Werner Zechner

Computed tomography‐based evaluation of template (NobelGuide™)‐guided implant positions: a prospective radiological study

OBJECTIVES This prospective study was intended to evaluate the overall deviation in a clinical treatment setting to provide for quantification of the potential impairment of treatment safety and reliability with computer-assisted, template-guided transgingival implantation. MATERIAL AND METHODS The patient population enrolled (male/female=10/8) presented with partially dentate and edentulous maxillae and mandibles. Overall, 86 implants were placed by two experienced dental surgeons strictly following the NobelGuide™ protocol for template-guided implantation. All patients had a postoperative computed tomography (CT) with identical settings to the preoperative examination. Using the triple scan technique, pre- and postoperative CT data were merged in the Procera planning software, a newly developed procedure - initially presented in 2007 allowing measurement of the deviations at implant shoulder and apex. RESULTS The deviations measured were an average of 0.43 mm (bucco-lingual), 0.46 mm (mesio-distal) and 0.53 mm (depth) at the level of the implant shoulder and slightly higher at the implant apex with an average of 0.7 mm (bucco-lingual), 0.63 mm (mesio-distal) and 0.52 mm (depth). The maximum deviation of 2.02 mm was encountered in the corono-apical direction. Significantly lower deviations were seen for implants in the anterior region vs. the posterior tooth region (P<0.01, 0.31 vs. 0.5 mm), and deviations were also significantly lower in the mandible than in the maxilla (P=0.04, 0.36 vs. 0.45 mm) in the mesio-distal direction. Moreover, a significant correlation between deviation and mucosal thickness was seen and a learning effect was found over the time period of performance of the surgical procedures. CONCLUSION Template-guided implantation will ensure reliable transfer of preoperative computer-assisted planning into surgical practice. With regard to the required verification of treatment reliability of an implantation system with flapless access, all maximum deviations measured in this clinical study were within the safety margins recommended by the planning software.

New safety margins for chin bone harvesting based on the course of the mandibular incisive canal in CT

OBJECTIVES Altered pulp sensitivity of anterior lower teeth is a frequent finding following chin bone harvesting. Persistent loss of tooth sensitivity has been reported in up to 20% of the patients. The aim of this study was to evaluate current recommendations for the location of the harvest zone with respect to the course of the mandibular incisive canal (MIC), the intrabony continuation of the mandibular canal mesial to the mental foramen. MATERIAL AND METHODS On computed tomographic (CT) scans of 50 dentate mandibles, the MIC was located and its distance to the root apices, to the labial bony surface, and to the inferior margin of the mandible was assessed. The risk of nerve injury and the percentage of patients suitable for chin bone grafting were calculated. RESULTS Respecting current recommendations for chin bone grafting, the content of the MIC was endangered in 57% of the CTs. Therefore, new safety margins are suggested: the chin bone should be harvested at least 8 mm below the tooth apices with a maximum harvest depth of 4 mm. CONCLUSIONS Applying the new safety recommendations and proper patient selection in chin bone harvesting could reduce the risk of altered postoperative tooth sensitivity due to injury of the mandibular incisive nerve.

Esthetic evaluation of single-tooth implants in the anterior maxilla following autologous bone augmentation.

OBJECTIVES Autologous bone augmentation to rebuild compromised alveolar ridge contour prior to implant placement allows for favorable three-dimensional implant positioning to achieve optimum implant esthetics. The aim of the present study was to evaluate peri-implant soft tissue conditions around single-tooth implants following bone grafts in the esthetic zone of the maxilla. MATERIALS AND METHODS Sixty patients underwent autologous bone augmentation of deficient maxillary sites prior to placement of 85 implants in the esthetic zone. In case of multiple implants per patient, one implant was randomly selected. Objective evaluation of 60 single-tooth implants was performed using the Pink-Esthetic-Score (PES) and Papilla Index (PI) and supplemented by subjective patient evaluation, as well as clinical and radiologic examination. RESULTS Objective ratings of implant esthetics were satisfactory (median PES: 11, median PI: 2) and significantly correlated with high patient satisfaction (mean VAS score: 80%). Both esthetic indices demonstrated respectable levels of inter- as well as intra-observer agreement. Poor implant esthetics (low PES and PI ratings) were significantly associated with increased anatomic crown height, while no influence of horizontal implant-tooth distance could be found. CONCLUSIONS The present investigation indicates that favorable esthetic results may be achieved in the augmented anterior maxilla. However, bony reconstruction of compromised alveolar ridges does not guarantee optimum implant esthetics.

Does Timing of Implant Placement Affect Implant Therapy Outcome in the Aesthetic Zone? A Clinical, Radiological, Aesthetic, and Patient‐Based Evaluation

PURPOSE To compare five different implant treatment protocols in the anterior maxilla, including immediate, early, and delayed implant placement, as well as implant placement in conjunction with simultaneous guided bone regeneration and implant placement 3 months following horizontal autologous bone block grafting. MATERIAL AND METHODS Aesthetic indices used included the Pink Esthetic Score (PES), Papilla Index (PI), Subjective Esthetic Score (SES), and White Esthetic Score (WES). Subjective evaluation of implant aesthetics was performed using a visual analogue scale (VAS). The VAS consisted of a 10 cm-long line representing the degree of discontent (0%) or satisfaction (100%). RESULTS A total of 153 implants in 153 patients (80 women, 73 men) were evaluated after a mean follow-up of 4.5 ± 2.9 years. Mean peri-implant bone loss was 1.6 ± 0.9 mm and not affected by treatment protocol, time after implant placement, or crown length. Papilla presence, by contrast, differed significantly between the protocols: Papilla formation was more pronounced following delayed and immediate implant placement. No statistical significance was found among treatment modalities with regard to PES, SES, or WES. Longer crowns were associated with lower PES and PI ratings and correlated with greater midfacial recession. SES was also influenced by time after implant placement and keratinized mucosa. Patient satisfaction differed significantly among treatment protocols, favoring immediate implant placement. Agreement between objective and subjective aesthetic ratings was low. CONCLUSION The present study suggests that comparable clinical, radiological, and aesthetic results can be achieved with all treatment protocols. Gingival recession, however, seems to occur in the long term irrespective of the technique used.

Thermal effects of a combined irrigation method during implant site drilling. A standardized in vitro study using a bovine rib model

OBJECTIVES The purpose of this study was to evaluate the temperature changes during implant osteotomies with a combined irrigation system as compared to the commonly used external and internal irrigation under standardized conditions. MATERIAL AND METHODS Drilling procedures were performed on VII bovine ribs using a computer-aided surgical system that ensured automated intermittent drilling cycles to simulate clinical conditions. A total of 320 drilling osteotomies were performed with twist (2 mm) and conical implant drills (3.5/4.3/5 mm) at various drilling depths (10/16 mm) and with different saline irrigation (50 ml/min) methods (without/external/internal/combined). Temperature changes were recorded in real time by two custom-built thermoprobes with 14 temperature sensors (7 sensors/thermoprobe) at defined measuring depths. RESULTS The highest temperature increase during osteotomies was observed without any coolant irrigation (median, 8.01°C), followed by commonly used external saline irrigation (median, 2.60°C), combined irrigation (median, 1.51°C) and ultimately with internal saline irrigation (median, 1.48°C). Temperature increase with different drill diameters showed significant differences (P < 0.05) regarding drill depth, confirming drill depth and time of drilling as influencing factors of heat generation. Internal saline irrigation showed a significantly smaller temperature increase (P < 0.05) compared with combined and external irrigation. A combined irrigation procedure appears to be preferable (P < 0.05) to an external irrigation method primarily with higher osteotomy depths. CONCLUSIONS Combined irrigation provides sufficient reduction in temperature changes during drilling, and it may be more beneficial in deeper site osteotomies. Further studies to optimize the effects of a combined irrigation are needed.

A novel standardized bone model for thermal evaluation of bone osteotomies with various irrigation methods

OBJECTIVES Based on a novel standardized bovine specimen, the aim of this study was to investigate thermal effects of different irrigation methods during intermittent and graduated drilling. MATERIAL AND METHODS Temperature changes during implant osteotomies (n = 320) of 10 and 16 mm drilling depths with various irrigation methods were investigated on manufactured uniform bone samples providing homogenous cortical and cancellous areas and analogous thermal conductivity comparable to human bone. Automated sequences were performed with surgical twist drills of 2 mm ∅ and conical drills of 3.5, 4.3 and 5 mm ∅. Real-time recording of temperature increase was done using two custom-built multichannel thermoprobes with 14 temperature sensors at a predefined distance of 1 and 2 mm to the final osteotomy. The effects of drilling depth, drilling diameter and irrigation methods on temperature changes were investigated by a linear mixed model. RESULTS Using this uniform bone specimen, the greatest temperature rise was observed without any coolant supply with 29.87°C, followed by external with 28.47°C and then internal with 25.86°C and combined irrigation with 25.68°C. Significant differences (P ≤ 0.0156) between drill depths of 10 vs. 16 mm could be observed with all irrigation methods evaluated. With each of the irrigation methods, significantly higher temperature changes (P < 0.0001) during osteotomies could be observed between twist drills of 2 mm ∅ and conical drills of 3.5, 4.3 and 5 mm ∅. During 10 and 16 mm drilling osteotomies, external irrigation showed significantly higher temperatures (P < 0.05) for all conical drills compared with internal or combined irrigation, respectively. Significantly lower temperatures (P < 0.05) could be detected with internal or combined irrigation for the use of conical drills with various diameters and drilling depths. CONCLUSIONS This fully standardized bone model provides optimized comparability for the evaluation of bone osteotomies and resulting temperature changes. As regards the efficiency of the various irrigation methods, it could be demonstrated that internal and combined irrigation appears to be more beneficial than external irrigation.

Clinical and radiological evaluation of a template‐guided (NobelGuide™) treatment concept

OBJECTIVES The study was designed to evaluate the clinical use of the NobelGuide(™) concept over a follow-up period of 12 months with respect to implant success and survival rates, development of soft tissue condition and recording of potential surgical and prosthetic complications. In addition, radiological assessment of peri-implant bone levels was performed at the 1-year follow-up post-implant placement. MATERIAL AND METHODS Thirty patients (male/female = 15/15) with partially dentate and edentulous mandibles and maxillae were included. All patients were planned and operated on using the computer-aided, template-guided treatment concept NobelGuide(™). Overall, 163 implants (NobelReplace(®) Tapered Groovy) were placed (mandible/maxilla = 107/56 implants). Recall appointments were performed after 1-2 weeks, 1, 3, 6 and 12 months after implant placement. Clinical parameters of the soft tissue conditions [e.g. bleeding on probing (BoP), pocket probing depth ≥3 mm (PPD), marginal plaque index (mPI)] and the dentists esthetic and functional evaluation using a visual analogue scale (VAS) were documented. Marginal bone level was evaluated on radiographs made at implant insertion and at the 1-year follow-up. RESULTS All 30 patients with 161 implants completed the 1-year follow-up resulting in a cumulative survival rate of 98.8% (two implant losses). Clinical parameters improved in a majority of the implants. The mean marginal bone level at implant insertion and at 1-year follow-up was reported with 0.17 mm (SD 1.24; n = 125) and -1.39 mm (SD 1.27; n = 110), respectively. The mean change in bone level from implant insertion to 1 year was -1.44 mm (SD 1.35; n = 98). CONCLUSIONS The 1-year follow-up showed a cumulative survival rate and success rate of 98.8% and 96.3%, respectively. Immediate or delayed loading of implants using a flapless, guided surgery approach (NobelGuide(™)) appears to be a viable concept demonstrating good clinical and radiographic outcomes at the 1-year time point.

Influence of Prosthetic Parameters on Peri-Implant Bone Resorption in the First Year of Loading: A Multi-Factorial Analysis

BACKGROUND The first year of prosthetic loading is crucial to peri-implant bone levels; however, contributing factors are yet barely understood. PURPOSE The purpose of the study is to investigate the influence of patient-, implant-, and prosthetic-related parameters on marginal bone resorption in partially edentulous patients within the first year of prosthetic loading. MATERIALS AND METHODS This retrospective multifactorial analysis involved the following influencing factors: patient gender and age, implant diameter, implant location and neck design, insertion torque, insertion depth, splinted versus single-tooth restorations, crown height space, and crown-to-implant ratio. RESULTS Mean peri-implant bone resorption around 200 dental implants was 0.98 ± 0.76 mm and significantly correlated to higher implant insertion depth (p < .001), whereas no association to prosthetic parameters could be observed. CONCLUSIONS Within the limits of the present analysis, it can be concluded that apical implant positioning may constitute a relevant determinant of early peri-implant bone resorption.

Evaluation of Three Different Validation Procedures regarding the Accuracy of Template-Guided Implant Placement: An In Vitro Study

PURPOSE The study aims to evaluate the accuracy of the NobelGuide™ (Medicim/Nobel Biocare, Göteborg, Sweden) concept maximally reducing the influence of clinical and surgical parameters. Moreover, the study was to compare and validate two validation procedures versus a reference method. MATERIAL AND METHODS Overall, 60 implants were placed in 10 artificial edentulous mandibles according to the NobelGuide™ protocol. For merging the pre- and postoperative DICOM data sets, three different fusion methods (Triple Scan Technique, NobelGuide™ Validation software, and AMIRA® software [VSG - Visualization Sciences Group, Burlington, MA, USA] as reference) were applied. Discrepancies between the virtual and the actual implant positions were measured. RESULTS The mean deviations measured with AMIRA® were 0.49 mm (implant shoulder), 0.69 mm (implant apex), and 1.98°mm (implant axis). The Triple Scan Technique as well as the NobelGuide™ Validation software revealed similar deviations compared with the reference method. A significant correlation between angular and apical deviations was seen (r = 0.53; p < .001). A greater implant diameter was associated with greater deviations (p = .03). CONCLUSION The Triple Scan Technique as a system-independent validation procedure as well as the NobelGuide™ Validation software are in accordance with the AMIRA® software. The NobelGuide™ system showed similar or less spatial and angular deviations compared with others.

Drilling- and Withdrawing-Related Thermal Changes during Implant Site Osteotomies

BACKGROUND Intrabony temperature increase is not only dependent on shearing energy and mechanical friction between bone and surgical drill but is also related to heat capacity and thermal conductivity of the surrounding bone and the applied surgical instrument. Thus time of occurrence of the highest temperature rise can be expected after the shearing process of the osteotomy, potentially affecting the process of osseointegration. PURPOSE The aim of this study was to evaluate temperature changes during the shearing and withdrawing processes during osteotomies. MATERIALS AND METHODS An overall 160 automated intermittent osteotomies (10/16 mm drilling depth) with 2 mm diameter twist drills and 3.5 mm diameter conical drills and different irrigation methods (without/external/internal/combined) were performed on standardized bone specimens. The drilling cycles were operated by a computer-controlled surgical system, while a linear motion potentiometer and multichannel temperature sensors in various intrabony levels ensured the real-time documentation of temperature changes during the shearing and withdrawing processes. RESULTS The highest temperature changes were invariably recorded during the process of withdrawal. Significantly lower temperature changes (p < .02) could be recorded at maximum drilling depths during the shearing process regardless of drilling depth, diameter or irrigation method. During coolant supply, 2 mm diameter twist drills showed higher temperatures (10 mm, p < .01/16 mm, p < .03) compared with 3.5 mm diameter conical implant drills. Internal (10 mm, p < .01) or combined irrigation (16 mm, p < .01) was associated with significantly lower temperatures compared with external irrigation by the use of conical implant drills. CONCLUSIONS Considering that heat generation during osteotomies is a multifactorial scenario, this study could demonstrate that the highest temperature rise during implant osteotomies occurs during the withdrawing process and that the time of occurrence is influenced by predominant factors such as osteotomy depth and mode of irrigation.