encompassing the total width of the furcation.Degree III: Horizontal “through-and-through” destruction of the periodontal tissue in the furcation. |
| Nyman and Lindhe84 | Pattern of destruction: Horizontal component.Class I: Horizontal loss of periodontal support not exceeding one-third of the width of the tooth.Class II: Horizontal loss of periodontal support exceeding one-third of the width of the tooth, but not encompassing the total width of the furcation.Class III: Horizontal “through-and-through” destruction of the periodontal tissue in the furcation. |
| Tarnow and Fletcher90 | Pattern of destruction: Vertical component.Subclass of Lindhe and Nyman87 classification.Subclass A: 0–3 mm probable depth from the roof of the furcation.Subclass B: 4–6 mm probable depth from the roof of the furcation.Subclass C: 7 mm or greater probable depth from the roof of the furcation. |
| American Academy of Periodontology Glossary of Periodontal Terms1 | Pattern of destruction: Horizontal component.Class I: Incipient loss of bone limited to the furcation flute that does not extend horizontally.Class II: A variable degree of bone loss in a furcation, but not extending completely through the furcation.Class III: Bone loss extending completely through the furcation. |
FURCATION ARROW
Early experimental studies evaluated the potential of radiographs to detect periodontal bony defects using human cadaver skulls.95–102 Prichard was the first to describe a “subtle shadow” in radiographs pointing toward the opening of the mesial furcation of maxillary first molars.99 Then, Hardekopf et al coined the term furcation arrow and defined it as a radiographic shadow associated with a proximal furcation involvement.8 Using skulls with furcation-involved molars, authors reported a significant association of Degree II and III furcation defects with the presence of furcation arrows in both mesial and distal furcation entrances when compared to noninvolved molars. For Degree I defects and noninvolved furcations, the incidence of furcation arrows was low and insignificant. Nonetheless, it was concluded that the absence of a furcation arrow does not necessarily mean an absence of a furcation involvement.8
Overall, the usefulness of the furcation arrow as a diagnostic marker is limited. When detected on radiographs, these can predict furcation involvements only in 70% of cases; yet, furcation arrows were also seen in less than 40% of sites with truly present furcation involvement. Consequently, the furcation arrow has a sensitivity of 38.7%, a specificity of 92.2%, a positive predictive value of 71.7%, and a negative predictive value of 74.6%.100
Currently, a combination of both clinical and conventional radiographic assessments remains as the gold standard approach for detecting furcation defects. Limited evidence supports the use of CBCT for periodontal disease diagnosis.101–103
Root Morphology
ROOT SURFACE AREA
Root surface area has been