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PRC Dentist Licensure practice questions

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Question 1Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

在牙釉质形成过程中，成釉细胞分泌的有机基质随即发生矿化，最终形成的牙釉质其主要无机成分是什么？

  1. 氟化钠
  2. 碳酸钙
  3. 羟基磷灰石 Correct answer.
  4. 磷酸三钙

Explanation

牙釉质是人体矿化程度最高的组织，无机物约占其重量的96%以上，其中绝大多数以羟基磷灰石晶体形式存在。晶体中还含少量碳酸根、氟、镁等替代离子，但主体矿物相仍是羟基磷灰石。

Question 2Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

牙髓组织的感觉神经纤维绝大多数属于哪一类？

  1. 有髓的Aδ纤维和无髓的C纤维 Correct answer.
  2. 细小的节后交感纤维
  3. 有髓的B类节前纤维
  4. 粗大的Aα运动纤维

Explanation

牙髓内的传入神经以Aδ纤维和C纤维为主，前者有髓、传导快，多分布于牙髓牙本质界附近，介导锐痛；后者无髓、传导慢，介导钝痛。牙髓中缺乏Aα运动纤维和B类纤维。

Question 3Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

下列哪种细胞负责牙本质的持续形成并在牙本质小管内伸出突起？

  1. 成纤维细胞
  2. 成釉细胞
  3. 成牙本质细胞 Correct answer.
  4. 成骨细胞

Explanation

成牙本质细胞位于牙髓外周，其胞体排列成层，细长的细胞突起伸入牙本质小管，终生不断形成牙本质。成骨细胞形成骨基质，成纤维细胞产生胶原，成釉细胞形成牙釉质。

Question 4Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

唾液中能水解细菌细胞壁肽聚糖、发挥非特异性抗菌作用的酶是？

  1. 唾液淀粉酶
  2. 碳酸酐酶
  3. 溶菌酶 Correct answer.
  4. 碱性磷酸酶

Explanation

溶菌酶可裂解肽聚糖骨架中N-乙酰胞壁酸与N-乙酰葡糖胺之间的糖苷键，使细菌细胞壁破裂，是唾液中重要的先天免疫成分。唾液淀粉酶消化淀粉，碳酸酐酶催化二氧化碳水化，碱性磷酸酶参与矿化相关反应。

Question 5Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

口腔中主要致龋菌变形链球菌利用蔗糖合成细胞外多糖、促进菌斑黏附的关键酶是？

  1. 脲酶
  2. 乳酸脱氢酶
  3. 唾液酸酶
  4. 葡糖基转移酶 Correct answer.

Explanation

变形链球菌分泌葡糖基转移酶，将蔗糖分解并聚合成果聚糖和葡聚糖，后者黏附于牙面并作为菌斑基质，是致龋的重要毒力因素。乳酸脱氢酶催化糖酵解产酸，脲酶分解尿素产氨，唾液酸酶水解糖蛋白末端唾液酸。

Question 6Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

牙周炎的主要致病菌群中，常被称为红色复合体的三种细菌是？

  1. 金黄色葡萄球菌、表皮葡萄球菌、腐生葡萄球菌
  2. 变形链球菌、血链球菌、唾液链球菌
  3. 伴放线聚集杆菌、黏性放线菌、内氏放线菌
  4. 牙龈卟啉单胞菌、福赛坦氏菌、齿垢密螺旋体 Correct answer.

Explanation

Socransky提出的红色复合体包括牙龈卟啉单胞菌、福赛坦氏菌和齿垢密螺旋体，三者与牙周附着丧失和深牙周袋关系最密切。其余组合分别属于致龋菌群、伴放线聚集杆菌相关菌群或皮肤葡萄球菌。

Question 7Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

关于牙釉质晶体的排列，下列描述正确的是？

  1. 釉质晶体只在釉柱头部出现
  2. 釉柱内晶体彼此平行，与釉柱长轴基本一致 Correct answer.
  3. 釉柱间质中不含任何晶体
  4. 釉柱内晶体完全垂直于釉柱长轴排列

Explanation

釉柱由大量羟基磷灰石晶体组成，柱内晶体长轴与釉柱走行方向大致平行，而柱间质中的晶体方向与釉柱成较大角度。这种排列差异形成釉质的光学各向异性，并影响酸蚀后的表面形态。

Question 8Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

牙本质小管内液体随外界刺激移动，从而激活牙髓神经末梢的学说称为？

  1. 流体动力学说 Correct answer.
  2. 神经传导学说
  3. 成牙本质细胞受体学说
  4. 化学介质学说

Explanation

流体动力学说认为，外界刺激使牙本质小管内液体发生快速移动，机械性地牵张或压迫牙髓内的Aδ神经末梢，产生疼痛。该学说能较好解释牙本质敏感症的发生机制。

Question 9Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

牙周膜的主要纤维束中，能抵抗牙齿向冠方脱位、维持牙齿正常位置的是？

  1. 根尖纤维
  2. 牙槽嵴纤维 Correct answer.
  3. 越隔纤维
  4. 水平纤维

Explanation

牙槽嵴纤维自牙槽嵴顶斜向根方走行，可抵抗牙齿的冠向移位，并防止牙龈被推离牙面。水平纤维抵抗水平力，根尖纤维防止牙齿向根方移位，越隔纤维连接邻牙。

Question 10Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

颞下颌关节的关节盘将关节腔分为上、下两层，其中进行铰链式开闭口运动的部位是？

  1. 关节盘内部
  2. 关节上腔
  3. 关节囊外间隙
  4. 关节下腔 Correct answer.

Explanation

颞下颌关节的下腔位于髁突与关节盘之间，主要完成铰链式转动；上腔位于关节盘与关节结节之间，完成滑动运动。开闭口初期为下腔转动，随后上腔滑动。

Question 11Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

支配下颌牙齿的痛觉传入纤维主要经哪条神经通路进入三叉神经脊束核？

  1. 下颌神经分支 Correct answer.
  2. 面神经分支
  3. 舌咽神经分支
  4. 上颌神经分支

Explanation

下颌牙齿的感觉由三叉神经第三支即下颌神经的分支（如下牙槽神经、颊神经等）传导，痛觉纤维进入脑干后终止于三叉神经脊束核。面神经与舌咽神经主要支配面部表情肌及舌后部感觉。

Question 12Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

维生素C缺乏导致牙龈出血、伤口愈合不良，其机制主要与下列哪项有关？

  1. 胶原中脯氨酸和赖氨酸残基羟化障碍 Correct answer.
  2. 铁吸收障碍导致血红蛋白合成减少
  3. 维生素K依赖性凝血因子合成障碍
  4. 钙吸收减少导致骨矿化不良

Explanation

维生素C是脯氨酰羟化酶和赖氨酰羟化酶的辅因子，缺乏时胶原三螺旋结构不稳定，血管壁和牙龈结缔组织脆性增加，表现为出血与愈合障碍。维生素K、维生素D和铁分别对应凝血、矿化和造血。

Question 13Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

糖酵解途径中催化磷酸果糖激酶-1反应的关键限速步骤是？

  1. 磷酸烯醇式丙酮酸转化为丙酮酸
  2. 6-磷酸果糖磷酸化为1,6-二磷酸果糖 Correct answer.
  3. 葡萄糖磷酸化为6-磷酸葡萄糖
  4. 丙酮酸还原为乳酸

Explanation

磷酸果糖激酶-1催化6-磷酸果糖磷酸化生成1,6-二磷酸果糖，是糖酵解最重要的限速步骤，受ATP、柠檬酸抑制，受AMP、果糖-2,6-二磷酸激活。己糖激酶反应虽也受调控，但主要限速点在磷酸果糖激酶-1。

Question 14Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

长期使用糖皮质激素的患者突然停药后出现肾上腺皮质功能不全，其机制是？

  1. 肾素-血管紧张素系统过度激活
  2. 肾上腺皮质肿瘤自主分泌皮质醇
  3. 下丘脑-垂体-肾上腺轴受抑制，ACTH分泌减少 Correct answer.
  4. 醛固酮合成酶基因突变

Explanation

外源性糖皮质激素通过负反馈抑制下丘脑CRH和垂体ACTH分泌，长期使用导致肾上腺皮质萎缩；骤然停药时内源性皮质醇不足，出现乏力、低血压等肾上腺皮质功能不全表现，故需逐渐减量。

Question 15Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

局部麻醉药阻断神经冲动的根本机制是？

  1. 阻断电压门控钠通道，抑制动作电位产生 Correct answer.
  2. 阻断乙酰胆碱酯酶，增加递质堆积
  3. 激动γ-氨基丁酸受体，抑制突触传递
  4. 增强钾通道开放，引起超极化

Explanation

局麻药为弱碱性分子，其非解离型穿透神经膜后在胞内解离，与电压门控钠通道内侧结合，阻断钠内流，使动作电位无法产生和传导。局麻药不影响钾通道开放或胆碱酯酶活性。

Question 16Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

阿司匹林不可逆抑制环氧化酶，其抗血小板作用持续时间较长的原因是？

  1. 阿司匹林与血小板膜受体永久结合
  2. 阿司匹林在血浆中半衰期极长
  3. 血小板无细胞核，不能合成新的环氧化酶 Correct answer.
  4. 阿司匹林抑制血小板生成

Explanation

阿司匹林通过乙酰化环氧化酶活性位点的丝氨酸残基使其不可逆失活。血小板无细胞核，无法合成新的酶，因此抗血小板作用持续至该批血小板寿命结束（约7～10天），而药物本身血浆半衰期很短。

Question 17Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

四环素类药物沉积于发育中的牙齿，最典型的表现是？

  1. 牙齿出现半月形切缘凹陷
  2. 牙齿呈灰黑色且牙根吸收
  3. 牙齿呈白色不透光斑块
  4. 牙齿呈黄褐色并出现釉质发育不全 Correct answer.

Explanation

四环素能与钙离子螯合，沉积于矿化中的牙齿和骨骼，使牙齿呈黄色、棕色或灰色，并常伴釉质发育不全，妊娠后期及8岁以下儿童应避免使用。白色不透光斑块多见于氟牙症，半月形切缘凹陷为梅毒牙特征。

Question 18Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

急性炎症时血管通透性增加，主要由下列哪种机制介导？

  1. 红细胞聚集堵塞毛细血管
  2. 内皮细胞增生形成新血管
  3. 血管平滑肌持续收缩
  4. 内皮细胞收缩使细胞间隙增大 Correct answer.

Explanation

组胺、缓激肽、白三烯等炎症介质使内皮细胞收缩，细胞间隙增宽，血浆蛋白和液体外渗，形成渗出液。内皮增生见于慢性炎症和肉芽组织形成，与急性期通透性增加无关。

Question 19Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

牙源性角化囊肿具有特征性的组织学表现是？

  1. 衬里上皮为复层鳞状上皮，基底细胞呈栅栏状排列，伴星网状层 Correct answer.
  2. 上皮内出现大量朗格汉斯细胞
  3. 上皮下可见玻璃样变基底膜
  4. 囊壁内可见大量胆固醇结晶裂隙

Explanation

牙源性角化囊肿的衬里为薄层复层鳞状上皮，表面呈波纹状角化，基底细胞排列整齐呈栅栏状，上皮与结缔组织交界平坦，无上皮钉突。胆固醇结晶裂隙多见于根尖囊肿，玻璃样变基底膜见于某些黏液囊肿。

Question 20Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

鳞状细胞癌在组织学上区分高分化与低分化的主要依据是？

  1. 角化珠形成和细胞间桥的多少 Correct answer.
  2. 肿瘤体积的大小
  3. 肿瘤发生部位的深浅
  4. 患者血清肿瘤标志物水平

Explanation

高分化鳞状细胞癌可见明显的角化珠和细胞间桥，细胞异型性小；低分化者角化珠稀少或缺如，细胞异型性和核分裂象明显。分化程度反映肿瘤细胞与正常鳞状上皮的相似程度，与体积和部位无直接关系。

Question 21Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

肉芽组织的主要成分是？

  1. 新生毛细血管、成纤维细胞和炎细胞 Correct answer.
  2. 致密骨组织和破骨细胞
  3. 成熟胶原束和少量成纤维细胞
  4. 脂肪细胞和大量红细胞

Explanation

肉芽组织由增生的新生毛细血管、成纤维细胞及浸润的巨噬细胞、中性粒细胞等炎细胞组成，是创伤修复早期的特征性组织，随后逐渐转变为瘢痕组织。成熟胶原束是瘢痕组织的特征。

Question 22Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

口腔黏膜中抗原呈递功能最强的细胞是？

  1. 朗格汉斯细胞 Correct answer.
  2. 黑素细胞
  3. 梅克尔细胞
  4. 角化细胞

Explanation

朗格汉斯细胞位于口腔黏膜上皮的棘层，属于树突状抗原呈递细胞，可摄取处理抗原并迁移至区域淋巴结，向T淋巴细胞呈递。黑素细胞合成黑色素，梅克尔细胞为机械感受器，角化细胞主要构成上皮屏障。

Question 23Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

补体经典激活途径的起始分子是？

  1. 旁路途径中备解素与C3b结合
  2. C3自发水解形成C3b
  3. 甘露糖结合凝集素与病原体表面甘露糖结合
  4. C1q与抗原抗体复合物中的IgG或IgM结合 Correct answer.

Explanation

经典途径由C1q识别结合于抗原的IgG或IgM的Fc段而启动，随后激活C1r、C1s，裂解C4和C2形成C3转化酶。甘露糖结合凝集素途径和旁路途径的启动方式与此不同。

Question 24Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

免疫球蛋白中能通过胎盘为新生儿提供被动免疫的主要是？

  1. IgA
  2. IgM
  3. IgG Correct answer.
  4. IgE

Explanation

IgG可通过胎盘滋养层细胞的FcRn受体主动转运至胎儿循环，是新生儿出生后数月内主要的被动免疫来源。IgM为五聚体不能通过胎盘，分泌型IgA经乳汁提供黏膜免疫，IgE参与I型超敏反应。

Question 25Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

I型超敏反应中，肥大细胞脱颗粒释放组胺的直接触发因素是？

  1. 补体C3b与细胞表面受体结合
  2. 抗原抗体复合物沉积于血管基底膜
  3. IgG与NK细胞表面FcγRIII结合
  4. 变应原交联细胞表面IgE并与FcεRI结合 Correct answer.

Explanation

变应原与肥大细胞表面已结合的IgE发生交联，使FcεRI聚集，启动信号转导引起脱颗粒，释放组胺、白三烯等介质。C3b介导调理吞噬，IgG与NK细胞结合介导ADCC，免疫复合物沉积属于III型超敏反应。

Question 26Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

牙体硬组织中，无机成分约占其总重量的96%～97%、有机物和水极少的是哪一层结构？

  1. 牙釉质 Correct answer.
  2. 牙髓
  3. 牙骨质
  4. 牙本质

Explanation

牙釉质是全身矿化程度最高的组织，无机物约占总重量的96%～97%，有机物和水仅占很小比例，因此质地脆硬且无细胞成分。牙本质无机物约占70%，牙骨质更低，牙髓则为疏松结缔组织。这一矿化梯度也决定了龋病在釉质与牙本质中进展速度不同。

Question 27Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

某患者因甲状腺手术误伤甲状旁腺，术后出现手足搐搦、Chvostek征阳性。其血生化最可能出现的变化是？

  1. 血钙降低、血磷升高 Correct answer.
  2. 血钙升高、血磷升高
  3. 血钙降低、血磷降低
  4. 血钙升高、血磷降低

Explanation

甲状旁腺激素的主要作用是动员骨钙入血、促进肾小管重吸收钙并抑制磷的重吸收。甲状旁腺功能减退时，骨钙动员和肾小管重吸收钙减少，同时肾排磷减少，故表现为低血钙伴高血磷。低血钙使神经肌肉兴奋性增高，出现手足搐搦。

Question 28Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

有机磷酸酯类中毒时，患者出现瞳孔缩小、流涎、支气管分泌物增多和肌束颤动。此时抢救应及早联合使用阿托品与碘解磷定，后者的主要作用机制是？

  1. 抑制乙酰胆碱释放，减少神经末梢递质
  2. 复活被抑制的胆碱酯酶，并直接与游离毒物结合 Correct answer.
  3. 阻断M胆碱受体，减轻毒蕈碱样症状
  4. 可逆性抑制胆碱酯酶，减少乙酰胆碱分解

Explanation

有机磷酸酯与胆碱酯酶结合形成磷酰化胆碱酯酶，使酶失活。碘解磷定等肟类化合物能夺取磷酰基使胆碱酯酶复活，并能直接与游离的有机磷酸酯结合而解毒。阿托品则仅阻断M受体、缓解毒蕈碱样症状，对骨骼肌的烟碱样症状无效，故须两者合用。

Question 29Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

在DNA复制过程中，能够以亲代DNA为模板、沿5′→3′方向延伸新链，同时具有3′→5′外切酶校对活性的酶是？

  1. DNA连接酶
  2. 拓扑异构酶
  3. RNA聚合酶
  4. DNA聚合酶Ⅲ Correct answer.

Explanation

原核生物中DNA聚合酶Ⅲ是主要的复制酶，催化dNTP加到引物3′-OH端，使新链沿5′→3′方向延伸，并具有3′→5′外切酶活性以切除错配碱基进行校对。RNA聚合酶用于合成引物，无校对功能；连接酶和拓扑异构酶不催化链的延伸。

Question 30Basic Medical Sciences (Anatomy, Physiology, Biochemistry, Pathology, Pharmacology, Microbiology/Immunology)

一名患者反复发生口腔念珠菌感染，外周血CD4⁺T细胞计数显著下降。下列哪项关于CD4⁺T细胞识别抗原的叙述最准确？

  1. CD4⁺T细胞识别由MHCⅠ类分子提呈的抗原肽
  2. CD4⁺T细胞通过CD8分子与抗原肽结合
  3. CD4⁺T细胞直接识别未经加工的游离抗原
  4. CD4⁺T细胞识别由MHCⅡ类分子提呈的抗原肽 Correct answer.

Explanation

CD4⁺T细胞的TCR识别的是由抗原提呈细胞表面MHCⅡ类分子提呈的经加工抗原肽，其辅助受体CD4结合MHCⅡ类分子的非多态区。MHCⅠ类分子提呈内源性抗原肽给CD8⁺T细胞。CD4⁺T细胞数量下降会削弱对真菌等胞外病原体的辅助免疫，故易发生念珠菌感染。

Question 31Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

Enamel is formed by which cell type during odontogenesis?

  1. Ameloblast Correct answer.
  2. Odontoblast
  3. Cementoblast
  4. Fibroblast of the dental papilla

Explanation

Ameloblasts differentiate from the inner enamel epithelium of the enamel organ and secrete the enamel matrix, which then mineralizes into the hardest tissue in the body. Odontoblasts arise from the dental papilla and form dentin, not enamel. This appositional sequence, dentin first then enamel, defines the reciprocal induction at the dentinoenamel junction.

Question 32Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

Which description best characterizes the arrangement of enamel rods (prisms) in human permanent enamel?

  1. They run strictly parallel to the dentinoenamel junction in all regions.
  2. They extend from the dentinoenamel junction toward the surface, generally perpendicular to it but with regional variation. Correct answer.
  3. They run only in the cervical third and are absent coronally.
  4. They are randomly oriented with no consistent direction.

Explanation

Enamel rods extend outward from the dentinoenamel junction toward the tooth surface, generally following a course roughly perpendicular to the junction, with decussation and regional deviation such as gnarled enamel under cusps. This orientation reflects the path of the ameloblasts as they retreat during secretion. Rod direction matters clinically because acid and caries spread along rod pathways.

Question 33Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

A 30-year-old reports sharp pain on drinking cold water that resolves within seconds after the stimulus is removed. Which pulpal condition is most consistent with this history?

  1. Asymptomatic apical periodontitis
  2. Reversible pulpitis Correct answer.
  3. Irreversible pulpitis
  4. Pulpal necrosis

Explanation

Reversible pulpitis produces sharp, brief provoked pain that subsides promptly once the stimulus is removed, and the pulp retains healing capacity. Irreversible pulpitis typically gives lingering pain after the stimulus ends, often spontaneous and worse at night. Necrotic pulps and asymptomatic apical periodontitis generally do not give sharp cold sensitivity.

Question 34Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

Which bacterial species is most strongly associated with the initiation of dental caries on smooth enamel surfaces?

  1. Actinomyces israelii
  2. Treponema denticola
  3. Porphyromonas gingivalis
  4. Streptococcus mutans Correct answer.

Explanation

Streptococcus mutans is acidogenic and aciduric, adheres to the acquired pellicle via glucosyltransferase-derived glucans, and dominates early smooth-surface caries. Its ability to lower pH and survive acid conditions drives demineralization. The other listed organisms are linked to periodontal disease or to root caries rather than smooth-surface initiation.

Question 35Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

During mandibular protrusion, which muscle group acts as the primary protruder of the mandible?

  1. Medial pterygoid
  2. Posterior fibers of the temporalis
  3. Masseter
  4. Superior head of the lateral pterygoid Correct answer.

Explanation

The superior head of the lateral pterygoid, with its horizontal fibers, pulls the condyle forward along the articular eminence, producing protrusion. The inferior head mainly assists opening and disc positioning. The other muscles named elevate or retrude the mandible.

Question 36Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

Which zone of the periodontal ligament is most directly responsible for transmitting tensile forces and is embedded in alveolar bone?

  1. Sharpey fibers Correct answer.
  2. Gingival fiber group
  3. Transseptal fibers
  4. Principal fibers of the apical region only

Explanation

Sharpey fibers are the terminal collagen bundles of the principal periodontal ligament fibers that embed into cementum on one side and alveolar bone on the other, transmitting occlusal forces. The transseptal fibers run between adjacent teeth, and gingival fibers support the marginal tissues. These fiber systems differ in location and function.

Question 37Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

Which salivary component provides the primary buffering capacity of stimulated whole saliva?

  1. Secretory IgA
  2. Amylase
  3. Bicarbonate Correct answer.
  4. Lysozyme

Explanation

Bicarbonate is the principal buffer in stimulated saliva, and its concentration rises with flow rate, raising pH and protecting enamel. Amylase digests starch, lysozyme is antibacterial, and secretory IgA is immunologic. Buffer capacity therefore depends heavily on flow rate and gland stimulation.

Question 38Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

A 45-year-old presents with a well-demarcated white plaque on the buccal mucosa that cannot be wiped off and has no identifiable cause. Which term best describes this lesion?

  1. Lichen planus
  2. Frictional keratosis
  3. Candidiasis
  4. Leukoplakia Correct answer.

Explanation

Leukoplakia is a clinical diagnosis of exclusion: a predominantly white patch that cannot be characterized clinically or pathologically as any other disease and cannot be rubbed off. Candidiasis can often be wiped off and shows hyphae, lichen planus has characteristic striae, and frictional keratosis has an identifiable mechanical cause. The distinction matters because leukoplakia carries malignant potential.

Question 39Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

Which feature distinguishes a radicular cyst from a dentigerous cyst on a radiograph?

  1. The radicular cyst is associated with the apex of a nonvital tooth. Correct answer.
  2. The radicular cyst surrounds the crown of an unerupted tooth.
  3. The radicular cyst contains multiple calcified bodies.
  4. The radicular cyst occurs only in the mandibular ramus.

Explanation

A radicular (periapical) cyst arises from epithelial rests in a periapical granuloma of a nonvital tooth and appears as a well-defined radiolucency at the root apex. A dentigerous cyst encloses the crown of an unerupted tooth and attaches at the cementoenamel junction. Location and the vitality status of the associated tooth are the key discriminators.

Question 40Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

Which cell type is the principal antigen-presenting cell of the oral epithelium?

  1. Merkel cell
  2. Keratinocyte of the stratum spinosum
  3. Langerhans cell Correct answer.
  4. Melanocyte

Explanation

Langerhans cells are dendritic antigen-presenting cells located mainly in the suprabasal layers of the oral epithelium. They capture antigen and migrate to regional lymph nodes to present it to T cells. Melanocytes produce pigment, Merkel cells are mechanoreceptors, and keratinocytes provide structural barrier function rather than primary antigen presentation.

Question 41Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

Which change in dentin occurs in response to slowly progressing caries, producing a zone of altered permeability?

  1. Tertiary dentin only
  2. Dead tract formation
  3. Sclerotic dentin Correct answer.
  4. Enamel tuft formation

Explanation

Slow caries stimulates peritubular dentin deposition and tubular sclerosis, forming sclerotic dentin that reduces permeability and slows lesion progression. Tertiary dentin is a reparative response at the pulp surface, and dead tracts result from odontoblast death. Enamel tufts are hypomineralized structures in enamel.

Question 42Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

Which immunoglobulin is the predominant type in whole saliva and is produced by plasma cells near salivary glands?

  1. IgM
  2. IgE
  3. IgA Correct answer.
  4. IgG

Explanation

Secretory IgA is the dominant immunoglobulin in whole saliva, produced by plasma cells and transported across glandular epithelium with a secretory component. It agglutinates bacteria and neutralizes antigens at mucosal surfaces. IgG enters saliva mainly from gingival crevicular fluid, while IgE and IgM are minor contributors.

Question 43Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

Which statement correctly describes the sequence of tooth eruption phases for a permanent mandibular first molar?

  1. It erupts after the permanent canine.
  2. It erupts before the permanent second molar and after the first premolar. Correct answer.
  3. It erupts after the permanent second molar.
  4. It erupts before all permanent incisors.

Explanation

The mandibular first molar typically erupts at about 6 years, before the second molar, which emerges around 12 years. Permanent incisors and first premolars appear around 6 to 10 years, so the first molar usually precedes the second molar and most premolars. This timing makes it the cornerstone of the developing occlusion.

Question 44Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

Which nerve branch supplies sensation to the buccal gingiva of the mandibular molars?

  1. Mylohyoid nerve
  2. Lingual nerve
  3. Buccal nerve Correct answer.
  4. Inferior alveolar nerve

Explanation

The buccal nerve, a branch of the mandibular division of the trigeminal nerve, provides sensory supply to the buccal mucosa and buccal gingiva of the mandibular molars. The inferior alveolar nerve supplies the teeth and chin, the lingual nerve supplies lingual gingiva and tongue, and the mylohyoid nerve is motor to the mylohyoid and anterior digastric.

Question 45Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

In the classic Miller classification of gingival recession, which class describes recession extending to the mucogingival junction with no attached gingiva remaining?

  1. Class III Correct answer.
  2. Class IV
  3. Class I
  4. Class II

Explanation

Miller Class III recession extends to or beyond the mucogingival junction, with loss of attached gingiva and possible interproximal bone loss. Class I and II are within the attached gingiva, and Class IV involves severe interproximal bone loss with poor prognosis. The classification guides predictability of root coverage procedures.

Question 46Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

Which histologic feature is characteristic of a pleomorphic adenoma of the minor salivary glands?

  1. Dense fibrous tissue with sparse cellularity
  2. Sheets of atypical squamous cells with keratin pearls
  3. Multiple layers of basaloid cells with cribriform spaces
  4. A mixture of epithelial and myxochondroid stromal elements Correct answer.

Explanation

Pleomorphic adenoma shows a biphasic pattern of epithelial cells and myxochondroid stroma, reflecting its mixed origin. This admixture of ductal cells and chondromyxoid matrix is the diagnostic hallmark. Squamous pearls suggest squamous cell carcinoma, and cribriform basaloid patterns suggest adenoid cystic carcinoma.

Question 47Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

Which bacterial species is the primary etiologic agent of necrotizing ulcerative gingivitis?

  1. Actinomyces viscosus
  2. Lactobacillus acidophilus
  3. Fusobacterium species with spirochetes Correct answer.
  4. Streptococcus mutans

Explanation

Necrotizing ulcerative gingivitis is a fusospirochetal infection in which Fusobacterium species act together with spirochetes such as Treponema, producing punched-out papillae and a fetid odor. The mixed anaerobic flora requires both components. Streptococci and lactobacilli are cariogenic, and Actinomyces is associated with root caries.

Question 48Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

Which structure marks the boundary between the enamel-covered crown and the cementum-covered root?

  1. Gingival margin
  2. Dentinoenamel junction
  3. Cementoenamel junction Correct answer.
  4. Cemento dentinal junction

Explanation

The cementoenamel junction is the cervical line where enamel and cementum meet, and its configuration influences root sensitivity and periodontal attachment. The dentinoenamel junction lies deep within the crown, and the gingival margin is a soft-tissue landmark. Recognizing this boundary is important when interpreting cervical lesions and recession.

Question 49Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

Which mechanism best explains the reduced pain threshold observed in dentin hypersensitivity at the cervical region?

  1. Fluid movement within exposed dentinal tubules stimulating pulpal nerve endings Correct answer.
  2. Increased enamel thickness at the cervical margin
  3. Continuous cementum formation over the root
  4. Direct nerve endings within enamel

Explanation

The hydrodynamic theory holds that fluid shifts within exposed dentinal tubules deform mechanoreceptors near the pulp, generating pain. Cervical exposure of tubules after recession increases this response. Enamel does not contain nerve endings, and increased enamel thickness would reduce rather than enhance sensitivity.

Question 50Oral Basic Sciences (Oral Anatomy & Histology, Oral Physiology, Oral Pathology, Oral Microbiology)

Which primary tooth is most frequently retained beyond its expected exfoliation time, often associated with impaction of the succeeding premolar?

  1. Maxillary primary central incisor
  2. Maxillary primary second molar Correct answer.
  3. Mandibular primary first molar
  4. Mandibular primary canine

Explanation

The maxillary primary second molar is commonly retained and can block eruption of the maxillary second premolar, whose eruption path is longer and more complex. Retention here often requires extraction to allow the premolar to emerge. Other primary teeth exfoliate more predictably.