Maxillary Sinus & Molar Roots

Updated: Jul 30, 2019

A few days back, I got a call from a nearby general dentist regarding a complication. Distobuccal root of the Maxillary left third molar was displaced into the maxillary sinus and Oro-Antral Communication had been created.


I was called in to retrieve the root from maxillary sinus and close the Oro-Antral Communication. See the surgery pics here.


When I was done with the closure, we sat down to have a discussion on the case.


The first question he asked me was how can I determine the correct position of tooth roots in relation of maxillary sinus just by looking at the preop radiographs.


He said that many of the times, in a radiograph, the root apices appear to be inside the maxillary sinus but still there is no OAC after extraction.


This is the question that I have been getting a lot and I intend to address that question today.


But first we need to understand why we see the whites in the radiographs.



Bone is made up of outer Cortical (compact) bone & central Cancellous (trabecular or spongy) bone. Watch video on this.


Cortical bone is more compact and dense with mineral content whereas cancellous bone is more porous and less dense. Thickness of this cortical bone may vary in every patient.


So, Cortical bone absorbs more x-rays and appear white on a radiograph whereas cancellous bone absorbs comparatively less number of x-rays and appear grey on a radiograph.


Now, in every bone cancellous bone is surrounded by the cortical bone. Cancellous bone is never in direct contact with any soft tissue naturally. There will always be a thin layer of cortical bone between cancellous bone and a non-bone tissue like nerve or periodontal ligament.


Hence on a radiograph, on one side of cortical bone there is cancellous bone (appears grey on radiograph) and on the other side there is soft tissue (appears black on radiograph). Hence, cortical bone is clearly demarcated on a radiograph.


That is why we see maxillary sinus floor or Mandibular nerve as thick white line with black or dark grey area on one side.

Outer layer of the bone is coritcal bone and the central zone is the cancellous bone. Cancellous bone is naturaly surrounded by cortical bone which appears as a white line on a radiograph.

Maxillary sinus is surrounded by a layer of cortical bone. That is why we see sinus floor as a white line in a radiograph.

For example, in an IOPA or an OPG we can clearly see a white line of maxillary sinus wall in posterior maxilla and white lines of mandibular canal in posterior mandible.


Maxillary sinus wall seen as a white line on an OPG

I’ll talk about maxillary sinus in this article and mandibular canal in the next article.


When we see the white line of maxillary sinus in an OPG or IOPA of posterior maxilla, we are actually viewing the lowest point of the maxillary sinus floor.


And whatever image we see is a 2-D images of all the hard tissues superimposed over one another.


Bucco-palatally there is good amount of bone between premolar root and maxillary sinus floor but on IOPA it appears as if the root of the premolar is inside the maxillary sinus. This is because of the 2 dimensional nature of the IOPA.

This 2D overlap of structures gives different appearance depending on the relationship of these structures.



Radiographic appearance


In the radiographic appearance, there have been different classification of Relationship of Molar roots with maxillary sinus. But we are concerned with only 3 broad categories.


They are - no overlap, Roots in the sinus and Overlap.


Let’s go into the details of these 3 categories.


No overlap


Here there is no or little pneumatization of the maxillary sinus. So, the sinus floor is away from the root apices.


So, on a radiograph we see a continuous white line representing the maxillary sinus floor that is at some distance from the premolar and molar roots.


Continuous white line representing the maxillary sinus floor that is at some distance from the premolar roots.

Chances of Oro-Antral Communication are rare. But if there is a thin layer of apical bone (1-2 mm) separating the root apices and sinus floor then an Oro-Antral Communication may be established if forceful instrumentation is done in the extraction socket.


Roots in the sinus


In this case there is extensive pneumatization. The sinus expands with age and engulfs the premolar and molar roots.


The white line representing the maxillary sinus floor forms a dome shape around the premolar and molar roots. This is because the PDL fibres are attached to the bone and prevent bone resorption around the roots.


White line representing the maxillary sinus floor forms a dome shape around the roots that are inside the the sinus.

Chances of Oro-Antral Communication in this scenario is almost 100 percent.


Although, rarely there may be an intact sinus membrane present after extraction of the tooth which prevents formation of an Oro-Antral Communication. Any instrumentation in this case will lead to Oro-Antral Communication.


Overlap


Here there is extensive pneumatization, but (luckily for the patient) maxillary sinus is not in direct contact with the premolar and molar roots. The sinus is either buccal or palatal to the root.


On a radiograph it appears as if the roots are inside the maxillary sinus cavity because the roots appear overlapped on the maxillary sinus floor. But at the same time, you can clearly see the continuous white line representing the maxillary sinus floor.


The continuous horizontal white line indicates that the roots are outside the sinus cavity.


Continuous white line representing the intact maxillary sinus floor. The white line is flat and there is no dome shape formation around the roots.

Chances of Oro-Antral Communication are rare. But if there is a thin layer of buccal or palatal bone (1-2 mm) between root and sinus floor then an Oro-Antral Communication may be established if forceful instrumentation is done in the extraction socket.


So, these are the things you need to be vigilant of while viewing the 2 dimensional radiographs of maxillary posterior teeth.


If you want to know the exact 3 dimensional relationship of the tooth root with the maxillary sinus floor then you should advise a CT-scan or a CBCT.


If you plan a dental extraction in maxillary posterior region and if you see the sinus floor in close approximation to the tooth roots, you should always inform the patient of the possible complication of Oro-Antral Communication (even if the chances of it are low).

Read here in detail about the different relationship between maxillary sinus floor and posterior maxillary teeth roots. This study talks about the relationship based on OPG and CT-scans.


EDIT :

I have been getting a lot of queries about what the yellow and blue lines (in the picture of the third category) represents.

So here it is.




Let me know in the comment section, how you manage the cases where maxillary sinus is close to the roots.


Also, do let me know what topics would you want me to write about next.


If you find my posts helpful then share it on Whatsapp, Facebook or Twitter or any other social media platform that you use.




1,502 views