Maxillary anterior and mandibular posterior residual ridge resorption in patients wearing a mandibular implant-retained overdenture

The mandibular implant-retained overdenture could improve masticatory function compared to the conventional complete denture. However, increased forces exerted by the overdenture could increase residual ridge resorption of the maxillary anterior and mandibular posterior areas. The aim of this study was to compare the effect of the mandibular implant-retained overdenture using two or four dental implants, or the conventional complete denture on resorption of the residual ridge of the maxillary anterior and mandibular posterior areas over a period of 10 years. In total, 120 patients, 30 patients treated with an overdenture on two implants (two-implant group), 30 patients with an overdenture on four implants (four-implant group) and 60 patients treated with a conventional full denture (conventional group), participated in this study. On panoramic radiographs, made before and 10 years after treatment, proportional area measurements were applied to determine changes in bone height. After 10 years, a statistically significant amount of bone resorption had occurred in the anterior maxilla in the two-implant group and in the four-implant group. A significant amount of bone resorption had occurred in the posterior mandible in all three groups. There were no statistically significant differences between the groups in both areas. Patients presented large individual differences. It is concluded that patients rehabilitated with implant-retained mandibular overdentures are not subjected to more residual ridge resorption in the anterior maxilla when compared to patients wearing a conventional full denture. Regarding the mandibular posterior residual ridge, resorption was irrespective of wearing an implant-retained mandibular overdenture or a conventional mandibular denture.     

Association between occlusal force distribution in implant overdenture prostheses and residual ridge resorption

This study aimed to investigate residual ridge resorption (RRR) of anterior and posterior maxillary and mandibular edentulous ridges, in patients treated with mandibular implant overdentures (IOD) and compare with conventional complete denture (CD) wearers, and to determine at each location, the association of RRR with the occlusal forces distribution and other patients’ variables. The anterior and posterior RRR of IOD (six males, 17 females) and CD (12 males, 11 females) groups were determined using baseline and follow‐up dental panaromic radiographs (DPT) (mean intervals 4 ± 1·8 years). The bone ratios were calculated using proportional area: anatomic to fixed reference areas and mean difference of ratios between the intervals determined RRR. The ridge locations included anterior and posterior maxillary and posterior mandibular arches. The T‐Scan III digital occlusal system was used to record anterior and posterior percentage occlusal force (%OF) distributions. There were significant differences in anterior and posterior %OF between treatment groups. Two‐way anova showed RRR was significant for arch locations (P = 0·005), treatment group (IOD versus CD) (P = 0·001), however, no significant interaction (P = 0·799). Multivariate regression analyses showed significant association between RRR and %OF at anterior maxilla (P = 0·000) and posterior mandible (P = 0·023) and for treatment groups at posterior maxilla (P = 0·033) and mandibular areas (P = 0·021). Resorption was observed in IOD compared to CD groups, with 8·5% chance of less resorption in former and 7·8% in the latter location. Depending on arch location, ridge resorption at various locations was associated with occlusal force distribution and/or treatment groups (implant prostheses or conventional complete dentures).     

A clinical investigation of the morphological changes in the posterior mandible when implant-retained overdentures are used

OBJECTIVES: The widespread use and broad acceptance of osseointegrated dental implants as a means of retaining and supporting mandibular overdentures provide potentially stable three-dimensional reference structures, which have been used to examine the morphological changes of the surface contours of the mandibular ridges distal to implants. Unlike traditional methods that tended to measure changes in ridge morphology and quantity radiographically, this prospective study investigated the changes in the sagittal surface contours of the posterior residual ridges over a 1-year period by an alternative, non-radiographic method using serial casts of residual ridges of a group of patients. MATERIAL AND METHODS: The residual ridges of the serial casts produced were examined using a profiling apparatus and computer software programs that allowed the orientation, digitised recording and measurement of the sagittal surface contours of the posterior residual ridges of mandibular casts in terms of area (cm(2)). RESULTS: Statistical analysis revealed that the detected reductive changes in the surface contour of the posterior residual ridges following the wearing of an implant-retained mandibular overdenture over a 1-year period were highly significant (P<0.001). CONCLUSION: It is concluded that the methodology presented in this study can be used reliably as an alternative to radiographical examination for detecting changes that occur in the distal residual alveolar ridges of the implant containing edentulous mandible when implant-retained overdentures are used. Thus, the method presented may be used to contribute to a reduced exposure to ionising radiation for patients wearing implant-retained overdentures.     

A prospective 15‐year follow‐up study of mandibular fixed prostheses supported by osseointegrated implants. Clinical results and marginal bone loss.

In this prospective study 47 edentulous patients were treated with mandibular fixed prostheses supported by osseointegrated Brånemark implants and followed for 12 to 15 years. Three 1%) of the 273 inserted implants were lost, two before and one six years after placement of the fixed prosthesis. The cumulative success rate CSR) of the implants was 98.9% both after 10 and 15 years. None of the fixed prostheses was lost and at the last follow‐up, all patients had stable fixed prostheses in function (CSR 100%). The marginal bone loss around the implants was small, on average 0.5mm during the first post surgical year and thereafter about 0.05mm annually. More bone was lost around the anterior implants than around the most posterior ones. Smoking and poor oral hygiene had significant influence on bone loss, while occlusal loading factors such as maximal bite force, tooth clenching and length of cantilevers were of minor importance. It is concluded that the long‐term results of the mandibular implant treatment were extremely successful, regarding both the fixed prostheses and implant stability. Bone resorption around the implants, albeit limited, was influenced by several factors, smoking and oral hygiene appeared to be most important.     

Glycosaminoglycans in peri‐implant sulcus fluid from implants supporting fixed or removable prostheses

Previous studies have indicated that examination of glycosaminoglycans (GAG) present in peri‐implant sulcus fluid (PISF) may be a useful indicator of metabolic activity of the supporting bone. The GAG content in PISF from osseointegrated implants ad modum Bråemark in the maxilla was quantified and analysed. The study comprised 2 groups with 10 patients in each group. In one group the patients wore removable prostheses; in group 2 the patients wore fixed prostheses. The groups were matched for age, sex and function period of their prosthetic appliances. Clinical data were recorded, and the levels of the GAG hyaluronan (HA) and chondroitin‐4‐sulphate (C4S) were assessed using cellulose acetate electrophoresis and densitometric scanning of Alcian blue‐stained strips against known GAG standards. PISF volumes and levels of C4S as potential bone marker showed no significant difference both groups median 0.003 μg). There was a somewhat higher median value for HA (0.015 μg) in the group of patients with removable prostheses compared with the group with fixed prosthesis =0.008 μg)(NS). HA is known to be present in high amounts in gingival tissue. As both plaque index and gingival bleeding were more frequent in patients with removable prostheses, this may be the reason for the somewhat higher value for HA in this group of patients. The difference in biomechanical properties of fixed and removable prostheses on implants do not appear to be reflected in the bone responses as measured by GAG content in PISF.     

局部注射葛根素对鼠拔牙后剩余牙槽嵴吸收影响的实验研究

目的观察中药葛根素对鼠拔牙后剩余牙槽嵴吸收的影响作用。方法制作大鼠下颌中切牙缺失模型,于剩余牙槽嵴的粘膜下注射葛根素,用X线片测量大鼠相对剩余牙槽嵴高度和骨密度值,HE染色观察不同时期剩余牙槽嵴的组织学形态改变。结果实验组剩余牙槽嵴相对高度均大于对照组（P〈0.05）;除一周组外,其余各实验组剩余牙槽嵴光密度测量值均大于对照组（P〈0.01）;组织学观察可见实验组大鼠剩余牙槽嵴表面的成骨质量较对照组高,骨吸收程度较对照组少。结论将葛根素注射于拔牙窝周围能够抑制剩余牙槽嵴的吸收并保存牙槽嵴的高度。     

Measurements of distances related to the mandibular canal in radiographs

Before implant surgery in the mandibular side segment, it is of utmost interest to locate the mandibular canal in radiographs to avoid interference with the neurovascular bundle during surgery. Six mandibular specimens were radiographically examined with 2 panoramic and 3 tomographic techniques. The distances between the superior border of the canal and the alveolar crest and between the mandibular base and the inferior border of the canal were measured. In addition, the height of the canal was measured. The measurements were performed by 3 or 4 observers and compared with measurements on contact radiographs of the same areas. Tomography gave more accurate values of the above distances than panoramic techniaues. The variation between observers in detecting the mandibular canal Aas large.     

A comparison of hydroxylapatite coated implant retained fixed and removable mandibular prostheses over 4 to 6 years

In a 6-year prospective clinical study, 181 hydroxylapatite coated endosseous dental implants were placed into the anterior mandible of 48 patients. Twenty-one patients were treated with fixed prostheses and 27 patients with an overdenture. When the implants were exposed all 181 had integrated. To date, there is 100% survival of all implants and they all retain a functioning prostheses. The initial results were very promising, in both groups the interval success was over 95% in the first 4 years of the study. However, by year 6, the interval success rates had fallen to 83% for both the fixed and removable groups. This study also compares the construction and maintenance complications for the two types of restorations. The clinical time taken, after implant exposure, to construct the prostheses was similar whether the fixed (mean of 8 visits) or removable option (mean of 7 visits) was chosen. However, the removable restoration cost less than half the price of the fixed when both technical time and implant component costs were evaluated. Maintenance for both groups was higher than expected, but patients required more appointments in the removable group both in the first year and beyond. Regarding the prostheses itself, the incidence of remakes, relines and general adjustments was higher in the removable group. This study has shown that the overdenture offers an effective and initially a more economical alternative to the fixed prostheses, in the treatment of the edentulous mandible. However, long-term maintenance of such a prosthesis can be significant.     

Stress distribution prevents ischaemia and bone resorption in residual ridge

Objective

Intensive mechanical stress and/or inflammation are known to induce alveolar bone resorption. This study investigated whether a distribution of mechanical stress would reduce residual ridge resorption or improve ischaemia.

Design

Thirty rats were divided into six experimental groups (n = 5). The control group received no intentional stimulation, but rats in the experimental groups wore denture stimulators made of acrylic resin or a soft lining material. The stimulator transmitted masticatory pressure to the rats’ palates for four weeks. The four types of soft lining materials investigated in this study dispersed the applied pressure, with compressive stress ranging from 20.8 to 90.8 kPa. Volumes of blood flow and bone resorption of denture foundations were measured every week for 4 weeks. Statistical evaluation of these results was performed using two-way ANOVA and Holm-Sidak test within 5% error limits.

Results

Non-viscoelastic material clearly induced bone resorption and ischaemia of denture foundations, while viscoelastic materials reduced these phenomena to different extents according to their viscoelastic properties. Ischaemia in the alveolar ridge preceded residual ridge resorption, because the amount of residual ridge resorption and blood flow rate showed a simple linear regression.

Conclusion

Animal model of this study suggested that a distribution or reduction of mechanical stress could improve blood flow and decrease alveolar ridge resorption.     

外斜线取骨自体骨移植及其他牙槽嵴骨增量法的研究进展

针对严重骨缺损且有种植修复意向的牙列缺损位点，自体骨移植是实现种植体三维方向充足骨量的“经典方案”，常用的口内供骨区有颏部和外斜线区域。相比颏部取骨，下颌骨外斜线取骨移植后神经并发症少，但跟其他牙槽嵴骨增量方式相比，术后骨吸收率大。本文重点讲述下颌骨外斜线块状取骨及其局限性，并阐述了其他临床应用广泛的牙槽骨增量方法，对比移植骨术后牙槽嵴宽度及高度变化、术后骨吸收率，为临床提供减小外斜线块状取骨局限性的其他骨增量方法。     

牙槽嵴骨吸收程度不同下颌中性区外形变化初探

目的 观察无牙颌患者在牙槽嵴骨吸收程度不同的情况下下颌中性区外形的变化,以期寻找恰当的义齿磨光面设计.方法 选择20例无牙颌患者,根据患者上下颌弓关系,分为3组.第一组:牙槽嵴轻度吸收患者:第一类无牙颌,上下颌弓关系正常,共6例;第二组:牙槽嵴中度吸收患者:第二类无牙颌,上下颌弓关系正常,共7例;第三组:牙槽嵴重度吸收患者:第三类无牙颌,上下颌弓关系为反(牙合),共7例.通过患者充分主动的肌功能整塑,较准确地形成中性区外形,以此作为义齿磨光面,使用三维牙颌模型激光扫描仪对上下颌模型及磨光面进行三维激光扫描和重建.分别在双侧磨牙区和前磨牙区作垂直于磨光面轴线的垂面,将磨光面及上下颌模型一并切开,得到截面.观察截面形态,并在各截面上测量下颌舌侧磨光面外形曲线拟合直线与(牙合)平面所成的角度.结果从截面形态可见,第一组患者颊舌侧磨光面形态均为凹形;第二组患者颊舌侧磨光面形态均未见明显凹陷,为略凸或直形;第三组患者磨光面形态呈倾斜状.第一、二、三组患者下颌舌侧磨光面外形曲线拟合直线与(牙合)平面所成的角度分别为(80.40±3.51)°、(90.38±2.71)°和(96.59±5.00)°.结论 牙槽嵴骨吸收程度不同,下颌中性区外形有所不同,提示临床上在设计义齿磨光面外形时,应考虑牙槽嵴的吸收程度及上下颌弓关系.     

Accuracy of implant‐supported prostheses in the edentulous jaw. Analysis of precision of fit between cast gold‐alloy frameworks and master casts by means of a three‐dimensional photogrammetric technique.

Distortions of 15 routine implant‐supported prostheses were measured in relation to the master casts after completion by means of a 3‐dimensional (3‐D) photogrammetric technique. All prostheses were designed as one‐piece gold‐alloy castings with resin teeth. Five of the prostheses were placed in the edentulous maxilla, and the remaining were placed in the lower jaw. Distortion of the cylinders was mostly observed in the horizontal plane (x‐and y‐axis) while the vertical aspect seemed to be more stable. The mean 3‐D center point distortion was 42 (SD 15) and 74 (SD 38)μm for the upper and lower jaws, respectively. The measurements revealed a range of3‐D center point distortion from 16 to 80 and 15 to 165 μm for the different jaws, respectively. The corresponding 3‐D mean angular distortion of the cylinders was 51 (SD 35)μm in lower and 70 (SD 75)μm in the upper jaws. A correlation was found between 3‐D center point distortion and the width as well as the curvature of the implant arch, indicating more displacement the wider and the more curved the arch was. The 3‐D center point distortion was also significantly higher in the upper jaws which could possibly be explained by the curvature of the implant arch and higher numbers of implants in the upper jaws. Further problems with the fit of upper jaw castings could be related to more alloy in the 1 castings and poor alignment of implants.     

Atrophy of the residual alveolar ridge following tooth loss in an historical population

Oral Diseases (2010) 17 , 33–44 Objectives: To study the natural aetiopathology of jaw atrophy after tooth loss, unaltered by prosthetic procedures, an historical population without modern dental treatment was examined. Methods: Based on the hypothesis that there are predictable changes in shape during jaw‐atrophy, frequency and degree of atrophy as well as clinical aspects of bone quality and resorption were determined in the skeletal remains of 263 individuals. The potential association between age and frequency/severity of atrophy was analysed. Results: Atrophy in at least one jaw segment was present in 45.2% of the analysed jaw specimens. The residual ridge underwent a series of changes in shape and height following the pattern of resorption described for modern populations. The severity of these alterations was associated with the age of the individual and the region within the jaw. Atrophy was frequently related to structural degradation of the covering cortical layer. Conclusions: These findings prove that atrophy of the jaw evidently does occur, displaying similar patterns of resorption in a population without modern prosthetics, where the negative effect of ill‐fitting dentures is excluded. The basic information about alterations of shape and the cortical layer covering the residual crest might help to provide a deeper insight into aetiopathological mechanisms of this common oral disease.     

Residual ridge resorption, lower denture stability and subjective complaints among edentulous individuals

Residual ridge resorption in the mandible after tooth loss may lead to worsening of complete denture stability and to various subjective complaints. The aim was to evaluate the association between radiologically assessed residual ridge resorption in the mandible, clinically assessed stability of lower complete denture and subjective complaints among elderly denture wearers. The study population consisted of 326 (115 men and 211 women) edentulous subjects aged 60-78years, all of whom were wearing complete dentures in the mandible. Data on subjective complaints were obtained from questionnaires and interviews. Denture stability was assessed clinically. Residual ridge resorption was analysed from panoramic radiographs. The results showed that women were significantly more often satisfied with their lower dentures and reported fewer problems with eating than men. They also had significantly more often residual ridge resorption than men. Among women, residual ridge resorption was significantly associated with poor chewing ability, low satisfaction with dentures and poor denture stability. Among men, residual ridge resorption did not associate with subjective complaints or denture stability. Poor satisfaction with dentures associated significantly with poor denture stability in both genders. In conclusion, these results highlight the importance of denture maintenance treatment. As the extent of residual ridge resorption in the mandible was the most important factor that increased dissatisfaction with lower complete dentures, it is also important to inhibit the progression of resorption by preventing tooth loss or by using implant-retained dentures.     

大鼠下颌切牙拔出后剩余牙槽嵴吸收模型的建立

目的:建立大鼠切牙拔除后剩余牙槽嵴吸收的实验动物模型并探讨其发生机制。方法:选用健康雄性Wistar大鼠30只,局麻下齐龈缘磨除右下颌切牙牙冠,每3天磨除1次,共3次,最后磨除后3d拔除右下颌切牙,术后0、1、2、4、8、12周分别处死大鼠。用软X线摄片测量大鼠下颌剩余牙槽嵴的长度和保存率,组织学方法评价大鼠下颌切牙拔牙窝的愈合情况。对18只健康雄性Wistar大鼠通过HE染色观察磨除牙冠后的不同时期牙周组织形态学改变。结果:牙槽嵴长度:4、8、12周拔牙侧与非拔牙侧相比明显降低(P<0.05);拔牙4周后牙槽嵴保存率明显降低。组织形态学:拔牙后2周,拔牙窝内可见新生骨,残存的血凝块减少;拔牙后4周骨改建活跃;拔牙后8周,拔牙窝内充满新生骨;拔牙后12周,新生骨和周围牙槽骨界限不清。牙冠磨除后,牙周组织出现水肿,主纤维束断裂,丧失功能排列,血窦增加,随时间改变逐渐加重。结论:可以采用拔除大鼠切牙的方法建立剩余牙槽嵴吸收的动物模型。     

Eight-year outcome of posterior inlay-retained all-ceramic fixed dental prostheses

Aim

The main goal of this prospective clinical study was to evaluate the outcome of inlay-retained fixed dental prostheses (FDPs) made from heat-pressed lithium-disilicate glass-ceramic.

Methods

Forty-five FDPs were placed in 42 patients (21 women, mean age 36.1 years and 21 men, mean age 42.0 years). The FDPs replaced 4 premolars and 19 molars in the maxilla and 4 premolars and 18 molars in the mandible. Preparations were performed in accordance with general principles for ceramic inlay restorations. Five of the 45 FDPs were hybrid-retained restorations, i.e. one abutment tooth with an inlay retainer and one with a full crown retainer.All FDPs were pressed in one piece using lithium-disilicate ceramic (IPS e.max Press, Ivoclar Vivadent). The minimum dimensions for the proximal connector were 4 mm in height and 4 mm in width (16 mm²) with a minimum occlusal ceramic thickness of 1.5 mm. The surfaces of the inlay retainer were conditioned by etching with hydrofluoric acid 5% and silane application. Standard adhesive luting techniques were performed using a dentin adhesive (Syntac Classic, Ivoclar Vivadent) and a resin composite (Variolink II, Ivoclar Vivadent). Clinical follow-up examinations were performed annually.

Results

The mean observation periods were 70 months (minimum 4, maximum 123 months). Twenty-seven FDPs (60%) failed during the observation period and had to be replaced. The Kaplan–Meier survival rate for inlay-retained FDPs was 57% after 5 years and 38% after 8 years, while for hybrid-retained FDPs it was 100% after 5 and 60% after 8 years.

Conclusions

Inlay-retained FDPs made from lithium-disilicate ceramic present a high clinical failure rate and therefore cannot be recommended.     

高钉帽磁性附着体义齿在下颌牙槽嵴低平患者的应用

目的 高钉帽磁性附着体义齿在下颌牙槽嵴低平患者中的临床应用观察。方法 对15例下颌牙槽嵴低平患者采用高钉帽磁性附着体可摘义齿修复并进行2年的随访观察。结果 高钉帽磁性附着体可摘义齿修复患者的基牙牙槽骨吸收少,基牙松动度改变小,满意度高。结论 对于下颌低平牙槽嵴患者且基牙牙周情况良好的患者,高钉帽磁性附着体可摘义齿是一种较好的修复方式。     

CBCT与全颌曲面断层在下颌后牙区种植术中的诊断价值比较

目的：比较牙科专用锥形束CT（CBCT）与全颌曲面断层片在下颌后牙区种植术中的诊断价值。方法：对57例（69侧）下颌后牙区种植术的患者进行术前术后的CBCT影像学检查,得到下颌骨多层位影像,将其与全颌曲面断层影像进行比较,判断其检查结果的一致性。采用SPSS13．0统计软件对结果进行x2检验。结果：牙槽骨骨量不足的阳性检出率,CBCT与全颌曲面断层片分别为30．43％和15．94％,P=O．0437,差异具有统计学意义;术后种植体未发生骨结合的检出率,CBCT和全颌曲面断层片分别为3．45％和9．20％,P=O．1193,差异无统计学意义。结论：CBCT与全颌曲面断层片相比,可以更准确评估下颌后牙区种植术前牙槽骨骨量,并在术后的检查中能更准确地反应种植体骨结合的情况。     

Clinical fit of four‐unit zirconia posterior fixed dental prostheses

The objective of this clinical study was to assess the internal and marginal accuracy of computer‐aided design/computer‐aided manufacturing (CAD/CAM)‐generated four‐unit all‐ceramic posterior fixed dental prostheses (FDPs). The data were compared with the results of three‐unit metal‐ceramic and all‐ceramic FDPs that were obtained in a previous study. Twenty‐four patients were provided with all‐ceramic posterior four‐unit FDPs made from semisintered blank zirconia material. Prior to definitive insertion the accuracy was evaluated using a replica technique with a light body silicone that was stabilized with a heavy body material. The replica samples were examined using microscopy. The median marginal gap of the 24 four‐unit FDPs was 77 μm. The median gap widths were 87 μm at the midaxial wall, 167 μm at the axio‐occlusal transition of the abutments, and 170 μm at centro‐occlusal location. Although the marginal accuracy of the four‐unit FDPs differed significantly from that of the three‐unit metal‐ceramic FDPs (median 54 μm), the values obtained were clinically satisfactory and showed that semisintered zirconia blanks could be used for the fabrication of four‐unit FDPs.