Effect of build angle and layer height on the accuracy of 3-dimensional printed dental models.

INTRODUCTION: Three-dimensional (3D) printing technologies are profoundly changing the landscape of orthodontics. To optimize treatment-oriented applications, dimensional fidelity is required for 3D-printed orthodontic models. This study aimed to evaluate the effect of build angle and layer height on the accuracy of 3D-printed dental models and if each of their influences on print accuracy was conditional on the other. METHODS: A maxillary cast was scanned using an intraoral scanner. One hundred thirty-two study models were printed at various combinations of build angle (0°, 30°, 60°, 90°) and layer height (20 µm, 50 µm, 100 µm) with a digital light processing printer (n = 11 per group). The models were digitally scanned, and deviation analyzed using a 3D best-fit algorithm in metrology software. RESULTS: A statistically significant interaction was consistently found between build angle and layer height for each positive deviation, negative deviation, and proportion out of bounds. Average deviations of all study models were within clinically acceptable ranges, but the least accurate models were printed at 0°/20 µm. Although there was a tendency for an oblique build angle of 30° or 60° with a smaller layer height of 20 µm or 50 µm to print the most accurate models, 95 % confidence intervals overlapped with all other angles and heights except for 0°/20 µm. CONCLUSIONS: Build angle and layer height have statistically significant interactive effects on the accuracy of 3D-printed dental models. Overall, digital light processing printers produced models within clinically acceptable bounds, but the choice of build angle and layer height should be considered in conjunction with the clinical application, desired print time, and preferred efficiency of each print job.

Review of Etiology of Posterior Open Bite: Is There a Possible Genetic Cause?

Posterior open bite (POB) is one of the most severe malocclusions that can impair patients' masticatory functions, yet it is also a condition that is poorly understood and not well studied. Most reported cases are either sporadic or idiosyncratic with a diverse yet poorly understood etiology. Although primary failure of eruption (PFE), lateral tongue thrust, and certain medical syndromes or pathology of the temporomandibular joints have all been shown to cause POB, the complex interplay of environmental and genetic factors makes its etiopathogenesis a difficult subject to understand and investigate. Here, we provide a comprehensive review of the etiology of posterior open bite. Additionally, a genetic cause for POB is proposed through a report of an apparently non-syndromic familial case series with high POB penetrance across two generations. Further investigations of the gene(s) and mechanism(s) involved can not only provide a unique opportunity to better understand POB and the intricate muscular-occlusal relationship, but also offer powerful insight into the most effective approaches to clinical management of these (and potentially other) malocclusions.

Perceptions of chin asymmetries among dental professionals and laypersons.

INTRODUCTION: Previous studies have looked at a variety of dental and facial asymmetries and compared their detection by dental professionals with those of laypersons. However, few studies have analyzed the diagnosis and perception of chin asymmetries. In this study, we assessed whether dental professionals can recognize and diagnose facial asymmetries of the chin better than laypeople. METHODS: Chin asymmetries were analyzed through a series of edited frontal photographs of 2 subjects (male and female). The transverse position of the chin was digitally altered from 0° (no alteration) to 6° (most severe alteration). Participant responses were collected from laypersons (n = 64), nonorthodontist dentists (n = 58), and orthodontists (n = 145). Participants graded the photographs according to esthetic appeal using a visual analog scale. Statistical analysis produced diagnostic threshold levels for identifying chin asymmetries. RESULTS: Nonorthodontist dentists and orthodontists were better able to diagnose transverse chin asymmetry in the female subject at a lower threshold level of 2° of deviation, compared with laypersons at a 3° deviation. Orthodontists could diagnose transverse chin asymmetry in the male subject at a lower threshold level of 1° of deviation, compared with laypersons and nonorthodontist dentists at a 2° deviation. All 3 groups of raters graded very small or no chin asymmetries (1° and 0°) as more attractive, whereas high degrees of chin asymmetries (5° and 6°) were graded as most unattractive by all 3 groups. CONCLUSIONS: Transverse asymmetries of the chin influence the perception of facial attractiveness by laypersons, nonorthodontist dentists, and orthodontists. Subjects with small asymmetries are graded as most attractive, and subjects with large asymmetries are graded as least attractive. Orthodontists were the harshest graders, followed by the nonorthodontist dentists, whereas laypersons were the most lenient. The accuracy of diagnosing chin asymmetries varied among laypersons, nonorthodontist dentists, and orthodontists. Laypersons were the least accurate in diagnosing transverse chin asymmetries in a female subject, and they were just as accurate as nonorthodontist dentists when diagnosing this asymmetry in a male subject. Nonorthodontist dentists were just as accurate as orthodontists when diagnosing transverse chin asymmetries in a female subject, and orthodontists were the most accurate in diagnosing transverse chin asymmetries in a male subject.