Molar progression table relating age to Age Reference Line.

1 ARL class as allocated to all jaws in the study
2 ARL age allocated based on a best fit with the Laws [12] and Lee et al. [3] data
3 The Laws [12] age class was allocated to photographs of the occlusal surface of all jaws in the study
4 The Lee et al. [3] median age as allocated to Laws [12] criteria. Some of the classes are inverted
* No difficulty in molar identification from birth to this age. There is little difficulty in identifying molar types 1, 2, and 3 which makes ageing relatively easy up to when M4 occupies the mesial position at 10 years of age and the ARL = M4L6.
** No difficulty in molar identification from here onward. To obtain further information with regard to Table 1, refer to the Notes below and Figure references in Column 5. Note 1. It is usually not difficult to differentiate between M3 and M4. If there is any doubt, this can be substantiated by measuring the distance from the ARP to the crest, and the inter ramus width (see Fig 2, Tables 2 and 3). In addition, it is useful to look at the first lamella of the molar in question, the first lamellae on M3 tends to fill the full width of the tooth whereas in M4 it tends to form a pillar on the lateral side. Note 2. Note how much smaller M4 is compared to M5 despite there being a difference of only 1 lamellae (Fig 10F). M4s are narrower and shallower and tend to have thinner enamel ridges. The base of the root in M5 is also much longer and the gap between the roots of L3 and L4 much wider. See Fig 10G and 10H for further development of M4. Note 3. The Rank M4L10 rarely occurs as this lamellae is usually very small and if present becomes eroded by the mesial end of M5. None were found in this study and therefore there is no photograph. If the ARP to crest is <25 cm then it is suggestive of this being an M4. If ARP to crest >25 cm this suggests it is an M5. Note 4. By this stage the M5 molar is unlikely to be confused with M4 and the alveolus of M6 is usually visible, indicating that this is M5, not an M6 (this cannot be completely relied upon as 7th molars do occur in a small percentage of mandibles). See Fig 9 of the development of M5 and M6 at this ARL (M5 and M6 at L stage 2 [Fig 9A] and L stage 3 [Fig 9B]). Note 5. The distal end of M5 is much rounder than the distal end of M6, which is more tapered throughout development. Note 6. From here on, male mandibles and molars are noticeably larger than females. Note 7. M5L11 may rarely occur, none were recorded in this study. Note 8. From the age of 35 (M6L6), packing bone can be seen developing behind the M6 alveolus, indicating that this is M6. If an M7 is developing they can usually be seen to be truncated and irregular in shape.
Molar progression table relating age to Age Reference Line.