The Frankfort horizontal as a basis for cephalometric analysis

[Search of a cephalometric reference line]

The variability of cephalometric reference lines is examined in this article with regard to typology, natural orientation of the head, orientation by the vestibular system, and anatomy. It appears that these lines have orientations that vary with individual subjects, that is, a line is not the same in a specific person as it is in a theoretical model that is based on average values. It follows from this that the deviation observed between a patient's measurement and the average could just as well reflect variations in the reference lines as it does of those of the structures being studied. Such a measurement cannot, accordingly, serve as the basis for a morphological diagnosis. To deal with this problem, we propose another cephalometric reference system that presents, for orthognathic diagnosis, many advantages over the traditional system but, itself, remains imperfect.

Comparison of reproducibility of natural head position using two methods

Lateral cephalometric radiographs have become virtually indispensable to orthodontists in the treatment of patients. They are important in orthodontic growth analysis, diagnosis, treatment planning, monitoring of therapy and evaluation of final treatment outcome.

AIM

The purpose of this study was to evaluate and compare the maximum reproducibility with minimum variation of natural head position using two methods, i.e. the mirror method and the fluid level device method.

MATERIALS AND METHODS

The study included two sets of 40 lateral cephalograms taken using two methods of obtaining natural head position: (1) The mirror method and (2) fluid level device method, with a time interval of 2 months. Inclusion criteria • Subjects were randomly selected aged between 18 to 26 years Exclusion criteria • History of orthodontic treatment • Any history of respiratory tract problem or chronic mouth breathing • Any congenital deformity • History of traumatically-induced deformity • History of myofacial pain syndrome • Any previous history of head and neck surgery.

RESULTS

The result showed that both the methods for obtaining natural head position-the mirror method and fluid level device method were comparable, but maximum reproducibility was more with the fluid level device as shown by the Dahlberg's coefficient and Bland-Altman plot. The minimum variance was seen with the fluid level device method as shown by Precision and Pearson correlation.

CONCLUSION

The mirror method and the fluid level device method used for obtaining natural head position were comparable without any significance, and the fluid level device method was more reproducible and showed less variance when compared to mirror method for obtaining natural head position.

CLINICAL SIGNIFICANCE

Fluid level device method was more reproducible and shows less variance when compared to mirror method for obtaining natural head position.

Reprodutibilidade da posição natural da cabeça em fotografias de perfil de crianças de 8 a 12 anos, com e sem o auxílio de um cefalostato

OBJETIVO: este estudo avaliou a reprodutibilidade da posição natural da cabeça (PNC) em crianças. MÉTODOS: foram fotografados 25 pacientes da Clínica Infantil do Curso de Graduação em Odontologia da Universidade Estadual de Maringá com idades entre 8 e 12 anos, sendo 12 do gênero feminino e 13 do masculino. As tomadas fotográficas registraram a PNC com uma câmera digital e foram realizadas com e sem o uso de um cefalostato. Uma linha vertical (LV) foi usada como referência para as mensurações. Após um intervalo de 15 dias, as fotografias foram repetidas, respeitando-se o mesmo protocolo utilizado na primeira série de tomadas fotográficas. A reprodutibilidade da PNC entre os dois momentos das tomadas fotográficas foi avaliada utilizando-se a medida angular entre a linha vertical de referência e uma linha do perfil, passando pelo pogônio tegumentar e pelo ponto labial superior. RESULTADOS E CONCLUSÃO: embora algumas variações de posição tenham sugerido que os pacientes dessa idade devam receber orientações adicionais quanto à PNC, não foram observadas diferenças significativas quanto à reprodutibilidade das fotografias tomadas no intervalo de 15 dias, com ou sem a utilização do cefalostato auxiliar. Dessa forma, a PNC mostrou-se como um método de boa reprodutibilidade em crianças.

Head orientation in CBCT-generated cephalograms

OBJECTIVE

To determine the reliability of obtaining two-dimensional cephalometric measurements using two virtual head orientations from cone-beam computed tomography (CBCT) models.

MATERIALS AND METHODS

CBCT scans of 12 patients (6 class II and 6 class III) were randomly selected from a pool of 159 patients. An orthodontist, a dental radiologist, and a third-year dental student independently oriented CBCT three-dimensional (3D) renderings in either visual natural head position (simulated NHP) or 3D intracranial reference planes (3D IRP). Each observer created and digitized four CBCT-generated lateral cephalograms per patient, two using simulated NHP and two using 3D IRP at intervals of at least 3 days. Mixed-effects analysis of variance was used to calculate intraclass correlation coefficients (ICCs) and to test the difference between the orientations for each measure.

RESULTS

ICC indicated good reliability both within each head orientation and between orientations. Of the 50 measurements, the reliability coefficients were > or =0.9 for 45 measurements obtained with 3D IRP orientation and 36 measurements with simulated NHP. The difference in mean values of the two orientations exceeded 2 mm or 2 degrees for 14 (28%) of the measurements.

CONCLUSIONS

The reliability of both virtual head orientations was acceptable, although the percentage of measurements with ICC >0.9 was greater for 3D IRP. This may reflect the ease of using the guide planes to position the head in the 3D IRP during the simulation process.

Soft Tissue Cephalometric Standards based on NHP in a Sample of Iranian Adults

BACKGROUND AND AIMS

This study aimed to establish soft tissue cephalometric standards in Iranian adults based on NHP, which can be used in diagnosis of orthodontic and orthognathic patients.

MATERIALS AND METHODS

A group of 46 individuals (24 males and 22 females) with normal occlusion and proportional facial profile were chosen from a large group of dental students. For the all of the chosen sample, lateral cephalograms were obtained with head oriented in natural position. On the basis of the true horizontal and true vertical lines, the standard values of 19 soft tissue measurements were determined using McNamara, Burstone and Viazis methods.

RESULTS

In this study, the mean value of SN deviation to true horizontal line was 6.6°. Comparison between two genders showed that females have more obtuse nasolabial angle and thinner soft tissue chin than males (P < 0.05). Linear measurements showed that the overall size of males was more than females (P < 0.05).

CONCLUSION

Cephalometric norms based on NHP were found to be more reliable in orthognathic pa-tients.

Relationship of TMJ osteoarthritis / osteoarthrosis to head posture and dentofacial morphology

OBJECTIVE

The purpose of this study was to test the hypothesis that there is a relationship between the temporomandibular joint (TMJ) osteoarthritis/osteoarthrosis (OA), head posture and dentofacial morphology.

DESIGN

Case-control study.

SUBJECTS AND METHODS

The subjects consisted of 34 Japanese females with TMJ OA (aged 24.7 +/- 6.1 years) and a control group of 25 healthy Japanese females (aged 23.6 +/- 1.3 years). Six cranio-cervical angular measurements were constructed for head posture analysis. Nine angular and three linear measurements were constructed for the skeletal hard tissue analysis. Five angular and one linear measurements were constructed for the dental hard tissue analysis. Unpaired t-tests were used to compare the mean differences of head posture measurements and dentofacial cephalometric measurements between the TMJ OA and the control group.

RESULTS

The TMJ OA group had significantly larger cranio-cervical angles (p < 0.05) and had more posteriorly rotated mandibles (p < 0.0001) than those in the control group. They also had a significantly shorter posterior facial height (p < 0.0001). The TMJ OA group had more retroclined lower incisors (p < 0.05).

CONCLUSION

These results suggest that an association may exist between TMJ OA, head posture and dentofacial morphology.

Can we reduce episodes of haemoglobin desaturation in full-term babies restrained in car seats?

OBJECTIVES

To determine whether episodes of haemoglobin oxygen (SpO2) desaturation in full-term infants restrained in car seats can be reduced by a simple foam plastic infant car seat insert designed to push the body forward, with space for the protuberant occiput to lie behind the spine, and so reduce flexion of the infant's head on the trunk.

METHODS

Eighteen healthy full-term babies were evaluated while restrained in an infant car safety seat with, and without, the foam insert. Infants were monitored in each position for 30 min with continuous polygraphic recording of respiratory and heart rate, nasal airflow and SpO2.

RESULTS

Placement of the insert in the car seat was associated with a significant reduction in the rate of apneas with a fall in SpO2 >5% (median, interquartile range: 4.4 (0, 10.6) vs. 9.2 (5.4, 15.2) events per hour, p=0.03). The one clinically severe episode of apnea, with a fall in SpO2 of more than 30%, occurred in the car seat without the insert.

CONCLUSIONS

A car seat insert that allows the newborn's head to lie in a neutral position during sleep may reduce the frequency of mild episodes of reduced SpO2 in some full-term newborn babies.

Three-dimensional recording of the human face with a 3D laser scanner

Three-dimensional recording of the surface of the human body or of certain anatomical areas has gained an ever increasing importance in recent years. When recording living surfaces, such as the human face, not only has a varying degree of surface complexity to be accounted for, but also a variety of other factors, such as motion artefacts. It is of importance to establish standards for the recording procedure, which will optimise results and allow for better comparison and validation. In the study presented here, the faces of five male test persons were scanned in different experimental settings using non-contact 3D digitisers, type Minolta Vivid 910). Among others, the influence of the number of scanners used, the angle of recording, the head position of the test person, the impact of the examiner and of examination time on accuracy and precision of the virtual face models generated from the scanner data with specialised software were investigated. Computed data derived from the virtual models were compared to corresponding reference measurements carried out manually between defined landmarks on the test persons' faces. We describe experimental conditions that were of benefit in optimising the quality of scanner recording and the reliability of three-dimensional surface imaging. However, almost 50% of distances between landmarks derived from the virtual models deviated more than 2mm from the reference of manual measurements on the volunteers' faces.

Accuracy and precision of the three-dimensional assessment of the facial surface using a 3-D laser scanner

Three-dimensional (3-D) recording of the surface of the human body or anatomical areas has gained importance in many medical specialties. Thus, it is important to determine scanner precision and accuracy in defined medical applications and to establish standards for the recording procedure. Here we evaluated the precision and accuracy of 3-D assessment of the facial area with the Minolta Vivid 910 3D Laser Scanner. We also investigated the influence of factors related to the recording procedure and the processing of scanner data on final results. These factors include lighting, alignment of scanner and object, the examiner, and the software used to convert measurements into virtual images. To assess scanner accuracy, we compared scanner data to those obtained by manual measurements on a dummy. Less than 7% of all results with the scanner method were outside a range of error of 2 mm when compared to corresponding reference measurements. Accuracy, thus, proved to be good enough to satisfy requirements for numerous clinical applications. Moreover, the experiments completed with the dummy yielded valuable information for optimizing recording parameters for best results. Thus, under defined conditions, precision and accuracy of surface models of the human face recorded with the Minolta Vivid 910 3D Scanner presumably can also be enhanced. Future studies will involve verification of our findings using test persons. The current findings indicate that the Minolta Vivid 910 3D Scanner might be used with benefit in medicine when recording the 3-D surface structures of the face.

A comparison of the head and cervical posture between the self-balanced position and the Frankfurt method

Head and cervical posture evaluation has been a concern for many years, not only because of the purported relationship that exists between head and cervical posture in the presence of temporomandibular disorders, neck pain and headache, but also because of the biomechanical relationship between the head and cervical spine and dentofacial structures. Many methods have been suggested in an attempt to establish the best way to evaluate the position of the head using teleradiographs and cephalometric analysis. However, there is still no agreement as to which procedure is the best. The objective of this study was to evaluate the differences that exist between craniocervical measurements in lateral teleradiographs when comparing the position of the head in the self-balanced position to the position of the head using the Frankfurt method (Frankfurt plane parallel to the floor). Sixty-eight subjects who sought dental treatment in community health centres in Talca, Chile participated in this study. Rocabado analysis was used to measure the craniocervical variables. The Cobb analysis was used to measure cervical lordosis. A paired student t-test was used to evaluate the differences between both procedures, using an alpha of 0.05 and a power of 0.90. The use of the cephalostat changed only the craniocervical angle (P < 0.001). However, this change was minimal. No changes related to gender and age were found. More studies are needed to determine the variation between different procedures and to define a good procedure for evaluating head posture.

Simple car seat insert to prevent upper airway narrowing in preterm infants: a pilot study

OBJECTIVES

To test prospectively the hypothesis that an infant car seat modification to allow the infant's head to rest in a neutral position on the trunk would prevent narrowing of the upper airway and thus reduce oxygen desaturation in preterm infants who are restrained in car seats.

METHODS

Seventeen preterm infants who were approved for discharge were evaluated in a car seat for newborns, with and without a foam insert that provided a slot for the back of the infants' head. Respiration timed inspiratory radiographs for assessment of upper airway dimensions were taken during quiet sleep in each position. Infants were monitored in each position for 30 minutes with continuous polygraphic recording of respiratory, cardiac, and nasal airflow activity and pulse oximetry.

RESULTS

Placement of the insert in the car seat was associated with a larger upper airway space (mean +/- standard deviation, 5.2 +/- 1.3 vs 3.6 +/- 1.4 mm). This radiologic improvement was associated with a significant reduction in the frequency of episodes of oxygen desaturation to <85% (1.5 +/- 2.1 vs 3.5 +/- 3.5 episodes/infant), of bradycardia <90 bpm (0.1 +/- 0.3 vs 1 +/- 1.7), and of arousal (median [25th, 75th], 2.5 [1.3, 4.0] vs 5.0 [4.0, 7.0]).

CONCLUSIONS

The cause of oxygen desaturation in preterm infants who are restrained in car seats is multifactorial. The present data strongly support the hypothesis that flexion of the head on the body is a significant contributor to these episodes and that the mechanism is posterocephalic displacement of the mandible, leading to narrowing of the upper airway. Critically, this pilot study demonstrates that the frequency of episodes of desaturation in a standard newborn car seat can be substantially reduced by placement of a simple foam insert that allows the infant to maintain the head in a neutral position on the trunk during sleep.

Orientation of craniofacial planes and temporomandibular disorder in young adults with normal occlusion

The aim of this study was to investigate the relationship between orientation of craniofacial planes relative to the true horizontal and temporomandibular disorder (TMD), in normal occlusion. Fourteen university dental students, with full natural dentition and bilateral Angle Class I occlusion, who exhibited signs and symptoms of TMD, were compared with 14 age- and sex-matched healthy controls. Frontal and lateral photographs were taken in natural head position with the subject standing up, clenching a Fox plane and having a facial arch positioned. Photographs were examined by a standardized image analysis. Inter-pupillary axis, Frankfurt, occlusal and Camper planes were evaluated. In frontal view, the Frankfurt plane was right rotated relative to the true horizontal both in TMD subjects (P < 0.01) and controls (P < 0.05), but rotation was larger in TMD subjects (mean difference between groups, 1.1 degrees, 95% confidence interval, 95% CI, 0.2-2.0 degrees ). No significant deviation from the horizontal or difference between groups was observed for the interpupillary axis and occlusal plane. In lateral view, the Frankfurt plane was upward-orientated relative to the true horizontal in TMD group (mean angular deviation 2.8 degrees, 95% CI, 1.0-4.6 degrees ). The occlusal and Camper planes were downward-orientated in both groups (P < 0.0001), but inclination of occlusal plane tended to be smaller in TMD subjects (mean difference between groups, -3.8 degrees, 95% CI, -7.6-0.1 degrees ). Angles between any craniofacial planes did not significantly differ between groups. The findings show that in young adults with normal occlusion, a weak association exists between the orientation of craniofacial planes in natural head position and signs and symptoms of TMD. Furthermore, they suggest that, within this population, TMD might be mainly associated with head posture rather than with craniofacial morphology.

Estimated natural head position and facial morphology

Estimated natural head position, or natural head orientation (NHO), has been proposed as a preferred reference position for assessing facial morphology. However, because this position is subjectively defined by the orthodontist, it could be influenced by facial form, which would be an undesirable attribute. The aim of this study was to assess whether NHO is influenced by facial morphology. Lateral photographs of 14 patients were used. Each was warped to produce 2 new images, with the chin positioned backwards or forwards relative to the original (+/-2 degrees change of the soft tissue N-Pg line). All 42 images were placed in circular frames and shown to 7 experienced orthodontists, who were asked to orient them to NHO. Image orientation between the 3 chin positions was measured and compared. The results showed that NHO depended on chin position. Images with protrusive chins were positioned with the head rotated more downwards (Frankfort plane 3.10 degrees relative to horizontal) than were images with retrusive chins (Frankfort plane 4.98 degrees ). The difference in head orientation measurements was half of the difference in chin position (1.88 degrees for a chin change of 4 degrees ). These findings call into question the validity of NHO for diagnosis because it depends on the same factor it aims to assess. Use of NHO would result in underestimating the true skeletal relationships.

Soft tissue cephalometric analysis: diagnosis and treatment planning of dentofacial deformity

This article will present a new soft tissue cephalometric analysis tool. This analysis may be used by the orthodontist and surgeon as an aid in diagnosis and treatment planning. The analysis is a radiographic instrument that was developed directly from the philosophy expressed in Arnett and Bergman "Facial keys to orthodontic diagnosis and treatment planning, Parts I and II" (Am J Orthop Dentofacial Orthod 1993; 103:299-312 and 395-411). The novelty of this approach, as with the "Facial Keys" articles, is an emphasis on soft tissue facial measurement.

Comparative study of diagnostic measures in borderline surgical cases of unilateral cleft lip and palate and noncleft Class III malocclusions

Patients with complete unilateral cleft lip and palate present difficult growth problems. Their anteroposterior discrepancies in jaw and dentition are frequently so severe that some epidemiologic studies report the necessity of orthognathic surgery in 25% of their sample. The aims of this study were three-fold: (1) to delineate diagnostic measures in borderline surgical cases of unilateral cleft lip and palate, (2) to verify the significance of negative overjet as a measure of anteroposterior discrepancy, and (3) to compare these diagnostic measures with those of borderline surgical cases of noncleft Class III malocclusions. The sample consisted of 29 patients with unilateral cleft lip and palate and 25 noncleft Class III Korean patients (mean age, 18.69 years); all had crossbites of all four incisors. Each of their pretreatment study casts and cephalograms were analyzed. The group with unilateral cleft lip and palate was divided into two subgroups on the basis of the method of their anterior crossbite resolution; 18 subjects were treated with orthodontics alone (Cleft-NS) and 11 subjects with orthognathic surgery (Cleft-Surg). The noncleft Class III group was divided into two subgroups; 6 of the subjects were orthodontically treated (Cl III-NS), and 19 were surgically treated (Cl III-Surg). The group with unilateral cleft lip and palate showed smaller SNA and SNB angles than the noncleft Class III group, but the ANB angles and the amount of anterior crossbites showed no statistical differences. When the Cleft-NS and the Cleft-Surg groups were compared, the ANB angle and the Wits measurements were significantly different. When the Cl III-NS and Cl III-Surg groups were compared, the SNB, ANB, L1GoGn, Wits, and the crossbite showed significant differences. For borderline surgical Class III unilateral cleft lip and palate cases, ANB angle, Wits appraisal, and ABGoGn angle were critical diagnostic parameters. On the other hand, the magnitude of anterior crossbite, the negative overjet, was shown not to be a significant measure of anteroposterior discrepancy.