Hannu Larjava

Professor

Relevant Degree Programs

 

Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - Mar 2019)
The role of integrin alphavbeta6 in impaired wound healing and hair follicle regeneration (2011)

Integrin αvβ6 is an epithelial-specific receptor that is absent from the healthy epidermis but synthesized de novo during wound repair. However, its function in wound repair is unknown. Integrin-mediated activation of transforming growth factor-β1 (TGF-β1) is the main activation mechanism of this key cytokine in vivo. It has been previously reported that chronic human wounds continue to express αvβ6 integrin and transgenic mice over-expressing αvβ6 integrin produce chronic hypertrophic wounds that contain high levels of TGF-β1. Therefore, we hypothesize that αvβ6 integrin-mediated regulation of TGF-β1 activity may play a role in the impaired wound healing process. To this end, a well-established dexamethasone-induced mouse impaired wound model was used in β6 integrin-deficient (β6-/-) and WT mice. The dexamethasone-treated β6-/- mice demonstrated an accelerated wound repair and enhanced keratinocyte proliferation in wound epithelium and particularly in the hair follicles, while the production of pro-inflammatory cytokines and TGF-β1 activation were reduced compared to the treated WT controls. TGF-β1 has been implicated as an endogenous inducer of hair follicle regression. Since hair follicles constitutively express αvβ6 integrin, we tested whether αvβ6 integrin-mediated TGF-β1 signaling regulates hair regeneration and hair follicle involution process. Using a depilation-induced mouse hair cycling model we showed that hair regeneration was accelerated and hair follicle regression retarded in the β6-/- mice compared to WT controls. These changes were associated with enhanced keratinocyte proliferation in both hair follicles and interfollicular epidermis (IFE). Additionally, the levels of TGF-β1 and Smad2 phosphorylation were significantly reduced in β6-/- follicles during early anagen and anagen-catagen transition. Our study also demonstrated that the expression of integrin αvβ6 was strongly upregulated and specifically enhanced in the bulge stem cell niche during early hair regeneration.In summary, the results indicate that αvβ6 integrin plays an important inhibitory role in keratinocyte proliferation in both the IFE and hair follicles after wounding. The downregulated TGF-β1 signaling in β6-/- mice may impact epidermal stem cell behavior via modulating the microenvironment of the bulge stem cell niche after injury, which suggests a possible manipulation target in the functions of epidermal stem cells in the future.

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The role of keratinocyte alpha v beta6 integrin in the regulation of transforming growth factor beta during wound healing (2010)

The stratified squamous epithelium of skin and mucosa is mostly formed from keratinocytes and protects the organism from its surrounding environment. Any damage to this protective layer is restored through re-epithelialization – an essential part of wound healing. Therefore, studying the regulatory mechanisms of keratinocytes during re-epithelialization is important in understanding the processes involved in both normal and impaired wound healing. The keratinocyte αvβ6 integrin is induced during wound healing. Interestingly, αvβ6 integrin can activate both fibrogenic transforming growth factor-β1 (TGF-β1) and anti-fibrogenic TGF-β3. The role of αvβ6 integrin, however, especially in regards to the regulation of TGF-βs, during wound healing, is largely unknown. In the present study, we investigated the potential for the αvβ6 integrin-mediated regulation of TGF-β1 and TGF-β3 during wound healing in gingival and skin wound tissue sections. Furthermore, we investigated the possible regulatory mechanisms of TGF-β1 activity by αvβ6 integrin in keratinocytes. Spatio-temporal co-accumulation of αvβ6 integrin with TGF-β1 and TGF-β3 in the wound epithelium suggested that αvβ6 integrin may locally regulate both isoforms during wound healing. Prolonged co-expression of αvβ6 integrin and TGF-β3 in the scar-free gingival wound epithelium may potentially have an important role in the protection of gingiva from scarring. Our in vitro data showed that keratinocytes responded differentially to low levels of endogenously produced TGF-β1 compared to high amount of extracellular matrix (ECM)-bound latent TGF-β1. While the data were suggestive of activating endogenous TGF-β1 by the keratinocyte αvβ6 integrin, high levels of ECM-associated TGF-β1 was removed by keratinocytes in the presence of αvβ6 integrin allowing them to overcome the TGF-β1-mediated inhibitory effects on the cell proliferation. Taken together, our data showed a potential for the αvβ6 integrin-mediated local regulation of TGF-β1 and -β3 during wound healing. Prolonged expression and co-accumulation of αvβ6 integrin and TGF-β3 may be important in the protection of gingival wounds from scar formation. Our finding of αvβ6 integrin-mediated removal of the matrix-bound TGF-β1 in keratinocytes may be important at the time of wound closure, when keratinocytes typically show increased proliferation rate despite high levels of TGF-β1 in the surrounding matrix.

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Master's Student Supervision (2010-2017)
In vitro evaluation of the effects of leukocyte-platelet rich fibrin on disinfection of a rough implant surface (2017)

Objectives: Peri-implantitis is a frequent and serious clinical problem affecting between 1 and 47% of implants. Bacterial contamination of the roughened implant surface plays a major role in the etiology and progression of the disease. Successful treatment of peri-implantitis requires disinfection of the rough implant surface. There is no generally accepted protocol for implant disinfection. Autologous leukocyte and platelet-rich fibrin (L-PRF) membranes can be produced from autologous human blood via a one-step centrifugation procedure. It was hypothesized that the antimicrobial defense system of L-PRF may decontaminate the SLAⓇ implant surface. The objective of this study was to test the efficacy of L-PRF for SLAⓇ implant surface disinfection.Methods: Collagen-coated SLAⓇ (sand blasted, large grit acid etched) titanium discs were inoculated with dispersed dental plaque with a minimum bacterial cell concentration of 3.2 × 10⁷ CFU/ml. After 21 days of anaerobic incubation at 37C, discs were rinsed with 12 ml 0.9% NaCl to remove unattached biofilm, and exposed for 48 hours to Leukocyte-Platelet Rich Fibrin (L-PRF) in DMEM. Disks with or without rinsing with 12 ml of 0.9 % NaCl were fixed for SEM. Bacterial counts and perforations in bacteria were quantified from standardized scanning electron micrographs of the implant surface. The rinsing solution was collected and Western blot analysis was performed. L-PRF disks were compared with the control group (rinse). Results: Difference in presence of bacteria displaying perforation of the cell wall between cell–rich L-PRF treated samples and rinsed control group was statistically significant (p
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Chemotherapeutic decontamination of dental implants colonized by multispecies oral biofilm (2015)

Objectives: A recent meta-analysis reported that 18.8% of patients treated with dental implants are affected by peri-implantitis. Chemotherapeutic agents are often used during surgical decontamination of the dental implant despite limited evidence to support their efficacy. It is also known that mature biofilms are more resistant to antimicrobial agents. No studies have tested disinfectants on mature multispecies oral biofilms on titanium substrata. The aim of this study is to develop a multispecies oral biofilm implant model and to determine its susceptibility to antimicrobial agents. The null hypothesis is that no chemical agent is more effective than saline rinse to decontaminate sandblasted acid etched (SLA) titanium dental implant.Methods: Collagen-coated SLA titanium discs were inoculated with dispersed dental plaque with minimum bacterial cell concentration of 3.2 × 10⁷ CFU/ml. After 21 days of anaerobic incubation, discs were rinsed with 0.9% NaCl to remove unattached biofilm, and exposed for 2 minutes to tetracycline paste, 1% chlorhexidine (CHX) gel, 35% phosphoric acid gel. Discs were rinsed again to remove the chemical agents. Bacterial counts were quantified from standardized scanning electron micrographs of the implant surface. Disinfectants were compared within each other and with the control groups (rinse and double-rinse).Results: After three weeks, the biofilm thickness on SLA discs was approximately 30 µm and showed the presence of multitude of rod and coccoid organisms. Rinsing the surfaces with 0.9% NaCl removed the majority of the biofilm. However, bacteria persisted in all specimens regardless of the treatment and none of the disinfectants was superior to the saline double-rinse group. CLSM analysis showed that CHX and Etch groups had a statistically significant reduction of viable bacteria within the biofilms, although small. New chemical and peeling-off techniques were also tested but did not remove significantly more bacteria than the double-rinse group.Conclusions: This mature multispecies biofilm model may be useful for the evaluation of decontamination of SLA implant surface. The tested chemical agents and the peeling-off techniques did not improve the decontamination effect when compared with the 0.9% NaCl rinse. CHX and Etch may provide a slight advantage in killing some of the remaining bacteria.

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Effect of kindlin-1 deficiency on inflammatory cytokine expression in gingival keratinocytes in the presence of oral biofilm (2015)

Kindler syndrome (KS) is an autosomal recessive skin disorder of unknown etiology resulting in congenital skin blisters, photosensitivity, generalized progressive poikiloderma, and mucosal alterations. Early onset and severe periodontal disease has been noted as a common clinical finding. Kindlin-1 is an intracellular focal adhesion protein that functions in cellular adhesion in the epidermis and mucosal tissues through interaction and activation of integrins. Kindlin-1 deficiency, as occurs in KS, results in impaired adhesion of the junctional epithelium to the basement membrane and may contribute to severe periodontal disease. We hypothesize that kindlin-1 deficiency may affect other aspects of keratinocyte behavior, including expression of cytokines and mediators involved in inflammation and repair. Expression of kindlin-1 was down-regulated in human gingival keratinocytes (HGK) and confirmed via Western blot analysis and RT-PCR. HGKs were exposed to varying concentrations of a native and heat-inactivated oral biofilm extract as well as a 3-week live oral biofilm. mRNA was isolated from control and kindlin-1 deficient HGKs and RT-PCR was used to assess relative gene expression of the following gene products: β6 integrin, fibronectin ED-A and ED-B, IL-1α, IL-1β, IL-6, IL-8, TNFα, TGFβ-1, TGFβ-3, MMP-1, MMP-2, MMP-9, and tenascin C. Kindlin-1 deficiency in HGKs was found to significantly up-regulate the expression of genes encoding for β6 integrin, IL-1α, and IL-1β. β6 integrin expression was increased in K1-deficient cells in the absence of biofilm treatment and when exposed to native biofilm extract. The pro-inflammatory cytokines IL-1α and IL-1β were significantly up-regulated in K1-deficient cells as compared to control cells in keratinocytes exposed to native oral biofilm extract, and in control cells exposed to heat- inactivated biofilm.iiMMP-2, MMP-9, IL-8, tenascin C, ED-B fibronectin, and TGFβ-3 were differentially regulated by the presence of biofilm extract or live biofilm in the gingival keratinocytes. TGFβ-3 and ED- B fibronectin expression were down-regulated in cell exposed to biofilm, while IL-1α, IL-1β, MMP-2, MMP-9, and tenascin C were up-regulated. Our findings suggest that the severe and early-onset periodontal disease found in patients with KS may be a result of enhanced expression of certain pro-inflammatory cytokines.

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Self-reported penicillin allergy and dental implant therapy outcome, a clinical retrospective study (2015)

Objectives: The histologic, clinical, and radiographic findings together indicated infection as a major etiology of implant failure. Antibiotics have been prescribed following implant surgery to control infection. Inability to take penicillin seems to be a determining factor in implants failure in particular, with certain types of implant-related procedures. The aim of this study was to investigate retrospectively whether self-reported allergy to penicillin contributes to higher rate of implant failure. Methods: The survival of 5576 implants (985 Nobel Biocare and 4591 Straumann) placed surgically by an experienced periodontist was assessed in patients with the age range of 20-89 (mean: 60 years old) and with the follow-up period of up to 10 years. 4132 implants followed for at least one year. The survival was defined as the implant remaining in the jaw. Pearson χ2 test and Logistic regression were applied to examine the relation between pairs of variables. All tests were 2-tailed with a significance level of 0.05. Results: Out of 5106 implants placed for patients taking penicillin, 0.8% failed, while out of 470 implants placed for patients with self-reported allergy to penicillin, 2.1% failed with statistically significant difference (P= 0.002). Odds of failure for implants placed in patients allergic to penicillin were 3.2 times higher than those for non-allergic patients while controlling for the other variables. Kaplan Meier test revealed statistically significant difference between survivals of implants placed in penicillin-allergic group compared with non-allergic group. 54% of implant failures in non-allergic group have occurred during the first 6 months of implant insertion, while in penicillin allergic group this amount was 80% with statistically significant difference. Immediate implant placement in fresh extraction socket had 10-times higher rate of failure in patients with self-reported allergy to penicillin. Significant association between smoking and implant failure was found (p=0.005). Implants in the area of second molars have the highest failure rate with more frequency in maxilla relative to mandible. Conclusion: Inability to take penicillin may contribute to higher rate of implant failure and thus, penicillin allergy test could be implemented in clinical settings to increase the likelihood of prescribing penicillin relative to its alternates.

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Replication of the implant peri-abutment epithelium : a novel approach to investigating epithelial attachment to the implant abutment. (2014)

Objective: A multicenter clinical trial was conducted to characterize the surface topography of the peri-abutment epithelium after removal of the dental implant healing abutment. Methods: The study included a total of 10 Straumann (S) and 19 Nobel Biocare (N) dental implants. All dental implants were placed by either a certified periodontist (private practice) or residents of the Graduate Periodontics clinic at the University of British Columbia (UBC). Photographs of the peri-abutment epithelium were taken and analyzed using Image J software for % area of redness. Silicone impressions of the peri-abutment epithelium were taken and used to fabricate epoxy replicas that were imaged under SEM. Student T-tests were used to analyze differences between groups (p 0.05). There was a positive correlation between the peri-abutment soft tissue height and % area of redness that was found to be statistically significant (p
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A clinical study of scar formation in the human palatal mucosa (2013)

Scar formation is a frequent consequence of wound healing and has widespread negative effects on individuals’ quality of life, both physically and psychologically. For most people, scars are unsightly, but in addition to this, they can result in serious morbidities such as pruritus, pain, contracture, and decreased heat tolerance in severe situations. The association between degree of scarring and depth of dermal injury has been recognized by surgeons for many years, however the cellular and molecular basis for these observations remains poorly understood. Interestingly, oral wounds have been shown to heal faster and with less clinical and histological scar formation than similar skin wounds. It was hypothesized that palatal wounds in general show relatively little scarring and also that there is increased scar formation of the palatal mucosa following a connective tissue graft (CTG) harvest (deep wound) than a free gingival graft (FGG) harvest (superficial wound). This was a retrospective clinical study carried out at the University of British Columbia, Faculty of Dentistry. Intraoral photographs were taken of the palate in 37 subjects. Each subject had undergone a CTG and/or FGG harvest by a Graduate Periodontics resident more than six months prior to the study. 23 FGG and 23 CTG scars were assessed. Two independent calibrated blinded examiners assessed the photographs using a modified version of the Manchester Scar Proforma. A value of zero, one, or two was given for each parameter, with no difference from normal tissue scored as zero and gross mismatch scored as two. The values for each parameter were summed to produce a total scar score, zero to six, for each site. The component parameters were also examined individually so that color, contour, and distortion could be evaluated independently. The results of this study demonstrated that scar formation in the palatal mucosa is minimal and in many cases, non-existent. CTG donor sites did not have more severe scar formation than FGG sites.

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Comparison of treatment protocols to reduce the total bacterial load in the implant screw hole (2013)

Objective: A prospective multi-centre clinical trial was conducted to assess the biofilm inhibitory potential of 1% chlorhexidine (CHX) gel in the internal cavity of implant screw holes, when utilized at the time of surgical implant placement. Methods: The study included a total of 40 Straumann (S) and Nobel Biocare (N) implants, divided into test (ST or NT) and control (SC or NC) based on the implant system. The implants were placed by two periodontists (private practice) as well as by senior Graduate Periodontics residents at the University of British Columbia. Total colony forming units (CFUs/ml) were assessed 3 months post surgery by means of aerobic and anaerobic culturing and Gram staining was conducted on 15 of the samples. Univariate Mann-Whitney U tests were used to analyze differences between groups (p 0.05). No statistical differences in term of CFUs/ml were evident when comparing aerobic and anaerobic culturing methods (p > 0.05). The use of 1% CHX gel significantly reduced biofilm formation in both the ST and NT samples when compared with controls (SC and NC) (p 0.05). Overall, 13 implants from the test population demonstrated CFUs/ml below a threshold of 1000 compared to only 1 implant from the control population. Microscopic analysis revealed the presence of mainly Gram-positive coccoid species in 14/15 samples; one sample consisted mainly of rod shaped bacteria. Conclusion: The application of 1% CHX gel in the internal implant cavity at the time of initial implant surgery greatly reduces the biofilm formation over a 3-month period.

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Role of Alpha v Beta 6 integrin in enamel biomineralization (2013)

No abstract available.

Clinical outcomes of the Nobel Active dental implant system after one year of loading : a retrospective multicentre analysis (2010)

Objective: A retrospective review of charts was conducted to assess the survival rate and marginal bone loss around Nobel Active implants after one year of loading. Methods: The study included 124 NobelActive dental implants that were placed by experienced practitioners in two private clinics and by senior Graduate Periodontics residents at the University of British Columbia. The effect of patient, medical condition, site, implant, surgeon’s experience and timing related risk factors on implant survival and marginal bone loss was evaluated. Implant failure was defined as the loss or removal of an implant. Radiographic measurements of marginal bone loss (mm) were made using Image J 1.42 software and Planmeca Romexis 2.2.7R software. Bivariate analyses were used to identify variables associated with implant failure and marginal bone loss. Risk factors that were shown to be significant (p
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Implant treatment outcomes at the University of British Columbia graduate periodontics clinic : a retrospective analysis (2010)

Objectives: Dental implants have predictable outcomes and high survival rates. However, a small subset of patients experience implant failure. A retrospective review of charts at UBC was conducted to determine how patient-, disease-, site-, surgeon- and implant design-centered risk factors affect the survival of implants.Methods: A review of implants placed between 1989-2006 was completed. Inclusion criteria required a one-year post-placement diagnostic radiograph. Implant failure was defined as the loss or removal of an implant at any time. Bivariate analyses were used to identify variables associated with implant failure. Risk factors with p-values
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