| BackgroundMaxillary sinus augmentation had developed into a mature technique since it was raised by Tatum in 1986.The maxillary sinus augmentation contained osteotome technique and lateral window technique.The classic technique for maxillary sinus floor-augmentaion is based on the insertion of bone graft substitutes into the space created between the Schneiderian membrane and the bony walls of the maxillary sinus.Autogenous bone was considered as the gold standard for bone graft materials.But due to its unpredictable absorption rate and a relatively small amount,bone substitute materials was used in clinic instead of autogenous bone.There are four kinds of bone substitue materials,include allograft,heterograft and artifical bone.Allograft and heterograft may cause different degrees of immune rejection and potential of the spread of disease,meanwhile losing part of the bone inductivity after the process of removing antigenicity.Artificial bone materials induce bone formation base on its osteoconductive potential,it is easily to experience injection and postoperative complication through a long time for the revascularization of creeping substitution process.The absorption of the artificial bone,determined by the size and porosity of the particle and the composition of chemical structure,may affect the formation and reconstruction of the new bone,and its manufacturing process is relatively complex,generating higher technical requirements.In conclusion,all kinds of bone substitute materials have its inherent shortcomings,there is no ideal clinical bone substitute material at present.The main function of bone substitute materials is to induce the formation of the new bone and maintain the space created between the Schneiderian membrane and the bony walls of the maxillary sinus.If the induction and the space can be achieved,is it accessible to perfome maxillary sinus lift without the use of bone substitute materials?Ellegaard reported a result of implant therapy involving a sinus membrane lift as well as conventional implant therapy in 24 periodontally compromised patients.Patients were included on the basis of being in need of at least two implants,one of which was to be placed in the maxillary sinus region and at least 3 mm bone height was required int the sinus region.A fenestration with a diameter of about 10mm was prepared in the lateral sinus wall approximately 5mm above the anticipated bottom of the sinus,the sinus membrane was lifted away from the margins of the fenestration and dissected form the osseous sinus floor,the implants were inserted into the sinus through the alveolar crest and the membrane was allowed to settle on the implants,thereby creating a void which would be filled with coagulum.A radiographic evaluation of the sinus implants revealed some new bone formation around the upper part of the implants extending into the sinus cavity in most of the sinus implants.Howver,the extent of new bone formation varied,and in two case did the originally denuded part of the implants appear to be completely surrounded by bone.Lundgren reported a clinic case which a patient referred for sinus augmentation,an intrasinus mucosal cyst was removed 3 months prior to the planned augmentation procedure,a replace bone window was prepared in the lateral aspect of the sinus wall,and the cyst was removed,the bony window was replaced.After 3 months of healing the space between the replaced bony window and the lifted sinus membrane was filled with newly formed bone.The surgical technique was repeated in a second patient and resulted in a similar bone reformation pattern.Lundgren performed a study to investigate whether sinus membrane elevation and the simultaneous insertion of implants without additional grafting material constitute a valid technique for bone formation of the maxillary sinus floor.A replaceable bony window was prepared in the lateral sinus wall with an oscillating saw.The sinus membrane was dissected,elevated superiorly,and sutured to the sinus wall to create and maintain a compartment for blood clot formation.One to three dental implant were inserted through the residual bone and protruded at least 5mm into the maxillary sinus.All implants remained clinically stable during the follow-up examination,and the comparisons of pre and postoperative CT radiography demonstrated new bone formation within the compartment created by the sinus membrane elevation procedure.The nongrafted maxillary sinus elevation gained more and more attention after this clinic coincidence and exploration.Scala proposed that the healing process of nongrafted maxillary sinus elevaton was initiated by the formation of a coagulum and followed by a provisional matrix and woven.Subsequently,a parallel-fiber bone replaced woven bone.Sprouts of woven bone,present to a moderate extent after 4 days,were more numerous after 10 and 20 days.After 30 days the window access appeared to be closed by a layer of newly formed trabecular bone.The blood clot is a necessary condition for the formation of new bone.Earlier study revealed that the space created between the Schneiderian membrane and the bony walls of the maxillary sinus was kept by the inserted implants.In physiological condition,the process of bone rebuilding were in a state of balance,includes bone deposition and bone resorption,the osteoclast were actived under the compressive stress and the resorption begin,the osteoblast were actived under the tensible stress and the deposition started.The presence of air pressure caused by respiration can motive the activity of osteoclast and evevtually lead to bone resorption.Asai performed a study which was undertaken to establish an experimental model for maxillary sinus augmentation in rabbits and to clarify the bone response to the occluded nasal ostium.In rabbits without ostial occlusion,the elevation of the sinus mucosa resulted in formation of a subantral hollow space filled with blood clots and granulation tissue 1 week after operation.The newly formed bone filled in the space had a central granulation tissue.The space was almost completely replaced by a normal sinus airspace after 3 weeks.In rabbits with ostial occlusion,a fully formed bone mass was seen after 3weeks.The mass had both mature trabeculae and peripheral cortical bone containing no sinus airspace after 6 weeks.This animal model for maxillary sinus augmentation improve the understanding of the bone formation procedure in humans and delineate how sinus air pressure caused by the occluded nasal ostium affects the quantity and fate of newly formed bone.Kim investigated the feasibility of maxillary sinus floor augmentation using the venous blood in conjunction with a sinus membrane elevation procedure,An implant that protruded 8mm into the maxillary sinus after sinus membrane elevation was placed in the maxillary sinus of six adult female mongrel dogs.The resulting space between the membrane and the sinus floor was filled with autologous venous blood retrieved from each dog.The implants were left in place for 6 months.During the experimental period,the created space collapsed and the sinus membrane fell down onto the implant.A small amount of new bone formation occurred in the space created by the collapsed membrane.The average height of newly formed bone around the implants in the sinus was 2.7 ± 0.7mm on the buccal side and 0.6 ± 0.3mm on the palatal side.The results of this pilot study indicate that blood clots do not have sufficient integrity to enable the sinus membrane to remain in an elevated position for therapeutically effective periods of time and the space need to be kept by a rigid device.Dental implant was the most comm device used for space maintaining,But sometimes the volume of bone in maxillary sinus region can not meet the requirement of stability and implants can not be insert simultaneously.So is it possible to design a space maintaining device for maxillary sinus membrane lifting?The space maintaining device can hold the maxillary sinus membrane at a certain height.Not only can prevent the collapse of the maxillary sinus membrane,but also can keep off the new bone formation away from the compressive stress area.The most common complication of the sinus augmentation was the perforation of membrane.Perforation temporarily lead to the loss of sealed healing environment.Drain of blood clot,mucus and bacteria invasion can increase the risk of infection.For a small range of perforation,the area can be self-repaired to achieve the objective of the elimination of perforation.What was the effect of perforation on new bone formation without graft materials and can the perforation be healed by the potential of self-healing?ObjectiveThe aim of the presnt study was to to design a space maintaining device and investigate the feasibility of maxillary sinus floor augmentation using the space maintaining device in a model with bone volume deficiency in the maxillary posterior region.The aim of the presnt study was to to evaluate the quantity and source of new bone formation through mere sinus membrane elevation and to assess the influence of perforation on nongrafted sinus floor technique.Materials and Methods1.The design of the space maintaining deviceThe space maintaining device was made of titatium which was purchased form theTengxin Company and was manufactured bt Tongjia Company.The thickness of space maintaining device was 0.2mm and the height was 4.5mm,the shape was consistent with the form of a cap and its supporting area was similar to a circular area.There are many holes with a diameter of 0.5mm cover the surface of the device and the distance between each hole was 0.5mm.2.Experimental animals and modelsA total of five adult male Beagle dogs,about 1 year of age and weighing 11-12.6kg were included in the study.The animals were maintained in individual cages at the Guangdong Laboratory Animals Monitoring Institute,Guangzhou,China.The license number was SCXK2013-0007 and the certificate number was 44006900000057.The aninmal were sedated with ketamine hydrochloride ketamine hydrochloride 15mg/kg body weight,administered intramuscularly.Before surgery or at any manipulation of the animals,general anesthesia was performed with pentobarbital sodium,30mg/kg body weight.The anesthesia was supplemented by local administration of 4%articaine with 1:100000 epinphrine.Before surgery,the animals received dental prophylaxis procedures,and all of the surgical sites were washed with 0.12%chlorhexidine gluconate solution.The surgeries were performed under sterile conditions.The model with bone volume deficiency in the maxillary posterior region was established by the extraction of the teeth in the maixillary region and the elimination of alveolar crest.CBCT was performed before the surgery to certificate the height of maxillary sinus region was below 2mm.3.Surgical procedureAfter a midcrestal and vertical releasing incisions,mucoperiosteal flaps were raised and reflected at the edentulous area.The lateral bone of infraorbital nerve were removed and the infraorbital neurovascular bundle were ligatured to exposure the lateral aspect of the maxillary sinus.A rectangular bony window,approximately 10 x 7 ± 2mm,was created and the Schneiderian membrane was carefully elevated using sinus floor elevators,a perforation of 2mm in diameter randomly created in one side.Five animals received a space-maintaining titanium device,approximately 8mm wide and 4.5mm high.The mucoperiosteal flap was sutured with absorbable sutures.The animals were fed with a soft diet during the first 15 days and were given an oral dose of gentamicin,80mg/kg,for 7 days.4.SacrificeThree animals were sacrificed 3 months after the surgery,and the other two animals were sacrificed 6 months after the initial surgery.The animals were anesthetized with pentobarbital sodium and the maxillar was retrieved en bloc and the surrounding soft tissues were detached,the specimens were subjected to postfixation with 4%paraformaldehyde in 0.1M sodium phosphate buffer.The specimens were measured with Micro-CT and dehydrated in a series of ethanol,embedded in methyl methacrylate and cut in a Mesio-distal plane using a diamond saw.The final specimen reduced to a thickness of about 50μm by microgrinding and polishing using a cutting grinding device.The specimens were stained with toluidine blue.The percentage of new bone、the percentage of new bone occupied in the lift space and mineralization in the hole were assessed by Image-Pro-Plus.Result1.General observationAll the animals were revived within one hour and the wound achieved healthy healing after one week,all animals are in good condition throughout the entire follow-up and no major complications occurred during the observation time.2.Observation of sampleAll maxillary sinus showed no inflammation.The bone window healed well and no displacement of the space maintaining device was observed.The space maintaining device were underneath the maixllary sinus membrane.No perforation were observed between the experimental group and the control group.The perforation in experimental group were compeletely repaired.3.Observation of the specimenThe specimen contain the device was transparent and presented with no bubble,the boundary between the device and the PMMA were clear.Part of the device falled off and the section was in coronal plane.4.Observation of Micro-CT(1)The space maintaining device layed on the floor of maxillay sinus cavity and the axial was not changed.No artifact was observed around the images.(2)There were no bone formation on the surface of the device,but new bone occupied the space underneath the device which still not full filled with.The new bone tissue was continuity with the maxillary sinus floor.The morphology of the new bone was unregular and the boundary between the new bone and the maxillary sinus floor was obvious.5.Histological observation(1)No displacement of the device was observed and the maxillary sinus membrane closely attached to the surface of the device.(2)The difference between perforation and intactness in histological observation showed no significance.The histological examination of the specimens showed bone formation was found underneath the space maintaining device and the shape of new bone was in accord with the outline of the elevated membrane.New bone was concentrated in the central of the device and did not full filled with the space underneath the device.New bone formation can be found on the lateral aspect of the device,but can not be found on the top supporting area of the device.(3)The boundary between the new bone and the maxillary sinus floor was obvious in 3 months group,the bone was composed of immature woven bone.Loose arrangement of trabecular bone staggered into a network,lacuna can be found betwenn tarbecular bone and cartilage pit distribute in the trabecular bone.The boundary between the new bone and the maxillary sinus floor was not obvious in 6 months group,the new bone was composed of mature bone and in continuity with the sinus floor.(4)mineralization can be found in the hole of the device and depositon were in accord with the shape of the hole,more in the aspect of the membrane and less in the aspect of the space,the mineralization was consisted of micro-mineralization which present in shape of spindle and ellipse.The arrangement of micro-mineralization was regular and boundary was obvious.The spindle-shaped micro-mineralizaiton located in the aspect of membrane and the elliptic micro-mineralizaiton located in the aspect of the space.The percentage of mineralization in the hole was 48%.(5)New bone area was 8.17 ± 9.76mm2、9.92 ± 8.05mm2 in the condition of membrane intactness and perforation after three months.New bone area was 5.46 ±6.24mm2、6.34 ± 2.98mm2 in the condition of membrane intactness and perforation after six months.The difference was not significant.New bone percentage was 16.29±11.22%、17.29 ± 6.58%in the condition of membrane intactness and perforation after three months.New bone percentage was 15.21 ± 12.86%、12.87 ± 8.44%in the condition of membrane intactness and perforation after six months.ConclusionThe space maintaining device showed good biological compatibility and no rejection occurred.The folding design can adapt to the anatomy of the maxillary sinus and easy to operate which can reduce the surgical trauma.The hole on the surface of the device contribute to the concentration and penetration of the blood clot and nutritions.The cap-shaped outline of the device contribute to support the sinus membrane and the covering membrane on the surface can lead to a holding force to reinforce the stability.New bone formation can be found in nongrafted sinus floor technique using space maintaining device and the shape of new bone was in accord with the outline of the elevated membrane and the small perforation has no effect on it.Mineralization can be found in the hole of the device and depositon were in accord with the shape of the hole,the sinus membrane maybe the source of the new bone and the new bone formation mechanism remains to be explored. |
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