Primary stability and self-tapping blades: biomechanical assessment of dental implants in medium-density bone

Novel approach to assessing the primary stability of dental implants under functional cyclic loading in vitro: a biomechanical pilot study using synthetic bone

PURPOSE

This pilot study was conducted to develop a novel test setup for the in vitro assessment of the primary stability of dental implants. This was achieved by characterising their long-term behaviour based on the continuous recording of micromotions resulting from dynamic and cyclic loading.

METHODS

Twenty screw implants, each 11 mm in length and either 3.8 mm (for premolars) or 4.3 mm (for molars) in diameter, were inserted into the posterior region of 5 synthetic mandibular models. Physiological masticatory loads were simulated by superimposing cyclic buccal-lingual movement of the mandible with a vertically applied masticatory force. Using an optical 3-dimensional (3D) measuring system, the micromotions of the dental crowns relative to the alveolar bone resulting from alternating off-centre loads were concurrently determined over 10,000 test cycles.

RESULTS

The buccal-lingual deflections of the dental crowns significantly increased from cycle 10 to cycle 10,000 (P<0.05). The deflections increased sharply during the first 500 cycles before approaching a plateau. Premolars exhibited greater maximum deflections than molars. The bone regions located mesially and distally adjacent to the loaded implants demonstrated deflections that occurred synchronously and in the same direction as the applied loads. The overall spatial movement of the implants over time followed an hourglass-shaped loosening pattern with a characteristic pivot point 5.5±1.1 mm from the apical end.

CONCLUSIONS

In synthetic mandibular models, the cyclic reciprocal loading of dental implants with an average masticatory force produces significant loosening. The evasive movements observed in the alveolar bone suggest that its anatomy and yielding could significantly influence the force distribution and, consequently, the mechanical behaviour of dental implants. The 3D visualisation of the overall implant movement under functional cyclic loading complements known methods and can contribute to the development of implant designs and surgical techniques by providing a more profound understanding of dynamic bone-implant interactions.

Effect of cutting flute design features on primary stability of immediate implant placement and restoration: a dynamic experimental analysis

Self-tapping implants with self-cutting flutes may influence primary stability, especially for the immediate implant placement and restoration protocol in which implants are affixed to the bone in the apical portion. Screw geometry differs between brands, and the effect of apical design on its clinical outcomes remains unclear. This study is aimed at investigating the influence of cutting flute shape (spiral, straight, and without flute) on primary stability by using a dynamic experimental test. Six types of dental implants were designed using computer-aided design and computer-aided manufacturing technology, consisting of three types of cutting flute shapes along with two types of screw features. A dynamic mechanical test was performed using a cyclic loading scheme. The mechanical behaviors of resistance to lateral load (RLL), maximum force, and energy dissipation were compared between groups. In the dynamic test, implants without cutting flute also exhibited higher values in RLL, maximum force, and energy dissipation. The aggressive thread implant with straight flute displayed higher RLL and had a significantly higher values in RLL (p = 0.033) at the threshold point of bone-implant interface breakdown. The implants without cutting flutes exhibited higher primary stability. Straight flute design would improve RLL for aggressive thread implant.

Influences of screw design features on initial stability in immediate implant placement and restoration

BACKGROUND

Self-tapping screws have been extensively used for dental implants. Their biomechanical behavior is highly associated with their clinical success, particularly for screws used for immediate implant placement and restoration, because occlusal forces can directly affect the loading transfer at the bone-implant interface after implantation. The effect of implant design on the initial stability of self-tapping screws remains unclear. This study explored the biomechanical behaviors of implant stability in standardized implants with different design features.

METHODS

Six types of dental implants were designed using computer-aided design/computer-aided manufacturing technology, including three types of cutting flute shapes (spiral, straight, and non-self-tapping) combined with two types of screw features. Peak insertion torque values were first recorded; initial stability levels were subsequently evaluated in terms of the maximum force and resistance to lateral loads using an electrodynamic test system.

FINDINGS

The peak insertion torque values, maximum force, and resistance to lateral loads of the non-self-tapping groups were higher than those of the self-tapping groups by 17%-90% (p < 0.01). The peak insertion torque values of the Straumann implant with a spiral flute was higher than that of the original straight flute by 20% (p < 0.001). However, compared with the original spiral flute, the Nobel Biocare implant with straight flute had a 23% higher maximum force (p = 0.016) and 24.5% higher resistance (p = 0.012) under lateral loading.

INTERPRETATION

Changing the flute design would affect initial implant stability. Non-self-tapping implants exhibited superior initial stability than did self-tapping implants.

How Do Parameters of Implant Primary Stability Correspond with CT-Evaluated Bone Quality in the Posterior Maxilla? A Correlation Analysis

The aim of the present study was to evaluate correlations between bone density and implant primary stability, considering various determinants such as age, gender, and geometry of implants (design, diameter). Bone density of edentulous posterior maxillae was assessed by computed tomography (CT)-derived Hounsfield units, and implant primary stability values were measured with insertion torque and resonance frequency analysis (RFA). A total of 60 implants in 30 partially edentulous patients were evaluated in the posterior maxilla with two different types of dental implants. The bone density evaluated by CT-derived Hounsfield units showed a significant correlation with primary stability parameters. The bone quality was more influenced by gender rather than age, and the type of implant was insignificant when determining primary stability. Such results imply that primary stability parameters can be used for objective assessment of bone quality, allowing surgical modifications especially in sites suspected of poor bone quality.

Comparison of nonself-tapping tapered implant and self-tapping hybrid implant in terms of implant stability at initial and second fixation: A prospective randomized clinical trial

BACKGROUND

Various features are provided in dental implants to improve initial fixation.

PURPOSE

To compare the implant stability of the nonself-tapping tapered implant and self-tapping hybrid implant over a 3-month healing period.

MATERIALS AND METHODS

A randomized controlled trial was conducted. Patients were randomly divided into tapered and self-tapping groups. Patients in the tapered group received NobelReplace Tapered (Nobel Biocare, Sweden) implants, while those in the self-tapping group received NobelSpeedy (Nobel Biocare, Sweden) implants. Implant stability was measured by resonance frequency analysis at surgery and 3 months following implant insertion. Data were analyzed using an independent t-test.

RESULTS

Forty-three patients (tapered group: 21, self-tapping group: 22) received a total of 88 implants. Initial stability in the tapered group was significantly higher (mean: 60.14, SD: 12.40) than that in the self-tapping group (mean: 54.72, SD: 7.92). Implant stability significantly increased 3 months after implantation in the tapered group (mean: 66.61, SD: 9.00) and self-tapping group (mean: 64.01, SD: 5.78). No significant intergroup difference in implant stability was noted 3 months after surgery.

CONCLUSIONS

The tapered shape affected initial fixation more than the self-tapping function. However, during the second fixation, both implants showed good stability, and the difference disappeared.

Effect of insertion factors on dental implant insertion torque/energy-experimental results

Anchorage of dental implants is quantified with a mechanical engagement to insertion, for example maximum insertion torque (MIT) and insertion energy (IE). Good anchorage of dental implants highly correlates to positive clinical outcomes. However, it is still unclear how bone density, drill protocol, surface finish and cutting flute affect anchorage. In this study, effects of the insertion factors on both MIT and IE were investigated using a full-factorial experiment at two levels: bone surrogate density (0.32 g/cm³ versus 0.48 g/cm³), drill protocol (Ø2.4/2.8 versus Ø2.8/3.2 mm), implant surface finish (machined versus anodized surface) and cutting flute (with versus without). Osteotomies were prepared on rigid polyurethane foam blocks with dimensions of 40 × 40 × 8 mm. Screw shaped dental implants with variable tapered body were consecutively inserted into and removed from the polyurethane foam blocks three times under constant axial displacement and rotational speed. Axial force and torque were recorded synchronously. Insertion energy was calculated from the area under the torque-displacement curve. In this study, we found the main insertion mechanics were thread forming for the first insertion. For the second and third insertions, the main mechanics shifted to thread tightening. Maximum insertion torque (MIT) responded differently to the four insertion factors in comparison to IE. Bone surrogate density, drill protocol and surface finish had the largest main effects for first MIT. For the first IE, drill protocol, surface finish and cutting flute were significant contributors. These results suggest that MIT and IE are influenced by different mechanics: the first MIT and the first IE were sensitive to thread tighten and forming, respectively. Together MIT and IE provide a complete assessment of dental implant anchorage.

The clinical significance of implant stability quotient (ISQ) measurements: A literature review

Implant stability quotients (ISQ values) are obtained in dental clinical practice on a non-invasive basis by resonance frequency measurement rapidly after surgical placement of implants. The ISQ-values are used as indicator for mechanical implant stability, and are believed to have predictive power for clinical outcome. It is the aim of this review to provide a synopsis of all factors described in the literature that influence ISQ measurements by performing an exhaustive literature review; moreover, this review aims at elucidating the key factors relevant for a rapid clinical predictive assessment. We searched systematically and exhaustively all major databases for publications relating to ISQ measurement methodology and for ISQ-influencing factor analyses. The reports identified were ordered in experimental (preclinical) studies and in clinical publications. We were able to identify 13 basic factors influencing ISQ-measurements. Among these, local bone quality, playing a key role in such measurements, was subdivided in four specific subfactors; thus a total of 17 individual factors was identified and reported to influence ISQ-measurements. A comprehensive list of these factors is provided in Table-form. A critical analysis points out that only 6 of these factors are of a sound predictive power useful for a rapid clinical assessment; and only two of these factors appear to have a well-documented scientific basis.

Effect of implant design on the initial biomechanical stability of two self-tapping dental implants

BACKGROUND

This study evaluated the effect of two self-tapping implants on implant stability in immediate implantation.

METHODS

Two types of self-tapping implants, straight flute (STF) and spiral flute (SPF) designs, were studied. Two synthetic bone blocks with varying densities (0.32 g/cm³ and 0.16 g/cm³) were chosen to simulate the bone quality of the anterior maxilla. Insertion torque values were measured by a torque testing machine during implant insertion. Four biomechanical tests were performed: resonance frequency analysis was conducted using the Osstell device, and the strengths of screw push-in, lateral bending, and pull-out were evaluated using an MTS machine. The strength for each design feature was obtained by averaging the results of 10 trials. In total, 40 specimens were tested for each bone density. Statistical difference was determined by one-way analysis of variance followed by Bonferroni post hoc multiple tests between groups.

FINDINGS

The STF and SPF groups exhibited similar insertion torque values (p = 0.525 in low-density bone, and p = 0.99 in high-density bone). A significant difference (p < 0.001) was observed in the push-in test between the two groups when low-density bone was tested. The SPF group exhibited a significantly higher lateral bending force (p = 0.001) and a higher stiffness (p < 0.001) than the STF group in high-density bone. The SPF design attained higher (p < 0.001) ISQ numbers than the STF design, but all numbers were below 60.

INTERPRETATION

Implant stability can be influenced by the apical fixture design of self-tapping implants in immediate implantation.

Development and application of a direct method to observe the implant/bone interface using simulated bone

BACKGROUND

Primary stability after implant placement is essential for osseointegration. It is important to understand the bone/implant interface for analyzing the influence of implant design on primary stability. In this study rigid polyurethane foam is used as artificial bone to evaluate the bone-implant interface and to identify where the torque is being generated during placement.

METHODS

Five implant systems-Straumann-Standard (ST), Straumann-Bone Level (BL), Straumann-Tapered Effect (TE), Nobel Biocare-Brånemark MKIII (MK3), and Nobel Biocare-Brånemark MKIV (MK4)-were used for this experiment. Artificial bone blocks were prepared and the implant was installed. After placement, a metal jig and one side artificial bone block were removed and then the implant embedded in the artificial bone was exposed for observing the bone-implant interface. A digital micro-analyzer was used for observing the contact interface.

RESULTS

The insertion torque values were 39.35, 23.78, 12.53, 26.35, and 17.79 N cm for MK4, BL, ST, TE, and MK3, respectively. In ST, MK3, TE, MK4, and BL the white layer areas were 61 × 103 μm(2), 37 × 103 μm(2), 103 × 103 μm(2) in the tapered portion and 84 × 03 μm(2) in the parallel portion, 134 × 103 μm(2), and 98 × 103 μm(2) in the tapered portion and 87 × 103 μm(2) in the parallel portion, respectively.

CONCLUSIONS

The direct observation method of the implant/artificial bone interface is a simple and useful method that enables the identification of the area where implant retention occurs. A white layer at the site of stress concentration during implant placement was identified and the magnitude of the stress was quantitatively estimated. The site where the highest torque occurred was the area from the thread crest to the thread root and the under and lateral aspect of the platform. The artificial bone debris created by the self-tapping blade accumulated in both the cutting chamber and in the space between the threads and artificial bone.

The influence of three different apical implant designs at stability and osseointegration process: experimental study in rabbits

OBJECTIVES

The aim of this study was to perform a histomorphometric and biomechanical comparison of three implants with different designs of the apical area to promote a better bone initial stability and its correlation with the osseointegration.

MATERIAL AND METHODS

Fifty-four tapered implants with same length, diameter and surface properties but with three different apical configurations (Group I: MK4: Group II: C1 and Group III: MK7) were inserted in the tibia of rabbits. Implant stability and bone formation were evaluated by resonance frequency analysis measured at 0, 6, 8 and 12 weeks and by histomorphometric analysis performed at 6, 8 and 12 weeks.

RESULTS

Statistical test to compare the stability through the implant stability quotient in the four times showed few differences between the groups and time periods proposed, with significance set at P < 0.05. In the bone-implant contact, by comparing the groups in the three times proposed, it was possible concluded that there is a similar behavior among the three implant design (P < 0.05).

CONCLUSION

With the limitations of this animal study, it can be concluded that the design of the apical area influences the implant stability and the bone-to-implant contact.

Integrative Performance Analysis of a Novel Bone Level Tapered Implant

Primary mechanical stability, as measured by maximum insertion torque and resonance frequency analysis, is generally considered to be positively associated with successful secondary stability and implant success. Primary implant stability can be affected by several factors, including the quality and quantity of available bone, the implant design, and the surgical procedure. The use of a tapered implant design, for instance, has been shown to result in good primary stability even in clinical scenarios where primary stability is otherwise difficult to achieve with traditional cylindrical implants—for example, in soft bone and for immediate placement in extraction sockets. In this study, bone-type specific drill procedures are presented for a novel Straumann bone level tapered implant that ensure maximum insertion torque values are kept within the range of 15 to 80 Ncm. The drill procedures are tested in vitro using polyurethane foam blocks of variable density, ex vivo on explanted porcine ribs (bone type 3), and finally in vivo on porcine mandibles (bone type 1). In each test site, adapted drill procedures are found to achieve a good primary stability. These results are further translated into a finite element analysis model capable of predicting primary stability of tapered implants. In conclusion, we have assessed the biomechanical behavior of a novel taper-walled implant in combination with a bone-type specific drill procedure in both synthetic and natural bone of various types, and we have developed an in silico model for predicting primary stability upon implantation.

The effect of the thread depth on the mechanical properties of the dental implant

PURPOSE

This study aimed to evaluate the effect of implant thread depth on primary stability in low density bone.

MATERIALS AND METHODS

The insertion torque was measured by inserting Ti implants with different thread depths into solid rigid polyurethane blocks (Sawbones) with three different bone densities (0.16 g/cm³, 0.24 g/cm³, and 0.32 g/cm³). The insertion torque value was evaluated with a surgical engine. The static compressive strength was measured with a universal testing machine (UTM) and the Ti implants were aligned at 30° against the loading direction of the UTM. After the static compressive strength test, the Ti implants were analyzed with a Measurescope.

RESULTS

The Ti implants with deeper thread depth showed statistically higher mean insertion torque values (P<.001). Groups A and group B had similar maximum static compressive strengths, as did groups C and D (P>.05). After the static compressive strength, the thread shape of the Ti implants with deeper thread depth did not show any breakage but did show deformation of the implant body and abutment.

CONCLUSION

The implants with deeper thread depth had higher mean insertion torque values but not lower compressive strength. The deep threads had a mechanical stability. Implants with deeper thread depth may increase the primary stability in areas of poor quality bone without decreasing mechanical strength.