10.59987/ads/2015.2.53-57
Aims. The aim of this study was to analyse the effects of nasal obliteration with regards to the linear dimensions of dissected hemimandibles of a homogeneous sample of young rats.
Methods. 68 pure breed male Sprague-Dawley rats, aged four weeks, were divided into four groups of 17: two control groups and two test groups. The first control group was sacrificed at the beginning of the observation period and the other one at the end. The test groups, one of which had the right nostril occluded by silicon material while the other had the left occluded, were sacrificed after eight weeks, at twelve weeks. After isolating the hemi-mandibles, four vertical and four sagittal measurements were taken; comparison was then made between the control groups and the experimental groups. The sagittal measurements are articular surface of the condyle-neck incisor (SARCIN), articular surface of the condyle-mental foramen (SARFORO), articular surface of the condyle-margo incisalis (SARMI), articular surface of the condyle-surface mesial of the first molar (SARSMM). The vertical measurements are superior condyle surface-base (SCOSUB), mesial surface of the first molar-base (SUMESM), maximum inferior arched concavity-base, (XCOARIB), maximum sigmoid notch concavity-base (XCOINSB).
Results. The sagittal and vertical measurements showed an increase in the values of the experimental group when compared to the controls.
Conclusion. An altered nasal respiration is able to influence the patterns of facial growth and in particular to induce an increase in the growth of the mandible.
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Craniofacial growth and respiration: a study on an animal model
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Craniofacial growth and respiration: a study on an animal model
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                                                                                                   Original article



    Craniofacial growth and respiration:
    a study on an animal model




                                                                                                     i
                                                                                                   al
                                                                                                on
    Luca Levrini, MD,DDSc,MSc1                                Conclusion. An altered nasal respiration is able to
    Alessandro Mangano, DDS,MSc1                              influence the patterns of facial growth and in par-
    Alessandro Ambrosoli, DDS,MSc1                            ticular to induce an increase in the growth of the
    Paola Merlo, DDS,MSc1                                     mandible.
    Carlo Mangano, MD,DDSc2




                                                                                       zi
    Alberto Caprioglio, DDS,MSc1                              Key words: craniofacial growth, respiration, or-
                                                              thodontics, growth patterns.




                                                                          na
    1   Department of Surgical and Morphological Sci-
        ences, University of Insubria, Varese, Italy          Introduction
    2   Private practice
                                                              Numerous studies conducted on animals have
                                                              demonstrated a strict correlation between craniofacial




                                                                er
    Corresponding author:                                     morphogenesis and the onset of functional anomalies
    Alessandro Mangano                                        (1). It has been shown that in bipedal rats (created by
    Department of Surgical and Morphological Sciences,        amputation of two paws) variations in body and head
    University of Insubria


                                                        t     posture have been brought about, with consequential
    Via Ravasi, 2
    21100 Varese, Italy
                                                     In       alterations in the craniofacial region (2). These varia-
                                                              tions consist above all in an opening of the angle of
    E-mail: ale.mangano10@gmail.com                           the base of the skull and an anterior displacement of
                                                              the occipital foramen. A theory has been put forward
                                                              that the craniofacial alterations may occur as a con-
                                                 ni
    Summary                                                   sequence of a lack in nasal airflow, which is indepen-
                                                              dent from the onset of oral respiration (3-5). Signifi-
    Aims. The aim of this study was to analyse the ef-        cant correlation between oral respiration and cranio-
                                    io

    fects of nasal obliteration with regards to the lin-      facial modifications were found in a study carried out
    ear dimensions of dissected hemimandibles of a            on a sample of 80 rats, in which one or both nostrils
    homogeneous sample of young rats.                         were occluded. Besides a reduction in overall growth
    Methods. 68 pure breed male Sprague-Dawley rats,          of the animals, where a clear-cut ponderal reduction
                           iz



    aged four weeks, were divided into four groups of         was shown, a reduction in the general dimensions of
    17: two control groups and two test groups. The first     the skull was also demonstrated. Important variations
    control group was sacrificed at the beginning of the      were found not only in the mandible but also in the
           Ed




    observation period and the other one at the end. The      pterygoid and tympanal areas. In particular, a post-
    test groups, one of which had the right nostril oc-       rotation of the viscerocranium and of the mandible
    cluded by silicon material while the other had the left   were noted, probably due to induced oral respiration.
    occluded, were sacrificed after eight weeks, at           In fact, under these conditions, the rodent is forced to
    twelve weeks. After isolating the hemi-mandibles,         an obligatory raising of the head in order to increase
    four vertical and four sagittal measurements were         the opening of the pharynx (6). In another study
IC




    taken; comparison was then made between the con-          made on rats, where a monolateral nostril occlusion
    trol groups and the experimental groups. The sagit-       had been carried out, a significant deviation of the
    tal measurements are articular surface of the             midline towards the side of the occlusion was noticed.
    condyle-neck incisor (SARCIN), articular surface of       This has therefore led to the belief that a lack of air-
C




    the condyle-mental foramen (SARFORO), articular           flow in the occluded fossa inhibits morphogenesis
    surface of the condyle-margo incisalis (SARMI), ar-       and, therefore, the passage of airflow through the
    ticular surface of the condyle-surface mesial of the      nasal cavity constitutes in itself a morphogenetic
    first molar (SARSMM). The vertical measurements           stimulus for the viscerocranium development (7).
                                                              The anatomic and structural differences between
©




    are superior condyle surface-base (SCOSUB), mesial
    surface of the first molar-base (SUMESM), maximum         man and other animals often make it difficult to com-
    inferior arched concavity-base, (XCOARIB), maxi-          pare the results obtained in these studies (8,9), par-
    mum sigmoid notch concavity-base (XCOINSB).               ticularly when comparing human anatomy with ro-
    Results. The sagittal and vertical measurements           dents’ anatomy. From this point of view, studies
    showed an increase in the values of the experi-           made on primates would appear to be much more re-
    mental group when compared to the controls.               liable (10,11). In all mammals respiration requires a

    Annali di Stomatologia 2015; VI (2): 53-57                                                                     53
    L. Levrini et al.


    highly specialised structure able to adapt to the vari-             test p=0.03. Using a general anaesthesia for animals
    ety of needs of every specie and to the different evo-              (Chetamine cloridate i.m.) the nostrils of groups A
    lutionary pressures (12). In the albino rat, even                   and B were occluded with silicon material. In order to
    though skeletal segments are comparable in number                   verify a comparison between the experimental mod-
    to those of the human skull (13), the respiratory func-             els and evaluate whether different ways of breathing




                                                                                                                 i
    tion is carried out differently. The topographic proxim-            had any influence on the health of the rats they were




                                                                                                               al
    ity between the epiglottis and the soft palate makes                weighed at the beginning and end of the observation
    the passage of air through the oral cavity extremely                period. The animals were then sacrificed at 12
    difficult thus making the rat’s respiration mainly nasal.           weeks. Soft tissues were then carefully removed from




                                                                                                            on
    Many studies conducted on human patients (14-28)                    the head until the cranium was completely isolated
    have shown cephalometrically a correlation between                  and the mandibles could be separated. The
    respiration and craniofacial development, but also an               mandibles were then divided into two hemi-
    interesting possible correlation between growth hor-                mandibles. Checking whether the nasal cavities had
    mone levels and the morphologic development of the                  indeed been obstructed, only 29 obstructions resulted




                                                                                                  zi
    upper and lower jaw (15).                                           out of 31 (the total number of possibly obstructed
    A very recent study conducted on newborn rats (29)                  nostrils corresponds to 31 due to the fact that 3 out of
    showed that a diet-induced hypermethioninemia in rat                the 34 rats with obstructed nostrils had died). The fi-




                                                                                    na
    dams results in growth retardations and histomorpho-                nal number of specimens of mandible was 29 be-
    logical changes of the spheno-occipital synchondro-                 cause two rats’ nasal cavities were not totally ob-
    sis, an important craniofacial growth centre in new-                structed and were discarded from the study. The 29
    borns: this may elucidate facial dysmorphoses report-               useful hemi-mandibles were photographed using a




                                                                          er
    ed in patients suffering from hypermethioninemia.                   digital camera (Polaroid Digital Microscope Camera):
    The hypothesis for this study is the possibility that               they were put onto the stage plate of a stereomicro-
    respiratory function may also modify skeletal growth                scope, on a black background with a millimetre mark-
    in the animal model. The type of modification induced               er and identity signs for the groups (Fig. 1); in order
    is not clinically relevant, due to the reasons cited


                                                              t         to guarantee the same position of the hemi-
    above concerning the lack of comparison possibilities
    between man and rat.
                                                           In           mandibles during the analysis, the latter where glued
                                                                        to a support that made the external face of the
                                                                        mandible parallel to the surface of the stage plate.
                                                                        The photographs were then transferred to a software
    Materials and methods                                               system (IMAT R-D) which allowed measurements up
                                              ni
                                                                        to approximately 0.1 mm to be taken. The linear mea-
    This study was carried out according to the declara-                surements were divided into sagittal (S) and vertical
    tion of Helsinki (1964). In this study 68 male pure                 (V); we decided not to evaluate the thickness of the
                                   io

    breed Sprague-Dawley rats were used. At the begin-                  mandibles because we considered that this value
    ning of the experiment the rats were 4 weeks old. The               was not useful to the purpose of our research, in that
    animals have been randomly divided into four groups
    of 17 (two experimental and two controls); of the two
                          iz



    experimental group, one had the right nostril occlud-
    ed with silicone material, while the other had the left
    nostril occluded. The animals belonging to two control
          Ed




    groups (groups C and D) had no nostril occluded and
    were sacrificed at two different times; respectively af-
    ter 4 weeks and after 12 weeks. Accommodation was
    made putting five rats per cage with water and food at
    their disposal (Tab. 1). A Student t-test was applied.
    The level of significance was set at 0.05. All statisti-
IC




    cal analyses were run on the statistical package
    SPSS (SPSS 17.0; SPSS Inc., Chicago, IL,USA).
    At the beginning of the observation period rats be-
    longing to Group C were sacrificed, in order to verify
C




    whether the growth of the rats was homogeneous or
    not: the measurements were quite the same, with a t-                Figure 1. One of the sample analyzed.


    Table 1. Subdivision of the rats in the four groups.
©




                    Group type           Number of rats         Nostril occluded          Sacrifice time          Average weight
    Group A         experimental         17                     left                      12 weeks                Gr 384 ± 23
    Group B         experimental         17                     right                     12 weeks                Gr 395 ± 32
    Group C         control              17                     none                      4 weeks                 Gr 72 ± 19
    Group D         control              17                     none                      12 weeks                Gr 388 ± 27


    54                                                                                     Annali di Stomatologia 2015; VI (2): 53-57
    Craniofacial growth and respiration: a study on an animal model


    the volume of the superior aerial column shall not be           S4: Articular surface of the condyle – Mental foramen
    modified by the thickness of this particular bone.              (SARFORO)
    The acquired data concerning the linear measure-                The average, standard deviation, mode and median
    ments measured on the rats’ mandible may be divid-              were calculated for every variable measured. The
    ed into two main groups: sagittal measurements (Fig.            statistical significance of the increases in evidence




                                                                                                             i
    2) and vertical measurements (Fig. 3).                          were ascertained with the use of t-test (p<0.05) for




                                                                                                           al
    With regard to the vertical values they were identified         correlated samples (matched data) in the sample and
    perpendicular to a reference line passing from the up-          the control group. Due to the uniform genetic and
    per reference point, the following distances were con-          phenotypical characteristics of the sample it was not




                                                                                                        on
    sidered:                                                        necessary to apply non parametric statistical tests,
    V1: Superior condyle surface - Base (SCOSUB)                    where the conclusions obtained are valid indepen-
    V2: Maximum concavity sigmoid notch - Base                      dently from the normality of the population and the
    (XCOINSB)                                                       homogeneity of the variance between the groups.
    V3: Medial surface of the first molar - Base (SUMESM)           The application of the t-test was, therefore, consid-




                                                                                             zi
    V4: Maximum concavity inferior arch - Base (XCOARIB)            ered to be sufficient.
    With regard to the sagittal values, the following dis-
    tances were considered (Figure below):




                                                                                 na
    S1: Articular surface of the condyle - Incisal margin           Results
    (SARMI)
    S2: Articular surface of the condyle – Medial surface           The sagittal measurements demonstrate a homoge-
    of the first molar (SARSMM)                                     nous increase in the values together with a reduction




                                                                      er
    S3: Articular surface of the condyle - Incisal neck             of the standard deviations (p<0.05). The SARCIN val-
    (SARCIN)                                                        ues increase compared to the control; after 8 weeks
                                                                    of obstruction in the upper nasal airways, a notice-
                                                                    able increase in the values and a decrease of the



                                                           t        standard deviation was observed.
                                                        In          The values of SARFORO, SARMI and SARSMM also
                                                                    present a similar trend with an increase in the dis-
                                                                    tances and a compression of the standard deviations
                                                                    (Tab. 2).
                                                                    When analysing the data concerning the vertical dis-
                                                 ni
                                                                    tances a tendency towards an increase in the linear
                                                                    values is noted, accompanied by a modest growth in
                                                                    the standard deviation.
                                    io

                                                                    The values SUMESM, XCOARIB, and XCOINSB all
    Figure 2. Sagittal measurements.
                                                                    demonstrate an increase in the linear dimensions and
                                                                    a modest increase in the standard deviation.
                                                                    Three rats died after nasal obstruction and, as al-
                           iz



                                                                    ready said before, the real obstruction of the nasal
                                                                    cavities was found in 29 out of 31. Considering the
                                                                    weight, no significant differences were observed be-
          Ed




                                                                    tween the test group and the control group.


                                                                    Discussion

                                                                    The lack of experimental studies on the modification
IC




    Figure 3. Vertical measurements.                                of maxillofacial growth in rats following obstruction of

    Table 2. Measurements found analysing the rats after they were sacrificed.
C




                                             Control                                          Experimental
                      Mean (mm)            S.D.         T-Test p<0.05        Mean (mm)         S.D.           T-Test p<0.05
    SARCIN            24,5                 0,6100       0                    24,8              0,6080         0
    SARFORO           20,2                 0,6661       0                    20,5              0,4740         0
©




    SARMI             29,9                 0,5690       0                    29,9              0,8480         0
    SARSMM            18,4                 0,4930       0                    18,7              0,3760         0
    SCOSUB            11,5                 0,4410       ns                   11,5              0,4500         ns
    SUMESM            6,8                  0,2150       0                    7                 0,3930         0
    XCOARIB           4,6                  0,1586       0                    4,8               0,2650         0
    XCOINSB           10,7                 0,3750       0                    10,9              0,4080         0


    Annali di Stomatologia 2015; VI (2): 53-57                                                                           55
    L. Levrini et al.


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                                                                                                               i
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    Annali di Stomatologia 2015; VI (2): 53-57                                                                                       57
