The mandibular dental arch: part II. Effects of lower incisor position on the soft tissue profile.

It has been demonstrated that there are reliable methods of predicting the ultimate position of the lower incisor and the soft tissue. However, the concept of treating this tooth to any one number for every individual was not supported by the evidence. An optimum system would allow the clinician to select and combine factors from all methods and arrive at a balance of esthetics, function, and stability, obtaining a suitable compromise for his individual patient. This is undoubtedly attempted intuitively by many experienced clinicians.     

The mandibular dental arch: part III. Buccal expansion.

The tendency toward relapse in intercuspid width has been examined with those cases having final intercuspid width less than 27 mm showing significantly less relapse than those cases with final intercuspid width of 28 mm or more. The point of contact between the cuspid and first premolar has been introduced as a key point on the arch, determining arch width. An individualized norm has been derived for this measurement as a function of the patient's tooth size, facial pattern, and other variables based upon stable normal occlusions in treated cases. Those cases expanded to a dimension exceeding the norm by more than 1 mm showed a greater propensity toward relapse. The group following the norm was significantly more stable than the over- and underexpansion groups at the .025 significance level. An individual norm for intermolar width based upon the patient's facial pattern (using frontal and lateral X-rays) has been established. Cases showing relapse showed considerably less space between the lower molar and the JAG plane, and greater lower face height than stable cases. The results show that the space available for the permanent dentition can be estimated in advance of treatment based on the patient's own skeletal measurements, thus minimizing unnecessary extractions, relapse, and extended treatment time due to errors in diagnosis.     

Correlation between maxillary central incisor crown morphology and mandibular dental arch form in normal occlusion subjects

The aim of this study was to evaluate the correlation between the morphology of the mandibular dental arch and the maxillary central incisor crown. Cast models from 51 Caucasian individuals, older than 15 years, with optimal occlusion, no previous orthodontic treatment, featuring 4 of the 6 keys to normal occlusion by Andrews (the first being mandatory) were observed. The models were digitalized using a 3D scanner, and images of the maxillary central incisor and mandibular dental arch were obtained. These were printed and placed in an album below pre-set models of arches and dental crowns, and distributed to 12 dental surgeons, who were asked to choose which shape was most in accordance with the models and crown presented. The Kappa test was performed to evaluate the concordance among evaluators while the chi-square test was used to verify the association between the dental arch and central incisor morphology, at a 5% significance level. The Kappa test showed moderate agreement among evaluators for both variables of this study, and the chi-square test showed no significant association between tooth shape and mandibular dental arch morphology. It may be concluded that the use of arch morphology as a diagnostic method to determine the shape of the maxillary central incisor is not appropriate. Further research is necessary to assess tooth shape using a stricter scientific basis.     

Correlations between lower incisor crowding and lower incisor position and lateral craniofacial morphology

Crowding of the lower incisors is a problem encountered frequently in orthodontic practice. Successful therapy may depend on the orthodontist's ability to evaluate factors contributing to the overall pattern. Two of these factors, vertical skeletal morphology and lower incisor position in the lateral cephalogram, were evaluated. Dental casts and cephalograms of 100 children with primary mandibular incisor crowding (that is, primary discrepancy between mesiodistal tooth width and available space of the dental alveolar process and apical base) were examined in this study. Results indicated the following: (1) all vertical skeletal and lower incisor position measurements closely duplicated published norms, (2) no correlation was found between lower incisor crowding and either skeletal morphology or lower incisor position, (3) a factor analysis did demonstrate, however, that other selected variables were interrelated, and (4) the cause of lower incisor crowding must be attributed to factors not examined in this study.     

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近年来,许多正畸医生对安氏Ⅱ1错畸形伴下颌前牙轻度唇向倾斜的患者多倾向于不拔牙治疗而运用唇挡这一功能性矫治器进行治疗,这一技术受到人们越来越多的关注。本文就唇挡的作用原理、制作要求、矫治效果及效果的稳定性等几方面加以综述。     

Changes in mandibular incisor position and arch form resulting from Invisalign correction of the crowded dentition treated nonextraction

Objective:To investigate changes in mandibular incisor position resulting from Invisalign correction of the crowded dentition without extraction.Materials and Methods:A retrospective chart review was completed on 61 adult White patients. Patients were categorized into three groups based on the value of pretreatment crowding of the lower dentition: 20 mild (2.0–3.9 mm), 22 moderate (4.0–5.9 mm), and 19 severe (>6.0 mm). Cephalometric radiographs were measured to determine lower incisor changes. Interproximal reduction and changes in arch width were also measured. Statistical evaluation of T₀ and T₁ values using paired t-tests and analysis of covariance were applied to evaluate mean value changes.Results:Lower incisor position and angulation changes were statistically significant in the severe crowding group. There were no statistically significant differences in lower incisor position between the mild and moderate crowding groups. There was a statistically significant increase in buccal expansion in each of the three groups.Conclusions:Invisalign^® treatment can successfully resolve mandibular arch crowding using a combination of buccal arch expansion, interproximal reduction, and lower incisor proclination. When there is <6 mm of crowding, lower incisor position remained relatively stable. The lower incisors proclined and protruded in the more severely crowded dentitions (>6 mm).     

The surgical-orthodontic correction of mandibular deficiency. Part I

Persons with mandibular deficiency and Class II malocclusions have a spectrum of esthetic, skeletal, and occlusal characteristics. In many of these patients optimal overall results are best obtained via a combined orthodontic-surgical approach. In such cases a critical patient evaluation is essential to decide (1) the optimal operation and (2) the appropriate orthodontic-surgical sequencing. In Part I of this article our method of making these two basic decisions is presented, the decisions being predicated upon achieving optimal esthetic, functional, and stable results. In addition, two of the possible orthodontic-surgical approaches--the augmentation genioplasty and the anterior maxillary ostectomy are discussed in detail. These approaches are illustrated with representative cases. In Part II of the article additional options for combined orthodontic surgical-management of this patient population will be discussed.     

The mandibular foramen: its anteroposterior position.

This study has been conducted on forty-five Asiatic skulls and sixty-two mixed skulls of black and white Americans to determine the anteroposterior relationship of the mandibular foramen. The mean size of the anterior dimension was greater than the mean size of the posterior dimension of the ramus in all instances. The mandibular foramen was found to be located in the third quadrant anteroposteriorly. The lingula was located just anterior to the mandibular foramen. There was no right- or left-side dominance in the ramus size and position of the mandibular foramen. No appreciable difference was noted in the location of mandibular foramen in the two groups studied.     

The child dental patient. Part I. The nature and prevalence of children's dental fears.

For various reasons, fear of dentists and dentistry is not uncommon among children. These fears not only disrupt the performance of clinical procedures, they also tend to undermine the relationship between dentist and child patient. It would seem to make sense then, to address this vexing problem in which two major issues are involved. The first is concerned with the prevalence of dental fears among children and the second deals with their management. For reasons of convenience, clarity and brevity, these issues are dealt with in two separate papers. The first paper (Part I) focuses on acquiring an understanding of the nature and prevalence of dental fears among children and the second (Part II) is concerned with investigating ways in which these fears could best be managed. Parts I and II appear in successive issues of the SADJ.