on the child’s birth certificate. All these parameters are essential in the comprehensive assessment of a child’s developmental progress.
Dental age
Dental age is another of these parameters and is a particularly relevant and important assessment used in advising as to the timing of proper orthodontic treatment. The tables and diagrammatic charts presented by Schour and Massler [1], Moorrees et al. [2, 3], Nolla [4], Demirjian et al. [5], Koyoumdjisky‐Kaye et al. [6], Willems et al. [7] and Liversidge et al. [8] demonstrate the stages of development of the teeth, from initiation of the calcification process through to the completion of the root apex and the average chronological ages at which each stage occurs. Normal and healthy tooth buds develop from initial calcification to root apex closure at a given rate for each of the teeth groupings. That is to say that incisors, canines, premolars, first, second and third molars, in the mandible and in the maxilla, differentiated between males and females, all have their individual specific time at which they reach the various developmental stages. These stages are empirically defined in the above classic works. Schour and Massler [1] produced an atlas from intra utero to adulthood, consisting of 21 consecutive drawings, which feature annual development schemes up to age 12 as well as 3 more schemes up to age 35 years. Nolla [4], on the other hand, used a radiographic assessment of tooth development at 10 different developmental stages, starting from the presence of the crypt through to root apex closure (apexification).
Estimating the stage of development based on the eruption time of teeth is an unreliable method of assessing dental age. Although eruption of each of the various groups of teeth normally occurs at a particular time (when there is half to two‐thirds of the final root length), nevertheless this may be influenced by local factors, which may cause premature or delayed eruption with a wide time‐span discrepancy. This may be true even when root development may be proceeding unhindered.
In contrast, examination of periapical or panoramic X‐rays is a far more accurate tool for dental age assessment. With few exceptions, mainly related to frank pathology, root development proceeds in a fairly constant manner and usually regardless of tooth eruption or the fate of the deciduous predecessor.
Let us take the case of a child of 11–12 years of age who has four erupted first permanent molars and only the permanent incisors, with deciduous canines and molars completing the erupted dentition. If practitioners were to refer only to the eruption chart, they would note that at this age all the permanent canines and premolars should have erupted. They may then conclude that the 12 deciduous teeth had been retained beyond their due time. The treatment that would appear to be the logical sequel to this observation would be the elective extraction of all the deciduous teeth!
This, however, is an overly simplistic diagnosis, since indeed there are two possible conclusions to the practitioner’s observations. It is of paramount importance to carefully study the radiographs in order to distinguish between these two possibilities and thereby avoid unnecessary harm being inflicted on the child and the parents.
The initial conclusion to which the practitioner came would indeed be correct if the radiographs were to show that the unerupted permanent canines and premolars had completed most of their expected root length, showing that the child’s dental age corresponded with his chronological age. In the present case (Figure 1.1), the deciduous teeth had not shed naturally, presumably due to insufficient resorption of their roots constituting an impediment to the normal eruption of the permanent teeth. Their permanent successors must then strictly be defined as having delayed eruption. The logical line of treatment would be to extract the deciduous teeth on the grounds that their continued presence defines them as over‐retained.
However, there is a second possibility, where the radiographs reveal relatively little root development, more closely corresponding on the tooth development chart (Figure 1.2) to the picture of a 9‐year‐old child. The child’s birth certificate has indicated the age of 12 years and this may well be corroborated by body size and development and even by intelligence level. Nevertheless, her dentition is that of a child three years younger, thus determining dental age as 9 years. Extraction of deciduous teeth in these circumstances would be the wrong line of treatment, since it is to be expected that these teeth will shed normally at the appropriate dental age. Early extraction may lead to the undesired characteristic consequences of early extraction, performed for a completely different reason.
Fig. 1.1 The advanced root development of the canines and premolars indicates a dental age of 12–13 years, despite the presence of 11 deciduous teeth in this 10‐year‐old child. This defines the deciduous teeth as over‐retained and extraction is their appropriate treatment. A note should be made and follow‐up is needed regarding the relatively slow eruptive progress of the second permanent molars.
Fig. 1.2 A 12‐year‐old patient with root development indicating the late dental age of 9 years. Extraction of deciduous teeth is contraindicated
An additional parameter of teeth development must also be considered. Although on average, central incisors, canines and first and second molars in the maxilla show identical rates of development of one side of the mouth compared to the other, this may not be true for certain specific teeth. There may be a marked variation between right and left sides in the development rate of maxillary lateral incisors and mandibular second premolars and, less commonly, of maxillary second premolars.
In the same way that we may determine the patient’s overall dental age, these identical principles also serve to enable us to diagnose the dental age of the patient’s individual unerupted permanent teeth. However, because developmental variation is found within these different groups of teeth, the developmental stage of a single tooth cannot be used as an indicator for overall dental development and dental age must be evaluated employing a comprehensive, all‐round assessment. Only then can a definitive determination be offered.
Accurate assessment of dental age is critical in deciding when to treat a patient in general and in regard to the treatment of impacted teeth in particular.
We are now in a position to define the terms that we shall use throughout this text, as follows:
Retained deciduous tooth: This term has a positive connotation and refers to a tooth that remains in place beyond its normal, chronological shedding time due to the absence, or retarded development, of the permanent successor. A radiograph of the permanent successor is required in order to determine the presence and developmental status of the unerupted permanent tooth.
Over‐retained deciduous tooth: In contrast, this term has a negative connotation and refers to a tooth whose unerupted permanent successor exhibits root development in excess of two‐thirds of its expected final length (Figure 1.3). Here too, a radiograph of the permanent successor is required in order to determine the status of the deciduous tooth and its implied treatment.Fig. 1.3 The mandibular left second deciduous molar is retained (extraction contraindicated), since the root development
