James L. Ackerman

Pharyngeal airway volume and shape from cone-beam computed tomography: Relationship to facial morphology

INTRODUCTION The aim of this study was to assess the differences in airway shape and volume among subjects with various facial patterns. METHODS Cone-beam computed tomography records of 62 nongrowing patients were used to evaluate the pharyngeal airway volume (superior and inferior compartments) and shape. This was done by using 3-dimensional virtual surface models to calculate airway volumes instead of estimates based on linear measurements. Subgroups of the sample were determined by anteroposterior jaw relationships and vertical proportions. RESULTS There was a statistically significant relationship between the volume of the inferior component of the airway and the anteroposterior jaw relationship (P = 0.02), and between airway volume and both size of the face and sex (P = 0.02, P = 0.01). No differences in airway volumes related to vertical facial proportions were found. Skeletal Class II patients often had forward inclination of the airway (P <0.001), whereas skeletal Class III patients had a more vertically oriented airway (P = 0.002). CONCLUSIONS Airway volume and shape vary among patients with different anteroposterior jaw relationships; airway shape but not volume differs with various vertical jaw relationships. The methods developed in this study make it possible to determine the relationship of 3-dimensional pharyngeal airway surface models to facial morphology, while controlling for variability in facial size.

Soft tissue limitations in orthodontics: Treatment planning guidelines

Orthodontists have traditionally viewed structural discrepancies as the major limitation of treatment. In reality, it is the soft tissues that more closely determine therapeutic modifiability. The boundaries of dental compensation for an underlying jaw discrepancy are established by pressures exerted on the teeth by the lips, cheeks, and tongue; limitations of the periodontal attachment; neuromuscular influences on mandibular position; and the contours of the soft tissue facial mask. The ability of the soft tissues to adapt to changes in tooth-jaw relationships are far narrower than the anatomic limits in correcting occlusal relationships. The tolerances for soft tissue adaptation from equilibrium, periodontal, and facial balance standpoints are in the range of 2 to 3 mm for expansion of the mandibular arch and even less for changes in condylar position. Thus, analysis of the soft tissues is the critical step in orthodontic decision making, and this can only be accomplished through physical examination of the patient. Although quantitative measurements cannot be rigorously applied, guidelines for soft tissue assessment, with particular emphasis on facial esthetics, are proposed. From this perspective, a contemporary philosophy of orthodontic practice is offered, with general indications and contraindications for nonextraction, extraction, and surgical treatment.

Cranial base superimposition for 3-dimensional evaluation of soft-tissue changes.

INTRODUCTION The recent emphases on soft tissues as the limiting factor in treatment and on soft-tissue relationships in establishing the goals of treatment has made 3-dimensional (3D) analysis of soft tissues more important in diagnosis and treatment planning. It is equally important to be able to detect changes in the facial soft tissues produced by growth or treatment. This requires structures of reference for superimposition and a way to display the changes with quantitative information. METHODS In this study, we outlined a technique for quantifying facial soft-tissue changes viewed in cone-beam computed tomography data, using fully automated voxel-wise registrations of the cranial base surface. The assessment of soft-tissue changes is done by calculation of the Euclidean surface distances between the 3D models. Color maps are used for visual assessment of the location and the quantification of changes. RESULTS This methodology allows a detailed examination of soft-tissue changes with growth or treatment. CONCLUSIONS Because of the lack of stable references with 3D photogrammetry, 3D photography, and laser scanning, soft-tissue changes cannot be accurately quantified by these methods.

Primary failure of eruption and PTH1R: The importance of a genetic diagnosis for orthodontic treatment planning

INTRODUCTION Primary failure of eruption (PFE) is characterized by nonsyndromic eruption failure of permanent teeth in the absence of mechanical obstruction. Recent studies support that this dental phenotype is inherited and that mutations in PTH1R genes explain several familial cases of PFE. The objective of our study was to investigate how genetic analysis can be used with clinical diagnostic information for improved orthodontic management of PFE. METHODS We evaluated a family (n = 12) that segregated an autosomal dominant form of PFE with 5 affected and 7 unaffected persons. Nine available family members (5 male, 4 female) were enrolled and subsequently characterized clinically and genetically. RESULTS In this family, PFE segregated with a novel mutation in the PTH1R gene. A heterozygous c.1353-1 G>A sequence alteration caused a putative splice-site mutation and skipping of exon 15 that segregated with the PFE phenotype in all affected family members. CONCLUSIONS A PTH1R mutation is strongly associated with failure of orthodontically assisted eruption or tooth movement and should therefore alert clinicians to treat PFE and ankylosed teeth with similar caution-ie, avoid orthodontic treatment with a continuous archwire.

Communication in orthodontic treatment planning: bioethical and informed consent issues.

Orthodontic treatment planning is an interactive process in which the patient or parent and the orthodontist serve as co-decision makers. As in most partnerships, there is a natural tension between the orthodontist and the patient because of differences in their frames of reference. The orthodontist generally is influenced more by the objective findings (the problem list), whereas patients are guided more by subjective issues related to their perceived needs, desires, and values. The art of careful probing and listening to the patient as part of the treatment planning process is an essential skill. One of the most difficult situations in contemporary orthodontics is presented by the patient with a jaw discrepancy for which the alternative treatments are orthodontic camouflage through dental compensation or surgical-orthodontic correction. Computer imaging to simulate the probable treatment outcomes can facilitate communication about these alternatives by eliminating misconceptions. Full disclosure and the consideration of all viable treatment alternatives have great benefits from a risk management standpoint, in addition to their bioethical merits.

Porous block hydroxyapatite in orthognathic surgery.

Seventy-six nonconsecutive patients undergoing orthognathic surgery, in whom blocks of porous hydroxyapatite were implanted into osteotomy gaps in lieu of autogenous bone grafts, are the subjects of this report. Surgical procedures include inferior maxillary repositioning (10 patients), maxillary advancement (24 patients), transverse maxillary expansions (17 patients) and inferior repositioning of the chin (25 patients). A total of 140 anatomic sites were implanted. Eleven patients later consented to open biopsy of the implant material at a mean 10.2 months following implantation. At the time of follow-up, mean 16.3 months, excellent osseous stability was observed. Three patients developed complications relative to the presence of the implant. Twenty-one of 24 biopsy specimens demonstrated an osseous union of implant to bone with osseous deposition within the implant pores. Radiographic follow-up revealed implant blocks to maintain their volume with no change in density or discreteness. The biological behavior and biomechanical properties of porous block hydroxyapatite are discussed. These implant characteristics make it a feasible bone graft substitute in orthognathic surgery and justify its continued use in this context.

A systematic modification of edgewise therapy

This article describes a highly systematic modifcation of the edgewise technique that incorporates the principle of light continuous force application. It is a re-evaluation of our earlier article in view of the experience gained in applying this treatment approach in a teaching clinic. The classification of cases according to retraction requirements, the appliance designs, and the use of four basic phases of treatment remains largely the same as previously described. Some of the variations and modifications that have been necessary because of new information and pedogogical considerations are discussed. The treatment of typical orthodontic problems with differing retraction requirements is illustrated.