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Peer-reviewed paper; submitted December 2021; accepted January 2022.
Dental health in a cohort of six-year-old
New Zealand children who were breastfed as
infants – a comprehensive descriptive study
Beckett DM, Wheeler BJ, Loch C, Mahoney EK, Drummond BK, Broadbent JM
Abstract
Background and objectives: Enamel defects occur during
tooth formation. Identifying variances in presentation
and prevalence between and within countries can help
researchers identify potential causes requiring further
investigation. Children with an early mixed dentition are
at an increased risk of dental caries and reliant on others
to control their diet and provide oral hygiene assistance.
Breastfeeding is recommended by the WHO for the first
six months of life and there has been some controversy
around breastfeeding in relation to dental caries risk.
This study investigated dental enamel defects and dental
caries in relation to tooth eruption, diet, and oral hygiene,
in a cohort of 6-year-old South Island, New Zealand
children who were breastfed as infants.
Methods: 120 children were followed prospectively
since birth as part of a breastfeeding study. Participants
completed a dental questionnaire and were dentally
examined for caries and developmental defects of
enamel at age 6 years.
Results: 82 participants were included in this study.
The mean age was 6.6 years, 52% were male, and
80% resided in areas of low or medium deprivation.
All participants had been breastfed for at least 5 months,
with 9% being breastfed beyond 2 years. Two thirds of
participants had at least one tooth affected by an enamel
defect, with a mean of 6.12 (SD 4.34) affected teeth/
affected participants, while half had experienced dental
caries. No statistically significant differences were found
with breastfeeding duration and dental caries, however
there was a trend towards increased dental caries
experience and severity with prolonged breast feeding
beyond 24 months.
Conclusions: The prevalence of enamel defects and
dental caries among participants was high relative to
national and international data. Breast feeding for
<24 months was not associated with dental caries.
Introduction
Contributing factors for dental caries include the
presence of dental anomalies, poor diet, poor oral
hygiene, and socio-economic deprivation (Schwendicke
et al. 2015). Children with an early mixed dentition are
at a high risk of dental caries due to the presence of
smaller and less resistant primary teeth, the eruption of
immature permanent teeth, and reliance on others to
control their diet and provide oral hygiene assistance
(Schwendicke et al. 2015). Regarding developmental
enamel defects, disturbances during secretion of
the enamel matrix can result in hypoplasia, while
disturbances or alterations during the maturation
(mineralisation) phase can result in hypomineralisation
(Elhennawy et al. 2017). Enamel hypomineralisation can
range in severity, and the appearance of affected enamel
may include demarcated opacities (creamy, white, yellow,
or brown), and may result in post-eruptive breakdown
(Elhennawy et al. 2017). Teeth with hypoplastic or severe
hypomineralisation defects can be hypersensitive, and
due to the weaker enamel structure and subsurface
porosities, these teeth may be more susceptible to dental
caries (Vargas-Ferreira et al. 2015). Hypomineralisation
can affect any tooth but is most frequently observed
on first permanent molars (FPMs) and permanent
incisors, and this condition is referred to as Molar
Incisor Hypomineralisation (MIH) (Weerheijm et al. 2003).
Approximately 15% of New Zealand children have MIH
(Mahoney and Morrison 2009; 2011). Second primary
molars form at around the same time as FPMs, and
approximately 5-6 % of children present with affected
enamel in these teeth, and sometimes also on primary
canines (Owen et al. 2017). Internationally, enamel defect
prevalence is anywhere between 10-50%, or 30% in the
primary dentition (Allazzam et al. 2014; Basha et al. 2014).
NZ studies report enamel defect prevalence as between
35 – 63%; however, the indexes used, teeth included, and
age of participants vary between studies (Kanagaratnam
et al. 2009; Mackay and Thomson 2005; Mahoney and
Morrison 2009; Suckling and Pearce 1984).
Breastfeeding is naturally the first nutrition for the
majority of infants worldwide and provides ideal early life
nutrition for children, with a recommendation from the
World Health Organisation for six months of predominant
or exclusive breastfeeding (WHO 2003). A recent
systematic review examined the relationship between
breastfeeding and early childhood caries and concluded
that breastfeeding up to 12-months protects against
tooth decay (Tham et al. 2015). Data on breastfeeding
beyond 12 months has produced mixed findings, with
nocturnal breastfeeding after 12 months-of-age (when
the primary teeth are erupting) appearing to have the
greatest associated risk of dental caries (Tham et al.
2015). Few studies have examined the epidemiology of
hypomineralisation in the context of prior breastfeeding.
One study has reported that children who were not
Volume 118 March 2022 5
breastfed could be considered at risk for developing
dental enamel defects, and another suggesting that
prolonged breastfeeding may increase the risk of
mineralisation defects (Alaluusua et al. 1996; Lunardelli
and Peres 2006).
Given the lack of clear data in this area, we conducted
a prospective observational study to investigate dental
health in a cohort of New Zealand children with a history
of exclusive or predominant breastfeeding for at least the
first 20 weeks post-partum (as per WHO standards (WHO
2003)). This study aimed to describe the oral health care
habits and stage of tooth eruption for participants, as
well as the prevalence and severity
of both dental caries and dental enamel defects.
Methods
Study population
Children from Dunedin New Zealand who participated
in a previous observational study investigating vitamin
D status throughout pregnancy and exclusive lactation
(n-127) (Wheeler et al. 2017), followed by a subsequent
randomized controlled trial (RCT) of a postnatal maternal
vitamin D intervention during exclusive breastfeeding
(Wheeler et al. 2016), were invited to participate in this
study. At the time of recruitment into the dental study,
participants were aged five to six years. The methods
of the previous studies have been described elsewhere.
(Wheeler et al. 2017; Wheeler et al. 2016) Inclusion criteria
were pregnant women intending to exclusively breastfeed
for at least 20 weeks postpartum and their babies (post
birth); and exclusion criteria were premature delivery
(prior to 37 weeks gestation), intent to use postnatal
vitamin D supplementation, and a history of disorders
known to affect calcium and/or vitamin D metabolism.
For the current study, inclusion criteria were participation
in the previous 2012 trial and being at least 5.5 years
of age at time of clinical assessment, and exclusion
criteria were inability to cope with a comprehensive
dental examination.
Study procedures
All parents gave informed consent for their children to
participate, and all children gave assent to be dentally
examined. Background demographic information
was collected using a questionnaire, and baseline
demographic information available through the previous
RCT was updated. Deprivation status was measured
using NZ Deprivation index 2018 (NZDep2018), a well-
recognized measure of socioeconomic deprivation in
New Zealand (University of Otago 2018). Standard oral
health information was collected to determine caries
risk status, exposure to sources of fluoride (toothpaste
levels, fluoridated water, mouth rinse, etc.), nutrition
(including sugar and dairy consumption), medical history,
and homecare habits such as toothbrushing frequency,
whether a caregiver helps with brushing, and if a
fluoridated toothpaste is used.
A comprehensive clinical dental assessment was
conducted (by DB) and calibration for dental caries
and enamel defects diagnosis was undertaken (by
EM). Tooth surfaces were examined both wet and dry,
using an overhead dental light, flat head dental mirror
and a periodontal probe to evaluate the integrity of the
enamel surfaces. Carious lesions were visually assessed
and classified using the International Caries Detection
and Assessment System (ICDAS-II) (Ismail et al. 2007).
Posterior Bitewing radiographs were taken at the
University of Otago Faculty of Dentistry if not available in
the previous twelve months from the child’s usual dental
provider. Lesions were classified using ICDAS-II, and
radiographs read by two calibrated paediatric dentists
(EM and BD). In cases of disagreement, two further
dental academics (DB – dental therapist and JMB –
dental public health specialist) reviewed these and
came to a consensus on the coding. Enamel defect
identification involved visual inspection of wet tooth
surfaces. Teeth were examined for the absence
or presence of demarcated and diffuse opacities,
hypoplasia and/or post eruptive enamel breakdown.
Atypical restorations, extractions, and delayed eruption
of teeth were recorded. Both the European Academy
of Paediatric Dentistry guidelines for diagnosis of MIH
(EAPD for MIH), and the Modified Defect of Dental
Enamel Index (DDE Index) were used to classify buccal,
lingual, and occlusal surfaces of all teeth present
(Clarkson and O’mullane 1989; Ghanim et al. 2017).
This study and the previous study approved by the
New Zealand Lower South Regional Ethics Committee
(H18/001) and (LRS/11/02/007). The original RCT study
was also registered prior to commencement with the
Australian New Zealand Clinical Trials Registry at
ww w.anzctr.o rg.auasACTR N1261100010 8910.
Statistical analyses
Caries severity was coded for analysis using both the
decayed, missing and filled teeth (dmft) index, and
decayed, missing and filled surfaces (dmfs) index
(Bödecker and Bödecker 1931). Primary and permanent
teeth mean scores were combined to create a count
for the whole mouth. Enamel defects were presented
within the categories of demarcated opacities, diffuse
opacities, hypoplastic defects, and unknow cause.
The mean number of defects were calculated across
participants with affected teeth only, and demarcated
opacities were dichotomised into mild (white or cream)
and moderate to severe (yellow/brown, PEB, atypical
restoration or extraction due to defect). Breast feeding
data were divided across three duration groups, less than
12 months, 12-23 months, and longer than 24 months.
Statistical analyses were conducted using I/C Stata
16.0. A p-value of <0.05 was deemed statistically
significant. Associations between independent
variables were tested for statistical significance using
the chi-square test for categorical variables while non-
parametric analyses (such as the Kruskal-Wallis H test or
Mann-Whitney U test) were used for skewed continuous
variables such as caries experience.
NZ DENTAL JOURNAL
6
Results
In total, 119 children were invited to participate in this
study; 38 eight had either left the area or declined
consent, and 81 were included (Figure 1). Most children
identified as NZ European, and the mean age was
6.6 years (SD 0.6). One in five children resided in areas
of high deprivation (NZ Dep score 8-10), while 37%
resided in areas of low deprivation (NZ Dep score 1-3).
Most mothers did not smoke during pregnancy (90%),
and no participants were born preterm. All participants
were born between November 2011 and September 2013
at the Queen Mary tertiary maternity unit in Dunedin, and
all were exclusively or predominantly breastfed for the
first 20 week of life (Table 1). Breastfeeding data post
20 weeks were missing for 4 participants (5%), and most
were breastfed for 12 months or longer.
Over half of the participants had experienced
dental caries by the time of dental assessment, and
the prevalence was similar among males and females
(Table 2). The mean number of decayed, missing or
filled teeth in both the primary and permanent dentitions
combined was 1.9 (SD 2.8). Data were right skewed, and
dmft scores ranged from 0 to 17. Only one participant
presented with caries in a permanent tooth. The mean
dmft/DMFT score was higher among those living in areas
of high deprivation at 2.6 (SD 4.2), than those living in
medium or low areas of deprivation at 1.8 (SD 2.2) and
1.7 (SD 2.6), respectively. When looking at duration of
breastfeeding, there were no statistically significant
% "
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Figure 1. Participation flowchart
Table 1. Participants’ characteristics
Characteristics Current Study
N=811
Did not participate
n=46
Sex
Male 42 (52.0) 26 (57.0)
Female 39 (48.0) 20 (43.0)
Mean age at dental exam (SD) 6.6 (0.6) N/A
Ethnicity, n (%)
NZ European 71 (88.0) 33 (72.0)
NZ Māori 6 (7. 0 ) 2 (4.0)
Other3 4 (5.0) 11 ( 24.0)
Deprivation Index2, n (%)
1-3 (Low ) 30 ( 3 7. 0 ) 14 (31.0)
4-7 (Medium) 35 (43.0) 19 (42.0 )
8-10 (Hig h ) 16 (20.0 ) 12 ( 2 7. 0 )
Mean gestation (weeks) 39.7 (1.1) 3 9 .7 (1.1)
Breastfeeding duration1
<12 months 24 (29.0) *
12-23 months 38 (46.0) *
24 + months 16 (20.0 ) *
Missing BF duration data 4 (5.0) *
Maternal characteristics
Maternal smoking during pregnancy, n (%)
Yes 8 (10.0) 1 (2.0)
No 73 (90.0) 45 (98.0)
Mean age at delivery 33.5 (4.6) 31.7 (5.3)
1 All children were breastfed until 20 weeks
2 NZ Deprivation Index 2018
3 Other ethnicity = Japanese (1), Sinhalese (2), Unknown (1)
* Breastfeeding information post 20 weeks unknown for participants who did not participate
Volume 118 March 2022 7
Table 2 . Dental caries experience and severity by participant characteristics, caries risk factors and enamel defects
Characteristics dmft/DMFT1
Mean (SD)
dmfs/DMFS2
Mean (SD)
Any caries present
N (%)
Overall 1.9 (2.8 ) 5.3 (10.6) 45 (56)
Sex
Male 1.9 (3.0) 5.7 (12.5) 22 (52)
Female 2.0 (2.5) 4.8 (8.1) 23 (59)
Ethnicity
NZ European 1.8 (2.9) 5.1 ( 11.0) 36 (51)
NZ Mā ori 2. 8 ( 3 .1 ) 5.7 (8.2) 5 (83)
Other 2.3 (1.0) 7.3 (5.8) 4 (100)
Deprivation
Low 1.7 (2.6) 4.4 7.6) 14 (47 )
Medium 1.8 (2. 2) 4.7 (7.9) 20 (57)
High 2.6 (4.2) 8.3 (18.3) 11 (69)
Breastfeeding duration
<12 months 1.7 (2.1) 3.9 (5.9) 15 (63)
12-23 months 1.6 (2.3) 4.3 (7.9) 18 (47)
=>24 months 2.8 (4.5) 8.8 (18.7) 9 (56)
Missing BF data 2.5 (2.1) 7.0 (5.4) 3 (75)
Traditional caries risk factors
Brushing frequency
Not daily 3.3 (4.2) 10.0 (15.6) 2 (67)
1 X per day 2.0 (2.5) 4.0 (6.3) 12 (6 0)
2 X per day 1.8 (2.9) 5.5 (12.0) 31 (53)
Adult helps brushing
No 2.1 (2.5) 5. 5 ( 8 .1 ) 26 (62)
Yes 1. 8 ( 3 .1 ) 5.0 (12.8) 19 (49)
Dairy consumption
Not daily 1.7 (2.3) 1.9 ( 2.7) 5 (50)
1-2 X per day 2.3 (3.1) 6.3 (13.0) 25 (66)
3+ X per day 1.6 (2.5 ) 5.0 (9.0) 14 (44 )
Missing data 2.0 (0.0) 8.0 (0.0) 1 (100 )
Daily sweet drinks
None 2.9 (3.0) 7.8 ( 9 . 3 ) 12 (63)
1 glass per day 1.6 (2.7 ) 4.2 (10.9) 30 (52)
2+ glasses per day 2.0 (2.2) 8 . 5 ( 11. 6 ) 3 (75)
Daily sweet foods
None 2.6 (2.4) 4.8 (5.7) 3 (60)
1 serve per day 1.3 (2.2) 3.1 (6.0) 15 (44)
2+ serves per day 2.3 (3.2) 7.1 ( 1 3 . 4 ) 27 (64)
Enamel defects
Present
Yes 2.3 (3.7) 6.5 (14. 3) 29 (36)
No 1.7 (2. 2) 4.6 (7.6) 52 (64)
Demarcated Opacity
Mild3 1.8 (2. 2) 4.7 (7.4) 45 (56)
Moderate to Severe4 1.5 (1.7) 4.2 (6.5) 27 (33)
1 dmft/DMFT: Number of decayed, missing or filled teeth in combined primary and permanent dentition.
2 dmfs/DMFS: Number decayed, missing or filled tooth sur faces. In combined primar y and permanent dentition.
3 Mild = white or cream demarcated opacity
4
Moderate/Severe = yellow/brown demarcated opacity, post eruptive breakdown, atypical restoration or extraction
due to enamel defect
NB: No statistically significant differences (p <0.05) were observed when looking at participant characteristics, caries risk factors,
enamel defect type, and dental caries experience/severity.
NZ DENTAL JOURNAL
8
differences between groups. Those who had breastfed
for less than 12 months had a mean dmft/DMFT of
1.7 (SD 2.1), while those who had breastfed for 12-23
months had a similar mean dmft/DMFT of 1.6 (SD2.3).
There was a slight increase in caries severity when
looking at those who had breastfed for longer than
24 months (dmft/DMFT 2.5: SD 2.1), but this was not
statistically significant.
Most children had access to fluoridated water supply
at their homes during early childhood, with only three
living in a non-fluoridated area. No children were taking
supplementary fluoride tablets. Most children were
brushing at least once a day (96%), and both caries
prevalence and severity at the tooth level followed a
gradient in the expected direction, with less caries
experience among those who brushed more frequently.
Participants who had parents helping them brush
their teeth had a lower caries prevalence (49%) than
those whose parents did not help (62%), although this
difference was not statistically significant (Table 2).
Participants who reported consuming two or more
servings of sweet drinks and sweet foods had a higher
prevalence of dental caries, and when looking at dmft/
dmfs scores, had the greatest number of teeth and
surfaces affected. Developmental enamel defects were
not associated with caries experience in this group, with
participants classified as having moderate to severe
demarcated opacities having a lower dmft/DMFT and
dmfs/DMFS than those with mild opacities or no enamel
defects at all, and this was not statistically significant
(Table 2).
Eruption of one or more permanent first molars had
been experienced by two in three participants, while
lower central incisors had erupted among three in four.
Most participants still had their mandibular primary
lateral incisors and maxillary central incisors in situ, and
almost all participants still had their primary maxillary
lateral incisors. Fourteen participants were missing one
or more teeth following extraction due to dental caries
(Figure 2).
Sixty four percent of participants had an enamel
defect affecting at least one tooth, with a total of 318
affected teeth, and a mean of 6.12 (SD 4.34) among
affected participants (Table 3). The most prevalent
enamel defect was demarcated opacities (58%), which
was comprised of either a white cream opacity, yellow/
brown opacity, or opacity with post eruptive breakdown.
Twenty-six participants (32%) had either a yellow/brown
opacity or post eruptive breakdown, with a total of 84
defects detected, and a mean of 3.23 (SD 2.67) defects
per affected participant. There were 224 demarcated
defects identified in total across all participants in both
the primary and permanent dentitions, with twice as
many in the primary dentition. The mean number of total
demarcated defects per affected participant was 4.8
(SD 3.3).
Five participants had atypical restorations, crowns or
extracted teeth that were known to be due to an enamel
defect but were unable to be classified. All restored or
extracted affected teeth were in the primary dentition.
Less than a quarter of participants had a diffuse opacity,
and of those affected, there were slightly more in the
permanent dentition than in the primary dentition.
Only six participants were identified as having a
hypoplastic defect, and these presented predominately
as pitting in permanent incisors. One participant had
more than one type of defect on the same tooth,
a demarcated opacity and a hypoplastic defect,
and these defects were counted twice, once in
each c ateg or y.
Sixty-two participants (77%) had at least one
permanent MIH index tooth present (Table 4).
Of participants with MIH index teeth present, over
two thirds had one or more tooth affected with MIH.
Figure 2. Number of participants and status of each tooth
Volume 118 March 2022 9
Table 3 . Primary and permanent teeth affected by enamel defects
Enamel defect type Prevalence Primary Teeth Permanent Teeth All teeth
N (%)
Total
number
of
defects
Defects per
affected
participant
Mean (SD)
Total
number
of
defects
Defects per
affected
participant
Mean (SD)
Total
number
of
defects
Defects per
affected
participant
Mean (SD)
Demarcated opacities
White/cream 45 (56) 100 2. 22 (1.78) 40 0.89 (1.17 ) 140 3.11 (1.7 6 )
Yellow/brown 23 (28) 30 1.30 (1.49 ) 30 1.30 (1.8 4) 60 2.61 (1. 92)
Post eruptive breakdown (PEB) 11 ( 14 ) 20 1.82 (2.09) 4 0.36 (0.67) 24 2.18 (1. 8 3 )
Either Y/B opacity or PEB 26 (32) 50 1.92 (2.61) 34 1.31 (2.0 2) 84 3.23 (2.67)
Total Demarcated 47 (58) 150 3 .19 ( 3 .1 8) 74 1.57 (2.22) 224 4.77 (3.27 )
Diffuse opacities 16 (20) 21 1.31 (1.54 ) 31 1.9 4 (2.72) 52 3.25 (2.44)
Hypoplastic defects 6 (7) 8 1.33 (1.21) 4 0.67 (0.86) 12 2.00 (0.63)
Unknown
Atypical restoration,
SSC, or extracted due to
enamel defect
5 (6) 31 6.20 (3.70) 0 0.00 (0.00) 31 6.20 (3.70)
Any defect 52 (64) 210 4.04 (3.91) 108 2.08 (2.71) 318 6 .12 (4.34)
*
Only 1 participant had a combination of defects on the same tooth (demarcated and hypoplastic)
and these have been counted twice – once for each defect type.
** The mean number of defects is for those with affected teeth only
Table 4 . Prevalence of Molar-Incisor Hypomineralisation (MIH) and/or Hypomineralised Primary Second Molar (PSM)
with summary of affected teeth
One or more index
teeth present1
N (%)
One or more
hypomineralised
teeth1
N (%)
Females: count
of MIH-affected
teeth1
(% of index teeth)
Males: count of
MIH-affected
teeth1
(% of index teeth)
Total MI2 62 (77) 25 (40) 14 (56) 11 ( 4 4 )
Total PSM3 80 (99) 31 (39) 15 (4 8) 16 (52)
Total MIH or PSM4 80 (99) 46 (58) 23 (50) 23 (50)
By specific teeth
Molar Tooth present
N (%)
16 49 (60) 9 (18) 6 (67) 3 (33)
26 49 (62) 13 (26) 10 (77) 3 (23)
36 51 (6 3) 8 (16) 5 (63) 3 (38)
46 50 (62) 4 (8) 3 (75) 1 (25)
Incisor
11 25 (31) 4 (16) 3 (75) 1 (25)
12 5 (6) 0 (0) 0 (0) 0 (0)
21 29 (36) 5 (17 ) 1 (20) 4 (80)
22 5 (6) 0 (0) 0 (0) 0 (0)
31 55 (68) 4 (7) 3 ( 75) 1 (25)
32 17 (21) 0 (0) 0 (0) 0 (0)
41 58 (72) 3 (5) 2 (67) 1 (33)
42 17 (21) 0 (0) 0 (0) 0 (0)
Second primary molar
55 73 (91) 15 (21) 8 (44) 10 (56)
65 74 ( 9 1) 18 (24) 8 (44) 10 (56)
75 73 (91) 14 (19) 8 (50) 8 (50)
85 74 ( 9 1) 14 (19) 9 (53) 8 (47)
1 Index Teeth able to be scored (not extracted, unerupted, or crowned for reason other than enamel defect)
2 Children with no permanent 1st molars or incisors excluded from this row
3 One child with no primary 2nd molars excluded this row
4 One child missing either permanent 1st molars, incisors, or primary 2nd molars excluded this row
NZ DENTAL JOURNAL
10
Most participants had their primary second molars
present, with 39% having at least one primary molar
affected by HPSM. In total, over half of all participants
showed evidence of either MIH or HMPS as categorized
by the EAPD for MIH classification. Maxillary teeth were
more likely to be affected than mandibular teeth, and this
was clinically evident across all primary and permanent
index teeth. There were no significant differences
between males and females for the prevalence of either
MIH or HPSM.
Discussion
This study presents detailed descriptive dental data on
a predominately NZ European cohort that was breastfed
for at least 5 months. The main finding is a high rate of
enamel defects in at least one tooth (64%), which were
of mixed type. In addition, more than half of participants
had experienced dental caries, with a mean dmft of
almost 2 in the combined dentition. A clear gradient was
evident when looking at tooth brushing habits and dental
caries, with those brushing twice a day having a lower
caries experience. Dental caries severity was no different
between children who had breastfed for less than
12 months and between 12-23 months, but increased
slightly for children who were breastfed beyond
24 months, however this difference was not statistically
significant. More severe dental caries was observed
for participants who reported consuming two or more
servings of sweet drinks or foods per day.
Our study used both EAPD for MIH and DDE indexes,
therefore was comparable with studies from other
regions of New Zealand (Kanagaratnam et al. 2009;
Mackay and Thomson 2005; Mahoney and Morrison
2009), although the number of index teeth included in the
analysis and age of participants differed. The distribution
of enamel defects in these NZ studies were similar to
our findings, with demarcated defects being the most
observed, followed by diffuse opacities and hypoplastic
defects. A fourth study used the FDI index, which differed
slightly to DDE and EAPD for MIH in the classification
of defects, however included all teeth in their analysis.
Overall prevalence of defects was similar to our data at
63% and 64% respectively (Suckling and Pearce 1984).
Prevalence of enamel defects in the NZ North Island
(20%–35%) appears less than the South Island (52%–
63%), and this warrants further investigation around
access to care and other potentially contributing factors.
The findings from our Dunedin study are consistent
with the South Island figures from other locations
(Kanagaratnam et al. 2009; Mackay and Thomson 2005;
Mahoney and Morrison 2009; Suckling and Pearce 1984).
Methodological differences may result in under or
over-estimate of findings. Participants in our study
were younger than the aforementioned NZ studies by
2-3 years, therefore did not all have their permanent
incisors or molars present. When looking only at
participants with at least one permanent incisor or
molar present, the prevalence of MIH in our study
was 40%, or 58% if including HFPM’s. Due to some
children not having all teeth erupted, this is likely to be
underestimated. This is significantly higher than MIH
prevalence reported in Wainuiomata (North Island),
with 15% of children with MIH (Mahoney and Morrison
2009). Two Southland studies reported enamel defects
for between 51.6 and 63% of participants, with the later
figure being from the study that included all teeth in their
analysis, which is consistent with our findings (at 64% of
participants) (Mackay and Thomson 2005; Suckling and
Pearce 1984).
The number of children recorded as having
experienced dental caries at the 2018 MOH 5-year-old
caries data for NZ was 40%, with a mean dmft of 1.8
(MOH 2018). When comparing with other countries with
a publically-funded child dental service, these figures
are slightly higher than for Australian children aged 6-7,
which reported 34% of children had experienced dental
caries, with an average dmft of 1.3 (AIHW 2020), and
almost double than 5-year-olds from England, with 23%
having experienced dental caries, with a mean dmft
of 0.8. The NZ Southern District Health Board (DHB)
(which encompasses Dunedin), reported that 33.7%
of children in the area had experienced dental caries,
with a mean dmft of 1.2 (MOH 2018). In this study, 56% of
participants had experienced dental caries with a mean
dmft of 1.9, which was higher than both the regional and
national figures for both prevalence and severity. Ethnic
and social disparities in dental caries experience are well
understood, with those living in areas of high deprivation,
or from ethnic minority groups, known to carry a greater
burden of disease(Beckett and Meldrum 2018). Given this
cohort was predominately
NZ European, and 80% were living in areas of medium
or low deprivation, these findings were unexpected.
NZ Ministry of Health (MOH) data is collected by dental
and oral health therapists employed by the Community
Oral Health Service, and radiographs are not routinely
taken before age 5. Radiographs are able to detect early
lesions that are often not clinically visible, therefore
the higher caries prevalence in our study could be
a reflection of the comprehensive assessments that
included posterior bitewing radiographs, and therefore
may represent a more accurate reflection of the true
caries experience for this age group in Dunedin than that
previously documented.
Exclusive breastfeeding for the first six months of
life is recommended by the WHO, and the findings
from this study support this recommendation (WHO
2003). Some concern has previously been raised
about longer breastfeeding durations, in particular the
potential risk seen with nocturnal feeding (Tham et al.
2015). However, following our detailed data collection
and assessments we identified no statistically significant
differences with breastfeeding duration and dental
caries. Importantly, breastfeeding up to 24 months
was not found to be a caries risk factor in this cohort.
There was a slight trend towards increased dental caries
severity with breast feeding beyond 24 months, which
potentially supports previous research that has found
that prolonged breastfeeding beyond 24 months may
increase the risk of dental caries (Tham et al. 2015).
As expected, participants in our study experienced
less dental caries if they brushed at least once a day,
Volume 118 March 2022 11
and had an adult who helped. Those who consumed
more servings of sugar per day through either drink or
food also experienced more dental caries. These findings
are consistent with what is known about the role of
diet and oral hygiene in dental caries (Andlaw 1978;
Hujoel et al. 2018). The lack of statistical significance
for this cohort is most likely due to the lower number
of participants, and findings can still be viewed as
clinically important and consistent.
Strengths of this study are the robust data collection
around breastfeeding and its duration, and the thorough
clinical assessments that included posterior bitewing
radiographs, and detailed caries information that was
recorded using ICDAS (Ismail et al. 2007). Defects were
categorised using both the DDE (on all teeth present) and
EAPD for MIH, to ensure all defect types on all teeth were
recorded, and MIH prevalence for index teeth could be
extrapolated and compared to other studies (Clarkson
and O’mullane 1989; Weerheijm et al. 2003). While this
study had low numbers of NZ Māori participants (7%),
this was consistent with the demographic characteristics
of Dunedin city overall (7.7%) (Statistics NZ 2013).
Dunedin also typically has low numbers of those living
in areas of high deprivation, with only 7.9% of areas
identified as highly deprived (Chiang and Exeter).
20% of participants in our study were categorised
as living in areas of high deprivation, therefore all
deprivation groups were well represented. Similar to
most studies, there are limitations in this investigation,
and due to it being a descriptive study, we were unable
to determine causation of either dental caries or enamel
defects. While the children in this study had a mean age
of 6.6 years, it became apparent that they were still too
young to have erupted all their permanent incisors and
molars. Given that only participants with at least one MIH
index tooth were included in the MIH analysis (77%), the
figures from our study are likely to be an underestimate
of the true figure; however still of clinical importance.
In summary, enamel defect prevalence was high
in this cohort, which corroborates previous studies
suggesting that enamel defects are more prevalent in
the South Island than the North Island of New Zealand.
Dental caries experience was high when compared with
national and international 5-year-old data, and good
oral hygiene practices and reduced sugar consumption
positively impacted on dental caries experience and
severity. No statistically significant different was found
between breastfeeding duration and caries risk.
Why this paper is important
1. Enamel defects appear more prevalent in the South
Island than the North Island of New Zealand, and
reasons for this need to be further investigated.
2. Dental caries prevalence and severity were high when
compared to Dunedin MOH caries data, and this is
likely due to the comprehensive assessment provided
that includes intra-oral radiographs, therefore a
more accurate representation of caries prevalence in
Dunedin NZ.
3. Breastfeeding duration does not appear to be a
prominent risk for caries. However, good oral hygiene
practices, parents assisting with toothbrushing, and
reduced sugar consumption positively impacted on
dental caries experience and severity, and this is in line
with current literature.
Ethical Approval
University of Otago Human Ethics Committee (Health)
31 January 2018. Reference number H18/001.
Acknowledgements
The authors acknowledge the participants and their
parents, as well as the generous sponsorship from the
Otago Medical Research Foundation (Laurenson Award)
and the Healthcare Otago Charitable Trust.
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Author details
Deanna Beckett, Lecturer Dip D.Therapy, DPH, MPH
Oral Sciences, Sir John Walsh Research Institute, University of Otago
Corresponding author: Deanna.beckett@otago.ac.nz
Benjamin John Wheeler, Associate Professor/Paediatric Endocrinologist MBCHB, DCH, CCE, FRACP, PhD
Women’s & Children’s Health, Dunedin School of Medicine, University of Otago
Jonathan Broadbent, Professor BDS PhD PGDipComDent
Oral Sciences, Sir John Walsh Research Institute, University of Otago
Carolina Loch, Senior Lecturer BSc MSc PhD
Oral Sciences, Sir John Walsh Research Institute, University of Otago
Dr Erin Mahoney, Clinical Lecturer BDS, MDSC, PhD, FRACDS, MRACDS
Paediatrics, University of Otago, Wellington
Bernadette Drummond, Professor BDS, MS, PhD, FRACDS, FDSRCSEd
Professor Emeritus, School of Dentistry, University of Leeds
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