Swedish Dental Journal

48 Pages·2013·1.36 MB·English

Swedish
Dental Journal
Scientific Journal of The Swedish Dental Association
2/13
No.
Vol.37 Pages 61-104
contents
Onset of Molar Incisor
Hypomineralization (MIH)
Fagrell, Salmon, Melin, Norén 61
Treatment with local hemostatic
agents and primary closure after tooth
extraction in warfarin treated patients
Svensson, Hallmer, Sahlström Englesson,
Svensson, Becktor 71
Comparison of diagnostic performance
on approximal caries detection among
Swedish and Chinese senior dental
students using analogue and digital
radiographs
Minston , Li, Wennberg, Näsström ,Shi 79
The prevalence and alterations of fur-
Onset of Molar Incisor Hypomineralization (MIH) page 61 cation involvements 13 to 16 years after
periodontal treatment
Johansson, Starkhammar Johansson, Ravald 87
Molar position associated with a
missing opposed and/or adjacent
tooth: a follow up study in women
Lindskog-Stokland, Hakeberg, Hansen 97
swedish dental journal vol. 25 issue 1 2001 3
Swedish
Dental Journal

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264 22 Klippan
swed dent j 2013; 37: 61-70  fagrell et al
Onset of Molar Incisor
Hypomineralization (MIH)

Tobias G. Fagrell1,3, Phil Salmon2, Lisa Melin3, Jörgen G. Norén3
Abstract 
 The etiological factors and timing of the onset of molar incisor hypomineralization
(MIH) are still not clear. The aim of this study was to examine ground radial and
sagittal sections from teeth diagnosed with MIH using light microscopy, polarized light
microscopy and X-ray micro-computed tomography (XMCT) and to estimate the onset
and timing of the MIH and to relate the hypomineralized enamel to the incremental
lines. Thirteen extracted permanent first molars diagnosed MIH, were analyzed with
light microscopy and XMCT.
The hypomineralized areas were mainly located in the mesio-buccal cusps, starting
at the enamel-dentin-junction and continuing towards the enamel surface. In a relative
gray scale analysis the values decreased from the EDJ towards the enamel surface.
The findings indicate that the ameloblasts in the hypomineralized enamel are capa-
ble of forming an enamel of normal thickness, but with a substantial reduction of their
capacity for maturation of enamel. Chronologically, it is estimated that the timing of the
disturbance is at a period during the first 6-7 months of age.
Key words  
Enamel, light microscopy, molar incisor hypomineralization, polarized light microscopy, X-ray micro-
computed tomography.
1Paediatric Dentistry Special Dental Service, Sahlgrenska University Hospital Mölndal, Mölndal, Sweden
2SkyScan, Kontich, Belgium
3Department of Pediatric Dentistry, Institute of Odontology at the Sahlgrenska Academy, University of Gothenburg,
Göteborg, Sweden
swedish dental journal vol. 37 issue 2 2013 61
swed dent j 2013; 37: 61-70  fagrell et al
Start för Molar Incisor Hypomineralization (MIH)
Tobias G. Fagrell, Phil Salmon, Lisa Melin, Jörgen G. Norén
Sammanfattning 
 De etiologiska faktorerna och timingen för start av mineraliseringsstörningen molar
incisor hypomineralization (MIH) är inte klarlagda. Syftet med denna studie var att
studera ourkalkade radiala och sagittala snitt från tänder med diagnosen MIH med
ljusmikoroskop, polarisationsmikroskop och röntgenmikro-datortomografi (XMCT)
och uppskatta tidpunkten för start av MIH, samt att relatera den hypomineraliserade
emaljen till emaljens inkrementlinjer. Totalt undersöktes 13 extraherade permanenta
förstamolarer med diagnosed MIH.
Den hypomineraliserade emaljen var främst lokaliserad till molarernas mesio-buck-
ala delar och började vid emalj-dentingränsen för att fortsätta ut mot emaljytan. I en
gråskaleanalys av XMCT-bilderna sågs att värdet minskade från emalj-dentingränsen
mot emaljytan.
Fynden pekar mot att ameloblasterna i den hypomineraliserade emaljen klarar att
bilda en emalj av normal tjocklek men har en kraftigt reducerad förmåga till matu-
ration av emaljen. Tidsmässigt uppskattas att störningen har uppkommit under de
första 6-7 levnadsmånaderna.
62 swedish dental journal vol. 37 issue 2 2013
onset of molar incisor hypomineralization (mih)
Introduction ming this is the use of X-ray micro computed to-
During the last decades much interest has been fo- mography (XMCT) (11, 13).
cused on a condition called Molar Incisor Hypomi- Micro computed tomography or "micro-CT" is
neralization (MIH) (15, 18, 29), which is a develop- X-ray imaging in 3D. The method is based on tomo-
mental disturbance of the enamel mainly occuring graphic X-ray scans with massively increased resolu-
in the permanent first molars. Clinical studies in tion, where very fine scale internal structure of ob-
almost all parts of the world have revealed an overall jects is imaged non-destructively (11). The sample's
prevalence of around 20% (17), but lower figures for internal 3D structure at high resolution may be pro-
the most severe forms with loss of substance (15, 18). vided, and in the case of a MIH tooth a 3D image
MIH is by definition a chronological developmen- is reconstructed of the hypomineralized enamel in
tal disturbance in the enamel. One characteristic of relation to the normal enamel and the dentin.
MIH is variation in the number of molars affected The aim of this study was to use light microscopy,
- some cases only one permanent first molar may be polarized light microscopy and X-ray micro-com-
affected while in other cases two, three or four mo- puted tomography, to examine radial and sagittal
lars. Furthermore, the degree of hypomineralization un-demineralized sections from teeth diagnosed
may vary between the first permanent molars in the MIH, and to determine the onset and timing of the
same dentition. enamel hypomineralization (relative to normative
From a clinical point of view MIH is associated development) in relation to the incremental lines.
with extensive objective and subjective problems
such as hypersensitivity of the affected teeth, enamel Material and methods
breakdown and problems with retention of fillings Tooth material
(14, 19). The condition often also leads to dental fear The tooth material consisted of 13 permanent first
and dental management problems(14). molars, collected from 9 individuals, with the diag-
Several attempts have been made to find the etio- nosis of MIH, extracted due to severe hypominera-
logical factors behind MIH and a number of pos- lized enamel and for orthodontic reasons. 8 teeth
sible factors have been suggested (1, 6). In a recent
 Figure 1. Schematic drawing of the study design.
paper it was shown that nutritional factors around 6
(MIH=Molar Incisor Hypomineralization, no=number; XMCT=X-
months postnatally may have an impact on the de- ray micro-computed tomography; LMSM=light microscopy-
velopment of MIH (10). stereo microscopy; POLMI=polarized light microscopy;
In a number of articles the histological, chemical GLM=gray level measurements.)
and mechanical properties of the hypomineralized
enamel has been described (9, 12, 20, 28, 30) someti-
mes even with conflicting results. Histologically the
hypomineralized enamel extends from the enamel-
dentin junction towards the enamel surface and the
disturbance has a distinct cervical border to nor-
mal enamel along a prism.
In order to be able to have a realistic discus-
sion of possible etiological factors the timing of
the onset of the disturbance must be thoroughly
elucidated, as well as the extension of the defect
within the crown. These parameters for the hypo-
mineralized enamel are crucial to know in order to
find a relevant time period for potential causative
factors. Most often only sagittal sections are made
but radial sections may provide information of re-
levance. Serial sectioning of un-decalcified dental
hard tissues may, at least for the moment, only be
performed using a saw microtome. For every sec-
tion of 100 μm there is a loss of 300 μm due to the
thickness of the saw blade. Therefore, substantial
and vital information is lost. One way of overco-
swedish dental journal vol. 37 issue 2 2013 63
fagrell et al
were maxillary molars and 5 teeth were mandibular size 15.80 μm, copper+aluminium filter (38 μm Cu,
molars. The study design is shown in Figure 1. Af- 0.5mm Al), rotation step 0.360°, 360° rotation, frame
ter extraction the teeth were stored in plastic tubes averaging 8, and geometrical correction, flat field
containing 70% ethanol. Four of the teeth derived correction and median filtering on.
from the same patient and were numbered 16, 26, 36 The software package CT Analyser (Version
and 46 according to their position in the permanent 1.11.6.0+, SkyScan N.V., Kontich, Belgium) was used
dentition. for analysis. For each sample in the study, the enamel
gray levels (0–255) were measured in two directions.
Cutting procedure The relative gray level in normal and hypomine-
The teeth were stored in 70% ethanol until further ralized enamel was measured in CT Analyser in a
preparation. After macro photos of the teeth were series of XMCT scans from the cuspal parts to the
taken, four teeth were selected for micro-CT X-ray cervical parts of the crown.
analysis. The remaining nine teeth were embedded
in an epoxy-resin (Epofix®, Electron Microscopy Relative gray level measurements
Sciences, Fort Washington, PA, USA) and serially The digital images taken in the stereo microscope of
sectioned with an approximate thickness of 120 μm, the sagittal and radial sections were analyzed with
in a Leica SP1600 Saw Microtome (Leica Mikrosys- ImageJ (Research Services Branch, National Insti-
teme Vertrieb GmbH, Wetzlar, Germany). tute of Mental Health, Bethesda, Maryland, USA).
Sagittal bucco-lingual sections were prepared
from six teeth and radial sections were prepared Ethical considerations
from three teeth. Before cutting a section an object All the examined teeth had been extracted due to
glass was glued onto the previously cut surface, with severe hypomineralized enamel and for orthodontic
a light curing one-component adhesive (Technovit reasons and given by the patient of his/her own free
7210 VLC, Heraeus Kulzer GmbH, Hanau, Germa- will. The teeth were stored in plastic tubes without
ny). This technique allows optimal positioning of any identification, which is why none of the teeth
the sample on the glass and prevents loss of enamel could be traced to any specific patient.
during the cutting procedure.
Results
Light microscopy - Stereo microscopy (LMSM) LMSM
All sagittal and radial sections were examined in Normal mineralized enamel appeared as translucent
a Leica M80 stereo microscope (Leica M80 with in incident light. The hypomineralized enamel most
8:1 zoom, 0.75x-6x, Leica Mikrosysteme Vertrieb often appeared as opaque with a whitish color, in
GmbH, Wetzlar, Germany) in incident light with a some cases slightly beige. Hunter-Schreger bands,
matt black background. Digital images were taken Retzius lines and the overall appearance of the ena-
of all sections using a Leica digital camera (Leica mel prisms were readily seen (Fig. 2) in both normal
DFC420 C, Leica Mikrosysteme Vertrieb GmbH, and hypomineralized enamel. The degree of opa-
Wetzlar, Germany) equipped with Leica Application queness reflects the degree of hypomineralization
Suite LAS V3.7.0 (Leica Microsystems AG, Heer- (degree of porosity), implicating that the more opa-
brugg, Switzerland). que the enamel appears in incident light, the more
porous it is.
Polarized light microscopy (POLMI) In all examined teeth the hypomineralized ena-
All sections were examined dry in air and after soa- mel was mainly located at the buccal cusps and the
king in water in an Olympus polarizing light mi- hypomineralized areas started at the enamel-dentin-
croscope (Olympus, Tokyo, Japan). Digital images junction (EDJ) and continued up to the enamel sur-
were produced using a Leica digital camera and face (Figs. 2 & 3). In 2 of the mandibular molars and
Leica Application Suite. 3 of the maxillary molars the hypomineralized area
  extended over to the occlusal area of the tooth (Fig.
X-ray Micro Computed Tomography (XMCT) 4). In all these teeth hypomineralized enamel was
The SkyScan 1172 (SkyScan N.V., Kontich, Belgium), also found in the lingual/palatinal part of the crown.
XMCT system was used to scan the teeth. The para- The largest extension of hypomineralized enamel
meters used were: camera pixel size 9.07 μm, source was found in the mesial part of the crowns, where
voltage 74 kV, source current 120 mA, image pixel also the most severely affected enamel was seen. The
64 swedish dental journal vol. 37 issue 2 2013
≥ ≤
onset of molar incisor hypomineralization (mih)
 Figure 2. Light microscopic images of an un-demineralized sagittal section of a permanent first molar seen in incident light
(left) and after water imbibition in polarized light (right). (HMIN=hypomineralized enamel; NE=normal enamel; D=dentin.)
 Figure 3. Un-demineralized sagittal section of a permanent
first molar seen in polarized light after water imbibition. A
hypomineralized lesion is seen as a darker area extending
from the enamel-dentin junction towards the surface with a  Figure 4. Light microscopic images of an un-demineralized
porous surface zone. To the left of the lesion the enamel has sagittal section of a permanent first molar seen in incident light
a normal degree of mineralization and a normal surface zone. with a hypomineralization extending over the occlusal area of the
(HMIN=hypomineralized enamel; NE=normal enamel; D=dentin; crown. (HMIN=hypomineralized enamel; NE=normal enamel;
PES=porous surface enamel; NES=normal enamel surface.) D=dentin.)
swedish dental journal vol. 37 issue 2 2013 65
fagrell et al
 Figure 5. Light microscopic images of an un-demineralized radial section of a permanent first molar seen in incident light (left)
and after water imbibition in polarized light (right). (HMIN=hypomineralized enamel; NE=normal enamel; D=dentin.)
cervical extension reached from half till 2/3 of the POLMI
coronal height. The enamel corresponding to the translucent areas
Enamel breakdown and loss of substance was seen seen in LMSM appeared when examined dry in air
in all mandibular molars. Caries lesions associated with a blue surface zone (negative birefringence) lea-
with the hypomineralized enamel were found in all ving the remaining portion of the enamel with a red
mandibular molars and in 2 maxillary molars. color (positive birefringence). After hydration the red
When comparing the 4 permanent first molars color turned blue, indicating a pore volume less than
from the same patient, one of the mandibular mo- 5% (Fig. 2). The overall morphology and structure
lars was more affected than the other three molars, were normal and the Hunter-Schreger bands and the
both with regard to the spatial extent and the degree Retzius lines were readily seen. The surface enamel ap-
of hypomineralization. peared normal. However, in some sections a thin hypo-
The central part of the hypomineralized enamel mineralized band could be seen extending over parts of
appeared distinct, but became gradually less discrete the enamel surface.
towards the cervical part of the section. The exten- When examined dry in air the enamel in the opaque
sion towards the enamel surface of the hypomine- areas had a color that ranged from dark brown to dark
ralized zone decreased in the adjacent sections. The yellow, the central part of the affected enamel being the
border between hypomineralized and normal ena- darkest color. After hydration the brown-yellow color
mel followed a prism and appeared not to be related remained in the central part, indicating a pore volume
to the incremental lines. of more than 5% (Fig. 3). The central part of the hy-
A surface zone of normal enamel was seen in most pomineralized enamel extended from the EDJ to the
sections. However, in some sections the hypomine- enamel surface, which either exhibited a thin normal
ralized enamel extended to the outermost enamel mineralized enamel surface or a porous enamel (Fig. 3).
surface, thus leaving part of the enamel surface with The porous surface zone varied in extent. The borders
a porous outer zone. of the central part of the hypomineralized enamel were
In the radial sections the hypomineralization sho- distinct and followed a prism. The enamel surface had
wed in principle the same pattern as in the sagittal a yellow color that remained yellow after soaking in
sections (Fig. 5). The hypomineralization starting water. The overall structure was less distinct compared
at the EDJ and, depending on severity, extended with normal enamel. The surrounding hypominerali-
towards the enamel surface. In areas with marked zed enamel changed in color to yellow or red, indica-
opacity no surface zone of normal mineralized ena- ting a pore volume of around 5%. The enamel surface
mel was found, which was present in other areas. appeared normal with a blue color.
66 swedish dental journal vol. 37 issue 2 2013
onset of molar incisor hypomineralization (mih)
 Figure 6. Example of an X-ray micro-computed tomography  Figure 7. 3D ribbon plot of relative gray level measurements
image of a MIH tooth. The more compact opaque areas represent from the enamel surface towards the enamel-dentin-junction
hypomineralized enamel. in X-ray micro-computed tomographic radial images of a tooth
diagnosed with MIH. (HM-Cor=hypomineralized enamel coronal
part; N-Cor=normal enamel coronal part; HM-Mid=hypomineralized
enamel middle part; N-Mid=normal enamel middle part; HM-
Cer=hypomineralized enamel cervical part; N-Cer=normal enamel
cervical part; ES=enamel surface; EDJ=enamel-dentin-junction;
RGV=relative gray value; RD=relative distance.)
HM - Cor
N - Cor
EDJ
HM - Mid
N - Mid
H - Cer
210 N - Cer
200
190
180
170
160
150 V
140 G
130 R
120
110
140 N - Cer
120100 H - Cer
80 N - Mid
60 EHSM - Mid
40 N - Cor
RD 20 0 HM - Cor
X-ray Micro Computed Tomography (XMCT)
The XMCT revealed the location of the hypomine-
ralized enamel as a coherent volume of tissue with gray values decreased from the EDJ towards the ena-
a higher degree of radio-lucency having its origin mel surface, while the values in normal enamel, ir-
at the enamel-dentin-junction (Fig. 6). The hypo- respective of location, had a slight increase towards
mineralized enamel was located on the buccal side the enamel surface. Both locations for measurement
of the tooth crown, the enamel around the mesio- in the cervical part of the enamel represented nor-
buccal cusp being the most affected, followed by the mal enamel.
disto-buccal cusp. However, the hypomineralized
enamel did not extend into the outermost part of
Timing of enamel hypomineralization
the cusp. A more limited hypomineralized area was Since the incremental lines were easily discernable it
seen in the disto-lingual cuspal area. Examination of became possible to estimate the appositional enamel
the sections from the tooth analyzed with XMCT in growth over a certain period of time. Even though
incident light and in POLMI confirmed the hypomi- incremental lines are found in the radial sections, the
neralized character of the radio-lucent volume seen sagittal sections from the central part of the crown
and its location. through a cusp are more suitable for estimating the
timing of the affected enamel.
Gray level measurements An estimation of the timing was performed on the
Radial XMCT images (27 images) were used to ana- most central mesial-sagittal sections and based on
lyze the relative gray value intensities of the enamel enamel development and secretion rate for molars
in two locations in each image (Fig. 7). Exactly the (5, 22). An image of the most central mesio-buccal
same two locations were measured in all images, section was compared with a schematic drawing of
thus values within the same section and from the the same area with incremental lines (Fig. 8).
coronal enamel to the cervical could be measured Hypomineralization started below the dentin
for normal and hypomineralized enamel. cusp in five of the first molars (2 mandibular, 3 max-
The relative gray scale values in the coronal and illary), whereas in the remaining two mandibular te-
middle parts of the enamel were markedly higher eth the hypomineralization started at the top of the
in normal enamel compared with hypomineralized dentin cusp. The relative extension of hypominera-
enamel. In the hypomineralized enamel the relative lized enamel towards the cervical part of the crown
swedish dental journal vol. 37 issue 2 2013 67
fagrell et al
 Figure 8. Light microscopic images of an un-demineralized refore, serial sectioning per se is not possible since
radial section of a permanent first molar seen in incident light for each section cut with a thickness of 100 μm there
with plotted incremental lines and corresponding time in days
is a loss of 300 μm. Three times more information
(relative values). (HMIN=hypomineralized enamel; NE=normal
is lost compared with what is gained. The inter-
enamel; D=dentin.)
pretation of histological sections in 3-dimensions
is extremely unreliable. However, the use of X-ray
micro-computed tomography may greatly improve
the possibility of understanding aberrations in the
mineralization process in all dimensions.
In the LMSM analyses the degree of opacity re-
flected the degree of hypomineralization (degree of
porosity), indicating that the more opaque the ena-
mel appears in incident light, the more porous it is.
This is in line with earlier studies where the color
of the hypomineralization was used as a variable to
determine the degree of hypomineralization (7, 11).
These findings were also confirmed in the POLMI
analyses showing a high degree of porosity in the
areas of hypomineralization.
Analyses of the enamel surface demonstrated a
thin normal outer layer of the enamel in some of the
teeth affected by MIH, which has previously been
shown (16). However, no normal enamel surface
zone was seen in the surface of more pronounced
hypomineralization, which could constitute a pos-
sible pathway for bacteria and other materials from
in six teeth (3 mandibular, 3 maxillary) was equal to
the oral cavity. Teeth affected by MIH are often as-
200 days and to a relative value of 300 days in one
sociated with different subjective symptoms, one of
maxillary first permanent molar.
them being hypersensitivity. In a previous study of
MIH-teeth bacteria were found both in hypomine-
Discussion ralized enamel and in the dentinal tubules (8, 9). The
This study has shown that the hypomineralized ena-
finding of a porous enamel surface would thus ex-
mel in first permanent molars associated with MIH
plain how bacteria can penetrate deep into the den-
was mainly located in the buccal enamel of the teeth
tin through the enamel.
and had a high degree of porosity extending from
The findings that the hypomineralized enamel
enamel-dentin-junction (EDJ) towards the enamel
starts at the EDJ extending towards the enamel sur-
surface. Its cervical extension was well demarcated
face and that the hypomineralization has a cervical
along a prism. The bulk of the lesions exhibited limitation along a prism, have also been shown in
an enamel surface with low degree of mineraliza- earlier studies (12, 11, 16), in contradiction however,
tion. The X-ray micro-computerized tomography to the result presented in a study by Farah 2010 (11).
revealed the hypomineralized enamel as a volume The start of the hypomineralization close to the EDJ
extending from the EDJ towards the surface. An es- indicated that an onset of the hypomineralization is
timation of onset and extension in time for the hy- early in the enamel mineralization. The gray value
pomineralized enamel ranged from the start of the analyses showed that the coronal enamel was more
enamel mineralization at the tip of the dentin cusp hypomineralized than the cervical enamel. The de-
up to a relative value of 200 days. gree of hypomineralization increased slowly towards
Sectioning of un-demineralized dental hard tis- the enamel surface in contrast to normal enamel,
sues creates certain problems due to hardness and which had a flat gradient of gray value.
brittleness, especially of enamel. Sectioning of teeth An understanding of the timing of crown for-
must be performed with a diamond-edged band mation is crucial in order to be able to identify the
saw. The thickness of the cutting blade determines time of a possible insult to the ameloblasts. Boyde
how much tooth substance is lost for every cut. The- (5) used a histologically derived method to calculate
68 swedish dental journal vol. 37 issue 2 2013