In recent years, with the spread of new 3D manufacturing technologies such as 3D printing, the demand for 3D coordinate data collection technology has been increasing. In the past, CAD/CAM systems were developed to streamline manual processes such as drafting and clay model making, which were used to describe design shapes as drawings. However, as the number of processes using digital data has increased, such as reverse engineering and computer-aided engineering (CAE), research and development on 3D measurement have been promoted. In this article, the principles and characteristics of typical methods used for 3D measurement in the industry are explained, and the techniques applied in digital impression devices are described and notes are summarized.

Nowadays, more than 10 brands of intraoral scanners (IOS) have been launched in Japanese market. Information such as price, size of the measuring device, measuring area, disinfection method for the scan tip was surveyed by asking sales representatives. The price at purchase was difficult to calculate because some products required purchasing the PC for the control, the prices ranged from 1 million to 6.9 millions yen. Almost all IOS did not required powder spraying before impression, and could obtain color images. The weight of IOS varied from 80 g to 525 g. Some IOSs digitized precise images around the abutment tooth, and the others did the uniform image.

With the progress of digital dentistry, the way of prosthesis fabrication has dramatically changed. Since the approval of zirconia in Japan in 2005, CAD/CAM technology capable of processing zirconia has gradually spread. And it accelerated when CAD/CAM crowns were covered by insurance in 2014. As of now, the intraoral scanner attracts worldwide attention, and it is becoming more popular in the self-pay treatment field in Japan, there are increasing opportunities to manufacture prostheses from the intraoral scanner data. In this paper, from the viewpoint of a dental technician, I will describe the differences between the digital method and the conventional one from several perspective.

In the case of occlusal reconstruction for partially edentulous dentition, it is often necessary to restore the occlusal vertical dimension (OVD). In such cases, it is important not to correct the OVD alone, but to reconstruct the occlusal plane and other occlusal factors as well.

When setting a new OVD, it is common to use facial measurements and physiologic rest position with reference to the OVD determined by the prosthesis in use. However, in some cases, it is necessary to raise the OVD beyond the physiologic rest position, and the occurrence of a new interocclusal rest space must be confirmed while carefully observing the condition of the muscles and TMJ adapted to the reduced OVD. Furthermore, in terms of the temporomandibular joint, it is necessary to raise the OVD within the range where the mandibular condyle is in the stabilized condylar position.

Purpose: In order to prevent aspiration pneumonia, it is important not only to care for the remaining teeth but also to clean the dentures. When it comes to long-term care, the dentures are managed by a third person such as a family member or a caregiver. In the future, it will be necessary for the staff of nursing care facilities, such as elderly homes and special elderly nursing homes, with little knowledge of denture care, to be involved. In this study, we conducted a questionnaire survey of the staff of long-term care facilities in an effort to use the data to help spread good denture care and improve the level of oral hygiene of elderly residents.

Methods: An anonymous questionnaire was given to all employees of four special-care elderly nursing homes and one group home in Gifu and Nagano prefectures about their knowledge of dentures and correct care practices.

Results: Of the 332 people included in the survey, 290 responded, with a response rate of 87.3%. The data revealed that the most common length of service was less than 5 years (56.9% of respondents). 84% of the employees had contact with dentures in the facility, and 53.1% had been taught about denture care in study sessions. Although 93.7% of the respondents knew about the relationship between oral care and aspiration pneumonia, only 28.6% had read magazines or books on denture care.

Conclusions: Knowledge of denture care and oral care is indispensable for the staff of facilities providing nursing care. The link between aspiration pneumonia and oral care is well known. Standards and manuals should be created so that oral care and denture care can be performed uniformly and correctly at each facility. It is necessary to hold seminars and study sessions for long-term care facility staff to disseminate knowledge.

Patients: Recently, as the number of patients with dementia increases, preemptive interventions to prevent dementia are expected. In the present case, a prosthetic treatment was performed on a toothless patient diagnosed as having mild cognitive impairment due to Lewy body disease, and changes in masticatory function and cognitive function were observed over time. Masticatory function was measured by using a glucosensor (GS-II, GC, Tokyo, Japan), and cognitive function was assessed using the Japanese version of the Montreal Cognitive Assessment (MoCA-J), which evaluates mild cognitive impairment at the non-dementia level, the Mini-Mental State Examination (MMSE) and the Hasegawa Dementia Rating Scale - Revised (HDS-R), which are screening scales for dementia. The Lawton Instrumental Activity of Daily Living (Lawton-IADL) was used to assess social functioning in a multilayered manner.

Discussion: During the 18-month follow-up, when a new complete denture was attached to the upper and lower jaws, the masticatory function improved and cognitive function remained at the level of mild cognitive impairment, and no progression to dementia was observed.

Conclusions: These results suggest that intervention in oral function by prosthetic treatment may be a preemptive preventive intervention against the progression of cognitive impairment and the onset of dementia.

Patient: A 71-year-old man presented with the chief complaint of masticatory disturbance caused by multiple missing teeth. At first, hopeless teeth were extracted, and provisional restorations and temporary dentures were inserted. Preprosthetic treatments were performed while remodeling the temporary dentures, and metal plate dentures were inserted in the defective area as the definitive prosthesis.

Discussion: The use of metal plate dentures and crown restorations of the remaining teeth enabled proper occlusal force distribution and correction of the occlusal plane, and also enabled stability of the dentures to be obtained.

Conclusion: In this case, oral rehabilitation was performed for the patient to treat the non-vertical stop occlusion. The metal plate dentures were applied as the definitive prosthesis, and good masticatory function was maintained over a long period.

Patient: The patient was a 71-year-old woman. In 1990, lingual cancer (T3N0M0) on the left side was diagnosed, and lingual resection and brachytherapy were performed. Then, in 2016, she was referred to our hospital with a chief complaint of mastication disorder due to loss of tooth 65| and dysphagia/dysarthria after surgery for lingual cancer.

Discussion: Tongue training was conducted in parallel with denture treatment, however, sufficient functional recovery of swallowing and articulation was not observed. Therefore, it was decided to insert a PAP. This was completed after confirming functional improvement by fluoroscopy of swallowing. The tongue pressure after using the PAP was higher than that before using it. In addition, although some problems in articulation remain, it has generally improved and the PAP is still functioning without problems.

Conclusion: Patient satisfaction increased with improvement of swallowing and articulation functions by a PAP.

Patient: The patient was a 72-year-old man with the chief complaint of spontaneous pain of gingiva in the anterior mandible. As severe infra-occlusion caused by missing teeth in the posterior region of the mandible and teeth attrition was observed, bite raising was performed by using a removable partial denture after the initial periodontic treatment and endodontic treatment. The provisional restoration was adjusted at the mandibular position with the increase of occlusal vertical dimension, and then the final prosthesis, which reproduced the form of the provisional restoration, was fabricated.

Discussion: The use of a provisional restoration and treatment denture made it possible to reflect the appropriate mandibular position and anterior guidance in the final prosthesis.

Conclusion: It is suggested that masticatory function and esthetics were improved by the prosthetic treatment with an appropriate occlusal vertical dimension and anterior guidance by bite raising for the patient with infra-occlusion.

Patient: A 29-year-old female complained of esthetic and masticatory disturbance with tooth erosion due to an eating disorder. All tooth crowns were remarkably eroded such that dentin was exposed, and the vertical dimension of occlusion (VDO) was decreased. VDO was ideally restored by referring to the mean anatomical crown length with occlusal overlay splints and provisional restorations. After long-term follow-up, the final prosthesis (all-ceramic crowns) with cuspid protected occlusion was applied.

Discussion: The occlusal overlay splint, which can be applied without tooth preparation, was helpful for occlusal reconstruction in a patient with mental instability.

Conclusion: In this patient with tooth erosion due to an eating disorder, a favorable outcome was achieved by oral rehabilitation with occlusal overlay splints and provisional restorations.

Patient: A 73-year-old man visited our clinic complaining of difficulty in chewing because of an unfitted mandibular telescopic denture. Although six maxillary teeth remained, all of the mandibular teeth needed to be extracted. Treatment dentures were delivered to provide occlusal stability, followed by fixed and removable partial dentures for the maxilla, and complete dentures for the mandible were delivered as the definitive prosthesis.

Discussion: The treatment dentures were effective for establishing functional stability, and were able to predict final prosthesis quality. As a result, high patient satisfaction was achieved.

Conclusion: Applying treatment dentures to improve occlusal stability resulted in a satisfactory therapeutic effect on a patient with an unfavorable edentulous situation.

Patient: A 64-year-old female patient complained of masticatory dysfunction caused by mobility of a maxillary right fixed bridge. The maxillary right canine with occlusal traumatic symptoms had been diagnosed by her previous dentist as indicated for extraction, but it was fixed with a provisional bridge to determine whether the tooth could recover. After this traumatic tooth was allowed to recover, the fabricated fixed bridge was finally attached after a follow-up observation by temporary cementation.

Discussion: There are no clear criteria for tooth preservation of occlusal traumatic teeth depending on bone resorption or tooth mobility. Therefore, it is important to plan a step-by-step prosthodontic treatment in which the availability of abutment teeth is determined after the acute traumatic symptoms have resolved.

Conclusion: A careful and step-by-step prosthodontic treatment for an occlusal traumatic tooth resulted in tooth preservation, restoration of masticatory function, and improvement of patient satisfaction.

Patient: A 76-year-old female complained of toothache and gingival swelling of the maxillary remaining teeth. Due to the non-maxillomandibular relationship and maladaptation to dentures, complete dentures were fabricated after improvement of the residual mucous membrane and mandibular position by temporary dentures.

Discussion: By using the functional closed mouth impression technique with tissue conditioner for this case with alveolar ridge resorption and dysfunctional movement, final complete dentures were made by taking an impression of the shape of the denture base in order to improve retention and stability.

Conclusion: These results suggested that complete dentures using the functional closed mouth impression technique with tissue conditioner are suitable for cases where impression-taking is difficult due to alveolar ridge resorption.

Patient: The patient was an 85-year-old female. Her chief complaints with regard to her mandibular complete denture included pain, difficulty in chewing, and movement during speech. Denture retention was difficult to obtain due to the patient’s extensive residual ridge resorption. A duplicate mandibular denture was made, and the dynamic impression technique was applied to make a new denture.

Discussion: Creating a duplicate denture allowed the functional denture form to be reflected on the new prosthesis. Because she used a duplicate denture during the period of denture fabrication, the patient was able to continue using her original denture.

Conclusion: In this case, where the patient displayed extensive residual ridge resorption, good results were obtained by preserving and modifying the old denture form as a duplicate denture.

Patient: An 81-year-old female complained of disturbance caused by poor stability of mandibular complete dentures, and discomfort when eating. The condition of the patient’s current dentures and the range of motion of the labial and buccal mucosa and tongue were examined by palpation and inspection. The examination revealed that the poor stability of the mandibular dentures was due to the inadequate shape of the denture base. Complete dentures were fabricated by using a closed mouth functional impression.

Discussion: The stability and retention of the complete dentures were improved by considering the shape of the denture base and using the closed mouth impression technique.

Conclusion: The main complaint was improved, and a good course was obtained by taking impressions in consideration of the external shape and floor morphology of the dentures.