Denture repair

 Today an elderly man dropped off a broken lower full denture which belonged to his wife. She was in a nursing home due to her severe dementia and had thrown her denture on the floor. It had split in half and was a clean break so was definitely repairable. I had a bit of free time and we had some cold cure acrylic in the back lab so I thought I would attempt the repair rather than send it out to our lab as they didn't offer same day work.

The steps I followed are below:

-Inspect the denture: If the break is clean and there aren't too many pieces then the denture is deemed repairable. With traumatic fractures, the denture usually breaks at the thinnest part of the denture which tends to be down the midline with lower full dentures or at the flanges for upper full dentures. If there is a fracture through the tooth arches it will almost always pass through the contact point and not fracture a tooth in half as this point is a weak spot. Put the pieces together and if they fit together reproducibly then you are good to proceed. To an extend, a traumatic fracture has a better prognosis compared to a fracture when the patient is chewing. If it fractures when the patient is chewing, their occlusion may be unfavourable or the denture may be ill fitting and be getting insufficient support from the soft tissues. If this is the case, even if you repair the denture you need to check and manage the occlusion if imbalanced and the patient may need a reline to reduce the risk of future fracture. If the denture is recently made or relined and it broke by trauma then a fracture repair may be sufficient.

-Stick the pieces together: Temporarily bond the pieces together with superglue. This is to hold them together while you create an index for repair. Superglue holds the pieces together very strongly and once I had stuck them together I put quite a bit of force on them and couldn't break the pieces apart. I can see why it is tempting for patients to do some DIY repairs but unfortunately superglue is water soluble and the bond comes undone before too long and then the pieces will not fit together as well. Use just a drop of superglue in the thickest cross sectional area of the fracture line. Once the pieces are joined together it will extrude all the excess glue and you don't want any to extrude any onto the fitting surface of the denture or it will set and be represented onto your index which will transfer a high spot to the final repair which may become a sore spot. The more glue you put, the longer you have to wait for the solvent to evaporate so just a drop will do. Use a pencil to make lines parallel to the fracture line as it can be difficult to see later.

-Create an index: You could pour fast setting stone in the fitting surface of the denture to act as the locator so that when you remove the acrylic around the fracture line the relationship of the pieces and the shape of the fitting surface is preserved. Even easier is to mix some putty and place it into the fitting surface of the denture and then push that onto the bench to make a flat surface. My base was quite thin and so there was some flexure of the whole putty when I was flowing in the acrylic. I would mix more putty and make a thicker base next time. Today I wanted a more accurate representation of the fitting surface so I extruded some light body after the putty had set and squashed it back onto the putty model like a reline impression. I only put a little amount where the fracture line was so it wasn't enough to cover the whole fitting surface. Ultimately this caused issues because I think it hindered perfect seating of the denture as the area at the fracture line was held up by the light body and the other areas had a microscopic gap underneath them causing inherent instability once the acrylic at the fracture line was cut away. 2 better ways of doing it would be flowing enough light body into the denture to cover the whole fitting surface or flowing light body into the denture at the ridge crest and pushing the unset putty into it. The latter way is better as the light body will bond better to the putty and the pressure required to push the denture onto the set putty with light body can cause distortion of the light body that will elastically spring back after you release the pressure and cause a distortion in your impression. 

-Index the polished and tooth surfaces: While the base putty was setting I used a wax knife to place V shaped grooves on the buccal and lingual. When the base was set I mixed another batch of putty and made 2 indexes recording the buccal and lingual surfaces up until the incisal edges. Later on I had difficulty locating these keys against the V shaped grooves as the acrylic flowed into the grooves. I solved this by placing the buccal key in and flowing the acrylic from the lingual. The lingual or palatal surfaces are smooth and are easy to adjust till they match the surrounding acrylic. What I would do next time is to skip the lingual key and make the buccal key as part of the base putty index i.e when you have put putty in the fitting surface and made a base, put more putty on the buccal of the fracture line up and until the incisal edge so the buccal and base keys are joined.

-Remove the denture after the putty has set and grind back the acrylic around the fracture line. Use an acrylic bur to remove a few mm of acrylic along the whole fracture line. This is to make space for new acrylic and to remove the superglue. Drill up till the denture teeth but try not to remove and of the tooth acrylic. This will help to have another point of contact to prevent lateral movement of the denture when it is replaced onto the key. Removing tooth acrylic will also affect the aesthetics. Cut horizontal notches into both side of the denture perpendicular to the fracture line. This increases retention and surface area for bonding.

-Mix cold-cure acrylic in a dish, wet all surfaces of the denture adjacent to the fracture line to activate the acrylic monomers. Air dry slightly and place them onto the putty index. Flow the acrylic into the fracture line and tap the key against the bench to flow it in. Don't pour it too quickly or you will trap air bubbles in. I poured it in quite fast and fiddled with it so had quite a large subsurface air bubble that I had to drill into and put a second round of acrylic in. The first time I attempted this I poured the acrylic in and tried to put the buccal and lingual keys on. For all of the reasons I mentioned before the fragments weren't stable and while the acrylic was setting the fragments kept separating as I handled it. You want the whole system to be stable enough so you can put everything together and not have to hold it still. This comes from accurate keys and less moving parts (i.e avoiding separate buccal and lingual keys). Before the acrylic set I scraped it off as best as I could and used a bur to grind the acrylic back some more. The second time around I put the buccal key on and held it in place while I flowed the acrylic in. This avoided the need to force the key on when it wasn't accurate due to acrylic flash. Flowing the acrylic in right after mixing worked well for me as waiting for the doughy stage and packing it in under pressure may have caused deformation of the index or displaced the fragments. The downside of using it in the flowy stage is that it can make a mess and will flow down gravity. To remedy this, while the acrylic is setting tip the base of the putty so that the acrylic doesn't flow out of the fracture site.

-Put the assembly in a pressure pot according to the manufacturers instructions: This reduces porosity of the acrylic which makes it feel smoother, avoids a white opaque appearance, leads to a better shine and increases the strength of the repair. I didn't have a pressure pot so I put it in a bowl of hot tap water at an angle to prevent flowing of the acrylic. After 30 minutes I removed it and trimmed all the flash off. Make sure you clean all the instruments and mixing bowl of acrylic before it sets or it will be very difficult to clean off after.

It was a good experience and I learnt quite a bit about what to do and what not to do during denture repair. To an extent I think I need more equipment i.e pressure pot to improve the outcome but a change in technique would be the most effective in making the process simpler and more predictable.