|Year : 2018 | Volume
| Issue : 3 | Page : 178-185
Hazards of soft modern food on the periodontium of adult albino rats
Gihan S Hassan, Reda G Saleh, Dalia H Zahran
Department of Oral Biology, Faculty of Dentistry, Tanta University, Tanta, Egypt
|Date of Submission||15-Feb-2018|
|Date of Acceptance||12-May-2018|
|Date of Web Publication||10-Oct-2018|
Dalia H Zahran
Department of Oral Biology, Faculty of Dentistry, Tanta University, Tanta
Source of Support: None, Conflict of Interest: None
The ever-increasing widespread use of modern fast food with its soft consistency strongly argues for its deleterious effects on the periodontium ligament (PDL).
The objectives of this study were to investigate the effect of soft diet consistency on the integrity of the periodontium of adult Albino rats and its reversibility by shifting into normal diet consistency.
Materials and methods
A total of 15 adult male Albino rats, 6 weeks of age were used. The animals were divided randomly into three equal groups; control group received hard diet for 6 weeks, the experimental group received soft diet for a period of 6 weeks while the recovery group received soft diet as experimental group and then changed to hard ordinary diet for another 4 weeks. At the end of the experimental period, all animals were anaesthetized and the mandible was dissected then the animals were euthanized. The periodontium of the molar region was examined by light microscope and scanning electron microscope. The thickness of PDL was also calculated and statistically analyzed.
Soft diet administration in the experimental group led to thick and proliferated junctional epithelium, dissimilarity of the width of the PDL on both sides of the root, bony projections at the wide side of the PDL, disorganized PDL bundles and resorption of alveolar bone, cementum and dentin at the narrow side of the PDL. In the recovery group, some improvement of the periodontium was evident as detected by light and scanning electron microscope examinations. Statistical analysis revealed that PDL thickness decreased significantly in the experimental group compared to other groups.
The soft consistency of modern fast food disturbs the structural integrity of the periodontium and their hazards can be prevented by avoiding fast food consumption.
Keywords: alveolar bone, cementum, junctional epithelium, periodontium, soft diet
|How to cite this article:|
Hassan GS, Saleh RG, Zahran DH. Hazards of soft modern food on the periodontium of adult albino rats. Tanta Dent J 2018;15:178-85
|How to cite this URL:|
Hassan GS, Saleh RG, Zahran DH. Hazards of soft modern food on the periodontium of adult albino rats. Tanta Dent J [serial online] 2018 [cited 2019 May 26];15:178-85. Available from: http://www.tmj.eg.net/text.asp?2018/15/3/178/243078
| Introduction|| |
Modern food is totally different from before in many aspects including its high carbohydrates, fat and sugar content and low vitamins content. In addition, most modern food with fewer raw materials has soft consistency. The intake of fast food has increased markedly since the 1970s  and fast food consumption has been linked to many health adverse effects, mainly due to its soft consistency and poor nutritional quality .
The periodontium is the tissue that supports and invests the tooth. It consists of the cementum which covers the roots of teeth; the alveolar bone which surrounds and supports the tooth root; and the periodontal ligament (PDL) which is situated between these two hard tissues and functions as a kind of hammock in which the tooth is nestled . It has been confirmed that masticatory function is an essential factor that strongly affects the structure and function of the alveolar bone and PDL ,,. There is sufficient evidence that food hardness is sensed during mastication and affects the masticatory forces .
It is also well documented that modern food with soft consistency leads to decreased strength of masticatory muscles (occlusal hypofunction) which in turn affects the architecture of the alveolar bone and PDL . There have been several animal studies to determine the relationship between occlusal hypofunction and the changes in the alveolar bone, PDL, tempromandibular joint, and condyle in adult rats ,,. According to these studies the alveolar bone in rats with occlusal hypofunction; achieved through soft diet; showed thinner, taller trabeculae and its density was low ,. Also, Denes et al.  confirmed the narrowing of the alveolar processes, decreased thickness of PDL and small alveolar socket surface in rats fed a soft diet.
Although previous studies discussed the influence of soft diet consistency on the PDL there is a few knowledge explaining these changes on the periodontium at the histological and scanning electron microscope (SEM) levels. Therefore the present study was designed to investigate the effect of diet consistency on the integrity of periodontium (gingiva, PDL, alveolar bone, and cementum) of adult Albino rats and whether these effects were reversible by changing the diet consistency to normal. These effects were assessed by both qualitative and quantitative methods.
| Materials and Methods|| |
Fifteen male Albino rats, 6 weeks of age, were obtained from the Histology Department, Faculty of Medicine in Tanta University and kept under the standard laboratory conditions. After 1 week of acclimatization, rats were randomly divided into three equal groups. Control group received hard (ordinary) diet for 6 weeks. Experimental group, received soft consistency diet for a period of 6 weeks by mixing the ordinary diet with water at a ratio of 1: 1. Recovery group, received soft consistency diet as experimental group and then changed to hard ordinary diet for another 4 weeks. All rats were fed diet and water ad libitum throughout the experimental period. At the end of experimental period, rats were anesthetized with ketamine chloride (Ketalar, 40 mg/kg body weight), Ketalar (par pharmaceutical companies, Inc.suffern, NY, USA) and the mandible was dissected and then the rats were euthanized by cervical dislocation. The mandibles was separated into two halves, one half was immediately fixed in buffered formaldehyde (pH: 7.4) for 48 h for light microscopic study. The other half was fixed in 2.5% glutaraldehyde for SEM study. Images of the hemotoxylin and eosin (H and E) stained sections was analyzed for PDL measurements using the ImageJ analysis system (ImageJ 1.48s), (Java-written Inc, Colorado, USA). Data were entered and coded into Microsoft Excel, (Microsoft inc, Las Vegas, USA). Statistical package for the social sciences version 22.0 was used for data analysis (SPSS; SPSS Inc., Chicago, Illinois, USA). Approval for this research was obtained from Research Ethics Committee, Faculty of Dentistry, Tanta University. The procedures were designed in accordance with the guidelines for the responsible use of animals in research as a part of scientific research ethics recommendation of the Ethical Committee, Faculty of Dentistry, Tanta University.
Histological procedures for light microscopic evaluation
The specimens were decalcified in 10% EDTA for 4 weeks. They were washed in tap water over night and then dehydrated in ascending grades of alcohol, cleared in xylol and embedded in paraffin wax (56–58°C mp). Sections (4–6 μm) were cut with rotary microtome (lyca) and then performed for H and E staining, Masson–Goldner trichrome staining (Sigma #HT15; Sigma-Aldrich, St. Louis, MI, USA) in accordance with the manufacturer's protocol and the periodontium was observed under the light microscope .
Scanning electron microscopic evaluation
Fresh specimens were fixed in (2.5% glutaraldehyde for 72 h). Two parallel cuts were done in the molar area with a rotary microtome followed by a freehand dissection of the buccal plate of bone to expose the molar roots and the surrounding PDL and alveolar bone [Figure 1]. These exposed surfaces were treated for 1/2 h with 5% sodium hypochlorite (commercial bleach) to remove organic tissues . The specimens were cleaned ultrasonically to remove bone dust and other debris. After cleaning, they were washed twice in buffer to remove any unreacted aldehyde. Postfixation was performed with (1% OsO4 for 24 h) followed by washing in PBS and dehydration in ascending grades of alcohol followed by two washes in acetone. Then they were dried, mounted on stubs and coated with gold using a sputter coater . The processed specimens were analyzed at 25 kV accelerating voltage by SEM (JSM 5600LV; JEOL, Tokyo, Japan) in EM Unit of Faculty of Medicine, Tanta University.
|Figure 1: Photomicrograph of mandibular bone specimen prepared for scanning electron microscope. (a) Before removal of buccal bone plate and (b) after removal of buccal bone plate.|
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Statistical analysis for periodontal ligament measurements
The slides were visualized in a LM (Leica DM500) equipped with built-in camera (Leica ICC50 HD Camera), (Leica Microsystem, China). Images of the H and E stained sections of the molar area were analyzed for PDL measurements using the ImageJ analysis system. In longitudinal sections, the distance from the root surface to the alveolar bone surface was recorded at the middle of the roots (two measurements for a single root; one in each side) in power fields at ×100 magnification. The measurement at each point was performed and repeated three times by the same investigator and the mean value was used.
Descriptive statistics were done by expressing mean and SD. Inferential statistics were done using the analysis of variance test followed by Student's t-test. Data were collected coded and analyzed using the statistical software 'SPSS 20' for windows (Chicago, USA). Statistical significance was set at the level of 0.05, P value of less than 0.05 was considered statistically significant.
| Results|| |
Histological examination of H and E stained sections showed normal architecture of the periodontium. The junctional epithelium consisted of thin nonkeratinizing stratified squamous epithelium with a straight basement membrane supported by dense computed tomography (CT) and the gingival collagen bundles were thick and well oriented [Figure 2]a. Active fibroblasts with rounded nucleus in gingiva and PDL were detected. The cellular cementum was thick and located in the apical third of the root. The alveolar bone showed smooth surface in the mesial side of the root. While the distal side showed irregular surface with areas of resorption and bone formation [Figure 2]b. The PDL has functionally oriented collagen bundles on both sides of the root [Figure 2]c.
|Figure 2: Photomicrographs of the control group. (a) Normal architecture of the junctional epithelium (arrow). (b) The alveolar bone (AV) shows smooth surface in the mesial side and irregular distal surface with areas of resorption lacunae and reversal lines (arrows). Normal architecture of cellular cementum (CC). The periodontal ligament (PDL) shows uniform thickness on both sides of the root. (c) Higher magnification of distal side illustrating well-organized principal fibers of PDL running between bone and cementum. The alveolar bone surface shows a resorption crater with osteoclastic activity and areas of bone formation. Enamel space (ES), dentin (d) (H and E original magnification, A and B ×10, C ×40).|
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Marked structural changes were observed in the periodontium of the experimental group. Gingiva: the junctional epithelium consisted of thick, proliferated epithelium supported with moderately inflamed highly vascular CT [Figure 3]a.
|Figure 3: Photomicrographs of the experimental group. (a) Thickened proliferated junctional epithelium (arrow). Disorganized collagen bundles with areas of hyalinization (arrow heads). (b) Dissimilarity of the periodontal ligament (PDL) width on both sides of the root and projections of alveolar bone (AV) at the wide side. (c) Partial separation between dentin and cellular cementum (arrows). Alveolar bone resorption (AV) in the distal side of the socket (arrow heads) and resorption of the dentin (asterisk). Dentin (d), enamel space (ES), gingival epithelium (GE) cellular cementum (CC) (H and E original magnification, A, B and C ×10).|
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Alveolar bone: on the compression side, resorption of alveolar bone [Figure 3]c with many resorption lacunae and osteoclasts were found [Figure 4]a.
|Figure 4: Photomicrographs of the experimental group showing disorganized and destructed periodontium. (a) Bone resorption lacunae containing osteoclasts along the alveolar bone surface (arrows). (b) Areas in which the periodontal ligament (PDL) seems to be divided into two halves with the one adjacent to the tooth showing disorganized principal fibers. (c) Area of cementum resorption (arrow) and hyalinization are visible at the narrow side of the PDL. Dentin (D), cementum (C), Alveolar bone (AV) (H and E original magnification, A, B and C ×40).|
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PDL: the orientation of the collagen bundles of the PDL was disturbed. The PDL thickness was uneven on both sides of the root [Figure 3]b and [Figure 3]c. The PDL seemed to be divided into two halves where the part adjacent to the tooth is more disorganized [Figure 4]b. In the narrow side of the PDL, signs of degeneration and hyalinization were obvious [Figure 4]c.
Cellular cementum: when compared to control group, dentin and cellular cementum was thicker on compression side only of the root with separation between dentin and cementum. Dentin resorption on its pulpal surface [Figure 3]c and cementum resorption [Figure 4]c were evident on the same side of the root.
In general, the periodontium of recovery group presented some improvement in its histological features compared to the experimental group.
Gingiva: the junctional epithelium was relatively thin compared to the experimental group, and the collagen fibers of the supporting CT were more organized [Figure 5]a.
|Figure 5: Photomicrographs of recovery group showing nearly organized periodontium. (a) The junctional epithelium is relatively thin (arrow). (b) The alveolar bone (AV) and cellular cementum (CC) show more regular surfaces. Signs of separation between dentin and cellular cementum at the apical third of the root are still evident (arrows). The periodontal ligament (PDL) still shows variations in thickness in the two sides. (c) The PDL principle fibers are more organized and highly vascular. Areas of new bone formation and reversal lines can be noticed (arrow). Dentin (d), Enamel space (ES) (H and E original magnification, A ×4, B ×10, and C ×40).|
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PDL: the PDL shows highly vascularity and still shows variations in thickness in the two sides [Figure 5]b. Collagen bundles were almost organized with many active fibroblasts [Figure 5]c.
Cellular cementum: it was slightly thicker on compression side of the root than the other side. Signs of separation between dentin and cementum were still present [Figure 5]b.
Alveolar bone: the surface of the alveolar bone was more regular compared to the experimental group. New bone formation and reversal lines were present [Figure 5]b and [Figure 5]c.
The histochemical results of Masson's trichrome (MT) stain of gingiva and junctional epithelium in the control group revealed thin junctional epithelium and proper arrangement of mild to moderate staining of fine and coarse gingival collagen fibers [Figure 6]a. The experimental group showed proliferated junctional epithelium and disorganized gingival collagen fibers with areas of hyalinization [Figure 6]b. In the recovery group, the thickness of juctional epithelium was almost normal. However, areas of hyalinization were still present in the gingival CT [Figure 6]c. MT staining of the control group revealed thick PDL collagen fibers [Figure 7]a. The experimental group showed mild staining of thin PDL fibers. Many inactive fibroblasts with dark-staining, elongated nuclei were detected. Also, there was loss of insertion of Sharpey's fibers especially on the bone side and constricted blood vessels [Figure 7]b. Moderate to intense staining coarse PDL fibers with many active fibroblasts were seen by MT staining [Figure 7]c.
|Figure 6: Photomicrographs of different treatment groups. (a) Well-organized dense gingival fibers of the control group and thin junctional epithelium (arrow). (b) Disorganized gingival fibers of the experimental group with multiple areas of hyalinization (arrows) and excessive proliferation of junctional epithelium (arrow heads). (c) Moderately organized gingival fibers of the recovery group and nearly normal junctional epithelium (arrow head). Areas of hyalinization are still present (arrow). Enamel space (ES), Gingival epithelium (GE), dentin (d) (Masson-Goldner trichrome; original magnification, A, B and C ×4).|
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|Figure 7: Photomicrographs of the periodontal ligament (PDL) of different treatment groups. (a) Well.organized thick collage fibers of the control group and multiple insertion of Sharpey's fibers. Many active fibroblasts can be observed. (b) Disorganized PDL collagen fibers of the experimental group with loss of Sharpey's fibers insertion especially in alveolar bone side. Constricted blood capillaries (arrow). (c) The PDL collagen fibers of the recovery group are more organized compared to the experimental group. Numerous wide blood vessels are visible (arrows). Dentin (d) (Masson-Goldner trichrome; original magnification, A, B and C ×40).|
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Scanning electron microscopic results
SEM analysis of the PDL in control group revealed thick well-organized collagen fiber bundles running from alveolar bone to cementum. The insertion of Sharpey's fibers into the alveolar bone was obvious [Figure 8]a. The collagen fibers of the PDL of the experimental group were disorganized and the insertion of Sharpey's fibers was not obvious as in control group [Figure 8]b. Some reorganized thick collagen fiber bundles were marked in the PDL of recovery group [Figure 8]c.
|Figure 8: Scanning electron microscope photograph of the periodontal ligament (PDL) of different treatment groups. (a) Thick collagen fibers of the PDL in the control group are running from cementum (c) to alveolar bone (AV) with obvious insertion of Sharpey's fibers (arrow). (b) The PDL of the experimental group shows disorganization of collagen fibers. Some of these fibers appeared thin (arrow) with areas of lack of insertion of Sharpey's fibers. (c) The PDL of the recovery group shows some thick reorganized collagen fibers.|
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The neurovascular canals were obvious on the alveolar bone of control group [Figure 9]a. Whereas, in the alveolar bone of the experimental group there were disorganized wide neurovascular canals and rough surface with multiple resorption lacunae [Figure 9]b. The alveolar bone of recovery group revealed slightly rough surface with fewer resorption lacunae and some wide neurovascular canals [Figure 9]c.
|Figure 9: Scanning electron microscope photograph of the alveolar bone surface of different treatment groups. (a) Normal architecture of the alveolar bone of the control group with narrow neurovascular canals (arrows). (b) The alveolar bone surface of the experimental group shows multiple bone resorption lacunae and widening of neurovascular canals (arrow). (c) The alveolar bone surface of the recovery group shows fewer resorption lacunae compared to the experimental group. Some neurovascular canals are normal (arrow) while others are slightly widened (arrow head).|
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The cementum surface of control group was smooth and regular [Figure 10]a, while that of the experimental group showed wide area of resorption [Figure 10]b. On the other hand, the cementum surface of recovery group, the resorption area was quite small, and patches of new cementum were present [Figure 10]c.
|Figure 10: Scanning electron microscope photograph of the Cemntum surface of different treatment groups. (a) Smooth cementum surface of the control group. (b) Areas of resorption of the cementum surface of the experimental group (asterisk). (c) Multiple patches of cementum in the recovery group (arrow) and small area of resorption (arrow head).|
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Statistical analysis for periodontal ligament measurements
The greatest mean value of quantitative PDL measurements was recorded in control group with the least value obtained in experimental group. Analysis of variance test revealed a highly significant difference between the three groups (P < 0.01; [Table 1], [Figure 11]).
|Figure 11: Column chart representing means of periodontal ligament (PDL) measurements.|
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The t-test revealed that the difference of PDL thickness between control groups and experimental group was statistically highly significant [Table 2], while it was statistically significant between control group and recovery group [Table 3]. With nonsignificant value between experimental group and recovery group [Table 4].
|Table 2: Comparison the means of periodontal ligament measurements in control groups and experimental group|
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|Table 3: Comparison of the means of periodontal ligament measurements in control group and recovery group|
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|Table 4: Comparison of the means of periodontal ligament measurements in experimental group and recovery group|
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| Discussion|| |
The present study was conducted to investigate the influence of soft consistency of modern food through consumption of soft diet on the periodontium of Albino rat. All constituents of the periodontium were observed in this study as they function together as one unit and the components of one periodontal part were found to influence the maintenance, repair or regeneration of the other structures . It is noteworthy to mention that various approaches have been used in the literature to achieve functionless model and decreased occlusal load, including extraction or occlusal reduction of the opposing teeth , bite opening by application of composite on the occlusal surfaces of molars  or by attaching appliances to maxillary and mandibular incisors of rats to produce masticatory hypofunction in molar region . These studies represented a functionless model which is different from the hypofunctional model used in the current study, where the soft diet feeding decreased the occlusal stimuli on teeth. In addition, the model used in our study made it possible to reestablish the normal occlusal stimuli by returning to the normal hard diet, which is not possible with other functionless models such as extraction of opposing teeth.
Histological assessment of the specimens from 12 weeks old rats fed hard diet (control group) showed normal architecture of the periodontium in rats at this age. However, the alveolar bone showed smooth surface mesially and irregular surface distally with areas of resorption lacunae and reversal lines. In rats, distal physiologic drift begins at the age of 12 weeks  in which alveolar bone remodeling occurs on one side of the socket and modeling on the other side. Although the tooth migrates, the width of PDL remains constant . Moreover, Levy and Mailland  reported two sides; the apposition side, showing regular bone deposition, while on the resorption side there were alternating areas of resorption and bone formation that preserved the attachment of Sharpey's fibers .
Additionally, MT stain was used in this study to determine the orientation and thickness of collagen fibers along with activity of fibroblasts in the periodontal tissues as the standard H and E stain offers only the morphological alterations ,,. The histochemical results of MT stain in control group revealed proper arrangement of mild to moderate staining of fine and coarse collagen fibers besides active fibroblasts with rounded nucleus in gingiva and PDL.
Whereas rats fed soft diet for 6 weeks revealed hypofunctional changes of the periodontium compared to control group. In agreement with our results, Ishida et al.  observed thickening of the junctional epithelium in hypofunctional teeth which was more obvious 4 weeks after extraction of their antagonist. Furthermore, the authors reported disorganization of the collagen fiber bundles in the connective tissue stroma of the gingiva especially in the dentogingival fibers. These changes may be caused by the decreased mechanical stimuli on teeth, which are essential for the maintenance and remodeling of the periodontal tissues, as a result of soft diet feeding. Moreover, the decreased functional load may reduce necessity for supporting the tooth that may result in the disappearance of the functional arrangement of collagen fibers in the gingiva.
In the present study, PDL fibers showed various degrees of disorganization and degeneration that could be explained by the variations of masticatory load and the length, size or inclination of the root. The MT stain and SEM examination confirmed the disorganization and thinning of the collagen fibers. Lack of Sharpey's fibers insertion into bone and cementum was explained by Deporter and Ten Cate  as a part of alveolus remodeling. Nevertheless, the area of loss of attachment coincided more with atrophy of Sharpey's fibers that was described in hypofunctional teeth ,.
It has been confirmed that the reduced masticatory load in hypofunction models resulted in a decrease in PDL thickness after 6 weeks  or after 8 weeks  with a lower rate of collagen fibers turnover. The dissimilarity of PDL thickness on both sides of the root observed here could be a result of tooth rotation as a consequence of occlusal hypofunction which coincided with Chattah  who stated that the multirooted molar could rotate at lower functional loads on the tooth, using the inter-radicular bone as a fulcrum and consequently alter the localized widening and narrowing of the PDL space . In addition the consumption of soft diet decreased the functional loads on the bone-PDL-tooth complex, therefore the distally directed forces due to innate distal drift in rats resulted in tooth movement . In this study, increased thickness of cellular cementum in compression side of the root was evident. This was in agreement with Tsuchiya et al.  who reported active cementum formation only on the distal surface of molar root perhaps due to less mechanical stress related to the diminished physiological distal drift as a result of reduced occlusal loads ,. Also, this was contradictory to Denes et al.  who suggested that bone deposition at one side of the alveolar socket was responsible for narrowing of the PDL that occurred as a result of disuse atrophy following defects in occlusal function.
The atrophy of the periodontium as a result of decreased masticatory load was explained by decreased expression of vascular endothelial growth factor and fibroblast growth factor as a consequence of occlusal hypofunction. It has been suggested that these growth factors have an important regulatory role in angiogenesis and expansion of blood vessels as mediators of occlusal stimuli which are essential to maintain the structural integrity of the periodontium . Also, these growth factors are involved in bone remodeling and therefore affect the thickness of PDL area . The PDL in the LM and SEM examination displayed the PDL composed of two separate parts; one related to cementum showed more disorganization than bone related PDL. This could be elucidated by thinner diameter of the cementum related fibers which make it readily affected than the other part.
In the current study, increased separation between the dentin and the cellular cementum at the apical third of the root, marked thickening of cementum of the experimental group and areas of cementum resorption (external root resorption) were detected by light and SEM examination. It is well known that the cellular cementum is mainly responsible for resistance to functional loads . Also, Nanci  confirmed that in rats, acellular cementum formation starts on mineralized root dentin, often in presence of epithelial cells which explains the separation between the two tissues by cells. Secondary cementum resorption in response to decreased occlusal load was also reported by Niver et al.  who demonstrated regional pitting on the root surface indicating resorption activity to cementum. Also, Hayashi et al.  reported several resorption lacunae containing odontoclasts on the root surfaced in hypofunctional teeth. The authors concluded that diet consistency markedly affects the functional loads experienced within the periodontium and that the masticatory hypofunction was not sufficient to maintain tissue homeostasis resulting in loss of PDL mechanical integrity and resorption of cementum and bone. In addition to the external root resorption observed here in experimental group, there was also internal resorption of the root (resorption of dentin). The internal resorption was attributed to the decreased occlusal stimuli that markedly affected the metabolism of PDL and dental pulp . Moreover, Shibutani et al.  disclosed that the microvasculature could spread the degeneration of PDL to the pulp.
In the current study, soft diet induced alveolar bone resorption and resorption lacunae containing osteoclasts were detected along the alveolar bone surface lining the sockets. It has been confirmed that occlusal stimuli are crucial to the underlying alveolar bone structure and decreased occlusal load by consumption of soft diet resulted in decreased width of the alveolar bone . Also, Shimizu et al.  demonstrated that soft diet feeding induced atrophic changes of the PDL and alveolar bone and led to disuse osteopenia of the alveolar bone. Moreover, animals fed soft diet had higher and narrower alveolar process with a trabecular bone network of low quality and quantity ,. The findings of several resorption lacunae with multinucleated osteoclasts along the alveolar bone surface in molars were reported by Hayashi et al.  after attaching anterior metal cap and bite plate to maxillary and mandibular incisors to simulate occlusal hypofunction in the molar region.
Interestingly, the results of MT and SEM from recovery group showed that when the normal function was restored by returning to normal hard diet, some improvement of the periodontium was observed. The restoration of masticatory function resulted in re-adaptation of the periodontium as indicated by the relatively thin junctional epithelium, more regular surfaces of cementum and alveolar bone, highly vascularized PDL with more regular principle fibers and the observation of new bone formation and reversal lines. The PDL thickness in recovery group was significantly different from control group, while there was no significant difference in PDL thickness between recovery group and experimental group. The recovery from the atrophic changes of the periodontium induced by soft diet and decreased occlusal stimuli has also been reported by several studies ,,. However, in the current study the reversibility of the atrophic changes of the periodontium was incomplete and a longer recovery period may produce further improvement.
In conclusion, the results of our study confirmed that normal occlusal stimuli are important for the maintenance and remodeling of the periodontium. Also, it is obvious that the change in diet consistency via consumption of modern food with soft consistency caused atrophic changes in the rat periodontium. Moreover, these changes could be improved by shifting to normal hard diet.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11]
[Table 1], [Table 2], [Table 3], [Table 4]