explored in the literature (Table 5-6).104–108 While initially investigated as an important factor to aid clinicians in decision making for root resection therapy,13 the calculation of this area is also helpful to determine the extent of disease progression and to assist in the selection between regenerative or resective approaches.
TABLE 5-6 Average root surface area (mm2) covered by cementum*
*Adapted from Schroeder.108
Hermann et al13 reported a total surface area for the maxillary first molar of 476.43 mm2. Interestingly, the authors went further to investigate the percentage of root surface area occupied by root trunk (32%), palatal (24%), mesiobuccal (25%), and distobuccal (19%) roots (Fig 5-3a). Later, similar studies were conducted around mandibular first molars.69,109 Dunlap and Gher reported a total surface area of 436.8 mm2, and the percentage of root surface area for the root trunk, distal, and mesial root were 30.5%, 32.4%, and 37%, respectively69 (Fig 5-3b). Box 5-3 includes a summary for the percentages of root surface area for each region in the root complex.13,68
Fig 5-3 Percentage of root surface area of maxillary (a) and mandibular (b) first molars.
BOX 5-3 Percentage of root surface area in the root complex
| Maxillary first molars(Hermann et al13) | Mandibular first molars(Gher and Dunlap68) | ||
| Root trunk | 32% | Mesial root | 37% |
| Mesiobuccal root | 25% | Distal root | 32.4% |
| Palatal root | 24% | Root trunk | 30.5% |
| Distobuccal root | 19% | ||
ROOT CONCAVITIES
Root concavities are common features of the root configuration and act as predisposing sites for periodontal breakdown.70 Additionally, the presence of these developmental depressions will impair mechanical instrumentation during nonsurgical and surgical therapy, especially for multirooted teeth.
Fox and Bosworth conducted a morphologic assessment to determine the presence of proximal concavities on extracted teeth among all tooth types.110 The authors concluded that nearly every tooth has concavities at or within 5 mm apical to its CEJ.110 For multirooted teeth specifically, Booker and Loughlin reported mesial concavity depths of 0.35 mm and 0.44 mm associated with single-rooted and two-rooted maxillary first premolars, respectively.74 Generally, these depressions tend to be deeper on the mesial aspects and middle third of the root surface.75 Conversely, Gher and Vernino reported a prevalence of 78% of concavities around maxillary premolars being not clinically relevant until 50% of interproximal bone loss had occurred.70
Bower also extensively explored the concavity depth and incidence around maxillary and mandibular first molars.111 Within the maxillary first molar, concavities are more likely found on mesiobuccal (94%) than distobuccal (31%) or palatal (17%) root surfaces. A higher incidence was also noted among mandibular first molars on both mesial (100%) and distal (99%) root surfaces (Table 5-7).74,111
TABLE 5-7 Prevalence and root concavity depth around maxillary and mandibular molars74,111
Root Proximity
DEFINITION AND CHARACTERISTICS
Root proximity has been defined as interradicular distances (IRDs) of less than or equal to 0.8 mm or less than 1 mm presenting as a risk marker for periodontal disease.112–119 In a classic study, Heins and Wieder examined the nature of IRD spaces using human histology and reported a distance ranging from 0.2 to 4.5 mm between second premolars, first molars, and second molars.120 Interestingly, sites exceeding 0.5 mm (89.6%) of IRD showed signs of cancellous bone flanked by lamina dura. When this distance is less than 0.5 mm, a fused lamina dura was observed with no signs of cancellous bone in between. Ultimately, sites with less than 0.3 mm of IRD were connected only by the PDL (Table 5-8).120
TABLE 5-8 Histologic features based on IRD120
| Interradicular distance | Histologic features |
| ≥ 0.5 mm | Cancellous bone, lamina dura, and PDL |
| < 0.5 mm | Lamina dura and PDL |
| < 0.3 mm | Only PDL |
Vermylen et al reported a 15.3% prevalence of root proximity among 5,122 interproximal sites from 197 patients.113 It is important to note that 68% of sites were located affecting primarily maxillary molars as well as central and lateral mandibular incisors.113 In a case control study, root proximity was encountered more often at the coronal and middle thirds of the root.115 Moreover, sites with bilateral root proximity had 3.6 times greater risk of developing periodontitis. Similarly, Kim et al examined 473 patients with a mean follow-up time of 23 years to evaluate the association between root proximity and the risk for alveolar bone loss.119 The mean IRD and alveolar bone loss was 1.0 mm and 0.61 mm, respectively. Sites with less than 0.6 mm of IRD presented an increased risk for alveolar bone loss than those with 0.8 mm or more, especially in mandibular anterior teeth.
Similarly, a higher risk for occurrence of intrabony defects has been associated with IRD between 2.1 to 4.1 mm.121 Trossello and Gianelly reported more bone loss at sites with less than 1 mm of root proximity (13.4%) and in patients who had received orthodontic treatment.112 On the other hand, Årtun et al examined 400 patients who completed orthodontic treatment with at least a 16-year follow-up. Among them, 25 patients (6%) with root proximity had no significant differences regarding inflammation, attachment level, and bone level in comparison with neighboring control sites.122
CLASSIFICATION FOR ROOT PROXIMITY
Vermylen et al proposed a classification system for root proximity to indicate location (apical, middle, and coronal third) and severity based on modification of the ruler used by Schei et al123 and findings from Heins and Wieder120 as depicted in Table 5-9.113
TABLE 5-9 Classification for root proximity by Vermylen et al113
| Location | A | Apical third of the root |
| B | Intervening (middle) third of the root | |
| C | Coronal third of the root | |
| Severity | 1 | > 0.5 and ≤ 0.8 mm. A small amount of cancellous bone is present between the adjacent roots. |
| 2 | > 0.3 and ≤ 0.5 mm. Only cortical and connective tissue attachment is present between the adjacent roots. | |
| 3 | ≤ 0.3 mm. Only connective tissue attachment is present between the adjacent roots. |
Root Surface Anomalies
INTERMEDIATE BIFURCATIONAL RIDGE