The results indicate the need for further quality studies on the involvement of the permanent successor tooth following trauma in the primary dentition, since we were only able to include 7 of the 18 studies as high quality according to the NOS scale.
The most common study design was cross-sectional. This is a type of observational study and therefore does not provide the same level of evidence as randomized controlled trials, although in some aspects of dental trauma, such as that dealt with by our review, randomized trials are not possible.
We found differences in the study designs analyzed, the type of trauma analyzed, the age of the participants, the follow-up time, etc. Because of this heterogeneity between studies, we were unable to perform a meta-analysis. Instead, we validated the studies based on selection criteria, comparability, and the measurement of results according to the NOS scale (Tables 1 and 2).
Of the seven high quality studies only three had a control group 5,10,18. There was a majority of observational studies and the lack of a control group could have influenced the results, as the alterations in permanent dentition observed may be due to other causes (molar incisor hypomineralization, amelogenesis imperfecta, fluorosis, or dilaceration, which may be idiopathic), and not only because of the trauma in the primary dentition. A control group design would therefore be more appropriate and present fewer biases 10.
Machado Lenzi et al 10 found that permanent teeth whose preceding primary teeth had trauma had a much higher risk of alterations when compared to the control group: 28.9% of the permanent teeth in the trauma group had alterations, while the prevalence of defects in the control group due to other causes was 7%. Andreasen et al 18 found a high frequency of alterations in the group without previous trauma, suggesting there are non-traumatic factors involved in the etiology of these changes. However, the same authors also stated, in another study, that a non-trauma etiology probably does not explain more than 3% of the alterations 5.
The objective of this systematic review was to determine whether evidence in the literature that trauma in primary dentition causes alterations in the development of permanent succession teething.
Any trauma to a primary tooth can damage the bud of the successor permanent tooth 17.
Discoloration of the enamel and/or hypoplasia were the most common sequelae in permanent teeth following trauma to its deciduous predecessor 1, 4–8,10,11,17,21. Several studies found that the predominance of enamel hypoplasia versus other developmental alterations is due to the fact that it can be caused by less severe trauma in primary teeth 10,17.
Most mineralization defects are located in the incisal half of the central and lateral incisors. In adjacent teeth, discoloration of the enamel may occur after being indirectly affected due to bleeding of the traumatized tooth10,17.
The type and severity of sequelae in the permanent teeth were associated with the developmental phase of the bud. When the studies considered the development of the permanent tooth at the time of the injury, discoloration of the enamel appeared to occur in the early stages of the formation of both the crown and the root, while enamel discoloration associated with hypoplasia was only found in teeth injured during the formation of the crown 5,6. Severe trauma to the permanent tooth bud at an early stage of odontogenesis may lead to complete deformation of the tooth, causing an odontoma-like formation 10.
Involvement of the crown occurred more often than root involvement or alterations in eruption. This may be attributed to the close relationship between the deciduous tooth root and the permanent tooth crown, and the fact that most traumatic injuries occur between one and four years of age, during the development of the permanent crown 6.
Some studies found that the types of trauma that cause the most sequelae are intrusions, followed by avulsions 6,20,22. Von Arx et al 17, found that more than half of cases with intrusive luxation developed permanent tooth malformations, but found no alteration of the permanent tooth in any case of corono-radicular fracture. Andreasen et al5injury to the permanent tooth is evident, since the socket is fractured or compressed. In the case of avulsion, the slight rotational motion caused by the root curvature may injure the tissues that separate the temporary tooth from the bud of the developing permanent tooth. Fracture of the alveolar bone, in addition to the dental injury, significantly increases the frequency of subsequent alterations in the permanent teeth.
Other studies, such as those by Guedes de Amorim et al 8 Ribeiro do Espírito Santo et al 21, found no significant relationship between the type of trauma and the consequences in the permanent teeth.
Due to their position in the dental arch, the upper incisors are the teeth most affected by trauma. They are the most exposed teeth, especially in cases where they are protruding or there is lip incompetence 1,11,17. The next most affected teeth are the upper and lower lateral incisors, and the upper canines, albeit with a large statistical difference 6.
Reports show that the severity of sequelae varies depending on the child’s age. Several studies analyzed the relationship between the child's age at the time of trauma and sequelae in permanent teeth 4,5,24. Damage secondary to trauma appears to be considerably greater when it occurs at a younger age. Studies report a higher percentage of permanent teeth abnormalities in patients aged < 2 years at the time of trauma 6,22. A high risk of sequelae in this age group may be associated with incomplete bone and permanent teeth 4,8. According to Von Arx et al 17, except for enamel discoloration, all other types of developmental alterations were, to some extent, correlated with the time when the lesion occurred in the primary teeth. The fact that enamel mineralization maturation continues until the time of eruption explains why enamel discoloration may affect all age groups 7,10.
Machado Lenzi et al 10 also found a lower prevalence of sequelae in children aged 5–7 years, while no 8-year-old with trauma presented sequelae.
Some studies found no correlation between the patient's age at the time of trauma and the development of permanent tooth alterations 6,11.
Epidemiological studies of dental trauma provide important data on prevalence and associated factors, which may aid the development of clinical action and prevention protocols. Early treatment of trauma helps avoid further consequences on the tooth involved and its successor 11.