3rd Level All 1st Term Lectures PDF

**Introduction to Fixed Prosthodontics\ Terminology and Classification Lec. 1** - ***Effects of tooth loss**:\ * Movement of teeth: -- tilting, migration, rotation and overeruption\ Alteration of occlusal plane\ Alteration of path of mandibular closure\ Alveolar bone re...

**Introduction to Fixed Prosthodontics\ Terminology and Classification Lec. 1** - ***Effects of tooth loss**:\ * Movement of teeth: -- tilting, migration, rotation and overeruption\ Alteration of occlusal plane\ Alteration of path of mandibular closure\ Alveolar bone resorption\ Effects of Mastication and Speech\ Appearance\ Psychological effects - **Terminology** ֎ **Prosthodontics:\ **Prosthodontics is that discipline of dentistry pertaining to the restoration of oral function, comfort, appearance and health by restoring natural teeth and replacing\ missing teeth and contiguous oral and maxillofacial tissue with artificial substitutes.\ ֎ **Fixed Prosthodontics:\ **Pertains to the restoration or replacement of teeth with artificial substitutes that are attached to natural teeth, roots, or implants and that are not readily removable.**\ **❖ **A Prosthesis:\ **Is any artificial replacement of a missing body part.**\ **֎ **Removable Prosthodontics:\ **Pertains to the replacement of missing teeth and adjacent oral structures with artificial substitutes that are readily removable.\ **Fixed prosthodontics:** is the art and science of restoring the damaged coronal portion of the teeth and / or replacing missing tooth/ teeth using an artificial substitutes like cast metal, metal-ceramic, or all-ceramic restorations, that permanently cemented in place to restore function, esthetic and contour.\ **The fixed prosthesis can be in the form of single cast or multiple unit of cast crowns joined together, commonly referred to as fixed partial denture or bridge.** - **Scope (Aims) of fixed prosthodontic treatment**\ ❑ The scope of fixed prosthodontic treatment can range from the restoration of a single tooth to rehabilitation of the entire occlusion that include:**\ 1. Restore function (mastication & speech)\ 2. Restore esthetics\ 3. Maintain health and integrity of dental arch\ 4. Maintain health of TM\ ** In many instances elevate the patient\'s self-image.\ \ ❑ The treatment of problems related to the temporomandibular joint and its neuromuscular components may also be possible by the use of fixed prostheses.\ However, with improper treatment, it is possible to create disharmony and damage to the stomatognathic system.**\ **❑**Types of Fixed Restorations**\ ✓ Crowns\ ✓ Bridges\ ✓ Inlays\ ✓ Onlays\ ✓ Veneer\ ✓ Post Crown**\ [THE CROWN:]\ a. Natural crown:\ **o **Anatomical crown**: Is the portion of the tooth covered by enamel, extending form the incisal edge or occlusal surface to the cervical line (CEJ).\ Decreased by age due to attrition or abrasion.**\ **o **Clinical crown:** It is the portion of the tooth that extends form the gingival crest to the incisal edge or occlusal surface.\ Increase by age due to passive eruption then gingival recession.\ o **OR:** it is that part of tooth which is visible in the mouth.\ **- Terminology**\ **b. Dental Crown: artificial Crown:\ **Is an Extra-coronal artificial replacement that restores missing tooth structure by surrounding most or all of the remaining structure with a substitutes material such as cast metal, porcelain or a combination of materials such as metal and porcelain.**\ ** **It is cemented to the tooth or implant using a suitable adhesive material (Cement).\ ** It reproduce both the form and function of the tooth and in some instance restore or enhance the appearance.**\ \ *[The crown: Cont.]***\ ❖ **Complete Veneer Crowns:\ **Restore all surfaces of the clinical crown. The restoration material may be all metal e.g. \"complete metal cast crown\", all porcelain (ceramic) e.g. \"porcelain jacket crown\". A metal ceramic combination e.g. \' 'Veneered and full veneered Crown\" or metal with processed resin e.g. "Veneered crown\".**\ **❖ **Partial Veneer Crowns:\ **Restore only a portion of the clinical crown.\ ❖ **Three-Quarter Crowns:\ **Restore the occlusal surface and three of the four axial surfaces.\ (not including the facial surface).**\ Terminology**\ ❖ **Reverse Three-Quarter Crowns:\ **Restore all surface except the lingual surface.**\ **❖ **Seven-Eighths Crowns:\ **Are extensions of the three-quarter crown to include a major portion of the facial surface, except the mesiobuccal cusp of maxillary molars.**\ **❖ **One-half crown veneers:\ **Restore the occlusal and mesial surfaces, as well as portions of the facial and lingual surfaces.**\ **✓ **Is a modified form of three-quarter crown.**\ ❖ **MacBoyle retainer:\ **Is a modified three-quarter crown, with its retention derived from grooves at the labio-proximal line angles usually used for mandibular anterior teeth.**\ **❖ **Pinledge Retainer:\ **Refers the modification of an anterior three-quarter crown preparation to obtain primary retention and resistance from long parallel pins in the lingual or palatal surface of the clinical crown.**\ **❖ **Laminates:\ **Are (thin plate of cosmetic materials) veneer restorations that restore the\ facial surface of a tooth for esthetic purposes.\ They are fabricated from resin or dental porcelain.\ **They bond to etched enamel with a composite resin luting agent.\ **\ **Inlay Retainer:\ **It is a classic intracoronal cast restoration that restores the proximal and occlusal surfaces without covering the cusp.\ **Onlay Retainer:\ **Is a modification of the inlay with cusp overlays on the occlusal surface to protect the integrity of the remaining tooth structure.**\ ** **Overlay Retainer???\ **❑ **Radicular Retained Restorations: (POST CROWN)\ **Radicular retained restorations consist of a post or dowel with an attached Core that obtains its retention and resistance to displacement forces from the prepared root portion of an endodontically treated tooth.**\ ** **This post and core (dowel and core) may be custom cast, or prefabricated.**\ ✓ **Temporary Crown:\ **Is a crown made and used temporarily for the protection of the prepared tooth till the crown or bridge is completed and ready for cementation.**\ \ **֎ **Bridge:\ (Fixed Partial Denture), (Fixed Prosthesis), (Fixed Replacement),\ (Fixed Appliance).\ ** Is a masticating or incisive surface of metallic and/or nonmetallic material spanning an edentulous space in the dental arch firmly anchored at one or both ends to the adjacent teeth or implants.\ \ **2. Retainer (Attachment), (Abutment Piece):\ **Is a restoration covering and rebuilding the prepared tooth and by means of which the pontics are anchored to the abutment teeth. **4. Connector Joint:\ **Is that part of the bridge that uniting the pontic (s) with retainer (s).\ o Joining the component parts of the bridge, it may be (rigid or non-rigid connector). ❑ **Types of Bridges: three types as following:\ 1. Basic Designs\ 2. Combinations\ 3. Variations** **1. Basic Designs:-**\ **A. Fixed - Fixed Bridge:\ **(Fixed Bridge), (Rigid Bridge), (Fixed Rigid Bridge) , (Stationary Fixed Bridge).\ ❑ Is a bridge where the abutment pieces (retainers) and pontics are all soldered together and the bridge is cemented at both ends to the abutment teeth.**\ **\ **B. Fixed - Supported Bridge: movable bridge\ **(Fixed-Movable), (Broken Stress Bridge), (Semi-Rigid), (Fixed-Semi-rigid Bridge).\ ❑ Is a bridge where the pontic is fixed to the retainer by a rigid connector at one end while the other end is connected by means of a non-rigid connector, allowing some individual movement of the abutment tooth.\ ❑ N.B: 11/16 of the force to fixed side and 5/16 to the supported side.**\ \ C. Cantilever Bridge:\ **(Swing on Bridge), (Free End Bridge)\ ❑ Is a bridge where the pontic is fixed to one or double retainers at one end only by rigid connector to derives its support while the other end is free (unsupported).\ **\ D. Spring Cantilever Bridge:\ **❑ Is a cantilever bridge where the pontic is fixed at the end of slightly resilient curved metal arm deriving its support from an abutment remote from the edentulous space.**\ 2. COMBINATION BRIDGE:\ **Employing more than one of the above types: For Example:**\ **❖ **Combine Fixed -- Fixed and Cantilever Designs.\ **❖ **Combine the Fixed--fixed and Fixed-- Movable Designs.** **3. VARIATION:**\ **\ A- Resin - bonded Restorations:\ **Are cast metal partial veneers that are bonded to etched enamel. (involves attaching pontic by a metal plate to the (unprepared or minimally prepared) lingual surfaces of adjacent teeth.\ **This type of prosthesis is commonly referred to as Rochette or Maryland bridge.\ B- Removable Bridge:\ **(Precision Attachment Bridge). (Removable Partial Denture with internal attachment).\ Is a bridge where each retainer consists of two parts (Key and keylock),\ One part (Key) fixed to the abutment tooth and the other part (keylock) soldered to the pontic.\ The bridge can be removed at the will of and by the patient for cleansing purposes**.** ❑ **INDICATIONS FOR FIXED PARTIAL DENTURE:**\ \ ❑ One or two adjacent posterior teeth are missing in the same arch (short span edentulous area).\ ❑ One or two adjacent and maximum Four missing anterior teeth.\ ❑ When the supportive tissues are healthy.\ ❑ Sound, defect free abutment teeth and normal pattern occlusion are present.\ ❑ The patient is in good heaths and desires to have the prosthesis placed.\ ❑ The patient has the skills and motivation to maintain good oral hygiene. ❑ **CONTRAINDICATIONS FOR FIXED PARTIAL DENTURE:\ **❑ More than two missing posterior and four anterior teeth.\ ❑ Lack of supporting tissue and alveolar bone.\ ❑ Presence of periodontal disease.\ ❑ Excessive mobility of abutment teeth.\ ❑ Patients with poor oral hygiene.\ ❑ Patients who cannot afford treatment. **[❑Classification of Fixed Restorations]**\ **1- CROWNS 2- BRIDGE**\ ***1- CROWNS:** classified according to the surface coverage in to:\ ***A- Full Coverage:** cover the entire coronal portion of the crown (all 5 surface of the tooth).\ **B- Partial Coverage:** cover just a portion of the clinical crown (less than 5 surface of the tooth).**\ A- Full Coverage: classified according to the Retention in to: (mainly retained by):\ i. Encircling the Preparation: complete encircling of the tooth (friction)\ 1) Metallic:\ **a) One Piece: \* Cast Crown. \* Swaged Crown.\ b) Two Piece: \* Swaged --- Cast Crown\ **2) Combined:\ **a) Veneered with acrylic or porcelain (labially or buccally).\ b) Full Veneered with acrylic or porcelain.\ **3) Non-metallic:\ **a) Porcelain Jacket Crown. b) Acrylic Jacket Crown. **ii- Post inserted in the root canal: post-crown\ **i. According to retention...... a) Post only b). Both Post and collar.\ ii. According to fabrication techniques: Readymade or costume made post\ iii. According to attachment techniques: Attached or detached (2 pieces or 3 pieces)\ iv. According to material types: Metallic / nonmetallic / combined.....\ **B. Partial Coverage: classified according to the Retention in to: (mainly retained by):\ 1) Grooves:\ **i. Three Quarter Crown 3/4.\ ii. Reverse ¾ crown\ iii. Half Veneer Crown 1/2.\ iv. Seven eight Crowns 7/8.\ v. MacBoyle Crown \"Retainer ".\ **2) Pins:** Pin-Ledge Retainer.\ **3) Enclasping the preparation:** Reverse Retention Retainer**.\ 4) Combined means of retention:\ ** **Modified types including both grooves and pins.** ***2- BRIDGES:* it classified as**\ **I. According to the Site:\ A. Anterior bridge:\ **a. Unilateral: 2 or 3 teeth anterior bridge which does not cross the midline and canine line.**\ **b. Bilateral: 3 or 4 teeth bridge which involves teeth on both sides of the midline. (cross the midline)**\ B. Posterior bridge:** dose not cross the canine line\ **C. Complex bridge:** anterior and posterior segments involving the canine line.\ or one of its terminals beyond the canine.\ **\ II- According to Retention:\ A. Simple Bridge:\ **i. Fixed-Fixed Bridge. See b4\ ii. Fixed-Supported Bridge. See b4\ iii. Cantilever Bridge. See b4\ iv. Spring Cantilever Bridge. See b4\ **v. Removable Bridge: (**Is a bridge where each retainer consists of two parts, one part fixed to the abutment tooth and the other soldered to the pontic)\ **B. Compound Bridge:\ **Employing more than one of the above types**.**\ **III- According to Material:\ A. Metallic:\ **a. precious alloy: Au, Pt. b.\ b. Semi-Precious Alloy: Ag, Pd.\ c. Non-precious Alloy: Cr. Ni. Co. Cu. Ti. Fe.**\ \ B. Combined:\ **a. Metallic with labial or buccal veneers. \"Porcelain or acrylic\"\ b. Metallic with full porcelain veneer.\ c. Non-Metallic with metal reinforcement or framework.**\ C. Non-Metallic:\ **a. All-Acrylic.\ b. All-Ceramic. C. Zirconia.\ **IV- According to the length of span:\ A. Short span:** One missing tooth\ **B. Long span:** More than two missing teeth???\ **\ V- According to the chronology of span /or time line:\ A. Temporary bridge:** used temporarily for the protection of prepared teeth, till the cementation of bridge is completed\ **B. Immediate bridge:** (Bridge with root extension pontic) constructed before extraction of teeth and seated in position immediately after extraction at the same visit\ **A. Definitive: (final) bridge**\ **\ **\ **Q: Classify the Fixed Restorations according to Support??? And give a short note about each Support???** 1. - **Factors affecting the path of insertion:\ **1) Reduction of opposing axial surfaces.\ a. Parallel to each other to give a line of insertion, or with\ b. Slight occlusal convergence to give a range of insertion...O.W?????\ 2) Rounding of axial line angles.\ To eliminate the cervical triangular undercut area at the axial line angle.\ 3) Alignment of Proximal grooves.\ In 3/4 crown-axial grooves on mesial and distal surface. Discussed later?????\ In 1/2 crown-axial grooves on the buccal and lingual surface.\ 4) Alignment Ledges and / or indentation. Discussed later?????\ 5) Alignment Pinholes. Discussed later?????**\ \ *To evaluate the preparation taper:\ ***view it with one eye from a distance of approximately thirty centimeters.\ If both eyes are open when the preparation is viewed → undercut may remain undetected.\ Where it is difficult to survey the preparation with direct vision use a dental mirror.\ **\ [In summary:]** the finish line of the preparation (all axial walls) should be seen either directly by eye vision or indirectly by dental mirror vision from a single direction without shifting of dentist head / eye or dental mirror. O.W U.C**\ III) ESTHETIC CONSIDERATIONS:\ *It is influenced by:\ ***1- Amount of teeth reduction and Type of teeth preparation (i.e.: full or partial coverage).\ 2- Marginal placement for either full or partial coverage restorations.\ 3- Types of materials: all ceramic have better esthetic result than metal ceramic restorations.\ 4- Other factors...(shade selection, cementation, surface characterization, optic illusions and so on......). - **1- Amount of teeth reduction\ *A) Full coverage METAL-CERAMIC RESTORATIONS:\ *1) Facial Tooth Reduction:\ ** A minimum reduction of 1.5 mm typically is required for optimal appearance. Adequate thickness of porcelain is needed to create a sense of color depth and translucency.**\ Reduction of the facial surface of anterior teeth should be done in two\ planes:\ o One parallel with the path of insertion (cervical 1/3), and one parallel\ with the incisal two-thirds of the facial surface of the tooth\ **o *If they prepared in a single plane, insufficient reduction will result in either cervical or incisal area of the preparation, which affect the esthetic or tissue health.**\ *****\ 2) Incisal Reduction: (1.5 -- 2 mm)\ ** The incisal edge of a metal-ceramic restoration has no metal backing and can be made with a translucency similar to that of natural tooth structure. (Excessive incisal reduction should be avoided as it reduces the\ R&R form of the preparation), So maximum amount of incisal reduction is.................???**\ 3) Proximal Reduction: (1-1.5 mm)\ ** The proximal surfaces of anterior teeth will look most natural *if they\ are restored as the facial or incisal edges*, without metal backing.**\ 4) Labial Margin shape and Placement:\ **Should flow the contour of gingiva???\ Supra or Subgingival \>\> as mentioned b4. (high lip line VS low lip line)**\ \ *B) Partial Coverage Metal-ceramic Restorations:\ i. Posterior partial-coverage restorations:-\ *1) Proximal Margin: *(for Maxilla and mandible)\ *** The mesial which is the more visible margin is critical to the esthetic result of a partial coverage restoration.\ The margin should be placed just buccal to the proximal contact area, where metal will be hidden by the distal line angle of the neighboring tooth.\ The distal margin of posterior partial-coverage restorations is less visible than the mesial margin, Sooo\...can be extended beyond the contact **area.\ \ 2) Facial Margin:\ For Maxilla:\ **The facial margin of a maxillary partial-coverage restoration should be extended just beyond the occluso-facial line angle.\ A short bevel is needed to prevent enamel chipping.\ If the *buccal margin* of *metal* is *correctly shaped*, it will *not reflect light* to an observer.**\ For Mandible:\ ** When mandibular partial cast crowns are made*, metal display is unavoidable because the occlusal surface of mandibular teeth can be seen during speech*.**\ A chamfer margin, rather than a bevel margin is recommended\ for the buccal margin because it provides a *greater bulk of metal around the highly stressed centric cusp*.\ **\ Q: What is the difference b/w upper and lower Partial coverage preparation for posterior teeth???**\ *ii. Anterior partial-coverage restorations:\ * ** The facial margin is extended just beyond the highest contour of\ the incisal edge *but not quite to the inciso-labial line angle.\ (between the highest point of the incisal contour and the inciso-facial angle)* **[Full Metal Crown. Lec. 4]** ***Full Metal Crown\ Definition:\ **❑ Is a full coverage restoration covering all axial surfaces as well as the occlusal surface of the tooth and made of metal.\ ❑ It is an all-metallic restoration that restore functional properties of the prepared tooth. (prepared clinical crown of natural teeth)\ It is one of the most commonly indicated crown restorations for posterior teeth. Because it made of metal. (Strong)\ It should be used when the patient doesn't mind the appearance of metal or when esthetic is not a factor.\ **\ **o **Types of metal alloys used for full metal crown:\ **1) High noble alloys (Gold alloys).\ 2) Low noble alloys (Silver-palladium and gold-palladium alloys).\ 3) Non-noble alloys or base metal alloys (Nickle-chromium alloy).**\ **o **Requirements (Criteria) of full metal crown preparation:\ **1) Removal of adequate amount of tooth structure.\ 2) Preservation of remaining tooth structure.\ 3) Reduction should produce a crown of acceptable strength.**\ **o **Indications of Full Metal Crown:\ **1) Single crown (restoration) for posterior teeth\ 2) Retainer for long span bridge.??????\ 3) Patient with ↑ caries index and poor oral hygiene.\ 4) Extensively damaged teeth by caries or trauma.\ 5) Endodontically treated teeth (because of brittleness).\ 6) Teeth with short clinical crown / sever attrition.\ 7) Correction of mal-aligned, rotated or tilted teeth to restore contact, contour and occlusion.\ 8) Support for R.P.D clasp.\ o **Contraindications of Full Metal Crown:\ **1) When more conservative treatment plan can be done (partial coverage).\ 2) When ↑ esthetic is desired esp. anterior teeth.\ 3) When less than maximum retention and resistance are needed. (i.e. in case of partial denture in the opposing arch)\ 4) When short span bridge can be done.\ 5) Young patient.?????\ **\ Advantages of Full Metal Crown:\ **1) Maximum Retention, Resistance and Strength than partial coverage.???\ 2) Allow modification of axial contour→ in case of mal-aligned teeth.\ 3) Can be used as a support for R.P.D.**\ Disadvantages of Full Metal Crown:\ **1) Less conservative than partial coverage restorations.\ 2) Can not allow for pulp vitality test of the abutment teeth.\ 3) Metal display ( ↓ Esthetic).\ 4) Can endanger pulp vitality or cause gingival inflammation!!!!!! (Very young patient). Allergic reaction.**\ **❑ **Tooth Preparation for All-metal Crowns:\ **o **Steps of Full Metal Crown Preparation:\ **1- Occlusal surface reduction.\ 2- Axial surface reduction:\ Buccal and Lingual surface preparation.\ Mesial and distal surfaces preparation.\ 3- Margin placement and Design (type of finish line).\ 4- Finishing and Smoothing the preparation**.\ **❑ **Depth Orientation Grooves (D.O.G):\ **❖ Are grooves prepared in the surface of the tooth to act as a guide or reference to determine the amount of tooth structure removed by preparation.\ ❖ If the preparation is done without these grooves, under or over preparation is possible and more time will be spent by repeated checking of the preparation.**\ 1) Occlusal Reduction:\ ** **Amount of reduction: 1-1.5mm\ ** **Aim**: to create a uniform space **(clearance) of 1-1.5mm** to provide enough thickness of metal for **structural durability**.\ **Instruments** **tapered diamond bur with rounded end.\ **3 Depth grooves of 1mm deep are placed in central / mesial/ and distal fossa then the tooth structure between the grooves\ are removed following occlusal anatomy...............**why?\ i) To preserve pulp vitality.\ ii) Allow even metal thickness** **structural durability.\ iii) To improve the retention and resistance features of the preparation.\ ** **Occlusal clearance** **1.5 mm on functional cusps.\ ** **1mm on non-functional cusps.\ In case of pulpless teeth** **the occlusal surface is prepared in tow planes buccal and lingual.\ N.B:\ ** **decrease Occlusal reduction** **thin metal** **perforation.\ ** **↑ increase Occlusal reduction** **decrease occluso-gingival height** **decrease** **retention.\ Q: How to check the occlusal reduction????\ **1. Using Utility Wax and Wax caliper: utility wax of 2mm thickness is placed on the occlusal surface & patient bite on it & then measure the thickness using Wax caliper)\ 2. Using Reduction gauge\ 3. Using occlusal clearance tab\ 4. Others???????????\ **Functional cusp bevel:\ Wide bevel is performed 45 degree inclination to the long axis of the tooth on:\ **❑ **Buccal inclines of lower buccal cusps (Fn. cusp).\ **❑ **Palatal inclines of upper palatal cusps (Fn. cusp).\ **Finally The occlusal clearance is then checked in centric and eccentric occlusal relations.\ **2) Axial Reduction:\ a. Buccal and Lingual surface preparation:\ ** **Instrument:** **tapered stone with round end.\ **3 depth groove of 1mm deep are placed on buccal and lingual surface // to path of insertion.\ One placed in the **center** of the wall and one in each **mesial** and **distal** transitional line angles of tooth **with 6 degree taper.\ ** **Direction of cutting:** is mesiodistally.\ **Amount of reduction:** is **0.8---1 mm.\ ** Remove the tooth structure between the grooves creating\ **chamfer finish line 0.5 mm thickness** to allow bulk of\ metal for structural durability.\ **Reduce half of the tooth leaving the other half as a reference guide for amount of reduction.\ \ b. Mesial and distal surfaces preparation (free the contact area)\ ** **Instrument:** **tapered stone with round end.\ ** **Direction of cutting:** is buccolingually\ **Amount of reduction:** is **0-8---1mm\ ** **The two proximal surfaces:** should be prepared parallel to each other or with slight occlusal convergence (2°---6°)\ **2) Axial Reduction: Cont.**\ **\ ** **Opening the contact:** is done by **fine tapered stone** (**long needle)** while protecting the adjacent teeth **by matrix band to avoid injury.\ **❑ **decrease** **Axial reduction** **thin restoration wall** **deformation.\ **❑ **↑ increase Convergence** **decrease** **retention.\ Note: to open the contact:-\ **❖Using a very thin long pointed taper diamond bur (long needle), that rested on the prepared tooth (to prevent any damage to the adjacent tooth), moving the bur up and down, the contact will be opened bucco-lingually.\ ❖ Once the contact is opened, a tapered stone with round end is used to\ plane the wall while forming a chamfer finishing line.**\ \ ** **The chamfer finish line should be smooth and continuous.**\ **\ 3)Margin Placement and design/ type:\ ** **Placement:\ ** Whenever possible finish line should be placed supra gingival\ whyyyyy?????????????? See be4\ Finish line is placed sub-gingival in the following cases ?????? See be4**\ ** **Types of margin (finish line):\ **❖ Chamfer Finish Line using A round-end tapered fissure bur during axial reduction.\ ❖ Knife edge finish line may also be used.\ ❖ Chisel edge finish line on the mesial and distal surfaces where there is no enough space to introduce tapered stone with rounded end to make chamfer.\ ❖ Bevel finish line on the buccal and lingual surfaces where there is initial cervical caries.**\ \ ** **Seating groove:** A seating groove is finally placed in the buccal surface of the lower molar and the palatal surface of the upper molar.\ **Advantages of placing a seating groove:\ ** It acts as a guide during the placement of the crown.\ Increasing the resistance (prevents the rotation of the crown).\ It improves the retention.\ **\ 4)*** ***Finishing and Smoothing the preparation:\ ** Finishing: done by Roundation of axial line and point angle using low speed?????**\ a) To remove cervical triangular undercut\ b) To establish a proper path of insertion\ c) To allow the continuity of finish line\ d) To prevent Stress concentration\ ** **Finishing will aid in:\ **i) Impression making.\ ii) Waxing.\ iii) Investing.\ iv) Casting.**\ ** **Smoothing the preparation: using fine grits stone and sand paper disc????**\ ❑ **Common Errors:\ ** **Over tapering of opposing axial walls** decrease **retention????\ Therefore, to overcome this error:\ i) Prepare a band of few mms of tooth structure with** **taper 6 degree.\ ii) Use grooves / boxes/ pinholes.??????????????\ \ Q: What are the results of:\ **1.Insuffecient and excessive occlusal reduction????\ 2.Insuffecient and excessive proximal reduction????* ***[Metal Ceramic Restoration Part I 3rd level. Lec. 5]*** - ***[Important notes to be remember??]\ **❑ The coping / framework provide strength and rigidity* *therefore the minimal thickness of gold framework is 0.3-0.5 mm while minimal thickness of base metal framework is 0.2-0.3mm whyyyyy??\ Because base metal alloys has high yield strength and high modulus of elasticity.\ The minimal thickness of porcelain is 0.7mm, otherwise high opacity\ decrease esthetic.\ The optimum thickness of porcelain is 1mm.\ The maximum thickness of porcelain is 1.5-2mm, otherwise fracture\ whyyy?? Because the porcelain layer away from the framework support will be subjected to tensile stresses* *fracture.* - ***Inclinations of*** ***Metal Ceramic Restoration.\ **1) Single crown or bridge retainer where esthetic is important.\ 2) Extensive destruction of anterior or posterior teeth.\ 3) Endodontically treated anterior or posterior teeth.\ 4) Need for recontouring axial surface or adjustment of minor mal-\ 5) In deep bite* *because all-ceramic cannot withstand ↑ forces.\ 6) Accommodate a rest of removal prosthesis ( i.e. Support R.P.D).\ 7) When partial coverage OR all ceramic is contraindicated. (Short\ teeth, bad habit / deep bite / parafunctional habits).\ 8) Teeth require fixed splinting. (i.e. Periodontically weakened teeth)\ 9) Where good occlusal surface is required.\ 10) ↑ Caries index and bad oral hygiene.* - ***Contraindication of [ Metal Ceramic Restoration]:\ **1) Young patient with large vital pulp.\ 2) Insufficient bulk of tooth structure (e.g. lower centrals* *therefore resin bonded restoration can be used).\ 3) When more conservative restoration can be applied ( e.g. ¾ or 7/8 crown).\ 4) When maximum esthetics is required. (so, use all ceramic)* - ***Advantages of*** ***Metal Ceramic Restoration:\ **1. It combines strength and esthetic.\ 2. ↑↑ increase Retention and ↑↑ Resistance.\ 3. Correction of axial contour.\ 4. Easy preparation than partial coverage.\ 5. Long term durability.\ 6. Compared to all ceramic: → ↑ Marginal fit.\ → Stronger.\ → Can accommodate all type of connector.\ → Can be used to correct the occlusal plane.\ 7. Can be used for tooth splinting.* - ***Disadvantages of [Metal Ceramic Restoration]*** 1. *Less conservative (need ↑ reduction for metal + porcelain).\ 2) The facial margin of anterior restoration is placed sub-gingival which may cause periodontal problems.\ 3) Compared to all ceramic → It has ↓decreased esthetic.\ 4) Difficult shade selection.\ 5) Liable for porcelain fracture* *due to improper metal framework design**.*** A. ***High Noble alloys:** They contain a minimum of 60% by weight of noble element and at least 40 % gold.\ o Gold-platinum-palladium\ o Gold-palladium-silver\ o Gold-palladium\ **B) Noble alloys:** They contain a minimum of 25% by weight of noble metal with no gold percentage requirement.\ o Palladium-silver\ o Palladium-cupper-gallium\ o Palladium-gallium\ **C) Base metal alloys:** Less than 25% by weight noble metal and with no requirement for gold.**\ **o Nickel-chromium\ o Cobalt-chromium\ o Titanium alloys**\ **❑ **Requirements of alloy used for metal-ceramic restorations:\ **1. The coefficient of thermal expansion of porcelain and metal should be compatible. (CTE of\ porcelain should be slightly lower than that of the metal).**\ **The optimal difference between the two would be **no greater than 0.5-1 x 10^-6^ °C. ???\ ** A **great difference** in their coefficient of thermal expansion **produce difference** in their **cooling rates** thus **shear stress** leading to **failure** of the **bond** between porcelain and metal.\ **2. The melting range temperature** of the metal should be **higher** than the **fusion** temperature of porcelain by **at least 170-280 °C. ???\ **If the difference is less than 170 °C, the metal coping may undergo flow or creep and deformation.\ **N.B:** Porcelains used for metal-ceramic restorations have a fusion temperature of about 980°C,\ noble alloys melt at nearly 1260 °C, base metal alloys nearly at 1300 °C.\ **N.B:** Porcelains should be high viscosity (maintain basic shapes during firing).\ **\ 3. The metal should be rigid enough** i.e. it should not flex during seating or when subjected to occlusal forces. Any **flexing of the metal will lead to shearing of the porcelain then fracture.\ N.B:** Porcelains should resist devitrification (firing porcelain too many times result in milky color and difficult to glaze).\ **N.B:** Porcelains should be chemically and optically stable.\ **\ **❑ **Techniques of fabrication of metal substructure:\ **1- Lost wax technique.\ 2- Electroforming/ Galvano-forming.\ 3- Metal foil systems (bonded foil system).\ 4- CAD/CAM system.**\ \ **❑ **Criteria of ideal tooth preparation to receive Metal-Ceramic restoration: (ANTERIOR TEETH)\ 1) Labial reduction → 1-1.5 mm with:\ **→ Shoulder F.L.\ → Deep chamfer.\ → Shoulder with bevel.* - ***Labial reduction must be prepared in 2 planes:\ **One parallel with the path of insertion (cervical 1/3rd ), and one parallel with the original contour (incisal 2/3rd) of the facial surface of the tooth.**\ 2) Incisal reduction →** Should allow for 2mm of clearance.\ -To ensure adequate thickness of restoration (Strength).\ -To increase esthetic (Translucency).**\ 3) Lingual reduction (Cingulum) → chamfer F.L 0.5mm.\ 4) Distinct junction (WING or HALF GROOVE)\ **o **May exist between both F.L →** shoulder F.L should extend 1mm lingual to proximal contact.**\ \ 5) Axial reduction with → 1-1.5 mm clearance with 6º degree of convergence.\ 6) In anterior teeth → palatal fossa is prepared with clearance 1mm if centric contact on metal.\ But : if centric contact on porcelain → clearance 1.5-2 mm.\ \ **❑ **Wingless Variation of Tooth Preparation:\ ** The labial shoulder gradually narrow towards the lingual chamfer → i.e. no distinct transition from shoulder to chamfer (NO WING OR HALF GROOVE).\ Done in the following cases:\ i) Narrow and thin teeth.\ ii) In young age patient due to large pulp horns to avoid pulp exposure.\ iii) Proximal caries.* **[All Ceramic Restoration Part I (3rd level). Lec.6]** ❑ **Historical background**:\ In 1886 → Land introduced the 1st all ceramic crown using platinum foil technique known as Porcelain Jacket Crown. (PJC)\ Unfortunately, due to their brittleness, these restoration were used only for single anterior restoration.**\ **\ In 1940 →The introduction of acrylic resin → ↓ popularity of all-ceramic crowns because of:\ →↑ Brittleness of all ceramic.\ → Less liability of A.R to fracture.\ → Low A.R cost.\ But: Acrylic Resin suffer from the following disadvantages:\ 1) ↑ Coefficient of thermal expansion and contraction than tooth structure (7 to 8 times), which lead to marginal leakage (percolation)\ 2) ↑ Wear.\ 3) Water sorption, Discoloration.\ 4) Monomer irritation. (less tissue biocompatibility).\ So, porcelain was then reintroduced, and the demand for porcelain have been increased because of its: →↑↑ Esthetic.\ →↑Tissue biocompatibility.\ Therefore several methods were developed in order to →\ reinforce dental ceramics. How????**\ **\ o In 1965, McLean and Hughes introduced the glass-alumina composite by\ incorporating 40% to 50% alumina crystals to the traditional porcelain. this\ resulted in block crack propagation and increase in strength by about 40% than\ the traditional porcelain.\ But, this alumina content porcelain was Opaque, (i.e: non-esthetic material). So....., it was used as a Core material to be veneered (surrounded) with an\ esthetic ceramic of relatively lower strength.\ o It similar to the metal-ceramic technique, although the color of the ceramic core\ could be easily masked than the metal substructure.\ \ o Continuous improvements in both materials and techniques have been achieved in an attempt to develop a ceramic material that combines good esthetics with high strength.\ o Recently, improved materials (as zirconia) & techniques (as CAD/CAM) have been introduced to overcome the drawbacks inherent disadvantages of ceramics (low tensile strength).\ **Definitions:\ All -- ceramic crown restoration:** It is Extra-coronal full coverage non-metallic restoration, Covering the prepared clinical crown, and Restoring the anatomy, esthetics and function.\ It acquires its retention from complete encircling (frictional retention) bonding.\ **Difference Between Ceramic and Porcelain:**\ **CERAMIC:** any product made from a nonmetallic inorganic material usually processed by firing at a high temperature to achieve desirable properties.\ **[ PORCELAIN:]** a specific compositional range of ceramic materials originally made by mixing:- Kaolin (hydrated aluminosilicate 1-10%), Quartz (silica 11-18%), and Feldspars (70-90%).....+ Coloring pigments.\ **[PORCELAIN] components:\ a) Kaolin or Clay: (1-10 %)\ Role:\ **i) When mixed with water → it become sticky therefore forming a workable mass of\ porcelain. (↑plasticity / workability).\ ii) Binds the particles together when the porcelain is unfired. (Responsible for strength of porcelain before firing (green strength)\ iii) ↑ opacity if more than 10%.\ **b) Quartz (Silica): (Sio2) (11-18 %)\ ** Pure quartz crystals.\ **Role:\ **i) → Remain unchanged during firing, therefore **forms network for other ingredients** (glass bridges) → ↑ strength\ (Responsible for strength and hardness of porcelain)\ (It helps the porcelain restoration to maintain its form during firing).\ **c) Feldspar: (70-90%)\ ** Potassium aluminum silicate.\ **Role:\ **i) On heating → under fusion forming glassy material which gives the porcelain its\ translucency.\ ii) Act as matrix → holds other components that don't undergo fusion.\ **d) Coloring pigments: (1-2%)\ **They are metal oxide in small quantities → to obtain shades (for example):-\ Indium oxide → yellow\ Iron oxide → (brown / black)\ Cobalt oxide → (blue)\ Lanthanide oxide → fluorescence\ Others........\ ❑ **Advantages of All ceramic restorations:** 1\. Excellent esthetic, Translucency & Color stability\ 2. Biocompatible to the gingival tissue. (subgingival finish line)\ \ \ 3. Slightly more conservative reduction of the facial surface than metal-ceramic restoration.?????\ 4. Chemical stability.\ 5. Coefficient of thermal expansion is similar to tooth structure. (No marginal percolation)\ ❑ **Disadvantages of All ceramic restorations:\ **1. High brittleness & liability to be fractured.\ 2. More expensive than full metal & PFM.\ 3. Among the least conservative preparation (By comparison, the proximal and lingual reduction are less conservative than those\ needed for a metal-ceramic crown (due to the shoulder F.L. prep.).\ 4. Reduced strength compared to metal-ceramic restoration.\ 5. Wearing of the opposing natural teeth.\ 6. Pulp vitality can\'t be done ???\ 7. Radiographic examination can\'t be done??? they are radio-opaque**\ **❑**Indications of All ceramic restorations:** 1\. As a single restoration for patient with high esthetic demands. (malformed tooth as peg shaped lateral / malposed / rotated or discolored anterior teeth).\ 2. As a retainer for all ceramic anterior bridge when esthetic is important.\ 3. When no more conservative treatment option can be done. (e.g. partial coverage).!!!!!\ 4. Favorable occlusion (i.e. favorable distribution of occlusal load)\ 5. Restoration of endodontically treated tooth & badly decayed teeth.\ 6. Fractured anterior teeth that cannot be restored with another restoration (but not more than 1/3 of tooth height).\ 7. Erosion / abrasion.\ 8. Proximal & facial caries that can no longer successfully restored with more conservative option. ❑**Contraindications of All ceramic restorations:** 1. **When high strength is required.????????????\ **2- When more conservative treatment option is indicated !!!!!!\ 3- Young age with large pulp size and high epithelial attachment) (as it require more reduction to avoid pulp exposure).\ 4- Un-favorable distribution of occlusal load: e.g.\ Deep bite?? opposing teeth occlude on the cervical 1/5 of the lingual surface produce tensile stresses Half-moon\" fracture.\ Edge to edge??? produce stress in the incisal area of restoration.\ Parafunctional habits (bruxism /clenching)?? Increase facture risk\ Bad habits (Nile biting / pencil chewing)?? Increase facture risk 1. **Incisal Reduction:\ **a. Amount of reduction: 1.5-2 mm for sufficient porcelain bulk (Esthetic and strength)\ b. Instrument: Tapered stone with round end / Flat end or wheel stone\ c. Direction of cutting: mesio-distally with an inclination 45 degree with the long axis toward the palatal surface in upper Anterior And toward the labial surface in lower anterior???? Why??\ To oppose the forces perpendicularly on the incisal edge and prevent porcelain shearing.\ **2) Facial / Labial Reduction:\ **a. Amount of reduction: → 1 mm creating shoulder finish line.\ b. Direction: mesio-distally in sweeping motion:→ prepared in 2 planes:-\ 1) Gingival (cervical) part which is parallel to the long axis of the tooth (path of\ insertion) and slightly tapered to the prepared cingulum (for retention and resistance).\ 2) Incisal part which is parallel to the original tooth contour.\ C. Instrument: → Tapered stone with flat end for incisal half and with rounded end for gingival half.\ D. Finish line: 1mm Round shoulder or Deep chamfer (tapered with round end\ stone is used)\ **3) Lingual Reduction:\ **a. Amount of reduction: 1mm. (in all centric & eccentric movements)\ b. Direction: → prepared in 2 parts.\ a) Concave lingual fossa: follow its concavity to allow even amount of clearance.\ b) Cingulum: mesio-distally in sweeping motion → prepared // or slight taper in\ relation to the cervical portion of the facial surface (retention and resistance).\ c. Instruments: → Wheel or football (oval shaped) stone for lingual fossa.\ → Tapered stone with flat end for cingulum.\ d. Finish line: 1mm Round shoulder or Deep chamfer (tapered with round end\ stone is used)**\ 4) Proximal Reduction;\ **a. Amount of reduction: → 1mm.\ b. Direction of cutting: is labio-lingually\ c. Instrument: → Fine tapered for opening of the contact\ → Tapered stone with flat end to create shoulder F.L????\ d. Finish line: 1mm Round shoulder or Deep chamfer (tapered with round end stone is used)\ **5) Finishing and Smoothening the preparation:**\ o All axial surface should be smoothed using finishing stone and burs.\ o Rounding sharp line angle. → O.W stress concentration → fracture.\ o Refine the established shoulder F.L using:\ → End cutting bur\ → Hand cutting instrument (Binangle chisel).**\ \ ** **[Partial Coverage Retainers (Partial Veneer Crowns). Lec.7&8]** ❑ **Definition:\ **It is an extra coronal restoration covering and rebuilding only the prepared part of the coronal portion of the tooth to which the pontic is connected and by which the bridge is supported.\ ❑ **Classification of partial coverage:\ I) According to means of retention:\ **1) By grooves → 3/4 , Reverse 3/4 , 1/2 , 7/8 and Macboyle retainers.\ 2) By pins → Pinledge retainer.\ 3) By Enclasping tooth structure → Reverse Retention Retainer.\ 4) By combination means of retention: Modified types including both grooves and pins.\ **2) According to position:\ **1) Anterior teeth → ¾ retainer, Macboyle, Pin-ledge retainer.\ 2) Posterior teeth → ¾ retainer, Revers ¾ , Proximal ½ , 7/8 and Reverse Retention Retainer.**\ 3) Recent classification:\ **1) Conventional Partial Coverage:\ Gains its retention through grooves / pinholes (macro-mechanical) e.g.: 3/4 , 1/2, 7/8 retainers.\ 2) Adhesive Partial Coverage:\ Gains its retention chemically / micromechanically e.g.: Laminate veneer and All-ceramic resin bonded retainers.\ **Advantages of partial coverage:\ **1) Conservation of tooth reduction.\ 2) Less pulpal and periodontal irritation.\ 3) Allow pulp vitality test.\ 4) Allow proper seating.\ 5) Allow easy removal of excess cement less hydraulic pressure.\ 6) Margins are accessible:\ to dentist for → finishing and\ to patient for → cleaning.\ **Disadvantages:\ **1. Less retentive than full coverage restoration.\ 2. May show some metal display or metal shadow in certain types.\ 3. Possibility of recurrent caries.\ 4. Difficult preparation → need skillful dentists.\ **Indications of partial coverage:\ **1. For posterior teeth → single restoration.\ → bridge retainer for short span bridge.\ 2. For anterior teeth → bridge retainer for short span bridge.\ 3. Used in long clinical crown, wide (M-D) and thick (B-Lg) teeth.\ 4. Used in splinting.\ 5. Used in re-establish incisal guidance.\ 6. Moderate loss of tooth with intact labial or buccal surface.\ 7. Patient with good oral hygiene.\ 8. Normal occlusion.\ 9. Teeth with normal axial inclination.\ 10.Vital tooth.\ \ ** Contraindications of partial coverage:\ **1. Short thin teeth.\ 2. R.C.T teeth.\ 3. Malformed teeth → peg-shaped tooth.\ 4. Developmental defects (e.g. hypo-calcified enamel).\ 5. Badly destructed teeth.\ 6. Patient with bad oral hygiene.\ 7. Extensive caries.\ 8. Others..........P.D diseases/ long span/ parafunctions????????**\ **❑ **Different types of Partial Veneer Crowns** 1. **MAXILLARY 3/4 CROWN:** - **Steps of preparation (teeth reduction):**\ A) Occlusal reduction\ B) Lingual reduction\ C) Proximal reduction\ D) Marginal placement\ E) proximal Grooves preparation\ F) Contra bevel\ G) Occlusal offset\ H) Smoothening and finishing\ **A) Occlusal reduction:**\ ►Depth cuts are placed: (D.O.G)\ → 1.5mm on functional cusp.\ → 1mm on nonfunctional cusp.\ ►Occlusal reduction is completed by removing tooth structure between depth cuts using tapered stone with round end.\ ►Functional cusp bevel on the functional cusp.**\ **\ **B) Lingual reduction:\ **►Depth cuts are placed (D.O.G).\ ►Instrument → tapered stone with round end.\ ►Eliminate the undercut cervical to height of contour → creating chamfer finish line.\ ►The reduced lingual surface should be:\ i. Follow the normal contour of the tooth → mesiodistally\ ii. Parallel to path of insertion with slight occlusal convergency.**\ C) Proximal reduction:**\ o Opening the contact → using fine tapered stone and stop just labial to the contact area.\ o Then, tapered stone with round end is used to complete the reduction → creating chamfer finish line.\ o The reduced proximal surfaces must be // to each other with slight occlusal convergency.**\ D) proximal Grooves:\ **o **Guidelines:\ **1- Parallel to the incisal 2/3 of the facial surface\ 2- Done by: Tapered fissure bur ???\ 3- Depth: 1.0 mm\ 4- Width: 1.0mm\ 5- High/ Length: It ends about O. 5 mm occlusal to the chamfer finish line??? to ensure marginal integrity..\ 6- Grooves on mesial and distal sides are parallel ???\ **D) proximal Grooves preparation:\ [1) Types/ forms:]**\ V-shaped → for ant. Teeth ↓↓ retention and ↑↑ conservative.\ U-shaped → for post. Teeth\ Box-shaped → for post. Teeth ↑↑ retention and ↓↓↓ conservative.\ → used in the following cases:\ i) Proximal caries.\ ii) Solder joint.\ iii) Precision attachment.\ **[2. Location:\ ]** On the buccal 1/2 of the proximal surface, Or\ At the line between buccal and middle thirds of proximal surface or 1mm lingual to Bucco-proximal line angle).????? why??\ To avoid metal display.\ To increase the amount of tooth structure lingual to the groove to increase retention and resistance to lingual displacement.\ **3. Depth:** → 1mm.**\ 4. Width:** → 1mm.**\ 5. Length: →** The gingival seat of the groove ends ½ mm away from F.L (Apron) to ensure maximum adaptation.**\ **❑ **The most important wall of the groove is the definite lingual wall??? → which resist lingual displacement.\ **\ **Clinical tips for groove preparation:-\ **(1) The groove outline should be drawn on the occlusal surface using sharp pencil.\ (2) The grooves should be placed buccally as much as possible without undermining the facial surface.\ (3) Grooves should be done first on:\ i) Distal surface of molars (Inaccessible).\ ii) Mesial surface of the premolars (Esthetic critical surface).**\ **\ (4) The buccal wall of the groove and lingual wall of the groove should be Parallel or slightly diverge occlusally.\ (5) The buccal wall of the groove should be flared buccally (bevel finish line) in order to:\ Avoid enamel undermining.\ Slight widening of the contact without metal display.**\ E) Contra bevel:** **(**facial or occlusal finishing bevel):\ → It is a bucco- occlusal bevel of width 0.5 mm.\ → It extends mesio-distally to join the buccal flare of the proximal groove.\ ❑ **Functions of Contra bevel:\ **i) To remove any unsupported enamel.\ ii)↑ Metal adaptation.\ iii) ↑ Metal thickness to protect buccal cusp from fracture.\ iv) Marginal integrity.\ **F) Occlusal offset:\ ** It is an **occlusal groove joining the 2 proximal Groove →** to provides thickness & bulk for the crown to withstand forces during function (structural durability)\. its 1mm ledge on the lingual incline of the facial cusp connecting the proximal grooves and assuming a V shape\ Depth 0.5-1 mm\ **Instrument:\ **Fissure bur no.(171)\ End cutting bur no.(957) is used to define the margin.\ **N.B:** it is essential for anterior partial coverage.\ \ N0te: **Three quarter crown preparation on a maxillary molar is\ similar to premolar\ Modifications of Posterior maxillary preparation:\ 7/8 crown:\ ** All surfaces are prepared except MB cusp area.\ Grooves → one mesially and one buccally.\ The buccal groove done on the middle of the buccal surface // to the path of insertion then the mesial wall of the groove is flared mesially.\ Used in upper 6 , 7.\ **II) Mandibular Posterior ¾ crown:\ A) ¾ crown on lower premolar:\ Differ from upper premolar in:\ **1) Third groove is made at the distal ½ of the buccal surface.\ o Depth 0.3-0.5mm.\ o Width 1mm.\ 2) Functional cusp is the buccal → therefore 1.5mm reduction, beveling and\ covering..............while lingual cusp → 1mm reduction.\ \ 3) Extend the preparation beyond the buccal functional cusp (1mm below occlusal contact creating chamfer / shoulder finish line).\ Causes of these modifications: (to improve the retention)\ i) The smaller size of lower premolars, therefore ↓retention.\ ii)The smaller lingual cusp of lower premolars, therefore ↓ retention.**\ **\ **B) 3/4 Crown on lower molar:\ **Same as lower premolar except no need for the third disto-buccal groove.\ Buccal cusp should be completely covered as it is the functional cusp ending with chamfer finish line 1 mm below occlusal surface (concave bevel)\ ** Modification of ¾ crown for mandibular premolars and molars:\ 1) Reverse Retention Retainer:\ ** The preparation is extend till bucco-proximal line angle i.e enclasping tooth structure.\ Proximo-buccal half grooves. (instead of M&D grooves)\ Used in lower premolar → to ↑ retention.\ **2) Reverse ¾ crown:\ ** All surfaces are prepared except lingual surface → and gains its retention by 2 grooves (M&D)\ Used in → lower premolar and molar with sever lingual inclination)\ Restoration of mandibular molar with damaged buccal surface and intact lingual surface.**\ 3) ½ crown:\ **Partial coverage restoration where mesial ½ of buccal and mesial ½ of lingual surfaces are prepared.\ Grooves → one buccally and one lingually. should be parallel to the path of insertion of the F.P.D.\ Indicated for the distal retainer of a fixed partial denture with tilted molar abutment.**\ ½ Crown preparation:** a. **Anterior ¾ crown:** +-----------------------+-----------------------+-----------------------+ | | **Anterior 3/4** | **Posterior 3/4** | +=======================+=======================+=======================+ | **1) Path of | Parallel to the | Parallel to the long | | insertion:** | incisal 2/3 of the | axis of the tooth. | | | labial surface. | | +-----------------------+-----------------------+-----------------------+ | **2) Grooves:** | → V-shaped groove. | → U or box-shaped | | | | groove. | | | → has no cervical | | | | stop | | +-----------------------+-----------------------+-----------------------+ | **3) Offset:** | (fade to zero) | → Has cervical step ½ | | | | mm away from F.L. | | | → Incisal offset is | (apron) | | | done. | | +-----------------------+-----------------------+-----------------------+ | **4) Cutting pin | A pin hole may be cut | → Occlusal offset is | | holes:** | on the cingulum area | optional. | | | → to ↑ retention. | | | | | No pin hole is done. | +-----------------------+-----------------------+-----------------------+ **N.B:\ Incisal offset:\ ** It is a V shaped groove having labial and lingual walls.\ The angle between the two walls may be right or slightly acute angle.\ The labial wall is twice the width as the lingual wall leaving dentin to support\ labial enamel plate.\ Done by small inverted bur.\ In canine the groove follows the form of the incisal edge.**\ \ Modification of ¾ crown for anterior teeth:\ a) Modification of Canine preparation to increase retention and resistance:**\ i. Added groove on one side of the cingulum.\ ( 2 proximal grooves + 1 cingulum groove)\ ii. Added pinhole.\ **b) Macboyle retainer:** Indicated in lower 1, 2, upper 2 (i.e. Thin labio-lingual teeth).\ The grooves are placed at labio-proximal line angle instead of M&D surface. (same to posterior revers retention retainer)\ Disadvantage → metal display. **c) Pinledge retainer:** **Definition:\ **It is a modified partial coverage gets its retention from 3 or more parallel\ pinholes prepared at the palatal or lingual surface of tooth.\ Designs of Pinledge preparation:\ 1. Conventional design: → if used as single restoration i.e involve only lingual surface.\ 2. Pinledge with proximal slice: → if used as bridge retainer (proximal slice to the surface adjacent to the edentulous area).\ 3. Pinledge with proximal groove: → if used as bridge retainer / proximal caries / to modify palatal surface to receive support of P.D.**\ Pin-ledge preparation:\ A- Ledges:\ **. Number of ledges: → 1 incisally\ (at the junction between 1st and 2nd incisal quarter)\ → 1 cervically. (at the cervical quarter).\. Depth: → 0.5-0.7mm\. Instrument: → small fissure bur...End???\. Direction: → Parallel to incisal edge and perpendicular to the long axis.\ Each ledge must have 2 walls → pulpal wall // to path of Insertion\ → cervical wall which is prepared 90º to pulpal wall\ **B) Indentation:\ **. Number of indentations: → 2 incisally\ → 1 cervically\. Depth: → 0.5mm\. Instrument: → small fissure bur...End???\. Direction: → away from pulp chamber.\ → parallel to path of insertion.\ (parallel to the incisal 2/3 of the labial surface).\ → parallel to each other.\. Function: → provide enough bulk of metal at the junction between pin and ledge\ → therefore prevent pin fracture.**\ (c) Pinholes:\ **. Number of pinholes: → 2 incisally\ → 1 cervically\. Depth: → incisally → 2.5 mm\ → cervically → 2 mm\. Diameter: → 0.3 mm\. Instrument: → small fissure bur...End???\. Direction: → away from pulp chamber.\ → parallel to path of insertion.\ (parallel to the incisal 2/3 of the labial surface).\ → parallel to each other\'s.\. Function: →↑ retention.\ \ ❑ **Pin-ledge preparation modification:\ **→ Additional 4th pin cervically.\ → Proximal grooves.\ \ ❑ **Impression making:\ ** Nylon bristles 25-50um in diameter are placed in the pinholes → then make\ impression (i.e. the bristles support the impression while removed from the mouth, otherwise → tearing ).\ After pouring the impression → serrated pins are used to construct wax pattern. **[Tissue Dilation and Fluid Control]. Lec.9** - **Definition:** → it is the process of temporary pushing of free gingival tissues away from tooth surface. **OR**\ It is a physical stretching of circumferential gingiva away from tooth surface. - **[Indications of Tissue Dilation:]\ **1) During clinical examination → for better diagnosis and detection of cervical caries.\ 2) During preparation → for accurate preparation of subgingival finish line without\ tearing of epithelial attachment and bleeding.\ 3) During impression → to expose preparation margin and finish line.\ 4) During try in → to check subgingival marginal accuracy.\ 5) During cementation → to make sure that there is no overhanging\ & for easier removal of excess cement.\ 6) During follow visits to check for incipient caries. - **Requirements (Aims) of tissue dilation:\ **1) Expose the prepared margin (finish line).\ 2) It must create proper space horizontally, to give bulk to the\ impression material to resist tearing. (Provide sufficient strength of impression\ material to prevent distortion or tearing the impression when removed or poured\ with stone).\ 3) Create vertical space to allow impression material to go beyond the finish line (The\ impression material could record the tooth structure at/ and beyond the margin).\ 4) It must create clean and dry field → i.e. free from blood, saliva and gingival fluid.\ 5) It must protect and maintain the health of the supporting periodontal tissues. - **Techniques of Tissue Dilation:\ *[According to the Method:]*** - **Disadvantages of Mechanical method:\ **1. Any of the above is pushed in the gingival sulcus for 12- 24 hrs. → tissue displacement. But if last more than 24 hrs. → Permanent tissue displacement or\ recession.\ 2. Final impression cannot be taken in the same visit.\ 3. It does not control bleeding.**\ II\]** **Mechano-chemical method:** It is the most efficient & most common\ technique used for tissue displacement.\ This is done by using cotton cord impregnated in one of the following chemicals:\ **1) Epinephrine 1/1000** 2. **Epinephrine 8%.... Contra-indicated in cardiac patient → Otherwise epinephrine syndrome:\ **i) Tachycardia\ ii) ↑ blood pressure.\ iii) Post operative depression.\ iv) Nervosity.**\ 3) Tannic acid (20-100%)** may cause tooth discoloration.\ **4) Aluminum chloride (5-25%)** may cause gingival inflammation / interferes with the setting of polyvinyl siloxane impression material.\ **5) Ferric sulphate (13.3%)** may cause gingival inflammation / Necrosis**\ 6) Aluminum solution →** most safe (100%).\ **7) Negatol solution (45%).\ 8) Sometimes: Eye or Ear drops.\ \ **Any of the above → Cords = mechanical action. (retraction of the gingival tissue)\ → Chemicals = chemical action (astringent action) With vasoconstriction of blood vessels. (hemostatic action that gives clean dry field)**\ ❑ Advantages of Mechano-chemical method:** - Bloodless **IV\]** **Recent retraction techniques:\ Recently Cordless retraction paste or gel is available:\ **e.g. Expasyl paste / Magic foam injected into the sulcus for 2 minutes\ then removed by irrigating water. (it contains hemostatic agent (aluminum chloride)\ Others: Gingi Trac/ Merocel strips/ Retraction capsule\ **Advantages of Recent retraction techniques:\ **i) Less pressure applied during application.\ ii) Application time is 2 minutes only.\ iii) Effective tissue retraction. - **examples for Recent retraction techniques\ 1- Magic foam gel:\ ** This material is based on polyvinyl siloxane, with the ability to expand and displace tissues once placed inside the gingival sulcus. This is used in combination with a compression cap.**\ 2- Expasyl paste:\ ** This is a viscous synthetic paste, which contains 10% aluminum chloride, 80% kaolin, with water and modifiers.**\ 3- Merocel strips:\ ** It is a synthetic polymer strips of 2 mm thickness, that has a sponge-like texture. It has the ability to absorb fluid once placed in the gingival sulcus,\ then swells and occupies the gingival sulcus. - **FLUID CONTROL\ Importance of Fluid Control:\ ** To provide Dry and Clean operating field.\ For better Access and Visibility.\ Provides Comfort for the patient.\ Protects from swallowing or aspirating foreign bodies.\ Success of adhesion and physical properties of dental materials.\ Infection control to minimize aerosol production.\ Less fogging of the dental mirror.\ Prevents contamination. - **Sources of moisture (fluids) in clinical environment:\ **A- Patient related source:\ Saliva: Salivary glands-parotid, submandibular, sublingual.\ Blood: Inflamed gingival tissues / iatrogenic damage.\ Gingival crevicular fluids.\ B- Dental equipments and materials related source:\ Rotary instruments. (high speed rotatory cutting instrument)\ Sonic and ultra sonic scallers.\ Triplex syringe, etchants.\ Irrigant solutions. - **[Methods of Fluid Control:]\ **Mechanical control.\ Chemical control.\ Others control. - **Mechanical methods of fluid control:\ ** Rubber dam.\ Suction tip devices.\ High volume vacuum.\ Saliva ejector.\ Sveedopter.\ Cotton rolls.\ Moisture absorbing card. - **Chemical methods of fluid control:\ ** Chemical agents that Administered for patient with excessive salivation:\ a. Anti-sialagogues.\ b. Local anesthetics.\ **\ ❑ Anti sialagogues:\ ** Gastrointestinal anti cholinergic drugs that inhibit action of myoepithelial cells of salivary gland.**\ Common drugs:\ ** Bromide (Banthine) 50mg. / 1hr before procedure.\ Propantheline bromide (Pro-Banthine) 15mg /1 hr. before procedure.\. Clonidine hydrochloride (Antihypertensive) 0.2mg / 1hr before procedure. (N.B: it causes drowsiness)\. Atropine 1 tablet of 0.4mg per day.**\ Contraindication of anti-sialagogues:\ ** Hypersensitivity to drugs.\ Glaucoma.\ Asthma.\ Congestive heart failure.\ Obstructive condition of Gl tracts or urinary tracts.**\ \ Q: What are the factors that affect the success of gingival tissue\ displacement?????????????\ \ 1- Type of Technique used:\ **a. Mechanical tech: not recommended.\ b. Mechano-chemical tech: (cord tech.) commonly used with cautions.\ c. Surgical tech: laser is the best one.\ d. Infusion tech.: (Cord/3minute then apply infuser (ferric sulphate 15-20%)\ e. Recent (cordless) technique: are preferable... advantages.....**\ 2- Mechano-chemical tech. considerations:\ a. Force applied to the cord:** **. Direction:** lateral with 45 degrees (preferred).\ apical/vertical (harmful)...trauma to the gingiva. Then recession. ** Magnitude:**1-2N/cm2.... (the best)\ more than 2.5/cm2...permanent damage.\ **b. Cord:-\ ** Diameter: small for anterior teeth, medium for posterior teeth, large (used with caution so not recommended.\ Design: plain, braided and knitted....**\ c. Cord tech: (numbers):-\ ** Single cord tech: used for single missing teeth with healthy gingiva.\ Double cord tech: used for\ Multiple preparation.\ Compromised gingival tissue health.\ Excessive gingival fluid exudate.**\ d. Time for cord application:\ ** 5- \