Comparative 3-dimensional Superimposition Analysis of Dentition in Horizontal and Vertical Grower During the Retention Phase -A Prospective Clinical Trial''

Orthodontic treatment is involved with the correction of irregular dental positions and skeletal structures. It is a specialized dental discipline that involves the application of biomechanical principles to correct dentofacial anomalies, thereby enhancing the morphological and functional harmony of the stomatognathic system. However, achieving stable results at the end of active treatment remains a significant challenge, as teeth and their supporting structures tend to revert to their original malocclusion following orthodontic and orthopedic changes. Such changes are attributed to either the tissue's " physiologic rebound " or normal development. The growth changes that take place after treatment can result in relapse of the occlusion and of the tooth alignment. Late growth changes in the jaws have been implicated as a factor contributing to post-treatment relapse, with some suggesting that disharmonious growth after treatment may compromise occlusal stability.

The cause of postorthodontic dental changes remains uncertain, although it appears to involve a combination of dental relapse and continued growth. Despite this uncertainty, research has shown that several variables studied remained stable after treatment. However, for those variables that did exhibit change, the majority seemed to be related primarily to growth alone or to a combination of growth and dental relapse. Furthermore, alterations attributed to growth consisted of variables that were directly or indirectly affected by continued craniofacial maturation, highlighting the significant role that growth plays in postorthodontic dental changes.

Natural growth and development continue throughout life, influencing the position and alignment of teeth. Understanding the interplay between orthodontic treatment, relapse, and natural growth is crucial for optimizing treatment outcomes and retention protocols.

Individuals can be broadly classified into two categories based on their growth patterns: horizontal growers and vertical growers.

Horizontal growers exhibit a more pronounced increase in mandibular length, whereas vertical growers display a greater increase in mandibular height. These distinct growth patterns can significantly influence orthodontic treatment outcomes and relapse tendencies.

Research suggests that growth and relapse contribute to post-treatment changes, with facial morphology and mandibular rotation influencing occlusal stability.

The study (2020) sheds light on the changes that occur in the lower incisors after orthodontic treatment, tooth movement by using a TDI (Tooth Displacement Index) where each single tooth is registered at the different follow-up. The study found that approximately 25% of the tooth movements observed at 6 years (T2) and 12 years (T3) after treatment were not present before treatment (T0). This suggests that these changes were due to natural growth rather than relapse from orthodontic treatment.

Several studies have demonstrated that facial morphology influences post-treatment changes. These changes in vertical parameters of growing individuals can be influenced by mandibular rotation accompanying growth and orthodontic treatment. Research suggests that different facial types with long-faced individuals demonstrate more mandibular backward rotation compared to those with shorter faces.

Researcher noted that forward rotation of the mandible, characteristic of short facial types, influences tooth eruption patterns and can increase the risk of deep bite and mandibular incisor crowding in extreme cases and individual variations in the direction of condylar growth during adolescence can be quite significant, ranging up to 45 degrees. This variability underscores the complex interplay between facial growth patterns and anterior occlusion, resulting in significant individual differences in the development of the mandibular dentoalveolar structure. This variability is aptly demonstrated by study (1963) on mandibular growth. Subjects with an upward and forward growing condyle (Figure A), exhibit pronounced mesial migration of the lower dentition, accompanied by limited forward movement of the incisors. In contrast, the second subject (Figure B) displays a more average vertical eruption pattern of the posterior teeth, with some degree of mesial migration and limited forward movement of the anterior teeth. The third subject, with a posterior condylar growth direction (Figure C), demonstrates vertical eruption of the posterior teeth with no mesial movement, and the incisors erupt vertically and posteriorly. Notably, the occlusal characteristics of these subjects differ significantly. The patient in Figure A presents with a deep bite, whereas the patient in Figure C exhibits a severe anterior open bite.

Bishara and Little also shed light on the long-term stability of orthodontic treatment. Bishara's study revealed that overbite relapse occurs more frequently than overjet relapse, and that the maxillary intercanine width is more stable than its mandibular counterpart. Little's investigation of 65 patients found significant individual variation in long-term treatment outcomes. Notably, all patients experienced a decrease in arch width and length over time, with two-thirds developing lower arch crowding after retention. These findings suggest that maintaining lower arch alignment is challenging, with success rates below 30%.

Research by Roberta A. Gardner's longitudinal study . The research reveals that the mandibular arch, particularly the lower incisors, undergo significant changes over time. Notably, relapse of mandibular incisor alignment and crowding is a common phenomenon, while inter-canine width tends to decrease. Additionally, some patients experience an increase in overbite. The study highlights that patients with initial severe crowding or irregularities are more prone to these changes.

A three-dimensional superimposition study conducted to assess these post-treatment tooth movement in the dentition. Utilizing advanced 3D superimposition techniques, researchers evaluated tooth movement patterns after orthodontic treatment. The results revealed significant displacements in the transverse and vertical dimensions, highlighting the complexity of tooth movement. By employing 3D superimposition, the study provided detailed insights into tooth movement patterns, underscoring the importance of precise retention strategies to maintain optimal treatment outcomes.

Hence, the present trial will be undertaken to assess the changes and compare If there is any difference in tooth movement in 3-Dimensional superimposition in the dentition in horizontal and vertical growers post orthodontically over a period of retention phase.

Inclusion criteria

• Fixed orthodontic cases with FMA of 26 0 or more for hyperdivergent cases and FMA Of 24 o or less for hypodivergent cases.
• Optimal functional occlusion at end of treatment (PAR score >70%).
• Littles irregularity index (Pre-treatment <6mm in both upper and lower arch).
• Nonsurgical and non-orthopedic patients and non syndromic patients.
• Optimal periodontal condition and Good oral hygiene (probing depth <3mm, gingival index score <1
• Good compliance regarding retainer wear

Exclusion criteria

• Subjects with incomplete orthodontic treatment.
• TMJ disorder patients.
• Any systemic disease affecting bone and general growth.
• Patients with incomplete records
• Patient who fail to follow up or undergo complete treatment.
• Patient with learning difficulties
• Patients having antibiotic therapy within previous 3 months and used anti inflammatory drugs in the month before the study