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DefinitionThe act of closure or being closedA static morphological tooth contact relationshipIncludes all factors concerned with the development and stability of the masticatory system and the use of teeth in oral motor behaviorIncludes the integrated system of functional units involving teeth, joints and muscles of the head and neck

Balanced occlusionBilateral contacts in all functional excursionsPrevent tipping of the denture basesNot necessarily existing in natural dentition because each tooth is a separate unitIntercuspal positionCentric occlusionConcepts developed in relation to orthodontics, complete dentures and full mouth rehabilitationNone are completely applicable to natural dentition

Each tooth occludes with 2 teeth of the opposing jawExceptionsMandibular central incisorMaxillary second molarOcclusion is supported and made more efficient after eruption of first permanent molarsInterdental spacing is important for future sufficiency of space in permanent teethProbability of crowding in permanent teeth is related to the amount of interdental spacing in primary dentition

Terminal plane relationshipFlush56% - Class I Angle’s molar relationship44% - Class II Angle’s molar relationshipDistal stepClass II Angle’s molar relationshipMesial stepA greater probability for Class I Angle’s molar relationshipA lesser probability for Class III Angle’s molar relationship

Factors influencing the effect of terminal plane relationship on Angle’s molar relationshipDifferential growth of the jawForward growth of the mandibleSufficient Leeway space to accommodate a mesial shift of the permanent molars

Leeway space is the amount of space gained by the difference in the mesiodistal diameter between deciduous molars and premolars

Anteroposterior relationshipIncisors: Class I, II, IIICanine: Class I, II, IIIMolars: Angle’s Class I, II, IIIFaciolingual relationshipPremolarsMolars

Class IClass IIClass IIIOverjetReverse overjetOverbite

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Class IClass IIClass III

Mandibular arch is wider than maxillary archEach tooth must be placed at the angle that best withstands the line of forces brought against it during functionIf the tooth is placed at a disadvantage, its longevity may be at riskAnterior teeth are placed at a disadvantage

Lingual cusp tips of maxillary posterior make contact with opposing fossae and marginal ridges of mandibular posterior teethBuccal cusp tips of mandibular posterior make contact with opposing fossae and marginal ridges of maxillary posterior teethLingual cusps of maxillary posterior teeth and buccal cusps of mandibular posterior teeth are called “supporting cusps” Areas of occlusal contact that a supporting cusp make with opposing teeth in centric occlusion are “centric stops”The tip of that cusp is also a centric stop

Angle’s Class IAngle’s Class IIAngle’s Class III

Curve of SpeeCurve of WilsonSphere of Monson

With the exception of mandibular incisors and maxillary third molars, each tooth contacts two antagonist teeth in the opposing archLoss of one tooth keeps the adjacent tooth in contact with opposing antagonistMesial or distal drifting into the space disturbs occlusal contact with antagonist teeth

LateralWorking sideNon-working sideIn complete denturesBalancing sideNon-balancing sideMovement in TMJTooth guidanceGroup functionCanine guidanceProtrusiveIncisal guidanceRetrusiveThe most retrusive position is the centric occlusion in complete dentures

مبسم الله الرحمن الرحي

We will start to talk about an important topic which is the OCCLUSION

SLIDE 2[Occlusion]

Definition

The act of closure or being closedApproximate or occlude of 2 jaws together that’s what do we mean by OCCLUSION

A static morphological tooth contact relationship.Notice it’s StaticThe relationship between upper & lower teeth then they are in contact

Includes all factors concerned with the development and stability of the masticatory system and the use of teeth in oral motor behavior.

So this definition or fact is more appropriate, because it’s including some …

Includes the integrated system of functional units involving teeth, joints and muscles of the head and neck.

This what we covered in the oral physiology when we talked about theDynamic Part of Occlusion. Se I won’t concentrate about it hereBecause it’s more related to Physiology.

SLIDE 3[Concepts of Occlusion]

We have some concepts of occlusion we’ll actually discusses here

Balanced Occlusion.

Bilateral contacts in all functional excursions.Means when we have the mandible against the maxilla & the teeth are in contact, teeth remain in contact.So, for example: if you are closing your mandible against the maxilla & you want to move the mandible 5 mm to the right or to the left, ofcourse the teeth will be in contact at the side that you move the teeth to, but we also need the teeth to be in contact at the other side. So, Balanced Occlusion means whatever you actually

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occlude your mandible or whatever the position of teeth of the mandible, the teeth remain in contact.

Q: Is Balanced Occlusion happening in people with teeth?NO, let’s take an example; the dentate person (like you) if he try to bite the mandible against the maxilla & try to move his mandible 5mm to the right or to the left, the teeth of the other side (the opposite side) won’t be in contact, this is important.[Balanced Occlusion doesn’t happening in reality]But we need it in cretin Situations.

Q: Why we don’t need Balanced Occlusion in dentate people?Simply, because each tooth of our teeth act as a single unit, each tooth has its own PDL & it’s connect to the bone.But imagine person with Upper & Lower Dentures, now if this person bite on centric occlusion & I ask him to move his mandible & remain in contact with the maxilla for 5 mm to the right, if he actually don’t have Balanced Occlusion, there will be a space in the other side (the Left Side) because the denture is considered as a single unit, complete unit not as the real teeth which each one of them act as a single unit, so when there is a space in the other side, the denture will falls down.So, Balanced Occlusion is needed when we construct upper & lower complete dentures.

Prevent tipping of the denture bases.It’s preventing denture’s movement.

Not necessarily existing in natural dentition because each tooth is a separate unit.

Intercuspal position.It’s the position where the cusps of the lower teeth are located in the fossae & marginal ridges of the upper teeth (opposing teeth). That mean when you close your mandible against the maxilla, the cusps of the lower teeth is present in the fossae & marginal ridges of the upper teeth.Remember we have the preperioceptor all the time guides the mandible to its right position [The Intercuspal position].

So, for example, when I ask you to close your mandible, you close it in the centric occlusion without a problem. You don’t think about it, because you have a preperioceptor in the PDL which all the time send information to the telling it about the position of the mandible & this actually leads the mandible to its correct relationship to the maxilla with biting.

Centric Occlusion.

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It’s a state where the teeth are in inercuspal position and the condoyles are located in a specific location in the glenoid fossa.So, the centric occlusion isn’t necessarily related to the teeth only, the Intercuspal position: it’s the position of the mandible to the maxilla or the maxilla to the mandible when the teeth are in maximum contact.

The CENTRIC OCCLUSION isn’t only describes the relationship between the Upper & Lower teeth, but it also illustrates the relationship between Upper & Lower part of TMJ.

Concepts developed in relation to orthodontics, complete dentures and full mouth rehabilitation.

Q: When do we need the OCCLUSION?We need it in orthodontics & in complete & partial constrictions.

None are completely applicable to natural dentition.This concept which is discussing especially BALANCED OCCLUSION isn’t necessarily applicable to the natural dentition.When you have all the teeth in your mouth, you don’t have a problem.All of them are functional, so any movement of the mandible won’t lead to dislocation of the teeth of the other side, because as we said each tooth is hold in the bone separately as a one unit.

SLIDE 4[Overview of Primary Occlusion]

Each tooth occludes with 2 teeth of the opposing jaw.This a general rule.So, any primary tooth should be occluding to 2 teeth in the opposing jaw, but we have exceptions:

Exceptions: Mandibular central incisor.

It makes contact with the maxillary central, because it’s smaller in size than the maxillary one.

Maxillary second molar.It makes occlude with the mandibular second molar only.

Occlusion is supported and made more efficient after eruption of first permanent molars.

The occlusion of primary teeth remains premature until the eruption of permanent first molar; they are stabilizing the primary epithelium.

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Interdental spacing is important for future sufficiency of space in permanent teeth.

If you examine the primary teeth of your little brothers & sisters, you will find spaces between them.The importance of these spaces is for permanent teeth to be erupting normally.

Probability of crowding in permanent teeth is related to the amount of interdental spacing in primary dentition.

SLIDE 5[Primary Molar relationship]Here we are talking about the relationship between the last deciduous molars.(Which are the second maxillary & mandibular deciduous molars).There is a relationship between the ends of the distal parts of these molar.

Terminal Plane Relationship.It’s also called Terminal Plane Relationship.

Flush:When the distal surface of the maxillary second deciduous molar is in lined with the distal surface of the mandibular second deciduous molar making one straight line - like (Case A) in the picture below - this is called Flush Relationship.

Sometimes the distal end of the mandibular second located distal to the distal end of the maxillary second molar; making what is called Mesial Step.- like (Case C) in the picture below - .

While in case of what the distal end of the maxillary second is masial to the distal end of the mandibular second making the Distal Step, is considered as Case B.- look at the picture below - .

56% - Class I Angle’s molar relationship.Now when we have flush terminal relationships like Case A in the picture below, in 56% this will lead to Class I Angle’s molar relationship.

44% - Class II Angle’s molar relationship.

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While it’s only in 44% will lead to Class II Angle’s molar relationship.

Distal step.When we have a distal step like in Case B, this will lead in all the cases to the Class II Angle’s molar relationship.Notice in the picture (Case B), if the permanent molars getting erupt here , the Upper molar will be anterior to the lower, so it will be Class II Angle’s molar relationship.

Mesial step.Like Case C we have:

A greater probability for Class I Angle’s molar relationship.

A lesser probability for Class III Angle’s molar relationship

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SLIDE 6[Primary Molar Relationship]

Factors influencing the effect of terminal plane relationship on Angle’s molar relationship.

Means what are the Factors that determine the flush terminal relationship will be for example Class I, II, and III Angle’s Molar Relationship?The factors include:

Differential growth of the jaw.The difference of the growth between the Upper & Lower Jaws.If for example we have a growth in the lower jaw more than the upper jaw & for that it may have class III.

Forward growth of the Mandible.All the time the Mandible grows forward more than the Maxilla.

Sufficient Leeway space to accommodate a mesial shift of the permanent molars.

• Leeway space is the amount of space gained by the difference in the mesiodistal diameter between deciduous molars and premolars.

You know the premolars will replace the deciduous molars, & their sizes MesioDistaly aren’t equal, they are less in size MesioDistaly than deciduous molars (Deciduous Molars are bigger than Premolars); this difference is called Leeway Space.So when these premolars getting erupt in these spaces which are larger in size than their sizes, this will lead the Maxillary Permanent Molar to be erupt more anterior or accommodate this space because its size is large. It’s also important to know that this Leeway Space is more in the Mandible than in the Maxilla, so for this reason the Lower Molars erupting more mesial to the Upper molars, that’s really which makes the Class I Angle’s molar relationship.

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SLIDE 7[Permanent Occlusion]

AnteroPosterior Relationship.

Incisors: Class I, II, III Canine: Class I, II, III Molars: Angle’s Class I, II, III

We don’t have only AnteroPosterior Relationship; not necessarily all the time AnteroPosterio, we also have:

Faciolingual relationship.

Premolars Molars

SLIDE 8[Incisal Relationship]

Class I: [Normal Case]:It’s when the incisal edge of the Lower incisors is just located in the lingual fossa of the Upper Incisor.

Class II:It’s when the Mandibular Incisor is slightly lower to its normal position.When the Lower Incisors edges lay Posterior to the Cingulum plateau of the Upper Incisors .Increase in the Overjet.Which divides into 2 divisions?

Division 1:In this case the upper incisor will be Proclained (moving more anterior).Here the Overjet will be More than normal case.

Division 2:While here the upper incisor will be Retroclined.Here the Overjet will be ZERO.

Class III:Where the Lower Incisors edges lie anterior to the cingulum plateau of the Upper Incisors, the Overjet is reduced or reversed.

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Overjet:: is the Horizontal Space between the incisal edges of the Upper & Lower Incisors.

Reverse OverjetWhen Overjet is reversed & the Lower Incisors become anterior to the Upper Incisors.

Overbite:It’s the Vertical Space between the incisal edges of the Upper & Lower Incisors.

SLIDE 10[Canine Relationship]

Class I: It’s when the tip of the Upper Canine is just in the Embrasure position between the lower canine & the Lower First Premolar.

Class IIIt’s when the tip of the upper canine is Anterior to theNormal Position which is in Class I.

Class III:It’s when the tip of the upper canine is Posterior tothat of the Class I.

SLIDE 11[Molars Relationship]

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Angle’s Class I.It’s when the tip of the MesioBucchal cusp of the Maxillary first molar located exactly opposite to the MesioBucchal groove of the Mandibular first molar.

Angle’s Class II:It’s when the tip of the MesioBucchal cusp of the maxillary first molar is located Anterior to the Normal Position which is in class I, (Protruding Case)

Angle’s Class III:While in this case if you notice, the tip of the MesioBucchal cusp goes Posterior to that of the class I & become in the embrasure site which is in between the lower first & second molars. And notice here the tip of the upper canine takes place where the upper molar should be located, (Retruding Case).

Protruding Case: is when the Upper Molar Protrude (Become Anterior) to its normal position.

Retrudind Case: is when the Upper Molar Retrudes (Become Posterior) to its normal position.

Not necessarily you should see same relationship of the incisors as well, sometimes you may found Class I Angle’s Molar relationship & at the same time Class II incisal relationship, but whenever have a sever class II Angle’s Molar relationship you

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should see a sever Class II incisal relationship, because sometimes the cause of Class II in incisal relationship is (Thumb Suckling).

SLIDE 12[Arch Occlusal Relationship]

So we are discussed the AnterioPosterior relationship between the Upper & Lower teeth, we also we have a relationship related to Lower teeth whish is (FacioLingual or BucchoLingual <MesioLateral> relationship).Like for example, what is the relationship between the Upper & Lower Molars in the FacioLingual dimension (Coronal Section)?

Now if you look to the drawing no. 5 which is illustrate the Normal Relationship between the Upper & Lower First premolars, notice that the Bucchal Cusp of the lower first premolar is in between the 2 cusps (Bucchal & Lingual cusps) of the upper premolar.

Regarding the molars, notice that in the drawing no. 6, the MesioBucchal cusp of the lower first molar located between the 2 cusps (MesioBucchal & DistoBucchal) of the upper first molar & this is the Natural Relationship. This makes some categorization of the cusps; that’s mean based on these relationships; we divide the cusps into 2 Categories:

1- Functional Cusp.

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Which are the cusps that are related to the opposing teeth or which are important in contact.

2- Non – Functional Cusp Which are the cusps that are without contact.

Let’s take for example the tooth which is in (drawing no. 5) Premolars Relationship. Here we have 1 bucchal cusp & 1 lingual cusp.

Which one of these cusps is in occlusion?The Bucchal CuspSo, we need the bucchal cusp of the lower premolar as the Functional Cusp.

Regarding the upper molars (drawing no. 6)Which the cusp is in contact?The Lingual Cusp.

So, this is actually important (the Lingual cusp of the Upper Molar & the Bucchal cusp of the Lower Molar), because let’s suppose we want to make a Filling to supports the heavy load & this filling is made on the Supporting Cusp (for example, the bucchal cusp), I have to know that this Bucchal Cusp is under the load, so this filling need to be very hard. But if I want to make a small filling on the lingual cusp of the lower molar, I have to know this cusp is Non – functional Cusp. It’s not in contact, it doesn’t have a pressure on it, and so it doesn’t matter if I put a filling less in hardness. So all the time we have to put very strong filling or restorations at the areas of the Functional Cusp or the areas of Occlusion.Because not all parts of the tooth make the occlusion.

SLIDE 13[Curves of Occlusion]

Curve of SpeeAs you see if you put the teeth together, their

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Occlusal surface are not actually Flat, that’smean if you bring the lower jaw & try to put itwith the upper one, you will be not able to fitall the teeth in the Flat Surface, because not all the teeth is organized to fit into the flat surface. See here in the picture if you join a line from the tip of the canine to the last cusp here which is the DB cusp of the Mandibular Third Molar & let the line to pass throw the cusps of all teeth, this line tend to curve & this curvature called Curve of Spee.

Curve of Spee:Defines as the Imaginary Line passing from the cusp tip of the Mandibular Canine to the cusp tip of the DB cusp of the Mandibular Third molar.

If you continue the curvature of this curve this line should pass throw the Head of Condyles & this is very important, because when you bite if the teeth arrangement is flat, all the teeth were touching a flat plane, so you will be not able to bite; because actually the mandible rotating around the condyle. So if you have a flat teeth upper & lower you will not be able to bite them together, because the posterior teeth will touch together & the anterior ones will remain without contact, with this curvature all the teeth will be in contact this is the AnterioPosterior curvature, this is a Carve of Spee

Curve of Wilson.Which is describes the MesioLateralcurvature, this picture is a coronal section &here we find this curvature, lets imagine thatthis curvature passes throw mandibular firstmolar from B cusp then L cusp, then L cusp & B cusp from the other side, this curve is called Curve of Wilson.

Curve of Wilson:Is define as the Imaginary Line passing throw the B & L cusps of the right side of the posterior teeth then it continues to the L & B cusps of the crown of the posterior teeth of the other side (Any Posterior Teeth).

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Sphere of MonsonIf you bring the Curve of Spee & Curve of Wilson together you get a sphere called Sphere of Wilson.Here this is the mandible & see all the teeth are touching the sphere.The center of this sphere is in the Glabella which is the area between the eyebrows & it’s an elevating ridge (Between Superciliary Ridge).

SLIDE 14[Inclinations & Angulations of the Roots of the teeth]If you notice here in the molars, the long axis of the two occluding molar are not vertical, & as you see here the long axis of the upper first molar is tip Outward that’s mean the upper molar is not existing vertical in the jaw, while in the lower molar it’s also not vertical but it’s tip Inward.Because of our teeth are not meeting cusp to cusp, we always have inclination, the upper molar incline Outward while the lower molar incline Inward, but if they are vertical, if the relationship between them is vertical, there will be imbalanced when we are apply the force from the maxilla to the mandible or from the mandible to the maxilla, this will lead to inclination of the teeth in a non functional way. But if we inclines the teeth slightly and in a correct way, there will be a stabilization between them, so because of the functional cusps (Bucchal Cusps) of the lower molars are located between the two cusps of the upper molars, you should actually make the long axis of the molars not vertically oriented, & this makes the arch of the mandible wider than the arch of the maxilla.

Mandibular arch is wider than maxillary arch. Each tooth must be placed at the angle that best withstands the

line of forces brought against it during function.The teeth are not vertically located in the jaw, & this makes the stabilization between the upper & lower teeth.

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If the tooth is placed at a disadvantage, its longevity may be at risk.

If one of our teeth -for example- is erupt in wrongly way, & its angle is not appropriate for its function, so the life time in our mouth or the longevity will be at risk.

Anterior teeth are placed at a disadvantage.That’s mean is their position, their angulations is not appropriate, their forces isn’t actually enough to keep them in its position. All the time the anterior teeth are not put exactly as molars, the molars are more stable than the Anterior teeth all the time tipped forward, but what’s actually stabilize that is the force of the Lips, Lips all the time apply force on the anterior teeth to inhibit them to do profanation, let’s assume theoretically cutting the upper & lower lips, after some years we will find anterior teeth getting exposed, pronounced anteriorly.So those people who have Incompliant Lips (lips which don’t meet, away from each other), always we see their anterior teeth to be Proclined.

SLIDE 15[Antagonist]

With the exception of mandibular incisors and maxillary third molars, each tooth contacts two antagonist teeth in the opposing arch.

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As we said before in the deciduous teeth each tooth should has a contact with 2 teeth, also here the permanent teeth follow the same rule. Let’s take an example; the Lower First Premolar normally should be contact to 2 teeth which are (the Maxillary canine & First premolar). Except the Mandibular central incisor which make a contact with the maxillary central & the maxillary third molar.This rule is applied in Normal Class I relationship, while in the case of the Class II relationship the situation is different & the exception will be the mandibular third molar not maxillary one.As the general rule: If you extract the lower third molar, you also should extract an upper third molar why?Because the upper third molar has only one antagonist (which is the lower third molar that will be extract) & this antagonist is loss, so there will be a supraeruption of the upper third which leads to imbalanced in the occlusion, so we should extract the upper third as well, & this in the normal case only in the Class I relationship. While in Class II the opposite is true, the lower third molar which is make the occlusion, so in this case if we extract the upper molar, we should extract the lower also. But if we extract the lower, we will not need to extract the upper because the antagonist is lost & the upper is still in contact with the mandibular second molar.

Loss of one tooth keeps the adjacent tooth in contact with opposing antagonist.

While each tooth has 2 antagonists, so if you lose one tooth, the other one will be in contact.

Mesial or distal drifting into the space disturbs occlusal contact with antagonist teeth.

If we have tooth with 2 antagonists & one of these antagonists get extracted, the tooth will be still in occlusion because it still have the other antagonist tooth, but if we need to extract the tooth which anterior or posterior to it, this will lead to Mesial or Distal drifting & this will disturbs the occlusion.So as the rule in dentistry: If you extract your tooth don’t be late, run to the nearest dentist and replace it.

SLIDE 16[Centric Spots]

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Lingual cusp tips of maxillary posterior make contact with opposing fossae and marginal ridges of mandibular posterior teeth.

Buccal cusp tips of mandibular posterior make contact with opposing fossae and marginal ridges of maxillary posterior teeth.

Lingual cusps of maxillary posterior teeth and buccal cusps of mandibular posterior teeth are called “supporting cusps”.

Areas of occlusal contact that a supporting cusp makes with opposing teeth in centric occlusion are “centric stops”.

Not all the surface of the tooth are in contact with the antagonist tooth, only a small areas which are called Centric Stops.

The tip of that cusp is also a centric stop.Always the tip of cusp (if this cusp is a supporting cusp only) considered as a Centric Stop, also the bottom of the fossa & the marginal ridges are considered as a Centric Stop.

Knowledge of centric stops is important in restorative dentistry. All the time you should know the area of a Centric Stops because these are the areas which caries the whole load.

SLIDE 17[Movement Away from the Centric Occlusion]

LateralIf you move the mandible laterally, we called the side where you move your mandible to it, the Working Side & the other side is called the Non – Working Side.

Working side.It’s the side which where the mandible is moving to.

Non-working side.It’s the opposite side to the Working Side.

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In complete dentures.

Balancing side.In the Complete Dentures instead of saying Working Side, we said Balancing Side.

Non-balancing side.Here (in Complete Denture) the Non – Working Side should have contacting teeth & that’s what we call it Balanced Occlusion, but as we said in the Dentate People in the normal dentition there will be no need to have the contact between teeth.

Movement in TMJ.When you move the mandible to the right side (for example), the TMJ in the opposite side will move forward & the TMJ which is in the same side will be constant.

Tooth guidance.When you move a group of the teeth laterally, we have one of the following cases:

Group function.It’s mean all the bucchal cusps of the lower teeth are in contact with all the bucchal cusps of the upper teeth.

Canine guidance.But sometimes because of the prominent of Canines, these canines only are the guidance.The canine guidance is risky because if you move your mandible to the lateral side, the whole load will be on the Canines.

Protrusive Incisal guidance.

All the time the incisal surface of the upper incisors is the guidance for the forward movement of the mandible.

Retrusive The most retrusive position is the centric occlusion in

complete dentures.We talked about it in the Oral Physiology.

THE END

Done By: Ramiz Alrashwani

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