Comparative evaluation of intraosseous temperature and drilling time using four different drill designs in implant site preparation

Abstract

Background

The aim of this study was to compare the thermal effects and drilling efficiency of four different implant osteotomy systems -conventional stainless steel drills (CS), velodrills (VD), ceramic drills (CD), and bone-enhancing drills (BE)- under standardized experimental conditions.

Methods

A total of 160 osteotomies were performed on fresh bovine rib bone blocks using four different drill systems. Each group included 40 repetitions. A standardized protocol was applied, including constant irrigation (50 ml/min), drilling speed (800 rpm), and axial load (2 kg). Each drill was used for the entire 40 repetitions per system. However, all drills were inspected before and after the experiments to ensure no visible damage, and the performance decline was analyzed over time. Temperature changes on the bone surface were recorded using a 14-bit digital infrared thermal camera. Drilling time was measured for each osteotomy. Statistical analysis was conducted using Dunn’s multiple comparisons test to evaluate differences between groups.

Results

The ceramic drill group (CD) exhibited the highest mean temperature (24.82 ± 2.69 °C) and the longest mean drilling time (17.07 ± 6.82 s). The conventional stainless steel drill (CS), velodrill (VD), and bone-enhancing drill (BE) systems demonstrated significantly shorter drilling times and lower temperature values. Statistically significant differences in temperature and drilling time were observed between CD and other systems (p < 0.0001). While all systems remained below the critical thermal threshold for bone necrosis, ceramic drills were significantly associated with greater thermal load and procedural duration (p < 0.0001).

Conclusion

Under standardized experimental conditions, all drill systems remained within safe thermal limits. However, ceramic drills generated more heat and required significantly longer drilling times compared to other systems. Conventional stainless steel and velodrill systems demonstrated promising thermal control and efficiency in this in vitro setting, which may inform clinical decisions. However, further validation including drill wear rate and biological response is necessary before clinical endorsement.

Background

Dental implant placement requires precise osteotomy techniques to ensure thermal safety and promote osseointegration. One of the critical determinants of implant success is the integrity of the bone tissue during and after the osteotomy procedure [1]. During implant site preparation, excessive heat generation can lead to thermal osteonecrosis, impairing bone healing and compromising osseointegration [2]. Eriksson and Albrektsson (1984) demonstrated that a temperature rise above 47 °C for more than one minute can cause irreversible bone damage, emphasizing the importance of minimizing thermal trauma during drilling [3].

Numerous factors influence the amount of heat generated during osteotomy, including drill design, material, diameter, speed, irrigation, and bone density [4]. Conventional stainless steel drills remain the most commonly used systems; however, innovations in drill geometry and materials have led to the development of alternative systems such as ceramic drills, velodrills, and bone-enhancing drills [5]. These systems aim to improve cutting efficiency, reduce surgical time, and minimize thermal elevation. Despite these innovations, the performance and safety of these systems under clinical conditions remain under investigation.

Ceramic drills, typically made from zirconia, are valued for their biocompatibility, corrosion resistance, and long-term sharpness [6]. However, their lower thermal conductivity and potential for increased friction have raised concerns about excessive heat generation during osteotomy [7]. Velodrills are designed to optimize bone cutting by distributing the cutting force along multiple diameters, potentially reducing overall resistance and thermal output. Bone-enhancing osteotomes, on the other hand, displace bone laterally rather than removing it, and are particularly beneficial in low-density bone regions, although their thermal behavior is not well understood [8].

Given the clinical implications of both heat generation and procedural efficiency, comparative studies of different osteotomy systems are essential for evidence-based surgical planning. The aim of the present study was to evaluate and compare four different drill systems -conventional stainless steel (CS), velodrill (VD), ceramic (CD), and bone-enhancing (BE)- in terms of the temperature they generate during osteotomy and the time required to reach the desired depth. By identifying differences in thermal performance and drilling efficiency, this study seeks to guide clinicians in selecting appropriate tools to optimize implant site preparation and promote favorable surgical outcomes.

Methods

This in vitro experimental study was conducted at the Research Laboratory of the Faculty of Dentistry, Istanbul University to compare the thermal changes and drilling durations associated with four different drill systems used during dental implant site preparation. A total of 40 drilling procedures were performed for each system. The sample size was determined based by a priori power analysis performed using G\Power Version 3.1.9.7, targeting a power of 0.8, an alpha of 0.05, and a medium effect size (f = 0.25) for one-way ANOVA, ensuring that the study had sufficient statistical power to detect significant differences between the experimental and control groups.

Measurements were evaluated both cumulatively and in time-based subgroups: the first 10, second 10, third 10, and final 10 drilling attempts. Fresh bovine ribs from cadavers were selected due to their cortical structure and mechanical properties resembling human mandibular bone. This model has been validated in previous implantology studies for simulating thermal and mechanical responses [9]. The samples were prepared with an average thickness of 2.0 mm and a length of approximately 10 cm. The bones were kept moist throughout the procedure using 0.9% sodium chloride solution to simulate physiological conditions. To standardize density, all bone segments were obtained from the same anatomical region (mid-diaphyseal rib segments) of bovine sources with similar age and weight, and bone mineral density was confirmed using a digital caliper measurement of cortical thickness combined with visual inspection for morphological similarity.

All procedures for each drill system were performed on bone samples with similar morphological characteristics with standardization was ensured by visual inspection to confirm comparable density across samples.

The evaluated drill systems included the stainless steel drill set (five steps) (Straumann AG, Basel, Switzerland), the velodrill system (six steps) (Straumann AG, Basel, Switzerland), the ceramic drill system (four steps) (Z-Systems AG, Oensingen, Switzerland) and the bone-enhancing drill system (eight steps) (Legend Group, Sialkot, Pakistan). All drill systems were used in accordance with the manufacturers’ recommended sequences and technical protocols. Final osteotomies were prepared to place an implant with a diameter of 4 mm and a depth of 10 mm.

All drilling procedures were conducted under standardized conditions. A constant rotational speed of 800 rpm was maintained using a standard implant motor (W&H, Bürmoos, Austria), and a vertical axial load of 2 kg was applied during drilling. External irrigation was provided using 0.9% saline solution at a flow rate of 50 mL/min, maintained at 23 °C. The ambient room temperature was controlled at 23 °C ± 1 °C. The drilling apparatus was fixed in place to eliminate operator-related variability and ensure consistent angulation and pressure (Fig. 1).

Fig. 1.

Experimental setup used for implant osteotomy and measurements

Bone surface temperatures during drilling were measured using a high-resolution infrared thermal imaging camera. A FLIR E6-XT (FLIR Systems Estonia OÜ, Tallinn, Estonia) 14-bit digital infrared camera with a thermal resolution of 240 × 180 pixels was used for this purpose. The camera was positioned perpendicularly at a fixed distance of 20 cm from the drilling site (Fig. 2). Prior to data collection, the thermal camera was calibrated according to the manufacturer’s instructions, including emissivity adjustment for bone tissue (ε = 0.96) and ambient temperature stabilization. Maximum temperature values were recorded before and immediately after each drilling procedure.

Fig. 2.

Measurement of the maximum temperature generated in the bone during drilling

Drilling duration was defined as the time elapsed from the initial contact of the drill with the bone surface until it reached a depth of 10 mm. This was measured using a digital stopwatch with millisecond precision. The drilling time served as an objective parameter reflecting the cutting efficiency of each drill.

In order to evaluate changes in drill performance over time, the 40 drilling attempts for each system were divided into four groups: first 10 (1–10), second 10 (11–20), third 10 (21–30), and final 10 (31–40) drills. In addition, a general analysis was conducted using the overall data from all 40 repetitions per system.

Statistical analyses were performed using GraphPad Prism Version 10.3.1 (GraphPad Software Inc., CA, USA). Normality of data distribution was assessed using the Shapiro–Wilk test. For normally distributed data, one-way analysis of variance (ANOVA) followed by Tukey’s post-hoc test was used. For non-normally distributed data, the Kruskal–Wallis test followed by Dunn’s multiple comparisons test was applied. A significance level of p < 0.05 was considered statistically significant.

Results

In this study, four different drill systems were evaluated in terms of the thermal changes they induced in bone tissue and the time required to reach the final drilling depth. The systems included a conventional stainless steel drill set (CS), velodrill system (VD), a ceramic drill set (CD), and a bone-enhancing drill system (BE). In total, one ceramic drill fractured during the 26th repetition. A new drill was used to complete the remaining procedures. The results were analyzed quantitatively for both temperature changes and drilling times, and the differences between groups were assessed using Dunn’s multiple comparisons test.

The highest mean temperature was recorded in the ceramic drill group (CD), with a mean value of 24.82 ± 2.69 °C (range: 23.10–33.80 °C). This was followed by VD (24.45 ± 1.15 °C), BE (24.40 ± 1.50 °C), and CS (23.79 ± 1.08 °C) (Table 1). Although all systems remained within clinically acceptable temperature limits (below the critical threshold of 47 °C for thermal bone necrosis), statistically significant differences were observed between certain systems (Fig. 3).

Table 1.

Mean bone surface temperature and drilling time for each osteotomy system

Drill Systems	Temperature (°C)		Drilling Time (sec)
	Mean	Min -Max	Mean	Min - Max
CS	23.79 ± 1.08	22.30–29.20	10.11 ± 5.94	4.58–35.62
VD	24.45 ± 1.15	22.90–28.20	10.24 ± 4.89	4.11–24.68
CD	24.82 ± 2.69	23.10–33.80	17.07 ± 6.82	3.51–31.08
BE	24.40 ± 1.50	22.90–29.80	9.87 ± 4.68	5.30–23.51

CS Conventional stainless steel drills, VD Velodrills, CD Ceramic drills, BE Bone-enhancing drills

* “Min” and “Max” values represent the minimum and maximum measurements recorded. Highlighted values represent the min and max measurements in total

Fig. 3.

Comparison of mean bone surface temperatures among different drill systems

According to Dunn’s multiple comparisons test for the overall drilling period (1–40), the CS group showed significantly lower temperatures compared to both the VD (p < 0.0001) and BE (p = 0.0125) groups. However, no significant difference was found between CS and CD (p = 0.0723), or between VD, CD, and BE. Interestingly, subgroup analysis (drilling repetitions 21–30) revealed significant differences between CS and VD (p < 0.0001), and CS and BE (p = 0.0379), indicating that temperature differences may become more prominent with increased usage (Table 2). To ensure consistency, each drill was used for 40 osteotomies, and changes in performance were monitored across 10-drill intervals.

Table 2.

Statistical test results for bone surface temperature between drill systems

Drill Systems	1–10	11–20	21–30	31–40	1–40
CS vs. VD	0,4018	0,5177	< 0,0001**	> 0,9999	< 0,0001**
CS vs. CD	0,1575	0,6021	0,1001	0,5985	0,0723
CS vs. BE	0,0014**	> 0,9999	0,0379*	> 0,9999	0,0125*
VD vs. CD	> 0,9999	> 0,9999	0,1987	0,4860	0,6798
VD vs. BE	0,3986	0,6036	0,0502	> 0,9999	0,5621
CD vs. BE	> 0,9999	0,7241	> 0,9999	> 0,9999	> 0,9999

Although p-values indicate statistically significant differences, the mean temperature differences ranged between 0.6 and 1.1 °C, suggesting modest practical implications in terms of clinical thermal safety

CS Conventional stainless steel drills, VD Velodrills, CD Ceramic drills, BE Bone-enhancing drills

*The values represent p-values obtained from Dunn’s multiple comparisons test

*Statistically significant differences (p < 0.05) are marked with asterisks (*p < 0.05, **p < 0.01, **p < 0.001)

The CD group exhibited the longest mean drilling time (17.07 ± 6.82 s), followed by VD (10.24 ± 4.89 s), CS (10.11 ± 5.94 s), and BE (9.87 ± 4.68 s) (Table 1). Notably, drilling times varied more widely in the CD group (range: 3.51–31.08 s), suggesting potential inconsistencies in cutting efficiency (Fig. 4).

Fig. 4.

Comparison of mean drilling time required by each drill system

Statistically, CS showed significantly shorter drilling times compared to CD in the total dataset (p < 0.0001) and in all subgroups from the 11th to the 40th repetition. Similarly, VD exhibited shorter times than CD for the total group (p < 0.0001) and in the 11–20 subgroup (p < 0.0001). BE also showed significantly shorter times than CD in multiple subgroups and the overall analysis (p < 0.0001) (Table 3).

Table 3.

Statistical test results for drilling time between drill systems

Drill Systems	1–10 P	11–20	21–30	31–40	1–40
CS vs. VD	0,9416	0,2556	> 0,9999	0,0043**	> 0,9999
CS vs. CD	0,9084	0,0036**	0,0206**	< 0,0001**	< 0,0001**
CS vs. BE	> 0,9999	0,3572	0,4905	0,6486	> 0,9999
VD vs. CD	> 0,9999	< 0,0001**	0,1670	0,3063	< 0,0001**
VD vs. BE	> 0,9999	0,0005**	0,0816	0,4515	> 0,9999
CD vs. BE	> 0,9999	0,7276	< 0,0001**	0,0011**	< 0,0001**

CS Conventional stainless steel drills, VD Velodrills, CD Ceramic drills, BE Bone-enhancing drills

*The values represent p-values obtained from Dunn’s multiple comparisons test

*Statistically significant differences (p < 0.05) are marked with asterisks (*p < 0.05, **p < 0.01, **p < 0.001)

These findings suggest that the ceramic drill system not only leads to prolonged drilling durations but also causes more thermal elevation, possibly due to its material properties and cutting efficiency.

Across both temperature and time parameters, the ceramic drills (CD) consistently performed worse than other systems, particularly in longer drilling durations and higher thermal elevations. On the other hand, the bone-enhancing drill (BE) and velodrill (VD) systems exhibited comparable performance to the conventional system (CS) in terms of drilling time, while slightly increasing temperature. The conventional stainless-steel drills (CS) demonstrated the most stable thermal profile with consistent drilling times across repetitions.

Discussion

This study investigated the thermal effects and drilling efficiency of four different implant osteotomy systems: conventional stainless steel drills (CS), velodrills (VD), ceramic drills (CD), and bone-enhancing drills (BE). The findings demonstrate that while all systems remained within the safe thermal threshold, the ceramic drill group (CD) produced significantly higher temperatures and required longer drilling times compared to the others. Importantly, during the experimental procedures, one of the ceramic drills fractured due to its brittle structure. As a result, the affected trials were excluded, and new bone samples along with a replacement ceramic drill were used to repeat the procedures under the same conditions. This incident highlights the potential mechanical limitations of ceramic drills, particularly under repeated or prolonged use. This result is consistent with Tur et al. (2023), who reported that ceramic drills, despite maintaining sharpness over time, tend to fracture more easily under cyclic mechanical stress due to their inherent brittleness [9].

Thermal injury is a major concern in implant osteotomy procedures, as temperatures exceeding 47 °C for more than one minute can lead to irreversible bone necrosis and impaired osseointegration [3]. Heat generated during drilling is primarily influenced by friction between the drill and bone surface, which is influenced by factors such as drill design, material, sharpness, speed, axial load, and irrigation [10]. Although none of the systems in this study reached critical temperature levels, the ceramic drill group exhibited the highest mean temperature (24.82 ± 2.69 °C) and the widest range (up to 33.80 °C). This elevation may be attributed to the lower thermal conductivity of ceramic materials, which impairs heat dissipation during high-friction cutting [11]. In comparison, metallic drills such as stainless steel possess superior thermal conductivity, allowing heat to be more effectively transferred away from the cutting site [9]. Our finding that ceramic drills produced higher temperatures aligns with the results of Scarano et al. (2020), who demonstrated through thermographic analysis that zirconia drills exhibit significantly less thermal dissipation during implant site preparation compared to steel drills [12].

Additionally, ceramic drills tend to retain sharpness longer due to their higher hardness, which theoretically could reduce friction and heat [13]. However, when drilling resistance increases -especially in dense bone or after repeated use- this advantage may diminish. In such scenarios, the lower capacity of zirconia to conduct heat away from the osteotomy site may lead to localized temperature accumulation [14]. Moreover, the relatively brittle nature of ceramic materials could contribute to micro-chipping or surface roughness that further increases friction during cutting [2]. In our study, the variability observed in ceramic drill performance across the repetitions may be explained by such microstructural alterations over time, potentially compromising their cutting efficiency despite initial sharpness.

Previous studies have shown conflicting results regarding the thermal behavior of ceramic drills. While some report superior cutting efficiency and reduced heat generation due to maintained sharpness, others highlight concerns about increased friction and heat accumulation, especially in dense bone substrates or during extended usage [13, 15]. Our results align more closely with the latter, suggesting that ceramic drills may not offer thermal advantages under continuous use without irrigation optimization. This discrepancy emphasizes the importance of considering not only drill material but also cumulative use and surgical conditions, such as irrigation efficacy and bone type, when evaluating thermal safety.

Drilling time is another critical parameter, as prolonged osteotomy not only increases operative time but also contributes to additional heat generation [4]. In this study, ceramic drills also required significantly longer drilling durations (mean: 17.07 ± 6.82 s), whereas the CS, VD, and BE systems demonstrated comparable and significantly faster performance. The extended time with CD may reflect reduced cutting efficiency due to tip geometry, increased tool-bone contact, or higher resistance in denser regions. Previous literature supports the idea that prolonged contact time between the drill and bone leads to a linear increase in heat, underscoring the importance of both drill geometry and speed in surgical planning [12, 16]. The prolonged drilling times observed in our study with ceramic drills are in agreement with Delgado-Ruiz et al. (2018), who reported increased osteotomy duration and corresponding heat accumulation when using slower or less efficient cutting instruments [17].

The VD and BE systems exhibited consistent performance across trials, with moderate thermal outputs and reduced drilling times. The BE system, which employs an osteotome-like expansion mechanism rather than rotational cutting, showed one of the shortest drilling durations (mean: 9.87 ± 4.68 s), likely due to its mechanical mode of action and the absence of extensive material removal. Although osteotome systems do not “cut” in the traditional sense, their controlled displacement of bone results in lower thermal accumulation. On the other hand, velodrills are engineered to sequentially increase in diameter during advancement, distributing the cutting load across multiple levels and potentially reducing bone resistance. This design is thought to enhance drilling efficiency and reduce the net energy required per unit time, which may explain the favorable performance observed in this study [18].

These findings are clinically relevant, as shorter drilling durations and reduced thermal outputs are desirable for preserving bone viability, especially in patients with compromised bone quality (e.g., irradiated bone, osteoporotic bone) [17]. Elevated bone temperature not only impairs healing but also increases the risk of early implant failure due to loss of primary stability [19]. In line with this, Rugova suggests that minimizing the number of drilling steps and thermal stress may enhance osseointegration more effectively than even advanced implant surface treatments, highlighting the biological significance of procedural simplification in implant site preparation [20]. Similarly, recent in vitro evidence comparing static computer-assisted implant surgery (S-CAIS) and conventional implant preparation (CIP) techniques demonstrated that drilling depth, irrigation mode, and drill diameter significantly affect temperature changes during osteotomy, particularly when larger diameter drills are used [21].

From a clinical perspective, the conventional stainless steel (CS) and velodrills (VD) appear to offer a balanced profile in terms of thermal safety and procedural efficiency. Although ceramic drills may still have advantages such as biocompatibility and resistance to corrosion, their thermal performance in repetitive clinical scenarios remains a potential limitation [22]. In cases requiring multiple osteotomies, dense cortical bone preparation, or limited irrigation, ceramic drills may inadvertently elevate intraosseous temperatures despite their cutting stability.

In this study, the higher heat generation and prolonged drilling times observed with ceramic drills suggest that their low thermal conductivity and cutting geometry may be more prone to performance decline over repeated use. Additionally, the fracture of a ceramic drill during the experiment highlights the mechanical limitations of this system under repetitive loading. In contrast, the conventional stainless steel, velodrill, and bone-enhancing systems maintained more stable thermal profiles and shorter drilling durations, indicating greater durability and clinical reliability. Based on our findings, ceramic drills should be carefully evaluated after 5–10 uses, while other systems may remain effective for up to 15–20 uses before reassessment is necessary. It is suggested as a hypothesis to be tested in future investigations or clinical trials.

All drill systems remained well below the critical thermal threshold for bone necrosis, indicating that—under adequate irrigation and controlled drilling parameters—implant site preparation can be performed safely. However, even sub-threshold temperature increases and prolonged drilling times may influence healing, particularly in compromised bone. In such cases, systems with low heat generation and shorter preparation times, such as stainless steel or velodrills, may better preserve bone viability, while ceramic drills may require closer monitoring and optimized irrigation to prevent localized heat buildup.

Surgeons should be cautious when using ceramic drills in cases requiring multiple osteotomies or prolonged preparation times, and ensure adequate irrigation and intermittent drilling techniques to mitigate heat buildup [23]. Additionally, careful monitoring of drill wear and adherence to manufacturers’ recommended usage cycles is essential for all systems [24].

Although drilling angle was standardized using a fixed apparatus in this study, literature suggests that angulation significantly affects temperature distribution and cutting efficiency [25]. Deviations from axial orientation may increase friction and heat, underscoring the need for strict control in clinical practice. Despite the standardized setup, several limitations exist in this study. First, temperature measurements were restricted to bone surface using infrared thermography. Intrabony temperatures, which are more critical for assessing thermal osteonecrosis risk, were not recorded. Second, the lack of histological validation limits the interpretation of biological consequences. Third, while performance decline was monitored through physical parameters, the absence of torque or force measurement may underestimate drill fatigue. Future studies should include in vivo settings with histological and mechanical outcomes.

Future studies should incorporate different bone densities (D1–D4 classification), assess drill wear over time, and investigate irrigation patterns’ contribution to thermal mitigation. Moreover, histological analysis of bone viability following osteotomy with different systems would complement these findings with biological evidence.

Conclusion

Under standardized in vitro conditions, all osteotomy systems remained below critical thermal thresholds. Ceramic drills generated significantly more heat and required longer durations, potentially due to their material properties. Stainless steel and velodrill systems offered favorable thermal and temporal performance. These findings may guide clinicians in selecting efficient and thermally safe tools, though further in vivo validation is recommended.

Authors’ contributions

B.G. conceptualized the study and M.A.E. designed the experiments. E.E. and B.K.Y. performed the experiments and tests in the study. B.K.Y. analyzed the data and B.G. wrote the manuscript. A.B.C. coordinated the revisions. All three authors read and approved the final manuscript.

Funding

This research was not supported by any scientific council.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

This study did not require ethical approval as it used only bovine cadavers and did not involve any human or live animal subjects. Therefore, consent was not valid for participation.

Consent for publication

Not applicable, as this research does not involve identifiable individual data or images.

Competing interests

The authors declare no competing interests.