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Temperature changes in bovine mandibular bone during implant site preparation: an assessment using infra-red thermography
Journal of Dentistry, Vol. 24,No. 4,pp.263-267,1996 CopyrightQ 1996ElsevierScienceLtd. AUrightsreserved Printedin GreatBritain 0300-5712/96 $15.00+ 0.00
0300-5712(95)00072-0
ELSEVIER
Temperature changes in bovine mandibular bone during implant site preparation: an ssessment using infra-red thermography i.C.Benington*, P.A.Biagioni , P. J. Crossey*, D. L. Hussey”, S. Sheridan* and P. -J. Lameyt *Division of Restorative Dentistry Belfast, Northern Ireland, UK
and
TDivision of Dental Surgery
School of Clinical Dentistry,
The Queen’s
University
of
ABSTRACT Objectives: Changesin bone temperature during the sequenceof drilling for implant site preparation
using the Branemark techniquewere monitored usingi&a-red thermography. Methods: Bovine mandibleswere usedto provide cortical bone of a similarquality to humanmandibular bone. To ensure the consistencyin the drilling procedure, one operator used a conventional dental handpiecewith a motor provided by Nobelpharma.The manufacturer’sspecificationswere followed during the implant site preparation,except that no irrigation wasemployedsincei&a-red radiation does not transmit through water. Thermal imageswere recorded using the Thermovision 900 system.A sequenceof imageswasrecorded during implant site preparation.Three drills were examinedin termsof temperature changesduring drilling over the entire area involved. The three drills usedwere a round bur, which determinesthe site of the fixture, a spiral drill (2 mm twist drill) which establishesthe direction of the implant and finally a pilot drill (3 mm)which progressivelyincreasesthe diameterof the site. Results: Average values (n = 10 drill sequences) for maximumrecorded temperature(Max T”C), change in temperature (ATC) from baselineand the area of involvement (mm’) for each drill in the 10 drill sequences were asfollows: round, spiral (2 mm) and pilot (3 mm) drills gavemaximumtemperaturesof 82.7”C, 130.1”Cand 126.3”C,respectively.The changesin temperature, AT”C, were 457°C 79.O”Cand 78.9”Cfor the round, 2 mm twist and 3 mm pilot drill, respectively.The averageareasrecordedfor the round, spiral and pilot drills were 49 mm’, 140.1mm2and 273.0mm’, respectively. Conclusions:It is concludedthat the methodologyemployedaccuratelyrecordedtemperaturechangesat and around the dental implant site, and provided preliminary baselinedata againstwhich the cooling efficacy of different irrigant systemsmay be compared.Copyright 0 1996Elsevier ScienceLtd. KEY WORDS:
Thermography,
J. Dent
24: 263-267
1996;
Implant (Received
preparation 29 September
1994;
reviewed
INTRODUCTION The success of an endosteal implant depends, in part, on its ability to achieve primary healing’. Implant bed preparation and healthy bone are critical precursors to primary healing. Thermal and mechanical damage to the bone must be minimised in the preparation of the implant bed. Drilling and trephining procedures during dental implant site preparation may cause not only mechanical damage to the bone involved, but a temperature increase in the bone directly adjacent to the implant site. Significant temperature increases can result in heat-induced bone tissue injury2. Temperature increases in bone during drilling have been measured before in uivo3, and studies have been performed on
Correspondence should be addressed to: Dr P.A. Biagioni, of Dental Surgery, School of Clinical Dentistry, The Queen’s sity of Belfast, Grosvenor Road, Belfast BT12 6BP, UK.
Division Univer-
15 November
1994;
accepted
27 March
1995)
drilling animal cortical bone for different implant systems in uitro4. Studies have been performed which most closely resemble a clinical situation when heat, caused by drilling cortical bone in vivo in patients and animals, was measured5. Temperature measurement was by means of a thermocouple situated at a distance of 0.5 mm from the drill site. Indeed, recent work has been undertaken using thermocouples as close as 0.1 mm to the drill site interface6. Unfortunately, thermocouple measurements only show temperature changes at one or a number of sites close to the drill site interface, and require a procedure for the insertion of the thermocouple which may itself result in a temperature increase and hence cause thermal damage adjacent to the area under investigation. One technique which may surmount these problems is electronic i&a-red thermography. This is a non-invasive scanning thermometric technique which allows for a thermal picture of the drill site and surrounding
264
J. Dent. 1996; 24: No. 4
tissue to be examined during the drilling procedure. This technique has been in clinical use since the early 1960s and is based on the laws of radiation. All bodies emit electromagnetic radiation to a greater or lesser degree, and the total energy emitted depends on the absolute temperature of the body. Therefore, if the energy emitted can be measured, then it is possible to accurately determine the temperature. This is essentially the basis for radiation thermography. The instrumentation is designed around an optical mechanical scanning system using mirrors and lenses to collect and focus the energy emitted from the body of interest on to an infra-red detector. The surface of interest is scanned point by point horizontally and on a number of vertical lines, and the image is built up in much the same way as a television image. The detector then converts the absorbed energy to an electrical signal which is then digitised into a 1Zbit format. These signals will be interpreted by a scanner unit and displayed as a high resolution thermal picture of the object in either a colour or grey scale. All measurements must be recorded within a controlled environment which is free from external radiation sources, convective air currents and extremes of humidity. This paper discusses the application of therm0 imaging in the determination of temperature changes in bone during the preparation of dental implant sites in bovine mandibular cortical bone in uitro.
METHODS
AND MATERIALS
Bone temperature measurements during dental implant site preparation were undertaken at a number of sites on bovine mandibular cortical bone which had been stripped, sectioned and frozen into pieces measuring approximately 6 cm x 6 cm in size. Care was taken to select sites where the bone was as homogenous as possible and where the cortical bone layer was of a similar thickness for all drill sites. The implant site was prepared to correspond to the initial stages of the Branemark technique. A conventional dental handpiece was used with a motor provided by Nobelpharma (Harrow, UK). The sections of bovine mandibular bone were held by a simple apparatus on a normal working surface. Manufacturer specifications were followed during the implant site preparation, but no irrigation was employed. One operator performed all the drilling procedures. Thermal images were recorded using the Agema Thermovision 900 system (Agema Infra-red Systems, Danderyd, Sweden). This is a cryogenically cooled long wave scanner using a mercury cadmium telluride detector with a spectral response of S-12pm and a sensitivity of 0.08”C at physiological temperatures of around 30°C. Each lens, filter and measurement range combination has its own calibration function. The constants for these functions are stored in the
scanner, and the system automatically chooses the correct constants for the combination in operation. A rotational speed of 2500 rpm was used with a locating drill, a 2 mm twist drill and a 3 mm twist drill in sequence similar to the Branemark technique. The therm0 imaging camera with the integral macro lens was positioned 0.05 m from the area of interest. The entire drilling sequence was recorded at a highest storing speed of three images per second in 1Zbit format and analysed on screen at a later date without any loss of accuracy. The Thermovision 900 System is a real time system, and storage speed is dependent on hard disk space at a rate of three images per second. Maximum temperature change and the area of involvement were noted. The procedure was repeated for a number of drilling sequences. Care was taken to avoid using a drill site where an area of temperature change had been recorded with the result that the distance between adjacent drill sites was approximately 4 cm.
RESULTS The mean baseline temperature of the bovine bone was 2O.W with a variation of 0.5”C. The changes in temperature (AT’%) from baseline were 45.7”C, 79.o”C and 78.9”C for the round, spiral and pilot drills, respectively. The area of thermal involvement also illustrated a gradual increase in area for each drill. The round drill on average affected an area of 49.2 mm’, whereas the 2 mm spiral drill altered the surface temperature over a mean area of 140.1 mm2 and the 3 mm pilot drill affected an area of 273.0 mm’. The complete drill sequence time, including changing of drills was 75 s, therefore approximately 25 s per drill. Figure 1 is a thermogram of the round, locating drill in operation. Point A represents the bone/drill interface, and it was at this point that the maximum temperature for any drill within any sequence was recorded. For the 10 round locating drills used, the maximum temperatures ranged between 61.4”C and 102.1”C, with an average maximum temperature of 82.7”C. This represents an average temperature increase (ATC) over 10 drilling sequences, from a baseline temperature of 45.7”C. Point B represents the outer edge of the affected area. This was delineated and the affected area calculated. For the round locating drill, this ranged from 17.3 mm2 to 68.0 mm2 with a mean area of 49.2 mm2 over the 10 drilling sequences. A representation of the 2 mm spiral drill in operation is illustrated in Fig. 2. The maximum temperatures using the spiral (2 mm) drill ranged between 107S”C and 152.8”C, with an average temperature for the 10 drilling sequences of 13O.l”C. This represents an average AT”C over 10 drilling sequences from the baseline of 79.O”C. The area of involvement ranged from 42.4 mm2 to 231.0 mm2 with an average of 140.1 mm2 over the 10 drilling sequences.
Benington
et al.: Thermographic
Fig. I. Thermogram of round locating bur in operation. Focal distance was 0.05 m. Drill shank and head (Point A) are shown withdrawing from the drill site (Point 6). The yellow coloured area (Point C) corresponds to the drill debris with the surrounding corona (Point D) illustrating direct changes in surface bone temperature from baseline. For all thermographic images shown, the palette used a black colouration depicting cold (20°C or less) through a continuous blue, green, yellow, red and white spectrum of 112 hues. White illustrates the highest temperatures (40°C or more). When co/our saturation in either black or white was achieved, accuracy was not lost. The level and span of temperatures can be varied during and after storage of the images.
The final 3 mm pilot drill is illustrated in Fig. 3. The maximum temperatures using the pilot (3 mm) drill ranged between 104.5”C and 159.3”C with an average temperature for the 10 drilling sequences of 126.3”C. This represents an average AT”C over 10 drilling sequences from the baseline of 78YC. The area of involvement ranged from 75.3 mm* to 428.4 mm2 with an average of 273.0 mm’.
Fig. 2. Thermogram illustrating the 2 mm spiral drill in operation at a focal length of 0.05 m. The spiral thread of the drill is visible as a lighter helix (Point A). As in Fig. 1, the white area (Point B) within the yellow coloured area, (Point C) represents the area of maximal thermal emission which corresponds to the drill/bone interface. Note that Points C and D have increased in diameter as compared with Fig. 1.
Fig. drill drill (D) the
assessment
265
of implant site preparation
3. This represents the thermal radiance during the 3 mm pilot sequence. Reflectance of heat emissions can be seen on the thread point (A). Note the change in diameter of areas (C) and as compared to previous figures. The white area (B) illustrates large temperature increase observed at this point.
DISCUSSION The critical temperature generated during surgical preparation for implant placement is generally regarded to be in the region of 56°C since this is the temperature at which alkaline phosphatase is denatured. However, hard tissue injury has been shown in bone temperatures below this proposed critical leve17. Therefore, there is a need for verification of critical temperatures during bone drilling. Most studies have used thermocouples as their measurement device. However, the relationship between thermocouple voltage and temperature is sometimes non-linear. Also, those used in medicine have to show their optimum thermo-electric characteristics over the range of body temperatures, and this will limit the type available. In addition, they only give spot temperature measurements at adjacent sites, not the overall thermal profile. In contrast, thermoimaging using electronic infra-red scanners allowed the temperature increase, that occurred when drilling bone for a dental implant site preparation, to be recorded and
04
0
/
/
I
I
:
I
:I
5
10
15
20
25
30
35
40
I
/
45
50
I:
55
60
~,
65
70
75
seconds Fig. 4. This is an example plot for the temperature recordings with time during a drilling sequence. The three drill types can be clearly identified by their isolated profiles.
266
J. Dent. 1996; 24: No. 4 Tab/e 1. Results
for each of the ten drill sequences
Type of bur
Max
T”C
Mean AT% from baseline
Average area hm3
1
Round Spiral (2 mm) Pilot (3 mm)
61.4 108.4 114.6
24.1 65.9 75.0
26.1 61.4 112.2
2
Round Spiral (2 mm) Pilot (3 mm)
91.9 132.3 153.4
52.5 64.4 79.0
68.0 207.5 428.4
3
Round Spiral (2 mm) Pilot (3 mm)
102.1 140.3 104.5
45.2 80.1 57.8
60.2 231 .O 386.7
4
Round Spiral (2 mm) Pilot (3 mm)
72.1 128.3 113.5
57.7 83.3 80.5
66.8 213.7 400.0
5
Round Spiral (2 mm) Pilot (3 mm)
83.9 143.4 121.5
42.9 77.5 72.8
47.3 144.4 347.0
6
Round Spiral (2 mm) Pilot (3 mm)
93.9 138.5 127.4
47.4 88.4 92.5
62.7 161.4 321.6
7
Round Spiral (2 mm) Pilot (3 mm)
91.5 152.8 141.6
70.1 94.1 92.9
59.4 149.9 308.3
8
Round Spiral (2 mm) Pilot (3 mm)
69.5 107.5 159.3
28.0 65.1 90.3
17.3 42.4 75.3
9
Round Spiral (2 mm) Pilot (3 mm)
78.0 123.8 104.8
40.2 81.6 70.6
44.8 59.4 89.8
10
Round Spiral (2 mm) Pilot (3 mm)
82.7 125.7 122.4
49.3 78.9 77.3
39.8 129.6 260.4
Average baseline temperature =20.8”C Average time taken for each drill sequence =75 s. The maximum temperatures as indicated in column 2 were measurements recorded at the bone/drill interface. Column 3 shows the mean change in temperature from baseline and column 4, the average area affected by a change in temperature regardless of the degree of elevated temperature.
temperature of 140°C 0.5 mm from the drill site while using standard unirrigated orthopaedic twist drills. Indeed, of their 158 examinations, 37 showed temperatures of 100°C or more. Their mean maximum temperature was 93.1”C. Lavelle and Wedgwood* also noted high temperatures using thermocouples. They found that (without irrigation) temperatures of around 74°C were observed at a distance 0.5 mm from the round bur drill site and 83°C from a semielliptical bur site. These results compare favourably with our study where the
followed continuously throughout the drilling procedure. As well as allowing identification of the point of maximal temperature increase and the area of bone thermally affected, accurate measurements of the temperature may be carried out, stored and retrieved without any loss of accuracy. The published results of other researchers, using thermocouples without irrigation, compared very favourably with those observed using infra-red thermography. Matthews et al.’ illustrated a maximum Tab/e II. Average maximal temperatures area of thermographic involvement during
(Max T”C), each drilling Max
Average
Round Spiral (2 mm) Pilot (3 mm)
T”C
82.7 130.1 126.3
increase sequence AT% 45.7 79.0 78.9
in temperature
(A TX)
Area
(mm’)
49.2 140.1 273.0
and
Benington et a/.: Thermographic assessment
average temperatures recorded for the round bur, 2 mm spiral bur and 3 mm pilot bur were 82.7”C, 13O.l”C and 126.3”C, respectively. The point of note is that these latter measurements were obtained non-invasively. Surface contact may be a source of error in measurements using thermocouples since all thermocouples must make contact with the surface, not necessarily in the correct plane, and therefore may alter the localised surface temperature. The temperatures measured, while irrigation is employed, vary, although the variation seems to depend more on the load and drill design rather than on the irrigant employed. Lavelle and Wedgwood’ showed differences with external and internal irrigation systems. However, temperatures of up to 72°C have been recorded using thermocouples for different irrigation systems during implant site preparation6. No irrigation was employed for several reasons during this preliminary investigation. Firstly, as the application of electronic infra-red thermography was a novel technique to implantology, it was necessary to achieve the absolute baseline values. In addition, water is opaque to infra-red radiation, and was therefore an unnecessary source of error at this preliminary level.
CONCLUSIONS In conclusion, electronic infra-red thermography is a viable technique to be employed in implantology research. Temperatures measured by thermography when compared to those reported for thermocouple systems
of implant site preparation
267
were similar. The two main advantages of thermography are that it is a non-invasive technique giving absolute temperature measurement, and allows the researcher to visualise, in a two-dimensional manner, the entire drilling sequence area.
References 1. Albrektsson T, Branemark P-I, Hansson H-A and Lindstrogm J. Osseointegrated titanium implants: Requirements for ensuring a long-lasting, direct bone-to-implant anchorage in man. Acta Orthop Stand 1981; 52: 155-170. 2. Eriksson AR and Albrektsson T. Temperature threshold levels for heat-induced bone tissue injury: A vital microscopic study in the rabbit. JProsthet Dent 1983; 50: 101-107. 3. Matthews LS and Hirsch C. Temperatures measured in human cortical bone when drilling. .I Bone Joint Sung Am 1972; 54: 297-308. 4. Jo H, Olin P and Schachtele C. Temperature changes in bone during dental implant site preparation. J Dent Res
1993; 72: 389. 5. Eriksson AR, Albrektsson T and Albrektsson B. Heat
caused by drilling cortical bone: Temperature measured in vivo in patients and animals. Acta Orthop Stand 1984; 55: 629-631. 6. Sutter F, Krekeler G, Schwammberger AE and Sutter FJ. Atraumatic surgical technique and implant bed preparation. Quintessence Znt 1992;23: 811-816. 7. Lundskog J. Heat and bone tissue. An experimental investigation of the thermal properties of bone tissue and threshold levels for thermal injury. Thesis, GGteborg: University of Giiteborg, 1972. 8. Lavelle C, Wedgwood D. Effect of internal irrigation on frictional heat generated from bone drilling. J Oral Surg 1980; 38: 499-503
0300-5712(95)00072-0
ELSEVIER
Temperature changes in bovine mandibular bone during implant site preparation: an ssessment using infra-red thermography i.C.Benington*, P.A.Biagioni , P. J. Crossey*, D. L. Hussey”, S. Sheridan* and P. -J. Lameyt *Division of Restorative Dentistry Belfast, Northern Ireland, UK
and
TDivision of Dental Surgery
School of Clinical Dentistry,
The Queen’s
University
of
ABSTRACT Objectives: Changesin bone temperature during the sequenceof drilling for implant site preparation
using the Branemark techniquewere monitored usingi&a-red thermography. Methods: Bovine mandibleswere usedto provide cortical bone of a similarquality to humanmandibular bone. To ensure the consistencyin the drilling procedure, one operator used a conventional dental handpiecewith a motor provided by Nobelpharma.The manufacturer’sspecificationswere followed during the implant site preparation,except that no irrigation wasemployedsincei&a-red radiation does not transmit through water. Thermal imageswere recorded using the Thermovision 900 system.A sequenceof imageswasrecorded during implant site preparation.Three drills were examinedin termsof temperature changesduring drilling over the entire area involved. The three drills usedwere a round bur, which determinesthe site of the fixture, a spiral drill (2 mm twist drill) which establishesthe direction of the implant and finally a pilot drill (3 mm)which progressivelyincreasesthe diameterof the site. Results: Average values (n = 10 drill sequences) for maximumrecorded temperature(Max T”C), change in temperature (ATC) from baselineand the area of involvement (mm’) for each drill in the 10 drill sequences were asfollows: round, spiral (2 mm) and pilot (3 mm) drills gavemaximumtemperaturesof 82.7”C, 130.1”Cand 126.3”C,respectively.The changesin temperature, AT”C, were 457°C 79.O”Cand 78.9”Cfor the round, 2 mm twist and 3 mm pilot drill, respectively.The averageareasrecordedfor the round, spiral and pilot drills were 49 mm’, 140.1mm2and 273.0mm’, respectively. Conclusions:It is concludedthat the methodologyemployedaccuratelyrecordedtemperaturechangesat and around the dental implant site, and provided preliminary baselinedata againstwhich the cooling efficacy of different irrigant systemsmay be compared.Copyright 0 1996Elsevier ScienceLtd. KEY WORDS:
Thermography,
J. Dent
24: 263-267
1996;
Implant (Received
preparation 29 September
1994;
reviewed
INTRODUCTION The success of an endosteal implant depends, in part, on its ability to achieve primary healing’. Implant bed preparation and healthy bone are critical precursors to primary healing. Thermal and mechanical damage to the bone must be minimised in the preparation of the implant bed. Drilling and trephining procedures during dental implant site preparation may cause not only mechanical damage to the bone involved, but a temperature increase in the bone directly adjacent to the implant site. Significant temperature increases can result in heat-induced bone tissue injury2. Temperature increases in bone during drilling have been measured before in uivo3, and studies have been performed on
Correspondence should be addressed to: Dr P.A. Biagioni, of Dental Surgery, School of Clinical Dentistry, The Queen’s sity of Belfast, Grosvenor Road, Belfast BT12 6BP, UK.
Division Univer-
15 November
1994;
accepted
27 March
1995)
drilling animal cortical bone for different implant systems in uitro4. Studies have been performed which most closely resemble a clinical situation when heat, caused by drilling cortical bone in vivo in patients and animals, was measured5. Temperature measurement was by means of a thermocouple situated at a distance of 0.5 mm from the drill site. Indeed, recent work has been undertaken using thermocouples as close as 0.1 mm to the drill site interface6. Unfortunately, thermocouple measurements only show temperature changes at one or a number of sites close to the drill site interface, and require a procedure for the insertion of the thermocouple which may itself result in a temperature increase and hence cause thermal damage adjacent to the area under investigation. One technique which may surmount these problems is electronic i&a-red thermography. This is a non-invasive scanning thermometric technique which allows for a thermal picture of the drill site and surrounding
264
J. Dent. 1996; 24: No. 4
tissue to be examined during the drilling procedure. This technique has been in clinical use since the early 1960s and is based on the laws of radiation. All bodies emit electromagnetic radiation to a greater or lesser degree, and the total energy emitted depends on the absolute temperature of the body. Therefore, if the energy emitted can be measured, then it is possible to accurately determine the temperature. This is essentially the basis for radiation thermography. The instrumentation is designed around an optical mechanical scanning system using mirrors and lenses to collect and focus the energy emitted from the body of interest on to an infra-red detector. The surface of interest is scanned point by point horizontally and on a number of vertical lines, and the image is built up in much the same way as a television image. The detector then converts the absorbed energy to an electrical signal which is then digitised into a 1Zbit format. These signals will be interpreted by a scanner unit and displayed as a high resolution thermal picture of the object in either a colour or grey scale. All measurements must be recorded within a controlled environment which is free from external radiation sources, convective air currents and extremes of humidity. This paper discusses the application of therm0 imaging in the determination of temperature changes in bone during the preparation of dental implant sites in bovine mandibular cortical bone in uitro.
METHODS
AND MATERIALS
Bone temperature measurements during dental implant site preparation were undertaken at a number of sites on bovine mandibular cortical bone which had been stripped, sectioned and frozen into pieces measuring approximately 6 cm x 6 cm in size. Care was taken to select sites where the bone was as homogenous as possible and where the cortical bone layer was of a similar thickness for all drill sites. The implant site was prepared to correspond to the initial stages of the Branemark technique. A conventional dental handpiece was used with a motor provided by Nobelpharma (Harrow, UK). The sections of bovine mandibular bone were held by a simple apparatus on a normal working surface. Manufacturer specifications were followed during the implant site preparation, but no irrigation was employed. One operator performed all the drilling procedures. Thermal images were recorded using the Agema Thermovision 900 system (Agema Infra-red Systems, Danderyd, Sweden). This is a cryogenically cooled long wave scanner using a mercury cadmium telluride detector with a spectral response of S-12pm and a sensitivity of 0.08”C at physiological temperatures of around 30°C. Each lens, filter and measurement range combination has its own calibration function. The constants for these functions are stored in the
scanner, and the system automatically chooses the correct constants for the combination in operation. A rotational speed of 2500 rpm was used with a locating drill, a 2 mm twist drill and a 3 mm twist drill in sequence similar to the Branemark technique. The therm0 imaging camera with the integral macro lens was positioned 0.05 m from the area of interest. The entire drilling sequence was recorded at a highest storing speed of three images per second in 1Zbit format and analysed on screen at a later date without any loss of accuracy. The Thermovision 900 System is a real time system, and storage speed is dependent on hard disk space at a rate of three images per second. Maximum temperature change and the area of involvement were noted. The procedure was repeated for a number of drilling sequences. Care was taken to avoid using a drill site where an area of temperature change had been recorded with the result that the distance between adjacent drill sites was approximately 4 cm.
RESULTS The mean baseline temperature of the bovine bone was 2O.W with a variation of 0.5”C. The changes in temperature (AT’%) from baseline were 45.7”C, 79.o”C and 78.9”C for the round, spiral and pilot drills, respectively. The area of thermal involvement also illustrated a gradual increase in area for each drill. The round drill on average affected an area of 49.2 mm’, whereas the 2 mm spiral drill altered the surface temperature over a mean area of 140.1 mm2 and the 3 mm pilot drill affected an area of 273.0 mm’. The complete drill sequence time, including changing of drills was 75 s, therefore approximately 25 s per drill. Figure 1 is a thermogram of the round, locating drill in operation. Point A represents the bone/drill interface, and it was at this point that the maximum temperature for any drill within any sequence was recorded. For the 10 round locating drills used, the maximum temperatures ranged between 61.4”C and 102.1”C, with an average maximum temperature of 82.7”C. This represents an average temperature increase (ATC) over 10 drilling sequences, from a baseline temperature of 45.7”C. Point B represents the outer edge of the affected area. This was delineated and the affected area calculated. For the round locating drill, this ranged from 17.3 mm2 to 68.0 mm2 with a mean area of 49.2 mm2 over the 10 drilling sequences. A representation of the 2 mm spiral drill in operation is illustrated in Fig. 2. The maximum temperatures using the spiral (2 mm) drill ranged between 107S”C and 152.8”C, with an average temperature for the 10 drilling sequences of 13O.l”C. This represents an average AT”C over 10 drilling sequences from the baseline of 79.O”C. The area of involvement ranged from 42.4 mm2 to 231.0 mm2 with an average of 140.1 mm2 over the 10 drilling sequences.
Benington
et al.: Thermographic
Fig. I. Thermogram of round locating bur in operation. Focal distance was 0.05 m. Drill shank and head (Point A) are shown withdrawing from the drill site (Point 6). The yellow coloured area (Point C) corresponds to the drill debris with the surrounding corona (Point D) illustrating direct changes in surface bone temperature from baseline. For all thermographic images shown, the palette used a black colouration depicting cold (20°C or less) through a continuous blue, green, yellow, red and white spectrum of 112 hues. White illustrates the highest temperatures (40°C or more). When co/our saturation in either black or white was achieved, accuracy was not lost. The level and span of temperatures can be varied during and after storage of the images.
The final 3 mm pilot drill is illustrated in Fig. 3. The maximum temperatures using the pilot (3 mm) drill ranged between 104.5”C and 159.3”C with an average temperature for the 10 drilling sequences of 126.3”C. This represents an average AT”C over 10 drilling sequences from the baseline of 78YC. The area of involvement ranged from 75.3 mm* to 428.4 mm2 with an average of 273.0 mm’.
Fig. 2. Thermogram illustrating the 2 mm spiral drill in operation at a focal length of 0.05 m. The spiral thread of the drill is visible as a lighter helix (Point A). As in Fig. 1, the white area (Point B) within the yellow coloured area, (Point C) represents the area of maximal thermal emission which corresponds to the drill/bone interface. Note that Points C and D have increased in diameter as compared with Fig. 1.
Fig. drill drill (D) the
assessment
265
of implant site preparation
3. This represents the thermal radiance during the 3 mm pilot sequence. Reflectance of heat emissions can be seen on the thread point (A). Note the change in diameter of areas (C) and as compared to previous figures. The white area (B) illustrates large temperature increase observed at this point.
DISCUSSION The critical temperature generated during surgical preparation for implant placement is generally regarded to be in the region of 56°C since this is the temperature at which alkaline phosphatase is denatured. However, hard tissue injury has been shown in bone temperatures below this proposed critical leve17. Therefore, there is a need for verification of critical temperatures during bone drilling. Most studies have used thermocouples as their measurement device. However, the relationship between thermocouple voltage and temperature is sometimes non-linear. Also, those used in medicine have to show their optimum thermo-electric characteristics over the range of body temperatures, and this will limit the type available. In addition, they only give spot temperature measurements at adjacent sites, not the overall thermal profile. In contrast, thermoimaging using electronic infra-red scanners allowed the temperature increase, that occurred when drilling bone for a dental implant site preparation, to be recorded and
04
0
/
/
I
I
:
I
:I
5
10
15
20
25
30
35
40
I
/
45
50
I:
55
60
~,
65
70
75
seconds Fig. 4. This is an example plot for the temperature recordings with time during a drilling sequence. The three drill types can be clearly identified by their isolated profiles.
266
J. Dent. 1996; 24: No. 4 Tab/e 1. Results
for each of the ten drill sequences
Type of bur
Max
T”C
Mean AT% from baseline
Average area hm3
1
Round Spiral (2 mm) Pilot (3 mm)
61.4 108.4 114.6
24.1 65.9 75.0
26.1 61.4 112.2
2
Round Spiral (2 mm) Pilot (3 mm)
91.9 132.3 153.4
52.5 64.4 79.0
68.0 207.5 428.4
3
Round Spiral (2 mm) Pilot (3 mm)
102.1 140.3 104.5
45.2 80.1 57.8
60.2 231 .O 386.7
4
Round Spiral (2 mm) Pilot (3 mm)
72.1 128.3 113.5
57.7 83.3 80.5
66.8 213.7 400.0
5
Round Spiral (2 mm) Pilot (3 mm)
83.9 143.4 121.5
42.9 77.5 72.8
47.3 144.4 347.0
6
Round Spiral (2 mm) Pilot (3 mm)
93.9 138.5 127.4
47.4 88.4 92.5
62.7 161.4 321.6
7
Round Spiral (2 mm) Pilot (3 mm)
91.5 152.8 141.6
70.1 94.1 92.9
59.4 149.9 308.3
8
Round Spiral (2 mm) Pilot (3 mm)
69.5 107.5 159.3
28.0 65.1 90.3
17.3 42.4 75.3
9
Round Spiral (2 mm) Pilot (3 mm)
78.0 123.8 104.8
40.2 81.6 70.6
44.8 59.4 89.8
10
Round Spiral (2 mm) Pilot (3 mm)
82.7 125.7 122.4
49.3 78.9 77.3
39.8 129.6 260.4
Average baseline temperature =20.8”C Average time taken for each drill sequence =75 s. The maximum temperatures as indicated in column 2 were measurements recorded at the bone/drill interface. Column 3 shows the mean change in temperature from baseline and column 4, the average area affected by a change in temperature regardless of the degree of elevated temperature.
temperature of 140°C 0.5 mm from the drill site while using standard unirrigated orthopaedic twist drills. Indeed, of their 158 examinations, 37 showed temperatures of 100°C or more. Their mean maximum temperature was 93.1”C. Lavelle and Wedgwood* also noted high temperatures using thermocouples. They found that (without irrigation) temperatures of around 74°C were observed at a distance 0.5 mm from the round bur drill site and 83°C from a semielliptical bur site. These results compare favourably with our study where the
followed continuously throughout the drilling procedure. As well as allowing identification of the point of maximal temperature increase and the area of bone thermally affected, accurate measurements of the temperature may be carried out, stored and retrieved without any loss of accuracy. The published results of other researchers, using thermocouples without irrigation, compared very favourably with those observed using infra-red thermography. Matthews et al.’ illustrated a maximum Tab/e II. Average maximal temperatures area of thermographic involvement during
(Max T”C), each drilling Max
Average
Round Spiral (2 mm) Pilot (3 mm)
T”C
82.7 130.1 126.3
increase sequence AT% 45.7 79.0 78.9
in temperature
(A TX)
Area
(mm’)
49.2 140.1 273.0
and
Benington et a/.: Thermographic assessment
average temperatures recorded for the round bur, 2 mm spiral bur and 3 mm pilot bur were 82.7”C, 13O.l”C and 126.3”C, respectively. The point of note is that these latter measurements were obtained non-invasively. Surface contact may be a source of error in measurements using thermocouples since all thermocouples must make contact with the surface, not necessarily in the correct plane, and therefore may alter the localised surface temperature. The temperatures measured, while irrigation is employed, vary, although the variation seems to depend more on the load and drill design rather than on the irrigant employed. Lavelle and Wedgwood’ showed differences with external and internal irrigation systems. However, temperatures of up to 72°C have been recorded using thermocouples for different irrigation systems during implant site preparation6. No irrigation was employed for several reasons during this preliminary investigation. Firstly, as the application of electronic infra-red thermography was a novel technique to implantology, it was necessary to achieve the absolute baseline values. In addition, water is opaque to infra-red radiation, and was therefore an unnecessary source of error at this preliminary level.
CONCLUSIONS In conclusion, electronic infra-red thermography is a viable technique to be employed in implantology research. Temperatures measured by thermography when compared to those reported for thermocouple systems
of implant site preparation
267
were similar. The two main advantages of thermography are that it is a non-invasive technique giving absolute temperature measurement, and allows the researcher to visualise, in a two-dimensional manner, the entire drilling sequence area.
References 1. Albrektsson T, Branemark P-I, Hansson H-A and Lindstrogm J. Osseointegrated titanium implants: Requirements for ensuring a long-lasting, direct bone-to-implant anchorage in man. Acta Orthop Stand 1981; 52: 155-170. 2. Eriksson AR and Albrektsson T. Temperature threshold levels for heat-induced bone tissue injury: A vital microscopic study in the rabbit. JProsthet Dent 1983; 50: 101-107. 3. Matthews LS and Hirsch C. Temperatures measured in human cortical bone when drilling. .I Bone Joint Sung Am 1972; 54: 297-308. 4. Jo H, Olin P and Schachtele C. Temperature changes in bone during dental implant site preparation. J Dent Res
1993; 72: 389. 5. Eriksson AR, Albrektsson T and Albrektsson B. Heat
caused by drilling cortical bone: Temperature measured in vivo in patients and animals. Acta Orthop Stand 1984; 55: 629-631. 6. Sutter F, Krekeler G, Schwammberger AE and Sutter FJ. Atraumatic surgical technique and implant bed preparation. Quintessence Znt 1992;23: 811-816. 7. Lundskog J. Heat and bone tissue. An experimental investigation of the thermal properties of bone tissue and threshold levels for thermal injury. Thesis, GGteborg: University of Giiteborg, 1972. 8. Lavelle C, Wedgwood D. Effect of internal irrigation on frictional heat generated from bone drilling. J Oral Surg 1980; 38: 499-503