1. The Twin Block Appliance
Nalaka Jayaratne BDS, PhD
Resident in Orthodontics,
University of Connecticut School of Dental Medicine
USA

2. History
• First used on Sept 7th, 1977 by William Clark
Clark W.J. Twin Block Functional Therapy: Applications in Dentofacial Orthopedics
(3rd Edition)

3. History
• First used on Sept 7th, 1977 by William Clark
• “Necessity is the mother of invention”
Clark W.J. Twin Block Functional Therapy: Applications in Dentofacial Orthopedics
(3rd Edition)

4. History
• First used on Sept 7th, 1977 by William Clark
• “Necessity is the mother of invention”
• Used for a son of a dental colleague with CII D1
who luxated Upper Cent. Incisor to
Clark W.J. Twin Block Functional Therapy: Applications in Dentofacial Orthopedics
(3rd Edition)

5. History
• First used on Sept 7th, 1977 by William Clark
• “Necessity is the mother of invention”
• Used for a son of a dental colleague with CII D1
who luxated Upper Cent. Incisor to
Clark W.J. Twin Block Functional Therapy: Applications in Dentofacial Orthopedics
(3rd Edition)

6. History
• First used on Sept 7th, 1977 by William Clark
• “Necessity is the mother of invention”
• Used for a son of a dental colleague with CII D1
who luxated Upper Cent. Incisor to
▫ Prevent lip trap posture mandible forward
▫ Prevent direct pressure on upper incisor
Clark W.J. Twin Block Functional Therapy: Applications in Dentofacial Orthopedics
(3rd Edition)

7. History
• First used on Sept 7th, 1977 by William Clark
• “Necessity is the mother of invention”
• Used for a son of a dental colleague with CII D1
who luxated Upper Cent. Incisor to
▫ Prevent lip trap posture mandible forward
▫ Prevent direct pressure on upper incisor
Clark W.J. Twin Block Functional Therapy: Applications in Dentofacial Orthopedics
(3rd Edition)

8. Concept
• Maximize growth response to functional mandibular proturusion
Clark W.J. Twin Block Functional Therapy:
Applications in Dentofacial Orthopedics (3rd
Edition)

9. Concept
• Maximize growth response to functional mandibular proturusion
Occlusal inclined plane
Displaces mandible downward and
forward
Unfavorable cuspal contacts of distal
occlusion replaced by favorable
proprioceptive contacts
Frees mandible from locked distal
functional position Clark W.J. Twin Block Functional Therapy:
Applications in Dentofacial Orthopedics (3rd
Edition)

10. 4

11. 4
• Protrusive function Sensory receptors in
muscles of mastication, teeth, tissues 
Functional response in underlying bone 
Adaptation to new favorable maxillomandibular
relation

12. 4
• Protrusive function Sensory receptors in
muscles of mastication, teeth, tissues 
Functional response in underlying bone 
Adaptation to new favorable maxillomandibular
relation
• Rapid soft-tissue changes  Muscles adapt

13. 4
• Protrusive function Sensory receptors in
muscles of mastication, teeth, tissues 
Functional response in underlying bone 
Adaptation to new favorable maxillomandibular
relation
• Rapid soft-tissue changes  Muscles adapt
• Bony changes gradual

14. Design
• Posterior bite-blocks with an inclined
plane
• Clasps
• Labial bow
• Screws – midline or saggital

15. What is the angle of the inclined plane of a twin block?

16. What is the angle of the inclined plane of a twin block?

17. Why is this angle selected instead of 45 degree inclined plane?

18. Answer
• 450 Inclined plane Apply equal downward and forward
component of force to the lower dentition Both
downward and forward stimulus to growth
Clark W.J. Twin Block Functional Therapy: Applications in Dentofacial Orthopedics (3rd Edition)

19. Answer
• 450 Inclined plane Apply equal downward and forward
component of force to the lower dentition Both
downward and forward stimulus to growth
• 700 Inclined plane More horizontal component of
forces More forward mandibular growth
Clark W.J. Twin Block Functional Therapy: Applications in Dentofacial Orthopedics (3rd Edition)

20. Should you instruct the patient to remove the twin block while
eating food?

21. Answer
• Twin blocks are designed to be worn 24hrs per
day to take full advantage of all functional forces
applied to the dentition, including forces of
mastication
Clark W.J. Twin Block Functional Therapy: Applications in Dentofacial Orthopedics (3rd Edition)

22. Types of Twin Blocks
1. Standard Twin Block
2. Sagittal Twin Block
11

23. 3. Reverse twin block
Clark W.J. Twin Block Functional Therapy: Applications in Dentofacial Orthopedics (3rd Edition)

24. Selection criteria for simple treatment

25. Selection criteria for simple treatment
1. Class II division 1 malocclusion (ideal but CII D2 & CIII can also
be treated)

26. Selection criteria for simple treatment
1. Class II division 1 malocclusion (ideal but CII D2 & CIII can also
be treated)
2. Uncrowded or decrowded dentition

27. Selection criteria for simple treatment
1. Class II division 1 malocclusion (ideal but CII D2 & CIII can also
be treated)
2. Uncrowded or decrowded dentition
3. Full unit distal occlusion

28. Selection criteria for simple treatment
1. Class II division 1 malocclusion (ideal but CII D2 & CIII can also
be treated)
2. Uncrowded or decrowded dentition
3. Full unit distal occlusion
4. Well-developed arches

29. Selection criteria for simple treatment
1. Class II division 1 malocclusion (ideal but CII D2 & CIII can also
be treated)
2. Uncrowded or decrowded dentition
3. Full unit distal occlusion
4. Well-developed arches
5. OJ < 10mm & deep overbite

30. Selection criteria for simple treatment
1. Class II division 1 malocclusion (ideal but CII D2 & CIII can also be
treated)
2. Uncrowded or decrowded dentition
3. Full unit distal occlusion
4. Well-developed arches
5. OJ < 10mm & deep overbite
6. Profile improve when the mandible is brought forward to correct OJ

31. Selection criteria for simple treatment
1. Class II division 1 malocclusion (ideal but CII D2 & CIII can also be
treated)
2. Uncrowded or decrowded dentition
3. Full unit distal occlusion
4. Well-developed arches
5. OJ < 10mm & deep overbite
6. Profile improve when the mandible is brought forward to correct OJ
7. Active grower

32. Bite registration

33. Bite registration
• Guide the mandible into planned position before
taking the bite

34. Bite registration
• Guide the mandible into planned position before
taking the bite
• A horseshoe-shaped wax bite rim is prepared

35. Bite registration
• Guide the mandible into planned position before
taking the bite
• A horseshoe-shaped wax bite rim is prepared
• Form the wax bite

36. Bite registration
1. Vertical opening :
• 2 mm interincisal space
• .

37. Bite registration
1. Vertical opening :
• 2 mm interincisal space
• Equivalent to an inter-premolar space of 5- 6 mm
• .

38. Bite registration
1. Vertical opening :
• 2 mm interincisal space
• Equivalent to an inter-premolar space of 5- 6 mm
2. AP :
• For most patients: edge to edge (if not uncomfortable)
• Facial profile should improve
• .

39. Bite registration
1. Vertical opening :
• 2 mm interincisal space
• Equivalent to an inter-premolar space of 5- 6 mm
2. AP :
• For most patients: edge to edge (if not uncomfortable)
• Facial profile should improve
• Maximum ~ 10mm
• .

40. Bite registration
1. Vertical opening :
• 2 mm interincisal space
• Equivalent to an inter-premolar space of 5- 6 mm
2. AP :
• For most patients: edge to edge (if not uncomfortable)
• Facial profile should improve
• Maximum ~ 10mm
• Must not exceed 70% of the total protrusive path (OJ measured with the mandible retruded
and in the position of maximum protrusion)
• .

41. Bite registration
1. Vertical opening :
• 2 mm interincisal space
• Equivalent to an inter-premolar space of 5- 6 mm
2. AP :
• For most patients: edge to edge (if not uncomfortable)
• Facial profile should improve
• Maximum ~ 10mm
• Must not exceed 70% of the total protrusive path (OJ measured with the mandible retruded and in the
position of maximum protrusion)
• .
Important to
1. Open the bite beyond the freeway space patient cannot retrude the mandible when in rest position

42. Bite registration
1. Vertical opening :
• 2 mm interincisal space
• Equivalent to an inter-premolar space of 5- 6 mm
2. AP :
• For most patients: edge to edge (if not uncomfortable)
• Facial profile should improve
• Maximum ~ 10mm
• Must not exceed 70% of the total protrusive path (OJ measured with the mandible retruded and in the
position of maximum protrusion)
• .
Important to
1. Open the bite beyond the freeway space patient cannot retrude the mandible when in rest position
2. Avoid making the blocks too thick  patient should be able to eat and speak comfortably with the
appliances in the mouth

44. Delivering the Appliance – Things to Explain

45. Delivering the Appliance – Things to Explain
1. Components and the function of the appliance Point out the 70 degree inclined planes.

46. Delivering the Appliance – Things to Explain
1. Components and the function of the appliance Point out the 70 degree inclined planes.
2. Explained that Twin Blocks achieve correction through the forces of occlusion.
 wear the appliances full time
 learn how to eat with the appliances in the mouth.
The twin block manual - Protec dental laboratory

47. Delivering the Appliance – Things to Explain
1. Components and the function of the appliance Point out the 70 degree inclined planes.
2. Explained that Twin Blocks achieve correction through the forces of occlusion.
 wear the appliances full time
 learn how to eat with the appliances in the mouth.
3. How to clean the appliances after each meal
The twin block manual - Protec dental laboratory

48. Delivering the Appliance – Things to Explain
1. Components and the function of the appliance Point out the 70 degree inclined planes.
2. Explained that Twin Blocks achieve correction through the forces of occlusion.
 wear the appliances full time
 learn how to eat with the appliances in the mouth.
3. How to clean the appliances after each meal
3. Prior to insertion, tell the patient about the improved facial esthetics they'll notice when
the appliances are fitted. After fitting, tell the patient that to permanently achieve the
facial esthetics, they will need to wear the appliances full-time throughout treatment. It
is helpful for the patient to see profile photo prior to and after fitting the appliance.
The twin block manual - Protec dental laboratory

49. Delivering the Appliance – Things to Explain
1. Components and the function of the appliance Point out the 70 degree inclined planes.
2. Explained that Twin Blocks achieve correction through the forces of occlusion.
 wear the appliances full time
 learn how to eat with the appliances in the mouth.
3. How to clean the appliances after each meal
3. Prior to insertion, tell the patient about the improved facial esthetics they'll notice when
the appliances are fitted. After fitting, tell the patient that to permanently achieve the
facial esthetics, they will need to wear the appliances full-time throughout treatment. It
is helpful for the patient to see profile photo prior to and after fitting the appliance.
4. Although the appliances will feel bulky initially to the patient, they will feel comfortable
in a few days.
The twin block manual - Protec dental laboratory

50. Vertical control

51. Vertical control
• Timing:1-2 months after the appliance was
inserted

52. Vertical control
• Timing:1-2 months after the appliance was
inserted
• Method: trimming the upper block to leave 1mm
clearance between bite and lower molar

54. What are the skeletal effects of Twin Block appliance?

62. Herbst vs. Twin Block: Which is better?

64. • OJ ≥ 7 mm
• second premolars erupted
• no craniofacial syndrome

67. Conclusions

68. Conclusions
• Phase I treatment is more rapid with the Herbst
appliance, but overall duration of treatment is
similar to that with the Twin-block

69. Conclusions
• Phase I treatment is more rapid with the Herbst
appliance, but overall duration of treatment is
similar to that with the Twin-block
• The Herbst appliance is prone to debonding and
component breakage

70. Conclusions
• Phase I treatment is more rapid with the Herbst
appliance, but overall duration of treatment is
similar to that with the Twin-block
• The Herbst appliance is prone to debonding and
component breakage
• There are no differences in the dental and skeletal
effects of treatment between the 2 appliances

71. Does Twin Block have an effect on the airway?

73. Methods
• Pre and post-treatment CBCT scans of 30
growing patients with TB treatment

74. Methods
• Pre and post-treatment CBCT scans of 30
growing patients with TB treatment
• 30 age-gender matched untreated controls with
the same diagnosis

75. Methods
• Pre and post-treatment CBCT scans of 30
growing patients with TB treatment
• 30 age-gender matched untreated controls with
the same diagnosis
• CBCT’s analyzed with MIMICS software

77. The pre- (T1) and post-treatment (T2) data of TB patients was registered.

78. The pharyngeal morphology and the hyoid bone were measured.

79. Findings
• During the TB treatment, the mandible moved
advanced by 3.52±2.14 mm in the horizontal
direction and 3.77±2.10 mm in the vertical
direction.
• The upper airway showed a significant
enlargement in nasopharynx, oropharynx and
hypopharynx.
• Hyoid bone moved to a more anterior

81. • 46 children (aged 9.7±1.5 years, BMI: 18.1±1.04 kg/m2 )

82. • 46 children (aged 9.7±1.5 years, BMI: 18.1±1.04 kg/m2 )
• Diagnosed with mandibular retrognathia and OSA by polysomnography (PSG)
but with no obesity or adenotonsillar hypertrophy

83. • 46 children (aged 9.7±1.5 years, BMI: 18.1±1.04 kg/m2 )
• Diagnosed with mandibular retrognathia and OSA by polysomnography (PSG) but
with no obesity or adenotonsillar hypertrophy
• PSG and cephalometric changes before and after appliance removal

84. • 46 children (aged 9.7±1.5 years, BMI: 18.1±1.04 kg/m2 )
• Diagnosed with mandibular retrognathia and OSA by polysomnography (PSG) but
with no obesity or adenotonsillar hypertrophy
• PSG and cephalometric changes before and after appliance removal
• AHI decreased from 14.08 ± 4.25 to 3.39 ± 1.86 (p < 0.01), and the lowest
SaO2increased from 77.78 ± 3.38 to 93.63 ± 2.66 (p < 0.01)

85. • 46 children (aged 9.7±1.5 years, BMI: 18.1±1.04 kg/m2 )
• Diagnosed with mandibular retrognathia and OSA by polysomnography (PSG) but with no obesity
or adenotonsillar hypertrophy
• PSG and cephalometric changes before and after appliance removal
• AHI decreased from 14.08 ± 4.25 to 3.39 ± 1.86 (p < 0.01), and the lowest SaO2increased from
77.78 ± 3.38 to 93.63 ± 2.66 (p < 0.01)
• Twin block appliance may improve the patient's facial profile and OSA symptoms in a group of
carefully selected children presented with both OSA and mandibular retrognathia symptoms

86. • 46 children (aged 9.7±1.5 years, BMI: 18.1±1.04 kg/m2 )
• Diagnosed with mandibular retrognathia and OSA by polysomnography (PSG) but with no obesity
or adenotonsillar hypertrophy
• PSG and cephalometric changes before and after appliance removal
• AHI decreased from 14.08 ± 4.25 to 3.39 ± 1.86 (p < 0.01), and the lowest SaO2increased from
77.78 ± 3.38 to 93.63 ± 2.66 (p < 0.01)
• Twin block appliance may improve the patient's facial profile and OSA symptoms in a group of
carefully selected children presented with both OSA and mandibular retrognathia symptoms

87. Take-home messages

88. Take-home messages
• Carful selection and an accurate bite registration
is important when using the Twin Block
appliance

89. Take-home messages
• Carful selection and an accurate bite registration
is important when using the Twin Block
appliance
• Patients should be encouraged to eat with the
appliance

90. Take-home messages
• Carful selection and an accurate bite registration
is important when using the Twin Block
appliance
• Patients should be encouraged to eat with the
appliance
• Twin Block appliances can improve the airway in
addition to the facial profile

91. Thank You