氩气源低温常压等离子体改善牙本质-自酸蚀粘接界面粘接效果的体外研究

目的 探讨氩气源低温常压等离子体（nonthermal argon atmospheric pressure plasma,NTAPP）射流处理不同时间对牙本质-自酸蚀粘接剂粘接界面粘接强度及牙本质润湿性的影响。方法 使用NTAPP发生装置（放电输入功率：9 W,氩气气体流量：5 L/min）,分别处理5组（n=6）人牙本质试件（0、5、10、15、20 s）后,使用S3 Bond粘接剂处理牙面,制作微拉伸粘接试件并测量各组即刻粘接强度。同样参数、同样分组条件下处理牙本质面后测量牙本质表面接触角。结果 随着NTAPP处理时间延长,牙本质即刻粘接强度呈显著上升趋势,以处理15 s组粘接强度最高（31.82±2.80）MPa。随着NTAPP处理时间延长,与阴性对照组牙本质表面接触角（75.57°±1.45°）相比,各实验组牙本质表面接触角均显著减小,以处理15 s组牙本质表面接触角（33.56°±2.14°）最低,湿润性最大。结论 NTAPP处理可显著增加牙本质表面湿润性,提高与自酸蚀粘接剂粘接界面的粘接强度,这与处理时间相关。     

ObturaⅡ热牙胶系统根管充填的微渗漏研究

目的:比较ObturaⅡ热牙胶系统在3种加热温度设定下充填根管后根尖封闭效果的差异,并与冷牙胶侧压充填技术的密封性进行比较.方法:28个离体单根管恒牙,根管预备后随机均分为4组:A组用传统的泠牙胶侧压充填法进行充填,B、C、D组用ObturaⅡ系统将牙胶分别加热至160℃、180℃、200℃进行充填.使用染料渗入法检测根尖微渗漏的发生情况.结果:ObturaⅡ热牙胶系统在160℃、180℃、200℃的温度设定下充填后的微渗漏与冷牙胶侧压法相比差异有统计学意义(P<0.05),但温度设定不同的热牙胶充填组间的微渗漏差异无统计学意义(P<0.05).结论:ObturaⅡ热牙胶系统加热温度设定在160℃、180℃、200℃进行充填时根尖封闭能力无显著差异,但其根管封闭能力明显优于冷牙胶侧压充填技术.     

可摘局部义齿支架的计算机辅助设计与快速制造

目的 自主开发可摘局部义齿支架三维设计软件及选择性激光熔融制造(selective laser melting,SLM)设备,探讨应用其进行可摘局部义齿支架设计并直接成形金属支架的方法 .方法 使用层析扫描仪获得两个牙列缺损模型的三维点云数据.使用自主开发的可摘局部义齿支架三维设计软件进行模型观测及可摘局部义齿支架(牙合)支托、卡环、舌杆、金属加强网、上颌大连接体等组件的设计.组件设计路线:首先确定组织面轮廓,利用轮廓线内的点云数据生成组织面.根据各个组件的特点,设定抛光面截面形态,结合轮廓线生成抛光面.各组件完成后,用小连接体连成完整支架.将完成的支架数据导入SLM设备中,直接成形金属支架.结果 应用自主开发的可摘局部义齿支架三维设计软件及SLM设备,成功进行了两个可摘局部义齿金属支架的计算机辅助设计及快速制造,在模型上试戴后目测金属支架适合性良好.结论 自主开发的具有完全自主知识产权的可摘局部义齿支架计算机辅助设计与辅助制作系统,可为可摘局部义齿金属支架的制作提供一种新的方法.     

北京市785名老年人口腔修复状况及其影响因素

目的:评估北京市60～84岁老年人的口腔修复情况及其影响因素.方法:收集北京市785名老年人上下颌的修复情况、社会经济信息和全身健康信息.结果:总义齿的修复率上颌要高于下颌,但上下颌均以75～84岁年龄组的修复率为最高;可摘局部义齿的修复率则相反,下颌要高于上颌.在教育程度较低和较高的两组人群中上颌行总义齿修复的比例分别为34.9%和22.5%,而口腔内拥有10个以上天然牙的比例为14.5%和40.9%.Logistic回归分析显示行总义齿修复的可能性与老龄化、低收入、低教育程度、吸咽和嗜酒密切相关,而与患慢性病的种数无关.结论:老龄化、低收入、低教育程度、吸咽、嗜酒和行总义齿修复显著相关.     

α2巨球蛋白对大鼠下颌骨放射性骨坏死的预防作用

目的: 观察和分析在X线照射前于大鼠下颌骨体局部注射α2巨球蛋白（alpha2-macroglobulin, α2M）是否对大鼠下颌骨放射性骨坏死（osteoradionecrosis,ORN）具有预防作用。 方法: 健康SD雄性大鼠18只,随机分为3组,每组6只。其中A组为空白对照组,B组为单纯X线照射组,C组为X线照射前左侧下颌骨局部注射α2M组。大鼠均经麻醉后使用3D打印装置固定,B、C组使用X线生物学辐照器对其左侧下颌骨进行精准照射,每天7 Gy,连续照射5 d;A组假照射;C组在第1次X线照射前30 min于大鼠左侧下颌骨体部骨膜下局部注射0.5 mL 2000 mg/L的α2M,A、B组在同样部位注射等量无菌生理盐水（normal saline,NS）。照射完成后第7天,拔除大鼠左侧下颌3颗磨牙。照射完成后第28天处死所有大鼠,从大体、影像学、病理学等方面系统评估各组大鼠的放射损伤。采用SPSS 13.0软件包对数据进行统计学分析。 结果: B组5只大鼠大体上体重明显减轻、照射区黏膜重度溃疡、受照侧颊部脱毛、咬合关系紊乱;影像学显示明显的骨质缺损;病理观察发现照射区皮质骨空白骨陷窝增多、死骨形成、纤维增生等骨坏死典型症状,证实发生下颌骨ORN,发生率为5/6;与B组相比,C组大鼠大体上仅表现为轻度体重下降及照射区脱毛,影像学上未见明显骨质缺损,病理观察仅见骨髓腔内轻微炎症,皮质骨无明显破坏,骨陷窝空虚率较B组显著降低（P<0.001）;C组大鼠下颌骨ORN发生率为零。 结论: X线照射前注射α2M对下颌骨ORN的发生具有较好的预防作用。     

不同位置咬合高点对颞下颌关节面压力分布影响的实验力学研究

目的研究36 面不同位置的咬合高点对颞下颌关节（TMJ）负荷的影响。 方法在已建立的人冰鲜头颅TMJ负荷分析模型上，定义36 面无咬合高点，以及咬合高点位于 面近中尖、中央窝和远中尖时为工况一、二、三和四，记录并分析力学试验机加载后双侧TMJ上下腔关节面综合力度中心、压力集中区位置、压力峰值和压力接触面积等，使用方差分析方法进行结果的统计分析。 结果（1）双侧TMJ关节面负荷的综合力度中心均往右侧关节下腔关节面偏移，工况三时较为明显；关节面压力集中区位置变化表现为：左侧的各关节面有不同程度的位移，而右侧则相对稳定。（2）相较于工况一，工况二、三、四时，左侧TMJ上、下腔关节面表面压力峰值总体呈减小趋势（F_上 = 4.49，P_上 = 0.63；F_下 = 7.11，P_下 = 0.01），右侧TMJ上下腔关节面表面压力峰值差异无统计学意义（F_上 = 0.60，P_上 = 0.04；F_下 = 1.13，P_下 = 0.39）。（3）相较于工况一，工况二、三、四时，双侧TMJ上、下腔关节面接触面积变化均无统计学意义（P>0.05）。 结论36 面不同位置的咬合高点会影响TMJ关节面的受力形式，造成关节结构之间受力环境的改变。     

儿童口腔尖锐湿疣的临床表现及HPV检测

目的:探讨儿童口腔粘膜尖锐湿疣的病毒类型、传播途径、临床病理特点及预后等。方法:回顾6 例被确诊为口腔粘膜尖锐湿疣患儿的临床特点及HE 切片,并对其中5 例采用免疫组化染色及原位杂交检测人乳头状瘤病毒(HPV)DNA。结果:儿童口腔尖锐湿疣多发生在2 岁左右,发病部位多位于腭部,并且多数有家族感染史,镜下见棘层上部或角化层常出现灶性凹空细胞,免疫组化检测结果显示5 例HPV 共同抗原全部阳性,5 例中有4 例HPV16P18- E6 阳性;原位杂交结果显示仅1 例HPV6 和HPV11 同时阳性,另1 例初发时HPV6 阳性而复发后呈阴性。结论:儿童口腔尖锐湿疣的病毒类型、传播途径可能与成人不同。     

上颌全口义齿的加强结构对基托下黏膜应力分布的影响

目的：分析上颌全口义齿加强前后及不同的加强设计，对基托下黏膜应力分布的影响。方法：采用三维有限元法，建立无加强（BS），铸造结构加强BA，BD和BDr等4种上颌全口义齿三维有限元模型。设定P1，M1，PMc和PMe等4种垂直加载条件，加载力合计98N。对全口义齿基托下黏膜的应力分布进行分析。结果：在相同加载条件下，黏膜应力峰值表示为按BS，BA，BD，BDr的顺序依次减小。BDr基托下黏膜应力峰值最小，应力分布更均匀和广泛。结论：使用覆盖牙槽嵴顶及后堤区的铸造加强结构的上颌全口义齿能够使基托下黏膜应力分布更均匀和广泛，有利于保护基托下黏膜组织。     

白芍总苷对糜烂型口腔扁平苔藓患者外周血中IFN-γ及IL-10表达的影响研究

目的:探讨白芍总苷对糜烂型口腔扁平苔藓患者外周血中IFN-γ及IL-10表达的影响。方法:选取于2014年2月~2015年3月我院皮肤科与口腔科收治的38例糜烂型口腔扁平苔藓患者为研究对象,随机分为对照组和研究组两组。对照组患者,18例,对照组患者,在清除患者口腔中残根、残冠以及牙石等,用0.1%的他克莫司软膏进行局部治疗,2次/d。研究组患者,20例,在对照组治疗的基础上采用口服白芍总苷胶囊进行治疗,比较两组患者一个疗程后的临床疗效,并采用ELISA法检测并比较治疗前后两组患者外周血中IFN-γ及IL-10的表达情况。结果:对照组,18例,其中有效者2例,好转者6例,无效者10例,总有效率为44.4%。研究组,20例,其中其中有效者8例,好转者7例,无效者5例,总有效率为75%。与对照组相比,研究组患者的总有效率显著升高,差异显著(P＜0.05)。治疗后研究组患者外周血中IFN-γ及IL-10的表达水平均显著升高,差异显著(P＜0.05),具有统计学意义。结论:白芍总苷治疗糜烂型口腔扁平苔藓具有较好的临床疗效,值得临床推广应用。同时,白芍总苷较好的临床疗效可能与其增高了患者外周血中IFN-γ水平及IL-10水平有关。     

老年人牙列缺损可摘局部义齿修复设计回顾性研究

目的:总结老年人多数牙列缺损的临床修复体会,探讨老年患者可摘局部义齿的设计。方法:对276例老年多数牙列缺损患者分别设计牙合垫式、连续卡环式、连续卡环加牙合垫式可摘局部义齿,其中179例余留牙有残根、残冠患者,先作根管治疗,然后按以上形式设计覆盖式可摘义齿。对修复效果作戴修复体时及戴后3月、3年随访,标准分为好、差两个等级。结果:276例复查结果:满意度调查,好均为100%,(P>0.05)。咀嚼功能检查,戴后3月,好为100%,3年好为99.3%,(P>0.05)。基牙牙周情况检查,戴后3月,好为100%,3年好为97.1%,(P>0.05)。结论:对老年人多数牙列缺损患者,应根据患者口腔情况设计最佳个体修复方案,制作适合老年人生理特点的可摘局部义齿。     

A novel oligopeptide simulating dentine matrix protein 1 for biomimetic mineralization of dentine

Objective

The objectives were to design and fabricate an oligopeptide that simulates dentine matrix protein 1 (DMP1) to study its ability to bind to dentine collagen fibrils and induce biomimetic mineralization for the management of dentine hypersensitivity.

Materials and methods

A novel oligopeptide was developed by connecting the collagen-binding domain of DMP1 to the hydrophilic C-terminal of amelogenin. Fluorescein isothiocyanate-coupled oligopeptide was applied to the completely demineralized dentine collagen and examined using fluorescent microscopy. The nucleation and growth of hydroxyapatite were initiated by immersing oligopeptide into calcium chloride and sodium hydrogen phosphate solutions. Scanning electron microscopy (SEM), transmission electron microscopy, and selected area electron diffraction (SAED) were used to examine the formation. Dentine slices were acid-etched, coated with oligopeptide, and immersed into a metastable calcium phosphate solution. Dentine mineralization was evaluated by SEM, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR).

Results

Fluorescent dentine collagen was identified in the specimens. The nucleation and growth of crystals were detected after immersing the oligopeptide into calcium chloride and sodium hydrogen phosphate solutions. Under SEM, crystals were observed covering the oligopeptide-coated dentine surface, within the demineralized dentine collagen matrix and occluding dentinal tubules. SAED, XRD, and FTIR confirmed that the crystals were hydroxyapatite.

Conclusion

A novel oligopeptide-simulating DMP1 was developed, that can bind to collagen fibrils, initiate mineralization, and induce biomimetic mineralization of dentine.

Clinical relevance

Biomimetic mineralization of dentine facilitated by this oligopeptide is a potential therapeutic technique for the management of dentine hypersensitivity.     

Biomimetic mineralisation of phosphorylated dentine by CPP-ACP

Objectives

Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) has the potential to induce the biomimetic mineralisation of dentine collagen fibrils. This study aimed to demonstrate in vitro the ability of CPP-ACP to form apatite crystals on phosphorylated dentine collagen fibrils.

Methods

Dentine slices with a 2-mm thickness were prepared from sound human third molars. The slices were etched with phosphoric acid to expose the collagen fibres. Sodium trimetaphosphate was then used to phosphorylate the exposed collagen fibres. CPP-ACP paste was topically applied to the surface of the phosphorylated slices, which were then immersed in a metastable calcium phosphate remineralising solution and incubated at 37 °C for 10 days. The CPP-ACP paste and the remineralising solution were replaced every two days. Phosphorylated dentine slices without a CPP-ACP application and non-phosphorylated dentine slices with a CPP-ACP application were prepared and used for comparison. The slices were examined using scanning electron microscope (SEM), diffuse reflectance-Fourier transform infrared spectroscopy (DR-FTIR) and X-ray diffraction (XRD).

Results

The SEM results revealed the presence of intrafibrillar and interfibrillar crystal nucleation and growth along the phosphorylated dentine collagen fibres. The DR-FTIR and XRD confirmed that the crystals were hydroxyapatite. No apatite crystal nucleation and growth were observed in either the slices that had no non-phosphorylation or those without CPP-ACP application.

Conclusions

CPP-ACP can induce the biomimetic mineralisation of dentine through apatite formation along and between the phosphorylated dentine collagen fibres.

Clinical significance

The in vitro study imitated the application of CPP-ACP to exposed dentine tooth surfaces in the mouth. This could lead to the development of a new therapeutic technique for the treatment of tooth hypersensitivity.     

AFM study of the effects of collagenase and its inhibitors on dentine collagen fibrils

Objective

This study evaluated the effects of exogenous collagenase and two collagenase inhibitors on the variation in microstructure of human collagen fibrils.

Methods

Dentine specimens which were sectioned from 6 freshly extracted human caries-free third molars were wet polished. Each specimen was divided into 4 parts which were treated as experimental groups (group 1, group 2, group 3) and the control group, respectively. All the specimens were etched and further treated with NaClOaq. Subsequently, the topography of each specimen was observed using atomic force microscopy (AFM) in tapping mode in air. Group 1 was then treated with a solution of collagenase II. Group 2 was treated with a solution of collagenase II and chlorhexidine (saturated solution). Group 3 was treated with a solution of collagenase II and captopril (0.3%). The control group was treated with a buffer solution. After 3 h and 6 h of treatment, the topography of the collagen fibrils was measured with AFM in air, respectively.

Results

AFM images of the dentine collagen fibrils were obtained after treatment with NaOClaq. Following further treatment with collagenase II, the topography of the collagen fibrils changed. Most reticular collagen fibrils disappeared after 6 h. After treatment with collagenase II in the presence of chlorhexidine or captopril for 3 h and 6 h, the morphology of the collagen fibres was not changed obviously.

Conclusions

Exogenous collagenase II effectively degraded human dentine collagen fibrils, and its collagenolytic activity was inhibited by the exogenous collagenase inhibitors, chlorhexidine and captopril.     

Influence of light irradiation of dentine primers on dentine-resin bond

Objective: The purpose of this study was to examine the influence of light irradiation of dentine primers that contain camphoroquinone (CQ) on the shear bond strength to dentine and their contact angle.

Method: Three dentine bonding systems which contain CQ, Imperva Bond, OptiBond and XR-Bond; and Light Bond, which does not contain CQ, were employed. Labial surfaces of freshly extracted lower bovine incisors were ground with no. 600 grit SiC paper. Dentine primers were applied to the dentine surfaces in two groups, irradiated and non-irradiated. A shear bond strength test was performed and the direct contact angle was measured.

Results: Statistical analysis (Newman-Keuls multiple comparison P < 0.05) of the data indicated that light irradiation of the dentine primer for systems containing CQ resulted in increased bond strength and decreased contact angle.

Conclusion: This study indicates that for these dentine bonding systems containing CQ in their primers, light irradiation of the dentine primer is effective in improving wettability and increasing the bond strength to dentine.     

Solvent composition of one-step self-etch adhesives and dentine wettability

Objectives

Our aim was to determine the wettability of dentine by four commercial self-etch adhesives and evaluate their spreading rate on the dentine surface. Any correlation with chemical composition was sought, particularly with the amount of solvent or HEMA present in the adhesive. The adhesives used were AdheSE One, Optibond All.In.One, Adper Easy Bond and XenoV.

Methods

Chemical compositions were determined by proton nuclear magnetic resonance (NMR) spectroscopy of the adhesives dissolved in dimethylsulfoxide. Apparent contact angles for sessile drops of adhesives were measured on dentine slices as a function of time for up to 180 s. The water contact angles were determined for fully polymerised adhesives.

Results

All adhesives were water-based with total solvent contents ranging from 27% to 73% for HEMA-free adhesives, and averaging 45% for HEMA containing adhesives. The contents in hydrophobic groups decreased as water contents increased. No differences were found in the adhesive contact angles after 180 s even though the spreading rates were different for the products tested.

Conclusion

Water contact angles differed significantly but were not correlated with HEMA or solvent presence. Manufacturers use different approaches to stabilise acid co-monomer ingredients in self-etch adhesives. Co-solvents, HEMA, or acrylamides without co-solvents are used to simultaneously etch and infiltrate dentine. A large proportion of water is necessary for decalcification action.     

Effect of triple antibiotic paste with or without ethylenediaminetetraacetic acid on surface loss and surface roughness of radicular dentine

This study aimed to compare the effect of two concentrations of triple antibiotic paste (TAP) with or without ethylenediaminetetraacetic acid (EDTA) on surface loss and surface roughness of radicular dentine. Human radicular dentine specimens were randomized into six experimental groups (n = 16 per group). The first and second groups were treated with 1,000 mg/mL or 1 mg/mL of TAP for 4 weeks. The third and fourth groups were treated with 1,000 mg/mL or 1 mg/mL of TAP for 4 weeks followed by 17 % EDTA for 5 min. The fifth group was treated with 17 % EDTA for 5 min and the sixth group received no treatment (control). Dentine surface loss and surface roughness were quantified after various treatments using optical and contact profilometry, respectively. One-way ANOVA followed by Fisher’s protected least significant differences was used for statistical analyses. All treatment groups showed significantly higher surface loss compared to the untreated dentine. Dentine treated with 1,000 mg/mL had significant increase in surface loss and surface roughness compared to dentine treated with 1 mg/mL of TAP. The use of EDTA after both concentrations of TAP did not have significant additive effect on surface loss and surface roughness of dentine. The clinically used concentration of TAP (1,000 mg/mL) caused significantly higher surface loss and surface roughness of radicular dentine compared to the use of 1 mg/mL of TAP. Furthermore, the substantial amount of dentine surface loss and surface roughness detected in the current study may be attributed to TAP rather than EDTA.     

Adsorption and interactions of dentine phosphoprotein with hydroxyapatite and collagen

Dentine phosphoprotein (DPP) has been proposed to both promote and inhibit mineral deposition during dentinogenesis. The present study aimed to investigate the molecular interactions of DPP and dephosphorylated DPP (DPP-p) with hydroxyapatite (HAP). Bovine DPP was purified and dephosphorylated by alkaline phosphatase to obtain DPP-p. DPP and DPP-p adsorption to HAP was determined along with their ability, when free in solution or bound to collagen, to influence HAP-induced crystal growth. Absorption isotherms suggested that lower DPP concentrations (1.5-6.25 microg ml(-1)) demonstrated a reduced affinity for HAP compared with higher protein concentrations (12.5-50.0 microg ml(-1)). Dephosphorylated DPP had a much reduced affinity for HAP compared with DPP. Dentine phosphoprotein inhibited seeded HAP crystal growth, in a dose-dependent manner, whilst removal of the phosphate groups reduced this inhibition. When bound to collagen fibrils, DPP significantly promoted the rate of HAP crystal growth over 0-8 min. Conversely, DPP-p and collagen significantly decreased the rate of crystal growth over 0-18 min. These results indicate a major role for the phosphate groups present on DPP in HAP crystal growth. In addition, concentration-dependent conformational changes to DPP, and the interaction with other matrix components, such as collagen, are important in predicting its dual role in the mineralization of dentine.     

Evaluation of the surface free energy on root canal dentine walls treated with chelating agents and NaOCl

AIM: To evaluate ex vivo the effects of combined and single use of EDTA, RC-Prep and NaOCl on the surface free energy of canal wall dentine using the captive bubble technique. METHODOLOGY: Eighteen extracted human pre-molar teeth were sectioned at the crown and the apical third, the remaining mid-root portion were bisected longitudinally. Thereafter, the root halves were embedded in resin blocks that exposed the dentine surface of the canal wall. The specimens were randomly assigned to six experimental groups (n = 6) after polishing. The root dentine surfaces of the first two groups were treated with 17% EDTA or RC-Prep followed by 2.5% NaOCl irrigation. Groups 3, 4 and 5 were treated with either 17% EDTA, RC-Prep or 2.5% NaOCl alone. Control specimens were irrigated with saline solution. The surface free energies of experimental groups were calculated by measuring air and octane contact angles on the canal wall dentine. Statistical analysis was performed using the Mann-Whitney U and Bonferroni post-tests at P = 0.05. RESULTS: Compared with the control group; combined and single use of EDTA, RC-Prep and NaOCl irrigation significantly decreased the surface free energy of canal wall dentine surfaces (P < 0.05). Among all groups tested, the use of NaOCl as a final flush following RC-Prep treatment yielded increased wettability. Nevertheless, this value remained lower than that of the control group. CONCLUSION: Use of chelating agents alone or in combination with NaOCl decreased the wettability of root canal wall dentine.     

ElectroBond application may improve wetting characteristics of etched dentine

Objective

To assess the efficacy of an electrically assisted application technique on dentine wettability (water contact angle measurements) and to determine the promoted surface roughness of dentine after applying 37% phosphoric acid etching, a self-etching primer or a self-etching adhesive system.

Methods

Wettability was assessed on 30 caries-free extracted human third molars. Specimens were sectioned parallel to the occlusal surface to expose moderately deep dentine and ground flat (water-wet 180-grit SiC) to provide uniform flat surfaces. 37% H₃PO₄, Clearfil SE Bond (CSEB) primer or Prompt-L-Pop (PLP) adhesive system were applied on dentine surfaces. In half of the specimens, the electric impulse-assisted application technique/ElectroBond-assisted application was followed. Contact angle measurements were performed to assess wettability using the Axisymmetric Drop Shape Analysis technique. Additional surfaces were conditioned for atomic force microscopy (AFM) analysis. Two-way ANOVA, Student's t and Student-Newman-Keuls tests were performed (P < 0.05).

Results

PLP-treated dentine showed the highest intertubular roughness and the lowest dentine wettability. ElectroBond application reduced water contact angles when dentine was treated with H₃PO₄ or Clearfil SE Bond primer, but not when dentine was treated with PLP.

Conclusions

The use of electric current improved wettability of dentine surface following application of phosphoric acid and a mild self-etch primer, but not self-etch adhesive.     

Effects of phosphoric acid and tannic acid on dentine collagen

We examined the effects of phosphoric acid, the most common enamel etchant in composite resin therapy, on dentine collagen. Dentine collagen pretreated with 7M phosphoric acid was shown to be more susceptible to trypsin digestion than untreated collagen. This susceptibility increased with increasing duration of exposure to the acid. The results indicate that phosphoric acid induces a conformational change in dentine collagen (denaturation or perturbation) similar to that observed with 0.39 M HCl, which has a similar pH value (0.65). However, phosphoric acid-pretreated dentine collagen, when treated with tannic acid for 2 h, became as resistant to tryptic digestion as intact dentine collagen. The present results suggest that tannic acid may work as a dentine conditioner in composite resin therapy, in view of the fact that phosphoric acid etchant is applied, either deliberately or inadvertently, to dentine, and would thus induce denaturation or perturbation of collagen.