ARTÍCULOS ORIGINALES DERIVADOS DE INVESTIGACIÓN

RADIOGRAPHIC DESCRIPTION OF TITANIUM AND FIBERGLASS POSTS CEMENTED IN HUMAN PREMOLARS SUBJECTED TO HIGH TEMPERATURES IN VITRO FOR FORENSIC PURPOSES

Johana Aramburo¹; Herney Garzón²; Juan Camilo Rivera³; Freddy Moreno⁴

¹ DMD, Colciencias Program of Young Researchers and Innovators, Universidad del Valle Office of the Vice President for Research (Cali, Colombia).
² DMD, Oral Rehabilitation Specialist, Professor at the Universidad del Valle School of Dentistry (Cali, Colombia), Dental Biomaterials Research Group, Universidad del Valle (Cali, Colombia). e-Mail: herneygarzon@hotmail.com
³ DMD, Endodontics Specialist, Professor at the Universidad del Valle School of Dentistry (Cali, Colombia), Dental Biomaterials Research Group, Universidad del Valle (Cali, Colombia).
⁴ DMD, MSc in Biomedical Sciences, Professor at the Universidad del Valle School of Dentistry (Cali, Colombia), Professor at the Pontificia Universidad Javeriana School of Health Sciences (Cali, Colombia).

SUBMITTED: APRIL 14/2013-APPROVED: MARCH 4/2014

Aramburo J, Garzón H, Rivera JC, Moreno F. Radiographic description of titanium and fiberglass posts cemented in human premolars subjected to high temperatures in vitro for forensic purposes. Rev Fac Odontol Univ Antioq 2015; 26(2): 314-335.

ABSTRACT.

Key words: forensic dentistry, identification of victims, dental tissues, endodontic materials, titanium posts, fiberglass posts, high temperatures, conventional radiography.

INTRODUCTION

Teeth are the hardest organs of the human body due to their high resistance to exposure to acids and high temperatures, as well as their high taphonomic resistance.^{1, 2} This makes them an efficient means to identify individuals or human remains based not only on their morphological characteristics (macro and microanatomy of dental and periodontal tissues), but also on dental treatments and the materials with which they were performed. Therefore, if there are dental records of an unknown individual who has died in extreme conditions, information obtained from his/her remains can be collated to initiate the process of dental identification.^3-5 The process of comparing information obtained from the body against dental life records is known as antemortem/ postmortem comparison and it allows determining whether the body or human remains belong to the missing individual.^{6, 7}.

Initially, this process uses circumstantial evidence collected at the site where the corpse or human remains are located, since the methods of visual identification by relatives may produce false positives because of the emotional impact of seeing a body affected by causes of death (mutilated, decaying, burned, charred, or incinerated human remains).^{4, 5}

Therefore, once the initial information is classified, further reliable information is obtained through different methods, including the observation and analysis of teeth—a process that has proven to be one of the most effective among other medico-legal methods and has been recognized in Colombia through Act 38 of January, 1993, which unifies the dactiloscopy system and adopts dental charts for identification purposes—.⁸

In the case of corpses or burned, charred, or incinerated human remains, the identification process becomes difficult depending on the postmortem conditions, associated with the total destruction of the epidermis and areas of necrosis in underlying tissues, which impedes identification by the conventional methods of visual recognition or fingerprint.³This is why comparisons are most frequently done using teeth and dental treatments such as prosthetic restorations and obturations, since dental materials are highly resistant to the action of high temperatures. This can been verified in the descriptions of the behavior of dental amalgams, composite resins, and different alloys by the University of Pavia Department of Odontostomatology,^9-11 the classifications of composite resins subjected to high temperatures, carried out in the University of Buffalo Department of Restorative Dentistry (USA), ^{12, 13} and the experiments on dental amalgam, composite resin, glass ionomer, zinc oxide cement, endodontic cement, and gutta-percha, conducted in Universidad del Valle School of Dentistry. ^14-17

The objective of this study was to perform a radiographic description of the behavior of two types of prefabricated posts cemented in human premolars subjected to high temperatures (200°C, 400°C, 600°C, 800°C, and 1000°C) to determine repetitive parameters of radiographic changes in dental tissues and materials, in order to identify and obtain useful radiographic markers that can help in forensic dental identification processes and in the documentation of medico-legal autopsy. Eventually, this will provide valuable information during postmortem dental registration (time of exposure to high temperatures, maximum reached temperature, relationship between dental tissues and dental materials) that can be collated with antemortem dental records, thus providing sufficient data leading to accurately identify a burned, charred or incinerated individual, besides supporting the use of conventional radiography with scientific evidence in these cases.

METHODS

This is a pseudo-experimental in vitro study on the behavior of the action of high temperatures on dental tissues (enamel, dentin, and cement), endodontic materials (Wave One^® gutta-percha by Dentsply Maillefer^®, Top Seal^® obturation material by Dentsply Maillefer^®, and Relyx TM ARC posts cementing material by 3M ESPE^®), titanium posts (Tenax^® Endodontic Post System by Coltene^®) and fiberglass posts (Tenax^® Fiber Trans by Coltene^®). To this end, a convenience sample of 30 upper and lower premolars, both right and left, was collected from individuals of both sexes aged 14 to 26 years, and extracted for orthodontic and periodontal reasons, presenting no tooth decay, restorations, endodontic treatments, pulp pathology, or congenital malformations.

The variables included in this study are connected to the radiographic changes of dental tissues, materials used in endodontic treatment, materials used for cementing posts, and prefabricated titanium and fiberglass posts. These changes will be grouped to facilitate the discussion, according to the tissues and dental materials with respect to temperature range, taking into account: 1. Maladaptation of obturation materials; 2. Fissures, cracks, cracked appearance, and fractures, and 3. Changes in density.

Sample collection

This study was first approved by the Universidad del Valle Ethics Committee in Humans, in accordance with Article 11 of Resolution No. 008430 of the Ministry of Social Protection,¹⁸ and the ethical principles for medical research on humans, as indicated by the World Medical Association in the Declaration of Helsinki.¹⁹ Prior authorization of the School of Dentistry Board of Directors and after patients signed an informed consent, the sample was obtained from extracted teeth meeting the inclusion criteria, at the Clinic of Oral Surgery of Universidad del Valle School of Dentistry.

Management and storage of samples

Immediately after the teeth had been extracted, they were washed with non-sterile water to eliminate blood residues and were put for one week in a dark container with 5% chloramine T fixative solution (100 g sodium tosylchloramide diluted in 2 liters of distilled water). Then they were placed in saline solution at a temperature of 37°C with a relative humidity of 100%; the saline solution was changed every two weeks, according to ICONTEC 4882\2000 standards²⁰ and ISO/TS 11405/2003 standards,²¹ until the procedures on the samples were started not later than two weeks afterwards. At this time, each tooth was taken a conventional DENTUS E Speed^® (AGFA^®) radiograph, in a Radiology Gendex^® 770^® equipment of 0.8 impulses. The following items were taken into account: the vertical position of the radiographic film to the longitudinal axis of teeth, the spatial orientation of the vestibular surface of teeth towards the cone of the equipment, the placement of teeth on the white side of the x-ray film with the identification point towards occlusal, and the standard location of the equipment cone at 10 cm. Similarly, the radiographs were revealed in a Gendex^® GXP^® automatic x-ray processor.

Preparation of cavities

One operator put each of the 30 teeth in a wax base and performed the opening of chambers (the teeth’s clinical crown was not removed) through a type I occlusal cavity using # 1 and 2 round diamond burs (Diatech^®) and Endo Z burs (Dentsply Maillefer^®). Once the cavity was prepared, each tooth went through prophylaxis with baking soda to disinfect the cavity and decrease the dentin’s surface tension, in order to optimize the adhesive properties of the materials used for cementing prefabricated posts.

Endodontic treatment

Once the canal was located, the working length was determined with K15 files (Dentsply Maillefer^®), visually monitoring the appearance of the file through the apical foramen and decreasing this length by 1 mm. The coronal cavity was sealed with a cotton pellet and Coltosol^® (Dentsply Maillefer^®) and the apical foramen with methacrylate. The temporary seal was removed eight days later, instrumenting with rotary Wave One Endomotor^® instrumentation equipment (Dentsply Maillefer^®) and Wave One Primary File 25^® reciprocating instrumentation files (Dentsply Maillefer^®) of 25 mm or Wave One Large File 40^® (Dentsply Maillefer^®), according to the canal’s diameter. During the three phases of instrumentation with reciprocating files, the samples were irrigated with 6 ml of 5.25% sodium hypochlorite (2 ml in phase one cervical third, 2 ml in phase two mid-third and 2 ml in phase three apical third), through Monoject^® (Kendal^®) irrigation needles at 2 mm from the working length. Finally, the canals were washed with distilled water and dried with Wave One (Dentsply Maillefer^®) paper cones. Obturation was performed eight days later with Primary File 25^® single-cone guttapercha (Dentsply Maillefer^®) or Wave One Large File 40^® (Dentsply Maillefer^®), according to the rotary instrument initially used and with Top Seal^® obturation material by Dentsply Maillefer^®, to the estimated length of the prefabricated posts, using the technique of vertical compaction with heat, using an Element Obturation Unit^® (Sybron Endo^®). The cervical third was not obturated to avoid contamination of dentin with the sealing cement, and the coronal cavity was sealed with a cotton pellet and Coltosol^®. All the procedures were performed following the directions of manufacturers, according to the protocols reported in the literature.^{22, 23}

Cementation of prefabricated posts

Cementation was performed depending on the group to which each tooth belong and according to the material of the cemented post. Thus, teeth were sorted out in two groups of 15 samples each (table 1) .

Group 1 (Coltene^® Tenax^® Endodontic Post System titanium posts):

The temporary obturation material was removed and the root canal was prepared and expanded with # 1 and 2 Peeso^® burs (Stainless^®), as well as with burs corresponding to the caliber of the prefabricated post. The canal was immediately applied Scotchbond^® 37% orthophosphoric acid (3M ESPE^®) for 15 s, thoroughly washed with water for 10 s, and dried with paper tips (Dentsply Maillefer^®). Two consecutive layers of Adapter Single Bond 2^® adhesive (3 M ESPE^®) were later applied, drying for 5 s and light curing for 10 s with a LED Elipar S10^® lamp (3 M ESPE^®). Finally, Relyx TM ARC^® cement (3M ESPE^®) was placed on a mixing block and mixed for 10 s to be applied inside and around the root canal and the prefabricated post using a periodontal probe. The post was fixed on the root canal and photo cured with a LED Elipar S10^® lamp (3M ESPE^®) for 40 s. Posts with caliber 1 (1.10 mm) and 2 (1.20 mm) were used. All the procedures were performed following the indications of manufacturers.

Group 2 (Coltene^® Tenax^® Fiber Trans fiberglass posts))

The temporary obturation material was removed and the root canal was prepared and expanded with # 1(and 2 Peeso^® (Stainless^®) burs, as well as with burs corresponding to the caliber of the prefabricated post. The canal was immediately applied Scotchbond^® 37% orthophosphoric acid (3M ESPE^®) for 15 s, thoroughly washed with water for 10 s, and dried with paper tips (Dentsply Maillefer^®). Two consecutive layers of Adapter Single Bond 2^® adhesive (3 M ESPE^®) were later applied, dried for 5 s and light cured for 10 s with a LED Elipar S10^® lamp (3 M ESPE^®). Finally, Relyx TM ARC^® cement (3M ESPE^®) was placed on a mixing block and mixed for 10 s to be applied inside and around the root canal and the prefabricated post using a periodontal probe. The post was fixed on the root canal and photo cured with a LED Elipar S10^® lamp (3M ESPE^®) for 40 s. All the procedures were performed following the manufacturers' instructions.

Crown sealing

Once posts had been cemented, the coronal cavity was sealed. Initially, Scotchbond^® 37% orthophosphoric acid (3M ESPE^®) was applied for 30 s, thoroughly washing with water, and drying with paper tips (Dentsply Maillefer^®). Adapter Single Bond 2^® adhesive (3M ESPE^®) was later applied and light cured for 20 s with a LED Elipar S10^® lamp (3M ESPE^®). Finally, the cavity was obturated with TPH3^® composite resin (Dentsply Maillefer^®) by the incremental technique. All the procedures were performed following the indications of manufacturers. After clinical manipulation of teeth, they were taken a conventional radiograph using the previously explained protocol.

Application of high temperature

This procedure was carried out following the technical and scientific protocol established in the Department of Odontostomatology of the University of Pavia (Italy),¹⁰ and the studies carried out in the School of Dentistry of Universidad del Valle (Colombia).²³ Once crown sealing was completed, the teeth were taken to individual trays made of refractory lining material (Cera-Fina^® Whipmix^®) to facilitate handling, and were subjected to direct heat in a muffle type oven (Thermolyne^®) previously calibrated to five different temperature ranges (200, 400, 600, 800, 1000°C), with an increase rate of 10° C per minute, from an initial temperature of 34° C (room temperature) until reaching each of the proposed ranges.

For example, the three teeth of the 200° C group were put in the oven, each on its respective tray, at a temperature range from 34° C to 200° C, allowing the oven to cool down back to room temperature and removing the trays with teeth. Then the three teeth of the 400° C group were put in the oven, each on its respective tray, at a temperature range from 34° C to 400° C, allowing the oven to cool down back to room temperature and removing the trays with teeth. The same procedure was conducted with teeth from the groups of 600° C, 800° C and 1000° C. The in vitro procedure proposed in this study is done in an oven and not in direct flame, bearing in mind that in different literature reports the maximum temperature reached is 1000° C, a peak that is reached in 25 to 30 min and later remains to approximately 500° C until all the oxygen is consumed or all the organic material is reduced to carbon (carbonization) or compounds of calcium, phosphate, silica, or other mineral nutrients (incineration).²⁴ In addition, this in situ "muffle effect" is what perioral tissues, facial musculature, bone tissue, and dental and periodontal tissues would comparatively do.²⁵

A tooth exposed to high temperatures may undergo the following changes: stay intact, or become burned (color change and formation of fissures and cracks), carbonized (reduced to carbon by incomplete combustion), incinerated (reduced to ashes) or burst (root and crown explosion). Therefore, the teeth will be very fragile and susceptible to alterations during handling at the time of removing them from the lining trays.

For this reason, once they are at room temperature the teeth will be covered with hairspray in order to structurally fix them without altering or changing their microstructure.²⁵

The teeth were later embedded in transparent acrylic resin (New Estethic^®) and taken a conventional radiograph with the previously explained protocol.

Observation

The radiographic analysis was done by comparing the teeth’s initial radiograph with the radiograph taken at the end of the clinical trials and the one taken after exposure to high temperatures. The radiographs were placed on a negatoscope to be observed with the help of a 10 x amplification magnifying glass. The following items were taken as reference: the temperature to which each sample was subjected, the radiographic changes compatible with fissures, cracks, fractures and fragmentation, according to changes in aspects such as density (radiopacity and radiolucency), limits, size and shape of the various structures.

RESULTS

Dental tissues

The samples subjected to 200 °C showed irregular enamel with small radiolucent lines compatible with fissures involving both enamel and dentin independently (figure 1). The samples subjected to 400 °C showed loss of enamel density and an irregular pattern of fissures in the entire surface. The dentin suffered a network of radiolucent lines compatible with micro-fractures, longitudinal radiolucent lines compatible with cracks affecting enamel and dentin, and a discontinuous radiolucent band between these two tissues, compatible with the separation of enamel at the amelodentinal junction. Although this change occurred in all the samples from this group, the extension varied in coronal direction (figure 2).

At 600° C the enamel experienced greater density loss, which provides the surface with a rugged appearance due to a network of radiolucent lines compatible with micro-fractures. Similarly, the enamel showed longitudinal radiolucent lines in its entirety, which continued through the dentin and fragmented it in several sections. Likewise, the dentin showed countless radiolucent lines compatible with cracks in different directions. A broad continuous radiolucent band was observed between the enamel and the dentin, corresponding with the separation of the enamel at the amelodentinal junction, and which is more evident in the cervical coronal thirds (figure 3).

At 800 °C the enamel lost continuity due to the presence of countless fractures that altered its structural integrity, in such a way that in two samples there were no traces of enamel. The coronal and radicular dentin was invaded by radiolucent lines compatible with fractures oriented in all directions. The samples that retained fragments of enamel showed a wide radiolucent band that separates both tissues at the amelodentinal junction (figure 4). Finally, at 1000° C the samples experienced coronal burst due to dentin fragmentation. However, some samples maintained the integrity of coronal dentin but completely lost the enamel due to their separation at the amelodentinal junction and subsequent fragmentation. The remnant coronal dentin showed a network of radiolucent lines compatible with micro-fractures (figure 5 y table 2).

(table 2)

Prefabricated posts

No significant changes were observed in samples subjected to 200°C and their posts (both metallic and fiberglass) were radiographically intact (figure 1). At 400° C the images are radiolucent between dentin and post due to loss of the material used in cementation of the nucleus. Similarly, there was a change in the radiographic density of the middle and apical thirds, associated with loss of endodontic obturation material (figure 2). At 600° C there were changes in the radiographic density of the endodontic obturation at the mid and apical thirds, and radiolucent images inside the canal due to loss of endodontic obturation material (figure 3). Finally, at 800 and 1000° C, the radiolucent images were much more evident inside the canal, associated with separation of the posts due to loss of the materials used for cementation, as well as loss of endodontic obturation material. There were no changes consistent with the structural alteration of the posts (figure 4 and figure 5, table 2).

DISCUSSION

Several authors have reported the importance of intra- and extra-oral radiography as identification methods in dentistry, based on the analysis of different radiolucent and radiopaque structures in teeth,^{26, 27} in addition to dental biomaterials, specifically those used in endodontic treatments, which have been used to guide and document processes of forensic dental identification in cases of burned, charred, or incinerated corpses.²⁸

This was demonstrated by Savio et al,11 who subjected human teeth to high temperatures (200, 400, 600, 800, 1000 and 1100° C) to describe radiographic changes. The authors analyzed dental tissues using conventional periapical radiographs, including criteria such as shape, dimensions, and relationships between radiopacity and radiolucity. This way, dental tissues had no radiographic changes at 200° C, while at 400° C there was a series of radiolucent lines compatible with fissures and fractures in coronal dentin.

At 600° C, some samples showed separation of the fragmented enamel from dentine (a wide radiolucent band between both tissues, compatible with the amelodentinal junction) as well as a network of radiolucent lines compatible with a reticulate pattern of fissures. At 800° C, teeth crowns were fragmented and after 1000° C the teeth were fragmented and the dental tissues had fissures and fractures in all directions. Finally, the authors concluded that the pattern of cracks and fractures is progressive as temperature increases, which means that higher temperatures result in fragmentation of dental tissues and separation of enamel from dentin. All of these changes in dental tissues (enamel and dentin) are consistent with those reported in the present study.

Although such in vitro studies prove that dental tissues and materials are highly resistant to the action of high temperatures and show specific changes in each temperature range to which they were subjected, it should be noted that these changes may vary in vivo due to extrinsic factors such as time of exposure to heat, nature of the cause of fire, participation of flammable substances, curve of temperature elevation, and substances used to extinguish the fire. Intrinsic factors should also be considered, such as the thermal expansion coefficient of tissues and materials, as well as their melting point.^{3, 4}

Similarly, by means of x-rays the present study allowed observing and describing one of the most characteristic changes of dental tissues: enamel burst in the cervical region followed by coronal detachment from the rest of the tooth, right at the interface of the amelodentinal junction. This phenomenon occurs because dentine, having a high organic content and 12% water, shrinks due to dehydration when subjected to high temperatures; it is then provided with some degree of resistance compared to the enamel,²⁹ which has a high inorganic content (from 96% to 99%), represented in a mineral structure formed by a large amount of calcium phosphate in the form of apatite crystals,³⁰ which means that, once subjected to high temperatures, this tissue loses its low content of water and collagen matrix, causing a sharp contraction and therefore fissures, cracks, and fractures, resulting in a cracked appearance.

This discrepancy in the behavior of tissues with respect to their dimensional stability is what causes that in the cervical third, enamel cracks at 200° C, that it separates from the dentin starting at 400° C and that, finally, the crown detaches as a cap, once dentin carbonizes and considerably reduces root volume starting at 800° C.^14,31,32 All these changes were reported in the studies by Günther and Schmidt, cited by Rötzscher et al,³³ Merlati et al,¹⁰ and Moreno et al.¹⁴

As for fissures, cracks, cracked appearance, and fractures of the dental tissues, starting at 400° C there are fissures in enamel and cement that from 600° C produce cracks that deepen up to the coronal and radicular dentin respectively, as observed in the radiolucent images, and starting at 800°C can generate root fractures in some teeth. This pattern of longitudinal and transversal fissures and cracks shown in radiographs corresponds to changes in the surface of enamel and cement, which acquires a chopped or cracking appearance that disappears with the fragmentation of enamel and the incineration of cement at 1000° C, as described by Merlati et al¹⁰ and Moreno et al.¹⁴

Changes in dental materials

In terms of the composite resin used for coronal seal, what is most striking is the gradual maladaptation associated to temperature increase, which becomes evident by the emergence of radiolucent images between material and dentin. Similar changes were reported by Merlati et al¹⁰ and Moreno et al.¹⁴

In terms of endodontic obturation materials, we did not find literature reports discussing the behavior of the endodontic cements used in our study. Therefore, the discussion focuses on gutta-percha. This thermoplastic material is characterized by a soft consistency between 25° C and 30° C, and a fluid consistency from 60° C and above—features that can be observed in vitro—. However, López et al²⁸ pointed out that, in vivo, gutta-percha is able to resist external heat, which agrees with this study, where gutta-percha can be differentiated from dental tissues inside the root canal even if it is incinerated at 800° C. Another interesting aspect of gutta-percha is that Moreno et al¹⁴reported a greater number of fractures and root bursts on teeth that were not endodontically treated, a situation that did not happen in this study, so one can infer that gutta-percha, inside the canal, can provide structural strength to charred and incinerated dental tissues, as happened in the study by Savio et al.¹¹

Prefabricated posts

No reports were found in the literature describing the behavior of these cemented elements on teeth subjected to high temperatures; however, it was determined that the posts are highly resistant, noting that teeth that had titanium posts cemented suffered greater thermal expansion at some point, which explains the greater amount of transverse cracks and root burst in some samples, while fiberglass posts practically incinerated starting at 800° C, and did not influence the behavior of roots.

Cement for resin posts

It was not possible to observe obturation material changes in all the radiographs; however, it was possible to observe radiolucent images between posts and dentin roots, compatible with structural loss of resin cement, which was described by stereomicroscopy by Aramburo et al,¹⁵and by scanning electron microscopy by Moreno and Mejía.¹⁷

CONCLUSIONS

Both dental tissues (enamel, dentin and cement) and the prefabricated posts evaluated in this study showed a series of specific radiographic changes in each described temperature range, so their behavior, in terms of radiopacity and radiolucency, provides information on the maximum degree of temperature that can be reached. Similarly, prefabricated titanium and fiberglass posts showed high resistance to high temperatures, and therefore they can be used in identification processes during ante-post mortem comparison, with the help of radiographs, in the case of corpses or burned, charred, or incinerated human remains. The results of the present study showed that being familiar with the behavior of dental tissues and materials to the action of high temperatures is of great importance to forensic dentistry during the processes of identification and documentation of medico-legal autopsy of an individual whose dead body or remains have been burned, charred or incinerated.

ACKNOWLEDGMENTS

The authors thank the Universidad del Valle Laboratory of Image Collection and Analysis for the advice provided during the analysis of the sample. This research project was conducted as part of the Colciencias Program of Young Researchers and Innovators "Virginia Gutiérrez de Pineda" and the Universidad del Valle Vice Presidency for Research, 2012-2013.

CONFLICT OF INTEREST

The authors declare having no conflict of interest.

REFERENCES