Relationship Between Basal Mesiodistal Crown Widths of Deciduous SecondMolars and the Permanent First Molars

Introduction

Deciduous teeth are crucial for mastication, alveolar growth, aesthetics, phonetics, and for the occlusal guidance to its ideal condition. To identify and address occlusal issues at any stage of dental development, examination of the deciduous dentition is necessary.¹ Dental crowding, especially in the anterior region, is among the most common malocclusions observed in children and frequently manifests during the transitional dentition phase. Dental crowding results from an imbalance between the size of the jaw and the teeth, which causes the teeth to overlap and rotate. Dental crowding can be attributed to three primary factors: excessively large teeth, unusually short jawbone bases, or a combination of both, all of which contribute to insufficient space within the dental arches.² Various theories have been put forward to explain the etiology of dental crowding, embracing the concepts of evolution, hereditary and environmental effects.³ A correct diagnosis and treatment to address probable abnormalities and malpositions in the growing dentofacial complex through orthodontic or myo-functional treatments can be made with an early crowding prediction based on obvious symptoms. Early correction of unfavourable aspects of a developing occlusion decreases the duration of therapy and improves stability, functionality, and aesthetic outcomes. Selection of appropriate treatment strategy may depend on the factors influencing crowding. Dental crowding can be corrected using a range of orthodontic techniques. For instance, to accommodate the total tooth mass into a given dental arch, permanent teeth extractions and mesiodistal tooth size reductions are the two approaches that are commonly undertaken. The goal of additional treatment methods is to widen the dental arches, creating space for the existing teeth. This involves palatal expansion and use of certain functional appliances. Any one of these methods is predicated on the implicit premise that dental crowding is caused by an imbalance in the relationship between the size of the teeth and the size of the jaw.¹

The mesiodistal crown diameter of teeth is a key factor influencing occlusal development during the transition of dentition, as well as the final positioning of teeth within the bony arches. The environment plays an epigenetic role on tooth size, which is polygenic in nature. In forensic and clinical dentistry, mesiodistal crown diameter, often known as tooth size, is useful for providing important information on biological issues and human evolution. Mesiodistal diameter is a tool used by anthropologists to chart the evolution of tooth size. Tooth size offers insights into the relationship between populations and their environmental adapta-tions.⁴ This study aimed to evaluate the feasibility of early prediction of dental crowding by conducting an initial assessment of the mixed dentition stage, focusing on the basal mesiodistal widths of the primary second molars, permanent first molars, and overall arch length. Determining the relationship between the arch length of children in the local Karnataka community and the basal mesiodistal widths of primary second molars and permanent first molars is one of the objectives of this study. This relationship is compared to the dentition's crowding and non-crowding.

Materials and Methods

A sample consisting of 150 casts of children in the mixed dentition phase was selected for the study after obtaining ethical clearance from the institution. These previously made study casts were retrieved from the records of the Department of Pediatric and Preventive Dentistry, Krishnadevaraya College of Dental Sciences, Bangalore. The selected casts were trimmed till the basal bone and were divided into two groups based on the dentition- Group 1: consisting of casts with crowded dentition and Group 2: consisting of casts with non-crowded dentition. Using a digital vernier calliper, mesiodistal dimensions of primary second molars (E) and permanent first molars (6) were recorded.

Results

A total of 150 dental casts were analyzed and catego-rized into two groups: Group 1 with crowded dentition and Group 2 with non-crowded dentition. In the non-crowded group, the mean basal mesiodistal width of the maxillary primary second molar was 8.1414 mm (right) and 8.1874 mm (left), while the maxillary permanent first molar measured 11.9512 mm (right) and 11.9472 mm (left). The average arch length in this group was 79.541 mm (Table 1).

In comparison, the crowded dentition group showed slightly larger measurements. The mean basal mesiodistal width of the maxillary primary second molar was 8.3436 mm (right) and 8.3846 mm (left), and for the maxillary permanent first molar, it was 12.1023 mm (right) and 12.2501 mm (left). The mean arch length available in the crowded group was 79.8205 mm (Table 2).

The mean basal mesiodistal width of mandibular primary second molar in non-crowded dentition was 9.1863 (R) and 9.14 mm (L). The mean basal mesiodistal width of mandibular permanent first molar in non-crowded dentition was 11.9588 (R) and 12.0015 mm (L). The mean arch length available for non-crowded dentition was 71.813 mm (Table 3). The mean basal mesiodistal width of mandibular primary second molar in crowded dentition was 9.5386 (R) and 9.4157 mm (L). The mean basal mesiodistal width of mandibular permanent first molar in crowded dentition was 12.0910 (R) and 12.0699 mm (L). The mean arch length available for crowded dentition was 71.8429 mm (Table 4).

Discussion

The development of dental crowding has been explained by a number of theories, including those involving evolution, heredity, and environmental factors. A study conducted by Bravo N et al., demonstrated a statistically significant correlation between the size of the permanent first molars and the deciduous second molars, suggesting that the dimensions of primary teeth can serve as predictive indicators for the size and space requirements of their permanent successors.⁵ Using a precision caliper oriented parallel to the occlusal and vestibular surfaces, the largest distance between the mesial and distal sites of contact represents the mesio-distal diameter of the tooth. Numerous studies have employed the method that Moorrees et al., described to estimate the mesio-distal crown diameter of the teeth.⁴ 

From this study, it can be inferred that in maxilla, in the mixed dentition phase, crowding can be predicted if -

• the MD width as measured from the base of primary second molar is more than 8.14 - 8.18 mm.
•  the  MD width of permanent first molar is more than 11.95 mm.

The arch length as measured from the base is less than 79.54 - 79.82 mm. We can also infer that in maxilla, in the mixed dentition phase, crowding can be predicted if-

• The MD width as measured from the base of primary second molar is more than 9.14 - 9.18 mm.
• The MD width of permanent first molar is more than 12.00 mm.
•  The arch length as measured from the base is less than 71.81 - 71.84 mm.

This can help understand the probability of occur-rence of crowding in the mixed dentition, so that the necessary interventions can be undertaken promptly. The treatment of malocclusion may benefit clinically from these findings. The treatment planning must focus on one of the three objectives when dental crowding or the discrepancy between the patient's jaw and teeth has been diagnosed. There are three possible approaches: (1) reducing the bulk of the teeth; (2) expanding the dental arch; or (3) the combination of both. The patient's current state (i.e., whether crowding is caused by excessively large teeth or excessively narrow dental arches) and the efficacy of the suggested treatment must be taken into account while choosing an acceptable course of treatment.²

 An accurate diagnosis and treatment plan to address probable abnormalities and malpositions in the growing dentofacial complex through orthodontic or myofunctional interventions may be made with an early crowding prediction that takes obvious symptoms into account.

Conclusion

The basal mesiodistal widths of the primary second molars and permanent first molars can serve as reliable indicators for the early prediction of dental crowding.

The findings of this study suggest a significant correla-tion between the mesiodistal crown dimensions of these teeth, which may act as a prognostic tool for assessing tooth-jaw size discrepancies and the likelihood of future crowding in the permanent dentition. Incorporating standardized tooth size measurements into early case history evaluations can enhance diagnostic accuracy. With detection possible as early as three years of age, clinicians can anticipate future dental development and educate parents on potential tooth size-arch length discrepancies. Early identification and intervention are critical, as spontaneous jaw growth may not adequately compensate for these discrepancies.

Conflict of Interest

Nil