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Evaluation of tensile bond strength of glass ionomer cements for orthodontic bonding
American Journal of Orthodontics and Dentofacial Orthopedics Volume 103, No. 6
regions for all healing times. Significantly higher amounts of woven hit, lamellar hit, and lamellar bone near the implant were also in the coronal region for all healing times. There was a trend toward more total bone contacting the implant in the coronal region with time. Torquing forces used to displace left side implants were significantly higher in the 12 week compared with the 4-week group, (1.74 k g - c m - 0.51) versus (1.08 kgcm --. 0.19). An overall trend was noted with increasing torque values measured as a function of time. The majority of the osseous healing response at the endosseous implant interfaces and a trend of bzcreasing bone to implant contact with time occurred hz the coronal implant region, hzcreashzg torque forces nzeasured as a function of time suggests an hzcrease hz "osseohztegration" with time. This study was supported . by N I D R Grant DE09237 01.
Quantification of pain thresholds in orthodontic patients using strain gage techniques. J.W. Cordero and K. E. Simmons, Indianapolis: hzdiana University School of Dentistry 1992 It is generally believed that pain is fairly common during the initial phase of orthodontic treatment and following regular arch wire adjustments. The purpose of this study was to assess the suitability of a pain model that uses the application of force between teeth as the noxious stimulus. Also, the time course of pain threshold alterations in patients subjected to orthodontic treatment was explored. A simple pressure algometer using strain gages was produced to apply and to measure the force required to reach the pain threshold of incisor teeth (centrallateral pairs) for 3 consecutive days. Fifteen orthodontic patients were used (9 females, 6 males) with incisors in good alignment and with interproximal contact. Each patient was used for both control and experimental measurements in each arch. Baseline pain threshold measurements were taken on the first day, and individual orthodontic springs placed on the experimental side. The control side was the adjacent central-lateral incisor pair on the other side of the arch where no spring was placed. Additional measurements were taken the second and third days in each quadrant. Significantly lower pain threshold levels were observed a day after the initial spring activation followed by an increase in the pain threshold the second day after spring activation. In the mandibular arch, the treatment by day interaction was significant, with the experimental side pain threshold substantially lower than control on the second and third days. There was a tendency for lower pain sensitivity in males for both arches. The present model was shown to be suitable to study pain thresholds associated with orthodontic forces, and the pressure algometer was able to quantify pahz threshold with objective measurements. The model could be used clinically to screen patients with low pretreatment pain thresholds so modifications of treatment me-
R e v i e w s and Abstracts
571
chanics or pharmacologic means could be used to allay patient pain. This study was funded by Indiana University School of Dentistry Faculty Research Fund #90-29.
Evaluation of tensile bond strength of glass ionomer cements for orthodontic bonding. FI. Sprayberry, Indianapolis: Indiana University School of Dentist~ 1992 Glass ionomer cements offer advantages over conventional composite resins when used for orthodontic bonding. These include chemical bonding to enamel, fluoride release, and ease of removal from enamel on debonding. This study evaluated the tensile bond strengths of three type I and three Type II glass ionomer cements when used to bond siainless steel orthodontic brackets to teeth. Bovine incisors were divided into six groups of 20 each. Each group had brackets bonded with one of the following glass iofiomer cements: SHOFU Glasionomer Type I (SG1), Fuji I (F1), Ketac-cem (KC), SHOFU Glasionomer Type II (SG2), Fuji II (F2), and Ketae-fil (KF). A new regimen of specimen preparation was used to align the brackets so that truer tensile forces could be generated at testing. Special attention was given to creating a system that would not allow any change in angulation of force when specimens were debonded. Specimens were stored in room temperature water for 2 weeks, thermocycled, returned to water storage for 2 additional weeks, and then tested for tensile bond failure on an Instron Testing Machine. The type of bond failure was assessed by light microscopic analysis of the debonded bracket bases. The finite element method was used to further evaluate the interface with varying angulation of force application at debonding. The mean tensile bond strength value of 0.82 --- 0.36 MPa for SG1 was significantly less (p < 0.05) than the values of 1.13 • 0.33 MPa for KC and 1.26 --- 0.40 MPa for FI. For the Type II glass ionomer cements, the mean tensile bond strengths of 2.00 • 0.28 MPa for KF and 1 . 9 7 - 0.29 MPa for F2 were significantly greater (p < 0.05) than the 0.95 "4- 0.35 MPa for SG2. The KF and F2 cements developed bond strengths which were significantly greater (p < 0.0001) than the Type I cements. Light micr0gcopic analysis of bond failure revealed a high degree of within group variability. As a result, trends relating failure mode to tensile bond strength could not be established. The finite clement method study showed that even a slight alteration in angulation of the force applied to the bracket greatly affected the maximum principal stress developed in the adhesive layer. An increase in maximum principal stress of - 1000 MPa was seen when a true tensile debonding force (0 ~ offset) wad adjusted to 12~ of offset. The results of this study hzdicate that Tkpe H glass iolwmers have potential for clinical orthodontic use attd that special atten-
572
Reviews and Abstracts
tion should be given to the angulation of force applied to brackets br laboratory bondhzg studies. This study was supported by an IUSD Biomedical Research Support Grant. Analysis of bone remodeling in the mandibular condyle of female retired-breeder rabbits following altered loading. J. T. Hunt, hzdianapolis: hMiana Universi~, School of Dentisto~ 1992 Previous studies have associated increased occlusal loads with degenerative changes of the temporomandibular joint (TMJ). The purpose of this study was to analyze the effects of increased occlusal loads in adult animals. Twelve female retired-breeder rabbits (mean age = 3 years, 1 month) were divided equally into 3 experimental groups and 1 control group. Each of the experimental rabbits received light-cured acrylic anterior splints at the beginning of the study to create a bilateral posterior openbite. Theoretically, this should have resulted in increased loads to the TMJ. The first two groups wore the appliances for 6 and 12 weeks before euthanasia. The third group wore the appliances for 12 weeks and then had them removed for 12 weeks before euthanasia. Fluorescent bone labels were used, and the specimens were analyzed histomorphometrically. The cartilage thickness was not statistically different between groups, nor were there any signs of cartilage degeneration. There was a trend, however, toward thinner condylar cartilage in the 12-week group. The 6-week group showed significantly less labeled subchondral bone than the control group (0.5 • 0.1% versus 2.6 • 0.3%, respectively; p < 0.05). The 6- and 12-week groups both revealed significantly less pcriosteal surface label of the condylar neck than the control group (1.5 - 0.8% and 5.3 --- 1.7% versus 22.0 --. 3.5%, respectively; p < 0.05). Likewise, they both showed significantly more label at the cartilage-bone interface (1.0 • 0.2% and 1.4 • 0.2% versus 0.4 • 0.2%, respectively; p < 0.05) and moderately more label along the trabecular surfaces than the control group. These results indicated that increased loading of the mandibular condyle initially (at 6 weeks) depressed remodeling of the subchondral bone and decreased periosteal bone formation. Modeling increased at the cartilage-bone interface and potentially along the trabecular bone surfaces. With continued elevated occlusal loads (at 12 weeks), modeling still was quite active at the cartilagebone interface and on the trabecular surfaces. Pcriosteal surface modeling remained depressed compared with'the control group, but remodeling in the subchondral bone region increased to that of the control group. The 12/12week group tended to show findings similar to the control group. This suggests that once loading was returned to normal, the condyle also returned toward preexperimental physiologic conditions. Although this sludy did not show the obvious degenerative changes typically equated with osteoarthrosis, the elevated modeling at the cartilage-bone brterface following
American Journal of Orthodontics and Dentofacial Orthopedics June 1993
increased joint loads was consistet,t with tlre earl), degenerative changes obsen'ed by Radhr et aL hr their jobrt-loadhrg model. However, the rapid osseous changes seen #r this study refirte the theory that the adult TMJ is unable to adapt to altered fttnctional Ioadh~g. This study was supported by an IUSD Biomedical Research Support Grant.
Histological and mechanical analysis of bone/implant interface in female retired-breeder rabbits. C . G . Bruch, hzdianapo/is: Indiana University School of Dentistt); 1992 Endosseous implants are now being used for multiple dental applications. The majority are placed in elderly patients. As such, the increased use of implants has raised questions about bone healing and metabolism associated with their placement. This study evaluated the mechanical and histologic aspects of the bone/metal interface of titanium implants placed in the femurs of 12 older (3 year old) female rabbits. Implants (Exp.) were placed in the distal metaphysis (M), and the diaphysis (D) of the left femurs. Right side limbs were sham operated and served as controls (Cont.). Rabbits were sacrificed at 6 (n = 1), 12 (n = 4), and 24 (n = 2) weeks of healing time. Multiple fluorochrome labels were given to mark sites of new bone formation. Microradiography and epifluorscent light microscopy were used to determine percent mineralized (MT) and unmineralized tissue (UT), bone/implant interface characteristics, and percent labeled bone volume (LV) and surface area (IS). D implants required about 20% more torque to mechanically disrupt the interface than the M implants. Values were as follows: M (combined groups) 33.4 N-cm ___ 15.5 and D (combined groups) 41.5 N-cm __. 16.0 (Mean __. SD, p < 0.07). Percent direct bone/implant contact increased only slightly with time as follows: M 11.2%, 9.5% --- 8.5%, and 13.9% _ 6.6%; and, D 11.7%, 10.2% .4- 2.4%, and 19.5% --- 0.35% for 6-, 12-, and 24-week specimens, respectively (Mean • SD). MT volume in D implanted specimens was less than control: Exp. = 91.1%--- 3.1%, Cont. = 95.5% _ 0.73% (Mean • SD),,and UT: Exp. 8.9% • 3.02%, Cont. = 4.6% • 0.73% (Mean • SD), more than in controls (p < 0.02). Implanted D specimens showed greater I S than controls, Exp. 62.1% • 12.7%, Cont. 30.2%--15.4% (Mean --- SD, p < 0.001). This difference decreased with time. PLV was significantly greater in implanted specimens than controls (p < 0.001). LV showed a difference with time between 6- and 12-week implanted specimens, 6 weeks-M = 24.6%, D = 21.2%, 24 weeksM = I1.1%, D = 9.6% (Mean • SD, p < 0.05). These data hrdicate that when flnplants were placed hr older rabbits, hractive bone became very active. They also suggest that bone qualit); trot quantity is responsible for hrterface strength. Supported by IUSD Research Committee and NIDR Grant DE 09237-01.
regions for all healing times. Significantly higher amounts of woven hit, lamellar hit, and lamellar bone near the implant were also in the coronal region for all healing times. There was a trend toward more total bone contacting the implant in the coronal region with time. Torquing forces used to displace left side implants were significantly higher in the 12 week compared with the 4-week group, (1.74 k g - c m - 0.51) versus (1.08 kgcm --. 0.19). An overall trend was noted with increasing torque values measured as a function of time. The majority of the osseous healing response at the endosseous implant interfaces and a trend of bzcreasing bone to implant contact with time occurred hz the coronal implant region, hzcreashzg torque forces nzeasured as a function of time suggests an hzcrease hz "osseohztegration" with time. This study was supported . by N I D R Grant DE09237 01.
Quantification of pain thresholds in orthodontic patients using strain gage techniques. J.W. Cordero and K. E. Simmons, Indianapolis: hzdiana University School of Dentistry 1992 It is generally believed that pain is fairly common during the initial phase of orthodontic treatment and following regular arch wire adjustments. The purpose of this study was to assess the suitability of a pain model that uses the application of force between teeth as the noxious stimulus. Also, the time course of pain threshold alterations in patients subjected to orthodontic treatment was explored. A simple pressure algometer using strain gages was produced to apply and to measure the force required to reach the pain threshold of incisor teeth (centrallateral pairs) for 3 consecutive days. Fifteen orthodontic patients were used (9 females, 6 males) with incisors in good alignment and with interproximal contact. Each patient was used for both control and experimental measurements in each arch. Baseline pain threshold measurements were taken on the first day, and individual orthodontic springs placed on the experimental side. The control side was the adjacent central-lateral incisor pair on the other side of the arch where no spring was placed. Additional measurements were taken the second and third days in each quadrant. Significantly lower pain threshold levels were observed a day after the initial spring activation followed by an increase in the pain threshold the second day after spring activation. In the mandibular arch, the treatment by day interaction was significant, with the experimental side pain threshold substantially lower than control on the second and third days. There was a tendency for lower pain sensitivity in males for both arches. The present model was shown to be suitable to study pain thresholds associated with orthodontic forces, and the pressure algometer was able to quantify pahz threshold with objective measurements. The model could be used clinically to screen patients with low pretreatment pain thresholds so modifications of treatment me-
R e v i e w s and Abstracts
571
chanics or pharmacologic means could be used to allay patient pain. This study was funded by Indiana University School of Dentistry Faculty Research Fund #90-29.
Evaluation of tensile bond strength of glass ionomer cements for orthodontic bonding. FI. Sprayberry, Indianapolis: Indiana University School of Dentist~ 1992 Glass ionomer cements offer advantages over conventional composite resins when used for orthodontic bonding. These include chemical bonding to enamel, fluoride release, and ease of removal from enamel on debonding. This study evaluated the tensile bond strengths of three type I and three Type II glass ionomer cements when used to bond siainless steel orthodontic brackets to teeth. Bovine incisors were divided into six groups of 20 each. Each group had brackets bonded with one of the following glass iofiomer cements: SHOFU Glasionomer Type I (SG1), Fuji I (F1), Ketac-cem (KC), SHOFU Glasionomer Type II (SG2), Fuji II (F2), and Ketae-fil (KF). A new regimen of specimen preparation was used to align the brackets so that truer tensile forces could be generated at testing. Special attention was given to creating a system that would not allow any change in angulation of force when specimens were debonded. Specimens were stored in room temperature water for 2 weeks, thermocycled, returned to water storage for 2 additional weeks, and then tested for tensile bond failure on an Instron Testing Machine. The type of bond failure was assessed by light microscopic analysis of the debonded bracket bases. The finite element method was used to further evaluate the interface with varying angulation of force application at debonding. The mean tensile bond strength value of 0.82 --- 0.36 MPa for SG1 was significantly less (p < 0.05) than the values of 1.13 • 0.33 MPa for KC and 1.26 --- 0.40 MPa for FI. For the Type II glass ionomer cements, the mean tensile bond strengths of 2.00 • 0.28 MPa for KF and 1 . 9 7 - 0.29 MPa for F2 were significantly greater (p < 0.05) than the 0.95 "4- 0.35 MPa for SG2. The KF and F2 cements developed bond strengths which were significantly greater (p < 0.0001) than the Type I cements. Light micr0gcopic analysis of bond failure revealed a high degree of within group variability. As a result, trends relating failure mode to tensile bond strength could not be established. The finite clement method study showed that even a slight alteration in angulation of the force applied to the bracket greatly affected the maximum principal stress developed in the adhesive layer. An increase in maximum principal stress of - 1000 MPa was seen when a true tensile debonding force (0 ~ offset) wad adjusted to 12~ of offset. The results of this study hzdicate that Tkpe H glass iolwmers have potential for clinical orthodontic use attd that special atten-
572
Reviews and Abstracts
tion should be given to the angulation of force applied to brackets br laboratory bondhzg studies. This study was supported by an IUSD Biomedical Research Support Grant. Analysis of bone remodeling in the mandibular condyle of female retired-breeder rabbits following altered loading. J. T. Hunt, hzdianapolis: hMiana Universi~, School of Dentisto~ 1992 Previous studies have associated increased occlusal loads with degenerative changes of the temporomandibular joint (TMJ). The purpose of this study was to analyze the effects of increased occlusal loads in adult animals. Twelve female retired-breeder rabbits (mean age = 3 years, 1 month) were divided equally into 3 experimental groups and 1 control group. Each of the experimental rabbits received light-cured acrylic anterior splints at the beginning of the study to create a bilateral posterior openbite. Theoretically, this should have resulted in increased loads to the TMJ. The first two groups wore the appliances for 6 and 12 weeks before euthanasia. The third group wore the appliances for 12 weeks and then had them removed for 12 weeks before euthanasia. Fluorescent bone labels were used, and the specimens were analyzed histomorphometrically. The cartilage thickness was not statistically different between groups, nor were there any signs of cartilage degeneration. There was a trend, however, toward thinner condylar cartilage in the 12-week group. The 6-week group showed significantly less labeled subchondral bone than the control group (0.5 • 0.1% versus 2.6 • 0.3%, respectively; p < 0.05). The 6- and 12-week groups both revealed significantly less pcriosteal surface label of the condylar neck than the control group (1.5 - 0.8% and 5.3 --- 1.7% versus 22.0 --. 3.5%, respectively; p < 0.05). Likewise, they both showed significantly more label at the cartilage-bone interface (1.0 • 0.2% and 1.4 • 0.2% versus 0.4 • 0.2%, respectively; p < 0.05) and moderately more label along the trabecular surfaces than the control group. These results indicated that increased loading of the mandibular condyle initially (at 6 weeks) depressed remodeling of the subchondral bone and decreased periosteal bone formation. Modeling increased at the cartilage-bone interface and potentially along the trabecular bone surfaces. With continued elevated occlusal loads (at 12 weeks), modeling still was quite active at the cartilagebone interface and on the trabecular surfaces. Pcriosteal surface modeling remained depressed compared with'the control group, but remodeling in the subchondral bone region increased to that of the control group. The 12/12week group tended to show findings similar to the control group. This suggests that once loading was returned to normal, the condyle also returned toward preexperimental physiologic conditions. Although this sludy did not show the obvious degenerative changes typically equated with osteoarthrosis, the elevated modeling at the cartilage-bone brterface following
American Journal of Orthodontics and Dentofacial Orthopedics June 1993
increased joint loads was consistet,t with tlre earl), degenerative changes obsen'ed by Radhr et aL hr their jobrt-loadhrg model. However, the rapid osseous changes seen #r this study refirte the theory that the adult TMJ is unable to adapt to altered fttnctional Ioadh~g. This study was supported by an IUSD Biomedical Research Support Grant.
Histological and mechanical analysis of bone/implant interface in female retired-breeder rabbits. C . G . Bruch, hzdianapo/is: Indiana University School of Dentistt); 1992 Endosseous implants are now being used for multiple dental applications. The majority are placed in elderly patients. As such, the increased use of implants has raised questions about bone healing and metabolism associated with their placement. This study evaluated the mechanical and histologic aspects of the bone/metal interface of titanium implants placed in the femurs of 12 older (3 year old) female rabbits. Implants (Exp.) were placed in the distal metaphysis (M), and the diaphysis (D) of the left femurs. Right side limbs were sham operated and served as controls (Cont.). Rabbits were sacrificed at 6 (n = 1), 12 (n = 4), and 24 (n = 2) weeks of healing time. Multiple fluorochrome labels were given to mark sites of new bone formation. Microradiography and epifluorscent light microscopy were used to determine percent mineralized (MT) and unmineralized tissue (UT), bone/implant interface characteristics, and percent labeled bone volume (LV) and surface area (IS). D implants required about 20% more torque to mechanically disrupt the interface than the M implants. Values were as follows: M (combined groups) 33.4 N-cm ___ 15.5 and D (combined groups) 41.5 N-cm __. 16.0 (Mean __. SD, p < 0.07). Percent direct bone/implant contact increased only slightly with time as follows: M 11.2%, 9.5% --- 8.5%, and 13.9% _ 6.6%; and, D 11.7%, 10.2% .4- 2.4%, and 19.5% --- 0.35% for 6-, 12-, and 24-week specimens, respectively (Mean • SD). MT volume in D implanted specimens was less than control: Exp. = 91.1%--- 3.1%, Cont. = 95.5% _ 0.73% (Mean • SD),,and UT: Exp. 8.9% • 3.02%, Cont. = 4.6% • 0.73% (Mean • SD), more than in controls (p < 0.02). Implanted D specimens showed greater I S than controls, Exp. 62.1% • 12.7%, Cont. 30.2%--15.4% (Mean --- SD, p < 0.001). This difference decreased with time. PLV was significantly greater in implanted specimens than controls (p < 0.001). LV showed a difference with time between 6- and 12-week implanted specimens, 6 weeks-M = 24.6%, D = 21.2%, 24 weeksM = I1.1%, D = 9.6% (Mean • SD, p < 0.05). These data hrdicate that when flnplants were placed hr older rabbits, hractive bone became very active. They also suggest that bone qualit); trot quantity is responsible for hrterface strength. Supported by IUSD Research Committee and NIDR Grant DE 09237-01.