Richard G. Alexander

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.

Bilateral congenital absence of maxillary lateral incisors: a craniofacial and dental cast analysis.

The dental casts and cephalometric records of forty-three patients exhibiting bilateral congenital absence of maxillary lateral incisors were evaluated to determine the nature and extent of any concurrent craniofacial and dental anomalies. The effects of bilateral orthodontic space closure were evaluated on a subsample of twenty-two cases. The data revealed normal dental arch length, arch width, overjet, and overbite, while significant tooth size discrepancies were found in several anterior and posterior teeth. Craniofacial deviations from normal included smaller maxillary length, smaller mandibular length, smaller anterior cranial base, and nasal bone. Vertical facial dimensions, both anterior and posterior, were significantly less, as was the mandibular plane angle. Soft-tissue examination revealed a 10 degrees greater nasiolabial angle, which was increased a further 5 degrees as a result of a mean incisor retraction of 1.5 mm during space closure. The craniofacial anomalies noted in the present sample were similar to those seen in persons with clefts and may reflect a common etiology related to a developmental disturbance during fusion of the facial processes in utero. In the treatment of patients with bilateral congenital absence of maxillary incisors, mechanotherapy designed to open the mandibular plane, increase the vertical dimension, and move the maxillary posterior teeth forward is recommended in order to prevent worsening the Class III tendency and to minimize maxillary incisor and upper lip retraction. Most cases will require significant mesiodistal reduction in tooth size in order to achieve an optimal occlusion.

Differential diagnosis and treatment planning for the adult nonsurgical orthodontic patient

Increasing numbers of adult patients are seeking orthodontic care and some, despite significant skeletal malocclusions, elect not to have combined orthodontic-surgical treatment. The purpose of this article is to outline some of the diagnostic and therapeutic principles that can be used in the adult nonsurgical orthodontic patient. The importance of realistic goal setting in the face of compromised occlusions is emphasized. Diagnosis should include evaluation of all three dimensions and recognize the limitations of therapy in each dimension for the nongrowing patient. Periodontal considerations, extraction decisions, and retention regimens are of vital importance to the achievement and maintenance of an optimum result. Clinical records will demonstrate four commonly seen problems and their resolution.

Finite element analysis of dual hydroforming processes

Abstract The tube hydroforming process has gained increasing attention in recent years. With the hydroforming process, manufacturers can realize substantial cost savings as it provides reduced part count, increased part strength and stiffness, and reduced weight. Coordination of the pressurization and feeding curves is critical to generate successful parts without fracture or wrinkling failure. Herein a new process parameter, counter pressure, is introduced to achieve favorable tri-axial stress state during deformation process. This paper will establish the merits of applying external counter pressure in tube hydroforming. It is observed that the counter pressure will provide back support to the tube material. Excessive thinning and premature wrinkling could be prevented. Thus, larger tube expansion could be achieved. The process will be referred as dual hydroforming.

The accuracy of computerized growth prediction in Class II high-angle cases.

This study was conducted to test the accuracy of a commercially available forecasting system in predicting the effects of growth and orthodontic treatment. The pretreatment cephalograms and wax bites of mandibular casts of thirty-three consecutively treated Class II patients with high mandibular plane angles, along with twenty-six criteria related to treatment preference, were submitted for analysis. All patients had already been treated on a nonextraction basis by a single practitioner using high-pull face-bow headgear. The computer-generated posttreatment predictions or visual treatment objectives (VTOs) were compared to the actual posttreatment cephalograms, using twenty-one linear and nine angular measurements. Fifteen of the thirty parameters evaluated showed statistically significant (P less than 0.01) differences between the actual posttreatment result and the computer prediction. The computer was found to be accurate in predicting the effects of growth and treatment on maxillary position and rotation, mandibular length, upper face height, and incisor positions. It was found to be inaccurate in predicting the effects of growth and treatment on maxillary length, mandibular rotation, lower anterior and posterior face heights, the horizontal and vertical positions of the molars, and over 50% of the soft-tissue parameters.

Second molar impaction associated with lip bumper therapy

INTRODUCTION: Although lip bumpers (LBs) provide significant clinical gain of mandibular arch perimeter in mixed-dentition patients, orthodontists are reluctant to use them due to the possibility of permanent second molar eruptive disturbances. OBJECTIVE: The present study was conducted to assess second molar impaction associated with the use of LBs, and to investigate how they can be solved. MATERIAL AND METHODS: Lateral and panoramic radiographs of 67 patients (34 females and 33 males) were assessed prior (T1) and post-LB treatment (T2). LB therapy lasted for approximately 1.8 ± 0.9 years. Concomitant rapid palatal expansion (RPE) was performed in the maxilla at LB treatment onset. Impaction of mandibular second molars was assessed by means of panoramic radiographs in relation to the position of first mandibular molars. Horizontal and vertical movements of first and second molars were assessed cephalometrically on lateral cephalometric radiographs based on mandibular superimpositions. RESULTS: Eight (11.9%) patients had impacted second molars at the end of LB therapy. Two patients required surgical correction, whereas five required spacers and one patient was self-corrected. Mandibular first molar tip and apex migrated forward 1.3 mm and 2.3 mm, respectively. Second molar tip showed no statistically significant horizontal movement. CONCLUSION: Although LB therapy increased the risk of second molar impaction, impactions were, in most instances, easily solved.