Use of 3D scanner in dentistry - Essay Example

3D Scanner Running Head: 3D SCANNER Uses of 3D Scanners in Dentistry and the Use of 3D Scanners to Measure Tooth Movements Before and After Orthognathic Surgery In HARVARD Style 3D Scanner 2 Introduction 3D scanners are devices that analyze objects of interest in order to collect data on its shape and appearance so that 3-dimensional, digital models are constructed, useful for a wide variety of applications. In dentistry, the conventional intraoral and panoramic radiography offer two-dimensional view of the oral structures. Because of superimposition, both technologies have a limited value in detecting subtle anatomical and pathological structures (Hirsch 2007). Digital 3D has increasingly been prominent in dental radiology since the advent of computed tomography. Soft tissue volumetric data and surface topography can be measured accurately, whereas in 2-dimensional radiography, only linear angles, areas and distances can be measured. The ability to capture images in 3 dimensions has opened up new ways for observation and analyses. Uses in Dentistry Prosthodontics. There are at least 2 methods of usage of the 3D scanner in prosthodontic restorations. One is the use of the scanner in the laboratory and the second is the use of intraoral camera in the dental office. In the first method, the process begins in the dental chair wherein if a crown, for example is needed, the damaged tooth is drilled and a plastic impression from the patient is taken. The impression is then sent to the laboratory where a stone master model and a crown made of wax are created using conventional methods. The 3D process starts with the scanner, where a model of the tooth stump is captured for 3 minutes with an accuracy of 20 micrometers (Geomagic 2004). The scanner, looking like a microwave oven with 3D Scanner 3 a turntable that tilts, captures then the data from different angles to produce 15 point clouds of geometric samples of the tooth stump model (Geomagic 2004). The data is then processed in the control software, which is pre-installed in the computer connected to the scanner. In the Everest System, the control software has 4 modules: the scan, surface, CAD and CAM modules (Geomagic 2004). In the scan unit, extremely accurate data of the models is created. In the surface module, a mathematical surface calculation is automatically performed, detecting undercuts and preparation lines. After preparation of the model, the file is then passed on to the CAD module. In the CAD module, the design of the final copings or bridges for example, happen on the computer screen providing a digital approach to traditional steps in the design process, as well as speeding the design (SensAble Technologies 2008). The CAM module calculates the cutting data, taking into account the processing properties specific to the material being used. The data is then transfered to the CNC system called the Everest Engine (Geomagic 2004). The system is a computerized grinding and five-axis cutting machine defining horizontal, vertical, pivot, and rotational travel. With the system, several workpieces are manufactured at one time. Sintering of materials for ceramic pieces, which takes about 12 hours is performed using a thermal unit controlled by a microprocessor. The finished piece is then ready for the patient with a guarantee of perfect fit and with no excess material to be removed. In the second method, the process begins also in the dental chair wherein if a crown for example is also needed, the decay is drilled and dentist prepares it by painting it with an imaging liquid, and a special opaque powder is used to cover it (Doyle 2000). A small handheld high precision intraoral measuring camera is then used and placed inside the mouth and the pictures are taken which then appears on the computer screen connected to the camera. The 3D Scanner 4 image on the screen eliminates the impression taking process abhorred by both dentists and patients. The CAD software is then used to design the crown. A fully automated process for milling that takes place for 10-15 minutes then takes place with the ceramic block being inserted into the milling unit. When the milling process is completed, the crown is then bonded into place using the conventional ceramic bonding techniques and then polished. In the US alone, over 50 million partials, crowns and bridges are created annually. Digital technology is projected to grow by 60% by the year 2012 (SensAble Technologies 2008). Plaster pouring, base and pin, die cutting, trimming and articulation are some of the steps eliminated in the laboratory (3M 2008). With the high precision intraoral camera, the patient can be serviced in one visit lasting only in a little over one hour. Inevitable human errors and the manual steps are eliminated with digital dentistry, creating near perfect impressions that almost eliminate refitting in crowns and bridges (Digital Dentist 2007). Patients can have restorative work done on their teeth in just one appointment, rather than the usual multiple visits and in the laboratory, it can translate into an increase in the production of high-quality pieces that technicians can produce in a given amount of time. Endodontics. The cone-beam computed tomography (CBCT) is a type of 3-dimensional scanner designed for high resolution imaging of hard tissues. It has a higher resolution than the computed tomography (CT), the high resolution being necessary to display the subtle structures like periodontal ligaments and the root canals (Hirsch 2007). The radiation is also significantly lower. An x-ray tube and a 2-dimensional image detector are mounted opposite each other and perform a 180 or 360 rotation. The resulting primary data are converted into slice data using the filtered back projection, afterwhich the slice data can then be viewed in 3D Scanner 5 user-defined planes (Hirsch 2007). The applications include root canal measurements, root inclinations in relation to the surrounding jaw, the true size, extent, nature and position of periapical and resorptive lesions, and the maxillary sinus and inferior dental nerve in relation to the root apices. Posterior teeth prior to periapical surgery may also be assessed, as a periapical disease may be detected early (Patel et al. 2007). Another type of 3D scanner for endodontic application is the 3D Accuitomo XYZ Slice View Tomograph (3DX). It is used for compact computed tomography in dentistry. It is also a high resolution scanner used to examine and diagnose the presence and expansion of periradicular lesions of single or multirooted tooth and other regions of interest in endotherapy (Nakata et al. 2006). Periodontology. The cone beam computed tomography 3D scanner is also being used for most of Periodontology applications. One type of CBCT scanner is the i-CAT cone beam imaging system which has the fastest scan time at 5, 8.5, and 26 seconds, with standard reconstruction taking less than 30 seconds. Anatomically different cephalometric 3- dimensional images of the entire skull are constructed - a complete orthodontic work-up of frontal and lateral cephalometric, TMJ, supernumerary, panoramic, airway and spinal studies. It provides the dentists with instant data for the best possible diagnosis, treatment and predictability (Imaging Sciences Int'l 2007). The applications include marginal bone contouring, 3D imaging of deep pockets and furcations in bone and pathology detection. Implantology. With the use of the cone beam computed tomography 3D scanner, the patient's anatomy is evaluated and the location and course of vital structures such as the inferior alveolar nerve are accurately identified. Other applications for implantology include 3D Scanner 6 screening and detection in pathology and dental implant placement (Imaging Sciences Int'l 2005). For the implant placement, a 3D model of the patient's mouth is taken. The model, which is a diagnostic wax up duplicating the proposed final restoration is then used as a scan guide for the 3-dimensional treatment planning, as all of the restorative and surgical information are evaluated on the screen. To prepare the exact locations for implant placement, the scan guide is then converted into a conventional surgical guide (Aclar 2008). The exact spot for the implant placement and the eventual insertion with the crown on top with it, by the surgeon in one minimally invasive surgery is made possible with the imaging technique (3D dental implants 2007). Orthodontics. The applications of 3D imaging in orthodontics include configuration of roots, anatomical situation, relation of teeth between periodontal ligament and resorptions, 3-dimensional treatment planning and 3-dimensional soft and hard tissue prediction (simulation). Pre- and post-orthodontic assessment of dentoskeletal relationships and facial aesthetics and orthodontic outcomes with regard to soft and hard tissue are also included (Hajeer et al. 2004). The cone beam computed tomography is used for the applications. Another method used is the 3D scanner which makes use of a 3D scanning hardware, automatic surfacing software, 3D animation programs and rapid manufacturing systems to produce customized, removable, clear plastic appliances called aligners. The appliance provides an innovative alternative to traditional braces. The process begins with the impression-taking of the patient. X-rays of the patient's teeth are then taken and a treatment plan is prescribed and the impression sent to the laboratory. Digitization and design of the patient's impression are done in 3D Scanner 7 the laboratory to produce precise, manufacturable digital models and start-to- finish animations of the patient's treatment plan. The clear, plastic aligners that are custom-fitted to the patient's teeth and mouth are then processed in the laboratory. The appliance is worn by the patient for about 2 weeks before switching on to the next in the series. Up to 60 pairs of upper and lower aligners may be used in a single treatment case (Rosenblatt 2008). Dentomaxillofacial Surgery/Orthognathic Surgery. The main applications include pre- and post-operative imaging for noting important landmarks and structures, displaced and/or impacted teeth, apical periodontitis and other chronic inflammation of the jaw, examination of the maxillary sinus, cysts of the jaw, trauma cases such as teeth and bone fractures and cleft palate malformation cases (Hirsch 2007). The applications make use also of the cone beam computed tomography. Another method of application is the use of 3D cephalometric data for 3D simulation. The movement of the teeth, jaw and face are simulated. A laser camera scanner obtains the teeth and facial data of the patient and the reconstruction and integration of the patient's jaw are made according to the 3D cephalometry using a projection-matching technique. The mandibular form is simulated by transforming a generic model to match the patient's cephalometric data. This system permits analysis of bone movement at each individual part, while also helping in the choice of optional osteotomy design considering the influences on facial soft-tissue form. Another method of application, is the use of an experimental Craniofacial Surgery Simulator. One of its uses is in patients with complex facial deformities - a condition that is one of the most challenging multidisciplinary tasks in medicine. Surgical correction of severe malformations has become possible with the recent advances in 3D imaging. The use of 3D 3D Scanner 8 imaging greatly facilitated the diagnosis of complex craniofacial deformities. The use of Craniofacial Surgery Simulator provides the ability to perform preoperative 'virtual surgery', thus reducing intraoperative patient risk and morbidity. The system is an interactive computer- assisted craniofacial surgical planning and visualization, especially simulation of soft tissue changes. Non-linear soft-tissue deformation due to bone realignment is computed by the system and is capable of simulating bone cutting and bone realignment with integrated collision detection (Girod 2008). Another method is the assessment of the dimensions and arrangement of facial soft tissues, which is important to plastic surgeons, orthodontists, and orthognathic maxillofacial surgeon evaluations. All quantitative data about the soft tissue that compliment the evaluation of hard-tissue relations are taken with the use the 3-dimensional laser surface scanning images pre- and post- operative in order to assess facial changes that occur as a result of orthognathic surgery. A 3-dimensional facial scanner routinely scans the subject's facial surfacefrom top to bottom with a projected class 2 laser stripe immediately before and two months afterorthognathic surgery. Three hundred sixty degrees (360) 3D images are created with the help of computer software. Cartesian coordinates from facial landmarks can be identified with the surface distance between them calculated using computer software. The same software can be used to construct axial images with the head and to measure the area and head volume of the head and face. This method provides additional information of the surface shape and the 3-dimensional superimposition reveals soft tissue changes in the lower face. How Use 3D Scanner to Measure Tooth Movements Before and After Orthognathic Surgery 3D Scanner 9 Orthognathic surgery is the surgery that corrects conditions of the face and jaw related to growth, TMJ disorders, sleep apnea; in the treatment of congenital conditions like cleft palate or to correct orthodontic problems that cannot be easily treated with braces. Bones can be cut and realigned, held in place with either screws or plates and screws. The following are the indicationsfor orthognathic surgery: 1. Soft tissue defects and facial skeletal discrepancies associated with documented sleep apnea and airway. 2. Facial skeletal discrepancies associated with documented TMJ pathology. 3. Gross jaws discrepancies (anteroposterior, transverse and/or vertical discrepancies) (Bill et al. 2006). Oral and maxillofacial surgeons perform Orthognathic surgery almost always in collaboration with orthodontic treatment, often including braces before and after surgery, and retainers after the removal of braces. It is also often needed in major craniofacial anomalies and reconstruction of cleft palate. Careful collaboration between the surgeon and orthodontist is needed to ensure that the teeth will fit correctly after the surgery. Input from a multidisciplinary team such as the Oral and maxillofacial surgeons, Orthodontists, and sometimes a Speech and language therapist during the planning stage for the surgery is sought and photographs and radiographs are taken to help in the treatment planning (Misckowski et al. 2006). To predict the shape of the patient's face after surgery and allow the patient to see the predicted results, a software with the use of a 3D scanner is used. The use of 3D scanner in measuring tooth movements offers many advantages: 1.) Accurate and complete movement of the entire jaw or tooth can be calculated using 3D Scanner 10 the 3-dimensional rigid body analysis; 2.) Detailed treatment options before beginning the treatment can be evaluated; 3.) A precise and complete analysis of treatment using the digital models can be obtained; 4.) Movement analysis and precise measurement can be performed; 5.) An accurate teeth matching and jaw matching results may be provided; the shape difference between two different sets of impressions for the same teeth may also be revealed; 6.) Virtual planning may also be obtained; 7.) The virtual treatment model can also serve as a motivating tool to patients; 8.) It can serve as a constant objective reference during office visits so that the planned treatment goals can be discussed; 9.) The virtual model can be shown to the patient to continually see where the outcome of the treatment will be; 10.) Treatment outcomes can be reliably compared so that treatment plans can allow the detailed study of many cases; 11.) An accurate tooth geometry and gingival model from the scanned geometry can be obtained; 12.) Feedback and interactivity to a user during the model creation can be provided so that virtual planning treatment will help the user make informed decisions about the treatment plan (Choi et al. 2007). To measure tooth movements before and after orthognathic surgery, several methods 3D Scanner 11 and processes are employed. First, digital models of the patient's dentition are taken one, before orthognathic surgery and second, after surgery. There are several methods and systems of measurements: 1. Matching two sets of teeth shapes and calculating the difference. In this method, the shape difference for each tooth of the jaw is calculated and a corresponding location for each shape difference is identified. The position of one set of teeth with respect to the other set of teeth is also located. It can mean placing the 2 jaw impressions in a single coordinate system by selecting a positioning reference and determining a positional difference for each corresponding teeth in the jaw impression. 2. Matching two impressions of a jaw having teeth thereon (Choi et al. 2007). 3. Surface-to-surface matching. Digital models offer a precise and complete analysis of tooth movements. To achieve this, the measurements are calculated. First, a handheld intraoral 3D device such as the OraScanner is used to produce the digital models. The process involves several steps: 1. "Whitening" of the dentition. The process involves an imaging liquid being painted to the dentition and then covering it with a special powder. 2. Series of pictures or snapshots covering the entire dentition is taken. 3. A point cloud is obtained by registering or mapping the individual pictures. 4. The tooth material and gingiva are modeled as individual 3D surface objects (Rubbert 2002). With the procedure taking less than 20 minutes, a complete digital representation of the 3D Scanner 12 measurements begin with the dental models being assigned with an appropriate coordinate system. A virtual model is then created by scanning and segmenting the 2 models to create virtual models. The data of the two models are retained as they are segmented. A body coordinate system is established to express a simple movement of teeth. Then, a common coordinate system is set for the teeth in the two models which is an important process in comparing the two models. This is made by performing a tooth-to-tooth geometric matching, done automatically by the software, which also determines the relative transform between the two teeth. A reference frame for measurement is then established from which the relative transform is interpreted. Having a correct reference frame means that if the two teeth D1 and D2 are in the same position in both models, then T is the relative transform. Once the reference frame is found, the difference in tooth position can be described in absolute or relative terms (Choi 2007). An external reference frame must also be incorporated so that the absolute movement of teeth can also be determined. Otherwise, only the relative movement of teeth can be calculated. The external fixed reference such as the rugae in the patient's mouth can be used. Though, some studies and one particular clinical data showed that changes in the perpendicular rugae position with respect to the palatal plane were observed and that it was concluded that the vertical palatal rugae position is not stable over time (Christou et al. 2005). Thus, it was recommended that other stable structures are necessary as references especially when used in long term analysis such as orthodontic treatment. Another method of measurement is by using the tooth by tooth approach. In tooth by tooth matching, the difference between tooth geometry in two different models is determined. Even though the same tooth is scanned, there may be slight differences between the two 3D Scanner 13 impressions, revealing the differences between two different models. From the process, the necessary coordinate transformations are also determined from the expected 3D coordinates for each tooth to the 3D coordinates for the corresponding tooth in the impression. The difference of the impression of the individual tooth is then ascertained. The process determines tooth alignment data in the current position. Another method is by using a report analysis generation process. Each individual tooth generates discrepancy information report in terms of rotation, translation, deviation and an average for all teeth. The teeth are positioned, then the process obtains a first transform for the first impression and a second transform for the second impression. Translation is then calculated and the average, maximum and minimum of the translations is determined. Rotation, move distance of a tooth and deviation can also be calculated. Another method is by comparing the pre-treatment case with the post-treatment case with the jaw impression. The teeth data from the pre-treatment case is compared against the teeth data with the current jaw impression. Next, the new jaw data is positioned in the previous coordinate system. The previous jaw data is then compared against the current jaw data. In this method, a visualization showing the discrepancy is obtained. Another method is by matching shapes based on rugae. Points on the first model are located and points on the second model that correspond to those points are obtained. These points are then matched and the models positioned in such a way that they closely align in the regions such as the rugae, by applying a transform T to one of the models. After the reference frame is obtained, the actual relative transform between teeth can be calculated. Relative movement is then measured between the corresponding teeth and compared 3D Scanner 14 to the reference teeth (Choi 2007). 3D Scanner 15 References Aclar, A, 2008, 'About dental complications and technological advancements', Dental Implants and Periodontics. Available from: Read More