Near-infrared light-boosted antimicrobial activity of minocycline/hyaluronan/carbon nanohorn composite toward peri-implantitis treatments.

Dental implant therapy is a reliable treatment for replacing missing teeth. However, as dental implants become more widely used, peri-implantitis increasingly has become a severe complication, making successful treatment more difficult. As a result, the development of effective drug delivery systems (DDSs) and treatments for peri-implantitis are urgently needed. Carbon nanohorns (CNHs) are carbon nanomaterials that have shown promise for use in DDSs and have photothermal effects. The present study exploited the unique properties of CNHs to develop a phototherapy employing a near-infrared (NIR) photoresponsive composite of minocycline, hyaluronan, and CNH (MC/HA/CNH) for peri-implantitis treatments. MC/HA/CNH demonstrated antibacterial effects that were potentiated by NIR-light irradiation, a property that was mediated by photothermal-mediated drug release from HA/CNH. These antibacterial effects persisted even following 48 h of dialysis, a promising indication for the clinical use of this material. We propose that the treatment of peri-implantitis using NIR and MC/HA/CNH, in combination with surgical procedures, might be employed to target relatively deep affected areas in a timely and efficacious manner. We envision that this innovative approach will pave the way for future developments in implant therapy.

Human adenovirus oncolytic properties and the inhibitory role of E4 orf4 and E4 orf6/7 on endogenously activated NF-κB.

Human adenovirus is a promising tool for cancer therapy as an oncolytic virus. To predict which region of the oncolytic adenovirus E4 gene could be deleted, we investigated the relationship between the E4 proteins and NF-κB. Here, we report that TLR2-dependent NF-κB activation in Ad5-infected cells was significantly inhibited 24 h post-infection. Among the six E4 proteins, E4 orf4 and E4 orf6/7 exhibited notable suppressive effects on NF-κB activation. However, only E4 orf4 was co-immunoprecipitated with the RelA protein, also known as p65. It appears likely that E4 orf6/7 represses NF-κB activation via E2F-dependent pathways. Our results suggest that both E4 orf4 and E4 orf6/7 are novel inhibitors of NF-κB activation. The inhibition of endogenous NF-κB activation by E4 proteins during the late phase of infection also appears to elucidate the previously reported suppression of E1A expression in the late phase of infection. These redundant suppressive effects of E4 orf4 and E4 orf6/7 on NF-κB suggest that these proteins may play a major role in the anticancer properties of oncolytic adenovirus.

An antibacterial conjugate of carbon nanohorns for NIR-light mediated peri-implantitis treatment.

This study developed a novel antibacterial conjugate based on carbon nanohorns for peri-implantisis, an inflammatory disease around dental implants, which may result in failing implants by bone loss around them. The conjugate demonstrates much better photodurability than commonly used indocyanine green and a significant antibacterial effect under NIR illumination.

Effect of sitting posture with and without sole-ground contact on chewing stability and masticatory performance.

PURPOSE: To verify the effect of sitting posture with and without sole-ground contact on chewing stability and masticatory performance. METHODS: Thirty healthy subjects were evaluated. The Conformat was used to analyze the center of sitting pressure (COSP), and the three-dimensional motion analysis system was used to analyze changes in head and trunk postures while subjects remained in a sitting position with and without sole-ground contact. The parameters of masticatory performance and movement were calculated as follows. For evaluating masticatory performance, the amount of glucose extraction (AGE) during chewing of a gummy jelly was measured. For evaluating masticatory movements, the movement of the mandibular incisal point was recorded using the Motion Visi-Trainer V1, and parameters of the stabilities of movement path and rhythm were calculated. RESULTS: Head and trunk sway values and the displacement of COSP were significantly smaller with sole-ground contact than those without sole-ground contact. The masticatory movement path with sole-ground contact showed less variation in the opening distance and more stable movement path compared to those without sole-ground contact. The AGE was significantly greater with sole-ground contact than that without sole-ground contact. CONCLUSION: Sitting posture with and without sole-ground contact affects chewing stability and masticatory performance.

Effect of masticatory movements on head and trunk sways, and sitting and foot pressure distributions during sitting position.

BACKGROUND: The head plays an important role in the postural control. Chewing co-activates jaw and neck muscles leading to coordinated jaw and head-neck movements. Therefore, to examine effect of masticatory movements on head and trunk sways, and sitting and foot pressure distributions during mastication is helpful in the attempt to understand the interrelationship between stomatognathic function and posture control system in the sitting position. OBJECTIVES: The purpose of this study was to test the hypothesis in healthy subjects that masticatory movements affect head and trunk sways and sitting and foot pressure distributions during sitting position. METHODS: A total of 30 healthy male subjects with an average age of 25.3 years (range, 22-32 years) were evaluated. The CONFORMat™ and MatScan™ system were used to analyse changes in sitting pressure distribution center of sitting pressure (COSP) and changes in foot pressure distribution center of foot pressure (COFP), respectively, and the three-dimensional motion analysis system was used to analyse changes in head and trunk postures while subjects remained sitting position with rest position, centric occlusion and chewing. The total trajectory length of COSP/COFP, COSP/COFP area, and head and trunk sway values were compared between the three conditions to evaluate whether masticatory movement affected the stability of head and trunk sways and sitting and foot pressure distributions. RESULTS: Total trajectory length of COSP and COSP area during chewing were significantly shorter and smaller respectively than it was in rest position and centric occlusion (p ⟨ .016). Head sway value during chewing was significantly larger than it was in rest position and centric occlusion (p ⟨ .016). CONCLUSION: Masticatory movements affect sitting pressure distribution and head movements during sitting position.

In vivo transmission electron microscopy of the alternating structure of the protrusions between adjacent macrophage-like cells on micropatterns.

OBJECTIVES: We investigated the behavior of macrophages in the defined microtopography of materials. METHODS: Patterned cyclo-olefin polymer films were implanted into the femurs of seven-week-old rats. After 1 and 4 weeks, the rats were fixed with glutaraldehyde and OsO4, and their bones were observed with transmission electron microscopy (TEM). RESULTS: TEM and segmentation revealed an alternating structure in which multiple protrusions of adjacent macrophage-like cells overlapped. They were approximately 2 µm long and almost uniform in width, and were induced by the limited topography. CONCLUSION: New structures appeared between the macrophage-like cells as a result of microtopography.

The impact of an additional implant under the saddle of removable partial dentures in Kennedy Class II edentulism on oral health-related quality of life and oral function: a case series report.

BACKGROUND: Implant-supported removable partial dentures (ISRPDs) provide effective prosthodontic treatment for partially edentulous patients. ISRPDs offer greater patient satisfaction and better oral function compared with removable partial dentures (RPDs) by enhancing denture stability and support. However, few clinical studies have focused on RPD design in patients with mandibular Kennedy Class II edentulism. The aim of this case reports was to investigate the oral function, oral health-related quality of life, and satisfaction of four patients with unilateral distal-extension mandibular RPDs with the same design which were replaced with ISRPDs. In addition, we investigated how each patient's evaluation varied with the change from RPD to ISRPD. CASE PRESENTATION: Four patients had unilateral distal-extension mandibular edentulism and were missing the first and second molars and the first and second premolars. They received one implant (4.0 mm in diameter, 8.0 mm in length; IAT EXA PLUS Bone level; Nippon Piston Ring Co. Ltd, Saitama, Japan) at the position equivalent to the first molar in the edentulous residual ridge perpendicular to the occlusal plane. Implant position was determined by surgical guide plate. RPDs were fabricated after the residual mucosal membrane had healed. The basic design of the RPD was as follows: a cobalt-chromium alloy cast metal framework denture with a lingual bar as the major connector, a double Akers clasp on the molars and an auxiliary retainer on the premolar as indirect retainers, and a wrought wire clasp and a cast cingulum rest (combination clasp) as direct retainers. Masticatory performance, occlusal force, oral health-related quality of life, and satisfaction were estimated at baseline, and at time points after insertion of the RPD and after insertion of the adapted ISRPD. Each evaluation item showed a tendency for improvement on insertion of the new RPD. Masticatory performance and satisfaction tended to be better after insertion of the ISRPD than after insertion of the RPD. CONCLUSION: Our findings suggest that ISRPDs provided better patient satisfaction and masticatory performance than RPDs in patients with mandibular Kennedy Class II edentulism. Trial registration UMIN Clinical Trials Registry and Japan Registry of Clinical Trials, UMIN000025283 and jRCTs012180003. Registered 19 February 2016 and 17 December 2018, https://www.umin.ac.jp/ and https://jrct.niph.go.jp/.

Effect of body posture on stability and balance of occlusal contacts.

OBJECTIVE: To evaluate the effect of body posture on occlusal contact. METHODS: A total of 30 healthy subjects were evaluated. T-Scan™ III was used to analyze the center of occlusal force (COF) and occlusal force distribution while subjects remained supine (SP), upright sitting with the head fixed (UP-HFI), upright sitting with the head free (UP-HFR), and natural standing (NS). RESULTS: The total trajectory length of COF was significantly longer in NS than in SP, UP-HFI, and UP-HFR. The COF area was significantly larger in UP-HFR than in SP and UP-HFI and also significantly larger in NS than in SP, UP-HFI, and UP-HFR. The anteroposterior occlusal force distribution (AOD) in NS shifted significantly forward, compared to SP, UP-HFI, and UP-HFR. AOD in UP-HFI and UP-HFR shifted significantly forward, compared to the SP position. CONCLUSION: Changes in body posture affect the stability and anteroposterior balance of occlusal contacts.

Inhibition of RANKL and Sema4D improves residual ridge resorption in mice.

Residual ridge resorption (RRR) is a chronic and progressive bone resorption following tooth loss. It causes deterioration of the oral environments and leads to the pathogenesis of various systemic diseases. However, the molecular mechanisms and risk factors for RRR progression are still unclear and controversial. In this study, we developed a tooth extraction model using mice for analyzing long-term morphological and gene expression changes in the alveolar bone. We further applied ovariectomy to this model to elucidate the effects of osteoporosis on RRR progression. As a result, the alveolar bone loss was biphasic and consisted of rapid loss in the early stages and subsequently slow and sustained bone loss over a long period. Histological analysis indicated that ovariectomy prolonged the activation of osteoclasts in the alveolar bone. Furthermore, the expressions of Tnfsf11 and Sema4d kept increasing for a long time in OVX mice. Administration of neutralization antibodies for receptor activator of NF-κB ligand (RANKL) effectively suppressed RRR. Similarly, inhibition of Semaphorin 4D (Sema4D) also improved alveolar bone loss. This study demonstrated that reduced ovarian function may be a risk factor for RRR and that RANKL and Sema4D suppression are potential treatments.

Single-Walled Carbon Nanotube Membranes Accelerate Active Osteogenesis in Bone Defects: Potential of Guided Bone Regeneration Membranes.

Carbon nanotubes (CNTs) are potentially important biomaterials because of their chemical, physical, and biological properties. Our research indicates that CNTs exhibit high compatibility with bone tissue. The guided bone regeneration (GBR) technique is commonly applied to reconstruct alveolar bone and treat peri-implant bone defects. In GBR, bone defects are covered with a barrier membrane to prevent the entry of nonosteogenic cells such as epithelial cells and fibroblasts. The barrier membrane also maintains a space for new bone formation. However, the mechanical and biological properties of materials previously used in clinical practice sometimes delayed bone regeneration. In this study, we developed a CNT-based membrane for GBR exhibiting high strength to provide a space for bone formation and provide cellular shielding to induce osteogenesis. The CNT membrane was made via the dispersion of single-walled CNTs (SWCNTs) in hyaluronic acid solution followed by filtration. The CNT membrane assumed a nanostructure surface due to the bundled SWCNTs and exhibited high strength and hydrophilicity after oxidation. In addition, the membrane promoted the proliferation of osteoblasts but not nonosteogenic cells. CNT membranes were used to cover experimental bone defects made in rat calvaria. At 8 weeks after surgery, more extensive bone formation was observed in membrane-covered defects compared with bone defects not covered with membrane. Almost no diffusion of CNTs was observed around the membrane. These results indicate that the CNT membrane has adequate strength, stability, and surface characteristics for osteoblasts, and its shielding properties promote bone formation. Demonstration of the safety and osteogenic potential of the CNT membranes through further animal studies should facilitate their clinical application in GBR.

Comparison of the prognosis of the remaining teeth between implant-supported fixed prostheses and removable partial dentures in partially edentulous patients: A retrospective study.

BACKGROUND: There have been several reports about the prognosis of teeth adjacent to edentulous spaces for implant-supported fixed prostheses (ISFPs) and removable partial dentures (RPDs). However, there are few reports about the prognosis of the other remaining teeth comparing ISFPs with RPDs. PURPOSE: The aim of this study was to evaluate and compare the prognosis of the remaining teeth for ISFPs and RPDs in terms of survival and complication-free rates. METHODS: Subjects were partially edentulous patients with ISFPs or RPDs inserted in 2003-2016. Teeth adjacent to edentulous spaces (A-teeth), teeth not adjacent to edentulous spaces (R-teeth), and teeth opposing edentulous spaces (O-teeth) were investigated. The endpoints were tooth extraction and complications. A multivariate cox regression model was used to estimate the risk factors for survival of the investigated teeth. RESULTS: A total of 233 (ISFP: 89, RPD: 144) patients were included in the statistical analyses. An IFSP prosthesis, when compared to an RPD prosthesis did not significantly decrease the tooth loss rate for A-teeth (hazard ratio [HR]: 0.76; 95% confidence interval [CI]: 0.30-1.92), for R-teeth (HR: 0.54; 95% CI: 0.28-1.05), or for O-teeth (HR: 0.45; 95% CI: 0.10-2.09). CONCLUSIONS: In partially edentulous spaces, the difference between ISFPs and RPDs does not affect the prognosis of teeth adjacent to edentulous spaces, teeth not adjacent to edentulous spaces, and teeth opposing edentulous spaces. Namely, our findings suggest that it depends largely on the tooth type, jaw, endodontic therapy performed, not on the type of prostheses.

Controlled release, antimicrobial activity, and oral mucosa irritation of cetylpyridinium chloride-montmorillonite incorporated in a tissue conditioner.

This study examined the controlled release of cetylpyridinium chloride (CPC) from a tissue conditioner (TC) containing CPC-montmorillonite (CPC-Mont), the associated antimicrobial activity, and oral mucosa irritation. The CPC release test was performed daily for 28 days in three test solutions: distilled water, 0.2 M NaCl, and 0.2 M HCl. The antimicrobial activities for 7, 14, 21, and 28 days against Candida albicans, Staphylococcus aureus, and Streptococcus mutans were assessed according to the JIS Z 2801/ISO 22196 standard. An oral mucosa irritation test was conducted using cheek pouches in five male hamsters according to the ISO 10993-10:2010 standard. The amount of CPC released each day and the cumulative amount released over 28 days (6.12 mg) were less than the daily safe maximum of sore throat medicines (8 mg). Additionally, TC with CPC-Mont could sustain antimicrobial activity against adherent bacteria for 14 days and has no oral mucosa irritation potential.

Carbon nanohorn coating by electrodeposition accelerate bone formation on titanium implant.

Direct contact between bone and implant materials is required for dental implants. Titanium is used for the implant material owing to its mechanical and biological properties. The anodisation as the surface treatment was employed to enhance osteogenesis around titanium. Moreover, carbon nanohorn (CNH), a type of nanometer-sized carbon material, was reported to promote the bone formation. Thus, it is expected that if the surface of anodised Ti (AnTi) is modified with CNHs, Ti-bone contact would be enhanced. In this study, the Ti surface was modified with CNHs by electrophoresis and obtained anodised titanium coated with CNHs (CNH/AnTi). In vitro, CNH/AnTi attracted osteoblastic cells more than AnTi, thereby the proliferation of osteoblastic cell was enhanced by CNH/AnTi more than by AnTi. In vivo, at 7 and 28 days after implantation of CNH/AnTi or AnTi into the rat femur, more aggressive bone formation was observed on the surface of CNH/AnTi than on AnTi. More importantly, the area where newly formed bone tissue directly attached to CNH/AnTi was significantly larger than that for AnTi, suggesting that "contact osteogenesis" was accelerated on CNH/AnTi during the early post-implantation period. CNH/AnTi would be advantageous especially for the early stages of bone regeneration after surgery.

Immunocytochemical assessment of cell differentiation of podoplanin-positive osteoblasts into osteocytes in murine bone.

In this study, we examined the immunolocalization of podoplanin/E11, CD44, actin filaments, and phosphorylated ezrin in the osteoblasts on the verge of differentiating into osteocytes in murine femora and tibiae. When observing under stimulated emission depletion microscopy, unlike podoplanin-negative osteoblasts, podoplanin-positive osteoblasts showed a rearranged assembly of actin filaments along the cell membranes which resembled that of embedded osteocytes. In the metaphysis, i.e., the bone remodeling site, CD44-bearing osteoclasts were either proximal to or in contact with podoplanin-positive osteoblasts, but the podoplanin-positive osteoblasts also localized CD44 on their own cell surface. These podoplanin-positive osteoblasts, which either possessed CD44 on their cell surface or were close to CD44-bearing osteoclasts, showed phosphorylated ezrin-positivity on the cell membranes. Therefore, the CD44/podoplanin interaction on the cell surface may be involved in the osteoblastic differentiation into osteocytes in the metaphyses, via the mediation of podoplanin-driven ezrin phosphorylation and the subsequent reorganized assembly of actin filaments. Consistently, the protein expression of phosphorylated ezrin was increased after CD44 administration in calvarial culture. Conversely, in modeling sites such as the cortical bones, podoplanin-positive osteoblasts were uniformly localized at certain intervals even without contact with CD44-positive bone marrow cells; furthermore, they also exhibited phosphorylated ezrin immunoreactivity along their cell membranes. Taken together, it seems likely that the CD44/podoplanin interaction is involved in osteoblastic differentiation into osteocytes in the bone remodeling area but not in modeling sites.

Influence of rigidity of retainers on dynamic behavior of implant-supported removable partial dentures.

BACKGROUND: Implant-supported removable partial dentures (ISRPDs) are an effective treatment for partially edentulous patients. ISRPDs improve patients' satisfaction and oral function to a greater extent than RPDs by improving denture stability and enhancing support. However, the effect of a type of direct retainer on displacement of the abutment teeth and dentures in ISRPDs remains unclear. Therefore, we made a resin mandibular model of unilateral mandibular distal-extension partial edentulism for mechanical simulation and compared the dynamic behavior of the abutment teeth and the denture base among different tooth-borne retainers with various rigidities for RPDs and ISRPDs. METHODS: A resin mandibular model for mechanical simulation that had unilateral mandibular distal-extension edentulism and was missing the first molar, second molar, first premolar, and second premolar, and a denture fabricated from the patient's computed tomography images were used. Three types of direct retainers with different connecting rigidities were evaluated. The vertical displacement of the denture base and buccal and lingual sides and the mesial displacement of the abutment teeth were measured. RESULTS: Regardless of the rigidity of the direct retainers and loading positions, the displacement of the denture bases in the ISRPDs was significantly smaller than that in the RPDs (P < 0.001). There was no significant difference in vertical displacement of the denture bases among direct retainers with various connecting rigidities in the ISRPDs. Conversely, horizontal displacement of the abutment teeth in both the RPDs and ISRPDs tended to be larger with the cone crown telescope, which has high rigidity, than with the cast cingulum rest and wire clasp, which have much lower rigidities. CONCLUSION: Our results suggested that cast cingulum rest and wire clasps as direct retainers are appropriate ISRPDs to minimize denture movement and suppress displacement of the remaining teeth in patients with unilateral mandibular distal-extension partial edentulism.

Development of tissue conditioner containing cetylpyridinium chloride montmorillonite as new antimicrobial agent: Pilot study on antimicrobial activity and biocompatibility.

PURPOSE: The mechanical properties, antimicrobial activity, and biocompatibility of a novel antimicrobial tissue conditioner containing cetylpyridinium chloride with montmorillonite (CPC-Mont) were evaluated. METHODS: To examine the mechanical properties of the novel material, hardness, consistency, and penetration tests were conducted. Antimicrobial activity against Candida albicans (C. albicans) and Staphylococcus aureus (S. aureus) was evaluated. Cell viabilities of fibroblasts and epithelial cells using eluates from materials were measured to evaluate cytotoxicity. In addition, to assess tissue response, animal experiments were conducted. RESULTS: The hardness test results were similar to those of other commercially available materials. The novel tissue conditioner showed good antimicrobial activity against C. albicans and S. aureus compared with other materials. This effect was sustained for a week for C. albicans. In the case of S. aureus, microbial growth was suppressed for up to 3 weeks. Cell viability of the novel material for the eluate at 1 day was significantly less than those of other material for both cells. However, the cell viability at 7 days showed no significant difference. Animal experiments demonstrated that inflammatory responses around materials were not observed on the oral mucosa as other material. CONCLUSION: Within the limitations of this in vitro and in vivo study, the results suggest that the newly developed tissue conditioner containing CPC-Mont has not only excellent antimicrobial properties, but also the same mechanical properties and biocompatibility as tissue conditioners on the market.

Proliferation of Saos-2 and Ca9-22 cells on grooved and pillared titanium surfaces.

BACKGROUND: Surface nanostructures in titanium (Ti) oral implants are critical for rapid osseointegration. OBJECTIVE: The purpose of this study was to evaluate the growth of osteoblast-like (Saos-2) and epithelial-like (Ca9-22) cells on nanopatterned Ti films. METHODS: Ti films with 500 nm grooves and pillars were fabricated by nanoimprinting, and seeded with Saos-2 and Ca9-22 cells. Cell viability and morphology were assessed by cell proliferation assay and scanning electron microscopy, respectively. RESULTS: As assessed after 1 hour, proliferation of Saos-2 cells was most robust on grooved films than on pillared and smooth films, in this order. These cells approximately doubled on grooved and pillared substrates in 24 hours and after 5 days, but not on smooth surfaces. In contrast, Ca9-22 cells favored smooth surfaces, followed by grooved and pillared films. Indeed, cells sparsely adhered to pillared films over 5 days of incubation (p < 0.05). CONCLUSIONS: The data show that Saos-2 and Ca9-22 cells respond differently to different nanostructures, and highlight the potential use of nanopatterns to promote bone regeneration or to prevent epithelial downgrowth at the implant-bone interface.

Inhibition of enamel demineralization by an ion-releasing tooth-coating material.

PURPOSE: To evaluate the inhibitory effect of a surface pre-reacted glass-ionomer (S-PRG) filler-containing tooth-coating material on enamel demineralization. The outer surface of the S-PRG filler is in a state in which ions are readily released. METHODS: Human enamel blocks were incubated in lactic acid solution (pH 4.0) with and without a disk (n=6) made of the cured tooth-coating material. Test solutions were changed every 24 hours and incubation was continued for 4 days. The pH and amount of fluoride released were measured with an electrode and ion meter, respectively. The concentrations of ions (aluminum, boron, calcium, phosphorus, silicon, sodium, and strontium) were measured by inductively coupled plasma atomic emission spectroscopy. The surface of the enamel block was observed with a scanning electron microscope. RESULTS: Enamel demineralization was not observed in an enamel block incubated with a disk of the tooth-coating material. Ions released from S-PRG filler had an acid buffering action in the low pH lactic acid solution. However, in the enamel block-only solution showing high levels of calcium ion release, the degree of demineralization was correlated with morphological changes of the enamel surface. CLINICAL SIGNIFICANCE: Due to the buffering effects of the pre-reacted glass-ionomer surface by ion release, the S-PRG filler-containing tooth-coating material inhibited enamel demineralization by neutralizing the acidic environment at an early time point.

Histochemical examination on the peri-implant bone with early occlusal loading after the immediate placement into extraction sockets.

Early and immediate loading of dental implants has become a routine procedure in dental practices throughout the world, but the histological feature of peri-implant bone has not been fully understood. Therefore, we aimed to elucidate the histological response of peri-implant bone bearing the early occlusal loading using rat models. Four-week-old male Wistar rats were subjected to extraction of their maxillary left first molars and had titanium implants inserted immediately into the post-extraction sockets. In experimental groups at 1 week after placement, implants were loaded for 1 or 2 weeks by adding adhesive resin on the top of the screws. In control groups, no adhesive resin was added to the implants. After 1 or 2 weeks with loading, rats were fixed with an aldehyde solution for histochemical assessment. Newly-formed bone adhered broadly to the implant surface in both the control and experimental groups. The experimental group loaded for 2 weeks showed thicker trabeculae between the implant threads compared to those in the control group. Osteopontin- and osteocalcin-positive cement lines, which are histological hallmarks of bone remodeling, were narrow and smooth in the experimental groups, while featuring a complex meshwork with thick scalloped lines in the control groups. The index of sclerostin-positive osteocytes located close to implants loaded for 2 weeks was significantly lower than in controls, suggesting that osteoblast activity was preserved. Summarizing, our experimental model suggested that early implant loading increases trabecular thickness in the peri-implant bone tissue in a process that involves the regulation of bone remodeling.

Significance of mandibular molar replacement with a dental implant: a theoretical study with nonlinear finite element analysis.

BACKGROUND: Dental implants are frequently applied to unilateral defects in the mandible. However, implant placement in the molar region of the mandible can be difficult due to anatomical structure. The aim of this study was to evaluate the distribution of occlusal force in a mandibular shortened dental arch (SDA) with implants. METHODS: Three-dimensional finite element (FE) models of the mandible with varying numbers of teeth and implants were constructed. Models Im6 and Im67 contained one and two implants in the defect of the left molar region, respectively. Models Im456 and Im4567 contained three and four implants in the defect of the left premolar and molar regions, respectively. Model MT67 contained a defect in the molar region with no implant placed. Model MT7 represented natural dentition without a left second molar, as a control. Modification of the condition of occlusal contacts assuming the intercuspal position was performed before analysis under load 400 N; therefore, the load condition as total force on the occlusal surface was 400 N. FE analyses were subsequently performed under load conditions of loads 100, 200, and 800 N. The distribution of reaction forces on the occlusal surface and the mandibular condyle was investigated. RESULTS: Force distribution in models Im67 and Im4567 appeared to be symmetrical under all load conditions. Occlusal force distribution in models Im6 and Im456 was similar to that in model MT7. However, the occlusal force at the second premolars on the defect side in those models was larger under loads 100 and 200 N. Conversely, the occlusal force on the first molars was much larger than that in model MT7 under load 800 N. CONCLUSIONS: Within the limitations of this theoretical study, we demonstrated that restoration with the same number of implants as missing teeth will show almost symmetric occlusal force distribution, and it will produce less biomechanically stress for a unilateral defect of the mandible. However, if restoration of a missing second molar with an implant is impossible or difficult, then an SDA with implants may also be acceptable except for individuals with severe bruxism.