James Mah

Radiation absorbed in maxillofacial imaging with a new dental computed tomography device

OBJECTIVE The purpose of this investigation was to measure the tissue-absorbed dose and to calculate the effective dose for the NewTom 9000, a new generation of computed tomographic devices designed specifically for dental applications. Comparisons are made with existing reports on dose measurement and effective dose estimates for panoramic examinations and other computed tomographic imaging modalities for dental implants. STUDY DESIGN Thermoluminescent dosimeters were implanted in a tissue-equivalent humanoid phantom at anatomic sites of interest. Absorbed dose measurements were obtained after single and double exposures. The averaged tissue-absorbed doses were used for the calculation of the whole-body effective dose. RESULTS The effective dose for imaging of maxillomandibular volume with a NewTom 9000 machine is 50.3 muSv. CONCLUSION The effective dose with the NewTom 9000 machine is significantly less than that achieved with other computed tomographic imaging methods and is within the range of traditional dental imaging modalities.

Oropharyngeal airway changes after rapid palatal expansion evaluated with cone-beam computed tomography

INTRODUCTION The aims of this retrospective study were to use cone-beam computed tomography (CBCT) to assess changes in the volume of the oropharynx in growing patients with maxillary constriction treated by rapid palatal expansion (RPE) and to compare them with changes in age- and sex-matched orthodontic patients. METHODS The experimental group consisted of 24 patients (mean age, 12.8+/-1.88 years) with maxillary constriction who were treated with hyrax palatal expanders; the control group comprised 24 age- and sex-matched patients (mean age, 12.8+/-1.85 years) who were just starting regular orthodontic treatment. Beginning and progress CBCT scans, taken in the supine position, were analyzed with software to measure volume, length, and minimal cross-sectional area of the oropharyngeal airway. The 2 groups were compared with paired t tests. RESULTS Only retropalatal airway volume was found to be significantly different between groups before treatment (P = 0.011), and this difference remained after treatment (P = 0.024). No other statistically significant differences were found relative to changes in volume, length, or minimum cross-sectional area of the oropharyngeal airway between the groups, but the molar-to-molar width after RPE increased significantly compared with the controls (P <0.001). CONCLUSIONS Narrow oropharyngeal airways in growing patients with maxillary constriction was demonstrated. But there was no evidence to support the hypothesis that RPE could enlarge oropharyngeal airway volume.

Major Gene and Multifactorial Inheritance of Mandibular Prognathism

Mandibular prognathism typically shows familial aggregation. Various genetic models have been described and it is assumed to be a multifactorial and polygenic trait, with a threshold for expression. Our goal was to examine specific genetic models of the familial transmission of this trait. The study sample comprised of 2,562 individuals from 55 families. Complete family histories for each proband were ascertained and the affection status of relatives were confirmed by lateral cephalograms, photographs, and dental models. Pedigrees were drawn using PELICAN and complex segregation analysis was performed using POINTER. Parts of some pedigrees were excluded to create one founder pedigrees, so the total N was 2,050. Analysis showed more affected females than males (P = 0.030). The majority of the pedigrees suggest autosomal dominant inheritance. Incomplete penetrance was demonstrated by the ratio of affected/unaffected parents and siblings. The heritability of mandibular prognathism was estimated to be 0.316. We conclude that there is a major gene that influences the expression of mandibular prognathism with clear signs of Mendelian inheritance and a multifactorial component.

Effects of surface conditioning on the shear bond strength of orthodontic brackets bonded to temporary polycarbonate crowns

INTRODUCTION An increase in the number of adults seeking orthodontic treatment has given rise to new problems for orthodontists, one of which is the need to bond orthodontic brackets to teeth restored with temporary crowns. Many prefabricated temporary crowns are composed of polycarbonates or thermoplastic polymers; bonding to these surfaces is complex because of the composition, surface integrity, and resistance of the crowns. The bond must be sufficient to resist breakage from the forces of orthodontic biomechanics and oral functions including mastication. The purpose of this study was to test, in vitro, the effect of different surface treatments on the shear bond strength of metal and ceramic orthodontic brackets bonded to temporary polycarbonate crowns. METHODS Eighty polycarbonate crowns for the maxillary right central incisor were evenly divided into 4 groups, and the facial surfaces were subjected to one of the following conditions: group A (control): no treatment; group B: the surface was sandblasted with 50 mum aluminum oxide particles; group C: the glazed surface was removed with a diamond bur; and group D: the surface was etched with 9.6% hydrofluoric acid. Precoated Victory metal brackets (3M Unitek, Monrovia, Calif) were bonded to the facial surface of half (n = 10) of the polycarbonate crowns in each group, and precoated Clarity ceramic brackets (3M Unitek) were bonded to the facial surface of the other half (n = 10). Each was debonded with a shear load in a universal testing machine at a crosshead speed of 0.254 mm per minute, and the adhesive remnant index (ARI) was used to analyze the sites of bond failure. Analysis of variance (ANOVA), post-hoc t test with the Bonferroni adjustment, Student t test, and chi-square test with the Yates correction were used for statistical analysis. RESULTS There was a significant difference between group B (sandblasting) and all other ceramic and metal groups. In the metal groups, there was a slight difference between group C (diamond bur) and group A (control). According to the ARI, sandblasting was the only surface treatment to significantly affect the adhesion of metal and ceramic brackets to polycarbonate crowns. There was no statistically significant difference between the metal and ceramic brackets in group B (sandblasting). There was a statistically significant difference between metal and ceramic brackets in each group, with the exception of group C (diamond bur), which was just below statistical significance. CONCLUSIONS Metal and ceramic orthodontic brackets bonded to temporary polycarbonate crowns will most likely not withstand the forces of orthodontic biomechanics. However, sandblasting polycarbonate crowns consistently increased the shear bond strength of metal and ceramic brackets. A diamond bur effectively roughens the surface of a polycarbonate crown but with no gain in bond strength. Likewise, etching the surface of polycarbonate crowns with 9.6% hydrofluoric acid is ineffective. Ceramic brackets bonded to sandblasted polycarbonate crowns produced the highest mean shear bond strength (2.87 MPa), although this value is far below bond strengths with natural tooth surfaces.

Treatment of an ankylosed maxillary incisor by intraoral alveolar bone distraction osteogenesis.

An ankylosed tooth and adjacent alveolar process can lead to the development of an open bite, an unesthetic smile line, and abnormal function in mastication. Intraoral alveolar bone distraction osteogenesis is an option for treating an ankylosed tooth. The purpose of this clinical report was to show the treatment of a growing patient with an ankylosed maxillary central incisor. A simple tooth-borne intraoral distractor was made with an expansion screw and 0.9-mm stainless steel wire, which enabled it to move easily. Intraoral alveolar bone distraction osteogenesis will give the best results in patients with favorable root length and severely resorbed alveolar bone in the vertical dimension.

Bone thickness of the anterior palate for orthodontic miniscrews

OBJECTIVE To determine the bone thickness in the anterior palate and to test whether there is any dependency between bone thickness and patients age or gender and whether there is any difference between left and right sides. MATERIALS AND METHODS Cone beam computed tomographic (CBCT) evaluations (n  =  431; 229 females, 202 males) of healthy orthodontic patients aged 9-30 years were selected from the database of the imaging center network Mesantis. In each CBCT image, palatal bone thickness was determined as the median and 2, 4, 6, and 8 mm paramedian bilaterally. Bone height was measured perpendicularly to the bony surface at 10, 12, 14, 16, 18, and 20 mm from the cementoenamel junction of the maxillary central incisor in the sagittal plane. RESULTS The greatest bone thickness was found in the lateral anterior palate. Palatal bone thickness of male patients was on average 1.2 mm greater than that of females. Bone height of 9-13-year-olds was less than that of older patients. No difference could be determined between the left and right side. CONCLUSIONS The lateral anterior palate offers the greatest bone thickness. Because there is considerable variation of bone thickness between individuals, a CBCT evaluation is recommended if maximum screw length is to be used.

Precision, repeatability and validation of indirect 3D anthropometric measurements with light-based imaging techniques

Currently, two-dimensional photographs are most commonly used to facilitate visualization, assessment and treatment of facial abnormalities in craniofacial care but are subject to errors because of perspective, projection, lack metric and 3-dimensional information. A variety of methods are available to generate 3-dimensional facial images such as laser scans, stereo-photogrammetry, infrared imaging and even CT, however each of these methods contain inherent limitations and as such no systems are in common clinical use. In this paper we will focus on the validation of indirect 3-dimensional landmark location and measurement of facial soft-tissue with light-based techniques. Precision, repeatability and validation of a light-based imaging system will be analyzed in this paper.

Third molar evaluation with cone-beam computerized tomography

Precise 3-dimensional localization of impacted mandibular third molars relative to the inferior dental canal (IDC) is critical to clinical management and surgical outcomes. Recently introduced dental 3-D volumetric imaging systems coupled with semi-automatic modeling techniques allows 3-D visualization of the IDC and the third-molar. Six impacted third molar sites were imaged with various 3-D volumetric imaging systems (NewTom 9000, Morita Accuitomo and Hitachi Mercuray). The spatial relationship of six impacted third-molars were visualized using imaging data obtained from these units. An interactive virtual model of a proposed third molar surgical site including the third molar and the inferior dental canal was developed.

Peridental bone changes after orthodontic tooth movement with fixed appliances: A cone-beam computed tomographic study

OBJECTIVE To quantify treatment-related changes in peridental bone height and thickness in orthodontic patients. MATERIALS AND METHODS Cone-beam computed tomographs (CBCTs) of 43 patients (24 female, 19 male; mean age: 25 years, 5 months) who underwent orthodontic treatment with multibracket appliances for at least 1 year were chosen for retrospective evaluation. Dehiscence depth and changes in bone width and tooth inclination were determined for 954 teeth. RESULTS There was a significant decrease in peridental bone height (dehiscence; -0.82 ± 1.47 mm) and bone thickness (-0.56 ± 0.7 and -0.69 ± 0.9 mm at 5 mm and 10 mm apical to the CEJ, respectively) during treatment (P < .001). A significantly greater dehiscence depth with increased vertical bone loss occurred in patients older than 30 years. In patients <30 years old, approximately 20% of the teeth showed defect depths >2 mm before treatment. In 90% of these patients, at least one tooth was affected. The maxillary canines and all mandibular teeth showed a higher risk for vestibular bone loss. Treatment changes in tooth inclination were correlated with horizontal bone loss. CONCLUSIONS Based on these results, it seems reasonable to recommend that peridental bone in orthodontic patients older than 30 be evaluated on a routine basis due to the risk of increased vertical bone loss. Ninety percent of patients younger than 30 showed reduced bone height (dehiscence) of the periodontium of at least one tooth.