Presentation regarding Functional orthopaedic appliance

1. Twin Block Appliance
 Dr. Sanjida Haque & Dr. Anas Imran
 Presented to Dr. Muhammad Khursheed Alam

2. Introduction
 Twin Blocks are simple removable bite blocks with occlusal
inclined planes which act as functional appliance.
 Functional appliance: “Change the posture of mandible by
holding it open (or) open and forward. (Profitt)
 Cuspal inclined planes guide the relationship of teeth to
provide constant proprioceptive stimulus for favorable growth
of supporting bone.
 Devised by William J. Clark 1982

3. History
In 1880 Kingsley’s “Jumping the bite” gave the
concept of advancing mandible by inclined plane.
Followed by Vorbissplate of Schwarz 1966
Then “Oliver” guide plane
Devincenzo and coworkers used 90⁰ occlusal plane
as opposed to 700 recommended by Clark.

4. Indications
 Uncrowded Class II Div I
 Deep bite Class II Div I
 Class II Div II
 Deep overbite
 Reduced overbite
 Class III
 Mixed dentition
 Asymmetry
 Also indicated in early click when condyle is displaced distal
to the articular disc.

5. Contraindications
Crowding
Very narrow maxilla
Skeletal Class II by maxillary prognathism
Skeletal asymmetry

6. Advantages
 Comfortable
 Aesthetic
 Function
 Patient compliance ( Can be worn Full-time)
 Speech
 Clinical management
 Arch development
 Mandibular repositioning

7. Advantages
 Vertical control
 Facial asymmetry
 Safety
 Efficiency
 Age of treatment( Can be worn in all ages)
 Integration with fixed appliance

9. Modifications
 Twin Block for Transverse Development with Schwarz appliance
 Sagittal Twin Block
 Combination of both sagittal and transverse
 Twin block with Habit breaker
 Reverse Twin Block
 Magnetic Twin Block
 Twin Block with Extraoral attachment for advancement
 Twin Block with biofinisher

10. Twin Block for Transverse Development
with Schwarz appliance

11. Sagittal Twin Block

12. Combination of both sagittal and
transverse

13. Twin block with Habit breaker

14. Reverse Twin Block

15. Magnetic Twin Block

16. Twin Block with Extraoral attachment for
advancement(Reverse Pull Face Mask)

17. Twin Block with biofinisher for TMJ therapy

18. Other Designs

19. Parts
Twin block consists of two separate removable appliances.
1. Upper part has expansion screw
Labial bow 3/3
Adams clasps
Sometimes Lip Pads
2: Lower part
Double Adams clasps
'C' clasps
Ball ended clasps

20. Dental Effects of Twin Block
 After studies on primates, carefully designed studies were done on human beings
 Dental effects include
1. Retroclination of upper incisors
2. Uprighting of lower incisor into ideal incisor relationship (Lund and Sandler
AJO1998)
3. Restrainment or slight distalization of upper molars
4. Significant advancement of lower molars correcting the distocclusion.
 Vertical selective eruption of lower molars aids in OB correction
Duggal R. J Ind Orthod Soc 2006; 39:30-41,

21. Musculo-Skeletal effects
 Harvold 1983 described it as (Tension Zone)
Mc Namara as Pterygoid Response
Pain felt by patient after wearing functional appliances in response to altered
occlusal function.
From the studies of histological changes in animal experiment , it may be deduced
that retraction of the condyle results in compression of connective tissue and
blood vessels and that ischaemia is cause of pain.
A new pattern of muscle behavior is quickly established whereby patient finds it
difficult and later impossible to retract the mandible to its former rertruded
position.
This results due to medial head of the lateral pterygoid muscle.

22. The lateral pterygoid muscle hypothesis
Suggests that both postural and functional activity in the masticatory
muscles increase after functional appliance insertion. This increased
activity, especially in the superior head of the lateral pterygoid muscle,
then acts as a stimulus to mandibular growth
(McNamara JA. Neuromuscular and skeletal adaptations to altered
function in orofacial region. AJO 1973)

23. Effects on Bone
Skeletal changes as a result of Twin block therapy
1. Forward growth/repositioning of the mandible
2. Increase in the angle SNB.
3. No significant maxillary restraint
4. Increase in low anterior facial height.
(Morris et al. 1998)(Mc Namara 1999)

24. Effects on soft tissue
 Rapid changes in craniofacial musculature due to altered muscle function
 As appliance is worn full time , even during eating, rapid soft issue adaptation
occurs.
 Significant facial changes within 2-3 weeks.
 Twin Block appliance increases the intermaxillary space so difficult to form an
anterior oral seal by contact between the tongue and the lower lip, and
patients adopt a natural lip seal without instruction.
 Good lip seal is a functional necessity to prevent food and liquid escaping
from the mouth
So, no need for lip exercises.

26. Construction
1. Good set of impressions
2. Accurate construction bite
3. Models mounted on an articulator

27. Bite registration
There are two types of bite gauges used to register
bite for twin block:
1. George bite gauge
2. Exactobite gauge

28. George bite gauge
 Has a sliding jig attached to a millimeter
scale
 Designed to measure the protrusion path
of the mandible and can record a protrusive
bite of no more that 70% of the total
protrusion path.

29. Exactobite gauge or Project Bite gauge
Incisal portion has three incisal grooves to be positioned on the
incisal edge of the upper incisor.
A single groove on the opposing side that engages the incisal
edge of the lower incisor.
The appropriate groove is selected.

30. Designed to record a protrusion bite for
construction of twin blocks.
Registers 2 mm vertical clearance between
the incisal edges of the upper and the lower
incisors.
5 or 6 mm of clearance in the first premolar
region and 2 mm of clearance distally in the
molar region
Ensures that space is available for vertical
development of posterior teeth to reduce the
overbite.

31. Procedure
First rehearse the procedure of bite registration with
patient using a mirror. The patient should be
instructed to occlude with the midlines coincident
and the upper
incisors occluding in the appropriate groove to
reduce the overjet when the mandible closes into the
incisal guidance groove.
A relatively firm wax which is dimensionally table is
used to register the occlusion.

32. Pictorial Procedure

33. Pt bites with incisors edge to edge.
~ 6mm separation of molars

34. Fold wax lengthwise twice to 1/3 size(6mm)
Do not flatten

35. Turn folded wax lengthwise and fold once
with spatula in between

36. Crimp lower edge against spatula
Do not flatten

37. Bite edge to edge on incisor area

38. Registered Bite

39. Guidelines
 Horizontal consideration:
According to the Roccabado (1992), the position of maximal
protrusion is not a physiological position and the range of
physiological movement of the mandible is only 70% of the
total protrusive path. This is also called freedom of movement.

40. Total protrusion path is calculated by measuring
the overjet in most retruded position and then in
the most maximal protrusion and finding the
difference between the two.
The initial activation should not exceed 70% of
the protrusive path.
Average 5-10mm on initial activation, depending
upon the freedom of movement in protrusion
function.
This degree of activation allows an overjet as
large as 10 mm to be corrected.

41. Midline consideration:
Centre lines should be coincident provided no dental
asymmetry is present

42. Vertical consideration:
 Two factors determine the amount of vertical clearance.
1)Thickness of the bite-block: Adequate vertical clearance
must be available between the cusps of the upper and lower
first premolars or deciduous molars to accommodate blocks
of sufficient thickness to activate the appliance.
 2)The vertical activation must open the bite beyond the
freeway space to ensure that the patient can not drop the
mandible into rest position and negate the proprioceptive
functional response of the inclined planes.

43. Intergingival height
To establish the correct vertical dimension
Measured from gingival margin of upper Incisor to
gingival margin of lower incisor when teeth are in
occlusion.
Comfort zone for intergingival height for patients is
generally found to be 17-19mm
Height of upper & lower
incisors minus overbite.

44. Horizontal VS Vertical growth pattern
Horizontal growth pattern - maintain edge to edge
incisor relationship more easily (provided the overjet is
not excessive)
Vertical growth patterns - may not tolerate the same
degree of sagital activation.
A smaller initial activation is necessary
Gradual mandibular advancement

45. Clinical Management
• Selectively 1-2mm trimmed upper bite blocks at
the region of lower 6 and 7s
• Active Phase is finished after achieving
1. correct class I Molar
2. ideal OJ and OB
3. three-point contact with incisors and molars.
Clark, W. J. (2002) Twin Block Functional Therapy.
Fife, UK:Elsevier
Active Phase: Fig A, B & C
(6-9 Months)

46. Clinical Management
Support Phase: (Fig D & E)
3-6 Months
Aim is to maintain correct incisor relation
until buccal relationships are fully
established.
For this Upper removable appliance with
inclined plane and a labial bow is fitted
Retentive Phase: ( 9 months)
Only night time wear is sufficient for
retention.
Clark, W. J. (2002) Twin Block Functional Therapy. Fife, UK:Elsevier

47. Patients Instructions
 With co-operation, results can be achieved in the least amount of time.
 How to insert the Twin Block – when placing the upper and lower plates in your
mouth, first position them on your teeth and then firmly press the appliances into
place using your thumbs. Never position them with your tongue and bite into place.
When removing the plates, ease the appliance off from each side. Do not flip the
appliance on and off your teeth with your tongue as this will result in a breakage.
 Full-Time Wear – both the upper and lower plates must be worn together full time,
including while you eat and sleep. The only exceptions are when you remove them
for cleaning and for contact sports and swimming (to avoid loss).

48. Patients Instructions (Cont.)
 Activation of the Screw – Always follow directions from your orthodontist. When
instructed, turn the screw once/twice every seven days in the direction of the
arrow, until advised to stop turning.
 Eating with the Twin Block – Eating with the appliance will give you much faster
results. Leaving the plates out for one meal is equivalent to losing 24 hours of
wearing. It may take a while to get used to eating, so initially eat foods which are
soft and easy to chew.
 Comfort – There should not be much discomfort, apart from some tenderness of
the facial muscles in the first few days, but this should soon disappear. Full-time
wear and eating with the appliance maintains proper fit and minimizes discomfort

49. Patients Instructions (Cont.)
 Difficulty Speaking and Excessive Saliva – It is normal that there will be some
difficulty with speech and excessive saliva the first few days, but this diminishes
with time.
 Oral Hygiene – Always keep your Twin Block and teeth clean. Brush the appliance
regularly using a toothbrush and soapy water or toothpaste, and if you can’t brush,
rinse the appliance and your mouth after eating.
 Appointments – keep all appointments. The upper plate needs to be adjusted once
a month.
 Breakages – are costly in both time and money. Don't fiddle with your plate or try to
alter or repair it yourself.