The literature referred to here provided information concerning the epidemiology of hypodontia and
its association with other developmental anomalies. Current research with the major developments in molecular biology has focused on the genetic component of the aetiology mainly on animals. Limited information has been gained
from human studies concerning the morphology of different teeth in hypodontia. The present research is both methodological and investigative in nature.
The aims of this study were to measure crown morphology of the permanent dentitions for hypodontia subjects divided
according to severity of hypodontia into mild, moderate and severe groups and a control group, and then to compare the measurements of groups. All subjects were of white Caucasian origin and were unrelated. The study groups were balanced for size (N = 40), gender (N = 20) and age. The effect of both severity of hypodontia and gender were examined. The total study population was N= 161.
A new measurement system using image analysis and new measurement index for tooth taper were developed,
validated and then utilised in the main study. The image analysis technique and tooth taper measurement were validated against the classical manual measurements and subjective scoring respectively. The errors of measurements were assessed by duplicate measurements to determine the intra- and inter-observer reproducibility. It was found that measurements for all study variables were repeatable without systematic error and with small method error. Comprehensive measurements (N = 15) were obtained from both the buccal and occlusal views for
the following dimensions of tooth crowns: The principal mesiodistal (MDb and MDo) and buccolingual (BL), proportional mesiodistal (MD25, MD50 and MD75) and
buccolingual (BLm and BLd), occlusogingival
(OG), perimeter (Pb and Po), area (Ab and Ao) and the distance between MDb and occlusal level (Db) and between MDo and buccal border of tooth crown
(Do). A number of indices (N = 5) to evaluate
tooth crown morphology were also calculated: Tooth
taper determination index (MD50/MD75), crown indices
of buccal morphology (CIBMI and CIBM2 i.
e. MDb/OG and Db/OG respectively) and crown indices of occlusal morphology
(CIOMI and CIOM2 i. e. MDo/BL and Do/BL
respectively). Two-way analysis of variance
followed by multi-comparison
tests with Bonferroni
adjustment
for
the significance
levels were employed
in
the main study.
The
results of the main study revealed significant differences between hypodontia groups
and control subjects
for
the following measurement variables: MDb, Db, OG, Pb, Ab,
MD25, MD50, MD75, tooth taper, CIBM2, MDo, Do, BL, Ao, Po, BLm and BLd.
Hypodontia subjects demonstrated
significantly smaller measurement values
than controls
except Db, tooth taper and CIBM2. The
severity of hypodontia affected
the degree of
difference in
tooth morphology;
for many variables
the more severe the hypodontia the
greater the difference from
controls. There were only a
few
significant
differences between
hypodontia
and control groups
for
the variables CIBM1, CIOM1 and CIOM2.
Gender differences (within groups)
indicated
that males
tend to show
larger measurements
than females
although
few findings
reached statistical significance.
The symmetry of right and
left measurements
(MDb and tooth taper), the number of cusps
in
the premolar and molar teeth and the intermaxillary
ratios were
investigated. The
findings
suggest that asymmetry
in bilateral measurements appeared to be increased in
hypodontia
subjects. Descriptive data also suggest that all the intermaxillary
ratios
tend to
be larger in hypodontia than the control group. There was a tendency for the reduction
in
the number of cusps
for hypodontia
subjects than controls. Again, these
findings were
related to severity of hypodontia.
Thus,
variation
in tooth morphology
in patients with hypodontia was clearly established.
The differences were related to the severity of the condition. However, there were also
variations
in
the measurements between individuals with hypodontia
of the same severity
group. A possible explanation
is the multifactorial aetiology of the condition.
In certain
groups, especially with severe hypodontia,
the small numbers of some tooth types which
developed may also have influenced the results.
CORE (COnnecting REpositories)
CORE (COnnecting REpositories)