Many years ago when I was teaching in the Grad Prosthodontic clinic, I saw a fixed case that the resident was going to try in and I quickly made a comment that the bridge had tight contacts. And the resident immediately asked me how I can tell that it had tight contacts. And my response was I can just tell from looking how the bridge was seated on the dies that it had tight contacts. And this of course came from my experience in doing my lab work and evaluating the type of contacts that I feel on models versus the type of contacts I feel clinically.
Years later, I realize that ability to spot a tight contact on the model will immediately allow me to create a mindset how to manage my time and energy during the try in process so that it can be looked after properly.
I don’t know about you but adjusting tight contacts can be tricky. Over adjusting contacts can lead to open contacts, food impaction and possibly compromise on the contour and aesthetics. But knowing how to spot and adjust the tight area can also be tricky, especially on posterior areas where direct vision is impossible, access to the proximal contacts can be challenging and the constant pooling of saliva in the area can discourage a lot of us from spending too much time on this aspect.
And I have done it myself in the past and I see many of my students have done it. With the presence of the periodontal ligament of the adjacent teeth that gives you a little wiggle room, with a bit more force, you can probably get the restoration seated anyway…and you justify that the teeth will adjust itself and settle right into the space.
Unfortunately, I have seen my own failures when I did that to the multiple crowns that I failed to properly adjust the contacts in the past. When you force the restoration into the space that had tight proximal contacts, you just created a non controlled fixed orthodontic appliance. Something will move and depending on where the weak link is, your teeth or other restoration may fracture, your teeth may loosen up periodontally or the occlusion may change unintentionally. So it’s important not to get into a habit of just “letting the restoration settle into the space” be your excuse not to properly adjust proximal contacts.
For me, I evaluate the contact by the ability of a piece of floss to snap through the interproximal contact. It should pass through the contact with a snap if you want a point contact for your restoration. For the anterior restoration, if you have a long broad contact for contour and aesthetics, it may not snap through a contact point but rather a contact area. That is ok too as long as it does not shred the floss. But if you cannot floss through properly, then the contact is too tight and requires adjustment.
Campagni suggested the use of shim stock to evaluate proximal contacts.[i] He suggested that the fixed partial denture be seated under finger pressure and adjusted until 0-0005-in. shim stock will pass through the proximal contacts with very slight resistance. But with two pieces, the shim stock should hold and not pass. I don’t routinely use shim stock to check proximal contacts but want to share this technique so others can try and evaluate for yourself.
In any case, if there is tightness in your proximal contact, I usually check on the models first to see if I can identify the area to be adjusted. This gives me better access to the area without having to worry about saliva and the patient’s tongue getting in my way. I put a piece of thin articulator paper to mark the tight spot and bring the indirect restoration in and out of the die to allow me to better mark the point of contact that may be responsible for the tight contact. Or sometimes I put pencil mark on the adjacent teeth and bring the indirect restoration and out of the die to mark the tight contact area to be adjusted.
If after adjustment, you see an open contact on the model but not in the mouth and you still can’t pass a piece of floss through the contact, then there is a discrepancy between the model and the patient’s mouth and you have check for that tight contact intra-orally. This gets tricky trying to put a piece of articulating paper without having the saliva contaminate the area.
If the surface to be adjusted is on porcelain and it is in the bisque baked stage, the rough porous surface will allow better marking. But it is important to keep the proximal contact area dry intra-orally so it can mark the tight contact area.
There are times after several adjustment, the glazed porcelain is gone and allows me to mark the entire proximal area by rubbing articulating paper against that surface or colour the entire proximal surface with pencil, then by sliding the restoration in and out of the prepared abutment, the coloured area that gets rubbed off is my area of adjustment. I have learned that Parkell has a brush on material that can be used for this purpose as well.[i]
Checking proximal contacts and adjusting for them can get messy. My preferred method of adjustment is using a heatless stone and then polishing the area with porcelain polishing kits.
I learned my mistake the hard way seeing my own failures when I didn’t take the time to check for these interproximal contacts. The errors increase exponentially when you are dealing with multiple single units. I hope this post will bring awareness to dental students of how important it is to check and adjust for these tight interproximal contacts. When you are learning to deal with single unit restoration, take the time do these little adjustments well. Then when you have to handle bigger cases, it will not be as overwhelming. It is these little fine details that will elevate your case from good to excellent. You can’t always rely on the lab to deliver the perfect restoration. You have to learn to look and do these little adjustments yourself.
Thank you for reading.
[i] Boice PA, Niles SM, Dubois LM. Evaluation of proximal contacts with shim stock. J Oral Rehabil. 1987 Jan;14(1):91-4. doi: 10.1111/j.1365-2842.1987.tb00697.x. PMID: 3469380.