Influence of clenching level on intercuspal contact area in various regions of the dental arch

The purpose of this study was to evaluate the relationship between the clenching level and the intercuspal contact area in different regions of the dental arch. Twenty-five healthy subjects with natural normal dentitions and good occlusal support performed clenching tasks in the intercuspal position at four different levels (10, 30, 70 and 100% levels of maximum voluntary contraction) through EMG visual feedback from bilateral masseter and anterior temporal muscles. Simultaneously, the occlusal contacts were recorded with a silicone occlusal contact checking material (Black Silicone, GC Dental Industrial Corp., Tokyo, Japan). The occlusal records were analysed by an image analyser. Every area of the thickness less than 50 microm was determined to be an occlusal contact area. The occlusal contact areas on the anterior teeth (incisors and canines), the premolars (first and second premolars) and the molars (first and second molars) were calculated separately. The posterior occlusal contact area increased with an increase in the clenching levels but that of the anterior did not. The results of this study indicate that the increase in clenching forces affects the anterior and posterior occlusal contact areas differently.     

正常接触位、下颌后退接触位咬合接触的计算机图像分析

目的 :研究正常牙合肌接触位及下颌后退接触位咬合接触的基本规律。方法 :采集 35名正常牙合肌接触位及下颌后退接触位的硅橡胶牙合记录 ,进行计算机图像分析。结果 :肌接触位 33人前牙无接触 ,单颌后牙区接触数为 16 .6± 7.2 ,所有受试者均为双侧接触。肌接触位咬合接触均在牙尖交错位重复出现。接触频率超过 5 0 %的部位位于上颌磨牙颊尖和舌尖的远中斜面 ,下颌磨牙颊尖和舌尖的近中斜面。下颌后退接触位所有受试者均为双侧接触 ,有接触的牙齿数目单颌单侧 2 .7± 0 .8,接触点数目单颌 8.0± 2 .3,前牙无接触 ,接触数目及比率从第二磨牙到第一前磨牙依次减少。接触频率超过 40 %以上的斜面上颌为前磨牙舌尖、磨牙远中舌尖及第二磨牙近舌尖的近中颊斜面 ,下颌为前磨牙及第二磨牙颊尖的远中舌斜面。结论 :以硅橡胶为记录材料准确采集到肌接触位及下颌后退接触位牙合记录 ,经计算机图像分析 ,得出其咬合接触的基本特征。     

Influence of clenching intensity on bite force balance, occlusal contact area, and average bite pressure.

It has been difficult for investigators to simultaneously and reliably evaluate bite force in the intercuspal position with the area and location of occlusal contacts. This study was designed to investigate the variations in these parameters with respect to two factors: three levels of clenching and the preferred chewing side. Human subjects with normal occlusion were examined with a recently developed system (Dental Prescale Occluzer, Fuji Film, Tokyo, Japan). The three levels of clenching intensity were assessed by masseteric EMG activity and included the maximum voluntary contraction, and 30% and 60% of the maximum. The results indicated that the bite force and occlusal contact area on the whole dental arch increased with clenching intensity. In contrast, the average bite pressure, obtained by dividing the bite force by the contact area, remained unchanged regardless of the clenching intensity. As the clenching intensity increased, the medio-lateral position of the bite force balancing point shifted significantly (P<0.01) from the preferred chewing side toward the midline. The antero-posterior position remained stable in a range between the distal third of the first molar and the mesial third of the second molar. The bite force and occlusal contact area, which were mainly on the molars, increased with the clenching intensity, whereas the proportions of these two variables on each upper tooth usually did not change significantly. The exception was the second molar on the non-preferred chewing side. When comparisons were made between pairs of specific upper teeth of same name, usually no significant difference was found in bite force or occlusal contact area, regardless of the clenching level. Again, the exception to this observation was the second molar on the preferred chewing side, which had a larger area at the 30% clenching level. The results in normal subjects suggest that as the clenching intensity increases in the intercuspal position, the bite force adjusts to a position where it is well-balanced. This adjustment may prevent damage and overload to the teeth and temporomandibular joints.     

Occlusal force distribution on the dental arch during various levels of clenching

The purpose of this study was to explore the occlusal force distribution on the dental arch in the intercuspal position and to evaluate the relationship between the clenching strength and the occlusal force distribution. These variables were recorded using the Dental Prescale System in 16 healthy young adults. The number of tooth contacts, occlusal force and occlusal contact area increased linearly as clenching strength increased. The distribution of the occlusal force was greatest at the molar region followed by the premolar and anterior teeth region. The proportion of occlusal force (occlusal force at each region/total occlusal force) on molar regions increased as clenching strength increased. On the contrary, the proportion of occlusal force on the premolar and anterior teeth regions decreased as clenching strength increased. These findings suggest that control of occlusal force is important in diagnosis of the nature of occlusal contacts.     

The anterior component of occlusal force. Part 1. Measurement and distribution

The purpose of this investigation was to design and develop instrumentation to measure the anterior component of occlusal force generated by a single tooth under a known axial load. An additional objective was to quantify the distribution and dissipation of this force as it progressed anteriorly. The anterior component of the occlusal force generated by the left second molar was calculated from frictional force measurements at each contact mesial to the first molars in both dental arches. The distribution of this force and its dissipation were determined for 15 subjects. When a load was placed on the posterior teeth, the anterior component of the occlusal force was found to progress anteriorly through interproximal contacts and not to progress beyond open contacts. The mean magnitude of this force for a conservative occlusal load of 20 pounds was unexpectedly high: 5 pounds against the premolars and 1 pound against the canines. In some subjects this force crossed the dental midline and continued around the arch to the canine of the contralateral side. The distribution and dissipation of the anterior component of the occlusal force anteriorly approximated an exponential decay function.     

EMG response to alteration of tooth contacts on occlusal splints during maximal clenching

Maximum clenching on an equilibrated occlusal splint yielded an increase of 17% in overall muscle activity over that of maximum intercuspation contributed mainly by masseter muscles. Maximum clenching on an anterior occlusal splint yielded a decrease of 13% in overall muscle activity compared with that of an equilibrated occlusal splint. When maximum clenching was performed with six left-sided teeth removed from contact while the left second molar remained in contact, there was no significant change in muscle activity when compared with that of an equilibrated occlusal splint. When left-sided muscles were compared with right-sided muscles for the same situation, there was no significant change. When maximum clenching was performed with all left-sided teeth removed from contact, there was a decrease of 21% in overall muscle activity compared with that of an equilibrated occlusal splint. When left-sided muscles were compared with right-sided muscles for the same situation, there was no significant change. Changes in the number of tooth contacts did not cause changes in the overall muscle activity during maximum clenching. Changes in the position of the tooth contacts altered the overall muscle activity during maximum clenching. Changes in occlusal contact symmetry did not cause changes in symmetry of muscle pairs during maximum clenching. Unilateral support produced the subjective response of pressure on the contralateral TMJ during maximum clenching.     

�dz�������볣��������γ���˫�ǰͻ�ٴ���Ч�Ƚ�

目的    探讨拔除第一磨牙矫治成人双颌前突错牙合的可行性。方法    选择2003年1月至2008年6月大连市口腔医院正畸科收治的成人双颌前突患者20例,按照磨牙是否存在病变或缺失分为试验组和对照组,每组10例。试验组：患者均存在1颗或多颗第一磨牙严重病损或者早失;矫治设计拔除病损侧的第一磨牙而保留健康的双尖牙,早失磨牙侧不再减数,健康侧常规拔除第一前磨牙。对照组：矫治设计常规减数4颗第一双尖牙。所有病例均使用直丝弓矫治器,采用传统支抗技术,通过头影测量分析各组疗效。结果    试验组和对照组治疗后头影测量显示,面凸角减小、上下唇角增加,反映侧貌突度减小。矫治后硬组织改变主要为上下前牙内收。试验组患者平均疗程（34.5±4.5）个月,磨牙拔牙间隙完全关闭;治疗后第三磨牙与对牙合的第二或第三磨牙均建立良好咬合关系,且第二磨牙与第三磨牙牙根平行状况良好。对照组患者平均疗程（22.5±3.5）个月,上前牙回收幅度较试验组明显。结论    对于第一恒磨牙存在严重龋坏或过早缺失的成人双颌前突患者,经过仔细的支抗设计和精心的临床操作,非常规拔除第一磨牙与常规减数第一双尖牙矫治均可获得较满意的临床治疗效果,但常规减数治疗上前牙回收幅度更大且疗程较短。     

Influence of Variation in Jaw Posture on Sternocleidomastoid and Trapezius Electromyographic Activity

This study was conducted in order to determine the influence of variation in the occlusal contacts on electromyographic (EMG) cervical activity in 20 patients with myogenic cranio-cervical-mandibular dysfunction. EMG recordings during maximal voluntary clenching were performed by placing surface electrodes on the left sternocleidomastoid and upper trapezius muscles in the following conditions: intercuspal position; edge to edge left laterotrusive contacts (ipsilateral); edge to edge right laterotrusive contacts (contralateral); edge to edge protrusive contacts; and retrusive occlusal contacts. A significant higher EMG activity was recorded in both muscles during maximal voluntary clenching in retrusive occlusal contact position, whereas no significant differences in EMG activity were observed between intercuspal position, ipsilateral, contralateral and protrusive contact positions. The EMG pattern observed suggests that a more frequent intensity and duration of tooth clenching in retrusive occlusal contact position could result in more clinical symptomatology in these cervical muscles in patients with myogenic cranio-cervical-mandibular dysfunction.     

牙齿楔状缺损与侧方工作侧咬合接触关系的调查

目的研究牙颈部楔状缺损与牙齿咬合接触的关系.方法选取123名中年机关干部.用0.02mm厚的超薄咬合纸,临床检查侧方运动工作侧上颌尖牙、第一、二前磨牙、第一磨牙颊尖各斜面上及咀嚼循环各个时期中的牙齿咬合接触情况;评估接触程度.结果患楔状缺损牙齿咬合接触程度明显高于未患楔状缺损牙.上颌尖牙和前磨牙楔状缺损患牙在远中(上第一磨牙的近、远中)斜面上咬合接触程度高于未患牙,患牙在咀嚼侧方运动循环的中、末(上第一磨牙在初、中或末)期咬合接触程度增加.结论牙颈部楔状缺损的发生与牙齿的咬合接触程度加重有关.     

牙齿楔状缺损与侧方工作侧咬合接触关系的调查

目的　研究牙颈部楔状缺损与牙齿咬合接触的关系。方法　选取 12 3名中年机关干部。用 0 .0 2mm厚的超薄咬合纸 ,临床检查侧方运动工作侧上颌尖牙、第一、二前磨牙、第一磨牙颊尖各斜面上及咀嚼循环各个时期中的牙齿咬合接触情况 ;评估接触程度。结果　患楔状缺损牙齿咬合接触程度明显高于未患楔状缺损牙。上颌尖牙和前磨牙楔状缺损患牙在远中 (上第一磨牙的近、远中 )斜面上咬合接触程度高于未患牙 ,患牙在咀嚼侧方运动循环的中、末 (上第一磨牙在初、中或末 )期咬合接触程度增加。结论　牙颈部楔状缺损的发生与牙齿的咬合接触程度加重有关。     

Extraction treatment of a Class II division 2 malocclusion with mandibular posterior discrepancy and changes in stomatognathic function

This case report describes the successful extraction treatment of a Class II division 2 malocclusion with mandibular posterior discrepancy and a congenitally missing maxillary lateral incisor on the left side. The posterior space in the mandibular arch was small, and the mandibular second molars were impacted, with distal tipping. The discrepancies in the maxillary and mandibular arches were resolved by extraction of the maxillary lateral incisor on the right side and the mandibular second premolars on both sides. The mesial movement of the mandibular first molars occurred appropriately, with the second molars moving into an upright position. A lip bumper was used with a preadjusted edgewise appliance in the maxillary dentition to reinforce molar anchorage and labial movement of the retroclined incisors. Despite the extraction treatment, a deep bite could be corrected without aggravation as a result of the lip bumper and utility arch in the mandibular dentition. Thus, an Angle Class I molar relationship and an ideal overbite were achieved. The occlusal contact area and masticatory muscle activities during maximum clenching increased after treatment. The maximum closing velocity and the maximum gape during chewing increased, and the chewing pattern changed from the chopping to grinding type. The findings in the present case suggest that the correction of a deep bite might be effective for improving stomatognathic function.     

Evaluation of masticatory activity during unilateral single tooth clenching using muscle functional magnetic resonance imaging

Masticatory muscle activity during teeth clenching is affected by occlusal pattern. However, few studies have performed simultaneous evaluation of all masticatory activities during teeth clenching under various occlusal conditions. The aim of this study was to use muscle functional magnetic resonance imaging (mfMRI) to evaluate the effects of changes in occlusal point on masticatory activity during single tooth clenching. Changes in mean proton transverse relaxation time (?T2) as an index of activity in all masticatory muscles during left unilateral clenching at the first molar or first premolar for 1 min were examined in nine healthy volunteers. Bite force was maintained at 40% of the maximum voluntary clenching force. The ?T2 values of the masseter and lateral pterygoid muscles were analysed separately for superficial and deep layers, and for superior and inferior heads. The ?T2 values for the ipsilateral deep masseter were significantly lower, and for the superior head of the ipsilateral lateral pterygoid muscles were significantly higher, after left first premolar clenching compared to left first molar clenching. These results quantitatively demonstrate a significant increase in activity of the superior head of the ipsilateral lateral pterygoid muscle and a significant decrease in activity of the ipsilateral deep masseter muscle with forward displacement of the occlusal contact point during unilateral tooth clenching.     

Influence of occlusal contacts on tooth displacement for mesio-distal direction

To fabricate a prosthesis which is functionally harmonized with the stomatognathic system, the interocclusal relationship must be reproduced as accurately as possible. This study investigated the influence of the occlusal contacts upon tooth displacement and clarified the optimal occlusal contacts for the prosthesis. The displacement paths of six maxillary left first molars of six adults in good general health were measured in this study. We gave each test tooth eight patterns of artificial occlusal contacts by attaching platinum foil on the occlusal surface. Subjects were asked to perform clenching at the intercuspal position (= ICP) with medium occlusal forces, and 3-dimensional tooth displacement paths were measured by the Type M-3 tooth displacement transducer. The following conclusions were obtained. 1. Using the Student's t-test for statistical analysis, it was suggested that the difference of the buccolingual location of occlusal contacts influenced the direction of the tooth displacement. 2. The tooth which had occlusal contact in the buccal cusp displaced in the mesio-buccal direction, so this may create a wide dental arch and a slight discrepancy was generated at the distal interproximal contact area of the tooth. 3. It was shown that the tooth which had occlusal contact in the buccal cusp rotated in the buccoapical direction in reverse to the natural tooth.     

Changes in tooth contacts following orthodontic treatment

Occlusal contacts in maximum intercuspation were examined in 38 patients at the end of the active phase of orthodontic treatment and again 3 months into the retention phase to assess the initial posttreatment occlusal changes. The sample consisted of 23 patients with conventional retainers and 15 patients with gnathological rubber tooth positioners. Polyether rubber impression bites were used to record occlusal contacts. The locations of the contacts were then transferred to study models. In the combined sample (N = 38), the total number of contacts increased 14% over the 3-month period. This was due entirely to an increase in the number of contacts on posterior teeth (premolars and molars). Those cases with fewer teeth in contact at the end of treatment developed more teeth in contact over the 3-month period. Although the group retained with positioners demonstrated a greater gain in the total number of teeth in contact over time when compared with the group with conventional retainers, the additional gain was minimal.     

楔状缺损与咬合力关系的研究

目的 临床研究楔状缺损与He力的关系。方法 将123例患不同程度楔状缺损的中老年患者，按楔状缺损的程度分为无、轻、中、重度4组；使用电阻应变式咬合力计测量上颌尖牙、第一、二双尖牙、第一磨牙牙齿咬合力；用光He法测定上颌牙齿最高He接触强度。结果 楔状缺损患牙的咬合力低于无楔状缺损牙。上颌第一双尖牙的楔状缺损患牙的最高He接触强度高于未患牙、楔状缺损组中的第一磨牙和第一双澡牙相对于其邻牙的最高He接触强度增高。结论 He力与楔状缺损的发生有关。     

255例牙冠折裂的临床分析

目的分析长期咀嚼过程中牙冠折裂的发生情况,并初步探讨冠折发生的相关因素。方法以2005年12月-2007年12月在兰州市第一人民医院口腔科就诊的255颗冠折牙为研究对象,对折裂牙的患者性别、年龄、牙位、折裂位置及形态等进行分析。结果255颗冠折牙中,1）上颌第一磨牙76颗（29.8%）,下颌第一磨牙45颗（17.6%）,上颌第二磨牙41颗（16.1%）,下颌第二磨牙37颗（14.5%）,上颌第二前磨牙32颗（12.5%）,上颌第一前磨牙15颗（5.9%）,下颌第二前磨牙9颗（3.5%）;2）折裂位置与窝沟重叠者158颗（62.0%）,发生于牙尖斜面者97颗（38.0%）。3）正常者85颗（33.3%）,面形态异常者55颗（21.6%）,型异常者115颗（45.1%）。结论牙位及形态等与牙冠折裂的发生具有一定的关系。力是牙冠折裂的基本因素,但不是唯一因素。     

Conservative interdisciplinary treatment of a case with multiple facial and condyle fractures

The purpose of this case report is to describe an interdisciplinary approach for a 51‐year‐old male who underwent multiple facial fractures including bilateral condyle fractures. The patient underwent emergency surgery, which included open reduction of the maxilla and mandibular symphysis and closed reduction of the bilateral condyle fractures. Although the patient recovered a comfortable range of mouth opening and alleviation of the temporomandibular joint (TMJ) symptoms after surgery, he suffered from a large anterior–posterior discrepancy due to less stability on the condyle‐fossa relationships and from open bite with contacts only on both second molars and right second premolars. In this case, first, to increase the occlusal contact, comprehensive orthodontic treatment was completed. Second, occlusal equilibration was selectively performed to relieve the interferences and establish a stable range of mandibular movement without any changes in the vertical dimension. Third, both the upper central incisors and left lateral incisor were minimally restored with splinted and single zirconia crowns, which had modified lingual contours to provide adequate anterior guidance permitting the anterior–posterior discrepancy of the posterior teeth during protrusion. This conservative interdisciplinary treatment, including open and closed reduction, orthodontic treatment, occlusal adjustment, and minimal prosthetic restorations, resulted in a stable mandibular position and recovery of mastication function.     

Influence of different condylar and incisal guidance ratios to the activity of anterior and posterior temporal muscle

OBJECT: Few studies quantify reactions of masticatory muscles during clenching at different occlusal positions in individuals with different anterior and posterior guidance relationship and different number of working-side occlusal contacts. The hypothesis that altered incisal guidance (IG) and a different number of working-side occlusal contacts in complete denture wearers (CDW) change a pattern of temporal muscle activity and loadings to the mandible during clenching in incisal and lateral positions was tested. DESIGN: EMG activity during clenching in incisal (IP) and left (LOP) and right lateral occlusal (ROP) positions was compared between dentate subjects (DS) with steeper IG than condylar guidance (PG) and canine or canine+first premolar guidance in laterotrusive movements with CDWs who had steeper PG than IG and group function. EMG values were expressed as percentages of maximum voluntary clenching in maximum intercuspation (ICP) in each individual. RESULTS: The CDWs exhibited significantly higher posterior temporal muscle (TP) activity in IP and during lateral biting on mediotrusive side than DSs. Their coronoid process had to be pulled backward by TP fibers to rotate condyle in a counter-clockwise direction (PG>IG); contrary DSs had to rotate condyle in a clockwise direction to compensate for vertical overlap (IG>PG). Group function allowed more working-side contacts in CDWs and significantly higher anterior temporalis (TA) activity. CONCLUSION: Alteration of IG-PG ratio and a number of occlusal contacts during lateral clenching change a pattern of TA and TP activity in CDWs and a direction of mandibular loadings, although age related changes might also be responsible.     

T-ScanⅡ咬合分析数据作为早期牙隐裂调(牙合)干预指标的应用研究

目的:探讨牙隐裂(cracked tooth syndrome,CTS)患者动态咬合特征,分析其异常(牙合)因素,探索T-Scan Ⅱ咬合力分析系统作为牙隐裂调(牙合)干预指标之一的可行性.方法:T-ScanⅡ咬合力分析系统记录15名早期牙隐裂患者调胎干预前后牙尖交错位(ICP)及左右侧方咬合的过程.定量测定(牙合)接...     

Effect of balancing-side occlusion on the ipsilateral TMJ dynamics under clenching

summary The effect of balancing-side occlusal contact patterns on ipsilateral TMJ dynamics was evaluated in this study. Vertical displacement of the balancing-side lower second molar during clenching at canine edge-to-edge position, with 0 and 1 mm of inter-canine distance, was measured for 42 normal subjects in relation to their balancing-side occlusal contact. Balancing-side occlusal contact was classified into four following patterns; (1) simultaneous balancing-side and working-side contact (without clenching); (2) balancing-side contact (with clenching only); (3) no balancing-side contact (with or without clenching); and (4) exclusive balancing-side contact (no working-side contact). The vertical displacement of the balancing-side condyle, calculated from the displacement of the balancing-side second molar, showed three different types of displacement pattern. These three types showed distinctive incidence in relation to the pattern of balancing-side occlusal contact. It was revealed that balancing-side occlusal contact can affect the ipsilateral TMJ dynamics.