Ralf J Kohal

Publications of Ralf J Kohal

• Sinus augmentation with bovine hydroxyapatite/synthetic peptide in a sodium hyaluronate carrier (PepGen P-15 Putty): a clinical investigation of different healing times.

  Authors: Frank Butz, Maria Bächle, Markus Ofer, Katja Marquardt, Ralf J Kohal

  The International journal of oral & maxillofacial implants. 11/2011; 26(6):1317-23.

  Augmentation of the sinus floor with autogenous bone often requires an extra donor site, which is associated with a risk of morbidity, and current grafting protocols involve healing times of up to 9Augmentation of the sinus floor with autogenous bone often requires an extra donor site, which is associated with a risk of morbidity, and current grafting protocols involve healing times of up to 9 months. In this prospective in vivo study, the time-dependent efficacy of PepGen P-15 Putty, a combination of bovine hydroxyapatite and synthetic peptide in a sodium hyaluronate carrier, was evaluated in sinus grafting. Twenty-four edentulous patients received bilateral sinus augmentations with PepGen P-15 Putty, which mimics the cell-binding domain of type I collagen responsible for cell migration, differentiation, and proliferation. The patients were randomly divided into four groups of six patients each, corresponding to 2, 4, 6, and 9 months of healing postaugmentation. After these time intervals, bone biopsy specimens were retrieved through the alveolar bone crest into the augmented sinus, and subsequently oral implants were placed. The specimens were immersed in buffered formalin, scanned with a desktop microcomputed tomography machine, and processed for histologic and histomorphometric evaluation. A mixed model was used for statistical analysis. Three-dimensional microcomputed tomography depicted the distinct structure of trabecular bone encompassing remnants of PepGen, and histologic evaluation revealed osteoblasts and osteoid with osteocytes in the vicinity of the PepGen particles at all healing stages. Histomorphometric results indicated an increase in the newly formed bone fraction in the specimens as follows: 21.3% (± 2.33) at 2 months, 21.9% (± 8.9) at 4 months, 28.5% (± 6.9) at 6 months, and 29.8% (± 11.8) at 9 months. The differences were statistically insignificant. All implants placed in the augmented sites integrated and were restored prosthetically. PepGen can be used successfully for maxillary sinus augmentation. These data provide evidence that implant placement, even after only 2 months of healing, may be possible.

• The effects of cyclic loading and preparation on the fracture strength of zirconium-dioxide implants: an in vitro investigation.

  Authors: Ralf J Kohal, Martin Wolkewitz, Anastasia Tsakona

  Clinical oral implants research. 02/2011; 22(8):808-14.

  Zirconia is a potential material for the fabrication of oral implants. The aim of this study was to evaluate the effects of cyclic loading and preparation on the fracture strength of a zirconiaZirconia is a potential material for the fabrication of oral implants. The aim of this study was to evaluate the effects of cyclic loading and preparation on the fracture strength of a zirconia implant system. Forty-eight one-piece implants were divided into two groups of 24 implants: group A (without modification) and group B (1 mm chamfer preparation). Groups A and B were divided into three subgroups of eight implants each (1 = no artificial load, 2 = artificial load [98 N; 1.2 million loading cycles], and 3 = artificial load [98 N; 5 million loading cycles]). After completion of the loading, the fracture strength of each implant was determined in a universal testing machine. A two-way analysis of variance was used, the continuous response variable (fracture strength in Newtons) is modeled as a function of preparation, cycles, and the corresponding interaction as explanatory variables. The mean fracture strength values obtained for the groups were: A1 (no preparation, no load) = 1928.73 N, A2 (no preparation, 1.2 million cycles) = 2044.84 N, A3 (no preparation, 5 million cycles) = 1364.50 N, B1 (preparation, no load) = 1221.66 N, B2 (preparation, 1.2 million cycles) = 967.11 N, and B3 (preparation, 5 million cycles) = 884.89 N. Fracture values were significantly different between subgroups A1 vs. A3 and B1 vs. B3. There was no significant difference between subgroups A1 vs. A2 and B1 vs. B2. Preparation as well as cyclic loading can decrease the fracture strength resistance of zirconia implants. Nevertheless, even the lowest values of mean fracture strength of the implants used in our study seem to withstand average occlusal forces even after an extended interval of artificial loading.

• Alumina-reinforced zirconia implants: survival rate and fracture strength in a masticatory simulation trial.

  Authors: Ralf-J Kohal, Martin Wolkewitz, Constanze Mueller

  Clinical oral implants research. 12/2010; 21(12):1345-52.

  Alumina-toughened zirconia (ATZ) is a possible alternative material to titanium for oral implants. No data are available on the fracture strength of ATZ oral implants. Purpose: The purpose of thisAlumina-toughened zirconia (ATZ) is a possible alternative material to titanium for oral implants. No data are available on the fracture strength of ATZ oral implants. Purpose: The purpose of this study was to examine one-piece implants made of ATZ ceramic under artificial loading conditions and to compare the fracture strength of these implants with implants fabricated from tetragonal zirconium dioxide poylcrystal (TZP)-A. A total of 72 implants, 48 ATZ implants (groups A and B) and 24 TZP-A implants (group C), were investigated. A chamfer preparation at the implant heads was performed on all implants of groups B and C. Eight implants of each group underwent 1.2 or five million thermomechanical loading cycles in the chewing simulator (load value: 98 N). Further eight implants of each group were not cyclic loaded. Finally, the fracture strength of all implants was determined using a universal testing machine. No implant fractured during loading in the chewing simulator. All implants were placed in the universal testing machine to evaluate fracture strength. The mean fracture strength values±standard deviations for the implants without artificial loading were 1734±165 N (ATZ, no preparation), 1220±85 N (ATZ, with preparation), and 578±49 N (TZP-A, with preparation); 1489±190 N (ATZ, no preparation), 1064±121 N (ATZ, with preparation), and 607±57 N (TZP-A, with preparation) with 1.2 million loading cycles; and 1358±187 N (ATZ, no preparation), 1098±97 N (ATZ, with preparation), and 516±45 N (TZP-A, with preparation) with five million cycles. The ATZ implants showed significantly higher mean fracture strengths compared with the TZP-A implants. Modification of the implant head using diamond burs and increased loading time also led to a significant decrease in fracture strength. The ATZ implants showed an increased mechanical stability compared with the TZP-A. Modification of the implant head resulted in a decrease in fracture strength. However, within the limits of this in vitro investigation it can be concluded that ATZ implants will withstand functional loading over an estimated period of 20 years.

• In vitro reaction of human osteoblasts on alumina-toughened zirconia.

  Authors: Ralf J Kohal, Maria Baechle, Jung S Han, Dennis Hueren, Ute Huebner, Frank Butz

  Clinical oral implants research. 09/2009;

  Abstract Objectives: Alumina toughening enhances the mechanical properties of zirconia ceramics but the biocompatibility of this material has rarely been addressed. In this study, we examined theAbstract Objectives: Alumina toughening enhances the mechanical properties of zirconia ceramics but the biocompatibility of this material has rarely been addressed. In this study, we examined the osteoblast response to alumina-toughened zirconia (ATZ) with different surface topographies. Material and methods: Human osteoblasts isolated from maxillary biopsies of four patients were cultured and seeded onto disks of the following substrates: ATZ with a machined surface, airborne-particle abraded ATZ, airborne-particle abraded and acid etched ATZ. Airborne-particle abraded and acid etched titanium (SLA) and polystyrene disks served as a reference control. The surface topography of the various substrates was characterized by profilometry (R(a), R(p-v)) and scanning electron microscopy (SEM). Cell proliferation, cell-covered surface area, alkaline phophatase (ALP) and osteocalcin production were determined. The cell morphology was analyzed on SEM images. Results: The surface roughness of ATZ was increased by airborne-particle abrasion, but with the R(a) and R(p-v) values showing significantly lower values compared with SLA titanium (Mann-Whitney U-test P<0.05). The proliferation assay revealed no statistically significant differences between the ATZ substrates, SLA titanium and polystyrene (Kruskal-Wallis test, P>0.05). All substrates were densely covered by osteoblasts. ALP and osteocalcin production was similar on the examined surfaces. Cell morphology analysis revealed flat-spread osteoblasts with cellular extensions on all substrates. Conclusions: These results indicate that ATZ may be a viable substrate for the growth and differentiation of human osteoblasts. Surface modification of ATZ by airborne-particle abrasion alone or in combination with acid etching seems not to interfere with the growth and differentiation of the osteoblasts. To cite this article: Kohal RJ, Baechle M, Han JS, Hueren D, Huebner U, Butz F. In vitro reaction of human osteoblasts on alumina-toughened zirconia. Clin. Oral Impl. Res. xx, 2009; 000-000.

• Biomechanical and histological behavior of zirconia implants: an experiment in the rat.

  Authors: Ralf J Kohal, Martin Wolkewitz, Marc Hinze, Jung-Suk Han, Maria Bächle, Frank Butz

  Clinical oral implants research. 05/2009; 20(4):333-9.

  OBJECTIVE: This study aimed at evaluating the integration of zirconia implants in a rat femur model. MATERIAL AND METHODS: Zirconia implants with two distinct surface topographies were compared withOBJECTIVE: This study aimed at evaluating the integration of zirconia implants in a rat femur model. MATERIAL AND METHODS: Zirconia implants with two distinct surface topographies were compared with titanium implants with similar topographies. Titanium and zirconia implants were placed into the femurs of 42 male Sprague-Dawley rats. Four groups of implants were utilized: machined zirconia implants, zirconia implants with a rough surface, machined titanium implants, and titanium implants with an electrochemically roughened surface. After a healing period of 28 days, the load-bearing capacity between the bone and the implant surface was evaluated by a push-in test. Additionally, after a healing period of 14 and 28 days, respectively, bone tissue specimens containing the implants were processed and histologically analyzed. RESULTS: The mean mineralized bone-to-implant contact showed the highest values after 14 and 28 days for the rough surfaces (titanium: 36%/45%; zirconia: 45%/59%). Also, the push-in test showed higher values for the textured implant surfaces, with no statistical significance between titanium (34 N) and zirconia (45.8 N). CONCLUSIONS: Within the limits of the animal investigation presented, it was concluded that all tested zirconia and titanium implant surfaces were biocompatible and osseoconductive. The presented surface modification of zirconia implants showed no difference regarding the histological and biomechanical results compared with an established electrochemically modified titanium implant surface.

• The gene-expression and phenotypic response of hFOB 1.19 osteoblasts to surface-modified titanium and zirconia.

  Authors: Bernhard Setzer, Maria Bächle, Marc C Metzger, Ralf J Kohal

  Biomaterials. 12/2008;

  The osteoblastic cell-line hFOB 1.19 with the potential to proliferate and differentiate revealed that cellular differentiation is not affected by material and roughness on newly developed zirconiaThe osteoblastic cell-line hFOB 1.19 with the potential to proliferate and differentiate revealed that cellular differentiation is not affected by material and roughness on newly developed zirconia implant materials. Materials under investigation were surfaces machined titanium (Ti-m), modified titanium (TiUnite((R))), machined zirconia (TZP-A-m), modified zirconia (ZiUnite((R))), machined alumina-toughened zirconia (ATZ-m) and modified alumina-toughened zirconia (ATZ-mod). After surface description by scanning electron microscopy (SEM) and atomic force microscopy (AFM), cellular proliferation (EZ4U, Casy1) and differentiation were examined after days 1, 3, 7, 14, 21, and 28. Osteogenic differentiation was visualized by alkaline phosphatase staining, mineralization assay (alizarin red) and by expression analysis (RT-PCR) of bone- and extracellular matrix-related genes. Proliferation on rough surfaces was reduced on both titanium and zirconia. Cell-attachment and cytoskeleton organization documented by confocal laser scanning microscopy (CLSM) elucidated attenuated cell attachment within the first 4h to be the reason for impaired proliferation. A specific up-regulation of m-RNAs in an early event (RUNX2, NELL-1, RUNX3, and BMP7) and a late event (Integrin B3) could be observed on TiUnite((R)) and ZiUnite((R)). For titanium an up-regulation of IBSP and Integrin B1 could be described at day 21. In total, differentiation was neither affected by material nor by roughness.

• [Borderline cases in implantology. Extensive bone augmentation and implants in extremely atrophied upper jaw: two case reports]

  Authors: Theodor Waldhorn, Ralf J Kohal

  Schweizer Monatsschrift für Zahnmedizin = Revue mensuelle suisse d'odonto-stomatologie = Rivista mensile svizzera di odontologia e stomatologia / SSO. 02/2008; 118(4):301-14.

  The placement of implants in the vertically and horizontally resorbed maxilla for a fixed prosthodontic reconstruction still presents a challenge to the therapist. To enable acceptable implantThe placement of implants in the vertically and horizontally resorbed maxilla for a fixed prosthodontic reconstruction still presents a challenge to the therapist. To enable acceptable implant placement and positioning, optimizing the residual bone is necessary. A new method for the reconstruction of the extremely atrophied maxilla is presented in two edentulous patients. This extensive osseous augmentation (GBR) was performed using bilateral sinus grafts, simultaneous ridge splitting and guided bone regeneration with bone harvested from intraoral sites and bone replacement material. In both patients, the osseous reconstruction of the residual ridge allowed the placement of implants for a fixed bridge reconstruction.

• Ceramic abutments and ceramic oral implants. An update.

  Authors: Ralf J Kohal, Wael Att, Maria Bächle, Frank Butz

  Periodontology 2000. 02/2008; 47:224-43.

• Behavior of CAL72 osteoblast-like cells cultured on zirconia ceramics with different surface topographies.

  Authors: Maria Bächle, Frank Butz, Ute Hübner, Emmanouil Bakalinis, Ralf J Kohal

  Clinical oral implants research. 03/2007; 18(1):53-9.

  OBJECTIVES: Because of its inherent strength, biocompatibility, and tooth-like color, zirconia ceramics have the potential to become an alternative to titanium as dental implant material. This studyOBJECTIVES: Because of its inherent strength, biocompatibility, and tooth-like color, zirconia ceramics have the potential to become an alternative to titanium as dental implant material. This study aimed at investigating the osteoblastic response to yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) with different surface topographies. METHODS: CAL72 osteoblast-like cells were cultured on machined (TZP-m), airborne particle abraded (TZP-s), and airborne particle abraded and acid-etched Y-TZP (TZP-sa) surfaces. Polystyrene and airborne particle abraded with large grit and acid-etched (SLA) titanium served as a reference control. The surface topography was examined by scanning electron microscopy (SEM) and profilometry. At culture days 3, 6, and 12, cell proliferation, at day 12 cell morphology, and cell-covered surface area were determined. RESULTS: The surface roughness of Y-TZP was increased by airborne particle abrasion and additionally by acid etching. No statistically significant differences were found between average roughness (R(a)) and maximum peak-to-valley height (R(p-v)) values of airborne particle abraded and acid-etched Y-TZP and SLA titanium. Whereas the cell proliferation assay revealed statistically significant greater values at day 3 for surface-treated Y-TZP and polystyrene cultures as compared with machined Y-TZP, no differences between the Y-TZP groups, SLA titanium, and polystyrene were observed at culture days 6 and 12. CONCLUSIONS: Cell morphology and cell-covered surface area were not affected by the type of substrate. The results suggest that roughened Y-TZP is an appropriate substrate for the proliferation and spreading of osteoblastic cells.

• Zirconia-implant-supported all-ceramic crowns withstand long-term load: a pilot investigation.

  Authors: Ralf J Kohal, Gerold Klaus, Jörg R Strub

  Clinical oral implants research. 11/2006; 17(5):565-71.

  OBJECTIVES: The purpose of this pilot investigation was to test whether zirconia implants restored with different all-ceramic crowns would fulfill the biomechanical requirements for clinical use.OBJECTIVES: The purpose of this pilot investigation was to test whether zirconia implants restored with different all-ceramic crowns would fulfill the biomechanical requirements for clinical use. Therefore, all-ceramic Empress-1 and Procera crowns were cemented on zirconia implants and exposed to the artificial mouth. Afterwards, the fracture strength of the all-ceramic implant-crown systems was evaluated. Conventional titanium implants restored with porcelain-fused-to-metal (PFM) crowns served as controls. MATERIAL AND METHODS: Sixteen titanium implants with 16 PFM crowns and 32 zirconia implants with 16 Empress-1 crowns and 16 Procera crowns each--i.e., three implant-crown groups--were used in this investigation. The titanium implants were fabricated using the ReImplant system and the zirconia implants using the Celay system. The upper left central incisor served as a model for the fabrication of the implants and the crowns. Eight samples of each group were submitted to a long-term load test in the artificial mouth (1.2 million chewing cycles). Subsequently, a fracture strength test was performed with seven of the eight crowns. The remaining eight samples of each group were not submitted to the long-term load in the artificial mouth but were fracture-tested immediately. One loaded and one unloaded sample of each group were evaluated regarding the marginal fit of the crowns. RESULTS: All test samples survived the exposure to the artificial mouth. Three Empress-1 crowns showed cracks in the area of the loading steatite ball. The values for the fracture load in the titanium implant-PFM crown group without artificial loading ranged between 420 and 610 N (mean: 531.4 N), between 460 and 570 N (mean: 512.9 N) in the Empress-1 crown group, and in the Procera crown group the values were between 475 and 700 N (mean: 575.7 N) when not loaded artificially. The results when the specimens were loaded artificially with 1.2 million cycles were as follows: the titanium implant-PFM crowns fractured between 440 and 950 N (mean: 668.6 N), the Empress-1 crowns between 290 and 550 N (mean: 410.7 N), and the Procera crowns between 450 and 725 N (mean: 555.5 N). No statistically significant differences could be found among the groups without artificial load. The fracture values for the PFM and the Procera crowns after artificial loading were statistically significantly higher than that for the loaded Empress-1 crowns. There was no significant difference between the PFM crown group and the Procera group. CONCLUSIONS: Within the limits of this pilot investigation, it seems that zirconia implants restored with the Procera crowns possibly fulfill the biomechanical requirements for anterior teeth. However, further investigations with larger sample sizes have to confirm these preliminary results. As three Empress-1 crowns showed crack development in the loading area of the steatite balls in the artificial mouth, their clinical use on zirconia implants has to be questioned.

• [Prosthetic treatment of a six-year-old child with hypodontia. A case report]

  Authors: Ahmed Shadi Akkad, M Bächle, Ralf J Kohal

  Schweizer Monatsschrift für Zahnmedizin = Revue mensuelle suisse d'odonto-stomatologie = Rivista mensile svizzera di odontologia e stomatologia / SSO. 02/2006; 116(6):626-40.

  The prosthetic treatment of young patients with congenital missing of several teeth is a challenge for the dentist. An early prosthetic management with regard to function, phonetics, esthetics isThe prosthetic treatment of young patients with congenital missing of several teeth is a challenge for the dentist. An early prosthetic management with regard to function, phonetics, esthetics is important to ensure a normal psychological development of these children and to promote a normal tooth and jaw development. On the basis of this case report about the prosthetic rehabilitation of a 6-year-old patient with congenital hypodontia of the primary and the permanent dentition, we give an overview of the literature available about this topic. A restorative dental management with removable prosthodontic appliances is described, and the prosthetic therapeutic alternatives are discussed.

• On-line analysis of CAL72 cells on two different titanium surfaces in a perfusion micro-bioreactor.

  Authors: Maria Bächle, Mohamed-Ali Mahi, Ralf J Kohal

  Dental materials : official publication of the Academy of Dental Materials. 08/2005; 21(7):633-40.

  OBJECTIVES: The aim of the present experiment was to test a prototype microsensoric measuring system (micro-bioreactor) for the investigation of the biocompatibility of different titanium surfaces inOBJECTIVES: The aim of the present experiment was to test a prototype microsensoric measuring system (micro-bioreactor) for the investigation of the biocompatibility of different titanium surfaces in a cell culture model. METHODS: Osteosarcoma cells of the cell line CAL72 were seeded onto titanium plates (10mm x 10mm x 1mm) and inserted into the culture chamber of the micro-bioreactor. Titanium plates with two different surface topographies (machined and titanium plasma-sprayed [TPS]) were used for this pilot investigation. Plastic plates served as controls. The online-sensoric device of the micro-bioreactor allowed the continuous monitoring of the metabolism of the cells and the control of the culture conditions. Over a period of 17 h changes in O(2)-consumption in the medium were measured by micro-electrodes and registered by the software of the system. The metabolic activity of the cells was calculated from the difference between the bypass and the chamber values. The cell proliferation and vitality were analyzed before and after the perfusion time in the micro-bioreactor. The cell morphology was studied using scanning electron microscopy. RESULTS: The cells on the machined surfaces showed the highest oxygen consumption after 15 h, after that it decreased. The cells on the TPS plates showed a lower oxygen consumption, which remained stable after 17 h. The highest oxygen consumption was seen with the cells on the control plastic plates. Concerning cell proliferation analysis, it could be shown that more vital CAL72 cells seeded onto TPS and plastic could be detected after the passage through the micro-bioreactor. Hence, the number of vital cells on the machined surface was reduced after the passage. SIGNIFICANCE: Within the limits of this experiment, the presented micro-bioreactor system could offer a valuable method to examine the dynamic interactions of cells and materials under defined in vitro experimental conditions. While the presented system is already successfully used in the ecological/ecotoxicological field, its routine use for investigating dental materials on a cellular level has to be evaluated.

• A systematic review of the influence of different titanium surfaces on proliferation, differentiation and protein synthesis of osteoblast-like MG63 cells.

  Authors: Maria Bächle, Ralf J Kohal

  Clinical oral implants research. 01/2005; 15(6):683-92.

  OBJECTIVES: Titanium is the standard material for dental and orthopaedical implants. The good biocompatibility has been proven in many experimental and clinical investigations. Different titaniumOBJECTIVES: Titanium is the standard material for dental and orthopaedical implants. The good biocompatibility has been proven in many experimental and clinical investigations. Different titanium topographies were tested in vitro using different cell culture models. The aim of this systematic review was to evaluate and summarize the medical/dental literature to assess on which kind of titanium surface structure the osteoblast-like osteosarcoma cells MG63 show the best proliferation and differentiation rate, and the best protein synthesis. METHODS: A systematic search was carried out using different on-line databases (PubMed, Web of Science, Cochrane Library, International Poster Journal), supplemented by handsearch in selected journals and by examination of the bibliographies of the identified articles. Inclusion and exclusion criterias were applied when considering relevant articles. Studies which met the inclusion criteria were included and data extraction was undertaken by one reviewer. RESULTS: The search yielded 348 references. Nine articles referring to nine different studies were relevant to our question. Additionally 8 less relevant articles were identified. It was found that regularly textured surfaces of pure titanium with R(a) values (average roughness) of around 4 mum are well-accepted by MG63 cells. CONCLUSIONS: The surfaces and culture conditions vary widely. Therefore it is still difficult to recommend one particular surface. It seems that there are no differences in cell proliferation and differentiation on surfaces treated by blasting and etching. Standardization in fabrication and size of the different test surfaces as well as homogeneity in culture times and plating densities should be aspects for future research.

• Loaded custom-made zirconia and titanium implants show similar osseointegration: an animal experiment.

  Authors: Ralf J Kohal, Dietmar Weng, Maria Bächle, Jörg R Strub

  Journal of periodontology. 10/2004; 75(9):1262-8.

  BACKGROUND: Zirconia might be an alternative material to titanium for dental implant fabrication. The aim of the present study was to investigate the histological behavior (osseointegration) ofBACKGROUND: Zirconia might be an alternative material to titanium for dental implant fabrication. The aim of the present study was to investigate the histological behavior (osseointegration) of loaded zirconia implants in an animal model and to compare it with the behavior of titanium implants. METHODS: Five months after extraction of the upper anterior teeth, 12 custom-made titanium implants (control group) and 12 custom-made zirconia implants (test group) were inserted in the extraction sites in six monkeys. Before insertion, the titanium implant surfaces were sandblasted with Al2O3 and subsequently acid-etched. The zirconia implants were only sandblasted. Six months following implant insertion, impressions were taken for the fabrication of single crowns. A further 3 months later, nonprecious metal crowns were inserted. Five months after insertion of the crowns, the implants with the surrounding hard and soft tissues were harvested, histologically prepared, and evaluated under the light microscope regarding the peri-implant soft tissue dimensions and mineralized bone-to-implant contact. RESULTS: No implant was lost during the investigational period. The mean height of the soft peri-implant tissue cuff was 5 mm around the titanium implants and 4.5 mm around the zirconia implants. No statistically significant differences were found in the extent of the different soft tissue compartments. The mean mineralized bone-to-implant contact after 9 months of healing and 5 months of loading amounted to 72.9% (SD: 14%) for the titanium implants and to 67.4% (SD: 17%) for the zirconia implants. There was no statistically significant difference between the different implant materials. CONCLUSION: Within the limits of this animal experiment, it can be concluded that the custom-made zirconia implants osseointegrated to the same extent as custom-made titanium control implants and show the same peri-implant soft tissue dimensions.

• A zirconia implant-crown system: a case report.

  Authors: Ralf J Kohal, Gerold Klaus

  The International journal of periodontics & restorative dentistry. 05/2004; 24(2):147-53.

  Exposed metal crown margins in the porcelain-fused-to-metal technique might be an esthetic problem. Therefore, all-ceramic crown systems are used for restoring teeth and dental implants. In addition,Exposed metal crown margins in the porcelain-fused-to-metal technique might be an esthetic problem. Therefore, all-ceramic crown systems are used for restoring teeth and dental implants. In addition, the gray color of a titanium implant might hamper the esthetic appearance of the entire reconstruction in cases of thin peri-implant soft tissue or tissue retraction. To further improve the esthetic aspect of dental implants, efforts are undertaken to develop implant systems fabricated out of tooth-colored materials that are biocompatible and able to withstand masticatory forces. One such material may be zirconia. The present article presents a case in which an all-ceramic custom-made zirconia implant-crown system was used for the replacement of a single tooth.

• Hard tissue reaction to dual acid-etched titanium implants: influence of plaque accumulation. A histological study in humans.

  Authors: Ralf J Kohal, Maria Bächle, Dominik Emmerich, Sven M Beschnidt, Jörg R Strub

  Clinical oral implants research. 09/2003; 14(4):381-90.

  OBJECTIVES: The aim of this investigation was to evaluate histologically, histometrically, and histomorphometrically the influence of plaque accumulation on the peri-implant hard tissues. MATERIALOBJECTIVES: The aim of this investigation was to evaluate histologically, histometrically, and histomorphometrically the influence of plaque accumulation on the peri-implant hard tissues. MATERIAL AND METHODS: Twelve fully edentulous subjects were selected for this investigation. Four to five standard titanium screw implants were placed interforaminally. Two small custom-made screw implants were incorporated in the region of the former first molar, one in each lower quadrant. One month after abutment connection, plaque control was terminated randomly at one of the custom-made implants and continued at the other implant. The custom-made implants and the surrounding tissue were harvested after different time points of plaque accumulation (7, 21, or 90 days). Thus, according to the plaque control program and implant removal time, there were six groups each with four implants for investigation. After histologic processing of the biopsies, histologic, histometric, and histomorphometric analyses were performed. RESULTS: Four of the 24 implants were unavailable for analysis. One implant was mobile at abutment connection and another implant was mobile 2 weeks after abutment connection; both implants had to be removed. The bone around two implants was destroyed during the removal with the trephine bur; therefore, these two implants could not be evaluated histologically either. No differences in the histologic appearance of the peri-implant bone between the different groups could be observed. Histomorphometrically, the implant surface in contact with mineralized bone as a fraction of the implant surface (measured from the buccal to the lingual implant shoulder) varied between 59% and 73%. The implant surface in contact with mineralized bone from the first bone-to-implant contact buccally to the first bone-to-implant contact lingually varied between 80.6% and 91.5%. The values for the distance from the implant shoulder to the first bone-to-implant contact, i.e. peri-implant bone loss, varied from 1.1 to 2.2 mm. No statistically significant differences could be found between any of the evaluated variables. CONCLUSIONS: This clinical investigation is the first to evaluate the hard tissue reactions to different plaque accumulation periods. Within the limits of this experiment, it can be concluded that the bone reaction toward the different plaque accumulation periods and in the different plaque control/accumulation groups were similar. It can be further concluded that the observed bone loss is rather attributed to the establishment of the biologic width than to plaque accumulation.

• [Bioresorbable barrier membranes for guided bone regeneration around dental implants]

  Authors: Ralf J Kohal, Markus B Hürzeler

  Schweizer Monatsschrift für Zahnmedizin = Revue mensuelle suisse d'odonto-stomatologie = Rivista mensile svizzera di odontologia e stomatologia / SSO. 02/2002; 112(12):1222-9.

  The aim of this study was to evaluate the efficacy of two bioresorbable barriers especially produced for guided bone regeneration. Six beagle dogs were used in this investigation. At the beginning ofThe aim of this study was to evaluate the efficacy of two bioresorbable barriers especially produced for guided bone regeneration. Six beagle dogs were used in this investigation. At the beginning of the study, all mandibular premolars were extracted and after a healing period of three months three screw-type machined implants were inserted in each side of the mandible. At the buccal aspect of each implant bed a dehiscence type defect with a coronoapical and mesiodistal extension of 5 mm was created. Then, one of the following four methods for defect treatment was applied: 1) guided bone regeneration (GBR) with a bioresorbable barrier (poly-L/DL-lactide) (test group 1), 2) GBR with a bioresorbable composite barrier [poly-L/DL-lactide reinforced with tricalciumphosphate (TCP)] (test group 2), 3) GBR with an expanded polytetrafluoroethylene barrier (GTAM) (control group 1), and 4) no treatment (control group 2). The animals were sacrificed six months after implant installation. During the healing period the most common problems encountered in the test groups 1 and 2 were soft tissue dehiscences and bioresorbable membrane exposures. Retrieved tissue specimens were processed for histological and histometric evaluation. The mean amount of vertical bone regeneration at the defect areas was 1.75 mm for test group 1, 1.82 mm for the test group 2, 2.38 mm for control group 1, and 1.93 mm for control group 2. When the amount of bone regeneration in contact to the implant surface was evaluated, the regeneration result was 1.45 mm for test group 1, 1.49 mm for test group 2, 2.08 mm for control group 1, and 0.91 mm for control group 2. For both measurements, no statistically significant differences could be observed between the different groups. The present animal experiment showed that the treatment of dehiscence type defects around machined implants with the two bioresorbable barriers showed only slightly superior results compared to the treatment without barriers (control group 2). The best results--although not statistically significant different from the other treatment groups--were obtained when nonresorbable barriers were used.

• The gene-expression and phenotypic response of hFOB 1.19 osteoblasts to surface-modified titanium and zirconia

  Authors: Bernhard Setzer, Maria Bächle, Marc C. Metzger, Ralf J. Kohal

  Biomaterials.

  The osteoblastic cell-line hFOB 1.19 with the potential to proliferate and differentiate revealed that cellular differentiation is not affected by material and roughness on newly developed zirconiaThe osteoblastic cell-line hFOB 1.19 with the potential to proliferate and differentiate revealed that cellular differentiation is not affected by material and roughness on newly developed zirconia implant materials. Materials under investigation were surfaces machined titanium (Ti-m), modified titanium (TiUnite®), machined zirconia (TZP-A-m), modified zirconia (ZiUnite®), machined alumina-toughened zirconia (ATZ-m) and modified alumina-toughened zirconia (ATZ-mod). After surface description by scanning electron microscopy (SEM) and atomic force microscopy (AFM), cellular proliferation (EZ4U, Casy1) and differentiation were examined after days 1, 3, 7, 14, 21, and 28. Osteogenic differentiation was visualized by alkaline phosphatase staining, mineralization assay (alizarin red) and by expression analysis (RT-PCR) of bone- and extracellular matrix-related genes. Proliferation on rough surfaces was reduced on both titanium and zirconia. Cell-attachment and cytoskeleton organization documented by confocal laser scanning microscopy (CLSM) elucidated attenuated cell attachment within the first 4 h to be the reason for impaired proliferation. A specific up-regulation of m-RNAs in an early event (RUNX2, NELL-1, RUNX3, and BMP7) and a late event (Integrin B3) could be observed on TiUnite® and ZiUnite®. For titanium an up-regulation of IBSP and Integrin B1 could be described at day 21. In total, differentiation was neither affected by material nor by roughness.

• Rehabilitation of an extensive anterior explantation defect--a case report.

  Authors: Sebastian D Horvath, Ralf J Kohal

  Quintessence international (Berlin, Germany : 1985). 42(7):539-45.

  This article illustrates the surgical and prosthetic rehabilitation of an extensive defect in the area of a mandibular lateral incisor following explantation of a dental implant. Bone and soft tissueThis article illustrates the surgical and prosthetic rehabilitation of an extensive defect in the area of a mandibular lateral incisor following explantation of a dental implant. Bone and soft tissue defects existed after removal of the implant. Guided bone regeneration, a subepithelial connective tissue graft, and gradual pontic contouring were used to attempt correction of the defect. The missing tooth was replaced by a single-retainer, all-ceramic, resin-bonded fixed partial denture. The gingival contours were reestablished, but without complete regeneration of the interdental papillae. This article describes the use of several regenerative techniques in the treatment of dental defects and underscores the difficulty of complete correction of papilla deficiencies.