3D modelling seems to have really taken off in recent years. In Durham we’ve been 3D modelling and printing for quite a while now and over the last few years have been involved with several interesting projects including ‘Skeleton Science’, which saw us modelling and printing a complete skeleton from our collection.
Given that many of the analyses that will be carried out on the Scottish Soldiers are destructive, one of the first things that we have had to do is record, in as much detail as possible, the bones and teeth that will be affected. For the most part the recording has consisted of high quality photographs of the remains but for some of the elements we have been exploring creating high quality 3D models too. Previously we have created our 3D models using a laser scanner but this time we have been exploring using photogrammetry.
Photogrammetry, broadly speaking, is the science of making measurements from photographs to locate the exact position of any number of individual surface points. By using software that integrates the ‘Structure from Motion’ (SfM) range imaging technique, a highly accurate 3D model can be produced from a series of overlapping 2D images. To derive 3D information (distance/depth) from 2D images, SfMsoftware uses the apparent difference in the relative position of numerous points on an object when seen from multiple angles, known as the Parallax. Using triangulation to estimate the changes in the camera’s position relative to the object, the software can calculate the distance and depth of the thousands or millions of points from which the object is composed.
To build the 3D models constructed as part of the Scottish Soldiers Project, we used the software package Agisoft Photoscan. Sharp, detailed images, of a type most suitable for use with Photoscan, were captured under diffuse light using a tripod and camera in a fixed position, while rotating the object on a turntable. To ensure a detailed and accurate model, good image overlap is necessary, so the same features on an object appear on multiple photos. To obtain good overlap, 72 images were captured of each object, 36 from a lower angle and 36 from a higher angle. The images were then masked and imported into the software to construct the final 3D model.
Because the majority of the analyses that will be carried out require samples to be taken from the teeth, we wanted to record some of the dental pathologies in detail before analysis began. Therefore all of the 3D models we have made so far are of the jaws and teeth of the Scottish Soldiers. The models of the lower (mandible) and upper (maxilla) jawbones were particularly difficult to make as many of the individuals’ teeth are very loose, meaning that whenever we moved the jaw bones all the teeth would fall out! This is why some parts of the model are missing – because we physically couldn’t photograph them and keep the teeth held in place. If you click on the arrows in the bottom right of each model once it’s loaded you can open it up in full screen and really explore them in detail.
This model is one of our favourites. It shows Skeleton 21, who is the individual with the really obvious pipe-smoking facets in his teeth that we discussed in our first blog post. We actually made this model in two separate parts – first the mandible alone and then the maxilla alone. We took the photographs for both with the teeth pointing upward (so that gravity held them in place). Once we had made the two models we were able to put them together and line up the dental wear facets (something that proved challenging and we still haven’t got quite perfect in this model) to show where the clay pipe stem would have been held between the teeth.
Mandible with calculus
This is the mandible of Skeleton 12. This individual had large quantities of calcified plaque on their teeth, called dental calculus or tartar. The calculus is the brownish rough material that is covering the tooth enamel, which is a creamy colour and smooth. Calculus is formed when the plaque (the soft whitish stuff you brush off with your tooth brush) is not removed regularly or effectively and begins to calcify. This is what the dentist or hygienist scrapes of your teeth when you visit. As it calcifies it traps particles of food, pollen and bacteria in it, which makes it a fascinating time capsule of oral health!
Tooth with cavity (tooth decay)
This is the lower left (his left – not yours) second molar from Skeleton 22. The tooth has a single large cavity in it. Dental cavities (also called dental caries) form when the bacteria in the mouth metabolise sugar. As they do this they produce acid that, over time, dissolves the mineral content of the dental enamel leading to a cavity. There is also a lot of calculus on the side of the mouth where the cavity is, suggesting it was painful for the individual to chew on this side of his mouth.
Mandible with abscess
This individual (Skeleton 19) has really interesting teeth – and teeth that made us feel very grateful for modern dentistry! There is a large dental abscess in this individual’s lower left jaw; the abscess has formed in conjunction with a cavity in the second premolar that has destroyed the entire crown of the tooth. This cavity would have allowed bacteria to get into the tooth’s root causing an infection, leading to a build-up of pus in the jaw bone beneath the tooth that would have been extremely painful. The pus had pushed out of the jaw through the bone and surrounding tissue and into the mouth, allowing the pus to drain. This is why there is a large U-shaped area of bone missing and the tooth root is exposed. The fine porosity surrounding the U-shaped area shows the bony reaction to the abscess. While sounding revolting, this would have actually alleviated some of the pain caused by the build-up of pressure in the abscess. If you look at the mandible of this individual you can see that there are slightly heavier calculus deposits on the teeth on the same side of the jaw as the abscess. The action of chewing food helps to remove plaque and so the build-up of calculus on the surrounding teeth tells us it would have been painful for the individual to chew on this side of his mouth.
This is a lower right canine from Skeleton 25. Nine of the individuals excavated from Palace Green had some form of unusual wear on their teeth. This tooth also has quite a lot of calculus on it. The wear on this tooth might have been caused by pipe smoking as there is a matching crescent shaped notch on the tooth from the upper jaw, suggesting that the teeth were used to hold a cylindrical object. However, it is an unusual location to hold a pipe – clenched between two pointy teeth. Normally (as in the first model) pipe wear spans two adjacent teeth as the notch between them creates a natural resting point for the pipe. It is possible that the wear in the canines of Skeleton 25 relates to some other activity as yet unidentified. There were also four individuals who had ‘V’ shaped notches in their teeth. These notches and grooves may indicate some form of habitual activity using the teeth as tools. One of the things that we are hoping to investigate further is the calculus deposits from individuals with unusual wear patterns on their teeth to try and identify what might have caused them. Sometimes fibres or particles from materials brought into contact with the teeth survive trapped in the calculus – if we are lucky enough to find some of these then it could help us identify what they were doing. Historical research into typical activities in the areas from which these individuals were recruited could also help.
Author: Kamal Badreshany
Kamal currently runs the Durham Archaeomaterials Research Centre (DARC) (www.darclab.com), an analytical research facility based in the Department of Archaeology that offers advanced chemical and materials analysis. He specialize in the analysis and geological characterization of ancient ceramics using archaeometric techniques, including ceramic petrography, scanning electron microscopy, and X-ray diffraction. Kamal has been working closely with the Scottish Soldiers project to digitally record the remains using photogrammetry, 3D models and 3D printing.