ESTABLISHMENT OF OCCLUSION AND INTER-ARCHADE ARRANGEMENT
PLAN :
1 Establishment of occlusion and organization of dental arches
1.1 Temporary dentition
1.1.1 Intra-arcade arrangement
1.1.2 Inter-arcade arrangement
1.2 Permanent dentition
1.2.1 Intra-arcade arrangement
1.2.2 Inter-arcade arrangement
1. Establishment of occlusion and organization of dental arches
1.1 Temporary dentition
1.1.1 Intra-arcade arrangement
- The shape of the temporary dental arches is practically comparable to a semicircle.
- The arches frequently present diastemas:
- Simiens: between II and III in the maxilla, and between III and IV in the mandible.
- From Bogue: Presence of inter-incisal diastema.
- Temporary teeth do not have a particular axis, they are implanted vertically.
- The occlusal plane is flat (Absence of curve of Spee).
Figure 1: Temporary dentition with diastemas
1.1.2 Inter-arcade arrangement
- The occlusion is of the interlocking type: a tooth is in occlusal relationship with 2 antagonist teeth except for the lower central incisors and the upper 2nd molars.
- The meshing is not very marked, with a weak incisal overlap.
- The upper arch circumscribes the lower one, with a slight incisal overhang and sometimes an end-to-end.
1.1.2.1 Canine occlusion
- It constitutes the reference point for the occlusion of temporary teeth.
- The tip of the upper canine should be in the space between the lower 1st molar and the lower canine (according to Müller).
1.1.2.2 Terminal plan
- It corresponds to the alignment of the distal faces of the upper and lower 2nd temporary molars, which prefigures the position of the 1st permanent molars, because the distal face of the 2nd temporary molar will serve as a guide for the eruption of the 6-year-old tooth.
CHAPMAN describes 3 types of relationships between the upper and lower molars:
- Terminal plane with mesial step:
The distal face of the 2nd lower molar is mesial to the upper. This is the most classic arrangement (a class I occlusion could be established) which can evolve into class III.
- Right terminal plan:
It is the cusp to cusp ratio that can give an Angle class I.
- Terminal plane with distal step :
The distal face of the lower V is distal to the upper one. This invariably leads to an Angle class II.
NB: In the context of preventive and interceptive orthodontics, our clinical examination must target three important points:
- The presence of diastemas.
- Canine occlusion.
- The terminal plan.
1.2 Permanent dentition
1.2.1 Intra-arcade arrangement:
The organization of dental units within their respective arches must certify their balance and stability, in order to ensure their functions.
This objective arises from:
- On the presence of compensation curves:
- On the orientation of dental axes.
- Continuity of the arches (presence of contact points).
1.2.1.1 Van Spee curve (sagittal):
- It is a sagittal curve with superior concavity, whose center belongs to the region of the Crista-Galli process.
- It represents the fictitious line which passes through the tip of the canines, and the summit of the vestibular cusps of the premolars and molar of the lower hemi-arch.
- Its extension joins on the one hand the anterior slope of the mandibular condyle and on the other hand the cleft lip.
- She is born around the age of 12, after the permanent teeth have come in.
- Its depth is closely related to the individual’s morphological type.
According to Andrews:
- A pronounced curve of Spee gives less space to the upper teeth and promotes an OJ and an overbite.
- A reversed curve of Spee would give relatively more space to the upper teeth.
- An occlusal plane without a curve of Spee is most often associated with good occlusion.
1.2.1.2 Wilson curve (frontal):
– It is a frontal curve with superior concavity, passing through the vestibular and lingual cusp summits of the premolars and molars.
-Due to the helical arrangement of the occlusal tables, this curve is all the more accentuated as the teeth are more posterior; because the angulation of the posterior teeth being more accentuated, the radius of this curve is reduced in the mesio-distal direction.
1.2.1.3 Orientation of dental axes
In the vestibulo-lingual direction:
- Positive inclination of the upper incisors (vestibulo version) and a vertical implantation of the upper canines.
- The lower incisor-canine block is straight.
- The occlusal tables of the PM and M are oriented vestibularly in the maxilla, and vice versa in the mandible.
In the mesio-distal direction:
The axes of the teeth of the two arches are oblique to a perpendicular to the occlusal plane:
In the maxilla:
– The incisors and canines are mesioverted, their inclination is said to be positive.
– The PMs are perpendicular to the occlusal plane.
– The 1st molar is slightly mesioverted.
– The 2nd and 3rd molars are distorted.
In the mandible:
– The incisors are straight or slightly mesioverted.
– The canines are also in mesioversion.
– The premolars are perpendicular to the occlusal plane (sometimes, the 2nd PM is disto-verted).
– The first molars have a variable inclination from -1° to +1°.
– The 2nd and 3rd molars have a mesial inclination.
All these modifications in the orientation of the dental axes reflect the architectural and skeletal adaptation of the teeth to the functional forces exerted on them .
1.2.1.4 Interproximal contact points:
– The support cusps are arranged according to the same curve in both the maxilla and the mandible: curve of the arch.
– The curve of the support cusps corresponds, on the opposing arch, to a curve of the fossae and the dimples.
– At the incisor-canine level, the incisor-canine arch is located in the extension of the curve of the support cusps.
– The essential element in the arrangement of an ideal dental arch is the proximal contact zone which ensures the continuity of this arch and the distribution of occlusal forces over the entire arch. Ideally, the contact points are located in the vestibulo-lingual direction at the junction of the vestibular third and the medial third; and in the vertical direction, at the junction of the occlusal third and the medial third. The contact points are punctiform, immediately after the phase of constitution of the young adult dentition. Then gradually become support surfaces with age (mesial forces).
1.2.2 Inter-arcade arrangement:
1.2.2.1 Static occlusion
– The dental occlusion is of the interlocking type, that is to say that each tooth articulates with 2 antagonistic teeth, with the exception of the lower central incisors and the upper 3rd molars.
– The occlusal morphology is composed of cusps and marginal ridges whose main characteristic is to present only convex surfaces, the natural occlusion of permanent teeth is therefore achieved by punctiform contacts, that is to say tangents between these convex surfaces.
– Occlusal stability (tripodism) is determined by dento-dental contacts, which depend on:
- From the point of contact surface which is established between the convex surfaces.
- From the position, at the level of the molars the contacts are distributed in such a way as to stabilize the mandible.
In the sagittal direction:
The maxillary arch is longer and wider than the mandibular arch:
At the incisal level:
There is a vestibular overhang of the maxillary teeth relative to
to the mandibular teeth (“over jet” = 2mm).
– If OJ > 2mm proclusion.
– If OJ < 2mm retroclusion.
At the canine level:
The tip of the upper canine should be in the embrasure
between the lower canine and the 1st lower PM (class I canine).
– If it is in distoclusion: canine class II.
– If it is in mesioclusion: canine class III.
At the molar level:
The 6-year tooth is the key to occlusion in the permanent dentition.
The ideal occlusion should be in Angle’s Class I relationship, in which the lower 1st molar is ½ cusp mesial to the upper.
– If it is in distoclusion: class II molar.
– If it is in mesioclusion: class III molar.
In the transverse direction:
- Anteriorly, the upper and lower interincisal points should coincide with each other and with the median sagittal plane.
- Laterally, the maxillary teeth circumscribe the mandibular teeth.
In the vertical direction:
- The overlap of the lower incisors by the upper ones “over bite” is approximately 2mm.
- Laterally, the coverage of the mandibular teeth by the maxillary teeth on the vestibular side, and of the maxillary teeth by the mandibular teeth on the lingual side depends on the depth of the fossae and the height of the cusps.
1.2.2.2 Dynamic occlusion
1.2.2.2.1 Resting position:
The position occupied by the mandible when the masticatory and postural muscles are in a state of minimal active physiological equilibrium (relaxation).
- The mandibular condyle is located in the anterior part of the glenoid cavity (upper part of the posterior slope of the temporal condyle).
- This position conditions: the free space of innocence which is:
- 1 to 3mm anteriorly.
- From 1.8 to 2.7 mm at the level of the mesial cusps of the 6.
- Necessary for neuromuscular balance.
1.2.2.2.2 Maximum intercuspation position:
- Also called centric occlusion, it implies the closing position which presents the maximum of surfaces and points of contact between the maxillary and mandibular dental arches.
- It is said to be physiological when in this position the mandibular condyles occupy symmetrical articular relationships and the musculature is in a comfortable position of balance.
- It is said to be ortho-functional when it ensures harmonious arrangements of the different elements of the masticatory system and it is said to be pathogenic when it alters this harmony.
- However, it is possible that it is not ortho-functional while not being pathogenic, due to a certain adaptation of the neuromuscular system. The patient finds a comfortable position, this is the “convenience intercuspidation position”.
1.2.2.2.3 Centered relation
- It is a mandibular-cranial relationship
- This is the position in which the mandibular condyles occupy the highest and most unforced rearward position in their glenoid cavities.
- It is a stable and reproducible position, it can be chosen as a reference position in the anatomical analysis of occlusion
- According to POSSELT, the RC does not coincide with the ICM in 90% of cases. There is therefore a discrepancy of 1.25 mm in adults and 0.85 mm in children.
- To be able to examine the contacts in RC, the patient must be in a state of psychological and emotional relaxation and muscular relaxation.
1.2.2.2.4 Protrusion
- Corresponds to the sliding of the free edges of the lower incisors along the palatal faces of the anterior-upper teeth from the ICM to the end-to-end, we will speak of an incisal guide.
- Accompanied by a total and immediate disocclusion of the posterior teeth.
- Drives the protrusion in a straight path
- In case of deviation, a working or non-working protrusive interference should be considered.
- The ideal incisal guide depends on 3 parameters:
- The position of contact between the free edge of the lower incisors and the palatal surface of the upper incisors.
- Palatal concavity.
- Inter-radicular orientation and degree of coverage.
- The curve of Spee; an exaggerated or irregular curve of Spee leads to posterior contact and thereby prevents disocclusion.
1.2.2.2.5 Diduction movement
- During lateral movements, the mandibular vestibular cusps slide laterally on the internal faces of the upper vestibular cusps which constitute the guide surfaces with their “protective” role.
- Lateral guidance can be achieved by the lower canine on the working side alone, which is called the “canine function”, or by a group of teeth, which is called the “group function”.
- On the non-working side, the disocclusion must be total and immediate.
Canine function:
This function involves:
– A canine Class I.
– Greater coverage of the canine compared to PM and I.
– Intimate contact between the upper and lower canines on the same side.
– An overhang lower than that of the incisors, ensuring immediate disocclusion
The canine function is considered by gnathologists as the best guide during the diduction movement.
Group function:
Several teeth on the working side ( canines + others) conduct the lateral movement ensuring a harmonious distribution of lateral forces.
We are talking about:
Previous group function.
Posterior group function: total or partial.
Noticed:
For some authors, notably PLANAS, dynamic occlusion as described by gnathologists is not optimal.
PLANAS speaks of balanced occlusion which allows to have contacts on the working side but also on the non-working side during the diduction movement.
It describes the Functional Masticatory Angles of Planas (AFMP) which must be small and equal, guaranteeing physiological chewing.
Bibliography:
CHÂTEAU. M: dentofacial orthopedics volume 1 “Fundamental bases” Edition Cdp 1980
BASSIGNY: Manual of dentofacial orthopedics Edition MASSON 1991
LEJOYEUX. E FLAGEUL. F: dentofacial orthopedics “a bioprogressive approach” Quintessence 1999
LANGLADE. M: Orthodontic therapy Maloine edition, Paris 1976
AKNIN. JJ: craniofacial growth 23-455-C-10 EMC 2008
ABJEAN.J, KORBBENDAU.JM: Occlusion “clinical aspects, therapeutic guidelines” 1980
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ESTABLISHMENT OF OCCLUSION AND INTER-ARCHADE ARRANGEMENT
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