This study was approved by the Research Ethics Committee of the University of Barcelona and the Children Hospital of Barcelona and conducted in a day care center, CAP, Montcada i Reixac. The participants’ legal guardians gave positive consent on the day of the clinical examination.
A cross-sectional observational survey was carried out on boys and girls aged 3 to 6 years and included clinical evaluations of malocclusions and structured interviews.
All the children in the study met the inclusion criteria which included children of both genders aged 3 to 6 years; children exclusively in the deciduous dentition phase; agreement to participate in the clinical exam; all the normal numbers, sizes, and shapes of deciduous teeth; no major tooth destruction or reconstruction; children with no systemic diseases and/or neurological diseases; and parental questionnaires about the child’s habits.
Children were excluded from the study if their parents did not agree to their participation, they have syndromes or systemic problems affecting craniofacial growth, they have the presence of at least one permanent tooth, they have loss of mesial-distal diameter due to caries, and they have previous orthodontic treatment.
All clinical exams were performed by an experienced examiner, a PhD student (GMLF) who had previous experience in cross-sectional data. The child remained seated on a chair in front of the examiner. The examinations were performed under artificial light, using latex gloves and a disposable spatula. The clinical exam was performed with the aid of a disposable tongue depressor source. To ensure that natural occlusion was evaluated, the child was asked to open and close his/her mouth several times and to swallow saliva before the examination began. When necessary, the mandible was gently guided towards centric occlusion by the examiner.
The outcomes related to the children’s dental arch characteristics were examined in the three dimensions with the following criteria.
The transverse relation was measured by direct inspection in the presence of posterior crossbite or if the absence was considered normal occlusion. One of five separate relationships was recorded considering the following categories: normal relationship; posterior unilateral crossbite left side; posterior unilateral crossbite right side; bilateral posterior crossbite—both hemi-arches; and just one tooth was crossed. Posterior crossbite is considered present when, in occlusion, one or more of the maxillary deciduous canine or molars occluded lingual to the buccal cusps of the opposing mandibular teeth. Upper midline shift was registered if the midline was displaced by at least 1 mm. In addition, midline deviation data was also collected and the distance between the upper and lower midlines in the frontal plane was considered.
The vertical relation (relationship of incisors) was measured by direct inspection: one of three separate relationships was recorded in normal, anterior open bite, and overbite. Overbite was obtained by measuring the vertical distance between the upper and lower central incisor edges with the teeth in occlusion . This distance was considered normal when the upper incisor covered the lower up to 3 mm and overbite for values greater than 3 mm. When there was no overlap between the upper and lower incisors, with a minimum space of 1 mm between both incisal edges, it was considered anterior open bite .
The sagittal interarch relationship was classified according to the deciduous canine relationship as angle class I, class II, or class III, with class I considered normal occlusion, class I canine and molars bilateral, or class I canine and molars unilateral, and class II or class III considered altered: class II bilateral, class II 1 (increased overjet), class II 2 (without overjet), class II subdivision (I o III), class II unilateral, others with no classification, and class III or anterior crossbite.
A questionnaire in the form of a structured interview was applied with mothers or guardians in order to find out about nutritive sucking habits (breastfeeding and bottlefeeding), non-nutritive sucking habits (pacifiers and finger sucking), and the presence of malocclusions. The data collected included the presence and the duration of non-nutritive sucking habits and, if the child had sucking, any type of non-nutritive sucking habits: pacifier-sucking habit and digit sucking.
Data analyses were performed using SPSS software 22.0. Data analysis included descriptive statistics (frequency distribution). Statistical significance for the association between the non-nutritive sucking habits and the development of malocclusion was determined using chi-square, and Fisher’s exact tests with odds ratio (OR) calculations were used for intergroup comparisons. Children with non-nutritive sucking habits were excluded from the analysis. The level of significance was set at 5 %.