Biostatistics The Bare Essentials

1. The Peer Assessment Rating
(PAR) Index

2. OCCLUSAL INDICES - TYPES
(A) Peer Assessment Rating (PAR) Index -
quantitative
(B) Index of Treatment Need (IOTN) -
has 2 components
Dental Health
Component (DHC)
Aesthetic
Component (AC)

3. THE PEER ASSESSEMENT RATING (PAR)
INDEX
Index needed to assess results of treatment
and treatment standards
British Orthodontic Standards Working Party
(1987) - agreed on individual features of
malocclusion

4. THE PEER ASSESSEMENT RATING (PAR)
INDEX
- has 7 components:
(a) AP
(b) transverse relationship of buccal occlusion
(c) vertical
(d) centreline discrepancy
(e) overbite
(f) contact point displacement
(g) overjet
anterior occlusion

5. THE PEER ASSESSEMENT RATING (PAR)
INDEX
Scores are summed to give an overall score
which reflects deviation from normal
Score = 0 indicates excellent occlusion
Increasing scores (rarely > 50) indicates
increasing degrees of malocclusion
Scores assigned to study models only

6. TRANSPARENT PAR RULERS IN BLACK AND RED

7. PAR RULER
Evaluates buccal occlusion, from the canine to the first molar present, in occlusion
Buccal occlusion, transverse relationship
Buccal occlusion, vertical relationsip
Evaluates the centreline shift in relation to the width of one lower central incisor. If an incisor has been lost,
then the measurement is not recorded. (WEIGHTING X4)
Records the vertical overlap or open bite of the upper anterior teeth. Overbite is recorded in relation to the
overlap of the lower incisor or the degree of open bite. The recording zone includes the lateral incisors
(WEIGHTING X2)
The recording zone is from the mesial of the canine on one side to the mesial of the canine on the other side.
Crowding and spacing are recorded as the shortest points between the contact points of adjacent teeth in
relation to the occlusal plance. The greater the displacement, the greater the score
Positive as well as negative overjet is recorded. The recording zone is from the right to left lateral incisors, the
most prominent point of the most prominent incisor being used. The ruler is held radial to the line of the arch
and parallel to the occlusal plane (WEIGHTING X6)

8. Evaluation of buccal occlusion:
A-P
Recording zone is from the canine
to the last molar, both sides
Score
Good interdigitation: 0
Less than ½ unit from full interdigitation: 1
Cusp to cusp: 2

9. Evaluation of buccal occlusion:
transverse dimension
Both sided recorded

10. Evaluation of buccal occlusion:
vertical
Lateral open bite is recorded
where at least 2 teeth show
LOB > 2mm

11. Score
A-P relationship: ½ unit II: 1
Transverse: 2 molar teeth in crossbite: 3
Vertical: no open bite 0
Total 4

13. Evaluation of centrelines:
weighting x4
Upper centre line
Lower centre line
Centreline displaced
greater than ½ lower
incisor width
= 2
Weighting x4
= 8

14. Evaluation of overbite:
weighting x2
PAR score: 2
weighting x 2
Score: 4

15. Contact point displacements
Where a displacement is
greater than a particular line,
but not as large as the next
line, the larger displacement is scored by convention

19. 3
4
0
3
3
3+4+0+3+3 = 13

20. 3 2
1
3
3
3+2+1+3+3 = 12

21. Evaluation of overjet:
weighting x6
Recording zone is INCISOR teeth
When recording the overjet the
ruler is held parallel to the
occlusal plane and radial to the
line of the arch.
The most prominent point of the
most prominent upper incisor
is used for measurement

22. Overjet score = 1
Weighting x 6
= 6 PAR points

23. PAR Scoring
exercise:
Models PR

24. 3
4
0
3
3
3+4+0+3+3 = 13

25. 3 2
1
3
3
3+2+1+3+3 = 12

26. R buccal segment relationship: A-P: < ½ unit discrepancy: 1
Transverse: 0
Vertical: 0

27. L buccal segment relationship: A-P: < ½ unit discrepancy: 1
Trans: 2 teeth in xbite: 3
Vertical: no discrepancy 0

28. Centreline: > ½ width lower incisor discrepancy: 2
Weighting x 4 Score: 8

29. Overbite: 0 – 1/3rd coverage of lower incisors: 0

30. Overjet: scores 3 on ruler Also: 2/ in crossbite with 3/: scores 2
Total for overjet: 3+2 = 5
Weighting: x6, therefore unweighted score of 5 x 6 = 30

31. Models P.R. pretreatment
Upper labial segment score: 3 + 4 + 0 + 3 + 3 = 13
Lower labial segment score: 3 + 2 + 1 + 3 + 3 = 12
R buccal segment score: 1 + 0 + 0 = 1
L buccal segment score: 1 + 3 + 0 = 4
Centreline score (x 4): 2 x 4 = 8
Overbite score (x 2): 0 x 2 = 0
Overjet (x 6): (3+2) x 6 = 30
Total: 68

32. PR post-treatment

33. Upper labial segment alignment: 0 + 0 + 0 (2/2 extracted)

34. Lower labial segment alignment: 0 + 0 + 0 (2/2 extracted)

35. R buccal segment relationship: A-P: 1
Trans: 0
Vert: 0

36. L buccal segment relationship: A-P: 1
Trans: 1 tooth in xbite: 2
Vertical: 0

37. Centreline:
< ¼ lower incisor
width discrepancy
Score 0 x 4 = 0
Overbite:
< 1/3rd lower incisor
coverage
Score 0 x 2 = 0

38. Overjet score
0 x 6 = 0

39. Models P.R. postreatment
Upper labial segment score: 0 + 0 + 0 = 0 (13)
Lower labial segment score: 0 + 0 + 0 = 0 (12)
R buccal segment score: 1 + 0 + 0 = 1 (1)
L buccal segment score: 1 + 2 + 0 = 3 (4)
Centreline score (x 4): 0 x 4 = 0 (8)
Overbite score (x 2): 0 x 2 = 0 (0)
Overjet (x 6): 0 x 6 = 0 (30)
Total: 4 (68)
Pretx
Reduction of 64 PAR points or 94% reduction

40. THE PEER ASSESSEMENT RATING (PAR)
INDEX
Changes in weighted PAR score:
< 30% - Worse / no different
> 30% - Improved
> 22 points or 70% (whichever is greater)
- Greatly improved

41. PAR SCORE TREATMENT CHANGE NOMOGRAM
0 60
30
10 20 40 50
GREATLY
IMPROVED
IMPROVED
WORSE-NO DIFFERENT
*A
*B *C
PRETREATMENT SCORES
POSTTREATMENT SCORES
0
45
15
30

42. 0
5
10
15
20
25
30
35
40
45
0 10 20 30 40 50 60
RECALL PATIENTS – END OF TREATMENT PAR SCORES
Improved:
18.4%
Greatly
improved:
82%
Worse – no different 0%

43. RECALL PATIENTS – PAR SCORES OUT OF RETENTION
0
5
10
15
20
25
30
35
40
45
0 10 20 30 40 50 60
Greatly
improved:
30%
Improved:
53.5%
Worse – no different 16%

44. 0
10
20
30
40
50
60
0 PAR 1 PAR 2 PAR 3
All PAR scores at start and end treatment and recall

45. 60
50
40
30
20
10
0
T1 T2 T3
Mean 35.07 6.09 16.32
S.D 7.37 4.41 7.92
Time 1 Time 2 Time 3
PAR SCORES AT TIMES 1, 2, AND 3
Mean relapse: 46%

46. UPPER LABIAL SEGMENT ALIGNMENT (PAR)
Time 1 Time 2 Time 3
14
12
10
8
6
4
2
0
-2
T1 T2 T3
Mean 5.45 0.14 1.88
S.D 2.84 0.4 1.66
Mean relapse: 34%

47. LOWER LABIAL SEGMENT ALIGNMENT (PAR)
N =
20
10
0
-10
Time 1 Time 2 Time 3
T1 T2 T3
Mean 3.64 0.09 2.21
S.D 2.77 0.35 1.89
Mean relapse: 60%

48. PAR SCORES AT RECALL
0
10
20
30
40
50
60
Excellent
< 5
Good
6-10
Fair
11-15
Other
16+
% of patients

49. OVERJET CHANGES (MILLIMETRES)
20
10
0
-10
Time 1 Time 2 Time 3
T1 T2 T3
Mean 10.2 4.1 5.6
S.D 2.4 1.88 2.12
mm

50. EXAMPLE 1: SABRINA
No relapse

51. Example 1: Sabrina PAR score start tx: 25

52. Sabrina: end of tx PAR score: 3

53. Sabrina 2 years out of retention: PAR score 2

54. EXAMPLE 2: ANDREA
30% relapse in PAR score

55. Andrea Initial PAR score 33

56. Andrea Postx PAR score 4

57. Andrea 2 years out of retention: PAR score 10

58. EXAMPLE 3: GERALDINE
50% relapse in PAR score

59. Geraldine Initial PAR score 42

60. Geraldine Postx PAR score 7

61. Geraldine: 2 years out of retention: PAR score 21

62. EXAMPLE 4: MARY
100% relapse in PAR score

63. Mary Pretx PAR score 30

64. Mary Postx PAR score 3

65. Mary: 2 years postretention PAR score 30

66. So, how do we compare?

67. Follow-up studies: PAR scores
100
80
60
40
20
0
Fox and
Chadwick, 1995
% PAR
score
reduction
T1 T2 T2a T3 T5 T10
End retention

68. Follow-up studies: PAR scores
Otuyemi and
Jones, 1996
Fox and
Chadwick, 1995
% PAR
score
reduction
T1 T2 T2a T3 T5 T10
End retention
100
80
60
40
20
0

69. Follow-up studies: PAR scores
Al Yami et al,
1999
Otuyemi and
Jones, 1996
Fox and
Chadwick, 1995
% PAR
score
reduction
T1 T2 T2a T3 T5 T10
End retention
100
80
60
40
20
0

70. Follow-up studies: PAR scores
Al Yami et al,
1999
Otuyemi and
Jones, 1996
Fox and
Chadwick, 1995
MPH 2003
% PAR
score
reduction
T1 T2 T2a T3 T5 T10
End retention
100
80
60
40
20
0
Woods et al, 2000
Linklater and Fox,
2002 (6.5 yrs postx)

71. (Not
to
scale.
Copyright
Victoria
University
of
Manchester)
THE PAR INDEX TRANSPARENT RULER
Evaluates buccal occlusion, from canine to the last molar present, with the
teeth in occlusion
ANT-POST
0 None
1<1/2 unit dis
2=1/2 unit dis
TRANSVERSE
0 None
1 xbite tend >= 1t
2 1 tooth in xbite
3 > 1 tooth in xbite
4 > 1 tooth in sb
VERTICAL
0 None
1 Openb 2t>2mm
CENTRELINE
0 <= 1/4
1 1/4 - 1/2
2 > 1/2
OVERBITE
0 0 - 1/3 Open b
1 1/3 - 2/3
2 >2/3
3 >= FTC
4
CONTACT Pt
0
1
2
3
4
5 Impacted tooth
THE
PAR INDEX
Manchester
OVERJET
4 >2t xb
3 2t xb
2 1t xb
1 e to e
0
Buccal occlusion transverse relationships
Buccal occlusion vertical relationships.
Records the centreline discrepancy in relation to the width of one of the lower
central incisors. If a lower incisor is missing, the measurement is not recorded..
WEIGHTING: x4
Records the vertical overlap or open bite of the anterior teeth. Overbite is recorded
in relation to the coverage of the lower incisors or the degree of anterior open bite.
The recordign zone includes the lateral incisors. WEIGHTING: x2
The recording zone is from the mesial of the canine on one side to the mesial of the
canine on the opposite side. Crowding and spacing are recorded as the shortest
distances between contact points of adjacent teeth in relation to the occlusal plane.
The greater the displacement, the greater the score
Positive as well as reverse overjet is recorded. The recording zone is from the left to
right lateral incisors, the most prominent point of any incisor being used. The ruler is
held parallel to the occlusalplane and radial to the line of the arch. WEIGHTING: x6