Heat Generation during Dental Implant Bed Preparation Using Surgical Guides with and without Internal Irrigation Channels Evaluated on Standardized Models of the Alveolar Bone

Featured Application

All-on-4 dental implants provide support for an entire dental arch. They are inserted in properly mineralized regions of the alveolar bone, and their performance depends on accurate positioning and angulation. Surgical guides ensure accurate implant placement, but they block the access of the irrigation fluid during surgical drilling. In this study, guided drilling was performed sequentially, in four target sites, with gradually increased diameters, according to the All-on-4 dental implant procedure. We monitored intraosseous temperatures next to each osteotomy, in the presence of two types of surgical guides: a classical guide, composed of a splint with a cylindrical sleeve, and a guide with internal cooling, which (i) incorporates an irrigation channel that orients the coolant jet toward the drill’s point of entry into the target tissues and (ii) provides space for the evacuation of the irrigation fluid. The results of this study point to the use of surgical guides with internal cooling as the most effective method.

Abstract

Dental implant bed preparation involves surgical drilling. Heat generated in this process can cause a temperature elevation beyond the bone damage limit (10 °C), affecting the osseointegration of the implant. Surgical templates ensure accurate implant placement, but they limit the access of the irrigation fluid. This study evaluated the hypothesis that surgical guides with internal cooling prevent bone heating more effectively than classical guides. To eliminate biological variability, this study was conducted on artificial bone pieces that mimic the bone density of the human mandible. We created a surgical template that incorporated four pairs of guides—one classical (CLA) and one with internal cooling (INT) in each pair. For each specimen, we randomly selected the type of surgical guide to start with and performed four osteotomies with a 2.7 mm-diameter drill; then, we widened each hole with a 3.3 mm drill and finalized it with a 3.7 mm drill. The temperature was recorded by thermocouples placed at 0.8 mm from the prospective edge of the final osteotomy. In 168 measurements (12 osteotomies on 14 specimens) conducted for each type of surgical guide, the mean temperature rise was 7.2 ± 4.9 °C (mean ± standard deviation) for CLA and 5.0 ± 3.8 °C for INT. The mean differences between temperature elevations were 1.5 °C, 2.1 °C, and 3.0 °C for the first, second, and third drill, and they were statistically significant: the p-values of Student’s t-test were 0.004, 0.01, and 0.001, respectively. Although the mean temperatures remained safe, temperature rises exceeded 10 °C in 23.8% (9.5%) of the osteotomies performed in the presence of CLA (INT). Taken together, our results suggest that surgical guides with internal cooling ensure a significant drop in the temperature rise caused by implant site drilling.

1. Introduction

Dental implant bed preparation consists in drilling a hole in the alveolar bone at the target site. This process results in heat generation due to bone deformation next to the cutting edge of the drill and friction between the drill’s cutting tip and the underlying bone [1]. The amount of heat dissipated in the adjacent bone depends on several factors, including bone density, drilling speed, applied thrust force, drill parameters (material, design, diameter, and wear [2]), drilling procedure, and irrigation conditions (coolant fluid flow rate and temperature) [3]. Overheating can lead to irreversible bone damage, poor osseous integration of the implant, and, eventually, implant failure [4]. Therefore, the thermodynamics of osteotomy is an active field of biomedical research, with important milestones and several open questions [5,6,7].

The biological impact of temperature elevations caused by surgical drilling depends on the thermal history of the heated bone, not just on its peak temperature [8]. Intravital microscopy experiments conducted on rabbit tibia indicated that a temperature increment of 10 °C maintained for one minute did not lead to significant bone resorption. However, capillaries dilate for about 5 days, during which some fat cells in the heated area die. With five minutes of exposure, 20–30% of bone tissue is resorbed and replaced by fat cells within a month. Heating bone to 50 °C for one minute kills most fat cells, leading to a 30% loss of bone [9]. Therefore, for heat exposures that last up to one minute, 47 °C is considered the threshold temperature for bone tissue damage [10]. This estimate aligns well with the outcome of an in vivo study conducted on adult patients who received osteotomies for maxillary dental implant placement. The distribution of apoptotic osteocytes around the osteotomy was compared with the calculated temperature field, and the results indicated a threshold temperature for osteocyte death of about 47 °C [5].

Dental implant bed preparation can be performed manually, in an open-flap procedure (whereby the soft tissue is temporarily peeled off the underlying bone), or in a guided, flapless manner (whereby a surgical guide is placed over the target site and the drill passes through a sleeve that controls its position and orientation during osteotomy). Flapless guided surgery is the fastest, most accurate, and least traumatic procedure [11,12,13], but it entails the most bone heating [14]. Indeed, a classical surgical guide, composed of a personalized splint outfitted with a cylindrical sleeve, shields the target site and deviates the irrigation fluid jet from the drill’s point of entry.

The first quantitative study of the impact of surgical guides on bone heating in the course of implant bed preparation was conducted by Misir et al. on bovine femoral cortical bone samples [15]. Their results confirmed the hypothesis that more heat is generated in guided osteotomy than in the free-hand approach. Although the differences between mean maximum temperatures were statistically significant, they remained within the safe zone (below 47 °C) [15].

These findings are encouraging, since the cortical layer of the bovine femur is thicker and denser than that of the human mandible [16], and, therefore, even less temperature elevation is expected in a clinical context. Nevertheless, further research is warranted because individual temperature rises might exceed the safety threshold. Furthermore, circulation also contributes to heat exchange in a living organism. In their in vivo rabbit tibia study, dos Santos et al. [17] reported a mean peak temperature of 31.8 °C (28.5 °C) and individual temperatures below 34.6 °C (30.5 °C) when 40 drillings were performed with (without) a surgical guide. Also, the in vitro study conducted by Boa et al. on bovine rib cortical bone pieces suggests that bone temperature remains in the safe zone during osteotomies performed using classical surgical guides and external irrigation with saline solution at room temperature [18]. They found that, despite the presence of the surgical guide, external cooling was effective: the mean temperature rise ranged from 3.3 °C to 5.2 °C when the irrigation was used, and from 7.0 °C to 9.4 °C in the absence of cooling. The bone damage threshold was exceeded only once when irrigation was applied, and in 32% of the cases when it was not [18].

To further improve cooling efficacy, Liu et al. proposed adding an internal irrigation channel to a surgical guide of regular geometry and found a roughly twofold reduction in the temperature rise elicited by guided drilling [19]. Tuce et al. proposed a digital design and three-dimensional (3D) printing workflow for incorporating an irrigation fluid channel in a personalized surgical guide suitable for dental implant site preparation [20]. Alevizakos et al. created a 3D-printed surgical template with a built-in coolant duct that enabled rinsing the burr at the point of entry into the target tissues. Most importantly, they applied it in the clinics [21]. Orgev et al. presented detailed design steps and a clinical application of a 3D-printed surgical template with an incorporated coolant pipe [22].

The successful clinical applications motivated quantitative studies of the rise in bone temperature during osteotomies performed using surgical templates with internally routed irrigation. The study of Stocchero et al., conducted on bovine rib pieces, had a surprising outcome: the surgical guide with internal irrigation had no significant advantage over the classical one in terms of the intraosseous temperature elevation [23]. The authors attributed this result to the clogging of the final portion of the irrigation channel by bone chips, as revealed by cone beam computed tomography of the surgical guides taken after the osteotomies. In contrast, Teich et al. observed a significant decrease in the temperature rise while using a surgical guide outfitted with a pair of internal irrigation channels [24]. Parvizi et al. developed an innovative surgical template that included both an entry and an exit channel for the irrigation fluid. They observed a significant drop in peak temperatures compared to a classical surgical guide with external irrigation [25]. Tuce et al. investigated the rise in bone temperature caused by guided drilling into the cortical layer of porcine femur pieces, and compared surgical guides with internal cooling pipe, guides with C-shaped open sleeve, and classical guides [26]. The mean temperature elevations were 2.1 °C, 2.7 °C, and 3.2 °C, respectively, demonstrating the value of internal cooling. Nevertheless, the differences between them were marginally insignificant according to the one-way analysis of variance (p = 0.056).

In this study, we sought to eliminate biological variability by using artificial bone models that mimic the geometry and density of the alveolar bone of the human mandible. We designed and printed a surgical template that wrapped the bone model and featured four pairs of guides—one classical and one with internal cooling in each pair. The guide with internal cooling incorporated just one irrigation fluid channel because we hypothesized that a coolant exit channel is not necessary if the guide provides a stand-off distance from the target site. On each bone specimen, surgical drilling was performed sequentially, starting with a cortical perforation drill of 2.7 mm in diameter followed by 3.3 mm and 3.7 mm drills. We monitored the intraosseous temperature using a thermocouple inserted in a predrilled hole whose bottom was 0.8 mm away from the anticipated margin of the final osteotomy. Our working hypothesis was that surgical templates with internal cooling are more effective than classical ones in limiting the rise in bone temperature caused by surgical drilling.

2. Materials and Methods

2.1. Designing and 3D-Printing the Surgical Guides

We tested the cooling efficacy of the surgical guides on 14 artificial bone models, trade name BS-001B (Bone Models, Castelló de la Plana, Spain). These models simulate bone properties with cortical density D1 and dense-to-porous cortical density D2. The use of standardized bones aims to minimize specimen variability and clearly highlight the difference between the two types of surgical guides.

We started by acquiring a CBCT scan of a standardized bone specimen. The resulting DICOM file was then imported into the Blue Sky Plan software, V4.13 64bit, (Blue Sky Bio, Libertyville, IL, USA) to design the surgical guides, as shown in Figure 1. We used the “Create model” function to generate the digital model of the bone (Figure 1A). For building the surgical guides, we simulated 8 implants, as shown in Figure 1B. The dimensions of the implants were as follows: 3 mm in diameter, 8 mm long, guiding tube diameter of 5.3 mm, 4 mm tall, and 10 mm offset. We generated the template after marking its limits, thus producing 8 classical surgical guides (Figure 1C).

Four of these guides were modified to include an incorporated irrigation channel. To achieve this, we simulated additional implants using the “Create Scan Appliance Guide” function for guides in positions 2, 4, 6, and 8, as shown in Figure 1D. These implants were designed to intersect the main implants at a 52° angle and were 2 mm in diameter, 8 mm long, with guiding sleeve diameter of 3 mm, height of 3 mm, and no offset. We chose a 3 mm diameter for the guiding sleeve to ensure a proper connection to the tubing of the physiodispenser.

Additionally, eight lateral implants were simulated normally to the main implant direction, as illustrated in Figure 1E. These were used to guide the drilling for the holes needed to host the thermocouples. They were designed to allow the positioning of the thermocouples at a depth of about 4.5 mm (slightly variable because of the irregular shape of the bone models) and 0.8 mm away from the edge of the final osteotomy.

Lastly, we designed four additional guides on the lower part of the template. These were used to drill the holes needed for securing the surgical guide to the bone models using fixation pins. Our design was inspired by the work of Parvizi et al. [25].

We exported the surgical guide design in Standard Tessellation Language (STL) format. The file was then loaded into the software of an AccuFab L4-D Digital Light Processing 3D printer (Shining 3D, Hangzhou, China) and the template was manufactured using SG1 Surgical Guide resin (Shining 3D, Hangzhou, China). After printing, the template was cleaned of uncured resin by bathing in rubbing alcohol for 5 min, followed by an ultrasonic distilled water bath for another 5 min. The cleaning protocol was repeated twice. In the end, the surgical template was cured for 30 min in a photopolymerization booth.

2.2. Thermodynamic Measurements

Figure 2 illustrates the experimental setup used for thermodynamic measurements [26]. The 3D-printed surgical guide was mounted on the bone model (1) and secured with locking pins (one of them is visible on the bottom part of the inset). This assembly was then placed horizontally and locked on the workbench using a vise (2). A Strong ACL(B)-42I (Saeshin, Daegu, Republic of Korea) handpiece (3) was attached to the rotating end of a 1.2 m-long wooden arm (4). To achieve a constant 2 kg-force axial load, as suggested by Misir et al. [15], we adjusted the position of a sliding weight (5) while measuring the force using a hanging scale (precision of 1 g). We recorded the temperature simultaneously near the 4 consecutive osteotomy sites with K-type thermocouples connected to a factory-calibrated Digi-Sense 20250-50 digital thermometer (Cole-Parmer Instrument Company LLC, Vernon Hills, IL, USA) (6). The thermocouple tips, coated in thermally conductive paste, were positioned at the bottom of predrilled holes inside the artificial bone models. These holes were oriented perpendicularly to the osteotomy and located 0.8 mm away from the edge of the largest-diameter drill. After inserting the thermocouples, we sealed the holes using Vaseline to keep the irrigation fluid away from the thermocouples. During drilling, the osteotomy sites were irrigated with distilled water at room temperature (25 °C), delivered by a Saeshin X-Cube (Saeshin, South Korea) physiodispenser at a rate of 40 mL/min.

When using the classical surgical guide, the coolant pipe was attached to the nozzle of the handpiece. In contrast, with the guide featuring an internally routed irrigation channel, the coolant pipe was connected directly to the incorporated tube (7).

The bone models were kept in a thermostatic distilled water bath at 25 °C for at least one hour before measurements. The specimens and the type of surgical guides being evaluated were chosen randomly at the beginning of each experiment. The drilling speed was set at 1500 rpm at a torque of 50 N·cm [15]. We consecutively used three drills (2.7 × 8 mm, 4 × 8 mm, and 4/4.3 × 8 mm) from the Easydent Regular/Wide Kit (Neodent, Curitiba, Parana, Brazil); their diameters were 2.7 mm, 3.3 mm, and 3.7 mm, respectively. We recorded the corresponding temperature curves at all four osteotomy sites. After measurements, the artificial bone specimens were placed back into the water bath to dissipate the heat generated while drilling.

2.3. Statistical Analysis

We determined ∆T, the difference between the peak temperature and the baseline temperature recorded prior to the osteotomy, for each of the drilling steps.

We used violin plots to visualize the distribution of ∆T in terms of median values and interquartile range, as well as to spot outliers.

To compare the efficacy of the two surgical guides, we determined the mean values and standard deviations (SD) of the temperature differences. We performed a Student’s independent samples t-test on these data to determine whether the observed differences were statistically significant, with the significance level set at p < 0.05. We also determined the percentage of cases in which the temperature rise exceeded 10 °C, considered to be the critical threshold for bone damage.

To further compare the two types of surgical guides, we built Bland–Altman plots to illustrate the discrepancies of ∆T between individual data points during each drilling stage. These diagrams illustrate the temperature differences of paired points plotted against their mean value. The bias, indicated with a dashed blue line, represents the mean difference of the data pairs. The lower and upper limits of agreement (LLA = Bias − 1.96 SD; ULA = Bias + 1.96 SD), delineating the 95% interval of agreement, are depicted by dashed red lines. Each plot includes specific values for the bias, LLA, and ULA, with their 95% confidence intervals represented by blue and red bands, reflecting agreement across the entire population. The reliability of these confidence intervals was further validated by assessing the normality of the distributions of differences using the Shapiro–Wilk test.

The entire statistical evaluation and plotting were performed in Python version 3.10.9, employing standard functions from well-established packages including NumPy (v1.23.5), pandas (v1.5.3), SciPy.stats (v1.10.0), pyCompare (v1.5.4), and matplotlib (v3.7.0).

3. Results

Figure 3 shows photographs of a standardized bone model specimen together with the 3D-printed surgical guide that was used in this study. Each bone was prepared for thermodynamic measurements by mounting the surgical template onto it and drilling the lateral holes used for inserting the thermocouples and the fixation pins. Although is not clearly visible from the photographs in Figure 3, the template bed did not rest perfectly on the bone models, thus permitting the evacuation of the irrigation fluid while drilling with the guide featuring internal cooling, as can be seen in Supplementary Video S1.

The rise in temperature induced by drilling was measured for both surgical guide types, in each bone, at four locations, and for all drill sizes. Using 14 artificial bones, the measurements generated 336 independent thermodynamic data points.

Representative heating curves are displayed in Figure 4. Here, each line represents the temperature measured near the osteotomy site at specific positions on the surgical guide. The three consecutive peaks on each curve correspond to the use of the three consecutive drills. The temperature rose sharply during the osteotomy, and the maximum values were used to calculate the temperature increments, ∆T = T_max − T_baseline. When the drill apex reached the target depth, drilling stopped and we moved to the next position. We continued this process until the largest drill was used on the final position.

It can be observed in Figure 4 that osteotomies with the larger-diameter drill led to higher ∆T values. This can be explained by the combined effect of two factors. First, the time between subsequent drills at the same position was insufficient for heat dissipation, so the local temperature did not return to the baseline value. Second, the edge of the final drill was closer to the neighboring thermocouple.

The examples plotted on the two panels of Figure 4 showcase the variability of the data recorded during the thermodynamic measurements. For example, in the top panel, the green curve corresponding to the third pair of guides (Region 3) exhibits overall slower rises during osteotomy and lower ∆T compared to measurements in other regions. Most likely, this happened because, in this particular instance, the thermocouple tip was located farther from the drilling site than planned, or due to inadequate contact between the thermocouple and the adjacent bone. The bottom panel shows noisy data for the orange (Region 2) and red (Region 4) curves immediately after reaching the peak values. This could indicate that the thermocouples moved slightly during drill repositioning for the next osteotomy. Such variability is expected in this type of experimental design.

Overlaid violin plots and box plots of the 336 independent determinations of ∆T are shown in Figure 5. Here, individual data points are represented by circular markers. The width of the violin plots indicates the probability density function, with wider sections representing domains where more data points are clustered. It can be observed that for the surgical guide fitted with an incorporated irrigation channel (INT), the temperature increments are more tightly clustered together at generally lower values compared to the classical guide (CLA).

In Figure 5, the boxes depict the interquartile range (IQR), which contains the middle 50% of the data, delimited by the first quartile (Q1) at the bottom and the third quartile (Q3) at the top. The horizontal line inside each box indicates the median (Q2) of each data set. The whiskers extending above and below the boxes represent the highest and lowest temperature increase values that are closer than 1.5 × IQR away from each of the Q3 and Q1 quartiles, respectively. Values outside this range are considered outliers and are depicted by diamond markers in Figure 5. It can be observed that the position of the median, Q1, Q3, and the upper whiskers are located at higher values for the classical design, regardless of the drill being used. This finding suggests that an internally cooled guide provides superior cooling of the osteotomy site compared to a classical one.

Table 1. Percentage of drilling instances in which the temperature increased by more than 10 °C for each of the two types of surgical guides.

	INT *	CLA **
Drill 1	1.79%	5.36%
Drill 2	8.93%	17.86%
Drill 3	17.86%	48.21%
Overall	9.52%	23.81%

* INT = Internal irrigation channel design. ** Classical design.

lists the percentage of drilling instances in which the temperature increased by more than 10 °C from the baseline. It can be seen that, at each stage of implant bed preparation, individual temperature elevations exceeded the bone damage limit more frequently in the presence of a classical guide than in the presence of a guide with incorporated coolant pipe.

Figure 6 compares the temperature rise while using the two surgical guides in terms of mean value and standard deviation. It can be observed that the internally routed irrigation channel design was more effective in dissipating the heat generated while drilling, showing a significantly lower mean temperature increase. The corresponding p-values from the independent samples t-test are specified above each pair of bars in Figure 6.

The discrepancies in temperature rise while drilling under the two types of surgical guides are depicted in Figure 7 using Bland–Altman plots. Compared to the classical guide, osteotomies performed with the guide with internally routed irrigation channel display negative biases of −1.48 °C, −2.08 °C, and −3.04 °C for the three drills, respectively. Furthermore, the confidence intervals of the biases do not include zero, indicating a systematic difference between the two surgical guide types. The discrepancy is particularly evident for the largest drill (Drill 3), where the data points are normally distributed (Shapiro–Wilk p-value of 0.15).

4. Discussion

This study confirmed the hypothesis that including an irrigation fluid channel in the design of a surgical template brings about a significant reduction in the temperature rise caused by dental implant bed preparation. To minimize the errors associated with differences between bone specimens, the study was conducted on artificial bone models whose architecture and material properties were similar to those of the human mandible. Also, to recapitulate a common clinical practice (the osteotomies involved in the All-on-4 dental implant insertion protocol), we performed sequential drillings at four target sites on each bone model with each type of surgical guide. The surgical template was designed to wrap the artificial bone specimen while leaving sufficient space between its bottom and the target surface to allow for the evacuation of the irrigation fluid (see Supplementary Materials, Video S1). It included four subunits (regions), each of them comprising a common cylindrical sleeve guide and a guide outfitted with an internal coolant pipe.

In sequential osteotomy, the bone does not return to the initial temperature between consecutive drillings, being on an upward heating slope. This is of no concern, however, because experimental [27] as well as computational [28] studies indicate that the maximum temperature reached in sequential drilling is much lower than the peak temperature attained in a single drilling of the same final diameter. Furthermore, the thermally affected layer resulting from predrilling is removed by the next drill, so the osseointegration of the implant depends on the temperature elevation caused by the final drilling. In this respect, computational models of the temperature field offer valuable insights since the most affected zone is next to the osteotomy margin, which escapes measurements [5,28].

Although it seems reasonable to assume that internal cooling is effective, the results reported in the literature are mixed. For example, Stocchero et al. monitored the intraosseous temperature during osteotomies performed on bovine ribs under four conditions [23]: (C1) combined external and internal irrigation in the presence of a surgical guide with an internal coolant tube, (C2) external irrigation in the presence of a classical surgical guide, (C3) no irrigation in the presence of a classical surgical guide, and (C4) free-hand surgery with external irrigation. Temperatures were recorded by K-type thermocouples at 1.5 mm from the edge of the final osteotomy at depths of 1.5 mm, 7 mm, and 12 mm from the bone crest. The largest temperature increments were observed in the cortical bone layer (at 1.5 mm depth); the medians of temperature elevations were 3.0 °C for C1, 2.3 °C for C2, 3.2 °C for C3, and 2.0 °C for C4, with no significant differences between them. The authors pointed out two potential causes of the inefficacy (or even a potential disadvantage) of the internal cooling system: (i) the internal coolant duct was partially clogged by bone chips (as revealed by CBCT), and (ii) the irrigation fluid delivered by the physiodispenser was distributed between the external and the built-in coolant pipes—therefore, the pressure gradient along the internal coolant duct could have been too low [23].

We can further speculate regarding the poor performance of internal cooling in the experiments of [23]. Although it was carefully conducted, with surgical templates specifically designed to fit each bone piece, it is not clear whether the precise fit did not impede the evacuation of the internally routed irrigation fluid. Using both internal and external irrigation, it was not possible to separately observe the flow of the fluid that exited the internal coolant duct.

Teich et al. tested a worst-case scenario of in vitro osteotomies performed in bovine metatarsal sections, along the cortical layer [24]. At a depth of 6 mm, the mean temperature rise caused by a drill of 1.9 mm in diameter was 26.4 °C for the conventional surgical template and 5.8 °C (significantly lower, p < 0.05) for an innovative surgical template with two internal coolant pipes that targeted the drill’s point of entry. Moreover, the authors created an actual dental implant drill guide of a similar concept and demonstrated its clinical benefits [24].

In an experimental model inspired by reference [23], Parvizi et al. clarified the role of coolant evacuation in the context of internally conducted irrigation [25]. Guided drilling performed with surgical guides that had both an entry channel and an exit channel built into the guide resulted in a mean temperature rise of less than 2 °C at 6 mm depth and 1 mm from the osteotomy margin. In the absence of the exit channel, the mean temperature elevation was higher by about 0.5 °C, and this difference was statistically significant [25].

Compared to our previous study of the thermodynamic performance of surgical guides with internal cooling [26], the present work looked at a different, sequential drilling protocol. Moreover, instead of porcine femur pieces, here we used standardized bone models that replicate the bone density of the human mandible (D1 for the cortical layer and D2 for the cancellous regions [29]). Unlike in [26], the mean temperature rise observed in the case of the surgical guide with internal cooling was significantly lower than in the case of the classical guide for each of the three drills (Figure 6). A potential cause of this discrepancy might be the lack of biological variability in the present investigation. Nevertheless, these two studies have the common feature that the guide with internal irrigation tubing ensures a narrower distribution of the temperature elevations than the classical guide, which indicates a more consistent cooling performance (compare Figure 5 of reference [26] with Figure 5 of this article).

The standard deviations of the temperature elevations were relatively high compared to the means, especially in the context of drillings performed with classical guides (Figure 6). The large coefficients of variability indicate that, even in the absence of biological factors, many sources of error are involved in these measurements. We sought to control several experimental conditions (specimen temperatures, drilling speed, axial force, coolant flow rate, osteotomy locations, thermocouple positioning), but vibrations caused by drilling might have affected the thermal contact between the thermocouple and the bottom of its housing. Also, the precise path of the irrigating fluid was beyond our control.

The present study suggests that an internal coolant pipe brings about a significant decrease in bone heating during guided osteotomy even in the absence of a dedicated irrigating fluid evacuation channel, provided that the surgical template’s bottom does not rest on the target surface. This requirement is satisfied by clinical surgical guides supported by adjacent teeth [22,24] as well as in open-flap drillings of a fully edentulous arch according to the All-on-4 protocol [30]. Nevertheless, the All-on-4 treatment concept can be implemented in a less traumatic manner, by guided flapless implant bed preparation [31]. A surgical template with internal cooling prepared for such an application should ensure sufficient distance between the guide and the targeted soft tissue to enable the evacuation of the coolant fluid.

Another advantage of the internal coolant pipe is demonstrated by the picture of the surgical template’s bottom taken right after the measurements (Supplementary Materials, Figure S1), which indicates that the irrigation fluid jet flushes away the bone chips extracted by the drill.

In addition to surgical drilling, dental implant procedures often require bone splitting, which is also associated with heat dissipation. The study by Alevizakos et al. revealed that surgical guides with internal irrigation channels ensured the lowest peak temperatures during bone splitting performed with a piezo-driven bone saw [32].

The mean temperature elevations observed in this study remained below the bone damage threshold even in osteotomies performed using a classical guide. Individual peak temperature rises, however, exceeded the 10 °C limit at 0.8 mm from the margin of the osteotomy in almost half of the final drillings conducted in the presence of the classical guide. In contrast, while using the guide with internal cooling, the critical limit was crossed in 17.9% of the final drillings. Hence, the internally routed irrigation reduced the probability of overheating 2.7-fold.

This study demonstrates the superiority of surgical guides with internal coolant pipes compared to classical surgical guides. Its conclusions are strengthened by the standardized drilling parameters (thrust force, torque, and coolant flow), and the relatively large sample size (n = 56 data points per condition). Nevertheless, caution needs to be exercised when trying to translate the results of this study to the clinical setting. The use of standardized, artificial bone models ensured better reliability, but it is also an important limitation. The temperature rises observed here differ from actual bone temperature elevations expected in a clinical setting. To evaluate the corresponding changes in bone temperature, comparative thermodynamic investigations will be needed, along the lines devised by Szalma et al. [33], and in vivo measurements conducted on animal models.

Further limitations of this study include the use of a single set of drills for all the osteotomies and the use of a single thermocouple per drilling site for temperature recordings. Drill wear is known to favor bone heating [7]. To mitigate its impact on our comparative study, we randomized the order of drillings performed with the two types of surgical guides. Nevertheless, drill wear most likely contributed to the wide distributions of the observed temperature changes. Temperature measurements conducted in a single point, subject to errors associated with thermocouple placement, provided a poor mapping of the temperature field created in the course of surgical drilling. Computer simulations revealed that most thermal damage is expected to occur within 0.5 mm of the edge of the osteotomy, which is precisely the region that drives osseointegration [5]. Thermocouples are large compared to the thickness of this region, and their placement precision is limited.

Future studies might rely on infrared thermography to characterize temperature distributions around the osteotomy site. One option is to apply the method devised by Ali et al. [34] to map the bone heating caused by drilling in the presence of surgical templates with different cylinder designs. In their study, infrared thermography demonstrated the advantage of cylinders endowed with windows over cylinders with small lateral orifices or solid cylinders.

5. Conclusions

This study evaluated the bone heating in the presence of external cooling applied during an All-on-4 implant bed preparation by using classical, cylindrical sleeve guides as well as by using surgical guides with internal coolant pipe that points the irrigation fluid jet towards the drill’s point of entry.

Our findings demonstrate that internally cooled surgical guides can be an effective solution in daily clinical practice, especially in All-on-4 treatments, to reduce the risk of thermal bone damage during dental implant placement. In this type of treatment, the primary stability of the implants is essential for immediate prosthetic loading, but the secondary stability can be affected by excessive bone heating. By significantly decreasing the temperature rise while drilling, internally cooled guides can help improve the success rate of dental implant procedures and reduce patient recovery time, providing a safer and more predictable approach for clinicians.

Our results suggest that including a coolant channel in the design of the surgical guide while also providing a stand-off distance between the bottom of the guiding sleeve and the target tissue can significantly reduce the intraosseous temperature rise caused by guided surgical drilling.