Mandibular incisor dimensions and crowding

Association between crowding estimation and extraction recommendations in orthodontics

INTRODUCTION

Little is known about how precisely orthodontists in the United States (US) assess crowding or at what range of crowding they recommend extraction. This study aimed to assess the relationship between estimated crowding in patients with a Class I relationship and extraction recommendation by orthodontists in the US. The secondary aims were to evaluate the accuracy and precision of clinician estimations and determine if clinician background traits play a role in extraction decision-making.

METHODS

An electronic survey was prepared using 4 patients with a Class I relationship with anterior crowding selected from a University Orthodontics Clinic and was sent to approximately 10,400 subjects through Facebook and the American Association of Orthodontists Partners in Research program.

RESULTS

From the 297 responses received, most clinicians recommended extraction once crowding reached 9-10 mm in either the maxilla or the mandible. The data from 2 patients suggest this decision was more strongly correlated with mandibular crowding. Clinician estimations varied widely but, on average, were precise within approximately 2 mm of objective measurements. There was a tendency to overestimate crowding, especially by Northeastern practitioners. Clinicians who reported routinely measuring crowding or who reported that they recommended extractions to >10% of their patients were 1.2-2.0 and 1.4-1.6 times more likely, respectively, to recommend extraction in the patients.

CONCLUSIONS

Crowding estimation was highly subjective and varied widely among clinicians. Most clinicians recommended extraction once maxillary or mandibular crowding approximated 9-10 mm. Some clinician demographics were correlated with the precision and accuracy of estimations and the likelihood of extraction in the patients.

Comparative Study of Tooth Size and Arch Dimensions in Class I Crowded, Proclined Malocclusion and Class I Normal Occlusion

Aim

The objectives are to compare the extent and to find whether it is arch dimension or tooth size that contributes to a greater extent to malocclusions such as dental crowding and proclination.

Materials and Methods

A total of 90 pretreatment models were selected and divided into three groups, namely uncrowded (Group-A), crowded (Group B), and proclination (Group-C). Measurements obtained were: (1) The largest mesiodistal width of each tooth on each arch (except the second and third molars), (2) Buccal inter-canine and inter-molar widths, (3) Lingual inter-canine and inter-molar widths, (4) Arch perimeters, and (5) Arch length.

Results

The mesiodistal teeth dimensions were higher in crowded and proclination group. Both inter canine width and inter molar width of maxilla were reduced in crowded group. Maxillary and mandibular arch perimeter and arch lengths were higher proclination group.

The rationale for orthodontic retention: piecing together the jigsaw

Retaining teeth in their corrected positions following orthodontic treatment is one of the most challenging aspects of orthodontic practice. Despite much research, the rationale for retention is not entirely clear. Teeth tend to revert to their pre-treatment positions due to periodontal and gingival, soft tissue, occlusal and growth factors. Changes may also follow normal dentofacial ageing and are unpredictable with great variability. In this overview, each of these factors are discussed with their implications for retention, along with adjunctive procedures to minimise relapse. The state of current knowledge, methods used to assess relapse, factors regarded as predictive of or associated with stability as well as overcorrection are outlined. Potential areas requiring further investigation are suggested. The way in which the clinician may manage current retention practice, with a need for individualised retention plans and selective retainer wear, is also considered.

Association between incisor positions and amount of interdental stripping in patients undergoing orthodontic treatment

INTRODUCTION

The study aimed to investigate the effect of a nonextraction treatment approach with interdental stripping (IDS) on the dentofacial structures in patients with dental and skeletal Class I, II, and III malocclusions.

METHODS

A total of 60 patients with mild-to-moderate crowding of the teeth and nonsevere skeletal malocclusion were included and divided into 3 groups: Class I, Class II, and Class III groups (n = 20 per group). In all patients, nonextraction orthodontic treatment was administered, and those who underwent IDS at the jaw quadrants as needed were evaluated. For pretreatment and posttreatment evaluation, lateral cephalometric radiography and 3-dimensional dental model scans were acquired for each patient. For statistical analysis, paired-samples t test and 1-way analysis of variance with Tukey post-hoc test were used for parametric variables, whereas the Wilcoxon paired signed rank test and Kruskal-Wallis test with Dunn post-hoc test were used for nonparametric variables.

RESULTS

An increase in the maxillary incisor angle was observed in patients with Class I and Class III malocclusions, whereas a decrease was observed in patients with a Class II malocclusion (P < 0.05). Mandibular incisor angles were significantly increased in the Class II malocclusion group (P < 0.05) but unchanged in the other groups. IDS was more frequently applied to the posterior aspect of the maxilla and mandible in patients with a Class II malocclusion than in patients with other malocclusion types, and the amount of IDS at the anterior aspect of the mandible was significantly higher in the Class III group.

CONCLUSIONS

Combined nonextraction orthodontic treatment and IDS yielded successful treatment outcomes. IDS application was localized to different jaw regions according to the different malocclusion types.

Perceptions of dental professionals and laypeople to altered maxillary incisor crowding

INTRODUCTION

The aim of this study was to determine how sensitive dental specialists and laypeople are to maxillary incisor crowding when viewed from the front.

METHODS

Computer technology was used to create a series of photographs of the incisors of a smiling woman viewed from the front. The photographs showed varying degrees of maxillary incisor crowding classified according to Little's irregularity index (LII). The incisors illustrated in the photos were ranked on a scale from perfect alignment to severely crowded. The rating was done by 4 groups of people: orthodontists, general dentists, laypeople with experience of orthodontic treatment, and laypeople with no history of orthodontic treatment.

RESULTS

The orthodontists and the general dentists noted misalignment of 1 central incisor when the LII reached 1.5 mm, whereas the laypeople with or without experience of orthodontic treatment were sensitive to 2.0 mm of crowding. When the LII reached 2.0 mm for 1 lateral incisor, it triggered the orthodontists to consider providing orthodontic treatment, whereas this degree of irregularity was ignored by the general dentists and laypeople. When both central incisors were misaligned, the orthodontists were sensitive to the fact at 2.0 mm of LII, whereas the general dentists and the laypeople with experience of orthodontic treatment became sensitive at 3.0 mm of LII, and the laypeople with no history of orthodontic treatment were sensitive at 4.0 mm of LII. When both lateral incisors were misaligned, the orthodontists noted the crowding at an LII of 3.0 mm, the general dentists became sensitive at an LII of 4.0 mm, whereas both the laypeople with experience of orthodontic treatment and the laypeople with no history of orthodontic treatment ignored it. When the crowding of all maxillary incisors reached an LII of 4 mm, both the orthodontists and the general dentists were alerted to the fact, but both the laypeople with experience of orthodontic treatment and the laypeople with no history of orthodontic treatment were sensitive only to a total incisor crowding equal to an LII of 6.0 mm.

CONCLUSIONS

Orthodontists are more critical than other groups when evaluating the misalignment of the maxillary incisors. It appears that the central incisors play a more important role than do the lateral incisors when dental crowding impacts smile esthetics. For all observer groups, it also appears that people are more sensitive to the misalignment of a single tooth than they are to the same level of crowding distributed over multiple teeth.

An odontometric study of tooth size in normal, crowded and spaced dentitions

OBJECTIVE

To assess the mesio-distal tooth width in normal, crowded, or spaced dentitions.

MATERIALS AND METHODS

A sample of 192 maxillary and mandibular dental casts of Libyan subjects was selected from a larger cohort. These subjects did not present with craniofacial anomaly, hypodontia, significant attrition, caries, restorations, or history of permanent tooth extraction or orthodontic treatment. The sample was divided into normal, crowded, and spaced groups according to tooth size/arch length discrepancy. Each group included 32 upper and lower dental casts with equal numbers of males (mean (SD) age = 14.7 (1.9) years) and females (mean (SD) age = 15.7 (2.5) years). The mesiodistal (MD) tooth width, sum of the MD tooth widths mesial to the first molars (TTM), sum of the MD width of the four incisors (I), and the sum of the MD width of canine and first and second premolars (CPP) were calculated for each group. The independent Student t-test was applied sequentially to detect significant differences between paired groups. The ANOVA test was undertaken to explore significant differences between the three groups. Pearson coefficient of correlation was used to evaluate the correlation between I and the corresponding CPP in maxillary and mandibular arches.

RESULTS

MD tooth width, TTM, I, and CPP were significantly wider in the crowded compared to normal and spaced dentitions (P<0.001), except for the width of the upper left lateral incisors in both normal and crowded groups. Although there was a trend for smaller tooth widths in spaced dentitions compared to normal ones, this was only significant in the maxillary left central incisor, maxillary right and left lateral incisors, maxillary right first premolar, mandibular right lateral incisor, and mandibular right canine (P<0.05). However, the maxillary TTM, I, and CPP in the normal group were significantly greater than in the spaced group (P<0.05). Significant positive correlations existed between the mean values of I and CPP in both the maxillary and mandibular dentitions of all groups (P<0.01).

CONCLUSIONS

It appears that in the studied Libyan population, the MD tooth width is a significant component of crowding/spacing.

Correlation between mandibular incisor crown morphologic index and postretention stability

INTRODUCTION

Considering postretention stability as a result of successful orthodontic treatment, we aimed to verify the influence of mandibular-incisor-crown morphology in the relapse of mandibular anterior crowding.

METHODS

The sample comprised 56 white subjects of both sexes with Class I and Class II malocclusions at pretreatment, treated with extraction of 4 first premolars and edgewise mechanics. No patient underwent interproximal stripping during or after treatment. Mean pretreatment age was 13.23 years. Mean treatment time was 2.11 years, and mean posttreatment evaluation time was 5.12 years. Mandibular anterior crowding was measured with the Little irregularity index, and the mesiodistal and buccolingual proportion of the mandibular incisor crowns was measured with the Peck and Peck index. The measurements were obtained from dental casts at the pretreatment, posttreatment, and postretention stages. The Pearson correlation coefficient was calculated to determine the correlation between mandibular-incisor-crown morphology and the amount of postretention-crowding relapse.

RESULTS

The mandibular-incisor-crown morphologic index was not significantly correlated with the amount of mandibular-anterior-crowding relapse.

CONCLUSIONS

Mandibular-incisor-crown morphology is not correlated with the amount of mandibular-anterior-crowding relapse.

Determinação das medidas dentárias mésio-distais em indivíduos brasileiros leucodermas com oclusão normal

Em 60 modelos de gesso ortodônticos foram medidas as larguras mésio-distais dos dentes, de segundo molar a segundo molar, em ambos os arcos, utilizando um paquímetro digital modificado. Este trabalho teve como objetivos determinar o valor médio para a largura de cada dente e observar a presença de dimorfismo sexual, em indivíduos brasileiros leucodermas, com a média de idade de 16,03 anos (25 do gênero masculino e 35 do gênero feminino), não tratados ortodonticamente e portadores de oclusão normal, apresentando no mínimo quatro das seis chaves de oclusão, conforme descrito por Andrews. Os valores das médias individuais dos dentes estudados foram utilizados para a elaboração de uma tabela, correspondentes aos arcos superior e inferior.

Intra-arch occlusal indicators of crowding in the permanent dentition

INTRODUCTION

The objective of this study was to identify the intra-arch occlusal characteristics that best discriminated 3 groups with different grades of dental arch discrepancies. This cross-sectional analysis was conducted in Lima, Peru, in 2003.

METHODS

Intra-arch measurements were made on 150 sets of dental casts of high school students (aged 12-16; 75 boys, 75 girls). Stepwise multiple discriminant analysis (SMDA) was used to obtain a better understanding of the morphological relationships between tooth and dental-arch variables and their relationship with crowding.

RESULTS

Mesiodistal tooth sizes and crown proportions of some teeth differed among significantly crowded, mild-to-moderately crowded, and spaced dental arches. Buccolingual tooth sizes were similar in the 3 groups. Of the arch dimensions evaluated, only intermolar arch width and arch length differed between the groups. An SMDA was developed to classify dental-arch discrepancies in the permanent dentition based on several intra-arch occlusal characteristics. The variable with the highest discriminatory capability between groups was arch length. When arch length was taken out of the SMDA, the explanatory capability from the variability on the dental arch discrepancies diminished from 51% to 14%. When the remaining arch dimension variable (intermolar width) was taken out, the explanatory capability diminished more (from 14% to 8%).

CONCLUSIONS

Although other tooth-size and arch dimensions are indicators of crowding, arch length is the most important factor.

Tooth-size discrepancies among different occlusion groups of southern Chinese children

The purpose of this study was to compare Bolton anterior and overall ratios among different occlusion groups of southern Chinese children. Fifty plaster casts with Class I occlusion, 30 with Class II occlusion, and 30 with Class III occlusion were selected from a random sample of 1247 12-year-old southern Chinese children in early permanent dentition in Hong Kong. For the anterior ratio, a statistically significant difference was found between the Bolton standard and the Class III occlusion group. For the overall ratio, statistically significant differences were found between the Bolton standard and the Class II occlusion group, and between the Class II and the Class III occlusion groups. Thus specific standards are required for Class II and Class III cases from the southern Chinese population.

Is the postretention relapse of maxillary and mandibular incisor alignment related?

Previous studies suggest a poor association between initial and postretention pattern of incisor irregularity. One explanation may be that the incisor movements are limited by the boundaries provided by the incisors in the opposite arch. If so, postretention malalignment of the maxillary and mandibular incisors may be related. To test this hypothesis, long-term postretention study models of 96 patients with acceptable occlusion at the time of appliance removal were examined. The occlusal surfaces of the postretention study models were photocopied, and tooth anatomical contact points were digitized. An algorithm was used to fit the dental arch to the digitized points. The amount of incisor rotation and anatomical contact point displacement of maxillary and mandibular anterior teeth, relative to their respective dental arches, were computer generated. Overbite, the number of occlusal contact points in the anterior segment, and concavity of the lingual surfaces of the maxillary incisors were recorded manually. Statistical analyses demonstrated a significant association (P <.05) between the overall irregularity of the maxillary and mandibular incisors. The association did not differ among subgroups that were stratified according to overbite or number of occlusal contacts. No associations were found for the overall amount of incisor rotation in the 2 arches (P >.05). The amount and direction of displacement of antagonistic pairs of maxillary and mandibular central incisors were also associated (P <.05), but not the amount and direction of rotation (P >.05). The lingual configuration of the maxillary incisors did not affect the pattern of mandibular incisor malalignment.

Nickel-titanium mandibular bonded lingual 3-3 retainer: for permanent retention and solving relapse of mandibular anterior crowding

An innovative technique that involves a nickel-titanium mandibular bonded lingual 3-3 retainer was used to treat relapse of mandibular anterior crowding. The purpose of this study was to demonstrate clinical procedures and to study the effects of a new mandibular bonded lingual 3-3 retainer on the mandibular dental arch. In 18 patients, changes in the irregularity index and in arch dimensions (intercanine width, arch length, and arch depth) were measured against the patients' mandibular dental casts, which were obtained at completion of the previous orthodontic treatment (T(0)). These measurements were taken at the beginning of retreatment (T(1)), and 2 (T(2)), 4 (T(3)), and 6 (T(4)) months after initiation of retreatment. During the period of relapse (T(0)-T(1)), the irregularity index increased from 1.3 to 3.5 mm and the mandibular arch dimensions decreased. Four months after a segment of.018-in nickel-titanium archwire was bonded lingually from canine to canine, the irregularity index decreased from 3.5 to 1.0 mm and the arch dimensions increased and recovered their original posttreatment dimensions. The nickel-titanium archwire was left in place for permanent retention after the period of retreatment. This simple technique effectively solved relapse of mandibular anterior crowding in 4 months. This mandibular bonded lingual 3-3 retainer could be used both actively, to re-treat mandibular anterior crowding without the use of lingual brackets, and passively, for maintenance as a bonded lingual retainer.

Triangular-shaped incisor crowns and crowding

The purpose of this study was to establish if there is a correlation between the shape of the labial crowns of the incisors and crowding. Plaster cast models of 69 untreated individuals (30 males and 39 females) were evaluated. The casts were selected randomly from the collection at Seoul National University and Ajou University. With the use of Little's irregularity index, the sample was divided into 2 groups, a crowded group and a normal group. Repeated measurements of the maximum mesiodistal width of the incisal and cervical areas of the incisors were taken by means of a digital vernier caliper and a ratio of these measurements was calculated. The mean value for the crowded group was significantly larger in the incisal area (P <.01) and smaller in the cervical areas (P <.01) than corresponding values in the normal group. These ratios were correlated with the irregularity index (Pearson r(2) from 55% to 65%). The value obtained from the incisor width ratio in the normal group can be useful for the diagnosis and treatment of crowded malocclusion.

Treatment of a Class I malocclusion with a carious mandibular incisor and no Bolton discrepancy

Occasionally orthodontists must plan treatment for a patient with extensive caries or a traumatic injury to one mandibular incisor. If the patient has a Bolton discrepancy, one treatment option could involve extraction of the affected mandibular incisor. However, if the patient does not have a Bolton discrepancy and a mandibular incisor is extracted, the treatment becomes more complicated. This case report will present and discuss the ramifications of extracting one mandibular incisor in a patient without an anterior tooth-size discrepancy. The CDABO Student Case Selection Committee chose this case for publication.

Stability and relapse of mandibular anterior alignment: University of Washington studies

For more than 40 years, research in the Department of Orthodontics, University of Washington (Seattle, WA) has focused on a growing collection of more than 800 sets of patient records to assess stability and relapse of orthodontic treatment. All patients had completed treatment a decade or more before the last set of data. Evaluation of treated premolar extraction patients, treated lower incisor extraction patients, treated non-extraction cases with generalized spacing, patients treated with arch enlargement strategies, and untreated normals showed similar physiologic changes: (1) Arch length decreases after orthodontic treatment. (2) Arch width measured across the mandibular canine teeth typically reduces posttreatment, whether or not the case was expanded during treatment. (3) Mandibular anterior crowding during the posttreatment phase is a continuing phenomenon well into the 20-to-40 years age bracket and likely beyond. (4) Third molar absence or presence, impacted or fully erupted, seems to have little effect on the occurrence or degree of relapse. (5) The degree of post-retention anterior crowding is both unpredictable and variable and no pretreatment variables either from clinical findings, casts, or cephalometric radiographs before or after treatment seem to be useful predictors.

Retention and stability: a review of the literature

Long-term posttreatment stability is an issue of great concern to all orthodontists. This article highlights the factors reported to play a role in posttreatment crowding and reviews the long-term retention studies evaluating the stability of various treatment modalities. Recommendations, based on well-documented basic principles, are made to try to insure greater posttreatment stability of our orthodontically treated cases.

The effect of premolar extractions on tooth-size discrepancy

The purpose of this study is to investigate whether the extraction of four premolars as a requirement of orthodontic therapy is a factor in the creation of tooth size discrepancies, and to determine whether any tooth extraction combinations create more severe discrepancies. The study is carried out on the pretreatment dental casts of 50 patients with malocclusions. The dental casts were selected according to the main criteria. No tooth-size discrepancy between the mandibular and maxillary dental arches should exist before treatment. Pretreatment mesiodistal dimensions of mandibular and maxillary teeth were measured, recorded on a computer program, and subjected to Bolton's analysis. Hypothetical tooth extractions were performed on each patient by the following combinations: all first premolars, all second premolars, upper first and lower second premolars, and upper second and lower first premolars. The resultant measurements were again subjected to Bolton's analysis to see whether a tooth-size discrepancy had been created. The results were evaluated statistically by the use of paired samples t test. The difference between the pretreatment and postextraction Bolton values was found statistically significant for the first premolar extraction and insignificant for the others. The removal of the four first premolars created the most severe tooth-size discrepancy, whereas the extraction of all four second premolars created fewer discrepancies and the smallest range in the size of discrepancies. The results of this study indicate a new point of view to the question of which teeth to extract when evaluated for tooth size aspect only.

Late lower arch crowding: the role of the transverse dimension

Fifty subjects who were followed longitudinally between 13 and 18 years showed an average increase in lower arch crowding of 2.36 mm. This increase in crowding was examined in relation to tooth width, arch width and jaw width, actual and relative, and to changes in these dimensions with correlation and multiple regression analyses. No relationship was found between width dimensions and late crowding in the lower arch.

The etiology of late lower arch crowding alternative to mesially directed forces: a review

The causes of late crowding in the lower arch alternative to mesially directed forces are reviewed under the headings: late mandibular growth, skeletal structure and complex growth pattern, soft tissue maturation, periodontal forces, tooth structure, occlusal factors, and connective tissue changes. A multifactorial basis for late lower arch crowding seems likely.

A long-term prospective evaluation of the circumferential supracrestal fiberotomy in alleviating orthodontic relapse

This prospective study conducted during a period of nearly 15 years initially involved 320 consecutively selected cases. The primary purpose of the investigation was to statistically evaluate the efficacy of the circumferential supracrestal fiberotomy (CSF) procedure in alleviating dental relapse following orthodontic treatment. The "Irregularity Index" method of Little for measuring the malposition of teeth was used to quantitatively record the relapse of the control and CSF cases at approximately 4 to 6 years after active treatment and again at 12 to 14 years after active treatment. The differences between the mean relapses of the control and the CSF cases were highly significant at both time intervals. The surgical procedure appeared to be somewhat more effective in alleviating pure rotational relapse than in labiolingual relapse. On a long-term basis, the CSF procedure was shown to be more successful in reducing relapse in the maxillary anterior segment than in the mandibular anterior segment. Nevertheless, a significant and unpredictable variation in individual tooth movement following orthodontic treatment was observed in both the control and CSF groups. No clinically significant increase in the periodontal sulcus depth nor decrease in the labially attached gingiva of the CSF teeth was observed at 1 and 6 months following the surgical procedure.

Nonextraction orthodontic therapy: posttreatment dental and skeletal stability

To assess the long-term stability of nonextraction orthodontic treatment, the dental cast and cephalometric records of 28 cases were evaluated. Thirty cephalometric and seven cast parameters were examined before treatment, posttreatment, and an average of almost 8 years postretention. Results showed overall long-term stability to be relatively good. Relapse patterns seen were similar in nature, but intermediate in extent, between untreated normals and four first premolar extraction cases. Significant decreases were seen in arch length and intercanine width during the postretention period despite minimal changes during treatment. Incisor irregularly increased slightly postretention; intermolar width, overjet, and overbite displayed considerable long-term stability. Mandibular incisor mesiodistal and faciolingual dimensions were not associated with either pretreatment or posttreatment incisor crowding. Class II malocclusions with large ANB values and shorter mandibular lengths showed increased incisor irregularity, shorter arch lengths, and deeper overbites at the postretention stage, suggesting that the amount and direction of facial growth may have been partially responsible for maturational changes seen during the postretention period.