Tarcila Triviño

A new concept of mandibular dental arch forms with normal occlusion

INTRODUCTION Because it is important to maintain dental arch dimensions during orthodontic therapy, all possible dental arch forms must be evaluated. METHODS A mathematical method associated with a polynomial function was used to evaluate the dental arch forms of 63 mandibular models of Brazilian adolescents in the permanent dentition with normal occlusion. A bead was glued to each tooth to simulate an orthodontic accessory and help in the measurement of distances between the center of the bead to the x- and y-axes. The dental casts were digitized, and images were plotted on a computer program to obtain the sixth-degree polynomial and the graph of this function. These segments were organized into 8 groups according to the form of the anterior curve of the dental arch; these were named forms A through H. Each group was subdivided into 3 subgroups: small, medium, and large sizes. RESULTS Form A was the most frequently observed at 22%, whereas form G was observed in only 2% of the total sample. Forms A, B, C, D, E, and F had more curve segments in medium size, and forms G and H had more curves in small size. A mean dental arch curve was calculated; however, this form coincided with form C, which had an incidence of 10%. CONCLUSIONS The mandibular dental arch is represented by 23 forms; thus, a normal dental arch cannot be represented by only 1 simple arch form.

Evaluation of distances between the mandibular teeth and the alveolar process in Brazilians with normal occlusion

INTRODUCTION The aims of this study were to evaluate the distances between the mandibular permanent teeth and the alveolar process in Brazilians with normal occlusion and to compare them with normal American values. METHODS We used 59 mandibular casts from untreated subjects who had permanent dentition and the 6 keys to normal occlusion. A computer program was used to calculate the distances between the dental reference points and the alveolar process for each tooth. The mean values were then compared to the normal values by applying the Student t test at a significance level of 0.05. RESULTS The results showed a progressive increase of these distances from the anterior region (incisors) to the posterior region (molars), from 0.00 to 2.49 mm. All measurements had statistically significant differences from the American sample, except for the values for canines and first premolars. CONCLUSIONS Brazilians with normal occlusion have more lingual crown positions for the incisors, second premolars, and molars compared with Americans with normal occlusion. Although these findings were statistically significant, they are unlikely to be clinically significant.

A forma do arco dentário inferior na visão da literatura

AIM: The main purposes of this study were to analyze the literature related to a relevant clinic aspect, the dental arch form, emphasizing the importance of maintaining the original form in order to obtain stability after the orthodontic treatment, as well as to evaluate the methods used for establishing the dental arch form and the arch form diagrams proposed by many authors. RESULTS AND CONCLUSIONS: It was verified that there is some controversy regarding the indication of an ideal average form and the selection of an individualized form from diagrams which provide varied formats for the dental arch. However, some progress was observed in the methodologies applied in recent studies, which will possibly provide more accuracy in arch form determination in the near future.

Avaliação rotacional mandibular após os efeitos da disjunção rápida da sutura palatina mediana

The studies concerning the rapid expansion of the median palatine suture, by using some appliances that expand the maxillary dental arch, show that the maxilla moves downward and forward, causing alterations in the occlusion, such as anterior bite opening and an increase of the angles of the occlusal and mandibular planes values. This study aimed at evaluating the alterations after the rapid maxillary expansion by using two types of expanders (Haas – GI and Hyrax – GII). The sample consisted of 93 lateral cephalometric radiographs from 31 Brazilian individuals (15 females and 16 males) between 9 and 16 years of age (mean age 13 years and 2 months). Radiographs were taken from each individual in the pre-expansion, immediately after expansion, and at the conclusion of the leveling stage. Angle measurements PP.GoMe, NBa. GoMe and NS.Gn showed a statistically significant increase in the pre-expansion and the leveling stages in both groups. The clockwise, downward and back rotational displacement of the mandible was verified by the statistically significant increase in the angle measurements studied in the postexpansion stage, remaining in the final leveling stage for both groups.