A digital approach to the evaluation of mandibular position by using a virtual articulator

The purpose of this technique report was to describe a fully digital technique to evaluate the mandibular position both in centric relation occlusion (CRO) and maximal intercuspation position (MIP). The procedure transfers data relative to the position of the maxillary and mandibular dentition to a virtual articulator based on a single cone beam computed tomography (CBCT) image. A CBCT scan of the patient was obtained in CRO, and the maxillary and mandibular casts were scanned both in CRO and MIP with an intraoral scanner. The model CRO scan data were registered on the dental part of the CBCT image by using a virtual articulator program, and a virtual facebow transfer process and mounting was performed. The virtual articulator was positioned in the right and left condyle medial pole and right orbitale. The mandibular position was evaluated in CRO and MIP by superimposing the data of the mandible position in both CRO and MIP. A quantitative 3D measurement was obtained by using the grid function. Based on this protocol, it is possible to use a fully digital approach to transfer the position of a patient’s maxillary dentition to a virtual articulator based on the data from a single CBCT scan and intraoral scans. This technique eliminates the traditional facebow transfer and mounting process and complicated laboratory procedures for evaluating mandibular positional changes in CRO and MIP.     

A fully digital workflow to register maxillomandibular relation using a jaw motion tracer for fixed prosthetic rehabilitation: A technical report

Objective

This technique aimed to describe a fully digital workflow to register maxillomandibular relation for fixed prosthetic rehabilitation.

Clinical Considerations

Mandibular kinematics could be reproduced in a four-dimensional (4D) virtual patient based on the intraoral scan, facial scan, cone beam computed tomography, and jaw motion trajectory, which helped record centric relation and determine a proper occlusal vertical dimension in a virtual environment. The therapeutic position could be exported directly to the dental computer-aided design software for digital waxing design with a facial scan. The 4D virtual patient was also used to verify the functional and esthetic outcomes of provisional restorations.

Conclusions

This novel approach digitized the process of determination, delivery, and double-check of maxillomandibular relation, thus contributing to the establishment of a completely digital workflow for fixed prosthetic rehabilitation.

Clinical Significance

Registration of maxillomandibular relation, including centric relation and occlusal vertical dimension is critical to the success of prosthetic rehabilitation. Traditional procedures are complex and time-consuming, and heavily rely on the clinical experience of dentists. A fully digital approach to creating a 4D virtual patient and registering the maxillomandibular relation is established, which guides to determine a proper occlusal vertical dimension in centric relation. Digital delivery and double-check can simplify the conventional procedure and ensure that the determined maxillomandibular relation is reliable.     

基于口内扫描的三维数字化牙列模型咬合匹配评价分析

目的    通过评价咬合接触面积及咬合接触点的分布,分析3个品牌口内扫描仪扫描牙列模型颊侧部分获取数字化咬合记录的可靠性。方法    使用3个品牌口内扫描仪（TRIOS、CS3600、CEREC Omnicam）分别扫描10副上下颌牙列模型后,通过扫描颊侧部分获得具有牙尖交错位三维空间位置关系的上下颌牙列数字化模型,以口外扫描仓获得的数字化模型为对照组,应用逆向工程软件的偏差分析功能显示下颌牙列模型上的咬合接触图像,测量上下颌间的咬合接触面积、咬合接触点的分布,并运用SAS统计学软件比较3个品牌口内扫描仪的咬合关系精确度。结果　全牙列咬合接触面积：TRIOS组为（15.160 ± 8.145）mm2,CEREC组为（13.153 ± 5.080）mm2,CS3600组为（27.509 ± 20.847）mm2,对照组为（23.194 ± 18.194）mm2;3个口内扫描仪组分别与对照组比较,差异均无统计学意义（P > 0.05）;CS3600组分别与TRIOS组和CEREC组比较,差异均有统计学意义（均P < 0.05）;而TRIOS组与CEREC组之间的差异无统计学意义（P > 0.05）。咬合接触面积分布统计图显示,3个品牌口内扫描仪所得的面积分布趋势基本相同,咬合接触面积磨牙区＞前磨牙区＞前牙区。咬合接触点分布统计图显示,3个品牌口内扫描仪全牙列咬合接触点分布呈左右对称,接触点数少于对照组;位于中央窝和边缘嵴处的接触点在口内扫描仪与对照组之间出现的重复率较高。结论    3个品牌口内扫描仪通过颊侧扫描记录上下颌位置关系,得到数字化咬合记录。在全牙列咬合接触面积方面,3个口内扫描仪均与口外扫描仓无明显差异;咬合接触面积的主要差异在于磨牙区,TRIOS和CEREC Omnicam 相比CS3600的磨牙区咬合接触面积更接近口外扫描仓。咬合接触点位于中央窝和边缘嵴处记录的准确性要高于颊舌尖斜面。     

Accuracy of transfer of bite recording to simulated prosthetic reconstructions

Objectives

A key aspect of complex restorative therapy is reconstruction of a new three-dimensional jaw relation. The objective of this study was to test the hypotheses that the initially recorded jaw relation would deviate substantially from the jaw position of the prosthetic reconstruction and that activity ratios of the jaw muscles would be significantly different for each of these jaw positions.

Materials and methods

In 41 healthy subjects, 41 examiners incorporated intraoral occlusal devices fabricated with all the technical details and procedures commonly used during prosthetic reconstructions. The jaw positions in centric relation with the incorporated occlusal devices were telemetrically measured in the condylar, first molar and incisal regions, relative to intercuspation. Electromyographic (EMG) activity of the temporalis and masseter muscles was recorded, and activity ratios were calculated for homonymous and heteronymous muscles.

Results

The recorded jaw relation differed significantly (p?<?0.001) from the jaw position reconstructed with the intraoral occlusal devices. The initially recorded jaw relation was reproduced with the intraoral occlusal device with spatial accuracy of approximately 0.3 mm in the condylar, molar and incisal regions. The EMG ratios between centric relations and the reconstructed positions were significantly different (p?<?0.05) for the temporal muscle and the temporalis/masseter ratio.

Conclusions

The findings revealed that three-dimensional jaw-relation recording may be reproduced in a simulated prosthetic reconstruction within the accuracy reported for replicate intraoral bite recordings.

Clinical relevance

Centric relation recordings may be reproduced in a prosthetic reconstruction with the spatial accuracy of 0.3 mm.     

Centric Relation Registration Using an Anterior Deprogrammer in Dentate Patients

A technique is described for registering centric relation in dentate patients using an anterior deprogrammer to prevent muscle splinting. Properly executed, the patient is able to close into centric relation unassisted, eliminating the possibility of operator-induced error associated with commonly accepted manipulative techniques. Verification is possible visually when articulating casts by confirming the precise alignment of the mandibular incisors with occlusal markings on the deprogrammer attached to the maxillary cast.     

Customized procedure to display T-Scan occlusal contacts

The virtual technique described in this article integrates reverse engineering and mandibular dynamics into dental computer-aided design and computer-aided manufacturing (CAD-CAM) systems. This technique aims to provide more objective information to the dental technician for the diagnosis, planning, and treatment phases. In order to carry out this protocol, the following devices, currently available in many practices, are necessary: an intraoral scanner, a T-Scan system, and some specific open reverse engineering software. By means of a virtual procedure, the T-Scan system detects the occlusal contacts, and the occlusal surfaces are obtained using an intraoral scanner. Once the alignment between the 3-dimensional occlusal surface and the T-Scan registration is carried out, the resulting contacts are projected onto the patient’s occlusal surfaces; in this way, occlusal forces are obtained over time. The results obtained with this procedure demonstrate the feasibility of integrating different tools and software and the full integration of this procedure into a dental digital workflow.     

Computer-assisted morphological analysis of dental casts with maxillary prognathism and reversed occlusion

The morphologic characteristics of the dentition with maxillary prognathism and reversed occlusion were examined by a computer-assisted dental cast analysing system. Dental casts with normal occlusion, maxillary prognathism and reversed occlusion were selected and measured by a 3D shape measuring system. The dental arches and anteroposterior occlusal curves were approximated numerically by the polynomial expression with a fourth order and second order coefficients, respectively. The coefficients were analysed statistically. Maxillary dental arches with mandibular prognathism showed a more acuminate shape (V-shape) with a significant larger second order coefficient, while arches with reversed occlusion showed more angulate shapes (U-shape) with significantly smaller second order coefficients compared with arches with normal occlusions. However, a notable difference in the shape of the mandibular dental arches was not observed. The mandibular dental arches with maxillary prognathism were positioned backward relative to maxillary dental arches, while the arches with reversed occlusion were positioned forward. The anteroposterior occlusal curves with maxillary prognathism showed larger curvatures in maxilla and mandible, while the curves with reversed occlusion showed smaller curvatures in mandible comparing with the curves with normal occlusion. These results suggest that the present method could offer a useful and objective examination technique for the diagnosis of malocclusion.     

A Digital Technique to Replicate Edentulous Arches with Functional Borders and Accurate Maxillomandibular Relationship for Digital Complete Denture

Correct functional border impression and jaw registration is a challenge when edentulous arches are directly digitized with an intraoral scanner. This article describes a digital workflow to replicate complete edentulous arches with full functional contour, and position them in the centric relation using an intraoral scanner, existing denture, and three‐dimensional image reversal technique. Based on the reconstructed images, the base and dental parts of the new denture can be designed efficiently and predictably.     

A single procedure for the registration of maxillo-mandibular relationships and alignment of intraoral scans of edentulous maxillary and mandibular arches

PurposeThe presented technique describes the intraoral scanning workflow to capture scans of edentulous arches and occlusion rims, align them as per maxillo-mandibular relationships registered in the occlusion rims, and incorporate data for tooth arrangement.MethodsOn preliminary intraoral scans of the edentulous arches, design the baseplates for the occlusion rims, make a 3D print of them and finalize by adding wax. Use occlusion rims to make jaw relation record and definitive intraoral scans. Use the “Pre-preparation scan” function to link scans of occlusion rims to scans of edentulous arches and align each other.ConclusionsMaking and aligning, in a single procedure, intraoral scans of the edentulous arches and occlusion rims incorporating maxillo-mandibular relationships and information for tooth arrangement, allow to proceed directly with the denture design, thus, being sensible from the treatment time efficiency point of view. The technique is applicable to both partial and complete edentulous maxillary and mandibular arches. Nonetheless, care should be taken in stabilizing occlusion rims, whose shape is characterized by a reduction in size of the baseplates. In addition, its accuracy in comparison with the current clinical best practice based on conventional procedure requires to be addressed by further research.     

An Efficient and Cost‐Effective Technique to Construct an Intraoral Central Bearing Tracing Device

Intraoral central bearing tracing has been shown to be a predictable way of recording and verifying centric relation position for patients. Existing tracing devices are challenging to use due to several significant clinical limitations. In comparison to commercially available counterparts, this article presents a technique that simplifies instrumentation and clinical steps to make an intraoral tracer for making centric relation records, determining occlusal vertical dimension, and detecting deflective occlusal contacts in edentulous patients.     

Using the neutral zone to obtain maxillomandibular relationship records for complete denture patients

A technique for obtaining maxillomandibular registration for complete denture patients is presented. The maxillary rim is formed with the use of conventional techniques. The mandibular rim is made from modeling plastic impression compound on a record base formed by the patient into the neutral zone. The mandibular rim then is reheated, and the patient determines the occlusal vertical dimension by swallowing. An imprint of the maxillary rim is made on the mandibular rim at the occlusal vertical dimension. The posterior extent of the mandibular rim is relieved 1 mm. Orientation notches are placed in both rims, and centric relation is recorded with a fast-setting vinyl polysiloxane material.     

内置式牵引成骨技术治疗颌骨畸形

目的 :探讨内置式牵引成骨技术在不同类型的牙颌面畸形治疗中的应用。方法 :应用 2种类型的内置式牵引装置 ,为严重的小颌畸形、上颌后缩畸形、半侧颜面萎缩畸形和下颌骨缺损畸形患者行下颌骨体水平方向延长、上颌骨水平前徙、下颌升支与上颌骨同期垂直向延长以及下颌骨体部双端式牵引延长 ,共 5例。结果 :5例牵引成骨手术 ,部分病例辅助正颌外科手术 ,均达到术前设计要求 ,临床效果满意。 2例因牵引方向导致的错牙合问题 ,在牵引结束时及时得以纠正。无伤口裂开、感染、骨坏死、骨不连等并发症。结论 :应用内置式牵引成骨技术可重建面部轮廓 ,恢复理想的咬合关系和口颌功能 ,创伤小 ,安全可靠     

Determination of the physiologic equilibrium point of the mandible by electronic means

The location of the physiologic equilibrium point of the mandible was determined by electronic means while the subjects clenched their teeth in centric relation with a force of 24 pounds. A total of 20 occlusal relationships were observed. In 14 Angle's Class I occlusal relationships, the equilibrium point, when projected at right angles to the midsagittal plane, was observed lined up within the mesial third of the mandibular first molar. In four Angle's Class II occlusal relationships, it was lined up within the distal half of the mandibular second premolar; and in two Class III Angle's occlusal relationships, it was lined up within the middle third of the mandibular first molar. When referenced to the maxillary arch, 16 occlusal relationships lined up within the mesial third of the first molar and four within the distal half of the second premolar. In the coronal plane, the equilibrium point was estimated as being in or close to the midsagittal plane. The biomechanical significance of the equilibrium point was discussed. The location of the equilibrium point was expressed mathematically using a model of the mandible as a beam on resilient supports. Further studies considering the clinical significance of the equilibrium point in relation to centric occlusion registrations and orthodontic treatment are suggested.     

无牙颌正中关系位的哥特式弓描记与转移

目前一般认为确定无牙颌水平关系即确定正中关系位,哥特式弓描记法是唯一在确定关系时可客观观察下颌后退程度的方法。它利用固定于上下颌弓上的装置记录下颌运动时的信息,描记出雨伞状的划痕,雨伞顶点即被认为是正中关系位点。本文详细介绍了利用哥特式弓描记法记录与转移正中关系位的临床规范操作方法,主要内容包括安装描记盘、固定描记针、口内描记、记录正中关系位和转移至牙合架等操作,每一步操作都通过相应的临床图片进行详细说明。     

Mounting casts on a mechanical articulator by using digital multisource data: A dental technique

A facebow transfer is typically used for mounting a maxillary gypsum cast in an ideal location in a mechanical articulator. However, the facebow transfer procedure is difficult and may cause the patient discomfort. This proposed technique uses a patient’s cone beam computed tomography (CBCT) data to reproduce the occlusal plane in relation to digital articulator scan data, align the patient’s gypsum cast or intraoral scan data on the reproduced plane, and then transfer the data to a mechanical articulator.     

Finite element analysis of stresses in the maxillary and mandibular dental arches and TMJ articular discs during clenching into maximum intercuspation, anterior and unilateral posterior occlusion

The objective of this study was to investigate distribution of stresses in the human TMJ discs, generated during clenching into various occlusal positions. The work presents a biomechanical finite element model of interaction of mandibular and maxillary dental arches and the TMJ discs of a particular person, based on real geometrical data obtained from spiral computed tomography two-dimensional images. 3D contour coordinates - point clouds were collected from these images and solid model was created. The system under investigation consisted of eight basic parts: two rigid structures representing the mandibular and maxillary dental arches, two mandibular condyles, two mandibular fossae of temporal bone, and solid models of two articular discs. The model of maxillary dental arch was fixed in space. The model of the mandibular dental arch was able to move in space synchronically with the mandibular condyles under action of applied forces, which were considered as prescribed and known at insertion points of masticatory muscles. The motion of the mandible was constrained by interdental contact interactions and contact interaction with articular discs, which were situated in between mandibular condyles and mandibular fossae of temporal bone. The model was implemented by using LS-DYNA finite element software. The obtained results presented a 3D view of stresses exhibited in the articular discs, as well as the real contact points of dental interactions at given masticatory geometry of a particular subject and the values of interaction forces. The expected practical value of the developed model is the facilitation of biomechanical evaluations of the influence of tolerances of teeth shapes and occlusal areas together with the supporting areas on the final stress distribution in the dental arches and articular discs.     

The effect of changing the maxillomandibular relationship by a bite plane on the habitual mandibular opening and closing movement

The relationship between the change of afferent information from occlusal contacts and its influence on the jaw muscles was investigated. For this purpose, the following questions were posed and experimental studies designed. If the subject was given habitual occlusal contacts in centric relations with a bite plane, were the habitual mandibular closing and opening movements influenced? Second, was it easier for the subjects to accomplish regular habitual mandibular opening and closing movements, when the bite plane was inserted and removed? From the results it could be concluded that the centric occlusal contacts in centric relation were more physiological for the jaw muscles. In addition, when the new occlusal position was coincident or close to the centric relation, it was easier for the subject to study and acquire the new habitual mandibular opening and closing movement.     

Critical assessment of a device to measure incisor crown inclination.

The aims of this study were to critically assess the use of a disposable device--the tooth inclination protractor (TIP)--to record incisor crown inclination and to compare its reliability and validity with that of traditional cephalometric radiographic analysis. The sample comprised 30 dental students with lateral cephalometric radiographs and dental casts. Four examiners were trained and calibrated to digitize radiographs and to use intraoral (on patients and dental casts) and extraoral (on dental casts) TIPs. The following angles were measured on the radiographs: maxillary incisor to maxillary plane, mandibular incisor to mandibular plane, maxillary incisor to occlusal plane, and mandibular incisor to occlusal plane. Measurements were also made with the TIP: maxillary incisor to occlusal plane and mandibular incisor to occlusal plane. All techniques were reliable between examiners. There were statistically significant systematic differences between the TIP and the radiographic assessments. The following differences were found. The TIP tended to record maxillary incisor crown inclination an average of 14 degrees less than maxillary incisor to maxillary plane. The TIP tended to record mandibular incisor crown inclination as similar to mandibular incisor to mandibular plane. The TIP recorded mandibular crown inclination 19 degrees less than mandibular incisor to occlusal plane. The disposable TIP was shown to be a simple, inexpensive, reliable, and valid method of assessing incisor inclination.     

Fabricating Complete Dentures with CAD/CAM and RP Technologies

Two techological approaches for fabricating dentures; computer‐aided design and computer‐aided manufacturing (CAD/CAM) and rapid prototyping (RP), are combined with the conventional techniques of impression and jaw relation recording to determine their feasibility and applicability. Maxillary and mandibular edentulous jaw models were produced using silicone molds. After obtaining a gypsum working model, acrylic bases were crafted, and occlusal rims for each model were fabricated with previously determined standard vertical and centric relationships. The maxillary and mandibular relationships were recorded with guides. The occlusal rims were then scanned with a digital scanner. The alignment of the maxillary and mandibular teeth was verified. The teeth in each arch were fabricated in one piece, or set, either by CAM or RP. Conventional waxing and flasking was then performed for both methods. These techniques obviate a practitioner's need for technicians during design and provide the patient with an opportunity to participate in esthetic design with the dentist. In addition, CAD/CAM and RP reduce chair time; however, the materials and techniques need further improvements. Both CAD/CAM and RP techniques seem promising for reducing chair time and allowing the patient to participate in esthetics design. Furthermore, the one‐set aligned artificial tooth design may increase the acrylic's durability.     

长正中《牙合》型下颌全口义齿近中移位量的初步研究

目的 探讨无牙颌患者戴用长正中<牙合>型全口义齿3个月后下颌义齿的近中移位量能否满足患者长正中量的自然要求,从而检验长正中<牙合>型全口义齿的设计理论. 方法 为10例无牙颌患者制作长正中<牙合>型、线性<牙合>型和解剖<牙合>型3种全口义齿,采用哥特式弓描记装置测量无牙颌患者的长正中量,采用三维精密平移台测量3种<牙合>型下颌义齿的近中移位量.对比分析不同<牙合>型下颌义齿近中移位量的差异,并与患者长正中量进行对比. 结果 10例无牙颌患者的长正中量为(1.02±0.36)mm,3种<牙合>型下颌义齿的近中移位量分别为:长正中<牙合>型(1.016±0.348)mm,线性<牙合>型(1.092±0.448)mm,解剖<牙合>型(0.409±0.253)mm. 结论 长正中<牙合>型全口义齿能满足患者长正中量的自然要求,以及在患者正中关系位至肌力闭合道终点的位置之间无障碍的义齿设计要求.