Dental eruption refers to the vertical displacement of a tooth from its initial non-functional towards its functional position. Tooth eruption disorders may be expressed in various clinical conditions, which may be grouped as “primary retention” and “secondary retention”. The purpose of this article is to review the literature and the clinical parameters of the various conditions related to tooth eruption disorders. Materials and Methods: The search strategy of this critical review included keywords in combination with MeSH terms in Medline, Scopus, and Cochrane Library until February 2022 and only in English. Results: “Primary Failure of Eruption” (PFE) occurs during the eruption process and includes clinical characteristics of both primary and secondary retention, which make diagnosis difficult. PFE is distinguished by Types I and II. In Type I, the defect in the eruption process occurs in all the relative teeth at the same time, whilst in Type II, the clinical expressions vary in multiple quadrants of the mouth, and the second molars erupt more. The variability of the PFE’s clinical spectrum seems to be connected to a genetic origin. The differential diagnosis among single ankylosis, secondary retention, and PFE is based on the occlusal relationship between the upper and the lower teeth distally, most commonly the first molar, which has not yet fully erupted. The treatment approach depends on many factors and combines surgical and orthodontic techniques.

One of the most common malocclusions encountered in everyday practice by orthodontists is skeletal Class II malocclusion, namely a protrusion of the maxilla, a retrusion of the mandible or a combination of both. To correct it, many clinicians use functional devices that guide the mandible into a more forward position. This stimulates bone growth, correcting the skeletal discrepancy. Controversy exists as to whether these appliances accelerate the growth rate, helping the mandible reach its final size earlier, or whether the growth of the mandible is observed as a positive response to the stimuli. This study examined whether the protrusion of the mandible in rats accelerates the growth rate or increases the overall growth of the mandible in the long run. Relapse was also assessed by removing the appliance prior to the end of the experiment. Seventy-two four-week-old Wistar rats were used. The treatment group, which consisted of 36 rats, had a device fitted on their upper incisors that led to a protrusion of their mandible. The device, a bite-jumping appliance, consisted of an iron-cast inclined plane and was fitted for 24 h a day, inducing a 3.5 mm anterior protrusion and 3 mm inferior displacement of the mandible. The control group consisted of 36 rats that were fed the same soft diet as the treatment group. Both groups were divided into three subgroups. The first was sacrificed 30 days after the onset of the experiment, the second at 60 days, and the last subgroup had the appliance removed for 30 days and was sacrificed 90 days after the onset of the experiment. At the beginning of the experiment, as well as at each time interval prior to the sacrifice of the animals, the appliances were removed, and cone beam-computed tomography was performed on every animal. Linear measurements were made on each 3D scan, measuring the growth of the mandible. Measurements of mandibular growth were higher compared to the control group. For instance, Gonion-Menton was 1.18 mm higher on month 2 compared to month 1 in the control group, whereas the same measurement marked a 1.82 mm difference in the experimental group. Condylion–Menton on the same intervals marked a 0.84 mm difference in the control, whereas a 1.35 mm difference was noted in the experimental group. Given the results, true mandibular growth is achieved using functional appliances for Class II malocclusion correction in rats.