- Email: [email protected]
Cone-beam computed tomography
HANDS ON ART Therapy Adjunctive cavity disinfection Background.—The Atraumatic Restorative Treatment (ART) approach was developed to enable practitioners in countries with limited oral health care systems to provide preventive and restorative dental care. It has also been shown to be cost-effective compared to traditional methods using amalgam and provides durable single-surface restorations in primary and permanent posterior teeth. Egypt has a particularly high prevalence and severity of dental caries among its younger population. The high number of caries is attributed to poor oral hygiene, minimal preventive care, financial barriers to the provision and receipt of care, poorly distributed oral healthcare personnel and dental equipment, and fear of the traditional restorative approaches. The ART approach was introduced in Egypt but because of resistance among dentists to the idea of leaving affected dentin in place when doing cavity cleaning, chlorhexidine rinsing of the cleansed cavity was added. A survey of adolescents was carried out, noting the survival of ART restorations with and without cavity disinfection after 5 years. Methods.—The 90 14- and 15-year-old students were divided into those receiving cavity disinfection with ARTrestorations and those not. The results were assessed using replica models after 1 and 5 years according to the ART criteria. Differences between the disinfected and nondisinfected restorations were categorized by gender, mean decayed/missing/filled teeth (DMFT) score at baseline, cavity size, and cavity type. Results.—After 1 year and 5 years, respectively, three and nine restorations failed. The percentage of survival for the disinfected ART restorations was 85%, compared
to 80% for the non-disinfected restorations. Over the 5-year evaluation period, these differences were not statistically significant. The percentage of survival was significantly higher for boys than for girls but no other factors differed between the two groups. Discussion.—The rate of survival for the ART restorations after 5 years was high at 80% to 85%. Disinfection with 2% chlorhexidine solution produced no significant effect on the survival of ART restorations for these adolescent patients, making it an unnecessary addition to the ART approach.
Clinical Significance.—Other Middle-Eastern countries have demonstrated good results with the ART approach, and Egypt proved to be no exception. Using the chlorhexidine cleansing was a compromise to help Egyptian dentists accept the modern concept of minimal intervention dentistry. It was shown to be unnecessary to reduce the bacterial load and increase the survival data for the dental restorations. Further use of replica models to provide a continuing evaluation of ART restorations will provide more evidence of effectiveness.
Farag A, van der Sanden WJM, Abdelwahab H, et al: 5-year survival of ART restorations with and without cavity disinfection. J Dent 37:468-474, 2009 Reprints available from JE Frencken; fax: þ31 24 354 0265; e-mail: [email protected]
Dental Imaging Cone-beam computed tomography Background.—Three-dimensional imaging of the teeth and jaws can be accomplished using cone-beam computed tomography (CBCT) (Fig 1). Although new to the
292
Dental Abstracts
field, this technology is becoming widely available and can be used for implant dentistry, endodontics, and oral surgery. The differences between conventional computed
CBCT is, however, not as well suited as CT for examining lesions involving both soft tissue and bone, because it is difficult to obtain good soft tissue detail. Dental Considerations.—CBCT technology has become widely available and costs less than CT scanners. The CBCT machines are available in many different formats and with various attributes. The footprint of the machine is comparable to that of a panoramic unit.
Fig 1.—An Accuitomo F170 (Morita Corp, Kyoto, Japan), a CBCT scanner with a variable FOV. (Courtesy of Dawood A, Patel S, Brown J: Cone beam CT in dental practice. Br Dent J 207:23-28, 2009.)
tomography (CT) and CBCT and their dental applications were examined. Conventional CT.—CT provides three-dimensional imaging through scans that are taken of the patient and are digitally processed to generate image data. CT gathers data using rows of detectors; the slices of these data are then stacked to produce a three-dimensional result (Fig 2). The current multislice technology permits rapid acquisition of large volumes of data. However, the x-ray dose is high, the equipment is quite expensive, and machine availability is generally limited to hospitals only. CBCT.—CBCT is a low-dose scanning system designed specifically for three-dimensional imaging of the maxillofacial skeleton. Most systems have scan times of less than 20 seconds, and use personal computers as data processors. CBCT exposes the entire section of the patient, using one detector and then uses the data to generate individual slice images (Fig 3). The most complex aspects of CBCT systems are the detector and the data processing capabilities. These systems are considerably less sophisticated in terms of hardware and software than CT systems, but produce comparable or better images of hard tissue structures of the jaws and skull. Also, the x-ray dose is much lower with CBCT systems.
Scanners can have a field of view (FOV) ranging from the entire skull to just a few teeth, with the x-ray dose increasing or decreasing depending on the volume exposed and the resolution. FOV is adjusted to limit radiation exposure to the area of interest. Digital files of data will increase with higher image resolution and a larger FOV, making storage space and security an issue. The ability to control the FOV and resolving power are important considerations in choosing a CBCT scanner. Along with greater FOV, greater resolution entails a higher radiation dose. It may be possible to achieve the objectives of an examination using a lower resolution setting or reduced exposure parameters, thus limiting the radiation dose. High-resolution scans are recommended for small FOV uses only. Occupational exposure to radiation is generally not an issue if the equipment is properly installed. CBCT units can have greater power and x-ray scatter than conventional radiographic units. Applying the principle used to obtain conventional x-rays safely, the operator should stand at least 8 m from a CBCT machine during patient exposures. It is important to note that the biological effect of a beam varies with the patient’s age and gender as well as the radiosensitivity of the exposed tissue. Factors influencing the appearance of the data obtained through CBCT include overall exposure parameters, efficiency of the detector, and the reconstruction. The best slice thickness for three-dimensional modeling seems to be <0.5 mm. Viewing the data on-screen is the optimal mode, and software and hardware for computer processing are considered essential components of the system. The software allows the scan data to be reconstructed in three orthogonal planes and often along a curved plane to yield a ‘‘panoramic’’ reconstruction. The area of interest can be emphasized by changing the window and level. The viewing software chosen should be based on what the dental practice will use most, including the ability to view results on various workstations and in more than one location. It should also allow exporting to third-party software to facilitate implant, maxillofacial, and orthodontic treatment planning. The results of a CBCT are required by law to be fully evaluated. Dentists are qualified to adequately evaluate
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2009
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Fig 2.—The benefits of three-dimensional imaging. A, An intraoral radiograph of an asymptomatic central incisor fails to show the true nature of the extensive lesion compared with re-sliced CBCT images: B, coronal; C, sagittal; and D, axial. (Courtesy of Dawood A, Patel S, Brown J: Cone beam CT in dental practice. Br Dent J 207:23-28, 2009.)
Fig 3.—Source and opposing flat panel detector rotating around the patient’s jaw, capturing image data in one sweep. (Courtesy of Dawood A, Patel S, Brown J: Cone beam CT in dental practice. Br Dent J 207:23-28, 2009.)
294
Dental Abstracts
the clinical findings on CBCT images of the immediate dentoalveolar region. Should a wider FOV be chosen, capturing the skull base, sinuses, and cervical spine, a full report may require the input of a dentomaxillofacial or head and neck radiologist. All CBCT operators must be adequately trained, including the referrer, generally the dentist who prescribes or requests the CT; the IRMER practitioner, who will justify the exposure by selecting appropriate cases, understanding the risks to the patient, being aware of the likely yield of the examination, and knowing how to manipulate and interpret the resulting imaging data to obtain the needed diagnostic information; and the operator, who obtains the radiograph safely, accurately, and with maximum dose optimization for the diagnostic application. Included in the training are how to use the specific machine, radiation hazards, imaging pitfalls, selection criteria, and interpretation of cross-sectional and three-dimensional images.
Clinical Significance.—When conventional two-dimensional imaging is insufficient, or access to technological processes such as guided surgery will improve patient management, it is appropriate to consider CBCT technology. CBCT scanners are simpler, more compact, and less expensive than conventional CT machines and produce images that are at least as good. The goal for any imaging system should be to obtain the best and most accurate diagnostic and treatment possibilities for the patient while minimizing radiation exposure or other harm. It is best to have everyone on the dental team trained in CBCT and the technologies related to it.
Dawood A, Patel S, Brown J: Cone beam CT in dental practice. Br Dent J 207:23-28, 2009 Reprints available from A Dawood, Dawood & Tanner Dental Practice, 45 Wimpole St, London, W1G 8SB UK; e-mail: [email protected]
Dental Materials Self-etching adhesive bond strengths Background.—Modern dentin bonding systems are based on creation of a hybrid resin–reinforced layer for dentin adhesion. The dentin layer is partially demineralized to expose collagen fibrils, and the adhesive monomers are infiltrated in and around the remaining collagen and mineral. To support the collagen fibers, moisture is needed on the dentin surface. With bonded restorations, achieving the correct dentin moisture content relies on clinical judgment and is an unreliable process. The laboratory bond strengths that are achieved with moist bonding, using the current etch-and-rinse hydrophilic bonding systems, range from 17 to 24 MPa, with corresponding clinical success. The self-etching adhesive systems offer a simpler technique, with fewer steps and no need for clinically judging the dentin moisture level. These systems condition, demineralize, and infiltrate both enamel and dentin at the same time. However, their hydrolytic stability has been questioned, as has their lower immediate enamel bond strength and long-term consistency of the enamel bond. Enamel marginal breakdown of restorations placed with these adhesives is a danger. Bond strength testing can help dentists understand and predict the clinical behavior of the various adhesive systems. We compared the shear bond strengths of 10 current self-etching adhesive systems to dentin and enamel. Methods.—A 600-grit silicon carbide paper was used to expose the dentin or enamel of flat bonding sites on 216 extracted human molars. The adhesive systems were applied,
with 24 bonded assemblies of Spectrum TPH prepared. These samples were stored in water at 37 C for 24 hours. Twelve specimens of each enamel and dentin group were debonded, and subjected to alternating thermocycling and water baths. The specimens were then loaded to failure in a testing machine. Results.—The mean shear bond strength values to enamel (Table 1) and dentin (Table 2) were measured for
Table 1.—Mean Shear Bond Strengths of Self-Etching Adhesives to Enamel (MPa) Product
MPa
24.0 4.3a 23.6 3.9a,b 23.2 4.1a,b 22.3 5.8a,b 21.4 4.2a,b,c 21.3 1.9a,b,c 20.0 3.1b,c 18.4 4.8c 17.8 2.9c,d 11.8 2.9d
Clearfil S3 Xeno V AdheSE One Clearfil SE Bond iBond SE Xeno IV Optibond All-in-One Adper Prompt L-Pop G-Bond iBond
Groups designated by a common symbol were statistically similar at a confidence level of 95%. (Reprinted with permission from General Dentistry, May/June 2009. On the Web at www.agd.org. ª Academy of General Dentistry. All rights reserved. Foster Printing Service: 866-879-9144, www.marketingreprints.com. License # GD-6188-MES)
Volume 54
Issue 6
2009
295
to 80% for the non-disinfected restorations. Over the 5-year evaluation period, these differences were not statistically significant. The percentage of survival was significantly higher for boys than for girls but no other factors differed between the two groups. Discussion.—The rate of survival for the ART restorations after 5 years was high at 80% to 85%. Disinfection with 2% chlorhexidine solution produced no significant effect on the survival of ART restorations for these adolescent patients, making it an unnecessary addition to the ART approach.
Clinical Significance.—Other Middle-Eastern countries have demonstrated good results with the ART approach, and Egypt proved to be no exception. Using the chlorhexidine cleansing was a compromise to help Egyptian dentists accept the modern concept of minimal intervention dentistry. It was shown to be unnecessary to reduce the bacterial load and increase the survival data for the dental restorations. Further use of replica models to provide a continuing evaluation of ART restorations will provide more evidence of effectiveness.
Farag A, van der Sanden WJM, Abdelwahab H, et al: 5-year survival of ART restorations with and without cavity disinfection. J Dent 37:468-474, 2009 Reprints available from JE Frencken; fax: þ31 24 354 0265; e-mail: [email protected]
Dental Imaging Cone-beam computed tomography Background.—Three-dimensional imaging of the teeth and jaws can be accomplished using cone-beam computed tomography (CBCT) (Fig 1). Although new to the
292
Dental Abstracts
field, this technology is becoming widely available and can be used for implant dentistry, endodontics, and oral surgery. The differences between conventional computed
CBCT is, however, not as well suited as CT for examining lesions involving both soft tissue and bone, because it is difficult to obtain good soft tissue detail. Dental Considerations.—CBCT technology has become widely available and costs less than CT scanners. The CBCT machines are available in many different formats and with various attributes. The footprint of the machine is comparable to that of a panoramic unit.
Fig 1.—An Accuitomo F170 (Morita Corp, Kyoto, Japan), a CBCT scanner with a variable FOV. (Courtesy of Dawood A, Patel S, Brown J: Cone beam CT in dental practice. Br Dent J 207:23-28, 2009.)
tomography (CT) and CBCT and their dental applications were examined. Conventional CT.—CT provides three-dimensional imaging through scans that are taken of the patient and are digitally processed to generate image data. CT gathers data using rows of detectors; the slices of these data are then stacked to produce a three-dimensional result (Fig 2). The current multislice technology permits rapid acquisition of large volumes of data. However, the x-ray dose is high, the equipment is quite expensive, and machine availability is generally limited to hospitals only. CBCT.—CBCT is a low-dose scanning system designed specifically for three-dimensional imaging of the maxillofacial skeleton. Most systems have scan times of less than 20 seconds, and use personal computers as data processors. CBCT exposes the entire section of the patient, using one detector and then uses the data to generate individual slice images (Fig 3). The most complex aspects of CBCT systems are the detector and the data processing capabilities. These systems are considerably less sophisticated in terms of hardware and software than CT systems, but produce comparable or better images of hard tissue structures of the jaws and skull. Also, the x-ray dose is much lower with CBCT systems.
Scanners can have a field of view (FOV) ranging from the entire skull to just a few teeth, with the x-ray dose increasing or decreasing depending on the volume exposed and the resolution. FOV is adjusted to limit radiation exposure to the area of interest. Digital files of data will increase with higher image resolution and a larger FOV, making storage space and security an issue. The ability to control the FOV and resolving power are important considerations in choosing a CBCT scanner. Along with greater FOV, greater resolution entails a higher radiation dose. It may be possible to achieve the objectives of an examination using a lower resolution setting or reduced exposure parameters, thus limiting the radiation dose. High-resolution scans are recommended for small FOV uses only. Occupational exposure to radiation is generally not an issue if the equipment is properly installed. CBCT units can have greater power and x-ray scatter than conventional radiographic units. Applying the principle used to obtain conventional x-rays safely, the operator should stand at least 8 m from a CBCT machine during patient exposures. It is important to note that the biological effect of a beam varies with the patient’s age and gender as well as the radiosensitivity of the exposed tissue. Factors influencing the appearance of the data obtained through CBCT include overall exposure parameters, efficiency of the detector, and the reconstruction. The best slice thickness for three-dimensional modeling seems to be <0.5 mm. Viewing the data on-screen is the optimal mode, and software and hardware for computer processing are considered essential components of the system. The software allows the scan data to be reconstructed in three orthogonal planes and often along a curved plane to yield a ‘‘panoramic’’ reconstruction. The area of interest can be emphasized by changing the window and level. The viewing software chosen should be based on what the dental practice will use most, including the ability to view results on various workstations and in more than one location. It should also allow exporting to third-party software to facilitate implant, maxillofacial, and orthodontic treatment planning. The results of a CBCT are required by law to be fully evaluated. Dentists are qualified to adequately evaluate
Volume 54
Issue 6
2009
293
Fig 2.—The benefits of three-dimensional imaging. A, An intraoral radiograph of an asymptomatic central incisor fails to show the true nature of the extensive lesion compared with re-sliced CBCT images: B, coronal; C, sagittal; and D, axial. (Courtesy of Dawood A, Patel S, Brown J: Cone beam CT in dental practice. Br Dent J 207:23-28, 2009.)
Fig 3.—Source and opposing flat panel detector rotating around the patient’s jaw, capturing image data in one sweep. (Courtesy of Dawood A, Patel S, Brown J: Cone beam CT in dental practice. Br Dent J 207:23-28, 2009.)
294
Dental Abstracts
the clinical findings on CBCT images of the immediate dentoalveolar region. Should a wider FOV be chosen, capturing the skull base, sinuses, and cervical spine, a full report may require the input of a dentomaxillofacial or head and neck radiologist. All CBCT operators must be adequately trained, including the referrer, generally the dentist who prescribes or requests the CT; the IRMER practitioner, who will justify the exposure by selecting appropriate cases, understanding the risks to the patient, being aware of the likely yield of the examination, and knowing how to manipulate and interpret the resulting imaging data to obtain the needed diagnostic information; and the operator, who obtains the radiograph safely, accurately, and with maximum dose optimization for the diagnostic application. Included in the training are how to use the specific machine, radiation hazards, imaging pitfalls, selection criteria, and interpretation of cross-sectional and three-dimensional images.
Clinical Significance.—When conventional two-dimensional imaging is insufficient, or access to technological processes such as guided surgery will improve patient management, it is appropriate to consider CBCT technology. CBCT scanners are simpler, more compact, and less expensive than conventional CT machines and produce images that are at least as good. The goal for any imaging system should be to obtain the best and most accurate diagnostic and treatment possibilities for the patient while minimizing radiation exposure or other harm. It is best to have everyone on the dental team trained in CBCT and the technologies related to it.
Dawood A, Patel S, Brown J: Cone beam CT in dental practice. Br Dent J 207:23-28, 2009 Reprints available from A Dawood, Dawood & Tanner Dental Practice, 45 Wimpole St, London, W1G 8SB UK; e-mail: [email protected]
Dental Materials Self-etching adhesive bond strengths Background.—Modern dentin bonding systems are based on creation of a hybrid resin–reinforced layer for dentin adhesion. The dentin layer is partially demineralized to expose collagen fibrils, and the adhesive monomers are infiltrated in and around the remaining collagen and mineral. To support the collagen fibers, moisture is needed on the dentin surface. With bonded restorations, achieving the correct dentin moisture content relies on clinical judgment and is an unreliable process. The laboratory bond strengths that are achieved with moist bonding, using the current etch-and-rinse hydrophilic bonding systems, range from 17 to 24 MPa, with corresponding clinical success. The self-etching adhesive systems offer a simpler technique, with fewer steps and no need for clinically judging the dentin moisture level. These systems condition, demineralize, and infiltrate both enamel and dentin at the same time. However, their hydrolytic stability has been questioned, as has their lower immediate enamel bond strength and long-term consistency of the enamel bond. Enamel marginal breakdown of restorations placed with these adhesives is a danger. Bond strength testing can help dentists understand and predict the clinical behavior of the various adhesive systems. We compared the shear bond strengths of 10 current self-etching adhesive systems to dentin and enamel. Methods.—A 600-grit silicon carbide paper was used to expose the dentin or enamel of flat bonding sites on 216 extracted human molars. The adhesive systems were applied,
with 24 bonded assemblies of Spectrum TPH prepared. These samples were stored in water at 37 C for 24 hours. Twelve specimens of each enamel and dentin group were debonded, and subjected to alternating thermocycling and water baths. The specimens were then loaded to failure in a testing machine. Results.—The mean shear bond strength values to enamel (Table 1) and dentin (Table 2) were measured for
Table 1.—Mean Shear Bond Strengths of Self-Etching Adhesives to Enamel (MPa) Product
MPa
24.0 4.3a 23.6 3.9a,b 23.2 4.1a,b 22.3 5.8a,b 21.4 4.2a,b,c 21.3 1.9a,b,c 20.0 3.1b,c 18.4 4.8c 17.8 2.9c,d 11.8 2.9d
Clearfil S3 Xeno V AdheSE One Clearfil SE Bond iBond SE Xeno IV Optibond All-in-One Adper Prompt L-Pop G-Bond iBond
Groups designated by a common symbol were statistically similar at a confidence level of 95%. (Reprinted with permission from General Dentistry, May/June 2009. On the Web at www.agd.org. ª Academy of General Dentistry. All rights reserved. Foster Printing Service: 866-879-9144, www.marketingreprints.com. License # GD-6188-MES)
Volume 54
Issue 6
2009
295