tips and tricks

 There are a few tips that I have learned over the years to reduce gagging during impressions but a common one that I use is to use a mandibular impression tray for the upper impression. This is useful when you just need an impression of the teeth and don't care about capturing the palate in your impression. The idea is that there is less impression material in the tray compared to a maxillary tray and when the excess spills over the tray edge when it is seated it doesn't shoot directly to the back of the tongue. I tray to use a fairly stiff mix for these impressions and when the excess runs over at the palatal aspect, I will use my finger to pull it fowards towards the incisors. This keeps it off the tongue and also locks the impression more firmly onto the tray. You do have to be aware that the lingual flange of lower trays are usually quite exaggerated so overseating the tray will hit onto the palate. This can help as it can be a positive seat to stop the tray overseating an...

Ensure the teeth are relatively clean of food and plaque prior to impressions. I can't count the number of times I have taken an impression and bits of interproximal food come out with the impression. Usually in perio patients and usually in posterior teeth. Really heavy plaque will affect your surface detail capture and food will affect your accuracy and look gross for the lab an on the model. It will also affect your impression disinfection.  If there is really heavy plaque, give the teeth a good prophy or teach the patient how to use a toothbrush and reschedule. If the patient has recently eaten, give their mouth a good rinse and floss. When I haven't done this and there is food that comes out with the first impression, usually the second impression goes well.

At one of my private practice jobs the material we use for fixed prosthodontic impressions is PVS putty with a light body wash. I have used this with reasonable success and it takes reasonable impressions as the viscosity of the putty pushes the light body down the tooth, however this can be disadvantageous sometimes as the putty itself fails to flow. Therefore it will be hopeless in capturing an impression of the sulcus if your light body hasn't made it in there. Additionally, if the tissue is quite floppy, it can displace the tissue out of the way but can just as easily push the tissue back onto your preparation undoing the action of your tissue retraction. Ideally you would put a medium/heavy bodied material on top of the light body to act as an intermediary between the two material viscosities. One issue I've been having coming into the summer months is that the putty reaches an early set stage extremely fast where it becomes stiffer and forms cracks and distortions when pr...

Following up on the difficult impression appointment from a previous post: https://dental-tidbits.blogspot.com/2021/04/difficult-impression-appointment.html The aim of preparation is to convert a difficult task to an easier one. The impression that I sent off that day turned out the be absolute rubbish and completely inappropriate for the final impression.  I could approach the case with a clear head and cleaned the old impression off the tray and placed adhesive long before the appointment. This way there was enough time for the solvent to evaporate and the adhesive to be effective.  I used light body PVS in every single cavity to block it out. I thought this would be difficult to handle but it was quite simple and if excess bled out of the cavity I could push it back in with an instrument. I had to change tips half way through because I was too slow in the placement and the material had early set half way through the blocking out. One thing I would change is to dry the teeth...

 Today I had a difficult impression appointment. The case is for a full upper immediate denture and the patient has almost all of his upper teeth that are badly broken down and carious. The issue with the impressions is that the material kept flowing into the carious areas, locking in and when I tried to remove the tray, the alginate would peel off the tray and tear. I retook the impression 4 times and in the end accepted a compromised result. I don't know how it will come back to bite me down the line but I know it will in some form or another. An important failure of mine here is that I didn't analyse how the first few impressions failed and try to learn from them for the next impression. Some thoughts: -The combination of locking in on the anterior and posterior teeth was enough to overcome the adhesion to the tray. When considering impression debonding it is merely a tug of war between the impression sticking to the tray and the impression sticking to the teeth. I think the...

 In my new role the very first patient I met was a difficult denture case. There are upper and lower canine to canines were remaining and the periodontal condition was so severe that the lower teeth are grade 3 mobile and less than 1mm of bone is holding the upper teeth in. In the public system, this would be an open and shut full clearance and delayed denture case as the teeth would clearly come out in the impression but in the private setting, the boss had treatment planned a phased immediate denture and had already extracted the posteriors. I had told him that I enjoy the denture process and mysteriously I have found all of his denture cases have been transferred to me.  So walking into the practice having this case in front of me I was faced with a challenge as I had a situation I had not encountered previously and had time pressure as he wanted the dentures made before his birthday in 3 weeks. It occurs to me that private patient's demands are more reasonable as they are ...

 I have recently started using alginate for my upper full denture impressions and zinc oxide eugenol for my lower full denture impressions as per Dr. Findlay Sutton's lectures. I find the alginate superbly accurate as it is hydrophillic and flows very well as well allowing good border moulding at the flanges.  A full lower impression I took today with Zinc oxide eugenol had a large deficiency on the labial flange area as I had insufficiently border moulded with greenstick. This would normally not be an issue as on seating the tray, the excess material would extrude out and fill the sulcus area, however, I had also requested tissue stops which the lab had placed at the 34 and 44 area. This prevented over seating of the tray and actually worked quite well to control the level of thickness of ZOE and to control placement of the tray. However, compared to alginate, as ZOE is much thicker and flows more poorly, my inadequate control of flange length meant that insufficient material...

 I was having a chat with one of my new graduate colleagues about one of his full denture cases. He was taking a jaw registration but I noted that his upper model had a deep horizontal divot running across the hard palate area. I was wondering how that had happened but when I saw the ZOE impression, it was apparent that he had not seated the impression fully in the palatal area, tried to reline the impression and again not seating it fully leading to a step in the model.  When using ZOE as an impression material for full upper dentures, the tray is made without spacing so while border moulding with greenstick, the tray is in intimate adaptation to the soft tissues. If the tray is then seated without sufficient pressure, there will be a significant thickness of impression material set onto the tray rather than a thin wash. This makes the previous border moulding step almost redundant and can fail to capture all areas of soft tissue, it will also lead to differential thickness o...

I was thinking during a walk today about an impression I had to take a while back where the 18 was very buccally tilted and overerupted. The issue was that the largest impression tray wasn't large enough to get around this abnormally positioned tooth and the tray wasn't seating. During my walk I asked myself what are the possible solutions to this problem. I cam up with a few: 1. Take a bad impression: Take an impression with a very overfilled tray and hope to get enough detail for what you want to achieve. The issue is the material around the 18 is unsupported and is likely to tear when you withdraw the impression, the differences in impression material thickness will result in inaccuracy and the tray seating onto a hard surface will cause rebound of the tray when you remove it resulting in further inaccuracy 2. Soften the tray in a flame and widen the tray around the tooth: This is what I did in the aforementioned situation. I used a bunsen burner to heat the tray in the...

So at my new job I've started to make dentures again. My first job had a prosthetist making all the dentures and my next job didn't offer denture services. The last full denture I made was probably 4 years ago in dental school. Starting to make dentures again is an exciting prospect because they were a part of dental school that I quite enjoyed. I am finding that I am remembering small tips here and there and learning new ones as I go along. Dentures are the most aesthetic restorations we can provide as we have full control over tooth shape, size, position and shade as well as gingival aesthetics. Each surface of a denture is important for different reasons. -The fitting surface is obvious important for a good fit against the soft tissues with no trauma to specific areas. -The peripheries are important in achieving a border seal to exclude air to allow a suction effect for retention. -The vertical aspects of the flanges seat against the ridges for resistance to horizontal ...

Some points on final impressions from Lincoln Harris' course: Every step of the appointment is important in the lead up to the impression; Local anaesthesia,  final preparations, tissue and moisture control and the impression itself. The issue is that we complete the most important step at the end when we are the most tired. If any of these steps are lacking then the final impression will be affected. -Final preparations should be as smooth as possible as it allows wettability of the impression material and final cement. There is an argument as to smooth preps vs rough preps and wettability vs retention for cement but if there is a rubbish final impression you won't have a well fitting crown to cement in the end. If the gum is inflamed the cord won't stay in. The gum needs tightness and elasticity to hold the cord in place or the cord will fall out. This is why in the initial appointment it is important to produce well fitting temporary crowns that will allow good tiss...

As opposed to bubble which are air inclusions, rag marks will appear as smooth, thin vertical lines in an impressions. Contrary to what I believed before, drag marks are unlikely due early removal of the impression material but more likely due to wet oral surfaces. the excess moisture is put under pressure from the seating impression and the path is is displaced through to escape the impression shows up as a drag mark. This is especially noticeable in hydrophobic impression materials such as PVS. Setting times for intraoral impression materials are minimum suggested times for the warm oral environment. Add at least a minute on top of the setting time when using intraoral impression materials for your putty keys for temporary mockups and crowns.

Stock impression trays are generally designed to fit all of the population however as for anything designed with the average in mind they tend to fit absolutely no one. A particular issue I find in choosing the right sized stock tray are the arch form and the space between the maxillary molars and the coronoid process. Patients with teeth crowded out of the arch or wider or narrower arch forms would benefit from a stock tray that is wider between the flanges, the peril of using this regularly however is it can encroach into the buccal and lingual soft tissue boundaries and make seating the impression more difficult. Individual modifications en be made to plastic stock trays by heating them in a flame till soft and bending the tray to suit the patient. This will then solidify when cool. A particular issue I had today was on two separate patients where the stock trays fit seemingly well on the maxillary arch however the flange area in the maxillary molar area was not caught in the im...

Boxing impressions can be beneficial before pouring up casts because upon removing the impression from the cast the cast will be of ideal shape and will require minimal adjustment. Inverting impressions onto a stone base can be harmful as if the stone base is too firm it can distort the stone overlying the impression especially over unsupported areas. Also, water in the stone mix rises upwards against gravity so inverting the impression will result in a higher concentration of water at the working surface resulting in a weaker cast predisposed to chipping. Boxing allows for the impression to be poured without inverting. Steps: 1. If it is a lower impression, the lingual area must be blocked out with a sheet of red wax. Trim a wax sheet to the approximated shape of the lingual area and seal 2-3mm from the sulcus depth with sticky wax or a hot wax knife. 2. Soften a sheet of red wax and fold over the long edge once. Cut a thin strip ~2mm wide. This will result in a strip ~3mm thick ...

Alginate can deteriorate in its powder form within 3 days of opening the container. Exposure to humidity or heat causes thin mixes, altered setting times, reduced strength, high deformation. Contamination with gypsum products in the bowl should be avoided as it can accelerate its set. Don't mix stone and alginate in the same bowls. The water powder ration affects the consistency and setting time of the materials and strength and quality of the impression. a thin mix will flow out of the tray and away from the tissues with increased tear risk. a thick mix will capture less fine detail. Ideally work with a predetermined amount of powder and alter the water. Primary mechanisms of alginate distortion is water absorption (imbibition-Do not wrap in wet paper towels or immerse in liquids) and evaporation of liquids (syneresis occures even at 100% humidity). Distortion exists if impressions are not poured up within 12 minutes of removal. Alginate can stick to teeth (hydroxyapatite)...