Effect Of Labial Muscle Movement On Alveolar Bone Resorption In The Maxillary Anterior Teeth After Tooth Extraction

Background:With the development of society,aesthetic effects have become the main focus of successful implant therapy.However,one of the greatest difficulties and pitfalls in inserting implants in esthetic areas,especially in the anterior maxilla,is bone resorption triggered by the tooth extraction.Although there are many methods that can make up for bone loss after extraction,it is still a research hotspot to preserve the autologous bone tissue.Among them,the effect of labial muscle movement on bone resorption in the anterior maxillary area has not been quantified.Objective: In this animal study,the upper anterior teeth losing model was created in order to exploring the effects of labial muscle movement on alveolar bone resorption in the maxillary anterior area,and guiding the application of the pressure bearing device after tooth extraction in clinical.Materials and methods:1.Preparation of lip baffles and measuring plates: Six beagle dogs,with a mean age and weight of 1 years and 10 kg,respectively,were used.Under general anesthesia,the maxillary model was taken to make lip baffles and measuring plates.The measurement holes were prepared at the positions of the distal alveolar crest and1 mm and 3 mm below the distal alveolar crest in incisor extraction sockets.2.Animal surgery: Six incisors were extracted from each Beagle dog after sterilization and anesthesia.According to whether the lip block was worn,it was divided into an experimental group(with a lip baffle)and a control group(natural healing).On the day of surgery,3 months and 6 months after surgery,the vertical distance between the measurement plate and the distal alveolar ridge and the horizontal distance between the measurement plate and the labial bone plate(1 mm and 3 mm below the distal alveolar ridge)were measured.Then bone resorption was calculated.The animals were sacrificed after 6 mouths.Specimens were taken for gross observation,Radiographic assessment and histological observation,then statistical analysis was performed on the observed data.Results:1.Gross observation:There is no death of experimental dogs.Three days after the operation,the diet and life-habit recover to normal,Overt signs of soft-tissue inflammation(swelling and redness)were seen in sites.The mucosa covering the sockets after 1 week of healing were considered to be clinically healthy.No inflammatory reaction and no symptoms of wound infection.At 3 months after operation,the shape of the extraction area in experimental groups were protruded compared with the control groups,and the experimental mucosa slightly proliferated.At 6 months after operation,the contour of the extraction area in control groups were protruded compared with the experimental groups,and there was tissue hyperplasia in the vestibular sulcus of the experimental group.2.Radiographic assessment:All extraction sockets healed uneventfully,and the contour of the extraction area on the control side was bigger than on the experimental side.A continuous bone cortex can be seen at the top of each extraction socket,and the bone density in the extraction socket is uniform,and mature trabeculae can be seen.3.Histologic examination:In all specimens,a thick,well-keratinized mucosa covered the healed socket.The connective tissue was devoid of inflammatory cell infiltrates but was characterized by the presence of a dense network of collagen fibers.In the socket,mineralized bone trabecula consisted by woven and lamellar bone connected the buccal and lingual crests.4.Statistical analysis:Three months after surgery,the vertical bone resorption of the distal alveolar crest in the experimental group and the control group were 2.30 ± 0.31 mm and 2.44 ±0.27 mm respectively;the horizontal bone resorption of the labial bone plate,which was 1mm below the distal alveolar crest in the experimental group and the control group,were 1.43 ± 0.44 mm and 1.05 ± 0.36 mm respectively.;the horizontal bone resorption of the labial bone plate,which was 3mm below the distal alveolar crest in the experimental group and the control group,were 1.28 ± 0.42 mm and 1.00 ±0.26 mm respectively.Six months after surgery,the vertical bone resorption of the distal alveolar crest in the experimental group and the control group were 2.37 ±0.33 mm and 2.54 ± 0.38 mm,respectively;the horizontal bone resorption of the labial bone plate,which was 3mm below the distal alveolar crest in the experimental group and the control group,were 1.87 ± 0.36 mm and 1.13 ± 0.29 mm,respectively;the horizontal bone resorption of the labial bone plate,which was 3mm below the distal alveolar crest in the experimental group and the control group,were 1.84 ± 0.32 mm and 1.07 ± 0.25 mm respectively.(Table 1)The maximum gray values measured in the extraction fossa of the experimental group and the control group by CBCT were 837.22 ± 56.51 Hu and847.00 ± 98.98 Hu respectively.(Table 2)Statistical analysis found that there was no significant difference in vertical bone resorption in the experimental group and the control group on 3 and 6 months after surgery(p> 0.05),which was not statistically significant;The horizontal bone resorption of the labial bone plate in control group was significantly lower than the experimental group on 3 and 6 months after surgery(p <0.05),which was statistically significant.Six months after operation,there was no significant difference in the new bone mineral density in the extraction socket between the experimental group and the control group(p> 0.05),which was not statistically significant.Conclusion:1.Within 6 months after tooth extraction,the height of alveolar ridges and labial bone mass in the extraction socket were significantly reduced.Among them,the height of the alveolar ridge and the amount of bone on the lip side changed significantly within 3 months,and 3 to 6 months after surgery the decrease of the height of the alveolar ridge became slower,and the bone resorption on the lip side became stable.2.Labial muscle movement has no significant effect on alveolar bone resorption and the healing of sockets in the anterior maxillary area,but some changes still need to be further explored.