[Music] foreign this video is sponsored by bootcamp.com check it out for inbde prep and use coupon code mental Dental for 10 off hey everyone Dr Ryan here and welcome back to our Dental Anatomy series this video is going to be about the mandibular first molar so here is a picture of the permanent mandibular first molar and different from my other videos in this series I'm showing you a photo with a restoration in the tooth and that's by Design to help you remember that this is the permanent tooth most likely to get carries and that's thanks to it erupting at the young age of six years old and also just having a lot of pits and fissures in it where carries can originate and we'll talk about that later in the video so using the universal tooth numbering system this would include tooth number 19 and number 30. now remember how the maxillary first molar was the widest tooth facial lingually in the entire mouth well the mandibular first molar is the widest tooth mesio distally in the entire mouth and spoiler alert this isn't the only example we'll see of how the mandibular first molar is a complete opposite of the maxillary first molar so we'll start like we always do with the facial aspect the first thing I want to point out are these two widespread Roots so you have two of them here there's one mesial and one distal and notice how the mesial root tends to curve more than the distal root does the facial cusps are generally pretty blunt and you can see the lingual cusps because they're slightly longer or taller although the mesiofacial cusp is the largest one by overall size this is the only tooth in the mouth that has two grooves on its facial surface so there's a facial groove right here and a disto facial groove right over there there's also often a facial pit right at the end of that facial Groove which is the opposite of the maxillary first molar where there's often a lingual pit at the end of its lingual Groove the reason why I point this out is because oftentimes if there's a pretty noticeably sized pit instead of just performing a sealant on the occlusal surface which is most commonly done you can sometimes when it's appropriate flow that sealant material into the facial pit for a mandibular first molar or the lingual pit of a maxillary first molar to do the best that you can proactively to prevent those areas from originating carries some dentists will call the facial height of Contour a cervical Ridge because it's fairly long but it's not quite as pronounced as it is in the mandibular second molar and we'll talk about that more in the next video the lingual Groove is very small and it's almost never fissured so you're not going to see a lingual pit on these teeth it's also right in line with the bifurcation the lingual head of Contour is a bit higher than it was on the facial surface and it's very prominent in order to hold the tongue back away from the teeth so there's not much to say here for the mesial aspect of this tooth the mesial surface of the root usually has a pretty deep root flute or depression that you can see in this picture and the same is true for the distal side of this root so that makes the mesial root overall by concave and it typically houses two separate root canals that are separated by this root fluting we'll get to see a better picture of that later in the video once again for the distal aspect we're going to see a shorter marginal Ridge which enables us to see more of the occlusal surface or occlusal table from this view there's also a flatter cervical line and the distal root is a little bit narrower than the mesial root which you can kind of see poking out behind there from this angle you can also appreciate the difference in cusp Heights that we briefly mentioned from the facial aspect so the blunt facial cusps versus The Tall lingual cusps and you might remember we saw the opposite Trend in the maxillary molars where the lingual cusps were more blunted while the facial cusps were taller so why is that a pattern that we're seeing well in the maxillary molars the lingual cusps were the holding cusps and in the mandibular molars the facial cusps take that role and we went over this when we talked about the maxillary molars but you can see that very well Illustrated in this picture where those holding cusps are the ones in contact most directly with the opposing teeth hence why they are by Design more blunted and that leaves the non-holding cusps taller in order to push away or keep away the soft tissues from impeding on the functioning teeth for this tooth the facial root trunk again area between cervical line and forcation is shorter than the lingual root trunk or in other words the facial cej is closer to the bifurcation than the lingual CJ is so I hope you didn't forget about our mini molar tooth that's the mandibular second premolar because there are some indirect resemblance to that tooth that tooth if you recall was a pentagon shape where I told you it looked like a house the occlusal table was like the walls of the house and the facial surface was like the roof of that house this tooth is also a pentagon shape but this time the roof corresponds to the fifth cusp the distal cusp sticking out to the side and the other four cusps create the four corners of the house now since these two teeth the mandibular first molar and the mandibular second premolar are right next to each other in the mouth My Hope Is that you can remember the two houses are neighbors with each other and unfortunately one of the houses got knocked down another cool thing is the maxillary first molar had three lingual cusps including the cusp of caribelli whereas the mandibular first molar has three facial cusps just the opposite so by that token it makes sense that this tooth would converge toward the lingual just the opposite that we saw in the maxillary first molar so the facial half is larger than the lingual half however there's a similarity between this tooth and the maxillary first molar and that the mesial half is wider than the distal half and so the tooth in other words converges towards the distal this is the biggest occlusal table in the entire mouth and so most chewing occurs on this tooth you might also remember the y-type mandibular second premolar that was the most common anatomical variety for that tooth and here now we have what I'm calling the y5 tooth and that's because there are five cusps mesio facial disto facial distal distolingual and mesial lingual and the major grooves of the tooth form a y hence y5 and so those grooves are the facial Groove which separates the mesio facial and distofacial cusps the disto facial Groove which separates the disto facial and the distal cusps and it's also the groove through which the oblique Ridge of the opposing maxillary first molar sits the lingual Groove separates the mesial lingual and distolingual cusps and then the central Groove travels from distal pit to mesial pit the central pit right in here is the deepest part of the occlusal surface as far as the pulp is concerned there are five pulp horns that's one for each of the cusp tips 65 percent of the time there are three canals that's two canals in the mesial root and one in the distal root 32 percent of the time they have four canals that would be two canals in the mesial root and two canals in the distal route and only about three percent of the time much less likely there's only two canals which would be one canal in the mesial root and one canal in the distal root which is not shown here in the diagram in this series when I get to this slide traditionally the dark gray area is showing you the widest portion of the crown basically the outline of the crown whereas the white inner part is showing a cross section slice right at the cej which this image shows really well so that would correspond to that white area there and then the gray inner parts correspond to the pulp what the pulp would look like at this slice so that makes the cross section of the cej kind of like a square or a rectangle shape but I don't care so much about that to be honest what I want you more to focus on is what we've talked about before with the mid root cross sections which are shown here so the distal root is oval shaped while the mesial root is biconcave since it has two concavities or we can call it ribbon shaped and if you go back to either of the mandibular incisor videos that's almost exactly what they looked like in cross section at the middle of their roots also as an aside these are the longest roots of all of the molars not all of the teeth though the canine Roots still hold the title for the longest roots in the entire mouth specifically the maxillary canine for a summary of the mandibular first molar the mesio distal Dimension is greater than the facial lingual Dimension which is greater than the occluso cervical dimension y5 is what I want you to remember why for the shape of the grooves five for the amount of cusps that there are in order from biggest to smallest we have mesio facial then mesial lingual distal lingual then disto facial and finally the small fifth distal cusp four grooves and three pits so the pattern is five four three which is the exact same pattern we saw on the maxillary first molar nice and easy to help us remember that it looks like a trapezoid from the facial view like all the molars do it's a rhombus from the side view that's leaning toward the lingual that's the same pattern that we've seen for all mandibular posterior teeth it looks like a pentagon from The occlusal View that's the crown of course whereas the cross section at the cej looks like a rectangle but I want you to remember that mesial root is biconcave or Ribbon shaped and then it consists of primarily five developmental lobes five pulp horns and three pulp canals that's it for this video thank you so much for watching please like this video If you enjoyed it and subscribe to this channel for much more 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