Study Model Analysis:◦ 1. The 1st permanent molar relationship.◦ 2. Nature of midline discrepancy if any◦ 3. Symmetry of the dental arches is determined.◦ 4. Curve of spee is checked to see if it can be leveled with

the activator.◦ 5. Crowding and any dental discrepancies

Functional Analysis:-◦ 1. Rest position◦ 2. Path of closure◦ 3. Prematurities◦ 4. THJ examination◦ 5. Interocclusal clearance◦ 6. Respiration

Cephalometric Analysis◦ 1. The direction of growth◦ 2. The difference between the position and the size of the

Jaw bases.

Before bite registration few analyses have to be done.

ANDRESEN'S first activators did not displace mandible beyond the physiologic rest position relative the vertical and was 3 mm short of the limit of the patient's tolerance relative to the protrusion.

First to oppose was SELMER-OSLEN◦ 1. Muscles couldn't be stimulated at night, for this

was the time nature used to give them rest.◦ 2. Forces delivered to the teeth by the appliance

were a form of potential energy and not kinetic energy.

◦ 3. Andresen's 2-4 mm opening in molar region is beyond physiologic rest position.

◦ 4. He said Andresen is wrong if he thought an appliance holding the jaws a 2 mm beyond is a truly functional passive appliance.

Construction bite

PAUL HERREN- activator didn't work according to Andresen's theories at all, even if it was constructed within the physiological limits of rest position. His construction bite is in sagittal direction, the mandible is positioned in an overcompensated by 3-4 mm. Vertical opening - 2-4 mm plus the deep bite that is already present.

The Louisiana state university acivator of ROBERT SHAYE (1982) essentially follows the same design and principles.

HARVOLD (1974) said you have got to go Stretch the muscles, the more stretch, the better. His construction bite - 3 mm short of patient's limit of tolerance in .protrusive position but with a 8-10 mm vertical opening beyond the rest Position.

WOODSIDE (1974-75) - said to go even further beyond rest position to 12-15 mm

GRABER and NEUMANN said use a combination of bite opening and protrusion to equal to 10 mm. In other words, if you open the bite 4 mm between the occlusions posteriorly then advance the mandible by 6 mm.

BALTERS of Germany advocated protrusive incisal end-to end with an interincisal opening of 2-3 mm.

Construction s/b made considering vertical, horizontal & transverse planes

1. The original sagittal jaw relationship may be maintained.

2. Mandible may be positioned forward to change the sagittal relationship equally on both sides.

3. The bite is changed on one side but is maintained as much as possible on the other side as with a unilateral Class II Div. 1 or class II Div. 2 or class III. This means that a normal midline relationship exists in postural rest, but a midline swing to the side that is forced in the habitual occlusal relationship.

4. The mandible is postured backward as much as possible in the fossa, opening the bite enough to try for an end to end Incisal relationship or as close to this as possible, in class III malocclusions.

Horizontal posturing of mandible

Dependent on three major considerations:

◦ (1) The kind dysgnathic problem (Sagittal and vertical relationships, morphogenetic growth pattern)

◦ (2) the developmental state, sex, and age of the patient (potential incremental change)

◦ and (3) the type of appliance to be used.

Vertical opening of mandible

Different sagittal and vertical dysplasias require different construction bite registrations.

For example, in deep bite Class II, Division 2 and Class III malocclusions, it is necessary to record the vertical distance between Incisal of lower incisors the upper and margins determining how wide open the construction bite should

In permanent dentition cases (specifically in Class II Division 2 malocclusions or class I Division 2 symptoms, or in anterior cross bites, e.g., Class III malocclusions), it is best to open the bite for the construction registration a distance of 1.5mm to 3 mm, vertically beyond the Incisal edges.

Type of malocclusion:

In the mixed dentition, it should be increased to 4 mm. to 7 mm. Thus, the original overbite is a determining factor.

In the Class II, Division 2 malocclusion and in the permanent dentition, the bite may have to be opened up to 9 mm. in the molar region and occasionally more.

Woodside feels it improves the chances of retention during sleep and enlists the viscoelastic properties of the stretched soft tissues.

The reason the bite can be opened so far is that type of Class II, Division 2 malocclusion most frequently has a palatal plane that is tipped down anteriorly along with a deep bite and an excessive curve of spee. A large bite opening can improve the maxillary incisor inclination because the anterior end of the palatal plane is withheld or tipped up and this also reduces the deep overbite because the lower incisors are under intrusive action as the maxillary base rotates upward and forward.

The wide open construction bite brings the mandible out of the range of any tooth guidance and resultant retrusive effect on the condyle and the path of closure.

Also such cases usually do not have a severe sagittal malrelationship and usually have a good chin-button morphological appearance so rocking open the bite, which drops the symphysis down and back, does not have a deleterious effect on the profile.

This is particularly true since in most of these cases there is a horizontal growth pattern.The large vertical opening improves the growth direction and allows the full eruption of the posterior teeth, which are usually in marked infraocclusion.

If only mandibular positioning is needed, or a small anterior posturing is required the (only maxillary teeth spaced & labially inclined ) , the vertical opening should be rised more in order to elicit more positive functional and viscoelastic response from musculature.

Class II, Division 1 problems demanding more horizontal posturing to establish correct maxillomandibular relationship, a smaller vertical opening is needed,

In cases with a more vertical growth direction and a deep overbite, a larger bite opening is desirable for the construction bite registration This allows some downward and backward compensation of maxillary growth (and palatal plane) to fit the mandibular growth pattern.

In Class II, Division I malocclusions in which ◦ (1) the sagittal malrelationship is the width of a

whole premolar;◦ (2) there is a severe curve of Spee◦ (3) the lower incisors are over erupted, impinge

on the palatal mucosa, the construction bite should not be higher than vertical end to end relationship.

This is because the interocclusal distance in the molar region, with infraocclusion of the molars and supraocclusion of the lower incisors, might exceed 7 mm which would be excessive because of the possible lateral spread of the tongue.

If moderate curve of Spee vertical opening s/b increased to allow for posterior eruption & getting favorable muscle balance. In such cases, 4mm. Between incisal edges is desirable, and it can occasionally be even more.

In the case of a synchronous downward and backward archform growth pattern and an average incisor overbite, caution is the watchword, so as not to accentuate the molar eruption too much, which will create a more retrusive profile and possibly induce an anterior open bite that will be difficult to close.

The interocclusal space should not exceed 4 mm in the molar region. The same applies to anterior open bite problems. The interocclusal acrylic table or tooth bed should not be ground away in such cases, but rather should maintain constant intrusive contact on the upper and lower posterior teeth in both arches.

Type of activator

If the upper and lower midlines do not coincide, a determination must be made as to the fault - maxillary or mandibular. The patient is observed in postural rest position to check the midlines and is then asked to slowly close the mouth into full habitual occlusion.◦ 1. Midlines of postural rest position and occlusion

coinciding - construction bite no change.◦ 2. Postural rest position coincides with midlines

while occlusal position does not, this is due to shift from one side to other, occlusal interferences should be checked. Construction bite should follow the resting Position midline relationship.

Transverse posturing of mandible

◦ 3. Midlines of both in rest and occlusion - caused by shifting of teeth in one jaw or the other. The construction bite should line up with the midlines of maxilla and mandible regardless of shifting of teeth. Dental midline discrepancies caused by shifting and malposition of the teeth can be corrected late with the fixed appliances. Occasionally a short pretreatment fixed appliance to correct midline.

The purpose of the construction bite is to fabricate an appliance that induces the following effects: ◦ (1) to bring the lower jaw into a tolerable forward

position with every occluding action of the mandible

◦ and (2) to "block the bite“ depressing the lower anterior teeth and stopping their eruption, while attempting to stimulate eruption of the posterior segments.

Construction bite planning

Taking the construction bite one should look at the bite in three different planes of space: sagittal , vertical and frontal.

Therefore it is first necessary to clarify three points using the procedure developed by Schwartz.

The usual intermaxillary relationship for the Class II problem is that of end to end an average incisal relationship. However. it should not exceed 7 mm to 8mm. Or quarters of the mesiodistal dimension of the first permanent molar. Anterior positioning of this magnitude is contraindicated in the following instances:

Anterior positioning mandible

If the overjet is too large (in extreme cases approach 18 mm) the anterior positioning becomes a stepwise progression to be accomplished in two or three phases.

If there is severe labial tipping of the

maxillary incisors. they should probably be uprighted first if possible by a prefunctional appliance.

If one of the incisors usually the lateral incisor has erupted markedly to the lingual the mandible must be postured anteriorly to an edge to edge relationship with the lingually malposed tooth otherwise labial movement of this tooth would not be possible. Eschler termed this a "pathological" construction bite.

In a normal case, the maximum forward movement of the mandible averages 9-10mm, but as little as 6-7mm. The optimal forward movement of the mandible for the construction bite is usually half the individual’s maximum range. There are three reasons for this –◦ more uncomfortable for the patient◦ The distance of 5mm is approximately is the

same as that between the points of the buccal cusps of the first molars. This is the amount of distance necessary to change a class II malocclusion into a class I occlusion.

THE EXTENT OF MAXIMUM FORWARD MOVEMENT OF THEMANDIBLE (SCHWARZ)

◦ It is claimed that one of the best positions for obtaining the desired histological transformation of the TMJ from a Class II malocclusion into a Class I is approximately half the distance that the condyle can move forward along the anterior wall of the fossa to the articular tubercle.

There are some guiding principles in maintaining a proper horizontal vertical relationship and determining the height of the bite-◦ The mandible must be dislocated from the resting

position in at least one direction - sagittally or vertically. This is essential in order to activate the associated musculature and induce a strain in the tissues.

Opening the Bite

◦ If the magnitude of the forward position is great (7mm- 8mm), the vertical opening should be minimal so as not to overstretch the muscles. This type of construction bite means an increased force component in the sagittal plane, enabling a forward positioning of the mandible. The primary neuromuscular activation is in the elevator muscles of the mandible.

◦ If the vertical opening must be extensive, the mandible must not be anteriorly positioned. If the bite opening is more than 6 mm, mandibular protraction must be very slight. Myotatic reflex activity of muscles of mastication can then be observed as can a stretching of the soft tissues. A more extensive bite opening is possible in functionally true deep-bite cases. If the bite registration is high both the muscles and the viscoelastic properties of the soft tissues are enlisted.

◦ The vertical force is increased and the sagittal force is decreased. This type of construction bite is not effective in achieving anterior positioning of the mandible, but the inclination of the maxillary base can be influenced.

One possible indication of this type of construction bite is in the case vertical growth pattern. In such cases, the vertical relationship, either deep bite or open bite, can be therapeutically affected by the activator.

The disadvantages of a wide construction bite are the difficulty in wearing appliance, with increased difficulty of patient to adaptation. Muscle spasms often occur in such cases, and appliance tends fall out of mouth. The wide open construction bite also makes the lip seal difficult. Yet the reestablishment of a normal lip seal is essential requisite of functional appliance therapy.

Clinical experience indicates that the opening of construction bite in excess by approximately 2mm individual's position is optimal.

Resting individuals the interocclusal clearance amounts to 2 mm to 3mm in the molar area. and 4mm. to 5mm in the incisor area.

An opening of 4 mm to 5mm in the Molar area and 6mm to 7mm in the incisor area frequently will desired.

The Extent of the Individual's Occlusal Clearance in the Resting Position: (Schwarz)

As we know from the study of rest position when mandible is open beyond this position. the condyle moves downward and forward on the articular eminence. Thus the bite open more than 5 mm. in the molar area, forward movement of 4mm. will suffice.

Highly experienced clinicians such as Petrik and Herren entirely disregard the rest position.

Petrik – The upper and lower incisal edges should meet in as close to an to edge relationship as possible in a horizontal plane. This maneuver will generally leave the incisors 1mm to 4mm. Apart at most, with a posterior bite opening of 4mm. to 7mm. Contrary to many other clinicians, Petrik also given preference to bring the mandible forward to the complete desired distance at once, not in stages.

The configuration of the original malocclusion and the movability of the mandible must be studied carefully before deciding which technique to follow.

Taking the construction bite is a most important step in the treatment. It should be done directly in the patient's mouth. No articulator duplicates the exact condylar pathway as in the patient.

If the forward positioning of the mandible is 7mm to 8mm the vertical opening must be slight to moderate(2mm-4mm).

If the forward positioning is not more than 3mm to 5mm the vertical opening should be 4mm to 6mm.

Lower midline shifts or deviations can be corrected by the activator only if there is actual lateral translation of the mandible itself. Functional cross bites that are observed in the functional analysis can be corrected by taking the proper construction bite.

General rules for the construction bite:

Both experimental research and clinical experience have shown that an increase in muscle activation with overextended appliances does not increase the efficiency of the activator.

Acc to Sander- the frequency of maximal biting into a 6mm. high construction bite is 12.5 percent of the sleeping time, whereas in an 11mm construction bite it is only 1.1 percent of the time. If the height is increased to 13mm as prescribed by Harvold, maximal biting takes place only 0.8 percent of the time.

First, a horseshoe-shaped wax bite rim is prepared for insertion between the maxillary and mandibular teeth.(2-3mm thicker than required)

Choice to keep bite on lower or upper arch If the rim is placed on lower arch –easy to guide mandible into desired position –class II

On the upper arch-mandible can be moved easily into retruded position required for construction of Class III activator

EXECUTION OF THE CONSTRUCTION BITE TECHNIQUE

Before taking the wax bite registration, the patient is seated in an upright position. The posture should be relaxed and not strained. The mandible is then gently guided the predetermined position. The operator guides but not force the jaw into the desired sagittal relationship. This exercise is repeated three or four times.

The patient is asked to repeat the exercise alone and then hold the forward position for a while to set up an exteroceptive engram that can be replicated when wax is placed between the teeth.

After the operator is relatively sure that the patient can replicate the exercise, the softened wax bite placed in the mouth in the manner already described.

Wax should not be too soft. During the closing movement, the operator controls the edge to edge incisal relationship and the midline registration.

To visualize the midlines & to establish correct reproduction of the incisal relationship, wax should be cut away from the labial surface of the central incisors.

In the final step, the wax is carefully removed from the mouth without distorting and is checked on the upper and the lower models and chilled.

After it has been fitted on casts, the margins are trimmed with a scissors, so the operator can be sure the wax is in close approximation to all the cusps of the teeth.

The hardened wax bite is then checked once again in the mouth.

The following step by step procedure for taking the construction bite is suggested:

1. Reproduce the maximum forward movement of the mandible and the correct occlusal clearance of postural rest. Observe whether a functional lateral shift occurs and register the true mandibular midline with a pencil on the labial surfaces of the upper and lower incisors on the casts and in the patient's mouth.

2. Determine the amount of mesial and vertical mandibular displacement necessary for the construction bite. It is helpful to mark the amount of mesial shift with a pencil on the buccal surfaces of the first molars.

3. Show the patient on the casts and in the mirror in which direction the mandible should be moved. Practice the forward mandibular movement by gently guiding the mandible in the desired direction.

Sequential steps for the construction bite: Schwartz

Advise the patient to move the jaw slowly according to the verbal instructions and to stop movement immediately when asked to do so. Talk to the patient in a calm, reassuring manner.

4. Soften a sheet of beeswax and make a tight roll, approximately 1 cm in diameter.

5. Shape the roll to conform to the lower dental cast, leaving the seam on the inside. Press the softened roll of wax on the lower arch so that only the buccal teeth are covered. In the front, the wax roll lies just lingual to the lower incisors. Make a groove on the wax to indicate the midline. Remove any excess wax that extends onto the retromolar tissue. The distal half of the last molar tooth should not be covered with wax.

6. Transfer the wax to the patient's mouth, fitting it on the lower arch in the same manner that it was fitted on the plaster cast.

7. Move the mandible forward as was previously practiced. If the registration fails, make a new wax roll and repeat.

8. Remove the wax bite from the mouth and chill it. With a sharp knife, trim the excess buccal wax until the occlusal surfaces of the molars are visible. By carefully checking the plaster casts, also remove all wax that is contacting the soft tissues, the interproximal papillae, and the palate. If this is not done, the wax bite cannot be seated properly on the casts.

9. Place the wax bite between the casts and check that the mandible is moved forward the desired amount in the three planes of space. If the construction bite is incorrect, replace it on lower cast, and soften its superior surface add a layer of warm wax. Repeat the procedure from No.6 through No.1O.

10.Replace the hard wax bite in the patient's mouth and have the patient close the jaw slightly more firmly to assure the correct fit.

Low CB with marked mandibular positioning High CB with slight mandibular positioning CB without forward mandibular positioning Posterior CB

Activator

BIONATOR

2-3 mm interincisal clearance at the centrals or laterals and a mandibular advancement so that lower centrals are 2-3 mm protruded beyond upper centrals or lateralsMixed dentition S:2mm V :2mm for 24hr wearPermanent dentition S:3mm V: 3mm for 12hr or more

FRANKEL

Balance between protractor and retractor muscles shouldnot be disturbed

Sagittal: not more than 2.5 – 3mm

Vertical: just to permit cross over of wires(2.5 – 3mm)

Transverse: midlines

TWINBLOCK

Sagittal : edge to edge oclusion of incisors

Vertical : thicker in premolar region

Transverse : midlines should coincide.