Role for CAD/CAM in Forensics?

INTRODUCTION
As the progression of technology accelerates, the profession of dentistry faces a dilemma: remain rigid and unchanged, or embrace the revolution. Although new technology has a definite learning curve and requires time for refinement, the decision to embrace new technology should be based on providing the highest quality of service. Although the decision may be influenced by other factors such as cost, the comfort level of the learner, and evidence-based research, the art and science of forensics remains unique.
Clinical dentistry demands that your patients receive the highest quality of care in a timely and compassionate manner. The profession is based on the delivery of a service or product. Forensic dentistry deals with the confirmation of an individual’s unique identity, whether as a confirmation of a crime or death.1 This process demands the highest possible degree of accuracy to satisfy the logistical and emotional needs of all parties involved. Application of proven technology must be utilized to maximize accuracy.

CAD/CAM in Dentistry
Dentistry has embraced technological advances in computer-aided dentistry and computer-aided manufacturing (CAD/CAM) for the past 3 decades. Computer-aided dentistry has been employed to digitize dental structures and the oral cavity for the virtual design of simple and complex prosthetic units.2 Computer-aided manufacturing has been utilized to manufacture everything from surgical stents to dental prostheses.3 The application of cone beam computed tomography (CBCT) with rapid prototyping develops a patient-specific surgical stent that has unparallel anatomical accuracy.4 The technology is here, and it will have an impact on all aspects of the dental profession.

Dental Forensics
The role of dentistry within forensic sciences deals with age estimation, bite-mark analysis, and postmortem identification.5 The postmortem identification process compares dental records (radiographs and models) of an individual before death (antemortem) to that after death (postmortem).6 Dental structures and restorations are compared, based on their uniqueness, to subjectively confirm a match with a level of certainty.6 The experience and expertise of the individual performing the comparison;7 the availability, quality, and age of the records; and the postmortem damage are limiting factors.8,9 A calculated and objective comparison utilizing technology would strengthen the validity of forensic dentistry.
Forensic sciences has employed CAD/CAM technology to assist in the 3-dimensional (3-D) reconstruction of crime scene investigations.10 The technology is still in its infancy yet offers enormous insight and evidence to the forensic field. The application of CAD/CAM to forensic dentistry must be realized.

CASE STUDY
Methodology

A clinical case has been investigated for the possibility of utilizing currently established CAD/CAM in-office technology to assist in recreating an antemortem record and compare it with a traumatic postmortem record. The individual in this study remains alive and well, and the postmortem consideration is only hypothetical.
A Q-Tray (Research Driven) was utilized with Template (CLINICIAN’S CHOICE) to obtain a segmental impression of the third quadrant. The impression was poured in stone, separated, and then repeated to create 2 identical models (Figure 1). One model was set aside and kept pristine and served as the antemortem record. The second model was placed in a white plastic bag and struck with a conventional hammer. The white bag ensured randomness and the impact from the hammer-represented trauma. The model was removed and served as the postmortem record (Figure 1).

Figure 1. Antemortem and postmortem models. Figure 2. Digitized postmortem model.
Figure 3. Delineation of dental structures. Figure 4. Morphogenisis of dental structures.
Figure 5. Reconstructed postmortem model.

An in-office E4D CAD/CAM unit (E4D Technologies) was employed to digitize the entire postmortem cast (Figure 2). The margins of the damaged dental structures were delineated (Figure 3). Parameters within the settings were changed, and morphogenesis was executed. The alteration of parameters and morphogenic ability represented a large component to the investigation, since the morphological result was the limiting factor. The morphogenesis produced a 3-D computer generated model of the teeth in which missing portions were recreated by the software (Figure 4).
Once dental structure design was achieved, the image was sent to the milling machine (E4D Technologies). A Paradigm MZ100 (3M ESPE) milling block (optimized composite resin) was utilized to mill the projected portions of the tooth that were lost to damage. An investigative question was whether or not an in-office unit could in fact mill the portions. The composite resin block was selected as the material of choice, as it could be milled in fine detail without requiring firing.
Once the portions were successfully milled, the sections were tried and fitted onto the postmortem cast. The segments were adhered to the cast using conventional epoxy cement (Figure 5).

RESULTS
Quantitative

The antemortem and postmortem casts were measured with a digital caliper in 3 dimensions: occlusal-gingival, buccal-lingual, and mesial-distal. The vertical measurement was taken from either the gingival margin or the inferior edge of the cast. Cast measurement reference points were identical in both samples as the pour-up used the same impression. The measurements for the antemortem cast and postmortem casts are presented in Tables 1 and 2, respectively.

Qualitative
Subjective comparison was achieved through the use of monochromatic infrared (IR) digital photography (720 nm) from the occlusal, facial, and lingual views (Figures 6 and 7). Images of the antemortem and postmortem casts were then resized to approximate each other. The postmortem images were reduced to 50% opacity and superimposed onto the antemortem image (Figure 8).

Figure 6. Postmortem record, occlusal view. Figure 7. Postmortem record, facial view.
Figure 8. Ante- and postmortem overlay.
Figure 9. Average value composite image, facial view. Figure 10. Average value composite image, occlusal view.

A composite image, utilizing an average value from each, was then processed to create an average image of the 2 models (Figures 9 and 10).

DISCUSSION
Quantitative measurements indicated deviations in the postmortem record for teeth Nos. 32, 33, and 35. Occlusal-gingival dimensions varied by 0.93,
-0.08, and 1.48. The buccal-lingual dimension varied with a difference of -0.07, -0.16, and 0.06 mm. Mesial-distal dimensions varied by -0.2, -0.13, and 0.01. The buccal-lingual measurement varied the least, with an average of 0.096 mm. The mesial-distal had an average variation of 0.113 mm and the occlusal-gingival dimension varied the most, with an average value of 0.83 mm. The large discrepancy in this dimension could be attributed to the establishment of an occlusal plane with limited amount of information provided by the segmental impression.
Qualitative variations from IR photography indicated that occlusal anatomy was lacking in the postmortem reconstruction. Reduction in the occlusal height changed the overall dimensions of the tooth morphology. Facial morphology of the postmortem model also exhibited lack of adequate height. The canine was absent of age-related wear. Similarly, lingual morphology lacked occlusal height.
The composite images represented an average of both ante- and postmortem casts. The facial view still represented inadequate detail based on occlusal height. The occlusal view represented a very close approximation to the antemortem record.
Further studies would be required to alter software algorithms and modify morphogenesis to accommodate segmental records, age, and parafunction to establish a proper occlusal plane. Greater sample sizes would be required to compare and validate the application of the technology. Future work considerations could explore the utilization of CBCT to generate data regarding dental, osseous, and soft tissues to create a 3-dimensional virtual antemortem record.

CONCLUSIONS
As a single case study, the purpose of this work was to explore the potential of utilizing in-office technology to offer another tool for the forensic dentist.
If identification of an individual is required, and there are no other means to offer assistance, then this approach may offer a starting point to inventory existing restorations for individual identification, especially in mass disaster and missing person cases.
CAD/CAM technology has the potential to lend a helping hand to the discipline of forensic dentistry in the identification and confirmation of an individual’s identity. Refinements to the hardware, software, and operator parameters are required to offer simple yet accurate results. Providing the forensic dentist with another tool could provide greater accuracy in objectively confirming the identification of individuals.


References

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  2. Kalman L. Utilization of an in-office CAD/CAM e.max Maryland bridge as a long-term anterior provisional. Oral Health. 2012;102(8):27-34.
  3. Crespi R, Vinci R, Capparé P, et al. A clinical study of edentulous patients rehabilitated according to the “all on four” immediate function protocol. Int J Oral Maxillofac Implants. 2012;27:428-434.
  4. Bornstein MM. The use of cone beam computed tomography for diagnostic imaging in oral implantology. Part one: the maxillary sinus. Forum Implantologicum. 2012;8(1):8-14.
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  9. Dierickx A, Seyler M, de Valck E, et al. Dental records: a Belgium study. J Forensic Odontostomatol. 2006;24:22-31.
  10. HGExperts.com. New computer aided design tools enhance forensic accident reconstruction. hgexperts.com/article.asp?id=4976. Accessed May 10, 2013.

Dr. Kalman is a Diplomate of the International Congress of Oral Implantologists. He is a full-time assistant professor at the Schulich School of Dentistry, University of Western Ontario. He can be reached at (519) 661-2111 ext 86097, at kalmanz@rogers.com or at researchdriven.ca.

Disclosure: Dr. Kalman is the developer of Q-Trays and is co-owner of Research Driven.