**Partial Coverage Restorations** **INLAY** **ONLAY** Dr V. Matsubara Image of three dental models showing partial coverage restorations (inlay and onlay) on molars. # **Partial Coverage Restorations** > [!info] > This lecture covers partial coverage restorations, with a specific focus on **inlays** and **onlays**. The content is designed to provide a comprehensive understanding of their application, from definitions and material science to clinical preparation techniques. It is recommended to supplement this lecture with the provided reference papers to expand knowledge on the topic. ## **INLAY** ## **ONLAY** **LEARNING OUTCOMES** - Explain the differences between inlays and onlays. - Discuss material options for inlays and onlays. - Outline the clinical indications and contraindications for inlays and onlays. - Evaluate the advantages and disadvantages of partial-coverage ceramic restorations. - Compare the use of direct composite versus indirect composite restorations. - Describe the key features of tooth preparation for inlays and onlays. - Review different techniques for temporizing inlay and onlay preparations. # **LEARNING OUTCOMES** - Explain the differences between inlays and onlays. - Discuss material options for inlays and onlays. - Outline the clinical indications and contraindications for inlays and onlays. - Evaluate the advantages and disadvantages of partial-coverage ceramic restorations. - Compare the use of direct composite versus indirect composite restorations. - Describe the key features of tooth preparation for inlays and onlays. - Review different techniques for temporizing inlay and onlay preparations. **Inlay and Onlay** **Indirect dental restorations** - Dental restoration made outside of the mouth to correspond to the form of the prepared tooth. - Cemented or bonded onto the tooth. At least 2 appointments required: - 1<sup>st</sup> Tooth preparation + impression/scan + temporarization - 2<sup>nd</sup> Try-in, Insertion # **Inlay and Onlay** ## **Indirect dental restorations** - Dental restoration made outside of the mouth to correspond to the form of the prepared tooth. - Cemented or bonded onto the tooth. At least 2 appointments required: - 1<sup>st</sup> Tooth preparation + impression/scan + temporarization - 2<sup>nd</sup> Try-in, Insertion - ==**Appointment 1:**== - ==Tooth investigation and treatment planning (removing old fillings, assessing remaining structure).== - ==Tooth preparation.== - ==Impression or digital scan.== - ==Bite registration.== - ==Placement of an interim (provisional) restoration.== - ==**Appointment 2:**== - ==Try-in of the final restoration.== - ==Cementation or adhesive bonding of the restoration.== # Inlay and Onlay **Inlay:** - Fixed intracoronal restorations that fit within the anatomic contour of the clinical crown. - Relies on the strength of the remaining tooth structure for support and retention Clinical image showing an inlay restoration in a molar tooth, alongside a model demonstrating the fit within the tooth structure. # **Inlay and Onlay Definitions** ## **Inlay** - Fixed intracoronal restorations that fit within the anatomic contour of the clinical crown. - Relies on the strength of the remaining tooth structure for support and retention. - ==It does not cover any cusps.== - ==*Requirement:* It relies on strong remaining tooth structure, as the cusps must be robust enough to bear occlusal loads independently. The inlay itself does not protect the cusps from fracture.== # Inlay and Onlay **Onlay:** - Partial-coverage restoration that restores one or more cusps and adjoining occlusal surfaces; or the entire occlusal surface - Retained by mechanical and/or adhesive means Glossary of Prosthetic Terms Clinical image showing a tooth with an onlay restoration. - *Inlay ‘fits into’* ## **Onlay** - Partial-coverage restoration that restores one or more cusps and adjoining occlusal surfaces; or the entire occlusal surface. - Retained by mechanical and/or adhesive means. - ==*Terminology:* When an onlay covers the entire occlusal surface, it may be referred to as an **overlay** or **tabletop**.== - ==*Function:* Onlays are designed to protect weakened cusps from occlusal forces, preventing cracks and fractures. This is known as **cuspal coverage**.== - ==They can be retained either mechanically (through preparation design) or, more commonly, through adhesive bonding systems.== # Inlay and Onlay **Inlay** *Inlay ‘fits into’,* **Onlay** *Onlay ‘fits onto’* *Incorporates cuspal coverage* --- **The Extent of Tooth Structure Loss** requiring replacement will define the need for an **INLAY** or **ONLAY** or a Full crown. **ONLAY** - the need for **tooth protection** with **CUSPAL COVERAGE** whilst trying to avoid a traditional full crown --- *Contemporary Fixed Prosthodontics, 4 ed* - *Onlay ‘fits onto’* - *Incorporates cuspal coverage* --- The Extent of Tooth Structure Loss requiring replacement will define the need for an **INLAY** or **ONLAY** or a Full crown. **ONLAY** - the need for **tooth protection** with **CUSPAL COVERAGE** whilst trying to avoid a traditional full crown. --- # Inlay and Onlay ## INLAY **Indications:** - Moderate-sized cavities **confined within the cusps**. - Teeth with at least **one sound marginal ridges**. - Replacement of **small defective restorations** (amalgam or composite) in the occlusal area. - Restorations requiring **better marginal fit and durability** than direct composite or amalgam. - Cases where **occlusal anatomy and contact points** need precise reproduction. **Contraindications:** - Extensive tooth destruction involving cusps. - Poor isolation or moisture control for bonding. - MOD cavities with weak cusps # **Indications and Contraindications** ## **INLAY** ### **Indications** - Moderate-sized cavities **confined within the cusps**. - Teeth with at least **one sound marginal ridges**. - Replacement of **small defective restorations** (amalgam or composite) in the occlusal area. - Restorations requiring **better marginal fit and durability** than direct composite or amalgam. - Cases where **occlusal anatomy and contact points** need precise reproduction. , ==especially for deep proximal boxes where direct placement is challenging and to ensure occlusal stability and prevent future periodontal issues.== ### **Contraindications** - Extensive tooth destruction involving cusps. - Poor isolation or moisture control for bonding. - MOD cavities with weak cusps. # Inlay and Onlay ## ONLAY **Indications:** - Large cavities involving **one or more cusps**, but **enough tooth structure (enamel)** remains for bonding. - Teeth with **fractured or weakened cusps** that need protection. - Replacement of **defective large restorations**. - Restorations of **endodontically treated teeth** when sufficient tooth structure is still present - Situations where **full crowns** are not indicated to preserve tooth structure (conservative preparation). - Replacement of a large MOD amalgams due to **poor aesthetics** **Contraindications:** - Teeth with severely compromised - lack of sound enamel for a predictable bonding - Severe parafunctional habits ## **ONLAY** ### **Indications** - Large cavities involving **one or more cusps**, but **enough tooth structure (enamel)** remains for bonding. - Teeth with **fractured or weakened cusps** that need protection. - Replacement of **defective large restorations**. , ==especially old MOD amalgams, to provide cuspal protection and prevent stress-induced fractures from composite shrinkage.== - Restorations of **endodontically treated teeth** when sufficient tooth structure is still present. , ==which are structurally compromised due to access cavity preparation and previous decay. Onlays or full crowns are necessary to protect the remaining cusps.== - Situations where **full crowns** are not indicated to preserve tooth structure (conservative preparation). , ==such as when preparing axial walls would leave them excessively thin (e.g., less than 1mm). An onlay preserves more tooth structure in the cervical area.== - Replacement of a large MOD amalgams due to **poor aesthetics**. ### **Contraindications** - Teeth with severely compromised - lack of sound enamel for a predictable bonding. ==Bonding to dentin and cementum is less predictable. In such cases, a restoration with mechanical retention (like a full crown) is preferred.== - Severe parafunctional habits. ==(e.g., bruxism), as the high forces can fracture ceramic restorations. A stronger material like monolithic zirconia in a full crown design may be a better option.== # Inlay and Onlay Tooth Structure Removal Associated with Various Preparation Designs for Posterior Teeth *Edelhoff & Sorensen 2002* - Typodont teeth: maxillary and mandibular premolars and molars were prepared in various crown preparation designs: MO/DO/MOD inlays, MOD onlay, partial crown, full crown. - Mean tooth structure removal was assessed by gravimetric analysis **Results:** - Inlays (MO): 27.2% - Full crown preparations: 67.5-75.6% (depending on the type of margin preparation) # **Tooth Structure Removal in Preparation Designs** *Edelhoff & Sorensen 2002* - Typodont teeth: maxillary and mandibular premolars and molars were prepared in various crown preparation designs: MO/DO/MOD inlays, MOD onlay, partial crown, full crown. - Mean tooth structure removal was assessed by gravimetric analysis. ### **Results** - Inlays (MO): 27.2% - Full crown preparations: 67.5-75.6% (depending on the type of margin preparation) - ==**Onlays:** Fall between inlays and full crowns in terms of tooth removal.== > [!info] > This data highlights the importance of choosing a conservative design like an onlay whenever clinically appropriate to preserve natural tooth structure. # Inlay and Onlay ## Inlay x Onlay Depend on the extension of the restoration: - When the width of an intracoronal cavity exceeds 1/2 the distance of the cusp tips, an onlay or crown is probably more suitable - Cuspal coverage is needed for endodontically-treated tooth **Occlusal table** **THINGS TO CONSIDER:** - enamel bonding vs dentin bonding - variance in bonding to different qualities of dentin - possibility of limited retentive form # **Considerations for Inlay vs. Onlay** ## **Extension of the Restoration** - When the width of an intracoronal cavity exceeds 1/2 the distance of the cusp tips, an onlay or crown is probably more suitable. > [!info] > If the width of the occlusal isthmus is greater than half the distance between the cusp tips, the cusps are likely undermined and require onlay coverage for protection. - Cuspal coverage is needed for endodontically-treated tooth. > [!info] > These teeth should receive either an onlay or a full crown for cuspal protection. A small inlay is not justified, as a direct composite is more conservative if the tooth structure is sufficient. ## **Occlusal table** ### **THINGS TO CONSIDER** - enamel bonding vs dentin bonding - variance in bonding to different qualities of dentin - ==Bonding to **sclerotic dentin** (often found under old amalgam fillings) is less predictable due to calcified tubules, resulting in lower bond strength. If bonding is compromised, the preparation may require more retentive features.== - possibility of limited retentive form # Inlay and Onlay ## Inlay x Onlay **A)** Tooth structure less than 2 mm **B)** Low quality of the enamel covering the cusp - unsupported enamel are likely to fracture under occlusal load Occlusal contacts on the margin of the preparation ## Cuspal coverage Diagram showing cuspal coverage with an arrow indicating occlusal force ## **Cuspal coverage** - **A)** Tooth structure less than 2 mm : ==If a cusp wall is less than 2mm in width, it is considered weak and should be covered with an onlay.== - **B)** Low quality of the enamel covering the cusp - unsupported enamel are likely to fracture under occlusal load Occlusal contacts on the margin of the preparation. > [!info] > The margin of the restoration should not be placed directly at the proximal contact point. The contact should ideally be on either the restoration or the natural tooth, away from the interface, to prevent fracture. # Inlay and Onlay **Clinical Rationale** *Generic approach* | Amalgam | Composite | Indirect restoration | |---------|-----------|----------------------| | Class I | Class II MO, DO | Class II MOD | | | | Class II MODL, MODB | | | | Multiple cusps missing | Diagram showing tooth restorations for different classes: Class I, Class II MO/DO, Class II MOD, Class II MODL/MODB, and Multiple cusps missing. # **Clinical Rationale** *Generic approach* | Amalgam | Composite | Indirect restoration | |---|---|---| | Class I | Class II MO, DO | Class II MOD | | | | Class II MODL, MODB | | | | Multiple cusps missing | # Inlay and Onlay ## Clinical Rationale ### Longevity of restorations in posterior teeth and reasons for failure **Annual failure rates in posterior stress-bearing restorations** | Restoration Type | Annual Failure Rate | |-------------------------------|---------------------| | Glass ionomers and derivatives | ~14.00% | | Direct composites | ~8.00% | | Ceramic restorations | ~7.00% | | Amalgam | ~6.00% | | Gold inlays and onlays | ~5.00% | | CAD/CAM ceramic restorations | ~4.00% | **Main reasons for failure**: secondary caries, fracture, marginal deficiencies, wear, and postoperative sensitivity. *Hickel R, et. al.: J Adhesive Dent 2001* ## **Longevity of restorations in posterior teeth and reasons for failure** ### **Annual failure rates in posterior stress-bearing restorations** | Restoration Type | Annual Failure Rate | |---|---| | Glass ionomers and derivatives | ~14.00% | | Direct composites | ~8.00% | | Ceramic restorations | ~7.00% | | Amalgam | ~6.00% | | Gold inlays and onlays | ~5.00% | | CAD/CAM ceramic restorations | ~4.00% | > [!tip] Gold Standard? > **CAD/CAM Ceramics** are considered a potential gold standard due to the high quality of modern materials and the precision of digital fabrication, which reduces technical errors. **Main reasons for failure**: secondary caries, fracture, marginal deficiencies, wear, and postoperative sensitivity. ### **Survival Rate vs. Success Rate** > [!info] > It is important to distinguish between two key metrics in clinical studies: > - ==**Survival Rate:** The restoration is still in place and functioning, but may have technical issues like chipping, wear, or marginal staining.== > - ==**Success Rate:** The restoration is in place, functioning, and has **no technical problems or failures**.== A restoration can **Inlay and Onlay** **Material / Fabrication method** - Precious alloys: Gold / Cast - Indirect composite resin (polymer-based) / CAD-CAM (chair side or lab) - Ceramic: Feldspathic, Leucite-reinforced ceramic, Lithium disilicate, Polymer-infiltrated ceramic, Alumina-based and Zirconia / Sintering, hot pressing, chairside CAD/CAM and laboratory CAD/CAM) ○ Survival rate: similar ○ Deterioration: Gold < Ceramic < Composite *Abduo et al. 2018, Angeletakia et al 2016* # **Material & Fabrication Methods** - **Precious alloys:** Gold / Cast - **Indirect composite resin (polymer-based):** CAD-CAM (chair side or lab) - **Ceramic:** - Feldspathic, Leucite-reinforced ceramic, Lithium disilicate, Polymer-infiltrated ceramic, Alumina-based and Zirconia / Sintering, hot pressing, chairside CAD/CAM and laboratory CAD/CAM) - **Survival rate:** similar - **Deterioration:** Gold < Ceramic < Composite *Abduo et al. 2018, Angeletakia et al 2016* # Inlay and Onlay *Longevity of ceramic onlays: A systematic review* *Abduo et al. 2018* - No indication that one ceramic material performs better than another, and the fabrication methods appear to minimally influence the ceramic onlay performance. - Survival rate: medium-term studies (2–5 years) - 91–100% long-term studies (more than 5 years) - 71–98.5% - Common cause of failure: 1<sup>st</sup> Ceramic fracture 2<sup>nd</sup> Debonding 3<sup>rd</sup> Caries - Deterioration of ceramic onlays: marginal integrity, margin discoloration, surface roughness, color match and anatomical form - Most common: loss of marginal integrity - Second: margin discoloration # **Longevity of Ceramic Onlays: A Systematic Review** *Abduo et al. 2018* - No indication that one ceramic material performs better than another, and the fabrication methods appear to minimally influence the ceramic onlay performance. > [!warning] Caveat > This conclusion should be interpreted with caution, as long-term, well-controlled clinical studies in prosthodontics are difficult to conduct and limited in number. - **Survival rate:** - medium-term studies (2–5 years) - 91–100% - long-term studies (more than 5 years) - 71–98.5% - **Common cause of failure:** - 1<sup>st</sup> Ceramic fracture - 2<sup>nd</sup> Debonding - 3<sup>rd</sup> Caries - **Deterioration of ceramic onlays:** marginal integrity, margin discoloration, surface roughness, color match and anatomical form - Most common: loss of marginal integrity - Second: margin discoloration # Inlay and Onlay **CAD/CAM polymer-based material – indirect composite restorations** - Indirect CAD/CAM resin composite materials - higher edge stability than ceramics, permitting restorations with very thin margins. - CAD/CAM composites: more homogenous and more abrasion-resistant restorations than direct composite resins. - Ceramics are generally superior to CAD/CAM polymer-based materials in terms of flexural strength, abrasion resistance and discoloration rates, whereas CAD/CAM polymer-based materials are more antagonist-friendly **Pressable lithium disilicate ceramic versus CAD/CAM resin composite restorations in patients with moderate to severe tooth wear: Clinical observations up to 13 years** *EDELHOFF ET AL. 2023* - Pressed LD single-tooth restorations showed lower long-term failure rates than RC. - CAD/CAM RC restorations showed higher abrasion and significantly higher discoloration rates - RC restorations exhibited more material fractures - Despite the technical problems, the survival rate for both was 100% # **Material Comparisons** ## **CAD/CAM polymer-based material – indirect composite restorations** - Indirect CAD/CAM resin composite materials - higher edge stability than ceramics, permitting restorations with very thin margins. - CAD/CAM composites: more homogenous and more abrasion-resistant restorations than direct composite resins. - Ceramics are generally superior to CAD/CAM polymer-based materials in terms of flexural strength, abrasion resistance and discoloration rates, whereas CAD/CAM polymer-based materials are more antagonist-friendly. , ==meaning they cause less wear to opposing teeth than harder ceramics. They are also easily repairable in the mouth.== ## **Pressable lithium disilicate ceramic versus CAD/CAM resin composite restorations in patients with moderate to severe tooth wear: Clinical observations up to 13 years** *EDELHOFF ET AL. 2023* - Pressed LD single-tooth restorations showed lower long-term failure rates than RC. - CAD/CAM RC restorations showed higher abrasion and significantly higher discoloration rates. - RC restorations exhibited more material fractures. - Despite the technical problems, the survival rate for both was 100%. - ==While the **survival rate** was similar, the pressable lithium disilicate had a **lower long-term failure rate** and was more resistant to abrasion.== # Inlay and Onlay ## Direct composite vs Indirect composite restorations ### DIRECT (Posterior composites) - Restores aesthetic and functionality - More affordable – single appointment - Maximum preservation of tooth structure (minimally-invasive dentistry) - Relatively short lifespan: microleakage, secondary caries, staining, fractures - Relies on remaining tooth structure for strength and integrity of restoration - Incomplete polymerization - Polymerisation shrinkage - Degrade chemically in the oral environment* - Lower wear resistance - Contacts & contours technique sensitive * Chemical agents found in saliva, food and beverages. - Intermittent exposure occurs during eating or drinking until teeth are cleaned. - Continuous exposure may occur as chemical agents can be absorbed by adherent debris (such as calculus or food particles) at the margins of restorations or be produced by bacterial decomposition of debris. Yep 2008 Chemical degradation of composite restoratives Angeletaki et al. 2016 # **Direct vs. Indirect Composite Restorations** # Inlay and Onlay ## Direct composite vs Indirect composite restorations ### DIRECT (Posterior composites) - Restores aesthetic and functionality - More affordable - single appointment - Maximum preservation of tooth structure (minimally-invasive dentistry) - Relatively short lifespan: microleakage, secondary caries, staining, factures - Relies on remaining tooth structure for strength and integrity of restoration - Incomplete polymerization - Polymerisation shrinkage - Degrade chemically in the oral environment* - Lower wear resistance - Contacts & contours technique sensitive ### INDIRECT (Composite) - Complete polymerization - Less porosity - Better control of contours & contacts - Better Marginal Adaptation and bond strength - Easier to repair (vs ceramic) - Less conservative (vs direct) - More expensive (vs direct) - Unpredictable color stability (vs ceramic) - Inferior mechanical properties (vs ceramic) - More wear and risk of fracture (vs ceramic) *Angeletaki et al. 2016* ## **DIRECT (Posterior composites)** - Restores aesthetic and functionality - More affordable - single appointment - Maximum preservation of tooth structure (minimally-invasive dentistry) - Relatively short lifespan: microleakage, secondary caries, staining, factures - Relies on remaining tooth structure for strength and integrity of restoration - Incomplete polymerization - Polymerisation shrinkage - Degrade chemically in the oral environment* - Lower wear resistance - Contacts & contours technique sensitive , ==especially for establishing tight proximal contacts and ideal occlusal anatomy in large restorations.== *\* Chemical agents found in saliva, food and beverages. Intermittent exposure occurs during eating or drinking until teeth are cleaned. Continuous exposure may occur as chemical agents can be absorbed by adherent debris (such as calculus or food particles) at the margins of restorations or be produced by bacterial decomposition of debris. Yep 2008 Chemical degradation of composite restoratives* ## **INDIRECT (Composite)** - Complete polymerization : ==Fabricated from a fully polymerized block, resulting in complete polymerization, less porosity, and no clinical shrinkage stress.== - Less porosity - Better control of contours & contacts - Better Marginal Adaptation and bond strength - Easier to repair (vs ceramic) - Less conservative (vs direct) - More expensive (vs direct) - Unpredictable color stability (vs ceramic) - Inferior mechanical properties (vs ceramic) - More wear and risk of fracture (vs ceramic) *Angeletaki et al. 2016* # Inlay and Onlay **CERAMIC ONLAY/INLAY** ## Advantages - Superior aesthetics – excellent translucency, shade stability, and enamel-like appearance. - High wear resistance – maintains anatomical form over time. - Excellent biocompatibility – inert and tissue-friendly. - Resists surface degradation and staining. - High compressive strength – suitable for posterior load-bearing areas when properly bonded. ## Disadvantages - Brittleness – prone to fracture under high occlusal stress if preparation or bonding is inadequate. - Irreparable – if fractured, usually requires replacement. - More invasive preparation – requires slightly more tooth reduction to allow adequate ceramic thickness. - Technique-sensitive bonding – requires resin cementation. - Higher cost – material and laboratory fees are more expensive. # **CERAMIC ONLAY/INLAY** ## **Advantages** - Superior aesthetics – excellent translucency, shade stability, and enamel-like appearance. - High wear resistance – maintains anatomical form over time. - Excellent biocompatibility – inert and tissue-friendly. - Resists surface degradation and staining. - High compressive strength – suitable for posterior load-bearing areas when properly bonded. - ==Ability to bond to tooth structure, reinforcing weakened cusps.== ## **Disadvantages** - Brittleness – prone to fracture under high occlusal stress if preparation or bonding is inadequate. - ==More abrasive to opposing natural dentition compared to composites or gold.== - Irreparable – if fractured, usually requires replacement. , ==as intraoral repair would require etching with hydrofluoric acid, which is not used clinically in the patient's mouth.== - More invasive preparation – requires slightly more tooth reduction to allow adequate ceramic thickness. - Technique-sensitive bonding – requires resin cementation. - Higher cost – material and laboratory fees are more expensive. # Inlay and Onlay **Clinical long-term results and 10-year Kaplan-Meier analysis of Cerec restorations** *Reiss & Walder 2000* - Inlays and onlays were manufactured using the Cerec technique (one single appointment CAD-CAM) - The clinical success was documented continuously for 9 to 12 years after the placement. **Results** - Probability of survival decreased to 90% after 10 years and 84.9% after 11.8 years - Restoration size and outline did not affect success rate - Premolars better than molars - Vital teeth better than non vital # **Clinical Long-Term Study: Cerec Restorations** *Reiss & Walder 2000* - Inlays and onlays were manufactured using the Cerec technique (one single appointment CAD-CAM). - The clinical success was documented continuously for 9 to 12 years after the placement. ## **Results** - Probability of survival decreased to 90% after 10 years and 84.9% after 11.8 years. > [!info] > This is considered a very good long-term outcome for large restorations. - Restoration size and outline did not affect success rate. - Premolars better than molars. ==(due to lower occlusal forces).== - Vital teeth better than non vital. # Inlay and Onlay ## TOOTH PREPARATION *Preparation guidelines for ceramic inlays/onlays differ from those for cast gold* **Box style – Conventional preparation** **Curved preparation – morphology driven preparation** # **TOOTH PREPARATION** > [!note] Two main philosophies exist for onlay preparation: > 1. **==(Old) Conventional Preparation:==** > - ==Characterized by **boxes, sharp angles, and retentive grooves**.== > - ==Designed for **mechanical retention** of restorations like cast gold onlays.== > - ==This design creates stress concentrations and is **unfavorable for brittle ceramic materials**.== > 2. **==Morphology Driven Preparation:==** > - ==Characterized by **smooth, flowing curves, rounded internal angles, and simple geometry**.== > - ==Designed for **adhesively bonded restorations** (ceramics, indirect composites).== > - ==This design minimizes stress concentration and allows for more even stress distribution, which is ideal for ceramics.== *Preparation guidelines for ceramic inlays/onlays differ from those for cast gold* - **Box style – Conventional preparation** - **Curved preparation – morphology driven preparation** # Inlay and Onlay **CERAMIC RESTORATIONS – PRINCIPLES OF PREPARATION** ## FAVORABLE DESIGNS - **Compressive stress** - **Curved transition** - **Simple geometry** - **Gradual cross sectional transition** ## UNFAVORABLE DESIGNS - **Tensile stress** - **No sharp edges** - **No complex geometry** - **No abrupt cross sectional transition** # **PRINCIPLES OF PREPARATION FOR CERAMIC RESTORATIONS** > [!info] Fundamental Principle > The fundamental principle is that ceramics perform well under **compression** but fail under **tension**. Preparation design must accommodate this property. ## **FAVORABLE DESIGNS** - ==Sufficient and even material thickness to distribute stress uniformly.== - ==Preparation follows the existing defect or restoration, removing only compromised tooth structure.== - **Compressive stress** - **Curved transition** - **Simple geometry** - **Gradual cross sectional transition** ## **UNFAVORABLE DESIGNS** - **Tensile stress** - **No sharp edges** - **No complex geometry** - **No abrupt cross sectional transition** # Inlay and Onlay **CERAMIC RESTORATIONS - PRINCIPLES OF PREPARATION** Box style preparation tends to produce tensile stresses on the internal surface Curved preparation tends to produce compressive stresses on internal surface Arnetzl GB & Arnetzl G 2006 - Box style preparation tends to produce tensile stresses on the internal surface. - Curved preparation tends to produce compressive stresses on internal surface. *Arnetzl GB & Arnetzl G 2006* # Inlay and Onlay **CERAMIC ONLAY AND INLAY** - No sharp internal line angles or points, only curved transitions - The prep extension depends on the extension the previous restoration or the caries lesion. # **Key Preparation Features for Ceramic Onlay and Inlay** - No sharp internal line angles or points, only curved transitions. - The prep extension depends on the extension the previous restoration or the caries lesion. # Inlay and Onlay ## CERAMIC ONLAY AND INLAY - All cavo-surface angles need to be **sharp, well defined** - **Butt joint (90°)** Hopp and Land 2013 Diagram showing ceramic onlay and inlay with labels for cavo-surface angle, external walls, internal walls, and beveled restoration margin. Includes a red 'X' indicating incorrect beveled margin and a clinical photo of a tooth with restoration. - All cavo-surface angles need to be **sharp, well defined**. - ==**Avoid bevels**, especially in occlusal contact areas. A beveled or undefined margin makes it impossible for the lab to know where the restoration should end, leading to over-extension and thin, chippable ceramic edges.== - **Butt joint (90°)** *Hopp and Land 2013* # Inlay and Onlay ## CERAMIC ONLAY AND INLAY - Greater than or equal to 10 degrees of divergence on buccal and lingual walls - 10 to 12 degrees of axial wall convergence *Hopp and Land 2013* - Greater than or equal to 10 degrees of divergence on buccal and lingual walls. > [!info] Path of Insertion > The preparation must have a single path of insertion with **no undercuts** to allow for passive seating. > - ==The main buccal and lingual walls should be **divergent** towards the occlusal surface.== > - ==The **axial walls** of any proximal boxes (mesial or distal) must be **convergent** towards the occlusal surface. This is a critical feature to ensure a single path of draw.== > - ==The traditional recommendation for the buccal-lingual width of the isthmus is a minimum of **2mm**.== - 10 to 12 degrees of axial wall convergence. *Hopp and Land 2013* # Inlay and Onlay - Avoid complex internal geometry to the preparation - Transition of material thickness should be gradual not abrupt - Avoid complex internal geometry to the preparation. - Transition of material thickness should be gradual not abrupt. # Inlay and Onlay - **No acute angles within preparation** - **Smooth flowing margins** - **No additional retention features** - **No tooth structure without support** - **Obtuse external line angles** Diagram showing correct and incorrect preparation for inlay and onlay restorations, highlighting acute angles (marked with red X) versus obtuse external line angles (marked with green check). - **No acute angles within preparation** . ==Milling machines use burs with a minimum diameter (e.g., 1.0-1.5 mm) and cannot physically mill a sharp internal corner. The machine will compensate by over-milling the area, creating a void that will be filled with a thick layer of cement, compromising the fit and stress distribution of the final restoration.== - **Smooth flowing margins** - **No additional retention features** - **No tooth structure without support** - **Obtuse external line angles** **Inlay and Onlay** Two dental burs: 1.0 mm step bur and 1.5 mm cylinder bur, used with a CEREC 3 milling unit. # Inlay and Onlay Reich S & Hofman J Diagram showing a cross-section through a ceramic crown with annotations for "1.2 mm minimum diameter" and "Crown lumen". A physical ceramic crown is also shown mounted on a pin. # Inlay and Onlay ## Position of Buccal margin **Avoid contact points** (a) Ultraconservative buccal cusp coverage. (b) Conventional buccal cusp coverage. (c) Full buccal cusp coverage (VONLAY). For aesthetics: the simplest and most ideal situation is for the restoration margins to be located in the incisal or cervical thirds. *Rocca et al 2015* ## **Position of Buccal margin** **Avoid contact points** - (a) Ultraconservative buccal cusp coverage. - (b) Conventional buccal cusp coverage. - (c) Full buccal cusp coverage (VONLAY). For aesthetics: the simplest and most ideal situation is for the restoration margins to be located in the incisal or cervical thirds. *Rocca et al 2015* # Inlay and Onlay - Absence of contact between the preparation and the adjacent teeth. - Drop down the margins in order to obtain an optimal, natural proximal emergence profile of the future restoration. Eg: closing diastemas ## **Proximal Margins and Emergence Profile** - Absence of contact between the preparation and the adjacent teeth. - Drop down the margins in order to obtain an optimal, natural proximal emergence profile of the future restoration. Eg: closing diastemas # Inlay and Onlay ## Margins - **No** aspect of the margin should be located in an **undercut** and **no unsupported enamel** Diagram showing correct and incorrect margin preparations with checkmarks and crosses. Labels: "Deep Chamfer, Modified Shoulder Supra or equigingival", "Feather edge Subgingival", "'Gutter' margin preparation" ## **Margins** - **No** aspect of the margin should be located in an **undercut** and **no unsupported enamel**. # Inlay and Onlay ## Margins - **Deep Chamfer, Modified Shoulder** - Supra or equigingival - **Feather edge** - Subgingival - **"Gutter" margin** - preparation - **Deep Chamfer, Modified Shoulder** - Supra or equigingival - **Feather edge** - Subgingival - **"Gutter" margin** - preparation **Inlay and Onlay** **Margins** - **Deep Chamfer, Modified Shoulder** Supra or equigingival ✅ - **Feather edge** Subgingival ❌ - **"Gutter" margin preparation** ❌ - **Deep Chamfer, Modified Shoulder** - Supra or equigingival ✅ - **Feather edge** - Subgingival ❌ - **"Gutter" margin preparation** - ❌ **Inlay and Onlay** Path of Insertion Diagram showing correct and incorrect paths of insertion for dental inlays/onlays, with a red 'X' marking the incorrect path and a photograph of a dental model on the right. ## **Path of Insertion** # Inlay and Onlay - **Smooth surfaces** Finishing of preparation should be with a bur with a grit size of no more 50 microns (Red band) ## **Surface Finish** - **Smooth surfaces** Finishing of preparation should be with a bur with a grit size of no more 50 microns (Red band). **Inlay and Onlay** Diagram comparing Inlay and Onlay restorations on teeth, with numbered annotations indicating specific areas of the tooth structure and restoration. Text below reads: "Accessibility of subgingival margins" # Inlay and Onlay ## Morphology Driven Preparation - Bonded restorations - **Immediate dentin sealing** and cavity design optimization (after tooth preparation): - avoid unnecessary removal of tooth structure - protect the pulpodentinal structures from any contamination/disturbance during temporarization - stabilize and improve the adhesive interface quality. - **Deep Margin Elevation** ## (Old) Conventional Preparation - Cemented or bonded - Deep occlusal box - Width of occlusal isthmus ≥ 2 mm - Geometrical reduction - More suitable for indirect non-adhesive restorations. *Veneziani 2017* # **Preparation Techniques** ## **Morphology Driven Preparation** - Bonded restorations - **Immediate dentin sealing** and cavity design optimization (after tooth preparation): - avoid unnecessary removal of tooth structure - protect the pulpodentinal structures from any contamination/disturbance during temporarization - stabilize and improve the adhesive interface quality. - **Deep Margin Elevation** ## **(Old) Conventional Preparation** - Cemented or bonded - Deep occlusal box - Width of occlusal isthmus ≥ 2 mm - Geometrical reduction - More suitable for indirect non-adhesive restorations. *Veneziani 2017* **Inlay and Onlay** **Morphology Driven Preparation** **MAXILLARY Mucospid and molars** - Butt joint (1.2–1.5 mm) - Interproximal box: always - Axial walls: apically to maximum contour line - Anatomical reduction of the occlusal surface - Convergent walls (6–10 degrees) - Inclined planes M–D, V–P (chamfer) - Axial walls, coronal to maximum contour line **MANDIBULAR molars and premolars** - Butt joint (1.2–1.5 mm) - Interproximal box: always - Axial walls: apically to maximum contour line - Anatomical reduction of the occlusal surface - Convergent walls (6–10 degrees) - Inclined planes M–D, V–P (chamfer) - Axial walls, coronal to maximum contour line *Veneziani 2017* ## **Morphology Driven Preparation Details** ### **MAXILLARY Mucospid and molars** - Butt joint (1.2–1.5 mm) - Interproximal box: always - Axial walls: apically to maximum contour line - Anatomical reduction of the occlusal surface - Convergent walls (6–10 degrees) - Inclined planes M–D, V–P (chamfer) - Axial walls, coronal to maximum contour line ### **MANDIBULAR molars and premolars** - Butt joint (1.2–1.5 mm) - Interproximal box: always - Axial walls: apically to maximum contour line - Anatomical reduction of the occlusal surface - Convergent walls (6–10 degrees) - Inclined planes M–D, V–P (chamfer) - Axial walls, coronal to maximum contour line *Veneziani 2017* # Inlay and Onlay ## Morphology Driven Preparation Veneziani 2017 Diagram showing tooth preparation for inlay/onlay, highlighting "Inclined plane (hollow chamber)" and "Butt joint" on a natural tooth, and "Perpendicular to long axis enamel prisms" with "Cavity-surface angle ≥ 90 degrees" on a blue tooth model. *Veneziani 2017* **Inlay and Onlay** Morphology Driven Preparation Veneziani 2017 Diagram showing tooth preparation for inlay and onlay, with arrows indicating areas of tooth structure removal. *Veneziani 2017* # Inlay and Onlay **AMOUNT OF REDUCTIONS** - 1 to 1.5 mm of axial wall reduction - 1.5 mm at least of occlusal reduction for cuspal coverage - Margin 1 mm if present # **AMOUNT OF REDUCTIONS** - 1 to 1.5 mm of axial wall reduction - 1.5 mm at least of occlusal reduction for cuspal coverage - Margin 1 mm if present **Inlay and Onlay** Checklist before impression or scanning: 1. Well defined sharp margins 2. No undercuts, no sharp internal line angles 3. Smooth surface 4. Accessibility to all margins, especially subgingival margins 5. Absence of contact between the prep margin and the adjacent tooth. 6. Adequate interocclusal space. # **Checklist before impression or scanning** 1. Well defined sharp margins 2. No undercuts, no sharp internal line angles 3. Smooth surface 4. Accessibility to all margins, especially subgingival margins 5. Absence of contact between the prep margin and the adjacent tooth. 6. Adequate interocclusal space. # Inlay and Onlay ## Interim Restoration Non-cemented “semi-rigid” light-curing resin **Telio** **Ivoclar** Prep isolated with Vaseline at the periphery and over the axial walls before applying the material Rocca et al 2015 # **Interim Restoration** ## **Non-cemented “semi-rigid” light-curing resin** **Telio** **Ivoclar** Prep isolated with Vaseline at the periphery and over the axial walls before applying the material. *Rocca et al 2015* # Inlay and Onlay **Interim Restoration** **Self-curing material** Jensen 2007 Image showing a 3M ESPE Cavitec W box, a jar of material, and two dental restorations labeled 'a' and 'b' ## **Self-curing material** *Jensen 2007* # Inlay and Onlay **DIRECT TECHNIQUE** Bis-Acryl composite Dental model, clear aligner, and composite material kit ## **DIRECT TECHNIQUE** Bis-Acryl composite # Partial Coverage Restorations - **Abduo and Sambrook.** Longevity of ceramic onlays: A systematic review *J Esthet Restor Dent.* 2018 May;30(3):193-215. - **Edelhoff et al.** Pressable lithium disilicate ceramic versus CAD/CAM resin composite restorations in patients with moderate to severe tooth wear: Clinical observations up to 13 years. *J Esthet Restor Dent.* 2023;35:116-128. - **Hickel and Manhart.** Longevity of restorations in posterior teeth and reasons for failure *J Adhes Dent.* 2001 Spring;3(1):45-64. - **Reiss and Walther.** Clinical long-term results and 10-year Kaplan-Meier analysis of Cerec restorations. *Int J Comput Dent.* 2000 Jan;3(1):9-23. - **Arnetzl & Arnetzl.** Biomechanical examination of inlay geometries--is there a basic biomechanical principle?. *Int J Comput Dent.* 2009;12(2):119-30. - **Edelhoff & Sorensen.** Tooth structure removal associated with various preparation designs for posterior teeth. *Int J Periodontics Restorative Dent.* 2002 Jun;22(3):241-9. - **Hopp & Land.** Considerations for ceramic inlays in posterior teeth: a review. *Clinical, Cosmetic and Investigational Dentistry* 2013:5 21-32 - **Rocca et al.** Evidence-based concepts and procedures for bonded inlays and onlays. Part II. Guidelines for cavity preparation and restoration fabrication. *Int J Esthet Dent.* 2015;10(3):392-413. - **Veneziani.** Posterior indirect adhesive restorations: updated indications and the Morphology Driven Preparation Technique. *INT J ESTHETIC DENT* 12:2 2017 - **Edelhoff et. All.** Clinical performance of occlusal onlays made of lithium disilicate ceramic in patients with severe tooth wear up to 11 years. *Dental Materials.* 35:9, 2019, Pages 1319-1330 # **References** - **Abduo and Sambrook.** Longevity of ceramic onlays: A systematic review *J Esthet Restor Dent.* 2018 May;30(3):193-215. - **Edelhoff et al.** Pressable lithium disilicate ceramic versus CAD/CAM resin composite restorations in patients with moderate to severe tooth wear: Clinical observations up to 13 years. *J Esthet Restor Dent.* 2023;35:116-128. - **Hickel and Manhart.** Longevity of restorations in posterior teeth and reasons for failure *J Adhes Dent.* 2001 Spring;3(1):45-64. - **Reiss and Walther.** Clinical long-term results and 10-year Kaplan-Meier analysis of Cerec restorations. *Int J Comput Dent.* 2000 Jan;3(1):9-23. - **Arnetzl & Arnetzl.** Biomechanical examination of inlay geometries--is there a basic biomechanical principle?. *Int J Comput Dent.* 2009;12(2):119-30. - **Edelhoff & Sorensen.** Tooth structure removal associated with various preparation designs for posterior teeth. *Int J Periodontics Restorative Dent.* 2002 Jun;22(3):241-9. - **Hopp & Land.** Considerations for ceramic inlays in posterior teeth: a review. *Clinical, Cosmetic and Investigational Dentistry* 2013:5 21-32 - **Rocca et al.** Evidence-based concepts and procedures for bonded inlays and onlays. Part II. Guidelines for cavity preparation and restoration fabrication. *Int J Esthet Dent.* 2015;10(3):392-413. - **Veneziani.** Posterior indirect adhesive restorations: updated indications and the Morphology Driven Preparation Technique. *INT J ESTHETIC DENT* 12:2 2017 - **Edelhoff et. All.** Clinical performance of occlusal onlays made of lithium disilicate ceramic in patients with severe tooth wear up to 11 years. *Dental Materials.* 35:9, 2019, Pages 1319-1330 [[MR6 Onlays.pdf#page=1|MR6 Onlays, p.1]] [[MR6 Onlays.pdf#page=2|MR6 Onlays, p.2]] [[MR6 Onlays.pdf#page=3|MR6 Onlays, p.3]] [[MR6 Onlays.pdf#page=4|MR6 Onlays, p.4]] [[MR6 Onlays.pdf#page=5|MR6 Onlays, p.5]] [[MR6 Onlays.pdf#page=6|MR6 Onlays, p.6]] [[MR6 Onlays.pdf#page=7|MR6 Onlays, p.7]] [[MR6 Onlays.pdf#page=8|MR6 Onlays, p.8]] [[MR6 Onlays.pdf#page=9|MR6 Onlays, p.9]] [[MR6 Onlays.pdf#page=10|MR6 Onlays, p.10]] [[MR6 Onlays.pdf#page=11|MR6 Onlays, p.11]] [[MR6 Onlays.pdf#page=12|MR6 Onlays, p.12]] [[MR6 Onlays.pdf#page=13|MR6 Onlays, p.13]] [[MR6 Onlays.pdf#page=14|MR6 Onlays, p.14]] [[MR6 Onlays.pdf#page=15|MR6 Onlays, p.15]] [[MR6 Onlays.pdf#page=16|MR6 Onlays, p.16]] [[MR6 Onlays.pdf#page=17|MR6 Onlays, p.17]] [[MR6 Onlays.pdf#page=18|MR6 Onlays, p.18]] [[MR6 Onlays.pdf#page=19|MR6 Onlays, p.19]] [[MR6 Onlays.pdf#page=20|MR6 Onlays, p.20]] [[MR6 Onlays.pdf#page=21|MR6 Onlays, p.21]] [[MR6 Onlays.pdf#page=22|MR6 Onlays, p.22]] [[MR6 Onlays.pdf#page=23|MR6 Onlays, p.23]] [[MR6 Onlays.pdf#page=24|MR6 Onlays, p.24]] [[MR6 Onlays.pdf#page=25|MR6 Onlays, p.25]] [[MR6 Onlays.pdf#page=26|MR6 Onlays, p.26]] [[MR6 Onlays.pdf#page=27|MR6 Onlays, p.27]] [[MR6 Onlays.pdf#page=28|MR6 Onlays, p.28]] [[MR6 Onlays.pdf#page=29|MR6 Onlays, p.29]] [[MR6 Onlays.pdf#page=30|MR6 Onlays, p.30]] [[MR6 Onlays.pdf#page=31|MR6 Onlays, p.31]] [[MR6 Onlays.pdf#page=32|MR6 Onlays, p.32]] [[MR6 Onlays.pdf#page=33|MR6 Onlays, p.33]] [[MR6 Onlays.pdf#page=34|MR6 Onlays, p.34]] [[MR6 Onlays.pdf#page=35|MR6 Onlays, p.35]] [[MR6 Onlays.pdf#page=36|MR6 Onlays, p.36]] [[MR6 Onlays.pdf#page=37|MR6 Onlays, p.37]] [[MR6 Onlays.pdf#page=38|MR6 Onlays, p.38]] [[MR6 Onlays.pdf#page=39|MR6 Onlays, p.39]] [[MR6 Onlays.pdf#page=40|MR6 Onlays, p.40]] [[MR6 Onlays.pdf#page=41|MR6 Onlays, p.41]] [[MR6 Onlays.pdf#page=42|MR6 Onlays, p.42]] [[MR6 Onlays.pdf#page=43|MR6 Onlays, p.43]] [[MR6 Onlays.pdf#page=44|MR6 Onlays, p.44]] [[MR6 Onlays.pdf#page=45|MR6 Onlays, p.45]] [[MR6 Onlays.pdf#page=46|MR6 Onlays, p.46]] [[MR6 Onlays.pdf#page=47|MR6 Onlays, p.47]] [[MR6 Onlays.pdf#page=48|MR6 Onlays, p.48]]