The resected mandible bone is a technically challenging specimen, especially if there is an attached tumor. The main difficulty is in presenting relationship between the bone and the soft tissue.
These remarks are intended to describe details of the processing of a mandible as an example of grossing of a complicated bone specimen. The same principles apply to a lung tumor and ribs, a soft tissue tumor of extremities, a brain tumor and the skull, etc. although texture of the bone is different. The maxillary bone has some substantial particularities in the grossing technique due to the fragility of the bones. The interaction of tools and technique is the main issue of these remarks.
Let’s take, for example, a hemi-mandible, composite resection due to squamous cell carcinoma involving the buccal mucosa and extending into underlying mandible bone. As it occurs in most cases, the diagnosis is known before the surgery. One of the questions of the pathology examination is the growth of the tumor in the bone and adjacent tissue.
It is assumed that all measurements, the appropriate marking, and photography have all been done according to the pathology manuals.
As a rule, the specimen arrives fresh. I am more comfortable working with a fresh specimen for the following reasons. First, although even overnight fixation does not go deep enough in the bone and soft tissue, it makes the tissue immediately attached to the bone (the main area of interest) a little brittle. Second, the natural colors of tissues contribute to the correct orientation in anatomical relationships of the specimen. Third, the colors for photography are impeded during fixation. Fourth, all sections get even fixation immediately after processing. Of course, fresh soft tissues require some technique in handling while operating with the knife and the saw. The overnight fixation has some advantages making the soft tissue harder and easier for sectioning. If there is not enough experience in handling soft tissue and bones, it is better to process fixated specimen. In a case of a bone tumor, the processing before fixation is almost obligatory (the fixation of the sections is more uniform, the natural colors of the tissues are maintained for photography).
Teeth are a substantial particularity in mandible bone processing. They should be taken out for two main reasons: first, extremely hard, they can interfere with bone cutting, second, the opened sockets allow the fixative to penetrate deeper and faster in the bone.
If the appropriate tools are used, the pulling out of teeth is not difficult, except some four-root teeth. The ubiquitous vise is the proper tool for the immobilization. Now I prefer the table vacuum vises that can be placed on the metallic surface of the standard grossing station table. (See “A Vise on the Surgical Pathology Grossing Table” in the link “Instruments and Gadgets”) It is flexible and makes the work much more convenient. The removable rubber jaw faces hold the bone firm with minimum damage to the soft tissue. The specimen is placed wrapped in soft paper or small bubble packing to preserve the soft tissue. The wrapping makes it easier to clean the vise. The mandible should be placed deep in the vise’s throat almost on the screw to keep the teeth just above the upper surface of the vise’s jaws. However, this is not always possible due to the thickness of the soft tissue. Sometimes both the need for firm immobilization as well as the required preservation of soft tissue from excessive squeezing calls for more superficial or eccentric placement of the mandible bone in the vise’s throat.
The teeth extraction procedure follows the dentist’s method. The first step is in crown’s lengthening to lower the gum allowing for the secure grasp of the pulling instrument. I use a Ferguson’s bone holding forceps or a bone nibbler. The alveolar gingiva should be detached from the crown as much as reasonably possible (loosening the gum as dentists say) otherwise the extracted tooth can take some diagnostic important soft tissue with it. Energetic rocking movements extract the tooth. Sometimes a light luxation is enough. The main direction is strait up. The dentist does not have this advantage because of the upper jaw. Of course, if there are only artificial crowns, the roots should be left alone. The teeth extraction after decalcification is impossible because the crowns detach from the roots by the instruments.
In general, the pulling of teeth is not a goal by itself. Sometimes only a “decrowning” (removing only the portion of the tooth above the gingiva) with a veterinary horseshoe puller is reasonable because the cementum and dentin of the roots do not interfere substantially with the bone cutting. A tooth can be left also as a location indicator. If the teeth extraction is too time consuming or more damaging than the benefit of this procedure, common sense should prevail. For example, in a case of Pindborg tumor (calcifying epithelial odontogenic tumor) in a 33 – years-old patient, one of the teeth (with a crown) was taken out because it was close to the area of tumor, but the next molar tooth was left alone because it was sitting too firm in this young man’s mandible. Pulling it out could bring more damage than good.
There are two options for immobilization during the bone cutting: keeping the mandible in the vise or placing it on a support board. Keeping it in the vise is reasonable when the amount of soft tissue is minimal. When a vise immobilizes the mandible, cutting the bone margins of resection is easier. In most cases, however, a firm horizontal immobilization device should be used. I prefer a hard pressed packing carton that has configurations that keep the soft tissue like as if in a mold. Pressed carton is firm enough to resist the pressure of the saw. The latter can go through the carton without any difficulty. The soiled carton is than discarded.(See “Hard- Pressed Packing Carton Gadgets” in “Instruments and Gadgets”)
After the bone’s margins are cut (I prefer using an oscillating saw), the next step is to find the most representative area and all cuts should be made in the same direction sideways from this area. An incision in soft tissue is made to the bone level. For cutting the bone, it is cut preferable to start with a thin easily manageable fret saw, than depending on the preferences can be used a Stryker saw or handsaw (I prefer the latter). If the thickness of soft tissue excides the 1/3 of the size of the Stryker saw blade, the handsaw is the tool of choice. The 24 TIN blade is the optimal. Sometimes it is reasonable to finish with the fret saw to prevent bone breaking while ending sawing. The general rule of sawing is applied: the sawing hand should become you are approaching the end of the sawing. It is always useful to have a kind of support of the soft tissue from the opposite side of the cut (“a third hand”) to prevent the soft tissue from flapping, especially if a mechanical saw is used.
The section of bone with the adjusted soft tissue rarely fits the processing cassette and may require some tailoring depending on diagnosis as well as goals of representation of anatomical relationships and pathology issues. A complete section sometimes requires several cassettes. If the section is too thick to close the cassette’s lid, it makes sense to leave it for fixation and only afterwards to adjust it to fit the cassette, although there are methods to trim bone that does not fit the cassette (See “Bones that do not fit the cassette” in Grossing Techniques).
The serial sectioning of the mandible bone is required if there is a bone tumor. In this situation it is reasonable to cut the bone in half at the mandible bone angle otherwise it is difficult to get perpendicular sections. In the case of a bone tumor, sometimes a resistance to the saw occurs in ramus as a result of an impacted tooth (wisdom) that is pushed by the tumor from the mandible bone body.
In a calcifying epithelial odontogenic tumor (Pindborg tumor) when unerupted or embedded tooth is involved a delicate cutting should be performed with a fret saw to maintain the integrity of very fragile structures of the bone in the tumor area.
It is necessary to object to the very popular practice of putting an entire or part of the mandible bone, with or with partially removed soft tissue, into decalcification solution after overnight fixation. The specimen is ruined because the soft tissue becomes detached from the bone.
Although every case does not require significant diagnostic answers, if a standard technique is not applied in all routine situations, a challenging case will become a failure. The employment of appropriate tools and technique makes mandible processing, though not always easy, a success.
Thanks to Dr. Stephen G. Marshall, D.D.S., Oral and Maxillofacial Surgery for valuable advice.