Novel Method for Measuring the Time of Death on Teeth ‒ Liquid Contents, Reflection Spectra

Novel Method for Measuring the Time of Death on Teeth ‒ Liquid Contents, Reflection Spectra

Novel Method for Measuring the Time of Death on Teeth ‒ Based on Liquid Contents, Reflection Spectra and Colour (Tooth Color)

Presentation of the First Analysis and Measurement Method That Is also Reference-Independent



The time of death is of considerable importance for investigations, is often one and sometimes the central key to solving criminal cases. It gives investigators a temporal framework and allows to reconstruct the chronology of the crime and, by checking of alibis, to narrow down the circle of suspects, excluding some and concentrating on others; and it can sometimes contribute to the reconstruction of the course of events. The time of death is also relevant in cases of natural death for the family register entry, insurance or succession and the request of the relatives for knowledge of the exact time or hour of death (see chapter 2).

But according to the author’s analysis, one of the greatest problems in forensic medicine must be the precise estimation of the time of death and estimations after two or three days ‒ it seems to be extremely difficult or impossible. In addition, there are a lot of influencing factors that may be unknown in the specific case. However, a number of factors can seriously influence the results or make it impossible to determine the time of death. All classical methods are limited to the first, second or third day after the onset of death. Such methods, which are based on such highly individual processes, contain uncertainty factors, intra- and inter-individual inaccuracies, which do not generally make estimations simple. In principle, there should be a need for new methods if a post-mortem interval is to be determined more precisely or also after longer times.


If the precision of the time statement is higher, the criminal investigation can be more targeted, more successful and economical.

The event of death and the subsequent onset are associated with very complex processes that alter a corpse and its tissues. If it would be possible to find a process of a particular tissue that behaves precisely like a clockwork and if it were also possible to set the time and condition state back to the moment of death, if the clock could run anew again and if it would also be possible to re-run the past time with all conditions states after the onset of death once again in real time at the same (identical) individual or object of investigation to be examined and if it is not just one clock, but several clocks of different complementary readings, it would be the perfect and most accurate method of measuring the time of death.

The author of the present work had observed that human teeth are much brighter and have another colour (value, hue, saturation) as well translucency ‒ less translucent and more opaque ‒ after death than in life. He sees a fundamental possibility in the use of processes ‒ that he has measured and analyzed at drying and rehydrating teeth ‒ and presented this novel method, for the first time. In addition, it is also the first reference independence method ‒ perhaps even the first reference-independent method of analysis or measurement in the natural sciences ‒ that does not require reference values obtained from other comparable samples (e.g. nomogram). In order to stay with the analogy, the tooth with its liquid has some clockworks and the measuring system provides also the clock face and hand or the display. The reversibility of the processes allows simulating and bypassing or eliminating inter-individual and intra-individual influencing factors ‒ for the first time.


2. Literature Review

2.1 Time of Death

An assessment of the potentials of a novel method for measuring the time of death on the basis of the tooth colour, the dental reflection spectrum and liquid content is possible taking into account the literature on existing possibilities in this field: “[...] suitable for the estimation of the time of death [are]: early signs of death (rigor mortis, livor mortis, body cooling), late signs of death (autolysis, putrefaction, conserving corpse changes[1]), examination of supravital response, […] reliable witness statements (e.g. in the case of fatal accidents), medical findings (e.g. echocardiogram/monitoring) and in special cases also ‒ in connection with findings (!) ‒ criminal investigation results (last seen alive, newspapers in the mailbox, condition of food, last phone call, etc.) […] With the information on the time of death, restraint is required; too far-reaching limitation of the time of death is to be avoided solely on the basis of the appearances of the corpse. In the case of corresponding entries regarding the time of death, relativizing additives such as ‛approximatelyʼ or ‛approximateʼ or indication of a time range are recommended. An uncritical transfer of third-party data must be avoided, it must be verified by means of own investigations […]” (Guidelines of the German Society of Forensic Medicine 2002).

In 2003, Madea and Dettmeyer published (minutes, hours or days post mortem) [2]:


Body core temperature (body cooling)

• Decrease in core body temperature (depth rectal temperature 8 cm above the sphincter ani), first temperature plateau of 2‒3 hours duration, then about 0.5‒1.5 °C/hours, depending on ambient temperature, storage, clothing, covering, body proportions, weather conditions etc.



  • Corneal opacity in open eyes after 45 minutes.
  • Corneal opacity in closed eyes after approx. 24 hours.


Livor mortis

  • Beginning of the livor mortis at the neck after 15‒20 minutes.
  • Confluction (approx. 1‒2 hours).
  • Full formation of the livor mortis after a few hours (approx. 6‒8 hours).
  • Disappearances by finger pressure (approx. 10 hours; 10‒20 hours).
  • Relocation (approx. 10 hours).


Rigor mortis

  • Beginning of the rigor mortis on the jaw joint after 2‒4 hours.
  • Complete rigidity after approx. 6‒8 hours.
  • Start of the resolution after approx. 2‒3 days (strongly dependent to the temperature).
  • Re-entry of the rigidity after breaking ‒ up to approx. 8 hours.
  • Complete resolution after 3‒4 days, at low ambient temperature also significantly longer than 1 week.


Mechanical excitability of skeletal muscles

  • Contraction up to 1.5‒2.5 hours.
  • Local contraction up to approx. 8 hours.

For orientation, however, the guidelines of the German Society of Forensic Medicine (2002) give the following values ‒ post mortem:


Livor mortis

  • Beginning (15‒30 minutes).
  • Confluction (approx. 1‒2 hours).
  • Full formation (approx. 6‒8 hours).
  • Disappearances              

     completely on thumb pressure up to approx. 20 hours),

     incomplete on sharp-edged pressure (tweezers) up to approx. 36 hours.

  • Relocation about 6‒12 hours.

     Complete up to 6 hours.


Rigor mortis

  • Beginning (jaw joint; 2‒4 hours).
  • Complete expression (approx. 6‒8 hours).
  • Re-entry after breaking up to approx. 8 hours.
  • Solution ‒ strongly dependent on ambient temperature (start of solution: after 2‒4 days and later).


Mechanical excitability of skeletal muscles

  • redirected contraction (so-called Zsako muscle phenomenon) to 1.5‒2.5 hours,
  • local contraction (idiomuscular contraction) up to 8 hours ‒ (extremely rare up to 12 hours).

A survey of other studies and publications showed other value ranges and variations (see [Pounder 1995]). Furthermore, the guidelines of the German Society of Forensic Medicine (2002) state[3]: “In order to be able to assess the degree of rigor mortis, it must be checked in small and large joints (jaw, finger, elbow, knee). The Zsako muscle phenomenon can be checked by striking with the percussion hammer in the area of ​​the mm. interossei over the back of the hand. Finger adduction occurs […] The idiomuscular bulge is preferably checked by vigorously striking the biceps brachii muscle. If the subcutaneous adipose tissue is more pronounced, the bulge is hardly visible, but it can be felt. Measurement of the so-called core body temperature (deep rectal temperature; body cooling): if done correctly, it is the best basis for determining the time of death. However, the use of a glass or electronic thermometer with a particularly long measuring attachment must be required, since it must be inserted at least 8 cm deep into the rectum. A clinical thermometer is generally not suitable. It is imperative to measure the ambient temperature at the place where the body is found. The time of day must be documented for both measurements. Approved thermometers are to be used. The measurement of the rectal temperature not only has a high value for the estimation of the time of death, but is also of great importance for the detection of febrile diseases [...] Changes in putrefaction allow an assessment of the time of death, but with a much wider range […] Eggs can be deposited very early due to insects, followed by maggots, pupation, empty pupae.[4] Outside and inside buildings, there may be various defects or changes caused by other animals: ants with etching marks, rodents, dogs, cats, foxes, birds […]” (Guidelines of the German Society for Forensic Medicine 2002).

Further approaches are seen at the level of biochemical analyses. The tyndallometry of the eye chamber liquid of K+ and the total protein should increase post mortem, Cl‒ and Na+ decrease. For this method, a time span of 98 hours (storage of the sample at 2°C) or 50 hours at an accuracy of +/‒24.8 hours (or 12.4 hours) and at 21°C storage of the sample +/‒13.0 or 12.2 hours is given. K+ and total protein should be significantly less influenced by the temperature than urea, Na+ and Cl‒ (Hagel 1999). The use of radio-carbon method (see [Taylor et al. 1989]) and further processes was discussed in connection with the determination of the death time. But up to now, such methods have no very high precision or are not applicable for such short time windows.

The analysis of the literature reveals the following: all processes used for estimating the time of death are caused by death. Such methods only work if the process triggered by death and used to determine the time of death has not yet been completed.

According to the general scientific laws, which must also apply here, they are strongly dependent on the ambient temperature and environment and various other inter- and intra-individual factors. 
When considering the literature, all previous methods of estimation the time of death taken together should be able to roughly narrow down the time of death on the first to second day after death or according to Arendt et al. (2003) within 72 hours. 

There is a certain time and precision gap between the classic estimation of the time of death and the determination of the time of lying. If a distinction is made between the determination of the time of death (using processes associated with body tissues that occur immediately as a result of death) and the corpse laying time estimation (using processes that result from the lying of a dead body in a specific location), the possibility of determination the time of death ends after one to three days at the latest. Influencing factors such as the physical conditions or condition of the body, cause of death, initial temperature of the body at the time of death, diseases, germ colonization, location, ambient temperature, sunlight, ventilation, moisture, animal feeding, displacement of the body and much, much more are likely to be decisive for the course of post mortem changes and the signs of death. Influencing factors that are not known or have changed may lead to incorrect results. If the death is more than 3 days ago, no time of death determination is possible.

In principle, there is a need for new methods if a time of death determination is to be made more accurate or even after longer periods of time than described post mortem.  
All previous methods are based on irreversible processes. In this respect, a method based on reversible processes could be advantageous and help to avoid or eliminate inter-individual scattering problems and intra-individual difficulties.


2.2 Applications of Spectrophotometry and Colorimetrics
      in Forensic Medicine; Drying and Colour

According to the authorʼs opinion, colour science and spectral analysis are likely to be underestimated by forensic medicine. But they should be fundamental. Perhaps the number of few studies with spectrophotometers or colorimeters could show little interest or knowledge of the potential and leads to wasted diagnostic options in any case: however, measurements were carried out on hair (Bohnert et al. 1998), artificially generated haematomas (Lins and Hamper 1970, Klein et al. 1992 and 1996), forensic relevant changes or bruises (Lins 1975, Trujillo et al. 1996, Bohnert et al. 2000), in connection with haemoglobin (Siek et al. 1984), on skin of living (Lins 1969) and dead (Lins 1968), green discoloration (Lins and Kutschera 1974), post-mortem pallor, lividity or hypostasis (Vanezis 1991, Vanezis and Trujillo 1996, Schaefer 2000), livores mortis (Schuller et al. 1987 and 1988, Kaatsch et al. 1993 and 1994), material, such as blood (Lins and Blazek 1982, Rommeiß et al. 2000) as well as white powder of different composition (Bohnert and Werp 1999).

Drying Materials become brighter and change their colour with the change in liquid content. This phenomenon can be observed in dry and wet textile fabric, on the more or less seawater-influenced sandy beach, at drying cement, lime or gypsum and depending on the weather at clay tiles or garden soil, and paint shows a different colour effect before and after drying. Even rain clouds look different from the brighter and friendlier cumulus clouds of a beautiful summer day.

For the first time, the author of the present work had described a method for measuring the time of death on the basis of dental drying. Furthermore, he is the first to investigate the relationship between dental liquid content and tooth colour colorimetrically and spectrophotometrically and to systematically research tooth colour with high-precision measurement systems and high-precision positioning systems.

  • [1] Mummification and adipocire could be meant.
  • [2] Translation from German.
  • [3] Translation from German.

[4] After death, various environmental conditions play most likely an important role regarding development, age determination of insects and the chronological sequence of settlement of different species influenced by several factors. In any case, entomological methods should be assessed differently from region to region due to specific flora and fauna. All entomological processes are likely to depend to a large extent on ambient temperature and climate ‒ according to the general physical, chemical, biological, biochemical and physiological principles.


André Hoffmann systematically researched the tooth colour at human teeth and dental shade guides with high-precision measuring systems and high-precision positioning system in vitro with highest precision. Due to this basic scientific research, he was able to quantify and isolate manifold factors influencing the colour of teeth. These include, for example, the light or measuring light and the type of light (illuminant) and illumination and colour temperature, the optical beam path of the light or the measuring geometry, the observation angle (2°, 10°), the size of the measuring surface, and measuring opening, the gloss effect, the liquid content (with scientific evidence of the relationship between liquid content and tooth colour), effect of drying, moisture and rehydration, the correlation between the liquid content and the gloss effect, the subjectivity of visual subjective shade matching, crown curvature, type of system (spectrophotometer, tristimulus colorimeter), measuring mode (contact or non-contact), system-object-relation, positioning, repeatability or reproducibility, lens shift, displacement between sample and measuring surface and further intra- and interindividual factors. In addition, subjective-visual determinations and objectified measurements were examined in subjective-objective comparisons using colour coordinates comparisons. All these influencing factors are investigated on moist, drying, drier (various specific dehydration and rehydration states) and dry teeth based on the brightness (L*), on colour measurement values, such as a*, b* (CIELAB), C*, h, (CIELCH), ΔE, the metamerism index, spectral values and curves, tabs of dental shade guides and tooth colour spaces

As part of this exploration, phenomena (e.g. changes and breaks in behaviour as well as highly individual developments in colour values, paradoxes between the values of subjective determination using tooth shade patterns and the values of objective measurements) were identified; and insights into the very complex colour dynamics through dehydration and rehydration were shown (up to more than >8 days). The development of the individual colour measurement values was based on the liquid flow through the tooth and its tissues, in particular during drying and rehydration, and gave information about dynamics and the temporal extent of these processes.

On the basis of this data, Hoffmann had developed several methods for research and practice, suggestions for feasible innovations, such as monitoring of dental treatment to protect against pulp damage based on drying, and reconstructing the colour of naturally moist teeth on those that have already dried, the identification of the living and the dead, human and animals via the “dental fingerprint” and a novel method of measuring the time of death for forensic medicine.

He also described a time limit of drying up to which relatively natural, suitable colour values and shade matching results can be obtained and after which no colour determination should be carried out; and he established the rehydration time after the end of the drying or dental treatment, which must be waited in order to regain a natural tooth colour and to get correct values and results again. 

His findings also show that teeth are able to store information, for example, on the condition (liquid content, colour values) and about the time within the drying and fluid reabsorption chronology. The author articulates a “dental chronometer” (“tooth clock”), “dental data storage” (“tooth data storage”) and a “dental memory” (“tooth memory”) and believes that significant progress in this area may include and could be achieved via a neural network for colour measurement apparatus.


First Systematic Research and Analysis of the Tooth Colour and Influencing Factors