Removable 3 22 (1) PDF - PRECLINICAL GUIDE FOR PARTIAL DENTURE PROSTHODONTICS

PRECLINICAL GUIDE FOR PARTIAL DENTURE PROSTHODONTICS Part 1 For 3rd year students Course title; removable Prosthodontics technology 3 Course code: RPROSD 311 Removable Prosthodontics Department 2024-2025 CONTRIBUTORS Dr. Sara Medhat Dr/Ahmed Atef Revised by Assoc. Prof. Iman Adel Head of the Removable Prosthodontics Department Dedication To my great Professors Especially Prof. Mahmoud El-Refaee Assoc. Prof. Iman Adel Prof. Mostafa Abdel Ghani To my supportive Family Dr. Sara Medhat i Acknowledgement I would like to express my sincere gratitude to the previous course coordinator Dr. Tarek Abdallah, for his invaluable assistance and guidance throughout the past years of this course. His support has been instrumental in shaping the course journey and I am truly appreciative of his dedication and expertise. ii ‫رؤية و رسالة الجامعة‬ ‫الرؤية‬ ‫تسعى الجامعة الحديثة للتكنولوجيا والمعلومات ان تكون احدى الجامعات الخاصة‬ ‫المتميزة والمؤثرة على المستوى المحلى واالقليمى‬ ‫الرسالة‬ ‫تعمل الجامعة الحديثة للتكنولوجيا والمعلومات على االرتقاء بالمستوى العلمى والجودة للخريج‬ ‫من خالل تقديم برامج تعليمية متطورة من اجل تلبية احتياجات سوق العمل الحالى والمستقبلى‬ ‫وتقديم خدمات للمجتمع واستشارات وابحاث اكاديمية وتطبيقية متميزة ومن خالل شراكة مع‬ ‫جامعات محلية واجنبية‪.‬‬ ‫رؤية و رسالة الكلية‬ ‫الرؤية‬ ‫تتطلع كلية طب الفم و األسنان – الجامعة الحديثة للتكنولوجيا و المعلومات إلى أن تكون‬ ‫من أكثر الكليات تميزا على المستوى المحلي و اإلقليمي في مجال طب األسنان‬ ‫الرسالة‬ ‫تلتزم الكلية بإعداد أطباء أسنان يتميزون بالجدارة المهنية قادرين على التوافق مع متطلبات‬ ‫سوق العمل و مواكبة التطور العلمي و اإلسهام فيه باألنشطة البحثية مع تلبية إحتياجات‬ ‫المجتمع في إطار قيم أخالقية‬ ‫‪Vision‬‬ ‫‪The College of Oral and Dental Medicine - Modern University for Technology‬‬ ‫‪and Information aspires to be one of the most distinguished colleges at the local‬‬ ‫‪and regional levels in the field of dentistry.‬‬ ‫‪iii‬‬ Mission The college is committed to prepare dentists who are distinguished by professional merit, able to comply with the requirements of the labor market and keep pace with scientific development and contribute to it through research activities while meeting the needs of the surrounding community within the framework of ethical values. iv ‫ر‬ ‫اإلستاتيجية‬ ‫الغايات واألهداف‬ ‫ز ز‬ ‫متمتة ف تعليم طب األسنان‬ ‫الغاية األوىل‪ :‬تحقيق قدرة تنافسية‬ ‫الهدف األول‪:‬‬ ‫إستاتيجيات التدريس والتعلم بما يتفق مع اتجاه الدولة المرصية لتطوير التعليم الجامع‪.‬‬‫تطوير ر‬ ‫الهدف ز‬ ‫الثان‪:‬‬ ‫ي‬ ‫للتنامج ونظم التقويم والكتاب الجامع واألنشطة الطالبية لتنمية مهارات‬ ‫تطوير المحتوى العلم ر‬ ‫متغتات سوق العمل‪.‬‬‫وخريج الكلية بما يتفق مع ر‬ ‫ر‬ ‫طالب‬ ‫الهدف الثالث‪:‬‬ ‫استيفاء أعداد أعضاء هيئة التدريس والهيئة المعاونة بما يتناسب مع أعداد الطالب‪.‬‬ ‫الهدف الرابع‪:‬‬ ‫استخدام تكنولوجيا المعلومات وأساليب التعلم الحديثة‪.‬‬ ‫ز‬ ‫ز‬ ‫الغاية الثانية ‪:‬‬ ‫العلم‬ ‫ي‬ ‫التمت واإلبداع يف مجال البحث‬ ‫الهدف األول‪:‬‬ ‫تلب حاجة‬ ‫تحفت منظومة البحث العلم بما يدعم تقديم خدمات بحثية ذات تطبيقات عالجية ر‬ ‫رز‬ ‫المجتمع المحل والدول‪.‬‬ ‫الهدف ز‬ ‫الثان‪:‬‬ ‫ي‬ ‫توسيع مجاالت التعاون ر‬ ‫والشاكة البحثية محليا واقليميا وعالميا‪.‬‬ ‫الهدف الثالث‪:‬‬ ‫تطوير البنية البحثية والتكنولوجية للكلية‪.‬‬ ‫الهدف الرابع‪:‬‬ ‫االلتام بأخالقيات البحث العلم وضمان حقوق الملكية الفكرية‬ ‫رز‬ ‫الهدف الخامس‪:‬‬ ‫نش األبحاث العلمية المحلية والدولية والحث‬ ‫تشجيع أعضاء هيئة التدريس والهيئة المعاونة عل ر‬ ‫عل المشاركة العلمية زف المؤتمرات‪.‬‬ ‫الهدف السادس‪:‬‬ ‫الخريجي زف سوق العمل‪.‬‬ ‫رز‬ ‫تلب احتياجات‬ ‫إنشاء برامج تعليمية لمرحلة الدراسات العليا ر‬ ‫ز‬ ‫ز‬ ‫المدن لتقديم خدمات عالجية ف طب األسنان‬ ‫ي‬ ‫الغاية الثالثة ‪ :‬التكامل مع المجتمع‬ ‫الهدف األول‪:‬‬ ‫التوسع زف التعاون مع مؤسسات المجتمع المدن المحيط لتلبية احتياجات المجتمع‪.‬‬ ‫ز‬ ‫‪v‬‬ ‫الهدف ز‬ ‫الثان‪:‬‬ ‫ي‬ ‫التوعية التثقيفية المستمرة داخليا وخارجيا لتلبية احتياجات المجتمع المحيط بالرعاية الصحية‬ ‫لألسنان‪.‬‬ ‫الهدف الثالث‪:‬‬ ‫التطوير المستمر للخدمات العالجية بالعيادات الخارجية للكلية‪.‬‬ ‫الهدف الرابع‪:‬‬ ‫رز‬ ‫الخريجي‪.‬‬ ‫دعم برامج التواصل مع‬ ‫ُ ز‬ ‫الغايــة ال ـرابعة‪ :‬التــمت واإلبــداع الـمؤسـ ي‬ ‫ـس‬ ‫الهدف األول‪:‬‬ ‫تطوير البنية التحتية والتكنولوجية للكلية‪.‬‬ ‫الهدف ز‬ ‫الثان‪:‬‬ ‫ي‬ ‫تنمية قدرات القيادات االكاديمية واالدارية الحالية والمستقبلية‪.‬‬ ‫الهدف الثالث‪:‬‬ ‫تنمية قدرات اعضاء هيئة التدريس والهيئة المعاونة والجهاز اإلداري‪.‬‬ ‫‪vi‬‬ List of contents Chapter Subject Page no. Chapter 1 INTRODUCTION AND 1 CLASSIFICATION Chapter 2 CLASSIFICATION OF 8 PARTIALLY EDENTULOUS ARCHES Chapter 3 LABORATORY 12 PROCEDURES FOR PARTIAL DENTURE CONSTRUCTION Chapter 4 COMPONENTS OF A REMOVABLE PARTIAL 28 DENTURE Chapter 5 MAJOR CONNECTORS 42 Chapter 6 RESTS AND REST SEATS 63 Chapter 7 TOOTH SELECTION FOR PARTIAL 78 DENTURE Chapter 8 FORCES ACTING ON PARTIAL DENTURES 84 vii CHAPTER I INTRODUCTION AND CLASSIFICATION Terminology ▪ Prosthetics: The art and science of replacing absent body parts ▪ Prosthesis: An artificial replacement for a missing body part. ▪ Prosthodontics or dental prosthetics: The branch of dental art and science that pertains to the replacement of missing teeth and oral tissues to restore and maintain oral form, function, appearance and health. ▪ Removable Prosthodontics is devoted to replacement of missing teeth and contagious tissues with prosthesis designed to be removed by the wearer. It includes; removable complete and removable partial Prosthodontics. ▪ Partially edentulous patient: Some of the natural teeth are present and some are absent, for such a patient a partial denture is to be constructed. Fixed partial denture: A restoration, which restores one or more missing teeth. It is permanently cemented to neighboring natural teeth resin bonded and cannot be removed by the patient. Removable partial denture: Any prosthesis that replaces some teeth in a partially edentulous patient and can be removed from the mouth by the patient. Bounded edentulous area: An edentulous area, which has an abutment Tooth on each side. (Distal extension edentulous area (free-end) An edentulous area with no posterior abutment. Extension base removable partial denture; A removable partial denture that is supported and retained by natural tooth at one end of the denture base only and in which a portion of a function load is carried by the residual ridge. 1 Tooth Borne (Tooth Supported) Removable partial denture; Removable prosthesis that depends entirely on the natural teeth for support. Abutment: tooth, or that portion of a dental implant that serves to support and/or retain a prosthesis. Denture base saddle: That part of a denture that rests on the oral mucosa and to which the teeth are attached. Unilateral removable partial denture: A removable denture restoring lost or missing teeth on one side of the arch only. Bilateral removable partial denture: A removable partial denture replacing teeth on both sides of the dental arch. Tooth- Supported removable partial denture, removable partial denture that is totally supported by natural teeth bounding the edentulous space Tooth - Tissue supported removable partial denture: Removable partial denture Saddle which gain its support from the residual ridge and abutment teeth. Tissue - Supported partial denture: Removable partial entirely from the mucosa and the underlying bone. This is usually acrylic removable partial denture without occlusal rest INDICATIONS FOR REMOVABLE PARTIAL DENTURES 1. No abutment tooth posterior to edentulous space (Free end edentulous area) Fig (1-1). 2. After recent extraction, usually done only to improve esthetics, or for patient satisfaction. 3. Long edentulous bounded span, too extensive for fixed restoration Fig (1-2). 4. Periodontally weak teeth not sufficiently sound to support fixed- partial denture. 5. With excessive loss of residual bone, the use of labial flange to restore lost tissues. 2 6. Need of bilateral bracing (cross arch stabilization). 7. Enhancing esthetics in anterior region, by the use of translucent artificial teeth instead of dull fixed partial denture pontic. 8. Young age (less than 17 years). 9. Immediate replacement. 10. Economic considerations, attitude and desire of the patient. Buccal frenum Fig (1-1) posterior teeth loss Fig (1-2) long span bounded PURPOSE OF REMOVABLE PARTIAL DENTURE 1-Preservation of the remaining teeth and tissues: The primary purpose of removable partial dentures must always be the preservation of the remaining teeth and soft tissues. The provision of partial dentures will prevent or at least minimize the following retrograde pathologic changes in the oral structures: A- Drifting and rotation of remaining teeth fig (1-3). B-Continuous eruption of unopposed teeth. fig (1-4). C- Overclosure and protrusion of the mandible. fig (1-5). 3 Fig (1-3) Drifting and rotation of remaining teeth. Fig (1-4) Continuous eruption of unopposed teeth. Fig (1-5) Overclosure and protrusion of the mandible. 4 D-Trauma to the oral mucosa: - A common situation is excessively deep anterior overbite and impingement of the lower teeth into the palatal mucosa.Overclosure and protrusion of the mandible and deep anterior overbite. E-Facial or temporomandibular joint pain, may result from occlusal derangement occurred due to drifting and super-eruption of the remaining teeth and overclosure and mandibular protrusion.p 2- To improve masticatory function: - Replacing the lost teeth in an arch will greatly improve the act of chewing, by eliminating space into which food escape from the occlusal table and also it contributes directly in mastication. 3- Improve aesthetics: - Restoration of lost facial contour, vertical dimension of the face and absent teeth will improve the patient appearance. 4- Restoration of speech: Missing of anterior teeth will result in defect in labio-dental sounds The artificial teeth should be placed in the position previously occupied by the natural teeth to correct the speech defects. (e.g. f,v and ph) and dental sounds (e.g. th and ch.). 5- Psychological benefits: - The provision of an acceptable partial denture will enhance comfort of the patient 5 HAZARDS OF IMPROPERLY DESIGNED PARTIAL DENTURES An improperly designed and constructed partial denture may adversely affect the tissues in the following manner 1- Stagnation of food around component parts of partial denture in contact with tooth surfaces that are not readily cleaned causes tooth decay. 2- Induce stresses on abutment teeth and tissues. If these stresses exceed the physiologic limits of tissue tolerance, pathologic and destructive changes may occur: a) Excessive stresses on abutment teeth cause periodontal membrane destruction, pocket formation, mobility, and even loss of these teeth. b) Inflammation, ulceration and gingival recession may occur due to excessive stresses and undue coverage of tissues with the restoration. Inadequate denture support due to inadequate stoppers, this causes displacement, of the restoration towards the tissues causing gum stripping. c) Stresses may also cause bone resorption and loss of the bony foundation necessary to support the prosthesis. 3- Improper occlusion of teeth or the presence of premature contact may cause T.M.J. disorders. ADVANTAGES OF REMOVABLE PARTIAL DENTURE OVER FIXED PARTIAL DENTURE: 1- They can be constructed for any case whilst fixed partial denture is confined to short spans bounded by healthy teeth and with a normal occlusion. 2- Cheaper than fixed partial denture. 3- They are more easily cleaned. 4. They are more easily repaired. 5- minimal tooth reduction is required 6 CONTRAIDICATIONS FOR REMOVABLE PARTIAL DENTURES: 1. Whenever fixed restorations and/or implant can be successfully used. 2. When oral hygiene is poor and high caries susceptibility. 3. Lack of patient cooperation or appreciation. 4. When the prognosis for the remaining natural teeth is doubtful (can't be used as abutment) and the residual ridges after extractions would be good. 7 CHAPTER II CLASSIFICATION OF PARTIALLY EDENTULOUS ARCHES I. classification according to the type of support into: 1- Tooth Supported RPD (Tooth-borne) removable partial denture: fig(2-1) Removable partial denture, which is totally supported by the natural teeth bounding the edentulous space. 2- Tissue Supported RPD (Tissue borne): : fig(2-2) Removable partial denture, which is entirely supported by the mucosa and the underlying bone. 3- Tooth and Tissue Supported RPD (Tooth and tissue borne):fig(2-3) Removable partial denture, which derives its support mainly from the tissues of the residual ridge and partly from the abutment teeth. 8 Fig (2-1) teeth supported RPD Fig (2-2) tissue supported RPD Fig (2-3) teeth tissue supported RPD III- Kennedy's classification: Fig (2-4) It is simple and can be easily applied to nearly all partially edentulous cases, according to the most posterior edentulous span or spans. Additional edentulous areas are referred to as modification spaces and are designated by their number These classes are: Class I: Bilateral edentulous areas located posterior to the remaining natural teeth. Class II: Unilateral edentulous area located posterior to the remaining natural teeth. Class III: Unilateral edentulous area with natural teeth, both anterior and posterior to it. Class IV: Single, bilateral edentulous area located anterior to the remaining natural teeth. 9 Fig (2-4) Kennedy clssification CLASSIFICATIONS of RPD The numeric sequence of the classification system is based on the frequency of occurrence of each class. Class I being the most common while class IV is the least common. Kennedy's classification was then modified by Applegate. Applegate's rules for applying Kennedy classification Fig (2-5) Rule l: Classification should follow mouth preparations, since further extractions may alter the class. Rule 2: If the third molar is missing and not to be replaced, it is not considered in the classification Rule 3: If the third molar is present and to be used as an abutment, it is considered in the classification Rule 4: If the second molar is missing and not to be replaced, because the opposing second molar is also missing, it is not considered in the classification. Rule 5: The most posterior edentulous area (or areas) always determines the classification. Rule 6: Additional edentulous areas other than those determining the class are referred to as modification spaces and are designated by their number. Rule 7: The extent of the modification is not considered, only the number of additional edentulous areas. Rule 8: There can be no modification areas in class IV arches, because if there is a posterior edentulous area beside the anterior one, the former will determine the class and the anterior edentulous area will be a modification to the class. 10 Fig (2-5) Applegate's rules 11 CHAPTER III LABORATORY PROCEDURES FOR PARTIAL DENTURE CONSTRUCTION The construction of metallic removable partial dentures comprises both, Clinical and laboratory steps that are done following the sequence shown in the table. Steps of partial denture construction Clinical steps Laboratory steps - Diagnosis and treatment planning: - Extra and intra-oral examinations. - X-ray Examinations. -primary impression: With an elastic -Pouring the impression in stone material as alginate impression plaster to construct a study cast. material in a perforated stock tray. Surveying the study cast. -Construction of the special tray on the study cast. -Mouth Preparation which includes a. Conservative, periodontal and surgical treatment. b. Preparation of occlusal rest seat, guiding planes and probable recontouring of abutments. Drawing the design of the partial denture. final impression -The final impression is poured in dental stone to obtain the master cast. Surveying the master cast. - Drawing the partial denture design on the master cast. -Modification of master cast for duplication -Duplication of the master cast into the refractory cast Construction of wax pattern on refractory cast spruing investment,wax elimination casting 12 pickling, finishing& polishing of metal framework Try-in of the metal frame work in the patient's mouth. Jaw relation registration Tooth Mounting casts on the articulator setting up of artificial selection Try-in of the denture -Flasking ,processing of acrylic resin -Finishing & polishing Delivery of removable partial denture and final adjustment Periodic check-up teeth 13 SURVEYING Dental surveyor: Fig (3-1) A paralleling instrument used in the fabrication of a removable partial denture. Surveying: The procedure of analyzing and delineating the contours of the abutment teeth and associated structures before designing a removable partial denture. Principles of surveying: If a vertical plane is brought into contact with a curved surface of the tooth and rotated around the tooth, it will draw an imaginary line. This line indicates the maximum convexity of the tooth surface (survey line). The area of the tooth gingival to this line is an undercut area (infrabulge) and that occlusal to this line is non-undercut area (suprabulge). If the position of the tooth is changed in relation to the vertical plane, the location of the survey line will change and the location and extent of undercut will change. Components of dental surveyor : 4 5 1 Fig (3-1) Dental surveyor 14 1- Base (B). 2-Vertical support arm. 3- Horizontal arm. 4- Vertical movable arm or spindle (VMA); moves down and up. 5- Chuck (C) or tool holder. 6- Surveyor table: It consists of a movable plate (MP) and a base (TB). Joined by a ball and socket joint (BS). The cast is attached to the movable plate and locked in place by a clamp (TLD). The ball and socket joint permits the cast to be tilted in various planes and can be fixed in any position by tightening the locking screw (LLD). 7- Surveyor tools: Fig (3-2) a- Analyzing rod is a straight metal shaft used to analyze the cast to evaluate the presence or absence of undercut (fig. 2-3). b- Undercut gauges, are used to identify the amount of the retentive undercut. It is available in three sizes; 0.01, 0.02 and 0.03 of an inch. c-Carbon marker and reinforcing sheath, used to draw the survey line of the teeth and to delineate an undercut area of the soft tissue of the ridge. d-Wax trimmer, used to eliminate or block out areas of undesirable undercut with wax. Also, used to prepare guiding planesinwaxpattern of fixed restorations. 15 Fig (3-2)Surveying tools Path of insertion (placement): Fig (3-3) The specific direction in which a prosthesis is placed upon the abutment teeth. The tilt of a cast determines the direction that the partial denture will take during placement and removal. There are four factors that must be considered when determining the most favorable tilt of a dental cast and correspondingly the path of insertion. These factors are: 1- The establishment of appropriate guiding planes. 2- The presence of suitable undercuts; 3- The elimination of hard and soft tissue interferences 4- The creation of desirable esthetics. 16 Fig (3-3) Path of insertion (placement): Survey process (Uses of dental surveyor): 1- Place the cast on the surveyor table and orient the plane of occlusion relatively horizontal. The final tilt of the cast for the ideal path of insertion is seldom more than 10° from this position. Fig (3-4) Fig (3-4) Place the cast on the surveyor table 2- Place the analyzing rod against the axial surface of the proposed abutments adjacent to the edentulous space. The tip of the rod should be at the level of the free gingival margin. 3- The establishment of appropriate guiding planes: The guiding planes are the proximal tooth surfaces that are prepared to be parallel to each other and to the path of insertion. These planes contribute to the stability of the partial denture. 17 Tilt the cast to gain maximum parallelism of axial surfaces of all of the proposed abutments. Check the mesial and distal tooth surfaces while tilting the cast anterior-posteriorly (A-P). While maintaining the same A-P tilt check facial and lingual parallelism. Lock the tilt of the cast when maximum parallelism is achieved. 4- Locating and measuring undercut areas of the teeth that may be used for retention. An undercut area is that portion of a tooth lies gingival to the survey line (height of contour). Use an undercut gauge to check for adequate and relatively equal retentive, undercuts for retentive arms on all abutments. Alter the tilt of cast if required. Fig (3-5) Fig (3-5) Locating and measuring undercut areas 5- The elimination of hard and soft tissue interferences: Certain structures within the oral cavity may interfere with the insertion of a removable partial denture. These structures may include teeth, bony prominences, soft tissue undercuts, and exostoses. These interferences would be eliminated surgically or by selecting a different path of insertion by changing the tilt of the cast or block out by wax. Fig (3-5) 18 Fig (3-5) block out the undercut The most common interferences: a- When the maxillary anterior ridge is edentulous and displays a noticeable undercut. Most of these undercuts can be controlled by giving the cast a posterior tilt. b-Noticeable undercuts are often encountered in anterior mandibular edentulous areas. Most anterior undercuts are controlled by giving the cast a posterior tilt. c- Palatal and mandibular lingual tori are relatively common and can produce significant difficulties in RPD therapy. Selection of the appropriate major connector can solve the problem. Otherwise, surgical removal of mandibular lingual tori provides an improved foundation for the RPD. d- The areas adjacent to the pear-shaped pads may exhibit significant undercuts. If the condition is unilateral, a slight lateral tilt of the surveying table may eliminate the undercut. Also, last mandibular molar may exhibit significant lingual undercuts. Tooth recontouring or restoration. may be carried out to eliminate the undercut. 6- The creation of desirable esthetics: The ideal position for a retentive clasp is in the gingival third of the clinical crown. Change the tilt of the cast if the selected path of insertion will cause an esthetic problem, when a clasp would have to be placed too far incisally on the facial surface of an anterior tooth. Large undercuts on the proximal surfaces of anterior teeth may create significant difficulties. These undercuts can produce triangular spaces that detract from the 19 appearance of the prosthesis and act as food traps. Undesirable undercuts may be minimized or eliminated by modifying the tilt of the cast. 7- Drawing the survey line on the abutment tooth: Fig (3-6) The survey line is a line encircling a tooth at its greatest circumference at a selected cast Max-comexity position. Lock the diagnostic cast in position on the surveying table and mark the heights of contour on the denture abutments and soft tissues with the carbon marker. When marking the heights of contour, ensure that the carbon tip follows close to the free gingival margin so that you do not register a false height of contour. The heights should be relatively equal occluso-gingivally. Fig (3-6) Drawing the survey line on the abutment tooth: 20 8- Recording the cast position in relation to the selected path of placement for future reference. This may be done by locating three parallel lines or three dots in the same horizontal plane on the cast (tripodization). Fig (3-7) Fig (3-7) Tripoding the cast Design Procedure 1- Surveyor with its tools. 2- Articulator; plasterless if possible or any simple hinge or mean value articulator. 3- Color pencils; red, blue, black, brown. Color Coding Color coding allows for easy understanding of the design marked on the diagnostic models by the technician and improves the communication between the dentist and laboratory. Commonly red, black, blue and brown colors are used. Red: Means 'required action' or the teeth require some preparation. It marks the teeth and soft tissues which are to be prepared, recontoured relieved. Solid red shows where occlusal rest is to be prepared. Diagonal red lines show where recontouring is necessary Tripod marks onare also marked in red.) 21 Black: Denotes survey lines on teeth and soft tissues. Instructions on cast base on type of tooth replacement, type of clasp, depth of undercut are also written in black. Blue: Denotes portions that will be made of acrylic; mostly denture bases and acrylic teeth. Brown: Denotes all metallic portions Procedure 1- Occluded diagnostic casts The following procedures are performed on occluded diagnostic a- Proposed rest areas are marked on the cast base below the tooth with a short line. b- Any cuspal relief needed to provide adequate occlusal clearance for the rest is marked in red on the tooth to be prepared. c- Line marked on lingual surface of upper anterior teeth demarcates incisal limits of metal extensions 2- Type of tooth replacement This is indicated by marking the type of replacement on the labial side of ridge of the missing tooth. The following symbols are used: a- Denture tooth; no symbol b- Tube tooth; T c- Facing; F d- Metal pontic; M 3- Select the final tilt of cast and Tripod the cast: The final tilt is selected and cast is locked in position. The areas that require modification are marked in red. The tilt of cast is recorded by tripoding for future reference. 22 4- Mark the survey lines and soft tissue undercuts The carbon marker is placed and survey line is marked in black on all the teeth. Soft tissue undercuts are also scribed for designing bar clasps. 5- Mark the areas to be prepared in the mouth Rests and indirect retainers are then marked in red. Areas to be recontoured are also marked in red as evenly spaced diagonal lines. 6- Mark the denture base area Outline the exact position and extent of the denture base area in blue. 7-Mark the major and minor connectors The framework with major and minor connectors is marked in brown to join the already marked rests, indirect retainers, denture base and replacement teeth 8- Mark the retentive terminal Desired undercut is measured with undercut gauge and location of retentive terminal is marked as a red line of 2 mm. 9. Draw the clasp arms With a brown pencil, the clasp arms are drawn to the correct size, shape and location and are connected to the other components. If wrought wire clasp is used, the symbol WW is marked on the cast base. Beading, waxing and relief of the master cast Beading the maxillary master cast: Fig (3-8) Beading is accomplished with a small spoon excavator by scraping along the anterior & posterior borders of the major connector. Beading depth & width should not exceed 0.5 to 1 mm and should fade-out (beveled) as the gingival margins are approached. Beading on the borders of maxillary major connectors. Beading is not made along the borders of the mandibular major connectors because of the thin underlying mucosa that cannot tolerate positive contact. 23 Fig(3-8) Beading the maxillary master cast The aims of beading: a. Compensate for metal solidification shrinkage and hence, ensures positive contact of the metal with palatal tissues. b. Prevent food particles from collecting under the RPD and better speech. d. Help in transferring the design to the refractory cast. Waxing the master cast: -Blocking-out the undesirable undercuts: Elimination of undesirable undercuts on the master cast before duplication has different forms. There are three patterns of block-out Paralleled Block-Out The block-out wax is trimmed parallel to the path of insertion & removal using the wax trimmer surveyor tool. While the cast is positioned in the predetermined tilt. It's made in the following areas 1. Beneath all minor connectors 2. Proximal tooth surfaces to be used as guiding planes. 3. Tissue undercuts to be crossed by rigid connectors 4. Tissue undercuts to be crossed by origin of bar clasps 5. Deep inter-proximal spaces to be covered by minor connectors or linguoplates beneath bar clasp arms to gingival crevice. 24 Shaped block-out : Fig(3-9) It is made in the form of ledges on the buccal & lingual surfaces of abutment teeth.It will help in proper positioning & carving of the clasp arms. Ledges for location of reciprocal clasp arms to follow height of contour so that they may be placed as cervical as possible without becoming retentive Ledges for location of retentive clasp arms to be placed as cervical as tooth contour permits; point of origin of clasp to be occlusal or incisal to height of convexity, crossing survey line at terminal fourth, and to include undercut area previously selected in keeping with flexibility of clasp type being used. Fig(3-9) Shaped block-out Arbitrary block-out (Smoothed arbitrary with wax spatula): Fig(3-10) This will cover the undercuts that may interfere with removal of the duplicating material otherwise it may be subjected to tearing or distortion. This includes: a. All gingival crevices to eliminate gingival crevice leveled arbitrarily with wax spatula. b. Gross tissue undercuts situated below areas involved in design of denture framework. c. Labial & buccal tooth surfaces and tissue undercuts not involved in denture design. Arbitrary block-out 25 Fig(3-10) Arbitrary block-out -Relief: Fig(3-11) Relief is made for creating a space between the metal framework & the cast as in the following areas: a. Beneath lingual bar connectors or the bar portion of linguoplates when indicated.Areas in which major connectors will contact thin tissue such as hard areas on lingual side of mandibular ridges & elevated median palatal raphe. b. Beneath framework extension onto ridge areas for attachment of resin bases Fig(3-11) Relief: 26 Tissue Stops: Fig(3-12) Tissue stops are made by removal of two small squares of 2 mm, usually an anterior and posterior, of relief wax at the distal end the edentulous ridge. -They will result in metal projections resting on ridge areas -It provides stability of the framework during clinical work & during acrylic resin processing. the pressure of packing later on. Hence, the framework maintains its position while being subjected to the pressure packing later on. Fig(3-12) Tissue Stops 27 CHAPTER IV COMPONENTS OF A REMOVABLE PARTIAL DENTURE A removable partial denture will have some of the following components Fig(4-1) 1- Major connector 2- Minor connector 3- Rests 4- Direct retainers (clasps) 5- Indirect retainers 6- One or more denture bases and replacement teeth. 7- Denture Base Connector: The parts of RPD that unites the framework with the resin forming the denture base. Fig (4-1) COMPONENTS OF A REMOVABLE PARTIAL DENTURE 28 These Components May Provide One Following Functions or More: 1-Support: a. The resistance of a denture to tissue- ward movement. b. Adequate and wide distribution of the load to the teeth and mucosa. Fig (4-2) support 2- Retention: The resistance of a denture to vertical displacement force (to move away from its tissue foundation). Fig (4-3) 3- Indirect retention: The resistance of denture rotation away from the tissues about an axis. 4- Bracing: The resistance of a denture to lateral forces. Fig (4-3) 29 Fig (4-3) support, retention ,bracing 5- Reciprocation: The resistance of lateral forces on the abutment during insertion and removal of the removable partial denture. Reciprocation is required as the denture is being displaced occlusally whilst the bracing function, comes into play when the denture is fully seated. 6- Stability: Fig(4-4) The resistance of a denture to tipping movement. Tipping movement: Vertical rotation around a line parallel to ridge crest(twisting of the denture base) Fig (4-4) Stability 30 DENTURE BASE (SADDLE) THE DENTURE BASE; Fig (4-5) The denture base is the part of the denture, which rests on the foundation tissues and to which artificial teeth are attached. The denture base helps in transferring occlusal stresses to the supporting oral structures. Fig (4-5) Denture base Requirements for an ideal denture base 1- Accuracy of adaptation to the tissues, with minimal dimensional changes. 2- Thermal conductivity. 3- Non-irritant and can maintain good finish and polish and easily kept clean. 4- Low specific gravity (light in weight) 5- Sufficiently strong to resist fracture or distortion. 6- Esthetically acceptable. 7- Can be relined. 8- Low cost. Functions of denture base: 1- Carry artificial teeth and transfer stresses to the supporting structures. 2- Add to esthetics by reproducing natural tissue contour. 3- -Stimulation of underlying tissues by the denture movement. 4- Prevent vertical and horizontal migration of the remaining natural teeth. 31 5- In addition, the distal extension base has the following functions: Support; the broad coverage provides the best support with minimal load per unit area. (Max. coverage) Retention; is provided by intimate contact of the base and palatal plates with the underlying tissues and by proper molding of the polished surface. Max. adaptation) Types of Denture Bases L According to location 1- Bounded partial denture bases The bounded partial denture base covers an edentulous span between two abutment teeth. The base may restore a short span or a long span edentulous area. 2- Free-end partial denture bases (distal-extension base) The base bounded by a natural tooth only on one side, while the other side is free. This type is sometimes called distal extension base II. According to Longevity 1-Permanent (with metallic or non-metallic framework) 2-Temporary (acrylic only) III. According to Material 1- Metal such as chrome cobalt alloy, gold, or stainless steel. Chrome cobalt alloy is the most commonly used alloy, the material is used in cast form only. It provides the needed rigidity for removable partial dentures even in thin section. It has low specific gravity which is nearly half that of gold and provides high resistance to corrosion. 2- Non-metallic Acrylic bases of temporary acrylic removable partial dentures. 3- Combined metal and acrylic resin. 32 Acrylic resin bases attached to metallic denture framework through metallic minor connectors. Types of denture bases I- Metallic denture bases (or framework material): Indications: 1- For short span tooth borne denture. 2- When there is insufficient vertical space for use of resin. 3- When there is a deep vertical overlap of anterior teeth. Fig (4-6) Metallic denture bases Advantages: 1- Accuracy and dimensional stability. 2- -High abrasion resistance. 3- Contributes to the health of the underlying tissues by its cleanliness. 4- Thermal conductivity may help in a patient’s acceptance to the denture. 5- High strength can be made in thin sections especially cobalt- chromium and titanium alloys. Disadvantages: 1- It cannot be relined. 2- Difficult in fabrication. 3- Poor esthetic. 33 4- Expensive. 1) Chrome cobalt alloy: This is the most commonly used alloy. The material is used in cast form only. It provides the needed rigidity for removable partial denture even in thin sections. Chrome cobalt alloy has low specific gravity which is nearly half that of gold and provides high resistance to corrosion. Fig (4-7) Chrome cobalt alloy of denture base 2) Cast gold alloy is more rigid than resins but less rigid than chrome cobalt alloy. It is heavier than chrome cobalt alloy for this reason the material is sometimes used in lower partial dentures to aid in their retention. 3) Stainless steel: Stainless steel is rarely used. It is less accurate than cobalt chrome or gold alloys. It is mainly used in the swaged form 4) Titanium alloy: Recently titanium alloy starts to compete chrome cobalt alloy due to its lighter weight however still the point of its complicated casting technique makes it more expensive 34 II- Acrylic denture base: Fig (4-8) Advantages: 1- Low specific gravity. 2- Ease of relining. 3- Good esthetics. 4- Low cost. 5- Ease of fabrication. Disadvantages: 1- Less accurate fitness and high dimensional changes. 2- No thermal conductivity. 3- Low strength, so it is made more thick and bulky. 4- Low abrasion resistance, so it becomes rough and tend to accumulate food particles and calcareous deposits. Fig(4-8) Acrylic denture base: 35 III- Combined metal and acrylic resin: Fig (4-9) Indications: 1- For free end saddle extension bases. 2- When denture base resin is needed to restore anatomic contour and esthetics. 3- When there is a need for relining. 4- For long span tooth supported saddle. Design considerations: 1- The open lattice design with large openings provides the greatest retention to the resin. The retentive mesh makes the resin packing more difficult and the bond between the resin and the metal is weak. 2- The internal and external finish lines should have less than 90° angle to provide mechanical retention for the resin. 3- A relief should be provided to the metal framework at the ridge area to provide a space to allow resin to completely surround it. 4- A metal stop should be used on the extension base framework for stabilization of the framework during packing of resin. Fig (4-9) Combined metal and acrylic resin: 36 Methods of Attaching Denture Bases Acrylic resin bases are attached to metallic denture framework by means of a minor connector designed so that a space exists between it and the underlying tissues of the residual ridge.The minor connectors are either made in the form of an open latticework (ladder-like pattern) or in a closed meshwork configuration (plastic mesh pattern).Minor connectors forming mandibular distal extension bases extend posteriorly about two-thirds the length of the edentulous ridge. They should be slightly extended onto the buccal and lingual surfaces of the ridge. This design adds strength to the acrylic denture base and helps to minimize distortion of cured resin bases, which occurs due to the release of strains after processing. However, minor connectors for maxillary distal extension bases may sometimes be extended to cover the entire length of the residual ridge Fig(4-10) 37 Fig(4-10) lattice and ladder pattern of metal framework Minor connectors forming denture bases should include tissue stops and finishing line: Tissue stops: Fig(4-10) Tissue stops are essential parts in the fitting surface of minor connectors. They are usually two or three in number that contact the cast. Tissue stops stabilize the framework on the master cast during processing as acrylic resin is packed in the retention spaces. Tissue stops elevate the minor connectors, forming the denture base, from the ridge, by providing a space equal to the thickness of acrylic bases.They are formed by making holes in the relief wax placed over the ridge during preparation of the master cast before duplication. 38 Fig(4-10) Tissue stops Finishing Lines: Fig(4-11) Finishing lines are butt joints created at the junction of major “Connectors with the denture bases”. In distal extension bases, these butt joint finishing lines, are made on both the external and internal surfaces of the major connector where acrylic resin is processed, while in short bounded metallic bases, the butt joint is required only on the external surface where acrylic resin is packed, for the attachment of teeth. Internal finish lines: Internal finish lines are formed by carving the relief wax used to create space for packing acrylic resin under mesh minor connector. This relief wax is applied on the master cast before duplication External finish lines: External finish lines are formed during the formation of the wax pattern by carving a sharp definite angle in the wax pattern at the junction between the major connector and the minor connectors forming the denture base. This angle should be less than 90 degrees to lock the acrylic resin securely to the minor connectors and for the acrylic base to blend smoothly and evenly with the major connector 39 Fig(4-11) Finishing Lines Denture base extension: Maximum coverage of the edentulous ridge is important for wide distribution of the occlusal load exerted during mastication. This helps in decreasing the force per unit area and keep the forces within the physiologic tissue tolerance. A) Antero-posterior extension: - In bounded spaces: It is determined by the abutment teeth. - In free-end spaces: The base extends from the abutment to cover the retromolar pad in the lower arch and the tuberosity in the upper. B) Buccally and Lingually, the denture flanges should extend to the functional depth of the vestibule as determined by the muscle function Relationship of denture base to abutment The ideal relationship between the denture base carrying the artificial teeth and the adjacent abutment should either be: Fig(4-12 ) 40 1-Close contact between the denture and the proximal surface of the abutment. In this condition relieving the gingival margin is necessary to avoid its traumatization. 2-Open Contact between artificial teeth carried by the denture base and the abutment above the contact point allowing enough space between them to create a cleansable area. On the other hand improper contact between the denture and the abutment tooth leaving only a small space between the neck of the abutment tooth and the artificial tooth is undesirable. This small space is difficult to clean predisposing to caries, gingivitis and pocket formation. Fig (4-12) close contact. & open contact (left) (right) Recent materials used in denture bases or framework: Modified poly-ether-ether-ketone (PEEK) (metal-free denture bases): Modified poly-ether-ether-ketone (PEEK), for example the biological high performance polymers (BioHPP) that can be used as a partial denture framework material or denture base as a substitute for metals: Fig(4-13) 41 These are new materials in prosthodontics. Compared to the metals used in dentistry. 1. An alternative material for the fabrication of distal extension removable dental prosthesis (RDP) frameworks. 2. This material can be used for patients allergic to metals, or who dislike the metallic taste, the weight, and the unpleasant metal display of the denture framework and retentive clasps. 3. A biocompatible, nonallergic, rigid material, with flexibility comparable to bone, high polishing and low absorption properties, lowplaque affinity, and good wear resistance. 4. Can be constructed either via CAD/CAM manufacturing or via the conventional lost wax technique. Fig (4-13) Modified poly-ether-ether-ketone (PEEK) Chapter V MAJOR CONNECTORS 42 The major connector connects the parts of the prosthesis located on one side of the arch with those on the opposite side. All other parts of the partial denture are attached to it either directly or indirectly. Requirements of major connectors: 1- Must be rigid to transmit stresses of mastication from one side of the arch to the other. 2- Must be properly located in relation to gingival and movable soft tissues. 3- Must not impinge on the gingival margin. 4- Provide an opportunity of positioning denture bases were needed. 5- Maintain patients comfort by covering little tissues, avoid food trap and avoid bony and soft tissue prominence during insertion and removal. MAXILLARY MAJOR CONNECTORS Design: 1. The borders are placed a minimum of 6 mm from gingival margins or are positioned on the lingual surfaces of the teeth. 2. Relief is normally not required under the major connector. 3. The posterior palatal bar or strap should be located as far posteriorly as possible without contacting the movable soft palate. 4. All borders should taper slightly towards the soft tissue. 5. Both anterior and posterior borders should cross the midline at right angles, never diagonally. 6. The thickness of the metal should be uniform throughout the palate. 7. The finished borders of the metal should be gently curved,never angular 8. The metal should be smooth but not highly polished on the tissue side. 9. All borders on the soft tissue should be beaded with the bead fading out near the gingival margin of the teeth. 43 TYPES OF MAXILLARY MAJOR CONNECTORS Requirements of Maxillary Major Connectors: 1. Rigidity is necessary to transmit stresses of mastication from one side of the arch to the other. 2. Must be properly located in relation to gingival and moving tissues. 3. Must not impinge on the marginal gingiva and never depend on the gingiva for support. The borders are placed a minimum of 6mm. away from gingival margins. 4. Should be self-cleansing and not allow trapping of food particles. 5. Relief is avoided under maxillary major connector except little relief may be required in the presence of palatal tori or prominent median palatine raphe. 6. The borders should run parallel rather than diagonal to the gingival margin and if they cross the gingival margin they should be crossed abruptly and at right angle to the margin in order to produce the least possible soft tissue coverage. 7. All borders should be tapered slightly towards the tissues, and should be smoothly curved. Hence they are less detectable by the tongue and not interfere with speech, in addition to minimizing patient discomfort. 8. Thickness of the metal should be uniform throughout the palate. 9. Bony or soft tissue prominences should be avoided. 10. The metal should not be highly polished on the tissue side. 11.The borders should be beaded. Beading of Maxillary Major Connectors: 1. A palatal major connector should have a specially prepared seal along the border of the connector where it contacts the soft tissues. 2. The seal is formed by beading the border of the major connector that displaces the soft tissues slightly, thus preventing food from collecting under the maxillary major connector and help in preventing over growth of the palatal tissues. 3. The bead is produced by scraping a groove approximately 3/4 to 1mm wide and deep at the edge of the design of the maxillary major connector. The groove 44 must fade out as it approaches within 6mm of the marginal gingiva. It also should fade out over the center of the cast when a hard midline suture is present. General form of maxillary major connectors Maxillary major connectors are either in the form of bars, straps or plates. The bars and straps are usually made of metals; the plates could be entirely made of metal or sometimes a combination of metal and non-metal. However bars cover less amount of tissues than plates. 1-Bars a. Bars are usually narrow,less than 8 mm in width (6-8 mm) and half oval in cross section. Their margins are beveled and gently curved. b. They cover less amounts of tissues. c. However, bars require more bulk of metal in order to gain the required rigidity; this bulk may interfere with proper speech and may be intolerable by patients. 2-Straps a. They are wide and thin palatal connectors, more than 8 mm in width to gain the necessary rigidity. b. Having a uniform thickness, its width could be increased in distal extension base. c. The palatal strap is well tolerated because it is not bulky. d. A wide strap helps in the distribution of stresses of mastication over a wider area of the palate and thus provides adequate support. 3-Extended palatal plates: a. They cover half or more of the palate. b. The maximum area coverage contribute to i. Wide distribution of the stresses falling on denture. ii. Better support and retention of the prosthesis. iii. Better horizontal stabilization of the prosthesis. 45 The following types of maxillary major connectors are used: 1- Single palatal bar. 2- Anteroposterior (or double) palatal bar. 3- Single palatal strap (Middle or Posterior Palatal Strap). 4- Horseshoe, or U-shaped connector (Anterior Palatal strap). 5- Closed horseshoe or anteroposterior palatal strap. 6- Complete palatal plate. I- SINGLE PALATAL BAR Fig (5-1) - It can be an anterior palatal bar (not used nowadays), middle or posterior palatal bar. Indications: Middle Bar: In tooth-borne (short, bounded spans) partial denture when second premolars and or first molars are missing. Posterior Bar: In tooth-borne (short, bounded spans) partial denture when second premolars and or first molars are missing. It can also be used in unilateral distal extension partial denture replacing one or two teeth. Design: 1- It is narrow in width and half oval in cross section with its thickest point at the center. 2- It is gently curved and should not form a sharp angle at the junction with the denture base. 3-It should not be placed further anterior to the second premolar. This position is favorable for the tongue action. Locations: Middle Bar: The bar crosses the middle portion of the palate away from the rugae area. Posterior Bar: It is located in close relation to the junction of the hard and soft palate, or placed in level with the second molar 46 Advantages 1- Limited tissue coverage 2- Not affect taste Fig (5-1) -MIDDLE (Left) ------------- POSTERIOR (right) PALATAL BAR Disadvantages: 1- For a single bar to maintain any degree of rigidity it should be bulky (less acceptable by the patient). Hence, It is rarely (not commonly) used nowadays. 2- It drives little support from the bony palate because its narrow Support anteroposterior width arch. 3- Its use is limited to replace one ore two teeth on each side of the one tooth Missing. 4- It cannot be used in cases having large torus palatinus or prominent median palatine raphe. II-ANTEROPOSTERIOR PALATAL BAR Fig (5-2) Indications: 1-It can be used in any class specially when the anterior and posterior abutments are widely separated. 2- When a patient objects a large amount of palatal coverage. 3- In patients with large palatal torus. 47 Design : 1- The anterior bar is flat but narrower than the palatal strap. 2- The posterior bar is half oval similar to the single bar but less bulky. 3- The two bars are joined by flat longitudinal bars on each side palate. Advantages: 1- It is rigid because it lies at different planes. 2- It offers little tissue coverage. Fig (5-2) ANTEROPOSTERIOR PALATAL BAR Disadvantages: anteroposterior bars should not be considered as the first choice because of the following disadvantages: 1- Provides little support from the palate. 2- The anterior bar covers the rugae area and may interfere with phonetics and patient's comfort. 3- Because the bars are narrow, extra bulk is required for rigidity. 48 III-SINGLE PALATAL STRAP (Middle or Posterior Palatal Strap) Fig (5-3) A-The middle (single) palatal strap is the most versatile and widely used maxillary major connector. Indications: 1- In most maxillary tooth borne partial dentures when posterior teeth are missing. 2-In tooth-mucosa borne partial dentures when the extension base is short. Location: The strap lies on the central portion of the hard palate, the anterior border lies just posterior to the commencement of the rugae area. The antero-posterior dimension of the middle palatal strap is usually a little greater than the posterior palatal strap. Design: 1- It consists of a wide, thin band of metal that crosses the palate. Its anterior border should be posterior to the rugae area and the posterior border should terminate short of the junction of the hard and soft palate. 2- Anteroposterior width is within the 8-12 mm range. 3- May be thickened in the middle for rigidity Fig (5-3) MIDDLE (left)-----------------------------POSTERIOR (right) PALATAL STRAP Advantages: 1- Rigid because it is wide and located in different planes. 2- It increases patient comfort because it is thin. 49 3-It provides support to the partial denture since it covers a relatively large area of the palate. Disadvantages: The patient may complaint from excessive palatal coverage. B-The posterior (single) palatal strap Indications: - In maxillary unilateral tooth borne RPDs of short span. Advantages: 1. It provides better support than a posterior palatal bar. 2. It distributes stresses of mastication over a wider area than a palatal bar. Disadvantages: 1. The increased coverage of the palate as compared to the palatal bar may be objectionable to some patients. 2. There may be some alteration of taste if made very wide. IV-HORSESHOE OR U-SHAPED (ANTERIOR PALATAL STRAP) CONNECTOR Fig (5-4) Indications: 1- When several anterior teeth are being replaced. 2- In tooth-borne partial dentures with anterior and posterior teeth are missing. 3- When a hard midline suture or palatal torus cannot be covered. Design: 1- It consists of U-shaped thin band of metal of 6-8 mm in width. 2-The borders must be either 6 mm away from the gingival margin or extend onto the lingual surfaces of the teeth with relief for the gingival margin. 50 3-The connector should be uniform in thickness, symmetric, and with curved and smooth borders Advantages: 1- It solves the problem of missing anterior teeth especially when there is deep anterior vertical overlap. 2- It offers a definite advantage in the presence of hard median suture or large torus. Disadvantages: 1- Tends to be less rigid than other connectors as a buccolingual movement may occur in the posterior area. 2- It covers the rugae area and interferes with phonetics) and patient's comfort. Fig (5-4) HORSESHOE OR U-SHAPED CONNECTOR V-ANTEROPOSTERIOR PALATAL STRAP Fig (5-5) Indications: 1- In tooth borne, and mucosa borne partial dentures when replacement of anterior and posterior teeth is required. 2- When a palatal torus exists. Design: It is also called closed horseshoe: 51 1- The anterior strap should be positioned as back as possible on the rugae area. 2-The posterior strap should be placed as far back as possible on the hard palate. 3-The borders of the connector should be placed 6 mm away from the gingival margins or should extend above the height of contour of the teeth. Advantages: 1- It is rigid because it lies at two different planes. 2- It provides good support to the partial denture. Disadvantages: May be not accepted by some patients due to multiple borders and coverage to the rugae area. Fig (5-5) ANTEROPOSTERIOR PALATAL STRAP VI-THE COMPLETE PALATAL PLATE Fig (5-6) Indications: 1- In long span bilateral tooth-mucosa borne partial denture with and without anterior teeth replacement. 2- Should be used whenever maximum tissue support is desired. 52 3- In patients with palatal defects. 4- Maximum palatal coverage should be considered in the presence of poor residual ridge, periodontal disease, increased muscular force and poor bone indices. 5-In transitional partial denture. Design: 1- The anterior border should be 6 mm away from the gingival margin. 2- Posterior borders are extended to the junction of movable and immovable soft palate (vibrating line). 3- The posterior border is beaded to prevent debris from collecting beneath the plate (beading corresponds to post damming of complete denture). Fig (5-6) THE COMPLETE PALATAL PLATE Advantages: 1- It offers maximum rigidity support and retention to the partial denture. 2- It is made in a uniform thin metal plate, which reproduce anatomic contour of the palate and feel natural to the patient. Disadvantages: 53 1- Often cannot be used in the presence of a palatal torus. 2-Complete palatal coverage may alter taste and tactile sensation. Types of palatal plates : 1- Complete cast metal plate covering the entire palate. It may not be relined easily 2- Complete resin plate, which can be relined or rebased 3-Combination of anterior metal with loops to retain posterior resin area. The resin area may be relined or rebased. MANDIBULAR MAJOR CONNECTORS Design : 1-Rigidity: Sufficient rigidity is important to provide wide distribution of stresses and bilateral stabilization. Consideration must be given to maintain rigidity of the connector without making it bulky and thus unacceptable to the patient. 2-Relief: Relief should be provided beneath the mandibular major connector to prevent inflammation of the delicate lingual mucosa. 3- The superior border of the lingual bar should be placed 3-5 mm below and parallel to the free gingival margin or for the lingual plate it should be extends to the cingulae of the anterior teeth in which the gingival margin should be relieved. 4- The lingual bar should be a half-pear shape in cross section, tapered superiorly with the broader and thicker portion at the inferior border. 5- The inferior border should be gently rounded above the moving tissues of the floor of the mouth. 6-Impingement of gingival tissues should be avoided. Bony or soft tissue prominences should be avoided during placement and removal. 54 TYPES OF MANDIBULAR MAJOR CONNECTORS I- Lingual bar. II- Sublingual bar. III- Double lingual bar. IV-Lingual plate. V- Labial bar. VI-Swing lock I-Lingual bar Fig (5-7) Indication: It is the first-choice major connector, should be used whenever the functional depth of the lingual vestibule equal or exceed 8 mm. Design: 1- The bar should be half pear-shaped in cross section. Superior inferior dimension is 5 mm, and it is 2 mm in thickness. 2- The superior border of the bar should be located at least 3 mm from the gingival margins of all adjacent teeth. 3- The Inferior border may be placed at the functional depth of the lingual vestibule. 4- Relief of the tissue surface of the bar major connector is necessary. 55 Fig (5-7) Lingual bar Advantages: 1- The simplest mandibular major connector with highest patient acceptance. 2- It does not cover the teeth or the gingival tissues. Disadvantages: If it is not properly designed it may not be rigid. Contraindicated in the following conditions: 1- Inadequate space between the free gingival margin and the floor of the mouth. 2- Extreme lingual inclination of lower anterior teeth. 3- Patients having high lingual frenular attachment. 4- The presence of bilateral torus mandibularis contraindicates the use of the lingual bar because they interfere with the proper placement of the bar. Tori require adequate relief, which minimize the rigidity of the connector. 5- The presence of an undercut on the lingual side of the ridge could cause gross food entrapment and discomfort in the presence of the lingual bar. Function: The lingual bar functions only as a major connector. It does not provide neithersupport nor indirect retention. 56 II-Sublingual bar Fig (5-8) Indication: When the lingual bar cannot be used because of a lack of functional depth of the lingual vestibule (depth of 5-7 mm). Design: 1- The sublingual bar is essentially a lingual bar rotated horizontally. 2- The superior border of the bar should be located at least 3 mm from the gingival margins of all adjacent teeth. Advantages: 1- It does not cover the teeth or tissues. 2- More rigid than a lingual bar in the horizontal plane. Disadvantages: A functional impression of the vestibule is required to accurately register the position and contour of the vestibule Fig (5-8) Sublingual bar III- The double lingual bar Fig (5-9) 57 Indication: 1- When indirect retention is required. 2- When periodontally affected teeth that require splinting are present. Design: 1. It is made of two bars; cingulum bar (Kennedy bar) and the conventional lingual bar. A rigid minor connector at the embrasure between the canine and first premolars joins the two bars. Rests are placed at each end of the upper bar attached to the minor connector. 2. The lower bar has the same design as a single lingual bar. 3. The upper bar is scalloped, and half-oval in cross section (2-3mm high, and 1 mm thick at its greatest diameter). Advantages: 1- Provides indirect retention. 2- Contributes to horizontal stabilization. 3- No gingival margin coverage. Disadvantages: 1- Tongue annoyance. 2- Food impaction if the upper bar is not in intimate contact with the teeth. Contraindicated When the teeth have short crown or inclined lingually 58 Fig (5-9) The double lingual bar IV-Lingual plate Fig (5-10) Indication: 1- When the functional depth of the lingual vestibule is not enough for bar placement (less than 5 mm). 2- When future loss of natural teeth is anticipated to facilitate addition of artificial teeth to the partial denture. 3- When splinting of anterior teeth is required. 4- When lingual tori are present. Fig (5-10) Lingual plate Design: 1- It consists of a pear shaped lingual bar with a thin metal extending upward from the superior border of the bar onto the lingual surfaces of the teeth above the cingula and survey lines. 2- In extension base partial denture the lingual plates should have a rest on each side to prevent labial movement of the teeth. 59 3- There should be adequate blockout and relief of the soft tissue undercuts, undercuts in the proximal areas of the teeth, the free gingival margins and the pear-shaped bar. Advantages: 1- The most rigid mandibular major connector. 2- It gives indirect retention to the partial denture. 3- Deflect food from impacting on lingual tissues. 4- Provide resistance against horizontal or lateral forces. 5- Permits the replacement of lost tooth without remaking the partial denture. 6- Help in splinting and prevent super-eruption of the anterior teeth. Disadvantages: Covers more tooth and gingival tissues than other mandibular major connectors. V-Labial bar Fig (5-11) Indications: 1- When the mandibular teeth are so severely inclined lingually as to prevent the use of lingual major connector. 2- When large lingual tori exist and their removal is contraindicated. Design: 1- It is a half pear shaped bar, runs across the mucosa labial to the anterior teeth 2- Labial vestibule should be adequate to allow the superior border to be place at leas 3 mm below the free gingival margins. 3- Relief is required beneath the bar. Advantages: It solves the problem of severely inclined teeth and avoids surgical intervention to remove a large torus. Disadvantages: 60 It tends to lack rigidity since it is considerably longer than a lingual bar. Also, it is the least comfortable mandibular major connector. Fig (5-11) Labial bar VI. The Swing Lock Partial Denture: Fig (5-12) The hinged continuous labial bar called the Swing-lock design partial denture is a modification of the labial bar. Design The labial bar is connected to a lingual plate major connector by a hinge device at one end and a locking device at the other end. Vertical minor connectors arise from the labial bar and may touch the anterior teeth either below or above the survey line. Advantages: 1- Helps in providing both retention and stabilization. 2- The labial bar together with the lingual plate provides the required rigidity, thus the labial bar does not require much bulk. Indications 61 1- Missing key abutments. 2- Unfavorable tooth and soft tissue contours. 3- Periodontally affected Teeth with questionable prognosis: The Swing lock partial denture provides splinting. Contraindications 1- Poor oral hygiene. 2- The presence of shallow buccal or labial vestibule. 3- The presence of high frenal attachment Fig (5-12) The Swing Lock Partial Denture: MINOR CONNECTORS A minor connector is a rigid component that links the major connector or base and other components of the partial denture such as rests, indirect retainers and clasps. Fig (5-13) Functions of minor connectors: 1. Joining different parts of the prosthesis to the major connector, or to denture bases. 2. Transfer functional stresses to the abutment teeth. 3. Transfer the effect of retainers, rests, and stabilizing units to the 62 denture. 4. Minor connectors contacting guiding planes add to the retention and stability of dentures. Design specifications: 1- Should have sufficient thickness for rigidity. 2- Should exhibit minimal gingival coverage; the lingual minor connector should cross the gingival margins directly, joining the major connector at rounded right angle. 3- Slight relief is required when crossing the gingival margin especially in tooth-mucosa borne dentures. 4- Should be highly polished to minimize plaque accumulation. 5- Should be located at least 5 mm from other vertical components. Fig (5-13) MINOR CONNECTORS 63 CHAPTER VI RESTS AND REST SEATS Definitions : A rest is a rigid extension of partial denture, which contacts a remaining tooth in a prepared rest seat to transmit vertical forces. A rest seat is the prepared surface of a tooth or a restoration into which a rest fits. Support:The quality of the prosthesis to resist displacement towards denture supporting structures. An onlay (overlay) is an enlarged occlusal rest covering the entire occlusal surface and extending buccally and lingually. Functions of rests: 1-Transmit the vertical forces to the abutment teeth (support). 2- Act as a vertical stop prevent injury of tissues under the denture. A denture without rests is called gum stripper. 3- It maintains the retentive clasp in position. 4- It may be used as indirect retainer. 5- Prevents food impaction, when it is placed on the proximal surface adjacent to the edentulous space. 6- Maintains occlusal contact with opposing teeth by preventing denture settling.ne 7- An onlay has the added functions of: a. Establishing more acceptable occlusal plane. b. Increasing the reduced vertical dimension of occlusion. c. Alteration of cusp height and angles to improve occlusion. 64 Requirements of rests: 1- Should have sufficient thickness of metal to prevent fracture, especially at the junction of the rest and minor connector. 2- Should be placed only on surfaces that will direct forces along the long axes of teeth. Should not be placed on inclined tooth surface (fig. 4-2). 3- Should be extended as close to the center of the tooth mesiodistally, as much as possible, to help axial direction of force. 4- Should be placed in rest seats, which have smooth rounded line angles to improve adaptation of casting. Types of rests: I- Occlusal rests; seated on the occlusal surfaces of a posterior tooth. II- Cingulum or lingual rest; seated on the lingual surface of a tooth. III- Incisal rest; seated on the incisal edge of a tooth. IV- Embrasure Hooks: Rests placed in embrasures between natural teeth 1- Occlusal Rests Types: 1- Conventional. 2- Extended. 3- Internal. 4- Onlay (Overlay). 5-Embrassure rest 65 1- Conventional occlusal rest Design: Fig (6-1) 1- The rest demonstrates a rounded triangular outline form when viewed from the occlusal. The base of the triangle resting on the marginal ridge and the rounded apex directed towards the center of the tooth. 2- The tissue surface of the rest should be smooth and rounded (spoon shape). All angles, walls and ledges should be avoided. 3- Its width varies from one third to one half the mesiodistal diameter of the tooth and should be one half the distance between the buccal and lingual cusp tips. 4- Floor of the rest seat should be inclined apically as it approaches the center of the tooth. The angle between the rest and the minor connector should be less than 90 degrees, to transmit the vertical forces along the long axis of the tooth (. If this angle is more than 90 degrees an inclined plane effect will occurs, which results in slippage of the rest and orthodontic movement of the abutment. N.B. The angle between the rest and the minor connector is less than 90 o. 5- Teeth marginal ridges should be reduced 1 to 1.5 mm for base metal alloys, and 2 mm for gold alloys, to give enough thickness of metal to avoid its fracture 6- The occlusal rest is prepared in sound enamel. It is prepared in enamel if there is law caries index and good oral hygiene. 7-When a metal restoration (inlay, onlay or crown) is planned for an abutment tooth, the rest seat must be carved in the wax pattern of the restoration and refined in the cast metal before the restoration is seated in the mouth 8- An amalgam restoration is not suitable to support an occlusal rest due to its tendency to flow. So, if amalgam is present (especially class II) it should be replaced by cast restoration. N.B. The Occlusal rests can be prepared in an old amalgam restoration. 66 8- The rest seats may be prepared in either a box shaped or saucer shaped form: "Saucer- Shaped Rest Seat: preparation have concave, spoon or saucer shaped form to prevent locking of the occlusal rest and transmission of lateral and tipping forces to the abutment. They are used in free end saddle cases and bounded cases having weak abutments. Boxed Shaped Occlusal Rest have vertical walls and flat floor, they are rarely used in bounded cases having strong abutments 9-In bounded partial denture: occlusal rests are placed in the near zone of the occlusal surface of the two abutments bounding the edentulous span. In free end partial dentures: the occlusal rest is placed on the far zone of the occlusal surface of the abutment, in order to decrease the torque action on the abutment tooth Fig (6-1) Conventional occlusal rest 67 2- Extended occlusal rest Indication: Fig (6-2) For tooth borne segments of partial dentures in which the most posterior abutment is mesially tipped molar. Advantages: 1- It promotes axial force direction. 2- Minimize further tipping of the abutment. 3- Minimize rotation of the abutment by its buccal and lingual dovetail extension. Design: An extended rest should be carried more than one-half way the mesiodistal width of the tooth, be approximately one-third the buccolingual width of the tooth, and at least of 1mm thickness. The preparation should be round with no undercuts or sharp angles N.B. Tipped molar (Mesially inclined mandibular molar): Failure to direct the stress axially may permit the forces of occlusion to tilt the tooth further mesially. The rest should be designed to prevent further tipping; it must direct forces down the long axis of the tooth by either of one of these ways: A) An additional occlusal rest in the distal fossa: A rest positioned in this way tends to counteract any tendency of the tooth to tip further mesially. B) A rest preparation that extended from the mesial marginal ridge to the distal triangular fossa to minimize further tipping. C) When a casting is required, such as full veneer crown or onlay, it should be constructed with flat occlusal surface perpendicular to the long axis. A one to two millimeters bevel on the buccal and lingual surfaces and a two to three millimeter guide plane on the mesial surface will provide bilateral bracing and prevent further tipping of the tooth. The occlusion is restored with a chrome cobalt or gold occlusal overlay as part of partial denture. Such type of rest 68 construction takes advantages of the inclined plane effect directing forces along the long axis of the tooth. Fig (6-2) Extended occlusal rest 3- Internal rest (attachments) The internal rest consists of narrow slot or key way, built into a metal casting that has been constructed for an abutment tooth, and into which is fitted a male attachment that has been made an integral part of removable partial denture framework(the milled rest,attachment) the semiprecision Fig (6-3) Indication: A bounded partial denture that is totally teeth supported. Advantages: 1- Provides support and lateral stabilization. 2-Elimination of visible buccal clasp arm is possible. 69 Design: 1- The form of the rest should be parallel to the path of insertion, slightly diverge occlusally, and slightly dovetailed to prevent dislodgment. 2- Support is derived from the floor of the rest, and lateral stabilization is obtained from the nearly parallel walls. Retention is derived from lingual clasp arms, lying in natural or prepared undercut Fig (6-3) Internal rest 70 4- Onlay Indication: Fig (6-4) In severely tilted posterior abutment of a tooth borne segment. Advantages: 1- Direct the forces along the long axis of the tooth. 2- Promote RPD stability by its buccal and lingual bevels and proximal guiding plane. 3- Minimize further tipping of the tooth. 4- Restore the occlusal plane. Design: 1- Cast restorations placed on tipped teeth may be fabricated with a flat occlusal surface perpendicular to the long axis. The tooth preparation for onlay must include removing or restoring pits, fissures, and grooves. A bevel of 1 to 2 mm on the facial and lingual surfaces and 2 to 3 mm guiding plane on the proximal. 2- The occlusion is restored with a base metal alloy or gold occlusal onlay as part of the partial denture framework. Occlusal rest seat preparation - The preparation of occlusal rest seat must follow proximal guiding plane preparation. First the marginal ridge is lowered, and the outline of the preparation is created by using No. 8 rounded diamond stone. A No. 6 round diamond point is then used to deepen the floor of the occlusal rest seat and to form the spoon shape. One must be careful not to carve an undercut to the path of insertion. Any sharp angles are smoothed through the use of no 4-round steel bur revolving in (reverse at moderate speed. A fluoride gel should be applied to abutment tooth following enamel preparation. 71 - Occlusal rest seat preparation in existing crown is the same as in sound enamel. To avoid perforation of the crown the rest seat can be made wider to compensate the shallow preparation. - In new cast crown, after tooth preparation for crown is complete, a depression is added to the preparation to accommodate the depth of the occlusal rest. Then the occlusal rest seat is prepared in the wax pattern. - Rest seat preparation for an embrasure clasp extends over the occlusal embrasure of two approximating posterior teeth. A round- diamond stone is used to establish the outline form for a normal occlusal rest in each the approximating fossae. A cylindrical diamond stone held horizontally from the buccal surfaces of the teeth pointing toward the lingual is used to carry extension of the occlusal rests over the buccal and lingual embrasures. Fig (6-4) Onlay 72 II- Lingual (Cingulum) Rests A- Cingulum Rest (inverted V Rest). B. Ball Rest. C. Canine Ledge. Indications: 1- When there is no posterior tooth to place an occlusal rest. Occlusal rest is preferred than lingual rest because of its mechanical advantage and ease of seat preparation. 2- The lingual or Cingulum rest is used primarily on maxillary canine, because the morphology of the tooth permits seat preparation. 3- It is rarely used on incisors when the canine is missing. In this situation, multiple rests must be used to distribute the force over a number of incisors. 4- To prepare a rest seat in enamel there should be: a- prominent cingulum: b- good oral hygiene. c- law caries index. Design: 1- The rest seat is half-moon shaped when viewed from the lingual. The broadest portion is in the middle of the lingual surface and 2- Rest is V shaped when viewed from the proximal, with rounded line angles. The V shaped preparation direct the force into apical direction along the long axis of the tooth. 3- Mesiodistal length of preparation should be a minimum of 2.5 mm, labiolingual width about 2 mm, and incisal_apical depth a minimum of 1.5 mm. 4- Often difficult to obtain a positive apically inclined rest seat due to tooth angulation or anatomy. The use of cast restoration may be required to establish a definite rest seat. 73 Composite buildups for cingulum rests: When a cingulum is poorly developed, with insufficient bulk for preparation for a cingulum rest seat, a rest seat can be made using composite resin. Research has demonstrated that these bonded rest seats can provide acceptable strength and longevity. Round lingual rest seat form: Round rest seats are occasionally prepared on the mesial of the canine teeth when the use of a typical cingulum rest is contraindicated (i.e. large restoration, lack of clearance with the opposing teeth, poorly developed cingulum). These rest seats are prepared spoon shaped, similar to an occlusal rest seat, with reduction of the mesial marginal ridge. Lingual or cingulum rest seat preparation Fig (6-5) A large diamond inverted cone stone is used to start the preparation. The preparation is finished using a green stone with round end in a low-speed handpiece. Care must be taken to round sharp angles. The preparation must be polished with the carborundum impregnated rubber wheels and points. The preparation should be directed so that it does not interfere with the path of placement of the prosthesis. cingulum rest seat is prepared by large, inverted cone bur. The preparation is finished using a green stone in a low-speed handpiece. Line angles must be rounded by round stone. 74 Fig (6-5) Lingual or cingulum rest seat preparation B. Canine Ledge Fig (6-6) It is a step-like preparation placed on the mesial or distal halves of the lingual surfaces of the maxillary canine. Usually at the junction of the gingival and middle one thirds. Having 1.5 mm depth.The ledge rest seat should be perpendicular to the long axis of the tooth. All undercuts and sharp line angles should be avoided. C. Ball Rest Fig (6-6) Cingulum ball rests with rounded outline are placed on the mesial or distal halves on the lingual surfaces of all anterior teeth, usually at the junction of the gingival and middle one thirds. Having 1.5 mm depth and 2.5 mm width. * Ball rest permits rotational movements to occur during function of tooth- mucosa born RPDs. * Such rest may be prepared on tooth surfaces with sufficient enamel thickness or may be prepared in restorations placed in teeth with inadequate enamel thickness (Amalgam or pin ledge, cast restoration, etc.). N.B. Improperly constructed cingulum rests placed on inclined surface of cuspid, causes movement of the rest in a gingival direction and labial movement of the tooth. 75 Fig (6-6) Canine Ledge. Ball Rest III- Incisal Rests Indication: 1-Incisal rests are used mostly on mandibular canines when the abutment is sound and when a cast restoration is not indicated. 2- It may be used as an auxiliary rest for indirect retention. Disadvantages: 1- The display of metal may be objectionable. 2- Greater mechanical leverage than lingual rests, due to the longer distance from the center of tooth rotation Design: 1- The incisal rest seat is prepared on the proximal line angle of the tooth, usually the distal for esthetic reason. 2- When seen from the facial surface, its floor is concave and inclined towards the center of the tooth to direct the forces along the long axis of the tooth 3- The outline form of the rest seat is saddle shaped (Convex), with buccal and lingual bevel, when viewed from the proximal. 4- All borders of rest seats are rounded, especially at the junction of the axial wall of the preparation and the floor of the rest seat. 5- It should be approximately 2.5 mm wide, and 1.5mm deep. 76 Incisal rest seat preparation Fig (6-7) An initial depth cut is made, using a tapered cylindrical stone, at the junction of the middle and the mesial or distal third of the abutment tooth. The walls of the rest seat are created by flaring the edges of the depth cut preparation and beveling the buccal and lingual walls with finishing bur. The preparation is then smoothed by rubber points. N.B. Whereas the most preferred site for a rest, is the occlusal surface of a molar and premolar. If anterior tooth is the only abutment available, a canine is preferred over an incisor. In the absence of canine multiple lingual rests are prepared on anterior teeth.1.5m Fig (6-7) Incisal rest seat preparation IV- Embrasure Hooks: Rests placed in embrasures between natural teeth extending slightly over the buccal or labial surface but never extend below the survey line. They provide support, splinting of natural teeth, resistance to lateral and anteroposterior movement and may act as indirect retainer. Fig (6-8) Disadvantages 1-Poor esthetics and wedging action on teeth. 2-Wedging action 77 Fig (6-8) Embrasure Hooks: CHAPTER VII TOOTH SELECTION FOR PARTIAL DENTURE Functions of denture teeth 1. Prevent migration of the remaining teeth. 2. Restore masticatory efficiency. 3. Retain proper interarch space. 4. Maintain esthetic of a normal facial contour. Factors affecting selection of RPD teeth: 1- The size, form and shade should resemble that of the remaining natural teeth. 2- Amount of available space; artificial teeth are placed within the available space incisogingival and mesiodistal. 3- Mechanical properties; the anterior teeth selection is affected by the opposing occlusion, abrasion resistance, resistance to fracture, bond strength to denture base and ease of adjustment. 4- Cusp height of opposing teeth; cusp height of the artificial teeth should be equal to or slightly greater than the opposing teeth. 5- Condition of the supporting tissues in distal extension base; if it is poor the occlusal forces are reduced by: 78 a- Using a small teeth faciolingually. b- Decreasing the number of posterior teeth. c- Space teeth with diastimas. d- Sharpening of the occlusal surface to increase the masticatory efficiency. e- Using acrylic teeth. Factors affecting arrangement of teeth in RPD: 1.Occlusal relationship of the remaining teeth. 2. Orientation of the occlusal plane. 3. Space available for restoration of missing teeth. 4. Arch integrity. 5. Tooth morphology Types of teeth I- Acrylic denture teeth Fig (7-1) Advantages: 1- bond with denture base resin. 2- Easily recontoured and polished. 3- May be used when space is limited. 4- Reduce wear of opposing restorations and natural teeth. 5- Reduce the stresses transferred to the ridge by its resilience. 6- Good esthetics. Disadvantages: 1- Law abrasion (wear) resistance. 2- May stain during use N.B. IPN resin teeth or modified cross linked acrylic teeth are a modification (type) of conventional acrylic resin teeth with cross linked polymer chains 79 providing improved wear resistance and strength compared to the conventional type. Fig (7-1) Acrylic denture teeth II- Porcelain denture teeth Advantages: 1- Increases abrasion resistance. 2- Increased stain resistance. 3- Natural appearance. Disadvantages: 1- Abrade the opposing natural and artificial teeth. 2- Cannot be used in close bite cases. 3- More susceptible to fracture. 4- Mechanical bond is required to denture base resins. 5- Polishing of ground surfaces is difficult. 6- Clicking during function. III- Facings Fig (7-2) If anterior teeth is to be replaced, metal packing with porcelain or resin facing may be used. It is usually used with metallic denture bases. Advantages: 1- Metal packing increase strength. 2- Can be used when there is insufficient interocclusal space to use resin to retain denture teeth. Disadvantages: 80 1- May exhibit flat appearance, lacking of depth. 2- Metal backing may affect shade. 3- Difficulty in fabrication of metal backing due to occlusion and articulation. Fig (7-2) Facings teeth IV-Tube teeth Fig (7-3) It is an acrylic or porcelain teeth in the form of a tube have a channel in its base to fit a post on the metal framework. Advantages: 1- Used as a single anterior or posterior tooth replacement, where space is available, with good esthetics 2- No need for flasking and processing the denture teeth. The tube teeth are cemented to the metal posts. Disadvantages: 1- It requires enough space mesiodistally and occlusogingivally. 2 - It is used with metallic denture base, which cannot be relined. Fig (7-3) Tube teeth V-Metal teeth Fig (7-4) 81 Advantages: 1- Can be used where space is limited for posterior teeth replacement. 2- Increased resistance to fracture and abrasion. Disadvantages: 1- May be unaesthetic; acrylic or composite veneer will improve it. 2- Difficult to adjust occlusion and articulation. Fig (7-4) Metal teeth 82 Acrylic Resin versus Porcelain Teeth Acrylic Teeth Porcelain Teeth Have strong chemical bond with Less efficient mechanical bonding denture bases. with denture bases. Tough, having good resistance to Tendency to fracture specially in patients breakage hence are used in closed havi

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