International Journal of Applied Dental Sciences 2023; 9(1): 156-159

ISSN Print: 2394-7489

ISSN Online: 2394-7497
IJADS 2023; 9(1): 156-159 Redefining tweed’s headplate correction and its
© 2023 IJADS
www.oraljournal.com
implications in dental arch space requirement
Received: 07-10-2022
Accepted: 19-11-2022
Dr. Mohsin Aslam Wani, Dr. Anjali Thapa, Dr. Payal Jyoti Dash and Dr.
Dr. Mohsin Aslam Wani Nadeem Hassan
MDS Orthodontics and
Dentofacial Orthopaedics,
DOI: https://doi.org/10.22271/oral.2023.v9.i1c.1673
Private Practitioner, Srinagar,
Jammu and Kashmir, India
Abstract
Dr. Anjali Thapa The cephalometric appraisal of mandibular incisor teeth in relation to the mandibular basal bone had its
MDS Orthodontics and origin in the clinical outcomes that Tweed observed in his treated cases. Although was an admirer of
Dentofacial Orthopaedics, Angle’s philosophy, failure to achieve functional and aesthetic harmony in some of the orthodontically
Private Practitioner, East treated cases prompted Tweed to introspect his methodology and revisit the records of his patients.
Sikkim, India Consequently, based on his clinical annotations and cephalometric aid, a Diagnostic Facial Triangle was
framed to assess the severity and difficulty in treating various degrees of malocclusions in routine
Dr. Payal Jyoti Dash orthodontic practice. Furthermore, a simple and effective method in the form of Headplate/Cephalogram
MDS Orthodontics and Correction was also developed to quantify the extent of space requirements for rectifying prognathic
Dentofacial Orthopaedics, Senior
dentures.
Lecturer, Sree Sai Dental College
& Research Institute,
Srikakulam, Andhra Pradesh, Keywords: Tweed, diagnostic facial triangle, mandibular incisor teeth, incisor mandibular plane angle
India (IMPA), headplate/cephalogram correction

Dr. Nadeem Hassan Introduction

MDS Orthodontics and In the evolutionary development of man, the size of the brain has increased, coupled with the
Dentofacial Orthopaedics,
reduction of the lower third of the face and the lingual tipping of the incisors on a horizontal
Private Practitioner, Patna,
Bihar, India axis, with their apex at or near the point of the rotation. Early anthropoids have shown
prominent supraorbital ridges that serve as buttresses to withstand the impact of occlusion, a
retreating frontal bone associated with procumbent mandibular incisors. However, in modern
man, the frontal bones have become more upright, and a long forehead has developed to
compensate for the disappearance of the supraorbital ridges. Likewise, the mandibular incisors
have become more upright with the reduction of the alveolar bone, loss of the simian shelf,
and the consequent development of the chin. All this evolutionary process is an excellent
example of functional adaptation [1]. Tweed intended to establish the practical relevance of
anthropometric measurement of the dentofacial region in the realm of orthodontic treatment by
demonstrating the harmony between his clinical results and the scientific facts. He believed
that orthodontic tooth movement can cause the failure of the treatment and arch collapse if the
incisor teeth are displaced off the medullary bone area of the mandibular body. Therefore,
Tweed advocated for the uprighting/lingual tipping of the incisors and reduction in tooth
material by means of extraction in pursuit of better aesthetic outcomes and stable results,
especially in cases where the incisor teeth were excessively proclined or where the
development of the jaw itself was primarily insufficient to accommodate the full complement
of teeth over medullary bone. This was in accordance with the evolutionary trends in the
development of man and that forward tipping of these teeth by any orthodontic means will
actually depict an evolution in the reverse direction. Since then, many clinicians have accepted
the principle of “uprighting”, or at least of not increasing the procumbence of the mandibular
Corresponding Author:
Dr. Mohsin Aslam Wani incisor teeth [2].
MDS Orthodontics and
Dentofacial Orthopaedics, Mandibular incisor position and angle in relation to the lower border of the mandible
Private Practitioner, Srinagar, Brodie demonstrated the angular constancy of the lower border or base of the mandible when
Jammu and Kashmir, India
related to any fixed point by always remaining virtually the same. In other words, the nature
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and pattern of growth of the mandibular body and the planes orthodontic normal patients, the mandibular incisors must be
formed by the mandibular base right from the natal phase to positioned at an angle of 90° or 0° with the normal range of -
adulthood are almost always parallel to one another [3]. 5° to +5°. Achieving this by over-expansion of the arches can
Margolis was the first to relate the axial inclination of the cause impaction of both the unerupted second and third
mandibular central incisor teeth with the sagittal plane, molars, thereby a major cause of relapse. Extraction was the
tangent to the most dependent points on the lower border of only alternative approach. Tweed also emphasized on the
the mandible. He named the angle formed by the interception importance of maintaining the integrity of the occlusal plane
of the long axes of the mandibular incisors with the plane during the duration of orthodontic treatment, especially in
formed by the lower border of the mandible, the incisor patients with favorable growth trends, and considered
mandibular plane angle (IMPA) [4]. Furthermore, in a study of controlled force application as the primary key for preventing
Caucasian children with normal dentitions and non- any undesirable changes in the occlusal plane. The advent of
prognathous faces, he observed that 90 percent of 300 cephalometry also benefited him in observing the growth
subjects examined had the mandibular incisors at right angles process and was also alarming at the behavior of the occlusal
to the mandibular plane and therefore the incisor mandibular plane during and following orthodontic treatment [8].
plane angle (IMPA) was 90 degrees, and the variation was
less than 5 degrees either way [5]. Margolis emphasized the The diagnostic facial triangle and Headplate /
philosophy which calls for distal movement of the denture in Cephalogram correction
prognathic faces to maintain its normal relationship with the In quest of converting unfavorable cases into favorable
rest of the head structures during orthodontic treatment and results, Tweed introduced two more angles following his
this according to him invariably depended upon the degree to visual clinical investigations of 100 samples, the Frankfort
which the mandibular incisors can be placed and maintained Mandibular Plane Angle (FMA) with a mean value of 25° and
in an upright position over the medullary bone of the body of consequently the Frankfort Mandibular Incisor Angle (FMIA)
the mandible [5]. of 65°. Frankfort-Horizontal Plane was drawn by connecting a
Brodie in 1940, observed the cephalometric records of 21 point 41/2 mm above the geometric center of the ear rod with
normal children, consisting of fourteen sets of headplates the lower border of the orbit. The mandibular plane is drawn
taken quarterly during the first year of life, semi-annually along the lower border of the mandible and is extended
from 1 to 5 years of age, and annually from then on. The posteriorly to connect with the Frankfurt plane. The third
average for these cases was an incisor mandibular plane angle plane of the triangle is formed by extending the long axis of
of 88.3°, therefore considered to be vertical or upright [6]. the mandibular central incisor to intersect the mandibular
Broadbent in 1941, collected data of normal dentofacial plane below and the Frankfurt plane above. This completed
developmental growth from the Bolton Study records of 3,500 the diagnostic facial triangle (Figure 2). In order to arrive at
white Cleveland children and observed the average of incisor an acceptable FMIA and to achieve mandibular incisor
mandibular plane angle (IMPA) to be 87.9°, which is within uprighting, a three-point formula was formulated by Tweed:
0.4° of the average for the normal reported by Brodie [7]. The 1. In patients with FMA greater than 30°, it will be
findings of Brodie and Broadbent were arrived at necessary to attain FMIA of 65°.
independently by them. 2. In patients with FMA ranging between 20° and 30°, an
average of 68° FMIA is acceptable.
The tweed discourse 3. In patients with FMA below 20°, an effort should be
Dr. Tweed was unhappy with his treatment results, even after made not to exceed an IMPA greater than 94° [8, 18].
advocating the non-extraction philosophy of Angles
Orthodontic treatment for more than 6 years, he was unable to Tweed’s Headplate Correction/Discrepancy is a clinical
achieve balance and harmony of the face in some of his method of calculating the amount of space that is required for
patients, consequently prompting him to change his practice, the uprighting/lingual tipping of the mandibular incisors in
rather drastically, his methods of procedure in entirety. The addition to the tooth material-arch length deficit. Earlier in the
two factors that influenced this change were, firstly, the facial Tweed era, this was done by drawing the diagnostic facial
contours of some of his patients that were not improved as a triangle directly on the Headplate/X-ray radiographic film
result of treatment, but rather progressed to become more with white ink. However, for more than the past 4 decades,
prognathous; and, secondly, in some other cases the teeth this procedure has been carried out on the roentgenographic
again became irregular, and a relapse of malocclusion was cephalometric tracing sheets, hence the alternate name,
seen even after the retention period was over [1]. In 1934, Cephalogram Correction [9].
Tweed undertook a retrospective analysis of his practice
results. He observed that those individuals possessing balance Steps to arbitrarily measure Headplate/Cephalogram
and harmony of facial proportions and a normal occlusion, correction (Method 1)
possess mandibular incisors upright over the basal bone. 1. Draw the diagnostic facial triangle as per the actually
Tweed defined normal as, in addition, to correct occlusal observed angles for the patient’s FMA, FMIA and IMPA.
relationship, must have all five of the other characteristics as 2. Draw a dotted line upward starting from the apex of the
outlined in the correct interpretation of Angle’s definition of mandibular incisor to intersect the FM plane at the
the line of occlusion and must possess a facial growth pattern desired/acceptable angle of FMIA and/or IMPA in
normal in its totality. The first angle of the diagnostic facial accordance with the Tweeds three-point rationale.
triangle IMPA was finally established after clinical research 3. This dotted line indicates the desired axial inclination of
covering a period of approximately 12 years. Moreover, he the mandibular incisor teeth.
concluded that the degree of disharmony in facial contour was 4. The distance between the solid line (actual inclination of
in direct proportion to the extent to which the denture base mandibular incisor) and the dotted line (desired/projected
mesially displaced into the protrusion and that in order to incisal inclination) is measured in millimeters along the
attain facial aesthetics similar to those found in non- occlusal plane of incisal edges (Figure 2) and multiplied
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by “2” (considering both sides of the dental arch), noteworthy to mention that Tweed’s diagnostic facial triangle
representing the amount of lingual tipping (headplate norms should only be used as a guide and not as an absolute
correction) necessary to satisfy the proposed FMIA [8, 9, benchmark for all diverse racial or ethnic groups. Hence,
10]
. using specific norms for specific races or ethnic groups will
help us in achieving more accurate diagnosis and treatment
This measurement obtained is combined with arch length planning [13, 16, 17, 19].
discrepancy to calculate the total discrepancy in millimeters.

Steps to precisely measure Headplate/Cephalogram

Correction (Method 2)
According to tweed, 12° of lingual inclination yields 5 mm of
space, or 1° = 0.8 mm approximately, for both sides of the
arch [11]. However, considering that a controlled crown tipping
of mandibular incisor tooth with negligible root apex
displacement is produced along an arc, the exact amount of
space (mm) obtained per degree of inclination change (°) can
be precisely calculated by following these steps:
1. Repeat steps 1, 2 and 3 as described above.
2. Use the Divider with a pencil holder. Place the metal
pointed tip of the divider at the apex of the mandibular
incisor tooth and extended the divider along its long axis,
such that the pencil tip touches the incisal edge of the
mandibular incisor over the solid axial inclination line.
3. Draw an arc, extending from the solid line (actual incisal
inclination) up to the dotted line (desired incisal
inclination). The circumference of the arc represents the
line of lingual tipping. (Figure 3) Fig 1: Tweed’s Diagnostic Facial Triangle
4. Use the mathematical formula:
, where S denotes arch length (cm), r is the
radius (axial length from apex to the incisal edge in cm),
is the angle formed between actual and proposed IMPA
axial lines.
5. Multiply it by “2” (considering both sides of the dental
arch) and dividing by "10" (converting cm into mm).
Therefore, the actual amount (mm) per degree change (°)
in the inclination of mandibular incisor teeth (headplate
correction) is obtained.
Fig 2: Tweed’s Headplate Correction-Method 1
Significance of Headplate/Cephalogram Correction
1. To determine the severity of malocclusion in mixed
dentition cases and perhaps undertake preventive and
interceptive treatment protocols such as serial extraction.
2. To determine the difficulty in treating the malocclusion
and therefore employ the favorable treatment mechanics
at the onset of fixed mechanotherapy.
3. To evaluate the extraction/non-extraction fate of the
permanent dentition [11].
Fig 3: Tweed’s Headplate Correction-Method 2
Conclusion
Determination of the lower incisor position and IMPA value Acknowledgement: Nil.
is crucial for orthodontic treatment planning. In Class II
subjects, with a proclined lower incisor, the apex lies near the Conflict of interest: Nil.
lingual cortex, whereas In Class III subjects, with a
retroclined lower incisor, the apex approaches the buccal Financial support: Nil.
cortex [12]. Several investigators have reported and signified
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How to Cite This Article

Mohsin AW, Anjali T, Payal JD, Nadeem H. Redefining tweed’s
headplate correction and its implications in dental arch space
requirement. International Journal of Applied Dental Sciences 2023;
9(1): 156-159.

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