Thermal Effect of Operatory Room Temperature, Surgical Drill Diameter, and Temperature of Irrigants at Different Depths of Implant Site Preparation - Thermographic Analysis on Goat Mandible.

BACKGROUND: Drilling of the implant site results in transient rise in temperature of the surrounding bone disrupting the bone healing process and implant stability. Overproduction of heat due to various factors at osteotomy site needs to be controlled as it hampers the final outcome of the procedure.
PURPOSE: The purpose of this study was to evaluate various factors related to implant drills responsible for heat generation and temperature rise during osteotomy.
MATERIALS AND METHODS: A total of 64 bone specimens with dimensions of 15 mm × 15 mm were obtained from goat mandibles and were equally divided into Groups A and B with operating room temperature maintained at 25°C and 30°C, respectively. Osteotomies were performed using drills with diameters (4.2 mm and 5.6 mm) at various drilling depths (10 mm and 13 mm) with external saline irrigation temperatures (4°C and 25°C). Temperature change was recorded by laser thermometer.
RESULTS: The surgical drill depths, diameters, and room temperatures made no differences in temperatures at implant drilling sites whereas the temperatures of the irrigants provide sufficient heat control during drilling.
CONCLUSION: Cooled saline provides beneficial effects in controlling the temperatures of osteotomy sites as compared to saline used at room temperature during implant site preparation. Copyright:

INTRODUCTION

Implant dentistry has gained importance in the modern era of dentistry and is considered as reliable treatment modality. Implants have been considered to be the possible closest substitute to natural, healthy teeth. It is considered as a preferable esthetic alternative for treating partial and complete edentulism, thus preserving the overall structures of the mouth.

During drilling of implant sites, applied forces are converted into heat, resulting in temperature rise and further destruction and impairment of the healing of the adjacent bone.[1] The temperature attained due to frictional heat generated during drilling process affects the normal bone tissue response.[2] The temperature threshold of 47°C exceeding 1 min impairs implant–bone contact, causes bone tissue necrosis, inhibits bone microcirculation, and activates bone destructive mechanism, thus hampering the regenerative potential of the bone, and therefore, it is considered to be a factor of early implant failure.[3] To reduce the overheating during drilling at bone–drill interface, sterile saline is a central strategy.[4] It removes the heated bone chips from the surgical drilling site and reduces friction during drilling further minimizing the production of the frictional heat.[5]

Climatic conditions in certain regions of India, specifically during summer season cross threshold temperature (47°C) leading to thermal bone necrosis. The body temperatures habitually fall by 0.5°C to 1.5°C; proposed reasons for this finding were loss of body heat by radiation in cold operating rooms, decrease in cellular oxidation, cutaneous vasodilation, and reduced muscular activity.[6]

Operating rooms could be classified by their effect on patients’ temperatures:[7]

Rooms below 21°C – All patients became hypothermic

21°C–24°C – 70% of the patients remained normothermic and 30% became hypothermic

24°C–26°C – All patients remained normothermic.

As there is variation in room temperature in different areas of India in different seasons, we consider to investigate its effect, so that we can standardize operatory room temperature before implant surgeries.

The purpose of the present study was to investigate the effect of the operatory room temperatures, surgical drill diameters, and irrigant temperature at different depths of implant site preparation.

MATERIALS AND METHODS

This in vitro study approved by the institutional experimentation committee was carried on bone blocks, obtained from goat mandible which simulates human jaw bone regarding bone density, relationship between cortical and cancellous bones, and thermal conductivity. All specimens were collected from the butchery. Samples were cut into equal sections of 15 mm thickness × 15 mm height to ensure uniform experimental conditions. A total of 64 specimens were obtained and were divided into Groups A and B with 32 specimens in each group, and impressions of bone specimens were made using silicone material and plaster casts were prepared. To maintain the physical and chemical properties, specimens were not used for few hours according to the guidelines established by Sedlin and Hirsch,[8] i.e., the specimens were kept moist in saline solution and stored in plastic bags at 10°C.

Thermal changes during implant osteotomies were recorded by an infrared or laser thermometer. It consists of a lens to focus the infrared thermal radiation onto sensor, which converts the radiant energy to an electrical signal that can be displayed in units of temperature after being compensated for surrounding temperature. The added advantage of this system is that temperature can be measured from a distance without actual contact with the object to be measured.

Emissivity represents the measured thermal changes at the osteotomy site. Layer of graphite spray of 0.95 emissivity was sprayed directly over the surface of the bone to cover it in order to void the difference between the cortical and cancellous bone layers. By using the graphite spray, the error of temperature difference between cortical and cancellous bones is cut down and the measurement of accuracy is thus improved. A bottle of saline was kept during the entire experiment in the heat-resistant bag to maintain the temperature of the solution. The same operator performed all the drillings in order to avoid the bias related to operator-related factors. Conventional physiodispenser dental handpiece was used. Drilling speed of 800 rpm was maintained throughout the procedure by the surgical motor unit, according to the recommendations of the manufacturer for a standard and atraumatic surgical protocol. For

Group A, the operating room temperature was maintained at 25°C and implant site preparation was done till 10 mm depth using drill with a diameter of 4.2 mm with irrigant temperatures first with 4°C and later with 25°C, and subsequently, drilling was done with 5.6 mm drill diameter and with the same irrigant temperatures. For the next set, the drilling was done till 13 mm depth and all the procedures were repeated with 10 mm drilling depth. For Group B, operating room temperature was maintained at 30°C and the same procedure was repeated with drilling depth till 10 mm and 13 mm [Tables 1 and 2]. At all the steps, temperature measurement was done using laser thermometer. The outcome evaluator and the statistician were blinded to all allocations of the intervention.

Table 1

Descriptive distribution of bone specimen with implant site preparation done till 10 mm depth

Group A: Room temperature 25°C				Group B: Room temperature 30°C
A1: Depth of osteotomy: 10 mm				B1: Depth of osteotomy: 10 mm
Group	Number of samples	Drill diameter	Irrigant temperature (°C)	Group	Number of samples	Drill diameter	Irrigant temperature (°C)
A1a	4	4.2	25	B1a	4	4.2	25
A1b	4	5.6	25	B1b	4	5.6	25
A1c	4	4.2	5	B1c	4	4.2	5
A1d	4	5.6	5	B1d	4	5.6	5

A1 – Depth of osteotomy: 10 mm; B1 – Depth of osteotomy: 10 mm; A1a – Subgroup a of group A1; A1b – Subgroup a of group A1; A1c – Subgroup a of group A1; A1d – Subgroup a of group A1; B1a – Subgroup a of group B1; B1b – Subgroup a of group B1; B1c – Subgroup a of group B1; B1d – Subgroup a of group B1

Table 2

Descriptive distribution of bone specimen with implant site preparation done till 13 mm depth

Group A: Room temperature 25°C				Group B: Room temperature 30°C
A2: Depth of osteotomy: 13 mm				B2: Depth of osteotomy: 13 mm
Group	Number of samples	Drill diameter	Irrigant temperature (°C)	Group	Number of samples	Drill diameter	Irrigant temperature (°C)
A2a	4	4.2	25	B2a	4	4.2	25
A2b	4	5.6	25	B2b	4	5.6	25
A2c	4	4.2	5	B2c	4	4.2	5
A2d	4	5.6	5	B2d	4	5.6	5

A2 – Depth of Osteotomy: 13 mm; B2 – Depth of Osteotomy: 13 mm; A2a – Subgroup a of group A2; A2b – Subgroup a of group A2; A2c – Subgroup a of group A2; A2d – Subgroup a of group A2; B2a – Subgroup a of group B2; B2b – Subgroup a of group B2; B2c – Subgroup a of group B2; B2d – Subgroup a of group B2

Statistical analysis

Data were analyzed using Student's t test. P > 0.05 suggests that the difference observed is nonsignificant and P < 0.05 will be considered significant.

RESULTS

Temperature changes of 64 drilling osteotomies at two different room temperatures were evaluated. The mean bone specimen baseline temperature before each osteotomy was 20.24 ± 0.60°C. All real-time measurement sequences presented an increase in temperature in superficial cortical and deeper cancellous bone areas for all investigated methods of implant osteotomies.

For intragroup comparison within Group A, no statistically significant difference could be observed between mean temperatures at 10 mm (26.37 ± 2.95) and 13 mm (27.37 ± 3.11) drilling depths at osteotomy sites [Table 3].

Table 3

Descriptive statistics of temperature changes (°C) during drilling of the implant sites with regard to the drilling depth at operating room temperature of 25°C

Drill diameter (mm) Room temperature 25°C	n	Mean±SD	P
4.2	4	25.9250±2.29111	0.38
5.6	4	27.8250±3.38662

Non-significant difference (P value ≤ 0.05 indicates statistically significant difference); P - Probability value, n - Sample size , SD - Standard deviation

No statistically significant difference could be observed between mean temperatures at 10 and 13 mm drilling depths with conical implant drills of 4.2 mm (25.92 ± 2.29) and 5.6 mm (27.82 ± 3.38) diameters [Table 4].

Table 4

Descriptive statistics of temperature changes (°C) during drilling of the implant sites with regard to the drill diameter at operating room temperature of 25°C

Depth (mm) Room temperature 25°C	n	Mean±SD	P
10	4	26.3750±2.95790	0.65
13	4	27.3750±3.11595

Non-significant difference (P value ≤ 0.05 indicates statistically significant difference); P - Probability value; n – Sample size

Irrigation of the surgical site with saline at 5°C (24.47 ± 0.78) temperature significantly reduced the bone temperature compared to saline at 25°C (29.27 ± 1.77) temperature regardless of the use of drill guide [Table 5].

Table 5

Descriptive statistics of temperature changes (°C) during drilling of the implant sites with regard to the temperature of the saline used as irrigants at operating room temperature of 25°C

Irrigant temperature (°C) Room temperature 25°C	n	Mean±SD	P
25	4	29.2750±1.77647	0.003*
5	4	24.4750±0.78049

*Significant difference at P≤0.05. SD – Standard deviation; n – Sample size; P – Probability value, n - Sample size

For intragroup comparison within Group B, at 10 mm (26.77 ± 3.05) and 13 mm (27.75 ± 3.11) drilling depths at osteotomy site, no statistically significant difference could be observed between mean temperature increases [Table 6].

Table 6

Descriptive statistics of temperature changes (°C) during drilling of the implant sites with regard to the drilling depth at operating room temperature of 30°C

Depth (mm) Room temperature 30°C	n	Mean±SD	P
10	4	26.7750±3.05982	0.67
13	4	27.7500±3.15013

*Significant difference at P≤0.05. SD – Standard deviation; n – Sample size; P – Probability value

Similarly, 4.2 mm (26.27 ± 2.29) and 5.6 mm (28.82 ± 3.46) drill diameter showed no statistically significant difference between mean temperature increases at osteotomy sites [Table 7].

Table 7

Descriptive statistics of temperature changes (°C) during drilling of the implant sites with regard to the drill diameter at operating room temperature of 30°C

Drill diameter (mm) Room temperature 30°C	n	Mean±SD	P
4.2	4	26.2750±2.29837	0.37
5.6	4	28.2500±3.46939

*Significant difference at P≤0.05. SD – Standard deviation; n – Sample size; P – Probability value

When drilling was performed under cooled saline, i.e., 5°C (24.82 ± 0.080), a significant decrease of bone temperature was observed compared to saline temperature of 25°C (29.7 ± 1.85) [Table 8].

Table 8

Descriptive statistics of temperature changes (°C) during drilling of the implant sites with regard to the temperature of the saline used as irrigants at operating room temperature of 30°C

Irrigant temperature (°C) Room temperature 30°C	n	Mean±SD	P
25	4	29.7000±1.85293	0.003*
5	4	24.8250±0.80156

*Significant difference at P≤0.05. SD – Standard deviation; n – Sample size; P – Probability value

Bone thermal changes at the surgical site were significantly affected by temperature of the saline used as irrigants whereas surgical drill depths and diameters made no significant difference in temperatures at osteotomy sites.

Intergroup comparisons between Groups A and B revealed no statistically significant difference in temperature of the bone at the surgical sites, with respect to change in room temperature.

DISCUSSION

Preservation of healthy bone during bone osteotomies for implant site preparation by surgical drills is an important prerequisite.[9] The thermal injury due to temperature rise at surgical site during osteotomies is affected by various factors such as bone mass, the amount of cortical versus cancellous bone at the surgical site, rotational drill speed, drill diameter, sharpening condition, drilling depth, and the force of drill application.[10111213] Regardless of the reason, this temperature increase can cause damage or necrosis of the bone, impairing the post-operative healing, affecting the osseointegration and finally hampering the retention of implant.[14]

For protecting the osteotomy site from thermal injury, saline irrigation with varied temperatures is routinely used. In the present study, the temperature change at the drilling site with saline at 5°C was 24.47 ± 0.78 and 24.82 ± 0.080 and at 25°C was 29.27 ± 1.77 and 29.7 ± 1.85 for Groups A and B, respectively. When drilling was performed under cooled saline, i.e., 5°C, a significant decrease of bone temperature was observed compared to saline temperature of 25°C regardless of the use of drill guide for both the groups. Adequate control of adjacent bone temperature might be possible by using irrigants cooled at 5°C during implant site drilling. Histological data have shown higher osteoblast activity and vigorous increase in bone marrow dynamics when osteotomy site is drilled under saline at 4°C compared to 25°C.[15] However, the effect of cooled saline on nerves, blood vessels, or other surrounding structures should also be considered when selecting a temperature of the irrigants in the clinical setting.[16]

In the literature, there are some studies which state that saline application has an effect on temperature rise of osteotomy site,[13] however, on the contrary, others indicate that application of saline solution to the rotational system at bone interface does not reduce the temperature during the osteotomy to any significant degree.[1718] In the present study, only external irrigation was used as contingent clogging and germ contamination can be seen with the use of internal irrigation. This finding is in favor of the study carried by Misir et al. where they documented higher jaw bone temperature at implant drilling site with combined irrigation when compared to external irrigation.[19]

In the present study, no significant difference was found in rise of temperature in relation to different drilling depths of 10 mm (26.37 ± 2.95 and 26.77 ± 3.05) and 13 mm (27.37 ± 3.11 and 27.75 ± 3.11) for Groups A and B, respectively, which is in accordance to the study carried by Reza Tabrizi et al.[20] The American Society of Heating, Refrigeration, and Air-Conditioning Engineers recommends that operating room temperatures be kept between 66°F and 68°F (18.8°C–20°C), with a humidity percentage of 70. The reason behind it is to reduce bacterial growth and comfort of patients and operators. In the author's knowledge, ours is the first study which focuses on the effect of the operating room temperature on the temperature of surgical site during osteotomies, where no significant difference could be found between the two given room temperatures (i.e., 25°C and 30°C) on bone temperature at surgical site. One of the limitations of the present study is that it is an in vitro study on nonvital bone where measurement of actual effect of heat on subsequent bone healing was not possible. Further studies are required with variable difference and more sample size to investigate these parameters before concluding its effect.

CONCLUSION

This study concluded that room temperature difference did not have a statistically significant effect on temperature generated at osteotomy sites. Difference between other parameters, i.e., drill diameter and drilling depth, was also statistically not significant. Difference between only one parameter was statistically significant, i.e., irrigant temperature while drilling. Lowering the temperature of irrigants helps to reduce the temperature at osteotomy site avoiding bone necrosis, thus facilitating osseintegration and finally retention of the implant.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.