10/09/2009 Available space for the incisors during dental development - a growth study based on physiologic age

Resident: J. Hencler
Date: 10/09/2009

Article title: Available space for the incisors during dental development - a growth study based on physiologic age

Author(s): Moorrees, DDS; Chadha, BDS
Journal: Angle Orthod.
Volume #35; Number 1; Pg 12-22
Year: 1965

Major topic: Spacing and crowding during incisor transition

Type of Article: Observational/investigative

Main Purpose:
Investigate available space for the incisors of the growing child by grouping children at similar stages of dental maturation with reference to tooth eruption instead of chronological age

Overview of method of research:
78 maxillary and 70 mandibular study casts were used for studying the available space in the incisor segment. Each tooth in an individual series of dental casts was classified according to one out of six stages:
1. Deciduous tooth present
2. Extracted
3. Exfoliated
4. The permanent successor emerging
5. ½ of the crown erupted
6. Fully erupted
The difference between each stage and the previous one in the series for each child was recorded, thus events occurring during specific eruption phases could be identified.

Findings:
Emergence of mandibular central and lateral incisors resulted in 1.6mm crowding in males and 1.8mm crowding in females. In the maxilla either a small excess or a small (0.2mm) lack of space for the erupting permanent incisors was encountered. Increments in the inter-canine distance and in arch length during eruption of the lateral incisors provided enough space for the alignment of these teeth, except in the mandible where 0.2 and 0.5mm crowding was noted for males and females, respectively. No changes were noted during the emergence of the permanent canines. Pattern of change in the maxillary and mandibular dentitions of the sexes was similar. Females recover better than males from the loss of available space. Graphs based on chronological age differed markedly from those based on dental age because they mask the severe changes and the amount of crowding encountered. After the eruption of the permanent canines the two methods of analysis gave similar end results for mean space values in the incisor segment.

Key points in the article discussion:
A precise description of dental development can make a more rational diagnosis in the mixed dentition possible, particularly with reference to the need for and timing of serial extraction. Available space is, to a large extent, dependent on tooth size so observing tooth emergence and eruption should provide a realistic account of the changes in available space. Contrastingly, combining early and late maturing children in the same chronological age has been shown to hide the actual loss of space during the incisor transition. The changes in arch length and arch width are consistent with the pattern of change in available space for the incisor segment. Incisors are largely relieved when the crowns of the lateral incisors are fully erupted while if growth increments in arch size are also completed at that time. A slight increase in arch width occurs in the maxillary arch when the permanent canines erupt. Increase in arch length is confined to the maxillary arch and explains why emerging incisors have nearly sufficient space for their alignment as opposed to the mandibular incisors. At the end of the incisor transition the spaces between the deciduous canines and molars are closed. Mesial migration of the permanent first molars occupies most of the leeway space between the crown diameters of the deciduous posterior teeth and their permanent successors reflected in a reduced arch length. The partitioning of leeway space is dependent on 1) the sequence of shedding and emergence of the deciduous second molars and the second premolars, respectively, 2) on the interdigitation of the cusps of the first permanent molars, and 3) on the position of the premolars in relation to the mesial aspect of the first molars. It appears that generally no significant relief of crowding in the incisor segment can be expected after the complete eruption of the lateral incisors. But we can prevent mesial migration of permanent first molars and use some leeway space to relieve minor incisor crowding.

Summary of conclusions:
The level of dental maturation gives decisive clues for diagnosis and treatment planning since it defines the timetable of individual development. Chronologically based methods often mask the characteristic features that distinguish one child from the next. The sources of variance for available space of the incisors are tooth size and growth of the alveolar processes.

Assessment of article:
Good article. Pertinent information that is still relevant today.