Thermal evaluation of pilot- and partially guided implant surgery – an in vitro study using automated robotic drilling

Abstract

Background

Since increased heat generation with guided implant surgery (GS) especially with pilot drills has been reported in the past, standardized investigation of pilot- and partially guided preparations was attempted.

Methods

A total of 160 automated and reproducible surgical procedures with stainless steel pilot drills of 2.0 and 2.8 mm have been performed on bovine testing samples for investigating GS vs. conventional drilling (CD). Preparations were performed in 2 preparation depths (10 / 12 mm) by using 2 cooling modes (external / without cooling). Real-time temperature measurements were conducted in 2 distances to the osteotomy site (1 / 2 mm). Temperature increase between the surgical preparation techniques was compared by a linear mixed model including all experimentally controlled variables.

Results

Comparison of pilot drills yielded significantly lower temperatures for GS in 2.0-mm diameter for preparation depths of 10 mm (p = 0.0107) and 12 mm (p = 0.0005) with external irrigation. 2.8-mm drills exerted higher temperatures during GS and external cooling, with significant outcome in 10-mm preparation depth (p = 0.0256).

Conclusions

Significant differences in temperature generation were obtained between pilot drills of different diameters, indicating sufficient irrigation of larger drill diameters during GS to be essential, even in sequential drilling preparations. The reported results of this investigation may be considered clinically relevant with regard to an observed impairment of cooling efficacy in larger drills during guided surgical preparations.

Background

Today, implant solutions in partially and fully edentulous patients, have become highly predictable treatment options for dental rehabilitation [1]. For facilitating precise and stable implant positioning during prosthodontic restoration at the dawn of dental implantology, guided concepts were initially proposed in the 1980s. These applications were mainly based on planning steps in conventional radiographs and diagnostic study casts [2, 3]. With the introduction of three-dimensional (3D) imaging tools and computing systems, computer-assisted guided implantation has become widely available for clinical application and can be considered an integral part of contemporary digital dentistry [4, 5]. While concepts of dynamic and robotic computer-assisted implant surgery may drive future innovations [6, 7], guided implant surgery (GS) remains the most commonly used and clinically established digital approach in implant dentistry today [8]. Depending on the applied surgical protocol, GS can include preparation steps only (pilot- or partially guided approach) or allow for subsequent implant insertion as well (fully guided approach) [8]. Systematic review and meta-analysis comparing fully guided vs. conventional implant procedures reported a high implant survival for both techniques, however, up to three times higher failure rates could be observed with freehand implant placement [9]. Regarding the implant placement accuracy by means of fully guided, partially guided surgery and freehand surgery, superior results were found for the GS groups, with highest precision in fully guided procedures and lowest in the freehand protocol [10]. Although pilot- or partially guided surgery can be considered less precise when compared to the fully guided approach and may require extensive surgical experience, valuable advantages of these techniques include the ability of the clinician to possibly adapt surgical steps and to place the implant freehand in delayed or immediate placement protocols [8, 10].

These results may support the claim for clinical prerequisites in successful implant therapy of the highly sensitive esthetic zone in the anterior maxilla, asserting ideal implant positioning in all 3 dimensions to be key for success. Additionally, it was highlighted that not only atraumatic preparation technique and the use of surgical guides may be recommended for success, but also the proper selection of non-oversized implants [11]. Advancements in implant technology and prosthetically driven treatment protocols facilitate immediate implant placement and restoration in combination with undersized preparation protocols, yielding promising esthetic results over at least 12 months of observation [12]. Most recently, beneficial long-term clinical results of 666 narrow-diameter implants in posterior regions have been reported, indicating favorable long-term success rates and patient satisfaction with diameter-reduced implants [13]. Similar results have been obtained by means of titanium-zirconium implants with reduced diameters and improved material properties over 10 years of observation, thereby further extending the indication for treatment in clinically challenging cases [14].

For successful implant placement, a paradigm of atraumatic surgical preparation was proposed by only creating the least possible surgical trauma during osseous tissue drilling [15]. Histologically, denaturation of proteins, dehydration, decreased osteoblastic and osteoclastic activity and ultimately cell death may be consequences of heat-induced trauma to the bone, which is called thermal osteonecrosis [16]. This process may be further enhanced by low thermal conductivity of human cortical and cancellous bone with a consequent increase of local tissue temperatures [16, 17]. Thermal osteonecrosis has been described to potentially cause early implant failures due to the inability to achieve proper osseointegration [18, 19]. Critical temperatures for the survival of bone during preparation seem to range from 44 to 47 °C with short exposure times to the heat source, as indicated by means of experiments in the bone growth chamber [20].

Although previous in vitro studies have compared guided and conventional implant osteotomy preparation [21–24], direct comparison of the reported findings remains difficult because of heterogeneous experimental designs, different testing materials, variations in guide design, and limited standardization of drilling motion and temperature assessment. In particular, the thermal behavior of pilot- and narrow-diameter drilling steps under highly standardized and reproducible conditions remains insufficiently understood. Therefore, the present study was designed to combine a standardized bovine testing model with automated robotic drilling and a controlled subgroup-based analysis of drill diameter, preparation depth, irrigation mode, and surgical technique. Our group recently reported thermal effects of static guided versus conventional implant bed preparation using sequential stainless steel twist drills in a standardized bovine model [25]. While that study mainly addressed a broader drill sequence including larger diameters, the present investigation was specifically designed to focus on pilot- and narrow-diameter drilling steps and their respective guiding concepts. Since higher temperatures have been reported with guided experimental procedures when compared to conventional drilling and highest temperatures have been described with pilot drills during incremental preparation [21], this investigation aims at further investigating pilot- and partially guided surgery in vitro. Based on the 3 R principles of replacement, reduction, and refinement in experimental research, this study aimed to test the working hypothesis that conventional drilling by means of pilot and narrow-diameter drills would display lower temperatures than pilot- or partially guided surgery.

Methods

Materials and guided design

The present study was conducted on the same standardized experimental platform as our previous investigation [25]; however, it addressed a distinct study objective, different drill system characteristics, and a narrower focus on pilot- and partially guided drilling steps. This in vitro investigation was based on artificially manufactured bovine testing samples (BoneSim™, Newaygo, MI, USA), previously established for standardized simulation of surgical preparations [25–33]. The testing samples provide constant cortical and cancellous Sects. (3 and 15 mm, respectively), human thermal conductivity of bone (0.3–0.4 W m^{− 1} K^{− 1}) [34] and mandibular bone density (bone type 2) [35]. The disk-shaped bone samples were trimmed into a rectangular shape (56 × 18 × 10 mm) with constant width (1 cm ± 0.05 mm) prior to the investigation due to quantitative and qualitative anatomic considerations of the mandibular alveolar structures in vitro (Fig. 1). A total of 32 bone disks were used, with each disk trimmed into one standardized rectangular bone block for the experiment. For each bone block, one new individual 3D-printed surgical guide was manufactured, resulting in 32 surgical guides in total.

Fig. 1.

Standardized bone model (BoneSim™) with constant cortical and cancellous layers

Testing samples with diverging measures (± 0.05 mm) in any direction were excluded from the experiment. In the present study, pilot surgical drills made of stainless steel (diameters 2.0 and 2.8 mm; Komet^®, Gebr. Brasseler, Lemgo, Germany) were used (Fig. 2).

Fig. 2.

Pilot implant drills made of stainless steel: 2.0, 2.8 ∅ (Komet^®, Gebr. Brasseler, Lemgo, Germany)

As commercially available bone samples were used for this in vitro investigation, ethics approval was not required. To ensure a workflow related to the clinical situation and for reproducible results in an in-vitro setting, recommended surgical and presurgical steps for guided surgery were used [5]. Prior to the investigational process, preplanning and preparation steps were performed: Multi-slice computed tomography (MSCT, voxel size 0.2 × 0.2 × 0.5 mm; Siemens, Erlangen, Germany) and scanning by means of an intraoral digital scanner (iTero; Align Technology Inc., San Jose, CA, USA) of the testing samples was performed. For precise positioning of the implants in vitro, data import in a software for guided preparation procedures (coDiagnostiX^® Version 10.8; DentalWings Inc., Montréal, Canada) was performed. In this way, positioning of five implants per bone specimen was ensured for two diameters (2.0, 2.8 mm) in two drilling depths (10, 12 mm) (Fig. 3).

Fig. 3.

3D-planning process including precise implant positioning of 5 implants per bone specimens for experimental surgical procedures

The design of the surgical guides for surgical preparation was based on guiding sleeves (titanium inner sleeves for depth stop drills, D3.5/d2.0/L5.0; steco-system-technik GmbH & Co KG, Hamburg, Germany) for 2.0-mm drills and sleeveless surgical preparation sites (H2 position) (Fig. 4) for guided surgical procedures for 2.8-mm drills using drill handle cylinders (Drill handle, diameter 2.8; Guided Implant Surgery Bone Level, Straumann^®, Basel, Switzerland) (Fig. 5), according to the manufacturer’s surgical protocol. The overall surgical guide design was comparable for both investigated groups with regard to guide base geometry, implant position planning, fixation design, and predefined thermocouple perforations. The relevant difference between the groups concerned the guiding concept used for the respective drill diameter: 2.0-mm preparations were performed with metallic guiding sleeves, whereas 2.8-mm preparations were performed with sleeveless guide sites in combination with corresponding drill handle cylinders according to the manufacturer’s protocol.

Fig. 4.

Printed surgical guides; (A) for 2.0-mm preparations based on guiding sleeves (Titanium inner sleeves for depth stop drills, D3.5/d2.0/L5.0; steco-system-technik GmbH & Co KG, Hamburg, Germany); (B) for 2.8-mm preparations using corresponding drill handle cylinders

Fig. 5.

Surgical drill handle for 2.8-mm preparations

Each guide was predesigned with two T-sleeves and template fixation pins. For ensuring intrabony temperature measurement during the entire experimental procedures, predefined perforations (diameter 1 mm; depths 3, 6, 9, 12, 15 mm) were preplanned on each side of the guide (Fig. 6).

Fig. 6.

Graphic illustration of the temperature measurement setup during guided experimental drilling in sagittal view: 10 individual temperature measurement sites at predefined depths; (A) thermocouple channels at 1 mm and (B) thermocouple channels at 2 mm radial distance from the preparation site

All digital planning steps were performed by the same senior physician G.D.S. After conclusion of preplanning, manufacturing was performed at the Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Austria. Therefore, data was exported and 3D-printing was completed using a rapid prototyping machine and photopolymer resin.

Robotic surgical simulator

A material testing machine was used for atraumatic and reproducible osteotomy preparations. The use of a software-controlled program (Nexygen™ Plus, Version 4.0, Lloyd Instruments™, Ametek Inc., Largo, FL, USA) ensured individual and atraumatic preparations for individual osteotomy sequences, preprogrammed with constant feed rate, depth and dwell time, according to previous publications in the field [25, 30–33, 36]: 10-mm preparation (drilling 21 s / withdrawing 11 s / total preparation process 32 s) and 12-mm preparation (drilling 26 s / withdrawing 13 s / total preparation process 39 s) were programmed with an active preparation feed rate of 2 mm/s for cortical bone regions, 1 mm/s in cancellous bone, and 1 mm/s for intermittent drilling and drill withdrawing. The programmed drilling–withdrawing sequence was designed to simulate an atraumatic intermittent osteotomy protocol under standardized conditions, including controlled withdrawal phases intended to limit continuous heat accumulation and to improve reproducibility across all preparations, as suggested in similar previous investigations [25, 31, 33]. For force measurement during preparation, a load cell was mounted at the crosshead of the apparatus. Track recording was performed externally by means of a draw-wire encoding device. Surgical preparations were performed by using a surgical handpiece (WS-75 E/KM 20:1, W&H, Bürmoos, Austria), mounted at the dowel, powered by an additional surgical motor unit (Implantmed SI-923; Surgical control S-N1, W&H, Bürmoos, Austria).

Temperature measurement and experimental preparation

Prior to temperature measurement, predrilling steps were performed for real-time temperature measurement in 2 constant radial distances (1 / 2 mm) to the osteotomy site in multiple depths (3, 6, 9, 12 and 15 mm) (Fig. 7): They included preparation of the individual temperature channels by using a customary drilling device and custom twist drills (diameter 1.2 mm) after pin fixation of 3D-printed acrylic templates. In order to optimize precision during predrilling, new and unused acrylic guides were used for each bone sample preparation. Depth control of the constant radial distances of the multi-twist drills was ensured by welding steel sleeves to the exact positions of the respective drills for predrilling.

Fig. 7.

Real-time measurement of temperature changes (∆T) in multiple channels with (A) recorded drilling pathway, (B) sensor distance S1 = 1 mm, and (C) sensor distance S2 = 2 mm from the preparation site; K1–K5 indicate the predefined measurement points from coronal to apical (K1 most coronal, K5 most apical)

Temperature measurement was performed using individual fine-wire Type K thermocouples (RS PRO, RS order no. 397–1589; RS Components Ltd, Corby, UK; 1 m length, 0.075 mm diameter, exposed welded junction). Data acquisition was performed using a multichannel measurement setup, consisting of a multifunction measurement and control module (USB-2416, 24-Bit, 1 KS/s, Temperature and Voltage Device; Measurement Computing Corp., Norton, MA, USA) and data acquisition software (DAQami, Version 4.2.1f0; Measurement Computing Corp., Norton, MA, USA). No additional in-house calibration was performed prior to the experiments. Instead, commercially available ANSI-compliant sensors with a manufacturer-specified accuracy of ± 1.5 °C were used consistently throughout the study. To ensure comparability, the same thermocouple type, predefined insertion geometry, and identical acquisition conditions were applied in all measurements.

Temperature recording started several seconds before the experimental drilling procedure and was concluded 1 min after the end of drilling (Fig. 7).

Five temperature sensors were bundled in a custom-made sensor array (distance of 3 mm between channels) after digital design and bonding. Before experimental preparations were commenced, heat transfer compound was applied in the temperature channels before insertion of the temperature sensors [25, 30–33, 36–38]. To avoid direct cooling of the thermocouples by the external irrigation fluid, the sensors were inserted from the outside into predefined temperature channels within the test specimen. Thus, no direct connection existed between the cooling fluid and the sensors during the drilling procedure. Thereafter, the respective guides were positioned and sample fixation was ensured by fixation pins.

The experimental protocol consisted of two surgical preparation techniques (conventional drilling and guided implant surgery, n = 2 × 80), 2 drills (2.0 / 2.8 mm, n = 2 × 80), 2 preparation depths (10 / 12 mm, n = 2 × 80), 2 irrigation methods (without / external irrigation, n = 2 × 80). The factorial experimental design comprised 16 groups in total, resulting from the combination of 2 surgical techniques (guided implant surgery and conventional drilling), 2 drill diameters (2.0 and 2.8 mm), 2 preparation depths (10 and 12 mm), and 2 irrigation methods (without and external irrigation). Each group consisted of 10 repeated preparations, resulting in a total sample size of 160 osteotomy procedures. As this was a controlled in vitro factorial experiment, the sample size was defined by the planned balanced design across all factor combinations, with 10 repeated preparations per experimental group.

For excluding potential bias due to drill wear, only new out-of-the-box instruments were used for each experimental preparation. Each constellation was executed with 10 identical repetitions (n = 160 preparations in total) under constant room temperature (21 ± 1 °C). In case of exceeding room temperature (T > 22 °C), the experiment was continued on the next day. Conventional guide-free drilling was used as control group and bone samples were allocated randomly to the individual experimental groups. Within the respective testing groups, there have been no exclusions of data points. Surgical drilling was performed by setting drilling speed to 800 rpm for a standard atraumatic preparation [25, 30–33, 36, 37, 39–41]. Prior to the experimental 2.8-mm drilling procedures, the osteotomy sites were predrilled using the smaller pilot drill in accordance with the sequential drilling protocol. The programmed preparation times of 32 s (10 mm) and 39 s (12 mm) refer only to the automated preparation cycle of the respective drill investigated and were recorded separately from the preceding predrilling step. Conventional drilling was performed by using guide-free preparations and guided preparations by using surgical guides and corresponding guiding sleeves (for 2.0-mm diameter burs) or drill handle cylinders (for 2.8-mm diameter burs).

Externally irrigated preparations were performed using room-temperature saline delivered through a custom irrigation tubing set at a constant flow rate of 50 mL/min. Cooling was standardized across all irrigated specimens by maintaining the same irrigation fluid, flow rate, tubing configuration, and experimental drilling protocol for every preparation. However, the actual distribution and flow pattern of the irrigant at the drill–bone interface were not directly measured in either guided or conventional drilling conditions. Surgical suction was performed during irrigated experimental preparations. Movement bias during experimental preparations was avoided by using a vise for sample fixation, mounted to the testing apparatus. The experiments were performed during the years 2023 and 2024. Blinding during the experimental procedures was not feasible, because the applied surgical technique and guide configuration were visible to the operators. However, the experimental workflow, drilling movements, and temperature acquisition were highly standardized and automated. Outcome assessment relied on objectively recorded sensor data, and statistical analysis was performed by M.M. on tabulated datasets without manual result interpretation.

Data processing and statistical analysis

Individual data processing was ensured for each individual preparation. Recorded parameters included real-time temperature (°C, δ = 0.01 s), extension of the drill (mm) and linear recording (V). Better comparison of the obtained results was ensured by calculation of temperature changes [ΔT(°C) = T_x – T₀] by subtracting the recorded absolute temperature [T_x] from the initial baseline temperature [T₀] for statistical analysis [25, 26, 30–33, 37, 38, 42, 43].

The recorded temperature changes were tabulated by means (± standard deviations). Location of highest temperature generation was tabulated (minimum, maximum, median). Temperature increase of different techniques was compared by means of a linear mixed model (variables: surgical technique, drill, preparation depth, cooling; interactions investigated up to four-way term). Adjustments for unequal variances were performed by the degrees-of-freedom adjustment of Kenward-Roger. Subgroup analyses were performed for significant interactions by testing preparation techniques with t-tests with unequal variances. A standard statistical software SAS^® (Version 9.4, SAS Institute Inc., Cary, NC, USA) was used for computing.

All p-values are two-sided, and p ≤ 0.05 was considered as statistically significant. The data that support the findings of this study are available from the corresponding author upon reasonable request.

Results

Within this investigation, a total of 160 experimental preparations were executed for obtaining temperature variations of guided implant surgery (GS) and conventional drilling (CD). Thereby, two drills (2.0 / 2.8 mm), two preparation depths (10 / 12 mm) and two irrigation modes (no irrigation / external irrigation) have been investigated.

Maximum temperature increase

The maximum heat generation was recorded over 2 × 5 temperature sensors per bur diameter with 10 identical repetitions. The respective results were tabulated in Table 1 as temperature increases [ΔT (°C)], presented as mean values and standard deviations (SD). Graphical illustration of the results is displayed in Fig. 8. The maximum heat generation recorded across all temperature sensors is summarized in Table 1 and illustrated in Fig. 8. Overall, non-irrigated preparations resulted in higher temperature increases than externally irrigated preparations in all investigated groups. Under external irrigation, GS with 2.0-mm drills yielded significantly lower temperatures than CD at both 10-mm and 12-mm preparation depths, whereas GS with 2.8-mm drills showed significantly higher temperatures than CD at 10-mm depth and no significant difference at 12-mm depth.

Table 1.

Comparison of maximum temperature increase: mean values and standard deviations of [ΔT (°C), mean (SD)] of the highest heat generation recorded across all 2 × 5 temperature measurement sites; two preparation depths, two drill diameters, and two irrigation modes were applied for testing guided implant surgery (GS) and conventional drilling (CD); p-values for subgroup analysis were calculated by t-tests after significant four-way interaction analysis by linear mixed model

Preparation depth		10 mm		12 mm
Diameter	Technique/p-value	Without cooling	External cooling	Without cooling	External cooling
2.0 mm	GS	19.19 (2.42)	9.44 (2.27)	20.03 (2.78)	12.09 (4.52)
	CD	23.43 (2.67)	13.4 (3.65)	26.84 (4.42)	22.1 (5.85)
	p -value	0.0016*	0.0107*	0.0009*	0.0005*
2.8 mm	GS	26.36 (4.57)	8.16 (2.43)	31.46 (4.60)	10.03 (2.83)
	CD	34.13 (5.69)	5.62 (2.23)	36.33 (3.48)	7.42 (3.12)
	p -value	0.0036*	0.0256*	0.0162*	0.0655

*p ≤ 0.05

Fig. 8.

Temperature increase of different drills (2.0, 2.8 ∅), cooling modes (without/external cooling) and preparation depths (10/12 mm) during CD (conventional drilling) and GS (guided implant surgery)

Temperature change and osteotomy preparation

Two different osteotomy techniques (GS vs. CD) were statistically compared by means of a linear mixed model after adjustment for the parameters diameter, cooling and preparation depth, as well as their interactions. With four-way interaction resulting in a statistically significant outcome (p = 0.0244) and means of the maximum temperature change were observed to be dependent on the diameter, irrigation and preparation depth, analyses of the respective subgroups were performed (Table 1; Fig. 8).

Results of statistical significance were found with all investigated constellations, except for 12-mm preparation depth using 2.8-mm burs and external cooling. Without irrigation, CD was found to result in statistically higher temperature changes when compared to GS in 10-mm preparation depth in both 2.0-mm (p = 0.0016) and 2.8-mm diameters (p = 0.0036), and in 12-mm preparation depth in both 2.0-mm (p = 0.0009) and 2.8-mm diameters (p = 0.0162) (Table 1; Fig. 8).

With external cooling, CD was found to result in statistically higher temperatures when compared to GS with 2.0-mm drill diameter in 10-mm (p = 0.0107) and in 12-mm preparation depth (p = 0.0005), whereas GS was found to result in statistically higher temperatures when compared to CD in 2.8-mm diameter and external irrigation during 10-mm preparation depth (p = 0.0256) (Table 1; Fig. 8).

Temperature increase and sensor depth

Drilling effect on the location of the maximum temperature increase (measurements at 3-, 6-, 9-, 12- and 15-mm depths) was described by median sensor location depths (minimum, maximum) in a distance of 1 and 2 mm to the preparation site for experimental tests (Table 2).

Table 2.

Location of highest temperature increase for individual sensor channels [median, minimum, maximum] in distance of 1 and 2 mm of two preparation depths with two drills and two cooling modes (GS = guided implant surgery, CD = conventional drilling)

Preparation depth			10 mm						12 mm
Irrigation mode			Without cooling			External cooling			Without cooling			External cooling
Diameter	Technique	Distance	Median	Min	Max	Median	Min	Max	Median	Min	Max	Median	Min	Max
2.0 mm	GS	1 mm	4.5	3	6	6	6	9	6	3	9	7.5	6	12
		2 mm	3	3	6	6	3	9	3	3	6	6	6	6
	CD	1 mm	3	3	6	6	6	9	4.5	3	9	9	6	12
		2 mm	3	3	6	6	6	6	3	3	6	9	6	9
2.8 mm	GS	1 mm	3	3	6	9	6	9	4.5	3	9	12	9	12
		2 mm	3	3	6	6	3	9	4.5	3	6	9	9	12
	CD	1 mm	4.5	3	6	9	6	12	6	3	9	12	9	12
		2 mm	3	3	6	9	6	9	6	3	6	12	9	15

2.0-mm drill

Highest temperature increase in burs of 2.0 mm and preparation depth of 10 mm was recorded in median between sensor locations of 3 and 4.5 mm without cooling and at 6 mm in irrigated sites. Maximum temperature increase in burs of 2.0 mm and preparation depth of 12 mm was recorded between sensor locations of 3 and 6 mm without cooling and 6 and 9 mm in irrigated sites (Table 2).

2.8-mm drill

Highest temperature increase in burs of 2.8 mm and preparation depth of 10 mm was recorded in median between sensor locations of 3 and 4.5 mm without cooling and 6 and 9 mm in irrigated sites. Maximum temperature increase in burs of 2.8 mm and preparation depth of 12 mm was recorded between median sensor locations of 4.5 and 6 mm without cooling and 9 and 12 mm in irrigated sites (Table 2).

Discussion

By using contemporary digital technology, fully guided implant procedures have been described with higher accuracy when compared to conventional freehand implant placement [10, 44]. Nevertheless, as higher temperatures were found with guided procedures and pilot drills were predominantly associated with the highest temperatures within the guided drilling process [21–24], further investigation in a standardized testing cycle seemed warranted. Hence, pilot- and partially guided procedures were compared to conventional guide-free preparations and non-irrigated preparations were performed as negative control within all constellations.

The results of our investigation are partially in alignment with previous studies, confirming higher temperature generation with pilot drills during incremental drilling and external irrigation in GS [21, 45]. In principle, the thermal results of this investigation may be viewed as real-time spot measurements of multiple depths in 2 distances to the osteotomy site. Multiple similar and non-standardized investigations used infrared thermography for temperature measurement [21, 22, 46], taking into account the possibility of imprecise temperature results in irrigated preparations [47, 48].

The present investigation should be interpreted in the context of our recently published in vitro study on heat generation during static guided versus conventional implant bed preparation using sequential stainless steel twist drills of 2.2, 2.8, and 3.5 mm in the same standardized bovine model. In that broader experimental setting, temperature differences between guided and conventional preparation became most apparent in the larger drill diameter range, particularly for 3.5-mm drills under specific irrigation conditions [25]. By contrast, the present study was designed as a focused follow-up investigation addressing the earlier stages of osteotomy preparation, namely pilot- and narrow-diameter drilling steps, which are frequently considered thermally critical during guided surgery. In addition, the present setup included different guiding concepts for the investigated drill diameters, i.e., sleeve-guided preparation for the 2.0-mm drill and partially guided preparation using a drill handle for the 2.8-mm drill, thereby allowing a more specific assessment of small-diameter guided drilling conditions.

The present study was able to demonstrate invariably higher temperatures without irrigation in all constellations, thereby confirming the effectiveness of external irrigation during both guided surgical procedures and conventional drilling [36, 37, 49–51]. Regarding the described critical temperature threshold for survival of bone of 44–47 °C [20], irrigated preparations were not observed to exceed the threshold in any diameter or surgical technique.

In the present investigation, higher temperatures were observed with CD when compared to GS during irrigated 2.0-mm preparations in both drilling depths. From a comparative perspective, this finding indicates that thermal behavior during guided preparation may differ even within a narrow drill diameter range. The contrasting pattern observed between the 2.0-mm sleeve-guided and the 2.8-mm partially guided setting further suggests that guide configuration and irrigation accessibility may be relevant factors in temperature development in addition to drill diameter itself. Although previous in vitro studies have shown that additional irrigation designs during GS may influence thermal outcomes [52], and although irrigation conditions were standardized across all irrigated groups, the present study did not directly assess irrigation fluid distribution or flow behavior around the guide. Therefore, no specific mechanistic conclusion can be drawn from these findings. Accordingly, the present observations should be interpreted as comparative thermal results of the investigated setups rather than as proof of a specific cooling mechanism. In this context, the findings may be viewed as the result of interacting biomechanical and fluid-dynamic factors, including drill diameter, cutting surface, frictional conditions, guide configuration, and coolant accessibility.

Non-irrigated controls displayed higher temperatures within the respective testing groups, with maximum temperatures in 2.8-mm preparations. Clogging of the drill flutes and impaired debris removal from the osteotomy site during non-irrigated partially guided preparations in combination with the use of drill handles may have contributed to the observed results. Clinically relevant preparations using external irrigation resulted in significantly reduced temperatures with a temperature maximum in 2.0-mm drills.

In addition, the present findings should be interpreted in the context of the investigated pilot- and narrow-diameter drills, as their smaller cutting surface and reduced frictional area may inherently contribute to lower absolute temperature generation than larger drill diameters. Drill geometry and flute characteristics were reported to additionally influence the thermal outcome, with lower temperature generation in two-fluted drills and higher cutting efficiency in three-fluted drills in vitro [53]. Since comparison of pilot- and partially guided technique versus conventional preparation only was attempted in the present investigation, consecutive two-fluted pilot drills of 2.0 and 2.8 mm with similar geometry were chosen for the experimental setup. Additionally, drill wear due to drill reuse has been described to negatively influence the thermal outcome during drilling of bone [54]. The use of metal guiding sleeves may thereby further contribute to increased drill wear and therefore to heat generation [55]. The present investigation consciously excluded wear-related factors to heat generation by only using new out-of-the-box drills for each experimental investigation.

Higher temperature generation was previously reported in 6- to 9-mm depth when compared to a cortical level during guided implant preparation [50]. The present investigation was able to confirm the occurrence of higher temperatures in medium and deeper bony layers, especially when external irrigation was used. This observation supports the cooling efficiency of external irrigation especially in superficial and medium bone levels during osteotomy [50, 56, 57]. Since different designs for surgical guides and sleeve geometry in GS have been proposed and investigated in the past [45, 46, 52, 58], comparability of the obtained testing results may be viewed as limited to a certain extent. In addition, refrigerated irrigation fluid in contrast to room-temperature saline, which has been used in this investigation, can be expected to further decrease generated temperatures during GS [22].

When the results of Tur et al. are interpreted together with those of the present study [25], a differentiated pattern emerges: in the previous study, larger drill diameters showed the most pronounced thermal differences between guided and conventional preparation, whereas the present investigation indicates that small-diameter guided preparation may behave differently depending on drill diameter and guide design. In the 2.0-mm sleeve-guided setting, guided preparation showed lower temperatures under external irrigation, while the 2.8-mm partially guided setting suggested impaired cooling efficiency during guided preparation. This combined interpretation supports the assumption that heat generation during guided implant surgery is not determined by drill diameter alone, but rather by the interaction of drill diameter, guide design, irrigation accessibility, and preparation depth. Taken together, the two studies may be interpreted as complementary investigations within the same standardized experimental platform, addressing different aspects of heat generation during guided osteotomy preparation. From a practical perspective, the present findings underline the importance of maintaining effective irrigation during guided osteotomy preparation, particularly when larger drill diameters and deeper preparation depths are used. Within the limitations of this in vitro model, the data suggest that clinicians should pay particular attention to cooling conditions during partially guided procedures and not assume equal irrigation efficacy across different drill diameters or guide configurations. Rather than supporting a direct change in clinical protocols, the present results should be understood as indicating situations in which thermal risk awareness may be especially relevant during guided implant preparation. In addition, the automated robotic drilling setup used in the present investigation allowed highly reproducible movement paths, depth control, and withdrawal sequences across preparations. This high degree of standardization may have reduced variability related to manual positional deviations and thereby improved the comparability of thermal measurements between groups. At the same time, robotic systems do not eliminate the need for human planning, programming, instrument replacement, and live supervision, and they cannot substitute for clinical judgement or patient-related intraoperative feedback.

The present investigation had some limitations. Since standardized and comparable testing results have been attempted, no direct simulation of human body conditions was possible in the present study. Therefore, in vivo temperatures during bone preparation may vary due to vital bone tissue, blood circulation and human body temperature. Additionally, conventional non-modified and externally irrigated GS was investigated. Consequently, different guide and sleeve geometries including open guided designs and the application of additional cooling strategies may alter the thermal outcome of the investigation. In addition, room-temperature saline was used for external irrigation in the present study. Although this approach ensured standardized cooling conditions across all irrigated groups, the use of refrigerated irrigation fluid might have resulted in lower absolute temperature increases. Furthermore, the drilling speed used in the present study was limited to 800 rpm as part of a standardized atraumatic preparation protocol. Although this approach ensured consistent experimental conditions across all groups, it may have contributed to lower absolute temperature increases than protocols using higher drilling speeds. Therefore, the present thermal results should be interpreted within the context of this controlled low-speed experimental design, while the relative comparison between the investigated groups remains valid. Moreover, the automated intermittent drilling–withdrawing protocol used in the present study may have reduced cumulative thermal elevation by introducing standardized withdrawal phases during osteotomy preparation. While this approach supported atraumatic and reproducible experimental conditions, it may also have limited the absolute temperature increase compared with more continuous drilling protocols. However, because the same programmed movement sequence was applied to all groups, the relative comparison between the investigated preparation techniques remains valid within the present study design. The present findings should therefore be interpreted within the context of a standardized experimental model in which both biomechanical factors, such as drill diameter, cutting surface, frictional area, drilling speed, and intermittent drilling movements, and fluid-dynamic factors, such as coolant delivery conditions and access to the drill–bone interface, may have influenced the absolute thermal values obtained.

Future studies may focus on exploring influencing factors within the heat generation process in more detail, such as the impact of different drill material compositions and alternative guided geometries. In this context, further standardized in vitro research is warranted not only for the further improvement of implant success rates, but also for the validation of novel techniques including dynamic and robotic implant preparation. Future studies may therefore also investigate factors contributing to heat generation during implant osteotomy in greater detail, including different drill materials, alternative guide geometries, and modified cooling strategies. In addition, emerging digital workflows such as dynamic navigation and robotic implant preparation should be evaluated under standardized in vitro conditions, as their specific drilling control, guidance principles, and irrigation access may influence thermal behavior differently from static guided and conventional procedures. Given that robotic approaches in dental implant surgery are still emerging, standardized in vitro investigations such as the present study may help to better understand procedure-related thermal effects before broader clinical application and validation.

Conclusion

External irrigation reduced temperature generation during osteotomy preparation with 2.0- and 2.8-mm pilot drills in both guided and conventional conditions. Within the standardized experimental setup, thermal differences between guided and conventional preparation depended on drill diameter and preparation depth, underlining the importance of effective irrigation especially in larger-diameter preparations.

Abbreviations

GS

Guided implant surgery

CD

Conventional drilling

3D

Three-dimensional

MSCT

Multi-slice computed tomography

ANSI

American National Standards Institute

∆T

Temperature increase

T_x

Recorded absolute temperature

T₀

Initial baseline temperature

SD

Standard deviation

PEEK

Polyetheretherketone

Authors' contributions

D.T. involved in design/concept, led experimental investigation and writing of manuscript Z.T. involved in experimental investigation K.G. and X.R. involved in experimental investigation and revised manuscript critically M.M. sample size calculation and statistical analysis of collected data E.U. involved in design/concept, supported investigation technically G.D.S. conceived ideas, involved in concept/design and experimental investigation, revised manuscript critically and secured investigation funding.

Funding

The authors were funded by their institutions (University Clinic of Dentistry, Medical University of Vienna; Center for Medical Physics and Biomedical Engineering, Medical University of Vienna; Institute of Clinical Biometrics, Center for Medical Data Science, Medical University of Vienna, Medical University of Vienna), and by Research Funding (17052021) of Austrian Society of Implantology (ÖGI).

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

For this in vitro investigation using artificially manufactured testing samples, ethics approval was not required.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.