According to the width and height of the maxillary alveolar ridge, the maxillary edentulous jaws can be divided into three categories by using modified lip-tooth-ridge (MLTR) classification. Class Ⅰ is characterized by sufficient bone available for implants in the vertical and horizontal aspects and is suitable for fixed implant-supported prostheses. Class Ⅱ is characterized by sufficient bone amount available for implants in a horizontal aspect but insufficient for lip support and is suitable for a fixed detachable implant-supported prosthesis. Class Ⅲ is characterized by inadequate amount of bone for implants (with vertical or horizontal components) and is suitable for the use of zygomatic implants or traditional complete denture. Patients belonging to Class Ⅰ can be further classified into two sub-categories according to the height of the alveolar ridge. The first subclass is characterized by minimal bone deficiency and is suitable for a conventional implant-supported “crown and bridge” prosthesis. The second subclass is characterized by a larger vertical deficiency than that of the first subclass and is suitable for implant-supported hybrid prosthesis. The MLTR classification system can help the dentist to determine whether the patient is suitable for implanting dentures and whether fixed denture or removable denture is appropriate for the patient, select indications, reduce complications, and achieve long-term results.
