Role of the Growth Hormone Receptor (GHR) Gene in Skeletal Class II Malocclusion and Its Significant Influence on the Skeletal Facial Profile in Both the Sagittal and Vertical Dimensions: A Systematic Review

This systematic review aims to determine the role of the growth hormone receptor (GHR) gene in skeletal malocclusion and its significant influence on the growth of the maxilla and the mandible in both sagittal and vertical dimensions. A search of the electronic databases of PubMed, Google Scholar, and Cochrane up to and including the year 2023 was made. In addition to this, a hand search of orthodontic and dentofacial orthopaedic journals was carried out. This search included randomized control trials. The Mesh terms used were "skeletal class II malocclusion", "mandibular retrognathism", "sagittal malocclusion", "genetic expression", "genetic factors", "genetic study", "genetic polymorphism", and "single nucleotide polymorphism". The inclusion criteria included studies such as clinical trials and orthopaedic appliances in the presurgical phase. The exclusion criteria for the study were studies not in the English language, case reports, case series, and studies with irrelevant data. It has been cited in various literature that polymorphic variations of the GHR gene could cause variations in mandibular morphogenesis affecting both the mandibular body length and ramal height. However, its effects are quite variable and are based on different population groups. Polymorphism of the GHR gene can be considered a reliable indicator predicting variations in affecting the growth of the mandible with greater significance in affecting the vertical ramal height compared to the body length of the mandible. Its effects on the maxillary skeletal base are rather limited comparatively.

Comparing the Efficiency of a Newly Designed Spring With the T Loop for Buccal Canine Disimpaction: A Finite Element Study

Disimpacting a buccally impacted canine precisely using frictionless mechanics is a challenge in orthodontics. Various mechanics can be used for aligning an impacted canine and a spring is one of the most versatile methods of accomplishing it. The present study describes a newly designed spring for canine disimpaction using the finite element method (FEM) model. In the present study, the efficiency of the newly designed spring was compared with the T loop. The FEM model of the maxilla was prepared. Harsha's Canine Disimpaction (HCD) spring and T loop with no pre-activation bends were utilized to disimpact the left maxillary canine using a 0.017 x 0.025 inch titanium molybdenum alloy wire. Efficiency of both springs in all dimensions (sagittal, vertical and transverse) was compared. Stress acting on the bone and teeth and number of activations needed for disimpaction were evaluated when the spring was activated by 3 mm. A movement/displacement of 0.8, 0.4 and 0.1 mm was seen in the sagittal (X), transverse (Y) and vertical (Z) planes, respectively, with the HCD spring, and 0.4, 0.1 and 0.1 mm seen in the X, Y and Z planes, respectively, with the T loop. A total of 12-13 and 80 activations were required as per the FEM simulation for disimpaction using the HCD spring and T loop, respectively. Stress concentration in the disto-cervical region was observed during disimpaction with both HCD spring and T loop. Within the constraints and limitations of the present study, it can be concluded that the HCD spring requires lesser activation and brings about greater control of canine disimpaction in all three dimensions when compared to the T loop.