Our results demonstrate that there is no evidence that a first (and only) test bite record is the best representation of the subject’s bite action. This is not a minor issue, considering that no protocol suggests performing more than one test bite record, which implies that slightest distortions may be overlooked if only one test bite record is considered. These slightest distortions do not necessarily represent errors in the recording procedures, but dynamic patterns that can manifest in varying degrees depending on multiple factors. In 2001, Sheasby & MacDonald stated that since the nature of the contact between teeth and the bitten substrate can influence the resulting bite mark, it is logical to postulate that the dynamics of the biting action may produce distortions known as “primary distortions”. According to these authors, these distortions are complex, unpredictable, and absolutely dependent and proportional to the degree of movement between the teeth and the bitten substrate (Sheasby and MacDonald 2001). It is extremely interesting to mention that although the authors report that each episode of contact is a unique dynamic event, and that the same dentition can produce bite marks with different forms of appearance (Sheasby and MacDonald 2001), we have not found a test bite protocol that explicitly considers performing more than one single record to control this phenomenon. The results of our research demonstrate that a first (and only) test bite may be masking slightest distortions that, at the time of the comparative analysis, may increase the chances of producing false positives or false negatives. Although registering the suspect’s incisal edges appears to be a simple protocol, problems can arise when introduced as evidence. Karazulas (1984) reported a case wherein test bites performed by the defense showed a different dental pattern different than the test bites produced by prosecution. The defendant was finally acquitted of the murder, but spent 7 years in prison and endured three trials before being proven innocent and released. Performing at least three test bites would not cause any delays or increased costs (most of the recommended materials are very economical and easy to manipulate), but would allow evaluation and selection of the highest quality sample (according to our results, any of the three registers may be the best representation of the subject’s bite), as well as help detect dynamic patterns of the bite. The latter statement is currently hypothetical -at least in the forensic discipline- but it is extremely attractive to start future lines of research.
The neuromuscular engram controls a complex spatial motion pattern and although this reflex primarily affects both masticatory muscles and occlusal-muscular relationships, the engram has received so little scrutiny (Lerman 2011). The intermaxillary functional relationship should be considered not by “dogmas” of static positions but in a dynamic three-dimensional framework, that is, through relative positions of teeth, mandible and maxilla in context with oral functions and appearance (Jokstad 2012). The usual technique for obtaining test bites is to take a record with the patient’s mouth passively closed based on centric relation (CR) (maximal intercuspation); this is performed on the assumption that the subject has a normal baseline psychoneuromuscular control, therefore, reproducible in time (ie, without habitual or conscious posturing) (Agbaje et al. 2013). However, number of residual teeth, occlusal support, maximum bite force, periodontal disease, difference in mandibular movement during mastication, changes in body posture, and even substrate consistency have all been described as factors that can affect neuromuscular control of chewing, muscle activity, masticatory performance (van der Bilt 2011; Kosaka et al. 2016; Sakaguchi et al. 2007) and, therefore, the final representation of the bite action: the bite mark.
Beyond these pathophysiological considerations of biting, there are other inherent limitations to the recording technique. Assuming that the operator has the necessary skills to perform quality test bites -another important factor considered by Yamashita et al. (2003)-, the success of tests can be conditioned by the material used and the type of bite mark. An ideal intermaxillary record material should be easy to manipulate, allow accurate records, and possess limited resistance before setting (to avoid dental or mandibular displacements during closure), then become rigid and with minimal dimensional changes after setting, even during storage (Sweeney et al. 2015; Ghazal et al. 2008). Considering that practically all materials recommended by the literature have demonstrated limitations to comply with all these aspects (Dailey 2011; Dailey et al. 2013; Ghazal et al. 2008), focus should be placed on taking special care throughout the technical procedure (Dailey et al. 2013). Although we only performed type 3 test bites (as typical bites found in cheese) -following the Webster’s classification (1982)-, the goal of the criterion defined by this author fell on the type of dental features that could be registered. The wax used in this research, although not certified by the ADA (some specific products are difficult to access in our country), met the standards required for testing. We firmly believe that performing at least three records for each individual will allow detection of vulnerabilities and selection of the most appropriate registry. It is evident that this technique is not extrapolated to other types of bite marks (two-dimensional or bite marks in skin). Likewise, in the future, this could revise current protocols of comparative analysis by reformulating, for these specific cases, a new strategy of comparison “between negatives”, which implies comparison of the bite marks to investigate the bite mark obtained from the suspect, and thereby seeking to replicate the bite (basically, the same principle of analysis of fingerprints). The classical methods suggest comparing negative representations of the biting teeth (the bite mark), with positive models of the suspect’s teeth, both in physical or digital comparisons and overlays (Dailey 2011). Would evaluation and comparison of negatives allow morphological detection and dynamic patterns, in order to identify the perpetrator? Again, perhaps new research along these lines will answer this question.
Bite mark comparison is often used in criminal prosecutions; however, the bite mark testimony continues to be criticized for lacking scientific studies that support this type of assessment (Committee 2009). Both the uniqueness of the human dentition and the possibility of the dentition transferring to the bitten substrate (with all possible distortion possibilities) are still basic problems inherent in bite mark analysis and interpretation (Committee 2009; Saks et al. 2016). Page et al. (2011) stated that “uniqueness is impossible to prove” and added “(mistakes and misidentifications) are made because of guesswork, poor performance, lack of standards, bias and observer error”. The dental information recorded on the bitten substrate should be compared to the dentition of the suspect, and although the uniqueness (the most basic concept supporting the bite mark analysis), sample selection or the applied imaging techniques still remain without scientific sufficiency (Franco et al. 2017), most current guidelines persist in considering the act of biting as only a mechanical bearing connecting two solid objects (jaws and their teeth), opening and closing with a simple hinge mechanism (American Board of Forensic Odontology 2017; Dailey et al. 2013). Although proven useful in certain experimental models, different devices designed to mimic the action of a human bite (Avon and Wood 2005; Chinni et al. 2013) are unlikely to reproduce the extreme complexity of the bite. The biomechanics of the biting action comprise not only the dental action but also the muscular relationships, occlusion, intentionality of aggression and the type of bitten material (Franco et al. 2017). Further technical attention should be given to the important phase of recording the suspect’s bite pattern. Something as easy as making three records (and not just one) could significantly help control these variables and thereby improve standards of bite mark evidence.
Although the authors could be expected to perform a microscopic evaluation of the test bites (or even the use of other technological tools of greater reliability), which would have increased the range of differences to give a better understanding of the distortions/differences possible in an experiment of this nature, the purpose of this research is to optimize/improve the current ABFO recommendations for collecting evidence of suspected dentition, which do not specify a necessary minimum number of test bites to be taken (accepting by default the possibility that it is only one) nor the way in which they should be evaluated (accepting by default the possibility of being evaluated only macroscopically). From the same point of view, our research is not intended to define the concept of “slightest distortions” when precisely they have not been studied under magnification (logically in the strict sense of the word). However, we consider that this first recognition of these small patterns precisely highlights the need to use better methodologies than to only evaluate them macroscopically. The use of a DMC comparison microscope (used for analyzing firearm barrels and bullets) in bite mark analysis has already been reported as an excellent tool to enhance the ability of the forensic odontologists to present evidence correctly (Rivera-Mendoza et al. 2017; Bernitz and Kloppers 2002). In the same way, and although this experimental model can only be evaluated on a special type of bite and substrate, the high values of interrater agreement would suggest the use of similar models of comparison between negatives (bite marks), but adapted to other substrates bitten.
Forensic odontology, "the application of the science of dentistry to the field of law", as defined by the U.S. National Academy of Sciences (Committee 2009) represents the point of contact of two radically different scenarios. Although from a scientific point of view it seems logical to think that more testing is better then less, extrapolate this to criminal proceedings when the universally accepted recommendations of ABFO do not make it explicit. Likewise, the controversy that mires bite mark analysis can be explained -at least in part- by the indifference that seems to exist in oral science, in scientific societies, and even in applied basic research. Although the minimalist “hinge” concept of the temporomandibular joint has been overcome decades ago in the world of oral physiology, it apparently still persists in certain forensic contexts, even determining the innocence or guilt of a defendant.
