Biomedical subjects

Carl N Stephan

Publications and source records attributed to Carl N Stephan.

4 recordsLinked to original sources

PubMed2003

Facial approximation: an evaluation of mouth-width determination.

Facial approximation techniques rely on the prediction of soft tissues from the skull, yet few prediction methods have been scientifically evaluated, despite being frequently used in the past. This study tests several published and commonly used methods for determining mouth width from the skull. The methods tested are: 1) that mouth width is equal to the distance between the pupils; 2) that mouth width is equal to the distance between the medial borders of the iris; and 3) that mouth width is equal to the distance between the most lateral junctions of the canines and the first premolars. The study primarily examines living Australian European and Central/South East Asian participants (of both sexes) using photogrammetric methods. The results of this study indicate that methods 1 and 3 are highly inaccurate. Method 1 overestimated mouth width, on average, by approximately 11 mm (SD, 4 mm), while method 3 underestimated mouth width by approximately 13 mm (SD, 3 mm). Method 2 was the most accurate of the methods evaluated, but on average underrepresented mouth width by approximately 2 mm (SD, 4 mm). All three methods produced mouth-width predictions that, in general, were statistically different from actual mouth widths (P < 0.05). A new guideline, describing mouth width as canine width plus 57% of the cumulative distance between the lateral canine borders and the pupil centers on each side was found not to differ at statistically significant levels from actual mouth widths (P > 0.05). On average, this guideline did not under/overestimate actual mouth width, with the difference between them being 0 mm (SD, 3 mm). The increased accuracy of this new guideline in comparison to others suggests that it is the most appropriate for facial approximation. However, it should be further tested using independent samples. The finding that commonly used mouth-width prediction guidelines are not accurate suggests that many facial approximations previously made have incorrect mouth widths. This could reduce the recognition of these facial approximations and may, especially if other guidelines are inaccurate, render the facial approximations unrecognizable as their respective target individual (individual to whom the skull belongs).

Adult↗

PubMed2003

Predicting mouth width from inter-canine width--a 75% rule.

It has been suggested that inter-canine width plus 57% of the cumulative distance between the lateral aspect of the canines and the pupil centers can be used to estimate mouth width. Evidence also suggests that the distance between the medial irises approximates actual mouth width fairly well. However, these soft tissue prediction guidelines are limited because they rely on accurate medio-lateral positioning of the pupils within the orbits, for which no systematic empirical evidence appears to exist at this stage. It would, therefore, be more appropriate to use only known hard tissue landmarks in mouth width prediction. This study reports the results of using inter-canine width as a percentage of mouth width for its prediction. This method seems favorable in comparison to the other guidelines because it is as accurate, uses known hard tissue landmarks, and does not rely on assumptions concerning pupil location. Estimating mouth width by using the canines alone, therefore, seems the best guideline to use in facial approximation techniques, at least given knowledge existing at this stage.

Anthropometry↗

PubMed2002

Do resemblance ratings measure the accuracy of facial approximations?

Since forensic facial approximations are used to promote recognition of a deceased person, an accurate forensic facial approximation (FFA) should be easily recognized as the person to whom the skull belonged (target individual). However, the accuracy of FFAs has been previously assessed by the direct comparison of an FFA to the corresponding target individual for similarity (i.e., a resemblance rating). Resemblance ratings may not indicate a facial approximation's accuracy since the resemblance of non-target individuals is not accounted for. This experiment tests the validity of using resemblance ratings to assess the accuracy of FFAs. The study indicates that there is no statistically significant difference between: (a) resemblance ratings of FFAs to target individuals and (b) resemblance ratings of FFAs to individuals incorrectly identified as the target individual. It is concluded that it is not possible from resemblance ratings to determine the accuracy and/or quality of a facial approximation since a non-target individual may receive a resemblance rating equal to, or higher than, the target individual.

Cephalometry↗

PubMed2002

Facial approximation: globe projection guideline falsified by exophthalmometry literature.

The projection of the cornea from the bony orbit has been determined, in facial approximation, by centrally locating the eyeball in the orbit and positioning the cornea so that its most anterior point falls in line with a tangent dropped from the mid-superior to the mid-inferior orbital rim. However, there appears to be no scientific evidence to justify this guideline; yet, there have been numerous studies that measure globe projection in living subjects, from the lateral orbit using an exophthalmometer. The aim of this study was to determine if the traditional facial approximation guideline is consistent with the exophthalmometry literature. MRI research shows that corneal projection is underestimated using the traditional facial approximation guideline. An underestimation is also strongly supported by statistical comparisons of globe projection measures taken using more traditional instruments (e.g., Hertel's exophthalmometer) to skull morphology (p < 0.006). It is suggested that the traditional facial approximation guideline not be used in future facial approximations since it appears to under-predict anterior globe projection by 4 mm on average. It is also suggested that average exophthalmometer values be used until more accurate and precise ways of determining globe projection have been determined.

Anthropometry↗