Development Dental Defects in Permanent Teeth Resulting From Primary Tooth Trauma. A Systematic Review.

Children are vulnerable to dental trauma, especially in the rst two year of life.The objective was to determine whether trauma in temporary teething causes alterations in the development of permanent teething. Searches were made in May 2020 using PubMed, MEDLINE, MEDES, Scopus, Lilacs, and Embase. Papers in English, German, and Spanish, without restrictions in the year of publication, were included. The quality of the studies was analyzed using the NOS Scale.The search retrieved 537 references, and 7 studies were included for a qualitative analysis. The results showed that trauma to a deciduous tooth can damage the bud of the permanent tooth. Enamel discoloration and/or hypoplasia were the most common sequelae in the permanent teeth after trauma to the primary predecessor. The type and severity of sequelae in the permanent tooth are associated with the development phase of the bud. Children with trauma of their primary teeth should receive check-ups until the eruption of the permanent teeth for the early diagnosis and treatment of possible sequelae. Intrusion of the primary tooth was the trauma that caused the most damage and enamel alterations the most frequent sequelae. consequences of primary tooth trauma in the development of the permanent teeth are enamel discoloration, enamel hypoplasia, coronal dilaceration, root dilaceration, odontoma-like malformations and alterations in eruption 5,8,9 . Constant follow-up, with complementary tests, such as radiographs, and appropriate clinical interventions, can minimize or even prevent damage to the successor tooth 10,11 .


Introduction
Children are especially vulnerable to dental trauma, especially in the rst two year of life, when they are starting to walk and socialize. The prevalence of trauma ranges from 4% to 33% 1 . Epidemiological data show that approximately 30% of children aged < 7 years have trauma in ≥ 1 temporary incisor, and about 40% of children go to the dentist for the rst time due to dental trauma 2 .
Dental injuries have been recognized as an oral public health problem 3 .Trauma lesions are considered emergency situations as they require immediate attention and may have important medical, aesthetic and psychological consequences for children and their parents 4 .
Due to the close relationship between the apex of primary teeth and the bud of permanent teeth, any lesion to the temporary teething may in uence the eruption of the permanent teeth 5 .
The severity of sequelae depends on the patient's age, the degree of root reabsorption, the type and extent of the trauma, and the degree of development of the permanent successor at the time of trauma. Intrusion and avulsion of temporary teeth are considered the types of trauma that have the most consequences in independently and resolved disagreements by consensus. In cases where consensus was not reached, the authors consulted a third author (A.V) who helped reach consensus.
Data extraction and quality assessment.
The same two authors (C.S., L.C.) extracted data from the articles included and evaluated the quality of the studies using the Newcastle-Ottawa scale (NOS) 16 and cohort studies. For cross-sectional studies, the NOS tool for cohort studies was used.
According to the NOS scale, each study may be assigned a maximum score of 9, based on 3 different categories, classifying the study as "high quality" if the total score is ≥ 7. In our review, we were able to assign a maximum score of 8 since, in the "comparability" category, we considered a maximum score of one point, rather than two, because the studies analyzed related the exposed and unexposed groups by population only, without considering other factors. Therefore, we determined that these studies had to reach a score of 6 to be classi ed as "high quality".
For some categories we had to determine appropriate cut-off points for evaluation. All authors agreed the following points: (a) a minimum of 50 children ( rst item in the selection category) was established as a representative sample, (b) the radiographic test ( rst item in the results category) was established as a common register for all studies and (c) an appropriate follow-up period up to the eruption of the permanent successor to the deciduous tooth with trauma (second item in the results category).

Results
The search strategy yielded 537 articles: 201 from Embase, 179 from Scopus, 92 from PubMed, 22 from Lilacs and 43 from MEDLINE. No items were found in MEDES. After removing all duplicate items, 310 remained. After applying the selection criterion, we included 18 articles in the review ( Fig. 1 Quality assessment. Using the NOS scale for cohort and cross-sectional studies, we found that none of the 15 studies reached the maximum score of 8, but four with a score of ≥ 6 were classi ed as high quality 1,6,11,17 (Table 1). Using the NOS scale for case-control studies we found that, although none of the 3 studies reached the maximum score of 8, they could be classi ed as high quality 5,10,18 ( Table 2). The remaining 10 studies were classi ed as low quality. Due to the lower evidence of the results in low quality articles, the systematic review only reports the results of the high-quality studies (Tables 3 and 4). ‡ We used the following criteria to assess the methodological quality of each study: representativeness of the exposed cohort (1); selection of the nonexposed cohort (2); ascertainment of exposure (3); demonstration that outcome of interest was not present at the start of study (4); comparability on the basis of confounding control in the design or analysis (5); assessment of outcome (6); duration of follow-up period (7); and adequacy of follow up (8). An "X" represents 1 point contributing to the total score, which represents the level of methodological quality we found for each study. Determining the methodological quality is important for determining the validity of the study results. Brazil Case-control X X X X X X X 7 † Source:(Wells et al., n.d.) ‡ We used the following criteria to assess the methodological quality of each study: adequate case de nition (1); representativeness of the case participants (2); selection of control participants (3); de nition of control participants (4); comparability on the basis of confounding control in the design or analysis (5); assessment of exposure (6); same methods for case control participants (7); and nonresponse rate (8). An "X" represents 1 point contributing to the total score. The total score represents the methodological quality we found for each study. Determining the methodological quality is important for determining the validity of the study results. Future researchers can note the placement of points for each study in this systematic review as a guideline for focusing the goals of future studies to increase the quality of the research on the topic. Table 3 Summary of the high-quality cohort and cross-sectional studies about consequences in permanent teeth after primary teeth injuries.    Four were cross-sectional studies: observational and descriptive studies in which researchers called children who had had trauma in the primary dentition to evaluate the consequences in the permanent dentition 1,6,11,17 . The remaining three were case-control studies 5,10,18 . Tables 3 and 4 summarize the data from high quality studies. The sample size varied from 78 to 879 children and 138 to 753 primary teeth with trauma. The children were aged between 0 and 17 years. All studies included children of both sexes: several found no differences between sexes in terms of the frequency of trauma 6,11 while others described a higher frequency in boys than in girls 1 .
Most studies included all types of trauma 1,5,10,17 two only studied intrusions 6,11 specify the type of trauma 18 . The types of trauma were classi ed according to the Andreasen 26 in most studies reviewed. In most of the articles the teeth most affected by trauma were the upper central incisors 1,6,10,11 consequences were described after intrusions 1,5,10,11,17 .
In most studies, researchers reported the results as prevalence rates with a P value when there were signi cant differences. Andreasen et al 5 between the type of trauma and the patient's age at the time of trauma, with the consequences on permanent teeth being less frequent when trauma occurred in children aged > 4 years, results similar to those of Lenzi et al 10 . Other studies found no signi cant relationship between the time of intrusion and sequelae in permanent dentition 6,11 .
The prevalence of permanent tooth alterations ranged from 4.5% 1 to 68.8% 11 , the most common being tooth enamel defects. Although many of the articles studied the consequences in both sets of teeth, we focused only on the consequences in permanent dentition.
Consequences in permanent dentition in high quality articles.
Hypoplasia and/or hypocalci cation were the most common malformations in permanent teeth in all studies 1,5,6,10,11,18 especially after intrusion or avulsion.
They included enamel discoloration, which ranged from white to yellow-brown, and defects of the enamel surface 17 . These lesions may be caused by environmental causes or genetic factors, emphasizing the need for a control group in studies 10 .
Alterations in eruption were much less common than enamel lesions 1,11 . In the study by Altun et al 6 , ectopic eruption was observed as a single sequela in 23 teeth and combined with other sequelae in 7 teeth.
Coronal or root dilaceration was rare or infrequent 1,5,6,11 . Alterations in the development of the remaining teeth involving the crown occurred more frequently than those in which the root was involved 6,17 .
Hypomineralization. Only one study mentioned two cases of hypomineralization due to injury to deciduous tooth 1 .
Odontoma was rare or uncommon and was only observed in groups who had trauma, indicating a direct relationship 10 .

Discussion
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 in uenced the results, as the alterations in permanent dentition observed may be due to other causes (molar incisor hypomineralization, amelogenesis imperfecta, uorosis, 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][5][6][7][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 tooth 10,17 .
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 coronoradicular fracture. Andreasen et al 5 injury 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, signi cantly increases the frequency of subsequent alterations in the permanent teeth.
Other studies, such as those by Guedes de Amorim et al 8  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 .

Conclusions
Children with dental trauma of the primary teeth should receive check-ups for the diagnosis and treatment of possible sequelae until the eruption of the permanent teeth.
The frequency of revisions will depend on the severity of the dental trauma, being more frequent the greater the severity. Intrusion is the trauma that causes the most damage and alterations in enamel development the most frequent sequelae.